Macroscopic and spectroscopic studies of the enhanced scavenging of Cr(VI) and Se(VI) from water by titanate nanotube anchored nanoscale zero-valent iron

Molybdenum-Oxysulfide-Functionalized MgAl-Layered Double Hydroxides─A Sorbent for Selenium Oxoanions

Effective removal of chemically toxic selenium oxoanions at high-capacity and trace levels from contaminated water remains a challenge in current scientific pursuits. Here, we report the functionalization of the MgAl layered double hydroxide with molybdenum-oxysulfide (MoO2S2) anion, referred to as LDH-MoO2S2, and its potential to sequester SeVIO42- and SeIVO32- from aqueous solution. LDH-MoO2S2 nanosheets were synthesized by an ion exchange method in solution. Synchrotron X-ray pair distribution function (PDF) and extended X-ray absorption fine structure (EXAFS) revealed an unexpected transformation of the MoO2S22- to Mo2O2S62- like species during the intercalation process. LDH-MoO2S2 is remarkably efficient in removing SeO42- and SeO32- ions from the ppm to trace level (≤10 ppb), with distribution constant (Kd) ranging from 104 to 105 mL/g. This material showed exceptionally high sorption capacities of 237 and 358 mg/g for SeO42- and SeO32-, respectively. Furthermore, LDH-MoO2S2 demonstrates substantial affinity and efficiency to remove SeO32-/SeO42- even in the presence of competitive ions from contaminated water. Hence, the removal of selenium (VI/IV) oxoanions collectively occurs through reductive precipitation and ion exchange mechanisms. This work provides significant insights into the chemical structure of the MoO2S2 anion into LDH and emphasizes its exceptional potential for high-capacity selenium removal and positioning it as a premier sorbent for selenium oxoanions.

Concurrent reductive decontamination of chromium (VI) and uranium (VI) in groundwater by Fe(0)-based autotrophic bioprocess

The co-presence of chromium (VI) [Cr(VI)] and uranium (VI) [U(VI)] is widely found in groundwater, imposing severe risks on human health. Although zerovalent iron [Fe(0)] supports superb performance for bioreduction of Cr(VI) and U(VI) individually, the biogeochemical process involving their concurrent removal with Fe(0) as electron donor remains unexplored. In the 6-d batch study, 86.1% ± 0.7% of Cr(VI) was preferentially eliminated, while 78.4% ± 0.5% of U(VI) removal was achieved simultaneously. Efficient removal of Cr(VI) (100%) and U(VI) (51.2% ∼ 100%) was also obtained in a continuous 160-d column experiment. As a result, Cr(VI) and U(VI) were reduced to less mobile Cr(III) and insoluble U(IV), respectively. 16 S rRNA sequencing was performed to investigate the dynamics of microbial community. Delftia, Acinetobacter, Pseudomonas and Desulfomicrobium were the major contributors mediating the bioreduction process. The initial Cr(VI) and hydraulic retention time (HRT) incurred pronounced effects on community diversity, which in turn altered the reactor's performance. The enrichment of Cr(VI) resistance (chrA), U(VI) reduction (dsrA) and Fe(II) oxidation (mtrA) genes were observed by reverse transcription qPCR. Cytochrome c, glutathione and NADH as well as VFAs and gas metabolites also involved in the bioprocess. This study demonstrated a promising approach for removing the combined contaminants of Cr(VI) and U(VI) in groundwater.

