SmMnO₃-decorated ZnO in a hexane-water interface for enhancing visible light-driven photocatalytic degradation of malachite green

Malachite green (MG) contributes to water contamination because its accumulation adversely impacts aquatic systems. For the first time, we prepare a high photoresponse of ZnO/SmMnO₃ heterojunction via a high-speed stirring method at the nonpolar–polar interface assisted by Alstonia scholaris leaves extract (ASLE) as natural hydrolyzing and stabilizing agents. The heterojunction formation boosts the photocatalytic activity of ZnO up to 91.74% under visible light irradiation. Photoluminescence analysis confirmed that modification with SmMnO₃ increases the separation of photogenerated charges and plummets the recombination rates of electron-holes, which induces high photodegradation of MG. With 3 mg of catalyst, the %TOC removal efficiency for MG degradation over ZnO/SmMnO₃ was found to be 53.09%, which is higher than that over ZnO. The kinetics model for the photocatalytic reaction was a pseudo-first-order with excellent stability in four consecutive cycles with no structural change. The radical trapping experiment suggests that h⁺ was the major species in the MG photodegradation reaction. Additionally, morphology and elemental analyses clearly present the formation of ZnO/SmMnO₃ heterojunction without any impurities. The current research demonstrates a simple and advanced technique to design heterojunction photocatalyst at the interface of hexane-water.