Catalytic oxidation of formaldehyde on ultrathin Co₃O₄ nanosheets at room temperature: Effect of enhanced active sites exposure on reaction path

This research precisely controlled the thickness of Co₃O₄ nanosheets to investigate the effect of active sites exposure on the reaction path of HCHO catalytic oxidation. X-ray absorption fine structure demonstrates that ultrathin Co₃O₄ nanosheets (Co₃O₄-2) with atomic layer thickness (~2 nm) exhibit stronger lattice disorder than Co₃O₄ nanosheets with a thickness of 20 nm (Co₃O₄-20). Aberration-corrected scanning transmission electron microscopy confirms that two-dimensional structure and disordered structure of Co₃O₄-2 enhances the surface exposure of active sites (Co3+ and oxygen vacancies). Therefore, Co₃O₄-2 can produce more reactive oxygen species, avoiding the side reaction path dominated by undesired intermediates over Co₃O₄-20, where active sites are blocked and HCHO oxidation is inhibited. Consequently, the HCHO removal efficiency (＞90%) and CO₂ conversion efficiency (＞90%) of Co₃O₄-2 are substantially higher than thicker Co₃O₄ nanosheets. This research provides an effective strategy to construct active sites and deep insights into the reaction path.