Foreign Anions Research Articles

Anion Exchange in Semiconductor Magic-Size Clusters.

Ion exchange is an effective postsynthesis strategy for the design of colloidal nanomaterials with unique structures and properties. In contrast to the rapid development of cation exchange (CE), the study of anion exchange is still in its infancy and requires an in-depth understanding. Magic-size clusters (MSCs) are important reaction intermediates in quantum dot (QD) synthesis, and studying the ion exchange processes can provide valuable insights into the transformations of QDs. Here, we achieved anion exchange in Cd-based MSCs and elucidated the reaction pathways. We demonstrated that the anion exchange was a stepwise intermolecular transition mediated by covalent inorganic complexes (CICs). We proposed that this transition involved three essential steps: the disassembly of CdE1-MSCs into CdE1-CICs (step 1), an anion exchange reaction from CdE1-CICs to CdE2-CICs (step 2), and assembly of CdE2-CICs to CdE2-MSCs (step 3). Step 3 was the rate-determining step and followed first-order reaction kinetics (kobs = 0.01 min-1; from CdSe-MSCs to CdS-MSCs). Further studies revealed that the activity of foreign anions only affected the reaction kinetics without altering the reaction pathway. The present study provides a deeper insight into the anion exchange mechanisms of MSCs and will further shed light on the synthesis of QDs.

Ultrafast alternating-current exfoliation toward large-scale synthesis of graphene and its application for flexible supercapacitors

To facilitate the transition of laboratory research to industrial applications, it is critical to establish a reliable protocol for the mass synthesis of high-quality graphene. Here, we present an efficient electrochemical intercalation-based exfoliation approach utilizing alternating current that allows for the production of sub-kilogram quantities of graphene. This strategy involves repeatedly intercalating foreign anions and cations into the interlayer gaps of dual-graphite electrodes, accelerating the graphite expansion process and maximizing the exfoliation efficiency of both electrodes while inhibiting excessive anodic oxidation. The exfoliation process leads to high-yield graphene nanosheets (92 %, primarily 1–3 layers) with minimal structural deterioration (ID/IG ratio of 0.05), high purity (2.1 at% oxygen), and outstanding electrical property (7.28 × 104 S m−1). Notably, our scaled-up manufacturing technique produces a record-breaking throughput of 135 g h−1, improving on the best-reported exfoliation efficiency with direct current by 35%. Furthermore, the as-made graphene demonstrates a large reversible capacity of 102 mF cm−2 for flexible supercapacitors, with robust cyclability with 99.5% after 10,000 cycles, excellent mechanical flexibility, and exceptional serial integration for adjustable voltage output. The efficient and scalable method presents a significant advancement in the large-scale manufacture of graphene, with potential for widespread industrial applications.

Employment of Co(II)–Fe(III) layered double hydroxide as magnetic adsorbent for rapid recovery of molybdenum-99

Co(II)–Fe(III) Layered double hydroxide (LDH) was prepared by co-precipitation methods for recovery of 99Mo(VI) from aqueous solutions. The data showed that 99Mo(VI) anions are efficiently adsorbed (R% ˃ 98), in the pH range 2.5–11. The kinetic data showed that about 82% of 99Mo(VI) are adsorbed onto the synthesized LDH in the first ten minutes, while the equilibrium is attained at 120 min. The thermodynamic parameters (ΔG°, ΔH° and ΔS°) are estimated in the temperature range 20–50 °C. The effect of different foreign anions, (Cl−, SO42−, CO32−and NO−3) at various concentrations is evaluated. The synthesized adsorbent showed maximum adsorption capacity of 255.175 mg g−1 for 99Mo(VI) at pH = 3.5, which is mostly higher than those reported in literature.