Highly efficient removal of Se(IV) using reduced graphene oxide-supported nanoscale zero-valent iron (nZVI/rGO): selenium removal mechanism

Se(IV) removal using nanoscale zero-valent iron (nZVI) has been extensively studied. Still, the synergistic removal of Se(IV) by reduced graphene oxide-supported nanoscale zero-valent iron (nZVI/rGO) has not been reported. In this study, nZVI/rGO was successfully synthesized for Se(IV) removal from wastewater. The effects of different environmental conditions (load ratio, dosage, initial pH) on Se(IV) removal by nZVI/rGO were investigated. When the load ratio is 10%, the dosage is 0.3 g/L, the initial pH is 3, and the removal rate is 99%. The adsorption isotherm and kinetics accorded with the Langmuir isotherm and first-order kinetics models (R² > 0.99). The fitted maximum adsorption capacity reached up to 173.53 mg/g. NZVI/rGo and Se(IV) is a spontaneous endothermic reaction (△G < 0, △H > 0) and is characterized by EDS, XRD, and XPS before and after the reaction, to further clarify the reaction mechanism. The XPS narrow spectrum analysis suggested that Se(IV) was reduced to elemental selenium (Se(0)), while the intermediate Fe(II) was oxidized to form hydroxide precipitation. Therefore, nZVI/rGO was favored for Se-contaminated wastewater remediation.

Selenium Oxoanions Removal from Wastewater by MoS42− Intercalated FeMgAl LDH: Catalytic Roles of Fe and Mechanism Insights

FeMgAl−MoS4 LDH was successfully synthesized by a one-pot hydrothermal process followed by ion-exchange methods, and this novel adsorbent was first conducted for aqueous selenite and selenate elimination. The Fe as a component for metal cation layers of LDHs could modulate the layer charge density, leading to more functional groups inserted into layers, and more importantly, this heterogeneous Fe can catalyze the surface reactions between Se(IV) or Se(VI) with S(-II) for oxoanions sequestration. The mechanisms are ion exchange between functional groups with HSeO3− and SeO32− for Se(IV) or SeO42− for Se(VI), followed by reduction by S(-II) from MoS42− groups. The existence of Fe in LDH cation layers, obviously enhanced the reactions (almost two times more for Se(IV) and three times more for Se(VI), respectively), resulting in satisfying adsorption capacities of 483.9 mg/g and 167.2 mg/g for Se(IV) and Se(VI), respectively. Mechanisms were further revealed by elementary analysis, XRD, FT−IR, SEM−EDX, and XPS, as well as the quantitative study. For sorption kinetics, the calculated values of capacities from the pseudo-second-order model are much closer to the experimental values. For sorption isotherms, Langmuir is better than the Freundlich isotherms model for closer capacities (505 mg/g for selenite and 172 mg/g for selenate). All these results demonstrated that the presence of heterogeneous Fe could catalyze the reduction of Se (IV/VI) for the aqueous system, and maybe other high oxidative states hazardous ions. So FeMgAl−MoS4 is a kind of novel adsorbent that offers a promising multi-functional and highly efficient solution for water selenium purification.

Highly efficient Cr(VI) removal from industrial electroplating wastewater over Bi2S3 nanostructures prepared by dual sulfur-precursors: Insights on the promotion effect of sulfate ions

In this work, different Bi₂S₃ nanostructures were prepared from various single and dual sulfide precursors via a solvothermal method. It was found that Bi₂S₃ nanostructures prepared from dual sulfur precursors of L-cysteine and ammonium sulfide exhibited highest Cr(VI) removal ability with maximum Cr(VI) removal capacity of 148.95 mg/g in Cr(VI) solution (pH = 2). More importantly, the removal capacity strikingly increased to 223.33 and 240.25 mg/g in two kinds of actual industrial electroplating wastewater. By analyzing the components of actual electroplating wastewater and the results of control experiments in the absence and presence of different ions in Cr(VI) solution, it was found that SO₄^2- played a critical role in the Cr(VI) removal over Bi₂S₃. The addition of SO₄^2- could promote the conversion of Cr(VI) to Cr(III) on the surface of Bi₂S₃, thus leading to the enhanced Cr(VI) removal ability in actual electroplating wastewater. The Bi₂S₃ maintained its original Cr(VI) removal ability after four cycles in the electroplating wastewater, indicating the moderate reuse ability of the sample. This work not only demonstrated an highly efficient nanomaterials for the Cr(VI) removal in industrial electroplating wastewater, but also provided an insight on the influence of the components in wastewater on Cr(VI) removal.

