Effect of humidity on the photocatalytic degradation of trichloroethylene in gas Phase over TiO2 thin films treated by different conditions

The effect of humidity on the photocatalytic degradation reaction of trichloroethylene (TCE) in gas phase was investigated by using pretreated TiO₂ sol-gel films. It was observed that the photocatalytic activity of the TiO₂ films depended more greatly on the pretreatment conditions, for example, UV pre-illumination, than on the moisture content. When the relative humidity was over 50%, the reaction rates decreased regardless of treatment conditions of the photocatalyst. The photocatalytic decomposition rate of TCE increased with the increase of light intensity. However, the influence of humidity on the reaction rate was less significant under the increased light intensity. The intermediates and byproducts of the reaction were not changed in different humidity conditions.     

Preparation of TiO2 ultrafine nanopowder with large surface area and its photocatalytic activity for gaseous nitrogen oxides

TiO₂ nanopowder with a large surface area and high crystallinity was synthesized by a thermal decomposition process. The physicochemical properties of the prepared powders were examined by X-ray diffraction, transmission electron microscopy and nitrogen adsorption-desorption isotherms. The nanocrystallites of the prepared powers were considerably smaller than those of the commercial photocatalyst (Degussa, P25), and the particles had a dense polyhedral structure. In addition, the particles had a mainly disordered mesoporous structure with a pore volume that varied according to the pore size in the range of 2-20 nm. The photocatalytic activity of the prepared photocatalyst was obviously higher than that of P25 on the photodegradation of gaseous nitrogen oxides under UV_{254 + 185 nm} lamp irradiation. Above 40% relative humidity, the NO_x removal efficiency of the prepared photocatalyst was 10% higher than that of P25. Furthermore, a suitable relative humidity and longer residence time were found to enhance the photocatalytic oxidation of gaseous nitrogen oxides by UV_{254 + 185 nm} lamp irradiation and TiO₂ nanoparticles.     

纳米光催化网ACH/TiO2动态降解甲苯气体

采用浸渍法将纳米TiO2颗粒负载在蜂窝活性炭(ACH)表面制备出光催化网ACH/TiO2,在自制光催化反应器中38 nm波长紫外光激发下进行甲苯的动态催化降解实验. 结果表明,ACH和TiO2具有良好的协同效应,能将可降解甲苯初始浓度从160 mg/m3提高至830 mg/m3. 在ACH/TiO2中TiO2含量12.5%±1%(w)、反应器内湿度30%、甲苯初始浓度410 mg/m3及气体流速1 L/min的条件下,ACH/TiO2降解甲苯气体效果最佳,降解率达90.0%. 水蒸气影响光催化降解甲苯气体,在稳定气流下光照降解甲苯气体效率可在6 h内维持稳定.     

负载TiO2纤维布的制备及光催化性能的研究

采用涂膜法直接将非晶态纳米TiO₂胶体负载于纤维布上，制备了纳米TiO₂光催化剂。采用扫描电子显微镜(SEM)、比表面及孔径分析仪观察了催化剂的表面形貌和结构特征。以甲基橙溶液、气态苯胺为研究对象，考察了负载TiO₂纤维布的光催化活性。结果表明，负载于纤维布上的TiO₂为锐钛矿型，具有中孔结构，且有较好的光催化降解能力。纳米TiO₂光催化降解气态苯胺的中间产物主要有苯酚、苯醌、亚硝基苯和偶氮苯等。推断了其光催化降解历程。     

A new kinetic model for titanium dioxide mediated heterogeneous photocatalytic degradation of trichloroethylene in gas-phase

This paper focuses on the kinetics of photocatalytic removal and carbon mineralization of gaseous trichloroethylene (TCE) on near-UV irradiated TiO₂ Degussa P25. Experiments were carried out in a flat-plate photoreactor at TCE inlet concentrations of 100–500 ppmv, relative humidities (RH) of 0–62% and gas residence times of 2.5–60.3 s. Gas residence time distribution (RTD) curves revealed an axial dispersed plug flow in the photoreactor with Peclet numbers above 59.4. For all experimental conditions, the carbon mineralization efficiency (5.1–73.0%) was lower than the removal efficiency (8.6–99.9%) and dichloroacetylchloride (DCAC) was detected as a gas-phase degradation product. TCE removal efficiencies increased with lower TCE inlet concentrations, lower RH and higher gas residence times. Evaluating different kinetic models by least squares analysis, it was shown that the Langmuir–Hinshelwood (LH) model could not give an adequate fitting to the experimental results. A new kinetic model, explicitly taking into account electron–hole pair reactions, was developed based on linear TCE adsorption–desorption equilibrium and first order reaction kinetics. The new kinetic model described the experimental results in a more accurate way, as exemplified by a more randomly distributed set of residuals and by a reduction of the sum of squares (SSQ) by a factor 1.7–8.5. The effect of TCE gas-phase concentration, RH and light intensity on adsorption–desorption kinetics, electron–hole concentrations and chemical conversion rates is discussed.     

