MOF-Templated Approach for Hollow NiO_x/Co₃O₄ Catalysts: Enhanced Light-Driven Thermocatalytic Degradation of Toluene

Catalysts with strong light absorption over a broad wavelength region and high catalytic performance are considered to be suitable materials for realizing efficient light-driven thermocatalytic environment purification. However, it still remains a challenge to acquire a highly efficient catalyst with tunable light absorption properties. In this report, structure management and secondary metal doping techniques were implemented to the catalysts for improving its solar-light utilization efficiency. We synthesized a series of hollow NiOx/Co3O4 composites derived from ZIF-67 by impregnation method and explored the light-driven catalytic activities on toluene oxidation under simulated sunlight. Remarkably, the prepared samples with strong light absorption and efficient photothermal conversion exhibit excellent catalytic activity under the full solar spectrum in toluene oxidation, which proceeds by a light-driven thermocatalysis. In terms of NiOx/Co3O4 composites, the 35-NiOx/Co3O4 catalyst shows the highest thermocatalytic activity (ca. 95% for conversion and ca. 80% for mineralization) in toluene oxidation (210 ppm, gas hourly space velocity = 32 000 mL/(g·h)). And the high light-driven catalytic performance over 35-NiOx/Co3O4 catalyst can be mainly explained by its strong light absorption, lager surface area, low-temperature reducibility, more active oxygen species, and more active Co3+ sites. Furthermore, the in situ diffuse reflectance infrared Fourier transform spectroscopy study on 35-NiOx/Co3O4 suggests that toluene is degraded via benzyl alcohol, benzaldehyde, and benzoate species as main intermediates and is finally decomposed to CO2 and H2O.