Enhanced removal of As (V) from aqueous solution using modified hydrous ferric oxide nanoparticles

Modified oyster shell powder with iron (II) sulfate heptahydrate to improve arsenic uptake in solution and in contaminated soils

Arsenic is a metalloid whose presence can be due to natural or anthropological causes. It is considered as a toxic chemical that puts human health at high risk. In this study, we evaluated a novel modified oyster shell (MOS) that was coated with iron (II) sulfate heptahydrate using two different proportions through batch sorption experiments in an arsenic solution and in arsenic-contaminated soils. The arsenic solution was prepared using As(III)-standard solution. The arsenic contaminated soils were extracted from a contaminated site in Cheonan, South Korea, where the average arsenic concentration of the soil was reported as 136.28 mg/kg. Different doses of oyster shell and modified oyster were used to understand the effect of the addition of iron (II) sulfate heptahydrate via sorption batch experiments in solution and sorption tests in soils. The sorption tests were conducted with 50 g of contaminated soil; then, 150 g of soils was used for the pot cultivation tests, and finally, 150 g of contaminated soils was used for column percolation test. Through the experiments, the authors observed a comparable improvement of arsenic stabilization from 10 to 60% with the addition of iron (II) sulfate heptahydrate to oyster shell.

Bioinorganic Nanoparticles for the Remediation of Environmental Pollution: Critical Appraisal and Potential Avenues

Nowadays, environmental pollution has become a critical issue for both developed and developing countries. Because of excessive industrialization, burning of fossil fuels, mining and exploration, extensive agricultural activities, and plastics, the environment is being contaminated rapidly through soil, air, and water. There are a variety of approaches for treating environmental toxins, but each has its own set of restrictions. As a result, various therapies are accessible, and approaches that are effective, long-lasting, less harmful, and have a superior outcome are extensively demanded. Modern research advances focus more on polymer-based nanoparticles, which are frequently used in drug design, drug delivery systems, environmental remediation, power storage, transformations, and other fields. Bioinorganic nanomaterials could be a better candidate to control contaminants in the environment. In this article, we focused on their synthesis, characterization, photocatalytic process, and contributions to environmental remediation against numerous ecological hazards. In this review article, we also tried to explore their recent advancements and futuristic contributions to control and prevent various pollutants in the environment.

Development of Efficient and Recyclable ZnO-CuO/g-C3N4 Nanocomposite for Enhanced Adsorption of Arsenic from Wastewater

Arsenic (III) is a toxic contaminant in water bodies, especially in drinking water reservoirs, and it is a great challenge to remove it from wastewater. For the successful extraction of arsenic (III), a nanocomposite material (ZnO-CuO/g-C₃N₄) has been synthesized by using the solution method. The large surface area and plenty of hydroxyl groups on the nanocomposite surface offer an ideal platform for the adsorption of arsenic (III) from water. Specifically, the reduction process involves a transformation from arsenic (III) to arsenic (V), which is favorable for the attachment to the -OH group. The modified surface and purity of the nanocomposite were characterized by SEM, EDX, XRD, FT-IR, HRTEM, and BET models. Furthermore, the impact of various aspects (temperatures, pH of the medium, the concentration of adsorbing materials) on adsorption capacity has been studied. The prepared sample displays the maximum adsorption capacity of arsenic (III) to be 98% at pH ~ 3 of the medium. Notably, the adsorption mechanism of arsenic species on the surface of ZnO-CuO/g-C₃N₄ nanocomposite at different pH values was explained by surface complexation and structural variations. Moreover, the recycling experiment and reusability of the adsorbent indicate that a synthesized nanocomposite has much better adsorption efficiency than other adsorbents. It is concluded that the ZnO-CuO/g-C₃N₄ nanocomposite can be a potential candidate for the enhanced removal of arsenic from water reservoirs.

UV-induced highly efficient removal of As(III) through synergistic photo-oxidation in the presence of Fe(II)

In polluted waters, arsenic (As) poses substantial risks to the environment and human health. Inorganic As mainly exists as As(V) and As(III), and As(III) usually shows higher mobility and toxicity and is more difficult to be removed by coagulation. The oxidation of coexisting Fe(II) can accelerate As(III) oxidation and removal by promoting the generation of reactive intermediates and Fe(III) coagulant in the presence of dissolved oxygen. However, the removal efficiency of As from acidic wastewaters is far from satisfactory due to the low Fe(II) oxidation rate by dissolved oxygen. Herein, UV irradiation was applied to stimulate the synergistic oxidation of Fe(II)/As(III), and the effects of coexisting Fe(II) concentration and pH were also evaluated. The synergistic oxidation of Fe(II)/As(III) significantly enhanced the removal of As from acidic waters. Under UV irradiation, Fe(II) significantly promoted the generation of reactive oxygen species (ROS), thereby facilitating As(III) oxidation. In addition, the formation of ferric arsenate and amorphous ferric (hydr)oxides contributed much to As removal. In the As(III)-containing solution with 200 μmol L^-1 Fe(II) at initial pH 4.0, the total arsenic (As(T)) concentration decreased from 67.0 to 1.3 and 0.5 μmol L^-1, respectively, at 25 and 120 min under UV irradiation. The As(T) removal rate increased with increasing Fe(II) concentration, and first increased and then decreased with increasing initial pH from 2.0 to 6.0. This study clarifies the mechanism for the synergistic photo-oxidation of Fe(II)/As(III) under UV irradiation, and proposes a new strategy for highly efficient As(III) removal from acidic industrial and mining wastewaters.

Arsenate removal on the iron oxide ion exchanger modified with Neodymium(III) ions

In this study the iron oxide ion exchanger with the quaternary ammonium groups, Ferrix A33E was modified with neodymium (III) ions in order to obtain the new material Ferrix A33E-Nd(III) characterized by greater sorption efficiency of arsenate(V) ions. A33E-Nd(III) was described by various techniques including scanning electron microscopy SEM, nitrogen adsorption/desorption isotherms, Fourier transform infrared spectroscopy FTIR and X-ray photoelectron spectroscopy XPS. The point of zero charge, pH_PZC was also determined. The kinetic and thermodynamic parameters of the arsenate(V) sorption were calculated. The experimental data was fitted to the four isotherm models - Langmuir, Freundlich, Dubinin-Radushkevich and Halsey. Kinetic and equilibrium studies allowed to get to know the behaviour of arsenate(V) ions during the sorption on A33E-Nd(III). The obtained material A33E-Nd(III)- was found to possess a larger maximum sorption capacity than A33E, great stability and the possibility of regeneration at least 3 times without a significant decrease in efficiency. This allows for the complete removal of As(V) ions from a solution with a concentration of 50 mg/dm³ in just 30 min. The Nd(III)-modification improved the sorption properties of the tested ion exchanger.

