Abstract
A TiO2–ZnO binary oxide system (with molar ratio TiO2:ZnO = 8:2) was synthesized by a hydrothermal method, assisted by calcination at temperatures of 500, 600 and 700 °C, using zinc citrate as the precursor of ZnO. The morphology (SEM, TEM), crystalline structure (XRD, Raman spectroscopy), diffuse reflectance spectra (DRS), chemical surface composition (EDXRF), porous structure parameters (low-temperature N2 sorption) and characteristic functional groups (FT-IR) of the TiO2–ZnO oxide materials were comprehensively analyzed. The novelty of this work is the observation of the coexistence of the crystalline structures of anatase and ZnTiO3 in TiO2–ZnO oxide materials. Moreover, it is shown that the obtained materials absorb visible radiation. The key stage of the study was the evaluation of the photocatalytic activity of the TiO2–ZnO binary oxide systems in the degradation of model organic pollutants: C.I. Basic Red 1, C.I. Basic Violet 10, C.I. Basic Blue 3 and 4-nitrophenol. For all synthesized materials, a high efficiency of degradation of the model organic impurities was demonstrated. The results show that the synthesized products may be materials of interest for use in the degradation of organic pollutants. Moreover, the kinetics of the photocatalytic degradation of selected organic compounds were determined based on the Langmuir–Hinshelwood equation, assuming a pseudo-first-order (PFO) reaction.
Highlights
Much attention has been paid in recent years to the discharge of sewage containing toxic organic pollutants such as synthetic dyes and phenol derivatives
The results show that the synthesized TiO2–ZnO binary oxide systems may be promising materials for the degradation of organic pollutants in visible light
The main objective of this work was the synthesis of a TiO2–ZnO oxide system using a ZnO precursor that had not previously been described: zinc citrate
Summary
Much attention has been paid in recent years to the discharge of sewage containing toxic organic pollutants such as synthetic dyes and phenol derivatives. The resulting wastewater contains 20–30% of the toxic pollutants, with an average concentration of 2000 ppm of organic dye (Esparza et al 2007). Synthetic dyes are produced and consumed in large quantities, and can cause considerable environmental pollution and serious health risks due to their stability and toxicity (Shukla and Gupta 1992). To reduce the negative impact on the environment, many methods of removing dyes from water and wastewater have been developed; conventional water treatment technologies such as solvent extraction and chemical treatment processes often produce hazardous by-products and generate large amounts of solid wastes, which is not environmentally friendly (Galindo et al 2001; Pandurangan et al 2001; Slokar and Le Marechal 1998)
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