Kinetic studies of direct blue photodegradation over flower-like TiO<Subscript>2</Subscript>

The kinetics of photocatalytic oxidation reaction for direct blue solution was studied by using flower-like TiO₂ under the irradiation of ultraviolet (UV) light. A series of possible affecting factors were studied, including pH value, the additive amount of light catalyst, H₂O₂ and with or without Ag modification. The kinetics of photocatalytic degradation under UV was found following a pseudo-second-order reaction kinetic model with high regression coefficients (R ²). It has been demonstrated that the initial concentration and its related factors have influenced the photocatalytic degradation efficiency and corresponding kinetic parameters. Also, the kinetic parameter k is increasing with the degradation efficiency.     

Kinetics and mechanism of photocatalytic degradation of metobromuron by TiO2 in simulated sunlight

The kinetics of photocatalytic degradation of metobromuron in aqueous solution, with TiO₂ as photocatalyst under simulated sunlight irradiation, have been systematically investigated. The single-variable-at-a-time method and the central composite design based on response surface methodology were used to study the individual and synergistic effects of several classical conditions on the efficiency of photocatalysis. Three different conditions, TiO₂ concentration, pH, and initial concentration of metobromuron, were found to independently determine the efficiency of degradation. The optimum degradation conditions were: TiO₂ concentration 3.00 g/L, pH 7.88, and initial concentration of metobromuron 60.23 μM. In addition, a mechanism of degradation of metobromuron is tentatively proposed on the basis of the experimental results and theoretical calculation of frontier electron densities and point charges. The results suggest that substitution of the Br atom, addition of ·OH radicals, and the cleavage of urea side chain are the predominant degradation pathways during the initial stage of photocatalytic degradation.     

UV-assisted degradation of propiconazole in a TiO2 aqueous suspension: identification of transformation products and the reaction pathway using GC/MS

Photocatalytic degradation of propiconazole, a triazole pesticide, in the presence of titanium dioxide (TiO₂) under ultraviolet (UV) illumination was performed in a batch type photocatalytic reactor. A full factorial experimental design technique was used to study the main effects and the interaction effects between operational parameters in the photocatalytic degradation of propiconazole in a batch photo-reactor using the TiO₂ aqueous suspension. The effects of catalyst concentration (0.15–0.4 gL^?1), initial pH (3–9), initial concentration (5–35 mg L^?1) and light conditions were optimised at a reaction time duration of 90 min by keeping area/volume ratio constant at 0.919 cm² mL^?1. Photocatalytic oxidation of propiconazole showed 85% degradation and 76.57% mineralisation under UV light (365 nm/30 Wm^?2) at pH 6.5, initial concentration 25 mg L^?1 and constant temperature (25 ± 1 °C). The Langmuir–Hinshelwood kinetic model has successfully elucidated the effects of the initial concentration on the degradation of propiconazole and the data obtained are consistent with the available kinetic parameters. The photocatalytic transformation products of propiconazole were identified by using gas chromatography–mass spectrometry (GC/MS). The pathway of degradation obtained from mass spectral analysis shows the breakdown of transformation products into smaller hydrocarbons (m/z 28 and 39).     

Photocatalytic degradation of triazine dyes over N-doped TiO2 in solar radiation

Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO₂ in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO₂ was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO₂ was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO₂ was 39.5, 86.0, and 96.3 mg g^?1 for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO₂ when compared with that of undoped TiO₂. Moreover, the degradation of RY 84 on N-doped TiO₂ in sunlight was faster than the commercial Aeroxide^® P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l^?1 Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO₂. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l^?1, due to the strong absorption of photons in the wavelength range 200–400 nm by the dye solution. LC–MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO₂.     

