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Opis: The efficient visible light driven photocatalytic reduction of hexavalent chromium, Cr(VI) was demonstrated using ZnO nanoparticles (NPs) decorated with oxo-clusters of transition metals. The ZnO NPs were synthesized by a facile one-pot solvothermal synthesis followed by a fast microwave-assisted (MW) grafting of transition metals on the surface of NPs. Nickel was found to be the most active transition metal for photocatalytic activity as demonstrated by reduction of Cr(VI) to Cr(III). The optimally grafted samples contained 0.5 wt% Ni and increased photocatalytic activity by almost one-fold. The oxo-clusters did not enter the lattice of ZnO but rather resided on the surface and their efficient bonding to the ZnO surface was proved by Raman, TEM and X-Ray absorption techniques. Influence of MW power was studied and shown that excessive power load leads to formation of elongated structures of ZnO which decreases the photocatalytic activity. It was demonstrated by measuring fluorescent radical products that electrons, efficiently transferred via oxygen, were the main active species in combination with the unchanged oxidation power of holes and • OH in the grafted samples. The applicability of the materials was tested in immobilized plug flow photoreactor system degrading five pharmaceuticals simultaneously where their long-term use was shown.
Ključne besede: Zinc oxide, Pharmaceuticals, Grafting, Cr(VI), Zn XANES, Zn EXAFS
Objavljeno v RUNG: 24.10.2024; Ogledov: 318; Prenosov: 3
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Opis: The effect of different water matrices on the photocatalytic degradation of dissolved pharmaceuticals was explored. The focus was on the degradation efficiencies in wastewater effluent from a bioreactor and water effluent from a central wastewater treatment plant and comparing the results with degradation in deionized H2O. The compounds tested included: oxytetracycline, marbofloxacin, ibuprofen, diclofenac, phenytoin, ciprofloxacin, sulfamethoxazole. For the experiments performed in this study, a compact packed-bed photocatalytic reactor was used in which the hybrid TiO2 photocatalyst (sol-gel/P25) was deposited on ~3 mm glass beads. As expected, the reactions proceed more slowly in wastewater than in deionized water, yet it is shown that removal of the compounds from the water is still possible even when other organic molecules are present. Total organic carbon measurements have shown that complete mineralization takes place albeit at slower rates than the initial degradation of parent compounds. The results show that an acidic pH can increase the reaction rates and the adsorption on the photocatalyst surface. Analyses of the degradation intermediates were performed using tandem liquid chromatography triple-quadrupole mass spectrometry system. Additionally, X-ray absorption spectroscopy was applied to get insight into the local structure of the photocatalyst before and after use. Understanding the effects that different wastewater compositions have on photocatalytic reactions will help to refine the potential applications of the technology.
Ključne besede: titanium dioxide, sol-gel processes, functionla applications, water treatment
Objavljeno v RUNG: 30.09.2022; Ogledov: 2193; Prenosov: 0
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Ključne besede: photocatalysts, TiO2, Cu/Zr, photodegradation, material characterization, photothermal spectrometry
Objavljeno v RUNG: 23.11.2021; Ogledov: 2561; Prenosov: 100
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Opis: Due to many advantageous physiochemical properties, titanium dioxide (TiO2) is the most widely used photocatalyst in numerous applications, such as wastewater treatment and air purification, self-cleaning surfaces and energy conversion (H2 generation). However, one of its disadvantages is the high electron-hole recombination rate, and coupling with other semiconductors is one of the strategies to improve it. The objective of this dissertation was to investigate how the photocatalytic activity of pure TiO2 can be improved by tin modification and to explain the mechanism of increased or hindered photoactivity in correlation with the structural properties of the modified TiO2 photocatalysts. A new low-temperature sol-gel synthesis route was developed to prepare Sn- or SnO2-modified