2,4-Dichlorophenol Degradation by an Integrated Process: Photoelectrocatalytic Oxidation and E-Fenton Oxidation

A new reactor system was designed for an integrated process involving photoelectrocatalytic oxidation (PECO) and electro-Fenton (E-Fenton) oxidation. Its efficiency was evaluated in terms of 2,4-dichlorophenol (2,4-DCP) degradation in aqueous solution. In this process, a TiO2 electrode and an iron (Fe) electrode were used as anodes in parallel, while graphite felt (GF) was used as a cathode. When an electrical current is applied between the anodes and the cathode, the iron anode can release Fe2+ and the GF cathode can generate H2O2 continuously in the reaction solution. Under UV-A illumination, while a H2O2-assisted PECO reaction occurs on the surface of the TiO2 photo anode, an E-Fenton reaction takes place in the solution. The experimental results demonstrated that 2,4-DCP degradation in aqueous solution was greatly enhanced because of the interaction between the two types of reactions. Moreover, the effect of pH as an important factor was investigated. It was found that the combined reaction becomes less pH sensitive than the typical E-Fenton reaction and may be suitable for application in a wide pH range.

Kinetic modeling of electro-Fenton reaction in aqueous solution

To well describe the electro-Fenton (E-Fenton) reaction in aqueous solution, a new kinetic model was established according to the generally accepted mechanism of E-Fenton reaction. The model has special consideration on the rates of hydrogen peroxide (H(2)O(2)) generation and consumption in the reaction solution. The model also embraces three key operating factors affecting the organic degradation in the E-Fenton reaction, including current density, dissolved oxygen concentration and initial ferrous ion concentration. This analytical model was then validated by the experiments of phenol degradation in aqueous solution. The experiments demonstrated that the H(2)O(2) gradually built up with time and eventually approached its maximum value in the reaction solution. The experiments also showed that phenol was degraded at a slow rate at the early stage of the reaction, a faster rate during the middle stage, and a slow rate again at the final stage. It was confirmed in all experiments that the curves of phenol degradation (concentration vs. time) appeared to be an inverted "S" shape. The experimental data were fitted using both the normal first-order model and our new model, respectively. The goodness of fittings demonstrated that the new model could better fit the experimental data than the first-order model appreciably, which indicates that this analytical model can better describe the kinetics of the E-Fenton reaction mathematically and also chemically.

Enhanced photocatalytic reduction reaction over Bi(3+)-TiO(2) nanoparticles in presence of formic acid as a hole scavenger

A series of Bi(3+)-doped TiO(2) (Bi(3+)-TiO(2)) catalysts with a doping concentration up to 2wt% were prepared by a sol-gel method. The prepared photocatalysts were characterized by different means to determine their chemical composition, surface structure and light absorption properties. The photocatalytic activity of different Bi(3+)-TiO(2) catalysts was evaluated in the photocatalytic reduction of nitrate in aqueous solution under UV illumination. In the experiments, formic acid was used as a hole scavenger to enhance the photocatalytic reduction reaction. The experiments demonstrated that nitrate was effectively degraded in aqueous Bi(3+)-TiO(2) suspension by more than 83% within 150min, while the pH of the solution increased from 3.19 to 5.83 due to the consumption of formic acid. The experimental results indicate that the presence of Bi(3+) in TiO(2) catalysts substantially enhances the photocatalytic reaction of nitrate reduction. It was found that the optimal dosage of 1.5wt% Bi(3+) in TiO(2) achieved the fastest reaction of nitrate reduction under the experimental condition. Bismuth ions deposit on the TiO(2) surface behaves as sites where electrons accumulate. Better separation of electrons and holes on the modified TiO(2) surface allows more efficient channeling of the charge carriers into useful reduction and oxidation reactions rather than recombination reactions. Two intermediate products of nitrite and ammonia during the reaction were also monitored to explore the possible mechanisms of photoluminescence quenching and photocatalytic reduction in the context of donor-acceptor interaction with electron trapping centers.

