Modulation of the Bifunctional Crvi to Criii Photoreduction and Adsorption Capacity in Zriv and Tiiv Benchmark Metal– Organic Frameworks

Supplementary Materials Modulation of the Bifunctional CrVI to CrIII Photoreduction and Adsorption Capacity in ZrIV and TiIV Benchmark Metal– Organic Frameworks

Paula G. Saiz 1,2,*,†, Ainara Valverde 1,3,*,†, Bárbara Gonzalez-Navarrete 4,†, Maibelin Rosales 4, Yurieth Marcela Quintero 4, Arkaitz Fidalgo-Marijuan 1,2, Joseba Orive 5, Ander Reizabal 1,3, Edurne S. Larrea 6,7, María Isabel Arriortua 1,2, Senentxu Lanceros-Méndez 1,8, Andreina García 4,9 and Roberto Fernández de Luis 1,*

1 BCMaterials, Basque Center for Materials, Applications and Nanostructures, UPV/EHU Science Park, 48940 Leioa, Spain; [email protected] (A.F.-M.); [email protected] (A.R.); [email protected] (M.I.A.); [email protected] (S.L.-M.); 2 Dept. of Geology, Science and Technology Faculty, University of the Basque Country (UPV/EHU), Barrio Sarriena s/n, Leioa, 48940 Bizkaia, Spain 3 Macromolecular Chemistry Group (LABQUIMAC), Department of Physical Chemistry Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Barrio Sarriena s/n, 48940 Leioa, Spain 4 Advanced Mining Technology Center (AMTC), University of Chile, Av. Tupper 2007 (AMTC Building), Citation: Saiz, P.G.; Valverde, A.; 8370451, Santiago, Chile; [email protected] (B.G.-N.); [email protected] (M.R.); Gonzalez-Navarrete, B.; Rosales, M.; [email protected] (Y.M.Q.); [email protected] (A.G.) Quintero, Y.M.; Fidalgo-Marijuan, 5 Dept. of Chemical Engineering, Biotechnology and Materials, Facultad de Ciencias Físicas y A.; Orive, J.; Reizabal, A.; Larrea, E.S.; Matemáticas, Universidad de Chile, Av. Beauchef 851, 8370451 Santiago, Chile; [email protected] 6 Arriortua, M.I.; Lanceros-Méndez, S.; Le Studium Research Fellow, Loire Valley Institute for Advanced Studies, 1 Rue Dupanloup, 45000 Orléans & Tours, France; [email protected] García, A.; de Luis, R.F. Modulation 7 CEMHTI—UPR3079 CNRS, 1 avenue de la Recherche Scientifique, 45100 Orléans, France of the Bi-Functional CrVI to CrIII 8 IKERBASQUE, Basque Foundation for Science, 48009 Bilbao, Spain Photo-Reduction and Adsorption 9 Mining Engineering Department, University of Chile, Av. Tupper 2069, 8370451, Santiago, Chile IV IV Capacity in Zr and Ti Benchmark * Correspondence: [email protected] (P.G.S) ; [email protected] (A.V.); Metal-orGanic Frameworks. Catalysts [email protected] (R.F.d.L.); Tel.: +34-946-12-88-11 2021, 11, 51. https://doi.org/ † These authors have contributed equally to the development of the work. 10.3390/catal11010051

Received: 25 November 2020 Accepted: 18 December 2020 Published: 1 January 2021 Table of Contents

Publisher’s Note: MDPI stays 1. Materials and processing methods S2 neutral with regard to jurisdictional 1.1. Chemicals S2 claims in published maps and 1.2. Synthesis of UiO-66 and MIL-125 materials S2 institutional affiliations. 2. Characterization techniques and procedures S3 2.1. Powder X-ray diffraction S3

