Active Sites in Copper-Based Metal–Organic Frameworks: Understanding Substrate Dynamics, Redox Processes, and Valence-Band Structure

Abstract

We have developed an integrated approach that combines synthesis, X-ray photoelectron spectroscopy (XPS) studies, and theoretical calculations for the investigation of active unsaturated metal sites (UMS) in copper-based metal–organic frameworks (MOFs). Specifically, extensive reduction of Cu+2 to Cu+1 at the MOF metal nodes was achieved. Introduction of mixed valence copper sites resulted in significant changes in the valence band structure and an increased density of states near the Fermi edge, thereby altering the electronic properties of the copper-based framework. The development of mixed-valence MOFs also allowed tuning of selective adsorbate binding as a function of the UMS oxidation state. The presented studies could significantly impact the use of MOFs for heterogeneous catalysis and gas purification as well as foreshadow a new avenue for controlling the conductivity of typically insulating MOF materials.

Sodalite‐type Cu‐based Three‐dimensional Metal–Organic Framework for Efficient Oxygen Reduction Reaction

“…This hinders to use these materials as cathode material in ad irect methanol fuel cell. [30] In present case, compound 1 exhibited excellent methanol tolerant activity.T he pores of the structure surrounded by p-electron clouds from tetrazole, which may prevent the methanol diffusion inside the pore.…”

“…Copper‐based materials are prone to methanol adsorption and oxidation. This hinders to use these materials as cathode material in a direct methanol fuel cell . In present case, compound 1 exhibited excellent methanol tolerant activity.…”

Recent advances in dual mode charge compensation for XPS analysis

“…Reduction of Cu(II) species during XPS analysis is well known with researchers taking different steps including cryogenic temperatures, application of a bias and rapid, multiple point acquisitions to minimise it. Controlling the reduction of Cu(II) during XPS analysis is especially important in the study of metal‐organic frameworks (MOFs), which are porous networks formed by bonds between organic linkers and metal ions. The growth in studying their surface chemistry is driven by their promise in areas such as energy storage, heterogeneous catalysis, and sensing applications …”

Selective Catalytic Chemistry at Rhodium(II) Nodes in Bimetallic Metal–Organic Frameworks

“…Previous studies by our group have established that reduction of Cu 2+ to Cu 1+ in pure CuBTC is induced by the combination of X-ray irradiation and heating to remove coordinating solvent molecules. [10] Thef act that the post-reaction CuRhBTC exhibits aC u(2p 3/2 )p eak identical to that of the pre-reaction MOF suggests that there is no change in oxidation state of the Cu ions after propylene hydrogenation ( Figure S3). Moreover,exposure of CuRhBTC to H 2 at room temperature does not cause significant reduction of Cu 2+ .…”