Degradation of endocrine disrupting chemicals in aqueous solution by interaction of photocatalytic oxidation and ferrate (VI) oxidation

In this study, the degradation of bisphenol A in aqueous suspension by interaction of photocatalytic oxidation and ferrate(VI) oxidation was investigated under different conditions. The results indicate that the formation of Fe(V) and Fe(IV) is in the photocatalytic reduction of Fe(VI) by electron (ecb-) on the surface of TiO2. The oxidation efficiency of the photocatalytic oxidation in the presence of Fe(VI) was much greater than that without. In addition, the decomposition of Fe(VI) under different conditions was also investigated. The results indicate that the Fe(VI) reduction was accelerated by photocatalytic reaction and the adsorption capacity of Fe(VI) on TiO2 surface decreased as pH increased. The characteristics of solid potassium ferrate prepared were investigated by X-ray diffraction. It was found that the potassium ferrate solid has a tetrahedral structure with a space group of D2h (Pnma) and a = 7.705 A, b = 5.863 A, and c = 10.36 A.

Levels of selenium, zinc, copper, and antioxidant enzyme activity in patients with leukemia

Essential elements, mainly selenium and zinc, were involved in protection against oxidative stress in cells. Oxidation could lead to the formation of free radicals that have been implicated in the pathogenesis of many diseases, including leukemia. Leukemia is a neoplastic disease that is susceptible to antioxidant enzyme and essential elements alterations. This study was undertaken to examine the levels of essential elements, antioxidant enzymes activities, and their relationships with different types of leukemia. Serum selenium, zinc, and copper concentrations, red blood cell glutathione peroxidase (GPx) activities, plasma Cu-Zn superoxide dismutase (Cu-Zn SOD) activities and lipid peroxidation (LPO) levels were determined in 49 patients with different types of leukemia before initial treatment. Serum selenium and zinc concentrations were lower in leukemia patients than those of controls (p<0.01). Serum copper concentration was higher in leukemia patients than that of controls (p<0.01). The activities GPx and Cu-Zn SOD were significantly increased in leukemia patients, especially with acute leukemia (AL), acute lymphoid leukemia (ALL), and acute nonlymphoid leukemia (ANLL) (p<0.05), whereas no difference was found between those of chronic myelogenous leukemia and the controls. The levels of LPO were normal as controls. Serum selenium concentration was not correlated with GPx, and serum levels of zinc and copper were not related to Cu-Zn SOD. Serum zinc levels had a negative correlation with the absolute peripheral blast cells, whereas serum copper had a positive correlation with the absolute peripheral blast cells. Increased GPx and Cu-Zn SOD activities and normal levels of LPO, which were a protective responses, were an indicator of mild oxidative stress; it might indicate that the essentials elements alterations in leukemia patients were mostly dependent on tumor activity. Changes of their levels demonstrated that there are low selenium, zinc, and high copper status in leukemia patients. The decrease of plasma zinc and increase of the Cu/Zn ratio could be the index that showed an unfavorable prognosis of acute leukemia.

A study of the preparation and reactivity of potassium ferrate

In the context of water treatment, the ferrate ([FeO(4)](2-)) ion has long been known for its strong oxidizing power and for producing a coagulant from its reduced form (i.e. Fe(III)). However, it has not been studied extensively owing to difficulties with its preparation and its instability in water. This paper describes an improved procedure for preparing solid phase potassium ferrate of high purity (99%) and with a high yield (50-70%). The characteristics of solid potassium ferrate were investigated and from XRD spectra it was found that samples of the solid have a tetrahedral structure with a space group of D(2h) (Pnma) and a=7.705A, b=5.863A, and c=10.36A. The aqueous stability of potassium ferrate at various pH values and different concentrations was investigated. It was found that potassium ferrate solution had a maximum stability at pH 9-10 and that ferrate solution at low concentration (0.25 mM) was more stable than at high concentration (0.51 mM). The aqueous reaction of ferrate with bisphenol A (BPA), a known endocrine disrupter compound, was also investigated with a molar ratio of Fe(VI):BPA in the range of 1:1-5:1. The optimal pH for BPA degradation was 9.4, and at this pH and a Fe(VI):BPA molar ratio of 5:1, approximately 90% of the BPA was degraded after 60s.