Recent advances in nanoremediation: Carving sustainable solution to clean-up polluted agriculture soils

Agriculture is one of the foremost significant human activities, which symbolizes the key source for food, fuel and fibers. This activity results in a lot of ecological harms particularly with the excessive usage of chemical fertilizers and pesticides. Different agricultural practices have remained industrialized to advance food production, due to the growth in the world population and to meet the food demand through the routine use of more effective fertilizers and pesticides. Soil is intensely embellished by environmental contamination and it can be stated as "universal incline." Soil pollution usually occurs from sewage wastes, accidental discharges or as byproducts of chemical residues of unrestrained production of numerous materials. Soil pollution with hazardous materials alters the physical, chemical, and biological properties, causing undesirable changes in soil fertility and ecosystem. Engineered nanomaterials offer various solutions for remediation of contaminated soils. Engineered nanomaterial-enable technologies are able to prevent the uncontrolled release of harmful materials into the environment along with capabilities to combat soil and groundwater borne pollutants. Currently, nanobiotechnology signifies a hopeful attitude to advance agronomic production and remediate polluted soils. Studies have outlined the way of nanomaterial applications to restore the eminence of the environment and assist the detection of polluted sites, along with potential remedies. This review focuses on the latest developments in agricultural nanobiotechnology and the tools developed to combat soil or land and or terrestrial pollution, as well as the benefits of using these tools to increase soil fertility and reduce potential toxicity.

Nanomaterials as adsorbents for As(III) and As(V) removal from water: A review

Freshwater demand will rise in the next couple of decades, with an increase in worldwide population growth and industrial development. The development activities, on one side, have increased the freshwater demand. However, the ground water has been degraded. Among the various organic and inorganic contaminants, arsenic is one of the most toxic elements. Arsenic contamination in ground waters is a major issue worldwide, especially in South and Southeast Asia. Various methods have been applied to provide a remedy to arsenic contamination, including adsorption, ion exchange, oxidation, coagulation-precipitation and filtration, and membrane filtration. Out of these methods, adsorption of As(III)/As(V) using nanomaterials and biopolymers has been used on a wide scale. The present review focuses on recently used nanomaterials and biopolymer composites for As(III)/As(V) sorptive removal. As(III)/As(V) adsorption mechanisms have been explored for various sorbents. The impacts of environmental factors such as pH and co-existing ions on As(III)/As(V) removal, have been discussed. Comparison of various nanosorbents and biopolymer composites for As(III)/As(V) adsorption and regeneration of exhausted materials has been included. Overall, this review will be useful to understand the sorption mechanisms involved in As(III)/As(V) removal by nanomaterials and biopolymer composites and their comparative sorption performances.

Synthesis of novel hierarchical micro/nanostructures AlOOH/AlFe and their application for As(V) removal

Hierarchical micro/nanostructured composites, which contain iron and/or its (hydr)oxides, demonstrate high rate and capacity of arsenic adsorption. The main objective of this paper is the use of novel low toxicity AlOOH/AlFe hierarchical micro/nanostructures for arsenic removal. AlOOH/AlFe composite was obtained by simple water oxidation in mild conditions using AlFe bimetallic nanopowder as a precursor. AlFe bimetallic nanopowder was produced by electrical explosive of two twisted wires in argon atmosphere. The productivity of the electrical explosion assembly was 50 g/h, with the consumption of the electrical energy was 75 kW·h/kg. AlFe bimetallic nanoparticles were chemically active and interacted with water at 60 °C. This nanocomposite AlOOH/AlFe is low cost and adsorbs more than 200 mg/g As(V) from its aqueous solution. AlOOH/AlFe composite has flower-like morphology and specific surface area 247.1 m²/g. The phase composition of nanostructures is present AlOOH boehmite and AlFe intermetallic compound. AlOOH/AlFe composite was not previously used for this. The flower-shape AlOOH morphology not only facilitated deliverability, but increased the As(V) sorption capacity by up to 200 mg/g. The adsorption kinetics has been found to be described by a pseudo-second-order equation of Lagergren and Weber-Morris models while the experimental adsorption isotherm is closest to the Freundlich model. This indicates the energy heterogeneity of the adsorbent surface and multilayer adsorption. The use of non-toxic nanostructures opens up new options to treat water affected by arsenic pollution.

Advancements in heavy metals removal from effluents employing nano-adsorbents: Way towards cleaner production

Due to the development in science field which gives not only benefit but also introducesundesirable pollution to the environment. This pollution is due to poor discharge activities of industrial effluents into the soil and water bodies, surface run off from fields of agricultural lands, dumping of untreated wastes by municipalities, and mining activites, which deteriorates the cardinal virtue of our environment and causes menace to human health and life. Heavy metal(s), a natural constituent on earth's crust and economic important mineral, due to its recalcitrant effects creates heavy metal pollution which affects food chain and also reduces the quality of water. For this, many researchers have performed studies to find efficient methods for wastewater remediation. One of the most promising methods from economic point of view is adsorption, which is simple in design, but leads to use of a wide range of adsorbents and ease of operations. Due to advances in nanotechnology, many nanomaterials were used as adsorbents for wastewater remediation, because of their efficiency. Many researchers have reported that nanoadsorbents are unmitigatedly a fruitful solution to address this world's problem. This review presents a potent view on various classes of nanoadsorbents and their application to wastewater treatment. It provides a bird's eye view of the suitability of different types of nanomaterials for remediation of wastewater and Backspace gives up-to-date information about polymer based and silica-based nanoadsorbents.

Arsenic: A Global Environmental Challenge

Arsenic is a naturally occurring metalloid and one of the few metals that can be metabolized inside the human body. The pervasive presence of arsenic in nature and anthropogenic sources from agricultural and medical use have perpetuated human exposure to this toxic and carcinogenic element. Highly exposed individuals are susceptible to various illnesses, including skin disorders; cognitive impairment; and cancers of the lung, liver, and kidneys. In fact, across the globe, approximately 200 million people are exposed to potentially toxic levels of arsenic, which has prompted substantial research and mitigation efforts to combat this extensive public health issue. This review provides an up-to-date look at arsenic-related challenges facing the global community, including current sources of arsenic, global disease burden, arsenic resistance, and shortcomings of ongoing mitigation measures, and discusses potential next steps.

