Enhanced removal of As(Ⅲ) and As(Ⅴ) from aqueous solution using ionic liquid-modified magnetic graphene oxide

Enhanced arsenic removal by graphene oxide chitosan composites through FeOx decoration: Influences and mechanism

Iron decoration has been recognized as one of the most important paths to enhance contaminant adsorption by carbon-based composites. In this study, varying amounts of Fe (II) are used for the modification of graphene oxide chitosan (GOCS) materials to assess the impact of iron oxide (FeOx) morphology on the composites and their efficiency in arsenic (As) removal. Results show that incorporating 0.08 mol Fe(II) into GOCS yields better As removal performance, leading to a remarkable enhancement by 5 times for As(V) and 6 times for As(III). The iron minerals in the material consist of goethite (FeO(OH)) and magnetite (Fe3O4), with FeO(OH) playing a predominant role in As removal through the complexation and electrostatic attraction of -OH and Fe - O groups. The adsorption capacity for As (Qe) decreases with the increasing pH and the mass and volume ratio (m/v) but increases with the increasing initial concentration (C0). Besides, the presence of SO42- and HPO42- can significantly reduce As removal by the FeOx-modified GOCS. Under the conditions of pH = 3, m/v = 1.0 g/L, and C0 = 10 mg/L, a maximum Qe value reaches 61.94 mg/g. The adsorption is well-fitted to a pseudo-second-order kinetic model and is an endothermic, spontaneous, and monolayer adsorption process.

Ionic Liquid Modified Polymer Gel for Arsenic Speciation

A new ionic liquid modified polymer gel containing methylimidazolium groups (poly(MIA)) is proposed as a sorbent for the separation and enrichment of trace inorganic and organic arsenic species in surface waters. The poly(MIA) was synthesized by chemical modification of polymeric precursor using post-polymerization modification of poly(glycidyl methacrylate-co-trimethylolpropane trimethacrylate). The composition, structure, morphology, and surface properties of the prepared particles were characterized using elemental analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and nitrogen adsorption-desorption measurements. Optimization experiments showed that at pH 8, monomethylarsonic acid (MMAs), dimethylarsinic acid (DMAs), and As(V) were completely retained on the poly(MIA), while the sorption of As(III) was insignificant. The desorption experiments revealed that due to the weaker binding of organic arsenic species, selective elution with 1 mol/L acetic acid for MMAs + DMAs, followed by elution with 2 mol/L hydrochloric acid for As(V), ensured their quantitative separation. The adsorption kinetic and mechanism were defined. The analytical procedure for As(III), As(V), MMAs, and DMAs determination in surface waters was developed and validated through the analysis of certified reference material.

3D-printed device for the kinetic determination of As(III) in groundwater samples by digital movie analysis

High concentrations of inorganic arsenic in groundwater for human consumption is a worldwide common problem. Particularly, the determination of As(III) becomes important, since this species is more toxic than organic, pentavalent and elemental arsenic forms. In this work, a 3D-printed device that included a 24-well microplate was developed to perform the colourimetric kinetic determination of arsenic (III) by digital movie analysis. A smartphone camera attached to the device was used to take the movie during the process where As(III) inhibited the decolourization of methyl orange. The movie images were subsequently transformed from RGB to YIQ space to obtain a new analytical parameter called "d", which was related to the chrominance of the image. Then, this parameter allowed the determination of the inhibition time of reaction (t_in), which was linearly correlated with the concentration of As(III). A linear calibration curve (R = 0.9995) in the range from 5 μg L^-1 to 200 μg L^-1 was obtained. The method was precise (RSD = 1.2%), and the limits of detection (LOD) and quantification (LOQ) were 1.47 μg L^-1 and 4.44 μg L^-1, respectively. These values were lower than the limit established by the World Health Organization for total arsenic in drinking water (10 μg L^-1). The accuracy of the method was assessed by a recovery study with optimal results (94.3%-104.0%). Additionally, the Analytical GREEnness metric approach was applied, obtaining a score 1.7 times higher than previously published works. The method is simple, portable and low-cost, being in compliance with various principles of green analytical chemistry.