Hydrothermally synthesized titanate nanomaterials for the removal of heavy metals and radionuclides from water: A review

Hazardous heavy metals and radionuclides in water and wastewater are of drastic concern owing to their detrimental impacts on the organisms as well as the circumambient ecosystem. To remove them as much as we can, both technique and materials were studied in the past years. The adsorption technique as superior water remediation method with the simplicity of design, environmental friendliness and high efficiency was well established. Consequently, it is practically important to explore advanced and economically feasible absorbents for removing these poisonous pollutants from aqueous solutions. So far, large numbers of experiments proved hydrothermally synthesized titanate nanomaterials (TNMs) could be a prospectively excellent adsorbent extracting heavy metals and radionuclides from water due to the high specific surface area, tunable pore size, abundant surface active sites, favorable hydrophilic properties. The objective of this work is to give an overview of hydrothermal synthesis, adsorption performance of TNMs for heavy metals and radionuclides, as well as the various influencing factors for water purification. It comprehensively reviews the structural changes and regenerability of TNMs after adsorption, and different modification methods adopted for improving removal capacity. Additionally, it uniquely highlights the efficient decontamination of the pollutants through a synergistic effect of adsorption and photocatalysis by TNMs. This review provides detailed information for the development, application, and research challenges faced by hydrothermally synthesized TNMs for the removal of heavy metals and radionuclides from aqueous solutions, which will serve as a reference guide for scientists in related fields.

Materials interacting with inorganic selenium from the perspective of electrochemical sensing

Inorganic selenium, the most common form of harmful selenium in the environment, can be determined using electrochemical sensors, which are compact, fast, reliable and easy-to-operate devices. Despite progress in this area, there is still significant room for developing high-performance selenium electrochemical sensors. To achieve this, one should take into account (i) the electrochemical process that selenium undergoes on the electrode; (ii) the valence state of selenium species in the sample and (iii) modification of the sensor surface by a material with high affinity to selenium. The goal of this review is to provide a knowledge base for these issues. After the Introduction section, mechanisms and principles of the electrochemical reduction of selenium are introduced, followed by a section introducing the modification of electrodes with materials interacting with selenium and a section dedicated to speciation methods, including the reduction of non-detectable Se(VI) to detectable Se(IV). In the following sections, the main types of materials (metallic, polymers, hybrid (nano)materials…) interacting with inorganic selenium (mostly absorbents) are reviewed to show the diversity of properties that may be endowed to sensors if the materials were to be used for the modification of electrodes. These features for the main material categories are outlined in the conclusion section, where it is stated that the engineered polymers may be the most promising modifiers.

Microwave-enhanced reductive immobilization of high concentrations of chromium in a field soil using iron polysulfide

High concentrations of Cr(VI) are often detected in contaminated soil. Yet, cost-effective remediation technologies have been lacking. In this study, we prepared a type of FeS_x based on commercial FeSO₄.7H₂O and CaS_x and tested a microwave-assisted technology based on FeS_x for reductive immobilization of high concentrations of Cr(VI) in a field contaminated soil. The as-prepared FeS_x particles appeared as a honeycomb-like and highly porous structure. The microwave-assisted FeS_x reduction process was able to rapidly reduce the TCLP-based reachability of Cr(VI) from 391.8 to 2.6 mg·L^-1. The dosage of FeS_x, S/Fe molar ratio, initial moisture content, microwave power, and irradiation time can all affect the treatment effectiveness. After 500 days curing under atmospheric conditions, the TCLP-leached concentration of Cr remained below the regulatory limit of 5 mg·L^-1, while other treatments failed to meet the goal. S_x^2- or S^2- served as the primary electron donors, whereas Fe facilitated the microwave absorption and the formation of the stable final product of FeCr₂O₄. S and Fe are mostly precipitated in soil. The microwave-assisted FeS_x reduction was shown to be an effective approach to rapidly reduce the leachability of Cr(VI) in contaminated soil, especially in heavily contaminated soil.

