The kinetics of photocatalytic degradation of trichloroethylene in gas phase over TiO2 supported on glass bead

In this investigation, a packed bed filled with coated titanium dioxide glass beads to study the kinetics of photocatalytic degradation of trichloroethylene under irradiation of 365 nm UV light. In the range of 100–500 ml/min of flowrate, the reaction rate for 6 μM TCE increased with an increasing flowrate upto 300 ml/min, while was not affected by the flowrate at the values higher than 300 ml/min. For moisture in the range of 9.4–1222.2 μM, the reaction rate of TCE was decreased with an increasing humidity. The adsorbed water on the catalyst surface could compete with the adsorption of TCE on the sites. The reaction rate of 6 μM TCE increased as the light intensity increased, and was proportional to the 0.61 order of the light intensity. Among the three L–H bimolecular form models, the experimental data had the best fit for one of models:

     

Gas-solid adsorption of selected volatile organic compounds on titanium dioxide Degussa P25

This paper focuses on the adsorption of gaseous trichloroethylene, toluene and chlorobenzene on the photocatalyst TiO₂ Degussa P25. An optimized EPICS (Equilibrium Partitioning In Closed Systems) methodology was used to study equilibrium partitioning. For the three compounds investigated, equilibrium adsorption was reached within of incubation. Adsorption isotherms, determined at a temperature (T) of and relative humidities (RH) of 0.0% and 57.8% were found to be linear (R²>0.993,n=5), indicating that no monolayer surface coverage was reached in the concentration interval studied ). Within the linear part of the isotherm, the influence of both relative humidity and temperature was investigated in a systematic way and discussed from a thermodynamic point of view. Data analysis resulted in a double linear regression for 22% ?RH?90% and . The equilibrium adsorption coefficient represents the equilibrium concentration ratio and ΔU_ads is the internal energy of adsorption . At RH=0.0%, experimental K values were a factor 5-10 higher than those expected from the regression equation, indicating that another adsorption mechanism becomes important below monolayer surface coverage of TiO₂ by water vapour molecules. Since surface interactions are of primary importance in photocatalytic reactions, this paper contributes to a better understanding of the basic mechanisms of TiO₂ mediated heterogeneous photocatalysis and is an interesting tool for developing optimized mathematical models.     

Electrochemically assisted photocatalytic degradation of methyl orange using anodized titanium dioxide nanotubes

The TiO₂ nanotubes have demonstrated potential in the photoelectrocatalytic degradation of methyl orange dye (MO). TiO₂ nanotubes were prepared using anodization of titanium foils in phosphoric acid (PA) and ethylene glycol (EG) by mechanical stirring and ultrasonic method. The TiO₂ nanotubes prepared in EG under ultrasound followed by annealing in nitrogen atmosphere showed higher activity towards dye degradation as compared to the stirring method. Dye degradation shows improved activity under an external bias compared to degradation performed in the absence of an external bias. An increase in the external bias from +0.0 to +0.1 V versus calomel electrode (SCE) is sufficient to improve the degradation rates of MO from 22% to 57% within the first 10 min. At +0.1 V, a complete degradation of 40 μM MO is observed within 30 min. The addition of oxidants such as oxygen and hydrogen peroxide demonstrate improvement in the MO degradation.     

A comparative photocatalytic activity of titanium dioxide and zinc oxide by investigating the degradation of vanillin

The photocatalytic degradation of an organic pollutant such as vanillin has been investigated in aqueous suspensions of titanium dioxide and zinc oxide by monitoring the change in substrate concentration employing UV spectroscopic analysis and decrease in Total Organic Carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation of the model compound was studied under different conditions such as pH, catalyst concentration, substrate concentration and in the presence of an electron acceptor such as hydrogen peroxide besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts, Hombikat UV100 and ZnO.     

Titanium dioxide mediated photocatalyzed degradation of a textile dye derivative, acid orange 8, in aqueous suspensions

Titanium dioxide mediated photocatalysed degradation of a textile dye derivative, acid orange 8(1), was investigated in aqueous suspensions of titanium dioxide by monitoring the depletion of total organic carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation kinetics were studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO₂ and in the presence of electron acceptors such as hydrogen peroxide (H₂O₂) and potassium bromate (KBrO₃) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient compared with other photocatalysts. The dye was found to be adsorbed on the surface of the photocatalyst at acidic pH.     

