Removal of Trace Arsenic to Meet Drinking Water Standards Using Iron Oxide Coated Multiwall Carbon Nanotubes

Magnetic nanocomposite adsorbents for abatement of arsenic species from water and wastewater

The presence of high concentrations of arsenic species in drinking water and other water bodies has become one of the most critical environmental concerns. Therefore, decontamination of arsenic-containing water is essential for improved health and environmental concern. In recent years, nano-adsorbents have been widely used for the adsorptive removal of arsenic from water. Separating existing nano-adsorbents from treated waters, on the other hand, is a critical issue for their potential applications in natural water treatment. To address these issues and to effectively remove arsenic from water, researchers looked at iron oxide-based magnetic nanocomposite adsorbents. The magnetic nanoadsorbents have the benefit of surface functionalization, making it easier to target a specific pollutant for adsorption, and magnetic separation. In addition, magnetic nanoparticles have a large surface area, high chemical inertness, superparamagnetic, high magnetic susceptibility, small particle size, and large specific surface area, and are especially easily separated in a magnetic field. Magnetic nano-adsorbents have been discovered to have a lot of potential for eliminating arsenic from water. The recent advances in magnetic nano-absorbents for the cleanup of arsenic species from water are summarized in this paper. Future perspectives and directions were also discussed in this article. This will help budding researchers for the further advancement of magnetic nanocomposites for the treatment of water and wastewater contaminated with arsenic.

Synergistically Improved Catalytic Ozonation Process Using Iron-Loaded Activated Carbons for the Removal of Arsenic in Drinking Water

This research attempts to find a new approach for the removal of arsenic (As) from drinking water by developing a novel solution. To the author’s knowledge, iron-loaded activated carbons (Fe-AC) have not been previously applied for the removal of As in a synergistic process using ozonation and catalytic ozonation processes. The As was investigated using drinking water samples in different areas of Lahore, Pakistan, and the As removal was compared with and without using catalysts. The results also suggested that the catalytic ozonation process significantly removes As as compared with single ozonation and adsorption processes. Moreover, a feed ozone of 1.0 mg/min and catalyst dose of 10 g was found to maintain a maximum removal efficiency of 98.6% within 30 min. The results of the catalyst dose–effect suggested that the removal of As tends to increase with the increase in catalysts amount. Hence, it is concluded that the Fe-AC/O3 process efficiently removes As in water. Moreover, it was established that the Fe-AC/O3 process might be regarded as an effective method for removing As from drinking water compared to the single ozonation and adsorption processes.

Development and Characterization of Silver-Doped Multi-Walled Carbon Nanotube Membranes for Water Purification Applications

A unique approach was utilized to develop multi-walled carbon nanotube (MWCNT) silver (Ag) membranes. MWCNTs were impregnated with 1 wt% Ag loading, which resulted in a homogeneous dispersion of Ag in MWCNTs. MWCNTs impregnated with Ag were then uniaxially compacted at two different pressures of 80 MPa and 120 MPa to form a compact membrane. Compacted membranes were then sintered at two different temperatures of 800 °C and 900 °C to bind Ag particles with MWCNTs as Ag particles also act as a welding agent for CNTs. The powder mixture was characterized by FESEM, thermogravimetric analysis, and XRD, while the developed samples were characterized by calculating the porosity of membrane samples, contact angle, water flux and a diametral compression test. The developed membranes showed overall large water flux, while maximum porosity was found to decrease as the compaction load and sintering temperature increased. The mechanical strength of the membranes was found to increase as the compaction load increased. The hydrophilicity of the membranes remained unchanged after the addition of Ag particles. The developed membranes would be useful for removing a variety of contaminants from water.

Heavy metal removal by biomass-derived carbon nanotubes as a greener environmental remediation: A comprehensive review

