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.