Evaluation of Metal–Organic Frameworks As Potential Adsorbents for Solar Cooling Applications

Review Evaluation of Metal–Organic Frameworks as Potential Adsorbents for Solar Cooling Applications

Muhammad Mujahid Raﬁque 1,2

1 Department of Mechanical Engineering, KFUPM, Dhahran 31261, Saudi Arabia; mujahidraﬁ[email protected] 2 Faculty of Mechanical Engineering, TU Freiberg 09599, Germany

Received: 12 May 2020; Accepted: 19 June 2020; Published: 23 June 2020

Abstract: The reduction of carbon dioxide emissions has become a need of the day to overcome different environmental issues and challenges. The use of alternative and renewable-based technologies is one of the options to achieve the target of sustainable development through the reduction of these harmful emissions. Among different technologies thermally activated cooling systems are one which can reduce the harmful emissions caused by conventional heating, ventilation, and air conditioning technology. Thermal cooling systems utilize different porous materials and work on a reversible adsorption/desorption cycle. Different advancements have been made for this technology but still a lot of work should be done to replace conventional systems with this newly developed technology. High adsorption capacity and lower input heat are two major requirements for efficient thermally driven cooling technologies. In this regard, it is a need of the day to develop novel adsorbents with high sorption capacity and low regeneration temperature. Due to tunable topologies and a highly porous nature, the hybrid porous crystalline materials known as metal–organic frameworks (MOFs) are a great inspiration for thermally driven adsorption-based cooling applications. Keeping all the above-mentioned aspects in mind, this paper presents a comprehensive overview of the potential use of MOFs as adsorbent material for adsorption and desiccant cooling technologies. A detailed overview of MOFs, their structure, and their stability are presented. This review will be helpful for the research community to have updated research progress in MOFs and their potential use for adsorption-based cooling systems.

Keywords: MOFs; thermal cooling; sustainable developments; solar energy

1. Introduction Energy consumption across diﬀerent sectors is increasing continuously with households as the major contributor which is responsible for one-third of the world’s total energy consumption [1]. The major portion of the energy in the household and almost 30% of the world’s total energy is consumed by heating, ventilation, and air conditioning (HVAC) equipment [2,3]. Furthermore, the energy demands for heating and cooling applications are increasing at a rapid rate and are accounting for more than 17% of worldwide consumption as can be observed from Figure1[ 4]. This demand is projected to increase at a rapid rate in the future as well. To combat this increasing demand for energy, a target of 20% reduction in primary energy use by 2020 has been set by EU-28 countries [5] and to achieve this milestone diﬀerent alternative energy technology needs to be introduced.

Appl. Syst. Innov. 2020, 3, 26; doi:10.3390/asi3020026 www.mdpi.com/journal/asi Appl. Syst. Innov. 2020, 3, 26 2 of 20

Appl.Appl. Syst. Syst. Innov. Innov. 2020 2020, ,3 3, ,x x FOR FOR PEER PEER REVIEW REVIEW 2 2 of of 19 19

FigureFigure 1. 1. Consumptions Consumptions of of global global ener energyenergygy in in different didifferentﬀerent sectors sectorssectors [5]. [[5].5].

DifferentDiDifferentﬀerent technologies technologiestechnologies and andand alternative alternativealternative coolin coolingcoolingg systems systemssystems based basedbased on onon thermal thermalthermal energy energyenergy including includingincluding absorption,absorption, adsorption, adsorption, and and desiccant desiccantdesiccant cooling coolingcooling have havehave been beenbeen investigated investigated in in recent recent years.years. The The basic basicbasic operatingoperating principle principle of of of a a thermal athermal thermal cooling cooling cooling system system system is is sh sh isownown shown in in Figure Figure in Figure 2 2 [6]. [6].2 [These These6]. Thesetechnologies technologies technologies are are based based are onbasedon the the process onprocess the process of of dehumidification dehumidification of dehumidiﬁcation and and cooling. cooling. and cooling.So Someme adsorbent adsorbent Some adsorbent materials materials materials are are used used arein in these these used systems insystems these whichsystemswhich havehave which thethe have potentialpotential the potential toto adsorb/absorbadsorb/absorb to adsorb water/waterabsorb momo waterlecules.lecules. molecules. DueDue toto thethe Due thermallythermally to the thermally operatedoperated operated nature,nature, thenature,the input input the energy energy input is energyis provided provided is provided in in the the form form in the of of form heat heat offo for heatr the the forcontinuous continuous the continuous operation operation operation of of these these of systems. thesesystems. systems. This This makesThismakes makes the the use use the of useof low-grade low-grade of low-grade thermal thermal thermal energy energy energy sources sources sources such such such as as solar,as solar, solar, biomass, biomass, biomass, waste, waste, waste, etc., etc., etc., more more more feasible. feasible. feasible.

FigureFigure 2. 2. Thermally Thermally activated activated cooling cooling system’s system’s working working principle principle [4]. [[4].4].

WhileWhile thermally thermally activated activated activated cooling cooling cooling systems systems systems offer offer off ader advantages advantagesvantages in in terms terms in terms of of energy energy of energy consumption consumption consumption and and and CO emissions [7,8], despite the advantages offered by thermally driven cooling systems, it is COCO2 2 emissionsemissions2 [7,8],[7,8], despitedespite thethe advantagesadvantages offereofferedd byby thermallythermally drivendriven coolingcooling systems,systems, itit isis observedobserved thatthatthat these thesethese systems systemssystems are areare comprised comprisedcomprised of large ofof large componentslarge componentscomponents which makewhichwhich them makemake bulky themthem and bulkybulky expensive. andand expensive.Furthermore,expensive. Furthermore,Furthermore, most of the adsorbentmostmost ofof thethe used adsorbentadsorbent for these used systemsused forfor has thesethese larger systemssystems water has uptakehas largerlarger capacity waterwater at uptakeuptake higher capacitypartialcapacity pressure. atat higherhigher Hence, partialpartial it pressure.ispressure. very di ffi Hence,Hence,cult to it implementit isis veryvery difficultdifficult these technologies toto implementimplement on these athese commercial technologiestechnologies and larger onon aa commercialscale.commercial These and and systems larger larger are scale. scale. available These These commercially systems systems are are available available but only commercially atcommercially a small scale but but and only only only at at aa a fewsmall small are scale scale installed and and onlyforonly large a a few few scale are are installed applicationsinstalled for for large [large9]. scale scale applications applications [9]. [9]. AdsorptionAdsorption andand desiccantdesiccant coolingcooling cooling technology technologytechnology can cancan be bebe used used used as as aas great aa greatgreat means meansmeans of general ofof generalgeneral cooling coolingcooling but, but,duebut, due todue the to to the above-mentionedthe above-mentioned above-mentioned issues, issues, issues, these these these systems syst systemsems have have have a lower a a lower lower coe coeffici coefficifficiententent of of performanceof performance performance (COP) (COP) (COP) as asshownas shown shown in in Figurein Figure Figure3[ 103 3 [10]. ].[10]. The The The average average average COP COP COP of theseof of these these systems systems systems is less is is less less than than than 1. This 1. 1. This This lower lower lower value value value of COP of of COP COP and andtheand bulky thethe bulkybulky nature naturenature of these ofof systems thesethese systemssystems are a big areare hurdle aa bigbig for hurdlehurdle its development forfor itsits developmentdevelopment and implementation. andand implementation.implementation. Concerning Concerningthis,Concerning different this,this, advancements differentdifferent advancements areadvancements required for areare adsorbent rerequiredquired materials forfor adsorbentadsorbent used for thesematerialsmaterials technologies usedused forfor to these lowerthese technologiestheirtechnologies weight, to cost,to lower lower and their their required weight, weight, temperature cost, cost, and and required ofrequired regeneration. temperature temperature of of regeneration. regeneration. Appl. Syst. Innov. 2020, 3, 26 3 of 20 Appl. Syst. Innov. 2020, 3, x FOR PEER REVIEW 3 of 19

FigureFigure 3.3. CoeCoefficientﬃcient of of performance performance (COP) (COP) as a functionas a func oftion temperature of temperature [10]. Reprinted [10]. Reprinted with permission with permissionfrom [10]. Copyrightfrom [10]. fromCopyright 2007 Elsevier.from 2007 Elsevier.

Metal–organicMetal–organic frameworks frameworks (MOFs) (MOFs) are are a a newly newly developed developed class class of of crystalline crystalline materials materials with with highlyhighly porous porous structure structure and and high high adsorption adsorption capaci capacity.ty. These These materials materials offer offer a a wide wide variety variety of of choices choices forfor itsits developmentdevelopment because because of of individual individual choices choices of linker of linker and metal-ligandand metal-ligand according according to the required to the requiredstructure structure and application. and application. These materials These materials have a high have surface a high area surface which area means which that means a small that quantity a small quantityof these materialsof these materials can replace can the replace bulk quantity the bulk of qu otherantity porous of other materials porous for materials a particular for a application. particular application.The MOF materials The MOF are materials widely used are forwidely gas storageused fo andr gas filtration storage processesand filtration nowadays. processes In recentnowadays. years, Inthese recent materials years, havethese made materials great have scientific made advances great scientific due to the advances above-mentioned due to the advantages. above-mentioned advantages.Keeping all aspects in mind, the main aim of this research work is to present a comprehensive overviewKeeping of MOFsall aspects for their in mind, potential the main use as aim adsorbents of this research for thermally work is activated to present cooling a comprehensive technologies. overviewThe brief of introduction MOFs for their of adsorption-based potential use as adsorb coolingents and for desired thermally behavior activated of adsorbent cooling technologies. material for Thecooling brief applications introduction is of described. adsorption-based The paper coolin providesg and desired a comprehensive behavior of overview adsorbent of material MOF-based for coolingcooling applications and its future is developments. described. The Furthermore, paper provides comparative a comprehensive studies related overview to MOFs of MOF-based and other coolingadsorbent and materials its future commonly developments. used for Furthermore, cooling applications comparative are reviewed. studies related The comprehensive to MOFs and plan other to adsorbentachieve the materials objectives commonly of this research used for can cooling be summarized applications as: are reviewed. The comprehensive plan to achieveDescription the objectives of alternative of this research cooling can be technologies summarized thatas: are both energy efficient and • • Descriptionenvironmentally of friendly.alternative cooling technologies that are both energy efficient and environmentallyResearch on thermal friendly. cooling systems for their development and promotion. • • ResearchA detailed on review thermal of availablecooling systems advanced foradsorbent their development materials and that promotion. can be employed for adsorption • • Abased detailed solar cooling.review of available advanced adsorbent materials that can be employed for adsorptionIntroduction based to MOFs solar ascooling. an alternative to other adsorbents. • • IntroductionThe recent development to MOFs as ofan MOFsalternative andtheir to other adsorption adsorbents. characteristics. •• TheFuture recent needs development for development of MOFs and and advancements their adsorption of MOF-based characteristics. cooling technology. •• Future needs for development and advancements of MOF-based cooling technology. It is predicted that the use of MOF materials for both adsorption-based cooling technology will helpIt for is theirpredicted development that the use and of promotion MOF materials on a commercialfor both adsorption-based scale. A suitable cooling MOF technology can be selected will helpbased for on their the development desired outcome and andpromotion further on tuned a commercial if needed. scale. The A use suitable of these MOF novel can structures be selected as basedan adsorbent on the desired for adsorbent-based outcome and coolingfurther tuned may perform if needed. better The as use compared of these tonovel other structures materials as that an adsorbentare widely for used adsorbent-based for these applications. cooling may In short, perform to find better out as this compared potential to through other materials a comprehensive that are widelyreview used of adsorbent-based for these applications. cooling systems,In short, desired to find adsorbent out this potential behavior through for these a technologies comprehensive and reviewcomparative of adsorbent-based adsorption properties cooling ofsystems, MOFs isdesire the aimd adsorbent of this paper. behavior for these technologies and comparative adsorption properties of MOFs is the aim of this paper. 2. Thermally Activated Cooling Systems The use of thermal energy for heating and cooling applications is one of the feasible options for the effective utilization of renewable energy sources such as solar, waste heat, biomass, etc. [11,12]. This can help to reduce the dependence on fossil fuels and to achieve the goals of sustainable development. Appl.Appl. Syst. Syst. Innov. Innov. 2020 2020, ,3 3, ,x x FOR FOR PEER PEER REVIEW REVIEW 4 4 of of 19 19

