Supporting Information

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1 Supporting Information Wiley-VCH Weinheim, Germany Synthesis of ZIF-8 and ZIF-67 by Steam-Assisted Conversion and an Investigation of Their Tribological Behaviors** Qi Shi, Zhaofeng Chen, Zhengwei Song, Jinping Li, and Jinxiang Dong* anie_ _sm_miscellaneous_information.pdf

2 Table of Contents Section S1. Materials and Instrumentation Section S2. Typical synthetic procedures for ZIFs by the solvent-free (melting) synthesis method, hydrothermal method, and steam-assisted conversion method Section S3. Solvent-free (melting) synthesis method: the formation of a eutectic mixture Section S4. Hydrothermal method: the characterization of dia(zn) and dia(co) Section S5. Steam-assisted conversion method: the characterization of ZIF-8 and ZIF-67 Section S6. Tribological behaviors of ZIF-8 and ZIF-67 2

3 Section S1. Materials and Instrumentation Materials: 2-methylimidazole (MIM, 99.0 %), zinc acetate dihydrate (Zn(OAc) 2 2H 2 O, 98.0 %) were purchased from Sigma-Aldrich Chemical Co., and cobalt acetate tetrahydrate(co(oac) 2 4H 2 O, 99.5 %), N,N-dimethylformamide (DMF, 99.5 %) were obtained from Sinopharm Group Chemical Reagent Co.. All raw chemicals were used without further purification. Distilled water (H 2 O) was prepared in our laboratory. Instrumentation: PXRD patterns were recorded with a X-ray diffractometer (Rigaku, MiniFlex Ⅱ) using Cu Kα radiation (λ= Å). Single-crystal data for dia(zn) was recorded on a single crystal X-ray diffractometer (Bruker, SMART-1000) using graphite-monochromated Mo Kα radiation (λ= Å). TG measurements were performed under a static air atmosphere on a thermogravimetric analyzer (NETZSCH, STA 409) at a heating rate of 10 C min 1. DSC thermograms were recorded on a differential scanning calorimeter (TA, Q100) under nitrogen atmosphere at a heating rate of 10 C min 1. SEM micrographs were obtained with a scanning electron microscope (JEOL, JSM-6360LV). Nitrogen sorption isotherms were measured by using an automated volumetric adsorption apparatus (Micromeritics, ASAP2010). IR spectra were recorded on an FT-IR spectrometer (Shimadzu, Prestige-21). 3

4 Section S2. Typical synthetic procedures for ZIFs by the solvent-free (melting) synthesis method, hydrothermal method, and steam-assisted conversion method Solvent-free (melting) synthesis method Zn(OAc) 2 2H 2 O (0.11 g, 0.5 mmol) and 2-methylimidazole (0.41 g, 5 mmol) were combined and sealed in a 30 ml Teflon-lined stainless steel autoclave. The mixture was heated at either 120 C or 150 C for 24 h. After cooling to room temperature, the solid products were left unwashed. According to XRD, no ZIF phase had been obtained. Moreover, the solid products were soluble upon washing with water, which further indicated none of the required crystallization had occurred. The detailed synthetic conditions are shown in Figure S2. Synthesis of dia(zn) and dia(co) by the hydrothermal method A typical procedure for the preparation of dia(zn) was as follows: Zn(OAc) 2 2H 2 O (0.11 g, 0.5 mmol) and 2-methylimidazole (0.41 g, 5 mmol) were dissolved in H 2 O (8 ml) in a 30 ml Teflon-lined stainless steel autoclave. The autoclave was then sealed and heated at 120 C for 24 h. After cooling to room temperature, the solid products were separated by filtration and washed with distilled water (yield: 0.08 g). The procedure for obtaining dia(co) was similar to that for dia(zn), except that Co(OAc) 2 4H 2 O was used instead of Zn(OAc) 2 2H 2 O (yield: 0.05 g). Synthesis of ZIF-8 and ZIF-67 by the steam-assisted conversion method H 2 O as liquid phase A typical procedure for the preparation of ZIF-8 was as follows: Zn(OAc) 2 2H 2 O (0.11 g, 0.5 mmol) and 2-methylimidazole (0.41 g, 5 mmol) were placed in a small teflon cup, which was supported by a teflon holder. Each cup and holder was placed in a Teflon-lined stainless steel autoclave. H 2 O (2.0 ml) was added to the bottom of each autoclave. The crystallization was then carried out at 120 C for 24 h. After cooling to room temperature, the solid products were separated by filtration and washed with distilled water (yield: 0.07 g). The detailed synthetic conditions are shown in Figure S10. The procedure for obtaining ZIF-67 was similar to that for ZIF-8, except that Co(OAc) 2 4H 2 O was used instead of Zn(OAc) 2 2H 2 O (yield: 0.06 g). DMF as liquid phase (for comparison) Following a similar protocol as for the synthesis by using H 2 O as the liquid phase, ZIF-8 and ZIF-67 could also be prepared by using organic solvents such as N,N-dimethylformamide (DMF) as the liquid phase. 4