The concentrations of heavy metal ions found in waterways near industrial zones are often exceed the prescribed limits, posing a continued danger to the environment and public health. Therefore, greater attention has been devoted into finding the efficient solutions for adsorbing heavy metal ions. This review paper focuses on the synthesis of carbon nanotubes (CNTs) from biomass and their application in the removal of heavy metals from aqueous solutions. Techniques to produce CNTs, benefits of modification with various functional groups to enhance sorption uptake, effects of operating parameters, and adsorption mechanisms are reviewed. Adsorption occurs via physical adsorption, electrostatic interaction, surface complexation, and interaction between functional groups and heavy metal ions. Moreover, factors such as pH level, CNTs dosage, duration, temperature, ionic strength, and surface property of adsorbents have been identified as the common factors influencing the adsorption of heavy metals. The oxygenated functional groups initially present on the surface of the modified CNTs are responsible towards the adsorption enhancement of commonly-encountered heavy metals such as Pb²⁺, Cu²⁺, Cd²⁺, Co²⁺, Zn²⁺, Ni²⁺, Hg²⁺, and Cr⁶⁺. Despite the recent advances in the application of CNTs in environmental clean-up and pollution treatment have been demonstrated, major obstacles of CNTs such as high synthesis cost, the agglomeration in the post-treated solutions and the secondary pollution from chemicals in the surface modification, should be critically addressed in the future studies for successful large-scale applications of CNTs.

Engineered Magnetic Carbon-Based Adsorbents for the Removal of Water Priority Pollutants: An Overview

This review covers the preparation, characterization, and application of magnetic adsorbents obtained from carbon-based sources and their application in the adsorption of both inorganic and organic pollutants from water. Different preparation routes to obtain magnetic adsorbents from activated carbon, biochar, hydrochar, graphene, carbon dots, carbon nanotubes, and carbon nanocages, including the magnetic phase incorporated on the solid surface, are described and discussed. The performance of these adsorbents is analyzed for the removal of fluoride, arsenic, heavy metals, dyes, pesticides, pharmaceuticals, and other emerging and relevant water pollutants. Properties of these adsorbents and the corresponding adsorption mechanisms have been included in this review. Overall, this type of magnetic adsorbents offers an alternative for facing the operational problems associated to adsorption process in water treatment. However, some gaps have been identified in the proper physicochemical characterization of these adsorbents, the development of green and low-cost preparation methods for their industrial production and commercialization, the regeneration and final disposal of spent adsorbents, and their application in the multicomponent adsorption of water pollutants.

Functionalized Carbon Nanotubes (CNTs) for Water and Wastewater Treatment: Preparation to Application

As the world human population and industrialization keep growing, the water availability issue has forced scientists, engineers, and legislators of water supply industries to better manage water resources. Pollutant removals from wastewaters are crucial to ensure qualities of available water resources (including natural water bodies or reclaimed waters). Diverse techniques have been developed to deal with water quality concerns. Carbon based nanomaterials, especially carbon nanotubes (CNTs) with their high specific surface area and associated adsorption sites, have drawn a special focus in environmental applications, especially water and wastewater treatment. This critical review summarizes recent developments and adsorption behaviors of CNTs used to remove organics or heavy metal ions from contaminated waters via adsorption and inactivation of biological species associated with CNTs. Foci include CNTs synthesis, purification, and surface modifications or functionalization, followed by their characterization methods and the effect of water chemistry on adsorption capacities and removal mechanisms. Functionalized CNTs have been proven to be promising nanomaterials for the decontamination of waters due to their high adsorption capacity. However, most of the functional CNT applications are limited to lab-scale experiments only. Feasibility of their large-scale/industrial applications with cost-effective ways of synthesis and assessments of their toxicity with better simulating adsorption mechanisms still need to be studied.

Fe3O4-Functionalized Boron Nitride Nanosheets as Novel Adsorbents for Removal of Arsenic(III) from Contaminated Water

We report the application of Fe3O4-functionalized boron nitride nanosheets (BNNS-Fe3O4 nanocomposite) for the remediation of As(III) ions from contaminated water. The specific surface area of the nanocomposite has been found as 179.5 m2 g-1. Due to its superparamagnetic nature at room temperature, the nanocomposite can be easily isolated from the solution under an external magnetic field. For As(III) ions, the maximum adsorption capacity of the nanocomposite is obtained as 30.3 mg g-1, which is approximately 4 times more than that of the bare BNNSs (8.5 mg g-1). The results from density functional theory calculations are also in close agreement with experimental findings and show that As(OH)3 binds more (∼4 times) efficiently to the BNNS-Fe3O4 nanocomposite than the bare BNNSs, implying a 4 times higher adsorption capacity of the nanocomposite. Especially, it is found that the synthesized nanocomposite could lessen the concentration of As(III) ions from 134 to 2.67 ppb in a solution at 25 °C. On increasing the temperature to 35 °C, the level of As(III) ions could be reduced from 556 to 10.29 ppb, which is close to the limit prescribed by the World Health Organization. The adsorbent was easily separable and showed regeneration properties. These outcomes depict the prospect of using BNNS-Fe3O4 nanocomposites as commercial adsorbents for the removal of As(III) ions from contaminated water.

