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A visible-light-driven photocatalyst, Cu2O-CuO/Sr3BiO5.4, was synthesized by the precipitation method using a new acidic system with basic ethylenediamine tetraacetic acid disodium salt (Na(2)EDTA) as the buffer reagent. Part of Cu2O was formed on the surface of Sr3BiO5.4 in situ during the calcination. 5.4 log inactivation of Escherichia coli K-12 and 27% degradation of naphthalene were achieved in 3 and 2 h, respectively, under the visible light irradiation provided by fluorescent lamps. The results of this study suggested that Cu2O-CuO on the surface of Sr3BiO5.4 is stable and can effectively promote the visible light photocatalytic activity of Sr3BiO5.4. (C) 2012 Published by Elsevier B.V.

Urgent development of effective and low-cost disinfecting technologies is needed to address the problems caused by an outbreak of harmful microorganisms. In this work, we report an effective photocatalytic disinfection of E. coli K-12 by using a AgBr-Ag-Bi(2)WO(6) nanojunction system as a catalyst under visible light (lambda >or= 400 nm) irradiation. The visible-light-driven (VLD) AgBr-Ag-Bi(2)WO(6) nanojunction could completely inactivate 5 x 10(7) cfu mL(-1) E. coli K-12 within 15 min, which was superior to other VLD photocatalysts such as Bi(2)WO(6) superstructure, Ag-Bi(2)WO(6) and AgBr-Ag-TiO(2) composite. Moreover, the photochemical mechanism of bactericidal action for the AgBr-Ag-Bi(2)WO(6) nanojunction was investigated by using different scavengers. It was found that the diffusing hydroxyl radicals generated both by the oxidative pathway and the reductive pathway play an important role in the photocatalytic disinfection. Moreover, direct contact between the AgBr-Ag-Bi(2)WO(6) nanojunction and bacterial cells was not necessary for the photocatalytic disinfection of E. coli K-12. Finally, the photocatalytic destruction of the bacterial cells was directly observed by TEM images and further confirmed by the determination of potassium ion (K(+)) leakage from the killed bacteria. This work provides a potential effective VLD photocatalyst to disinfect the bacterial cells, even to destruct the biofilm that can provide shelter and substratum for microorganisms and resist to disinfection.

Forest landscapes represent the major land-cover type for the watersheds of the East River, which is the source of water for 40 million people in South China. Forest soils with high levels of organic carbon are a potential terrestrial source of dissolved organic carbon (DOC) into the East River. DOC is of great concern, since it can form carcinogenic disinfection byproducts (DBPs) during drinking water treatment. In this study, soils from three altitudes (200, 450 and 900 m) in the Xiangtou Mountain Nature Reserve in South China, representing soils from evergreen moon forest, transitional evergreen broadleaf forest, and evergreen broadleaf forest, respectively, were evaluated for their potential contributions of DBP precursors into the East River. The water extractable organic carbon (WEOC) in three forest soils was physically and chemically fractionated into particulate organic carbon (1.2-0.45 microm), colloidal organic carbon (0.45-0.22 microm), and dissolved organic carbon (DOC) (0.22 microm), hydrophobic acid (HPOA), transphilic acid and hydrophilic acid and were analysed for the formation potentials of trihalomethanes (THMs), haloacetonitriles (HANs), and chloral hydrate (CHD). Also, soils were incubated at 15, 25 and 35 degrees C for 14d in darkness to examine the impact of temperature effects on the availability and characteristics of WEOC. The extraction study showed that the amount of WEOC was proportional to soil organic carbon content, of which about 1% was water extractable. Regardless of soil type, DOC and HPOA were the most reactive fractions in forming THMs, CHD, and HANs. Production of DOC and HPOA in WEOC increased over 14 d incubation as incubation temperature increased, but the temperature did not alter the distribution of physical and chemical fractions and their reactivity in DBP formation. Results suggest higher inputs of DOC and DBP precursors from forest watersheds into source water may result in a warmer environment.

Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic pollutants and their low water solubility limits their degradation in aqueous solution. The presence of water-miscible solvent such as acetone can increase the water solubility of PAHs, however acetone will also affect the degradation of PAH. In this study the effects of acetone on the photocatalytic degradation efficiency and pathways of 5 selected PAHs, namely naphthalene (2 rings), acenaphthylene (3 rings), phenanthrene (3 rings), anthracene (3 rings) and benzo[a]anthracene (4 rings) were investigated. The Microtox toxicity test was used to determine whether the PCO system can completely detoxify the parental PAHs and its intermediates. The addition of 16% acetone can greatly alter the degradation pathway of naphthalene and anthracene. Based on intermediates identified from degradation of the 5 PAHs, the location of parental PAHs attacked by reactive free radicals can be correlated with the localization energies of different positions of the compound. For toxicity analysis, irradiation by UV light was found to induce acute toxicity by generating intermediates/degradation products from PAHs and possibly acetone. Lastly, all PAHs (10 mg l(-1)) can be completely detoxified by titanium dioxide (100 mg l(-1)) within 24h under UVA irradiation (3.9 mW cm(-2)).

AgBr was creatively immobilized on a magnetic substrate (SiO 2 -coated Fe 3 O 4 nanoparticle, SFN) to achieve magnetic separation after visible light-driven photocatalytic oxidation (PCO). The resulted Ag/AgBr/SFN was characterized by TEM, vibrating sample magnetometer and other techniques. It is found that the average diameter of the Ag/AgBr/SFN particle is less than 20 nm. The typical superparamagnetic behavior of Ag/AgBr/SFN implies that the catalyst can be magnetically separated. The physicochemical features of the used Ag/AgBr/SFN after visible light irradiation were not dramatically changed by X-ray diffraction, UV–Vis diffuse reflectance spectra and Fourier transform-infrared analysis. SiO 2 interlayer was proven to slightly increase the degradation efficiency for an azo dye Acid Orange 7. UV–Vis spectra and HPLC analysis indicated that the dye was oxidized and decomposed. The photoactivity of Ag/AgBr/SFN was partly maintained after successive PCO under visible light. In order to evaluate the roles of e − –h + pairs and reactive oxygen species, the quenching effect was examined by employing Ag/AgBr/SFN and commercial TiO 2 (P-25) under visible light ( λ > 400 nm) and UV-A irradiation, respectively. Active h + and the resulting OH played the major roles for degradation. The effect of active h + and OH were proven to be highly dependent on the concentration of photocatalysts. The effect of OH was more obvious for P-25, while that of active h + was more predominant for Ag/AgBr/SFN.

A semiconductor-based photocatalyst system, consisting of two visible-light-driven (VLD) components and one electron-transfer system, has a great potential to efficiently photocatalytically degrade pollutants. In this paper, we have reported a simple strategy for constructing an all-solid-state AgBr-Ag-Bi 2 WO 6 nanojunction by a facile deposition-precipitation method with Bi 2 WO 6 as the substrate. Two visible-light active components (AgBr, Bi 2 WO 6 ) and the electron-transfer system (Ag) are spatially fixed in this nanojunction system. Due to the presence of double visible-light active components, such a AgBr-Ag-Bi 2 WO 6 nanojunction system has the broadened visible-light photo-response range, and it also exhibits higher photocatalytic activity than photocatalysts containing single visible-light active component, such as Bi 2 WO 6 , Ag-Bi 2 WO 6 and AgBr-Ag-TiO 2 composite, for the degradation of the azo dye, Procion Red MX-5B and colorless pollutant pentachlorophenol. In addition, the initial dye concentration and pH value could greatly affect its photocatalytic activity, and the recycling experiments confirm that it is essentially stable during the photocatalytic process. In particular, the photocatalytic activity of AgBr-Ag-Bi 2 WO 6 nanojunction is superior to the sum of the activities of two individual photocatalysts (AgBr-Ag-TiO 2 and Bi 2 WO 6 ) that contain the same weight of AgBr or Bi 2 WO 6 , indicating the presence of a synergic effect between two visible-light active components in AgBr-Ag-Bi 2 WO 6 nanojunction. On the basis of the photocatalytic results and energy band diagram, the photocatalytic process that may have occurred on the AgBr-Ag-Bi 2 WO 6 nanojunction system is proposed; the vectorial electron transfer driven by the two-step excitation of both VLD components (AgBr and Bi 2 WO 6 ) contributes to its high photocatalytic activity. Therefore, this work provides some insight into the design of novel and efficient photocatalysts with multi-visible-light active components for enhancing VLD photocatalytic activity.