Understanding the adsorption of iron oxide nanomaterials in magnetite and bimetallic form for the removal of arsenic from water

Arsenic decontamination is a major worldwide concern as prolonged exposure to arsenic (>10 µg L-1) through drinking water causes serious health hazards in human beings. The selection of significant, cost-effective, and affordable processes for arsenic removal is the need of the hour. For the last decades, iron-oxide nanomaterials (either in the magnetite or bimetallic form) based adsorptive process gained attention owing to their high arsenic removal efficiency and high regenerative capacity as well as low yield of harmful by-products. In the current state-of-the-art, a comprehensive literature review was conducted focused on the applicability of iron-based nanomaterials for arsenic removal by considering three main factors: (a) compilation of arsenic removal efficiency, (b) identifying factors that are majorly affecting the process of arsenic adsorption and needs further investigation, and (c) regeneration capacity of adsorbents without affecting the removal process. The results revealed that magnetite and bimetallic nanomaterials are more effective for removing Arsenic (III) and Arsenic (V). Further, magnetite-based nanomaterials could be used up to five to six reuse cycles, whereas this value varied from three to six reuse cycles for bimetallic ones. However, most of the literature was based on laboratory findings using decided protocols and sophisticated instruments. It cannot be replicated under natural aquatic settings in the occurrence of organic contents, fluctuating pH and temperature, and interfering compounds. The primary rationale behind this study is to provide a comparative picture of arsenic removal through different iron-oxide nanomaterials (last twelve yearsof published literature) and insights into future research directions.

Removal of As(III)/As(V) from aqueous solution using newly developed thiosalicylic acid coated magnetite [TSA@Fe3O4] nanoparticles

The aim of this study was to develop an affordable adsorption methodology for removal of As(III)/As(V) from contaminated water. Herein, novel adsorbent TSA@Fe₃O₄ nanoparticles (NPs) were synthesized by decorating thiosalicylic acid (TSA) on magnetite nanoparticles (Fe₃O₄ NPs) and employed for removal of As(III)/As(V) species from artificially contaminated natural water systems. TSA@Fe₃O₄ NPs demonstrated excellent adsorption efficiency (AE) and 98% of As(V) and 93% of As(III) was removed at optimized experimental conditions. The adsorption kinetic and equilibrium isotherm studies were conducted preferentially for As(III) adsorption. Adsorption followed the pseudo-second-order kinetic (R² = 99%) and adsorption data fitted well in Langmuir isotherm model (R² = 99%) and maximum adsorption capacity (Q_max = 34.1 mg/g) was calculated for 5 mg/L of As(III) by using 10 mg of TSA@Fe₃O₄ NPs. The effect of pH, contact time, adsorption dosages, and competitive anions was also examined to identify optimum experimental conditions. The adsorbent was characterized by advanced instrumental techniques to investigate the physicochemical properties and stability of NPs. To comprehend the interactions of As(III) species with adsorbent NPs, NPs were analyzed using XPS and Raman spectroscopy techniques. Both the techniques confirmed that As(III) and As(V) species present simultaneously on adsorbent surface. The TSA@Fe₃O₄ was regenerated using 0.1 M NaOH. The findings of this study suggested that TSA@Fe₃O₄ NPs could be considered a potential adsorbent for effective remediation of As(III) and As(V) from contaminated natural water systems.

Aqueous phase synthesis of ion-imprinted cryogel for paper-based colorimetric detection of As(V) with high selectivity

A novel hydrophilic As(V) ion-imprinted cryogel (IIC) was green prepared by cryogelation in aqueous environment which was coincident with the adsorption condition and can improve the specific recognition performance. The methacrylamido propyl trimethyl ammonium chloride (MPTAC) was selected as the functional monomer and the saturated adsorption capacity of the prepared IIC and NIC were 55.0 mg/g and 29.4 mg/g, and with high imprinting factor of 1.87. Additionally, the prepared IIC showed admirable reusability and high selectivity, and the recovery was in the range 81.2-97.9% with RSD range of 1.9-4.3%, which was similar to the value obtained by hydride generation atomic absorption spectrometry. IIC can be used as solid material for colorimetric detection at the ultraviolet wavelength of 858 nm without color interference of material matrix, in the range 5-200 μg/L (R² = 0.990) with a detection limit of 0.970 µg/L. Obviously, this synthetic strategy provides a simple, efficient, and green method for the preparation of water-compatible ion-imprinted polymers providing selective separation and detection of trace As(V) in real complex samples.

Graphene-Based Adsorbents for Arsenic, Fluoride, and Chromium Adsorption: Synthesis Methods Review

Water contamination around the world is an increasing problem due to the presence of contaminants such as arsenic, fluoride, and chromium. The presence of such contaminants is related to either natural or anthropogenic processes. The above-mentioned problem has motivated the search for strategies to explore and develop technologies to remove these contaminants in water. Adsorption is a common process employed for such proposals due to its versatility, high adsorption capacity, and lower cost. In particular, graphene oxide is a material that is of special interest due to its physical and chemical properties such as surface area, porosity, pore size as well as removal efficiency for several contaminants. This review shows the advances, development, and perspectives of materials based on GO employed for the adsorption of contaminants such as arsenite, arsenate, fluoride, and hexavalent chromium. We provided a detailed discussion of the synthesis techniques and their relationship with the adsorption capacities and other physical properties as well as pH ranges employed to remove the contaminants. It is concluded that the adsorption capacity is not proportional to the surface area in all the cases; instead, the synthesis method, as well as the functional groups, play an important role. In particular, the sol-gel synthesis method shows better adsorption capacities.