Structure Determination and Relative Properties of Novel Cubic Borates MM‘4(BO3)3 (M = Li, M‘ = Sr; M = Na, M‘ = Sr, Ba)

A series of novel borates, MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba), have been successfully synthesized by standard solid-state reaction. The crystal structures have been determined from powder X-ray diffraction data. They crystallize in the cubic space group Iad with large lattice parameters: a = 14.95066(5) A for LiSr4(BO3)3, a = 15.14629(6) A for NaSr4(BO3)3, and a = 15.80719(8) A for NaBa4(BO3)3. The structure was built up from 64 small cubic grids, in which the M' atoms took up the corner angle and the BO3 triangles or MO6 cubic octahedra filled in the interspaces. The isolated [BO3]3- anionic groups are perpendicular to each other, distributed along three 100 directions. The anisotropic polarizations were counteracting, forming an isotropic crystal. Sr and Ba atoms were found to be completely soluble in the solid solution NaSr(4-)xBax(BO3)3 (0 < or = x < or = 4). The photoluminescence of samples doped with the ions Eu2+ and Eu3+ was studied, and effective yellow and red emission was detected, respectively. The results are consistent with the crystallographic study. The DTA and TGA curves of them show that they are chemically stable and congruent melting compounds.

Development of an E-H2O2/TiO2 photoelectrocatalytic oxidation system for water and wastewater treatment

In this study, an innovative E-H2O2/TiO2 (E-H2O2 = electrogenerated hydrogen peroxide) photoelectrocatalytic (PEC) oxidation system was successfully developed for water and wastewater treatment. A TiO2/Ti mesh electrode was applied in this photoreactor as the anode to conduct PEC oxidation, and a reticulated vitreous carbon (RVC) electrode was used as the cathode to electrogenerate hydrogen peroxide simultaneously. The TiO2/Ti mesh electrode was prepared with a modified anodic oxidation process in a quadrielectrolyte (H2SO4-H3PO4-H2O2-HF) solution. The crystal structure, surface morphology, and film thickness of the TiO2/Ti mesh electrode were characterized by X-ray diffraction and scanning electron microscopy. The analytical results showed that a honeycomb-type anatase film with a thickness of 5 microm was formed. Photocatalytic oxidation (PC) and PEC oxidation of 2,4,6-trichlorophenol (TCP) in an aqueous solution were performed under various experimental conditions. Experimental results showed that the TiO2/Ti electrode, anodized in the H2SO4-H3PO4-H2O2-HF solution, had higher photocatalytic activity than the TiO2/Ti electrode anodized in the H2SO4 solution. It was found that the maximum applied potential would be around 2.5 V, corresponding to an optimum applied current density of 50 microA cm(-2) under UV-A illumination. The experiments confirmed that the E-H2O2 on the RVC electrode can significantly enhance the PEC oxidation of TCP in aqueous solution. The rate of TCP degradation in such an E-H2O2-assisted TiO2 PEC reaction was 5.0 times that of the TiO2 PC reaction and 2.3 times that of the TiO2 PEC reaction. The variation of pH during the E-H2O2-assisted TiO2 PEC reaction, affected by individual reactions, was also investigated. It was found that pH was well maintained during the TCP degradation in such an E-H2O2/TiO2 reaction system. This is beneficial to TCP degradation in an aqueous solution.

Enhanced photocatalytic degradation of VOCs using Ln3+-TiO2 catalysts for indoor air purification

Two types of lanthanide ion-doped titanium dioxide (Ln3+-TiO2) catalysts including La3+-TiO2 and Nd3+-TiO2 were prepared by a sol-gel method. The effects of the lanthanide ion doping on the crystal structure, surface area, adsorption properties, pore size distribution, and surface chemical state of the catalysts were investigated by means of XRD, BET, and XPS. As results, the crystal size decreased significantly, while the specific surface area, t-plot total surface area, micropore volume, and the total pore volume increased owing to the lanthanide ion doping. The nitrogen adsorption-desorption isotherms of the catalysts showed that the N2 adsorption ability of the Ln3+-TiO2 catalysts was better than the TiO2 catalyst. Among them, the 0.7% Ln3+-TiO2 catalysts demonstrated the highest adsorption ability. The photocatalytic activity of the catalysts was investigated in the experiments of the photocatalytic degradation of benzene, toluene, ethylbenzene and o-xylene (BTEX) in a gaseous phase. The photocatalytic efficiency of the TiO2 catalysts with the lanthanide ion doping was remarkably enhanced by BTEX removal. The 1.2% Ln3+-TiO2 catalysts achieved the highest photocatalytic activity. The enhanced photodegradation of BTEX is possibly due to the improved adsorption ability and the enhanced electron-hole pairs separation due to the presence of Ti3+ on the surface of Ln3+-TiO2 catalysts and the electron transfer between the conduction band/defect level and lanthanide crystal field state.

