Photocatalytic Reduction of Cr^Ⅵ by Natural Sphalerite Suspensions under Visible Light Irradiation

The photocatalytic reductive capability of a natural semiconducting mineral, sphalerite has been studied for the first time. The sphalerite from the Huangshaping deposit of Hunan Province performed great photoreductive capability that 91.95% of the Cr^6＋ was reduced under 9 h visible light irradiation, higher than the 70.58% under 9.5 h UV light irradiation. The highly reductive ability results from its super negative potential of electrons in the conduction band. Furthermore, Fe substitution for Zn introduces donor states, and the oxidation process of Fe^2＋ to Fe^3＋ makes it an effective hole-scavenger. Cd and Cu substitute for Zn also reduce the bandgap and help broaden the absorbing edge towards the visible light. These substituting metal ions in natural sphalerite make it a hyper-active photocatalyst and very attractive for solar energy utilization.

A Comparative Study on Biosorption of Cr (VI) by <i>Fusarium solani</i>under Different Growth Conditions

Biosorption of Cr(VI) from aqueous solution was studied in a batch bioreactor using the resting cells of Fusarium solani isolated from soil. The specific Cr(VI) removal decreased with increase in pH from 2.0 to 6.0 and increased with increase in initial Cr(VI) concentration, upto 500 mg?l–1. By increasing biomass concentration from 2.0 - 5.0 g?l–1, the specific metal removal remained almost constant. The maximum specific Cr(VI) removal was 60 mg?g–1 achieved at 500 mg?l–1 initial Cr(VI) concentration and by using resting cells (36 h old). The Langmuir adsorption isotherm constants, Q0 and b were observed to be 57.1 mg?g–1 and 0.06 l?mg–1 respectively. These results were compared with the Cr(VI) removal obtained in earlier studies conducted by the present authors using non living and growing cells of F. solani.

Adsorption of Cr(VI) by modified chitosan from heavy-metal polluted water of Xiangjiang River, China

Methacrylic acid was used together with a molecular imprinting technique to modify chitosan. In addition, the adsorption kinetics and adsorption isotherms were recorded and the results were analyzed to investigate reparative adsorption for Cr（VI） from the polluted Xiangjiang River water. A comparative X-ray analysis shows that the degree of crystallization in the imprinted polymer was significantly weakened, the area of the non-crystalline region was larger. There were more adsorption sites in the imprinted polymer, and the adsorption capacity towards Cr（VI） was increased. The adsorption capacity of the imprinted polymer towards Cr（VI） increased with time and reaches saturation after 8 h. The optimal adsorption time was 4-8 h after the adsorption starting and the optimal pH value for the solution was in the range of 4.5-7.5. When the chitosan reaches saturation, the adsorption capacity achieves a state of equilibrium, and the maximum Cr（VI） extraction rate reaches 33.7%. Moreover, the adsorption capacity of the imprinted polymer towards Cr（VI） increases with increasing chitosan concentration. In this situation, the Cr（VI） extraction rate shows little variation, and the maximum removal rate can reach 98.3%. Furthermore, the Cr（VI） extraction rate increases with an increase in the degree of deacetylation in the chatoyant and chitosan, with the best adsorption effect corresponding to 90% deacetylation. Fitting the adsorption data to the quasi first- and second-order kinetic models yields correlation coefficients of 0.9013 and 0.9875, respectively. The corresponding rate constants for the two models are 0.0091 min-1 and 7.129 g/（mg.min）, respectively. Hence, the adsorption using Cr（VI）-imprinted chitosan is more consistent with the second-order kinetics. Comparing the data to Freundlich and Langrnuir adsorption isotherms shows that the latter has a better linear fit and a maximum adsorption capacity of 15.784 mg/g.

Solvent impregnated resin prepared using ionic liquid Cyphos IL 104 for Cr(VI) removal

Ionic liquid (IL) trihexyl (tetradecyl) phosphonium bis 2,4,4-trimethylpentylphosphinate (Cyphos IL 104) was impregnated on XAD-7 resin. The solvent impreganated resin (SIR) was prepared and applied in Cr(VI) removal. The morphology and the thermal stability of the resins were explored. The effects of equilibrium time and initial pH value on Cr(VI) adsorption were investigated. Adsorption isotherm, separation and desorption of the SIR, and selectivity of SIR were also explored. The results show that Cyphos IL 104 exists in the inner XAD-7 resin, and the optimum pH value range of the SIR for Cr(VI) extraction is 0 to 2. When NaOH used as desorption solution, the Cr(VI) can be effectively desorbed from the SIR.

