Removal of arsenic(V) from spent ion exchange brine using a new class of starch-bridged magnetite nanoparticles

High-efficiency removal of As(iii) from groundwater using siderite as the iron source in the electrocoagulation process

Electrocoagulation technology, due to its simplicity and ease of operation, is often considered for treating arsenic-contaminated groundwater. However, challenges such as anode wear have hindered its development and application. This study aims to develop a siderite-filled anode electrocoagulation system for efficient removal of As(iii) and investigate its effectiveness. The impact of operational parameters on the removal rate of As(iii) was analyzed through single-factor tests, and the stability and superiority of the device were evaluated. The response surface methodology was employed to analyze the interactions between various factors and determine the optimal operational parameters by integrating data from these tests. Under conditions where the removal rate of As reached 99.3 ± 0.37%, with an initial concentration of As(iii) at 400 μg L-1, current intensity at 30 mA, initial solution pH value at 7, and Na2SO4 concentration at 10 mM. The flocculant used was subjected to characterization analysis to examine its structure, morphology, and elemental composition under these optimal operational parameters. The oxidation pathway for As(iii) within this system relies on integrated results from direct electrolysis as well as ˙O2 -, ˙OH, and Fe(iv) mediated oxidation processes. The elimination of arsenic encompasses two fundamental mechanisms: firstly, the direct adsorption of As(iii) by highly adsorbent flocculants like γ-FeOOH and magnetite (Fe3O4); secondly, the oxidation of As(iii) into As(v), followed by its reaction with siderite or other compounds to generate a dual coordination complex or iron arsenate, thus expediting its eradication. The anodic electrocoagulation system employing siderite as a filler exhibits remarkable efficiency and cost-effectiveness, while ensuring exceptional stability, thereby providing robust theoretical underpinnings for the application of electrocoagulation technology in arsenic removal.

Effects of Halides on Organic Compound Degradation during Plasma Treatment of Brines

Plasma has been proposed as an alternative strategy to treat organic contaminants in brines. Chemical degradation in these systems is expected to be partially driven by halogen oxidants, which have been detected in halide-containing solutions exposed to plasma. In this study, we characterized specific mechanisms involving the formation and reactions of halogen oxidants during plasma treatment. We first demonstrated that addition of halides accelerated the degradation of a probe compound known to react quickly with halogen oxidants (i.e., para-hydroxybenzoate) but did not affect the degradation of a less reactive probe compound (i.e., benzoate). This effect was attributed to the degradation of para-hydroxybenzoate by hypohalous acids, which were produced via a mechanism involving halogen radicals as intermediates. We applied this mechanistic insight to investigate the impact of constituents in brines on reactions driven by halogen oxidants during plasma treatment. Bromide, which is expected to occur alongside chloride in brines, was required to enable halogen oxidant formation, consistent with the generation of halogen radicals from the oxidation of halides by hydroxyl radical. Other constituents typically present in brines (i.e., carbonates, organic matter) slowed the degradation of organic compounds, consistent with their ability to scavenge species involved during plasma treatment.

Iron oxide nanoparticles in the soil environment: Adsorption, transformation, and environmental risk

Iron oxide nanoparticles (IONPs) have great application potential due to their multifunctional excellence properties, leading to the possibility of their release into soil environments. IONPs exhibit different adsorption properties toward environmental pollutants (e.g., heavy metals and organic compounds), thus the adsorption performance for various contaminants and the molecular interactions at the IONPs-pollutants interface are discussed. After solute adsorption, the change in the environmental behavior of IONPs is an important transformation process in the natural environments. The aggregation, aging process, and chemical/biological transformation of IONPs can be altered by soil solution chemistry, as well as by the presence of dissolved organic matter and microorganisms. Upon exposure to soil environments, IONPs have both positive and negative impacts on soil organisms (e.g., bacteria, plants, nematodes, and earthworms). Moreover, we compared the toxicity of IONPs alone to combined toxicity with environmental pollutants and pristine IONPs to aged IONPs, and the mechanisms of IONPs toxicity at the cellular level are also reviewed. Given the unanswered questions, future research should include prediction and design of IONPs, new characterization technology for monitoring IONPs transformation in soil ecosystems, and further refinement the environmental risk assessment of IONPs. This review will greatly enhance our knowledge of the performance and impact of IONPs in soil systems.

Starch-Based Polymer Materials as Advanced Adsorbents for Sustainable Water Treatment: Current Status, Challenges, and Future Perspectives

Over the past three decades, chemical and biological water contamination has become a major concern, particularly in the industrialized world. Heavy metals, aromatic compounds, and dyes are among the harmful substances that contribute to water pollution, which jeopardies the human health. For this reason, it is of the utmost importance to locate methods for the cleanup of wastewater that are not genuinely effective. Owing to its non-toxicity, biodegradability, and biocompatibility, starch is a naturally occurring polysaccharide that scientists are looking into as a possible environmentally friendly material for sustainable water remediation. Starch could exhibit significant adsorption capabilities towards pollutants with the substitution of amide, amino, carboxyl, and other functional groups for hydroxyl groups. Starch derivatives may effectively remove contaminants such as oil, organic solvents, pesticides, heavy metals, dyes, and pharmaceutical pollutants by employing adsorption techniques at a rate greater than 90%. The maximal adsorption capacities of starch-based adsorbents for oil and organic solvents, pesticides, heavy metal ions, dyes, and pharmaceuticals are 13,000, 66, 2000, 25,000, and 782 mg/g, respectively. Although starch-based adsorbents have demonstrated a promising future for environmental wastewater treatment, additional research is required to optimize the technique before the starch-based adsorbent can be used in large-scale in situ wastewater treatment.