2.2. Transmission Electron Microscopy S3 Copyright: © 2020 by the authors. 2.3. Thermogravimetric analysis S4 Submitted for possible open access 2.4. Sorption measurements S4 publication under the terms and 2.5. UV-Vis spectroscopy S5 conditions of the Creative Commons 2.6. Inductively coupled plasma atomic emission spectroscopy S6 Attribution (CC BY) license 3. Performance assessment S6 (http://creativecommons.org/licenses 3.1. Adsorption and photo-reduction experiments S6 /by/4.0/). 3.2. Adsorption models used to fit the kinetics data S7 3.3. Adsorption models used to fit the breakthrough adsorption curves data S7 4. Supplementary figures S8 5. Supplementary tables S11 6. References S11

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1. Materials and Processing Methods 1.1. Chemicals All chemicals and solvents used were obtained commercially. Zirconium(IV) chloride (99.5%, Alfa Aesar), titanium (IV) isopropoxide (97%, Aldrich), terephthalic acid (BDC) (97%), 2-aminoterephthalic acid (BDC-NH2) (99%, Sigma Aldrich), and N,N-dime- thylformamide (DMF) (99.8%, Sigma Aldrich), were used for the MOFs synthesis. All the chemicals were used as provided.

1.2. Synthesis of UiO-66 and MIL-125 materials UiO-66 MOFs were prepared through a slightly modified solvothermal synthesis based on the previously reported one by Audu et al. [1]. First, 0.5418 g of zirconium chloride were dissolved in 60 mL of DMF under magnetic stirring in a Pyrex® autoclave. Sub- sequently, 0.4185 g of BDC-NH2 and 1.5 mL of HCl (in the case of defective samples) are added to the solution, leading to a white or yellow suspension in the reactors vessel. Af- terwards,1.5 mL of distilled water were added to the zirconium chloride solution under continuous stirring at room temperature. Once a clear solution was obtained, the Pyrex® reactor was closed and placed in a preheated oven at 80°C for 24 hours. After that, the sample was allowed to cool down to room temperature and the obtained yellow powder was recovered by centrifugation and washed three times overnight with methanol. Fi- nally, the compound was dried at 80°C during 12 hours [2], [3]. The UiO-66 compound was synthetized in the same conditions that UiO-66-NH2, but using the same molar amounts of terephthalic acid instead of 2,5-dihydroxyterephthalic acid (doBDC). MIL-125 samples were prepared through two different synthesis methods. First, the MIL125-R was synthetized by a reflux method. For that, the terephthalic acid was dissolved in DMF in a glass balloon which leads to a yellow suspension. This suspension was subsequently heated to 110 °C and lead under magnetic stirring. After 30 minutes, MeOH was added to the solution and the reflux was turned on. 30 minutes later the Ti(iPrO)4 was added. The mixture was left under slow magnetic stirring at 110 °C during 3 days. After that reaction time, the precipitate was centrifuged and washed with methanol to remove the unreacted ligand. Finally, the obtained precipitate was dried at 80 °C. On the other hand, MIL125-H was synthetized by a hydrothermal synthesis following the same proto- col described previously by Dan-Hardi et al. [4]

2. Characterization Techniques and Procedures 2.1. Powder X-ray diffraction The powder X-ray diffraction (PXRD) patterns of the MOF samples were measured at room temperature using a Panalytical X´pert CuKα diffractometer in the following conditions: 2θ range = 5–70°, step size = 0.05°, exposure time = 10 s per step. Panalytical X´pert is a polycrystalline sample diffractometer with theta-theta geometry, a programmable slit, secondary graphite monochromator adjusted to a copper radiation and fast solid state PixCel detector adjusted to a 3.347º active length in 2θ(°). The equipment allows perform- ing high quality measurements for the subsequent data processing. Full peak fit profile matching of the MOF samples was performed. The final fittings are shown in Figure S1.