Carbon-based adsorbents as proficient tools for the removal of heavy metals from aqueous solution: A state of art-review emphasizing recent progress and prospects

Carbon-centric adsorbents (CCA) are diverse forms, from simple biochar (BC) to graphene derivatives, carbon nanotubes (CNTs), and activated carbon (AC), which have been vastly explored for their removal of a plethora of pollutants, including heavy metals (HM). The prominent features of CCA are their operational attributes like extensive surface area, the occurrence of flexible surface functional groups, etc. This work offers a comprehensive examination of contemporary research on CCA for their superior metal removal aptitude and performances in simulated solutions and wastewater flows; via portraying the recent research advances as an outlook on the appliances of CACs for heavy metal adsorption for removal via distinct forms like AC, BC, Graphene oxide (GO), and CNTs. The bibliometric analysis tool was employed to highlight the number of documents, country-wise contribution, and co-occurrence mapping based on the Scopus database. The coverage of research works in this review is limited to the last 5 years (2017-2021) to highlight recent progress and prospects in using CCAs such as AC, BC, GO, and CNTs to remove HM from aqueous media, which makes the review unique. Besides an overview of the common mechanisms of CACs, the future scope of CAC, especially towards HM mitigation, is also discussed in this review. This review endorses that further efforts should be commenced to enhance the repertory of CCAs that effectively eliminate multiple targeted metals in both simulated and real wastewater.

Characterization and Mechanistic Study of Heavy Metal Adsorption by Facile Synthesized Magnetic Xanthate-Modified Chitosan/Polyacrylic Acid Hydrogels

A simple method was used to synthesize magnetic xanthate-modified chitosan/polyacrylic acid hydrogels that were used to remove heavy metal ions from an aqueous solution. Xanthate modification of chitosan significantly improved adsorption performance: individual adsorption capacities of the hydrogel for Cu(II), Cd(II), Pb(II), and Co(II) ions were 206, 178, 168, and 140 mg g^-1, respectively. The magnetic hydrogels had good regeneration ability and were effectively separated from the solution by use of a magnet. Adsorption kinetic data showed that the removal mechanism of heavy metal ions from the solution by magnetic hydrogels occurs mainly by chemical adsorption. The equilibrium adsorption isotherms were well-described by the Freundlich and Langmuir equations. Positive values were found for the Gibbs standard free energy and enthalpy, indicating an increase in the disorder at the solid-liquid interface during adsorption. Magnetic xanthate-modified chitosan-based hydrogels that exhibit high adsorption efficiency, regeneration, and easy separation from a solution have broad development prospects in various industrial sewage and wastewater treatment fields.

Ionic liquid based composites: A versatile materials for remediation of aqueous environmental contaminants

Water pollution is one of the most aggravated problems threatening the sustainability of human race and other life forms due to the rapid pace of civilization and industrialization. A long history exists of release of hazardous pollutants into the water bodies due to selfish human activities since the Industrial Revolution, but no effort has been completely successful in curbing the activities that result in the degradation of our environment. These pollutants are harmful, carcinogenic and have adverse health effects to all forms of life. Thus, remarkable efforts have been geared up to obtain clean water by exploiting science and technology. The application of Ionic liquids (ILs) as sustainable materials have received widespread attention since the last decade. Their interesting properties, simplicity in operation and satisfactory binding capacities in elimination of the contaminants makes them a valuable prospect to be utilized in wastewater treatment. Immobilizing and grafting the solid supports with ILs have fetched efficient results to exploit their potential in the adsorptive removal processes. This review provides an understanding of the recent developments and outlines the possible utility of IL based nano adsorbents in the removal of organic compounds, dyes and heavy metal ions from aqueous medium. Effect of several parameters such as sorbent dosage, pH and temperature on the removal efficiency has also been discussed. Moreover, the adsorption isotherms, thermodynamics and mechanism are comprehensively studied. It is envisioned that the literature gathered in this article will guide the budding scientists to put their interest in this area of research in the days to come.

Recent Advances in Ionic Liquids and Ionic Liquid-Functionalized Graphene: Catalytic Application and Environmental Remediation

Applications of ionic liquids (ILs) for the modification physicochemical properties of porous materials have been extensively studied with respect to various applications based on the understanding and development of properties of ILs. In this review, IL–graphene composites are discussed and provided a perspective of composites of IL. IL has been used as a medium to improve the dispersibility of graphene, and the resulting composite material shows excellent performance in gas separation and catalysis during environmental treatment. The applications of ILs and IL–functionalized graphene are discussed in detail with the actual environmental issues, and the main challenges and opportunities for possible future applications are summarized.

