Efficient Cu2+, Pb2+ and Ni2+ ion removal from wastewater using electrospun DTPA-modified chitosan/polyethylene oxide nanofibers

Preparation of magnetic DTPA-modified chitosan composite microspheres for enhanced adsorption of Pb(II) from aqueous solution

In this study, magnetic DTPA-modified chitosan composite microspheres (MDCM) were prepared by reverse emulsion-double crosslinking method (carbodiimide followed by glutaraldehyde) for removal of Pb(II) from aqueous solution. The obtained magnetic adsorbents were characterized by FTIR, SEM, XRD, VSM, BET, and 13C NMR. The effects of the pH, contact time, initial concentration, and competitive metal cations (Na(I), Ca(II), or Mg(II)) on Pb(II) adsorption were investigated. The results revealed that MDCM exhibited high removal performance over a wide pH range and in the presence of competitive metal cations. The maximum adsorption capacity of MDCM for Pb(II) is 214.63 mg g-1 at pH 3, which is higher than most recently reported magnetic adsorbents. Adsorption kinetics and isotherms can be described by the pseudo-second-order model and Langmuir model, respectively. In addition, MDCM is easy to regenerate and can be reused five cycles with high adsorption capacity. Finally, the adsorption mechanism was further revealed by FTIR and XPS analysis. Overall, MDCM has practical application potential in removing Pb(II) from contaminated wastewater due to its high adsorption efficiency, good reusability, and convenient magnetic separation.

A magnetically recyclable carboxyl-functionalized chitosan composite for efficiently removing methyl orange from wastewater: Isotherm, kinetics, thermodynamic, and adsorption mechanism

In this study, a kind of magnetically recyclable adsorbent for dyes was synthesized by grafting diethylenetriamine pentaacetate acid (DTPA) to the composite of Fe3O4 microspheres and crosslinked chitosan (CS). The microstructures, molecular structure, crystal structure, and magnetic hysteresis loops of the chitosan matrix adsorbent before and after grafting was characterized. The results suggested that DTPA was covalent bonded with the composite of Fe3O4 microspheres and chitosan. The modified composite has larger specific surface area and can realize rapid solid-liquid separation. Batch experiments were conducted to optimize the parameters affecting the adsorption of methyl orange (MO). The adsorption process could be better described by pseudo-second-order kinetics model and Langmuir isotherm equation, and its saturated adsorption capacity of the modified adsorbents was 1541.5 mg·g-1 at 25 °C, which was 1.40 times of that the unmodified adsorbent (1104.1 mg·g-1). The obtained values of the thermodynamic parameters indicated that the adsorption was a spontaneous process. The regeneration experiment proved the stability and reproducibility of the adsorbent even after five cycles of adsorption-desorption. The primary adsorption mechanism was electrostatic interaction and hydrogen bonding. The adsorbent could be potentially applied for removing dyes from wastewater in wide pH of range, especially acid wastewater.

Advances in electrospun materials for the adsorption and separation of environmental pollutants: A comprehensive review

Despite a broad range of new techniques developed, adsorption methods remain one of the technologies of choice for the removal of contaminants. However, significant progress has also been made in these, which finds reflection in a new spectrum of adsorbents that can be used. This comprehensive review discusses properties, advantages, and perspectives on the use of custom-made electrospun adsorbents in the processes of heavy metals, agrochemicals, and microplastic contaminants removal from the environment. It presents the versatility and adaptability of materials that can be used as electrospun fibers matrix, also considering the mechanism and parameters of the sorption process carried out with them. The presented review proves, that due to the use of new, custom-made sorbents, such as electrospun materials, the adsorption processes still possess great application potential and development opportunities to provide an attractive and effective alternative to other remediation techniques.

Co-exposure of microplastics and heavy metals in the marine environment and remediation techniques: a comprehensive review

Microplastics (MPs) and heavy metals are significant pollutants in the marine environment, necessitating effective remediation strategies to prevent their release into the sea through sewage and industrial effluent. This comprehensive review explores the current understanding of the co-exposure of MPs and heavy metal-enriched MPs, highlighting the need for effective remediation methods. Various mechanisms, including surface ion complexation, hydrogen bonding, and electrostatic forces, contribute to the adsorption of heavy metals onto MPs, with factors like surface area and environmental exposure duration playing crucial roles. Additionally, biofilm formation on MPs alters their chemical properties, influencing metal adsorption behaviors. Different thermodynamic models are used to explain the adsorption mechanisms of heavy metals on MPs. The adsorption process is influenced by various factors, including the morphological characteristics of MPs, their adsorption capacity, and environmental conditions. Additionally, the desorption of heavy metals from MPs has implications for their bioavailability and poses risks to marine organisms, emphasizing the importance of source reduction and remedial measures. Hybrid approaches that combine both conventional and modern technologies show promise for the efficient removal of MPs and heavy metals from marine environments. This review identifies critical gaps in existing research that should be addressed in future studies including standardized sampling methods to ensure accurate data, further investigation into the specific interactions between MPs and metals, and the development of hybrid technologies at an industrial scale. Overall, this review sheds light on the adsorption and desorption mechanisms of heavy metal-enriched MPs, underscoring the necessity of implementing effective remediation strategies.