海藻酸钠基凝胶吸附材料对Cr(VI)吸附性能研究

海藻酸钠(SA)是一种天然生物质材料,其来源广、价格低,聚乙烯亚胺是一种含有氨基(-NH_(2))的水溶性高分子聚合物,螯合重金属离子能力强,众多研究者将二者结合其制备成吸附剂去除水溶液中的金属离子。本研究以海藻酸钠为基体,加入碳酸钙和聚乙烯亚胺,以戊二醛为交联剂,经冷冻干燥后形成吸附较好的海藻酸钠-聚乙烯亚胺吸附材料。采用吸附实验研究了材料对水中Cr(VI)的吸附性能,并研究初始浓度、溶液pH、吸附时间、吸附剂用量等对吸附效果的影响。实验结果表明:在Cr(VI)溶液初始浓度为15 mg/L、吸附剂用量0.4 g、吸附时间200 min,吸附温度为313 K时,Cr(VI)去除率达90%以上。

电纺丝制备磁性单晶BiFeO_(3)纳米纤维并用于Cr(VI)的可见光催化还原

本工作提出一种将溶胶凝胶与静电纺丝结合的分步快速烧结技术,成功制备了单晶BiFeO_(3)纳米纤维。通过热重差热分析(TG-DTG)、XRD、SEM、TEM、EDS、紫外可见漫反射光谱和氮气吸附脱附曲线等测试对所制备材料的结构和形貌进行表征。同时,考察了BiFeO_(3)纳米纤维在可见光下对水中Cr(VI)的光催化还原性能。结果显示,相比于传统方式制备的纳米颗粒,该材料因更大的比表面积而具有更高的光催化活性。空穴消耗剂酒石酸的加入能够促进该材料对Cr(VI)的光催化还原反应,使还原效率提高87%。总之,本文制备的BiFeO_(3)材料能在可见光下响应,并在常温下具有弱磁性,能通过磁场力回收,在环境净化领域具有广阔的应用前景。

A functionalized activated carbon adsorbent prepared from waste amidoxime resin by modifying with H_(3)PO_(4) and ZnCl_(2) and its excellent Cr(Ⅵ)adsorption

With the application of resins in various fields, numerous waste resins that are difficult to treat have been produced. The industrial wastewater containing Cr(Ⅵ) has severely polluted soil and groundwater environments, thereby endangering human health. Therefore, in this paper, a novel functionalized mesoporous adsorbent PPR-Z was synthesized from waste amidoxime resin for adsorbing Cr(Ⅵ). The waste amidoxime resin was first modified with H3PO4 and ZnCl_(2), and subsequently, it was carbonized through slow thermal decomposition. The static adsorption of PPR-Z conforms to the pseudo-second-order kinetic model and Langmuir isotherm, indicating that the Cr(Ⅵ) adsorption by PPR-Z is mostly chemical adsorption and exhibits single-layer adsorption. The saturated adsorption capacity of the adsorbent for Cr(Ⅵ) could reach 255.86 mg/g. The adsorbent could effectively reduce Cr(Ⅵ) to Cr(Ⅲ) and decrease the toxicity of Cr(Ⅵ) during adsorption. PPR-Z exhibited Cr(Ⅵ) selectivity in electroplating wastewater. The main mechanisms involved in the Cr(Ⅵ) adsorption are the chemical reduction of Cr(Ⅵ) into Cr(Ⅲ) and electrostatic and coordination interactions. Preparation of PPR-Z not only solves the problem of waste resin treatment but also effectively controls Cr(Ⅵ) pollution and realizes the concept of “treating waste with waste”.