Thermally regenerable FeS/N-doped biochar catalyzed peroxydisulfate oxidative destruction of aqueous triclosan

Ferrous sulfide loaded on N-doped biochar (FeS/NBC) was prepared to pyrolyze jute fibers pretreated with (NH4)2Fe(SO4)2. FeS/NBC-catalyzed degradation of triclosan was assessed by peroxydisulfate oxidation. The effects of solution pH, foreign anions and peroxydisulfate concentration were investigated. It is found that neutral pH was conducive to removal of triclosan, achieving about 99% triclosan removal and 65% mineralization level. The presence of HCO3− and HPO42− will inhibit triclosan degradation, but Cl− showed a considerable promotion. Importantly, the spent FeS/NBC catalyst can be regenerated via a reheat treatment to completely recover the catalytic activity. Electron paramagnetic resonance and quenching experiments demonstrated that radicals (OH, SO4−O2−) and non-radical (1O2) were the major reactive species in the reaction. GC–MS analysis identified that the residual intermediates from cycloaddition and ether bond breakage existed in the reaction solution, and recommended radical-dominated and singlet oxygen-assisted degradation pathways. The evaluation of actual samples showed that the presence of Cl− could enhance the removal of triclosan, and the generation of chlorine-based radicals was suggested as the main reason for this result. This study proved FeS/NBC-PDS system could efficiently remove triclosan in water, and the catalyst can be regenerated by a simple reheat treatment.

Self-assembled titanium-deficient undoped anatase TiO2 nanoflowers for ultralong-life and high-rate Li+/Na+ storage

Anatase TiO2 is a promising safe and high-rate anode for Li- and Na-ion batteries owing to its moderate redox potential and multi-dimensional ion diffusion paths. However, the capacity, rate and cycle life of anatase TiO2 are severely hindered by the low Li+/Na+ diffusion coefficients. Ti vacancies have been predicted to significantly improve Li+ diffusion kinetics by previous theoretical calculations. However, experimental evidence is still lacking because the existing methods to create Ti vacancies commonly rely on aliovalent doping, i.e., the co-existence of Ti vacancies and foreign anions precludes revelation of the true role and contribution of Ti vacancies alone. The current work reports the synthesis of mesoporous flower-like titanium-deficient anatase TiO2 (TDAT). The formation mechanisms of the Ti vacancies and the micro-architectures are tentatively discussed. Its undoped nature allows elucidation of the unambiguous roles of Ti vacancies on Li+/Na+ storage. Electrochemical results show high capacity, high rate and ultra-long cycle stability for both Li+/Na+ storage in TDAT. DFT calculations reveal that the presence of Ti vacancies results in reduced energy barrier for Li+/Na+ intercalation, enhanced diffusion kinetics, additional Li+/Na+ storage sites and diffusion pathways. For Na+ storage, it achieves a high capacity of 219.9 mAh g−1 at 50 mA g−1, and superior stability over ultra-long 15,000 cycle test at 2000 mA g−1. This work complements with the prevailing view of anion vacancy for improved Li+/Na+ storage.

Desorption of Coffee Pulp Used as an Adsorbent Material for Cr(III and VI) Ions in Synthetic Wastewater: A Preliminary Study.

Some of the diverse agro-industrial waste generated in primary or secondary stages have proved to be promising biomaterials for treating aqueous effluents contaminated, in this case, with heavy metals. Therefore, it is necessary to know their optimal operating conditions and the regeneration or reusability of the solid by-product, an aspect related to desorption. Considering the above, this article presents the findings of a preliminary study related to the desorption process of coffee pulp without physicochemical modification (Castilla variety), an agricultural waste used as a sorbent of Cr(III and VI) ions in synthetic wastewater. The desorption efficiency of four eluting agents at defined concentrations (0.10M)—HC1, HNO3, H2SO4, and EDTA—was evaluated in a time interval of 1 to 9 days. Likewise, the proposals for the sorption and/or desorption mechanisms proposed and reported in the literature with respect to the use of biosorbents derived from the coffee crop are presented. With respect to the results, the coffee pulp used in previous studies of the adsorption of chromium species mentioned (optimal conditions in synthetic water of particle size 180 μm, dose 20 g·L−1, agitation 100 RPM, room temperature, time of 90 to 105 min) showed efficiencies in the removal of Cr(III) and Cr(VI) of 93.26% and 74.80%, respectively. Regarding the extracting substances used, H2SO4 0.10 M was the one that presented the highest desorption percentage in both chromic species, with a desorption of 45.75% Cr(VI) and 66.84% Cr(III) in periods of 5 and 9 days, respectively, with agitation of 100 RPM and room temperature. Finally, the dissemination of preliminary results on the desorption of coffee pulp contaminated with chromic species without physicochemical modification is novel in this study, as similar work with this specific material has not yet been reported in the literature. On the other hand, the limitations of the study and future research are related to the evaluation at different concentrations and of other extractor solutions that allow improving the efficiency of desorption of these chemical species in a shorter time from the coffee pulp (with and without modification) as well as the reuse cycles. As a result, the desorption of coffee pulp used as an adsorbent material in real water could help researchers identify the possible interfering factors that affect the process (foreign anions and cations, organic matter, environmental conditions, among others).