A Strategy to Valorize a By-Product of Pine Wood (Pinus pinaster) for Copper Removal from Aqueous Solutions

This study describes the valorization of a pine wood by-product (Pinus pinaster) in the form of individualized fibers to a complex copper or more broadly metals present in an aqueous solution using a batch process. The adsorption results show that pine fibres activated by sodium carbonate are effective in recovering copper ions from monocontaminated or polycontaminated solutions of varying concentrations in a few minutes. One gram of material captures 2.5 mg of copper present in 100 mL of solution at pH 5 in less than 10 min. The results are perfectly reproducible and independent of pH between 3 and 5. The presence of the Na+ cation at concentrations of 0.1 M has no impact on material performance, unlike that of Ca2+ ions, which competes with Cu2+ ions for active sites. The adsorption process can be considered as rapid, as most of the copper is adsorbed within the first 10 min of exposure. Investigation of modeling possibilities shows some limitations. Indeed, the Weber and Morris and Elovich models show poor possibilities to describe all the kinetic data for copper adsorption on fibres. This may prove that the mechanism is far more complex than simple physisorption, chemisorption and/or diffusion. Complexation by wood fibers can be extended to solutions containing several types of metals. The results of this study show that the field of selective metal recovery could be a new way of valorizing by-products from the wood industry.

Electrospun Nanofiber Membrane: An Efficient and Environmentally Friendly Material for the Removal of Metals and Dyes

With the rapid development of nanotechnology, electrospun nanofiber membranes (ENM) application and preparation methods have attracted attention. With many advantages such as high specific surface area, obvious interconnected structure, and high porosity, ENM has been widely used in many fields, especially in water treatment, with more advantages. ENM solves the shortcomings of traditional means, such as low efficiency, high energy consumption, and difficulty in recycling, and it is suitable for recycling and treatment of industrial wastewater. This review begins with a description of electrospinning technology, describing the structure, preparation methods, and factors of common ENMs. At the same time, the removal of heavy metal ions and dyes by ENMs is introduced. The mechanism of ENM adsorption on heavy metal ions and dyes is chelation or electrostatic attraction, which has excellent adsorption and filtration ability for heavy metal ions and dyes, and the adsorption capacity of ENMs for heavy metal ions and dyes can be improved by increasing the metal chelation sites. Therefore, this technology and mechanism can be exploited to develop new, better, and more effective separation methods for the removal of harmful pollutants to cope with the gradually increasing water scarcity and pollution. Finally, it is hoped that this review will provide some guidance and direction for research on wastewater treatment and industrial production.

Bioremediation of Wastewater Using Yeast Strains: An Assessment of Contaminant Removal Efficiency

The main goal of wastewater treatment is to significantly reduce organic compounds, micronutrients (nitrogen and phosphorus) and heavy metals and other contaminants (pathogens, pharmaceuticals and industrial chemicals). In this work, the efficiency of removing different contaminants (COD, NO₃^-, NO₂^-, NH₄⁺, PO₄^3-, SO₄^2-, Pb²⁺, Cd²⁺) from synthetic wastewater was tested using five different yeast strains: Kluyveromyces marxianus CMGBP16 (P1), Saccharomyces cerevisiae S228C (P2), Saccharomyces cerevisiae CM6B70 (P3), Saccharomyces cerevisiae CMGB234 (P4) and Pichia anomala CMGB88 (P5). The results showed a removal efficiency of up to 70% of COD, 97% of nitrate, 80% of nitrite, 93% of phosphate and 70% of sulfate ions for synthetic wastewater contaminated with Pb²⁺ (43 mg/L) and Cd²⁺ ions (39 mg/L). In contrast, the results showed an increase in ammonium ions, especially in the presence of Pb²⁺ ions. The yeast strains showed a high capacity to reduce Pb²⁺ (up to 96%) and Cd²⁺ (up to 40%) ions compared to the initial concentrations. In presence of a crude biosurfactant, the removal efficiency increased up to 99% for Pb²⁺ and 56% for Cd²⁺ simultaneously with an increase in yeast biomass of up to 11 times. The results, which were obtained in the absence of aeration and in neutral pH conditions, proved a high potential for practical applications in the biotreatment of the wastewater and the recovery of Pb and Cd ions, with a high benefit-cost ratio.

Recent Advances in Chitosan-Based Applications-A Review

Chitosan derived from chitin gas gathered much interest as a biopolymer due to its known and possible broad applications. Chitin is a nitrogen-enriched polymer abundantly present in the exoskeletons of arthropods, cell walls of fungi, green algae, and microorganisms, radulae and beaks of molluscs and cephalopods, etc. Chitosan is a promising candidate for a wide variety of applications due to its macromolecular structure and its unique biological and physiological properties, including solubility, biocompatibility, biodegradability, and reactivity. Chitosan and its derivatives have been known to be applicable in medicine, pharmaceuticals, food, cosmetics, agriculture, the textile and paper industries, the energy industry, and industrial sustainability. More specifically, their use in drug delivery, dentistry, ophthalmology, wound dressing, cell encapsulation, bioimaging, tissue engineering, food packaging, gelling and coating, food additives and preservatives, active biopolymeric nanofilms, nutraceuticals, skin and hair care, preventing abiotic stress in flora, increasing water availability in plants, controlled release fertilizers, dye-sensitised solar cells, wastewater and sludge treatment, and metal extraction. The merits and demerits associated with the use of chitosan derivatives in the above applications are elucidated, and finally, the key challenges and future perspectives are discussed in detail.

