Novel chitosan/poly(vinyl) alcohol thin adsorptive membranes modified with amino functionalized multi-walled carbon nanotubes for Cu(II) removal from water: Preparation, characterization, adsorption kinetics and thermodynamics

Modified chitosan: Insight on biomedical and industrial applications

Chitosan (CS), a by -product of chitin deacetylation can be useful in a broad range of purposes, to mention agriculture, pharmaceuticals, material science, food and nutrition, biotechnology and of recent, in gene therapy. Chitosan is a highly desired biomolecule due to the existence of many sensitive functional groups inside the molecule and also because of its net cationicity. The latter provides flexibility for creating a wide range of derivatives for particular end users across various industries. This overview aims to compile some of the most recent research on the bio-related applications that chitosan and its derivatives can be used for. However, chitosan's reactive functional groups are amendable to chemical reaction. Modifying the material to show enhanced solubility, a greater range of application options and pH-sensitive targeting and others have been a major focus of chitosan research. This review describes the modifications of chitosan that have been made to improve its water solubility, pH sensitivity, and capacity to target chitosan derivatives. Applying the by-products of chitosan as antibacterial, in targeting, extended release and as delivery systems is also covered. The by-products of chitosan will be important and potentially useful in developing new biomedical drugs in time to come.

Research Progress on Metal Ion Recovery Based on Membrane Technology and Adsorption Synergy

The development of modern industry will generate more and more waste containing metal ions. It is necessary to take appropriate measures to recover these ions, whether from the perspective of environmental protection or improving economic benefits. So far, scientists have studied many methods for recovering metal ions. Among these methods, adsorption and membrane separation have received widespread attention due to their own characteristics. Combining adsorption and membrane separation methods can better leverage their respective advantages to improve the ability of recovering metal ions. This review, therefore, focuses on the synergistic recovery of metal ions by adsorption and membrane separation methods. This article first briefly explains the theoretical principles of membrane separation and adsorption synergy, and then focuses on several technologies that have received attention in different chapters. In these chapters, membrane technology is briefly introduced, followed by the situation and progress of synergistic application with adsorption technology. Then, the article compares and elaborates on the advantages and disadvantages of the above technologies, and finally summarizes and looks forward to these technologies being used to solve the difficulties and challenges in industrial application.

Carbon nanotubes buckypapers: A new frontier in wastewater treatment technology

Occurrence of contaminants in water is one of the major global concerns humanity is still facing today: most of them are extremely toxic and dangerous for human health, obliging their removal for a proper and correct process of sanitation. Among wastewater treatment technologies, in the view of development of sustainable and environmentally friendly processes, membrane adsorption has proved to be a fast and simple method in the removal of pollutants, offering great contaminants recovery percentages, fast adsorbent regeneration and recycle, and easy scale-up. Due to their large surface area and tunable chemistry, carbon nanotubes (CNTs)-based materials revealed to be extraordinary adsorbents, exceeding by far performances of ordinary organic and inorganic membranes such as polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, ceramics, currently employed in membrane technologies for wastewater treatment. In consideration of this, the review aims to summarize recent developments in the field of carbon nanotubes-based materials for pollutants recovery from water through adsorption processes. After a brief introduction concerning what adsorption phenomenon is and how it is performed and governed by using carbon nanotubes-based materials, the review discusses into detail the employment of three common typologies of CNTs-based materials (CNTs powders, CNTs-doped polymeric membranes and CNTs membranes) in adsorption process for the removal of water pollutants. Particularly focus will be devoted on the emergent category of self-standing CNTs membranes (buckypapers), made entirely of carbon nanotubes, exhibiting superior performances than CNTs and CNTs-doped polymeric membranes in terms of preparation strategy, recovery percentages of pollutants and regeneration possibilities. The extremely encouraging results presented in this review aim to support and pave the way to the introduction of alternative and more efficient pathways in wastewater treatment technologies to contrast the problem of water pollution.

