Photodegradation of contaminants using Ag@AgCl/rGO assemblages: Possibilities and limitations

Plasmonic photocatalysts of the form Ag@AgCl/rGO were synthesized by a deposition-precipitationphotoreduction method and the composite materials characterized using Raman spectroscopy, attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The as-prepared plasmonic photocatalysts exhibited enhanced photoactivity for the degradation of formic acid (FA) under visible light irradiation, however, both the Ag@AgC1 and the graphene oxide support underwent continuous transformation during photolysis. The high activity was attributed principally to the ability of the composite Ag degrees/AgCl system to absorb light in the visible wavelength region and to retard the recombination of electron-hole pairs. While the presence of the reduced graphene oxide (rGO) support may also have contributed to a reduction in rate of electron-hole pair recombination, the effect was not found to be particularly significant. HO trapping experiments with phthalhydrazide as well as the influence of t-butanol on FA degradation suggested that either photo-formed holes or surface chlorine atoms were the main reactive species inducing degradation of FA under visible light irradiation. Total free chlorine, but not hydrogen peroxide, could be detected by N,N-diethyl-p-phenylenediamine (DPD) spectrophotometry suggesting that while photogenerated holes decay via reaction with chloride ions, photogenerated electrons decay via a pathway other than reaction with oxygen. Possible reaction mechanisms that conform to these observations are discussed. Although this system has potential for the oxidative degradation of contaminants, greater understanding of the factors that promote excessive Ag(I) reduction, concomitant formation of Ag(0) and eventual deactivation of the catalyst is needed. (C) 2013 Elsevier B.V. All rights reserved.