Treatment of fluorinated wastewater with chitosan modified activated sludge lysis ash

Preparation of a novel environmentally friendly and cost-effective composite adsorbent for fluoride removal is presented in this work. An activated sludge lysis ash/chitosan (ASLA/C) composite adsorbent was synthesised using an in situ coprecipitation method, and the removal effect of the material was analysed by static adsorption, isothermal adsorption and kinetic adsorption tests. Langmuir model could better describe the adsorption process and the adsorption was in accordance with the kinetic equation of the pseudo-second-order kinetics reaction. The values of adsorption thermodynamic and kinetic parameters were indicated that the adsorption of fluoride ions is a spontaneous, heat-absorbing entropic process, and the reaction was carried out by a combination of mechanisms, such as electrostatic adsorption, ion exchange, surface complexation and hydrogen bonding. The experimental results indicated that ASLA/C can be used as a cheap and readily available alternative efficient adsorbent where the maximum fluorinate absorption was observed with 7.714 mg g^-1, while solving the problem of waste from activated sludge lysis disposal and realizing the environmental benefits of waste.

Synthesis of 2,5-Dialkyl-1,3,4-oxadiazoles Bearing Carboxymethylamino Groups

A series of new symmetrical 2,5-dialkyl-1,3,4-oxadiazoles containing substituted alkyl groups at the terminal positions with substituents, such as bromine, isopropyloxycarbonylmethylamino, and carboxymethylamino, were successfully synthesized. The developed multistep method employed commercially available acid chlorides differing in alkyl chain length and terminal substituent, hydrazine hydrate, and phosphorus oxychloride. The intermediate bromine-containing 2,5-dialkyl-1,3,4-oxadiazoles were easily substituted with diisopropyl iminodiacetate, followed by hydrolysis in aqueous methanol solution giving the corresponding 1,3,4-oxadiazoles bearing carboxymethylamino substituents. The structure of all products was confirmed by conventional spectroscopic methods including ¹H NMR, ¹³C NMR, and HRMS.

Evaluation of diethylenetriaminepentaacetic acid modified chitosan immobilized in amino-carbmated alginate matrix as a low cost adsorbent for effective Cu(II) recovery

In present work, facile synthesis of a biocompatible hybrid biosorbent based on diethylenetriaminepentaacetic acid (DTPA) modified chitosan immobilized in organo-functionalized sodium alginate matrix (DTPA-MCSA) was carried out. DTPA-MCSA was casted in microspherical hydrogel beads. Three dimensional microporous geometry of the biosorbent remained well preserved as observed in SEM analysis which revealed the improved mechanical strength of the alginate matrix. Surface functionalization of base biopolymers was confirmed by FTIR and SEM analysis. Equilibrium sorption studies using DTPA-MCSA for Cu(II) from aqueous medium were carried out in batch mode and found considerably dependent on pH, contact sorption time, temperature and initial copper concentration. Isothermal sorption data showed close correlation with Langmuir model as evident from nonlinear fitting of data (R 2 ˜ 0.99) at different temperatures. The experimental sorption capacity (q e) was found nearly 67 mg/g using 100 mg/L initial concentration of copper ions. Kinetic studies were conducted using different initial concentrations for better elucidation of results and it showed better correlation with pseudo second order rate equation which unveiled that strong ion pair coordination and complexation exist between Cu(II) and newly grafted chelating sites of DTPA-MCSA. Thermodynamic parameters suggested that the adsorption process is spontaneous and endothermic. The results concluded that DTPA-MCSA could be a better candidate for adsorptive remediation of copper ions from liquid waste.

Synthesis of Gum Arabic Magnetic Nanoparticles for Adsorptive Removal of Ciprofloxacin: Equilibrium, Kinetic, Thermodynamics Studies, and Optimization by Response Surface Methodology

Given the increasing risks that antibiotic abuse poses to microecology and human health, it is imperative to develop incredibly powerful adsorbents. This study investigated the use of environmentally sustainable polymeric nanocomposite based on gum arabic (GA) and magnetic nanoparticles (MNPs) synthesized via co-precipitation method to form gum arabic magnetitic nanoparticles (GA-MNPs) as an efficient adsorbent for ciprofloxacin (CIP) removal from aqueous solution. The physicochemical properties and morphology of the synthesized GA-MNPs were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Energy Dispersive X-Ray Analysis (EDX). The experiment was designed by response surface methodology (RSM) and the Central Composite Design (CCD) was utilized to optimize the operating variables: contact time (0–120 min), pH (3–10), adsorbent dosage (0.10–0.40 g/L), and concentration of adsorbate (5–100 mg/L). Results showed that 96.30% was the maximum percentage of CIP removed. The adsorption effect of the CIP molecule on the surface of the GA-MNPs was investigated using regression analysis and analysis of variance. Furthermore, Freundlich Isotherm and Pseudo Second order kinetic equations have the highest consistency with experimental investigations suggesting double-layer adsorption. This implies that chemisorption was the mechanism involved. In addition, the calculated thermodynamic parameters were postulating an exothermic and spontaneous method in nature. Owing to its adsorption selectivity and recyclability, GA-MNPs could be classified as an environmentally friendly, less expensive, and highly efficient promising adsorbent for remediation of CIP from aqueous solution.