ZVI impregnation altered arsenic sorption by ordered mesoporous carbon in presence of Cr(Ⅵ): A mechanistic investigation

It is challenging to efficiently remove arsenate (As(Ⅴ)) and chromate (Cr(Ⅵ)) simultaneously. Herein, ordered mesoporous carbon (OMC) was fabricated with averaged pore diameter of 6.5 nm and surface area of 997 m² g^-1. Zerovalent iron (ZVI) impregnation reduced surface area of ZVI/OMC (432 m² g^-1) and increased I_D/I_G ratio by 13%. Maximal Cr(Ⅵ) and As(Ⅴ) sorption capacities at pH 3 were 0.66 and 0.019 mmol g^-1 by OMC, and 0.71 and 0.39 mmol g^-1 by ZVI/OMC, respectively. Reduction accounted for over 55% for Cr(Ⅵ) and As(Ⅴ) removal followed by complexation and precipitation. Better ZVI/OMC performance was ascribed to higher electron transfer rate and lower electrical resistance than OMC as per electrochemical analysis. Upon Cr(Ⅵ) introduction, As(Ⅴ) removal increased to 0.28 mmol g^-1 by OMC, but decreased to 0.16 mmol g^-1 by ZVI/OMC. OMC could preferably reduce CrO₄^2- to Cr³⁺ by hydroxyl group, which enhanced its zeta potential facilitating As(Ⅴ) sorption. Regarding ZVI/OMC, Fe⁰ and Fe oxide in ZVI/OMC exhibited better affinity to As(Ⅴ), but the competition for the similar active sites resulted in compromised As(Ⅴ) and Cr(Ⅵ) removal. Thus, the novel OMC is advantageous for removal of binary As(Ⅴ) and Cr(Ⅵ), but ZVI/OMC is robust to detoxify single heavy metal.

Smectite-supported chain of iron nanoparticle beads for efficient clean-up of arsenate contaminated water

Prolonged exposure to inorganic arsenic (As) via drinking water is a major concern as it poses significant human health risks. Removal of As is crucial but requires effective and environment-friendly clean-up technology to avoid any additional risk to the environment. In this study, we developed Australian smectite (smec)-supported nano zero-valent iron (nZVI) composite for arsenate i.e., As(V) sorption. We used a range of tools, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and energy dispersion X-ray (EDS) spectroscopy to characterise the material. SEM and TEM images and elemental mapping of the composite reflect that the smectite layer was surrounded by a chain of iron nanobeads evenly distributed on clay particles, which is quite exceptional among currently available nZVIs. The maximum As(V) sorption capacity of this composite was 23.12 mg/g in the ambient conditions. Using X-ray photoelectron spectroscopy we unveiled chemical states of As and Fe before and after the sorption process. Additionally, the release of iron nanoparticles from the composite at various pHs (3-10) were found negligible, which demonstrates the effectiveness of smec-nZVI to remove As(V) from contaminated water without posing any secondary pollutant.

Enhancing arsenic sequestration on ameliorated waste molasses nanoadsorbents using response surface methodology and machine-learning frameworks

The development of a novel nanobiosorbent derived from waste molasses for the adsorptive removal of arsenic (As) has been attempted in this study. Waste molasses were chemically ameliorated through a solvothermal route for the incorporation of iron oxide, thereby producing iron oxide incorporated carbonaceous nanomaterial (IOCN). Synthesis of IOCN was confirmed through transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and atomic emission spectroscopy (AES) analysis. The surface area and porous behavior of IOCN were elucidated by Brunauer-Emmett-Teller (BET) assessments. The experimental conditions for adsorption were first modeled using response surface methodology (RSM) based on the central composite design (CCD), considering the parameters: adsorbate dosage, adsorbent dosage, pH, and contact time. RSM optimizations were improved upon using a three-layer feed-forward multilayer perceptron (MLP) based Artificial Neural Network (ANN) model. Optimization through ANN model resulted in the increase of the maximal As adsorption efficiency to ~ 96% for IOCN. The IOCN isotherm plots show the best fit for the Sips isotherm, and the reaction kinetics follows the pseudo-second-order model, indicating the chemisorption mechanism for As adsorption. Evidence for direct coordination of As to the surface of adsorbents was further confirmed by FTIR spectroscopic studies before and after As adsorption. The high adsorption efficiencies and the low-cost facile synthesis of the IOCN nanosorbent from agro-industrial waste indicate their potential for commercial applications.

Iron(III)-Oxo Cluster Chemistry with Dimethylarsinate Ligands: Structures, Magnetic Properties, and Computational Studies

A program has been initiated to develop Fe^III/oxo cluster chemistry with the "pseudocarboxylate" ligand dimethylarsinate (Me₂AsO₂^-) for comparison with the well investigated Fe^III/oxo/carboxylate cluster area. The synthesis and characterization of three polynuclear Fe^III complexes are reported, [Fe₁₂O₄(O₂C^tBu)₈(O₂AsMe₂)₁₇(H₂O)₃]Cl₃ (1), Na₂[Fe₁₂Na₂O₄(O₂AsMe₂)₂₀(NO₃)₆(Me₂AsO₂H)₂(H₂O)₄](NO₃)₆ (2), and [Fe₃(O₂AsMe₂)₆(Me₂AsO₂H)₂(hqn)₂](NO₃) (3), where hqnH is 8-hydroxyquinoline. The Fe₁₂ core of 1 is a type never previously encountered in Fe^III carboxylate chemistry, consisting of two Fe₆ units each of which comprises two {Fe₃(μ₃-O^2-)} units bridged by three Me₂AsO₂^- groups and linked into an Fe₁₂ loop structure by two anti-anti η¹:η¹:μ Me₂AsO₂^- groups, a bridging mode extremely rare with carboxylates. 2 also consists of two Fe₆ units, differing in their ligation from those in 1, and this time linked together into a linear structure by a central {Na₂(NO₃)₂} bridging unit. 3 is a linear Fe₃ complex with no monatomic bridges between Fe^III ions, a very rare situation in Fe^III chemistry with any ligands and unprecedented in Fe carboxylate chemistry. The distinct differences observed in arsinate vs carboxylate ligation modes are rationalized largely based on the greater basicity of the former vs the latter. Variable-temperature dc and ac magnetic susceptibility data reveal all Fe₂ pairwise interactions to be antiferromagnetic. For 1 and 2, the different J_ij couplings were estimated by use of a magnetostructural correlation for high nuclearity Fe^III-oxo clusters and by density functional theory calculations using broken symmetry methods, allowing identification of their relative spin vector alignments and thus rationalization of their S = 0 ground states. The J_ij values were then used as input values to give excellent fits of the experimental χ_MT vs T data. For 3, the fits of the experimental χ_MT vs T data to the Van Vleck equation or with PHI gave a very weak J₁₂ = -0.8(1) cm^-1 (H = -2JŜ_i·Ŝ_j convention) between adjacent Fe^III ions and an S = ⁵/₂ ground state. These initial Fe^III arsinate complexes also provide structural parameters that help validate literature assignments of arsinate binding modes to iron oxide/hydroxide minerals as part of environmental concerns of using arsenic-containing herbicides in agriculture.