Recent advances of carbon-based nano zero valent iron for heavy metals remediation in soil and water: A critical review

Heavy metal pollution in soil and water has presented a new challenge for the environmental remediation technology. Nano zero valent iron (nZVI) has excellent adsorbent properties for heavy metals, and thus, exhibits great potential in environmental remediation. Used as supporting materials for nZVI, carbon-based materials, such as activated carbon (AC), biochar (BC), carbon nanotubes (CNTs), and graphene (GNs) with aromatic rings formed by carbon atoms as the skeleton, have a large specific surface area and porous structure. This paper provides a comprehensive review on the advancement of carbon-based nano zero valent iron (C-nZVI) particles for heavy metal remediation in soil and water. First, different types of carbon-based materials and their combination with nZVI, as well as the synthesis methods and common characterization techniques of C-nZVI, are reviewed. Second, the mechanisms for the interactions between contaminants and C-nZVI, including adsorption, reduction, and oxidation reactions are detailed. Third, the environmental factors affecting the remediation efficiency, such as pH, coexisting constituents, oxygen, contact time, and temperature, are highlighted. Finally, perspectives on the challenges for utilization of C-nZVI in the actual contaminated soil and water and on the long-term efficacy and safety evaluation of C-nZVI have been proposed for further development.

Dispersive solid phase extraction based on reduced graphene oxide modified Fe3O4 nanocomposite for trace determination of parabens in rock, soil, moss, seaweed, feces, and water samples from Horseshoe and Faure Islands

This study reports an efficient, green, sensitive and simple analytical protocol for trace determination of methyl paraben, ethyl paraben, propyl paraben, butylparaben and benzyl paraben by high-performance liquid chromatography-ultraviolet detection (HPLC-UV). The analytes were preconcentrated using an ultrasonication supported (US) dispersive solid phase extraction (DSPE) method based on reduced graphene oxide (rGO) modified iron nanoparticles (US-Fe₃O₄@rGO-DSPE). A reversed-phase C18 column and an isocratic elution program comprising of 20 mM phosphate buffer (pH 4.50) and acetonitrile(58:42, v/v) were used to elute and separate the analytes for detection. The limits of detection determined for the analytes were very low and were in the range of 0.02 - 0.16 ng mL^-1. The coefficients of determination obtained for the analytes ranged from 0.9973 to 0.9998, and this validated good linearity of the method.Percent relative standard deviations obtained in the range of 2.5 - 10.6% verified the method's high intraday repeatability. Accuracy of the proposed method was assessed with spiking experiments performed on complex sample matrices. Percent recoveries calculated for spiked soil, artificial seawater and seaweed samples were in acceptable ranges of 95 - 121%, 87 - 117% and 85 - 111%, respectively. These figures of merit suggest that HPLC-UV coupled with the US-Fe₃O₄@rGO-DSPEmethod is suitable for the determination of parabens in Antarctic samples.

Magnetic dispersive solid phase extraction based on carbonized cellulose-ferromagnetic nanocomposite for screening phthalate esters in aqueous samples

In this work, a sorbent of the carbonized cellulose-ferromagnetic nanocomposite has been proposed for the magnetic dispersive solid phase extraction of some plasticizers in aqueous samples. Carbonized cellulose nanoparticles were prepared by treatment of cellulose filter paper with concentrated sulfuric acid and then loaded on Fe₃O₄ nanoparticles using coprecipitation. This sorbent is compatible with aqueous samples and can be considered as a viable sorbent for extraction of plasticizers from aqueous samples. In this study, magnetic dispersive solid phase extraction is followed by a dispersive liquid-liquid microextraction method. This combination makes the proposed approach as an efficient clean-up method with high enrichment factors for the selected analytes. The enriched analytes are monitored by gas chromatography equipped with a flame ionization detector. Parameters affecting the method efficiency were investigated in details. Under the optimized extraction conditions, limits of detection could reach up to of 0.15-0.50 µg L^-1. The satisfactory enrichment factors of 286-403 were obtained, and the extraction recoveries were found to be in the range of 57-80%. Relative standard deviations were in the range of 3-7% for intra-day and inter-day precisions for six replicate extractions at 25 µg L^-1 of each plasticizer. Calibration curves were linear in wide ranges with coefficients of determination ≥ 0.995. Eventually, efficiency of the prepared sorbent was confirmed by the extraction of some plasticizers from real samples including fruit juices, mineral water, injection solution, cola, and yoghourt drink packed in plastic containers.