Arsenic in drinking water: overview of removal strategies and role of chitosan biosorbent for its remediation

Accessibility to clean drinking water often remains a crucial task at times. Among other water pollutants, arsenic is considered a more lethal contaminant and has become a serious threat to human life globally. This review discussed the sources, chemistry, distribution, and toxicity of arsenic and various conventional technologies that are in option for its removal from the water system. Nowadays, biosorbents are considered the best option for arsenic-contaminated water treatment. We have mainly focused on the need and potential of biosorbents especially the role of chitosan-based composites for arsenic removal. The chitosan-based sorbents are economically more efficient in terms of their, low toxicity, cost-effectiveness, biodegradability, eco-friendly nature, and reusability. The role of various modification techniques, such as physical and chemical, has also been evaluated to improve the physicochemical properties of biosorbent. The importance of adsorption kinetic and isotherm models and the role of solution pH and pH_PZC for arsenic uptake from the polluted water have also been investigated. Some other potential applications of chitosan-based biosorbents have also been discussed along with its sustainability aspect. Finally, some suggestions have been highlighted for further improvements in this field.

Amine-bilayer-functionalized cellulose-chitosan composite hydrogel for the efficient uptake of hazardous metal cations and catalysis in polluted water

Herein, we represent a novel ecofriendly bilayer-amine group incorporated microcrystalline cellulose (MCC)/chitosan (CS) hydrogel, fabricated via integrating polydopamine (PDA) and polyethyleneimine (PEI) for reliable and effective extraction of copper (Cu²⁺), zinc (Zn²⁺), and nickel (Ni²⁺) ions from effluents. Owing to abundant adsorptive sites, the MCC-PDA-PEI/CS-PDA-PEI hydrogel showed excellent Cu²⁺, Zn²⁺, and Ni²⁺ adsorbabilities of ~434.8, ~277.7, and ~261.8 mg/g, respectively, in a single-ion adsorption system with the adsorption kinetics and isotherm complied with pseudo-second-order and Langmuir models, respectively. In a multi-ion adsorption system, hydrogel removes mixed metal cations with slightly higher selectivity for Cu²⁺. In accordance with X-ray photoelectron and Fourier-transform-infrared spectrometric analyses, a plausible binding mechanism of metal cations on the as-prepared hydrogel was proposed by chelation between hydrogel functional groups and metal ions. In the repetitive adsorption/desorption experiments, the hydrogel retained >40% metal ion adsorption and desorption capacities after four cycles. Furthermore, the Cu²⁺-adsorbing hydrogel could serve as a support for the in situ development of Cu nanoparticles, which showed excellent catalytic performance as demonstrated by the transformation of 4-nitrophenol (4-NP) to 4-aminophenol. This work provides a novel ecofriendly, reusable, and highly-efficient adsorbent, as well as a biocatalyst for remediation of heavy metal cations and 4-NP polluted effluents.

Extraction of Palladium(II) with a Magnetic Sorbent Based on Polyvinyl Alcohol Gel, Metallic Iron, and an Environmentally Friendly Polydentate Phosphazene-Containing Extractant

In this work, a highly efficient and environmentally friendly method for extracting palladium from hydrochloric acid media was developed. The method uses a magnetic sorbent carrying an organophosphorus extractant, which is not washed from the sorbent into the aqueous phase. The extractant was characterized by 1H, 13C, and 31P NMR spectroscopy and MALDI TOF mass spectrometry, and the palladium complex based on it was characterized by IR spectroscopy. According to an in vitro microbiological study, the extractant was non-toxic to soil microflora. It was established that the water uptake and saturation magnetization of the magnetic sorbent were sufficient for use in sorption processes. The sorption efficiency of palladium(II) with the developed sorbent can reach 71% in one cycle. After treatment of the spent sorbent with 5 M hydrochloric acid, palladium was completely extracted from the sorbent. The new sorbent is proposed for the extraction of palladium from hydrochloric acid media obtained by the leaching of electronic waste.

Electrospun chitosan/polyethylene oxide nanofibers mat loaded with copper (II) as a new sensor for colorimetric detection of tetracycline

Using electrospun chitosan/polyethylene oxide nanofibers mat (CS/PEO NFM) as carrier, Cu@CS/PEO NFM, a new tetracycline (TC) solid-state colorimetric sensor, were simply prepared by directly immobilizing Cu²⁺ on surface of CS/PEO NFM. After immersing in TC solutions, Cu@CS/PEO NFM can display visible color changes to the naked eye within 5.0 min, and the TC concentration-dependent color changes can also be quantitatively analyzed with a smartphone. Because Cu²⁺ can enhance the adsorption of CS/PEO NFM for TC, Cu@CS/PEO NFM possess a more sensitive response ability to TC, ensuring that the colorimetric sensing detection will not be interfered by other coexisting drugs. Due to the reversible combination of chitosan and Cu²⁺, the colorimetric sensing ability of Cu@CS/PEO NFM can be regenerated even after being reused at least 4 times. In addition, the naked eye detection limit of Cu@CS/PEO NFM-based colorimetric sensing is 65 μg kg^-1, which does not exceed the maximum residue limit in milk samples set by China (100 μg kg^-1). The obtained results fully indicated the practical application value of this method in preventing the hazard of TC residues.

Enhanced adsorption of copper ions from aqueous solution by two-step DTPA-modified magnetic cellulose hydrogel beads

Copper contamination of water is one of the most pressing environmental problems which has attracted extensive concern in recent decades. In this study, a series of magnetic adsorbents were synthesized by two-step modified cellulose with N-[3-(trimethoxysilyl)propyl]ethylenediamine (KH-792) and diethylenetriaminepentaacetic acid (DTPA) using for removal of Cu(II) from aqueous solutions. Adsorption performance of Cu(II) was systematically investigated under various treatment conditions as the effect of solution pH, contact time, initial concentration and temperature. The adsorption process was found to match better with the pseudo-second-order kinetics model, and the equilibrium adsorption data were well described by Langmuir model, which meant predominant governance of monolayer chemical adsorption. The analysis of FTIR and XPS confirmed the possible adsorption mechanism between Cu(II) and the synthesized adsorbents was electrostatic attraction and the chemical coordination. Compared with MCCs and APMC, DPMC showed higher adsorption capacity of Cu(II), reaching maximum adsorption capacity of 298.62 mg·g^-1 at pH 6. Given this, ease of preparation, low cost and excellent reusability, DPMC will be promising adsorbent for application in Cu(II) removal from wastewater.

