Supplementary Information Room-Temperature Synthesis of UiO-66 and Thermal Modulation of Densities of Defect Sites

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1 Supplementary Information Room-Temperature Synthesis of UiO-66 and Thermal Modulation of Densities of Defect Sites Matthew R. DeStefano, Timur Islamoglu, Sergio J. Garibay, Joseph T. Hupp*, and Omar K. Farha*,, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia

2 Table of Contents Section S1. Materials and Methods 2-3 Table S1. Experimental parameters for the synthesis of UiO-66 and its derivatives. 3 Figure S1. SEM images of UiO-66, UiO-66-NH 2, UiO-66-OH and UiO-66-NO 2 and their associated histograms. 4-5 Table S2. Values of parameters for BET surface area determination for the room temperature UiO-66 series. 5 Figure S2. PXRD patterns of simulated UiO-66 and thermally modulated UiO Figure S3. PXRD evidence of missing cluster defects in thermally modulated UiO Table S3. Values of parameters for BET surface area determination of the thermally modulated UiO-66 series. 7 Figure S4. DFT pore size distribution of thermally modulated UiO Figure S5. Titration and first derivative curves of thermally modulated UiO-66 samples. 9 Table S4. Calculated pk a s and equivalence points for thermally modulated UiO-66 samples. 10 Figure S6. Titration and first derivative curve acetic acid in 0.01 M NaNO 3 solution. 10 Section S2. Method for calculating the number defect sites from potentiometric acid-base titrations and an accompanied example References

3 Section S1. Materials and Methods Section S1-A. Materials All reagents were used as received. Zirconium(IV) propoxide solution (70 wt. % in 1- propanol), terephthalic acid, 2-aminoterephthalic acid, 2-nitroterephthalic acid, acetic acid ( 99.7%) and N,N-dimethylformamide were purchased from Sigma Aldrich. 2-hydroxyterephthalic acid was purchased from TCI America. Section S1-B. Methods Powder X-Ray Diffraction (PXRD) patterns were collected on a Rigaku Smartlab instrument with a 9 kw Cu rotating anode radiation source coupled to a multilayer optic. Samples were analyzed from 2<2θ<50 with a step size of 0.05 and scan rate of 5 /minute. N 2 Adsorption and Desorption Isotherms were collected at 77 K on either a Micrometrics ASAP 2020 (for UiO-66 synthesized at various temperatures) or Micrometrics Tristar II 3020 (for UiO- 66 functionalized derivatives). Prior to analysis, all samples were activated on a Micrometrics Smart VacPrep System. Thermally modulated UiO-66 samples and UiO-66-NH 2 were activated at 150 C for 12 hours while UiO-66-OH and UiO-66-NO 2 were activated at 80, 120 and 150 C for three hours at each temperature. A minimum of 50 mg was used for each analysis. Brunauer-Emmet-Teller (BET) surface areas (SAs) were calculated by adhering to the consistency criteria outlined by Rouquerol et al, among others. 1-4 With respect to the BET equation, " "# $(&' " " # ) = & + +'& (p $ * + $ * + p. ), p p. is the relative pressure, n is the amount of gas adsorbed, n 0 is the amount of gas necessary to form a monolayer on the adsorbent and C is the BET constant. Application of the consistency criteria was accomplished by (1) selecting a range from n(1 p p. ) vs p p. where n(1 p p. ) is increasing, (2) ensuring that the value of the BET constant, C, be positive, (3) that the relative pressure p p. at which the monolayer forms, be within the range of which p p. is chosen and (4) maximize the best fit line s R 2 value. Pore size distributions were calculated from the adsorption-desorption isotherms by using the density functional theory N 2 cylindrical pores oxide surface model. Potentiometric Acid-Base Titrations were performed with a Metrohm Titrando 905 autotitrator equipped with Dosino 800 dosing units (20 ml and 10 ml) using a procedure previously reported. Prior to each titration, calibrations were performed with 2.00 and 9.00 Metrohm buffer solutions. Sample preparation entailed using a minimum of 40 mgs of sample (previously activated for 12 H at 150 C on a Micrometrics Smart VacPrep system) that were crushed into a fine powder with a plastic spatula in a 100 ml beaker. An equivalent volume of a 0.01 M NaNO 3 solution was added (50 ml for 50 mg) and allowed to equilibrate for 18 H. Preceding each titration, a stir bar was added to the beaker and the ph was adjusted to a value of 3.00 with 0.1 M HCl. Following, the solution was titrated with a 0.1 M NaOH solution to a ph value of with an injection volume of ml at a rate of ml minute -1. In order to better visualize the equivalence points, the first derivative of the titration curve (ph vs. Volume of 0.1 M NaOH Added) was taken (dph/dv vs. Volume of 0.1 M NaOH Added). The first derivative plots were &, +4& 2

