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Nanoscale zero-valent iron (nZVI) shows excellent reduction of Cr(Ⅵ), but the passivation on its outer surface can restrict its longevity and performance. To tackle this problem, this work introduced

In a natural environment, Fe(ii) adsorbed onto the surfaces of natural particles to form various surface complex species can influence the transformation of contaminants. The reductive reactivity of the [[triple bond, length as m-dash]Fe(iii)]/[[triple bond, length as m-dash]Fe(ii)] couples are close correlated with the surrounding conditions. In this study, we investigated the effects of Si(iv) on the reductive reactivity of [[triple bond, length as m-dash]Fe(iii)]/[[triple bond, length as m-dash]Fe(ii)] couples adsorbed onto γ-Al

A fermentative facultative anaerobe, strain HS01 isolated from subterranean sediment, was identified as Aeromonas hydrophila by 16S rRNA sequence analysis. The biotransformation of 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT), 1,1-dichloro-2,2-bis(4-chlorophenyl) ethylene (DDD), and 1,1-dichloro-2,2-bis (4-chlorophenyl) ethane (DDE) by HS01 was investigated in the presence of goethite and anthraquinone-2,6-disulphonic disodium salt (AQDS). The results demonstrated that HS01 was capable of reducing DDTs, goethite and AQDS. And goethite can significantly enhance the reduction of DDT, DDD and DDE to some extent, while the addition of AQDS can further accelerate the reduction of Fe(III) and DDTs. The products of DDT transformation were identified as a large amount of dominant DDD, and small amounts of 1-chloro-2,2-bis-(p-chlorophenyl)ethane (DDMU), unsym-bis(p-chlorophenyl)-ethylene (DDNU), and 4,4'-dichlorobenzophenone (DBP). The results of cyclic voltammetry suggested that AQDS could increase the amounts of reactive biogenic Fe(II), resulting in the enhanced transformation of DDTs. This investigation gives some new insight in the fate of DDTs related to iron- and humic-reducing bacteria.

The kinetics of the reduction dissolution of iron oxides was studied by using Klebsiella pneumoniae L17 in a pH 7.0 bicarbonate buffer. The microbial reduction of various iron oxides was measured in the absence and presence of AQDS (9,10-anthraquinone-2,6-disulfonic acid), and the results of their rates vs. the surface areas of iron oxides suggested that the iron oxide reduction rate by L17 was obviously affected by the surface area but did not completely depend on it especially for hydrous ferric oxide. Increasing the crystalline degree of hematite decreased the rate of iron reduction, indicating that a higher crystalline degree inhibited microbial iron reduction. Increasing the AQDS concentration significantly increased the rate of HFO reduction, which suggested that the addition of AQDS significantly accelerated the microbial reduction of crystalline Fe(III) oxides. From the increased production of AH2DS (2,6-anthrahydroquinone disulfonate) and cell numbers, it can be concluded that the enhancement may be because of the growth in cells and abiotic Fe(III) reduction by AH2DS. X-ray diffraction, Fourier transform infrared spectra and scanning electron microscopy all indicated that secondary minerals (e.g., vivianite (Fe3(PO4)2) and siderite (FeCO3)) were the biogenic Fe(II) solids formed upon the bioreduction of iron oxides.

The concentrations, distribution and sources of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in 30 agricultural soil and 16 vegetable samples collected from subtropical Shunde area, an important manufacturing center in China. The total PAHs ranged from 33.7 to 350 microg/kg in soils, and 82 to 1,258 microg/kg in vegetables. The most abundant individual PAHs are phenanthrene, fluoranthene, chrysene, pyrene and benzo(b)fluoranthene for soil samples, and anthracene, naphthalene, phenanthrene, pyrene and chrysene for vegetable samples. Average vegetable-soil ratios of total PAHs were 2.20 for leafy vegetables and 1.27 for fruity vegetables. Total PAHs in vegetable samples are not significantly correlated to those in corresponding soil samples. Principal component analyses were conducted to distinguish samples on basis of their distribution in each town, soil type and vegetable specie. Relatively abundant soil PAHs were found in town Jun'an, Beijiao, Chencun, Lecong and Ronggui, while abundant vegetable PAHs were observed in town Jun'an, Lecong, Xingtan, Daliang and Chenchun. The highest level of total PAHs were found in vegetable soil, followed by pond sediment and "stacked soil" on pond banks. The PAHs contents in leafy vegetables are higher than those in fruity vegetables. Some PAH compound ratios suggest the PAHs derived from incomplete combustion of petroleum, coal and refuse from power generation and ceramic manufacturing, and paint spraying on furniture, as well as sewage irrigation from textile industries. Soil PAHs contents have significant logarithmic correlation with total organic carbon, which demonstrates the importance of soil organic matter as sorbent to prevent losses of PAHs.

