Su Zhi, Miao Yu-Run, Zhang Guanghui, Miller Jeffrey T, Suslick Kenneth S
Department of Chemistry , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , USA . Email:
School of Chemistry and Materials Science , Nanjing Normal University , Nanjing , Jiangsu 210023 , P. R. China.
Chem Sci. 2017 Dec 1;8(12):8004-8011. doi: 10.1039/c7sc03786d. Epub 2017 Oct 9.
The internal free volume of porous materials diminishes upon mechanical compression, and such volume collapse can have chemical consequences. We report here the endothermic bond breakage in a metal-organic framework (MOF) during compression-induced collapse. Upon bulk compression at 1.9 GPa, the effective number for Zr-O bonds between Zr(iv) ions and carboxylate groups in UiO-66 decreased from 4.0 to 1.9, as determined by EXAFS, and the internal free volume was synchronously collapsed. Consistent with the EXAFS data, IR spectra confirmed conversion of - bridging carboxylates to monodentate ligation, thus establishing mechanochemical reactions induced by external compression of MOFs. Substantial mechanical energy (∼4 kJ g) was absorbed by UiO-66 nanocrystals during compression, as demonstrated from nanocompression of single crystals (600 nm) during scanning electron microscopy, which establishes the potential application of MOFs as mechanical energy absorbers for hydrostatic and shock compression.
多孔材料的内部自由体积在机械压缩时会减小，这种体积坍塌可能会产生化学后果。我们在此报告了在压缩诱导坍塌过程中金属有机框架（MOF）内的吸热键断裂。通过EXAFS测定，在1.9 GPa的体压缩下，UiO-66中Zr(iv)离子与羧酸根基团之间Zr-O键的有效数量从4.0降至1.9，同时内部自由体积同步坍塌。与EXAFS数据一致，红外光谱证实了 - 桥连羧酸盐向单齿配位的转化，从而确定了由MOF外部压缩诱导的机械化学反应。在扫描电子显微镜下对单晶（600 nm）进行纳米压缩表明，UiO-66纳米晶体在压缩过程中吸收了大量机械能（约4 kJ g），这确立了MOF作为静水压力和冲击压缩机械能吸收器的潜在应用。
