Dual-photon-driven hydrogen evolution in copper-based photocatalysts under near-infrared and visible light.

Abstract

While the dynamic restructuring of Cu-metalated metal-organic frameworks for photocatalysis has recently been explored, its effect on electronic excitation remains under-investigated. For better mechanistic understanding, we study the light-induced activity of Cu-metalated UiO-66(COOH)₂ metal-organic framework, known as UiO-66(COOH)₂-Cu under varied irradiations, using gas-phase formic acid dehydrogenation at ambient conditions as a model reaction. A photocatalytic logic gate behavior is observed. The UiO-66(COOH)₂-Cu remains photo-catalytically OFF under visible (>390-720 nm) or near-infrared (>700 nm) light alone, but shows high H₂ production of 6.1 mmol·g⁻¹·h⁻¹ (ON state) when both are applied (≥390 nm). Operando Fourier transform infrared spectroscopy and X-ray absorption spectroscopy demonstrate that both visible and near-infrared irradiations are required for metalated Cu^2+/1+ restructuring inside the framework to form photoactive Cu⁰/Cu⁺ binary center, and thereafter for the photocatalytic dehydration of formic acid. X-ray absorption spectroscopic analysis suggests a distinct initiation behavior of Cu⁺ and Cu⁰ species under visible and near-infrared irradiation, respectively. However, operando Fourier-transform infrared spectroscopy reveals a cascade mechanism requiring both irradiations to progress the catalytic reaction. This photocatalytic logic gate behavior also appears in bare Cu⁰/Cu₂O system used as reference. These findings provide insights into dual-photon-driven photocatalysis and aid advanced hydrogen catalyst design.