Enhanced Photocatalytic Degradation of Bisphenol A in Aqueous Solution by Ag-Doping ZnO

The metal-doping into the photocatalyst was evaluated for the photocatalytic degradation of bisphenol A in aqueous solution with ZnO powder. Au/ZnO, Ag/ZnO and Cu/ZnO were tested in the present work. Ag-doping ZnO was effective for the improvement of efficiency for the photocatalytic degradation of bisphenol A in water. The optimum doping concentration of silver was found to be 3 wt%. The pseudo first-order rate constant with 3 wt% Ag/ZnO was 1.3 times better compared with bare ZnO. The photocatalytic degradation of treatment for the wastewater containing bisphenol A is simple, easy handling and low cost.

Enhanced Removal of Arsenite from Ground Water by Adsorption onto Heat-Treated Rice Husk

The effect of heat treatment for rice husk was investigated on the removal of arsenite in ground water by the adsorption onto the rice husk surface. The heat treatment was performed at the temperature from 80oC to 300oC in the closed system under anoxic environment. The continuous adsorption column method was applied for the removal of arsenite. The removal efficiency (75%) with rice husk treated at 150oC was better compared to those (54%) obtained with untreated rice husk. Therefore, the heat treatment of rice husk at relatively low temperature was effective for the enhancement of arsenic removal from water. The treatment conditions of As removal from aqueous solution were optimized. The developed treatment technique was applied into the real ground water sample in Bangladesh. The As concentration in sample water after treatment was approximately 18 and 8 μg/L, which was below the WHO guideline value of maximum admissible level of arsenic in ground water for Bangladesh (50 μg/L). The developed technique might become a potential avenue for simple and low cost arsenic removal methods.

Removal of Methylene Blue, Rhodamine B and Ammonium Ion from Aqueous Solution by Adsorption onto Sintering Porous Materials Prepared from Coconut Husk Waste

The present work was done in order to develop and find out suitable conversion methods for coconut husk wastes into value-added products. It is well-known that coconuts husk waste is hydrophobic therefore ethanol with different doses was used as a surfactant to enhance the removal efficiency. Treated samples at different adsorbent amounts, sintering temperatures & sintering time, stirring time, pH, and solution temperatures for color removal of Methylene Blue (MB) & Rhodamine B (RhB) and ammonium concentration were evaluated by using UV-Visible Spectroscopy. At 300°C, results showed complete removal for MB and more than 75% for RhB, whereas removal of ammonium ion reached around 52% when sintering product from husk waste was used. Further investigation was carried out for ammonium ion to understand the desorption kinetic behaviors and isotherm models. Kinetics indicated that desorption of ammonium ion followed pseudo-first order equation. Adsorption thermodynamic parameters such as ΔG, ΔH, and ΔS followed Van’t Hoff plot for adsorption and found to be negative which indicated that the adsorption process for ammonium onto coconut husk was physical, spontaneous and exothermic.

Optimization of Conditions for the Photocatalytic Degradation of EDTA in Aqueous Solution with Fe-Doped Titanium Dioxide

The conditions for photocatalytic degradation of ethylenediaminetetraacetic acid (EDTA) in aqueous solution with Fe-doped titanium dioxide (TiO2) were optimized. The degradation efficiencies with Fe-doped TiO2 were better, compared with those obtained with bare TiO2 and Pt-doped TiO2. The effect of various experimental factors, such as photocatalytic dosage, temperature, solution pH and light intensity on the photocatalytic degradation of EDTA by Fe-doped TiO2 was investigated. The photocatalytic degradation treatment for the wastewater containing EDTA is simple, easy handling and low cost.

Evaluation of Reaction Mechanism for Photocatalytic Degradation of Dye with Self-Sensitized TiO₂under Visible Light Irradiation

The dye-sensitized TiO2 method is one of the most promising methods for the visible-light-induced detoxification of pollutants. The reaction mechanism for photocatalytic degradation of orange II (OII) and rhodamine B (RhB) with self-sensitized TiO2 under visible light irradiation (λ > 400 nm) has been evaluated. Radical scavenger studies were carried out to investigate the active species involved in the photodegradation of 5 mg/L of initial concentration of OII and RhB at room temperature. The trapping effects of different scavengers results proved that the oxidation of OII and RhB mainly occurred by the direct oxidization of h+ and ·O2- radicals, while the ·OH radicals played only a relatively minor role in the direct oxidization process.