Modelling and optimization of factors influencing adsorptive performance of agrowaste-derived Nanocellulose Iron Oxide Nanobiocomposites during remediation of Arsenic contaminated groundwater

Nanocellulose Iron Oxide Nanobiocomposites (NIONs) were synthesized from rice husk and sugarcane bagasse derived nanocelluloses for adsorptive removal of arsenic and associated contaminants present in groundwater samples. These NIONSs were superparamagnetic, hence magnetically recoverable and demonstrated promising recyclability. Synthesis of NIONs was confirmed by Transmission electron microscopy (TEM), X-Ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopic (XPS). FTIR and XPS data together with adsorption kinetics provide insights into probable adsorption mechanism of Arsenic by NIONs. The experimental conditions for 10 different variants were modelled using response surface methodology (RSM) based on central composite design (CCD), considering the parameters; adsorbate dosage, adsorbent dosage, pH and contact time. The results identified the best performing variants and the optimal conditions for maximal absorption (~99%). These results were validated using a three-layer feed-forward Multilayer Perceptron (MLP) based Artificial Neural Network (ANN) model. Both RSM and ANN chemometric models were in close conformity for optimized conditions of highest adsorption by specific variants. The standardized conditions were used to expand the study to field-based arsenic contaminated groundwater samples and their performance to commercial adsorbents. NIONs show promising commercial potential for water remediation applications due to their high adsorptive performance, magnetic recoverability and recyclability.

Review: Efficiently performing periodic elements with modern adsorption technologies for arsenic removal

Arsenic (As) toxicity is a global phenomenon, and it is continuously threatening human life. Arsenic remains in the Earth's crust in the forms of rocks and minerals, which can be released into water. In addition, anthropogenic activity also contributes to increase of As concentration in water. Arsenic-contaminated water is used as a raw water for drinking water treatment plants in many parts of the world especially Bangladesh and India. Based on extensive literature study, adsorption is the superior method of arsenic removal from water and Fe is the most researched periodic element in different adsorbent. Oxides and hydroxides of Fe-based adsorbents have been reported to have excellent adsorptive capacity to reduce As concentration to below recommended level. In addition, Fe-based adsorbents were found less expensive and not to have any toxicity after treatment. Most of the available commercial adsorbents were also found to be Fe based. Nanoparticles of Fe-, Ti-, Cu-, and Zr-based adsorbents have been found superior As removal capacity. Mixed element-based adsorbents (Fe-Mn, Fe-Ti, Fe-Cu, Fe-Zr, Fe-Cu-Y, Fe-Mg, etc.) removed As efficiently from water. Oxidation of AsO₃^3- to AsO₄^3-and adsorption of oxidized As on the mixed element-based adsorbent occurred by different adsorbents. Metal organic frameworks have also been confirmed as good performance adsorbents for As but had a limited application due to nano-crystallinity. However, using porous materials having extended surface area as carrier for nano-sized adsorbents could alleviate the separation problem of the used adsorbent after treatment and displayed outstanding removal performances.

Assessment of Aspergillus niger Strain's Suitability for Arsenate-Contaminated Water Treatment and Adsorbent Recycling via Bioextraction in a Laboratory-Scale Experiment

In this work, the viability of bioaccumulation and bioextraction processes for arsenic removal from contaminated waters, as well as the recycling of arsenate-treated amorphous ferric oxyhydroxide adsorbent (FeOOH) were evaluated using the common soil microscopic filamentous fungus Aspergillus niger. After treating the contaminated arsenate solution (100 mg As L-1) with FeOOH, the remaining solution was exposed to the growing fungus during a static 19-day cultivation period to further decrease the arsenic concentration. Our data indicated that although the FeOOH adsorbent is suitable for arsenate removal with up to 84% removal efficiency, the fungus was capable of accumulating only up to 13.2% of the remaining arsenic from the culture media. This shows that the fungus A. niger, although highly praised for its application in environmental biotechnology research, was insufficient for decreasing the arsenic contamination to an environmentally acceptable level. However, the bioextraction of arsenic from arsenate-treated FeOOH proved relatively effective for reuse of the adsorbent. Due to its production of acidic metabolites, which decreased pH below 2.7, the fungal strain was capable of removing of up to 98.2% of arsenic from the arsenate-treated FeOOH adsorbent.

As(V) and As(III) sequestration by starch functionalized magnetite nanoparticles: influence of the synthesis route onto the trapping efficiency

We report the effect of the synthesis route of starch-functionalized magnetite nanoparticles (NPs) on their adsorption properties of As(V) and As(III) from aqueous solutions. NP synthesis was achieved by two different routes implying the alkaline precipitation of either a mixed Fe²⁺/Fe³⁺ salt solution (MC samples) or a Fe²⁺ salt solution in oxidative conditions (MOP samples). Syntheses were carried out with starch to Fe mass ratio (R) ranging from 0 to 10. The crystallites of starch-free MC NPs (14 nm) are smaller than the corresponding MOP (67 nm), which leads to higher As(V) sorption capacity of 0.3 mmol g_Fe ^-1 to compare with respect to 0.1 mmol g_Fe ^-1 for MOP at pH = 6. MC and MOP starch-functionalized NPs exhibit higher sorption capacities than a pristine one and the difference in sorption capacities between MOP and MC samples decreases with increasing R values. Functionalization tends to reduce the size of the magnetite crystallites and to prevent their agglomeration. Size reduction is more pronounced for MOP samples (67 nm (R0) to 12 nm (R10)) than for MC samples (14 nm (R0) to 9 nm (R10)). Therefore, due to close crystallite size, both MC and MOP samples, when prepared at R = 10, display similar As(V) (respectively, As(III)) sorption capacities close to 1.3 mmol g_Fe ^-1 (respectively, 1.0 mmol g_Fe ^-1). Additionally, according to the effect of pH on arsenic trapping, the electrostatic interactions appear as a major factor controlling As(V) adsorption while surface complexation may control As(III) adsorption.

