Remediation of a chlorinated aromatic hydrocarbon in water by photoelectrocatalysis

Photoelectrocatalysis driven by visible light offers a new and potentially powerful technology for the remediation of water contaminated by organo-xenobiotics. In this study, the performance of a visible light-driven photoelectrocatalytic (PEC) batch reactor, applying a tungsten trioxide (WO₃) photoelectrode, to degrade the model pollutant 2,4-dichlorophenol (2,4-DCP) was monitored both by toxicological assessment (biosensing) and chemical analysis. The bacterial biosensor used to assess the presence of toxicity of the parent molecule and its breakdown products was a multicopy plasmid lux-marked E. coli HB101 pUCD607. The bacterial biosensor traced the removal of 2,4-DCP, and in some case, its toxicity response suggests the identification of transient toxic intermediates. The loss of the parent molecule, 2,4-DCP determined by HPLC, corresponded to the recorded photocurrents. Photoelectrocatalysis offers considerable potential for the remediation of chlorinated hydrocarbons, and that the biosensor based toxicity results identified likely compatibility of this technology with conventional, biological wastewater treatment.     

Fe/Si/TiO2三元复合光催化剂的性能研究

用溶胶-凝胶法制备了Fe/Si/TiO2三元复合光催化剂,利用X射线衍射(XRD)和紫外-可见漫反射光谱(DRS)对样品进行了分析表征,并以甲基橙为模拟污染物,考察了其光催化活性.结果表明,Fe/Si/TiO2三元复合光催化剂与TiO2相比,光催化活性明显提高;当煅烧温度为900℃、添加Fe的摩尔分数为0.050%时,光催化活性最佳.     

Catalytic TiO2 oxidation of ethanethiol for environmentally begnin air pollution control of sulphur compounds

Volatile organic compounds containing reduced sulphur such as thiols and thioethers are released mostly from biological activities and a number of manufacturing processes, such as papermaking and petroleum refining. Environmentally benign and cost-effective air pollution control technology for reduced sulphur compounds is still a topic of research, e.g., in pulp and paper industry. Due to its advantages, photocatalytic oxidation over titanium dioxide presents a potential alternative for the air treatment strategies. The temperature influence on the reaction pathway and kinetics of gas-phase photocatalytic oxidation and thermal catalytic decomposition of ethanethiol over Degussa P25 TiO₂ was established by a continuous flow method in a simple tubular reactor at temperatures from 373 to 453 K. Kinetic parameters for ethanethiol were: adsorption enthalpy −45 kJ mol⁻¹ and activation energy 42 kJ mol⁻¹. Sulphur dioxide, carbon monoxide, carbon dioxide, acetic acid and water were identified as by-products.     

Decomposition of 1,4-dioxane by vacuum ultraviolet irradiation: Study of economic feasibility and by-product formation

We report the first use of vacuum ultraviolet (VUV) treatment to decompose 1,4-dioxane, a persistent organic contaminant that is difficult to remove by conventional drinking water treatment processes. The efficiency of VUV treatment was compared to that of VUV- and UV-based advanced oxidation processes (AOPs) (VUV/TiO₂, VUV/H₂O₂, UV/TiO₂, and UV/H₂O₂), and by-product formation was investigated. VUV treatment decomposed 1,4-dioxane more rapidly than did UV and UV/TiO₂ treatments. The decomposition rate was enhanced when VUV irradiation was combined with TiO₂ or H₂O₂. VUV/H₂O₂ decomposed 1,4-dioxane more rapidly than UV/H₂O₂ at a low H₂O₂ dose (1 mg/L), but the rate difference became small at a high H₂O₂ dose (5 mg/L). Electrical energy per order analysis revealed that VUV treatment, and the VUV- and UV-based AOPs, were economically feasible for 1,4-dioxane decomposition. Using raw water samples, we investigated by-product formation during VUV treatment and the effect of VUV irradiation on chlorinated disinfection by-product formation potential. Although the samples contained high concentrations of bromide, no bromate was produced by VUV treatment. VUV treatment slightly decreased trihalomethane formation potential (THMFP), whereas haloacetic acid formation potential (HAAFP) was unchanged, and total aldehyde concentration increased. The trend in HAAFP agreed with that had been reported for the VUV irradiation with much higher dose (Buchanan et al., 2006), whereas the trend in THMFP was different from that with much higher dose. THMFP, HAAFP, and aldehyde concentration were reduced by subsequent treatment with granular activated carbon (GAC) or biological activated carbon (BAC). Nitrite was produced by VUV treatment but disappeared after subsequent BAC treatment. These results suggest that VUV treatment should be combined with GAC or BAC treatment to suppress by-product formation.     

