Effects of Fe(II) and humic acid on U(VI) mobilization onto oxidized carbon nanofibers derived from the pyrolysis of bacterial cellulose.

The effects of Fe(II) and humic acid on U(VI) immobilization onto oxidized carbon nanofibers (Ox-CNFs, pyrolysis of bacterial cellulose) were investigated by batch, spectroscopic and modeling techniques, with results suggesting that, Ox-CNFs exhibited fast adsorption rate (adsorption equilibrium within 3 h), high adsorption performance (maximum adsorption capacity of 208.4 mg/g), good recyclability (no notable change after five regenerations) in the presence of Fe(II) towards U(VI) from aqueous solutions (e.g., 40 % reduction and 10 % adsorption at pH 8.0), which was attributed to the various oxygen-containing functional groups, excellent chemical stability, large specific surface area and high redox effect. U(VI) adsorption increased with increasing pH from 2.0 to 5.0, then high-level plateau and remarkable decrease were observed at 5.0-6.0 and at pH > 6.0, respectively. According to FT-IR and XPS analysis, a negative correlation between U(VI) reduction and organic in the presence of Fe(II) implied that U(VI) reduction was driven by Fe(II) while inhibited by humic acid. The interaction mechanism of U(VI) on Ox-CNFs was demonstrated to be adsorption and ion exchange at low pH and reduction at high pH according to XPS and surface complexation modeling. These findings filled the knowledge gaps pertaining to the effect of Fe(II) on the transformation and fate of U(VI) in the actual environment. This carbon material with distinctive performance and unique topology offers a potential platform for actual application in environmental remediation.

The modified biochar from wheat straw by the combined composites of MnFe2O4 nanoparticles and chitosan Schiff base for enhanced removal of U(VI) ions from aqueous solutions.

In the last few decades, U(VI) is a significant environmental threat. The innovative and environmentally friendly adsorbent materials for U(VI) removal were urgent. Preparation of the modified biochar from wheat straw by combined composites of MnFe2O4 nanoparticles and chitosan Schiff base (MnFe2O4@CsSB/BC) was characterized, and adsorption experiments were carried out to investigate the performance and interfacial mechanism of U(VI) removal. The results showed that MnFe2O4@CsSB/BC exhibited high adsorption capacity of U(VI) compared with BC. The adsorption process of U(VI) removal by MnFe2O4@CsSB/BC could be ascribed as pseudo-second-order model and Langmuir model. The maximum adsorption capacity of U(VI) removal by MnFe2O4@CsSB/BC reached 19.57 mg/g at pH4.0, 30 mg/L of U(VI), and 25 °C. The possible mechanism was a chemical adsorption process, and it mainly contained electrostatic attraction and surface complexation. Additionally, it also was an economic and environmental friendly adsorbent.

Effective elimination of hexavalent chromium and lead from solution by the modified biochar with MgMn2O4 nanoparticles: adsorption performance and mechanism.

Heavy metal pollution is one of the environmental problems that need to be solved urgently. The adsorption method is thought as the most effective and economical treatment technology. Nature biochar usually showed unsatisfactory adsorption capacity due to its relatively small adsorption capacity and slow adsorption rate. The metal of Mn has been widely applied in the modification of biochar, which could effectively improve the adsorption capacity of biochar. However, leaching of Mn2+ on the adsorbent materials would appear during the adsorption process. And it would increase the risk of secondary pollution. The multifunctional binary modified biochar could improve the adsorption capacity of environmental pollutant removal. In addition, it could also act as a metal support carrier, reducing the risk of secondary pollution. A novel effective biochar loaded by Mg-Mn binary oxide nanoparticles (MgMn2O4@Biochar) was prepared and applied for the Cr(VI) and Pb(II) removal in aqueous solution. The characteristic of MgMn2O4@Biochar was analyzed by SEM, TEM, FTIR, and XRD. The irregular and somewhat flaky shaped particles of different shape and sizes clustered on the surface of MgMn2O4@Biochar appeared. Abundant functional groups of O-H, -C-OH, C-O, and C-OOH could be observed on the surface of MgMn2O4@Biochar. The elements of Mg and Mn elements besides of C, O, and Si elements were presented on the surface of MgMn2O4@Biochar. The wt% of C, O, Mg, Mn, and Si were 42.82%, 48.99%, 2.83%, 4.44%, and 0.93%, respectively. The operational parameters had an important influence on adsorption capacity of Cr(VI) and Pb(II) removal. The results showed that the adsorption capacity of MgMn2O4@Biochar for Cr(VI) and Pb(II) would reach 33.5 mg/g and 536 mg/g, respectively, within 360 min. Additionally, the adsorption processes of Cr(VI) and Pb(II) in solution could be described with pseudo-second-order. For Cr(VI), the Langmuir model was suitable to the adsorption process. However, the adsorption process of Pb(II) in solution could be described with Freundlich model. Furthermore, it could be concluded that the possible mechanism of Cr(VI) and Pb(II) removal by MgMn2O4@Biochar was physical adsorption, surface complexation reaction, and electrostatic adsorption.

