Abstract
The construction of heterostructured photocatalyst with an appropriate energy band structure will help realize highly efficient photo-excited charge separation. In this study, ternary CuO/CeO2/ZnO nano-particle (NP) composites were synthesized by a facile two-step sol-gel method, which exhibit significantly enhanced photocatalytic degradation performance for various organic pollutants under UV and visible light excitation. The photo-responses to both UV and visible light, as well as the visible light absorption and utilization rates of ZnO are found to be synergistically intensified by CeO2 and CuO co-coupling. The first-order kinetic constants (K) of 3%CuO/CeO2/ZnO for methylene blue (MB) degradation are ~3.9, ~4.1 and ~4.8 times higher than ZnO under UV light, visible light and simulated sunlight illumination, respectively. The roles of CuO and CeO2 in optical properties and photo-degradation under UV and visible light were explored. Besides, the photogenic holes (h+) of ZnO, CeO2, and the produced hydroxyl radicals (·OH) are proved to be the main active species under UV light. Dissimilarly, under visible light, the superoxide radicals (·O2−) formed by the reactions between oxygen molecules and the photo-generated electrons (e−) of CuO moving towards the catalysts surface are also found to be important for promoting dye decomposition. The improved photo-responses, the well-matched band structure that facilitates charge transfer processes, and the highly efficient utilization of the photo-excited carriers of the ternary nano-heterostructure are suggested to be the key factors for the remarkable enhancement of photocatalytic performance of ZnO nano-photocatalyst. This work offers a low-cost strategy to acquire highly active UV and visible light-driven photocatalyst.
Highlights
Demands of the tangible current severe worldwide situation, from cleaning, energy harvesting to environment remediation techniques, are expecting the development and adoption of highly efficient photocatalytic system [1]
We explore whether CuO, CeO2 co-coupled ZnO, can analogously exhibit improved photocatalytic efficiency as a ternary hetero-structured photocatalyst system
Ce, Cu elements were respectively sourced from zinc acetate dihydrate (Zn(CH3COO)2·2H2O, Chengdu Kelon Chemical Reagent Co., LTD., Chengdu, China, ≥99.0%), cerium nitrate hexahydrate (Ce(NO3)3·6H2O, Chengdu Kelon Chemical Reagent Co., LTD., ≥99.0%) and copper acetate monohydrate (Cu(CH3COO)2·H2O, Chengdu Kelon Chemical Reagent Co., LTD., ≥99.0%) to prepare ZnO, CeO2/ZnO and CuO/CeO2/ZnO nano-particles (NPs)
Summary
Demands of the tangible current severe worldwide situation, from cleaning, energy harvesting to environment remediation techniques, are expecting the development and adoption of highly efficient photocatalytic system [1]. Classical wide band-gap metal oxide semiconductors (MOSs), such as ZnO (Eg = 3.37 eV), TiO2 (Eg = 3.20 eV), SnO2 (Eg = 3.80 eV), etc., cannot meet the requirements of a superior catalytic platform because of the limited sunlight utilization and low photo-generated charge carrier separation efficiency [1,2,3]. Numerous approaches have been explored to extend the solar absorption range of those MOSs, as well as improve the lifetime of photo-excited charge carriers. The band structure of as-treated semiconductor can be maneuvered by the defects states to extend light response range, surface defects serve as highly active sites for photocatalytic reactions [4]. In spite of the high activity of as-treated photocatalysts, these methods rely on cumbersome and expensive synthetic craft
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