Physical properties of nano-titania hollow fibers and their photocatalytic activity in the decomposition of phenol

A series of nano-titania (TiO₂) photocatalytic materials with a hollow fiber structure were successfully prepared using tetra-n-butyl titanate (Ti(OC₄H₉)₄) as precursor and cotton fiber as the template. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and N₂ adsorption-desorption measurements were employed to characterize the morphology, crystal structure, and surface structure of the samples. The photocatalytic activities of the samples were studied by phenol photodegradation in water under UV irradiation. The effect of calcination temperature, photocatalyst dosage, initial concentration of phenol and irradiation time on the photodegradation of phenol was studied. Results showed that the TiO₂ fiber materials have hollow structures, indicating that these materials had a large specific surface area. The fiber structure material showed better photocatalytic properties for the degradation of phenol than pure TiO₂ under UV light, and the sample calcined at 500°C exhibited the highest phenol photodegradation efficiency. In addition, the possibility of cyclic usage of the photocatalyst was also confirmed, the photocatalytic activity of TiO₂ fiber remained ca. 90% of photocatalytic activity of the fresh sample after being used four times. Moreover, TiO₂ fiber was easily recovered by centrifugal separation from water.     

Solvothermal synthesis of WO3/TiO2/carbon fiber composite photocatalysts for enhanced performance under sunlight illumination

Carbon fiber (CF)‐based WO₃/TiO₂ composite catalysts (WO₃/TiO₂/CF) were successfully synthesized by solvothermal method. The catalysts were characterized by XPS, SEM, BET, XRD, FTIR, Raman and UV–Vis. The analyses confirmed the WO₃/TiO₂ nanoparticles with high crystallinity deposited on the carbon structure. The photocatalytic degradation of Orange II azo dye under UV and sunlight illumination with the synthesized catalyst was explored. The composite catalyst displayed high performance (85%) for Orange II degradation while that of for WO₃/TiO₂ was found as 76%. The effects of CF amount, solution pH, initial dye concentration and catalyst dose on photocatalytic performance were studied. It was found that the degradation efficiency increased from 68% to 90% with the increasing CF amount from 3 wt% to 5 wt%, while the further increase in CF amount (7–10 wt%) decreased the photodegradation due to the blocking the active sites of WO₃/TiO₂. The enhanced photocatalytic efficiency was mainly attributed to the electrical properties of the CF and reduced bandgap.     

Fabrication of electrospun polyethersulfone/titanium dioxide (PES/TiO2) composite nanofibers membrane and its application for photocatalytic degradation of phenol in aqueous solution

The main objective of this research is to use the photocatalytic properties of PES/TiO₂ nanofibers membranes to remove the phenol as a toxic pollutant in various effluents. The uniform fibers in terms of minimum bead formation and fibers diameter were fabricated. Therefore, more TiO₂ catalysts are on the surface of the fibers which increase the active surface area of nanoparticles and consequently improve the phenol degradation efficiency. The effects of TiO₂ concentration on hydrophilicity, mechanical properties, porosity, mean pore size, and water flux of membranes were studied. The PES/TiO₂ nanofibers were evaluated for phenol degradation under UVA irradiation through a transparent membrane module. The amount of removable phenol was analyzed with high‐performance liquid chromatography. Central composite design was used as a statistical experimental design. Finally, the effect of TiO₂ content in nanofibers and initial phenol concentrations were investigated as well as pH values in synthetic wastewater, on phenol degradation. The results from analysis of variance (ANOVA) analysis indicated that TiO₂ content in nanofibers was the most important and effective parameter on phenol degradation. It was also presented that there is no significant interaction between parameters so that the effect of each parameter was investigated separately. Maximum phenol degradation was 43.0 ± 0.3% and found under conditions of TiO₂ content, initial phenol concentration, and pH value of 8%, 120 ppm, and 7, respectively.     

Photodegradation of Congo red in aqueous solution on ZnO as an alternative catalyst to TiO2

In this research, the efficiency of ZnO and TiO₂ was compared by photocatalytic degradation of Congo red azo dye. The effects of some parameters such as pH, dye concentration and irradiation time on the degradation rate of dye solution were also examined. In addition, the aggregation feature of Congo red was studied by using UV-Vis spectroscopy techniques. The recovery of the ZnO catalyst was also investigated.     