Arsenic Contamination in Groundwater: Geochemical Basis of Treatment Technologies

Arsenic (As) is abundant in the environment and can be found in both organic (e.g., methylated) and inorganic (e.g., arsenate and arsenite) forms. The source of As in the environment is attributed to both natural reactions and anthropogenic activities. As can also be released naturally to groundwater through As-bearing minerals including arsenopyrites, realgar, and orpiment. Similarly, agricultural and industrial activities have elevated As levels in groundwater. High levels of As in groundwater pose serious health risks and have been regulated in many developed and developing countries. In particular, the presence of inorganic forms of As in drinking water sources gained widespread attention due to their cellular and enzyme disruption activities. The research community has primarily focused on reviewing the natural occurrence and mobilization of As. Yet, As originating from anthropogenic activities, its mobility, and potential treatment techniques have not been covered. This review summarizes the origin, geochemistry, occurrence, mobilization, microbial interaction of natural and anthropogenic-As, and common remediation technologies for As removal from groundwater. In addition, As remediation methods are critically evaluated in terms of practical applicability at drinking water treatment plants, knowledge gaps, and future research needs. Finally, perspectives on As removal technologies and associated implementation limitations in developing countries and small communities are discussed.

Groundwater arsenic contamination: impacts on human health and agriculture, ex situ treatment techniques and alleviation

Groundwater is consumed by a large number of people as their primary source of drinking water globally. Among all the countries worldwide, nations in South Asia, particularly India and Bangladesh, have severe problem of groundwater arsenic (As) contamination so are on our primary focus in this study. The objective of this review study is to provide a viewpoint about the source of As, the effect of As on human health and agriculture, and available treatment technologies for the removal of As from water. The source of As can be either natural or anthropogenic and exposure mediums can either be air, drinking water, or food. As-polluted groundwater may lead to a reduction in crop yield and quality as As enters the food chain and disrupts it. Chronic As exposure through drinking water is highly associated with the disruption of many internal systems and organs in the human body including cardiovascular, respiratory, nervous, and endocrine systems, soft organs, and skin. We have critically reviewed a complete spectrum of the available ex situ technologies for As removal including oxidation, coagulation-flocculation, adsorption, ion exchange, and membrane process. Along with that, pros and cons of different techniques have also been scrutinized on the basis of past literatures reported. Among all the conventional techniques, coagulation is the most efficient technique, and considering the advanced and emerging techniques, electrocoagulation is the most prominent option to be adopted. At last, we have proposed some mitigation strategies to be followed with few long and short-term ideas which can be adopted to overcome this epidemic.

Recent advances in the hybridization of cellulose and semiconductors: Design, fabrication and emerging multidimensional applications: A review

Cellulose is a plentiful, biodegradable, renewable, and natural polymer in the world that can be widely utilized in the production of polymer nanocomposites. Cellulose is developed in nanomaterials owing to its remarkable inherent features of low density, non-toxicity, and affordability, as well as the amazing sample characteristics of strength and thermal stability. Recently, there has been a lot of interest in organic-inorganic composites because of their adaptable qualities. Cellulose and semiconductors have exciting properties, and new combinations of both materials may result in efficient functional hybrid composites with distinct properties. Lately, a huge study was reported on cellulose and semiconductor-based nanocomposites. In this review, we summarize the present research development in the preparation methods, structure, features, and possible applications of multifunctional cellulose and semiconductor-based nanocomposites. The cellulose/semiconductor based nanocomposites have massive potential applications in the areas of photodegradation of organic dyes, hydrogen production, metal removal, biomedical, and sensor applications. It is also assumed that this article will promote additional investigation and will establish innovative capabilities to enhance novel cellulose and semiconductor based nanocomposites with new and exciting applications.

FeSx@MOF-808 composite for efficient As(III) removal from wastewater: behavior and mechanism

Arsenic is extremely toxic to humans with water as its carrier. One challenge for arsenic control is the complete elimination of As(III) due to its high toxicity, mobility, and solubility. Herein, an active FeS_x@MOF-808 composite was fabricated to enhance the As(III) removal for wastewater remediation. The FeS_x@MOF-808 showed better As(III) adsorptive performance (Q_e = 73.60 mg/g) compared with Fe₂S₃ (Q_e=12.38 mg/g), MOF-808 (Q_e = 27.85 mg/g), and Fe@MOF-808 (Q_e=34.26 mg/g). This can be attributed to an improved porous structure provided by MOF-808 and abundant reactive sites provided by FeS_x. Calculated by the Langmuir model (R² =0.9965), the maximum adsorption capacity (Q_max) of FeS_x@MOF-808 for As(III) removal at 298 K and pH = 7 was 203.28 ± 6.43 mg/g, which is beyond most of the traditional materials and MOFs. Additionally, FeS_x@MOF-808 exhibited good stability in a wide pH range (1-13). Results also showed that the different Fe/S ratios (1:0-1:8) and FeS_x loading amount (0.00625-0.25 mmol) have effects on the FeS_x@MOF-808 performance. By kinetics studies, XPS, and DFT calculation, the mechanisms for arsenic by FeS_x@MOF-808 were proposed. Multiple reaction mechanisms combine the adsorption by the MOF-808 support, the co-precipitation of iron oxides via hydroxyl (Fe-OH) groups, and most importantly, the precipitation through the break of Fe-S and the bond of As-S.

