Effect of microwave on the synthesis of polyacrylamide-g-chitosan gel for azo dye removal

Fabrication of millimetre-sized amphoteric chitosan/alginate hollow vesicles for the adsorption of anionic and cationic dyes

In the face of complex dye wastewater, the development of amphoteric adsorbents for effective removal is imperative. Herein, millimetre-sized amphoteric chitosan/sodium alginate hollow vesicles were successfully prepared via a facile hydrothermal stirring method. The abundant functional groups, uniformly distributed micropores, and inner cavities contribute to enhance the adsorption capacity towards various types of charged dyes, including methylene blue (144.8 mg/g), acid blue-113 (654.9 mg/g), and methyl orange (400.3 mg/g). The vesicles worked well in the pH range of 3-11 and salt concentration up to 100 mmol/L, and remained >92 % of the original adsorption capacity after four cycles. The adsorption is a thermodynamic spontaneous process and the adsorption mechanism is monolayer chemisorption. Importantly, the vesicles possess semi-permeable membrane properties and excellent selectivity, making them favourable for complex wastewater treatment. The environment-friendly and high-performance amphoteric vesicles made from natural marine polysaccharides offer new possibilities for the development of effective absorbents.

Chitosan-based adsorbents for remediation of toxic dyes from wastewater: A review on adsorption mechanism, reusability, machine learning based modeling and future perspectives

The disposal of recalcitrant dyes in aquatic environments from various industrial sectors is a threat to both the plant and animal kingdom. The presence of dyes in various water bodies undermines the availability of uncontaminated drinking water and may result in serious health-related issues and diseases. Therefore, it is of utmost importance to get rid of these harmful dyes from the aquatic environment. Hence various treatment techniques came to the fore, but they have their corresponding advantages and disadvantages. Several researchers have reported the adsorption of dyes with carbon-based composites, polymeric materials, and metal-based nanoparticles. However, the one with biocompatible materials or biopolymers deserves special attention as they are benign from an environmental viewpoint. We have chosen chitosan as our material of interest and elaborated on the positive aspects of chitosan as an excellent candidate for dye adsorption. Although a plethora of review articles has been disseminated in the past to underscore the utilization of chitosan-based adsorbents in the extraction of dyes, this manuscript endeavors to furnish a thorough examination of the complete adsorption process, encompassing its parameters and kinetics, thus facilitating a reader lacking foundational knowledge in this field to attain a more comprehensible understanding of the subject matter. This review also integrates a comprehensive overview of optimization methodologies for dye adsorption and examines relevant patents-an area that, to the best of our knowledge, has not been thoroughly addressed in previous review articles. Conclusively, it can be stated that chitosan can efficiently adsorb dye from wastewater showing good performance even after five cycles of adsorption/desorption. Moreover, several software programs can be used for optimizing maximum dye adsorption capacity of chitosan which shows well alignment with experimental results, thus making it suitable for real-life applications.

Recent advances in CO2 capture and mineralization using layered double hydroxide-based materials: A review

The continuous release of substantial amounts of carbon dioxide (CO2) to the atmosphere has resulted in numerous severe adverse effects. Several materials have been synthesized and utilized for CO2 capture. One class of such materials is layered double hydroxides (LDHs), which have emerged as promising materials for CO2 capture due to their tunable properties, high surface area, and excellent CO2 adsorption capabilities. Although there are some review articles on CO2 capture and conversion using various materials, there is still a notable lack of thorough reviews focusing on the utilization of LDH-based materials for CO2 capture. Additionally, the field of CO2 capture and mineralization using LDH-based materials is rapidly evolving, necessitating up-to-date comprehensive reviews to analyze, evaluate, and condense the dispersed information found in recently published research articles. Accordingly, this review article provides a comprehensive overview of recent advancements in CO2 capture using LDH-based materials. After briefly introducing the topic, different synthesis protocols of LDH-based materials are briefly reviewed. Then, CO2 capture using LDHs, calcined LDHs, impregnated LDHs, composites containing LDHs, amine functionalized LDHs, and during steam methane reforming, are thoroughly analyzed and discussed. Additionally, the effects of synthesis method and post treatment of LDH-based materials on CO2 capture, effect of modification and functionalization on LDHs, and the effects of various process conditions including temperature, pressure, water vapor, and gas composition on the performance of CO2 capture by LDH-based materials are reviewed. Limitations, challenges, obstacles, and remaining knowledge gaps are highlighted, and future research works to address them are proposed.