Landscape patterns are known to influence many ecological processes, but the relationship between landscape patterns and soil pollution processes is not well understood. Based on 300 top soil samples, land use and cover map for the Pearl River Delta (PRD) of 2005, this study explored the characteristics and spatial pattern of heavy metal contamination of agricultural top soils and examined the impacts of landscape patterns on the heavy metal contamination in the buffers of soil samples. Research methods included geostatistical analysis, landscape pattern analysis, single-factor pollution indices, and Pearson correlation analysis. We found that: 1) out of the 235 agricultural soil samples, 3.8%, 0.4%, 17.0% and 9.4% samples exceeded the Grade II national standard for As, Pb, Cd and Ni concentrations respectively. High pollution levels were found in three cities, Guangzhou, Foshan and Zhongshan; 2) soils in the farmland were more polluted than those in the forest and orchard land, and there were no differences among different agricultural land use types in contamination level of each heavy metal (except Cd); and 3) the proportion, mean patch area as well as the degree of landscape fragmentation, landscape-level structural complexity and aggregation/connectivity of water at the buffer zone were significantly positively correlated with the contamination level of each of the four heavy metals in agricultural top soils. Part of the landscape pattern of urban land in the buffer zone also positively correlated with Pb and Cd levels (P0.05). On the contrary, the proportion, mean patch area and aggregation degree of forest land negatively correlated with soil Pb and Ni levels (P0.05); and 4) the closer to the industry land were the soil samples, the more polluted the soils were for Pb, Cd and Ni. Only landscape diversity was found to be positively correlated with soil Cd contamination. The study results provide new information and scientific basis for heavy metal pollution control and remediation, especially for agricultural soils in the PRD.

To understand the photodegradation of azo dyes in natural aquatic environment, a novel photo-Fenton-like system, the heterogeneous iron oxide-oxalate complex system was set up with the existence of iron oxides and oxalate. Five iron oxides, including gamma-FeOOH, IO-250, IO-320, IO-420 and IO-520, were prepared and their adsorption capacity was investigated in the dark. The results showed that the saturated adsorption amount (gamma(max)) was ranked the order of IO-250 > IO-320 > gamma-FeOOH > IO-420 > IO-520 and the adsorption equilibrium constant (Ka) followed the order of IO-250 > IO-520 > gamma-FeOOH > IO-420 > IO-320. The effect of initial pH value, the initial concentrations of oxalate and orange I on the photodegradation of orange I were also investigated in different iron oxide-oxalate systems. The results showed that the photodegradation of orange I under UVA irradiation could be enhanced greatly in the presence of oxalate. And the optimal oxalate concentrations (C(ox)0) for gamma-FeOOH, IO-250, IO-320, IO-420 and IO-520 were 1.8, 1.6, 3.5, 3.0 and 0.8 mM, respectively. The photodegradation of orange I in the presence of optimal C(ox)0 was ranked as the order of gamma-FeOOH > IO-250 > IO-320 > IO-420 > IO-520. The optimal range of initial pH was at about 3-4. The first-order kinetic constant for the degradation of orange I decreased with the increase in the initial concentration of orange I. Furthermore, the variation of pH, the concentrations of Fe3+ and Fe2+ during the photoreaction were also strongly dependent on the C(ox)0 and iron oxides.