2.2. Transmission Electron Microscopy The morphology of the MOF samples was observed by transmission electron microscopy (TEM) using a Philips Supertwin CM200 transmission microscope operated at 200 kV and equipped with a LaB6 filament and EDAX-DX-4 microanalysis system. The equipment incorporates double tilting sample holder, a Megaview III rapid acquisition camera, and a high resolution (4K x 4K) and high sensitivity digital camera. Powder samples were previously dispersed in ethanol by applying ultra-sonication during 10 min. Then the na- noparticles suspension was dropped on a copper grid placed on the sample holder and

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dried under vacuum overnight. Before introducing the samples into the microscope, they were thoroughly dried under ultra-vacuum during 15 min.

2.3. Thermogravimetric analysis Thermogravimetric analysis (TGA) was performed under synthetic air (25 mL/min) with a NETZSCH STA 449F3 DSC–TGA thermo-balance instrument. This equipment allows adjusting the heating rate, controlling the measurement atmosphere and selecting the temperature program. An alumina crucible containing ca. 25 mg of the sample was heated at 5 °C min–1 in the temperature range of 30–700 °C. Thermogravimetric analysis was employed to quantify the defect degree within the UiO-66 MOFs structure. The linker-defect positions average per formula was estimated from the weight loss associated to the organic linker calcination step (at an approximate temperature of 300 °C) [5], [6] observed in the TGA curve (Figure S3a). Assuming that the complete dehydration of the zirconium hexanuclear clusters occurs before the organic linker calcination step, the theoretical weight loss associated to the linker release as a func- tion of the defect degree can be calculated (Table S2) based on the following equation:

Zr6O6+x(Linker)6-x  Zr6O12 (1) where X is the defect degree. The theoretically calculated data can be fitted to a linear equation (Figure S3b) that has been used to determine the experimental defects per formula from the experimental weight-loss obtained from the thermogravimetric curves.

2.4. Sorption measurements

CO2 sorption isotherms were measured at 273 K using a Quantachrome ISorb instrument. Approximately 10-20 mg of the MOF particles were degassed at 120°C in high vacuum for at least 12 h before the measurement. The surface area value was obtained by the fitting of the adsorption data to a linearized form of the Brunauer–Emmett–Teller (BET) equation [7]. The correlation coefficient was higher than 0.999 for all samples. Results are shown in Figure S4.

2.5. UV-Vis spectroscopy The laser absorptivity of the powder samples was measured using diffuse reflectance spectroscopy (DRS). DRS was carried out in the 200-2200 nm wavelength range with 1 nm spectral resolution using an ultraviolet, visible, near-infrared (UV-Vis-NIR) V-770 Jasco spectrophotometer equipped with a 150 mm diameter integrating sphere coated with Spectralon. A Spectralon reference was used to measure the 100% reflectance and internal attenuators were used to determine zero reflectance in order to remove background and noise. The powders were placed in a quartz cuvette, sealed, and mounted on a Teflon sample holder for the DRS measurement. The measured reflectance spectra were subsequently converted to Kubelka-Munk (K-M) absorption factors to evaluate the absorption spectra of the powders. This conversion was performed using the K-M equation: f (R)=(1R2)/2R , with R representing the measured reflectivity of the powders. UV-Vis spectra for liquid samples were recorded using a Spectronic 20 Genesys spectrophotometer. Absorbance at single wavelength at the maximum of the fingerprint peak absorbance for chromate CrVI (λmax = 540 nm) was recorded. For CrVI quantification in the photoreduction experiments, a simplified methodology based on a previously reported one for 1,5-Diphenylcarbazide was used. [8], [9] Highly concentrated CrVI stock solution was prepared with distilled water. Several solutions of lower concentrations were prepared in order to obtain the calibration curve at the above-mentioned wavelength.

2.6. Inductively coupled plasma atomic emission spectroscopy An Oriba Yobin Yvon Activa atomic emission spectrometer with inductively-coupled plasma (ICP-AES) was used to quantify chromium total concentration in solution. The

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system is equipped with a glass and Teflon nebulizer system, which enables samples from acidic digestion to be determined using HF. The equipment is controlled by a computer with Activa Analyst 5.4 software. It allows sequential multi-elemental analysis as well as numerous analytical requirements to be met due to the large linear interval that charac- terizes this technique, which in turn facilitates the analysis of majority and minority ele- ments. For the adsorption assays, samples were diluted until the detection limits of the equipment and triplicate measurements were performed.