2.2. Thermally Thermally Activated Activated Cooling Cooling Systems Systems

Appl.The Syst.The use Innov.use of of2020 thermal thermal, 3, 26 energy energy for for heating heating and and cooling cooling applications applications is is one one of of the the feasible feasible options options4 offor for 20 thethe effectiveeffective utilizationutilization ofof renewablerenewable energyenergy sourcessources suchsuch asas solar,solar, wastewaste heat,heat, biomass,biomass, etc.etc. [11,12].[11,12]. ThisThis cancan helphelp toto reducereduce thethe dependencedependence onon fossfossilil fuelsfuels andand toto achieveachieve thethe goalsgoals ofof sustainablesustainable development.Thedevelopment. naturally The availableThe naturally naturally energy available available sources energy energy can be sources sources used to can can drive be be used thermallyused to to drive drive activated thermally thermally cooling activated activated systems cooling cooling such systemsassystems adsorption suchsuch asas [13 adsorptionadsorption,14] and desiccant [13,14][13,14] and coolingand desiccantdesiccant [4]. Apart cocoolingoling from [4].[4]. that, ApartApart absorption fromfrom that,that, cooling absorptionabsorption is also cooling ancooling option isis alsothatalso an canan optionoption make thatthat use can ofcan these makemake low-grade use use ofof thesethese energy low-gradelow-grade sources energyenergy eﬀectively sourcessources [15 effectivelyeffectively]. A classiﬁcation [15].[15]. AA classificationclassification of thermally ofactivatedof thermally thermally cooling activated activated is presented cooling cooling is inis presented Figurepresented4. in in Figure Figure 4. 4.

FigureFigure 4. 4. Classifications ClassificationsClassiﬁcations of of thermally thermally activated activated cooling. cooling.

TheThe working working of of thermally thermally activated activated cooling cooling technology technology is is based based on on two two processes, processes, which which are are adsorptionadsorption and andand regeneration regeneration asas illustratedillustrated illustrated inin in FigureFigure Figure5 .5. 5. During During During the the the process process process of of of adsorption, adsorption, adsorption, process process process air air air is ispassedis passedpassed through throughthrough a dehumidiﬁcation aa dehumidificationdehumidification unit unit composedunit composcompos ofed someed ofof adsorbentsomesome adsorbentadsorbent material. material.material. The adsorbent TheThe adsorbentadsorbent material materialadsorbsmaterial theadsorbsadsorbs moisture thethe moisturemoisture from the from processfrom thethe air processprocess depending airair dependingdepending upon its adsorptionuponupon itsits adsorptionadsorption capacity. capacity. Thecapacity. adsorbed TheThe adsorbedmoistureadsorbed moisture bymoisture the adsorbent byby thethe adsorbentadsorbent material material ismaterial removed isis removedremoved during the duringduring regeneration thethe regenerationregeneration process. process.process. Thermal ThermalThermal energy, energy,dependingenergy, depending depending upon the upon upon required the the required required regeneration regeneration regeneration temperature te temperaturemperature is provided is is provided provided during during during this step. this this step. Instep. this In In way,this this way,theway, process the the process process of adsorption of of adsorption adsorption and desorptionand and desorption desorption continues continues continues in a cyclic in in a a cyclic cyclic loop [loop 16loop]. [16]. [16].

Figure 5. Two-step process of thermally activated cooling. FigureFigure 5. 5. Two-step Two-step process process of of thermally thermally activated activated cooling. cooling. Thermally driven cooling technology provides many advantages over conventional HVAC devices ThermallyThermally drivendriven coolingcooling technologytechnology providesprovides manymany advantagesadvantages overover conventionalconventional HVACHVAC which are based on the vapor compression cycle [17]. The direct use of thermal energy and low heat of devicesdevices whichwhich areare basedbased onon thethe vaporvapor compressioncompression cyclecycle [17]. [17]. TheThe directdirect use use ofof thermal thermal energyenergy and and regeneration are some of the advantages offered by this technology [18–20]. A summary of the potential lowlow heat heat of of regeneration regeneration are are some some of of the the advantag advantageses offered offered by by this this technology technology [18–20]. [18–20]. A A summary summary advantages offered by this technology is summarized in Figure6. Silica gel is widely used as adsorbent ofof the the potential potential advantages advantages offered offered by by this this technology technology is is summarized summarized in in Figure Figure 6. 6. Silica Silica gel gel is is widely widely material for different cooling applications [21–23] such as trigeneration [24,25], air conditioning for usedused as as adsorbent adsorbent material material for for different different cooling cooling applic applicationsations [21–23] [21–23] such such as as tr trigenerationigeneration [24,25], [24,25], air air automotive [26], and solar cooling [27,28]. However, adsorption at higher pressure is one of the major conditioningconditioning for for automotive automotive [26], [26], and and solar solar cooling cooling [27,28]. [27,28]. However, However, adsorption adsorption at at higher higher pressure pressure problems of silica gel utilization as adsorbent. This means that water adsorbed/desorbed by silica gel will be a part of its total adsorption capacity at lower pressure or normal operating conditions of the cycle. This will result in a large amount of adsorbent material required to achieve the desired Appl. Syst. Innov. 2020, 3, x FOR PEER REVIEW 5 of 19

Appl.is one Syst. of Innov. the2020 major, 3, 26 problems of silica gel utilization as adsorbent. This means that water5 of 20 adsorbed/desorbed by silica gel will be a part of its total adsorption capacity at lower pressure or normal operating conditions of the cycle. This will result in a large amount of adsorbent material outputrequired and to bulkyachieve systems the desired having output high and capital bulky cost syst [29ems–31 ].having Therefore, high capital new and cost advanced [29–31]. adsorbentTherefore, materialsnew and advanced are required adsorbent which materials can exhibit are betterrequired properties which can according exhibit better to the properties system requirements. according to Thethe system performance requirements. improvement The performance of these systems improvem is theent only of waythese forward systems for is the only development way forward and promotionfor the development of this technology. and promotion of this technology.

Figure 6. Advantages of thermal cooling technology.

3.3. Physical Adsorbents and Desired Adsorption BehaviorBehavior TheThe adsorption adsorption process process is categorized is categorized as physic as physicalal and chemical and chemical adsorption adsorption and for adsorption- and for adsorption-basedbased cooling; the cooling; phenomenon the phenomenon of physical of physical adsorption adsorption takes place takes place[32]. [The32]. materials The materials used used for forphysical physical adsorption adsorption are are known known as asphysical physical adsorbents. adsorbents. The The ideal ideal adsorbents adsorbents should should have have a higher enthalpyenthalpy ofof adsorption,adsorption, highhigh porosity,porosity, largelarge surfacesurface area, area, and and high high uptake uptake capacity capacity [ 33[33,34].,34]. RegardlessRegardless ofof the the type type of of adsorbent, adsorbent, material material with with high high uptake uptake at lower at lower partial partial pressure, pressure, and having and stepwisehaving stepwise isotherm isotherm is preferred is preferred as this will as give this better will egivefficiency better and efficiency performance and [performance35,36]. Furthermore, [35,36]. theFurthermore, phenomenon the phenomenon of hysteresis of is hyst undesirederesis is for undesired the adsorption for the adsorption process as process this will as cause this will a loss cause of inea lossfficiency. of inefficiency. Many researchers Many researchers have used have silica used gel [37silica,38], gel zeolite [37,38], [39 ,zeolite40], and [39,40], functional and adsorbentfunctional materialadsorbent such material as FAM such Z05 as FAM [41], Z01Z05 [41], [42], Z01 Z02 [42], [43], Z02 and [43], [44] and for [44] different for different applications. applications. All these All adsorbentsthese adsorbents show goodshow adsorption good adsorption characteristics, characteristic especiallys, especially silica gel silica and gel zeolites. and zeolites. It is found It is that found the usethat of the zeolite use of in zeolite natural in gas-driven natural gas-driven heat pumps heat can pumps reduce thecan energyreduce requirements the energy requirements of a conventional of a householdconventional boiler household by up to boiler 30% [by40 ].up to 30% [40]. 2 ActivatedActivated carboncarbon (AC) (AC) is is an an eff effectiveective adsorbent adsorbent which which has has a surface a surface area ofarea 500–1500 of 500–1500 m /g [45m2]/g and [45] it canand adsorb it can refrigerantsadsorb refrigerants such as R134a,such as ammonia, R134a, ammo ethanol,nia, and ethanol, methanol and withmethanol a high with uptake a high rate [uptake46–48]. ACratehas [46–48]. a low AC adsorption has a low heat adsorption (1800–2000 heat kJ/ kg)(1800–2000 and poor kJ/kg) thermal and conductivity poor thermal (0.4 conductivity W/(m K)) [(0.449]. 2 · TheW/(m surface·K)) [49]. area The of surface silica gel area is 100of silica to 1000 gel mis 100/g and to 1000 it has m a2/g regeneration and it has a temperatureregeneration oftemperature 50–120 ◦C dependingof 50–120 °C on depending its type. It hason largeits type. adsorption It has large capacity, adsorption low mass capacity, transfer, low and mass large transfer, adsorption and heat large of 2500–2800adsorption kJ heat/kg. of Low 2500–2800 mass transfer kJ/kg. Low is not mass a desirable transfer phenomenon is not a desirable for thermally phenomenon activated for thermally cooling systems.activated Thecooling zeolites systems. have aThe high zeolites adsorption have heat a high (3000–4500 adsorption kJ/kg) heat and (3000–4500 poor thermal kJ/kg) conductivity and poor (0.2 W/(m K)) which reduces its heat transfer performance [50,51]. Zeolites can be regenerated at thermal conductivity· (0.2 W/(m·K)) which reduces its heat transfer performance [50,51]. Zeolites can abe temperature regenerated of at 200–300 a temperature◦C which of is 200–300 not desirable °C wh forichcooling is not desirable applications. for cooling The porosity applications. and surface The areaporosity of commercially and surface usedarea adsorbentsof commercially along used with theiradsorbents potential along applications with their are potential presented applications in Table1. are presented in Table 1.