γ-FeOOH was prepared by hydrothermal process and went through the phase transformation from lepidocrocite to maghemite firstly and then to hematite with the increase of sintering temperature. The iron oxides sintered at 250, 320, 420 and 520 °C for 2 h were named as IO-250, IO-320, IO-420 and IO-520, respectively, and characterized by X-ray diffractograms (XRD) and Brunauer–Emmett–Teller (BET) methods. XRD results showed that IO-250 and IO-320 had a mixed crystal structure of maghemite and hematite while IO-420 and IO-520 were pure hematite. BET results showed that the specific surface area decreased significantly with the increase of sintering temperature. The effect of iron oxides and oxalate on the photodegradation of 2-mercaptobenzothiazole (MBT) was investigated. The degradation of MBT depended strongly on the dosage of iron oxides and the initial concentration of oxalic acid ( C ox 0 ). The optimal dosages of iron oxides were 0.40, 0.35, 0.30, 0.25 and 0.25 g/L for γ-FeOOH, IO-250, IO-320, IO-420 and IO-520, respectively, and the optimal C ox 0 was 1.0 mM for all the five iron oxides. The results showed that MBT photodegradation could be enhanced greatly in the presence of oxalic acid. The first-order kinetic constants k for MBT degradation was ranked the order as IO-320 > IO-250 > IO-420 > IO-520 > γ-FeOOH in the presence of oxalate with the optimal C ox 0 of 1.0 mM. The oxalate photodegradation, the pH value in the solution and the concentration of Fe2+ and Fe3+ along with the reaction time were also investigated. The results showed that they also depended on iron oxides and C ox 0 . IO-420 and IO-520 with hematite structure and higher stability had a lower activity for oxalate adsorption and photodegradation, and then less formation of Fe3+ and Fe2+, while γ-FeOOH and IO-250 with a lower stability had much higher activity for oxalate adsorption and photodegradation, and then much more Fe3+ and Fe2+ formed in the solution. The excessive Fe3+ inhibited the formation of H2O2 while the much less Fe2+/3+ led to a much less Fe2+/3+-oxalate complex on the surface of iron oxides or in the solution. Therefore, IO-320 had the most photoactivity among them because of the mixed crystal structure and the suitable concentration of Fe3+ and Fe2+.

A new type of photoelectrode was innovated by anodising titanium mesh in H2SO4 solution and named Ti/TiO2 mesh electrode. The structural and surface morphology of the Ti/TiO2 mesh was examined by X-ray diffraction, Laser Raman spectra and scanning electronic microscopy (SEM). The results indicated that its crystal structure, morphology and the size of pore were affected greatly by the anodisation voltage, current density. The photoelectrocatalytic (PEC) oxidation of methyl orange (MO) solution using the Ti/TiO2 mesh was investigated. The results demonstrated that Ti/TiO2 mesh prepared at 160 V and 110 mA cm(-2) had the best PEC activity. The PEC oxidation efficiency could be significantly enhanced by applying an optimal electrical bias voltage between the working electrode and counter electrode. It was found that the best performance of PEC oxidation was achieved by applying an electrical bias of 0.6 V. It is suggested that the recombination of electrons and holes was hindered owing to applying electrical bias voltage.

With the use of an alkaliphilic bacterium, Corynebacterium humireducens MFC-5, this study investigated the reduction of goethite (α-FeOOH) and degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) mediated by different humic substances (humics) and quinones in alkaline conditions (pH of 9.0). The results indicated that (i) using sucrose as the electron donor, the strain MFC-5 was capable of reducing anthraquinone-2,6-disulfonic acid (AQDS), anthraquinone-2-disulfonic acid (AQS), anthraquinone-2-carboxylic acid (AQC), humic acid (HA) and fulvic acid (FA), and its reducing capability ranked as AQC > AQS > AQDS > FA > HA; (ii) the anaerobic reduction of α-FeOOH and 2,4-D by the strain was insignificant, while the reductions were greatly enhanced by the addition of quinones/humics serving as redox mediators; (iii) the Fe(III) reduction rate was positively related to the content of quinone functional groups and the electron-accepting capacities (EAC) of quinones/humics based on fourier-transform infrared spectroscopy (FT-IR) and electrochemical analyses; however, such a relationship was not found in 2,4-D degradation probably because quinone reduction was not the rate-limiting step of quinone-mediated reduction of 2,4-D. Using the example of α-FeOOH and 2,4-D, this study well demonstrated the important role of humics reduction on the Fe(III)/Fe(II) biogeochemical cycle and chlorinated organic compounds degradation in alkaline reducing environments. Funding Information This study was supported by the National Natural Science Foundation of China (Nos 41101211, 31070460, 41101477), and The Project Sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.