3. Performance Assessment 3.1. Adsorption and photo-reduction experiments Adsorption kinetics curves: Adsorption kinetics experiments for the different MOF samples were conducted at room temperature, 200 mg of MOF adsorbent were dispersed in 50 mL of a 5 ppm CrVI or CrIII solution. The solutions were stirred under magnetic stirring at 400 rpm and samples were taken at different times. After that, the suspension was filtrated with a hydrophilic 0.20 µm filter, acidified for its stabilization, and finally ana- lyzed by means of ICP-AES. Adsorbents were dried and collected for future characterization after the adsorption experiments. pH of the chromium solutions was kept below 3.5 to prevent chromium oxide precipitation. The absence of chromium oxide precipitation was confirmed experimentally, monitoring the CrIII concentration on the CrIII stock solution over a period of two months, which remained constant. Photoreduction curves: Photo-reduction experiments were conducted in a 5 ppm CrVI solution using 0.25 g/L and under UVA light. 50 mg of the MOF samples were dispersed in 100 mL of a 5 ppm CrVI solution under stirring in the dark. Once adsorption equilibrium conditions were achieved, light was turned on and 5 mL aliquots were taken at different times under illuminated conditions. The experiments were performed in a LuzChem LZC- 4V photoreactor equipped with 14 lamps emitting in the ultraviolet range. Additional experiments were performed using visible lamps and also under a concentration of 0.35 g/L.

3.2. Adsorption models used to fit the kinetics data 3.2.1. Bangham model [10]:

/ 𝑞 =𝑘 ·𝑡 (2)

where 𝑞 is the amount of adsorbate adsorbed at a time t, 1/m provides an idea of the kinetics order of the system and 𝑘 is the constant rate of the adsorption process.

3.2.2. Pseudo Second Order model [10]:

𝑑𝑞 =𝑘 (𝑞 −𝑞 ) (3) 𝑑𝑡

-1 where 𝑘 (min·g·mg ) is the pseudo second order constant rate.

3.3. Adsorption models used to fit the breakthrough adsorption curves data 3.3.1. Thomas model [11]: Thomas model assumes Langmuir type adsorption kinetics and enables calculating the maximum solid phase concentration of the sorbate (in our case CrVI), as well as the absorption constant rate.

𝐶 1 = (4) 𝐶 ( ) 1+ 𝑒( · )

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where C0 and Ct are the influent and effluent concentrations (mg/mL), Kth is the Thomas constant rate (mL/mg min), q0 is the maximum dynamic adsorption capacity (mg/g), m is the mass of the adsorbent (g) and Q is the flow rate (mL/min).

3.3.2. Yoon-Nelson model [11]: Yoon-Nelson model assumes that the probabilities of adsorption and breakthrough rates of the adsorbate at the column/adsorbent are inversely proportional. The model does not require input information about the nature of the adsorbent neither of the physical characteristics of the adsorption bed. The expression of the Yoon-Nelson kinetic model is defined as follows:

() 𝐶 𝑒 (5) = ( ) 𝐶 1+𝑒

where, kYN is the rate constant (min-1), τ is the time required for 50% adsorbate breakthrough (min) and t is time (min).

4. Supplementary Figures

Figure S1. Powder X-ray diffraction profile matching analysis of: (a) MIL125-R, (b) MIL125-H, (c) UiO-66, (d) UiO-66- NH2 and (e) UiO-66-NH2-def samples.

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100 (d)

50 Weight Loss (%) 40 UiO-66 UiO-66-NH2 UiO-66-NH2-def 30 MIL125-H MIL125-R 20 0 100200300400500600 Temperature (ºC)

Figure S2. TGA curves measured for the different MOF samples.