Synthesis and ab initio X-ray powder diffraction structure of the new alkali and alkali earth metal borate NaCa(BO3)

A sodium calcium borate, NaCaBO3, has been synthesized by the solid-state reaction method and the structure solved from X-ray powder diffraction data. The compound crystallizes in space group Pmmn and has a desired structure type containing isolated planar BO3(3-) anions. Mixed occupancy is found to exist in the Ca site, with partial replacement by Na. One Ca/Na mixed atom and one Na atom are at sites with mm2 symmetry, and a second Ca/Na mixed atom, an Na atom, two B and two O atoms are on mirror planes.

Computer programs for unit-cell determination in electron diffraction experiments

A set of computer programs for unit-cell determination from an electron diffraction tilt series and pattern indexing has been developed on the basis of several well-established algorithms. In this approach, a reduced direct primitive cell is first determined from experimental data, in the means time, the measurement errors of the tilt angles are checked and minimized. The derived primitive cell is then checked for possible higher lattice symmetry and transformed into a proper conventional cell. Finally a least-squares refinement procedure is adopted to generate optimum lattice parameters on the basis of the lengths of basic reflections in each diffraction pattern and the indices of these reflections. Examples are given to show the usage of the programs.

Syntheses, Thermal Stability, and Structure Determination of the Novel Isostructural RBa3B9O18 (R = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb)

A novel borate compound YBa(3)B(9)O(18) has crystallized in a melt of BaYB(9)O(16). Single-crystal X-ray diffraction measurements reveal that YBa(3)B(9)O(18) adopts a hexagonal space group P6(3)/m with cell parameters of a = 7.1761(6) A and c = 16.9657(6) A. The structure is made up of the planar B(3)O(6) groups parallel to each other along the (001) direction, regular YO(6) octahedra, and irregular BaO(6) and BaO(9) polyhedra to form an analogue structure of beta-BaB(2)O(4). A series of isostructural borate compounds RBa(3)B(9)O(18) (R = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) were prepared by powder solid-state reactions. The DTA and TGA curves of YBaB(9)O(16) show an obvious weight loss at about 955 degrees C associated with a decomposition into YBO(3), B(2)O(3), and YBa(3)B(9)O(18) due to its incongruent melting behavior. The DTA and TGA curves of YBa(3)B(9)O(18) show that it is chemically stable and a congruent melting compound. A comparison of the structures of YBa(3)B(9)O(18) and beta-BaB(2)O(4) is presented.

JECP/PCED—a computer program for simulation of polycrystalline electron diffraction pattern and phase identification

A computer program for simulation of polycrystalline electron diffraction pattern and phase identification is described. In addition to simulating electron diffraction pattern for a single phase, the program has the ability to model two phases with selected mass ratio. Experimental polycrystalline electron diffraction patterns can be directly compared to simulated patterns for phase identification. Examples of how to use the program are also given.

Three-dimensional reconstruction of the ν-AlCrFe phase by electron crystallography

The three-dimensional (3D) structure of the huge quasicrystal approximant nu-AlFeCr (space group P6(3)/m, a = 40.687 and c = 12.546 A) was solved by electron crystallography. High-resolution transmission-electron-microscopy (HREM) images and selected-area electron diffraction patterns from 13 different zone axes were combined to give a 3D potential map. 124 out of 129 unique atoms were found in the 3D map. Procedures for ab initio structure determination by 3D reconstruction are given. It is demonstrated that 3D reconstruction from HREM images is very powerful for solving structures--even very complicated ones. There is no limit in terms of the number of unique atoms in a structure that can be solved by 3D reconstruction.