A strain of humic substance- and Fe(III)- reducing bacterium was isolated from the subterranean forest sediment and designated as MFC-3. The strain is facultative anaerobic, Gram-negative, motile and rod (1.0-3.0 microm long, 0.5-1.0 microm wide) and identified as Pantoea agglomerans with the 16S rDNA sequence analyses. Batch experiments were conducted to investigate its humic substance-and Fe(III)-respiring activity. The results showed that MFC-3 was capable of anaerobic respiration on anthraquinone-2,6-disulphonate (AQDS) as the sole terminal electron acceptor with glucose as the electron donor. Within 48 h, MFC-3 could reduce 0.3 mmol x L(-1) AQDS at the expense of 4.5 mmol x L(-1) glucose, and the population of bacteria was increased by 7 times. The strain could use sucrose, glucose, citrate, lactate and formate as electron donors for anaerobic respiration, and the reduction rates of AQDS ranked as sucrose (77%)glucose (66%)citrate (50%)lactate (33%)glycerol (25%)formate (17%). MFC-3 can also effectively reduce four types of Fe(III) oxides. After 25 d, the total Fe(II) concentration in the tests of using ferrihydrite, alpha-FeOOH, gamma-FeOOH or alpha-Fe2 O3 as electron acceptor reached 2.5, 2.1, 2.3 and 0.8 mmol x L(-1), respectively. As a strain of environmental origin, MFC-3 is quite useful for the study of extracellular respiration and bioremediation of chlorinated organic pollutants in Fe(III)/humic substance-rich environments.

This work studied the ability of Comamonas koreensis CY01 to reduce Fe(III) (hydr)oxides by coupling the oxidation of electron donors and the enhanced biodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by the presence of Fe(III) (hydr)oxides. The experimental results suggested that strain CY01 can utilize ferrihydrite, goethite, lepidocrocite or hematite as the terminal electron acceptor and citrate, glycerol, glucose or sucrose as the electron donor. Strain CY01 could transform 2,4-D to 4-chlorophenol through reductive side-chain removal and dechlorination. Under the anaerobic conditions, Fe(III) reduction and 2,4-D biodegradation by strain CY01 occurred simultaneously. The presence of Fe(III) (hydr)oxides would significantly enhance 2,4-D biodegradation, probably due to the fact that the reactive mineral-bound Fe(II) species generated from Fe(III) reduction can abiotically reduce 2,4-D. This is the first report of a strain of C. koreensis capable of reducing Fe(III) (hydr)oxides and 2,4-D, which extends the diversity of iron-reducing bacteria associated with dechlorination.

This study was conducted to investigate the effects of soil properties on the heavy metal accumulation in flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) at the field scale. The concentrations of cadmium (Cd), mercury (Hg), and chromium (Cr) in topsoil and vegetable samples from Nanhai district of Foshan city in the Pearl River Delta (PRD) were analyzed. The results showed that 56.5% of the soil samples exceeded the grade II of the Chinese Soil Environmental Quality Standard (GB 15618-1995) for Hg concentrations, while 8.70% and 17.4% of the vegetable samples exceeded the criteria of the Chinese Safety Qualification of Agricultural Products (GB 18406.1-2001) for Cd and Hg concentrations, respectively. The calculated bio-concentration factor (BCF; i.e., the ratio of the metal concentration in the edible parts of flowering Chinese cabbage to that in soil) values were ranked as: Cd (0.1415) > Cr (0.0061) > Hg (0.0012) (p < 0.01), which demonstrated that Cd was easier to be accumulated in the edible parts of flowering Chinese cabbage than Hg and Cr. Furthermore, the following relationships between (bio-concentration factor) BCF values (BCFs) and soil physicochemical properties were concluded from our results: i) the mean BCFs of coarse-textured soils were higher than those of fine-textured soils; ii) the BCFs decreased with increasing soil pH; iii) the soils with high organic matter(OM) and Cation exchange capacity (CEC) have low BCFs, resulting from their high sorption capacities for Cd, Hg, and Cr. The stepwise linear multiple regression analyses showed that total metal concentrations and available calcium in soils were two main factors controlling the accumulation of Cd, Hg, and Cr in the flowering Chinese cabbage.