Encapsulins from Ca. Brocadia fulgida: An effective tool to enhance the tolerance of engineered bacteria (pET-28a-cEnc) to Zn2

Zn²⁺ is largely discharged from many industries and poses a severe threat to the environment, making its remediation crucial. Encapsulins, proteinaceous nano-compartments, may protect cells against environmental stresses by sequestering toxic substances. To determine whether hemerythrin-containing encapsulins (cEnc) from anammox bacteria Ca. Brocadia fulgida can help cells deal with toxic substances such as Zn²⁺, we transferred cEnc into E.coli by molecular biology technologies for massive expression and then cultured them in media with increasing Zn²⁺ levels. The engineered bacteria (with cEnc) grew better and entered the apoptosis phase later, while wild bacteria showed poor survival. Furthermore, tandem mass tag-based quantitative proteomic analysis was used to reveal the underlying regulatory mechanism by which the genetically-engineered bacteria (with cEnc) adapted to Zn²⁺ stress. When Zn²⁺ was sequestered in cEnc as a transition, the engineered bacteria presented a complex network of regulatory systems against Zn²⁺-induced cytotoxicity, including functions related to ribosomes, sulfur metabolism, flagellar assembly, DNA repair, protein synthesis, and Zn²⁺ efflux. Our findings offer an effective and promising stress control strategy to enhance the Zn²⁺ tolerance of bacteria for Zn²⁺ remediation and provide a new application for encapsulins.

Recent advances in starch-based magnetic adsorbents for the removal of contaminants from wastewater: A review

Considerable concern exists regarding water contamination by various pollutants, such as conventional pollutants (e.g., heavy metals and organics) and emerging micropollutants (e.g., consumer care products and interfering endocrine-related compounds). Currently, academics are continuously exploring sustainability-related materials and technologies to remove contaminants from wastewater. Magnetic starch-based adsorbents (MSAs) can combine the advantages of starch and magnetic nanoparticles, which exhibit unique critical features such as availability, cost-effectiveness, size, shape, crystallinity, magnetic properties, stability, adsorption properties, and excellent surface properties. However, limited reviews on MSAs' preparations, characterizations, applications, and adsorption mechanisms could be available nowadays. Hence, this review not only focuses on their activation and preparation methods, including physical (e.g., mechanical activation treatment, microwave radiation treatment, sonication, and extrusion), chemical (e.g., grafting, cross-linking, oxidation and esterification), and enzymatic modifications to enhance their adsorption properties, but also offers an all-round state-of-the-art analysis of the full range of its characterization methods, the adsorption of various contaminants, and the underlying adsorption mechanisms. Eventually, this review focuses on the recycling and reclamation performance and highlights the main gaps in the areas where further studies are warranted. We hope that this review will spark an interdisciplinary discussion and bring about a revolution in the applications of MSAs.

Influence of aggregation and sedimentation behavior of bare and modified zero-valent-iron nanoparticles on the Cr(VI) removal under various groundwater chemistry conditions

Aggregation behaviors of bare, and sodium polyacrylate (PAA) and starch modified zero-valent-iron nanoparticles (nZVI), as well as their effects on the Cr (VI) removal were investigated by simulating the groundwater. Results showed that increased concentration of PAA (1-6 wt%) and starch (0.1-0.6 wt%) alleviated the aggregation of modified nZVI (abbreviated as P-nZVI and S-nZVI), while there was an optimum dosage of 4 wt% PAA and 0.3 wt% starch for the Cr (VI) removal, respectively. Moreover, as one of the fundamental water chemistry parameters, Ca²⁺ (0, 5, and 10 mg L^-1) greatly promoted the aggregation of modified nZVI, and decreased the Cr (VI) removal efficiency by them via forming bidentate bridging structure (between Ca²⁺ and PAA) or complexes (between Ca²⁺ and starch). Additionally, fulvic acid (FA) (0, 2, 5, and 10 mg L^-1) decreased the Cr (VI) removal by P-nZVI because of the significantly improved electronic repulsion. However, FA enhanced the aggregation of S-nZVI, but diminished its performance on Cr (VI) removal due to the bridging effect between FA and starch. The present study was of great importance in predicting the migration of nZVI and contaminants removal under complex geological conditions in groundwater.

Gas Hydrate-Based Heavy Metal Ion Removal from Industrial Wastewater: A Review

Innovating methods for treating industrial wastewater containing heavy metals frequently incorporate toxicity-reduction technologies to keep up with regulatory requirements. This article reviews the latest advances, benefits, opportunities and drawbacks of several heavy metal removal treatment systems for industrial wastewater in detail. The conventional physicochemical techniques used in heavy metal removal processes with their advantages and limitations are evaluated. A particular focus is given to innovative gas hydrate-based separation of heavy metals from industrial effluent with their comparison, advantages and limitations in the direction of commercialization as well as prospective remedies. Clathrate hydrate-based removal is a potential technology for the treatment of metal-contaminated wastewater. In this work, a complete assessment of the literature is addressed based on removal efficiency, enrichment factor and water recovery, utilizing the gas hydrate approach. It is shown that gas hydrate-based treatment technology may be the way of the future for water management purposes, as the industrial treated water may be utilized for process industries, watering, irrigation and be safe to drink.

Alleviating the burden of ion exchange brine in water treatment: From operational strategies to brine management

Ion exchange (IX) using synthetic resins is a cost-efficient technology to cope with a wide range of contaminants in water treatment. However, implementing IX processes is constrained by the regeneration of IX resins that generates a highly concentrated brine (i.e., IX brine), the disposal of which is costly and detrimental to ecosystems. In an effort to make the application of IX resins more sustainable in water treatment, substantial research has been conducted on the optimization of IX resins operation and the management of IX brine. The present review critically evaluates the literature surrounding IX operational strategies and IX brine management which can be used to limit the negative impacts arising from IX brine. To this end, we first analyzed the physicochemical characteristics of brines from the regeneration of IX resins. Then, we critically evaluated IX operational strategies that facilitate brine management, including resin selection, contactor selection, operational modes, and regeneration strategies. Furthermore, we analyzed IX brine management strategies, including brine reuse and brine disposal (without or with treatment). Finally, a novel workflow for the IX water treatment plant design that integrates IX operational strategies and IX brine management is proposed, thereby highlighting the areas that make IX technology more sustainable for water treatment.