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.

The potential use of straw-derived biochar as the adsorbent for La(III) and Nd(III) removal in aqueous solutions

Recent attention on the lanthanides (Ln) contaminant such as lanthanum (La) and neodymium (Nd) extensively used in industry has aroused the great desire for the effective adsorbent. Biochar, relying on its high selectivity and optional ease, is regarded as a promising adsorbent for lanthanides removal although the evaluation of the efficiency and mechanism of La(III) and Nd(III) adsorption on biochar still lags. Here, we investigated the aqueous adsorption processes through SEM, TEM, EDS, FTIR and Raman spectra, XPS, and batch experiments. The porous structure of biochar and the complex functional groups on its surface contributed to the La(III) and Nd(III) removal processes. The kinetic of La(III) and Nd(III) adsorption agreed well with the pseudo-second-order kinetic model. The adsorption capacity showed a strong positive correlation with pH value. However, it was only slightly altered and robust in La(III) and Nd(III) adsorption respectively. The isotherm results reflected significant fitting to the Sips model as well as Langmuir and Freundlich model. Thermodynamic demonstrated the spontaneity, endothermic nature, and temperature favor of the adsorptions on biochar surface (La: ΔH⁰=35.39 (kJ/Mol), ΔS⁰=104.71(J*Mol^-1*K^-1) and ΔG⁰<0; Nd: ΔH⁰=16.71(KJ/mol), ΔS⁰=119.41(J*Mol^-1*K^-1) and ΔG⁰<0). Both the La(III) and Nd(III) removal processes combined physical and chemical adsorptions. Therefore, biochar could be a potential green material for the lanthanum and neodymium adsorption with high efficiency.

Fabrication, characterization and U(VI) sorption properties of a novel biochar derived from Tribulus terrestris via two different approaches

Water contamination due to radionuclides is considered a crucial environmental issue. In this study, Tribulus terrestris plant biomass was used as a precursor for obtaining biochar (BC), that was further modified by two different methods using FeCl₃ to obtain two different magnetic biochars. Both (one-step biochar, called 1S-BC, and two-steps biochar, called 2S-BC) were studied to investigate their capability for adsorbing/removing uranium (VI) from aqueous solutions. The U(VI) removal efficacy of both biochars was tested for different values of pH, ionic strength, initial concentration of U(VI) and temperature. Experimental adsorption data fitted well to the Freundlich model (achieving as highest value for adsorption capacity K_F = 49.56 mg g^-1 (mg L^-1)^-1/n, R² = 0.99). Thermodynamic studies revealed that adsorption was endothermic, characterized by inner-sphere complexation, and entropy-driven with a relatively increased randomness in the solid-solution interface. X-ray photoelectron spectroscopy (XPS) revealed that U(VI) sorption took place by surface complexation between U(VI) and oxygen containing functional groups on both biochars. Five consecutive regeneration cycles verified an excellent reusability for 1S-BC. The overall results allow to conclude that the FeCl₃ modification of the biochar obtained from Tribulus terrestris plant biomass could give an efficient alternative adsorbent for U(VI) removal in a variety of environmental conditions, promoting protection of the environment and human health, as well as facilitating resource utilization and sustainable management of the materials studied.

Fabrication of MOF-derived tubular In2O3@SnIn4S8 hybrid: Heterojunction formation and promoted photocatalytic reduction of Cr(VI) under visible light