超临界 CO2 辅助制备 TiO2 外负载火山岩复合体及其光催化降解亚甲基蓝性能

 以钛酸丁酯为前驱体, 封堵的火山岩为载体, 通过超临界 CO₂ 辅助制备了 TiO₂ 外负载火山岩复合体, 并将其用于光催化降解亚甲基蓝反应, 考察了溶液 pH 值及催化剂浓度对反应性能的影响. 结果表明, TiO₂ 外负载火山岩复合体的光催化性能优于纯 TiO₂ 和 TiO₂ 体负载火山岩复合体. 这是由于外负载复合体对亚甲基蓝的高吸附性、小晶粒尺寸的 TiO₂ 颗粒以及吸附和光催化降解间的协同效应. 亚甲基蓝浓度为 1.5 mg/L, 溶液 pH 为 8, 催化剂浓度为 6.8 mg/L 时, 外负载 TiO₂ 火山岩复合体上亚甲基蓝降解速率最高, 且使用后的催化剂仍具有高的光催化活性.     

Comparison of photocatalysis degradation of 4-nitrophenol using N,S co-doped TiO2 nanoparticles synthesized by two different routes

The photocatalytic degradation of 4-nitrophenol as pollutant in aqueous solutions was investigated under visible light irradiation over two different N?CS-codoped anatase TiO₂ catalysts prepared by sol?Cgel methods using titanium isopropoxide and titanium tetrachloride as two different precursors. The catalysts were characterized by XRD, SEM, DRS, EDAX and FT-IR. The effects of various operating parameters including the initial concentration of 4-nitrophenol (2?C14?ppm), solution pH (5?C8) and kinetic reactions were studied. The optimum solution pH was at around 6. For comparison purpose, the photodegradation activity of the commercial Degussa P-25 TiO₂ catalyst has also been studied. The results indicated that photocatalytic activity of N?CS-codoped TiO₂ with titanium isopropoxide as precursor was higher than N?CS-codoped TiO₂ with titanium tetrachloride as precursor and Degussa P-25.     

Photocatalytic Degradation of Styrene in Aqueous Solution: Central Composite Design Optimization

In this study, the response surface methodology was first applied to optimize the photocatalytic degradation of styrene in aqueous phase under UV/TiO₂ system. Twenty experiments were done by adjusting three parameters (styrene concentration, TiO₂ dose, and pH) at five levels. Optimal experimental conditions for arbitrary aqueous styrene concentration (115 mg L^?1) were found: initial pH 7 and TiO₂ loading 2 g L^?1 with photocatalytic degradation efficiency of 79.2%. Furthermore, the main degradation intermediate produced was identified by GC/MS. The total organic carbon results revealed that the photocatalysis process could be effectively mineralized. Kinetics of the photocatalytic reaction followed a pseudo-first-order model.     

Degradation of ofloxacin by UVA-LED/TiO<Subscript>2</Subscript> nanotube arrays photocatalytic fuel cells

The degradation of ofloxacin (OFX) at low concentration in aqueous solution by UVA-LED/TiO₂ nanotube arrays photocatalytic fuel cells (UVA-LED/TiO₂ NTs PFCs) was investigated. TiO₂ nanotube arrays (TiO₂ NTs) photoanode prepared by anodization-constituted anatase–rutile bicrystalline framework. The results indicated that the degradation efficiency of OFX by UVA-LED/TiO₂ NTs PFC was significantly enhanced by 14.3% compared with UVA-LED/TiO₂ NTs photocatalysis. The pH affected the degradation efficiency markedly; the highest degradation efficiency (95.0%) and the pseudo-first-order reaction rate constant k value (0.049 min^?1) were achieved in neutral condition (pH 7.0). The degradation efficiency increased with the increasing concentration of dissolved oxygen (DO) in the UVA-LED/TiO₂ NTs PFC. The main reactive species of OFX degradation are positive holes (h⁺) and superoxide ion radicals (O ₂ ^·? ) in a DO sufficient condition. Furthermore, the possible pathways of OFX degradation were proposed.     