Differentiating Nanomaghemite and Nanomagnetite and Discussing Their Importance in Arsenic and Lead Removal from Contaminated Effluents: A Critical Review

Arsenic and lead heavy metals are polluting agents still present in water bodies, including surface (lake, river) and underground waters; consequently, the development of new adsorbents is necessary to uptake these metals with high efficiency, quick and clean removal procedures. Magnetic nanoparticles, prepared with iron-oxides, are excellent candidates to achieve this goal due to their ecofriendly features, high catalytic response, specific surface area, and pulling magnetic response that favors an easy removal. In particular, nanomagnetite and maghemite are often found as the core and primary materials regarding magnetic nanoadsorbents. However, these phases show interesting distinct physical properties (especially in their surface magnetic properties) but are not often studied regarding correlations between the surface properties and adsorption applications, for instance. Thus, in this review, we summarize the main characteristics of the co-precipitation and thermal decomposition methods used to prepare the nano-iron-oxides, being the co-precipitation method most promising for scaling up processes. We specifically highlight the main differences between both nano-oxide species based on conventional techniques, such as X-ray diffraction, zero and in-field Mössbauer spectroscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism, the latter two techniques performed with synchrotron light. Therefore, we classify the most recent magnetic nanoadsorbents found in the literature for arsenic and lead removal, discussing in detail their advantages and limitations based on various physicochemical parameters, such as temperature, competitive and coexisting ion effects, i.e., considering the simultaneous adsorption removal (heavy metal-heavy metal competition and heavy metal-organic removal), initial concentration, magnetic adsorbent dose, adsorption mechanism based on pH and zeta potential, and real water adsorption experiments. We also discuss the regeneration/recycling properties, after-adsorption physicochemical properties, and the cost evaluation of these magnetic nanoadsorbents, which are important issues, but less discussed in the literature.

Fast removal of heavy metals from water and soil samples using magnetic Fe3O4 nanoparticles

Heavy metal discharge from anthropogenic sources on open soil surfaces and in natural water bodies poses serious environmental and health concerns. In addition to the contamination reduction of metals at the source, post-discharge removal of metals using nanoparticles is one of the remediation technologies being explored nowadays due to its cost-effectiveness, being environment-friendly, and easy application as a technique. In this work, magnetic iron oxide (Fe₃O₄) nanoparticles were synthesized chemically and then used for the removal of heavy metals (Cd, Cr, Cu, Fe, Ni, Pb, and Zn) from water and soil samples. The heavy metal removal efficiency of these iron oxide nanoparticles for different metals in water was best observed at a pH of 4.5 and varied between 63.5 and 98.3%. However, the removal efficiency of these nanoparticles from the soil sample was only measured at a pH of 0.7, and heavy metal removal efficiency varied between 69.6 and 99.6%. In both soil and water samples, the most efficient remediation time was less than 20 min, after which desorption and even dissolution of the nanoparticles can occur at a highly acidic pH. Among all selected metals for removal, lead showed the best adsorption and hence removal efficiency. The nanoparticles were characterized using the TEM, XRD, and FTIR techniques. The adsorption efficiency of various metals was estimated by using atomic absorption spectroscopy. The results suggest that the removal efficiency and stability of adsorbed products can further be improved by adjusting the pH higher towards 7 and also perhaps by modifying the nanoparticles with functional groups. The primary advantage of the magnetic un-coated nanoparticles is easy and efficient removal of the nanoparticles from the treated solutions by using an ordinary magnet.

Enhanced removal of zinc and cadmium from water using carboxymethyl cellulose-bridged chlorapatite nanoparticles

Zinc (Zn²⁺) and cadmium (Cd²⁺) in water pose serious threats to human health and the environment. In search for a more effective treatment technology, we prepared a type of carboxymethyl cellulose (CMC) bridged chlorapatite (CMC-CAP) nanoparticles and tested the material for removal of Zn²⁺ and Cd²⁺ from water. CMC macromolecules were attached to CAP by bidentate bridging and hydrogen bonding, preserving the high adsorption capacity of CAP nanoparticles while allowing for easy gravity-separation of the nanoparticles. CMC-CAP showed rapid adsorption kinetics and 22.8% and 11.2% higher equilibrium uptake for Zn²⁺ and Cd²⁺, respectively, than pristine CAP. An extended dual-mode isotherm model, which takes into account both sorption and chemical precipitation, provided the best fits to the sorption isotherms, giving a maximum Langmuir sorption capacity of 141.1 mg g^-1 for Zn²⁺ and 150.2 mg g^-1 for Cd²⁺ by CMC-CAP. Na⁺ at up to 5 mM showed modest effects on the uptake of the heavy metals, while 2-5 mM of Ca²⁺ exerted notable inhibitive effects. Dissolved organic matter (up to 5 mg L^-1 as TOC) inhibited the Zn²⁺ uptake by 16.5% but enhanced the Cd²⁺ removal by 8.6%. Material characterizations and surface binding analyses revealed that ion exchange, surface precipitation, and surface complexation were the removal mechanisms for the heavy metals. This study demonstrates stabilizer bridging may serve as a convenient strategy to facilitate water treatment uses of nanoparticles.