Characteristics of Amine Surfactant Modified Peanut Shell and Its Sorption Property for Cr（VI）

Modified peanut shell （MPS） was prepared by amination reaction with peanut shell （PS） as the starting material The sorption of Cr（VI） oxyanions on MPS in static and column tests were investigated. In addition, the sorption isotherm and kinetic models were applied to confirm the sorption capacity and the sorption mechanisms. BET surface area anysis showed the physicochemical characterist!cs of the samples. The results of zeta potential,Fourier transform infrared （FT-IR） and Raman spectra analysis illustrated that chemical adsorption and ion exi change are the potential sorption mechanism. The static sorption test showed that the maximum sorption capacity （qm） of MPS for Cr（VI） increased with temperature, which indicated that the Cr（VI） sorption rocess was endothermic. The saturated sorption capacity of Cr（VI） in the colunm sorption test was 138.34 mg.g-1, which accounted for 93.9% of the qmax at 25 ℃. The regeneration capacity of MPS was evaluated using HC1 solution as an eluent. The high regeneration efficiency （82.6%） validated the dominance of the ion exchange mechanism in the Cr（VI） sorption process with C1ions displacing Cr（VI） oxyanion on MPS. The Langmuir isotherm model showed a higher correlation coefficient than the other adsorption isotherm models. And in the kinetic study, a pseudo-second-order model fit the data best.

MoSe2/ZnO/ZnSe hybrids for efficient Cr（Ⅵ） reduction under visible light irradiation

Photocatalysis activated by visible light remains highly challenging.Here,we report novel MoSe2/ZnO/ZnSe(ZM)hybrids fabricated via a simple hydrothermal method for photocatalytic reduction of Cr(VI)under visible light irradiation.ZM hybrids show improved photocatalytic reduction ability under visible light irradiation compared to pure ZnO owing to good visible light absorption and rapid electron transfer and separation.The ZM hybrid shows the highest Cr(VI)reduction rate of 100%.Moreover,the photocatalytic Cr(VI)reduction process is mainly controlled by photoinduced electrons.

微纳米黄铁矿对水中Cr(VI)的还原固定研究

通过机械活化的方法对天然黄铁矿进行处理,利用X射线衍射仪(XRD)、高分辨率透射电子显微镜(TEM)对其进行表征,采用批实验的方法探究不同投加量、不同温度和不同pH的条件下,黄铁矿微粒对水中Cr(VI)的还原固定效果。结果表明,经过机械活化之后天然黄铁矿粒径在100 nm左右,达到微纳米级别;黄铁矿微粒对水中Cr(VI)的去除率随着投加量的增加不断增大,1.0 g的黄铁矿微粒可以完全去除浓度为10 mg·L^(-1)的Cr(VI)溶液;随着温度的升高,黄铁矿微粒对水中Cr(VI)的去除率升高,温度为45℃、反应时间为2 h,去除率可以达到97.8%;溶液初始pH值在2~7内,黄铁矿微粒对Cr(VI)的去除率随着pH值的升高逐渐降低,pH为2时去除率最高,为95%;通过尝试动力学拟合,黄铁矿微粒去除水中Cr(VI)的过程符合准二级动力学。

Preparation of chitosan modified fly ash under acid condition and its adsorption mechanism for Cr(VI)in water

Chitosan-coated fly ash(CWF)was prepared by the acid leaching-coating method.Chitosan and fly ash were crosslinked in the solution of acetic acid and sulfuric acid.The microstructure of CWF was conducted by scanning electron microscope(SEM)and X-ray diffraction(XRD).The removal of Cr(VI)from water by CWF was studied by adsorption experiments.The composite prepared by the experiment developed a pore structure and a crystal structure similar to SiO_(2) and chitosan chain-like coating was formed on the surface of fly ash.The new modified material has larger surface roughness,specific surface area and more adsorption channels.The Cr(VI)was enriched in modified materials by electrostatic adsorption between CrO_(4)^(2−)、CrO_(7)^(2−)and-NH_(3)^(+) group and surface acid functional groups.The movement of Cr(VI)in solution is a diffusion process from the main body of the liquid phase to the surface of the liquid film.