Removal of U(vi) from aqueous solutions by an effective bio-adsorbent from walnut shell and cellulose composite-stabilized iron sulfide nanoparticles.

FeS nanoparticles were easily aggregated and oxidized in the natural environment. It was important to stabilize the iron sulfide nanoparticle composite with a stabilizer. Biochar could be used as an effective carrier to inhibit the agglomeration and oxidization of FeS nanoparticles. An efficient and novel bio-adsorbent (CFeS-WS) from walnut shell (WS) and cellulose composites-stabilized iron sulfide nanoparticle was synthesized by the modified method. The removal of U(vi) ions from an aqueous solution by CFeS-WS was carried out. The experimental results indicated that numerous functional groups were observed on the surface of CFeS-WS. In addition, the biochar was loaded successfully with cellulose and FeS nanoparticle composites. The cellulose and biochar effectively prevented the agglomeration of FeS nanoparticles. The adsorption process of U(vi) ions by CFeS-WS was more consistent with the pseudo second-order kinetic model and Langmuir isotherm model. The adsorption process of U(vi) ions was an endothermic and chemical reaction process. The proposed reaction mechanism of the U(vi) ion removal by CFeS-WS mainly consisted of the ion exchange reaction, reduction reaction, hydrogen bonding and functional group, and pore of the adsorbent filling. According to the results of the recycle experiment, it indicated that the chemical stability of CFeS-WS was good.

Functionalized porous nanoscale Fe3O4 particles supported biochar from peanut shell for Pb(II) ions removal from landscape wastewater.

The large amounts ofheavy metal from landscape wastewater have become serious problems of environmental pollution and risks for human health. The development of efficient novel adsorbent is a very important for treatment of heavy metal. The functionalized porous nanoscale Fe3O4 particles supported biochar from peanut shell (PS-Fe3O4) for removal of Pb(II) ions from aqueous solution was investigated. The characterization of PS-Fe3O4 composites showed that biochar was successfully coated with porous nanoscale Fe3O4 particles. The pseudo second-order kinetic model and Langmuir model were more fitted for describing the adsorption process of Pb(II) ions in solution. The adsorption process of Pb(II) ions removal by PS-Fe3O4 composites was a spontaneous and endothermic process. The adsorption mechanisms of Pb(II) ions by PS-Fe3O4 composites were mainly controlled by the chemical adsorption process. The maximum adsorption capacity of Pb(II) ions removal in solution by PS-Fe3O4 composites reached 188.68 mg/g. The removal mechanism included Fe-O coordination reaction, co-precipitation, complexation reaction, and ion exchange. PS-Fe3O4 composites were thought as a low-cost, good regeneration performance, and high efficiency adsorption material for removal of Pb(II) ions in solution.

MXenes as emerging nanomaterials in water purification and environmental remediation.

Environmental pollution has accelerated and intensified because of the acceleration of industrialization, therefore fabricating excellent materials to remove hazardous pollutants has become inevitable. MXenes as emerging transition metal nitrides, carbides or carbonitrides with high conductivity, hydrophilicity, excellent structural stability, and versatile surface chemistry, become ideal candidates for water purification and environmental remediation. Particularly, MXenes reveal excellent sorption capability and efficient reduction performance for various contaminants of wastewater. In this regard, a comprehensive understanding of the removal behaviors of MXene-based nanomaterials is necessary to explain how they remove various pollutants in water. The eliminate process of MXene-based nanomaterials is collectively influenced by the physicochemical properties of the materials themselves and the chemical properties of different contaminants. Therefore, in this review paper, the synthesis strategies and properties of MXene-based nanomaterials are briefly introduced. Then, the chemical properties, removal behaviors and interaction mechanisms of heavy metal ions, radionuclides, and organic pollutants by MXene-based nanomaterials are highlighted. The overview also emphasizes associated toxicity, secondary contamination, the challenges, and prospects of the MXene-based nanomaterials in the applications of water treatment. This review can supply valuable ideas for fabricating versatile MXene nanomaterials in eliminating water pollution.

