Supporting information Mechanical Properties of Microcrystalline Metal-Organic Frameworks (MOFs) Measured by Bimodal Amplitude Modulated-Frequency Modulated Atomic Force Microscopy Yao Sun, Zhigang Hu, Dan Zhao,,,* and Kaiyang Zeng, * Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, 117576 Singapore Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, 117585 Singapore Correspondence and requests for materials should be addressed to Dr. Kaiyang Zeng (mpezk@nus.edu.sg) or Dr. Dan Zhao (chezhao@nus.edu.sg). S-1
Experimental Details Materials and equipments All of the reagents used were obtained from commercial suppliers and were used without further purification. Field-emission scanning electron microscope (FE-SEM) analyses were conducted on an FEI Quanta 600 SEM (20 kv) equipped with an energy dispersive spectrometer (EDS, Oxford Instruments, 80 mm 2 detector). Powder X-ray diffraction patterns were obtained on Bruker D8 Advance X-ray Powder Diffractometer equipped with a Cu sealed tube (λ = 1.54178 Å) at a scan rate of 0.02 deg s -1. TGA were performed using Shimadzu DTG 60AH Thermal Analyzer under flowing N 2 gas, with a heating rate of 10 C min -1. Solvothermal synthesis of pristine UiO-66 (Zr) 1 and UiO-66 (Hf) 2 In a typical process, benzene-1, 4-dicarboxylic acid (BDC) (83 mg) and ZrCl 4 (120 mg) or HfCl 4 (160 mg) dissolved in 20 ml of DMF/formic acid (18/2, v/v) mixed solvent were loaded into a Teflon lined autoclave and heated at 123 C for 40 hours. The product was soaked in anhydrous methanol for 3 days at room temperature, during which time the extract was decanted and fresh methanol was added every day. Then the sample was treated with anhydrous dichloromethane similarly for another 3 days. This process was carried out to wash out residual reagents in the pores. After removal of dichloromethane by decanting, the sample was dried under a dynamic vacuum at 120 C for 24 h to yield the final product with a yield of 52% based on the overall weight of ligand and metal salt. S-2
Modulated Hydrothermal (MHT) Synthesis of UiO-66-type MOFs 2-3 The ligands include 2-Aminoterephthalic acid (ATC), 2,5-Dihydroxyterephthalic acid (DOBDC), 1,2,4,5-benzenetetracarboxylic acid (BTEC) and 2,3,5,6-Tetrafluoro-1,4-benzenedicarboxylic acid (TFBDC). In a typical process, ligands (5 mmol) and ZrCl 4 (1.2 g, 5 mmol) or HfCl 4 (1.6 g, 5 mmol) were co-dissolved in a mixture of 50 ml water/acetic acid (30:20, v/v) in a flask. The flask was then placed in a 100 C oil bath for 24 h to yield about 1.8 g of colorless powder (yield: ~70% based on total mass of the reagents). The obtained MOF powders were washed by water thrice and soaked in methanol for another 3 days at room temperature, during which time the extract was decanted and fresh methanol was added every day. After removal of methanol by decanting, the sample was dried under a dynamic vacuum at 100 C for 24 h to give dry MOFs. Preparation of dispersed MOF nanoparticles on silicon substrate for AFM studies In a typical process, around 10 mg MOF powder was dispersed into 20 ml ethanol. After mild sonication, 100 µl of the resultant colloidal solution was pipetted onto clean silicon wafer substrate. The silicon wafer substrate was then left dry at 80 C for 2 h. Determination of defect concentration 4 The loss of ligands can be determined from the plateau in the temperature range from 300 to 500 C of TGA curves under air, refers to a chemical formula per Zr atom of ZrO(CO 2 ) 2 (C 6 H 4 ). Assuming BDC ligands are completely burned out at such a high temperature, final residual should be ZrO 2, the moles of Zr can be calculated. The Ligand to metal ratio (α) should be equal to 1 theoretically. If it is not, it means that the as-synthesized material is defective. In general, 12 ligands S-3