Evaluation of the Cr(VI) and other toxic element contamination and their potential sources:The case of the Thiva basin(Greece)

An integrated approach was performed on the soil, plant-crops and groundwater system at the Thiva basin, to evaluate the extent and intensity of the heavy metal contamination, the percentage of metals transferred into plants/crops （bio-accumulation） and the potential sources of contamination. Heavy metal contents （230--310 Cr, 1200--2200 Ni, 50--80 Co, 880--1150 Mn and 44,500--66,200 Fe all in ppm ） in the Thiva soils are higher than those in the Assopos basin. An increasing trend in the heavy metal contents, from the Assopos to the Thiva basin （Mouriki）, indicates that the metal source is probably the Ni-laterites and ophiolites, located towards north. On the other hand, groundwater samples from domestic and irrigation wells throughout the Thiva basin exhibit relatively low （8--37 ppb） concentrations in Cr compared to the Assopos （up to 150 ppb）. The plots of Cr versus Mg/Ca, Mg/Na versus Ca/Na, B versus Si/（Si ＋ Na） and Mg/Si versus Ca/Si ratios revealed a low degree of salinization in the Thiva compared to that in the Assopos （Avlida） basin. The low Cr concentration （average 23 ppb, during dry period） in the Thiva wells may be related with their depth （〉120 m）, in contrast to shallow wells in the central Euboea （hundreds ppb Cr） and points to a solution of a crucial environmental problem in Euboea and Assopos basin by using the deep karst-type aquifer instead the shallow-Neogene one. The average Cr contents （dry weight） ranges from 1.7 to 4.6 ppm （average 2.2） in carrots, potatoes and onions. The percentage of soil metals Crto^i, Cr（Vl）, Ni, Mn and Fe ranges between 0.06 and 3.2 （average （/.53 ~ 0.4）, whilst that for Cu and Zn ranges from 16 to 81 （average 36 ~ 24）. The Cr transfer to plants is low, due to the high resistance of chromite （main host of Cr）, but the determined Cr contents in plant- crops in the Thiva basin are higher than normal or sufficient vahles. Although mininml uptake for growth and production for Cr, Ni, Zn and Cn is still lacking, fnrthermorc research is required in order to restrict heavy metal accumulation and enstlre sustainability.

Facile fabrication of ZnIn2S4/SnS2 3D heterostructure for efficient visible-light photocatalytic reduction of Cr（Ⅵ）

Photocatalytic method has been intensively explored for Cr(VI)reduction owing to its efficient and environmentally friendly natures.In order to obtain a high efficiency in practical application,efficient photocatalysts need to be developed.Here,ZnIn2S4/SnS2 with a three-dimensional(3D)heterostructure was prepared by a hydrothermal method and its photocatalytic performance in Cr(VI)reduction was investigated.When the mass ratio of SnS2 to ZnIn2S4 is 1:10,the ZnIn2S4/SnS2 composite exhibits the highest photocatalytic activity with 100%efficiency for Cr(VI)(50 mg/L)reduction within 70 min under visible-light irradiation,which is much higher than those of pure ZnIn2S4 and SnS2.The enhanced charge separation and the light absorption have been confirmed from the photoluminescence and UV-vis absorption spectra to be the two reasons for the increased activity towards photocatalytic Cr(VI)reduction.In addition,after three cycles of testing,no obvious degradation is observed with the 3D heterostructured ZnIn2S4/SnS2,which maintains a good photocatalytic stability.

Enhanced photocatalytic Cr(Ⅵ) reduction and diclofenac sodium degradation under simulated sunlight irradiation over MIL-100(Fe)/g-C_3N_4 heterojunctions

Metal‐organic framework MIL‐100(Fe)and g‐C3N4 heterojunctions(MG‐x,x=5%,10%,20%,and 30%,x is the mass fraction of MIL‐100(Fe)in the hybrids)were facilely fabricated through ball‐milling and annealing,and characterized by powder X‐ray diffraction,Fourier transform infrared spectroscopy,thermogravimetric analysis,transmission electron microscopy,UV‐visible diffuse‐reflectance spectrometry,and photoluminescence emission spectrometry.The photocatalytic activities of the series of MG‐x heterojunctions toward Cr(VI)reduction and diclofenac sodium degradation were tested upon irradiation with simulated sunlight.The influence of different organic compounds(ethanol,citric acid,oxalic acid,and diclofenac sodium)as hole scavengers and the pH values(2,3,4,6,and 8)on the photocatalytic activities of the series of MG‐x heterojunctions was investigated.MG‐20%showed superior photocatalytic Cr(VI)reduction and diclofenac sodium degradation performance than did the individual MIL‐100(Fe)and g‐C3N4 because of the improved separation of photoinduced electron‐hole charges,which was clarified via photoluminescence emission and electrochemical data.Moreover,the MG‐x exhibited good reusability and stability after several runs.

