Study on Influencing Factors of Photocatalytic Performance of Cds/Tio2 Nanocomposite Concrete

Nanotechnology Reviews 2020; 9: 1160–1169

Research Article

Kang He, Yu Chen*, and Mengjun Mei Study on inﬂuencing factors of photocatalytic performance of CdS/TiO2 nanocomposite concrete

https://doi.org/10.1515/ntrev-2020-0074 received June 01, 2020; accepted September 02, 2020 1 Introduction

Abstract: In this study, a high-energy ball mill was used Since the industrial revolution, fossil energy has become - to composite nano TiO2 and CdS, and three kinds of an indispensable energy source for human beings, but - nanocomposite photocatalysts TiO2, CdS/TiO2 R400, and the environmental pollution problems caused by it have - CdS/TiO2 R600 were prepared, which can respond to become more and more serious; on the other hand, with visible light. The photocatalytic concrete test block was the increase in the number of cars, the emissions of prepared by mixing the nanocomposite photocatalyst automobile exhausts have become larger and larger. and other masses with cement by incorporation method. Among them, nitrogen oxides (NOx) and SO2 seriously ff To study the e ect of the photocatalyst content on the affect the quality of urban air and threaten the health of photocatalytic performance of nanoconcrete, a total of urban residents. When academia discovered that water ( ) four catalyst contents 0, 2%, 5%, and 8% were set. The molecules on the surface of titanium dioxide electrode ff - ( ) e ects of high temperature treatment 400°C and would decompose under ultraviolet light, this new ff ( ) di erent light sources ultraviolet and visible light on material TiO attracted much attention. With the ffi 2 photocatalytic e ciency were also considered. The deepening of research, the concept of using nanocom- ffi - results show that the catalytic e ciency of CdS/TiO2 posite treat pollutants has been proposed and accepted R400 under two light sources is higher than that of the by many people [1,2]. TiO2 has the advantages of safety other two photocatalysts. Compared to ultraviolet light and non-toxicity, low price, high catalytic activity, and sources, the photocatalytic efficiency of CdS/TiO nano- 2 good stability. It is recognized as the best photocatalyst composite concrete under visible light is lower, and the and has a good application prospect in the field of efficiency is below 9%. The optimal amounts of CdS/TiO2 environmental pollution treatment. However, TiO2 has a nanocomposite photocatalyst under ultraviolet and wide bandgap (anatase phase 3.2 eV), which can only be visible light are 2% and 5%, respectively. The high- excited by ultraviolet light source, and the utilization temperature treatment can improve the photocatalytic rate of sunlight is only 3% to 5%, which greatly limits performance of CdS/TiO nanocomposite photocatalyst 2 the application of TiO under general conditions [3]. by 2% to 3%. 2 Therefore, by modifying TiO2, expanding its response range to sunlight, and improving the utilization rate of sunlight has become a research hotspot. There are many Keywords: photocatalytic concrete, nanocomposite, studies on the modification of TiO2 photocatalysts. In CdS/TiO2, degradation rate, visible light terms of semiconductor recombination, semiconductor materials with a more negative conduction band

potential and smaller forbidden bandwidth than TiO2,

such as CdS, PbS, CdSe, and Cu2O nanoparticles, are used for sensitization [4–8]. The semiconductor CdS has  a bandgap of 2.42 eV and an excitation wavelength of * Corresponding author: Yu Chen, College of Civil Engineering, 495 nm or less, which has a good absorption effect on Fuzhou University, Fuzhou, 350116, China, sunlight. Through the synergistic effect of different e-mail: [email protected], tel: +86 18030219629 Kang He, Mengjun Mei: College of Civil Engineering, Fuzhou forbidden bandwidths between semiconductors, the University, Fuzhou, 350116, China light stability of the catalyst is enhanced, and the