Tubular In₂O₃@SnIn₄S₈ hierarchical hybrid photocatalyst was firstly fabricated by a two-step method. The morphology and composition were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The XRD results show that the obtained In₂O₃ microtubes were highly crystallized, while the SnIn₄S₈ flakes prepared at low temperature were poorly crystallized. The SEM image of the hybrid shows that numerous SnIn₄S₈ nanoflakes were assembled over the surface of In₂O₃ microtubes. In₂O₃ served as dispersing-templates have reduced the agglomeration of SnIn₄S₈ flakes. Meanwhile, the heterojunctions formed at the interfaces between In₂O₃ and SnIn₄S₈ could facilitate the interfacial charge transfer, as well as promote the photocatalytic activity of the hybrid. In the treatment of Cr(VI)-containing wastewater, the In₂O₃@SnIn₄S₈ hybrid not only exhibited strong adsorption ability, but also showed remarkably enhanced photocatalytic activity compared with pure SnIn₄S₈. The photocatalytic reaction constant k for In₂O₃@SnIn₄S₈ was approximately 2.54 times higher than that of SnIn₄S₈. The efficient activity of this hybrid photocatalyst should be ascribed to the promoted separation efficiency of electron/hole pairs, which was proved by the following three-dimensional excitation-emission matrix fluorescence spectra (3D EEMs), photocurrent responds, and EIS characterizations.

Phosphate adsorption performance and mechanisms by nanoporous biochar-iron oxides from aqueous solutions

To evaluate the adsorption mechanism and performance of phosphate onto the composite of low-cost biochar and iron oxide, four biochar-iron oxides, namely biochar-magnetite (BC-M), biochar-ferrihydrite (BC-F), biochar-goethite (BC-G), and biochar-hematite (BC-H), were prepared by fabricating iron oxide to porous biochar. The biochar-iron oxides had huge surface areas of 691-864 m²/g and average pore diameters of 3.4-4.0 nm. Based on the characterization analysis of FTIR, XRD, XPS, and zeta potential, the interactions of electrostatic attraction, ligand exchange, and deposition dominated the phosphate adsorption onto biochar-iron oxides. The maximum adsorption capacity of phosphate followed the order of BC-G > BC-F > BC-H > BC-M. The isotherm data of BC-M and BC-H were well fitted by the Langmuir and Freundlich models, while those of BC-G and BC-F followed the Langmuir model. In addition, BC-M, BC-F, BC-G, and BC-H owned excellent regeneration ability and adsorption performance in practical (simulated) wastewater environment. Then the biochar-iron oxides exerted extensive and satisfactory prospect in wastewater remediation and recycling application in soil.

Nanoscale zero valent iron supported on MgAl-LDH-decorated reduced graphene oxide: Enhanced performance in Cr(VI) removal, mechanism and regeneration

The scaled application of nanoscale zero-valent iron nanoparticles (nZVI or Fe° NPs) in environmental remediation is challenged by easy surface passivation and particle aggregation. To improve this situation and enhance their performance in Cr(VI) removal from water phase, we present one novel strategy to hybridize nZVI with layered double hydroxide (LDH) decorated reduced graphene oxide (rGO). The as-prepared ternary (Fe@LDH/rGO) composites possess better dispersibility, improved hydrophilicity and more positive surfaces that allows higher removal efficiency and capacity for Cr(VI) oxyanions. Composition proportion are optimized and influences of surroundings (solution pH, Cr(VI) concentration and temperature) are evaluated. Also, we demonstrate that Fe@LDH/rGO can be reused with suitable post-treatments, which combines alkaline solution desorption and NaBH₄ revivification possess. Cr desorption and Fe leaching ratio during regeneration should be critical indicators that determine the recovery efficiency. Synergistic effect within this ternary system not only contributes to its superiorities in stability, but also continuous iron corrosion via the formation of micro Fe-C batteries, where rGO acts as cathode and alternative electron conductor. The present work suggests great potentials of Fe@LDH/rGO composites in groundwater remediation.