Three-dimensional, printed water-filtration system for economical, on-site arsenic removal

The threat of arsenic contamination to public health, particularly in developing countries, has become a serious problem. Millions of people in their daily lives are still highly dependent on groundwater containing high levels of arsenic, which causes excessive exposure to this toxic element, due to the high cost and lack of water-treatment infrastructures. Therefore, a technique for large-scale treatment of water in rural areas to remove arsenic is needed and should be low-cost, be easily customized, and not rely on electrical power. In this study, in an effort to fulfill those requirements, we introduce a three-dimensional (3D), printed water-filtration system for arsenic removal. Three-dimensional printing can provide a compact, customized filtration system that can fulfill the above-mentioned requirements and that can be made from plastic materials, which are abundant. Armed with the versatility of 3D printing, we were able to design the internal surface areas of filters, after which we modified the surfaces of the 3D, printed filters by using iron (III) oxide as an adsorbent for arsenite. We investigated the effects of the controlled surface area on the flow rate and the deposition of the adsorbent, which are directly related to the adsorption of arsenic. We conducted isotherm studies to quantify the adsorption of arsenic on our 3D, printed filtration system.

Synthesis and characterization of a novel magnetic calcium-rich nanocomposite and its remediation behaviour for As(III) and Pb(II) co-contamination in aqueous systems

Herein, a novel magnetic calcium-rich biochar (MCRB), prepared by loading Fe₃O₄ nanoparticles (Fe₃O₄ NPs) on crab shell-derived biochar, was studied for remediation of arsenic and lead co-contamination. Characteristics of the MCRB demonstrated that Fe₃O₄ NPs adhered on the biochar matrix uniformly. Batch experiments on the effects of pH, contact time and initial concentrations revealed that for both metals, removal by the MCRB was pH-dependent with an optimal pH of 6, and that the MCRB had a strong ability for removing arsenic and lead with maximum removal capacities of 15.8 and 62.4 mg g^-1, respectively. The mechanisms of the simultaneous removal of arsenic and lead involved both competitive and synergistic effects. The As(III) addition enhanced Pb(II) removal by 5.4-18.8%, while the presence of Pb(II) suppressed As(III) removal by 5.8-17.8%. Competitive complexation of the two metals with biochar was responsible for the suppression, while the enhancement was due mainly to the formation of the Pb(II)-As(III)-FeO ternary surface complex with As(III) as the bridging molecule. These new insights can further our understanding of the application of MCRB as a potential material for use in the treatment of arsenic and lead co-contamination.

Critical review of magnetic biosorbents: Their preparation, application, and regeneration for wastewater treatment

The utilisation of magnetic biosorbents (metal or metal nanoparticles impregnated onto biosorbents) has attracted increasing research attention due to their manipulable active sites, specific surface area, pore volume, pore size distribution, easy separation, and reusability that are suitable for remediation of heavy metal(loid)s and organic contaminants. The properties of magnetic biosorbents (MB) depend on the raw biomass, properties of metal nanoparticles, modification/synthesis methods, and process parameters which influence the performance of removal efficiency of organic and inorganic contaminants. There is a lack of information regarding the development of tailored materials for particular contaminants and the influence of specific characteristics. This review focuses on the synthesis/modification methods, application, and recycling of magnetic biosorbents. In particular, the mechanisms and the effect of sorbents properties on the adsorption capacity. Ion exchanges, electrostatic interaction, precipitation, and complexation are the dominant sorption mechanisms for ionic contaminants whereas hydrophobic interaction, interparticle diffusion, partition, and hydrogen bonding are the dominant adsorption mechanisms for removal of organic contaminants by magnetic biosorbents. In generally, low pyrolysis temperatures are suitable for ionic contaminants separation, whereas high pyrolysis temperatures are suitable for organic contaminants removal. Additionally, magnetic properties of the biosorbents are positively correlated with the pyrolysis temperatures. Metal-based functional groups of MB can contribute to an ion exchange reaction which influences the adsorption capacity of ionic contaminants and catalytic degradation of non-persistent organic contaminants. Metal modified biosorbents can enhance adsorption capacity of anionic contaminants significantly as metal nanoparticles are not occupying positively charged active sites of the biosorbents. Magnetic biosorbents are promising adsorbents in comparison with other adsorbents including commercially available activated carbon, and thermally and chemically modified biochar in terms of their removal capacity, rapid and easy magnetic separation which allow multiple reuse to minimize remediation cost of organic and inorganic contaminants from wastewater.