Electrochemical processes for the treatment of contaminant-rich wastewater: A comprehensive review

Global water demand and environmental concerns related to climate change require industries to develop high-efficiency wastewater treatment methods to remove pollutants. Likewise, toxic pollutants present in wastewater negatively affect the environment and human health, requiring effective treatment. Although conventional treatment processes remove carbon and nutrients, they are insufficient to remove pharmaceuticals, pesticides, and plasticizers. Electrochemical processes effectively remove pollutants from wastewater through the mineralization of non-biodegradable pollutants with consequent conversion into biodegradable compounds. Its advantages include easy operation, versatility, and short reaction time. In this way, this review initially provides a global water scenario with a view to the future. It comprises global demand, treatment methods, and pollution of water resources, addressing various contaminants such as heavy metals, nutrients, organic compounds, and emerging contaminants. Subsequently, the fundamentals of electrochemical treatments are presented as well as electrochemical treatments, highlighting the latest studies involving electrocoagulation, electroflocculation, electroflotation, capacitive deionization and its derivatives, eletrodeionization, and electrochemical advanced oxidation process. Finally, the challenges and perspectives were discussed. In this context, electrochemical processes have proven promising and effective for the treatment of water and wastewater, allowing safe reuse practices and purification with high contaminant removal.

A review on hybrid membrane-adsorption systems for intensified water and wastewater treatment: Process configurations, separation targets, and materials applied

In the era of rapid and conspicuous progress of water treatment technologies, combined adsorption and membrane filtration systems have gained great attention as a novel and efficient method for contaminant removal from aqueous phase. Further development of these techniques for water/wastewater treatment applications will be promising for the recovery of water resources as well as reducing the water tension throughout the world. This review introduces the state-of-the-art on the capabilities of the combined adsorption-membrane filtration systems for water and wastewater treatment applications. Technical information including employed materials, superiorities, operational limitations, process sustainability and upgradeing strategies for two general configurations i.e. hybrid (pre-adsorption and post-adsorption) and integrated (film adsorbents, low pressure membrane-adsorption coupling and membrane-adsorption bioreactors) systems has been surveyed and presented. Having a systematic look at the fundamentals of hybridization/integration of the two well-established and efficient separation methods as well as spotlighting the current status and prospectives of the combination strategies, this work will be valuable to all the interested researchers working on design and development of cutting-edge wastewater/water treatment techniques. This review also draws a clear roadmap for either decision making and choosing the best alternative for a specific target in water treatment or making a plan for further enhancement and scale-up of an available strategy.

Progresses in lignin, cellulose, starch, chitosan, chitin, alginate, and gum/carbon nanotube (nano)composites for environmental applications: A review

Water sources are becoming increasingly scarce, and they are contaminated by industrial, residential, and agricultural waste-derived organic and inorganic contaminants. These contaminants may pollute the air, water, and soil in addition to invading the ecosystem. Because carbon nanotubes (CNTs) can undergo surface modification, they can combine with other substances to create nanocomposites (NCs), including biopolymers, metal nanoparticles, proteins, and metal oxides. Furthermore, biopolymers are significant classes of organic materials that are widely used for various applications. They have drawn attention due to their benefits such as environmental friendliness, availability, biocompatibility, safety, etc. As a result, the synthesis of a composite made of CNT and biopolymers can be very effective for a variety of applications, especially those involving the environment. In this review, we reported environmental applications (including removal of dyes, nitro compounds, hazardous materialsو toxic ions, etc.) of composites made of CNT and biopolymers such as lignin, cellulose, starch, chitosan, chitin, alginate, and gum. Also, the effect of different factors such as the medium pH, the pollutant concentration, temperature, and contact time on the adsorption capacity (AC) and the catalytic activity of the composite in the reduction or degradation of various pollutants has been systematically explained.

Synthesis of triethylenetetramine modified sodium alginate/CuS nanocrystal composite for enhanced Cr(VI) removal: Performance and mechanism

Photocatalysis has been widely used for the removal of hexavalent chromium from wastewater as an efficient and environmental friendly method. However, conventional photocatalysts generally exhibit poor adsorption properties toward Cr(VI), resulting in unsatisfactory performance in high concentrated wastewaters. In this study, we synthesized a novel composite material with high Cr(VI) adsorption ability by blending prepared CuS nanocrystals into triethylenetetramine modified sodium alginate for the enhanced photocatalytic removal of Cr(VI). Effect of CuS dosage, pH value, light source and intensity were discussed for the optimum Cr(VI) removal conditions. The synthesized composite has shown good adsorption performance toward Cr(VI) and the overall removal rate reached 98.99 % within 50 min under UV light irradiation with citric acid as hole scavenger. Adsorption isotherm, thermodynamics, and kinetics with corresponding model fitting were discussed, which suggested that the monolayer and chemical adsorption dominated the adsorption process. Characterization results indicated that amino and hydroxyl groups contributed electrons in the photocatalysis reaction for the reduction of Cr(VI) to Cr(III). CuS nanocrystals can enhance the surface charge and light absorbance ability of the composite, and the Cr(VI) removal was governed by electrostatic interaction and photo-induced redox reaction.

