Effect of synthesis medium on structural and photocatalytic properties of ZnO/carbon xerogel composites for solar and visible light degradation of 4-chlorophenol and bisphenol A

Abstract

The effect of synthesis medium (ethanol and water) on ZnO/Carbon xerogel photocatalysts was studied in order to increase the efficiency of the photocatalytic degradation of 4-chlorophenol and bisphenol A. The use of carbon xerogel is justified due to its excellent electrical conductivity, high surface area and porosity. The effect of the carbon content in the composites was also evaluated. The composites were characterized using scanning electron microscopy, transmission electron microscopy, dispersive energy spectrometry, X-ray diffractometry, infrared spectroscopy, nitrogen isotherms, differential scanning calorimetry, thermogravimetry, electrochemical impedance spectroscopy and Raman spectroscopy. All materials present the hexagonal crystalline structure of zinc oxide. Materials without carbon in their composition also presented the zinc hydroxychloride monohydrate phase. X-ray diffractograms and bandgap values obtained confirm the incorporation of carbon in the crystalline structure of zinc oxide. Materials produced in ethanol medium have lower values of crystallite and particle size, as well as higher graphite contents in their composition and higher specific surface area. All materials displayed photocatalytic activity when subjected to visible and solar radiation. Materials produced in ethanol displayed superior performance when compared to those synthesized in aqueous medium. The maximum values found for the degradation of 4-chlorophenol and bisphenol A were 88% and 78%, respectively, after 5 h. The mechanism of photocatalysis is strongly influenced by the generation of hydroxyl radicals and the materials were stable for three cycles of reuse. The electrochemical impedance spectroscopy confirms that the charge separation efficiency was optimized in the presence of the carbon xerogel and when the composite was produced in ethanol medium.