Recent Developments in the Application of Nanomaterials in Agroecosystems

Nanotechnology implies the scientific research, development, and manufacture, along with processing, of materials and structures on a nano scale. Presently, the contamination of metalloids and metals in the soil has gained substantial attention. The consolidation of nanomaterials and plants in ecological management has received considerable research attention because certain nanomaterials could enhance plant seed germination and entire plant growth. Conversely, when the nanomaterial concentration is not properly controlled, toxicity will definitely develop. This paper discusses the role of nanomaterials as: (1) nano-pesticides (for improving the plant resistance against the biotic stress); and (2) nano-fertilizers (for promoting the plant growth by providing vital nutrients). This review analyzes the potential usages of nanomaterials in agroecosystem. In addition, the adverse effects of nanomaterials on soil organisms are discussed. We mostly examine the beneficial effects of nanomaterials such as nano-zerovalent iron, iron oxide, titanium dioxide, nano-hydroxyapatite, carbon nanotubes, and silver- and copper-based nanomaterials. Some nanomaterials can affect the growth, survival, and reproduction of soil organisms. A change from testing/using nanomaterials in plants for developing nanomaterials depending on agricultural requirements would be an important phase in the utilization of nanomaterials in sustainable agriculture. Conversely, the transport as well as ecological toxicity of nanomaterials should be seriously examined for guaranteeing its benign usage in agriculture.

Fabrication and evaluation of silica embedded and zerovalent iron composited biochars for arsenate removal from water

Waste date palm-derived biochar (DPBC) was modified with nano-zerovalent iron (BC-ZVI) and silica (BC-SiO₂) through mechanochemical treatments and evaluated for arsenate (As(V)) removal from water. The feedstock and synthesized adsorbents were characterized through proximate, ultimate, and chemical analyses for structural, surface, and mineralogical compositions. BC-ZVI demonstrated the highest surface area and contents of C, N, and H. A pH range of 2-6 was optimum for BC-ZVI (100% removal), 3-6 for DPBC (89% removal), and 4-6 for BC-SiO₂ (18% removal). Co-occurring PO₄^3- and SO₄^2- ions showed up to 100% reduction, while NO₃^- and Cl^- ions resulted in up to 26% reduction in As(V) removal. Fitness of the Langmuir, Freundlich and Redlich-Peterson isotherms to As(V) adsorption data suggested that both mono- and multi-layer adsorption processes occurred. BC-ZVI showed superior performance by demonstrating the highest Langmuir maximum adsorption capacity (26.52 mg g^-1), followed by DPBC, BC-SiO₂, and commercial activated carbon (AC) (7.33, 5.22, and 3.28 mg g^-1, respectively). Blockage of pores with silica particles in BC-SiO₂ resulted in lower As(V) removal than that of DPBC. Pseudo-second-order kinetic model fitted well with the As(V) adsorption data (R² = 0.99), while the Elovich, intraparticle diffusion, and power function models showed a moderate fitness (R² = 0.53-0.93). The dynamics of As(V) adsorption onto the tested adsorbents exhibited the highest adsorption rates for BC-ZVI. As(V) adsorption onto the tested adsorbents was confirmed through post-adsorption FTIR, SEM-EDS, and XRD analyses. Adsorption of As(V) onto DPBC, BC-SiO₂, and AC followed electrostatic interactions, surface complexation, and intraparticle diffusion, whereas, these mechanisms were further abetted by the higher surface area, nano-sized structure, and redox reactions of BC-ZVI.

Smart synthetic maghemite nanoparticles with unique surface properties encode binding specificity toward AsIII

Pristine ɣ-Fe₂O₃ nanoparticles, called surface active maghemite nanoparticles (SAMNs) display unprecedented colloidal stability and specific binding properties. Herein, the interactions of SAMNs with As^V and As^III as surface molecular probes were comparatively studied. Thermodynamic and kinetic characterizations, along with chemical and structural analysis of SAMN@As complexes, evidenced two distinct binding modalities. Arsenite, emerged as an elective and specific ligand for SAMNs, whereas arsenate adsorption was more labile, pH dependent and ruled by different binding possibilities. In particular, As^III oxyacid exclusively interacts through inner-sphere coordination occupying available surface crystal positions resembling a key-lock fitting, while As^V leads to both outer-sphere and inner-sphere complexes. Noteworthy, discrimination between As^V and As^III was never reported for nanostructured maghemite evidencing the importance of synthetic route on surface properties of the nanomaterial. The present report, besides enriching the chemistry of nanosized iron oxides, suggests SAMNs application for the remediation of water contaminated by As^III, the most threatening As species in water.

Efficient removal of As(Ш) via the synergistic effect of oxidation and absorption by FeOOH@MnO2@CAM nano-hybrid adsorption membrane

Due to the neutral charge of As(III) oxy-ions that make approaching the traditional adsorbent very improbable compared to the As(V) case, making it harder to be separated. To enhance the adsorption of As(Ш), the FeOOH coated cellulose acetate (CA) membrane doped with MnO₂ nanoparticles (FeOOH@MnO₂@CAM) was fabricated and then to removes As(Ш) in water through the synergistic effect of oxidation and adsorption, and the maximum adsorption capacity can reach 50.34 mg/g. FeOOH@MnO₂@CAM was fabricated with CA as a substrate by dipping-precipitation phase inversion and hydrothermal method. Langmuir and pseudo-second-order model showed that As(Ш) was adsorbed by chemical interactions through the monolayer and thermodynamic showed that As(Ш) adsorption was an exothermic and spontaneous process. The results of the pH study showed that as the pH increases from 3 to 11, the adsorption capacity of As(Ш) decreases from 50.34 to 14.32 mg/g, which was attributed to the acidic environment promoting the protonation of the surface of FeOOH@MnO₂@CAM, which increases the electrostatic attraction, and the alkaline environment increases electrostatic repulsion due to deprotonation. The competitive ions exhibited the PO₄^3- significantly reduce the adsorption capacity of As(Ш)，and as the PO₄^3- content increases, the adsorption capacity of As(Ш) decreases from 29.76 to 18.57 mg/g, which was attributed to the similar chemical properties of PO₄^3- and arsenate. Importantly, FeOOH@MnO₂@CAM still maintains an adsorption capacity of 20.19 mg/g after seven cycles, demonstrating that it is a kind of environmentally friendly material to remove As(Ш) in the water environment.