Novel synthesis of nanoscale zerovalent iron from coal fly ash and its application in oxidative degradation of methyl orange by Fenton reaction

We firstly developed a novel synthesis method of nanoscale zerovalent iron (NZVI) using Fe sources in coal fly ash (CFA) for the oxidative degradation of methyl orange by Fenton reaction. Hydrochloric acid (HCl) and methyl isobutyl ketone (MIBK) were used for Fe dissolution from CFA and selective Fe(III) chelation, respectively. Among varied HCl concentrations, 7 N HCl showed the best performance for the oxidation of aqueous Fe(II) to Fe(III) and efficient chelation of Fe(III) with MIBK. The NZVI-CFA was synthesized by adding NaBH₄ to a solution of Fe(III)-chelated MIBK, yielding NZVI transformation >95% from Fe(III) in HCl. Various surface analyses were performed to characterize the NZVI-CFA, which was almost identical to typical NZVI-Bare. HCl and MIBK could be reused several times, indicating potential reusability of chemicals used in the synthesis. Remarkable >96% decolorization of methyl orange was obtained by the NZVI-CFA-induced Fenton reaction at pH 3, with a ∼22% decrease in total organic carbon in 7 min. The heterogeneous Fenton reaction initiated by NZVI-CFA with H₂O₂ showed reactivity similar to that of the homogeneous Fenton reaction (i.e., aqueous Fe(II) with H₂O₂), indicating the importance of homogeneous reaction for the oxidative degradation of methyl orange.

Optimizing the removal of nitrate from aqueous solutions via reduced graphite oxide-supported nZVI: synthesis, characterization, kinetics, and reduction mechanism

Graphene has been considered an ideal absorbent and excellent carrier for nanoparticles. Reduced graphite oxide (rGO)-supported nanoscale zero-valent iron (nZVI@rGO) is an effective material for removing nitrate from water. nZVI@rGO nanocomposites were prepared by a liquid-phase reduction method and then applied for nitrate-nitrogen (NO₃^--N) removal in aqueous solution under anaerobic conditions. The experimental results showed that the stability and activity of the nZVI@rGO nanocomposites were enhanced compared with those of nZVI. The influence of the reaction conditions, including the initial concentration of NO₃^--N, coexisting anions, initial pH of the solution, and water temperature, on NO₃^--N removal was also investigated by batch experiments. In a neutral or slightly alkaline environment, 90% of NO₃^--N at a concentration less than 50 mg/L could be removed within 1 h, and nitrogen production was approximately 15%. The process of NO₃^--N removal by nZVI@rGO fits well with different reaction kinetics. In addition, magnetite was the main oxidation product. RGO-supported nZVI might become a promising filler in the permeable reactive barrier process for groundwater remediation.

Stability and stabilizing efficiency of Mg-Fe layered double hydroxides and mixed oxides in aqueous solutions and soils with elevated As(V), Pb(II) and Zn(II) contents

Although the mechanisms of metal(loid) removal from aqueous solutions using LDHs (layered double hydroxides) and mixed oxides (thermally treated LDHs; CLDHs) have been studied, research dealing with their stability, stabilizing efficiency and remediation potential for contaminated soils remains scarce. We present a complex study investigating the stabilizing efficiency of Mg-Fe LDHs and CLDHs at different conditions, including aqueous solutions and real soils with highly elevated As(V), Pb(II) and Zn(II) concentrations. All studied materials showed excellent (ad)sorption efficiency for As(V), Pb(II) and Zn(II) in aqueous solutions. Additionally, the reconstruction ability of CLDHs at different conditions that could improve their adsorption properties was also evaluated, and the dependence on time, pH and the concentrations of metal(loid)s was shown. In general, CLDHs showed higher stability and stabilizing efficiency in aqueous and soil solutions; however, LDHs were more efficient in contaminated soils. Furthermore, solid state analyses coupled with geochemical modeling showed the formation of new phases corresponding to Mg‑carbonates/silicates on the surfaces of LDH/CLDH after their incubation in soils. Both LDHs and CLDHs significantly decreased the bioavailable/labile fraction of As(V) and Zn(II) in the studied soils. In general, our work shows Mg-Fe LDHs and CLDHs as prospective materials for water and soil remediation.