Photocatalytic degradation of trichloroethylene over TiO<Subscript>2</Subscript>/SiO2 in an annulus fluidized bed reactor

The effects of superficial gas velocity (Ug), wavelength and intensity of ultraviolet (UV) light, oxygen and H₂O concentration on the photocatalytic degradation of TCE (Trichloroethylene) over TiO₂/SiO₂ catalyst have been determined in an annulus fluidized bed photoreactor. The key factor in determining the performance of the annulus fluidized bed photoreactor is found to be an optimum superficial gas velocity (Ug) that provides the optimum UV lighttransmit through the proper size of bubbles in the photoreactor. The degradation efficiency of TCE increases with light intensity but decreases with wavelength of the UV light and H₂O concentration in the fluidized bed of TiO₂/silica-gel photocatalyst. The optimum concentration of O₂ for TCE degradation is found to be approximately 10%. The annulus fluidized bed photoreactor is an effective tool for high TCE degradation with efficient utilization of photon energy. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

Investigation into Photocatalytic Degradation of Gaseous Benzene in a Circulated Photocatalytic Reactor (CPCR)

Due to the fact that suspended TiO₂ powder enjoys free contact with gaseous pollutant molecules in photocatalytic reactors, it can generally achieve better efficiency than immobilized TiO₂ catalysts. However, difficulties with the separation of this catalyst powder from treated pollutants and its re‐use often limit its application. Therefore, a circulated photocatalytic reactor (CPCR) was designed to enhance the performance of the photocatalytic degradation of gaseous benzene. TiO₂ film photocatalysts were prepared by the sol‐gel method at low temperatures and coated onto the inner wall of this reactor by a bonding agent composed of poly‐(2, 2‐dimethyl)‐acrylic ethylene ester emulsion in which TiO₂ powder was characterized by FTIR, TEM and SEM. In particular, the influences of initial concentration and gas flow rate of benzene on the degradation conversion, D_p, apparent reaction rate constants, k_r, initial degradation rate, r, and the deactivation and regeneration of catalyst in the CPCR, were investigated. The results indicated that the degradation conversion, apparent reaction rate constants and initial degradation rate were closely correlated to the initial concentration of benzene. To elucidate the factors governing the observations, the adsorption characteristics and kinetics of the photocatalytic degradation of benzene were analyzed using the Langmuir adsorption isotherm and Langmuir‐Hinshelwood kinetic model. It was found that the reaction kinetics were best described by a fixed pseudo‐first‐order kinetic equation of photocatalytic degradation of gaseous benzene in the CPCR.     

Kinetic study for photocatalytic degradation of volatile organic compounds in air using thin film TiO2 photocatalyst

The present paper examined the kinetics of photocatalytic degradation of volatile organic compounds (VOCs) including gaseous trichloroethylene (TCE), acetone, methanol and toluene. Variable parameters were initial concentration of VOCs, water vapor content and photon flux of ultra-violet (UV) light. A batch photo-reactor was specifically designed for this work. The photocatalytic degradation rate increased with increasing the initial concentration of VOCs, but maintained almost constant beyond a certain concentration. It matched well with the Langmuir–Hinshelwood (L–H) kinetic model. For the influence of water vapor in a gas phase photocatalytic degradation rate, there was an optimum concentration of water vapor in the degradation of TCE and methanol. And, water vapor enhanced the photocatalytic degradation rate of toluene, whereas it inhibited that of acetone. As for the effect of photon flux, it was found that photocatalytic degradation occurs in two regimes with respect to photon flux.     