5 Section S3. Solvent-free (melting) synthesis method: the formation of a eutectic mixture Figure S1. DSC traces of hydrated Zn(OAc) 2 (a), MIM (b), and Zn(OAc) 2 -MIM mixtures with molar ratios of about 1:2 (c), 1:4 (d), and 1:10 (e). (a): The trace indicates two thermal events: the endothermic event around 107 C (minimum) is attributed to dehydration of water so as to form anhydrous Zn(OAc) 2 ; the later endothermic events at around 249 and 256 C (minimum) could be attributed to the melting of Zn(OAc) 2. (b): The thermal effect in the trace at about 147 C (minimum) corresponds to the melting of MIM; the endothermic event is followed by and overlaps with another endothermic trend, which can be attributed to thermal decomposition of MIM. (c), (d) (e): Since the thermal event corresponding to melting of Zn(OAc) 2 is not present in these DSC traces, it is logical to conclude that these endothermic events below 150 C (c: 113 C, d: 117 C, e: 137 C) are caused by the formation of eutectic mixtures. Furthermore, the second endothermic event in trace (e), at around 180 C, could be attributed to the decomposition of excess MIM. The presence of excess MIM in the mixture giving trace (e) was also confirmed by powder diffraction experiments. Figure S2. PXRD patterns of unwashed products in solvent-free (melting) synthesis at 120 C (left) and 150 o C (right) for 24 h with different molar ratios of Zn(OAc) 2 -MIM mixtures: (c) 1:2, (d) 1:4, (e) 1:10; patterns (a) and (b) are those of the reagents Zn(OAc) 2 and MIM, respectively. Based on the DSC data, we assume that a eutectic mixture is formed upon heating a mixture of Zn(OAc) 2 and MIM below the melting point of MIM. In the absence of solvent, the reactant mixtures of Zn(OAc) 2 -MIM (molar ratios of 1:2 and 1:4 ) upon heating at 120 C, could quickly turn an orange liquid quickly (eutectic mixture). These were kept for 24 h and then 5

6 cooled to room temperature to produce an orange solid. However, the PXRD analysis of the unwashed products showed that solvent-free (melting) synthesis had not lead to any detectable ZIF crystalline phase with the disappearance of the Zn(OAc) 2 and MIM. Remarkably, at an MIM/Zn(OAc) 2 molar ratio of 10, the product appeared as a eutectic mixture embedded in the excess of MIM. In fact, the orange products were found to be soluble upon washing with water, further indicating that none of the desired crystalline phase had been obtained. Furthermore, heating of a mixture of Zn(OAc) 2 and MIM at 150 C (the melting point of MIM) for 24 h had a similar effect. 6