Open Access. © 2020 Kang He et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 International License. Study on inﬂuencing factors of photocatalytic performance of CdS/TiO2 nanocomposite concrete  1161

recombination probability of photo-generated carriers is by TiO2 using a spectrophotometric method. The results reduced, so that the photocatalytic performance of the showed that the photocatalytic degradation rate of material is eﬀectively improved [9]. The role of TiO2 rhodamine B by TiO2 was higher in acidic conditions phase composition, nanocrystalline sizes, carbon con- than in alkaline conditions. Yang et al. [25] prepared tent in its diﬀerent forms in establishing static and silver and vanadium oxide co-doped TiO2 by a one-step dynamic magnetic response of our samples will be sol–gel solvothermal method in the presence of a discussed by Typek et al. [10]. Ruot et al. [11] used nano- triblock copolymer surfactant (P123). Song et al. [26]

TiO2 cement paste and cement mortar to degrade prepared Cu and N co-doped TiO2 nanoparticles and rhodamine B. The results show that the type of cement studied the effects of different amounts of Cu and N has little effect on the photocatalytic performance. Shen doping on the photocatalytic activity of TiO2. Shen et al. et al. [12] covered the surface of the prepared concrete [27] prepared N and Ce co-doped TiO2 by sol–gel with tens of nanometers of C–S–H and TiO2 nanoparti- method. The co-doped TiO2 can photocatalytically cles. The results show that photocatalytic ultra-smooth degrade nitrobenzene under visible light. concrete surfaces can effectively degrade methylene blue Nanoconcrete as an effective combination of nano- (MB). Teh et al. [13] discovered through research that technology and traditional civil engineering has broa- higher specific surface area can promote the adsorption dened the application range of nanotechnology and of more reactant molecules to the catalyst surface, nanomaterials, and also solved many problems that thereby avoiding the recombination of photo-generated traditional concrete materials are difficult to solve. This electron–hole pairs. The low grain size increases the area has also produced a lot of research results in recent specific surface area of the catalyst and promotes the years [28–32]. Zhang et al. [33] evaluated the flexural photogenic support to turn to the surface of the catalyst strength and durability (carbonization resistance, pene- to enhance the interaction with the reactant molecules tration resistance, cracking resistance, freeze–thaw

[14]. Wang et al. [15] prepared a concrete pavement with resistance) of nano-SiO2 cement-based composite mate- emulsified asphalt as the carrier and nano-TiO2 as a rials through experimental research. Tekin et al. [34,35] photocatalytic coating. The results showed that the studied the effects of WO3 and Bi2O3 additives on the nano-TiO2 content in the coating was 8% and the micron and nanometer scales on the radiation shielding 2 spraying amount was 400 g/m . The sidewalk NOx properties of hematite serpentine concrete (HSC).He degradation rate was the highest. Two asphalt emulsions et al. [36] replaced the traditional concrete in GFRP and one cement mortar are used in the right lane and concrete composite columns with a new type of emergency lane of highway sections. After comparison, nanoconcrete and carried out a series of experimental it was found that the asphalt emulsion-based substrate studies on the mechanical properties of this new type of still has a good NO degradation effect after 572 days [16]. composite column. Cheng et al. [37–41] added a certain

Wang et al. [17–19] used photocatalytic degradation of amount of nano-siO2 to concrete to improve the phenol with anatase phase TiO2 with different grain sizes durability of concrete. Al-Swaidani [42] studied the to investigate the effect of grain size on the photo- efficiency of adding concrete binder to volcanic slag on catalytic performance of anatase phase TiO2. The results a nanometer scale. In recent years, a new method for show that when the grain size is increased from 6.6 to producing heterogeneous photocatalysts, a high-energy