Coupling copper and hydrogenated TiO2 to bare TiO2 structures for improved photocatalytic performance

Coupling of metals and hydrogenated TiO₂ (HT) to bare TiO₂ may improve synergistically the photocatalytic activity of TiO₂ for pollutant decomposition. Herein, we address this issue by investigating the photocatalytic performances of Cu‐loaded HT (CuHT)/bare TiO₂ (CuHTT) heterojunction nanocomposites for the degradation of harmful n‐butanol under simulated solar light illumination. CuHTT with a CuHT‐to‐TiO₂ composition ratio of 0.1 showed a photocatalytic efficiency exceeding those of four reference photocatalysts, exhibiting the advantages of improved visible light absorption efficiency, charge carrier separation, and adsorption capacity. Increasing the CuHT‐to‐TiO₂ ratio from 0.01 to 0.1 improved the photocatalytic efficiency of CuHTT, whereas a further increase to 0.9 resulted in a decreased photocatalytic efficiency. Moreover, the photocatalytic efficiency improved as relative humidity increased from 20% to 70%, decreasing upon its further increase to 95%. The efficiencies of n‐butanol to CO₂ conversion over CuHTT were lower than the corresponding decomposition efficiencies. Incompletely oxidized CO and three organic vapors (butanal, propanal, and 1‐propanol) were determined as major intermediates. A possible mechanism for CuHTT‐catalyzed photodegradation under simulated solar illumination was proposed.     

Enhanced visible‐light‐driven photocatalytic activities of LiInO2 by Mo6+‐doping strategy

A novel visible‐light‐driven photocatalyst of Mo‐doped LiInO₂ nanocomposite was successfully synthesized through a sol‐gel method. The effect of Mo‐doping concentrations on the microstructures and properties of LiInO₂ was characterized by X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectroscopy, photoluminescence, and ultraviolet‐visible absorption spectra. The photocatalytic properties of the as‐prepared samples were evaluated by the photocatalytic degradation of methylene blue (MB) dye under visible‐light irradiation. The results demonstrated that the photocatalytic activity of 6% Mo‐LiInO₂ reached to 98.6%, which was much higher than that of the undoped photocatalyst LiInO₂ (only 46.8%). The enhanced photocatalytic activity is ascribed to Mo‐doping strategy. The holes play an important role in the process of the photodegradation of MB. The superior photocatalytic activity of the as‐prepared Mo‐LiInO₂ nanocomposites suggests a potential application for organic dye degradation of wastewater remediation. This work provides a further understanding on tailoring the band structure of semiconductor photocatalyst for enhancing visible‐light absorption and promoting electron‐hole separation by Mo‐doping strategy.     

Preparation, characterization and activity evaluation of p–n junction photocatalyst p-CaFe2O4/n-ZnO

p–n junction photocatalyst p-CaFe₂O₄/n-ZnO was prepared by ball milling of ZnO in H₂O doped with p-type CaFe₂O₄. The structural and optical properties of the p–n junction photocatalyst p-CaFe₂O₄/n-ZnO were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflection spectrum (DRS) and fluorescence emission spectra. The photocatalytic activity of the photocatalyst was evaluated by photocatalytic degradation of methylene blue (MB). The results showed that the photocatalytic activity of the p-CaFe₂O₄/n-ZnO was higher than that of ZnO. When the amounts of doped p-CaFe₂O₄ were 0.0 wt.% and 1.0 wt.%, the photocatalytic degradation efficiencies were 50.1 and 73.4%, respectively. Effect of ball milling time on the photocatalytic activity of the photocatalyst was also investigated. The mechanisms of influence on the photocatalytic activity were also discussed by the p–n junction principle.     

Parameter effect on photocatalytic degradation of phenol using TiO2-P25/activated carbon (AC)

P25 powder embedded and TiO₂ immobilized on activated carbon (TiO₂-P25/AC) was prepared by P25 powder modified sol-gel and dip-coated method. The photocatalysts were characterized by XRD, BET, SEM and their photocatalytic activities were evaluated through phenol degradation in a fluidized bed photoreactor. The addition of P25 in the photocatalysts could significantly enhance the photocatalytic activity, and the optimum loading of P25 was 3 g L^?1. The operating parameter results indicated that the optimum pH for phenol degradation was 5.2; the effect of air flow rate gave an optimal value of 2 L min^?1; the increasing of UV light intensity led to an increase of degradation efficiency due to more photons absorbed on the surface of the photocatalyst. The kinetics of the phenol degradation fitted well with the Langmuir-Hinshelwood kinetics model. Finally, the photocatalytic ability of TiO₂-P25/AC was reduced only 10% after five cycles for phenol degradation.     

