Sulfamethoxazole removal from polluted water by immobilized photocatalysis

The photocatalytic activity of TiO₂ deposits (Degussa P25 and Millennium PC500) has been studied using sulfamethoxazole (SMX) as a model water pollutant and a UV fluorescent lamp as a light source (365 nm). Both catalysts have shown very similar properties in the photocatalytic degradation of SMX. Special attention has been given to the effect of the irradiation time, pH, and pollutant concentration. No mass-transfer limitations are observed. The degradation of SMX is accelerated at low concentration, and the photocatalytic degradation kinetics obey the Langmuir–Hinshelwood model, allowing the adsorption and apparent rate constants to be determined for both catalysts.     

TiO2/活性炭复合体对罗丹明B的光催化降解

以紫外灯为光源,通过对可溶性染料罗丹明B的降解反应,考察TiO2／活性炭复合体的光催化活性,探讨了光催化反应中溶液的pH值、光强、反应温度和罗丹明B的起始浓度对催化反应的影响,结果表明,TiO2／活性炭复合体具有很高的光催化活性,对罗丹明B的降解过程遵循Langmuir-Hinshelwood动力学方程,降解速率受pH值、罗丹明B起始浓度和入射光强度的影响很大,反应温度对降解速率影响很小．在研究范围内,pH6和40W的入射光强度有利于光催化降解．     

Ag–TiO2 doped photo catalytic degradation of Procion blue H-B dye in textile washwater

The photocatalytic degradation of Procion blue H-B dye in biodegraded textile washwater has been investigated for the complete removal of color and maximum reduction of chemical oxygen demand (COD). Pseudomonas putida was utilized for obtaining biodegraded textile washwater. In this process, silver-doped TiO₂ photocatalyst was prepared and experiments were carried out to study the effects of UV and mercury lamp irradiations on COD reduction and removal of color. The thus prepared silver-doped TiO₂ catalyst was characterized by thermogravimetric and differential thermal analysis, UV-visible spectrometer, X-ray diffraction, scanning electron microscope, energy dispersive X-ray microanalysis, and BET surface area techniques. Adsorption studies were also carried out to evaluate the fitness of isotherm models. The results show that the silver-doped TiO₂ has enhanced the photodegradation of Procion blue H-B dye under UV and mercury lamp irradiations. The enhanced activity of silver-doped TiO₂ is due to the enrichment of electron–hole separation by electron trapping of silver particles.     

HO ‐ initiated oxidation of acridine and aminacrine in aqueous media: Kinetic model

The photodecomposition of diluted aqueous solutions of acridine and aminacrine in the presence of hydrogen peroxide was studied. Irradiation was carried out with a low pressure mercury vapour lamp. The kinetic model describes the photodegradation rate of the organic compound with respect to the technological parameters of the reactor and provides the reaction rate constants of hydroxyl radicals towards these two molecules. This model was extented to high hydrogen peroxide concentrations ([H₂O₂] > 200 μmol/l) by considering the reactivity of hydroxyl radicals towards hydrogen peroxide. This assumption allows us to define an optimal hydrogen peroxide concentration.     

部分水溶性偶氮染料的光催化降解研究

本研究以高压汞灯为光源,系统地研究了１６种偶氮染料在水溶液中的ＴｉＯ２光催化降解。结果表明,这些偶氮染料的光解为一级动力学反应,采用ＴｉＯ２光催化降解方法处理所研究的偶氮染料是可行的,并初步探讨了染料的结构与光解反应表观速率常数之间的关系。     

几种环境激素酞酸酯的光催化降解研究

在紫外光照射下,以TiO2为催化剂,研究邻苯二甲酸二丁酯(DBP)、邻苯二甲酸二环己酯(DCHP)和邻苯二甲酸丁基苄基酯(BBP)水溶液的光催化降解规律,不同结构特征的酞酸酯在降解过程中pH值均表现为先升高,再降低的趋势.降解为表观一级反应.采用色质联用技术(GC-MS)分别对上述物质降解过程中生成的中间体进行分析,提出了可能的降解机理.     