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.

Encapsulation of starch hydrogel and doping nanomagnetite onto metal-organic frameworks for efficient removal of fluvastatin antibiotic from water

Growing interests and efforts have been recently focused on design and assembly of novel hydrogel nanosorbents for removal of drugs from wastewater. Therefore, this work is aimed to immobilize and encapsulate starch hydrogel matrix onto metal organic frameworks (MOFs) and dope with nanomagnetite. The magnetic MOFs-Starch hydrogel (NFe₃O₄@Zn(GA)/Starch-Hydrogel) was synthesized via microwave irradiation process and characterized with high surface area (528.39 m²/g), mesoporous with pore size 2.90 nm and highly crystalline structure. The maximum swelling ratio (1000.0 %) was optimized at pH 10, 180 min and 25 °C. The validity of NFe₃O₄@Zn(GA)/Starch-Hydrogel for adsorptive removal of Fluvastatin statin drug provided maximum equilibrium adsorption capacity 782.05 mg g^-1. The Langmuir isotherm and pseudo-second kinetics models were correlated well with the computed correlation coefficient values 0.9991 and 0.9997, respectively. The validity of NFe₃O₄@Zn(GA)/Starch-Hydrogel for removal of FLV statin drug from real water matrices was confirmed in the range 96.15-99.99 %.

Selective and simultaneous detection of cadmium, lead and copper by tapioca-derived carbon dot-modified electrode

The need for the sensing of environmental pollutants cannot be overemphasized in the twenty-first century. Herein, a sensor has been developed for the sensitive and selective detection of copper (Cu²⁺), lead (Pb²⁺) and cadmium (Cd²⁺) as major heavy metals polluting water environment. A screen-printed carbon electrode (SPCE) modified by fluorescent carbon dots (CDs) and gold nanoparticles (AuNPs) was successfully fabricated for sensing Cu²⁺, Pb²⁺ and Cd²⁺. Differential pulse voltammetry (DPV) and cyclic voltammetry (CV) were deployed for the analysis of ternary analytes. CV was set at a potential range of - 0.8 to + 0.2 V at a scan rate of 100 mV/s, and DPV at a potential range of - 0.8 to + 0.1 V, scan rate of 50 mV/s, pulse rate of 0.2 V and pulse width of 50 ms. DPV technique was applied through the modified electrode for sensitive and selective determination of Cu²⁺, Pb²⁺ and Cd²⁺ at a concentration range of 0.01 to 0.27 ppm for Cu²⁺, Pb²⁺ and Cd²⁺. Tolerance for the highest possible concentration of foreign substances such as Mg²⁺, K⁺, Na⁺, NO₃^-, and SO₄^2- was observed with a relative error less than ± 3%. The sensitivity of the modified electrode was at 0.17, 0.42 and 0.18 ppm for Cd²⁺, Pb²⁺ and Cu²⁺, respectively, while the limits of detection (LOD) achieved for cadmium, lead and copper were 0.0028, 0.0042 and 0.014 ppm, respectively. The quality of the modified electrode for sensing Cu²⁺, Pb²⁺ and Cd²⁺ at trace levels is in accordance with the World Health Organization (WHO) and Environmental Protection Agency (EPA) water regulation standard. The modified SPCE provides a cost-effective, dependable and stable means of detecting heavy metal ions (Cu²⁺, Pb²⁺ and Cd²⁺) in an aqueous solution. Graphical abstract .

Controlled synthesis of iron oxyhydroxide (FeOOH) nanoparticles using secretory compounds from Chlorella vulgaris microalgae

FeOOH nanoparticles are commonly synthesized at very high temperature and pressure that makes the process energy consuming and non-economic. Recently, novel approaches were developed for the fabrication of these particles at room temperature. But, the main problem with these methods is that the prepared structures are aggregates of ultra-small nanoparticles where no intact separate nanoparticles are formed. In this study, for the first time, secretory compounds from Chlorella vulgaris cells were employed for the controlled synthesis of FeOOH nanoparticles at room atmosphere. Obtained particles were found to be goethite (α-FeO(OH)) crystals. Controlled synthesis of FeOOH nanoparticles resulted in uniform spherical nanoparticles ranging from 8 to 17 nm in diameter with 12.8 nm mean particle size. Fourier-transform infrared and elemental analyses were indicated that controlled synthesized nanoparticles have not functionalized with secretory compounds of C. vulgaris, and these compounds just played a controlling role over the synthesis reaction.

A comprehensive study on the bacterial biosorption of heavy metals: materials, performances, mechanisms, and mathematical modellings

Discharges of waste containing heavy metals (HMs) have been a challenging problem for years because of their adverse effects in the environment. This article provides a comprehensive review of recent findings on bacterial biosorption and their performances for sequestration of HMs. It highlights the significance of HM removal and presents a brief overview on bacterial functionality and biosorption technology. It also discusses the achievements towards utilisation of bacterial biomass with biosorption of HMs from aqueous solutions. This article includes different types of kinetic, equilibrium, and thermodynamic models used for HM treatments using different bacterial species, as well as biosorption mechanisms along with desorption of metal ions and regeneration of bacterial biosorbents. Its fast kinetics of metal biosorption and desorption, low operational cost, and no production of toxic by-products provide attraction to many researchers. Bacteria can easily be produced using inexpensive growth media or obtained as a by-product from industries. A systematic comparison of the literature for a metal-binding capacity of bacterial biomass under different conditions is provided here. The properties of the cell wall constituents such as peptidoglycan and the role of functional groups for metal sorption are presented on the basis of their biosorption potential. Many bacterial biosorbents as reported in scientific literature have a high biosorption capacity, where some are better than commercial adsorbents. Based on the reported results, it seems that most bacteria have the potential for industrial applications for detoxification of HMs.