Stability of hemicarbonate under cement paste-like conditions

Hemicarbonate is observed in hydrated cement paste even after prolonged hydration and in the presence of calcium carbonate, although monocarbonate is expected to be thermodynamically more stable. In this study, we demonstrate that hemicarbonate is significantly stabilized by the incorporation of foreign anions in its structure, resulting in the formation of solid solutions. We analyse the hemicarbonate-Friedel's salt and the hemicarbonate-monosulfate solid solutions under cement-like conditions. A combination of X-Ray diffraction in wet and dry conditions, Raman spectroscopy, energy dispersive spectroscopy and thermodynamic modelling allows us to differentiate between observed structure and composition. We argue that in modern cement paste, hemicarbonate is stabilized by the sulfates and/or chloride in the pore solution. We also demonstrate that the basal spacing of the hemicarbonate-Friedel's salt solid solution can be used to calculate its stoichiometry only when measured in wet conditions.

Single-step removal of arsenite ions from water through oxidation-coupled adsorption using Mn/Mg/Fe layered double hydroxide as catalyst and adsorbent

This study developed a layered double hydroxides (Mn/Mg/Fe-LDH) material through a simple co-precipitation method. The Mn/Mg/Fe-LDH oxidized arsenite [As(III)] ions into arsenate [As(V)] anions. The As(III) and oxidized As(V) were then adsorbed onto Mn/Mg/Fe-LDH. The adsorption process of arseniate [As(V)] oxyanions by Mn/Mg/Fe-LDH was simultaneously conducted for comparison. Characterization results indicated that (i) the best Mg/Mn/Fe molar ratio was 1/1/1, (ii) Mn/Mg/Fe-LDH structure was similar to that of hydrotalcite, (iii) Mn/Mg/Fe-LDH possessed a positively charged surface (pHIEP of 10.15) and low Brunauer–Emmett–Teller surface area (SBET = 75.2 m2/g), and (iv) Fe2+/Fe3+ and Mn2+/Mn3+/Mn4+ coexisted in Mn/Mg/Fe-LDH. The As(III) adsorption process by Mn/Mg/Fe-LDH was similar to that of As(V) under different experimental conditions (initial solutions pH, coexisting foreign anions, contact times, initial As concentrations, temperatures, and desorbing agents). The Langmuir maximum adsorption capacity of Mn/Mg/Fe-LDH to As(III) (56.1 mg/g) was higher than that of As(V) (32.2 mg/g) at pH 7.0 and 25 °C. X-ray photoelectron spectroscopy was applied to identify the oxidation states of As in laden Mn/Mg/Fe-LDH. The key removal mechanism of As(III) by Mn/Mg/Fe-LDH was oxidation-coupled adsorption, and that of As(V) was reduction-coupled adsorption. The As(V) mechanism adsorption mainly involved: (1) the inner-sphere and outer-sphere complexation with OH groups of Mn/Mg/Fe-LDH and (2) anion exchange with host anions (NO3−) in its interlayer. The primary mechanism adsorption of As(III) was the inner-sphere complexation. The redox reactions made Mn/Mg/Fe-LDH lose its original layer structure after adsorbing As(V) or As(III). The adsorption process was highly irreversible. Mn/Mg/Fe-LDH can decontaminate As from real groundwater samples from 45–92 ppb to 0.35–7.9 ppb (using 1.0 g/L). Therefore, Mn/Mg/Fe-LDH has great potential as a material for removing As.