7 Section S4. Hydrothermal method: the characterization of dia(zn) and dia(co) Figure S3. Ball-and-stick (left) and Wire-frame (right) diagrams (parallel to the crystallographic b-axis) for dia(zn) (Hydrogen atoms have been omitted for clarity; Zinc=red; carbon = gray; nitrogen = blue). Figure S4. Experimental XRD pattern of sample (blue pattern) and XRD pattern simulated from crystal structure data (red pattern): (left) dia(zn), (right) dia(co). Figure S5. TG curves for dia(zn) (left) and dia(co) (right). 7

8 Figure S6. PXRD patterns for dia(zn) (left) and dia(co) (right) that had been heated to different temperatures in air for 5 h. Figure S7. Nitrogen gas adsorption isotherms at 77 K for dia(zn) (left) and dia(co) (right). Figure S8. SEM micrographs of typical samples: dia(zn) (left) and dia (Co) (right). 8

9 Section S5. Steam-assisted conversion method: the characterization of ZIF-8 and ZIF-67 Figure S9. Experimental XRD pattern of sample (blue pattern) and XRD pattern simulated from crystal structure data (red pattern): (left) ZIF-8 [1], (right) ZIF-67 [2]. [1] K. S. Park, Z. Ni, A. P. Côté, J. Y. Choi, R. D. Huang, F. J. Uribe-Romo, H. K. Chae, M. O Keeffe, O. M. Yaghi, Proc. Natl. Acad. Sci. USA 2006, 103, [2] R. Banerjee, A. Phan, B. Wang, C. Knobler, H. Furukawa, M. O Keeffe, O. M. Yaghi, Science 2008, 319, Figure S10. PXRD patterns of the products in steam-assisted synthesis of ZIF-8 at 120 C (left) and 150 C (right) for 24 h with different molar ratios of Zn(OAc) 2 -MIM: (a) 1:2, (b)1:4, and (c)1:10. The effects of the MIM/Zn(OAc) 2 molar ratio and synthesis temperature were studied. The MIM/Zn(OAc) 2 molar ratio was varied from 2 to 10. Surprisingly, at an MIM/Zn(OAc) 2 ratio of 2, only an unknown phase was found. At an MIM/Zn(OAc) 2 ratio of 4, a mixture of ZIF-8 and the unknown phase was formed at 120 C. Pure ZIF-8 was obtained at MIM/Zn(OAc) 2 ratios higher than 10. So, it is important to add MIM in excess to the zinc source, contrary to previously reported protocols. However, the data shown in Figure S10 (right) indicate that the reaction at higher temperature is advantageous for the synthesis of ZIF-8. At an MIM/Zn(OAc) 2 ratio of 4, pure ZIF-8 was obtained at 150 C. 9

10 Figure S11. (a) comparison of the TG curves for ZIF-8 samples obtained by using H 2 O and DMF as the liquid phase; (b) comparison of the TG curves for ZIF-67 samples obtained by using H 2 O and DMF as the liquid phase; (c) the TG curves of as-synthesized and activated samples (dried at 150 C) of ZIF-8 (H 2 O as liquid phase); (d) the TG curves of as-synthesized and activated samples (dried at 150 C) of ZIF-67 (H 2 O as liquid phase). TG analysis under the air atmosphere performed on ZIF-8 (H 2 O as liquid phase) showed a gradual weight loss of 20 wt % between 35 and 300 C, probably due to the loss of H 2 O molecules. A plateau in the temperature range between 300 and 350 C was observed, and framework decomposition in the temperature range of C; and the final product was identified as ZnO by PXRD. The TG curve of ZIF-8 (DMF as liquid phase) exhibits a gradual weight loss up to 550, corresponding to the decomposition of guest molecules (i.e. DMF) and framework before formation of the final product ZnO. Similarly, TG of ZIF-67 (H 2 O as liquid phase) showed loss of H 2 O molecules below 250 C (ca. 20 wt %), followed by a plateau in the temperature range between 250 and 300 C. And the framework collapsed in the temperature range of C before formation of the final product (Co 3 O 4 ). TG of ZIF-67 (DMF as liquid phase) showed loss of guest molecules (i.e. DMF) below 240 C (ca. 20 wt %), followed by a gradual weight loss up to 410 C. In TG analysis of the ZIF-8 and ZIF-67 samples that has been heated at 150 C for 10 h, a long plateau was observed at temperatures up to 300 C and 250 C, respectively, at which decomposition of the framework structure commenced. It has been shown that, guest molecule H 2 O in the sod cages may be removed even at a temperature of 150 C in air. 10