Multi-templates surface molecularly imprinted polymer for simultaneous and rapid determination of sulfonamides and quinolones in water: effect of carbon-carbon double bond

In this work, the effect of a carrier modified with a carbon-carbon double bond (C=C) on preparing multi-templates surface molecularly imprinted polymer MIP (C=C@MIP) for simultaneous detection of sulfonamides and quinolones was investigated. The results showed that the adsorption capacities of the C=C@MIP were obviously higher than those of MIP, which is the carrier without modified C=C, suggesting that C=C played a key role in preparing MIP with higher adsorption capacities. Then, C=C@MIP was used as adsorbents for solid-phase extraction (SPE) and coupled with high-performance liquid chromatography (HPLC) for the simultaneous determination of sulfonamides and quinolones in water. The method showed excellent applicability, with the adsorption capacities of 19.92, 16.38, 12.92, 18.37, 14.49, 12.01, 16.98, 23.33, and 14.29 mg/g for SDZ, STZ, SMZ, SMX, SDM, ENRO, OFL, LOME, and GATI, respectively. The spiked recoveries and relative standard deviations (RSDs) of sulfonamides and quinolones using C=C@MIP were 81.59-100.7 % and 3.75-7.37 %, respectively. The limits of detection (LODs) for SDZ, STZ, SMZ, SMX, SDM, ENRO, OFL, LOME, and GATI were 0.013, 0.012, 0.012, 0.013, 0.014, 0.012, 0.013, 0.015, and 0.015 μg/L, respectively.

Synthesis of 3D graphene-based materials and their applications for removing dyes and heavy metals

Contamination of water streams by dyes and heavy metals has become a major problem due to their persistence, accumulation, and toxicity. Therefore, it is essential to eliminate and/or reduce these contaminants before discharge into the natural environment. In recent years, 3D graphene has drawn intense research interests owing to its large surface area, superior charge conductivity, and thermal conductivity properties. Due to their unique surface and structural properties, 3D graphene-based materials (3D GBMs) are regarded as ideal adsorbents for decontamination and show great potential in wastewater or exhaust gas treatment. Here, this minireview summarizes the recent progress on 3D GBMs synthesis and their applications for adsorbing dyes and heavy metals from wastewater based on the structures and properties of 3D GBMs, which provides valuable insights into 3D GBMs' application in the environmental field.

Comprehensive evaluation of ionic liquid [Bmim][PF6] for absorbing toluene and acetone

Absorption is an eminent technology for volatile organic compounds (VOCs) elimination with the merits of high efficiency and low cost. Absorbent plays a critical role in the absorption process, and the thermal stability, saturation capacity, and regeneration performance should be concerned. As a kind of green and eco-friendly solvent, ionic liquid (IL) is expected to be a substitute for the conventional VOCs absorbent. In this study, 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF₆]) is employed to absorb the modeling VOCs (toluene and acetone). Moreover, the used [Bmim][PF₆] is recovered by thermal distillation and the reusability is then conducted by consecutive batch experiments. Based on that, the thermal stability of [Bmim][PF₆] is comprehensively examined, in which the kinetic and thermodynamic parameters are also calculated. Results reveal that [Bmim][PF₆] owned promising toluene absorption performance with inlet concentration of 3000 mg/m³ and flow rate of 300 mL/min at 20 °C, it possesses the saturated adsorption capacity of 5.16 mg/g. [Bmim][PF₆] also shows satisfying thermal stability up to 610 K. In addition, thermal distillation is proved to be a reliable regeneration route on account of the recovered [Bmim][PF₆] remained satisfying capacity even after five cycles.

Investigation of the combined use of capping and oxidizing agents in the immobilization of arsenic in sediments

The combined use of capping (lanthanum modified bentonite; LMB) and oxidizing (calcium nitrate; CN) agents was investigated to immobilize arsenic (As) in sediments. The vertical changes in labile As and dissolved As were measured using diffusive gradients in thin films (DGT) and Rhizon devices. The results showed that the combined application of LMB and CN had the optimal effect on the immobilization of both DGT-labile As and dissolved As, compared to single treatments using LMB or CN. After 60 days of incubation, the maximum reduction efficiencies of DGT-labile As at sediment depths were 76.4%, 70.8%, and 44.9% of those treated with LMB + CN, CN, and LMB, respectively. After 32 days of incubation, the average concentrations of dissolved total As throughout the depths decreased from 7.71 μg/L after the control treatment without any amendments to 5.25, 4.03, and 3.15 μg/L after the addition of LMB, CN, and LMB + CN, respectively. The larger part of exchangeable As at sediment depths was converted into the reducible As mainly bound Fe/Mn oxide-hydroxides after combining LMB and CN. Due to the As(III) existing mainly in the form of electrically neutral H₃AsO₃ in sediments, it is hard to adsorb As(III) for the LMB and iron/manganese oxide-hydroxides formed by the oxidation effect of calcium nitrate. Thus, the single or combined LMB and CN use had much weaker effect on the immobilization of As(III) compared with As(V). The results of current study indicated that the combined use of LMB and CN could be a promising method to control the potential release of As from the sediment to the overlying water. However, this method needs further improvement to achieve a better immobilization effect on As(III) in sediments.