Preparation of Ag@AgCl-doped TiO2/sepiolite and its photocatalytic mechanism under visible light

A cube-like Ag@Ag Cl-doped TiO_2/sepiolite(denoted Ag@Ag Cl–TiO_2/sepiolite) was successfully synthesized via a novel method. X-ray diffraction, scanning electron microscopy, energy dispersion X-ray fluorescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and diffuse reflectance ultraviolet–visible spectroscopy were performed to determine the structure and physicochemical properties of Ag@Ag Cl–TiO_2/sepiolite. SEM micrographs revealed that Ag@Ag Cl nanoparticles and TiO_2 film are well deposited on the surface of tube-like sepiolite. As a result, Ag@Ag Cl–TiO_2/sepiolite exhibits a red shift relative to TiO_2/sepiolite. Photocatalytic experiments demonstrated that the dosage of catalysts plays an important role during photocatalysis. The photoelectrochemical activities of Ag@Ag Cl–TiO_2/sepiolite and TiO_2/sepiolite were also investigated. Photocurrent responses confirmed that the ability of Ag@Ag Cl–TiO_2/sepiolite to separate photo-generated electron–hole pairs is stronger than that of TiO_2/sepiolite. Methylene Blue degradation is also improved under alkaline conditions and visible light irradiation because more UOH is produced by visible light excitation.This excellent catalytic ability is mainly attributed to the formed Ag nanoparticles and the Schottky barrier at the Ag/TiO_2 interface. Active species analysis indicated that UO2-and h+are implicated as active species in photocatalysis. Therefore, catalysts are excited to produce abundant electron–hole pairs after they absorb photons in photocatalysis.     

Photocatalytic reduction of organic pollutant under visible light by green route synthesized gold nanoparticles

We report a rapid method of green chemistry approach for synthesis of gold nanoparticles(AuNPs)using Lagerstroemia speciosa leaf extract(LSE). L. speciosa plant extract is known for its effective treatment of diabetes and kidney related problems. The green synthesis of Au NPs was complete within 30 min at 25°C. The same could also be achieved within 2 min at a higher reaction temperature(80°C). Both UV–visible spectroscopy and transmission electron microscopy results suggest that the morphology and size distribution of Au NPs are dependent on the pH of gold solution,gold concentration,volume of LSE,and reaction time and temperature. Comparison between Fourier transform infrared spectroscopy(FT-IR)spectra of LSE and the synthesized Au NPs indicate an active role of polyphenolic functional groups(from gallotannins,lagerstroemin,and corosolic acid)in the green synthesis and capping of Au NPs. The green route synthesized Au NPs show strong photocatalytic activity in the reduction of dyes viz.,methylene blue,methyl orange,bromophenol blue and bromocresol green,and 4-nitrophenol under visible light in the presence of Na BH_4. The non-toxic and cost effective LSE mediated Au NPs synthesis proposed in this study is extremely rapid compared to the other reported methods that require hours to days for complete synthesis of Au NPs using various plant extracts. Strong and stable photocatalytic behavior makes Au NPs attractive in environmental applications,particularly in the reduction of organic pollutants in wastewater.     

Photodegradation of fungicide triadimefon and pesticide pirimicarb in aqueous TIO2 suspension

Two agrochemicals composed of nitrogen‐containing heterocyclic ring, triadimefon and pirimicarb, were degraded photocatalytically. The disappearance and TOC elimination rates of triadimefon were close to those of pirimicarb, whereas the photolysis of triadimefon was 4 times slower than that of pirimicarb. For triadimefon its aromatic moiety degraded quickly and Cl^‐ was released immediately, while triazole moiety degraded slowly. The formation rates of NH⁺ ₄ and NO₃ ^‐ by the degradation of triazole moiety were influenced by the rest of the molecule. The difference between disappearance and TOC elimination rates of both triadimefon and pirimicarb were far larger than those of aromatic compounds.     