Effect of Shewanella oneidensis MR-1 on U(VI) sequestration by montmorillonite.

Bacteria may change the physicochemical properties of montmorillonite and further effect the disposal of high-level radioactive waste. Therefore, we explored the influence of Shewanella oneidensis MR-1 on the elimination of representative radionuclide U(VI) by montmorillonite (MMT). The batch experiments showed that MR-1 significantly enhanced the removal efficiency of U(VI), the adsorption capacity of MMT improved from 8.4 to 16.1 mg/g after addition of MR-1, and the adsorption type changed from Langmuir to Freundlich. FTIR and XPS analysis revealed that hydroxyl, phosphate, carbonyl and amine in MMT + MR-1 were primary actors in the elimination of U(VI). The U 4f high-resolution XPS spectrum of MMT + MR-1 showed U(VI) and U(IV) peaks at the same time, indicating that the adsorption process was accompanied by the reduction reaction, which may be due to the extracellular respiration of MR-1. These investigations are significant to insight the potential significance of microbial processes for the transport and elimination of U(VI) in repositories, which in return will contribute to their safe disposal.

Orderly Porous Covalent Organic Frameworks-based Materials: Superior Adsorbents for Pollutants Removal from Aqueous Solutions.

Covalent organic frameworks (COFs) are a new type of crystalline porous polymers known for chemical stability, excellent structural regularity, robust framework, and inherent porosity, making them promising materials for capturing various types of pollutants from aqueous solutions. This review thoroughly presents the recent progress and advances of COFs and COF-based materials as superior adsorbents for the efficient removal of toxic heavy metal ions, radionuclides, and organic pollutants. Information about the interaction mechanisms between various pollutants and COF-based materials are summarized from the macroscopic and microscopic standpoints, including batch experiments, theoretical calculations, and advanced spectroscopy analysis. The adsorption properties of various COF-based materials are assessed and compared with other widely used adsorbents. Several commonly used strategies to enhance COF-based materials' adsorption performance and the relationship between structural property and sorption ability are also discussed. Finally, a summary and perspective on the opportunities and challenges of COFs and COF-based materials are proposed to provide some inspiring information on designing and fabricating COFs and COF-based materials for environmental pollution management.

Applications of water-stable metal-organic frameworks in the removal of water pollutants: A review.

Because the pollutants produced by human activities have destroyed the ecological balance of natural water environment, and caused severe impact on human life safety and environmental security. Hence the task of water environment restoration is imminent. Metal-organic frameworks (MOFs), structured from organic ligands and inorganic metal ions, are notable for their outstanding crystallinity, diverse structures, large surface areas, adsorption performance, and excellent component tunability. The water stability of MOFs is a key requisite for their possible actual applications in separation, catalysis, adsorption, and other water environment remediation areas because it is necessary to safeguard the integrity of the material structure during utilization. In this article, we comprehensively review state-of-the-art research progress on the promising potential of MOFs as excellent nanomaterials to remove contaminants from the water environment. Firstly, the fundamental characteristics and preparation methods of several typical water-stable MOFs include UiO, MIL, and ZIF are introduced. Then, the removal property and mechanism of heavy metal ions, radionuclide contaminants, drugs, and organic dyes by different MOFs were compared. Finally, the application prospect of MOFs in pollutant remediation prospected. In this review, the synthesis methods and application in water pollutant removal are explored, which provide ways toward the effective use of water-stable MOFs in materials design and environmental remediation.

High effective enrichment of U(VI) from aqueous solutions on versatile crystalline carbohydrate polymer-functionalized graphene oxide.

