Sunlight-driven photocatalytic degradation of 4-nitrophenol and adsorptive removal of Mn (II) ions from industrial wastewater by biogenic synthesized CuO/SnO2 heterojunction

Abstract

Toxic substances like organic pollutants and heavy metal ions require urgent removal from contaminated water for protection of human health. The presence of these pollutants in water beyond the permissible limits has negative consequences for human health, the climate, and the environment. Experts have paid close attention to eliminate these hazardous substances from natural water by using heterojunctions over the last decade. From this perspective, CuO/SnO2 heterojunction has been constructed for the first time by green synthesis route using fruit part of Carica papaya extract. The fabricated heterojunction photocatalyst was characterized using several sophisticated techniques like UV–vis, FTIR, XRD, field-emission scanning electron microscopy, energy-dispersive spectroscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and BET-BJH. Catalytic potential of the CuO/SnO2 heterojunction was descriptively explored for reducing 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) under direct sunlight irradiation. Complete conversion of toxic 4-NP into 4-AP was achieved in 20 min with a rate constant of 0.23 min−1, and the intermediates formed were analyzed by LC-MS. Furthermore, the heterojunction was used for removing toxic Mn2+ ions from industrial effluents. The influence of various experimental conditions on adsorption, including pH of the solution, amount of adsorbent, time of contact, and temperature, was carefully examined. The Langmuir, Freundlich, and Temkin isotherm models were used to study the equilibrium adsorption behavior of the heterojunction. The maximum adsorption by the CuO/SnO2 heterojunction was determined to be 227 mg/g. The biogenic synthesized heterojunction successfully removed Mn2+ ions from the real samples of industry effluents. Hence, biogenic CuO/SnO2 heterojunction could be used as a novel material for the reduction of 4-NP and adsorptive removal of Mn2+ ions.