per inorganic Zr 6 O 4 (OH) 4 cluster is expected, but the defect concentration could be quantified as 12(1-α)/12. Gas sorption measurements Gas sorption isotherms of these MOFs were measured up to 1 bar using a Micromeritics ASAP 2020 surface area and pore size analyzer. Before the measurements, MOF powder (~100 mg) was degassed under reduced pressure (< 10-2 Pa) at 150 C for 12 h. UHP grade N 2 were used for all the measurements. Oil-free vacuum pumps and oil-free pressure regulators were used to prevent contamination of the samples during the degassing process and isotherm measurement. The temperatures at 77 K were maintained with a liquid nitrogen bath. Pore size distribution data were calculated from the N 2 sorption isotherms at 77 K based on non-local density functional theory (NLDFT) model or Barrett-Joyner-Halenda (BJH) model in the Micromeritics ASAP2020 software package (assuming slit pore geometry). S-4
Figure S1. Powder x-ray diffraction patterns of UiO-66(Zr)-type MOFs. S-5
Figure S2. Power x-ray diffraction patterns of UiO-66(Hf)-type MOFs. S-6
Figure S3. FESEM images of UiO-66-type MOFs: (a) UiO-66(Zr); (b) UiO-66(Zr)-NH2; (c) UiO-66(Zr)-(OH)2; (d) UiO-66(Zr)-(COOH)2; (e) UiO-66(Zr)-F4; (f) UiO-66(Hf); (g) UiO-66(Hf)-NH2; (h) UiO-66(Hf)-(OH)2; (i) UiO-66(Hf)-(COOH)2; (j) UiO-66(Hf)-F4. S-7
Figure S4. TGA curves of UiO-66(Zr)-type MOFs. S-8
Figure S5. TGA curves of UiO-66(Hf)-type MOFs. S-9
Figure S6. N 2 sorption isotherms of UiO-66(Zr)-type MOFs at 77 K. S-10
Figure S7. N 2 sorption isotherms of UiO-66(Hf)-type MOFs at 77 K. S-11
Figure S8. AM-FM stiffness images of UiO-66-type MOFs: (a) UiO-66(Zr); (b) UiO-66(Zr)-(OH)2; (c) UiO-66(Zr)-NH2; (d) UiO-66(Zr)-(COOH)2; (e) UiO-66(Zr)-F4; (f) UiO-66(Hf); (g) UiO-66(Hf)-(OH)2; (h) UiO-66(Hf)-NH2; (i) UiO-66(Hf)-(COOH)2; (j) UiO-66(Hf)-F4. S-12
Figure S9. AM-FM elastic modulus images of UiO-66(Zr) (1 st row) and UiO-66(Hf) (2 nd row) using Magnesium (1 st column), Tin (2 nd column) and glass (3 rd column) as the reference material respectively. S-13
Table S1. Porosities of the synthesized UiO-66-type MOFs. BET SA a) Pore volume b) UiO-66(Zr) 1525 0.66 UiO-66(Hf) 940 0.42 UiO-66(Zr)-NH 2 833 0.76 UiO-66(Hf)-NH 2 1067 0.52 UiO-66(Zr)-(OH) 2 1150 0.87 UiO-66(Hf)-(OH) 2 922 0.40 UiO-66(Zr)-(COOH) 2 494 0.29 UiO-66(Hf)-(COOH) 2 378 0.26 UiO-66(Zr)-(F) 4 833 0.41 UiO-66(Hf)-(F) 4 329 0.25 a m 2 g -1 ; b cm 3 g -1. S-14
Table S2. Probe specifications of AC160TS (Asylum Research, Oxford Instruments, CA, USA). Specifications First eigenmode resonant frequency, khz Second eigenmode resonant frequency, MHz First eigenmode stiffness k, N/m First eigenmode InvOLS, a) nm/v Cantilever dimension (L, W, H), µm Tip radius of curvature, nm Coating (tip and cantilever) Values 300 1.67 33~37 54.93 160, 40, 3.7 8±2 None a) InvOLS: inverse optical lever sensitivity S-15
References 1. Hu, Z.; Zhang, K.; Zhang, M.; Guo, Z.; Jiang, J.; Zhao, D., A Combinatorial Approach towards Water-Stable Metal-Organic Frameworks for Highly Efficient Carbon Dioxide Separation. ChemSusChem 2014, 7 (10), 2791-2795. 2. Hu, Z.; Nalaparaju, A.; Peng, Y.; Jiang, J.; Zhao, D., Modulated Hydrothermal Synthesis of UiO-66(Hf)-Type Metal Organic Frameworks for Optimal Carbon Dioxide Separation. Inorg. Chem. 2016, 55 (3), 1134 1141. 3. Hu, Z.; Peng, Y.; Kang, Z.; Qian, Y.; Zhao, D., A Modulated Hydrothermal (MHT) Approach for the Facile Synthesis of UiO-66-Type MOFs. Inorg. Chem. 2015, 54 (10), 4862-4868. 4. Valenzano, L.; Civalleri, B.; Chavan, S.; Bordiga, S.; Nilsen, M. H.; Jakobsen, S.; Lillerud, K. P.; Lamberti, C., Disclosing the Complex Structure of UiO-66 Metal Organic Framework: A Synergic Combination of Experiment and Theory. Chem. Mater. 2011, 23 (7), 1700-1718. S-16