Remediation of carcinogenic arsenic by pyroaurite-based green adsorbent: isotherm, kinetic, mechanistic study, and applicability in real-life groundwater

The removal of the harmful carcinogen arsenic from drinking water by a green technology is a major concern in the field of environmental engineering. The sorptive profile of arsenic remediation by calcined Mg-Fe-layered double hydroxide, fabricated by a one-pot synthesis technique, was investigated to delineate its applicability in real-life water. The physicochemical properties of adsorbent, as demonstrated from spectroscopy and microscopy, which described the existence of amorphous material with significant surface roughness possess selectivity towards arsenic. The isotherm and kinetic along with thermodynamic modeling exhibited the occurrence of spontaneous (ΔG⁰ value = - 8.084 kJ/mol to - 10.942 kJ/mol), endothermic (ΔH⁰ value = 12.135 kJ/mol), and physisorption reactions (E_ad = 4.103-5.832 kJ/mol, E_a = 11.546 kJ/mol, S* = 0.0005 << 1, and ΔH_x = 9.23-16.29 kJ/mol) with high uptake rate and adsorption potential of adsorbent. The isotherm and kinetics were demonstrated by Temkin (R² = 0.944-0.969) and Elovich (R² = 0.996-0.998) models, respectively, with high statistical significance. The intraparticle diffusion model which established the rate-limiting step is the combination of both film and pore diffusions. The applicability of layered double hydroxide (LDH) material in the real-life water was confirmed by isotherm and kinetic modeling along with the regeneration/reuse potential. The adsorptive removal of arsenic by the LDH material exhibited to be a promising technique without creating any secondary hazard.

A Hybrid {Silk@Zirconium MOF} Material as Highly Efficient AsIII-sponge

Exposure of humans to Arsenic from groundwater drinking sources is an acute global public health problem, entailing the urgent need for highly efficient/low-cost Arsenite (As^III) up-taking materials. Herein we present an innovative hybrid-material, ZrMOF@SF_d operating like an “As^III-sponge” with unprecedented efficiency of 1800 mg As^III gr⁻¹. ZrMOF@SF_d consists of a neutral Zirconium Metal-Organic Framework [ZrMOF] covalently grafted on a natural silk-fiber (SF_d). ZrMOF itself exhibits As^III adsorption of 2200 mg gr⁻¹, which supersedes any -so far- known As^ΙΙΙ-sorbent. Using XPS, FTIR, BET-porosimetry data, together with theoretical Surface-Complexation-Modeling (SCM), we show that the high-As^ΙΙΙ-uptake is due to a sequence of two phenomena:[i] at low As^III-concentrations, surface-complexation of H₃AsO₃ results in As^III-coated voids of ZrMOF, [ii] at increased As^III-concentrations, the As^III-coated voids of ZrMOF are filled-up by H₃AsO₃via a partitioning-like mechanism. In a more general context, the present research exemplifies a mind-changing concept, i.e. that a “partitioning-like” mechanism can be operating for adsorption of metalloids, such as H₃AsO_3, by metal oxide materials. So far, such a mechanism has been conceptualized only for the uptake of non-polar organics by natural organic matter or synthetic polymers.

Hollow Polyaniline Microsphere/Fe3O4 Nanocomposite as an Effective Adsorbent for Removal of Arsenic from Water

Polyaniline hollow microsphere (PNHM)/Fe₃O₄ magnetic nanocomposites have been synthesized by a novel strategy and characterized. Subsequently, PNHM/Fe₃O₄-40 (Fe₃O₄ content: 40 wt.%) was used as an adsorbent for the removal of arsenic (As) from the contaminated water. Our investigations showed 98–99% removal of As(III) and As(V) in the presence of PNHM/Fe₃O₄-40 following pseudo-second-order kinetics (R² > 0.97) and equilibrium isotherm data fitting well with Freundlich isotherm (R² > 0.98). The maximum adsorption capacity of As(III) and As(V) correspond to 28.27 and 83.08 mg g⁻¹, respectively. A probable adsorption mechanism based on X-ray photoelectron spectroscopy analysis was also proposed involving monodentate-mononuclear/bidentate-binuclear As-Fe complex formation via legend exchange. In contrast to NO₃⁻ and SO₄²⁻ ions, the presence of PO₄³⁻ and CO₃²⁻ co-ions in contaminated water showed decrease in the adsorption capacity of As(III) due to the competitive adsorption. The regeneration and reusability studies of spent PNHM/Fe₃O₄-40 adsorbent showed ~83% of As(III) removal in the third adsorption cycle. PNHM/Fe₃O₄-40 was also found to be very effective in the removal of arsenic (<10 μg L⁻¹) from naturally arsenic-contaminated groundwater sample.

Sustainable Low-Concentration Arsenite [As(III)] Removal in Single and Multicomponent Systems Using Hybrid Iron Oxide-Biochar Nanocomposite Adsorbents-A Mechanistic Study

Rice and wheat husks were converted to biochars by slow pyrolysis (1 h) at 600 °C. Iron oxide rice husk hybrid biochar (RHIOB) and wheat husk hybrid biochar (WHIOB) were synthesized by copyrolysis of FeCl₃-impregnated rice or wheat husks at 600 °C. These hybrid sorbents were characterized using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, physical parameter measurement system, and Brunauer-Emmett-Teller (BET) surface area techniques. Fe₃O₄ was the predominant iron oxide present with some Fe₂O₃. RHIOB and WHIOB rapidly chemisorbed As(III) from water (∼24% removal in first half an hour reaching up to ∼100% removal in 24 h) at surface Fe-OH functions forming monodentate ≡Fe-OAs(OH)₂ and bidentate (≡Fe-O)₂AsOH complexes. Optimum removal occurred in the pH 7.5-8.5 range for both RHIOB and WHIOB, but excellent removal occurred from pH 3 to 10. Batch kinetic studies at various initial adsorbate-adsorbent concentrations, temperatures, and contact times gave excellent pseudo-second-order model fits. Equilibrium data were fitted to different sorption isotherm models. Fits to isotherm models (based on R ² and χ²) on RHIOB and WHIOB followed the order: Redlich-Peterson > Toth > Sips = Koble-Corrigan > Langmuir > Freundlich = Radke-Prausnitz > Temkin and Sips = Koble-Corrigan > Toth > Redlich-Peterson > Langmuir > Temkin > Freundlich = Radke-Prausnitz, respectively. Maximum adsorption capacities, Q _RHIOB ⁰ = 96 μg/g and Q _WHIOB ⁰ = 111 μg/g, were obtained. No As(III) oxidation to As(V) was detected. Arsenic adsorption was endothermic. Particle diffusion was a rate-determining step at low (≤50 μg/L) concentrations, but film diffusion controls the rate at ≥100-200 μg/L. Binding interactions with RHIOB and WHIOB were established, and the mechanism was carefully discussed. RHIOB and WHIOB can successfully be used for As(III) removal in single and multicomponent systems with no significant decrease in adsorption capacity in the presence of interfering ions mainly Cl^-, HCO₃ ^-, NO₃ ^-, SO₄ ^2-, PO₄ ^3-, K⁺, Na⁺, Ca²⁺. Simultaneous As(III) desorption and regeneration of RHIOB and WHIOB was successfully achieved. A very nominal decrease in As(III) removal capacity in four consecutive cycles demonstrates the reusability of RHIOB and WHIOB. Furthermore, these sustainable composites had good sorption efficiencies and may be removed magnetically to avoid slow filtration.