Appl. Syst. Innov. Innov. 20202020,, 3,, x 26 FOR PEER REVIEW 6 of 19 20

Table 1. Properties of commonly used adsorbents and their potential uses. Table 1. Properties of commonly used adsorbents and their potential uses. Adsorbent Properties Potential Applications Adsorbent Properties Potential Applications 2 Organic removal Surface area: 500–1500 m /g Organic removal Activated Carbon Surface area: 500–1500 m2/g Separation of air Activated Carbon Porosity: 0.3–1.5 cm3/g Separation of air Porosity: 0.3–1.5 cm3/g Purification of gases Purification of gases Surface area: 300–400 m2/g Air separation Activated Alumina Surface area: 300–400 m2/g Air separation Activated Alumina 3 Porosity:Porosity: 0.25 cmcm3//gg Gas purificationpurification 2 SurfaceSurface area: area: 100–1000 m m2/g/g DesiccantDesiccant HVACHVAC systems systems SilicaSilica Gel Gel Porosity:Porosity: 0.4–1.2 0.4–1.2 cmcm33//gg HumidityHumidity controlcontrol of of air air DeodorizationDeodorization of of air air SurfaceSurface area: area: 2800–3500 2800–3500 m m2/2g/g GasGas masksmasks MolecularMolecular Sieves Sieves (Zeolites) (Zeolites) 3 Porosity:Porosity: 1.4–2 cmcm3//gg WastewaterWastewater purification purification Storage material material

4. MOF-Based MOF-Based Adsorption Adsorption Cooling MOFs are novel crystalline porous materials with high porosity, flexibleflexible structure, and high adsorption capacity. The basic structure of an MOF is shown in Figure7 7[ [52].52]. A typical typical MOF material material consists of an organic linker and a metal ion. The The choice choice of of metal metal ion ion and and organic organic linker linker offers offers a great variety ofof flexibilityflexibility forfor didifferentfferent applications. applications. The The combination combination of of metal metal ion ion and and organic organic linker linker can can be bechosen chosen depending depending upon upon the the gases gases and and how how much much is is to to be be adsorbed adsorbed/absorbed./absorbed. TheseThese materials can have great heat and mass transfer potential dependingdepending upon the choice of structure.structure. The associated properties of MOFs offer offer a broader look and possib possibilityility of of developing developing the the MOF-based MOF-based cooling cooling system. system.

Figure 7. BasicBasic structure structure of a metal–organic framework (MOF) [52]. [52].

MOFs have recently attracted great interest in the gas storage sector, but there have been some reports ofof aspiringaspiring coolingcooling applications. applications. The The potential potential use use of of MOFs MOFs for for cooling cooling applications applications needs needs to beto beexplored explored because because of their of their high high mass mass loading loading capacity capacity and relativelyand relatively low heats low heats of adsorption. of adsorption. They couldThey provecould prove to be anto excellentbe an excellent adsorbent adsorbent for adsorption for adsorption chillers chillers and desiccant and desiccant dehumidifiers. dehumidifiers. The wide The varietywide variety of topologies, of topologies, the highthe high scope scope of porosityof porosity and and surface surface area area [ 53[53,54],,54], andand postpost/pre-synthesis/pre-synthesis functionalization possibilities [55–59] [55–59] make MOFs suit suitableable for a wide variety of applications such as storage [60,61], [60,61], adsorption and separation [[62–65],62–65], and catalysis [[66–69].66–69]. Computational studies have have shown shown that that the use of an MOF in adsorption chillers can help to achieve a coefficient coefficient of performance greater than oneone [[70].70]. This is a great achievement because these systems always had a COP value of lessless thanthan one.one. Only limited work is available for MOF-based cooling such as that of Henninger et al. [[71],71], who depicted the potential use of MOFs in adsorption technology. The instability of MOFs is a hurdle for their use as an adsorbent for cooling applications but, to date, manymany stablestable MOFsMOFs have have been been developed. developed. Many Many MOFs MOFs are are less less stable stable toward toward water water [72 [72––75] 75]but but more more stable stable towards towards methanol, methanol, ethanol, ethanol, and and ammonia ammonia [76 [76].]. That That is is why why the the choicechoice ofof aa suitable MOF material should also consider the nature of the working fluid.fluid. Appl. Syst. Innov. Innov. 20202020,, 33,, x 26 FOR PEER REVIEW 7 of 19 20

de Lange et al. [77] tested 18 different MOFs in combination with either methanol or ethanol as a workingDe Lange pair et al.for [ 77their] tested potential 18 diff erentapplications MOFs in in combination heat pumps. with The either results methanol showed or ethanol that thermodynamicallyas a working pair CAU-3, for their UiO-67, potential and ZIF-8 applications can be employed in heat pumps.with both Themethanol results and showed ethanol thatbut UiO-67thermodynamically will show some CAU-3, instability UiO-67, during and ZIF-8 the operation. can be employed CAU-3 and with ZIF-8 both will methanol be more and effective ethanol and but stableUiO-67 for will utilization show some in adsorption instability duringchillers thewith operation. both methanol CAU-3 and and ethanol. ZIF-8 will be more effective and stableMotkuri for utilization et al. [78] in adsorptionobserved and chillers reported with the both behavior methanol of andmicroporous ethanol. and mesoporous MOFs for theirMotkuri adsorption et al. [ 78capacity.] observed The and saturation reported uptake the behavior capacity of for microporous microporous and MOFs mesoporous at low saturation MOFs for their adsorption capacity. The saturation uptake capacity for microporous MOFs at low saturation pressure (P/Po = 0.02) is observed to be greater than 4 mmol g−1. In contrast, an uptake capacity of pressure (P/P = 0.02) is observed to be greater than 4 mmol g 1. In contrast, an uptake capacity of greater than 14o mmol g−1 is observed for mesoporous MOFs at a− P/Po of 0.4. It can be concluded that, 1 dependinggreater than upon 14 mmol the grequired− is observed water foruptake, mesoporous the desired MOFs framework at a P/Po of of 0.4. material It can becan concluded be employed that, whichdepending can be upon very the advantageous required water for uptake, adsorp thetion-based desired frameworkcooling applications of material [79–82]. can be employed which can beThe very specific advantageous pore volume for adsorption-based and surface area cooling of MOFs applications strongly [ 79affect–82]. their water adsorption propertiesThe specific for adsorption pore volume or desi andccant surface cooling. area of MIL-100(Cr) MOFs strongly and a ffMIL-101(Cr)ect their water have adsorption been identified properties to possessfor adsorption large orwater desiccant adsorption cooling. quantity MIL-100(Cr) and andexceptional MIL-101(Cr) hydrothermal have been identified stability toby possess numerous large researchers,water adsorption as can quantity be observed and exceptional from Figure hydrothermal 8 [83]. The high stability adsorption by numerous uptake researchers,makes these as MOFs can be a feasibleobserved adsorbent from Figure for8 [adsorp83]. Thetion-based high adsorption cooling uptakesystems. makes Better these adsorption MOFs a characteristics, feasible adsorbent lower for requiredadsorption-based heat, and coolingstable nature systems. have Better increased adsorption the interest characteristics, of these materials lower required to be used heat, as adsorbents and stable fornature cooling have applications. increased the interest of these materials to be used as adsorbents for cooling applications.

Figure 8. AdsorptionAdsorption isotherms isotherms of of MIL-101(Cr MIL-101(Cr)) and MIL-100(Cr) compounds [83]. [83].

5. Historical Historical Background Background of of MOFs MOFs as Adsorbents Adsorbents Aristov [[84]84] inin thethe year year 2007 2007 initially initially suggested suggested the the idea idea of MOF-basedof MOF-based heat heat pumps pumps and sinceand since then thenseveral several MOFs MOFs had been had studied been studied and investigated and invest forigated their adsorptionfor their adsorption and water uptakeand water capabilities. uptake capabilities.Cu-BTC, MIL-101Cr, Cu-BTC, andMIL-101Cr, CPO-27 areand some CPO-27 of the are widely some researchedof the widely MOFs researched for their potentialMOFs for use their as potentialadsorbent use materials. as adsorbent The structural materials. details The structural of Cu-BTC details (HUST-1) of Cu-BTC can be found(HUST-1) in references can be found [85,86 in]. referencesThe process [85,86]. of water The adsorption process of and water uptake adsorption capacity ofand MOF uptake materials capacity are investigatedof MOF materials by [87 ,are88]. investigatedThe water uptake by [87,88]. capacity The water of CU-BTC uptake capacity was found of CU-BTC to be 6% was by found weight to be at 6% 22 by◦C weight and 2.7 at 22 mbar. °C andRezk 2.7 et al.mbar. [15 ]Rezk concluded et al. [15]that, concluded among di that,ﬀerent among MOFs, different the water MOFs, uptake the water capacity uptake of Cu-BTC capacity and of Cu-BTCFeBTC is and found FeBTC to be is thefound highest. to be Thisthe highest. large uptake This large capacity uptake is because capacity of is their because high porosityof their high and porositysurface area. and surface In another area. studyIn another related study to Cu-BTC, related to Gul-E-Noor Cu-BTC, Gul-E-Noor et al. [87] et showed al. [87] that showed the Cu-BTCthat the Cu-BTCnetwork network can be decomposed can be decomposed because ofbecause the presence of the presence of water of in itswater structure. in its structure. The adsorptionadsorption characteristics characteristics of MIL-101Crof MIL-101Cr have have been been investigated investigated widely widely [14,89]. [14,89]. Ehrenmann Ehrenmann et al. [89] etfound al. [89] that found MIL-101Cr that MIL-101Cr has a high-water has a high-water uptake capacity uptake at capacity low operating at low pressure operating and pressure there will and be there only willa slight be only decrease a slight in itsdecrease adsorption in its capacity adsorption over capacity time. Rezk over et time. al. [14 Rezk,15] concludedet al. [14,15] that, concluded with ethanol that, withas a working ethanol pair,as a working the adsorption pair, the behavior adsorption of MIL-101Cr behavior is of better MIL-101Cr as compared is better to MIL-100Cr,as compared MIL-53Cr, to MIL- 100Cr, MIL-53Cr, CPO-27Ni, Cu-BTC, and Fe-BTC. The results also showed that MIL-101Cr is stable Appl. Syst. Innov. 2020, 3, 26 8 of 20

CPO-27Ni, Cu-BTC, and Fe-BTC. The results also showed that MIL-101Cr is stable after 20 cycles at 25 ◦C. CPO-27 (MOF-74) is another MOF family which is attractive for use in adsorption applications. CPO-27 has four types: CPO-27Zn [90], CPO-27Co [91], CPO-27Ni [92], and CPO-27Mg [93]. Glover et al. [93] stated that all these four types of CPO-27 show a competitive water adsorption behavior. A summary of three main MOFs which can be potentially employed for adsorption-based cooling application is presented in Table2.

Table 2. Characteristics of CU-BTC, MIL-101Cr, and CPO-27.

