article · Chemical Engineering Journal
Single semiconductor photocatalysts often suffer from limited charge separation, which hampers their ability to break down pollutants. To address this, a four-component heterojunction combining copper phosphate, barium tungstate, carbon-coated magnesium oxide, and layered double hydroxide was synthesised via a solvothermal route. By modulating the band structures across these materials, a triple S-scheme heterojunction was established. This architecture provides two reductive and two oxidative sites, significantly enhancing charge mobility and driving the generation of reactive oxygen species under visible light. When tested on the pharmaceutical pollutant naproxen, a formulation with higher barium tungstate content degraded the drug twice as fast as one richer in layered double hydroxide and carbon-coated magnesium oxide. Although copper leaching affected catalyst stability, the multiple active sites preserved functional performance during degradation.
Pharmaceutical residues such as naproxen frequently persist in wastewater, resisting conventional water treatment methods. Designing advanced multi-component photocatalysts that operate effectively under visible light offers a route to degrade persistent drug contaminants into less harmful by-products. This approach deepens understanding of complex semiconductor interfaces, supporting the development of cleaner technologies for environmental pollution remediation and cleaner water systems.
The research presents an early-stage laboratory development aimed at environmental pollution remediation, specifically for degrading pharmaceutical contaminants in wastewater. Potential end users include municipal water treatment facilities and industrial wastewater managers seeking advanced oxidation processes. However, practical application remains distant, as catalyst formulation requires optimisation to resolve copper leaching issues and must be tested in complex, real-world effluent conditions before scale-up is feasible.
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• Triple S-scheme is designed through band structure modulation for NPX degradation. • Four-component semiconductor heterojunctions charge transfer was confirmed. • Triple and quadruple S-scheme were described as novel heterojunctions. • Two reductive and oxidative sites improved OH • > • O 2 − > h + generation for NPX mineralization. • High catalyst stability despite leaching of Cu 3 (PO 4 ) 2 due to multiple active sites. The limited charge carrier separation and transportation in single semiconductor photocatalysts has lobbied research and development in rational design and fabrication of heterojunction photocatalysts which has become a hot topic in the last decade. In-depth investigation of a four-component semiconductors interfacial charge transfer analysis considering the contribution of all components was done for the first time to deduce triple S-scheme heterojunction. This work investigated four-component semiconductors (Cu 3 (PO 4 ) 2 , BaWO 4 , C-MgO and LDH) heterojunction photocatalyst formation by the solvothermal method for visible light degradation of NPX. The degradation rate of CBLM-B (0.0429 min −1 ) with high BaWO 4 content was two times the degradation rate of CBLM-A (0.0203 min −1 ) with high LDH/C-MgO content. XPS, electrochemistry, and band structure analysis were used to propose a triple S-scheme heterojunction with high electron mobility and charge separation that enhanced the formation of OH • > • O 2 − > h + species as supported by radical trapping experiments due to presence of two oxidative and two reductive sites for stable generation of ROSs. Internal electric field (IEF) and band bending modulated an S-S interfacial strategy at the three junctions. Cu leaching affected the catalyst stability, and NPX degradation pathways were investigated with QTOF-HPLC-MS. This work demonstrated band structure adjustment for design of highly efficient triple S-Scheme heterojunctions application in environmental pollution remediation as a new development to advance scientific knowledge on four-component heterojunctions which may also be described using the Z-scheme charge transfer model.
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DOI: 10.1016/j.cej.2024.155094
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