The suitability of Ce3+-modified ZnO photocatalyst for the mineralization of monochlorophenol isomers in sunlight exposure

Abstract

The photocatalytic activity of Ce³⁺-modified hexagonal ZnO for the degradation/mineralization of monochlorophenol isomers (2-chlorophenol, 3-chlorophenol and 4-chlorophenol), in natural sunlight exposure, is reported. Compared to bare ZnO, the modified catalysts showed superior activity for the mineralization of MCP isomers. The identification of the intermediates disclosed that the mode of degradation of chlorophenol substrates also varies with increased Ce³⁺ loading. Increased mineralization was discovered with increasing concentration of Ce³⁺ at the surface of ZnO. The correlation of the results obtained by various analytical tools revealed that the photocatalytic removal of MCP isomers initially proceeds with the cleavage of the aromatic ring, the release of chloride ions and the formation of oxygenated intermediates. Finally, the intermediates are oxidized further by the oxidizing species to mineralization. The efficacy of the synthesized catalysts was tested for the mixture of chlorophenol isomers. Based on the intermediates formed, the major contribution of superoxide anion radicals was evidenced in the removal process. The Ce³⁺ impregnation protected the surface of ZnO against photocorrosion.