Name of MOF Water Uptake Capacity Remarks 6% by weight CU-BTC Not stable 0.324 kgref/kgads 1.01 kg /kg MIL-101Cr ref ads Stable 0.3 kgref/kgads

CPO-27 0.1 to 0.5 kgref/kgads -

A comparative numerical analysis carried out by Bareschino et al. [94] showed that the desiccant wheel emended with MIL101@GO-6 (MILGO) has performed better in comparison to conventionally available silica gel-based desiccant wheels. Kuesgens et al. [95] tested several MOF materials and concluded that MIL-101 (Cr) has promising characteristics for use in adsorption-based cooling. Similarly, Khutia et al. [96] found that MIL-101 (Cr) has a high water uptake capacity which is desirable for their use in adsorption chillers. Yan et al. [97] employed the MIL-101 (Cr) structure and developed a novel structure, MIL101@GO-6, which has a water uptake capacity sic times higher than silica gel’s. Moreover, other different MOFs have also been investigated for their potential use in adsorption-based applications such as ISE-1 [98], 3D pillared-layer [99], MOF-5 [100], MOF-177 [100], copper-based MOF [101], MOF-801 [102], and MOF-841 [102]. Tannert et al. [103] reported desirable water uptake characteristics and thermal stability of that Al-based metal–organic framework MIL-53(Al)-TDC which has an average heat of adsorption of only 1 2.6 kJ g− . This indicates the low heat requirement of these MOFs which can be provided by the residual heat from the condenser [104]. In another study, Brandt et al. [105] concluded that MOF-177, NH2-MIL-125(Ti), and MIL-160 show excellent adsorption characteristics and they are stable under both humid and dry conditions. Shi et al. [106] also highlighted the use of MOFs to achieve higher COP of adsorption-based cooling and identified the 10 best MOFs. MOFs have the potential to be ideal adsorbent materials for this application, as they can be tuned to have desired adsorption behavior for different refrigerants. Different MOFs have also shown good characteristics for adsorption of water, methane, or other gases. Wu et al. [107] designed 424 types of tetrazolated-based MOFs and selected Zr-fcu-MOF-2Py material with the highest methane adsorption capacity. Li et al. [108,109] identified 15 MOFs with good adsorption performance of CO2 in the presence of H2O from 5109 computational ready experimental metal–organic frameworks (CoRE-MOFs). Erdos et al. [110] identified six MOFs that could satisfy the high-efficiency adsorbents in adsorption heat pumps. Chen et al. [111] found zirconium-based MOFs to be a suitable adsorbent for cooling applications. Xia et a. [112] concluded from their theoretical model that the use of COF-5 MOF enables adsorption-driven heat pumps to operate with a high coefficient of performance. UiO-66 has also been reported to be a promising adsorbent for cooling applications due to the high specific cooling effect [113,114].

6. Comparison of MOFs with Other Adsorbents Figure9 provides a comparison of conventional adsorbents and MOFs in terms of their surface area and pore volume [4]. In general, MOFs showed exceptionally high porosity, well-defined molecular adsorption sites, and a large surface area (up to 5500 m2/g) in comparison to currently used adsorbents like silica gel (1000 m2/g), zeolite (900 m2/g), and activated carbon (1300 m2/g), which suffer from low water uptake. The HKUST-1 has 93.2% better uptake as compared to silica gel RD-2060. This is Appl. Syst. Innov. 2020, 3, x FOR PEER REVIEW 9 of 19 Appl. Syst. Innov. 2020, 3, x FOR PEER REVIEW 9 of 19 6. Comparison of MOFs with Other Adsorbents 6. Comparison of MOFs with Other Adsorbents Figure 9 provides a comparison of conventional adsorbents and MOFs in terms of their surface area Figureand pore 9 provides volume a [4].comparison In general, of conventionalMOFs showed adsorbents exceptionally and MOFs high inporosity, terms of well-definedtheir surface moleculararea and adsorptionpore volume sites, [4]. and In ageneral, large surface MOFs area showed (up to 5500exceptionally m2/g) in comparison high porosity, to currently well-defined used 2 adsorbentsAppl.molecular Syst. Innov. adsorption like2020 silica, 3, 26 sites,gel (1000 and am large2/g), surfacezeolite (900area (upm2/g), to 5500and mactivated/g) in comparison carbon (1300 to currently m2/g), which9 used of 20 2 2 2 sufferadsorbents from lowlike watersilica geluptake. (1000 The m /g),HKUST-1 zeolite has (900 93 m.2%/g), better and uptakeactivated as comparedcarbon (1300 to silicam /g), gel which RD- 2060.suffer This from is lowdue waterto the uptake.higher surface The HKUST-1 area of HKUS has 93T-1.2% as better can also uptake be observed as compared from toFigure silica 10 gel [115]. RD- due to the higher surface area of HKUST-1 as can also be observed from Figure 10[ 115]. This could This2060. could This islead due to to a theconsiderable higher surface increase area in of refrigerant HKUST-1 flowas can rate, also cooling be observed capacity, from and/or Figure reduction 10 [115]. lead to a considerable increase in refrigerant flow rate, cooling capacity, and/or reduction of the ofThis the could size oflead the to adsorption a considerable cooling increase system. in refrigerantThis also highlights flow rate, th coolingat the usecapacity, of MOFs and/or will reduction improve size of the adsorption cooling system. This also highlights that the use of MOFs will improve the theof the efficiency size of theof adsorption-based adsorption cooling cooling system. systems. This also It can highlights also be notedthat the that use the of advanced MOFs will MOFs improve are efficiency of adsorption-based cooling systems. It can also be noted that the advanced MOFs are being beingthe efficiency investigated of adsorption-based with time which cooling is providing systems. a po Itssibility can also to be increase noted that the thermalthe advanced performance MOFs are of investigated with time which is providing a possibility to increase the thermal performance of thermal thermalbeing investigated cooling technologies. with time which is providing a possibility to increase the thermal performance of coolingthermal technologies.cooling technologies.

Figure 9. Comparison of conventional adsorbents and MOFs [4]. Figure 9.9. Comparison of conventional adsorbents and MOFs [[4].4].

Figure 10. Physical properties of three different MOFs [115]. Figure 10. Physical properties of three different MOFs [115]. Figure 10. Physical properties of three different MOFs [115]. The ratio between water uptake at equilibrium and maximum water uptake capacity concerning partialThe pressure ratio between for three water materials uptake shows at equilibrium that HKUST-1 and maximum is more e waterffective uptake than silicacapacity gel RD-2060concerning in The ratio between water uptake at equilibrium and maximum water uptake capacity concerning partialadsorbing pressure water for vapors three closermaterials to its shows maximum that HKUST-1 water uptake, is more in effective particular than at lowsilica partial gel RD-2060 pressure in partial pressure for three materials shows that HKUST-1 is more effective than silica gel RD-2060 in adsorbingvalues [115 water]. Figure vapors 11 reports closer the to comparisonits maximum between water dehumidificationuptake, in particular efficiency at low (η partial) predicted pressure by adsorbing water vapors closer to its maximum water uptake, in particular at low dehpartial pressure valuesthe model [115]. developed Figure 11 by reports Bareschino the compar et al. [94ison] for between silica gel anddehumidification MILGO (MIL101@GO-6)-based efficiency (ηdeh) predicted desiccant values [115]. Figure 11 reports the comparison between dehumidification efficiency (ηdeh) predicted bywheel. the model The simulations developed wereby Bareschino carried in et the al. same[94] for operating silica gel conditions and MILGO for both(MIL101@GO-6)-based desiccant wheels. by the model developed by Bareschino et al. [94] for silica gel and MILGO (MIL101@GO-6)-based desiccantIt can be observedwheel. The that simulations a MILGO-based were carried desiccant in wheelthe same has operating better dehumidification conditions for performanceboth desiccant as desiccant wheel. The simulations were carried in the same operating conditions for both desiccant compared to the silica gel desiccant wheel. The water adsorption isotherms of conventional adsorbents and MOFs are presented in Figures 12 and 13, respectively [4]. It can be noticed from the adsorption isotherms that the water uptake performance of MOFs is better with MIL-101(Cr) showing the highest capacity to adsorb water vapors. Appl.Appl. Syst.Syst. Innov.Innov. 20202020,, 33,, xx FORFOR PEERPEER REVIEWREVIEW 10 10 ofof 1920 wheels.wheels. ItIt cancan bebe observedobserved thatthat aa MILGO-baseMILGO-basedd desiccantdesiccant wheelwheel hashas betterbetter dehumidificationdehumidification performanceperformance asas comparedcompared toto thethe silicasilica gelgel desiccantdesiccant wheel.wheel. TheThe waterwater adsorptionadsorption isothermsisotherms ofof conventionalconventional adsorbentsadsorbents andand MOFsMOFs areare presentedpresented inin FiguresFigures 12Appl.12 andand Syst. 13,13, Innov. respectivelyrespectively2020, 3, 26 [4].[4]. ItIt cancan bebe noticednoticed frfromom thethe adsorptionadsorption isothermsisotherms thatthat thethe waterwater uptakeuptake10 of 20 performanceperformance ofof MOFsMOFs isis betterbetter wiwithth MIL-101(Cr)MIL-101(Cr) showingshowing thethe highesthighest capacitycapacity toto adsorbadsorb waterwater vapors.vapors. TheThe typetype ofof isothermisotherm furtherfurther revealsreveals thatthat thethe MILMIL groupgroup ofof MOFsMOFs areare moremore suitablesuitable forfor The type of isotherm further reveals that the MIL group of MOFs are more suitable for applications at applicationsapplications atat highhigh relativerelative pressurepressure [116],[116], whilewhile CPOCPO willwill bebe betterbetter atat aa loloww relativerelative pressurepressure rangerange high relative pressure [116], while CPO will be better at a low relative pressure range [117–119]. [117–119].[117,118,119]. The enthalpy of adsorption which is the heat released during the process of adsorption is crucial TheThe enthalpyenthalpy ofof adsorptionadsorption whichwhich isis thethe heatheat relereleasedased duringduring thethe processprocess ofof adsorptionadsorption isis crucialcrucial for the selection of an adsorbent as it determines the heat required for regeneration. This directly forfor thethe selectionselection ofof anan adsorbentadsorbent asas itit determinesdetermines thethe heatheat requiredrequired forfor regeneration.regeneration. ThisThis directlydirectly influences the efficiency of an adsorption cooling or heating system; the lower the adsorption heat of influencesinfluences thethe efficiencyefficiency ofof anan adsorptionadsorption coolingcooling oror heatingheating system;system; thethe lowerlower thethe adsorptionadsorption heatheat ofof a material, the less energy will be required to regenerate the material and the higher the efficiency will aa material,material, thethe lessless energyenergy willwill bebe requiredrequired toto reregenerategenerate thethe materialmaterial andand thethe higherhigher thethe efficiencyefficiency be. The calculated enthalpy of adsorption for different MOF materials is presented in Figure 14[ 77]. willwill be.be. TheThe calculatedcalculated enthalpyenthalpy ofof adsorptionadsorption foforr differentdifferent MOFMOF materialsmaterials isis presentedpresented inin FigureFigure 1414 The CAU family of MOFs has the enthalpy of adsorption in the range of 44–52 kJ/mol, whereas the [77].[77]. TheThe CAUCAU familyfamily ofof MOFsMOFs hashas thethe enthalpyenthalpy ofof adsorptionadsorption inin thethe rangerange ofof 44–5244–52 kJ/mol,kJ/mol, whereaswhereas MIL group has it in the range of 40–72 kJ/mol. The value of adsorption enthalpy for the UiO group of thethe MILMIL groupgroup hashas itit inin thethe rangerange ofof 40–7240–72 kJ/mol.kJ/mol. TheThe valuevalue ofof adsorptionadsorption enthalpyenthalpy forfor thethe UiOUiO groupgroup MOFs is found to be between 48 and 53 kJ/mol. In general, most of the MOFs have a lower enthalpy of ofof MOFsMOFs isis foundfound toto bebe betweenbetween 4848 andand 5353 kJ/mol.kJ/mol. InIn general,general, mostmost ofof thethe MOFsMOFs havehave aa lowerlower enthalpyenthalpy adsorption in comparison to conventional adsorbent materials. This further indicates that the MOF ofof adsorptionadsorption inin comparisoncomparison toto conventionalconventional adsorbadsorbentent materials.materials. ThisThis furtherfurther indicatesindicates thatthat thethe MOFMOF materials have the potential to increase the efficiency of adsorption-based cooling technologies due to materialsmaterials havehave thethe potentialpotential toto increaseincrease thethe efficiefficiencyency ofof adsorption-basedadsorption-based coolingcooling technologiestechnologies duedue the lower requirement of energy for the regeneration process [77]. toto thethe lowerlower requirementrequirement ofof energyenergy forfor thethe regenerationregeneration processprocess [77].[77].

deh FigureFigure 11. 11. ComparisonComparison between between dehumidification dehumidiﬁcationdehumidification eefficiencyefficiencyﬃciency (((ηηηdehdeh)) for for a a MIL101@GO-6 MIL101@GO-6 (MILGO) (MILGO) and andand aa silicasilicasilica gel-based gel-basedgel-based desiccant desiccantdesiccant wheel wheelwheel as a asas function aa functionfunction of the ofof relative thethe relativerelative humidity humidityhumidity (ϕ) of process ((φφ)) ofof air processprocess [94]. Reprinted airair [94].[94]. ReprintedwithReprinted permission withwith permissionpermission from [94]. Copyrightfromfrom [94].[94]. CopyrightCopyright 2017 Elsevier. 20172017 Elsevier.Elsevier.

