Nanostructured Cobalt Oxide Catalyst with a Three-Dimensional Flower-Like Structure for Photothermal Purification of Formaldehyde

Formaldehyde (HCHO), an indoor volatile organic compound (VOC), significantly impacts human health, driving the market demand for more effective degradation technologies. Photothermal catalysis offers a sustainable, efficient, and energy-saving solution for indoor HCHO purification. In this study, we investigated the photothermal catalytic efficiency of HCHO using synthesized copper foam (CF)-based monolithic catalysts. By loading nanostructured cobalt oxide with varying morphologies onto the CF surface, it was observed that cobalt oxide with a three-dimensional (3D) flower-like structure exhibited the highest photothermal performance. Under ultraviolet–visible–near-infrared (UV–vis–NIR) light irradiation alone, this structure achieved a surface temperature of 148.5 °C and demonstrated removal efficiencies of 96.5% and 94.6% for 300 ppm of HCHO in batch and fixed-bed reactors, respectively. The high efficiency of HCHO purification is attributed to the enhanced oxygen mobility from the catalyst, which activates the Mars–van Krevelen (MvK) oxidation pathway of the C–H bond at elevated temperatures. Additionally, short-wave light excitation induces electron transitions, initiating a mechanism involving free radical oxidation. This study highlights the potential of conventional transition metal catalysts as efficient photothermal catalysts for indoor air purification.