Adsorptive nanocomposite membranes for heavy metal remediation: Recent progresses and challenges

Heavy metal contamination in aqueous system has attracted global attention due to the toxicity and carcinogenicity effects towards living bodies. Among available removal techniques, adsorptive removal by nanosized materials such as metal oxide, metal organic frameworks, zeolite and carbon-based materials has attracted much attention due to the large active surface area, large number of functional groups, high chemical and thermal stability which led to outstanding adsorption performance. However, the usage of nanosized materials is restricted by the difficulty in separating the spent adsorbent from aqueous solution. The shift towards the use of adsorptive composite membrane for heavy metal ions removal has attracted much attention due to the synergistic properties of adsorption and filtration approaches in a same chamber. Thus, this review critically discusses the development of nanoadsorbents and adsorptive nanocomposite membranes for heavy metal removal over the last decade. The adsorption mechanism of heavy metal ions by the advanced nanoadsorbents is also discussed using kinetic and isotherm models. The challenges and future prospect of adsorptive membrane technology for heavy metal removal is presented at the end of this review.

Magnetite-Coated Boron Nitride Nanosheets for the Removal of Arsenic(V) from Water

It is widely known that the existence of arsenic (As) in water negatively affects humans and the environment. We report the synthesis, characterization, and application of boron nitride nanosheets (BNNSs) and Fe₃O₄-functionalized BNNS (BNNS-Fe₃O₄) nanocomposite for removal of As(V) ions from aqueous systems. The morphology, surface properties, and compositions of synthesized nanomaterials were examined using scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, surface area analysis, zero-point charge, and magnetic moment determination. The BNNS-Fe₃O₄ nanocomposites have a specific surface area of 119 m² g^-1 and a high saturation magnetization of 49.19 emu g^-1. Due to this strong magnetic property at room temperature, BNNS-Fe₃O₄ can be easily separated in solution by applying an external magnetic field. From the activation energies, it was found that the adsorption of As(V) ions on BNNSs and BNNS-Fe₃O₄ was due to physical and chemical adsorption, respectively. The maximum adsorption capacity of BNNS-Fe₃O₄ nanocomposite for As(V) ions has been found to be 26.3 mg g^-1, which is 5 times higher than that of unmodified BNNSs (5.3 mg g^-1). This closely matches density functional theory simulations, where it is found that binding energies between BNNS-Fe₃O₄ nanocomposite and As(OH)₅ are 5 times higher than those between BNNSs and As(OH)₅, implying 5 times higher adsorption capacity of BNNS-Fe₃O₄ nanocomposite than unmodified BNNSs. More importantly, it was observed that the synthesized BNNS-Fe₃O₄ nanocomposite could reduce As(V) ion concentration from 856 ppb in a solution to below 10 ppb (>98.83% removal), which is the permissible limit according to World Health Organization recommendations. Finally, the synthesized adsorbent showed both separation and regeneration properties. These findings demonstrate the potential of BNNS-Fe₃O₄ nanocomposite for commercial application in separation of As(V) ions from potable and waste water streams.

Challenges and opportunities in functional carbon nanotubes for membrane-based water treatment and desalination

Environmental applications of carbon nanotubes (CNTs) have grabbed worldwide attentions due to their excellent adsorption capacities and promising physical, chemical and mechanical properties. The functionalization of CNTs, which involves chemical/physical modification of pristine CNTs with different types of functional groups, improves the capabilities of CNT for desalination and/or removals of waterborne contaminants. This paper intends to provide a comprehensive review of functional CNT materials (f-CNT) and their existing and potential applications in membrane-based water treatment and desalination processes, with focuses on critical evaluation of advances, knowledge gaps and future research directions. CNT nanocomposite membranes have been studied at bench scale to efficiently remove a variety of waterborne contaminants and salts, while future improvement is under way with development in CNT functionalization techniques. The CNT-based membrane applications are found to possess a variety of advantages, including improve water permeability, high selectivity and antifouling capability. However, their applications at full scale are still limited by their high cost. Finally, we highlight that f-CNT membranes with promising removal efficiencies for respective contaminants be considered for commercialization and to achieve holistic performance for the purpose of water treatment and desalination.

