ZnWO4 powders with grain size in range 20 nm–10 µm have been synthesized by a simple combustion method and subsequent calcinations. The photocatalytic activities of powders were tested by degradation of methylene blue solution under UV light. The luminescence spectra and luminescence decay kinetics were studied and luminescence decay time dependence on average powder-grain size was obtained. The correlation between self-trapped exciton luminescence decay time and photocatalytic activity of ZnWO4 powders was shown. A model explaining the excitonic luminescence decay time correlation with photocatalytic activity was proposed.
The industrial hydrated amorphous titanium dioxide (TiO2ċ xH2O) was modified by treatment inside a chemical reactor under elevated pressure at low temperatures for 4 hours in an ammonia atmosphere. On the basis of the FTIR/DRS analysis the presence of nitrogen was confirmed. The XRD patterns of all of the catalysts exhibit mainly the diffraction lines of anatase phases. The photocatalytic activity of the modified photocatalysts was determined and compared to TiO2-P25 (Degussa, Germany). The high rate of phenol and dye degradation was obtained for the catalysts modified at 180°/15atm. TiO2-P25 showed similar activity in phenol decomposition like TiO2-15bar, whereas it was more active in dye decomposition.
The antifungal activity of four commercial photocatalytic paints (KEIM Ecosil ME, Titanium FA, Photo Silicate and Silicate D) in natural indoor light was investigated. The paints contained TiO2 in rutile and anatase crystalline forms as evidenced by means of the X-ray diffraction analysis. In most cases the paints inhibited growth of fungi viz. Trichoderma viride, Aspergillus niger, Coonemeria crustacea, Eurotium herbariorum, and Dactylomyces sp. The KEIM Ecosil ME paint displayed the highest antifungal effect in the light, which could be explained with the highest anatase content. The paint antifungal activity and the fungal sensitivity to the TiO2-mediated photocatalytic reaction both decreased in the following orders: KEIM Ecosil ME > Titanium FA > Photo Silicate > Silicate D and T. viride > Dactylomyces sp. > A. niger > E. herbariorum.
In presented studies the photocatalytic decomposition of NOx on gypsum plates modified by TiO2-N,Cphotocatalysts were presented. The gypsum plates were obtained by addition of 10 or 20 wt.% of different types of titanium dioxide, such as: pure TiO2 and carbon and nitrogen co-modified TiO2 (TiO2-N,C) to gypsum. TiO2-N,C photocatalysts were obtained by heating up the starting TiO2 (Grupa Azoty Zakłady Chemiczne Police S.A) in the atmosphere of ammonia and carbon at the temperature: 100, 300 i 600ºC. Photocatalyst were characterized by FTIR/DRS, UVVis/DR, BET and XRD methods. Moreover the compressive strength tests of modified gypsum were also done. Photocatalytic activity of gypsum plates was done during NOx decomposition. The highest photocatalytic activity has gypsum with 20 wt.% addition of TiO2-N,C obtained at 300ºC.
The photocatalytic efficiency of alkali niobate-based compounds (Li, Na, K) for hydrogen generation has been investigated. The systematic study showed that the highest photocatalytic activity was observed in the case of Na/Nb2O5 catalyst which contained sodium niobate (NaNbO3) phase and that the most efficient electron donor for hydrogen generation was formic acid. In addition, the effect of organic donor (HCOOH) concentration on the amount of the evolved hydrogen was studied.
The photocatalytic reduction of carbon dioxide with hydrogen was studied by Temperature-Programmed Surface Reaction (TPSR). This process was carried out in a flow reactor that was especially designed and constructed for this purpose. Titanium dioxide (TiO2, Degussa P-25) was used as supports for platinum, ruthenium and nickel catalysts. The experimental results indicated that the activity of photoreduction of CO2 changes as follows: Ru/TiO2 > Ni/TiO2 > = Pt/TiO2 > TiO2.