Photocatalytic oxidation using a new catalyst--TiO2 microsphere--for water and wastewater treatment

Since the suspended TiO2 powder enjoys free contact with UV irradiation in a photoreactor system, it can generally achieve better efficiency than the immobilized TiO2 catalysts. However, the separation and reuse of this catalyst powder from treated water often limit its application in practice. In this study, a new type of TiO2 catalyst called TiO2 microsphere was prepared by a sol-spraying-calcination method, which can easily settle in its aqueous suspensions under gravity. The SEM image of the TiO2 microsphere samples demonstrated that they had an almost spherical shape with a particle size of 30-160 microm, while the XRD analysis indicated that these TiO2 microspheres still had a crystal size of 8.1 nm. Since these TiO2 microspheres had a porous structure with higher specific surface area and pore volume than normal TiO2 powders, they appeared to have strong adsorption ability in its aqueous suspensions. The photocatalytic activity of the TiO2 microspheres was evaluated in the photodegradations of salicylic acid (SA) and sulfosalicylic acid (SSA). The experimental results showed that the reaction rate using the TiO2 microspheres was similar to that using the TiO2 powders in the SA suspensions and even higher than that in the SSA suspensions. Chemical and physical properties of the TiO2 microspheres and powders that are attributed to photoactivity were discussed based on the Langmuir-Hinshelwood kinetic model. The prepared TiO2 microsphere samples were reused in the photooxidation reaction more than 50 times. It was found that there was no significant weakening in their photoactivity and no change in their particle shape. This TiO2 microsphere catalyst can be simply used to conduct an effective photooxidation in its suspension for water and wastewater treatment with ease of recovery from treated water.

The enhancement of TiO2 photocatalytic activity by hydrogen thermal treatment

In this study, conventional TiO2 powder was heated in hydrogen (H2) gas at a high temperature as pretreatment. The photoactivity of the treated TiO2 samples was evaluated in the photodegradation of sulfosalicylic acid (SSA) in aqueous suspension. The experimental results demonstrated that the photodegradation rates of SSA were significantly enhanced by using the H2-treated TiO2 catalysts and an optimum temperature for the H2 treatment was found to be of 500-600 degrees C. The in situ electron paramagnetic resonance (EPR) signal intensity of oxygen vacancies (OV) and trivalent titanium (Ti3+) associated with the photocatalytic activity was studied. The results proved the presence of OV and Ti3+ in the lattice of the H2-treated TiO2 and indicated that both were contributed to the enhancement of photocatalytic activity. Moreover, the experimental results presented that the EPR signal intensity of OV and Ti3+ in the H2-treated TiO2 samples after 10 months storage was still significant higher than that in the untreated TiO2 catalyst. The experiment also demonstrated that the significant enhancement occurred in the photodegradation of phenol using the H2-treated TiO2.

MAP precipitation from landfill leachate and seawater bittern waste

The leachates generated at Hong Kong landfill sites contain high strength of ammonium-nitrogen (NH4+-N) over 3,000 mg l(-1) and are generally inhibitive to most biological treatment processes. To remove the NH4+-N from the landfill leachates and also recover the nitrogen as a struvite fertilizer, a lab-scale study was performed to investigate the feasibility of NH4+-N removal and struvite crystallization using different magnesium sources. Three combinations of chemicals, MgCl2 x 6H2O+Na2HPO4 x 12H2O, MgO+H3PO4 and MgSO4 x 7H2O+Ca(H2PO4) x H2O, were first used at different molar ratios to precipitate NH4+-N from the leachate. The experimental results indicated that NH4+-N was removed by 92%, 36% and 70% respectively at pH 9.0 and a molar ratio of Mg:N:P=1:1:1. Two synthetic seawater bitten wastes containing Mg2+ at 9,220 mg l(-1) and 24,900 mg l(-1) respectively were then used as a magnesium source, while 85% H3PO4 chemical was used as a phosphorus source. The results revealed that NH4+-N was removed by 80% and 72% respectively, while a molar ratio of Mg:N:P=1:1:1 was applied. In the final stage of experiments, the magnesium-ammonium-phosphate (MAP) precipitates were examined by SEM, EDS and XRD. The SEM micrographs of the MAP precipitates showed a typical morphology of elongated tubular and short prismatic crystals. The EDS and XRD results indicated that the chemical composition of the MAP precipitates depended on the chemicals used and experimental conditions. The study confirmed that the recovery of NH4+-N from landfill leachate and seawater bitten wastes could be effectively achieved by MAP precipitation to obtain struvite crystals with a composition of 5.1%N, 10.3%Mg and 16.5%P.