Hydrogel Composition Effects on Performance as Single-Walled Carbon Nanotube Purification Media

Hydrogel microsphere media allows for postsynthetic purification of single-walled carbon nanotubes (SWNTs), affording characterization and application of their unique (n,m) chirality-dependent properties. This work reports the characterization of five hydrogel resins, Sephacryl S-100, S-200, S-300, S-400, and S-500, and the implementation of each as a SWNT purification medium. The physiochemical properties of each resin were explored spectroscopically through elemental analyses and with both light and electron microscopy. Both surface porosity and hydrogel swelling ratio were found to increase as the concentration of component allyl dextran (aDEX) decreased, each with an increasing Sephacryl S-number. Conversely, invariant properties included a hydrogel microsphere size distribution and concentrations of components methylenebisacrylamide and ammonium persulfate. When employed within gel-based SWNT purification schemes in overloading conditions, Sephacryl formulations of larger S-number adsorbed fewer SWNTs, but the chirality dependence of SWNT adsorption and elution was approximately consistent across all resins. In underloading conditions, approximately one-third of introduced SWNTs passed through each resin unabsorbed, while the resins showed varying chirality-dependent adsorption efficiencies. These observations collectively identify aDEX-rich gel regions as being responsible for SWNT purification, along with a SWNT-exclusive parameter other than chirality (speculated as length) that convolutes the effectiveness of gel-based single-chirality purification.

Novel Chitosan-ZnO nanocomposites derived from Nymphaeaceae fronds for highly efficient removal of Reactive Blue 19, Reactive Orange 16, and Congo Red dyes

The primary aim of this investigation was to synthesise novel adsorbent by incorporating greenly synthesized zinc oxide nanoparticles into chitosan matrix (G-ZnO-Cs). The production of ZnO Nanoparticles via a green approach involved the utilization of extracts derived from Nymphaeaceae fronds. This assertion was substantiated by the application of Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD) analytical techniques. Several Analytical methods such as Fourier Transform Infrared spectroscopy (FT-IR), Energy Dispersive X-ray Analysis (EDAX), FESEM, Thermogravimetric Analysis (TGA), XRD, Brunauer-Emmett-Teller (BET) analysis, and point-of-zero charge determination were used to characterize G-ZnO-Cs. Further study investigates the impact of five key processing parameters, namely pH, interaction duration, G-ZnO-Cs dosage, temperature, and initial concentration of dyes, on the removal of three organic dyes Reactive Blue 19 (RB 19), Reactive Orange 16 (RO 16), and Congo Red (CR) The adsorption process of Reactive Blue 19 (RB 19), Reactive Orange 16 (RO 16), and Congo Red (CR) dyes on G-ZnO-Cs were determined to comply to the pseudo-second-order (PSO) and Langmuir models, as determined through equilibrium and kinetic experiments. The highest adsorption capabilities for RB 19, RO 16 and CR dye were revealed to be 219.6 mg/g, 129.6 mg/g, and 118.8 mg/g, respectively. The elimination success rate of the fixed-bed column approach for treating huge volumes was highlighted in the conducted research. Moreover, the G-ZnO-Cs composite exhibited significant reusability due to its ability to undergo elution and simultaneous regeneration processes.

