Loosening metal nodes in metal-organic frameworks to facilitate the regulation of valence

Abstract

The valence of metal nodes in metal-organic frameworks (MOFs) determines their performance in applications while developing an efficient approach for valence regulation is challenging. Here we present a strategy to make the valence regulation much easier by loosening metal nodes by thermal pretreatment. The typical MOF, HKUST-1, with the tunable valence of Cu nodes, was used as a proof of concept. Thermal pretreatment (producing HK-T) changes the chemical environment and loosens Cu nodes, endowing them with enhanced reducibility. In the subsequent vapor-induced reduction, the yield of Cu⁺ from Cu²⁺ conversion in HK-T (producing HK-T-V) reaches 69%, which is higher than that in pristine HKUST-1 (producing HK-V) with a Cu⁺ yield of 19% as well as the reported yields of target-valence metal nodes in various MOFs (6%–30%). The obtained HK-T-V possessing abundant Cu⁺ sites can capture 0.809 mmol/g thiophene in adsorptive desulfurization, 2.5 times higher than HK-V and superior to most reported adsorbents.