Figure 12. Water adsorption isotherms of conventional adsorbents at 25 °C [4]. Figure 12. Water adsorption isothermsisotherms ofof conventionalconventional adsorbentsadsorbents atat 2525 ◦°CC[ [4].4]. Appl. Syst. Innov. 2020, 3, 26 11 of 20 Appl. Syst. Innov. 2020, 3, x FOR PEER REVIEW 11 of 19 Appl. Syst. Innov. 2020, 3, x FOR PEER REVIEW 11 of 19

Figure 13. Water adsorption isotherm of MOFs at 25 °C [4]. Figure 13. WaterWater adsorption isotherm of MOFs at 25 ◦°CC[ [4].4].

Figure 14. Average enthalpyenthalpy of of adsorption adsorption of of di differentﬀerent MOFs MOFs [77 [77].]. Reprinted Reprinted with with permission permission from from [77]. Figure 14. Average enthalpy of adsorption of different MOFs [77]. Reprinted with permission from [77].Copyright Copyright 2015 2015 ACS ACS Publication. Publication. [77]. Copyright 2015 ACS Publication. Apart from the above-mentioned studies, a few reviews involving related topics of CO capture Apart from the above-mentioned studies, a few reviews involving related topics of CO2 capture Apart from the above-mentioned studies, a few reviews involving related topics of CO2 capture with MOFs have appeared very recentlyrecently [[120–12120–1244].]. Demirocak Demirocak et et al. al. [125] [125] also also compared the with MOFs have appeared very recently [120–124]. Demirocak et al. [125] also compared the performance of HKUST-1 with zeolite for coolingcooling applications using the TRNSYS model. The MOF performance of HKUST-1 with zeolite for cooling applications using the TRNSYS model. The MOF adsorbent for solar adsorption refrigeration is is a nanocomposite made made from from an MOF matrix with adsorbent for solar adsorption refrigeration is a nanocomposite made from an MOF matrix with carbon nanotubes incorporatedincorporated thereintherein and and is is preferably preferably used used as as a powdera powder [126 [126,127].,127]. A A comparison comparison of carbon nanotubes incorporated therein and is preferably used as a powder [126,127]. A comparison ofdi ﬀdifferenterent adsorbent adsorbent materials materials including including MOFs MOFs is is presented presented in in Table Table3 [3 128[128].]. ItIt cancan bebe observed that ofMIL different 101(Cr)-H adsorbentO has materials a better water including uptake MOFs capacity is presented and it canin Table be regenerated 3 [128]. It can at abe temperature observed that of MIL 101(Cr)-H22O has a better water uptake capacity and it can be regenerated at a temperature of 90 MIL90 to 101(Cr)-H 140 C. The2O has temperature a better water required uptake for capacity the regeneration and it can of be SAPO regenerated 34-H O at is a alsotemperature below 100 of 90C. to 140 °C. ◦The temperature required for the regeneration of SAPO 34-H2O is2 also below 100 °C. The◦ to 140 °C. The temperature required for the regeneration of SAPO 34-H2O is also below 100 °C. The higherThe higher uptake uptake capacity capacity and and lower lower requirement requirement of ofregeneration regeneration temperature temperature is is an an indication indication that higher uptake capacity and lower requirement of regeneration temperature is an indication that MOFs can be a suitable material for adsorption cooling. MOFs can be a suitable material for adsorption cooling.

Appl. Syst. Innov. 2020, 3, 26 12 of 20

Table 3. Characteristics comparison of adsorbent materials [128].

Is Working Uptake Is Is Working Refrigerant Working Pair Temperature Capacity Refrigerant Refrigerant Pressure Thermally ( C) (kg /kg ) Toxic? Flammable? ◦ ref ads Stable? Activated Positive 80 to 200 0.29 Yes Yes Yes carbon-NH3 Activated Vacuum 80 to 100 0.45 No Yes Yes carbon-Methanol Activated Vacuum 80 to 120 0.19 Yes Yes Yes carbon-Ethanol

Silica gel-H2O Vacuum 50 to 120 0.30 Yes No No

Zeolite-H2O Vacuum 200 to 300 0.17 Yes No No

SAPO 34-H2O Vacuum 80 to 90 0.29 Yes No No

MIL 101(Cr)-H2O Vacuum 90 to 140 1 Yes No No

7. The Future of MOF-Based Adsorption Cooling While maximum adsorption capacity of silica gel is good, the working pair of silica gel and water shows a low hydrophilic characteristic and has lower water uptake, especially at lower partial pressure. The limitations of available adsorbent materials arise in the need for the development of alternative materials with higher adsorption capacity, lower regeneration temperature, and stable nature at high temperatures. The above-mentioned literature shows that MOF materials can prove to be a good alternative to commercially available adsorbent materials for these cooling technologies. Currently, more than 20,000 MOF structures are known due to the flexible and rich variety of topologies associated with these crystalline materials. The porosity and surface area of these materials is increasing with the development of each new structure. Apart from that, the associated properties of these materials can be tuned by pre- or post-methods according to the desired behavior. The research for the use of MOFs for cooling applications is a topic of interest but is still at the initial stage. Water uptake capacity, regeneration temperature, and stability are the basic figure of merits for an MOF to be used for thermal cooling applications. New advancements are in progress to make these materials best fit for this technology but most of the developed MOFs still face issues of instability that need to be overcome. Most of the MOF compounds are synthesized at a lab-scale and only a few are available at commercial scale. These materials should be tested under real conditions to check their suitability for adsorption-based cooling. A summary of different adsorption and regeneration characteristics of MOF materials is presented in Figure 15. It can be observed that the MOF materials have a lower value of regeneration temperature and better sorption capacity, which are the positive attributes to be a good adsorbent for cooling applications. Despite promising sorption properties, the thermal stability of MOFs is still a challenge and only a few MOFs have been reported which are stable at higher temperatures. The effective use of these materials will allow the exploitation of yet mostly unused low-temperature heat sources of energy which will lower the use of carbon-emitting fuels. Appl. Syst. Innov. 2020, 3, 26 13 of 20 Appl. Syst. Innov. 2020, 3, x FOR PEER REVIEW 13 of 19

Figure 15. AdsorptionAdsorption and and regeneration regeneration characteristics characteristics of MOFs. of MOFs.

8.8. Concluding Concluding RemarksRemarks GlobalGlobal energyenergy consumptionconsumption shows shows a acontinuous continuous rise rise with with households households and and buildings buildings as major as major contributorscontributors toto thisthis increase.increase. Due Due to to improved improved living living style style and and climatic climatic changes, changes, the thedemand demand for for HVACHVAC technology technology toto provideprovide indoor comfort comfort conditions conditions is isincreasing increasing at a at rapid a rapid rate. rate. The Thereduction reduction ofof energy energy consumption consumption and the the use use of of environment-friendly environment-friendly HVAC HVAC technology technology is a ismust a must to achieve to achieve lowlow energy energy andand sustainablesustainable goals. goals. In In this this regard regard,, adsorbent-based adsorbent-based thermal thermal cooling cooling technology technology is a is asuitable alternative alternative to to conventional conventional cooling cooling syst systems.ems. Adsorption-based Adsorption-based cool coolinging systems systems are available are available commercially and most of them use silica gel or zeolite as adsorbents because of their suitable commercially and most of them use silica gel or zeolite as adsorbents because of their suitable adsorption characteristics. These systems currently face issues of lower performance and bulky adsorption characteristics. These systems currently face issues of lower performance and bulky nature. The development and promotion of these systems are directly related to their performance nature. The development and promotion of these systems are directly related to their performance improvement. One way of achieving performance improvement is the development and utilization improvement. One way of achieving performance improvement is the development and utilization of of new adsorbents such as MOFs. The MOF structures have recently received considerable interest newdue adsorbents to their enhanced such as properties MOFs. The and MOF structures. structures New have concepts recently and received reports considerablehave been published interest due torecently their enhanced and successfully properties with and the structures. tools and promisin New conceptsg applications and reports for MOF. have While been the published instability recently of andMOFs successfully could be a with hurdle the for tools their and use promising as an adsorbent applications for cooling for MOF.applications, While theto date instability many stable of MOFs couldMOFs be have a hurdle been developed. for their use as an adsorbent for cooling applications, to date many stable MOFs have beenThis developed.paper describes the exploration and production of MOF-based cooling technologies. The centralThis idea paper of this describes study is the to highlight exploration the andpotential production use of MOFs of MOF-based for adsorption cooling and desiccant technologies. Thecooling central systems. idea of The this potential study is of to MOFs highlight as adsorb the potentialents in adsorption-driven use of MOFs for adsorptioncooling is thoroughly and desiccant coolingaccessed. systems. The main The findings potential of this of paper MOFs can as adsorbentsbe summarized in adsorption-drivenas: cooling is thoroughly accessed.• Regardless The main of the ﬁndings type of of adsorbent, this paper a canmaterial be summarized with high uptake as: at lower partial pressure and having stepwise isotherm will be preferred for adsorption-based cooling applications. This type Regardless of the type of adsorbent, a material with high uptake at lower partial pressure and • of adsorbent material will give better efficiency and performance. having stepwise isotherm will be preferred for adsorption-based cooling applications. This type of adsorbent material will give better eﬃciency and performance. Appl. Syst. Innov. 2020, 3, 26 14 of 20

The adsorption-based cooling with conventional adsorbent material such as silica gel or zeolites • normally have a COP value less than one but the simulation studies available in the literature showed that the use of MOF in these technologies can help to achieve a coeﬃcient of performance greater than one. Better adsorption characteristics, lower required heat, and stable nature has increased the interest • of these materials to be used as adsorbents for cooling applications. MIL-101Cr has a high water uptake capacity at low operating pressure and there will be only a slight decrease in its adsorption capacity over time. The results presented in the literature showed that HKUST-1 has 93.2% better uptake as compared • to silica gel RD-2060. The high-water uptake capacity of HKUST-1 shows that it could be a suitable adsorbent material for adsorption-based cooling. Furthermore, the literature survey showed that Cu-BTC and CPO-27 are some of the other widely • researched MOFs for their potential use as adsorbent materials for these applications. HKUST-1/water, MIL101/water, UiO-66/water, COF-5/ethanol and Maxsorb III/ethanol working • pairs have the potential to increase the performance of adsorption cooling technologies.