Preparation and performance evaluation of chitosan/polyvinylpyrrolidone/polyvinyl alcohol electrospun nanofiber membrane for heavy metal ions and organic pollutants removal

In this work, a novel electrospun chitosan (CS)/polyvinylpyrrolidone (PVP)/polyvinyl alcohol (PVA) nanofibrous membrane was prepared to remove heavy metal ions and organic pollutants from water. The nanofiber morphologies were adjusted through the optimal electrospinning process parameters. Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations indicated that a well-crosslinked CS/PVP/PVA nanofiber film was formed. Under the optimize conditions, the obtained CS/PVP/PVA nanofiber membranes exhibited porous and uniform nanofibrous structures with an average diameter of 160 nm and a pure water permeability of 4518.91 L·m^-2·h^-1·bar^-1. In addition, the adsorption and separation performance of CS/PVP/PVA nanofiber membranes were evaluated with Cu(II), Ni(II), Cd(II), Pb(II) and Methylene Blue (MB), Malachite Green (MG) as target ions and dyes. The results showed that the retention rate of CS/PVP/PVA nanofiber membranes for Cu(II), Ni(II), Cd(II), Pb(II), MG and MB can reach 94.20%, 90.35%, 83.33%, 80.12%, 84.01% and 69.91%, respectively. The adsorption capacities of Cu(II), Ni(II), Cd(II), Pb(II), MG and MB were 34.79, 25.24, 18.07, 16.05, 17.86 and 13.27 mg g^-1. The adsorption kinetics of heavy metal ions and dyes by the nanofiber membranes can be explained by the Langmuir isotherm model and represented by the pseudo-second-order kinetic mechanism that determined the spontaneous chemisorption process. This study provides a synthetic approach to membranes for the removal of organic and heavy metal micropollutants from water.

Preparation of aminated porous polyacrylonitrile nanofibers as adsorbent for methyl orange removal

In this study, porous electrospinning polyacrylonitrile nanofiber (PPAN) surface functionalization with amine groups is studied for methyl orange (MO) dye removal from aqueous solution. A series of adsorption experiments were carried out to investigate the influence of initial solution pH value, contact time, initial solution concentration, and adsorption temperature on the adsorption performance. The experimental results showed that the removal of MO on these PPAN-PEI and PPAN-TEPA nanofibrous mats was a pH-dependent process with the maximum adsorption capacity at the initial solution pH of 3, and that the PPAN-PEI and PPAN-TEPA nanofibrous mats could be regenerated successfully after 4 recycling processes. The adsorption equilibrium data were all fitted well to the Langmuir isotherm equation, with maximum adsorption capacity of 1414.52 mg g⁻¹ and 1221.09 mg g⁻¹ for PPAN-PEI and PPAN-TEPA, respectively. The kinetic study indicated that the adsorption of MO could be well fitted by the pseudo-second-order equation and Weber–Morris model. Thermodynamic parameters such as free energy, enthalpy, and entropy of adsorption of the MO were also evaluated, and the results showed that the adsorption was a spontaneous exothermic adsorption process.

Amino functionalized porous polyacrylonitrile electrospun nanofibers were fabricated, which have good adsorption performance for MO in an acidic environment.

Research progress in the removal of heavy metals by modified chitosan

Chitosan and its modifiers have been widely studied for their good biocompatibility and excellent adsorption properties for heavy metal ions. The synthesis and application of modified chitosan, the effects of process variables (such as pH, amount of adsorbent, temperature, contact time, etc.), adsorption kinetics, thermodynamics and the adsorption mechanism on the removal of heavy metal ions are reviewed. The purpose is to provide the latest information about chitosan as adsorbent and to promote the synthesis of modified chitosan and its application in the removal of heavy metals.

Granulation of Nickel-Aluminum-Zirconium Complex Hydroxide Using Colloidal Silica for Adsorption of Chromium(VI) Ions from the Liquid Phase

We combined a nickel-aluminum-zirconium complex hydroxide (NAZ) with colloidal silica as a binder to prepare a granulated agent for adsorbing heavy metals from aqueous media. Three samples with different particle diameters were prepared to evaluate the effects on the properties: small (NAZ-S), medium (NAZ-M), and large (NAZ-L). We confirmed the granulation of the prepared samples at a binder content of 25%. NAZ-S had the largest specific surface area and number of hydroxyl groups, followed by NAZ-M and then NAZ-L. Regarding the adsorption capacity, NAZ-S adsorbed the most chromium(VI) ions followed by NAZ-M and then NAZ-L. The binding energy of Cr(2p) at 575-577 eV was detected after adsorption, and the effects of the temperature, contact time, and pH on the adsorption of chromium(VI) ions were evaluated. We identified the following adsorption mechanism: ion exchange with sulfate ions in the interlayer region of the NAZ samples. Finally, the chromium(VI) ions adsorbed by the NAZ samples were easily desorbed using a desorption solution. The results showed that NAZ offers great potential for the removal of chromium(VI) ions from aqueous solutions.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