Development of bark-based magnetic iron oxide particle (BMIOP), a bio-adsorbent for removal of arsenic (III) from water

Novel low-cost bark-based magnetic iron oxide particles (BMIOPs) were synthesized and investigated for the removal of As(III) in drinking water. The synthesized BMIOP had a saturation magnetization value of 38.62 emug^-1 which was found to be enough for the magnetic separation of exhausted BMIOP after As(III) adsorption. Parameters like agitation speed, adsorbent dosage, contact time, pH, temperature, and initial concentration were thoroughly investigated. Langmuir, Freundlich, and Dubinin-Radushkevich isotherms were used for the modeling of experiments and observed a maximum adsorption (19.61 mg g^-1) of As(III) by Langmuir isotherm. Kinetics of As(III) sorption were well correlated with the coefficients in pseudo-first-order than the pseudo-second-order rate equation. Thermodynamic parameter investigation revealed that As(III) sorption process is endothermic, feasible, and spontaneous. BMIOP emerged as less expensive adsorbent for the abatement of arsenic ion from the drinking water. BMIOP showed 13.58 mg g^-1 adsorption capacity when As(V) alone is present, while it is 9.43 and 7.04 mg g^-1 for As(V) and As(III), respectively, when present together in the water. Graphical Abstract ᅟ.

Remediation of As(III) and Cd(II) co-contamination and its mechanism in aqueous systems by a novel calcium-based magnetic biochar

A novel calcium-based magnetic biochar (Ca-MBC), made by pyrolyzing the mixture of rice straw, iron oxide (Fe₃O₄) and calcium carbonate (CaCO₃), was developed in this study for remediation of co-pollution of arsenic and cadmium. Characteristics of the material showed that Fe₃O₄ and CaCO₃ were adhered on the surface of biochar. The experiments on the effects of pH, adsorption kinetics and isotherm revealed that the Ca-MBC had a great ability to adsorb arsenic and cadmium within 0.5 h for cadmium and 12 h for arsenic with a maximum adsorption capacity of 6.34 and 10.07 mg g^-1, respectively, and that the adsorption of both metals was pH-dependent from 2 to 12 with an optimal pH of pH 5. The mechanism of co-adsorption of Cd(II) and As(III) included both competitive and synergistic effects. The presence of As(III) enhanced Cd(II) adsorption by 3-16% while Cd(II) addition suppressed As(III) adsorption by 15-33%. The synergistic effects on As(III) and Cd(II) adsorption had resulted from the electrostatic interaction and the formation of type B ternary surface complexes. These new insights provide valuable information for the application of Ca-MBC as a potential adsorbent in treatment of water contaminated with As(III) and Cd(II).

Dry reforming of methane over palladium-platinum on carbon nanotube catalyst

A dry reforming (DR) catalyst based on bimetallic Pd-Pt supported on carbon nanotubes is presented. The catalyst was prepared using a microwave-induced synthesis. It showed enhanced DR activity in the 773-923 K temperature range at 3 atm. Observed carbon balances between the reactant and product gases imply minimal carbon deposition. A global three-reaction (reversible) kinetic model-consisting of DR, reverse water gas shift, and CH₄ decomposition (MD)-adequately simulates the observed concentrations, product H₂/CO ratios, and reactant conversions. Analysis shows that, under the conditions of this study, the DR and MD reactions are net forward and far from equilibrium, while the RWGS is near equilibrium.

A review of functionalized carbon nanotubes and graphene for heavy metal adsorption from water: Preparation, application, and mechanism

Carbon-based nanomaterials, especially carbon nanotubes and graphene, have drawn wide attention in recent years as novel materials for environmental applications. Notably, the functionalized derivatives of carbon nanotubes and graphene with high surface area and adsorption sites are proposed to remove heavy metals via adsorption, addressing the pressing pollution of heavy metal. This critical revies assesses the recent development of various functionalized carbon nanotubes and graphene that are used to remove heavy metals from contaminated water, including the preparation and characterization methods of functionalized carbon nanotubes and graphene, their applications for heavy metal adsorption, effects of water chemistry on the adsorption capacity, and decontamination mechanism. Future research directions have also been proposed with the goal of further improving their adsorption performance, the feasibility of industrial applications, and better simulating adsorption mechanisms.

