Abstract
Mixed oxides containing zinc and lanthanum were prepared by coprecipitation in alkaline medium, followed by calcination at 400 °C. The initial precipitation product and the calcined form were characterized by Brunauer–Emmett–Teller (BET) method adsorption of nitrogen at −196 °C, Scanning Electron Microscopy/Electron-Probe Microanalysis (SEM/EPM), Ultraviolet—Diffuse Reflectance Spectroscopy (UV-DRS) and Infrared (IR) spectroscopy. The band gap slightly changes from 3.23 eV to 3 eV by calcination. The photocatalytic performance of the solids were investigated in diluted aqueous medium, by using clofibric acid (CA), a stable and toxic molecule used as precursor in some pesticides and drugs, as test compound, possibly found in the wastewaters in low concentrations. The effects of the degradation extent, determined by high performance liquid chromatography (HPLC) and total organic carbon (TOC) measurements, were investigated at different initial concentrations of CA. Within about 60 min the CA degradation is almost total at low concentration values (3 ppm) and reaches over 80% in 180 min for an initial concentration of 50 ppm. Moreover, the CA removal performance of photocatalyst remains excellent after three cycles of use: the removal yield was practically total after 60 min in the first two cycles and reached 95% even in the third cycle.
Highlights
The scientists’ concern for the green elimination of various persistent organic contaminants from wastewaters resulted, among others, in a high interest paid for obtaining highly performant materials for the photocatalytic reactions mediated by semiconductive solids, by oxidation reactions [1,2,3,4].This class of reactions belong to the so-called AOPs (Advanced Oxidation Process), being very popular especially for the purification of wastewaters from low amounts of pesticides, drug compounds, dyes, disinfectants and other very stable and non-biodegradable chemicals, which depreciate the water quality, despite their ppm-range concentrations [5,6]
The same allure of the XRD spectra was obtained by Maninkidan et al [17] on ZnO doped with up to 7% La, though the La to Zn ratio in the preparation was higher in our case
It should be noticed that, the ZnO XRD pattern as well as scanning electron microscopic (SEM) (JSM-7100, Jeol Ltd., Tokyo, Japan) images of pure ZnO prepared following a similar protocol as the one used in this work are available in the previous study of Lutic et al [22] and the obtained results clearly showed that the morphology of pure ZnO was really very different than that of the material obtained by coprecipitation of Zn and La
Summary
The scientists’ concern for the green elimination of various persistent organic contaminants from wastewaters resulted, among others, in a high interest paid for obtaining highly performant materials for the photocatalytic reactions mediated by semiconductive solids, by oxidation reactions [1,2,3,4]. This class of reactions belong to the so-called AOPs (Advanced Oxidation Process), being very popular especially for the purification of wastewaters from low amounts of pesticides, drug compounds, dyes, disinfectants and other very stable and non-biodegradable chemicals, which depreciate the water quality, despite their ppm-range concentrations [5,6]. A special attention was paid to the investigation of the effects of some relevant process parameters such as the initial pollutant content and catalyst load, as well as to the evaluation of its photocatalytic performance by reusing the same solid in several reaction cycles
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