The removal of uranium on various sorbents has been widely employed in recent times. However, the limited sorption capacities of these sorbents inhibit the actual application of the radionuclide in actual environments. The development of a novel material with high sorption capacity and superior regeneration for the removal of uranium is highly desirable. Therefore, a versatile class of crystalline carbohydrate polymers (COF) was prepared from organic compounds. Moreover, COF-functionalized graphene oxide (COF/GO) was synthesized and tested for the removal of U(VI) from aqueous solutions. The batch characterization showed that COF was vertically oriented on the surface of GO using diboronic acid as nucleation sites. The maximum removal capacity of U(VI) on COF/GO reached 117.67 mg g-1, and was attributed to a huge void ratio and various oxygen-bearing functional groups. In addition, the inner-sphere surface-complexation dominated the U(VI) removal, and the adsorption mechanism of inner-sphere surface-complexation was transferred into surface precipitation with increasing reaction time. COF/GO can be converted into conductive carbon and reduced GO (C/rGO) nanocomposite, which has high specific capacitance. These results suggested that GO-based materials can be considered as promising candidates for the enrichment of U(VI) and energy storage.

Recent advances in metal-organic framework membranes for water treatment: A review.

Among many separation membranes reported to date, the favorable polymer affinity and unique physio-chemical performances of metal-organic frameworks (MOFs) including ultra-high surface area, regular and highly controlled porosity have drawn widespread attention in industrial and academic communities. In this comprehensive review, the developmental timeline of MOF containing membranes for water treatment were clarified. The removal efficiencies, elimination mechanisms, as well as possible influencing factors of various MOF containing membranes that applied to water treatment were systematically summarized. The excellent removal performances of MOF containing membranes for various pollutants were determined by the size-exclusion, π-π stacking interaction, electrostatic interaction, hydrogen bonding and so on. Since the progress of engineered MOF containing membranes for practical wastewater treatment applications lags, we further analyzed the potential environmental application of MOF containing membranes from four aspects (stability of MOFs, antifouling performance of membranes, compatibility between MOF fillers and polymer matrix, dispersity of MOF nanoparticles in matrix), hoping to provide some meaningful insights.

Reductive and adsorptive elimination of U(VI) ions in aqueous solution by SFeS@Biochar composites.

The novel biochar supported by starch and nanoscale iron sulfide (SFeS@Biochar) composites were successfully prepared through coupling of biochar derived from peanut shell with nanoscale ferrous sulfide and starch under nitrogen atmosphere. It had the advantages of biochar, starch, and nanoscale ferrous sulfide. Therefore, it could overcome some shortcomings. The nanoscale ferrous sulfide particles and starch were thought to be loaded successfully on the surface of the biochar by SEM, EDS, BET, XRD, FT-IR, and XPS techniques. High uptake capacity of U(VI) by SFeS@Biochar could be attributed to reactive reaction of FeS nanoparticles and adsorptive of a lot of functional groups. The proposed reaction mechanisms of the U(VI) uptake by SFeS@Biochar were electrostatic attraction, surface complexation, precipitation, and reductive reaction. It also might be an improved environmentally friendly material for U(VI) removal.

Adsorption and reduction of Cr(VI) from aqueous solution using cost-effective caffeic acid functionalized corn starch.

Herein, a potential bio-adsorbent (DACS-CA) was formed via immobilizing caffeic acid (CA) on dialdehyde corn starch (DACS) for Cr(VI) removal. The characterization techniques such as IR, Raman, XPS and 13C NMR were performed to analyze surface elements and functional groups on the as-prepared sorbents. Batch experiments revealed that the maximum Cr(VI) removal amount (96.45 mg/g) took place at a pH value of 3.0, adsorption temperatures of 333 K and solid-liquid ratio of 0.2. The isotherms studies found that the Cr(VI) removal of DACS-CA was monolayer adsorption, while the kinetics analysis revealed that chemisorption was the main power for removal process. Characterization analysis found that about Cr(VI) (53.02%) and Cr(III) (46.98%) species co-existed onto the surface of DACS-CA, which implied that a redox reaction may be occurred between Cr(VI) and the bio-adsorbent. Namely, Cr(VI) was first loaded on DACS-CA via electrostatic interaction, subsequently Cr(VI) was partially transformed into Cr(III) by reductive functional groups, meanwhile the resulting Cr(III) was immobilized by the carboxyl groups of DACS-CA. Thus, this bio-adsorbent could serve as an efficient sorbent for the removal of Cr(VI) from wastewater in environmental pollution cleanup.