Incorporation of MIL-101 (Fe or Al) into chitosan hydrogel adsorbent for phosphate removal: Performance and mechanism

Metal-organic frameworks (MOFs) have become popular adsorbents for phosphate removal. However, in their special form (powder), the obvious disadvantage is poor recyclability and difficult operation. Therefore, this study incorporate MIL-101 (Al/Fe) into chitosan for phosphate removal. Batch experiments with different adsorption parameters including pH, reaction time, temperature, ionic strength are studied. The kinetics and thermodynamic study prove that the pseudo-second-order model and the Langmuir model could describe the phosphate adsorption on MOFs-chitosan adsorbents accurately, indicating that chemical adsorption and monolayer adsorption in the adsorption process. The maximum adsorption capacities for phosphate reached 49.8 ​mg/g (MIL-101(Al)-CS). A thermodynamics calculation results (△G ​< ​0, △H ​> ​0, and △S ​> ​0), indicating that phosphate adsorption onto MOFs-chitosan adsorbents is endothermic, spontaneous, and disordered. The main mechanisms of phosphate removal consists of electrostatic attraction and ligand exchange. MOFs-chitosan adsorbents has excellent selectivity to phosphate when adsorption process with foreign anion. In addition, adsorption capacity of MOFs-chitosan adsorbents can maintain 92% of the initial adsorption capacity after ten adsorption-desorption cycles. These findings demonstrate that MOFs-chitosan adsorbents is a promising adsorbent for phosphate removal. The current study provided a strategy for the design of adsorbents from the viewpoint of chemical structures.

Synthesis of two cationic Coordination polymers for the exploration of anion exchange properties

Anion exchange materials are important for their application in toxic anion control process. Coordination Polymers (CPs) with weakly coordinated anions and lattice anions may be practically useful in anion exchange process. To explore this anion exchange properties by Coordination Polymers (CPs) we have synthesized two water insoluble cationic CPs {[Mn(bix)3(H2O)2].bix.(NO3)2}n(1), {[Cd(bix)2(NO3)2].(H2O)2}n(2) by using N,N-donors linkers bix {bix = 1,4-bis(imidazol-1-ylmethyl)- benzene}. Structure of complex 1 is 1D and contains lattice NO3– anion and the complex 2 is 2D and contains weakly coordinated NO3–anion. Both these complexes along with another previously published structurally similar CP {[Cd(bix)2(NO3)2]}n (3), response in anion exchange studies with foreign anions. All the anion exchange processes have been monitored by FT-IR spectroscopy and PXRD measurements.

Reduction in Technogenic Burden on the Environment by Flotation Recovery of Rare Earth Elements from Diluted Industrial Solutions

Unconventional raw materials are widely used in construction sectors; for example, phosphate sludge with the addition of rare earth elements (REE) when producing brick. The second example is nanostructured composite systems of REE when forming covers of construction materials. This article studies flotation recovery of REE, the impact of chlorides on distribution coefficient, and pH recovery. The study proves the possibility of effective REE recovery from diluted industrial solutions and, consequently, the significant decrease in their content in wastewaters, which allows the improvement of the ecological situation in the industrial plant areas. In this article, optimum flotation conditions of REE by flotation are given by the example of yttrium (III) and lanthanum (III) salts. The processes of rare earth elements recovery by sodium dodecyl sulphate as salts of various compositions were studied. Distribution coefficients for target components as a function of aqueous phase pH and the presence of foreign anions were determined. The analysis of dependences obtained by the comparison of rare earth elements’ chloro and hydroxo complexes stability constants was made. The products of REE obtained by the authors will be used when manufacturing various kinds of building materials: carbon cement, baked brick, light construction materials, and high-tensile steel.

Kinetics, degradation mechanisms and antibiotic activity reduction of chloramphenicol in aqueous solution by UV/H2O2 process.