Stabilization treatment of arsenic-alkali residue (AAR): Effect of the coexisting soluble carbonate on arsenic stabilization

Arsenic-alkali residue (AAR) from antimony smelting is highly hazardous due to its ready leachability of As, seeking for proper disposal such as stabilization treatment. However, As stabilization in AAR would be challenging due to the high content of coexisting soluble carbonate. This study conducted the stabilization treatments of AAR by ferrous sulfate and lime, respectively, and revealed the significant influence of coexisting carbonate. It was found that ferrous sulfate was more efficient than lime, which required only one-tenth of dosages of lime to reduce the As leaching concentration from 915 mg/L to a level below 2.5 mg/L to meet the Chinese regulatory limit. The combining qualitative and quantitative analyses based on XRD, SEM-EDS, and thermodynamic modeling suggested that the formation of insoluble arsenate minerals, ferrous arsenate or calcium arsenate, was the predominant mechanism for As stabilization in the two treatment systems, and their efficiency difference was primarily attributed to the coexisting carbonate, which had a slight effect on ferrous arsenate but severely obstructed calcium arsenate formation. Moreover, the examination of As leaching concentrations in 1-year-cured samples indicated that the long-term stability of ferrous sulfate treatment was far superior to that of lime treatment. This study provides ferrous salts as a promising and green scheme for stabilization treatment of AAR as well as other similar As-bearing solid wastes with coexisting soluble carbonate.

Carrier-microencapsulation of arsenopyrite using Al-catecholate complex: nature of oxidation products, effects on anodic and cathodic reactions, and coating stability under simulated weathering conditions

Mining activities often generate large amounts of sulfide-rich wastes containing arsenopyrite (FeAsS), which when dissolved releases toxic arsenic (As) and generates acid mine drainage (AMD) that are both disastrous to the environment. To suppress arsenopyrite dissolution, a technique that selectively coats sulfide minerals with a protective layer of Al-oxyhydroxide called Al-based carrier-microencapsulation (CME) was developed. Although a previous study of the authors showed that Al-based CME could significantly limit arsenopyrite dissolution, nature of the coating formed on arsenopyrite, including its electrochemical properties, is still not well understood. Moreover, stability of the coating once exposed to weathering conditions remains unclear. Better understanding of these important issues would greatly improve Al-based CME especially in its application to real mine wastes. In this study, nature of the coating formed by Al-based CME was investigated using SEM-EDX, DRIFTS and XPS while the electrochemical properties of the coating were evaluated by cyclic voltammetry and chronoamperometry. Meanwhile, stability of the coating was elucidated using consecutive batch leaching experiments and weathering cell tests. SEM-EDX, DRIFTS and XPS results indicate that the protective coating formed on arsenopyrite by Al-based CME was mainly composed of bayerite (α-Al(OH)₃), gibbsite (γ-Al(OH)₃), and boehmite (γ-AlO(OH)). These Al-based coatings, which have insulating properties, made arsenopyrite less electrochemically active. The coatings also limited the extent of both the anodic and cathodic half-cell reactions of arsenopyrite oxidation that suppressed As release and acid generation. Weathering cell tests indicated that the oxidation of CME-treated arsenopyrite was effectively limited until about 15 days but after this, it started to gradually progress with time due to the increasing acidity of the system where Al-based coatings became unstable. Nonetheless, CME-treated arsenopyrite was less oxidized based on the released amounts of Fe, As and S suppressed by 80, 60 and 70%, respectively, compared with the one treated with control.

Removal of Arsenic(III) from water using magnetite precipitated onto Douglas fir biochar

Magnetic Fe₃O₄/Douglas fir biochar composites (MBC) were prepared with a 29.2% wt. Fe₃O₄ loading and used to treat As(III)-contaminated water. Toxicity of As(III) (inorganic) is significantly greater than As(V) and more difficult to remove from water. Removal efficiency was optimized verses pH, contact time and initial concentration. Column sorption and regeneration were also studied. Adsorption kinetics data best fitted the pseudo second order model (R² > 0.99). Adsorption was analyzed with three isotherm models at 20, 25 and 40 °C. The Sips isotherm showed the best fit at 25 °C with a 5.49 mg/g adsorption capacity, which is comparable with other adsorbents. MBC gave faster kinetics (~1-1.5 h) at pH 7 and ambient temperature than previous adsorbents. The Gibbs free energy (ΔG) of this spontaneous As(III) adsorption was -35 kJ/mol and ΔH = 70 kJ/mol was endothermic. Experiments were performed on industrial and laboratory wastewater samples in the presence of other co-existing contaminants (pharmaceutical residues, heavy metals ions and oxi-anions). The composite reduced the arsenic concentrations below the WHO's safe limit of 0.2 mg/L for waste water discharge. X-ray photoelectron spectroscopy (XPS) studies found As(III) and less toxic As(V) on Fe₃O₄ surfaces indicating adsorbed (or adsorbing) As(III) oxidation occurred upon contact with O₂ and possibly dissolved Fe(III) or upon drying under oxic conditions. Under anoxic conditions magnetite to maghemite transformation drives the oxidation. A pH-dependent surface chemisorption mechanism was proposed governing adsorption aided by XPS studies vs pH.

Iron oxide Permeated Mesoporous rice-husk nanobiochar (IPMN) mediated removal of dissolved arsenic (As): Chemometric modelling and adsorption dynamics

Adsorption based technologies are most widely used to mitigate the global predominance of heavy-metal groundwater contaminants like Arsenic (As), owing to their high efficiency and economic operation. The current study involves the optimization of Iron oxide Permeated Mesoporous rice-husk nanobiochars (IPMN) for As removal, which were synthesized through a chemically amended pyrolytic approach. The IPMN variants were screened based on preliminary OVAT (one-variable-at-a-time) studies for As removal. Chemometric investigations employing a central composite design matrix of Response surface methodology was further used to understand the influence of the process parameters on the adsorption of As on the most efficient IPMN variant. A Multi-Layered-Perceptron based artificial neural network was further used to confirm the veracity of the experimental and predictive conditions, to derive the optimal condition for the best adsorption efficiency. In addition, the dynamics of As adsorption by the optimal IPMN variant was modelled using pseudo-first-order (Lagergren) and pseudo-second-order (Ho) rate kinetic equations followed by isotherm studies using non-linear regression of Langmuir, Freundlich and Sips adsorption isotherms. The IPMNs have an appreciably higher uptake capacity (>90%) for dissolved As, as compared to the native milled rice husk (∼20%), alongside a substantial recyclability, thereby establishing their potential as a highly efficient, economical and sustainable nanobiochar for As removal.

