Ozone-Based Advanced Oxidation Processes for Primidone Removal in Water using Simulated Solar Radiation and TiO2 or WO3 as Photocatalyst.
ABSTRACT: In this work, primidone, a high persistent pharmacological drug typically found in urban wastewaters, was degraded by different ozone combined AOPs using TiO2 P25 and commercial WO3 as photocatalyst. The comparison of processes, kinetics, nature of transformation products, and ecotoxicity of treated water samples, as well as the influence of the water matrix (ultrapure water or a secondary effluent), is presented and discussed. In presence of ozone, primidone is rapidly eliminated, with hydroxyl radicals being the main species involved. TiO2 was the most active catalyst regardless of the water matrix and the type of solar (global or visible) radiation applied. The synergy between ozone and photocatalysis (photocatalytic ozonation) for TOC removal was more evident at low O3 doses. In spite of having a lower band gap than TiO2 P25, WO3 did not bring any beneficial effects compared to TiO2 P25 regarding PRM and TOC removal. Based on the transformation products identified during ozonation and photocatalytic ozonation of primidone (hydroxyprimidone, phenyl-ethyl-malonamide, and 5-ethyldihydropirimidine-4,6(1H,5H)-dione), a degradation pathway is proposed. The application of the different processes resulted in an environmentally safe effluent for Daphnia magna.
Project description:TiO<sub>2</sub> is an attractive catalyst for the photocatalytic degradation of organic pollutants. However, owing to its large band gap, it can only be activated by ultraviolet (UV) light, which constitutes a small portion of solar energy. Therefore, there has been significant interest in extending its light absorption range from UV to visible light. In this study, fluorinated TiO<sub>2</sub> hollow spheres (FTHSs) were prepared via a rapid and simple wet chemical process using ammonium hexafluorotitanate, and then FTHS/WO<sub>3</sub> heterostructures with different weight ratios of the FTHS and WO<sub>3</sub> nanoparticles were synthesized via a simple wet impregnation method. The formation of the hybrid structure was confirmed by various characterization techniques. The photocatalytic activity of the synthesized photocatalysts in the photodegradation of rhodamine B, a model pollutant, was evaluated under visible light irradiation. The FTHS/WO<sub>3</sub> heterostructures exhibited significantly improved photocatalytic activity compared to the bare FTHS or WO<sub>3</sub> nanoparticles. The photodegradation efficiency of the FTHS/WO<sub>3</sub> heterostructure in the present study was up to 0.0581 min<sup>-1</sup>. Detailed mechanisms that lead to the enhanced photocatalytic activity of the heterostructures are discussed. In addition, comparative experiments reveal that the photodegradation efficiency of the FTHS/WO<sub>3</sub> heterostructure under visible light irradiation is superior to that of the P25/WO<sub>3</sub> heterostructure prepared from the commercially available TiO<sub>2</sub> catalyst (P25) via the same impregnation method.
Project description:Nanoparticulate double-heterojunction photocatalysts comprising TiO<sub>2(Anatase)</sub>/WO<sub>3</sub>/TiO<sub>2(Rutile)</sub> were produced by a sol-gel method. The resulting photocatalysts exhibit clear synergistic effects when tested toward the degradation of methyl orange under both UV and visible light. Kinetic studies indicate that the degradation rate on the best double-heterojunction photocatalyst (10 wt % WO<sub>3</sub>-TiO<sub>2</sub>) depends mainly on the amount of dye concentration, contrary to pure oxides in which the degradation rate is limited by diffusion-controlled processes. The synergistic effects were confirmed through systematic and careful studies including holes and OH radical formation, X-ray diffraction, electron microscopy, elemental analysis, UV-vis diffuse reflectance spectroscopy, and surface area analysis. Our results indicate that the successful formation of a double heterojunction in the TiO<sub>2(Anatase)</sub>/WO<sub>3</sub>/TiO<sub>2(Rutile)</sub> system leads to enhanced photoactivity when compared to individual oxides and commercial TiO<sub>2</sub> P25.
Project description:Humic acid (HA) is the main component of organic matter in effluent from wastewater treatment. The effective removal of HA is significant. In this study, a novel catalyst was prepared using a transition metal oxide as the active component and Al<sub>2</sub>O<sub>3</sub> as a granular carrier. The mechanism of catalytic ozonation of HA under neutral pH conditions and its efficiency were investigated. Under the chosen conditions (an ozone concentration of 2.2 mg/L, 50 mg/L HA solution, catalyst dosage of 5 g/L and initial pH of 6.49), the Cu/Ce-Al<sub>2</sub>O<sub>3</sub> bimetallic catalyst led to 54.79% TOC removal rate after 30 min; the removal rate by ozone alone was only 20.49%. The characteristics of organic compounds determined by FT-IR and GC-MS showed that organic compounds were degraded significantly by the catalytic treatment. The addition of catalysts could effectively degrade toxic intermediates and reduce the acute toxicity produced by ozonation. Humic acid substances were largely removed and transformed into biodegradable intermediates. This study proposes a new and efficient ozonation catalyst for practical applications in advanced wastewater treatment.