26.6 nm, the photocatalytic degradation rate of TiO2 ball milling method, has been proposed. The high- nanoparticles in the anatase phase increases signifi- energy ball milling method is also called mechanochem- cantly. They believe that the increase in grain size of the ical method. The substance undergoes chemical changes anatase phase TiO2 can suppress the undesired hydro- or physical and chemical changes due to the action of quinone–benzoquinone redox reaction, thereby pro- mechanical forces. The method can realize a reaction moting the complete decomposition of phenol and that can occur only under chemical or high-temperature phenolic compounds. Saeli et al. [20–22] prepared a conditions under normal temperature conditions. In this lime mortar containing 5 wt% Ag-TiO2 and studied the paper, a high-energy ball mill was used to combine TiO2 removal activity of nitrous oxide (NOx) and volatile and CdS through mechanochemical action to make a organic compounds (VOC). The addition of dopants did CdS/TiO2 nanocomposite photocatalyst. Then, the nano- not significantly change the physical properties or curing composite CdS/TiO2 was replaced by cement by an of the lime mortar but showed excellent photocatalytic incorporation method, and the effects of different activity in sunlight. Chen et al. [23,24] studied the effect dosages (0, 2%, 5%, and 8%) on the photocatalytic of pH on the photocatalytic degradation of rhodamine B performance of concrete were studied. 1162  Kang He et al.

2 Testing process 2.3 Preparation of composite catalyst

2.1 Materials and instruments First, weigh 2 g CdS powder and 18 g TiO2 powder into a 500 mL corundum ball mill pot with a mass ratio of 1:9. The material of the ball in the tank is zirconium dioxide. The main instruments and consumables in this test The planetary ball mill is used for ball milling at a speed include QM-QX2L omnidirectional planetary ball mill; of 400 rpm for 2 h, as shown in Figure 1, and the powder UV-2600 ultraviolet visible spectrophotometer; TG16-WS was then weighed and ground with a rotating ball at a high-speed centrifuge; CJJ78-1 magnetic stirrer; SX-4-10 speed of 600 rpm for 2 h. medium temperature box resistance furnace; FA1004 CdS and TiO2 powder were added to a 500 mL analytical balance; small pure slurry mixer; 250 W high- corundum ball mill at a mass ratio of 1:9 for ball milling pressure mercury lamp; 500 W long arc xenon lamp; treatment, as shown in Figure 1. The ball milling rates 500 mL/1,000 mL beakers; 5 mL pipettes; pipette tips; are 400 rpm and 600 rpm, corresponding to two diﬀerent

5 mL centrifuge tubes; 4 mL quartz cuvettes; PO42.5 CdS/TiO2 nanocomposite photocatalyst CdS/TiO2-R400

Portland cement; 2 mm machine sand. The reagents used and CdS/TiO2-R600, respectively. The ball-milling treat- in the catalytic performance test are shown in Table 1. ment time for both nanocomposite photocatalyst was 2 h. Due to the heat generated during the ball milling process, the tank body became hot. Therefore, the ball milling tank could not be taken out immediately after the 2.2 Photocatalytic performance evaluation ball milling was finished. After the ball milling tank was method cooled to room temperature, it could be removed to avoid burns. After taking out the ball mill tank, an As there is currently no uniform photocatalytic perfor- appropriate amount of absolute ethanol was added to mance evaluation method in the world, this paper uses the tank, and the powder of the composite material was the latest x method, the method used in this experiment diffused into the absolute alcohol with sufficient agita- was to use a Shimadzu UV-2600 UV-visible spectro- tion. Finally, the processed composite material powder photometer to measure the absorbance (Abs) of the was poured into a stainless steel tray and dried in a methyl orange solution at a peak of 464 nm. Then drying box. The solid material was collected and ground according to the initial and the absorbance of the solution into a mortar. One part was directly put into the labeling at each time point A0 and An, use formula (1) to analyze record in the sample bottle, and the other part was put the degradation of methyl orange. The degradation rate of into the calcining kettle and put into the muffle furnace methyl orange is used to represent the catalytic perfor- for calcination at 400°C for 4 h. After being calcined and mance of photocatalytic concrete, and the catalytic cooled for 12 h, it was taken out into the sample bottle performance of composite catalysts is evaluated. and labeled with the record. AA− Degradation rate = 0 n (1) A0

In formula (1), A0 is the initial absorbance of methyl 2.4 Preparation of photocatalytic concrete orange when photocatalytic concrete is added and the equilibrium of adsorption and desorption is reached. An In this experiment, the photocatalytic concrete was is the absorbance of methyl orange solution at each time made by the internal mixing method. Materials used in point after light. making concrete: PO42.5 Portland cement, ordinary ﬁne