Highly efficient U(VI) capture by amidoxime/carbon nitride composites: Evidence of EXAFS and modeling.

The recovery of uranium from wastewater and safe treatment of U(VI)-containing wastewater are of great important to ensure the sustainable development of nuclear-related energy. Although abundant studies of U(VI) sorption on various adsorbents have been widely achieved, U(VI) sorption at extreme pH and trace concentration is challenging issues due to limited sorption activity of natural adsorbents. The development of novel materials with highly efficient and excellent selectivity for capturing U(VI) from nuclear-related wastewater and seawater is highly desirable. In this study, amidoxime/carbon nitride (AO/g-C3N4) was fabricated and captured U(VI) under a variety of water chemistry. We demonstrated that AO/g-C3N4 exhibited the high adsorption capacities (312 mg/g at pH 6.8), fast removal equilibrium (>98% at 10 min) and superior selectivity for U(VI) compared with the other radionuclides (e.g., 19.76 mg/g of Cs(I)). In addition, AO/g-C3N4 exhibited the high uranium extraction capacity from natural seawater (9.55 mg/g at saturation time of 5.5 days) compared to vanadium (1.85 mg/g). U(VI) adsorption behavior at different pH can be excellently fitted by the surface complexation modeling with three inner sphere surface complexes (i.e., SOUO2(CO3)23-, SO(UO2)3(OH)50 and SOUO2+ species). According to XPS (X-ray Photoelectron Spectroscopy) analysis, the strong complexation of U(VI) with AO groups retained in C3N4 nanosheet. The split of U-Oeq2 subshell and the occurrence of U-C shell further demonstrated inner-sphere surface complexation by EXAFS (X-Ray Absorption Fine Structure) spectra analyses. These results revealed that the high potential of AO/g-C3N4 materials for selective U(VI) capture from wastewater and seawater.

Recent advances on preparation and environmental applications of MOF-derived carbons in catalysis.

Carbon materials derived from metal organic frameworks (MOFs) have excellent properties of high surface area, high porosity, adjustable pore size, high conductivity and stability, and their applications in catalysis have become a rapidly expanding research field. In this review, we have summarized the synthesis strategies of MOF-derived carbons with different physical and chemical properties, obtained through direct carbonization, co-pyrolysis and post-treatment. The potential applications of derived carbons, especially monometal-, bimetal-, nonmetal-doped and metal-free carbons in organo-catalysis, photocatalysis and electrocatalysis are analyzed in detail from the environmental perspective. In addition, the improvement of catalytic efficiency is also considered from the aspects of increasing active sites, enhancing the activity of reactants and promoting free electron transfer. The function and synergy of various species of the composites in the catalytic reaction are summarized. The reaction paths and mechanisms are analyzed, and research ideas or trends are proposed for further development.

The photocatalytic reduction of U(VI) into U(IV) by ZIF-8/g-C3N4 composites at visible light.

The development of new photocatalyst towards the highly efficient photo-reduction of U(VI) was highly desirable. In this study, ZIF-8/g-C3N4 photocatalyst was fabricated to photo-reduce U(VI) from aqueous solutions under different water chemistry. It is demonstrated that ZIF-8/g-C3N4 exhibited the fast-photocatalytic rate (completely photoreduction within 30 min), high photocatalytic activity (Kd > 105 mL/g) and superior chemical stability (No significant decrease after fifth cycles). The photoreduction rate of U(VI) significantly decreased with increasing pH, H2O2 radicals and photo-generated electrons play an important role in U(VI) photoreduction by quenching experiments and ESR analysis. According to XPS and XANES analysis, adsorbed U(VI) was partly photo-reduced into U(IV) by ZIF-8/g-C3N4 photocatalyst. The highly efficient removal of U(VI) on ZIF-8/g-C3N4 photocatalyst was attributed to the synergistic effect of ZIF-8 and g-C3N4 photocatalyst. The present study may provide a new strategy to apply new photocatalyst for in-situ photoreduction of U(VI) in actual environmental remediation.

High efficiency removal of Pb(ii) in aqueous solution by a biochar-supported nanoscale ferrous sulfide composite.