While MOF materials have a huge potential for adsorption-based cooling technologies, additional research is required to develop the perfect models to accurately predict the performance of MOF-based cooling systems.

Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

1. Isaac, M.; Van Vuuren, D.P.Modeling global residential sector energy demand for heating and air conditioning in the context of climate change. Energy Policy 2009, 37, 507–521. [CrossRef] 2. Rezk, A.R.M. Theoretical and Experimental Investigation of Silica Gel/Water Adsorption Refrigeration Systems. Ph.D. Thesis, University of Birmingham, Birmingham, UK, 2012. 3. Sharafian, A.; Bahrami, M. Assessment of adsorber bed designs in waste-heat driven adsorption cooling systems for vehicle air conditioning and refrigeration. Renew. Sustain. Energy Rev. 2014, 30, 440–451. [CrossRef] 4. AL-Dadah, R.; Mahmoud, S.; Elsayed, E.; Youssef, P.; Al-Mousawi, F. Metal-organic framework materials for adsorption heat pumps. Energy 2020, 190, 116356. [CrossRef] 5. Eurostat Database for Energy Statistics. Available online: http://ec.europa.eu/eurostat/web/energy/ publications (accessed on 24 March 2018). 6. Rafique, M.M.; Gandhidasan, P.; Rehman, S.; Al-Hadhrami, L.M. A review on desiccant based evaporative cooling systems. Renew. Sustain. Energy Rev. 2015, 45, 145–159. [CrossRef] 7. Rafique, M.M.; Rehman, S. Solar Electrification and Zero Energy Rural Communities. In Smart Village Technology; Springer: Cham, Switzerland, 2020; pp. 329–340. 8. Rehman, S.; Rafique, M.M.; Alhems, L.M.; Alam, M. Development and Implementation of Solar Assisted Desiccant Cooling Technology in Developing Countries: A Case of Saudi Arabia. Energies 2020, 13, 524. [CrossRef] 9. Rafique, M.M.; Gandhidasan, P.; Bahaidarah, H.M.; Shakir, M.A. Thermal and exergetic performance evaluation of an absorption type desiccant dehumidifier. Environ. Prog. Sustain. Energy 2018, 37, 1411–1423. [CrossRef] 10. Balaras, C.A.; Grossman, G.; Henning, H.M.; Ferreira, C.A.I.; Podesser, E.; Wang, L.; Wiemken, E. Solar air conditioning in Europe—An overview. Renew. Sustain. Energy Rev. 2007, 11, 299–314. [CrossRef] 11. Rafique, M.M.; Gandhidasan, P.; Bahaidarah, H.M. Liquid desiccant materials and dehumidifiers—A review. Renew. Sustain. Energy Rev. 2016, 56, 179–195. [CrossRef] 12. Tatsidjodoung, P.; Le Pierrès, N.; Luo, L. A review of potential materials for thermal energy storage in building applications. Renew. Sustain. Energy Rev. 2013, 18, 327–349. [CrossRef] Appl. Syst. Innov. 2020, 3, 26 15 of 20

13. Wongsuwan, W.; Kumar, S.; Neveu, P.; Meunier, F. A review of chemical heat pump technology and applications. Appl. Therm. Eng. 2001, 21, 1489–1519. [CrossRef] 14. Fadhel, M.I.; Sopian, K.; Daud, W.R.W.; Alghoul, M.A. Review on advanced of solar assisted chemical heat pump dryer for agriculture produce. Renew. Sustain. Energy Rev. 2011, 15, 1152–1168. [CrossRef] 15. Srivastava, N.C.; Eames, I.W. A review of adsorbents and adsorbates in solid–vapour adsorption heat pump systems. Appl. Therm. Eng. 1998, 18, 707–714. [CrossRef] 16. Jeremias, F.; Fröhlich, D.; Janiak, C.; Henninger, S.K. Water and methanol adsorption on MOFs for cycling heat transformation processes. New J. Chem. 2014, 38, 1846–1852. [CrossRef] 17. Moran, M.J.; Shapiro, H.N.; Boettner, D.D.; Bailey, M.B. Fundamentals of Engineering Thermodynamics; John Wiley & Sons: Hoboken, NJ, USA, 2010. 18. Rafique, M.M. Design and Economic Evaluation of a Solar Household Electrification System. Lamp 2018, 5, 25. 19. Henning, H.M. Solar assisted air conditioning of buildings—An overview. Appl. Therm. Eng. 2007, 27, 1734–1749. [CrossRef] 20. Meunier, F. Adsorption heat powered heat pumps. Appl. Therm. Eng. 2013, 61, 830–836. [CrossRef] 21. Xia, Z.Z.; Chen, C.J.; Kiplagat, J.K.; Wang, R.Z.; Hu, J.Q. Adsorption equilibrium of water on silica gel. J. Chem. Eng. Data 2008, 53, 2462–2465. [CrossRef] 22. Gong, L.X.; Wang, R.Z.; Xia, Z.Z.; Chen, C.J. Adsorption equilibrium of water on a composite adsorbent employing lithium chloride in silica gel. J. Chem. Eng. Data 2010, 55, 2920–2923. [CrossRef] 23. Chen, C.J.; Wang, R.Z.; Xia, Z.Z.; Kiplagat, J.K. Study on a silica gel–water adsorption chiller integrated with a closed wet cooling tower. Int. J. Therm. Sci. 2010, 49, 611–620. [CrossRef] 24. Li, S.; Wu, J.Y. Theoretical research of a silica gel–water adsorption chiller in a micro combined cooling, heating and power (CCHP) system. Appl. Energy 2009, 86, 958–967. [CrossRef] 25. Grisel, R.J.; Smeding, S.F.; De Boer, R. Waste heat driven silica gel/water adsorption cooling in trigeneration. Appl. Therm. Eng. 2010, 30, 1039–1046. [CrossRef] 26. De Boer, R.; Smeding, S.F.; Mola, S. Silicagel-Water Adsorption Cooling Prototype System for Mobile Air Conditioning. In Proceedings of the Heat Powered Cycles Conference, Berlin, Germany, 7–9 September 2009. 27. Jakob, U.; Mittelbach, W. Development and Investigation of a Compact Silica Gel/water Adsorption Chiller Integrated in Solar Cooling Systems. In Proceedings of the VII Minsk International Seminar “Heat Pipes, Heat Pumps, Refrigerators, Power Sources”, Minsk, Belarus, 8–11 September 2008; pp. 8–11. 28. Chang, W.S.; Wang, C.C.; Shieh, C.C. Design and performance of a solar-powered heating and cooling system using silica gel/water adsorption chiller. Appl. Therm. Eng. 2009, 29, 2100–2105. [CrossRef] 29. Chua, H.T.; Ng, K.C.; Malek, A.; Kashiwagi, T.; Akisawa, A.; Saha, B.B. Multi-bed regenerative adsorption chiller—Improving the utilization of waste heat and reducing the chilled water outlet temperature fluctuation. Int. J. Refrig. 2001, 24, 124–136. [CrossRef] 30. Rafique, M.M. A statistical analysis of desiccant dehumidifier for air conditioning application. Int. J. Hybrid Inf. Technol. 2015, 8, 245–256. [CrossRef] 31. Rafique, M.M.; Rehman, S.; Alhems, L.M.; Lashin, A. Parametric Analysis of a Rotary Type Liquid Desiccant Air Conditioning System. Energies 2016, 9, 305. [CrossRef] 32. Rafique, M.M.; Gandhidasan, P.; Rehman, S.; Alhems, L.M. Performance analysis of a desiccant evaporative cooling system under hot and humid conditions. Environ. Prog. Sustain. Energy 2016, 35, 1476–1484. [CrossRef] 33. Wang, D.C.; Li, Y.H.; Li, D.; Xia, Y.Z.; Zhang, J.P. A review on adsorption refrigeration technology and adsorption deterioration in physical adsorption systems. Renew. Sustain. Energy Rev. 2010, 14, 344–353. [CrossRef] 34. Ullah, K.R.; Saidur, R.; Ping, H.W.; Akikur, R.K.; Shuvo, N.H. A review of solar thermal refrigeration and cooling methods. Renew. Sustain. Energy Rev. 2013, 24, 499–513. [CrossRef] 35. Aristov, Y.I. Challenging offers of material science for adsorption heat transformation: A review. Appl. Therm. Eng. 2013, 50, 1610–1618. [CrossRef] 36. Glaznev, I.S.; Ovoshchnikov, D.S.; Aristov, Y.I. Kinetics of water adsorption/desorption under isobaric stages of adsorption heat transformers: The effect of isobar shape. Int. J. Heat Mass Transf. 2009, 52, 1774–1777. [CrossRef] Appl. Syst. Innov. 2020, 3, 26 16 of 20