Strategies to improve the adsorption properties of graphene-based adsorbent towards heavy metal ions and their compound pollutants: A review

Heavy metal-containing wastewater can be treated by adsorption technology to obtain ultra-low concentration or high-quality treated effluent. Due to the constraints of the specific surface area, surface electrical structure and spatial effect of conventional adsorbents, it is often difficult to obtain adsorbents within high adsorption capacity. Graphene has characteristics of large specific surface area, small particle size, and high adsorption efficiency. It is considered as one of the research hotspots in recent years. However, despite graphene's unique properties, graphene-based adsorbents still have some drawbacks, i.e. graphene nanosheets are easier to be stacked with each other via π-π stacking and van der Waals interactions, which affect the site exposure, impede the rapid mass transport and limit its adsorption performance. Special strategy is needed to overcome its drawbacks. This work summarizes recent literatures on utilization of three strategies-surface functionalization regulation, morphology and structure control and material composite, to improve the adsorption properties of graphene-based adsorbent towards heavy metal removal. A brief summary, perspective on strategies to improving adsorption properties of graphene-based materials for heavy metal adsorption are also presented. Certainly, this review will be useful for designing and manufacturing of graphene-based nanomaterials for water treatment.

Accumulation, transformation and subcellular distribution of arsenite associated with five carbon nanomaterials in freshwater zebrafish specific-tissues

Although carbon nanomaterials (CNMs) commonly exist throughout the aquatic environment, their effect on arsenic (As) distribution and toxicity is unclear. In this study, arsenite accumulation, transformation, subcellular distribution, and enzyme activity were assessed in adult zebrafish (Danio rerio) intestines, heads and muscles, following co-exposure to arsenite and CNMs with different structures (single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), fullerene (C₆₀), graphene oxide (GO), and graphene (GN)). Results show that GN and GO promoted As toxicity in D. rerio, as carriers increasing total As accumulation in the intestine, resulting in arsenite adsorbed by GO and GN being released and transformed mainly into moderately-toxic monomethylarsonic acid (MMA), which was mostly distributed in organelles and metallothionein-like proteins (MTLPs). Moreover, GO and GN influenced As species distribution in D. rerio due to the excellent electron transfer ability. However, the effect was marginal for SWCNT, MWCNT and C₆₀, because of the different structure and suspension stability in fish-culture water. In addition, in the muscle and head tissues, As was mainly distributed in cellular debris in the forms of dimethylarsinic acid (DMA) and arsenobetaine (AsB). These findings help better understand the influence of CNMs on the mechanism of As toxicity in natural aquatic environments.

Highly selective removal and recovery of Ni(II) from aqueous solution using magnetic ion-imprinted chitosan nanoparticles

Nickel (Ni) is one of the most common heavy metals. In this study, nano-sized magnetic ion-imprinted polymers (MIIPs) were synthesized using chitosan as the functional monomer, and used for selective adsorption and recovery of Ni(II) from solutions. The results showed MIIPs possessed high sorption selectivity for Ni(II), and the change in pH (5.0-9.0) exerted insignificant influence on the ion adsorption, allowing almost complete elution and recovery of adsorbed Ni(II) ions by using 0.5% EDTA-Na solution. Moreover, the sorption capacity of the recycled MIIPs decreased by only about 10% after 15 adsorption-desorption cycles. The time required for establishing the adsorption equilibrium was less than 1 h. The sorption process was predominant and endothermic, and could be well described by both Langmuir isotherm model and pseudo-second-order kinetic model. Therefore, the synthesized MIIPs was a suitable adsorbent for highly selective, fast and efficient removal and recovery of low-concentration Ni(II) ions from wastewaters.