4 then subjected to Lorentzian function curve-fitting with Origin Pro V8.5 multiple peak fitting function. The associated pk a values were determined by first identifying the equivalence volumes on the first derivative plots (inflection points on ph vs ph vs. Volume of 0.1 M NaOH Added graph) and taking the ph at one-half of the titrant volume added to reach the equivalence point. Quantitative determination of the number of defect sites via potentiometric acid-base titration is explained in Section S3. Scanning Electron Microscopy (SEM) images were taken using a Hitachi SU8030 at the EPIC facility (NUANCE Center-Northwestern University). Histograms were constructed by measuring the length of 40 particles for each sample. Metal-Organic Framework Equivalents of BDC Linker BDC Linker Mass (mg) with Respect to Zr(OPr)4 UiO UiO-66-NH UiO-66-OH UiO-66-NO Table S1. Experimental parameters for the synthesis of UiO-66 and its derivatives. 3

5 a b c 4

6 d Figure S1. Scanning electron microscopy (SEM) images and associated histograms of (a) UiO (b) UiO-66-NH 2 (c) UiO-66-OH and (d) UiO-66-NO 2. Table S2. BET SAs, total pore volumes and pertinent information for satisfying the BET SA consistency criteria for the room-temperature synthesized UiO-66 derivatives. 5

7 Figure S2. Normalized (with respect to the 111 reflection at 7.3º) powder x-ray diffraction (PXRD) patterns of simulated and thermally modulated UiO-66-T (T = 25, 45, 60, 80, 95, 110 and 130ºC) samples from The intensity from is magnified 10x for clarity. 6

8 Figure S3. PXRD pattern from 2-9 for thermally modulated UiO-66 samples. The evolution of a broad peak at 4 degrees with decreasing synthesis temperature has been attributed to two overlapping reflections that arise when nanosize reo regions are present in the fcu structure. 5-6 These nanoregions result when a quarter of the SBU clusters in the unit cell are missing, yielding under coordinated clusters in the framework, giving rise to defect sites. Table S3. Pertinent values with respect to consistency criteria for determining the BET SAs of thermally modulated UiO-66 samples. 7

9 Figure S4. Normalized (with respect to pore at ~11 angstroms) pore size distribution of thermally modulated UiO-66 samples. 8

10 a b c d e f Figure S5. Acid- base titration curves (red) and first derivative curves (blue) of thermally modulated UiO-66 samples (a) 45 C (b) 60 C (c) 80 C (d) 95 C (e) 110 C and (f) 130 C. 9

11 Sample Mass of Sample (mg) Bridging -OH pk a Bridging OH Equivalence Point (ml) Acetate pk a Acetate Equivalence Point (ml) Zr-OH 2 pk a Zr-OH 2 Equivalence Point (ml) UiO UiO UiO UiO UiO UiO UiO Table S4. Mass of samples, calculated pk a s and corresponding equivalence volumes for thermally modulated UiO-66 samples that were analyzed by potentiometric acid-base titration. ph Volume 0.1 M NaOH (ml) Figure S6. Titration curve of acetic acid in 0.01 M NaNO 3 solution. The first equivalence point (EP) at ml is attributed to the NaNO 3 solution while the second EP at 0.86 ml is attributed to acetic acid (pk a = 4.92) dmv (ph) 10