11 Figure S12. PXRD patterns of samples that had been heated to different temperatures in air for 5 h: (a) ZIF-8 (H 2 O as liquid phase); (b) ZIF-8 (DMF as liquid phase); (c) ZIF-67 (H 2 O as liquid phase); (d) ZIF-67 (DMF as liquid phase). a b c d Figure S13. SEM micrographs of typical samples: (a) ZIF-8 (H 2 O as liquid phase); (b) ZIF-8 (DMF as liquid phase); (c) ZIF-67 (H 2 O as liquid phase); (d) ZIF-67 (DMF as liquid phase). 11

12 Figure S14. FT-IR spectra of typical samples: (left) ZIF-8 and (right) ZIF-67 (H 2 O as liquid phase). Figure S15. Nitrogen gas adsorption isotherms at 77 K for typical samples: ZIF-8 (left) and ZIF-67 (right). N 2 adsorption was examined for ZIF-8 and ZIF-67 (H 2 O as liquid phase). The as-synthesized samples were dried at 200 C in air for 3 h to yield an activated sample for gas adsorption measurements. Before the measurement, the samples were dried again by using the degas function of the surface area analyzer for 5 h at 150 C. Figure S16. PXRD patterns of unwashed products in steam-assisted synthesis of ZIF-8 with different times: (c) 10 min, (d) 1h, (e) 3h, (f) 6 h, (g) 12 h, and (h) 24 h. Patterns (a) and (b) are those of the reagents Zn(OAC) 2 and MIM, respectively. (Composition of the solid phase: 0.5 Zn(OAc) 2 :5 MIM; the amount of solid phase: 0.52 g; the inner volume of autoclave: 30 ml; crystallization temperature: 120 C; liquid water: 2.0 ml) 12

13 Figure S17. Effect of the amount of water added (to the eutectic mixture reactants) in the synthesis of ZIF-8 at 120 C (left); effect of the amount of water added (at the bottom of autoclave) in the synthesis of ZIF-8 by the steam-assisted conversion method at 120 C (right). (Composition of the eutectic mixture or solid reactants: 0.5 Zn(OAc) 2 :5 MIM; the amount of eutectic mixture or solid reactants: 0.52 g) Figure S18. Effect of the amount of water added (to the eutectic mixture reactants) in the synthesis of ZIF-67 at 120 C (left); effect of the amount of water added (at the bottom of autoclave) in the synthesis of ZIF-67 by the steam-assisted conversion method at 120 C (right). (Composition of the eutectic mixture or solid reactants: 0.5 Co(OAc) 2 :5 MIM; the amount of eutectic mixture or solid reactants: 0.53 g) Here, we reported quantitative studies of the effect of water on the synthesis of ZIFs with steam-assisted conversion method. For comparison, water was also added quantitatively into the eutectic mixture on the synthesis of ZIF utilizing an ionothermal/eutectic mixture system. In order to obtain clear and unambiguous results we varied only the amount of water added (0.05 ml 4.0 ml) and the other conditions remain fixed. Either in the eutectic mixture (Zn(OAc) 2 /Co(OAc) 2 MIM) regime or by steam-assisted conversion conditions, under low levels of water (0.05 ml 0.1 ml) no product was obtained after 24 h of heating at 120 C. In the case of eutectic mixture (Zn(OAc) 2 MIM) regime, ZIF-8 was prepared at intermediate levels of water ( ml) and with the addition of larger quantities of water (4.0 ml) dense dia(zn) was main product (Figure S17 left). In the case of eutectic mixture (Co(OAc) 2 MIM) regime, the addition of intermediate H 2 O resulted in either poorly crystallised ZIF-67 (0.3 ml) or a mixture of ZIF-67 and small unidentified phase ( ml), and even more water added (4.0 ml) dense dia(co) was produced (Figure S18 left). In contrast, in the case of the steam-assisted conditions, the ZIF-8 or ZIF-67 was found across all levels of water content ( ml) (Figure S17 right and Figure S18 right). Increasing the amount of water added resulted in the formation and further growth of ZIF-8 or ZIF-67, crystallization occurred with 0.3 ml of water, while the crystallinity of product had a higher value when 2.0 ml of liquid water was added to the autoclave. 13