Enhanced adsorptive removal of Cr(VI)in aqueous solution by polyethyleneimine modified palygorskite

Polyethyleneimine(PEI)modified palygorskite(Pal)was used for the adsorption of Cr(VI)in aqueous solution.The absorbent was characterized by Fourier transform infrared spectroscopy(FT-IR)and thermogravimetric analysis(TGA).Characterized results confirmed that the Pal has been successfully modified by PEI.The modification of PEI increased the Cr(VI)adsorption performance of the Pal by the adsorption combined reduction mechanism,and amino groups of the adsorbent play the main role in the enhanced Cr(VI)adsorption.The maximum adsorption capacity was 51.10 mg·g^-1 at pH4.0 and 25°C.The adsorption kinetics of Cr(VI)on the adsorbent conforms to the Langmuir isotherm model.The maximum adsorption occurs at pH3,and then the adsorption capacity of PEI-Pal was decreased with the increase of p H values.The adsorption kinetics of Cr(VI)on PEI-Pal was modeled with pseudo-second-order model.The addition of Cl^-,SO4^2-and PO4^3-reduced the Cr(VI)adsorption by competition with Cr(VI)for the active sites of PEI-Pal.The Cr(VI)saturated PEI-Pal can be regenerated in alkaline solution,and the adsorption capacity can still be maintained at 30.44 mg·g^-1 after 4 cycles.The results demonstrate that PEI-Pal can be used as a potential adsorbent of Cr(VI)in aqueous solutions.

High efficient removal and mineralization of Cr(VI)from water by functionalized magnetic fungus nanocomposites

A hydroxyl-functionalized magnetic fungus nanocomposite(MFH@GO)was prepared by a simple one-pot method for the removal of Cr(VI)from wastewater.The adsorption behavior of MFH@GO to Cr(VI)in wastewater was discussed in detail.At pH of 5.0 and temperature of 323.15 K,MFH@GO had higher adsorption capacity to Cr(VI)(58.4 mg/g)than the unmodified fungus and GO.Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),thermogravimetry and differential thermal analysis(TG-DTA),scanning electron microscopy and energy dispersive X-Ray spectroscopy(SEM-EDX)were employed to determine the characteristics of MFH@GO.Results showed that magnetic graphene oxide nanoparticles significantly enhanced the physiochemical properties of the fungi.In addition,the adsorption mechanisms analyses show that Cr(VI)could be reduced and mineralized into ferric chromate in residues.These results suggested that MFH@GO could be used as an promising and alternative biosorbent for removal of Cr(VI)from industrial wastewater.

Removal of Cr (VI) from Aqueous Solution Using Ultrafine Coal Fly Ash

Coal fly ashes WSRA and BQRA were ball milled for 5 h to produce their ultrafine coal fly ashes WSUA and BQUA, respectively. Batch kinetic, isotherm and pH effect on adsorption were studied to evaluate removal of Cr （VI） from aqueous solutions by ultrafine coal fly ashes comparing with raw coal fly ashes. The kinetics of adsorption indicates the process to be intraparticle diffusion controlled and follows the Lagergren first-order kinetics for all coal fly ashes. The first-order rate constants （k1） of Cr （VI） adsorption onto WSRA, WSUA, BQRA and BQUA are 1.981, 1.497, 2.119 and 1.500 （×10^-2） min^-1, respectively. The adsorption capacities of WSUA and BQUA are much better than those of WSRA and BQRA. Equilibrium adsorption data of all coal fly ashes well satisfy the Langmuir isotherm. The adsorbed amounts of Cr （VI） onto WSUA and BQUA decrease from pH 2 to pH 6 and then increase up to pH 12.