Designer carbon nanotubes for contaminant removal in water and wastewater: A critical review

The search for effective materials for environmental cleanup is a scientific and technological issue of paramount importance. Among various materials, carbon nanotubes (CNTs) possess unique physicochemical, electrical, and mechanical properties that make them suitable for potential applications as environmental adsorbents, sensors, membranes, and catalysts. Depending on the intended application and the chemical nature of the target contaminants, CNTs can be designed through specific functionalization or modification processes. Designer CNTs can remarkably enhance contaminant removal efficiency and facilitate nanomaterial recovery and regeneration. An increasing number of CNT-based materials have been used to treat diverse organic, inorganic, and biological contaminants. These success stories demonstrate their strong potential in practical applications, including wastewater purification and desalination. However, CNT-based technologies have not been broadly accepted for commercial use due to their prohibitive cost and the complex interactions of CNTs with other abiotic and biotic environmental components. This paper presents a critical review of the existing literature on the interaction of various contaminants with CNTs in water and soil environments. The preparation methods of various designer CNTs (surface functionalized and/or modified) and the functional relationships between their physicochemical characteristics and environmental uses are discussed. This review will also help to identify the research gaps that must be addressed for enhancing the commercial acceptance of CNTs in the environmental remediation industry.

Green synthesis and evaluation of an iron-based metal–organic framework MIL-88B for efficient decontamination of arsenate from water

A sustainable approach for the preparation of MIL-88B(Fe) was developed involving the use of a safer solvent and reduced energy input, exhibiting great performance as sorbent in water purification.

Effective aqueous arsenic removal using zero valent iron doped MWCNT synthesized by in situ CVD method using natural α-Fe2O3 as a precursor

This research presents an efficient system for removing aqua's arsenic based on in situ zero valent iron doping onto multiwall carbon nanotube (MWCNT) through MWCNT growth onto the natural α-Fe₂O₃ surface in chemical vapor deposition (CVD) reactor. The as-synthesized magnetic nanohybrid was characterized by XRD, VSM, FE-SEM and TEM techniques. The result of XRD analysis revealed that MWCNT has been successfully generated on the surface of zero valent iron. Moreover, the material showed good superparamagnetic characteristic to be employed as a magnetic adsorbent. The hematite, nanohybrid and its air oxidized form were used for removing aqueous arsenite and arsenate; however, non oxidized material exhibited greater efficiency for the analytes uptake. Equilibrium times were 60 and 90 min for arsenate and arsenite adsorption using nanohybrid and oxidized sorbent but the equilibrium time was 1320 min using hematite. The adsorption efficiencies of hematite and oxidized sorbent were 18, 74% and 26, 77% for arsenite and arsenate, respectively, at initial concentration of 10 mg L^-1. At this situation, the removal efficiencies were 96 and 98.5% for arsenite and arsenate adsorption using raw nanohybrid. Thermodynamic study was also performed and results indicated that arsenic adsorption onto nanohybrid and oxidized sorbent was spontaneous however hematite followed a nonspontaneous path for the arsenic removal.

Cr(VI) Adsorption to Magnetic Iron Oxide Nanoparticle-Multi-Walled Carbon Nanotube Adsorbents

  The aim of this study was to investigate the Cr(VI) adsorption to magnetic iron oxide(MIO) nanoparticle- multi-walled carbon nanotubes (MWCNTs) in aqueous solutions using batch experiments. Results show that the maximum adsorption capacity of Cr(VI) to MIO-MWCNTs was 11.256 mg/g. Kinetic model analysis demonstrates that the pseudo-second-order model and Elovich model are suitable for describing the kinetic data. Thermodynamic analysis indicates that Cr(VI) adsorption to MIO-MWCNTs decreased with increasing temperature from 5-60 °C, indicating the spontaneous and exothermic nature of the sorption process. Equilibrium isotherm analysis demonstrates that the Redlich-Peterson model suitably describes the equilibrium data. In the pH experiments, Cr(VI) adsorption to MIO-MWCNTs decreased gradually from 5.70-2.13 mg/g with increasing pH from 3.0-7.3. Sequential extraction indicates that, among the five binding forms of Cr(VI) associated with MIO-MWCNTs, the predominant contributions are the fraction bound to Fe-Mn oxides (57.82%) and the residual (23.38%).