High-efficiency adsorption of Cd(II) and Co(II) by ethylenediaminetetraacetic dianhydride-modified orange peel as a novel synthesized adsorbent

The treatment of heavy metal (HM) wastewater is a critical and considerable challenge. Fruit peel-based HM adsorption is a promising way for the water pollution control and the reuse of agricultural waste. In this study, a novel adsorbent based on orange peel was synthesized for the first time by introducing abundant -COO groups with ethylenediaminetetraacetic dianhydride (EDTAD) to eliminate Cd(II) and Co(II) of sewage solution. The synthesized adsorbent displayed excellent adsorption capacity of 51.020 and 40.486 mg/g for Cd(II) and Co(II), respectively, and the adsorption equilibrium was achieved within 5 min, following the Langmuir isotherm model and the pseudo-second-order model. Surface characterization of adsorbents by scanning electron microscopy-energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy confirmed that ion exchange, complexation, and physical adsorption could occur during the adsorption process. The rapid and highly efficient adsorption performance suggests EDTAD-modified synthesized orange peel possesses great potential for HM removal from sewage systems.

Fabrication and characterization of a toughened spherical chitosan adsorbent only through physical crosslinking based on mechanism of Chain Rearrangement

Chitosan extracted from natural products has gained tremendous attention in the field of adsorption and separation due to its inherent biocompatibility and potential applications. In this research, we synthesized a new type of spherical chitosan adsorbent (SCA) by controlling the mass transfer rate of the entanglement of the polymer chains in the recombination process. This SCA is a highly crystalline polymer material with outstanding mechanical strength, high adsorption capacity, a porous surface and suitable particle size distribution. The value of the sphericity of attrition of this SCA was 89.8%, which is the same as that of the commercial macroporous resin with a polystyrene matrix. The X-ray diffraction (XRD) patterns and differential scanning calorimetry (DSC) curves showed a significant change from powder to spherical structure and confirmed that the SCA is highly ordered and crystalline. Optical microscopy (OM) and scanning electron microscopy (SEM) demonstrated that the SCA was composed of a tightly stacked fiber structure, indicating the homogeneity of the polymerization. The porous structure of the surface provided a channel for mass transfer, which was indicated by a test of the ion exchange capacity and the adsorption performance of the SCA with Cu(ii) as the adsorbed subject. The adsorption capacity was higher than those of all reported non-composite chitosan materials. Therefore, we have successfully synthesized a completely green, nontoxic and environmentally friendly adsorbing resin equipped with excellent mechanical properties and adsorption capacity for future applications in many new fields.

Highly crystalline spherical chitosan ion exchange resins with numerous available functional groups and excellent mechanical performance can be produced on a large scale.

Xanthate-Modified Magnetic Fe3O4@SiO2-Based Polyvinyl Alcohol/Chitosan Composite Material for Efficient Removal of Heavy Metal Ions from Water

Chitosan has several shortcomings that limit its practical application for the adsorption of heavy metals: mechanical instability, a challenging separation and recovery process, and low equilibrium capacity. This study describes the synthesis of a magnetic xanthate-modified polyvinyl alcohol and chitosan composite (XMPC) for the efficient removal and recovery of heavy metal ions from aqueous solutions. The XMPC was synthesized from polyvinyl alcohol, chitosan, and magnetic Fe₃O₄@SiO₂ nanoparticles. The XMPC was characterized, and its adsorption performance in removing heavy metal ions was studied under different experimental conditions. The adsorption kinetics fit a pseudo-second-order kinetic model well. This showed that the adsorption of heavy metal ions by the XMPC is a chemical adsorption and is affected by intra-particle diffusion. The equilibrium adsorption isotherm was well described by the Langmuir and Freundlich equations. The XMPC reached adsorption equilibrium at 303 K after approximately 120 min, and the removal rate of Cd(II) ions was 307 mg/g. The composite material can be reused many times and is easily magnetically separated from the solution. This makes the XMPC a promising candidate for widespread application in sewage treatment systems for the removal of heavy metals.

A Review: Adsorption and Removal of Heavy Metals Based on Polyamide-amines Composites

In recent years, the problem of heavy metal pollution has become increasingly prominent, so it is urgent to develop new heavy metal adsorption materials. Compared with many adsorbents, the polyamide-amine dendrimers (PAMAMs) have attracted extensive attention of researchers due to its advantages of macro-molecular cavity, abundant surface functional groups, non-toxicity, high efficiency and easy modification. But in fact, it is not very suitable as an adsorbent because of its solubility and difficulty in separation, which also limits its application in environmental remediation. Therefore, in order to make up for the shortcomings of this material to a certain extent, the synthesis and development of polymer composite materials based on PAMAMs are increasingly prominent in the direction of solving heavy metal pollution. In this paper, the application of composites based on PAMAMs and inorganic or organic components in the adsorption of heavy metal ions is reviewed. Finally, the prospects and challenges of PAMAMs composites for removal of heavy metal ions in water environment are discussed.

A comprehensive review on electrospun nanohybrid membranes for wastewater treatment

Electrospinning, being a versatile and straightforward method to produce nanofiber membranes, has shown significant advancement in recent years. On account of the unique properties such as high surface area, high porosity, mechanical strength, and controllable surface morphologies, electrospun nanofiber membranes have been found to have a great potential in many disciplines. Pure electrospun fiber mats modified with different techniques of surface modification and additive incorporation have exhibited enhanced properties compared to traditional membranes and are even better than the as-prepared electrospun membranes. In this review, we have summarized recently developed electrospun nanohybrids fabricated by the incorporation of functional specific nanosized additives to be used in various water remediation membrane techniques. The adsorption, filtration, photocatalytic, and bactericidal capabilities of the hybrid membranes in removing common major water pollutants such as metal ions, dyes, oils, and biological pollutants have been discussed. Finally, an outlook on the future research pathways to fill the gaps existing in water remediation have been suggested.