Effect of molecular properties on the photocatalytic degradation rates of dichlorophenols and dichloroanilines in aqueous TiO2 suspensions

The kinetics of the photocatalytic degradation of 10 different dichlorophenols and dichloroanilines have been investigated experimentally and theoretically. With the intention of finding certain molecular indices in order to determine the degradation rates of aromatic pollutants, geometry optimizations of the compounds have been performed with the semiempirical PM3 method. The molecular orbital calculations have been carried out by an SCF method using the RHF formalism. The correlations between the apparent first-order rate constants and the calculated molecular properties of the compounds have been examined. Four different structure–activity relationships have been developed expressing the logarithms of the rate constants in terms of the Hammett constants, electron densities of the substituents, the coefficients and the energies of the highest occupied molecular orbitals HOMO, and 1-octanol/water partition coefficients log?K _OW.     

Decolorisation of Acid Blue 74 by ultraviolet/H<Subscript>2</Subscript>O<Subscript>2</Subscript>

The photodegradation of Acid blue 74 in aqueous solution employing a H₂O₂/ultraviolet system in a photochemical reactor was investigated. The kinetics of decolorization were studied by application of a kinetic model. The results show that the reaction of decolorization followed pseudo-first order kinetics. We demonstrate that there is an optimum H₂O₂ concentration, at which the rate of the decolorization reaction is maximum. Irradiation at 253.7 nm of the dye solution in the presence of H₂O₂ results in complete discoloration after ten minutes of treatment.     

Polyoxometalates for photocatalytic degradation of aqueous dyestuff solutions and quantitative structure–property relationship study on photolysis rate constants

Polyoxometalate, K₆TiW₁₁O₃₉Sn·7H₂O (TiW₁₁Sn), was synthesized and characterized. TiW₁₁Sn and K₆ZrW₁₁O₃₉Sn·12H₂O (ZrW₁₁Sn) were evaluated for their photocatalytic degradation of triarylmethane (brilliant green and acid blue 9), bisazo (C.I. reactive black 5), and monoazo dyestuffs (C.I. reactive red 24, C.I. reactive red 194, and C.I. reactive orange 5) with natural sunlight in homogeneous aqueous solutions. TiW₁₁Sn and ZrW₁₁Sn effectively and photocatalytically decolorized the dyestuffs. The TiW₁₁Sn- and ZrW₁₁Sn-mediated photocatalytic degradation of the dyestuffs involved a pseudo-first-order reaction and was modeled by Langmuir–Hinshelwood-type kinetics. The observed pseudo-first-order rate constants (K^/) of triarylmethane dyestuffs were generally bigger than that of the azo dyestuffs. Quantitative structure–property relationship models of the K^/ of the dyestuffs were developed using partial least-square regression. The cumulative variance of the dependent variable explained by the partial least-square components was > 0.753 for each optimal model. This value indicated that the model had good predictive ability and robustness. The K^/ values of the dyestuffs were related to the energy of the lowest unoccupied molecular orbital, and the most positive net atomic charges on a sulfur atom of dyestuffs. The linear correlation coefficients between the predicted and experimental values were all > 0.9950.     

Selective reduction of NO by photo-SCR with ammonia in an annular fixed-film photoreactor

Gaseous NO was photocatalytically reduced at room temperature by photo-assisted selective catalytic reduction (photo-SCR) with ammonia over TiO₂ in this study. NO reduction efficiency and N₂ selectivity were determined from gases composition at the outlet stream of photoreactor. Effect of operating conditions, e.g. light intensity and inlet concentrations of ammonia and oxygen, on the NO reduction efficiency and N₂ selectivity were discussed to determine the feasible operating condition for photocatalytic reduction of NO. Experimental results showed that selective catalytic reduction of NO with ammonia over TiO₂ in the presence of oxygen was a spontaneous reaction in dark. The photoirradiation on the TiO₂ surface caused remarkable photocatalytic reduction of NO to form N₂, NO₂, and N₂O under 254 nm UV illuminations, while almost 90% of N₂ selectivity was achieved in this study. The ammonia and oxygen molecules played the roles of reductant and oxidant for NO reduction and active sites regeneration, respectively. The reduction of NO was found to be increased with the increase of inlet ammonia and oxygen concentrations until specific concentrations because of the limited active sites on the surface of TiO₂. The kinetic model proposed in this study can be used to reasonably describe the reaction mechanism of photo-SCR.     

TiO2 photocatalyzed degradation of diazinon in an aqueous medium

The photocatalytic degradation of diazinon was studied over TiO₂ catalysts. The kinetics obtained demonstrated that powder titania (t_1/2 = 9.7 min) was more efficient compared to pure titania thin film catalysts (t_1/2 = 29.4 min). Mineralization of organic carbon to CO₂ after 360 min of irradiation was found to be 75% while heteroatoms (P, S, N) were mineralized into phosphate, sulfate and nitrate ions, respectively. A microtox test was performed to evaluate the toxicity of solutions treated by catalysts. Illumination of diazinon in the presence of TiO₂ gave rise to several intermediates that have been identified by means of solid phase extraction and gas chromatography-mass spectrometry, while a simple degradation pathway is proposed.     

