A visible light-responsive PmAP/rGO/MnO2 heterojunction: a promising photocatalyst for the degradation of reactive blue 19 and azithromycin†

Abstract

The design and synthesis of a poly-m-aminophenol ternary heterojunction photocatalyst (PmAP/rGO/MnO₂) using a combination of hydrothermal and in situ chemical oxidation methods were reported in this study. Various characterization techniques were utilized to examine the structural, morphological, and elemental composition of the catalyst. The rod-like MnO₂ structure identified in the synthesized ternary composite suggests the in situ formation of MnO₂ particles within the PmAP–rGO composites. The PRM-5 composite is characterized by a band gap of 1.74 eV, which is crucial for improving light absorption capacity and promoting the generation of photoactivated charges. The reduced photoluminescence (PL) intensity of PRM-5 compared to that of the neat samples, as observed in PL spectra, indicates suppressed recombination of charge moieties. Electrochemical impedance spectroscopy (EIS) Nyquist plots of PRM-5 indicated that the composite exhibits a lower charge transfer resistance (0.44 Ω), enabling a more efficient interfacial charge transfer process. The composite achieved over 90% photocatalytic degradation of azithromycin (Azx) and reactive blue (RB 19) at a concentration of 40 mg L⁻¹ within 120 minutes of visible light exposure. Scavenging analysis identified ˙O₂⁻ and ˙OH radicals as the main active charged moieties involved in the degradation process. GC-MS analysis further verified the breakdown of reactive blue-19 and Azx into smaller, non-hazardous components. The ternary photocatalyst maintained its performance even after five consecutive cycles, retaining about 81% of its degradation efficiency. The PmAP/rGO/MnO₂ ternary composite shows potential as a visible light active photocatalyst for effectively degrading organic water pollutants, providing a solution to the challenges posed by the textile industry and the presence of antibiotics in water sources.