Porous SnCo2O4-rGO nanohybrids for visible-light photocatalytic degradation of methylene blue and 4-nitrophenol reduction

In this study, cube-shaped SnCo2O4–rGO nanohybrids were successfully synthesized via a one-pot co-precipitation method and investigated its catalytic efficiency for light-induced redox reactions. Structural and morphological characterizations were performed using p-XRD, FESEM, TGA, XPS, BET and Raman spectroscopy. The analyses confirmed formation of spinel SnCo2O4 embedded within layered rGO matrix. Methylene blue (MB), a widely used cationic dye and 4-nitrophenol (4-NP), a persistent phenolic compound, have been frequently identified in water bodies causing water contamination. High surface area, abundant oxygen vacancies and reduced band gap of SnCo2O4–rGO nanohybrid made it utilized for photocatalytic MB degradation and 4-NP reduction under simulated visible light irradiation. The incorporation of rGO not only provided a conductive network for charge transport but also effectively suppressed the recombination of photogenerated charge carriers, as validated by photoluminescence and the reduction in charge-transfer resistance observed in electrochemical impedance spectroscopy. The reaction kinetics for MB degradation and 4-NP reduction were monitored using UV–Visible spectroscopy and photocatalytic reactions demonstrated a high degradation efficiency of 93.01% for MB degradation and 97.01% conversion of 4-NP reduction under optimised conditions within 120 min. Furthermore, formation of intermediates during MB degradation was confirmed by HRMS, followed by TOC analysis to confirm the mineralisation efficiency of SnCo2O4-rGO. Scavenger studies demonstrated the role of hydroxyl radicals, superoxide anions and electrons played during photocatalytic process. Comparative analysis with pristine SnCo2O4 indicated a superior rate constant for the hybrid nanocatalyst. Additionally, the SnCo2O4–rGO nanocatalyst displayed excellent photostability and reusability, retaining its activity over five successive cycles without a significant loss in efficiency.