Diatom Biosilica Doped with Palladium(II) Chloride Nanoparticles as New Efficient Photocatalysts for Methyl Orange Degradation

A new catalyst based on biosilica doped with palladium(II) chloride nanoparticles was prepared and tested for efficient degradation of methyl orange (MO) in water solution under UV light excitation. The obtained photocatalyst was characterized by X-ray diffraction, TEM and N₂ adsorption/desorption isotherms. The photocatalytic degradation process was studied as a function of pH of the solution, temperature, UV irradiation time, and MO initial concentration. The possibilities of recycling and durability of the prepared photocatalysts were also tested. Products of photocatalytic degradation were identified by liquid chromatography–mass spectrometry analyses. The photocatalyst exhibited excellent photodegradation activity toward MO degradation under UV light irradiation. Rapid photocatalytic degradation was found to take place within one minute with an efficiency of 85% reaching over 98% after 75 min. The proposed mechanism of photodegradation is based on the assumption that both HO^• and O₂^•− radicals, as strongly oxidizing species that can participate in the dye degradation reaction, are generated by the attacks of photons emitted from diatom biosilica (photonic scattering effect) under the influence of UV light excitation. The degradation efficiency significantly increases as the intensity of photons emitted from biosilica is enhanced by palladium(II) chloride nanoparticles immobilized on biosilica (synergetic photonic scattering effect).     

光催化降解甲醛废气的研究

通过使用自制的光催化剂(二氧化钛、三氧化钨)分别负载在玻纤上,对甲醛气体进行光催化降解。以动态法考察了温度、湿度对光催化降解甲醛的影响。实验结果表明:随着温度、湿度的升高,光催化降解甲醛气体的降解率先升高后降低。最佳反应条件为:反应温度38℃,反应湿度40%,以WO3/TiO2/玻纤为光催化剂,甲醛降解率达到76%。并对WO3/TiO2/玻纤光催化降解甲醛的反应动力学进行了初步研究,结果表明:以WO3/TiO2/玻纤为光催化剂,光催化降解甲醛反应符合一级反应动力学规律。     

Hybrid photocatalysts for the degradation of trichloroethylene in air

Hybrid photocatalysts based on an adsorbent SiMgOx and a photocatalyst TiO₂ were developed in a plate shape. The ceramic surface was coated with TiO₂ by the slip-casting technique. The effect of the support in the photocatalytic degradation of trichloroethylene (TCE) was analyzed by modifying TiO₂ loading and the layer thickness. Photocatalysts were characterised by N₂ adsorption–desorption, mercury intrusion porosimetry, SEM, UV–vis spectroscopy and XRD. A direct relationship between the TiO₂ content and the photocatalytic activity was observed up to three layers of TiO₂ (0.66 wt.%). Our results indicate that intermediate species generated on the TiO₂ layer can migrate through relatively long distances to react with the OH⁻ surface groups of the support. By increasing the TiO₂ loading of the photocatalyst two effects were observed: trichloroethylene conversion is enhanced, while the efficiency of the oxidation process is decreased at expenses of increasing the selectivity to COCl₂ and dichloroacetylchloride (DCAC). The results are discussed in terms of the layer thickness, TiO₂ amount, TCE conversion and CO₂, and COCl₂ selectivity.     

Photocatalytic decolorization of rhodamine B by fluidized bed reactor with hollow ceramic ball photocatalyst

Photocatalytic degradation of organic contaminants in wastewater by TiO₂ has been introduced in both bench and pilot-scale applications in suspended state or immobilized state on supporting material. TiO₂ in suspended state gave less activity due to its coagency between particles. Recent advances in environmental photocatalysis have focused on enhancing the catalytic activity and improving the performance of photocatalytic reactors. This paper reports a preliminary design of a new immobilized TiO₂ photocatalyst and its photocatalytic fluidized bed reactor (PFBR) to apply photochemical degradation of a dye, Rhodamine B (RhB). But it was not easy to make a cost-effective and well activated immobilized TiO₂ particles. A kind of photocatalyst (named Photomedium), consisting of hollow ceramic balls coated with TiO₂-sol, which was capable of effective photodegradation of the dye, has been presented in this study. The photocatalytic oxidation of RhB was investigated by changing Photomedia concentrations, initial RhB concentrations, and UV intensity in PFBR This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Polymer material-supported titania nanofibers with different polyvinylpyrrolidone to TiO2 ratios for degradation of vaporous trichloroethylene