Hemin-Modified Multi-Walled Carbon Nanotube-Incorporated PVDF Membranes: Computational and Experimental Studies on Oil-Water Emulsion Separations

The separation of oil/water emulsions has attracted considerable attention for decades due to the negative environmental impacts brought by wastewater. Among the various membranes investigated for separation, polyvinylidene fluoride (PVDF) membranes have shown significant advantages of ease of fabrication, high selectivity, and fair pore distribution. However, PVDF membranes are hydrophobic and suffer from severe fouling resulting in substantial flux decline. Meanwhile, the incorporation of wettable substrates during fabrication has significantly impacted the membrane performance by lowering the fouling propensity. Herein, we report the fabrication of an iron-containing porphyrin (hemin)-modified multi-walled carbon nanotube incorporated PVDF membrane (HA-MWCNT) to enhance fouling resistance and the effective separation of oil-in-water emulsions. The fabricated membrane was thoroughly investigated using the FTIR, SEM, EDX, AFM, and contact angle (CA) analysis. The HA-MWCNT membrane exhibited a water CA of 62° ± 0.5 and excellent pure water permeance of 300.5 L/m2h at 3.0 bar (400% increment), in contrast to the pristine PVDF, which recorded a CA of 82° ± 0.8 and water permeance of 59.9 L/m2h. The hydrophilic HA-MWCNT membrane further showed an excellent oil rejection of >99% in the transmembrane pressure range of 0.5−2.5 bar and a superb flux recovery ratio (FRR) of 82%. Meanwhile, the classical molecular dynamics (MD) simulations revealed that the HA-MWCNT membrane had greater solvent-accessible pores, which enhanced water permeance while blocking the hydrocarbons. The incorporation of the hemin-modified MWCNT is thus an excellent strategy and could be adopted in the design of advanced membranes for oil/water separation.

Insights into the Synergistic Removal of Copper(II), Cadmium(II), and Chromium(III) Ions Using Modified Chitosan Based on Schiff Bases-g-poly(acrylonitrile)

Chitosan has received broad consideration as an adsorbent for all pollutants because of its low cost and great adsorption potential. However, its shortcomings, including sensitivity to pH, poor thermal stability, and poor mechanical strength, limit its use. The functional groups of chitosan can be modified to enhance its performance by the grafting technique and Schiff base modification. The grafting process used acrylonitrile (Ch-g-PAN) as a monomer and potassium persulfate as an initiator. After that, the modification via preparation of the Schiff base reaction using salicylaldehyde (Ch-g-Sch I) and P-anisaldehyde (Ch-g-Sch II) was carried out. The synthesized copolymers were detailed and characterized through several spectroscopic and microscopic techniques including infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. In addition, Ch-g-Sch I and Ch-g-Sch II were applied in the removal of different metal ions such as Cu²⁺, Cd²⁺, and Cr³⁺. The maximum adsorption capacity of Ch-g-Sch I for Cd²⁺ was 183.7 mg g^-1 in 24 h, while in the case of Ch-g-Sch II, the maximum adsorption capacity for Cd²⁺ was improved to 322.9 mg g^-1 for the same time. Moreover, adsorption thermodynamic analysis displays that the all ion adsorption process was not random and the pseudo-second-order model fitted with experimental results. Finally, Ch-g-Sch I and Ch-g-Sch II were applied as designs for industrial wastewater treatment with significant efficiency.