Single-Particle Investigation of Environmental Redox Processes of Arsenic on Cerium Oxide Nanoparticles by Collision Electrochemistry

Quantification of chemical reactions of nanoparticles (NPs) and their interaction with contaminants is a fundamental need to the understanding of chemical reactivity and surface chemistry of NPs released into the environment. Herein, we propose a novel strategy employing single-particle electrochemistry showing that it is possible to measure reactivity, speciation, and loading of As³⁺ on individual NPs, using cerium oxide (CeO₂) as a model system. We demonstrate that redox reactions and adsorption processes can be electrochemically quantified with high sensitivity via the oxidation of As³⁺ to As⁵⁺ at 0.8 V versus Ag/AgCl or the reduction of As³⁺ to As⁰ at -0.3 V (vs Ag/AgCl) generated by collisions of single particles at an ultramicroelectrode. Using collision electrochemistry, As³⁺ concentrations were determined in basic conditions showing a maximum adsorption capacity at pH 8. In acidic environments (pH < 4), a small fraction of As³⁺ was oxidized to As⁵⁺ by surface Ce⁴⁺ and further adsorbed onto the CeO₂ surface as a As⁵⁺ bidentate complex. The frequency of current spikes (oxidative or reductive) was proportional to the concentration of As³⁺ accumulated onto the NPs and was found to be representative of the As³⁺ concentration in solution. Given its sensitivity and speciation capability, the method can find many applications in the analytical, materials, and environmental chemistry fields where there is a need to quantify the reactivity and surface interactions of NPs. This is the first study demonstrating the capability of single-particle collision electrochemistry to monitor the interaction of heavy metal ions with metal oxide NPs. This knowledge is critical to the fundamental understanding of the risks associated with the release of NPs into the environment for their safe implementation and practical use.

Application of modified electrospun nanofiber membranes with α-Fe2O3 nanoparticles in arsenate removal from aqueous media

In the present study, electrospun nanofiber membranes (ENMs) of polyacrylonitrile (PAN) were modified by dispersing α-Fe₂O₃ nanoparticles, synthesized using a thermal solvent process, in a PAN solution. The morphology and physiochemical properties of the prepared ENMs and the α-Fe₂O₃ were characterized using FESEM, EDX, BET, XRD, FTIR, porosity, and contact angle measurement. XPS was used to investigate the interaction of ENM with arsenate (As(V)) during the adsorption. Moreover, the effect of pH, the equilibrium isotherm, and the kinetics were investigated in batch experiments. The Langmuir isotherm best correlated the experimental results, indicating monolayer adsorption on ENMs, and the kinetics was best fitted, R² > 0.99, by the pseudo-second-order model. In addition, the effects of certain conditions on the filtration performance were examined, such as feed concentration and transmembrane pressure (TMP). By passing sodium hydroxide (0.1 M) for 20 min, the membrane was regenerated. The increase in TMP, along with the presence of co-ions including chloride, nitrate, and sulfate, had negative impacts on the removal of As(V). The results show that the modified ENMs with α-Fe₂O₃ nanoparticles are applicable for As(V) ion removal and possibly for eliminating other heavy metals from aqueous media.

In-situ reductive degradation of chlorinated DNAPLs in contaminated groundwater using polyethyleneimine-modified zero-valent iron nanoparticles

Zero-valent iron nanoparticles (ZVIN) have found applications in many strategies for on-site soil and groundwater decontamination. A number of studies have reported the prospective utilization of ZVIN in the reduction of chlorinated organic compounds such as dense non-aqueous phase liquids (DNAPLs) in groundwater. Due to their bioaccumulation and carcinogenesis, DNAPLs in groundwater are a human health hazard and pose environmental risks. Therefore, decontamination of these contaminants is necessary. This study presents the in-situ remediation of trichloroethylene (TCE), perchloroethene (PCE), and 1,2-dichloroethene (1,2-DCE) DNAPLs through the direct injection of polyethylenimine (PEI)-coated ZVIN (PEI-ZVIN composite materials) to facilitate the reduction of contaminants in low-permeability media. A field test was conducted at the premises of a petrochemical company, situated in the Miaoli County of Northern Taiwan that discharged significant amounts of DNAPLs. After in-situ injection and one-day of reaction with groundwater contaminants, ZVIN was further characterized to examine its efficacy in the reduction of pollutants. After the direct injection of PEI-ZVIN, a notable reduction in the concentration of DNAPLs was recorded with conversion from toxic to non-toxic substances. Use of resistivity image profiling (RIP) technique suggested similar conductivity data for the PEI-coated ZVIN suspension and groundwater samples. X-ray absorption near edge structure (XANES) and X-ray absorption fine structure (EXAFS) studies depicted that the oxidation of ZVIN and PEI-ZVIN was occurring after the reductive reaction with contaminated groundwater. The reacted samples had bond distance values of 1.98, 2.00, 1.96, and 1.94 Å. Combining floating surface-coated ZVIN and RIP technique seems promising and environmentally attractive.

Nanomaterials for the Removal of Heavy Metals from Wastewater

Removal of contaminants in wastewater, such as heavy metals, has become a severe problem in the world. Numerous technologies have been developed to deal with this problem. As an emerging technology, nanotechnology has been gaining increasing interest and many nanomaterials have been developed to remove heavy metals from polluted water, due to their excellent features resulting from the nanometer effect. In this work, novel nanomaterials, including carbon-based nanomaterials, zero-valent metal, metal-oxide based nanomaterials, and nanocomposites, and their applications for the removal of heavy metal ions from wastewater were systematically reviewed. Their efficiency, limitations, and advantages were compared and discussed. Furthermore, the promising perspective of nanomaterials in environmental applications was also discussed and potential directions for future work were suggested.

3‑Mercapto‑propanoic acid modified cellulose filter paper for quick removal of arsenate from drinking water

This paper reports a simple, facile and rapid preparation of 3‑mercapto‑propanoic acid (MPA) modified cellulose filter paper (MPA-Cell paper) for arsenate removal from drinking water. The MPA was covalently grafted to the cellulose filter paper (Cell) by esterification process through the formation of O‑acylisourea intermediate and characterized by the FTIR, SEM, EDS and XPS analyses. The arsenate adsorption efficiency was studied for batch and semi-continuous systems while exploring the adsorption kinetics, isotherm and the effect of pH for the former. The experimental data fitted well with Langmuir, Dubinin-Radushkevich (DR) and pseudo second order kinetic models. The mechanism of adsorption was studied by FTIR spectroscopy utilizing the adsorption isotherm, kinetic model and XPS results. The modified filter paper performed well at nearly neutral pH in arsenate removal through adsorption and demonstrated a significant arsenate uptake capacity of 92.59 mg/g. The DR and FTIR results indicated that the adsorption of arsenate ion occurred through ion exchange process. The MPA-Cell paper could have a potential use as low-cost but efficient commercial adsorbent for arsenate abatement from contaminated drinking water by both batch as well as semi-continuous operating systems. The MPA-Cell paper could purify ground water containing high level of arsenate.