Distribution behavior of superparamagnetic carbon nanotubes in an aqueous system

This study investigates the distribution behavior of superparamagnetic multiwalled carbon nanotubes (SPM-MWCNTs) in an aqueous system containing Lake Tai sediment. Specifically, the effects of dissolved organic matter (DOM) and sediment on SPM-MWCNTs under various conditions and the interaction forms between them were evaluated through a modified mathematical model and characterization. The results showed that DOM can stabilize SPM-MWCNTs by providing sterically and electrostatically stable surfaces, even under high sodium concentrations. The fitting accuracy of the Freundlich adsorption isotherm is higher than that of the Langmuir adsorption isotherm. Therefore, the adsorption of SPM-MWCNT on the sediment should proceed through a multiple, complex and heterogeneous adsorption mechanism. Characterization analyses indicated that DOM may serve as a bridge for the inorganic adsorption between SPM-MWCNTs and sediment. This study is the first to investigate the distribution behavior of magnetite coated carbon nanotubes (CNTs), which simplified the separation and quantification considerably. The findings of this study will serve as a valuable reference for future studies of magnetic CNTs.

Modeling of adsorption behavior of the amine-rich GOPEI aerogel for the removal of As(iii) and As(v) from aqueous media

In the present study, a PEI cross-linked graphene oxide aerogel (GOPEI) was prepared.

Novel 3D lightweight carbon foam as an effective adsorbent for arsenic(v) removal from contaminated water

An efficient removal of pentavalent arsenic (As(v)) from water has been developed using novel three-dimensional (3D) light weight carbon foam which exhibit adoption capacity of 38.4 μg g⁻¹.

Amorphous carbon nanotubes as potent sorbents for removal of a phenolic derivative compound and arsenic: theoretical support of experimental findings

Amorphous carbon nanotubes can be uses as potential material for water purification.

Kinetic, isotherm and thermodynamic studies of adsorption behaviour of CNT/CuO nanocomposite for the removal of As(iii) and As(v) from water

A CNT/CuO nanocomposite prepared by precipitation method was characterized and utilized as a nanoadsorbent for the adsorption of As(iii)/As(v) from water. Maximum uptake capacities of 2267 μg g⁻¹for As(iii) and 2395 μg g⁻¹for As(v) were achieved.

Selective Adsorption of Gd(3+) on a Magnetically Retrievable Imprinted Chitosan/Carbon Nanotube Composite with High Capacity

A novel magnetic imprinting nanotechnology for selective capture of Gd(3+) from a mixed solution of rare earth ions was developed by simply adding Gd(3+)-imprinted chitosan/carbon nanotube nanocomposite (IIP-CS/CNT) and silica-coated magnetite nanoparticle (SiO2@Fe3O4). The IIP-CS/CNT was prepared for the first time via a facile "surface deposition-crosslinking" method, exhibiting a well-defined coating structure. Interestingly, the neighboring IIP-CS/CNT monomers were held together as bundles, like a network, containing abundant interstitial spaces. When IIP-CS/CNT and SiO2@Fe3O4 were dispersed in a mixed solution of rare earth ions, the magnetic SiO2@Fe3O4 submicrospheres would be trapped in or adhere to the IIP-CS/CNT network, leading to the magnetization of IIP-CS/CNT; meanwhile, Gd(3+) ions could be selectively captured by the magnetized IIP-CS/CNT. Saturation adsorption capacity for Gd(3+) was up to 88 mg g(-1) at 303.15 K, which is significantly higher than the Gd(3+) adsorption capacities for the reported rare earth ion-imprinted adsorbents over recent years. The selectivity coefficients relative to La(3+) and Ce(3+) were 3.50 and 2.23, respectively, which are very similar to those found for other reported CS-based imprinted materials. Moreover, the imprinted adsorbents could be easily and rapidly retrieved by an external magnetic field without the need of additional centrifugation or filtration, greatly facilitating the separation process. Test of reusability demonstrated that the magnetized IIP-CS/CNT could be repeatedly used without any significant loss in binding capacity. Overall, this work not only provides new insights into the fabrication of magnetic imprinted CS-based composite, but also highlights its application for selective adsorption toward rare earth ions.

p-Aminophenol sensor based on tetra-β-[3-(dimethylamine)phenoxy] phthalocyanine cobalt(ii)/multiwalled carbon nanotube hybrid

The hybrid tetra-β-[3-(dimethylamine)phenoxy] phthalocyanine cobalt(ii)/multiwalled carbon nanotube was designed and synthesized, which can serve as an efficient catalyst for sensitive p-aminophenol detection due to synergistic effects between phthalocyanine and the carbon.