Construction of a 3D flower-like NiO/Mn3O4 heterojunction using Tulsi leaf extract for enhanced photodegradation of thiamethoxam pesticide and organic dyes under direct sunlight

Abstract

The construction of high-efficiency photocatalysts for photocatalytic disintegration of organic contaminants is a significant challenge. Herein, novel porous flower-like NiO/Mn₃O₄ heterojunction photocatalysts were successfully designed via a green synthesis route employing Tulsi leaf extract. The NiO/Mn₃O₄ heterojunction photocatalyst exhibited exceptional activity in the decomposition of thiamethoxam pesticide and crystal violet and rhodamine B dyes. The studied X-ray diffraction pattern established the existence of both NiO and Mn₃O₄ in the heterojunction photocatalyst. Field emission scanning electron microscopy micrographs substantiated the porous flower-like structure of the photocatalyst. Surface study demonstrated the surface area, micropore volume and mean pore diameter of the photocatalyst to be 119.93 m² g⁻¹, 0.1859 cm³ g⁻¹ and 3.78 nm, respectively, which are highly favourable for surface interactions. Photocatalytic experiments revealed that the heterojunction (NM-I) showed the highest photocatalytic efficiency for the degradation of thiamethoxam pesticide (93% in 90 min) and crystal violet (93.6% in 80 min) and rhodamine B (93.2% in 80 min) dyes with a rate constant of 0.0212, 0.0378 and 0.0355 min⁻¹, respectively. The performance of the NiO/Mn₃O₄ heterojunction was optimized by investigating the roles of certain variables, including pH, catalyst dosage, and scavengers, in degrading organic pollutants. Moreover, liquid chromatography–mass spectrometry was utilized to predict a tenable mechanism for thiamethoxam disintegration. In addition, the catalyst showed excellent stability and reusability, and was simple to extract from the solution. After five cycles, thiamethoxam, crystal violet and rhodamine B elimination efficiencies were 82%, 84%, and 87%, respectively.