Composite MOF foams: the example of UiO-66/polyurethane

Transcription

1 Composite MOF foams: the example of UiO-66/polyurethane Moisés L. Pinto,* a,b Sandra Dias, a João Pires, a a Department of Chemistry and Biochemistry, and CQB, Faculty of Sciences, University of Lisbon, Ed. C8, Campo Grande, Lisboa, Portugal. Fax: ; Tel: b Department of Chemistry, CICECO, University of Aveiro, Aveiro, Portugal. moises.pinto@fc.ul.pt Characterization Nitrogen adsorption isotherms, at -196 ºC, were obtained in an automatic apparatus (ASAP 21; Micromeritics). Before the adsorption experiments, the samples were outgassed under vacuum better than 1-2 Pa for 2.5 h at 12 ºC. This relatively low temperature was used to prevent polyurethane decomposition. The adsorption isotherms were analyzed by the Brunauer Emmett Teller (BET) equation, for the estimation of the specific surface area (A BET ), and by the t-plot method using the Harkins Jura equation, for the estimation of the microporous volume. The n-hexane and benzene adsorption isotherms, at 25 ºC, were obtained by the gravimetric method in a balance suited for vacuum (Disbal, C.I. Electronics). Samples of about 5 mg were outgassed with a heating program of 2 ºC min -1 from room temperature to 12 ºC and kept at this temperature for 2.5 h, under a final vacuum better than 1-2 Pa. The vapor was then introduced in the system, and allowed to equilibrate with the sample. Pressure readings were made with a capacitance transducer (CMR 262, Pfeiffer Vacuum). The temperature was controlled using a water bath (GD12, Grant), with.5 ºC precision. The vapors were purified in situ by freeze vacuum thaw cycles. The weighting scale was connected to a computer and the weight was recorded by software (Labweigh; C.I. Electronics) at constant time intervals. In some cases, several hours were necessary until equilibrium was attained (constant weight). The adsorbed amounts were converted to liquid volume using the respective molar volume at 25 ºC. TG-DSC experiments were performed in an apparatus (Setaram, TG-DSC 111) between 3 and 6 ºC. The experiments had a precision of.1 mg and.5 mw. Samples of about 15 mg in steel crucibles were used, with a heating rate of 1 ºC min -1, in air (Air Liquid, 2% vol.

2 oxygen in nitrogen) with a flux of.5 cm 3 s -1 measured with a glass fluxmeter (Brooks Instruments N.V., tube size R-2-15-AA). SEM micrographs were obtained in a Jeol JSM-52 LV equipment, after been gold plated. Powder XRD data was obtained in a Philips Analytical PW 35/6 X Pert Pro, equiped with a X Celerator detector.

3 Results DRIFT UiO-66 a b c d e Absorvance / au wave number (cm -1 ) 9 Composite 3 a b c d e Absorbance / au wave number (cm -1 ) 11 9 Figure S1 DRIFT spectra of the UiO-66 and composite 3, after several cleaning steps: a) as synthesised material, b) after soxhlet extraction with dichloromethane and c), d) and e) after successive cycles of heating at 15ºC under vacuum for 4 hours.

4 DRX a.u. UiO-66 activated UiO Θ Figure S2 Powder XRD of the UiO-66 and UiO-66 after the activation procedure.

5 TG-DSC To estimate the content of UiO-66 on the composites A and B, the mass of sample at 15 ºC was considered as the dry mass for all the samples. As can be seen in Figure S1, this corresponds to a point after the initial due to the dehydration of the materials. The mass difference between the mass at 15 ºC and at 55 ºC is considered as the due to the decomposition of the materials and the formation of ZrO 2, since after 55 ºC the mass becomes constant for all cases (Figure S1). For the case of UiO-66 a theoretical mass of 43.5% should be obtained at the end, assuming the decomposition of the BDC linkers. Experimentally, at 55 ºC we have obtained 4% of the initial mass at 15 ºC and this value supports the assumption made for the complete decomposition of the UiO-66 to ZrO 2. For the composites, at 55 ºC we have obtained 28% and 25% of the initial mass at 15 ºC, which we assume that is ZrO 2 formed from the decomposition of the UiO-66 since at 55 ºC the polyurethane is completely decomposed in air. Comparing the content of ZrO 2 formed from the composites with that formed from pure UiO-66, we can estimate a content of 71% and 64% of UiO-66 for the composite A and B. Powder XRD of the UiO-66 and composite 3 calcined in air (Figure S4) shows is that in both cases the same solid is obtained at the end of the calcinations and TG-DSC experiments. The powder pattern is compatible with ZrO 2, mainly in the cubic phase (ICDD PDF# ) with some minor part in the monoclinic phase (ICDD PDF# 36-42). This supports the estimation of the UiO-66 content on the composite materials presented above, based on the mass remaining at the end of the TG-DSC experiments.

6 8 UiO Exo heat flow PUF 15 Exo. 1 5 DTG Composite A Exo heat flow Composite B Exo heat flow Figure S3 TG-DSC of the pure UiO-66, pure PUF, and composites A and B, in air.

7 * calcined composite A a.u. calcined UiO-66 * cubic phase monoclinic phase * Θ Figure S4 Powder XRD of the white powder obtained after calcinations of UiO-66 and composite A under air. Diffraction data for cubic and monoclinic ZrO 2 is indicated.