100 58

Zr O (BDC) (b) y = 54.833 - 5.043x R= 0.99824 (a) 6 6 X 56 y = 56.764 - 5.0386x R= 0.9981 90

54 Zr O (BDC-NH2) 6 6 X 80 52

70 50 Weigth loss (%) loss Weigth WeightLoss (%) 60 48

49.5% BDC UiO66-NH2 52.4% 46 50 UiO66-NH2 def BDC-NH2 UiO66 53.2% 44 280 320 360 400 440 480 520 560 600 00.511.52 Temperature (ºC) Linker defects per formula

Figure S3. (a) Normalized TGA curves from 280 °C for the UiO-66 samples. (b) Theoretically calculated weight loss associated to linker defects in UiO-66-R (R=-H and NH2) compounds.

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140 0.25 (a)MIL125-H (b) MIL125-R 120 UiO66 UiO66-NH2 0.2 UiO66-NH2-def 100

0.15

-P) 80 0 )/(v·(1-x)) 0 60 v·(P 0.1 (P/P y = 2.8915 + 202.47x 40 MIL125-H y = 4.2969 + 120.26x MIL125-R 0.05 UiO66 y = 9.9813 + 159.3x 20 UiO66-NH2 y = 11.514 + 159.66x UiO66-NH2-def y = 17.128 + 231.3x 0 0 0 0.2 0.4 0.6 0.8 0 0.10.20.30.40.50.60.70.8 P/P P/P 0 0

Figure S4. (a) CO2 adsorption isotherm measured for the different samples and (b) Fitting of the CO2 adsorption isotherms with a linearized BET model.

100 35 III (a) CrVI (b) Cr 30 80 MIL-125-H MIL-125-H

MIL-125-R ) MIL-125-R )

-1 25 UiO-66-NH2-def UiO-66-NH2-def -1 UiO-66-NH2 UiO-66-NH2 60 UiO-66 20 UiO-66

15 (min/mg·g

40 t (min/mg·g t t/q

t/q 10 20 5

0 0 0 50 100 150 200 0 50 100 150 200 250 Time (min) Time (min)

Figure S5. (a) Cr(VI) and (b) Cr(III) adsorption kinetics for the different samples adjusted to the pseudo second order

model.

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Figure S6. Image of the UiO66-NH2/sand column experiment in closed circuit mode.

5. Supplementary Tables Table S1. Cell parameters obtained from the Le Bail fitting of the XRD patterns of the different MOF samples.

Sample a parameter (Å) c parameter (Å) UiO-66 20.671(3) --- UiO-66-NH2 20.693(3) --- UiO-66-NH2-def 20.698(2) --- MIL125-H 18.649(2) 18.136(2) MIL125-R 18.668(2) 18.156(2)

Table S2. Theoretical weight loss assigned to the organic linker calcination in UiO66 and UiO66-NH2 samples calculated for different defects degrees. Defects Molecular Weight Molecular Weight Formula % Diff degree Formula Weight (Zr6O12) Diff

0 Zr6O6,0(BDC)6,0 1628,03016 739,3368 888,69336 54,587033

0,5 Zr6O6,5(BDC)5,5 1553,97238 739,3368 814,63558 52,4227837

1 Zr6O7,0(BDC)5,0 1479,9146 739,3368 740,5778 50,0419281 UiO66 1,5 Zr6O7,5(BDC)4,5 1405,85682 739,3368 666,52002 47,4102348

2 Zr6O8,0(BDC)4,0 1331,79904 739,3368 592,46224 44,4858588

0 Zr6O6,0(BDC-NH2)6,0 1699,98 739,3368 960,6432 56,5090883

2 0,5 Zr6O6,5(BDC-NH2)5,5 1619,92 739,3368 880,5832 54,3596721

1 Zr6O7,0(BDC-NH2)5,0 1539,86 739,3368 800,5232 51,986752

6 7,5 4,5

UiO66-NH 1,5 Zr O (BDC-NH2) 1459,81 739,3368 720,4732 49,3539022

2 Zr6O8,0(BDC-NH2)4,0 1379,76 739,3368 640,4232 46,4155505

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