37. Yonezawa, Y.; Matsushita, M.; Oku, K.; Nakano, H.; Okumura, S.I.; Yoshihara, M. Morikawa, Adsorption Refrigeration System. U.S. Patent No. 4,881,376, 21 November 1989. 38. Wang, R.Z.; Oliveira, R.G. Adsorption refrigeration—An efficient way to make good use of waste heat and solar energy. Prog. Energy Combust. Sci. 2006, 32, 424–458. [CrossRef] 39. Invensor. Available online: http://www.invensor.com/en/technology/cooling-system.htm (accessed on 17 November 2017). 40. Dawoud, B.; Hoefle, P.; Bornmann, A.; Chmielewski, S.; Marburger, C. Vacuum Sorption Apparatus. U.S. Patent No. 8,544,293, 1 October 2013. 41. Shimooka, S.; Oshima, K.; Hidaka, H.; Takewaki, T.; Kakiuchi, H.; Kodama, A.; Matsuda, H. The evaluation of direct cooling and heating desiccant device coated with FAM. J. Chem. Eng. Jpn. 2007, 40, 1330–1334. [CrossRef] 42. Kakiuchi, H.; Shimooka, S.; Iwade, M.; Oshima, K.; Yamazaki, M.; Terada, S.; Takewaki, T. Novel water vapor adsorbent FAM-Z01 and its applicability to an adsorption heat pump. Kagaku Kogaku Ronbunshu 2005, 31, 361–364. [CrossRef] 43. Kakiuchi, H.; Shimooka, S.; Iwade, M.; Oshima, K.; Yamazaki, M.; Terada, S.; Watanabe, H.; Takewaki, T. Water vapor adsorbent FAM-Z02 and its applicability to adsorption heat pump. Kagaku Kogaku Ronbunshu 2005, 31, 273–277. [CrossRef] 44. MITSUBISHI PLASTICS, Zeolitic Water Vapor Adsorbent: AQSOA. Available online: http://www. aaasaveenergy.com/products/001/pdf/AQSOA_1210E.pdf (accessed on 16 March 2018). 45. Wang, L.W.; Wang, R.Z.; Oliveira, R.G. A review on adsorption working pairs for refrigeration. Renew. Sustain. Energy Rev. 2009, 13, 518–534. [CrossRef] 46. Saha, B.B.; Habib, K.; El-Sharkawy, I.I.; Koyama, S. Adsorption characteristics and heat of adsorption measurements of R-134a on activated carbon. Int. J. Refrig. 2009, 32, 1563–1569. [CrossRef] 47. Habib, K.; Saha, B.B.; Rahman, K.A.; Chakraborty, A.; Koyama, S.; Ng, K.C. Experimental study on adsorption kinetics of activated carbon/R134a and activated carbon/R507A pairs. Int. J. Refrig. 2010, 33, 706–713. [CrossRef] 48. Askalany, A.A.; Saha, B.B.; Ahmed, M.S.; Ismail, I.M. Adsorption cooling system employing granular activated carbon–R134a pair for renewable energy applications. Int. J. Refrig. 2013, 36, 1037–1044. [CrossRef] 49. Zhequan, J.I.N.; Bo, T.I.A.N.; Liwei, W.A.N.G.; Ruzhu, W.A.N.G. Comparison on thermal conductivity and permeability of granular and consolidated activated carbon for refrigeration. Chin. J. Chem. Eng. 2013, 21, 676–682. 50. Dawoud, B.; Sohel, M.I.; Freni, A.; Vasta, S.; Restuccia, G. On the effective thermal conductivity of wetted zeolite under the working conditions of an adsorption chiller. Appl. Therm. Eng. 2011, 31, 2241–2246. [CrossRef] 51. Yang, R.T. Adsorbents: Fundamentals and Applications; John Wiley & Sons: Hoboken, NJ, USA, 2003. 52. Sharmin, E.; Zafar, F. Introductory Chapter: Metal Organic Frameworks (MOFs). In Metal-Organic Frameworks; IntechOpen: London, UK, 2016. 53. Farha, O.K.; Eryazici, I.; Jeong, N.C.; Hauser, B.G.; Wilmer, C.E.; Sarjeant, A.A.; Snurr, R.Q.; Nguyen, S.T.; Yazaydin, A.O.; Hupp, J.T. Metal–organic framework materials with ultrahigh surface areas: Is the sky the limit. J. Am. Chem. Soc. 2012, 134, 15016–15021. [CrossRef] 54. Furukawa, H.; Ko, N.; Go, Y.B.; Aratani, N.; Choi, S.B.; Choi, E.; Yaghi, O.M. Ultrahigh porosity in metal-organic frameworks. Science 2010, 329, 424–428. [CrossRef][PubMed] 55. Yang, Q.; Wiersum, A.D.; Llewellyn, P.L.; Guillerm, V.; Serre, C.; Maurin, G. Functionalizing porous zirconium terephthalate UiO-66 (Zr) for natural gas upgrading: A computational exploration. Chem. Commun. 2011, 47, 9603–9605. [CrossRef] 56. Cmarik, G.E.; Kim, M.; Cohen, S.M.; Walton, K.S. Tuning the adsorption properties of UiO-66 via ligand functionalization. Langmuir 2012, 28, 15606–15613. [CrossRef][PubMed] 57. Tanabe, K.K.; Wang, Z.; Cohen, S.M. Systematic functionalization of a metal organic framework via − a postsynthetic modification approach. J. Am. Chem. Soc. 2008, 130, 8508–8517. [CrossRef] 58. Kim, M.; Cahill, J.F.; Su, Y.; Prather, K.A.; Cohen, S.M. Postsynthetic ligand exchange as a route to functionalization of ‘inert’metal–organic frameworks. Chem. Sci. 2012, 3, 126–130. [CrossRef] Appl. Syst. Innov. 2020, 3, 26 17 of 20

59. Goesten, M.G.; Juanalcaniz, J.; Ramosfernandez, E.V.; Gupta, K.B.S.S.; Stavitski, E.; van Bekkum, H.; Gascon, J.; Kapteijn, F. Sulfation of metal–organic frameworks: Opportunities for acid catalysis and proton conductivity. J. Catal. 2011, 281, 177–187. [CrossRef] 60. Murray, L.J.; Dincă, M.; Long, J.R. Hydrogen storage in metal–organic frameworks. Chem. Soc. Rev. 2009, 38, 1294–1314. [CrossRef] 61. Choi, H.J.; Dincă, M.; Dailly, A.; Long, J.R. Hydrogen storage in water-stable metal–organic frameworks incorporating 1, 3-and 1, 4-benzenedipyrazolate. Energy Environ. Sci. 2010, 3, 117–123. [CrossRef] 62. Gücüyener, C.; van den Bergh, J.; Gascon, J.; Kapteijn, F. Ethane/ethene separation turned on its head: Selective ethane adsorption on the metal organic Framework ZIF-7 through a gate-opening mechanism. − J. Am. Chem. Soc. 2010, 132, 17704–17706. [CrossRef][PubMed] 63. van den Bergh, J.; Gücüyener, C.; Pidko, E.A.; Hensen, E.J.; Gascon, J.; Kapteijn, F. Understanding the Anomalous Alkane Selectivity of ZIF-7 in the Separation of Light Alkane/Alkene Mixtures. Chem. A Eur. J. 2011, 17, 8832–8840. [CrossRef][PubMed] 64. Li, J.R.; Kuppler, R.J.; Zhou, H.C. Selective gas adsorption and separation in metal–organic frameworks. Chem. Soc. Rev. 2009, 38, 1477–1504. [CrossRef] 65. Couck, S.; Denayer, J.F.; Baron, G.V.; Rémy, T.; Gascon, J.; Kapteijn, F. An amine-functionalized MIL-53 metal organic framework with large separation power for CO and CH . J. Am. Chem. Soc. 2009, 131, − 2 4 6326–6327. [CrossRef][PubMed] 66. Gascon, J.; Hernández-Alonso, M.D.; Almeida, A.R.; van Klink, G.P.; Kapteijn, F.; Mul, G. Isoreticular MOFs as eﬃcient photocatalysts with tunable band gap: An operando FTIR study of the photoinduced oxidation of propylene. ChemSusChem 2008, 1, 981–983. [CrossRef][PubMed] 67. Gascon, J.; Aktay, U.; Hernandez-Alonso, M.D.; van Klink, G.P.; Kapteijn, F. Amino-based metal-organic frameworks as stable, highly active basic catalysts. J. Catal. 2009, 261, 75–87. [CrossRef] 68. Hasegawa, S.; Horike, S.; Matsuda, R.; Furukawa, S.; Mochizuki, K.; Kinoshita, Y.; Kitagawa, S. Three-dimensional porous coordination polymer functionalized with amide groups based on tridentate ligand: Selective sorption and catalysis. J. Am. Chem. Soc. 2007, 129, 2607–2614. [CrossRef] 69. Lee, J.; Farha, O.K.; Roberts, J.; Scheidt, K.A.; Nguyen, S.T.; Hupp, J.T. Metal–organic framework materials as catalysts. Chem. Soc. Rev. 2009, 38, 1450–1459. [CrossRef] 70. Jenks, J.J.; Motkuri, R.K.; TeGrotenhuis, W.; Paul, B.K.; McGrail, B.P. Simulation and experimental study of metal organic frameworks used in adsorption cooling. Heat Transf. Eng. 2017, 38, 1305–1315. [CrossRef] 71. Henninger, S.K.; Schmidt, F.P.; Henning, H.M. Water adsorption characteristics of novel materials for heat transformation applications. Appl. Therm. Eng. 2010, 30, 1692–1702. [CrossRef] 72. Burtch, N.C.; Jasuja, H.; Walton, K.S. Water stability and adsorption in metal–organic frameworks. Chem. Rev. 2014, 114, 10575–10612. [CrossRef] 73. Canivet, J.; Fateeva, A.; Guo, Y.; Coasne, B.; Farrusseng, D. Water adsorption in MOFs: Fundamentals and applications. Chem. Soc. Rev. 2014, 43, 5594–5617. [CrossRef] 74. Ul Qadir, N.; Said, S.A.; Bahaidarah, H.M. Structural stability of metal organic frameworks in aqueous media–Controlling factors and methods to improve hydrostability and hydrothermal cyclic stability. Microporous Mesoporous Mater. 2015, 201, 61–90. [CrossRef] 75. Low, J.J.; Benin, A.I.; Jakubczak, P.; Abrahamian, J.F.; Faheem, S.A.; Willis, R.R. Virtual high throughput screening conﬁrmed experimentally: Porous coordination polymer hydration. J. Am. Chem. Soc. 2009, 131, 15834–15842. [CrossRef] 76. Critoph, R.E.; Zhong, Y. Review of trends in solid sorption refrigeration and heat pumping technology. Proc. Inst. Mech. Eng. Part E J. Process Mech. Eng. 2005, 219, 285–300. [CrossRef] 77. de Lange, M.F.; van Velzen, B.L.; Ottevanger, C.P.; Verouden, K.J.; Lin, L.C.; Vlugt, T.J.; Kapteijn, F. Metal–Organic Frameworks in Adsorption-Driven Heat Pumps: The Potential of Alcohols as Working Fluids. Langmuir 2015, 31, 12783–12796. [CrossRef][PubMed] 78. Motkuri, R.K.; Annapureddy, H.V.; Vijaykumar, M.; Schaef, H.T.; Martin, P.F.; McGrail, B.P.; Thallapally, P.K. Fluorocarbon adsorption in hierarchical porous frameworks. Nat. Commun. 2014, 5, 4368. [CrossRef] 79. Henninger, S.K.; Jeremias, F.; Kummer, H.; Schossig, P.; Henning, H.M. Novel sorption materials for solar heating and cooling. Energy Procedia 2012, 30, 279–288. [CrossRef] Appl. Syst. Innov. 2020, 3, 26 18 of 20