Hydrogels Based on Chitosan and Nanoparticles and Their Suitability for Dyes Adsorption from Aqueous Media: Assessment of the Last-Decade Progresses

Water is one of the fundamental resources for the existence of humans and the environment. Throughout time, due to urbanization, expanding population, increased agricultural production, and intense industrialization, significant pollution with persistent contaminants has been noted, placing the water quality in danger. As a consequence, different procedures and various technologies have been tested and used in order to ensure that water sources are safe for use. The adsorption process is often considered for wastewater treatment due to its straightforward design, low investment cost, availability, avoidance of additional chemicals, lack of undesirable byproducts, and demonstrated significant efficacious potential for treating and eliminating organic contaminants. To accomplish its application, the need to develop innovative materials has become an essential goal. In this context, an overview of recent advances in hydrogels based on chitosan and nanocomposites and their application for the depollution of wastewater contaminated with dyes is reported herein. The present review focuses on (i) the challenges raised by the synthesis process and characterization of the different hydrogels; (ii) the discussion of the impact of the main parameters affecting the adsorption process; (iii) the understanding of the adsorption isotherms, kinetics, and thermodynamic behavior; and (iv) the examination of the possibility of recycling and reusing the hydrogels.

Polysaccharide nanocomposites in wastewater treatment: A review

In modern times, wastewater treatment is vital due to increased water contamination arising from pollutants such as nutrients, pathogens, heavy metals, and pharmaceutical residues. Polysaccharides (PSAs) are natural, renewable, and non-toxic biopolymers used in wastewater treatment in the field of gas separation, liquid filtration, adsorption processes, pervaporation, and proton exchange membranes. Since addition of nanoparticles to PSAs improves their sustainability and strength, nanocomposite PSAs has gained significant attention for wastewater treatment in the past decade. This review presents a comprehensive analysis of PSA-based nanocomposites used for efficient wastewater treatment, focusing on adsorption, photocatalysis, and membrane-based methods. It also discusses potential future applications, challenges, and opportunities in adsorption, filtration, and photocatalysis. Recently, PSAs have shown promise as adsorbents in biological-based systems, effectively removing heavy metals that could hinder microbial activity. Cellulose-mediated adsorbents have successfully removed various pollutants from wastewater, including heavy metals, dyes, oil, organic solvents, pesticides, and pharmaceutical residues. Thus, PSA nanocomposites would support biological processes in wastewater treatment plants. A major concern is the discharge of antibiotic wastes from pharmaceutical industries, posing significant environmental and health risks. PSA-mediated bio-adsorbents, like clay polymeric nanocomposite hydrogel beads, efficiently remove antibiotics from wastewater, ensuring water quality and ecosystem balance. The successful use of PSA-mediated bio-adsorbents in wastewater treatment depends on ongoing research to optimize their application and evaluate their potential environmental impacts. Implementing these eco-friendly adsorbents on a large scale holds great promise in significantly reducing water pollution, safeguarding ecosystems, and protecting human health.

Chitosan Hydrogels for Water Purification Applications

Chitosan-based hydrogels have gained significant attention for their potential applications in water treatment and purification due to their remarkable properties such as bioavailability, biocompatibility, biodegradability, environmental friendliness, high pollutants adsorption capacity, and water adsorption capacity. This article comprehensively reviews recent advances in chitosan-based hydrogel materials for water purification applications. The synthesis methods, structural properties, and water purification performance of chitosan-based hydrogels are critically analyzed. The incorporation of various nanomaterials into chitosan-based hydrogels, such as nanoparticles, graphene, and metal-organic frameworks, has been explored to enhance their performance. The mechanisms of water purification, including adsorption, filtration, and antimicrobial activity, are also discussed in detail. The potential of chitosan-based hydrogels for the removal of pollutants, such as heavy metals, organic contaminants, and microorganisms, from water sources is highlighted. Moreover, the challenges and future perspectives of chitosan-based hydrogels in water treatment and water purification applications are also illustrated. Overall, this article provides valuable insights into the current state of the art regarding chitosan-based hydrogels for water purification applications and highlights their potential for addressing global water pollution challenges.