Indirect photocatalytic reduction of arsenate to arsenite in aqueous solution with TiO_2 in the presence of hole scavengers

The indirect photocatalytic reduction of arsenate to arsenite in aqueous solution with titanium dioxide(TiO_2)was investigated with various hole scavengers such as methanol, ethanol, 2-propanol, formaldehyde, acetone,formic acid and acetic acid. Although the direct photocatalytic reduction of arsenate to arsenite with TiO_2 was impossible, an indirect reduction of As(V) was possible in the presence of sacrificial electron donors to form strongly reductive radicals. The addition of ethanol was very effective for indirect photocatalytic reduction of As(V) in aqueous solution with TiO_2 photocatalyst. The indirect photocatalytic reduction rate of As(V) may be related with both the reaction rate constants of reaction of hydroxyl radicals with hole scavenger and the reactivities for the radicals M· which are produced by the reaction of ·OH with hole scavenger.

Degradation of Reactive Yellow 86 with photo-Fenton process driven by solar light

The decolorization of Reactive Yellow 86 （RY 86）, one of reactive azo dyes, was investigated in the presence of Fenton reagent under solar light irradiation. The decolorization rate was strongly influenced by pH, initial concentrations of H202 and Fe（II）, and so on. An initial concentration of 40 mg/L was decolored more than 90% after 20 min under optimum conditions. The activation energy of the solar photo-Fenton reaction was 1.50 kJ/mol for RY 86 in the temperature range of 10-60℃. In the kinetic study, the rate constant of RY 86 with OH- radicals could be estimated to be 1.7 × 10^10 L/（mol.sec）. The decolorization efficiency of RY 86 under solar light irradiation was comparable to the artificial light irradiation. The decrease of TOC as a result of mineralization of RY 86 was observed during photo-Fenton process. The rate of RY 86 mineralization was about 83% under UV irradiation after 24 hr. The formation of chloride, sulfate, nitrate and ammonium ions as end-products was observed during the photocatalytic process. The decomposition of RY 86 gave two kinds of intermediate products. The degradation mechanism of RY 86 was proposed on the base of the identified intermediates.

Enhanced hydrogen production from aqueous methanol solution using TiO2/Cu as photocatalysts

The photocatalytic hydrogen production from aqueous methanol solution using titanium dioxide （TiO2） was investigated in the addition of metal particles including copper, lead, tin, and zinc. The results show that only the addition of copper particles enhances the hydrogen production. The copper usage and reaction temperature were further optimized for TiO2/Cu photocatalyts. Under the optimal conditions, the hydrogen production using TiO2/Cu as photocatalysts is approxi- mately 68 times higher than that obtained with only TiO2.

Simultaneous removal of trihalomethanes by bimetallic Ag/Zn:kinetics study

In the present work,bimetallic silver/zinc was applied into the degradation of trihalomethanes,THMs:CHCl_(3),CHBrCl_(2),CHBr_(2)Cl,and CHBr_(3).The kinetics reaction rates and removal efficiencies of the THM compound mixtures,in the aqueous solutions,were investigated.Batch experiments were conducted under mild conditions,ambient temperature,and pressure.The primary degradation reaction followed a pseudo-first-order kinetic law.The first-order rate constants and the degradation efficiencies followed the decreasing order of CHBr_(3)>CHBr_(2)Cl>CHBrCl_(2)>CHCl_(3).The bond dissociation energy and hydrophilic/hydrophobic characteristics of the THM compounds may become the most important parameters affecting the degradation kinetics and efficiency by bimetallic Ag/Zn.

Determination of aniline derivatives in water samples after preconcentration with oxidized multiwalled carbon nanotubes as solid-phase extraction disk

A sensitive and selective preconcentration method using solid-phase extraction （SPE） disk made from oxidized multiwalled carbon nanotubes （OMWCNTs）, has been developed for the determination of aniline derivatives, such as 2-nitroaniline （2-NA）, 4- nitroaniline （4-NA）, and 2,4-dichloroaniline （2,4-DCA） in water samples. Anilines were extracted onto OMWCNT disk and then determined by high performance liquid chromatography （HPLC） with UV detector. Several parameters on the recovery of the analytes were investigated. The experimental results showed that it was possible to obtain quantitative analysis when the solution pH was 8 using 200 mL of validation solution containing 2 ug of anilines and 10 mL of acetonitrile/ethanol （8/2, v/v） as an eluent. Relative standard deviations for five determinations were 7.5% （2-NA）, 6.5% （4-NA） and 3.8% （2,4-DCA） under optimum conditions. The linear range of calibration curves were 0.5 ng.mL 1 to 15 ng.mL-1 for each analyte with good correlation coefficients. The detection limits （3S/N） of 2-NA, 4-NA and 31 pg.mL -1 and 26 pg.mL-1 was successfully applied to 2,4-DCA were 30pg.mL -1, respectively. Our method the determination of aniline compounds in fiver water sample with high precision and accuracy.