In this study, the aim was to explore the effectiveness of the UV/H2O2 photolysis (UVP) process in terms of antimicrobial activity reduction and increasing the mean oxidation number of carbon (MONC) under the degradation of chloramphenicol (CHPL) drug. CHPL degradation kinetics and the effects of foreign anions on CHPL degradation were explored in this study. The order of the inhibition effect was found as Cl- > NO3- > HCO3- due to their different in HO• radical scavenging capacity. A pseudo-first-order model for CHPL degradation was well established, and the rate constant (kobs) was 2.93 × 10-2 min-1 (R2 = 0.98) in UVP. Thirteen intermediate products were detected in MS-chromatogram and were identified through different proposed degradation pathways. The cleavage of the amide side chain in CHPL was more effective in CHPL degradation due to an electrophilic attacks by HO. radicals on it. The inactivation rates of E. coli were decreased due to the reduction of -NO2 group into -NH2 functional group in CHPL that leads to the production of low toxic compounds on CHPL degradation.

Efficient macroporous adsorbent for phosphate removal based on hydrate aluminum-functionalized melamine sponge

Effective removal of phosphate from aqueous solution is of great significance in environmental protection. In this paper, the concept of developing a hierarchical and cost-effective aluminum functionalized melamine foam (MF) as phosphate adsorbent is presented. The material with 3D interconnected network, flexibility and ultralow density was fabricated via a simple adsorbing method based on hydrate aluminum and commercially available MF sponge. For use as an adsorbent, performance of the as-prepared MF-HA sponge was assessed with various pH, temperatures, adsorption time, initial P concentrations, ionic strengths and co-existing ions. The experimental results demonstrated that MF-HA performed well in a wide pH range of 4–10 and in the presence of foreign anions, with high maximum uptake capacity of 36.21 mg P/g. Furthermore, for the as-prepared material, the phosphate removal performance at different temperatures established the endothermic nature of the adsorption process. Moreover, MF-HA sponge could be directly separated from the solution and showed a satisfactory recyclability. The adsorbing strategy to design and fabricate the novel sponge with resultant high adsorption efficiency, cost-effectiveness, preferable selectivity, environmental friendliness, and easy separation from water may promote sponge functionalization for applications in extensive wastewater treatment areas.

S-TiO2/UiO-66-NH2 composite for boosted photocatalytic Cr(VI) reduction and bisphenol A degradation under LED visible light

Series sulfur-doped TiO2/amine-functionalized zirconium metal organic frameworks (S-TiO2/UiO-66-NH2) composites (U1Tx) were facilely fabricated from the as-prepared S-TiO2 and UiO-66-NH2 via ball-milling method. The photocatalytic activities of U1Tx toward Cr(VI) reduction and bisphenol A (BPA) degradation were tested under low-power LED visible light. The results demonstrated that U1T3 exhibited better photocatalytic performances than the pristine S-TiO2 and UiO-66-NH2 due to the improved separation and migration of electrons and holes. Furthermore, the influence factors like pH values and foreign ions on the photocatalytic performances of U1Tx were also investigated. The Box-Behnken design methodology was utilized to further clarify that the inorganic foreign anions and dissolved organic matters could exert significant effects on photocatalytic Cr(VI) reduction performance. As well, the possible pathway of BPA degradation was depicted. After four runs of Cr(VI) removal, it was found that U1T3 exhibited preferable reusability and water stability. The probable reaction mechanism was proposed and verified by active species capture experiments, electron spin resonance determination and electrochemical analyses.