Table 1: Main reagents

Name Molecular formula Quality of raw materials Place of origin

Anatase titanium dioxide TiO2 Analytical pure Shanghai, China Cadmium sulﬁde CdS Analytical pure Shanghai, China

Methyl orange C14H14N3NaO3S Analytical pure Shanghai, China

Absolute ethanol C2H5OH 99.5% Tianjin, China Study on inﬂuencing factors of photocatalytic performance of CdS/TiO2 nanocomposite concrete  1163

Figure 1: Preparation of nanocomposite catalyst. (a) Ball mill (b) preparing process. sand with a particle size greater than 2 mm, water. The solution. Finally, the beaker was moved to a photo- mixing ratio of cement:water:sand was 1:0.4:1. Each catalytic reaction box and stirred with a magnetic stirrer concrete test block has a diameter of 80 mm and a for 30 min before the photocatalytic treatment. When the thickness of 10 mm. The average mass is 100 g. A total of solution reached the equilibrium of adsorption and three nanocatalysts were prepared in this experiment, as desorption, 4 mL of supernatant was removed and placed shown in Table 2. To study the effect of high temperature in a centrifuge tube. At the same time, as shown in Figure on the photocatalytic efficiency of the catalyst, each type 3(a), when the ultraviolet light source in the box was of nanocatalyst has two temperature treatment methods, turned on, 4 mL of supernatant was extracted every one is room temperature and the other is 400°C. The 30 min. The total duration of light in each experiment was photocatalytic concrete test blocks were prepared by 2 h. The other group used the same materials and steps replacing the catalyst with cement based on the and was irradiated with fluorescent light for 2 h, as shown principles of 0%, 2%, 5%, and 8% mass, respectively. in Figure 3(b). Then, when the solution was centrifuged, Figure 2 shows all the nanocatalysts and their corre- the supernatant was collected. Spectrophotometer mea- sponding photocatalytic nanoconcrete samples in the surement was used to measure the absorbance of the experiment. After the test block was manufactured, it solution at different exposure times. According to the was placed in a standard curing room for 7 days. After absorbance A corresponding to different photocatalytic the curing was completed, the photocatalytic perfor- time, the degradation rate of methyl orange was obtained, mance of the test block could be tested. and the photocatalytic performance of the nanocomposite catalyst was evaluated.

2.5 Photocatalytic performance test

About 300 mL of 10 mg/L methyl orange solution was poured into the beaker, and then the cured photocata- 3 Test results and analyses lytic concrete test block was put into the methyl orange 3.1 Photocatalytic performance of Table 2: Nanocomposite catalyst nanoconcrete

Name Ingredient Working speed of Mass ratio A set of plain concrete control group was set up in the ball mill (rpm) (CdS/TiO2) experiment. The photocatalytic performance of the plain —— TiO2 TiO2 concrete test block under ultraviolet light and ﬂuores- CdS/TiO -R400 CdS and TiO 400 rpm 1:9 2 2 cent light was tested to obtain the methyl orange self- CdS/TiO2-R600 CdS and TiO2 600 rpm 1:9 degradation rate in the presence of the plain concrete. 1164  Kang He et al.

Figure 2: Nanocatalysts and photocatalytic nanoconcrete samples. (a) Nanocatalyst sample. (b) Photocatalytic nanoconcrete samples.