Effects of ionic strength on removal of toxic pollutants from aqueous media with multifarious adsorbents: A review

Adsorption is one of the most widely used and effective wastewater treatment methods. The role of ionic strength (IS) in shaping the adsorption performances is much necessary due to the ubiquity of electrolyte ions in water body and industrial effluents. The influences of IS on adsorption are rather complex, because electrolyte ions affect both adsorption kinetics and thermodynamics by changing the basic characteristics of adsorbents and adsorbates. For a given adsorption system, multiple or even contradictory effects of IS may coexist under identical experimental conditions, rendering the dominant mechanism recognition and net effect prediction complicated. We herein reviewed the key advancement on the interaction and mechanisms of IS, including change in number of active sites for adsorbents, ion pair for metal ions, molecular aggregation and salting-out effect for organic compounds, site competition for both inorganic and organic adsorbates, and charge compensation for adsorbent-adsorbate reciprocal interactions. The corresponding fundamental theory was thoroughly described, and the efforts made by various researchers were explicated. The structural optimization of adsorbents affected by IS was detailed, also highlighting polyamine materials with exciting "salt-promotion" effects on heavy metal removal from high salinity wastewater. In addition, the research trends and prospects were briefly discussed.

Efficient multistep arsenate removal onto magnetite modified fly ash

The modification of the fly ash (FA) by magnetite (M) was performed to obtain FAM adsorbent with improved adsorption efficiency for arsenate removal from water. The novel low cost adsorbents are characterized by liquid nitrogen porosimetry (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), Mössbauer spectroscopy (MB) and Fourier transform infrared (FTIR) spectroscopy. The optimal conditions and key factors influencing the adsorbent synthesis are assessed using the response surface method (RSM). The adsorption experiment was carried out in a batch system by varying the contact time, temperature, pH, and mass of the adsorbent. The adsorption capacity of the FAM adsorbent for As(V), calculated by Langmuir model, was 19.14 mg g^-1. The thermodynamic parameters showed spontaneity of adsorption with low endothermic character. The kinetic data followed the pseudo-second-order kinetic model (PSO), and Weber-Morris model indicated intra-particle diffusion as rate limiting step. Alternative to low desorption capability of the FAM was found by five consecutive adsorption/magnetite precipitation processes which gave exhausted layered adsorbent with 65.78 mg g^-1 capacity. This research also has shed light on the mechanism of As(V)-ion adsorption, presenting a promising solution for the valorization of a widely abundant industrial waste.

Arsenic availability and uptake by edible rape (Brassica campestris L.) grown in contaminated soils spiked with carboxymethyl cellulose-stabilized ferrihydrite nanoparticles

This study investigated arsenic (As) availability and uptake by rape (Brassica campestris L.) during two harvest periods of carboxymethyl cellulose (CMC)-stabilized ferrihydrite (HFO) nanoparticles for in situ treatment As-contaminated soil. Application of modified HFO nanoparticles in soils not only provided a larger specific surface area but also markedly improved stability against aggregation and recrystallization. For 90-day incubation, bare HFO particles were gradually converted to the crystalline Fe(III) oxide form, although this was not observed for the 0.5% CMC-HFO nanoparticles. CMC-modified HFO nanoparticles could be more effective in lowering the As uptake by rape and available As in soils than bare HFO particles. Compared the control without amendments, As contents in rape and available As in soils decreased 69.7 and 59.0%, respectively, during the second harvest when soils were amended with 0.5% HFO nanoparticles. And the soil-solution distribution coefficient (K _d ) increased by 2.6 and 2.8 times for the first and second harvest. Furthermore, the ratio of amorphous and free Fe-oxides (Fe_o/Fe_d) showed significant negative linear correlations with As_plant (P < 0.01), available As (P < 0.05), and nonspecifically sorbed As in soil (P < 0.01). In contrast, Fe_o/Fe_d was positively correlated with K _d and amorphous crystalline Fe/Al oxide-sorbed As, which suggests that a larger amount of As is associated with Fe(hydr)oxide in the amorphous phase or smaller particles.

Nanofibers of resorcinol-formaldehyde for effective adsorption of As (III) ions from mimicked effluents

In the present study, the core-shell structured RF/PVA nanofibers have been developed and used for the adsorption of As³⁺ ions from the mimicked liquid effluents. Efficient-facile fabrication of the structured nanofibers (300-417 nm diameter) was accomplished using facile electrospinning technique. Chi parameter (χ = 25.56) and free energy of mixing (E_mix = 17.19 kcal/mol) calculated via molecular dynamics simulations depicted compatibility of the polymeric system resulting supermolecular core-shell nanofibers, whose adsorption results were also supported by the FE-SEM, FT-IR, and UV-VIS spectroscopy analysis. The adsorption analysis was performed using both linear and non-linear regression methods, for kinetic models and adsorption isotherms. The developed nanofibers demonstrated an adsorption capacity of 11.09 mg/g at a pH of 7, and an adsorption efficiency of 97.46% on protracted exposure, which is even adaptable at high temperatures with 93.1% reclamation. FE-SEM analysis and FT-IR spectra confirm the adsorption of As (III) ions on RF/PVA nanofibers and the presence of embedded hydrophilic oxygen sites for metal ion adsorption. The developed RF/PVA nanofibers demonstrate scalability in fabrication, low-cost, recycling, and less solid waste generation, depicting the large-scale applicability in removing arsenic ions from effluent waste. Graphical Abstract ᅟ.

Biotechnological Advances for Restoring Degraded Land for Sustainable Development

Global land resources are under severe threat due to pollution and unsustainable land use practices. Restoring degraded land is imperative for regaining ecosystem services, such as biodiversity maintenance and nutrient and water cycling, and to meet the food, feed, fuel, and fibre requirements of present and future generations. While bioremediation is acknowledged as a promising technology for restoring polluted and degraded lands, its field potential is limited for various reasons. However, recent biotechnological advancements, including producing efficient microbial consortia, applying enzymes with higher degrees of specificity, and designing plants with specific microbial partners, are opening new prospects in remediation technology. This review provides insights into such promising ways to harness biotechnology as ecofriendly methods for remediation and restoration.