2D → 3D corrugated structure self‐assembled from 4,4′‐methylenebis(N‐(pyridin‐2‐ylmethylene)aniline and terephthalic acid: Crystal structure and selective anion separations via anion exchange

A new flexible cationic Zn(II)metal organic framework, {[Zn2(BDC)1.5(L)(DMF)]NO3·DMF·solvent}n, MOF 1, which is a corrugated two‐dimensional network, was synthesized by self‐assembly of Zn(NO3)2.6H2O with 4,4′‐methylenebis(N‐(pyridin‐2‐ylmethylene)aniline as a neutral ligand and terephthalic acid in dimethyl formamide (DMF) as solvent and characterized by X‐ray diffraction. Because of the presence of uncoordinated nitrate (NO3−) ions in the channels, the compound was employed for ion‐exchange applications. We report a detailed study of the host–guest interaction for a cationic metal–organic framework (MOF) that can reversibly capture nitrate. The recrystallization of the MOF was evaluated by monitoring the anion exchange dynamics using a combination of powder X‐ray diffraction and Fourier transform infrared spectra with various kinds of foreign anions. This MOF showed fast and highly efficient Cr2O72− and CrO42−, N3−, MnO4−, and SCN− exchange. The trapping capacities of Cr2O72−, CrO42−, N3−, MnO4−, and SCN− were 105,138, 44,104, and 25mg/g at 25°C after 3h, respectively, and there was good recyclability for capturing N3− and SCN−. {[Zn2(BDC)1.5(L)(DMF)]NO3}n exhibited anion exchange selectivity of SCN− in a solution containing a mixture of 0.025mmol N3−, SCN−, CrO4−2−, Cr2O72−, and MnO4− for 3h and exhibited anion exchange selectivity for SCN− and Cr2O72− in a solution containing a mixture of 0.001mmol N3−, SCN−, CrO42−, Cr2O72−, and MnO4−.

Pressure-induced isostructural phase transition in α-Ni(OH)2 nanowires**Project supported by the National Key Research and Development Program of China (Grant No. 2018YFA0305900), the National Natural Science Foundation of China (Grant Nos. 11874172, 11374120, 11634004, and 51320105007), and the Fund from Jilin University for Science and Technology Innovative Research Team (Grant No. 2017TD-01).

High pressure structural phase transition of monoclinic paraotwayite type α-Ni(OH)2 nanowires with a diameter of 15 nm–20 nm and a length of several micrometers were studied by synchrotron x-ray diffraction (XRD) and Raman spectra. It is found that the α-Ni(OH)2 nanowires experience an isostructural phase transition associated with the amorphization of the H-sublattice of hydroxide in the interlayer spaces of the two-dimensional crystal structure at 6.3 GPa–9.3 GPa. We suggest that the isostructural phase transition can be attributed to the amorphization of the H-sublattice. The bulk moduli for the low pressure phase and the high pressure phase are 41.2 (4.2) GPa and 94.4 (5.6) GPa, respectively. Both the pressure-induced isostructural phase transition and the amorphization of the H-sublattice in the α-Ni(OH)2 nanowires are reversible upon decompression. Our results show that the foreign anions intercalated between the α-Ni(OH)2 layers play important roles in their structural phase transition.

Postsynthesis Growth of CoOOH Nanostructure on SrCo0.6Ti0.4O3−δ Perovskite Surface for Enhanced Degradation of Aqueous Organic Contaminants

The deployment of an efficient catalyst is critical for successful application of peroxymonosulfate-based advanced oxidation processes to the rapid degradation of retardant organics in wastewater. Considering the rich properties of perovskite oxides and their drawbacks of low specific area and easy cation leaching, we reported a facile postsynthesis hydrothermal treatment method for preparing SrCoTiO@CoOOH (SCT@CoOOH) nanocomposite as an efficient catalyst for PMS activation here. Surprisingly, CoOOH nanosheets were grown in situ over the surface of SCT substrate, resulting in a significantly increased surface area (22.1 m g), enhanced charge transfer capability, more generated surface oxygen defects and a strongly synergistic effect created between the bulk SCT and CoOOH surface layer. Remarkably, SCT@CoOOH exhibited higher (1.7 times) catalytic activity (0.84 mg L min) for phenol degradation than SCT. Additionally, suppressed cobalt leaching was demonstrated in the SCT@CoOOH/PMS system. Notably, singlet oxygen as additional oxidative species were formed to accelerate phenol degradation in the radical-based SCT@CoOOH/PMS system due to the surface oxygen defects. The beneficial effect of higher pH value and different influence of foreign anions on the reation rate were also investigated. As a universal method, it may be also useful for the development of innovative functional materials for other various applications.