Synergism of solar-driven interfacial evaporation and photo-Fenton Cr(Ⅵ) reduction by sustainable Bi-MOF-based evaporator from waste polyester

The integration of interfacial solar steam generation and photocatalytic degradation technology has pro-vided a promising platform to simultaneously produce freshwater and degrade pollutants.However,con-structing low-cost,multi-functional evaporators for treating Cr(Ⅵ)-polluted water remains challenging,and the synergistic mechanism on Cr(Ⅵ)reduction is fuzzy.Herein,we propose the combined strategy of ball milling and solution mixing for the sustainable production of Bi-MOF microrod from waste poly(ethylene terephthalate),and construct Bi-MOF-based solar evaporators for simultaneous photo-Fenton Cr(Ⅵ)reduction and freshwater production.Firstly,the evaporator comprised of Bi-MOF microrod and graphene nanosheet possesses high light absorption,efficient photothermal conversion,and good hydro-philic property.Attributing to the advantages,the hybrid evaporator exhibits the evaporation rate of 2.16 kg m^(-2) h^(-1) and evaporation efficiency of 87.5%under 1 kW m^(-2) of irradiation.When integrating with photo-Fenton reaction,the Cr(Ⅵ)reduction efficiency is 91.3%,along with the reaction kinetics of 0.0548 min^(-1),surpassing many advanced catalysts.In the outdoor freshwater production and Cr(Ⅵ)reduction,the daily accumulative water yield is 5.17 kg m^(-2) h^(-1),and the Cr(Ⅵ)reduction efficiency is 99.9%.Furthermore,we prove that the localization effect derived from the interfacial solar-driven evap-oration enhances H_(2)O_(2) activation for the photo-Fenton reduction of Cr(Ⅵ).Based on the result of density functional theory,Bi-MOF microrod provides rich active centers for H_(2)O_(2) activation to produce active sites such as e-or-O_(2).This study not only proposes a new strategy to construct multi-functional solar evaporators for freshwater production and catalytic reduction of pollutants,but also advances the chem-ical upcycling of waste polyesters.

Bifunctional TiO2 Catalysts for Efficient Cr（VI） Photoreduction Under Solar Light Irradiation Without Addition of Acids

Bifunctional TiO2 photocatalysts co-doped with nitrogen and sulfur were prepared by the controlled thermal decomposition of ammonium titanyl sulfate precursor. They have both photocatalytic activity and Brφnsted acidity, and thus are active in the photoreduction of Cr（VI） under solar light irradiation without the addition of acids. The activity is superior to that of Degussa P25 in the acidified suspension at the same pH adjusted by H2SO4.

Optimization of Cr(VI) bioremediation in contaminated soil using indigenous bacteria

Bench-scale soil column experiments were carried out to evaluate the effectiveness of Cr（VI） bioremediation process in soils by using indigenous bacteria with the addition of bacteria nutrient media. Effects of particle size, spray intensity, initial Cr（VI） concentration, circulation mode and soil depth on Cr（VI） remediation were studied. Results show that soils after 6 d remediation with spray intensity controlled in the range of 29.6-59.2 mL/min could well fulfill the requirement of concrete aggregate and roadbed material usage, for the leaching toxicity concentration of the Cr（VI） in treated soils under the chosen condition is far less than 5 mg/L The leaching toxicity and fractions of both hexavalent chromium and trivalent chromium from remediated soils were determined and compared with that of untreated soil. The results show that water soluble Cr（VI） declines from 1520.54 mg/kg to 0.68 mg/kg, exchangeable Cr（VI） decreases from 34.83 mg/kg to 0.01 mg/kg and carbonates-bonded Cr（V1） falls from 13.55 mg/kg to 0.68 mg/kg. Meanwhile, a corresponding increase in carbonate-bonded Cr（III）, Fe and Mn oxides-bonded Cr（III） and organic matter-bonded Cr（III） are found. It reveals that indigenous bacteria can leach out water soluble Cr（VI）, exchangeable Cr（VI） and carbonates-bonded Cr（VI） from contaminated soil followed by converting into carbonate-bonded Cr（III）, Fe and Mn oxides-bonded Cr（IlI）, organic matter-bonded Cr（III） and residual Cr（III）.