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This work investigated the photocatalytic degradation of the 4-chloro-2-methylphenoxyacetic acid herbicide and its primary intermediate (4-chloro-2-methyl phenol) using the coupled catalyst TiO2 modified with the iron oxide species, FeOOH and Fe2O3 (FeOx, 0.5 wt.%), under UV–Vis radiation assisted with persulfate or peroxymonosulfate. The FeOx–TiO2 composite prepared by microwave-assisted sol–gel method was characterized by X-Ray Diffraction, Nitrogen Physisorption, UV–Vis Diffuse Reflectance Spectroscopy, Fourier Transform Infrared Spectroscopy, Atomic Absorption Spectroscopy, Photoluminescence, X-Ray Photoelectron Spectroscopy, Thermogravimetric Analysis, Scanning Electron Microscopy, and Transmission Electron Microscopy. The anatase phase was conserved in the FeOx–TiO2 material. The coupling of FeOx in TiO2 decreased the crystallite size and enhanced the specific surface area and visible light response. A response surface methodology based on Central Composite Design was used to obtain the optimal oxidant agent (persulfate or peroxymonosulfate), oxidant dosage, and solution pH conditions to enhance the 4-chloro-2-methylphenoxyacetic acid mineralization. The 87.04% of 4-chloro-2-methylphenoxyacetic acid mineralization was achieved by FeOx–TiO2 composite with persulfate (5 mM) under UV–Vis radiation at pH 7 in 150 min showing a synergic effect. This result allowed the complete elimination of 4-chloro-2-methylphenoxyacetic acid and the by-product 4-chloro-2-methyl phenol generated during the reaction compared to 61.6 and 27.9% mineralization obtained with FeOx–TiO2 + hυ and persulfate oxidation + hυ, respectively. The photogenerated electrons in FeOx–TiO2 improved mineralization efficiency that allows the persulfate activation. Besides, the coupling between FeOx and TiO2 suppresses the electron/hole (e−/h+) pair recombination of FeOx–TiO2 photocatalyst. [ABSTRACT FROM AUTHOR]

Photocatalytic degradation of 4-chloro-2-methylphenoxyacetic acid (MCPA) in aqueous solution using Cr(III)-doped TiO under UV and visible light was investigated. The semiconductor material was synthesized by a microwave-assisted sol-gel method with Cr(III) doping contents of 0.02, 0.04, and 0.06 wt%. The catalyst was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), nitrogen physisorption, UV-Vis diffuse reflectance spectroscopy (DRS), and atomic absorption spectroscopy (AAS). The photocatalytic activity for the photodegradation of MCPA was followed by reversed-phase high-performance liquid chromatography (HPLC) and total organic carbon (TOC) analysis. The intermediates formed during degradation were identified using gas chromatography-mass spectrometry (GC-MS). Chloride ion evolution was measured by ion chromatography. Characterization results showed that Cr(III)-doped TiO materials possessed a small crystalline size, high surface area, and mesoporous structure. UV-Vis DRS showed enhanced absorption in the visible region as a function of the Cr(III) concentration. The Cr(III)-doped TiO catalyst with 0.04 wt% of Cr(III) was more active than bare TiO for the degradation of MCPA under both UV and visible light. The intermediates identified during MCPA degradation were 4-chloro-2-methylphenol (CMP), 2-(4-hydroxy-2-methylphenoxy) acetic acid (HMPA), and 2-hydroxybuta-1,3-diene-1,4-diyl-bis (oxy)dimethanol (HBDM); the formation of these intermediates depended on the radiation source. [ABSTRACT FROM AUTHOR]

In this study, the photocatalytic removal of an emerging contaminant, diclofenac (DCF) sodium, was performed using the nitrogen-doped WO/TiO-coupled oxide catalyst (WO/TiO-N). The catalyst synthesis was accomplished by a sol-gel method using tetrabutyl orthotitanate (CHOTi), ammonium p-tungstate [(NH)HWO·4HO] and ammonium nitrate (NHNO) as the nitrogen source. For comparison, TiO and WO/TiO were also prepared under similar conditions. Analysis by X-ray diffraction (XRD), N adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV-Vis spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS) were conducted to characterize the synthesized materials. The photocatalytic efficiency of the semiconductors was determined in a batch reactor irradiated with simulated solar light. Residual and mineralized DCF were quantified by high-performance liquid chromatography, total organic carbon analysis and ion exchange chromatography. The results indicated that the tungsten atoms were dispersed on the surface of TiO as WO. The partial substitution of oxygen by nitrogen atoms into the lattice of TiO was an important factor to improve the photocatalytic efficiency of WO/TiO. Therefore, the best photocatalytic activity was obtained with the WO/TiO-N catalyst, reaching 100% DCF transformation at 250 kJ m and complete mineralization at 400 kJ m of solar-accumulated energy. [ABSTRACT FROM AUTHOR]