Activity and product distribution of alumina supported platinum and palladium catalysts in the gas-phase oxidative decomposition of chlorinated hydrocarbons

The complete catalytic oxidation of 1,2-dichloroethane (DCE) and trichloroethylene (TCE) over alumina supported noble metal catalysts (Pt and Pd) was evaluated. Experiments were performed at conditions of lean hydrocarbon concentration (around 1000 ppm) in air, between 250°C and 550°C in a conventional fixed bed reactor. The catalysts were prepared in a range of metal contents from 0.1 to 1 wt%. Palladium catalysts resulted to be more active than platinum catalysts in the oxidation of both chlorinated volatile organic compounds. DCE was completely destructed at 375°C, whereas TCE required 550°C. HCl was the only chlorine-containing product in the oxidation of DCE in the range of 250–400°C. Tetrachloroethylene was observed as an intermediate in the oxidation of TCE, being formed to a significant extent between 400°C and 525°C. CO was also detected in the oxidation of both DCE and TCE over Pd catalysts, though at temperatures of complete destruction, CO₂ was the only carbon-containing product. The Pt catalysts were selective to CO₂ at the studied conditions.     

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.     

纳米TiO2光催化降解有机污染物的研究与应用

以光催化剂TiO2为例,讨论了光催化降解有机污染物的机理,总结了TiO2光催化剂在降解有机污染物(氯代物与芳香族化合物、含氮化合物、表面活性剂、染料、农药等)方面的应用,并对TiO2光催化氧化法的发展与应用前景进行了展望。     

Study on the photocatalytic degradation of trichlorfon in suspension of titanium dioxide

In this paper, the photocatalytic degradation of trichlorfon, an organophosphorous pesticide, was studied by using TiO₂ as a photocatalyst. The effects of various parameters, such as the amount of the photocatalyst, illumination time, reaction temperature, electron acceptors, metal ions, anions, and initial pH value on the photocatalytic degradation of trichlorfon were investigated. The best conditions for the photocatalytic degradation of trichlorfon were obtained. The results show that the optimum amount of the photocatalyst used is 8.0 g L^− 1. The photodegradation efficiency of trichlorfon increases with the increase of the illumination time or reaction temperature. The photodegradation efficiency of trichlorfon is increased rapidly by adding a small amount of H₂O₂, K₂S₂O₈, KBrO₃, Fe³⁺ and Cu²⁺, however, with the addition of Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Co²⁺ and Ni²⁺, or with the addition of trace amount of SO₄²⁻, Cl⁻, Br⁻, there are no obvious effects on the photocatalytic degradation reactions. Alkaline mediums are favorable for the photocatalytic degradation of trichlorfon. The possible roles of the additives on the reactions and the possible mechanisms of effect were also discussed.     

A kinetic study of organic compounds (acetone,toluene, n-hexane and n-decane) adsorption behavior on activated carbon under supercritical carbon dioxide conditions at temperature from 313 to 353 K and at pressure from 4.2 to 15.0 MPa

Adsorption kinetics of four volatile organic compounds (VOCs) (acetone, toluene, n-hexane and n-decane) on activated carbon under supercritical carbon dioxide (scCO₂) conditions was studied. Breakthrough curve measurements of VOCs in scCO₂ were performed with a fixed bed method for activated carbon (ca. mean particles diameter: 100 μm, specific surface area: 1300 m²/g and mean pore diameter: 0.687 nm, respectively). The measured breakthrough curves could be correlated with a kinetic model by using only one fitting parameter (effective diffusion coefficient in pore) within 10% of average relative deviation. The determined effective diffusion coefficient decreased with decreasing temperatures and increasing pressures at all conditions. Additionally, a generalized model of the determined effective diffusion coefficients was developed, and the proposed model could satisfactorily describe temperature and pressure dependence at all VOCs conditions.     

Application of immobilized titanium dioxide photocatalysts for the degradation of creatinine and phenol, model organic contaminants found in NASA''s spacecrafts wastewater streams

In this project, immobilized titanium dioxide photocatalysis was utilized as a post-treatment technology for the destruction of model organic contaminants found in wastewater streams produced on-board during space exploration. Phenol, a known human carcinogen, and creatinine, a human metabolite found in urine, were the compounds tested in this study. Phenol and creatinine have cyclic structures consisting of six and five member rings, respectively. In addition, creatinine is a methyl guanidine derivative, with almost 40% (w/w) nitrogen. The degradation and carbon mineralization efficiencies of the target contaminants were investigated at different initial concentrations. Their photocatalytic degradation appears to follow pseudo-first-order reaction with phenol giving higher organic carbon reduction rates than creatinine. The presence and position of the functional groups of creatinine (amine, imine and peptide bond) are primarily responsible for the significantly slower mineralization. The degradation of creatinine was also tested at different pH_o values. Statistical analysis showed that there is an effect of pH on the treatment of creatinine. Besides the carbon mineralization, the extent of nitrogen mineralization and the mass balance of nitrogen were conducted for three pH values (pH_o 3.0, 6.2 and 11.0). Overall, the transformation of nitrogen was low, and the total maximum conversion (<20%) occurred at basic conditions.