Recyclable Composite Membrane of Polydopamine and Graphene Oxide-Modified Polyacrylonitrile for Organic Dye Molecule and Heavy Metal Ion Removal

Developing efficient and recyclable membranes for water contaminant removal still remains a challenge in terms of practical applications. Herein, a recyclable membrane constituted of polyacrylonitrile-graphene and oxide-polydopamine was fabricated and demonstrated efficient adsorption capacities with respect to heavy metal ions (62.9 mg g^-1 of Cu²⁺ ion, CuSO₄ 50 mg L^-1) and organic dye molecules (306.7 mg g^-1 of methylene blue and 339.6 mg g^-1 of eriochrome black T, MB/EBT 50 mg L^-1). The polyacrylonitrile fibers provide the skeleton of the membrane, while the graphene oxide and polydopamine endow the membrane with hydrophilicity, which is favorable for the adsorption of pollutants in water. Benefitting from the protonation and deprotonation effects of graphene oxide and polydopamine, the obtained membrane demonstrated promotion of the selective adsorption or desorption of pollutant molecules. This guarantees that the adsorbed pollutant molecules can be desorbed promptly from the membrane through simple pH adjustment, ensuring the reusability of the membrane. After ten adsorption-desorption cycles, the membrane could still maintain a desirable adsorption capacity. In addition, compared with other, similar membranes reported, this composite membrane displays the highest mechanical stability. This work puts forward an alternative strategy for recyclable membrane design and expects to promote the utilization of membrane techniques in practical wastewater treatment.

Performance improvement of PES membrane decorated by Mil-125(Ti)/chitosan nanocomposite for removal of organic pollutants and heavy metal

The Mil-125(Ti)-CS nanocomposite was successfully synthesized and characterized by using scanning electron microscopy (SEM) images, Fourier-transform infrared (FTIR) analysis and X-ray diffraction (XRD). Then, to improve the membrane performance, the synthesized Mil-125(Ti)-CS nanocomposite was embedded into the polyethersulfone (PES) membrane matrix. The nanofiltration membranes were fabricated via phase inversion method. Presence of chitosan in the structure of Mil-125(Ti) has increased the compatibility of nanoparticles with the polymer and also improved the hydrophilicity of the resulted membranes. The water contact angle of bare membrane (58°) was reduced to 40° by blending of 1 wt% nanocomposite led to increasing the pure water flux. However, the incorporation of more than 1 wt% of the nanocomposite caused the accumulation of nanocomposites and this was reduced the pore radius and permeability. The membrane containing 1 wt% nanocomposite was displayed the highest flux recovery ratio (FRR) ∼ 98% in bovine serum albumin (BSA) filtration. The membranes containing Mil-125(Ti)-CS also showed good performance against fouling. The performance of membranes was evaluated by treatment of six reactive dyes, antibiotic (cefixime), heavy metal, NaCl and Na₂SO₄ solutions. Addition of Mil-125(Ti)-CS NPs at low concentrations resulted in membranes with high pure water flux, higher separation efficiency, and remarkable anti-fouling behavior.

Preparation and characterization of graphitic carbon nitrides/polyvinylidene fluoride adsorptive membrane modified with chitosan for Rhodamine B dye removal from water: Adsorption isotherms, kinetics and thermodynamics

In the present study, a PVDF/g-C₃N₄/chitosan (PCC) membrane was used for the removal of Rhodamine B from aqueous solutions. Water flux for PCC membrane decreased from 49.87% to 14.76% by the addition of chitosan from 2% to 4%. Afterward, batch adsorption conditions were optimized for a PVDF/g-C₃N₄/chitosan membrane applying Box-Behnken design algorithm. The maximum RB removal efficiency was 72.74% at 2 mg/L of initial RB concentration, pH = 3, 2 g of g-C₃N₄ and 3% of chitosan at the optimum conditions. The Freundlich isotherm and pseudo-second order models were satisfactorily describing the equilibrium and kinetic of adsorption, respectively. Thermodynamic parameters were disclosed that the adsorption of RB onto PCC was exothermic (ΔH° = -21.35 kJ mol^-1) and spontaneous (ΔG° < 0) with the generation of energy (ΔS° = +92.42 kJ mol^-1) at the interface of solid/liquid. Thus, this novel membrane could be employed as an effective adsorbent to remove of RB dye from aqueous solutions.