Project description:This paper presents an intensification study of an ozonation process through an ultrasonic pre-treatment for the elimination of humic substances in water and thus, improve the quality of water treatment systems for human consumption. Humic acids were used as representative of natural organic matter in real waters which present low biodegradability and a high potential for trihalomethane formation. Ultrasonic frequency (98 kHz, 300 kHz and 1 MHz), power (10-40 W) and sonicated volume (150-400 mL) was varied to assess the efficiency of the ultrasonic pre-treatment in the subsequent ozonation process. A direct link between hydroxyl radical (HO) formation and fluorescence reduction was observed during sonication pre-treatment, peaking at 300 kHz and maximum power density. Ultrasound, however, did not reduce total organic carbon (TOC). Injected ozone (O<sub>3</sub>) dose and reaction time were also evaluated during the ozonation treatment. With 300 kHz and 40 W ultrasonic pre-treatment and the subsequent ozonation step (7.4 mg O<sub>3</sub>/L<sub>gas</sub>), TOC was reduced from 21 mg/L to 13.5 mg/L (36% reduction). HO attack seems to be the main degradation mechanism during ozonation. A strong reduction in colour (85%) and SUVA<sub>254</sub> (70%) was also measured. Moreover, changes in the chemical structure of the macromolecule were observed that led to the formation of oxidation by-products of lower molecular weight.
Project description:Extending the absorption range of TiO<sub>2</sub> nanofibers to visible light is a great improvement of the photocatalytic property of TiO<sub>2</sub>. In this study, TiO<sub>2</sub>/WO<sub>3</sub>/C/N nanofibers were prepared by electrospinning using precursors soluble in water then annealing in argon. Titanium(IV) bis(ammonium lactato)dihydroxide (TiBALDH) and ammonium metatungstate (AMT) were used as the precursor for TiO<sub>2</sub> and WO<sub>3</sub> respectively. Different volume ratios of the precursors were added to a solution of PVP before electrospinning. The fibers were studied by XPS, SEM-EDX, TEM, FTIR, XRD, Raman spectroscopy and UV-VIS diffuse reflectance spectroscopy (DRS). The photocatalytic degradation of methylene blue by the fibers in visible light was investigated. The fibers had anatase TiO<sub>2</sub> and monoclinic WO<sub>3</sub>. Based on UV-VIS DRS and Kubelka-Munk function the fibers could absorb visible light. Moreover, 100% TiBALDH had an indirect band gap of 2.9 eV, and the band gap decreased with increase in AMT, i.e., for 0% TiBALDH, band gap was 2.4 eV. The fibers degraded methylene blue dye in visible light, and 90% TiBALDH had the highest photocatalytic activity, i.e., it degraded 40% of the dye after 240 min.
Project description:Heterogeneous photocatalysis of TiO<sub>2</sub> is one of the most efficient advanced oxidation processes for water and air purification. Here, we prepared hierarchical TiO<sub>2</sub> layers (Spikelets) by hollow-cathode discharge sputtering and tested their photocatalytic performance in the abatement of inorganic (NO, NO<sub>2</sub>) and organic (4-chlorophenol) pollutant dispersed in air and water, respectively. The structural-textural properties of the photocatalysts were determined via variety of physico-chemical techniques (XRD, Raman spectroscopy, SEM, FE-SEM. DF-TEM, EDAX and DC measurements). The photocatalysis was carried out under conditions similar to real environment conditions. Although the abatement of NO and NO<sub>2</sub> was comparable with that of industrial benchmark Aeroxide<sup>®</sup> TiO<sub>2</sub> P25, the formation of harmful nitrous acid (HONO) product on the Spikelet TiO<sub>2</sub> layers was suppressed. Similarly, in the decontamination of water by organics, the mineralization of 4-chlorophenol on Spikelet layers was interestingly the same, although their reaction rate constant was three-times lower. The possible explanation may be the more than half-magnitude order higher external quantum efficacy (EQE) compared to that of the reference TiO<sub>2</sub> P25 layer. Therefore, such favorable kinetics and reaction selectivity, together with feasible scale-up, make the hierarchical TiO<sub>2</sub> layers very promising photocatalyst which can be used for environmental remediation.