Selenium content of rice,mixed plant foods and fish from Bangladesh

Static and dynamic adsorption studies of Co (II) ions have been undertaken at fixed pH and ionic strength taking binary biopolymeric beads of cross-linked calcium alginate and carboxy methylcellulose as biosorbents. The adsorption data were applied to Langmuir and Freundlich isotherm equations and various static parameters were calculated. The dynamic nature of adsorption process was quantified in terms of several kinetic constants such as rate constants for adsorption (K) and Lagergreen rate constant (K _ad). The influence of various experimental parameters such as solid-to-liquid ratio, pH, and temperature, the presence of salts and chemical composition of biopolymeric beads were investigated on the adsorption of cobalt ions.     

Ultraviolet-H2O2 oxidation of surfactants

This paper describes a study of the treatment of surfactant synthetic solutions by chemical and photolytic oxidation. Synthetic solutions of linear alkylbenzene sulfonates (LAS) are treated in this work as this is a model compound commonly used in the formulation of detergents, with a great presence in urban and industrial waste-waters. The application of ultraviolet (UV) radiation combined with hydrogen peroxide to oxidize linear alkylbenzene sulfonates (LAS) is shown to be suitable as a primary oxidation step since conversions of about 50% of the original compounds are achieved in the most favorable cases. Initially, the influence of the operating variables on the degradation levels is analyzed in this work. A kinetic model that considers the contributions of both direct photolysis and radical attack is also worked out. Direct photolysis is performed to determine the quantum yield in the single photodecomposition reaction. In addition, the rate constant of the reaction between hydroxyl radicals and linear alkylbenzene sulfonates in the oxidizing system H₂O₂/UV is determined for different operational conditions. Finally, the contribution of each oxidation pathway is quantified, resulting in a higher contribution of the radical reaction than of photolysis in all cases.     

Efficient photocatalytic degradation of Rhodamine B dye using ZnO/graphitic C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanocomposites synthesized by microwave

Semiconductor photocatalysis is a solution to issues of environmental pollution and energy shortage because photocatalysis can use solar energy to degrade pollutants. The photocatalytic activity can be improved by using composites of ZnO and other semiconductors. Here, composites of ZnO and polymeric graphite-like C₃N₄ (g-C₃N₄) with high photocatalytic activities were prepared by microwave synthesis. Products were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible and Fourier transform infrared spectroscopy. The photocatalytic degradation of Rhodamine B was tested under irradiation from a Xe lamp. Results show that adding graphite-like C₃N₄ promotes the photocatalytic activity of ZnO. Composites with 1.0 wt% g-C₃N₄ showed the best photodegradation efficiency, and the reaction average energy was approximately 33.71 kJ mol^?1.     

Photocatalytic degradation of aqueous methyl-tert-butyl-ether (MTBE) in a supported-catalyst reactor

Contamination of groundwater by methyl-tert-butyl ether (MTBE) poses increasing problems to water companies. Here we demonstrate the feasibility of using a cylindrical, supported-catalyst reactor for photocatalytic degradation of MTBE in water. It was shown that photocatalytic degradation of MTBE follows pseudo first-order kinetics. The maximum reaction rate constant observed was 0.47 hr^–1. The reaction rate increases linearly with increasing light intensity. It was also found that the reaction rate is linearly proportional to the ratio of catalyst surface area to volume of reactor. Complete degradation of MTBE was reached with an excess supply of oxygen.     

Photodegradation of an azo dye by silver-doped nano-particulate titanium dioxide

The synthesis of silver doped nano-particulate titanium dioxide (Ag/TiO₂) using a microemulsion method and an investigation of its photocatalytic activity for the degradation of Acid Red 27 in distilled water under UV-irradiation is reported. The prepared Ag/TiO₂ is characterized using transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The size of the Ag nanoparticles is around 5–15?nm, with almost uniform distribution on the TiO₂ particles. The efficiency of the photocatalytic process is evaluated to establish the optimum conditions, found to be at 2?wt% of Ag loading on TiO₂, catalyst dosage of 400?mg?L^?1, and calcination temperature of 300°C. Complete decolorization of the dye solution on Ag/TiO₂ was observed in 20?min of UV irradiation in the optimum conditions.     