Chitin and derivative chitosan-based structures - Preparation strategies aided by deep eutectic solvents: A review

The high molecular weight of chitin, as a biopolymer, challenges its extraction due to its insolubility in the solvents. Also, chitosan, as the N-deacetylated form of chitin, can be employed as a primary material for different industries. The low mechanical stability and poor plasticity of chitosan films, as a result of incompatible interaction between chitosan and the used solvent, have limited its industrialization. Deep eutectic solvents (DESs), as novel solvents, can solve the extraction difficulties of chitin, and the low mechanical stability and weak plasticity of chitosan films. Also, DESs can be considered for the different chitosan and chitin productions, including chitin nanocrystal and nanofiber, N,N,N-trimethyl-chitosan, chitosan-based imprinted structures, and DES-chitosan-based beads and monoliths. This review aims to focus on the preparation and characterization (chemistry and morphology) of DES-chitin-based and DES-chitosan-based structures to understand the influence of the incorporation of DESs into the chitin and chitosan structure.

Magnetite nanoparticles decorated on multi-walled carbon nanotubes for removal of Cu2+ from aqueous solution

Acid-functionalized multi-walled carbon nanotube (MWCNTs-COOH) was prepared by acid treatment followed by decoration with magnetite (Fe₃O₄) nanoparticles (Fe₃O₄/MWCNTs-COOH) by co-precipitation of Fe²⁺/Fe³⁺ in the colloidal suspension of MWCNTs-COOH. The adsorption capacity and separation efficiency of these two adsorbents were investigated for the removal of Cu²⁺ ions in aqueous solution as water treatment adsorbents. The effect of reaction conditions, such as contact time, initial concentration of Cu²⁺ ions, and adsorbent dosage, on the adsorption capacity of MWCNTs-COOH was investigated. It was found that contact time of 10 min, adsorbent dosage of 0.2 g/L and 15 mg/L as initial concentration of Cu²⁺ ions are ideal conditions for maximum adsorption capacity (10.45 mg/g). The adsorption capacity of synthesized Fe₃O₄/MWCNTs-COOH containing different weight percent of Fe₃O₄ (10, 25, 50 wt%) was explored for removal of Cu²⁺ ions from aqueous solution and the best results achieved with 25 wt% Fe₃O₄/MWCNTs-COOH, which exhibited optimum adsorption capacity of 9.50 mg/g and 97% separation efficiency. Further, Langmuir and Freundlich isotherm models were applied to validate experimental data obtained in this work for Cu²⁺ adsorption.

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.

Novel PVDF-PVP Hollow Fiber Membrane Augmented with TiO2 Nanoparticles: Preparation, Characterization and Application for Copper Removal from Leachate

High proportion of copper has become a global challenge owing to its negative impact on the environment and public health complications. The present study focuses on the fabrication of a polyvinylidene fluoride (PVDF)-polyvinyl pyrrolidone (PVP) fiber membrane incorporated with varying loading (0, 0.5, 1.0, 1.5, and 2.0 wt%) of titanium dioxide (TiO₂) nanoparticles via phase inversion technique to achieve hydrophilicity along with high selectivity for copper removal. The developed fibers were characterized based on scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), permeability, porosity, zeta potential, and contact angle. The improved membrane (with 1.0 wt% TiO₂) concentration recorded the maximum flux (223 L/m²·h) and copper rejection (98.18%). Similarly, 1.0 wt% concentration of TiO₂ nanoparticles made the membrane matrix more hydrophilic with the least contact angle of 50.01°. The maximum copper adsorption capacity of 69.68 mg/g was attained at 1.0 wt% TiO₂ concentration. The experimental data of adsorption capacity were best fitted to the Freundlich isotherm model with R² value of 0.99573. The hybrid membrane developed in this study has considerably eliminated copper from leachate and the concentration of copper in the permeate was substantially reduced to 0.044 mg/L, which is below standard discharge threshold.

A systematic review on carbohydrate biopolymers for adsorptive remediation of copper ions from aqueous environments-Part B: Isotherms, thermokinetics and reusability

The presence of copper in aquatic environment is a serious threat for human health and ecosystem conservation. Adsorption is a powerful, operable and economic method for remediation of copper ions from aqueous phase. Carbohydrate biopolymers have emerged as promising, effective and environmental-friendly adsorbents for copper remediation. In part A of this review, different types of carbohydrate biopolymer adsorbents were surveyed focusing on prevalent and novel synthesis and modification methods. In current work (part B of the review), isothermal, thermodynamic and kinetic aspects of the copper adsorption by carbohydrate-based adsorbents as well as the regeneration and reusability of the biopolymer adsorbents are overviewed. Adsorption capacity, time required for equilibrium (adsorption rate), thermal-sensitivity of the adsorption, favorability extent, and sustainability of the adsorbents and adsorption processes are valuable and useful outcomes, resulted from the thermokinetic and reusability investigations. Such considerations are critical for the process design and scale up regarding technical, economical and sustainability of the adsorption process.