Carbon can form different structures with TiO2: carbon-doped TiO2, carbon coated TiO2 and composites of TiO2 and carbon. The presence of carbon layer on the surface of TiO2 as well as the presence of porous carbon in the composites with TiO2 can increase the concentration of organic pollutants on the surface of TiO2, facilitating the contact of the reactive species with the organic molecules. Carbon-doped TiO2 can extend the absorption of the light to the visible region by the narrowing of the band gap and makes the photocatalysts active under visible light irradiation. TiO2 loaded carbon can also work as a photocatalyst, on which the molecules are adsorbed in the pores of carbon and then they undergo the photocatalytic decomposition with UV irradiation. Enhanced photocatalytic activity for the destruction of some organic compounds in water was noticed on the carbon coated TiO2 and TiO2 loaded activated carbon, mostly because of the adsorptive role of carbon. However, in carbon-doped TiO2, the role of carbon is somewhat different, the replacement of carbon atom with Ti or oxygen and formation of oxygen vacancies are responsible for extending its photocatalytic activity towards the visible range.
Ammonia-modified TiO2 (TiO2/N), prepared in a pressure reactor was used as the well- active and longlife photocatalyst for the azo dye (Reactive Red 198) decomposition. The effect of aeration and the different value of the pH of the reaction medium on the photocatalytic degradation of Reactive Red 198 in water has been investigated. It has been reported that the degradation is greatly influenced by the reaction pH and the faster decomposition of azo dye took place at pH 3.5. When the solution was acidic, a larger amount of azo dye on the positively charged surface of TiO2 photocatalysts was adsorbed. From the obtained results it can be seen that the effectiveness of the decolourisation of the solution was faster by using the nitrogen-modified TiO2.
The photocatalytic production of hydrogen over several chemical compounds based on sodium niobates and tantalates has been investigated. The photocatalysts have been prepared by an impregnation method of Nb2O5 and Ta2O5 in the aqueous solution of sodium hydroxide and then the calcination at the temperature range of 450 - 800°C. In this report, we present the study showing that of the catalysts explored, the highest photocatalytic activity was shown in a sample obtained at the temperature of 450°C and containing NaTaO3 as a main phase.
In this work photocatalytic properties of TiO2 thin films doped with different amount of Tb have been described. Thin films were prepared by high energy reactive magnetron sputtering process. Comparable photocatalytic activity has been found for all doped TiO2 thin films, while different amounts of Tb dopant (0.4 and 2.6 at. %) results in either an anatase or rutile structure. It was found that the terbium dopant incorporated into TiO2 was also responsible for the amount of hydroxyl groups and water particles adsorbed on the thin film surfaces and thus photocatalytic activity was few times higher in comparison with results collected for undoped TiO2 thin films.
The removal of a non-steroidal anti-inflammatory drug (NSAID) diclofenac sodium salt (DCF, C14H10Cl2NNaO2) from water in two hybrid systems coupling photolysis or photocatalysis with direct contact membrane distillation (DCMD) is presented. A UV-C germicidal lamp was used as a source of irradiation. The initial concentration of DCF was in the range of 0.005-0.15 mmol/dm3 and the TiO2 Aeroxide® P25 loading (hybrid photocatalysis-DCMD) ranged from 0.05 to 0.4 g/dm3. Regardless of the applied hybrid system and the initial concentration of DCF, the model drug was completely decomposed within 4h of irradiation or less. Mineralization was less efficient than photodecomposition. In case of the hybrid photolysis-DCMD process the efficiency of TOC degradation after 5h of irradiation ranged from 27.3-48.7% depending on the DCF initial concentration. The addition of TiO2 allowed to improve the efficiency of TOC removal. The highest degradation rate was obtained at 0.3 gTiO2/dm3. During the process conducted with the lowest DCF initial concentrations (0.005-0.025 mmol/dm3) a complete mineralization was obtained. However, when higher initial amounts of DCF were used (0.05-0.15 mmol/dm3), the efficiency of TOC degradation was in the range of 82.5-85%. The quality of distillate was high regardless of the system: DCF was not detected, TOC concentration did not exceeded 0.7 mg/dm3 (1.9 mg/dm3 in permeate) and conductivity was lower than 1.6 μS/cm.