The enhancement of photodegradation efficiency using Pt-TiO2 catalyst

This study investigates the mechanism of photosensitization and the recombination of excited electron-hole pairs affected by depositing platinum (Pt) on the surface of titanium dioxide (TiO2). A new catalyst of Pt-TiO2 was prepared by a photoreduction process. Being model reactions, the photocatalytic oxidation of methylene blue (MB) and methyl orange (MO) in aqueous solutions using the Pt-TiO2 catalyst was carried out under either UV or visible light irradiation. The experimental results indicate that an optimal content of 0.75%Pt-TiO2 achieves the best photocatalytic performance of MB and MO degradation and that the Pt-TiO2 catalyst can be sensitized by visible light. The interaction of Pt and TiO2 was investigated by means of UV-Vis absorption spectra, photoluminescence emission spectra, and X-ray photoelectron emission spectroscopy. The Pt0, Pt2+ and Pt4+ species existing on the surface of Pt-TiO2, and the Ti3+ species existing in its lattice may form a defect energy level. The Pt impurities, including Pt, Pt(OH)2, and PtO2, and the defect energy level absorb visible light more efficiently in comparison with the pure TiO2 and hinder the recombination rate of excited electron-hole pairs.

Enhancement of photocatalytic oxidation of humic acid in TiO2 suspensions by increasing cation strength

This study aimed at improving the photocatalytic (PC) oxidation of humic acids (HA) in TiO2 suspensions by adding cationic ion such as calcium or magnesium. A set of tests was first conducted in the dark to study the adsorption of HA onto TiO2 in suspensions at different pH and calcium concentrations. The experiment demonstrated that the adsorption of HA onto the TiO2 particles was either pH-dependent or calcium strength-dependent due to electrostatic interaction and calcium ion bridging. The photodegradation of HA in the presence of UV irradiation was investigated as a function of pH and the concentration of calcium and magnesium ions. The results showed that the adsorption behavior between HA and TiO2 played a very important role during the PC oxidation process. The PC oxidation could be enhanced at neutral pH by increasing the cation strength. The kinetics of HA PC degradation in TiO2 suspensions with different initial concentrations was also studied using the Langmuir-Hinshelwood model.

Photoelectrocatalytic degradation of humic acid in aqueous solution using a Ti/TiO2 mesh photoelectrode

Humic acid (HA) is one of natural organics existing in water supply as a precursor of trihalomethanes formation in chlorination. The photo-degradation of HA in aqueous solution by photoelectrocatalytic (PEC) oxidation using a Ti/TiO2 mesh electrode was investigated in terms of UV absorbance at 254 nm, colour and TOC concentration. The key factors affecting the PEC oxidation efficiency were studied, including the concentration of electrolyte, electrical bias applied. pH value of HA solution, the intensity of incident light and the area of Ti/TiO2 mesh photoelectrodes. The first-order kinetic model was applied to describe the PEC oxidation, in which the kinetic constant k was verified by the experimental data as a function of the concentration of electrolyte, light intensity, the area of Ti/TiO2 mesh electrode and the voltage of electrical bias applied. It was found that there was an optimal bias voltage of 1.63 V and low pH value was favourable for TOC removal in HA solution. Our investigation showed that PEC oxidation was a convenient way to mineralise the organic matters with high efficiency.