Enhanced Cr(VI) removal from water using a green synthesized nanocrystalline chlorapatite: Physicochemical interpretations and fixed-bed column mathematical model study

Apatite-based minerals have attracted much attention in the remediation of heavy metal-contaminated environment. However, exploring apatite with efficient adsorption performance for inorganic oxyanions such as Cr(VI) remains a challenge. Herein, a novel nanocrystalline chlorapatite (ClAP) was promptly prepared by a green method using eggshell wastes as calcium source with the purpose to enhance Cr(VI) adsorption capability. The generated ClAP was characterized by XRD, SEM-EPMA, TEM, FTIR, and BET analyses. Batch and column experiments were subsequently carried out to explore the influencing factors, adsorption capacity and removal mechanism. Results showed that ClAP exhibited excellent stability and adsorption performance for Cr(VI) (63.47 mg g^-1), which was much greater than that of hydroxyapatite and most reported materials. The adsorption process was fitted well by the pseudo-second-order model and the Langmuir model. In fixed bed column experiments, a novel time-fractional derivative model exhibited much better suitability in interpreting the observed breakthrough curves of Cr(VI) than traditional models. Furthermore, the reusability of ClAP in column was evaluated. Results showed that the adsorption capacity maintained well after consecutively reused for five cycles. Studies of the effect of pH, as well as FTIR and XPS investigations indicated that Cr(VI) adsorption was mainly ascribed to electrostatic interactions and surface complexation, while the reduction of Cr(VI) to the low-toxicity Cr(III) also existed in the adsorption process. The ClAP adsorbent was also successfully used for Cr(VI) remediation from real wastewater. Hence, nanocrystalline ClAP can be a promising material for enhancing the elimination of oxyanion contaminants such as Cr(VI) from water.

A critical review on the electrospun nanofibrous membranes for the adsorption of heavy metals in water treatment

Electrospun nanofibrous membranes (ENFMs) have many superior advantages, such as large specific surface area, high porosity, easy modification, good flexibility, and easy separation for recycling, which are consider as excellent adsorbents. In this paper, the research progress in the adsorption of heavy metals in water treatment by ENFMs is reviewed. Three types of ENFMs, including organic polymer ENFMs, organic polymer/inorganic material composite ENFMs and inorganic ENFMs are summarized, and their adsorption capacities for heavy metals in water are compared. The adsorption selectivity and capacity of ENFMs for heavy metals are depended largely on the type and number of functional groups on the surface of membranes, and usually the more the functional groups, the higher the adsorption capacity. The adsorption mechanisms of ENFMs are also mainly determined by the type of functional groups on the membrane. At present, the main challenge is to achieve the mass production of high-quality nanofibers and their actual application in the treatment of heavy metal-containing wastewater. Therefore, more consideration should be focused on the improvement of stability, mechanical strength and reusability of ENFMs. This review may provide an insight for the development of ENFMs-based adsorbents for heavy metals separation and water purification in the future.

Cu(II)-Regulated On-Site Assembly of Highly Chemiluminescent Multifunctionalized Carbon Nanotubes for Inorganic Pyrophosphatase Activity Determination