TiO2 photocatalysts. In both cases, organic tin and titanium precursors were used. Tin in the form of Sn cations was used to prepare Sn-modified TiO2. In this case, the precursors went through the sol-gel reaction together to form a Sn-TiO2 sol. In the case of SnO2 modification, the SnO2 sol was prepared separately and additionally mixed with the TiO2 sol to form a TiO2/SnO2 bicomponent semiconductor system. Different molar ratios of tin to titanium were prepared to investigate the correlation between the tin concentration and the photocatalytic properties of the photocatalysts in the form of thin films. The results were used to optimize the synthesis conditions to obtain an improved activity of the modified TiO2 photocatalysts under UV-irradiation. The photocatalytic activity of the thin films was determined by measuring the degradation rate of an azo dye. An increase of up to 40 % in the photocatalytic activity of the dried samples (at 150 °C) was achieved when the TiO2 was modified with the Sn or SnO2 in a concentration range of 0.1 to 1 mol.%. At higher Sn or SnO2 loadings and after calcination of the samples at 500 °C, the photocatalytic activity of the photocatalyst was reduced compared to the unmodified TiO2. Different characterization techniques (UV-Vis, XRD, nitrogen physisorption, TEM, SEM and XAS) were employed to clarify the mechanism responsible for the enhanced and hindered photocatalytic performance of the Sn- and SnO2-modified TiO2 photocatalysts. The results showed that a nanocrystalline structure is already achieved in the samples by the low-temperature film treatment (drying at 150 °C) and that the photocatalytic efficiency is mainly influenced by the crystalline phase composition: anatase/rutile in the case of Sn-modified and TiO2/SnO2 in the case of SnO2-modified TiO2. The crystal size and specific surface area differ insignificantly between the equally thermally treated samples and partly explain the differences in photoefficiency of the calcined samples compared to the dried samples. The structural study at the atomic level, using the Sn K-edge EXAFS, revealed that Sn cations act as nucleation sites for the anatase to rutile transformation in the Sn-modified TiO2 photocatalysts, while in the SnO2-modified TiO2 samples the nanocrystalline cassiterite SnO2 is bound to the TiO2 nanocrystallites via the Sn-O-Ti bond. In both cases, the advantage of coupling the two semiconductors was achieved by separating the charge carriers and thus prolonging their lifetime for accessibility to participate in the redox reactions. The maximum activity enhancement was achieved in the low concentration range (0.1–1 mol.%), which means that an optimal ratio and contact of the two phases are obtained for the given physical parameters, such as particle size, shape and specific surface area of the catalyst.
Ključne besede: Sn-modified TiO2, SnO2-modified TiO2, low-temperature sol-gel, thin films, photocatalytic activity, anatase/rutile system, Sn K-edge EXAFS, dissertations
Objavljeno v RUNG: 09.06.2021; Ogledov: 6135; Prenosov: 173
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Opis: The Sn-modified TiO2 photocatalysts are prepared by low-temperature sol-gel processing based on organic titanium and tin precursors with varied Sn concentrations (from 0.1–20 mol .%). The role of Sn dopant as the promotor of the formation of TiO2 rutile crystalline phase is explained and the optimal Sn concentration for preparation of efficient Sn-modified titania photocatalyst is determined. Up to 40 % increase in photocatalytic activity is achieved in Sn-modified TiO2 photocatalytic thin films dried at 150 °C with low Sn concentrations in the range from 0.1 to 1 mol .%. At low Sn concentrations optimal ratio between anatase and rutile (nano)crystals is obtained, which facilitates charge separation at the TiO2 photocatalyst’s surface. When the concentration of Sn increases above 5 mol.% or when the films are calcined at 500 °C, the relative amount of rutile phase with inferior photocatalytic activity, increases and the nanocrystals of titania grow, leading to fewer active sites per unit mass and the reduction of activity in comparison to unmodified TiO2.
Ključne besede: Anatase-rutile Sn-modified TiO2 XAS analysis Photocatalytic activity
Objavljeno v RUNG: 10.02.2020; Ogledov: 3792; Prenosov: 0
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