The purpose of the study is to compare problem based learning (PBL) and lecture-based learning (LBL) in Hong Kong secondary students’ science achievement. Secondary One students were divided into two groups: group A (n = 37), was taught two topics: “Human Reproduction” and “Density” through PBL; group B (n = 38) was taught the same topics by LBL. Multiple choice questions and short structured response items were used to assess students’ academic performance. Pre and post tests were categorized into three domains: knowledge, comprehension and application according to Bloom’s Taxonomy (Bloom 1956). The results of this study suggest first that PBL is at least as effective as LBL in gaining the knowledge required to achieve the syllabus’ learning objectives; secondly, the PBL group shows a significant improvement in students’ comprehension and application of knowledge over an extended time. Seemingly, PBL is favored for knowledge retention compared to a more conventional teaching approach, by these early adolescent children in Hong Kong. An ongoing longitudinal study on students’ interactions will further determine whether students taught through PBL develop improved learning in relation to high order skills, in a local situation which still tends to focus on factual recall but where higher skills are being demanded by systemic reform.

Natural rutile, which contains substituting metal ions as V5+ and Fe3+, was found to exhibit good photoactivity in visible light. The result showed that 60.59% of methyl orange (MO) was photodegraded after 1 h visible light irradiation. Compared with P25 TiO2, the efficiency and mechanism of MO degradation by natural rutile was discussed. The visible light response was due to the substituting ions altering the band structure, and the effective photoactivity was related to the presence of H2O2 and surface hydroxyl groups. Moreover, the substituting metal ions in their high oxidation states could capture photogenerated electrons to suppress electron–hole combination.

Polychlorinated biphenyls (PCBs) are wide spread environmental pollutants. This research focused the optimum physico-chemical conditions under which photocatalytic oxidation (PCO) can be used to degrade 2,2 � ,3,3 � -tetrachlorobiphenyl (tetra-CB). Among the optimal physico-chemical conditions studied were UV intensity, hydrogen peroxide (H2O2) and titanium dioxide (TiO2) concentrations, initial pH, and possible reaction intermediates were also determined. The results indicate that the optimal physico-chemical conditions necessary for the degradation of tetra-CB by PCO were UV intensity at 3.16 mW/cm 2 ,3 0 mM of H 2O2 and 100 mg/l of TiO2. In contrast to the results of PCO studies on other organic compounds, the optimum pH for PCO degradation of tetra-CB was 5.5. The removal efficiency was also higher under acidic conditions than alkaline conditions. Although degradation intermediates such as 1,3-bis(1,1-dimethylethyl)benzene, 2,4-bis(1,1-dimethylethyl)phenol, and 3,5-di- tert-butyl-4-hydroxybenzaldehyde were identified at an early stage in the reaction process, they were not completely degraded even after 7 h of PCO reaction. © 2004 Elsevier B.V. All rights reserved.

In situ grab sampling from source waters and water extraction from source materials are common methods for determining disinfection by-product (DBP) formation potential (FP) of water samples or reactivity of dissolved organic matter (DOM) in forming DBPs during chlorination. However, DOM, as the main DBP precursor, collected using these techniques may not represent the DOM reacting with disinfectants due to biogeochemical alterations during water conveyance to drinking water treatment facilities. In this study, we exposed leachates from fresh litter and associated decomposed duff to natural sunlight or K-12 for 14 d and evaluated the changes, if any, on the propensity to form trihalomethane (THM), haloacetonitrile (HAN), and chloral hydrate (CHD) during chlorination. Sunlight treatment did not significantly change dissolved organic carbon (DOC) concentration but caused a 24 to 43% decrease in the specific ultraviolet absorbance (SUVA) at 254 nm, indicating that UV-active chromophores were transformed or degraded. There were significant increases ( < 0.05) in specific HAN formation potential (HAN-FP) and specific CHD formation potential (CHD-FP) (i.e., HAN and CHD formation potentials per unit carbon), but no change in specific THM formation potential (THM-FP) after sunlight exposure. In contrast, bacterial treatment did not show any significant effect on SUVA, specific chlorine demand, or any specific DBP-FPs, although bacterial colony counts suggested DOM in leachates was utilized for bacterial growth. Results of this study confirmed that the reactivity of DOM in forming DBPs could be different after biogeochemical processes compared with its source materials. For this study, photochemical reactions had a greater effect on DBP-FPs than did microbial degradation.