To understand the degradation of endocrine disrupting chemicals (EDCs) with existence of iron oxides and polycarboxylic acids in the natural environment, the photodegradation of bisphenol A (BPA) at the interface of iron oxides under UV illumination was conducted. Four iron oxides were prepared by a hydrothermal process and then sintered at different temperatures of 65, 280, 310, and 420 °C named “IO-65,” “IO-280,” “IO-310,” and “IO-420,” respectively. The prepared iron oxides were characterized by X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) methods. The XRD pattern of IO-65 showed a crystal structure of lepidocrocite ( γ -FeOOH) and that of IO-420 demonstrated a crystal structure of hematite ( α -Fe 2 O 3 ), while IO-280 and IO-310 have the mixed crystal structures of maghemite ( γ -Fe 2 O 3 ) and hematite. The BET results revealed that the specific surface areas decreased with the increase of sintering temperature. The results demonstrated that the photodegradation of BPA depends strongly on the properties of iron oxides and oxalate, and pH. The properties of iron oxides influenced strongly the dependence of the BPA degradation on the oxalate concentration. The optimal initial concentrations of oxalate for BPA degradation under UV illumination were determined to be 2.0, 2.0, 2.4, and 2.0 mM for IO-65, IO-280, IO-310, and IO-420, respectively. The first-order kinetic constants k for BPA degradation under UV illumination in the presence of oxalate with the optimal initial concentration are ranked as IO-280 > IO-310 > IO-65 > IO-420. The experiments demonstrated that the optimal pH value should be in the range of 3–4. Furthermore, the dependence of BPA degradation should be also attributable to the formation of the dissolved Fe–oxalate in the solution and the adsorbed Fe–oxalate on the surface of iron oxides, and also the formation of hydrogen peroxide.

Distribution and speciation of heavy metals of agricultural soils(85 surface soil samples and 4 soil profiles) in Dongguan were investigated, while total Cr, Cu, Ni, Pb, Zn(abbreviated as Cr, Cu, Ni, Pb, Zn) and available Cu, Zn(Av-Cu, Av-Zn) were analyzed by a flame absorption spectrophotometer(AAS), and total Cd(Cd) was analyzed using graphite furnace AAS. The content of Cd, Cu and Ni was partially much more than the second grade of GB15618-1995 even though the mean contents of all heavy metal were less than the threshold value of the second grade and only the mean content of Pb was more than the value of national background. Results of descriptive statistic showed that the mean content of heavy metals should depend on land utilization and spatial location at some extent. The heavy metal contents were higher in the Southwest and Northwest than in the Central. In addition, the mean contents of Zn and Pb in Dongguan paddy soils were significantly higher than those of Pearl River Delta(PRD) and Taihu Lake region(TLR). Correlation analyses indicated that there existed significant correlation between Cr and Ni in orchard soils, and among Zn, Cd and Cu, between Av-Cu and Cu, between Av-Zn and Cr, Ni, pH value in vegetable soils, and a weak relationship between Cd, Cu and Pb, between Av-Zn and Zn. Principal component analyses(PCA) showed that the order of importance should be ZnPbCrNiCu.

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.

Environmental Context. Conventional titanium dioxide catalysts can assist oxidation reactions upon ultraviolet light irradiation. Such photocatalysts are used to degrade organic pollutants in water to less harmful inorganic materials. By modifying the catalyst with luminescent lanthanide ions, the pollutant degradation reaction takes place upon visible light illumination. 2-Mercaptobenzothiazole, a poorly biodegradable and malodourous pollutant used both as a corrosion inhibitor and antifungal agent, is shown to be efficiently mineralized to carbon dioxide, water, ammonium, nitrate, and sulfate with this new catalyst. Abstract. A series of neodymium ion-doped titanium dioxide (Nd3+-TiO2) catalysts were prepared by means of a sol–gel method. The physical and chemical properties of the catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) N2 sorbtion method, UV-visible diffusive reflective spectroscopy (DRS), and photoluminescence (PL) analyses. The adsorption behaviour and photocatalytic activity of Nd3+-TiO2 under visible light irradiation were evaluated for aqueous 2-mercaptobenzothiazole (MBT) solution. The analytical results of XRD and BET demonstrate that the neodymium ion doping could reduce the crystallite size and increase the specific surface area of TiO2 catalysts. The analytical results of DRS show that Nd3+ doping did not shift the main absorption band edge significantly, but some new absorption peaks attributable to 4f internal electron transition existed in the visible region. It was further confirmed that significant PL emission occurred in the visible range of 350–700 nm, attributable to the electron transfer between Nd3+ and TiO2 owing to introduction of a Nd 4f level. The experimental results of adsorption isotherm tests demonstrate that both the saturated adsorption amount (Γmax) and adsorption equilibrium constant (Ka) of Nd3+-TiO2 catalysts increased significantly with the increased Nd3+ dosage. Furthermore, the Nd3+-TiO2 catalysts demonstrated significant activity towards photocatalytic degradation of MBT in aqueous solution under visible light irradiation, whereas the TiO2 catalyst did not. An optimal dosage of Nd3+ doping was found to be 0.7%. We propose that the introduction of the Nd 4f level plays a crucial role in visible photosensitization and enhancement of the electron–hole separation.