12 Section S2. Calculation of the Number of Defect Sites via Potentiometric Acid-Base Titrations Explanation of Calculations: Owing to the fact that titrations are quantitative in nature and that defect sites inherently have titratable protons (under our conditions with a solution ph of 3), we are able to determine the number of defect sites in each sample. We assume that (1) each missing linker introduces two defect sites (one on each SBU it is connected to), (2) that each defect site is occupied by either an acetate moiety from the modulator or a terminal OH/-OH 2 pair derived from trace water in the employed solvents and (3) that the acetate anion will produce one titratable proton per defect site while the OH/-OH 2 pair will produce a total of three. In order to determine the number of acetate or OH/-OH 2 pairs that are present, we simply calculate the amount of NaOH titrant consumed for each species. With respect to the acetate anions, we take the difference in the amount of NaOH titrant consumed between the second (acetate) and first (µ 3 -OH) equivalence points. In a similar fashion, the amount of OH 2 species that are present can be found by taking the difference in NaOH titrant consumed between the third (Zr-OH 2 ) and second (acetate) equivalence points. From these findings, the total number of titratable protons from an OH/-OH 2 pair can be calculated by multiplying the previously determined number of OH 2 protons by three (each terminal water is deprotonated once, yielding an additional terminal hydroxyl group which we assume to be equivalent to the terminal hydroxyl group that was already present in the pair). The relative amounts of titrated protons from acetates and OH/-OH 2 pairs, with respect to each other, are then calculated and assigned the variables y and z, respectively. These values are then related to the molecular formula of UiO-66 that incorporates acetate and OH/-OH 2 pair compensating missing linker defects, Zr 6 O 4 (OH) 4 (bdc) 6-x [(OH 2 )(OH)] z*2*x (C 2 O 2 H 3 ) y*2*x, where x is the number of missing linkers in an ideal Zr 6 O 4 (OH) 4 (bdc) 6 cluster. Following, the number of missing linkers can be realized by comparing the experimental value of titrated protons from the calculated theoretical values with different numbers of missing linkers. 11

13 Example Calculation (UiO-66-25): References. (1) Rouquerol, J.; Llewellyn, P.; Rouquerol, F. Is the BET equation applicable to microporous adsorbents? Stud. Surf. Sci. Catal. 2006, 160, (2) Duren, T.; Millange, F.; Ferey, G.; Walton, K. S.; Snurr, R. Q. Calculating geometric surface areas as a characterization tool for metal-organic frameworks. J Phys Chem C 2007, 111 (42), (3) Senkovska, I.; Kaskel, S. Ultrahigh porosity in mesoporous MOFs: promises and limitations. Chem. Commun. 2014, 50 (54), (4) Wang, T. C.; Bury, W.; Gomez-Gualdron, D. A.; Vermeulen, N. A.; Mondloch, J. E.; Deria, P.; Zhang, K.; Moghadam, P. Z.; Sarjeant, A. A.; Snurr, R. Q.; Stoddart, J. F.; Hupp, J. T.; Farha, O. K. Ultrahigh Surface Area Zirconium MOFs and Insights into the Applicability of the BET Theory. J. Am. Chem. Soc. 2015, 137 (10),

14 (5) Cliffe, M. J.; Wan, W.; Zou, X. D.; Chater, P. A.; Kleppe, A. K.; Tucker, M. G.; Wilhelm, H.; Funnell, N. P.; Coudert, F. X.; Goodwin, A. L. Correlated defect nanoregions in a metal-organic framework. Nat. Commun. 2014, 5. (6) Shearer, G. C.; Chavan, S.; Bordiga, S.; Svelle, S.; Olsbye, U.; Lillerud, K. P. Defect Engineering: Tuning the Porosity and Composition of the Metal-Organic Framework UiO-66 via Modulated Synthesis. Chem. Mater. 2016, 28 (11),