A novel method, which determines the concentrations of speciated Cr(III) and Cr(VI) with the presence of Cr(III)-organic complexes (particularly chromium dyes), was developed based on a column solid phase extraction using Amberlite XAD-4 resin (XAD-4). Acid Yellow 99 (AY99), a chromium monoazo dye, used as a model organic compound, could be quantitatively recovered at pH 5 with low recoveries of Cr(III) and Cr(VI) (below 5%). After Cr(VI) being converted to Cr(III)-diphenylcarbazone (Cr-DPC) by 1, 5-diphenylcarbazide, Cr(VI) was quantitatively recovered at pH 1 with the recovery of Cr(III) below 5%. The recoveries of AY99, Cr(III) and Cr(VI) by the newly developed method were 94.7±1.7, 103.0±2.5 and 96.7±3.6%, respectively. In addition, the recoveries of organics (i.e. proteins, amino acids, and organic acids) complexing with chromium ion were all below 5% at pH 1 and had little interference to the selective determination of Cr(VI) concentration. The adsorption capacity and detection limit of XAD-4 for Cr(VI) was 281.6±2.8 µg g-1 and 1.37 µg L-1, respectively.

Litter materials from forested watersheds can be a significant source of dissolved organic matter (DOM) to surface waters that can contribute to the formation of carcinogenic disinfection by-products (DBPs) during drinking-water chlorination. This study characterized the reactivity of DOM from litter leachates of representative vegetation in oak woodlands, a major plant community in the Foothill Region of California. Leachates from fresh and decomposed litter (duff) from two oak species, pine, and annual grasses were collected for an entire rainy season to evaluate their reactivity to form DBPs on chlorination. Relationships among specific ultraviolet absorbance (SΔUVA), fluorescence index (FI), specific differential ultraviolet absorbance (SΔUVA), specific chlorine demand (SCD), and the dissolved organic carbon:dissolved organic nitrogen (DOC:DON) ratio to the specific DBP formation potential (SDBP-FP) were examined. The DOM derived from litter materials had considerable reactivity in forming trihalomethanes (THMs) (1.80-3.49 mmol mol), haloacetic acid (HAAs) (1.62-2.76 mmol mol(-1)), haloacetonitriles (HANs) (0.12-0.37 mmol mol(-1)), and chloral hydrate (CHD) (0.16-0.28 mmol mol). These values are comparable to other identified watershed sources of DBP precursors reported for the California Delta, such as wetlands and organic soils. Vegetation type and litter decomposition stage (fresh litter versus 1-5 yr-old duff) were key factors that determined characteristics of DOM and their reactivity to form DBPs. Pine litter had significantly lower specific THM formation potential compared with oak and grass, and decomposed duff had a greater DON content, which is a precursor of HANs and other nitrogenous DBPs. The SΔUVA and SDBP-FP were temporally variable and dependent on vegetation type, degree of decomposition, and environmental conditions. Among the optical properties of DOM, SΔUVA was the only parameter that was consistently correlated with SDBP-FP.