The removal of azo dye Acid Red 18 in hybrid photocatalysis/membrane processes systems was investigated. The photocatalytic reactions were conducted in the reactor with photocatalyst suspended in the solution. The reaction solution was recirculated through the ultrafiltration system. A commercially available titanium dioxide (Aeroxide® P25, Degussa, Germany) was used as a photocatalyst. The solution after the photocatalytic/UF reaction was applied as the feed for the membrane distillation process. The changes of various parameters, including the concentration of the dye, pH and the conductivity of the solution, TOC and TDS content were analyzed during the process.It was found that azo dye Acid Red 18 could be successfully decolourised in the hybrid photocatalysis/UF system. The catalyst particles were retained in the feed solution by means of the ultrafiltration membrane so the obtained permeate was free of TiO2. The application of ultrafiltration together with the photocatalytic process results in the separation of photocatalyst from the treated solution but does not give the complete removal of organic matter from the reaction mixture. Membrane distillation applied with the permeate after the photocatalysis/UF process as a feed gives a complete separation of TOC from the treated solution and the obtained product is practically pure water.
In this work photocatalytic properties of TiO2 thin fi lms doped with 8.51 at. % of Nd were described. The self-cleaning phenomenon of thin fi lms was discussed together with the structural, optical and surface properties of prepared thin fi lms. Transparent coatings based on titanium dioxide were manufactured by high-energy reactive magnetron sputtering process. Incorporation of Nd during sputtering process results in amorphous behavior, without a signifi cant infl uence on transparency and colour as compared to the undoped TiO2-rutile matrix. Nevertheless, doping with neodymium doubles the photocatalytic activity of the matrix due to higher quantity of photo-generated charge carriers and more effi cient mechanism of energy transfer.
The aim of the presented work was the removal of organic dye, Acid Red 18, from water using a novel reactor with the photoactive refill. Titanium dioxide was immobilized on the base material as a thin layer from the alcoholic suspension followed by thermal stabilization. The prepared coating exhibits high stability in repeated cycles of water treatment. The complete removal of colour was achieved in a relatively short time of 14 hours. The proposed reactor with the photoactive refill solves the problem of the necessity of the replacement of the reactor or parts of the reactor when the photocatalysts activity decreases. In the case of activity drop of the photocatalyst, only the photoactivve refill can be easily replaced.
The presented studies have focused on the influence of TiO2 properties, such as crystalline phase, crystallite size and surface area, on the effectiveness of degradation of azo dyes in water under UV irradiation. Two monoazo dyes: Acid Red 18 (AR18, C20H11N2Na3O10S3) and Acid Yellow 36 (AY36, C18H14N3NaO3S), and one polyazo dye Direct Green 99 (DG99, C44H28N12Na4O14S4) were applied as model compounds. The photocatalysts were prepared from a crude titanium dioxide obtained directly from the production line (sulfate technology) at the Chemical Factory "Police" (Poland). The crude TiO2 was calcinated in air for 1-4h at the temperatures ranging from 600 to 800°C. The BET specific surface area of TiO2 decreased gradually with increasing the calcination temperature. The crude TiO2 exhibited specific surface area of 277 m2/g. In case of the catalysts heated at 600, 700 and 800°C the BET surface area amounted to 62.3-53.3, 33.4-26.8 and 8.9-8.3 m2/g, for the calcination time of 1-4h, respectively. The crystallite size of anatase increased with increasing heat treatment temperature and ranged from 19 to 53 nm, for the temperatures of 600-800°C, respectively. The catalysts annealed at 600 and 700°C contained primarily anatase phase (94-97%), whereas the photocatalysts heated at 800°C were composed mainly of rutile (97-99%). The highest effectiveness of azo dyes degradation was obtained in case of the photocatalyst calcinated for 1h at 700°C. The photocatalyst was composed mainly of anatase (97%) with crystallite size of 27 nm. The most effectively photodegraded was AR18, having the molecular weight of 640.4 g/mol. The most difficult to degrade was AY36 exhibiting the lowest molecular weight from all the dyes used (375.4 g/mol).