Enhanced As(Ш) removal from aqueous solutions by recyclable Cu@MNM composite membranes via synergistic oxidation and absorption

Arsenic contamination threatens the safety of drinking water in many parts of the world, especially As (Ш), which is more toxic and more difficult to remove than As (Ⅴ). Hence, in terms of environmental protection and sustainable development, it is very important to remove As (Ш) from the environment to reduce the damage to ecosystems and human health. Since there is no effective method for removing As (Ш), it is essential to oxidize As (Ш) into easily removable As (Ⅴ) to achieve effective separation. Herein, a novel copper-coated MnO₂ nanowires membrane (Cu@MNM) which combines the oxidation properties of MnO₂ and the catalytic and absorption properties of nanoscale Cu (NSCu), was developed based on in situ chemical deposition NSCu on the surface of ultralong MnO₂ nanowires. The as-prepared Cu@MNM shows excellent arsenic separation properties with the maximum rejection rate of 96%. The results of pH studies indicate that acidic conditions promote the separation of As (Ш) by Cu@MNM, while alkaline conditions are inhibitory due to deprotonation of Cu@MNM surface enhances electrostatic repulsion. The results of the interfering ions show that the phosphate ions have a strong inhibitory effect on arsenic separation. In addition, Cu@MNM has been shown to be remarkably recyclable and can still achieve a separation efficiency of 60% after five cycles. Therefore, the prepared Cu@MNM with the high arsenic retention efficiency and excellent recycling capabilities has the potential to become an excellent candidate for practical application in arsenic separation.

Arsenic(III) Removal by Nanostructured Dialdehyde Cellulose-Cysteine Microscale and Nanoscale Fibers

Arsenite (As(III)) contamination in drinking water has become a worldwide problem in recent years, which leads to development of various As(III) remediation approaches. In this study, two biomass-based nanostructured materials, microscale dialdehyde cellulose-cysteine (MDAC-cys) and nanoscale dialdehyde cellulose-cysteine (NDAC-cys) fibers, have been prepared from wood pulp. Their As(III) removal efficiencies and mechanism were determined by combined adsorption, atomic fluorescence spectrometry, microscopy (scanning electron microscopy, transmission electron microscopy, and atomic force microscopy), and spectroscopy (Fourier transform infrared, 13C CPMAS NMR) methods. The adsorption results of these materials could be well described by the Freundlich isotherm model, where the maximum adsorption capacities estimated by the Langmuir isotherm model were 344.82 mg/g for MDAC-cys and 357.14 mg/g for NDAC-cys, respectively. Both MDAC-cys and NDAC-cys materials were further characterized by X-ray diffraction and thermogravimetric analysis, where the results indicated that the thiol groups (the S content in MDAC-cys was 12.70 and NDAC-cys was 17.15%) on cysteine were primarily responsible for the adsorption process. The nanostructured MDAC-cys system appeared to be more suitable for practical applications because of its high cost-effectiveness.

Self-enhanced and efficient removal of arsenic from waste acid using magnetite as an in situ iron donator

High arsenic-containing waste acid from the heavy nonferrous metallurgical sector (Cu, Pb, Zn, Ni, Sn, etc.), one of the most dangerous arsenic hazardous wastes with extremely high arsenic concentrations, has presented enormous challenges to the environment and caused severe environmental pollution over the past few decades due to the lack of affordable and environmentally friendly disposal technologies. Here, we report a green process for the self-enhanced and efficient removal of arsenic from waste acid using magnetite as an in situ iron donator. Firstly, the room-temperature predissolution of magnetite in waste acid provides initial iron ions as a starting precipitator of arsenic, simultaneously providing a suitable pH range and an active surface that are ready for the nucleation and growth of scorodite. Afterwards, arsenic is precipitated in form the of scorodite, which is driven by a mutually improved cycle composed of arsenic precipitation and magnetite dissolution on the surface of magnetite particles. This cycle creates a low supersaturation of iron and constant pH in the waste acid, ensuring the continuous precipitation of arsenic as well-crystallized and environmentally stable scorodite by using magnetite as an in situ iron donator via the reaction of 2Fe₃O₄ + 6H₃AsO₄ + H₂O₂ = 6FeAsO₄ + 10H₂O. Under optimal conditions, including a 6-h room-temperature predissolution, a 12-h atmospheric reaction at 90 °C and a pH of 2.0 with a magnetite dosage at the Fe₃O₄/As molar ratio (the molar ratio of Fe₃O₄ in magnetite to As in waste acid) of 1.33, 99.90% of arsenic was successively removed from waste acid with an initial arsenic concentration of 10300 mg/L. In combination with the good adaptability of this process, the performed case study and prospective process show the successful removal of arsenic from waste acid as well as great potential for large-scale applications.