Highly efficient and ultrafast removal of Cr(VI)in aqueous solution to ppb level by poly(allylamine hydrochloride) covalently cross-linked amino-modified graphene oxide

We herein report a facile strategy to prepare poly(allylamine hydrochloride) cross-linked amino-modified graphene oxide (PAH-ASGO) by Schiff-base reactions. The resulting PAH-ASGO exhibited a maximum adsorption capacity of 373.1 mg/g for Cr(VI), which was nearly 9 times higher than that of pure graphene oxide, exceeding that of most GO-based materials previously reported. More significantly, PAH-ASGO can effectively diminish the Cr(VI) concentration from 9.9 mg/L to the extremely low level of 0.004 mg/L within 10 s, far below the maximum allowable level of Cr(VI) (0.05 mg/L) in drinking water. In addition, the adsorbents still displayed excellent removal efficiency of 91.8% after 10 cycles. Considering the broad diversity, we developed also a magnetic PAH-ASGO/Fe₃O₄ adsorbent by a simple cross-linking reaction to achieve rapid separation of PAH-ASGO from their aqueous solution. Finally, the PAH-ASGO was successfully utilized to treat the actual industrial effluent.

Ti (IV) modified vinyl phosphate magnetic nanoparticles for simultaneous preconcentration of multiple arsenic species from chicken samples followed by HPLC-ICP-MS analysis

Ti (IV)-modified vinyl phosphate magnetic nanoparticles (Fe₃ O₄ @SiO₂ @KH570-PO₄ -Ti (IV)) was prepared for simultaneous extraction of multiple arsenic species, followed by high performance liquid chromatography (HPLC)- inductively coupled plasma mass spectrometry (ICP-MS) analysis. Inorganic arsenic (iAs), dimethyl arsenic acid (DMA), monomethyl arsenic acid (MMA), p-amino phenyl arsenic acid (p-ASA), 4-hdroxyphenylarsenic acid (4-OH), phenyl arsenic acid (PAA), and 3-nitro-4-hydroxyphenylarsenic acid (ROX) were investigated as interest analytes. It was found that they were quantitatively adsorbed on Fe₃ O₄ @SiO₂ @KH570-PO₄ -Ti (IV) at pH 5, and desorbed completely with 0.1 mol/L sodium hydroxide solution. Enrichment factor of 100-fold was obtained by consuming 100 mL sample solution. Under the optimal conditions, the method combining MSPE with HPLC-ICP-MS presented a linear range of 1-5000 ng/L for seven arsenic species. The limits of detection were 0.39, 0.60, 0.23, 1.85, 0.54, 0.48, and 0.84 ng/L for DMA, MMA, p-ASA, iAs, 4-OH, PAA, ROX, with the relative standard deviations (c = 10 ng/L, n = 7) of 3.6, 3.9, 5.5, 12.4, 6.1, 5.8, 5.0, respectively. The accuracy of the method was validated by analyzing BCR 627 Tuna fish. The application potential of the method was further evaluated by chicken muscle and liver samples. No target arsenic species were detected in these samples, and good recoveries (80.6-123%) were obtained for the spiked samples at low, medium, and high concentration levels.

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.

Adsorption Separation of Cr(VI) from a Water Phase Using Multiwalled Carbon Nanotube-Immobilized Ionic Liquids

Three types of multiwalled carbon nanotubes (MWCNTs, MWCNTs-OH, and MWCNTs-COOH) were used as carriers and five types of ionic liquids (ILs) were immobilized on each carrier by an impregnation method. Boehm titration, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, specific surface area analysis by the Brunauer-Emmett-Teller method, and thermogravimetric analysis were performed to investigate [C4mim]HSO₄ adsorption by the MWCNTs. The MWCNT-immobilized IL was used for Cr(VI) removal from a water phase. The adsorption properties of MWCNTs-COOH-immobilized [C4mim]HSO₄ were investigated by single-factor analysis. The results showed that the Cr(VI) removal rate was 52.14% and the adsorption capacity was 31.29 mg/g. The optimum adsorption conditions were as follows: initial Cr(VI) concentration, 60 mg/L; adsorbent dosage, 50 mg; pH 2.0; adsorption temperature 40 °C; and adsorption time, 200 min. Adsorption isotherm data fitted the Freundlich model, which indicates that the adsorption process was in line with the multimolecular layer adsorption theory. The Cr(VI) adsorption behaviors of the three adsorbents were consistent with a pseudo-second-order dynamic model. Thermodynamic analysis of the reaction systems was also performed. The Cr(VI) removal rates of MWCNTs-3, MWCNTs-OH-3, and MWCNTs-COOH-3 were 27.97, 9.39, and 7.34% lower than the initial removal rates after five cycles.