Project description:We report the synthesis of a three-dimensional graphene (3DG)-TiO<sub>2</sub> nanocomposite by covalently attaching P25 TiO<sub>2</sub> nanoparticles onto pristine 3DG through a perfluorophenyl azide-mediated coupling reaction. The TiO<sub>2</sub> nanoparticles were robustly attached on the 3DG surface, with minimal particle agglomeration. In photocatalytic CO<sub>2</sub> reduction, the 3DG-TiO<sub>2</sub> nanocomposite demonstrated excellent activity, about 11 times higher than that of the P25 TiO<sub>2</sub> nanoparticles. The enhanced activity can be partially attributed to the highly dispersed state of the P25 TiO<sub>2</sub> nanoparticles on the 3DG substrate. This 3DG-based system offers a new platform for fabricating photocatalytic materials with enhanced activities.
Project description:The mechanism of photodegradation of organic pollutants in seawater by TiO<sub>2</sub>-based catalysts irradiated by visible light was first explored by adding holes and free radical traps. The results showed that the photogenerated holes formed by the catalyst played a key role in the degradation of organic pollutants, regardless of whether the photodegradation occurred in seawater or pure water. Considering that the Yb-TiO<sub>2</sub>-rGO catalyst has a strong adsorption for organics, the salt ion almost did not interfere with the adsorption of pollutants by Yb-TiO<sub>2</sub>-rGO. Therefore, the degradation performance of Yb-TiO<sub>2</sub>-rGO did not remarkably change in the two water systems. For P25-ZN with a weak adsorption capacity for organics, several salt ions in the seawater hindered the contact of pollutants with the catalyst surface. Thus, the degradation rate of P25-ZN for phenol was significantly reduced. After the solvothermal reduction treatment for catalysts using ethylene glycol (EG) as the solvent, the increase in the Ti<sup>3+</sup> content in the catalyst improved the visible-light response and activity of the catalyst. In addition, a small amount of EG grafted on the catalyst surface promoted the photocatalytic reaction process on the catalyst surface, thereby effectively resisting the interference of salt ions.
Project description:The electro-peroxone (E-peroxone) process is an emerging electrocatalytic ozonation process that is enabled by in situ producing hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) from cathodic oxygen reduction during ozonation. The in situ-generated H<sub>2</sub>O<sub>2</sub> can then promote ozone (O<sub>3</sub>) transformation to hydroxyl radicals (•OH), and thus enhance the abatement of ozone-refractory pollutants compared to conventional ozonation. In this study, a chemical kinetic model was employed to simulate micropollutant abatement during the E-peroxone treatment of various water matrices (surface water, secondary wastewater effluent, and groundwater). Results show that by following the O<sub>3</sub> and •OH exposures during the E-peroxone process, the abatement kinetics of a variety of model micropollutants could be well predicted using the model. In addition, the effect of specific ozone doses on micropollutant abatement efficiencies could be quantitatively evaluated using the model. Therefore, the chemical kinetic model can be used to reveal important information for the design and optimization of the treatment time and ozone doses of the E-peroxone process for cost-effective micropollutant abatement in water and wastewater treatment.
Project description:Nanosized titanium oxide (TiO<sub>2</sub>) material is a promising photocatalyst for the degradation of organic pollutants, whereas the difficulty of its recycling hinders its practical application. Herein, we reported the preparation of a novel titanium oxide/polysulfone (TiNPs/PSF) composite hollow microspheres by the combination of Pickering emulsification and the solvent evaporation technique and their application for the photodegradation of methyl blue (MB). P25 TiO<sub>2</sub> nanoparticles dispersed on the surface of PSF microspheres. The porosity, density and photoactivity of the TiNPs/PSF composite microsphere are influenced by the TiO<sub>2</sub> loading amount. The composite microsphere showed good methyl blue (MB) removal ability. Compared with TiO<sub>2</sub> P25, and PSF, a much higher MB adsorption speed was observed for TiNPs/PSF microspheres benefited from their porous structure and the electrostatic attractions between the MB+ and the negatively charged PSF materials, and showed good degradation efficiency. For TiNPs/PSF composite microsphere with density close to 1, a 100% MB removal (10 mg L<sup>-1</sup>) within 120 min at a catalyst loading of 2.5 g L<sup>-1</sup> can be obtained under both stirring and static condition, due to well dispersing of TiO<sub>2</sub> particles on the microsphere surface and its stable suspending in water. For the non-suspended TiNPs/PSF composite microsphere with density bigger than 1, the 100% MB removal can be only obtained under stirring condition. The removal efficiency of MB for the composite microspheres retained 96.5%, even after 20 cycles. Moreover, this composite microsphere also showed high MB removal ability at acidic condition. The high catalysis efficiency, excellent reusability and good stability make this kind of TiNPs/PSF composite microsphere a promising photocatalyst for the water organic pollution treatment.