Application of Response Surface Methodology and Desirability Function in the Optimization of Adsorptive Remediation of Arsenic from Acid Mine Drainage Using Magnetic Nanocomposite: Equilibrium Studies and Application to Real Samples

A magnetic multi-walled carbon nanotube/zeolite nanocomposite was applied for the adsorption and removal of arsenic ions in simulated and real acid mine drainage samples. The adsorption mechanism was investigated using two-parameter (Langmuir, Freundlich, Temkin) and three-parameter (Redlich–Peterson, and Sips) isotherm models. This was done in order to determine the characteristic parameters of the adsorptive removal process. The results showed that the removal process was described by both mono- and multilayer adsorptions. Adsorption studies demonstrated that a multi-walled carbon nanotube/zeolite nanocomposite could efficiently remove arsenic in simulated samples within 35 min. Based on the Langmuir isotherm, the adsorption capacity for arsenic was found to be 28 mg g⁻¹. The nanocomposite was easily separated from the sample solution using an external magnet and the regeneration was achieved by washing the adsorbent with 0.05 mol L⁻¹ hydrochloric acid solution. Moreover, the nanoadsorbent was reusable for at least 10 cycles of adsorption-desorption with no significant decrease in the adsorption capacity. The nanoadsorbent was also used for the arsenic removal from acid mine drainage. Overall, the adsorbent displayed excellent reusability and stability; thus, they are promising nanoadsorbents for the removal of arsenic from acid mine drainage.

Ultrafast and deep removal of arsenic in high-concentration wastewater: A superior bulk adsorbent of porous Fe2O3 nanocubes-impregnated graphene aerogel

Bulk adsorbents for fast and deep removal of arsenic in water is highly demanded for practical treatment process, especially fixed-bed column process. In this study, a superior bulk adsorbent of porous Fe₂O₃ nanocubes-impregnated porous graphene aerogel (PGA/PFe₂O₃) is prepared using a simple template engineering. The maximum capacity for As(III) and As(V) reaches as high as 172.27 and 217.34 mg g^-1 of Fe₂O₃, respectively. The adsorption equilibrium times of As(III) and As(V) on PGA/PFe₂O₃ are only 30 and 5 min, respectively (m/V = 0.5 g L^-1, C₀ = 5 mg L^-1). Significantly, the high concentrations of As(III) and As(V) can be reduced below 10 μg L^-1 within only 60 and 5 min, respectively. The aerogel is conducive to fast diffusion of arsenic and porous Fe₂O₃ nanocubes provide abundant adsorption sites. Moreover, the adsorbent exhibits an outstanding reusability. The adsorbent also shows a strong anti-interference to aquatic environment. A real realgar tailing wastewater (C₀ = 3.076 mg L^-1 for As(III) and 3.225 mg L^-1 for As(V)) can be deep treated (below 10 μg L^-1) within 4 h (m/V = 0.6 g L^-1). The bulk adsorbent of PGA/PFe₂O₃ presents a high column treatment capacity of arsenic-containing groundwater (4750 BV for As(III), 5730 BV for As(V)), producing only 12 BV eluent. This work develops a superior bulk adsorbent for large-scale treatment of arsenic-containing wastewater.

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.

Sensing Coated Iron-Oxide Nanoparticles with Spectral Induced Polarization (SIP): Experiments in Natural Sand Packed Flow-Through Columns

The development of nanoparticle-based soil remediation techniques is hindered by the lack of accurate in situ nanoparticle (NP) monitoring and characterization methods. Spectral induced polarization (SIP), a noninvasive geophysical technique, offers a promising approach to detect and quantify NPs in porous media. However, its successful implementation as a monitoring tool requires an understanding of the polarization mechanisms, the governing NP-associated SIP responses and their dependence on the stabilizing coatings that are typically used for NPs deployed in environmental applications. Herein, we present SIP responses (0.1-10 000 Hz) measured during injection of a poloxamer-coated superparamagnetic iron-oxide nanoparticle (SPION) suspension in flow-through columns packed with natural sand from the Borden aquifer. An advective-dispersive transport model is fitted to outflow SPION concentration measurements to compute average concentrations over the SIP spatial response domain (within the columns). The average SPION concentrations are compared with the real and imaginary components of the complex conductivity. Excellent correspondence is found between the average SPION concentrations in the columns and the imaginary conductivity values, suggesting that NP-mediated polarization (that is, charge storage) increases proportionally with increasing SPION concentration. Our results support the possibility of SIP monitoring of spatial and temporal NP distributions, which can be immediately deployed in bench-scale studies with the prospect of future real-world field applications.

Fabrication of Stabilized Fe⁻Mn Binary Oxide Nanoparticles: Effective Adsorption of 17β-Estradiol and Influencing Factors

Fe–Mn binary oxide nanoparticles (FMBON) were reported to be high performance as adsorbent for pollutants removal from aqueous solution. However, there are still limitations in practice application due to the FMBON tend to aggregate into the micro millimeter level. In order to avoid the agglomeration of nanoparticles, this work synthesized the stabilized Fe–Mn binary oxide nanoparticles (CMC-FMBON) by using water-soluble carboxymethyl celluloses (CMC) as the stabilizer. The characteristics of CMC-FMBON and FMBON were measured by using Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Zeta potential. This work systematically investigated the adsorption capacity of CMC-FMBON for 17β-estradiol (E2) and the influences of external environmental factors on E2 removal. The results indicated that CMC-FMBON had much smaller particles, wider dispersion and larger surface area than the FMBON. CMC-FMBON showed better adsorption performance for E2 than FMBON with the maximum adsorption capacity of CMC-FMBON and FMBON were 124.10 and 98.14 mg/g at 298 K, respectively. The experimental data can be well fitted by the model of pseudo-second-order and Langmuir model. The E2 removal by CMC-FMBON was obviously dependent on pH with the maximum adsorption occurring when the pH was acidic. The removal capacity of CMC-FMBON increased when enhancing ionic strength in solution. Background electrolytes promoted slightly E2 adsorption process whereas the presence of humic acid inhibited the E2 removal. π-π interactions, hydrogen bonds, and oxidation might be responsible for E2 removal. This research suggested that the CMC-FMBON has been considered to be a cost-efficient adsorbent for removing E2 from water.