Exposure and Health Effects of Cadmium

The results of a study of photocatalytic degradation of phenol using aqueous oxygenated TiO₂ (anatase) suspensions in a batch Pyrex photoreactor are reported. The influence on the photodegradation rate of various parameters as pH, phenol and TiO₂ content, oxygen partial pressure, anions present in the dispersions was investigated. A complete oxidation of phenol was observed. Intermediate compounds, catechol and quinone, were detected. It was observed that the photodegradation also proceeded with sunlight radiation. A mechanistic and kinetic model, which accounts for the results obtained, is given. Likely reasons for inactivity of the rutile modification for this reaction are also given.     

Recovery of seven kinds of cfc and cfc replacements on high‐surface area activated carbon

The adsorption isotherms, the constants of the Dubinin—Radushkevich plots, and the constants of the Langmuir plots of chlorofluorocarbon (CFC) and CFC replacements on high‐surface area activated carbon were investigated to estimate the recovery efficiency of CFC and CFC replacements. The adsorption and desorption of HFC134a on a high‐surface area activated carbon was much easier than that of CFC 113 and the CFC replacements. The recovery efficiency of CFC replacements depends on the hydrogen atoms in molecule. It is possible that the saturated amount adsorbed in the pores or on the surface of the activated carbon could be evaluated by the W_s constant of the the Langmuir equation and the W_o constant of the Dubinin‐Radushkevich equation. The a constant of the Langmuir equation and the BE_o constant of the Dubinin‐Radushkevich equation depend on the molecular composition.     

Fenton process for degradation of selected chlorinated aliphatic hydrocarbons exemplified by trichloroethylene, 1,1-dichloroethylene and chloroform

The degradation of selected chlorinated aliphatic hydrocarbons (CAHs) exemplified by trichloroethylene (TCE), 1,1-dichloroethylene (DCE), and chloroform (CF) was investigated with Fenton oxidation process. The results indicate that the degradation rate was primarily affected by the chemical structures of organic contaminants. Hydroxyl radicals (·OH) preferred to attack the organic contaminants with an electron-rich structure such as chlorinated alkenes (i.e., TCE and DCE). The dosing mode of Fenton’s reagent, particularly of Fe²⁺, significantly affected the degradation efficiency of studied organic compound. A new “time-squared” kinetic model, C = C _o exp(?k _obs t ²), was developed to express the degradation kinetics of selected CAHs. This model was applicable to TCE and DCE, but inapplicable to CF due to their varied reaction rate constants towards ?OH. Chloride release was monitored to examine the degree of dechlorination during the oxidation of selected CAHs. TCE was more easily dechlorinated thanDCE and CF.Dichloroacetic acid (DCAA) was identified as the major reaction intermediate in the oxidation of TCE, which could be completely removed as the reaction proceeded. No reaction intermediates or byproducts were identified in the oxidation of DCE and CF. Based on the identified intermediate, the reaction mechanism of TCE with Fenton’s reagent was proposed.     

Removal of congo red and basic violet 1 by chir pine (Pinus roxburghii) sawdust,a saw mill waste: batch and column studies

The efficiency of chir pine sawdust (CPS) for adsorptive removal of the dyes, congo red (CR) and basic violet 1 (BV), from aqueous solution was evaluated using batch and column studies. The equilibrium was attained in 60 min for CR and 45 min for BV. The adsorption of BV obeyed the Langmuir isotherm model while the Freundlich isotherm fitted the equilibrium data of CR adsorption. The Langmuir monolayer adsorption capacities (Q_o) of CPS for BV and CR were 11.3 and 5.8 g kg^?1, respectively. The kinetic data for CR were best fitted to the Lagergren pseudo-first-order model and for BV to the pseudo-second-order model. The intra-particle diffusion was found to be the rate-controlling step for CR adsorption, while the adsorption kinetics of BV were controlled by both intra-particle and liquid-film diffusion. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic in nature. The adsorption activation energy (E_a) for CR (124 kJ mol^?1) implied chemical adsorption while that for BV (5.4 kJ mol^?1) indicated physical adsorption. An increase in the Thomas model constant (K_Th) with increasing flow indicated that for both dyes the mass transport resistance decreased during adsorption. Thus, CPS may be an efficient low-cost adsorbent for decolorization of dye-containing wastewaters.