Biochar Supported Oxygen Rich TiO₂-CuO Heterojunction Photocatalyst for the Degradation of Dimethyl Phthalate: Optimization, Degradation Kinetics and Mechanisms

With the extensive usage of plastic items, phthalate esters entered into the environment, and then imparts a threat to human and the ecological systems. Therefore, current study focuses on the degradation of DMP by synthesizing novel photocatalysts. TiO₂ is one of the well-studied photocatalyst but had not shown the photocatalytic activity in longer wavelength and also suffers from the recombination of electron–hole pairs. Hence, these limitations need to be addressed to enhance the photocatalytic performance of TiO₂. In this work, p–n heterojunction of n-type O₂-TiO₂ nanocrystalline materials and p-type CuO was synthesized and then impregnated into the biochar. Properties of the synthesized photocatalyst was characterized using different characterization techniques such as XRD, XPS, Raman spectroscopy, and diffuse reflectance spectroscopy. Among all the synthesized photocatalysts, O₂-TiO₂/CuO (90:10)/BC650 had shown lowest energy band gap of 2.48 eV and least photoluminescence intensity. Further, detailed mechanisms and the performance of photocatalysis were discussed. At optimum conditions, 93% degradation of DMP was achieved using O₂-TiO₂/CuO (90:10)/BC650 at pH 3, catalyst dose of 0.75 mg L⁻¹ under 120 min reaction time. In addition, TOC removal of 91% at optimum conditions was accomplished suggesting the accumulation of by-products is insignificant. The photocatalytic breakdown of DMP was primarily caused by the free radicals, transforming DMP molecules into CO₂ and H₂O by dealkylation and decarboxylation. Therefore, current study could provide strategies for the preparation of highly effective p–n heterojunction photocatalysts for the mineralization of DMP and also for the treatment of other recalcitrant organic pollutants (ROPs).