A biochar-supported nanoscale ferrous sulfide composite was prepared and applied for the treatment of Pb(ii) ions in aqueous solution. The experimental results of SEM, EDS, XRD, and FT-IR spectroscopy clearly implied that the biochar was successfully modified with nanoscale ferrous sulfide composite. The maximum adsorption capacity of Pb(ii) ions by FeS@biochar reached 88.06 mg g-1. Compared with other reported adsorbents, the removal rate of Pb(ii) ions by FeS@biochar was higher. The pseudo-second-order kinetic model and Langmuir isotherm model could better fit the experimental adsorption results. The removal rate of Pb(ii) ions by FeS@biochar was controlled by the chemical reaction and monolayer adsorption on the surface of FeS@biochar. The mechanisms of Pb(ii) removal from aqueous solutions by biochar involved electrostatic attraction, hydrogen bonding, physical adsorption, ion exchange, and chemical precipitation. Additionally, the chemical stability and reusability of FeS@biochar were good. It is also an environment-friendly material for low-cost wastewater treatment.

Bismuth oxychloride-based materials for the removal of organic pollutants in wastewater.

Various kind of organics are toxic and detrimental, resulting in eutrophication, black, odorous water and so on. Photocatalysis has been deemed to be a promising technology which can decompose different kinds of organic pollutants under visible light irradiation, finally achieving non-poisonous, harmless CO2, water and other inorganic materials. Bismuth oxychloride (BiOCl) is considered as a promising photocatalyst for the efficient degradation of organic pollutants due to its high chemical stability, unique layered structure, resistance to corrosion and favorable photocatalytic property. However, BiOCl can only absorb UV irradiation because of its wide band gap of 3.2 eV-3.5 eV that limits its photocatalytic performance. Herein, a lot of methods have been reviewed to improve its photocatalytic activity. We introduced the unique and special layered structure of BiOCl, the typical and common synthesis methods that can control the morphology, and the most important part is varies of modification routes of BiOCl and the application of BiOCl-based materials for photocatalytic degradation of organic pollutants. Besides, we summarized the crucial issues and perspectives about the application of BiOCl in pollution management.

XANES and EXAFS investigation of uranium incorporation on nZVI in the presence of phosphate.

Effect of phosphate on the reduction of U(VI) on nZVI was determined by batch, XPS, XANES and EXAFS techniques. The batch experiments showed that nZVI was quite effective for the removal of uranium under the anaerobic conditions, whereas the addition of phosphate enhanced uranium removal over wide pH range. At low pH, the reduction of U(VI) to U(IV) significantly decreased with increasing phosphate concentration by XPS and XANES analysis. According to EXAFS analysis, the occurrence of UU shell at 10 mg/L phosphate and pH 4.0 was similar to that of U(IV)O2(s), whereas the UP and UFe shells were observed at 50 mg/L phosphate, revealing that reductive co-precipitate (U(IV)O2(s)) and precipitation of uranyl-phosphate were observed at low and high phosphate, respectively. The findings are crucial for the prediction of the effect of phosphate on the speciation and binding of uranium by nZVI at low pH, which is significant in controlling the mobility of U(VI) in contaminated environments.

Stomata prioritize their responses to multiple biotic and abiotic signal inputs.

Stomata are microscopic pores in leaf epidermis that regulate gas exchange between plants and the environment. Being natural openings on the leaf surface, stomata also serve as ports for the invasion of foliar pathogenic bacteria. Each stomatal pore is enclosed by a pair of guard cells that are able to sense a wide spectrum of biotic and abiotic stresses and respond by precisely adjusting the pore width. However, it is not clear whether stomatal responses to simultaneously imposed biotic and abiotic signals are mutually dependent on each other. Here we show that a genetically engineered Escherichia coli strain DH5α could trigger stomatal closure in Vicia faba, an innate immune response that might depend on NADPH oxidase-mediated ROS burst. DH5α-induced stomatal closure could be abolished or disguised under certain environmental conditions like low [CO2], darkness, and drought, etc. Foliar spraying of high concentrations of ABA could reduce stomatal aperture in high humidity-treated faba bean plants. Consistently, the aggressive multiplication of DH5α bacteria in Vicia faba leaves under high humidity could be alleviated by exogenous application of ABA. Our data suggest that a successful colonization of bacteria on the leaf surface is correlated with stomatal aperture regulation by a specific set of environmental factors.