Selective Ethanol Oxidation to Acetaldehyde on Nanostructured Zeolitic Imidazolate Framework-8-Wrapped ZnO Photothermocatalyst Thin Films

Photothermocatalytic ethanol oxidation to acetaldehyde offers an alternative technology in synthesizing high-value-added chemicals. However, the practical application is hindered by the competition from overoxidation leading to complete mineralization. Herein, the 1D nanostructured ZnO@zeolitic imidazolate framework-8 (ZIF-8) composite is reported as an efficient photothermocatalyst, which shows improved conversion efficiency and high catalytic selectivity and durability compared with the parent ZnO nanorods, for continuous ethanol oxidation in a flow system. The ZnO@ZIF-8 composite achieves a high selectivity of 91.5% toward acetaldehyde production. The underlying mechanism is probed using electrochemical impedance spectroscopy, N-2 adsorption-desorption isotherms, transient open-circuit potential, and steady-state and time-resolved photoluminescence spectroscopy. Collectively, the probings show that the improved performance originates from 1) facilitated charge separation; 2) lowered oxidation potential holes; 3) enlarged surface area; and 4) preferred reaction routes. This work provides a new perspective for the design of a hybrid photothermocatalyst for selective solar energy conversion into desirable chemicals.