A novel signal-on chemiluminescence (CL) assay for pyrophosphatase (PPase) activity determination was innovatively developed based on the Cu(II)-regulated on-site assembly of highly chemiluminescent Cu(II), N-(aminobutyl)-N-(ethylisoluminol) (ABEI), gold nanodot, and chitosan multifunctionalized carbon nanotubes (Cu(II)/ABEI-Au/cs-CNTs). First, ABEI-functionalized gold nanodots (ABEI-Au) were assembled on the surface of chitosan-modified carbon nanotubes (cs-CNTs) via the reduction of HAuCl₄ with ABEI in a cs-CNT suspension to form ABEI-Au/cs-CNTs. Then, it was found that the catalyst Cu(II) can be selectively, efficiently, and quickly adsorbed onto ABEI-Au/cs-CNTs via the high-affinity interactions between Cu(II) and cs-CNTs to form novel hybrid nanomaterials Cu(II)/ABEI-Au/cs-CNTs. The CL intensity of Cu(II)/ABEI-Au/cs-CNTs was enhanced by about 2 orders of magnitude compared with that of ABEI-Au/cs-CNTs. Furthermore, it was found that in the presence of pyrophosphate ions (PPi), PPi could coordinate with Cu(II) to form a stable PPi-Cu(II) complex and block the assembly of Cu(II)/ABEI-Au/cs-CNTs. After the addition of PPase, PPase could catalyze the hydrolysis of PPi into Pi and release Cu(II) from the PPi-Cu(II) complex. The released free Cu(II) could trigger the on-site assembly of highly chemiluminescent Cu(II)/ABEI-Au/cs-CNTs, resulting in an enhanced CL intensity. The enhanced CL intensity had a good linear relationship with the activity units of PPase ranging from 0.025 to 0.5 U, with a detection limit of 9 mU. The method was employed to monitor the PPase inhibitor efficiently. Cu(II)/ABEI-Au/cs-CNTs with excellent CL may also find more applications in the development of novel CL analytical methods.

Membrane bioreactors troubleshooting through the preparation of a high antifouling PVDF ultrafiltration mixed-matrix membrane blended with O-carboxymethyl chitosan-Fe3O4 nanoparticles

Polymeric ultrafiltration (UF) membranes often used in membrane bioreactor (MBR) prone to be fouled by fouling agents. Therefore, in this paper, the antifouling characteristics of polyvinylidene fluoride (PVDF) UF membranes for wastewater treatment are improved through modifying membranes by O-carboxymethyl chitosan (OCMCS)-functionalized Fe₃O₄ nanoparticles (OCMCSFe₃O₄). The modifier agent was manufactured by the adsorption of OCMCS on Fe₃O₄ nanoparticles, which were synthesized via co-precipitating method. Antifouling performance of membranes was assessed by permeation tests done using activated sludge suspension as a biological foulant, then the calculation of the pure water flux recovery ratio (FRR) and fouling resistance parameters. Also, to investigate the protein rejection of membranes, permeation tests were conducted by the bovine serum albumin (BSA) solution. According to the obtained results, surface hydrophilicity of the embedded membranes was improved in the low concentrations of the modified nanoparticles. However, the high quantity of the OCMCS-Fe₃O₄ nanoparticles (>0.1 wt. %) in the casting solution lessened membrane performance owing to the agglomeration of the nanoparticles in the polymer matrix. Although, the 1 wt. % OCMCS-Fe₃O₄ membrane revealed considerably higher PWF and permeation than that of the other membranes. It was because of defects and cracks in the membranes. The 0.05 wt. % OCMCS-Fe₃O₄/PVDF membrane exhibited the highest FRR (95.7%) and protein rejection value (48%) and the lowest irreversible fouling resistance (Rir) value (4.2%). It is concluded that the blended membranes with modified nanoparticles resulted in a high-flux ultrafiltration membrane comparable with microfiltration membrane, while its separation properties remained similar to UF membrane.

Chitosan-based sorbent for efficient removal and extraction of ciprofloxacin and norfloxacin from aqueous solutions

Nanosheets prepared from magnesium oxide, chitosan and graphene oxide (MgO/Chit/GO) were hydrothermally synthesized and used as a sorbent for removal of ciprofloxacin and norfloxacin from aqueous solutions. Residual antibiotics in sample were determined by HPLC/UV instrument. The sorbent was characterized by FTIR, XRD, BET, SEM, and TEM. Its high adsorption capacity is attributed to the high surface area (294 m².g^-1) as compared to bare MgO/chit or bare GO. The pore size of the mesoporous sorbent typically is 15 Å. The adsorption isotherms for the two model antibiotics studied (norfloxacin, ciprofloxacin) can be described with the Langmuir model, and the maximum adsorption capacities are 1111 and 1000 mg.g^-1 for ciprofloxacin and norfloxacin, respectively. The analysis of the kinetic data revealed that the synthesized sorbent followed pseudo-second-order kinetics and the maximum equilibrium was at over 120 and 150 min for ciprofloxacin and norfloxacin, respectively. Therefore, it is introduced as an economical, eco- friendly, and high-performance sorbent for removal of antibiotics from aqueous solutions. Graphical abstract Schematic presentation of dispersion of magnesium oxide/chitosan/graphene oxide (MgO/chit/GO) nanosheets in waste water for removal of ciprofloxacin and norfloxacin as water pollutants.