Titanium dioxide thin films doped with the same amount of neodymium were prepared using two different magnetron sputtering methods. Thin films of anatase structure were deposited with the aid of Low Pressure Hot Target Magnetron Sputtering, while rutile coatings were manufactured using High Energy Reactive Magnetron Sputtering process. The thin films composition was determined by energy dispersive spectroscopy and the amount of the dopant was equal to 1 at. %. Structural properties were evaluated using transmission electron microscopy and revealed that anatase films had fibrous structure, while rutile had densely packed columnar structure. Atomic force microscopy investigations showed that the surface of both films was homogenous and consisted of nanocrystalline grains. Photocatalytic activity was assessed based on the phenol decomposition. Results showed that both thin films were photocatalytically active, however coating with anatase phase decomposed higher amount of phenol. The transparency of both thin films was high and equal to ca. 80% in the visible wavelength range. The photoluminescence intensity was much higher in case of the coating with rutile structure.
This paper deals with the problem of the photocatalytic reactor construction. The supported TiO2 on γ- Al2O3 modified with Mo or V addition was used as the photocatalyst, whereas phenol and formaldehyde were chosen as the model pollutants. The counter - current contact of reagents and catalysts is the main advantage of the construction and enables a significant COD reduction of the highly concentrated wastewaters.
Photocatalysis process belongs to an advanced oxidation technology for the removal of persistent organic compounds and microorganisms from water. It is the technology with a great potential, a low-cost, environmental friendly and sustainable treatment technology to align with the “zero” waste scheme in the water/wastewater industry. At present, the main technical barriers that impede its full commercialization remained on the post-recovery of the catalyst particles after water treatment. This paper reviews the background of the process and photooxidation mechanisms of the organic pollutants and microorganisms. The review of the latest progresses of engineered-photocatalysts, photo-reactor systems, and the kinetics and modeling associated with the photocatalytic and photodisinfection water and wastewater treatment process, has been presented. A number of potential and commercial photocatalytic reactor configurations are discussed, in particular the photocatalytic membrane reactors. The effects of key photo-reactor operation parameters and water quality on the photoprocess performances in terms of the mineralization and disinfection are assessed.
PL
Proces fotokatalizy należy do wysoko zaawansowanych technik utleniania o możliwościach usuwania trwałych związków organicznych i mikroorganizmów z wody. Jest to technologia o dużym potencjale, niskich kosztach, przyjazna dla środowiska oraz o cechach zrównoważonego rozwoju i "zerowym" odprowadzaniu odpadów w przemysłowych systemach wodno-ściekowych. Obecnie, główne bariery techniczne, które ograniczają pełną komercjalizację metody, są związane z zagospodarowaniem cząstek katalizatora po uzdatnianiu wody (ścieków). W pracy przedstawiono podstawy teoretyczne procesu oraz mechanizmy fotoutlenienia zanieczyszczeń organicznych i mikrobiologicznych. Dokonano również przeglądu ostatnich postępów w badaniach inżynierii fotokatalizatorów, systemów fotoreaktorów oraz kinetykę fotomineralizacji i fotodezynfekcji i ich modelowanie związane z procesami fotokatalitycznego oczyszczania wody (ścieków). Omówiono wiele potencjalnych i komercyjnych konfiguracji reaktorów fotokatalitycznych, w szczególności membranowych reaktorów fotokatalitycznych oraz wpływ parametrów operacyjnych i jakości wody na efektywność mineralizacji i dezynfekcji.
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