Multifunctional Zn0.3Al0.4O4.5 crystals: An efficient photocatalyst for formaldehyde degradation and EBT adsorption

The Zn_0.3Al_0.4O_4.5 nanoparticles (ZnAlONPs) with size of 70–90 nm are used as an efficient photocatalyst for formaldehyde (HCHO) degradation and effective adsorbent for the removal of eriochrome black-T (EBT) dye from synthetic aqueous solution. Degradation of HCHO reactions were studied using TiO₂ (homemade), TiO₂ (P-25) and ZnAlONPs by irradiating under 18 W daylight lamp source for photocatalytic degradation. The HCHO degradation rate is about 67, 76 and 89% for TiO₂ (homemade), TiO₂ (P25) and ZnAlONPs during 2 h reaction, respectively at initial formaldehyde gas concentration of 20 ppm. Maximum adsorption capacity was optimized by changing the parameters such as pH, EBT concentration and adsorbent dosage. A  200 mg of ZnAlONPs are useable for quick removal of EBT (>95%). Langmuir isotherm model showed a maximum adsorption capacity of 90.90 mgg⁻¹. The ZnAlONPs could be successfully reused upto 5^th adsorption/desorption cycle for EBT dye removal from water samples.     

Photocatalytic Degradation of Oxytetracycline in Aqueous Solutions with TiO2 in Suspension and Prediction by Artificial Neural Networks

In this study, the photocatalytic degradation of oxytetracycline (OTC) in aqueous solutions has been studied under different conditions such as initial pollutant concentrations, amount of catalyst, and pH of the solution. Experimental results showed that photocatalysis was clearly the predominant process in the pollutant degradation, since OTC adsorption on the catalyst and photolysis are negligible. The optimal TiO₂ concentration for OTC degradation was found to be 1.0 g/L. The apparent rate constant decreased, and the initial degradation rate increased with increasing initial OTC concentration with the other parameters kept unchanged. Subsequently, data obtained from photocatalytic degradation were used for training the artificial neural networks (ANN). The Levenberg–Marquardt algorithm, log sigmoid function in the hidden layer, and the linear activation function in the output layer were used. The optimized ANN structure was four neurons at the input layer, eighteen neurons at the hidden layer, and one neuron at the output layer. The application of 18 hidden neurons allowed to obtain the best values for R² and the mean squared error, 0.99751 and 7.504e–04, respectively, showing the relevance of the training, and hence the network can be used for final prediction of photocatalytic degradation of OTC with suspended TiO₂.     

Degradation and isomerization of 1,2-dichloroethenes by photocatalytic reactions

The photocatalytic degradation and isomerization of trans- and cis-1,2-dichloroethenes (1,2-DCEs) by TiO₂ photocatalyst have been investigated using gas chromatography. The reaction half-life of 1,2-DCEs in nitrogen was longer than in dry air and oxygen, and the initial concentration of them affects the extent of the isomerization. The results indicate that the oxygen molecule and chlorine atoms play an important role in the degradation and isomerization of 1,2-DCE. It is also apparent that the photocatalytic degradation of 1,2-DCEs occurs on the TiO₂ surface.     

Synthesis,characterization and photocatalytic application of TiO2/magnetic graphene for efficient photodegradation of crystal violet

A magnetized nano‐photocatalyst based on TiO₂/magnetic graphene was developed for efficient photodegradation of crystal violet (CV). Scanning electron microscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy and elemental mapping were used to characterize the prepared magnetic nano‐photocatalyst. The photocatalytic activity of the synthesized magnetic nano‐photocatalyst was evaluated using the decomposition of CV as a model organic pollutant under UV light irradiation. The obtained results showed that TiO₂/magnetic graphene exhibited much higher photocatalytic performance than bare TiO₂. Incorporation of graphene enhanced the activity of the prepared magnetic nano‐photocatalyst. TiO₂/magnetic graphene can be easily separated from an aqueous solution by applying an external magnetic field. Effects of pH, magnetized nano‐photocatalyst dosage, UV light irradiation time, H₂O₂ amount and initial concentration of dye on the photodegradation efficiency were evaluated and optimized. Efficient photodegradation (>98%) of the selected dye under optimized conditions using the synthesized nano‐photocatalyst under UV light irradiation was achieved in 25 min. The prepared magnetic nano‐photocatalyst can be used in a wide pH range (4–10) for degradation of CV. The effects of scavengers, namely methanol (OH^? scavenger), p‐benzoquinone (O₂^?? scavenger) and disodium ethylenediaminetetraacetate (hole scavenger), on CV photodegradation were investigated.     