80. Mahzoon, S.; Fatemi, S.; Hashemi, S.J. Modeling Based Investigation of Ultraﬁne SAPO-34 Core-shell

Adsorbent in Cyclic Adsorption Process for Purification of Natural Gas from CO2. J. ISSN 2012, 1929, 1248. [CrossRef] 81. Chen, H.J.; Cui, Q.; Li, Q.G.; Zheng, K.; Yao, H.Q. Adsorption-desorption characteristics of water on silico-alumino-phosphate-34 molecular sieve for cooling and air conditioning. J. Renew. Sustain. Energy 2013, 5, 053129. [CrossRef] 82. Ng, E.P.; Mintova, S. Nanoporous materials with enhanced hydrophilicity and high water sorption capacity. Microporous Mesoporous Mater. 2008, 114, 1–26. [CrossRef] 83. Zheng, X.; Ge, T.S.; Wang, R.Z. Recent progress on desiccant materials for solid desiccant cooling systems. Energy 2014, 74, 280–294. [CrossRef] 84. Aristov, Y.I. Novel materials for adsorptive heat pumping and storage: Screening and nanotailoring of sorption properties. J. Chem. Eng. Jpn. 2007, 40, 1242–1251. [CrossRef] 85. Castillo, J.M.; Vlugt, T.J.; Calero, S. Understanding Water Adsorption in Cu BTC Metal Organic Frameworks. − − J. Phys. Chem. C 2008, 112, 15934–15939. [CrossRef] 86. Gul-E-Noor, F.; Jee, B.; Pöppl, A.; Hartmann, M.; Himsl, D.; Bertmer, M. Effects of varying water adsorption on a Cu 3 (BTC) 2 metal–organic framework (MOF) as studied by 1 H and 13C solid-state NMR spectroscopy. Phys. Chem. Chem. Phys. 2011, 13, 7783–7788. [CrossRef][PubMed] 87. Gul-E-Noor, F.; Michel, D.; Krautscheid, H.; Haase, J.; Bertmer, M. Time dependent water uptake in Cu 3 (btc) 2 MOF: Identification of different water adsorption states by 1 H MAS NMR. Microporous Mesoporous Mater. 2013, 180, 8–13. [CrossRef] 88. Wang, Q.M.; Shen, D.; Bülow, M.; Lau, M.L.; Deng, S.; Fitch, F.R.; Semanscin, J. Metallo-organic molecular sieve for gas separation and purification. Microporous Mesoporous Mater. 2002, 55, 217–230. [CrossRef] 89. Ehrenmann, J.; Henninger, S.K.; Janiak, C. Water Adsorption Characteristics of MIL-101 for Heat-Transformation Applications of MOFs. Eur. J. Inorg. Chem. 2011, 2011, 471–474. [CrossRef] 90. Dietzel, P.D.; Johnsen, R.E.; Blom, R.; Fjellvåg, H. Structural changes and coordinatively unsaturated metal atoms on dehydration of honeycomb analogous microporous metal–organic frameworks. Chem. A Eur. J. 2008, 14, 2389–2397. [CrossRef][PubMed] 91. Caskey, S.R.; Wong-Foy, A.G.; Matzger, A.J. Dramatic tuning of carbon dioxide uptake via metal substitution in a coordination polymer with cylindrical pores. J. Am. Chem. Soc. 2008, 130, 10870–10871. [CrossRef] [PubMed] 92. Dietzel, P.D.; Panella, B.; Hirscher, M.; Blom, R.; Fjellvåg, H. Hydrogen adsorption in a nickel based coordination polymer with open metal sites in the cylindrical cavities of the desolvated framework. Chem. Commun. 2006, 956–961. [CrossRef] 93. Glover, T.G.; Peterson, G.W.; Schindler, B.J.; Britt, D.; Yaghi, O. MOF-74 building unit has a direct impact on toxic gas adsorption. Chem. Eng. Sci. 2011, 66, 163–170. [CrossRef] 94. Bareschino, P.; Diglio, G.; Pepe, F.; Angrisani, G.; Roselli, C.; Sasso, M. Numerical Study of a MIL101 Metal Organic Framework Based Desiccant Cooling System for Air Conditioning Applications. Appl. Therm. Eng. 2017, 124, 641–651. [CrossRef] 95. Küsgens, P.; Rose, M.; Senkovska, I.; Fröde, H.; Henschel, A.; Siegle, S.; Kaskel, S. Characterization of metal-organic frameworks by water adsorption. Microporous Mesoporous Mater. 2009, 120, 325–330. [CrossRef] 96. Khutia, A.; Rammelberg, H.U.; Schmidt, T.; Henninger, S.; Janiak, C. Water sorption cycle measurements on functionalized MIL-101Cr for heat transformation application. Chem. Mater. 2013, 25, 790–798. [CrossRef] 97. Yan, J.; Yu, Y.; Ma, C.; Xiao, J.; Xia, Q.; Li, Y.; Li, Z. Adsorption isotherms and kinetics of water vapor on novel adsorbents MIL-101 (Cr)@ GO with super-high capacity. Appl. Therm. Eng. 2015, 84, 118–125. [CrossRef] 98. Henninger, S.K.; Habib, H.A.; Janiak, C. MOFs as adsorbents for low temperature heating and cooling applications. J. Am. Chem. Soc. 2009, 131, 2776–2777. [CrossRef][PubMed]

99. Karra, J.R.; Grabicka, B.E.; Huang, Y.G.; Walton, K.S. Adsorption study of CO2, CH4,N2, and H2O on an interwoven copper carboxylate metal–organic framework (MOF-14). J. Colloid Interface Sci. 2013, 392, 331–336. [CrossRef] 100. Kondo, A.; Daimaru, T.; Noguchi, H.; Ohba, T.; Kaneko, K.; Kanoh, H. Adsorption of water on three-dimensional pillared-layer metal organic frameworks. J. Colloid Interface Sci. 2007, 314, 422–426. [CrossRef] Appl. Syst. Innov. 2020, 3, 26 19 of 20

101. Lincke, J.; Lassig, D.; Moellmer, J.; Reichenbach, C.; Puls, A.; Moeller, A.; Glaser, R.; Kalies, G.; Staudt, R.; Krautscheid, H. A novel copper-based MOF material: Synthesis, characterization and adsorption studies. Microporous Mesoporous Mater. 2011, 142, 62–69. [CrossRef] 102. Furukawa, H.; Gaándara, F.; Zhang, Y.B.; Jiang, J.; Queen, W.L.; Hudson, M.R.; Yaghi, O.M. Water adsorption in porous metal–organic frameworks and related materials. J. Am. Chem. Soc. 2014, 136, 4369–4381. [CrossRef] 103. Tannert, N.; Ernst, S.J.; Jansen, C.; Bart, H.J.; Henninger, S.K.; Janiak, C. Evaluation of the highly stable metal–organic framework MIL-53 (Al)-TDC (TDC= 2, 5-thiophenedicarboxylate) as a new and promising adsorbent for heat transformation applications. J. Mater. Chem. A 2018, 6, 17706–17712. [CrossRef] 104. Cui, S.; Qin, M.; Marandi, A.; Steggles, V.; Wang, S.; Feng, X.; Nouar, F.; Serre, C. Metal-Organic Frameworks as advanced moisture sorbents for energy-eﬃcient high temperature cooling. Sci. Rep. 2018, 8, 15284. [CrossRef][PubMed] 105. Brandt, P.; Nuhnen, A.; Lange, M.; Möllmer, J.; Weingart, O.; Janiak, C. Metal–Organic Frameworks with

Potential Application for SO2 Separation and Flue Gas Desulfurization. ACS Appl. Mater. Interfaces 2019, 11, 17350–17358. [CrossRef][PubMed] 106. Shi, Z.; Liang, H.; Yang, W.; Liu, J.; Liu, Z.; Qiao, Z. Machine learning and in silico discovery of metal-organic frameworks: Methanol as a working ﬂuid in adsorption-driven heat pumps and chillers. Chem. Eng. Sci. 2020, 214, 115430. [CrossRef] 107. Wu, X.; Peng, L.; Xiang, S.; Cai, W. Computational design of tetrazolate-based metal–organic frameworks for CH 4 storage. Phys. Chem. Chem. Phys. 2018, 20, 30150–30158. [CrossRef]

108. Li, S.; Chung, Y.G.; Snurr, R.Q. High-throughput screening of metal–organic frameworks for CO2 capture in the presence of water. Langmuir 2016, 32, 10368–10376. [CrossRef] 109. Li, W.; Xia, X.; Cao, M.; Li, S. Structure–property relationship of metal–organic frameworks for alcohol-based adsorption-driven heat pumps via high-throughput computational screening. J. Mater. Chem. A 2019, 7, 7470–7479. [CrossRef] 110. Erdös, M.; de Lange, M.F.; Kapteijn, F.; Moultos, O.A.; Vlugt, T.J. In Silico Screening of Metal–Organic Frameworks for Adsorption-Driven Heat Pumps and Chillers. ACS Appl. Mater. Interfaces 2018, 10, 27074–27087. [CrossRef] 111. Chen, H.; Chen, Z.; Farha, O.K.; Snurr, R.Q. High Propane and Isobutane Adsorption Cooling Capacities in Zirconium-Based Metal–Organic Frameworks Predicted by Molecular Simulations. ACS Sustain. Chem. Eng. 2019, 7, 18242–18246. [CrossRef] 112. Xia, X.; Liu, Z.; Li, S. Adsorption Characteristics and Cooling/Heating Performance of COF-5. Appl. Therm. Eng. 2020, 176, 115442. [CrossRef] 113. Xia, X.; Cao, M.; Liu, Z.; Li, W.; Li, S. Elucidation of adsorption cooling characteristics of Zr-MOFs: Effects of structure property and working fluids. Chem. Eng. Sci. 2019, 204, 48–58. [CrossRef] 114. Sarker, M.; Song, J.Y.; Jhung, S.H. Carboxylic-acid-functionalized UiO-66-NH2: A promising adsorbent for both aqueous-and non-aqueous-phase adsorptions. Chem. Eng. J. 2018, 331, 124–131. [CrossRef] 115. Rezk, A.; Al-Dadah, R.; Mahmoud, S.; Elsayed, A. Characterisation of metal organic frameworks for adsorption cooling. Int. J. Heat Mass Transf. 2012, 55, 7366–7374. [CrossRef] 116. Elsayed, E.; Raya, A.D.; Mahmoud, S.; Elsayed, A.; Anderson, P.A. Aluminium fumarate and CPO-27 (Ni) MOFs: Characterization and thermodynamic analysis for adsorption heat pump applications. Appl. Therm. Eng. 2016, 99, 802–812. [CrossRef] 117. Elsayed, A.; Elsayed, E.; Raya, A.D.; Mahmoud, S.; Elshaer, A.; Kaialy, W. Thermal energy storage using metal–organic framework materials. Appl. Energy 2017, 186, 509–519. [CrossRef] 118. Youssef, P.G.; Dakkama, H.; Mahmoud, S.M.; AL-Dadah, R.K. Experimental investigation of adsorption water desalination/cooling system using CPO-27Ni MOF. Desalination 2017, 404, 192–199. [CrossRef] 119. Dakkama, H.J.; Youssef, P.G.; Al-Dadah, R.K.; Mahmoud, S. Adsorption ice making and water desalination system using metal organic frameworks/water pair. Energy Convers. Manag. 2017, 142, 53–61. [CrossRef] 120. Elsayed, A.; Al-Dadah, R.; Mahmoud, S.; Elshaer, A.; Bowen, J. Investigation of Efficient Adsorbents Using Transient Analysis of Adsorption Chillers with Simulink. In Proceedings of the International Conference on Heat Transfer and Fluid Flow, Prague, Czech Republic, 11 12 August 2014. − Appl. Syst. Innov. 2020, 3, 26 20 of 20

121. Nunez, T.; Henning, H.M.; Mittelbach, W. Adsorption Cycle Modeling: Characterization and Comparison of Materials. In Proceedings of the International Sorption Heat Pump Conference, Munich, Germany, 24–26 March 1999; ZAE Bayern: Garching, Germany. 122. Green, D.W.; Perry, R.H. Perry’s Chemical Engineers’ Handbook, 8th ed.; McGraw-Hill: New York, NY, USA, 2008. 123. Mu, B.; Walton, K.S. Thermal analysis and heat capacity study of metal–organic frameworks. J. Phys. Chem. C 2011, 115, 22748–22754. [CrossRef] 124. Song, L.F.; Jiao, C.L.; Jiang, C.H.; Zhang, J.; Sun, L.X.; Xu, F.; Cao, Z. Heat capacities and thermodynamic properties of MgNDC. J. Therm. Anal. Calorim. 2011, 103, 365–372. [CrossRef] 125. Demirocak, D.E.; Kabir, M.M. Performance of a Solar Thermal Adsorption Cooling System Based on Metal Organic Frameworks in Texas. In Proceedings of the InASME 2016 10th International Conference on Energy Sustainability, American Society of Mechanical Engineers, Charlotte, NC, USA, 26–30 June 2016. 126. Said, S.A.M.; Ahmed, S.; Qadir, N.U. Metal Organic Framework Adsorbent for Solar Adsorption Refrigeration. U.S. Patent No. 9,480,967, 1 November 2016. 127. Markus, S.; Mueller, U.; Kiener, C. Porous Metal Organic Frameworks as Desiccants. U.S. Patent Application 12/863,339, 23 January 2009. 128. Shi, B. Development of an MOF Based Adsorption Air Conditioning System for Automotive Application. Ph.D. Thesis, University of Birmingham, Birmingham, UK, 2015.

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