Polymer-supported TiO₂ nanofibers with different polyvinylpyrrolidone (PVP)-to-TiO₂ (PT) ratios were synthesized and their photocatalytic efficiencies were examined for the decomposition of trichloroethylene (TCE). The spectral results of the TiO₂ nanofibers confirmed the presence of TiO₂ crystal phases in the nanofibers. The TiO₂ nanofiber with the highest PT ratio of 1:1.3 showed the highest TCE decomposition (94%), followed by TiO₂ nanofibers with PT ratios of 1:0.7 (91%), 1:0.35 (88%), and 1:0.1 (84%). The conditions of low input concentration and humidity were suggested for the optimal decomposition of TCE. Consequently, the TiO₂ nanofiber webs could be used effectively to decompose TCE.     

Enhanced photocatalytic performance of Bi2Fe4O9/graphene via modifying graphene composite

Bi₂Fe₄O₉ (BFO) is one of the most important photocatalyst materials and its composition with graphene may leave an optimizing effect on the photocatalytic performance. In this paper, reduced graphene oxide (RGO) with various contents is selected to be composited with BFO successfully via one‐step hydrothermal method. A series of BFO‐xRGO (x=0, 1.25, 2.50, 3.75, 5, 6.25, and 7.50 wt.%) were prepared and the effects of RGO content on crystalline, light absorption, impedance, and photocatalytic degradation rate of methyl violet (MV) solution are characterized. The entire film samples exhibit enhanced photocatalytic efficiency. Especially, with 5 wt.% RGO content added, the film sample shows the best photocatalytic degradation efficiency with a MV solution degradation rate of 95%. This implies that the composition of RGO allows BFO‐based thin film as an efficient photocatalyst candidate, and as well, the BFO/RGO composite possesses the potential for better use in the related photocatalyst applications.     

Response surface optimization of the photocatalytic degradation of atenolol using immobilized graphene-TiO2 composite

Photocatalytic processes using semiconductors have been widely explored due to their fascinating benefits in environmental remediation. In this study, a four-factor three-level Box-Benkhen design (BBD) was employed to assess the photocatalytic degradation of atenolol (ATL) using immobilized graphene-TiO₂ as a photocatalyst. The four variables that were considered in the BBD model were the photocatalyst concentration (10%-20%), pH (4-9), ATL concentration (10-30 mg/L), and light intensity (60-260 W/m²). A monolithic-type swirl-flow reactor, which allowed the immobilization of the photocatalyst, was employed in a semi-batch system to study the photocatalytic degradation kinetics of ATL. The optimum conditions where the highest rate constant (0.667 min⁻¹) was observed were graphene-TiO₂ concentration of 10%, pH of 6.5, ATL concentration of 30 mg/L, and light intensity of 160 W/m². The developed model well predicted the observed values indicated by a high R² of 0.897. Reaction rate constants obtained herein using graphene-TiO₂ in immobilized form were compared with slurry system and TiO₂.     

Purification of textile wastewater by using coated Sr/S/N doped TiO<Subscript>2</Subscript> nanolayers on glass orbs

Simultaneous doping of TiO₂ nanoparticles with three elements including Sr, S, and N is reported. The resulting material shows superior photocatalytic performance toward degradation of textile waste under visible and sunlight. The pure and doped TiO₂ nanolayers were prepared by sol-gel method and were fixed on a bed of glass orbs. The immobilized TiO₂ were characterized by a variety of techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), spectroscopy diffusion reflection (DRS), energy dispersive X-ray spectrometry (EDS) and elemental analysis (CHNS). The photocatalytic activity of the prepared fixed-bed materials toward degradation of the textile wastes was determined by using ultraviolet-visible spectroscopy (UV-Vis) and measurement of the chemical oxygen demand testing (COD). The best photocatalytic activity was observed with the use of Sr/S/N-TiO₂ nano-layers. Afterwards, the experimental conditions were optimized by tuning reaction parameters, including amount of doped metal ion on photocatalyst structure, sample solution pH and photoreactor output flow rate. The results confirmed that at natural pH 5.9 of sample solution, maximum decomposition of 91-99% of azo dyes was obtained in 8 h under visible irradiation. Finally, the experiments were repeated under 1.5 AM sunlight with high volume of reactants in order to confirm the cost-effectiveness of the designed photocatalyst.