Sunlight responsive WO 3 /ZnO nanorods for photocatalytic degradation and mineralization of chlorinated phenoxyacetic acid herbicides in water

Abstract

Highly effective WO3/ZnO nanorods (NRs) were synthesized via a hydrothermal-deposition method for degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under natural sunlight. The structural properties of WO3/ZnO NRs such as morphology, crystal structure, porous properties and light absorption characteristics were investigated in detail. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that the prepared samples were two-phase photocatalysts consisted of WO3 and ZnO NRs. The UV-vis diffuse reflectance spectroscopy result showed that the addition of WO3 altered the optical properties of the photocatalysts. In contrast with the pure ZnO NRs, commercial anatase TiO2 and commercial WO3, the WO3/ZnO NRs showed excellent sunlight photocatalytic activities in degrading 2,4-D. The optimal WO3 loading and calcination temperature were also determined. Based on the band position, the synergetic effect of WO3 and ZnO NRs was the source of the enhanced photocatalytic activity as validated by PL and terephthalic acid-photoluminescence measurements. The reaction intermediates and degradation pathways of 2,4-D were elucidated by a HPLC method. In addition, the extent of mineralization during the 2,4-D degradation was also estimated using total organic carbon (TOC) and ion chromatography (IC) analyses.