One-dimensional graphene for efficient aqueous heavy metal adsorption: Rapid removal of arsenic and mercury ions by graphene oxide nanoribbons (GONRs)

There is a knowledge gap for the application of one-dimensional graphene in the adsorption process. Our hypothesis was based on the fact that graphene oxide nanoribbons (GONRs) as one-dimensional graphene with more desired edges and specific surface area than other carbonaceous nanomaterials have more oxygen containing functional groups (active sites) on their edges and basal planes and therefore are more capable in adsorption of pollutants. In this regard, we synthesized GONRs by unzipping of multi-walled carbon nanotubes (MWCNTs) and investigated the adsorption behavior of GONRs by ultrasonic-assisted adsorptive removal of As(V) and Hg(II) ions from aqueous solution. The obtained results showed that As(V) ions are more favorably adsorbed onto the GONRs than Hg(II) ions and with increasing initial As(V) and Hg(II) ions concentration to 300 ppm, the equilibrium adsorption uptake of the synthesized GONRs increases to 155.61 and 33.02 mg/g for As(V) and Hg(II) ions, respectively through a rapid separation process in just 12 min. Also, three kinetic models and Freundlich and Langmuir adsorption isotherms were applied to evaluate the obtained experimental results. Our findings highlight the potential application of GONRs as one-dimensional graphene adsorbent with more desired edges than MWCNTs and graphene oxide (GO) and high adsorption capacity for selective removal of heavy metals.

Adsorptive removal of heavy metal ions using graphene-based nanomaterials: Toxicity, roles of functional groups and mechanisms

The endless introduction of toxic heavy metals through industrialization has worsened the heavy metal pollution in the environment. Thus, the need for its effective removal has become more crucial than before. Studies on graphene-based nanomaterials and their use in removing heavy metals are gaining tremendous traction over the past decade. The properties of graphene oxide (GO), such as large surface areas, desired functional groups and excellent mechanical properties are advantageous. Nevertheless, due to its tendency to agglomerate and difficulty in phase separation after treatment, the functionalization of GO using various materials of different surface functional groups is an ongoing study. The surface modification of GO is done by using various materials to introduce heteroatoms, which have high affinity for heavy metals. This review summarizes the utilization of different surface functional groups, such as oxygen-containing, nitrogen-containing, and sulphur-containing functionalized graphene oxide composites in the adsorption of cationic and oxyanionic heavy metals. The toxicity of these heavy metals is also addressed. Furthermore, the interactions between adsorbents and heavy metals which are influenced by pH and surface functional groups, are also discussed in detail. This is followed by the review in adsorption isotherms and kinetics. Future research needs are also offered.

Effect of UV radiation on the structure of graphene oxide in water and its impact on cytotoxicity and As(III) adsorption

Graphene oxide (GO) is widely used in different applications, however once released into the environment it can change its structure and affect the transport of important contaminants such as arsenic. In this work we show that UV radiation, even in the range of 28-74 μW/cm² of irradiance up to 120 h of exposure, can induce important changes in the structure of graphene oxide, by eliminating -OH and CO functional groups. This reduction affected the stability of graphene oxide in water by decreasing its zeta potential from -41 to -37 mV at pH=7 with the increase of the exposure time. Our results showed that after 24 and 120 h of UV exposure, As(III) adsorption capacity decreased from 5 mg/g to 4.7 and 3.8 mg/g, respectively, suggesting a lower capacity to transport contaminants with time. Computer modelling showed that even a degraded GO structure can have an interaction energy of 223.84 kJ/mol with H₃AsO_3. Furthermore, we observed that the cytotoxicity of graphene oxide changed after being irradiated at 74 μW/cm² for 120 h, showing 20% more cell viability compared to as-produced GO. Our results stress the importance of considering the microstructural and compositional changes that GO undergoes even under low irradiance and short periods, when studying its fate and behavior in the environment and possible applications in water treatment.

Comparative Study on the Regeneration of Fe3O4@Graphene Oxide Composites

In this study, two kinds of composites with the structure of graphene oxide (GO) sheets wrapped magnetic nanoparticles were investigated on their regeneration. The composites have a similar core-shell structure, but the interactions between the core and shell are quite different, which are electrostatic and covalent. They were characterized by scanning/transmission electron microscopy, power X-ray diffraction, and vibrating sample magnetometer analysis. Their morphologies and structures of the samples had been revealed using methylene blue and Pb(II) as adsorbates during regeneration. The results showed that the composites with covalent bonding interaction could maintain a stable core-shell structure and present a good regeneration performance for adsorption-desorption of methylene blue and Pb(II). The composites with electrostatic interaction could approximately preserve its core-shell structure and could be recyclable for adsorption-desorption of methylene blue, however, they would disintegrate its core-shell structure during adsorption/desorption of Pb(II), thus greatly decreasing their regeneration performance. The regeneration mechanisms of the composites were analyzed, which could provide a useful theoretical guide to design the GO sheets wrapped magnetic nanoparticles composites.