Altering defect population during the solvothermal growth of ZnO nanorods for photocatalytic applications

Abstract

High abundance and low toxicity make zinc oxide very attractive for broad application in the field of photocatalysis for remediation of toxic compounds from water. Its performance could be elegantly improved by inducing native defects into ZnO semiconductor nanocrystals. However, this typically requires post-processing at high temperatures, during which many of the benefits of the original batch of monodisperse small grains are lost due to agglomeration and/or crystal growth. Within this research we show how variations in defect population are inherent to recrystallization process and that they can be tuned to some extent by choosing optimal pathways. The defects were studied by Raman, photoluminescence and EPR spectroscopy, while the surface chemistry of the ZnO nanorods, solvothermally recrystallized from ZnO nanodots, was evaluated by X-ray photoelectron spectroscopy. The produced nanorods with different dimensions were also utilized to show how effective the samples are for degradation of a model pollutant, namely caffeine. Unexpectedly, we found that the surface chemistry of our samples is not the main factor in photocatalytic efficiency. Instead, we show that the differences in photocatalytic activity are mainly determined by the defect population within the bulk formed during the recrystallization process under altered solvothermal conditions.