Then it was compared with three kinds of photocatalytic groups is partially due to the difference between the concrete under ultraviolet light and visible light to two light source lamps. In this test, the ultraviolet decompose methyl orange. light source is a mercury lamp, which generates less As shown in Figure 4(a), under ultraviolet light heat during work and has less impact on the experi- irradiation, the degradation rate of methyl orange in the ment; while the visible light source is a xenon lamp, plain concrete test block group gradually increased with which generates a large amount of heat during work, the increase in the light time. In the 2% photocatalytic which raises the temperature of the methyl orange concrete group, with the increase of light time, the solution. When the solution was exposed to light for degradation rate of methyl orange gradually increased, 2 hours, the temperature of the solution system and the increasing trend was more obvious. As shown in reached 60°C, and the solubility of methyl orange Figure 4(b), under visible light irradiation, the degradation reached the maximum at about 55°C. Therefore, when rate of methyl orange was almost zero in the first 30 min of thetemperatureofthesolutionisincreasedduetothe the plain concrete test block group, and the degradation xenon lamp irradiation, the undissolved methyl rate (absolute value) gradually increased with the increase orange fine particles in the original solution diffuse in the light time. In the 2% photocatalytic concrete group, into the solution, the color of the solution deepens, the degradation rate slowly increased in the first 60 min, and the absorbance increases. Therefore, in visible and the degradation rate began to decrease with time. light, the degradation rate of methyl orange in the Comparing Figure 4(a) and (b), it is found that the plain concrete group is negative and the absolute large difference in degradation rate between the two value is increasing.

Figure 3: Photocatalytic reaction box. (a) UV light source. (b) Visible light source. Study on inﬂuencing factors of photocatalytic performance of CdS/TiO2 nanocomposite concrete  1165

Figure 4: Comparison of photocatalytic performance between plain concrete and nanocomposite concrete. (a) Ultraviolet light (b) visible light.

3.2 Effect of catalyst types on R600, respectively. To further study the difference photocatalytic performance of between the photocatalytic performance of three dif- nanoconcrete ferent catalysts under ultraviolet and visible light sources, two sets of tests were set up, as shown in ( ) ( ) The photocatalytic performance of photocatalytic con- Figure 5 a and b , and each group covered 2%, 5%, and crete is related to the type of catalyst incorporated. This 8% catalyst contents. As shown in Figure 5(a), under the test evaluated the catalytic performance of three action of ultraviolet light source, when the catalyst different photocatalytic concretes, TiO2 concrete, CdS/ content is the same, the photocatalytic performance of - - TiO2-R400 concrete, and CdS/TiO2-R600 concrete. It CdS/TiO2 R400 in the three nanocomposite photocata needs to be explained here that the degradation rate of lytic concrete is slightly higher than the other two the ordinate in Figure 5 is the degradation rate of the catalysts, but the gap between the three catalysts is methyl orange test solution obtained by the photocata- within 2%. Therefore, under the action of the ultraviolet lytic reaction of each group of samples after 2 h. In light source, the difference between the three different Figure 5, the black, red, and blue columns correspond to catalysts is not obvious, and the catalytic efficiency of nanocomposite photocatalytic concrete added with three the three nanocomposite photocatalytic concretes is different catalysts TiO2, CdS/TiO2-R400, and CdS/TiO2- between 50% and 65%.

Figure 5: Photocatalytic eﬃciency of photocatalytic concrete with diﬀerent catalyst types. (a) Ultraviolet light (b) visible light. 1166  Kang He et al.

As shown in Figure 5(b),CdS/TiO2-R400 concrete has methyl orange increases first and then decreases, and the best catalytic effect under visible light irradiation, there is an optimal dosage of 5%. Compared with the followed by CdS/TiO2-R600 concrete, and the worst effect photocatalytic efficiency of three nanocomposite cata- is pure TiO2 concrete. Theoretically, pure TiO2 concrete lysts under the action of ultraviolet light source, the has very low catalytic activity under visible light. Because amount of catalyst in the visible light source has a no filter was set during the visible light irradiation in this significant effect on the photocatalytic performance of experiment, TiO2 absorbed part of the ultraviolet light in nanoconcrete. This law is especially evident in CdS/TiO2- the xenon light source, so that pure TiO2 concrete showed R400 concrete and CdS/TiO2-R600 concrete. When the catalytic activity under visible light. catalyst content is 5%, their photocatalytic efficiency is almost doubled when the content is 2% and 8%. However, nanocomposite photocatalytic concrete has low photocatalytic efficiency under visible light, and all 3.3 Effect of catalyst content on the catalytic efficiency is below 9%. catalytic performance of nanoconcrete

