Free-Standing Porous Cuprous Oxide Microspheres Exert Distinctive Catalytic Degradation of Nitroarenes and Dyes

Nitroarenes and organic dyes are hazardous pollutants that pose significant risks to environmental and human health. Herein, free-standing porous cuprous oxide microspheres (pCOMs) were synthesized via a simple surfactant-free reduction of copper sulfate using hydrazine monohydrate at room temperature and evaluated as catalysts for the degradation of nitroarenes and dyes. The synthesized pCOMs were comprehensively characterized by PXRD, FTIR, FESEM, TEM, XPS, BET, zeta potential, and TGA analyses, confirming the formation of phase-pure mesoporous Cu 2 O microspheres with accessible pore channels and mixed Cu + /Cu 2+ surface states. Nitrogen adsorption–desorption studies revealed a type-IV isotherm with a BET surface area of 5.3 m 2 g –1 and predominant mesopores of 35–40 nm diameter. The catalytic activity of pCOMs was investigated for the reduction of 4-nitrophenol (4-NP), 2-chloro-4-nitroaniline, and 2-chloro-5-nitrobenzoic acid, as well as the degradation of methylene blue (MB), bromocresol green (BCG), and rhodamine B (RhB) in the presence of NaBH 4 . The pCOMs exhibited rapid catalytic performance, achieving degradation efficiencies of 99.96%, 96.20%, and 82.16% for 4-NP, 2-chloro-4-nitroaniline, and 2-chloro-5-nitrobenzoic acid, respectively, within 60–150 s, while complete degradation of MB, BCG, and RhB occurred within seconds. Kinetic studies revealed pseudo-first-order behavior with an apparent rate constant of 0.05255 s –1 for 4-NP reduction. Comparative experiments demonstrated that porous microspheres significantly outperformed solid Cu 2 O microspheres. XPS analysis before and after catalysis indicated the involvement of reversible Cu + /Cu 2+ redox transitions during the catalytic process. Furthermore, the catalyst retained 94.72% of its activity after five consecutive cycles, highlighting its excellent stability and reusability. These findings establish free-standing porous Cu 2 O microspheres as efficient, recyclable, and noble-metal-free catalysts for rapid environmental remediation applications.