Adsorption for copper(II) ion with chitosan-SP/PET composite adsorbent enhanced by electric field

A method combining adsorption with electric field-driven ion enrichment to remove the trace metal ions in wastewater was investigated. Composite adsorbent prepared from chitosan (CS) and sodium phytate (SP) supported into polyethylene glycol terephthalate (PET) nonwoven fabric by nonsolvent induced phase separation was employed and located near the cathode in a pair of titanium plate electrodes. Results showed the removal rate of copper ions (Cu(II)) adsorbed onto CS-SP/PET adsorbent was increased from 56% to 88% for 10 mg L−1 Cu(II) solution when the applied voltage was from 0 to 1.2 V. The adsorption behavior was well correlated with the Langmuir isotherm model. And adsorption process fitted well for pseudo-second-order kinetic equation, suggesting that chemical adsorption was rate-limiting step. And the energy consumption was economical, about 4.35 × 10−3 kW·h for 1 m3 of water with 10 mg L−1 Cu(II). It was suggested that the adsorption performance for Cu(II) with CS-SP/PET adsorbent was enhanced due to the enrichment of Cu(II) under electric field. This work provides a new way to remove trace heavy metal ions from wastewater.

Functional Chitosan Derivative and Chitin as Decolorization Materials for Methylene Blue and Methyl Orange from Aqueous Solution

Dyes are classified as one of the major pollutants of water. They have negative impacts not only on environment but also on human health. In fact, wastewater that contains these harmful substances requires many types of treatments. Therefore, alternative methods and adsorption agents are needed. Herein, we propose to evaluate the decolorization of methylene blue (MB) and methyl orange (MO) as two models of soluble dyes from water using chitin and chitosan-graft-polyacrylamide. Furthermore, the applicability of these biomacromolecules as alternative adsorption agents, their sticking probability and desorption were also examined. Experimental parameters such as dye concentration, contact time, pH solution, adsorbent dosage and temperature were thoroughly examined for the grafted chitosan and chitin. The activation energy ( E a ) and the thermodynamic variables (i.e., standard Gibb's free energy ( Δ G 0 ), standard enthalpy ( Δ H 0 ), and standard entropy ( Δ S 0 )) were determined using the Van't Hoff and Arrhenius equations. The sticking probability ( S *) model for MB and MO removal by chitin and the chitosan derivative demonstrated that both dyes were successfully removed under the proposed conditions. Desorption studies of MB and MO showed the reusability of both materials, suggesting their application for removing dyes from aqueous solution.

Carbon nanostructures for advanced nanocomposite mixed matrix membranes: a comprehensive overview

The highly progressive membrane separation technology challenges conventional separation processes such as ion exchange, distillation, precipitation, solvent extraction, and adsorption. The integration of many desired properties such as low energy consumption, high removal efficiency, affordable costs, suitable selectivity, acceptable productivity, ease of scale-up, and being environmentally friendly have made the membranes capable of being replaced with other separation technologies. Combination of membrane technology and nanoscience has revolutionized the nano-engineered materials, e.g. nanocomposites applied in advanced membrane processes. Polymer composites containing carbon nanostructures are promising choices for membrane fabrication owing to their enhanced chemistry, morphology, electromagnetic properties, and physicochemical stability. Carbon nanostructures such as carbon nanotubes (CNTs), nano graphene oxides (NGOs), and fullerenes are among the most popular nanofillers that have been successfully applied in modification of polymer membranes. Literature review shows that there is no comprehensive overview reporting the modification of mixed matrix membranes (MMMs) using carbon nanofibers, nano-activated carbons, and carbon nanospheres. The present overview focuses on the applications of carbon nanostructures mainly CNTs and NGOs in the modification of MMMs and emphasizes on the application of CNTs and NGO particles.