Photocatalytic removal of NOx using cobalt oxide/graphitic carbon nitride nanocomposites under visible light irradiation

Abstract

The development of efficient photocatalysts for the selective conversion of nitrogen oxides (NO_x) into valuable products is essential for promoting environmental sustainability and addressing air pollution. This study presents the synthesis and application of Co₃O₄/g-C₃N₄ nanocomposites as high-performance photocatalysts for the oxidation of NO_x to nitric acid (HNO₃) under visible light irradiation. The synthesized nanocomposites exhibited a large surface area and high porosity, which are critical for maximizing interaction with pollutants. Additionally, their efficient light absorption characteristics enhance photocatalytic activity. The incorporation of hole scavengers was found to significantly improve photocatalytic performance by suppressing charge recombination. Remarkably, the NO_x-to-HNO₃ conversion efficiency increased from 25.5% for pure Co₃O₄ to 86.5% for the nanocomposites, reaching 92% with t-butanol as a hole scavenger, under visible light irradiation at room temperature for 2 hours. The photodegradation rate of NO_x followed the order: Co₃O₄/g-C₃N₄ NCs> g-C₃N₄ NPs> Co₃O₄ NPs, indicating the synergistic effect of the nanocomposite. This significant improvement is attributed to the synergistic effects of the nanocomposite structure, visible light absorption, and efficient charge separation, enabling the stepwise oxidation of NO to HNO₃ under mild conditions. This research demonstrates the potential of advanced photocatalysts for the simultaneous remediation of NO_x emissions and production of valuable chemicals.