14 Figure S19. Effect of the amount of water added (to the eutectic mixture reactants) in the synthesis of ZIF-8 at 150 C (left); effect of the amount of water added (at the bottom of autoclave) in the synthesis of ZIF-8 by the steam-assisted conversion method at 150 C (right). (Composition of the eutectic mixture or solid reactants: 0.5 Zn(OAc) 2 :3.0 MIM; the amount of eutectic mixture or solid reactants: 0.36 g) Figure S20. Effect of the amount of water added (to the eutectic mixture reactants) in the synthesis of ZIF-67 at 150 C (left); effect of the amount of water added (at the bottom of autoclave) in the synthesis of ZIF-67 by the steam-assisted conversion method at 150 C (right). (Composition of the eutectic reactants or solid reactants: 0.5 Co(OAc) 2 :3.0 MIM; the amount of eutectic mixture or solid reactants: 0.37 g). Similar experiment was also carried out at 150 C. At 150 C the ZIF-8 or ZIF-67 was found again across various amounts of water (0.5 ml-4.0 ml) by the steam-assisted conversion method (Figure S19 right and Figure S20 right). In contrast, a mixture of ZIF-8 and dia(zn) or Co 3 O 4 was dominate product in the case of eutectic mixture regime (Figure S19 left and Figure S20 left). There are therefore one or more variables effecting ZIF-8 or ZIF-67 crystallization in the case of eutectic mixture regime. The data shown indicate that phase region is broad for crystallization of ZIF-8 or ZIF-67 by steam-assisted conversion. 14

15 B Section S6. Tribological behaviors of ZIF-8 and ZIF-67 Tribological behaviors. The tribological behaviors of samples (ZIF-8, ZIF-67, PTFE) as additives in base oil were investigated using a four-ball machine. The balls (diameter 12.7 mm) used in the test were made of GCr15 bearing steel (SAE52100 steel) with an HRc of The base oil employed in this work was mineral oil (100 SN), which has a viscosity of mm 2 /s at 40 C, a viscosity index of 68, and a flash point of 196 C. It should be noted that the samples (ZIF-8 and ZIF-67) were carefully milled prior to use until an edge length of about several hundred nanometers was obtained (Figure S21). Figure S21. SEM images for typical samples after milling: ZIF-8(left), ZIF-67(right). The anti-wear properties (wear scar diameters, WSD) of the samples as additives in base oil were evaluated with a four-ball tester operated at a rotating speed of 1200 rmin 1 (rpm) and room temperature of 25 C. The test duration was 60 min and the load applied was 147 N. At the end of each test, the wear scar diameters (WSD) on the three stationary balls were measured by means of a digital-reading optical microscope to an accuracy of 0.01mm in the directions parallel and perpendicular to the sliding motion. The load-carrying capacity (the maximum non-seizure loads, P B ) of the samples was determined according to the China National Standard method GB/T , which is similar to ASTM D2783. For each sample, three identical tests were performed so as to minimize data scattering. The average wear scar diameter of the three identical tests was calculated as the wear scar diameter in this work. The morphologies of the worn surfaces (scars) of the ball were examined by means of SEM (Figure S22). a b c d Figure S22. SEM images of worn surfaces on balls lubricated with: (a) pure oil, and oil containing different additives (b) ZIF-8, (c) ZIF-67, and (d) PTFE. 15