Zn:In(OH)ySz solid solution nanoplates (Zn:In(OH)ySz-SSNs) with uniform nanoparticle size were synthesized through a simple sodium dodecyl sulfate (SDS)-assisted hydrothermal process. To achieve better photoabsorption in the visible light (VL) region and suitable redox potentials of the Zn:In(OH)ySz solid solution (Zn:In(OH)ySz-SS), the substitution of S(2-) for OH was carried out by adjusting the concentration of thiourea and SDS in the synthesis solution, while the doping of Zn2+ was realized by adjusting Zn2+ concentration. In addition, the morphology and crystallinity of Zn:In(OH)ySz-SSs were also controlled by the concentration of SDS. Using Rhodamine B (RhB) as a target pollutant the photocatalytic performance of these Zn:In(OH)ySz-SSs with different components, diameter sizes, and morphologies was investigated. Remarkably, Zn:In(OH)ySz-SSNs prepared with atomic ratio of Zn2+ and In3+ of 0.6, 45 mmol L(-1) thiourea, and 26 mmol L(-1) SDS, have the highest visible-light-driven (VLD) photocatalytic activity, exceeding 95% for the degradation of RhB after 60 min. The investigation of photocatalylic mechanism further indicates that the holes, superoxide radical (*O2(-)) and surficial hydroxyl radical (*OHs) are the major reactive species for the photocatalytic reactions. More importantly, for the first time, a simple and versatile strategy is developed to confirm the fact that direct contact between the Zn:In(OH)ySz-SS and RhB is the prerequisite for the photocatalytic degradation of RhB. Therefore, we report not only the preparation of a novel and effective VL-driven photocatalyst, but also provide mechanistic insight into semiconductor photocatalysis.

Di(2-ethylhexyl)phthalate (DEHP) is a ubiquitous environmental contaminant due to its extensive use as a plasticiser and its persistence. Currently, there is no cost-effective treatment method for its removal from industrial wastewater. In a previous study, DEHP was effectively adsorbed from aqueous solution by biosorption onto chitinous materials. Biosorption can pre-concentrate DEHP from the aqueous phase for further treatment. As biosorption cannot degrade DEHP, in this study the degradation (and detoxification) of DEHP adsorbed onto chitinous material by photocatalytic oxidation (PCO) is attempted. PCO relies on hydroxyl radical (∙OH), which is a strong oxidising agent, for the oxidative degradation of pollutants. It is a non-selective process which can degrade DEHP adsorbed onto chitinous material. The first part of this study is the optimisation of the degradation of adsorbed DEHP by PCO. Adsorption was carried out in the physicochemical conditions optimised in the previous study, with 500 mg/L chitin A and 40 mg/L DEHP at initial pH 2, 22±2 °C and 150 rpm agitation for 5 min. After optimisation of PCO, a 61% removal efficiency of 10 mg/L of DEHP was achieved within 45 min under 0.65 mW/cm2 of UV-A with 100 mg/L TiO2, and 10 mM of H2O2 at initial pH 12. The optimisation study showed that UV-A and TiO2 are essential for the degradation of DEHP by PCO. The degradation intermediates/products were identified by GC–MS analysis. GC–MS results showed that the di(2-ethylhexyl) side chain was first degraded, producing phthalates with shorter side chains. Further reaction produced phathalic anhydride and aliphatic compounds such as alkanol and ester. The toxicities of parental and degradation intermediates in the solution phase and on chitinous materials were followed by the Microtox® test. Results indicated that toxicity can be removed after 4 h treatment by PCO. Thus the decontamination of DEHP by integrating biosorption and PCO is feasible.

The adsorption of Cu 2 + from aqueous solution by magnetite-immobilised chitin (MC) was studied in batch mode. Two conventional adsorbents, cation exchange resin (CER) and activated carbon (AC) were used for the comparison. The physicochemical parameters including pH, concentration of adsorbent, temperature and initial Cu 2 + concentration were optimised. Under the optimised conditions, the removal efficiencies of Cu 2 + for MC, CER and AC were 91.67, 93.36 and 89.16%, respectively. In addition, the removal capacities of Cu 2 + for MC, CER and AC were 56.71, 74.84 and 6.55 mg/g, respectively. The adsorption isotherm studies indicated that the adsorptive behaviour of Cu 2 + on three adsorbents could be well described by the Langmuir model. The maximum adsorption capacities ( q max ) for MC, CER and AC were 53.19, 89.29 and 5.82 mg/g, respectively. The applicability of the kinetic model has been investigated for MC. Experimental results indicated that a pseudo-second-order reaction model provided the best description of the data with a correlation coefficient 0.999 for different initial Cu 2 + concentrations. The rate constants were also determined. Various thermodynamic parameters such as standard free energy (Δ G 0 ), enthalpy (Δ H 0 ) and entropy (Δ S 0 ) were calculated for predicting the adsorption nature of MC. The results indicated that this system was a spontaneous and endothermic process.