Removal of radioselenium oxyanions from aqueous solutions by adsorption onto hydrous zirconium oxide

Adsorption of 75Se(IV) oxyanions onto hydrous zirconium oxide (HZO) is investigated. At pHs 2.2 and 5.3, most of Se(IV) are removed within 5 min and the equilibrium is attained at 40 min. Kinetic and equilibrium data are analyzed by several kinetic and isotherm models, respectively. Adsorption of Se(IV) at different pHs (1.5–12) is dependent on its initial concentration. HZO exhibited a high adsorption capacity for Se(IV), Qmax = 213.19 mg/g, which is higher than those reported for other adsorbents. Thermodynamic studies revealed that the present adsorption process is feasible, spontaneous and endothermic. Adsorption of Se(IV) in presence of foreign anions is also evaluated.

Detoxification of U(VI) by Paecilomyces catenlannulatus investigated by batch, XANES and EXAFS techniques

Paecilomyces catenlannulatus (P. catenlannulatus) as a genus of entomogenous fungus presented a variety of surface reactive groups by batch characterizations. The detoxification of U(VI) by P. catenlannulatus was investigated under different water chemistry (pH, incubation time, foreign anions and U(VI) concentration) by batch techniques. Approximately 75% of U(VI) was reduced to U(IV) (i.e., U(IV)O2(s)) by P. catenlannulatus at pH 5.5 and 7 days under glovebox conditions, therefore the formation of precipitates decreased the toxicity of U(VI) for P. catenlannulatus. In addition, phosphate facilitate the U(VI) reduction, whereas carbonate and sulfate inhibited the U(VI) reduction. The activities of catalase (CAT), superoxide dismutase (SOD) and glutathione (GSH) level were stimulated exposure to 1-30 mg/L U(VI), indicating that CAT, SOD and GSH were antagonized for the oxidant stress derived from U(VI) at low concentrations. According to XPS and XANES analysis, the occurrence of U(IV) revealed the reduction of adsorbed U(VI) to U(IV) by P. catenlannulatus. The results of EXAFS analysis indicated that the fitting of U-O and U-U shell for U-loaded P. catenlannulatus was similar to that of U(IV)O2(s)). The formation of U-bearing precipitates decreased the toxicity of U(VI) for P. catenlannulatus. These findings indicated that P. catenlannulatus is capable to detoxify U(VI) by extracellar/intracellar defense systems. Therefore, P. catenlannulatus can be utilized as a promising bioadsorbents for remediation of uranium-contaminated wastewater in environmental cleanup.

Ethylenediamine grafted to graphene oxide@Fe3O4 for chromium(VI) decontamination: Performance, modelling, and fractional factorial design.

A method for grafting ethylenediamine to a magnetic graphene oxide composite (EDA-GO@Fe3O4) was developed for Cr(VI) decontamination. The physicochemical properties of EDA-GO@Fe3O4 were characterized using HRTEM, EDS, FT-IR, TG-DSC, and XPS. The effects of pH, sorbent dose, foreign anions, time, Cr(VI) concentration, and temperature on decontamination process were studied. The solution pH can largely affect the decontamination process. The pseudo-second-order model is suitable for being applied to fit the adsorption processes of Cr(VI) with GO@Fe3O4 and EDA-GO@Fe3O4. The intra-particle diffusion is not the rate-controlling step. Isotherm experimental data can be described using the Freundlich model. The effects of multiple factors on the Cr(VI) decontamination was investigated by a 25−1 fractional factorial design (FFD). The adsorption process can significantly be affected by the main effects of A (pH), B (Cr(VI) concentration), and E (Adsorbent dose). The combined factors of AB (pH × Cr(VI) concentration), AE (pH × Adsorbent dose), and BC (Cr(VI) concentration × Temperature) had larger effects than other factors on Cr(VI) removal. These results indicated that EDA-GO@Fe3O4 is a potential and suitable candidate for treatment of heavy metal wastewater.