For the same nanocomposite photocatalytic concrete, when the amount of the catalyst is changed, its 3.4 Effect of high temperature on catalyst photocatalytic performance will fluctuate. For this performance reason, this experiment designed a total of 2%, 5%, and 8% of three catalyst levels. Similarly, Figure 6(a) Because the composite CdS/TiO2 catalyst is collided by represents the degradation rate of nanocomposite the balls at high speed in the ball mill tank, the crystal photocatalytic concrete under ultraviolet light source, structure will have defects. The high-temperature calci- and Figure 6(b) represents the degradation rate under nation can reduce the defects of the crystal structure and visible light source. reduce the impurities. However, the effect of high- As shown in Figure 6(a), when the catalyst types are temperature treatment on the performance of composite the same, under ultraviolet light irradiation, the degra- CdS/TiO2 catalysts needs to be clarified. In this test, a dation rate of methyl orange gradually decreases as the part of the composite catalyst was first placed in a muffle amount of the catalyst increases. When the catalyst furnace and calcined at a high temperature of 400°C for content is 2%, the photocatalytic concrete has the best 2 hours, and then the calcined composite catalyst was catalytic performance, and the law is the same for the used to make photocatalytic concrete. The manufac- three different types of catalysts. turing method was the same as that of the catalyst Under visible light irradiation, in Figure 6(b), with without the high temperature treated concrete. After the increase of the dosage, the degradation rate of curing, test its photocatalytic performance, compare the

Figure 6: Photocatalytic efficiency of photocatalytic concrete with different catalyst contents. (a) Ultraviolet light, (b) visible light. Study on influencing factors of photocatalytic performance of CdS/TiO2 nanocomposite concrete  1167

Figure 7: Comparison of photocatalytic performance of catalysts treated at diﬀerent temperatures under ultraviolet light sources. (a) TiO2 concrete, (b) CdS/TiO2-R400 concrete, (c) CdS/TiO2-R600 concrete.

Figure 8: Comparison of photocatalytic performance of catalysts treated at different temperatures under visible light sources. (a) TiO2 concrete, (b) CdS/TiO2-R400 concrete, (c) CdS/TiO2-R600 concrete. catalytic performance of the concrete test block made of As shown in Figure 8, under the action of visible the composite catalyst calcined at high temperature with light, the catalytic efficiency of CdS/TiO2-R400 and the concrete test block made of the untreated composite CdS/TiO2-R600 catalysts was slightly improved after catalyst, and explore the effect of high temperature on 400°C high-temperature treatment. The photocatalytic the performance of the composite photocatalyst. efficiency of the TiO2 catalyst after 400°C high- Under the action of ultraviolet light source, the red temperature treatment decreased when the content lines representing the degradation rate of the nanocom- was 5%. However, the catalytic efficiency of the TiO2 posite photocatalytic concrete after the catalyst is treated catalyst under visible light is less than 1.2%, so this at 400°C in Figure 7 are above the catalyst at normal discrete fluctuation cannot be considered and does not temperature. Therefore, the high-temperature treatment affect the evaluation of the effect of high temperature at 400°C promoted the photocatalytic performance of the on the nanocatalyst. three nanocatalysts. As shown in Figure 7(a) and (b), for catalysts TiO2 and CdS/TiO2-R400, the increase in photocatalytic efficiency after 400°C high-temperature treatment does not change with the increase in the 4 Conclusions dosage of catalyst. As shown in Figure 7(a) and (b), the two lines are approximately parallel. However, as shown The differences in photocatalytic efficiency of three ( ) - ff in Figure 7 c , for catalyst CdS/TiO2 R600, the e ect of different nanocomposite catalysts, TiO2, CdS/TiO2- - 400 high temperature treatment on the improvement of R400, and CdS/TiO2-R600, are more pronounced under photocatalytic efficiency is significantly less than the the action of visible light than under the action of dosage of 2% and 8% when the catalyst content is 5%. ultraviolet light. However, the catalytic efficiency of CdS/ 1168  Kang He et al.

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