Targeted nanoparticle binding & detection in petroleum hydrocarbon impacted porous media

Targeted nanoparticle binding has become a core feature of experimental pharmaceutical product design which enables more efficient payload delivery and enhances medical imaging by accumulating nanoparticles in specific tissues. Environmental remediation and geophysical monitoring encounter similar challenges which may be addressed in part by the adoption of targeted nanoparticle binding strategies. This study illustrates that engineered nanoparticles can bind to crude oil-impacted silica sand, a selective adsorption driven by active targeting based on an amphiphilic polymer coating. This coating strategy resulted in 2 mg/kg attachment to clean silica sand compared to 8 mg/kg attachment to oil-impacted silica sand. It was also shown that modifying the surface coating influenced the binding behaviour of the engineered nanoparticles - more hydrophobic polymers resulted in increased binding. Successful targeting of Pluronic-coated iron oxide nanoparticles to a crude oil and silica sand mixture was demonstrated through a combined quantitative Orbital Emission Spectroscopy mass analysis supported by Vibrating Scanning Magnetometer magnetometry, and a qualitative X-ray micro-computed tomography (CT) visualization approach. These non-destructive characterization techniques facilitated efficient analysis of nanoparticles in porous medium samples with minimal sample preparation, and in the case of X-Ray CT, illustrated how targeted nanoparticle binding may be used to produce 3-D images of contaminated porous media. This work demonstrated successful implementation of nanoparticle targeted binding toward viscous LNAPL such as crude oil in the presence of a porous medium, a step which opens the door to successful application of targeted delivery technology in environmental remediation and monitoring.

Rational design of carbonaceous nanofiber/Ni-Al layered double hydroxide nanocomposites for high-efficiency removal of heavy metals from aqueous solutions

Heavy metal pollution of water sources has raised global environmental sustainability concerns, calling for the development of high-performance materials for effective pollution treatment. Herein, we report a facile approach to synthesize carbonaceous nanofiber/NiAl layered double hydroxide (CNF/LDH) nanocomposites for high-efficiency elimination of heavy metals from aqueous solutions. The CNF/LDH nanocomposites were characterized by three-dimensional architectures formed by the gradual self-assembly of flower-like LDH on CNF. The nanocomposites exhibited excellent hydrophilicity and high structural stability in aqueous solutions, guaranteeing the high availability of active sites in these environments. High-efficiency elimination of heavy metal ions by the CNF/LDH nanocomposites was demonstrated by the high uptake capacities of Cu(II) (219.6 mg/g) and Cr(VI) (341.2 mg/g). The sorption isotherms coincided with the Freundlich model, most likely because of the presence of heterogeneous binding sites. The dominant interaction mechanisms consisted of surface complexation and electrostatic interaction, as verified by a combination of X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy analyses and density functional theory calculations. The results presented herein confirm the importance of CNF/LDH nanocomposites as emerging and promising materials for the efficient removal of heavy metal ions and other environmental pollutants.

Removal of Cr (VI) from Simulated and Leachate Wastewaters by Bentonite-Supported Zero-Valent Iron Nanoparticles

Zero-valent iron (Fe⁰) nanoparticles (NPs) have shown excellent ability to remove contaminants hexavalent chromium (Cr(VI)) from aquatic systems. Use of support materials can help to prevent oxidation and aggregation of Fe⁰NPs, and thus enhance their remediation efficiency. However, most previous studies were conducted using artificially synthetic wastewater, and little is known on the remediation effects of supported Fe⁰NPs on actual wastewaters containing Cr(VI). Here, bentonite-supported Fe⁰NPs (BFe⁰NPs) with 1–5% of bentonite were prepared and characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Batch experiments were performed to study Cr(VI) removal by the selected BFe⁰NPs from a simulated wastewater and a leachate wastewater originating from a Cr slag heap-polluted soil. The results show that Fe⁰NPs were uniformly dispersed on the bentonite, leading to a decreased aggregation of NPs, and the optimal mass ratio of bentonite was 4%. Batch experiment results show that lower pH values favored Cr(VI) removal by BFe⁰NPs. The removal percentage of Cr(VI) was higher than 90% for both wastewaters when the pH value was 2.0, but decreased significantly as pH value increased. Cr(VI) removal reaction was quite fast within the initial 10 min, and at least 85% of Cr(VI) was removed for both wastewaters. Cr(VI) removal percentage increased with increasing BFe⁰NPs dosages ranging from 30 to 60, but remained almost unchanged when the Fe/Cr mass ratio increased to above 60. The reaction of BFe⁰NPs to remove Cr(VI) followed the pseudo second-order reaction model. In most cases, the removal rates of Cr(VI) were higher in simulated wastewater than in leachate wastewater, but all approached 100% at the optimal conditions. Our present results show that BFe⁰NPs with 4% bentonite are efficient for treatment of Cr(VI)-containing wastewaters.