Arsenic removal approaches: A focus on chitosan biosorption to conserve the water sources

Globally, millions of people have no access to clean drinking water and are either striving for that or oppressed to intake polluted water. Arsenic is considered one of the most hazardous contaminants in water bodies that reaches there due to various natural and anthropogenic activities. Modified chitosan has gained much attention from researchers due to its potential for arsenic removal. This review focuses on the need and potential of chitosan-based biosorbents for arsenic removal from water systems. Chitosan is a low-cost, abundant, biodegradable biopolymer that possesses unique structural aspects and functional sites for the adsorption of contaminants like arsenic species from contaminated water. The chitosan-based biosorbents had also been modified using various techniques to enhance their arsenic removal efficiencies. This article reviews various forms of chitosan and parameters involved in chitosan modification which eventually affect the arsenic removal efficiency of the resultant sorbents. The literature revealed that the modified chitosan-based sorbents could express higher adsorption efficiency compared to those prepared from native chitosan. The sustainability of the chitosan-based sorbents has also been considered in terms of reusability. Finally, some recommendations have been underlined for further improvements in this domain.

Diethylenetriaminepentaacetic acid-thiourea-modified magnetic chitosan for adsorption of hexavalent chromium from aqueous solutions

Chromium pollution is a serious environmental problem given that like most heavy metals, Cr tends to persist and accumulate in the environment. In this study, diethylenetriaminepentaacetic acid-thiourea-modified magnetic chitosan (DTCS-Fe₃O₄) was synthesized for use as an adsorbent for Cr(VI) removal from aqueous solutions. The effects of various treatment conditions on the Cr(VI) adsorption performance of DTCS-Fe₃O₄ composite as well as the kinetics were elucidated. Moreover, by observing the structure and morphology of DTCS-Fe₃O₄, the possible Cr(VI) adsorption mechanism was proposed. DTCS-Fe₃O₄ exhibited a maximum adsorption capacity of 321.3 ± 6.0 mg g^-1. Further, the adsorption process, which followed the Langmuir model for monolayer adsorption, was predominantly governed by chemical adsorption, and could be fitted using the pseudo-second-order kinetics model. Furthermore, given its ease of preparation, low cost, and remarkable performance, it is expected that the DTCS-Fe₃O₄ composite would find wide practical application in the removal of toxic Cr(VI) from wastewater.

N-methylene phosphonic chitosan aerogels for efficient capture of Cu2+ and Pb2+ from aqueous environment

In this paper, N-methylene phosphonic acid chitosan (NPCS-PEI) was synthesized from chitosan, phosphorous acid, formaldehyde and hyperbranched polyethyleneimine (PEI), and Cu²⁺ and Pb²⁺ removal performance was examined in aqueous solution. NPCS-PEI exhibited three-dimensional porous architectures, with a specific surface area of 490.61 m²/g. The effects of pH, initial concentration, adsorption time, temperature and ionic strength on the adsorption capacity were investigated. The adsorption kinetics indicated that Cu²⁺ and Pb²⁺ adsorption onto NPCS-PEI follows a pseudo-second-order model. The adsorption isotherms agree well with the Langmuir isotherm model, and the maximum adsorption capacities of Cu²⁺ and Pb²⁺ on the NPCS-PEI are approximately 276.12 and 645.16 mg/g, respectively. The adsorption efficiency of NPCS-PEI remained above 85% after 5 adsorption-desorption successive cycles. Moreover, the NPCS-PEI aerogels had selective adsorption toward Cu²⁺. The FTIR and XPS analysis proved that amino, hydroxyl, and phosphonic acid groups were involved in the chelation with metal ions.

Efficient removal of diethyl dithiocarbamate with EDTA functionalized electrolytic manganese residue and mechanism exploration

The recycling of solid wastes is obligable as it can reduce the environmental pollution and prevent the diffusion of secondary pollution. In this study, a novel cheap adsorbent was prepared by modifying electrolytic manganese residue (EMR) with EDTA. The maximum adsorption capacity of adsorbents for diethyl dithiocarbamate (DDTC) was 133.46 mg/g under initial pH of 7.32 at room temperature. Adsorption kinetics study revealed the DDTC adsorption on EDTA-EMR is mainly controlled by chemisorption and isotherm studies implied the adsorption is a monolayer process. Mechanism exploration found that the DDTC molecules could enter into the holes of EDTA-EMR, and the transition metal-based sorption sites were crucial for the target molecule immobilization and chelation. High pH value (> 10) was found to have inhibited the adsorption capacity of adsorbent, which should be due to the fact that the decreasing of functional groups on adsorbents surface and the competition between DDTC and OH^-. The ionic strength has negligible effect on the adsorption and the as-synthesized adsorbents showed excellent performance after five cycles. The overall results reveal that EDTA-EMR is a promising adsorbent ascribed by its low cost, good recyclability and excellent adsorption capacity.