Photoelectrocatalytic oxidation of rhodamine B in aqueous solution using Ti/TiO2 mesh photoelectrodes

To further improve the photooxidation techniques for water and waste-water purification, a Ti/TiO2 mesh electrode, was successfully prepared by anodizing Ti mesh in 0.5M H2SO4 solution. The structural and surface morphology of the Ti/TiO2 electrode was examined by Raman spectroscopy and scanning electronic microscopy (SEM) respectively. The examination results indicated that its structure and properties were affected by its growth rate in the anodization process, and anatase TiO2 was dominant in its composition. The photocatalytic (PC) oxidation and photoelectrocatalytic (PEC) oxidation of rhodamine B in aqueous solution using the Ti/TiO2 electrode were investigated and compared. The experimental results demonstrated that the PEC oxidation by applying an electrical bias between the Ti/TiO2 electrode and Pt electrode could significantly enhance the degradation rate of rhodamine B compared with the PC oxidation. It was found that the best performance of PEC oxidation was achieved by applying the electrical bias of 0.6 V. The mechanism of rhodamine B degradation in the PEC process was discussed by studying the changes of absorbance spectrum and proton nuclear magnetic resonance spectroscopy of rhodamine B during the PEC degradation. The experimental results illustrated that both de-ethylation and chromogen destruction of rhodamine B under UV-light irradiation in the PEC degradation took place simultaneously.

SmeDEF multidrug efflux pump contributes to intrinsic multidrug resistance in Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an emerging nosocomial pathogen that displays high-level intrinsic resistance to a variety of structurally unrelated antimicrobial agents. Efflux mechanisms are known to contribute to acquired multidrug resistance in this organism, and indeed, one such multidrug efflux system, SmeDEF, was recently identified. Still, the importance of SmeDEF to intrinsic antibiotic resistance in S. maltophilia had not yet been determined. Reverse transcription-PCR confirmed expression of the smeDEF genes in wild-type S. maltophilia, and deletion of smeE or smeF in wild-type strains rendered the mutants hypersusceptible to several antimicrobials, suggesting that SmeDEF contributes to intrinsic antimicrobial resistance in this organism. Expression of smeDEF was also enhanced in an in vitro-selected multidrug-resistant mutant, although deletion of smeF but not of smeE in these mutants compromised antimicrobial resistance. Apparently, hyperexpressed SmeF is capable of functioning with additional multidrug efflux components to promote multidrug resistance in S. maltophilia.

Further formation of trihalomethanes in drinking water during heating

This study was aimed at investigating the further formation of trihalomethanes (THM) in drinking water when it is being heated at home. Experimental results confirmed that there could be a further significant formation during heating drinking water. Overall variation of THM concentration in water during the heating depended on its formation rate and volatilisation rate. The rate of THM formation was mainly affected by not only both the concentrations of THM precursors, such as humic substances and residual chlorine, but also temperature and reaction time. The rate of THM volatilisation depended on water temperature and the extent of water agitation in the water heaters. It was concluded that the THM residuals in drinking water could be effectively eliminated to a very low level, if the boiling of water was kept in the open for few minutes after water boiling.

Fluoroquinolone susceptibilities of efflux-mediated multidrug-resistant Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Burkholderia cepacia

The antibacterial activities of seven fluoroquinolones (ciprofloxacin, BAYy3118, clinafloxacin, gemifloxacin, moxifloxacin, sparfloxacin and trovafloxacin) against isogenic efflux-mediated multidrug-resistant strains of Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Burkholderia cepacia, were compared. The results indicate that these fluoroquinolones are all substrates for the multidrug efflux systems of these organisms. Clinafloxacin was found generally to be the most active agent against multidrug-resistant strains.

Some questions about landscape modelling

The paper discusses mainly about the modelling process and related problems with examples from Chinese and French cases. Five practical problems must be solved for modelling the functioning of any landscape: (1) The field data are necessarily taken with a sampling procedure that implies a spatial (and often temporal) scale. (2) Every landscape modelled has to be identified, delimited and characterised before application of the hierarchical theory. (3) The functioning of a landscape involves data of multiple types (climate, soil, vegetation, fauna, buildings, communications, economy, aesthetics, etc.) which must be integrated in a holistic approach. (4) Every landscape is spatially heterogeneous, and the structure of the model must be more or less isomorphic with its heterogeneity. (5) The evolution of the landscape must be modelled on a rather long period of time. For all these reasons, it is necessary to build ad hoc models. Object-oriented computing languages may be useful for this purpose.