Mechanistic insights into sequestration of U(VI) toward magnetic biochar: Batch, XPS and EXAFS techniques

The magnetic iron oxide (Fe₃O₄) nanoparticles stabilized on the biochar were synthesized by fast pyrolysis of Fe(II)-loaded hydrophyte biomass under N₂ conditions. The batch experiments showed that magnetic biochar presented a large removal capacity (54.35mg/g) at pH3.0 and 293K. The reductive co-precipitation of U(VI) to U(IV) by magnetic biochar was demonstrated according to X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption near edge structure analysis. According to extended X-ray absorption fine structure analysis, the occurrence of U-Fe and U-U shells indicated that high effective removal of uranium was primarily inner-sphere coordination and then reductive co-precipitation at low pH. These observations provided the further understanding of uranium removal by magnetic materials in environmental remediation.

Impact of water chemistry on surface charge and aggregation of polystyrene microspheres suspensions

The discharge of microplastics into aquatic environment poses the potential threat to the hydrocoles and human health. The fate and transport of microplastics in aqueous solutions are significantly influenced by water chemistry. In this study, the effect of water chemistry (i.e., pH, foreign salts and humic acid) on the surface charge and aggregation of polystyrene microsphere in aqueous solutions was conducted by batch, zeta potentials, hydrodynamic diameters, FT-IR and XPS analysis. Compared to Na⁺ and K⁺, the lower negative zeta potentials and larger hydrodynamic diameters of polystyrene microspheres after introduction of Mg²⁺ were observed within a wide range of pH (2.0-11.0) and ionic strength (IS, 0.01-500mmol/L). No effect of Cl^-, HCO₃^- and SO₄^2- on the zeta potentials and hydrodynamic diameters of polystyrene microspheres was observed at low IS concentrations (<5mmol/L), whereas the zeta potentials and hydrodynamic diameters of polystyrene microspheres after addition of SO₄^2- were higher than that of Cl^- and HCO₃^- at high IS concentrations (>10mmol/L). The zeta potentials of polystyrene microspheres after HA addition were decreased at pH2.0-11.0, whereas the lower hydrodynamic diameters were observed at pH<4.0. According to FT-IR and XPS analysis, the change in surface properties of polystyrene microspheres after addition of hydrated Mg²⁺ and HA was attributed to surface electrostatic and/or steric repulsions. These investigations are crucial for understanding the effect of water chemistry on colloidal stability of microplastics in aquatic environment.

HNO3 modified biochars for uranium (VI) removal from aqueous solution

The HNO₃ treatment was used to chemically modify the biochars produced from wheat straw (WH) and cow manure for U(VI) removal from aqueous solution. Macroscopic experiments proved that the enrichment of U(VI) on the biochars was regulated by surface complexation and electrostatic interactions. FTIR and XPS analyses confirmed that the highly efficient adsorption of U(VI) was due to the carboxyl groups on the biochar surfaces. The reducing agents of the R-CH₂OH groups facilitated U(VI) adsorption on the untreated biochars. Owing to the higher contents of surface COO groups and more negative surface charge, the modified biochars showed enhanced U(VI) adsorption ability than the untreated ones. The maximum adsorption capacity of U(VI) by the oxidized WH was calculated to be 355.6 mg/g at pH 4.5 and 298 K, which was an improvement of 40 times relative to the untreated WH and was higher than that of most carbon-based adsorbents.