Efficient degradation of methyl orange via multilayer films of titanium dioxide and silicotungstic acid

We report layer-by-layer (LbL) assembly of TiO2 and H4 SiW12 O40 (SiW 12 ) multilayer film on silicon wafers and glass slides for photocatalytic degradation of methyl orange (MO). The photocatalytic efficiency of the obtained multilayer film increases along with the decrease of pH and salt concentration of the incubation solution. The results show that MO can be almost removed in pH2.0 solution without salt addition in the first 60 min incubation when MO concentration is lower than 15 mg/L. Different salts show an apparent inhibitory effect on photocatalytic degradation of MO with the order of ZnCl2 >KCl> NaCl>LiCl. The TiO2 /SiW12 multilayer film maintains photocatalytic activity even after five degradation cycles. The reaction of MO photodegradation accords with an apparent first-order dynamics.     

Visible light induced photocatalytic degradation of phenol by polymer-modified semiconductors: Study of the influencing factors and the kinetics

To investigate the influencing factors and the kinetics of photocatalytic degradation of phenol, experiments were carried out using conjugated polymer poly(fluorene-co-thiophene) (PFT) sensitized TiO₂ and ZnO under LED (light-emitting diode) lights of the wavelength of 450–475 nm. Influencing factors, such as initial phenol concentration, photocatalyst dosage and pH value on the photocatalytic degradation of phenol were studied in detail. The reaction kinetics was found to follow pseudo first-order law.     

Photoelectrocatalytic degradation of 3-nitrophenol at surface of Ti/TiO2 electrode

The widely utilization of phenol and its derivatives such as 3-nitrophenol (3-NP) has led to the worldwide pollution in the environment. In this study, Ti/TiO₂ photoelectrode was prepared with anodic oxidation of Ti foil electrode and then the photoelectrocatalytic (PEC) degradation of 3-NP was performed via this electrode, comparing with photocatalytic (PC), electrooxidation and direct photolysis by ultraviolet light. A significant photoelectrochemical synergetic effect in 3-NP degradation was observed on the Ti/TiO₂ electrode and rate constant for the PEC process of Ti/TiO₂ electrode was about three times as high as its PC degradation process. 3-NP concentration monitoring was carried out with differential pulse voltammetry. Results showed that PEC degradation has highest effect on concentration decreasing of 3-NP at solution and degraded it about 38 %, while other processes degradation efficiencies were about 4, 7, and 12 % for electrooxidation, direct photolysis and photocatalytic degradation, respectively. Finally, effects of solution pH and applied potential on degradation efficiency were studied and results showed that optimum pH for degradation is equal 4.00 and optimum potential is 1.2 V vs. Ag|AgCl|KCl (3M) reference electrode.     

A Sharp Jump in Photocatalytic Activity of Elemental Sulfur for Dye Degradation in Alkaline Solution

Elemental sulfur is a low-cost and abundant substance as one of the largest by-products of the oil industry which was widely used in many industrial activities. Cyclo-octasulfur (S₈) is one of the sulfur allotropes that is a very stable substance in standard conditions. In this study, we report a low-cost and fast method for the degradation of methyl violet in water under visible light and also sunlight by using elemental sulfur (S₈). The results show that sulfur is a good photocatalyst which operates under visible light and can be utilized for degradation of methyl violet. The photocatalytic degradation of methyl violet in acidic, neutral, and alkaline media was investigated, and it was found that the photocatalytic efficiency increases dramatically in alkaline solution. The effects of the initial concentration of the dye, photocatalyst dosage, solution pH, and photocatalyst reusability were investigated. The kinetics of the reaction were studied in detail, and the photocatalytic rate equation was presented.