Photodegradation of malachite green and malachite green carbinol under irradiation with different wavelength ranges

The dye malachite green (MG) is used worldwide as a fungicide in aquaculture. It is a toxic substance which in aqueous solutions is partly converted into its non-ionic colorless form (leucocarbinol). The equilibrium between these two forms is pH-dependent (pK = 6.9). To assess the photodegradation of MG under sunlight conditions, both species were irradiated separately in aqueous solutions with different pH values (4.0 and 12.0) using various ultraviolet and visible wavelength ranges (UV/VIS). A 700 W high-pressure mercury lamp with special filters was used. No artificial photooxidizers such as H₂O₂ or TiO₂ were added. MG leucocarbinol proved to be much more sensitive to irradiation than the dye form. Quantum yields Φ were calculated for some wavelength ranges as follows: MG carbinol: Φ_(280-312nm) is 4.3 × 10⁻³, Φ_(313-410nm) is 5.8 × 10⁻³, and MG dye: Φ_(280-312nm) is 4.8 × 10⁻⁵, Φ_(313-365nm) is 1.1 × 10⁻⁵, and Φ_(>365nm) is 0, respectively. Therefore, the solar photolysis of MG is an important sink and primarily depends on the photodegradation of the colorless leucocarbinol. During the irradiation of MG leucocarbinol with wavelengths >365 nm, an intermediate was formed which has photocatalytical properties.     

Highly efficient Zr doped-TiO2/glass fiber photocatalyst and its performance in formaldehyde removal under visible light

Zr-doped-TiO_2 loaded glass fiber(ZT/GF) composite photocatalysts with different Zr/Ti ratios were prepared with a sol–gel process. Zr4+can replace Ti4+in the TiO_2 lattice, which is conducive to forming the anatase phase and reducing the calcination temperature. The glass fiber carrier was responsible for better dispersion and loading of Zr-doped-TiO_2 particles, improving the applicability of the Zr-doped-TiO_2. The ZT/GF photocatalysts were characterized by X-ray diffraction(XRD), scanning electron microscope(SEM), Fourier transform infrared spectroscopy(FT-IR), ultraviolet–visible spectroscopy(UV–vis) and Barrett–Joyner–Halenda(BJH). The performance of photocatalysts with different loading was evaluated in formaldehyde degradation under visible light at room temperature. ZT/GF0.2exhibited the highest activity, with a formaldehyde removal rate as high as 95.14% being observed, which is better than that of the photocatalyst particles alone. The stability of the catalyst was also tested, and ZT/GF exhibited excellent catalytic performance with 94.38%removal efficiency, even after seven uses.     

Combined effects of adsorption and photocatalysis by hybrid TiO2/ZnO-calcium alginate beads for the removal of copper

The use of nanosized titanium dioxide(TiO_2) and zinc oxide(ZnO) in the suspension form during treatment makes the recovering and recycling of photocatalysts difficult.Hence,supported photocatalysts are preferred for practical water treatment applications.This study was conducted to investigate the efficiency of calcium alginate(CaAlg) beads that were immobilized with hybrid photocatalysts,TiO_2/ZnO to form TiO_2/ZnO-CaAlg.These immobilized beads,with three different mass ratios of TiO_2:ZnO(1:1,1:2,and 2:1) were used to remove Cu(Ⅱ) in aqueous solutions in the presence of ultraviolet light.These beads were subjected to three cycles of photocatalytic treatment with different initial Cu(Ⅱ) concentrations(10-80 ppm).EDX spectra have confirmed the inclusion of Ti and Zn on the surface of the CaAlg beads.Meanwhile,the surface morphology of the beads as determined using SEM,has indicated differences of before and after the photocatalytic treatment of Cu(Ⅱ).Among all three,the equivalent mass ratio TiO_2/ZnO-CaAlg beads have shown the best performance in removing Cu(Ⅱ) during all three recycling experiments.Those TiO_2/ZnO-CaAlg beads have also shown consistent removal of Cu,ranging from 7.14-52.0 ppm(first cycle) for initial concentrations of10-80 ppm.In comparison,bare CaAlg was only able to remove 6.9-48 ppm of similar initial Cu concentrations.Thus,the potential use of TiO_2/ZnO-CaAlg beads as environmentally friendly composite material can be further extended for heavy metal removal from contaminated water.