Preparation of composite sludge carbon-based materials by LDHs conditioning and carbonization and its application in the simultaneous removal of dissolved organic matter and phosphate in sewage

In this work, a novel carbon-based hydrotalcite-like compounds materials (LDO-SBCs) were prepared by coupling layered double hydroxides (LDHs) conditioning and pyrolytic carbonization, and characterized by X-ray diffraction (XRD), Thermogravimetric Analyzer (TGA), X-ray photoelectron spectroscopy (XPS) and Brunner-Emmet-Teller (BET) measurements. The synthesized LDO-SBCs composites were used in wastewater treatment for simultaneous removal of phosphate and dissolved organic matter (DOM). The adsorption of DOM and phosphate were well conformed to pseudo-second-order mode. Adsorption equilibrium was better fitted by Langmuir model for phosphate, while Freundlich model for DOM. Compared with the raw sludge carbon, the removal efficiency of DOM and phosphate by LDO-SBCs were increased by 8% and 13%, respectively. Based on the fluorescence spectrum and parallel factor analysis (PARAFAC), LDO-SBCs performed well in promoting the removal of protein substances (TPN and APN). Pore filling, hydrogen bonding, electrostatic adsorption and surface complexation might be dominant in the adsorption of DOM, while, surface complexation and ion exchange between the LDO layers were mainly responsible for the adsorption of phosphate. The difference of adsorption capacity of LDO-SBCs was related to the superior channel structure of composite materials and the composition of interlayer anions of LDO.

The adsorption performance and micro-mechanism of MoS2/montmorillonite composite to atenolol and acebutolol: Adsorption experiments and a novel visual study of interaction

MoS₂/montmorillonite (MoS₂/Mt) composite was successfully synthesized through a simple hydrothermal method, and its adsorption performance for two emerging contaminants-atenolol (ATE) and acebutolol (ACE) was researched. The batch experiments revealed that the adsorption process can be described by the Pseudo-second order model and Langmuir model, and the adsorption capacity of MoS₂/Mt, MoS₂ and Mt for ATE were 132.08 mg/g, 60.68 mg/g and 74.23 mg/g, for ACE were 113.82 mg/g, 33.01 mg/g and 36.05 mg/g, respectively. Besides, Fourier-transform infrared spectroscopy (FTIR), BET specific surface area measurement and X-ray photoelectron spectroscopy (XPS) were also employed to analyze the adsorption mechanism. Moreover, quantitative molecular surface analysis and weak intermolecular interaction analysis with independent gradient model were combined to probe the microscopic interaction between the adsorbent and adsorbate. The results indicated the interactions included hydrogen bonding and vdW interaction. Mt and MoS₂ interacted more strongly with ATE than ACE, which revealed the reason MoS₂/Mt, Mt and MoS₂ possessed higher adsorption capacity for ATE.

Antibacterial Activity and Protection Efficiency of Polyvinyl Butyral Nanofibrous Membrane Containing Thymol Prepared through Vertical Electrospinning

Human safety, health management, and disease transmission prevention have become crucial tasks in the present COVID-19 pandemic situation. Masks are widely available and create a safer and disease transmission-free environment. This study presents a facile method of fabricating masks through electrospinning nontoxic polyvinyl butyral (PVB) polymeric matrix with the antibacterial component Thymol, a natural phenol monoterpene. Based on the results of Japanese Industrial Standards and American Association of Textile Chemists and Colorists methods, the maximum antibacterial value of the mask against Gram-positive and Gram-negative bacteria was 5.6 and 6.4, respectively. Moreover, vertical electrospinning was performed to prepare Thymol/PVB nanofiber masks, and the effects of parameters on the submicron particulate filtration efficiency (PFE), differential pressure, and bacterial filtration efficiency (BFE) were determined. Thorough optimization of the small-diameter nanofiber-based antibacterial mask led to denser accumulation and improved PFE and pressure difference; the mask was thus noted to meet the present pandemic requirements. The as-developed nanofibrous masks have the antibacterial activity suggested by the National Standard of the Republic of China (CNS 14774) for general medical masks. Their BFE reaches 99.4%, with a pressure difference of <5 mmH2O/cm2. The mask can safeguard human health and promote a healthy environment.

A Highly Expanded Polycarboxylate Gel and New Environmental Response Effects for Efficiently Adsorbing and Recovering Cu(II) from Water

A new highly expanded polycarboxylate gel (EPCG) was accidentally formed in a facile cross-linking copolymerization system. When used as an adsorbent material, the EPCG could be quickly expanded 29.44 times in water to have a high permeability inside for realizing the efficient adsorption toward Cu(II) from water. The adsorption capacity of EPCG toward Cu(II) was 261.70 mg/g, which was higher than that of all the selected existing adsorbents reported in recent years. The adsorption rate of expanded EPCG was 3.61 times higher than that of the previous polyantionic gel. Similarly, due to the high expansion and high permeability of EPCG, the EPCG skeleton could be further coated with an alkaline NaOH, forming a novel NaOH-coated EPCG material, and its adsorption capacity toward Cu(II) was further improved to 333.21 mg/g compared to that of pure EPCG adsorbent. Moreover, the EPCG wastes after adsorbing Cu(II) could be fully desorbed to be regenerated for reuse. A total of 99.39% of the adsorbed Cu(II) was desorbed from EPCG wastes to be recovered. The adsorption capacity of regenerated EPCG reused for adsorbing Cu(II) was 259.05 mg/g, which was very near that of the original EPCG. In addition, a series of simulation experiments and instrumental analysis were adopted to confirm the new environmental response effects as the key factors in the purification of Cu(II)-containing wastewater, including "expansion-shrink," "alkali-coating," and "acid-desorption" responses.