Scavenging of copper(II) ions, phosphate(V) ions, and diuron from aqueous media by goethite modified with chitosan or poly(acrylic acid)

Goethite was modified by chitosan (CS) or poly(acrylic acid) (PAA) to improve its adsorptive abilities toward components of agrochemicals, i.e., copper ions (Cu), phosphate ions (P), and diuron. The pristine goethite effectively bound Cu (7.68 mg/g, 63.71%) and P (6.31 mg/g, 50.46%) only in their mixed systems. In the one adsorbate solutions, the adsorption levels accounted for 3.82 mg/g (30.57%) for Cu, 3.22 mg/g (25.74%) for P, and 0.15 mg/g (12.15%) for diuron. Goethite modification with CS or PAA did not yield spectacular results in adsorption. The maximum increase in adsorbed amount was noted for Cu ions (8.28%) after PAA modification as well as for P (6.02%) and diuron (24.04%) after CS modification. Both goethite modifications contributed to clear reduction in desorption of pollutants (even by 20.26% for Cu after PAA coating), which was mainly dictated by electrostatic attractive forces and hydrogen bonds formation occurring between macromolecules and impurities. The only exception in this phenomenon was Cu desorption from CS-modified solid-the polymer made it higher (to 95.00%). The Cu adsorption on PAA-modified goethite enhanced solid aggregation and thus facilitated metal cation separation from aqueous media. Consequently, the goethite modification with PAA was considered more promising for environmental remediation.

Magnetic Fe3O4 embedded chitosan-crosslinked-polyacrylamide composites with enhanced removal of food dye: Characterization, adsorption and mechanism

The water solubility in acid solution, relative low adsorption capacities and unsatisfactory separation performance limit application of traditional chitosan-based adsorbents in wastewater treatment. To break the limitation, a hydrophilic magnetic Fe₃O₄ embedded chitosan-crosslinked-polyacrylamide composites (abbreviated as m-CS-c-PAM) were prepared by a two-step method. The m-CS-c-PAM composites were systematically characterized using SEM, XRD, FTIR, VSM, TGA and BET. Sunset yellow (SY) was selected as model food dye to investigate adsorption kinetics and thermodynamic parameters of food dye adsorption onto m-CS-c-PAM. Compared with magnetic Fe₃O₄/chitosan, m-CS-c-PAM can adapt to a wider range of pH (2-10) and resist the presence of inorganic salts. m-CS-c-PAM was proved to have high adsorption capacity (359.71 mg g^-1) for SY dye at 298 K, much higher than magnetic Fe₃O₄/chitosan and many reported adsorbents. Moreover, m-CS-c-PAM could be rapidly and efficiently separated from treated solution within 15 s by an external magnet and regenerated by NaOH solution. With its excellent adsorption capacity, pH-independent adsorption capability for food dye, easy and convenient separation ability, satisfactory reusability, m-CS-c-PAM can be a promising material for food wastewater treatment.

Engineered biochar supported layered double hydroxide-cellulose nanocrystals composite-: Synthesis, characterization and azo dye removal performance

In this work, engineered biochar decorated layered double hydroxides and cellulose nanocrystals (B-CuFe-CNC) biocomposites were synthesized by the facile ultrasonicated-co-precipitation technique. The biocomposite was investigated for purification of Eriochrome Black T (EBT) dye from water. The characterization results showed that the presence of CNC in biochar-layered double hydroxides resulted in a two-dimensional rod-like structure with excellent crystallinity, improved surface functionalities, and provides an attractive platform for the enhanced adsorption of azo anionic dye molecules. The adsorption system was appropriately demonstrated by the BBD-RSM (R² > 0.994). The biocomposite exhibited higher EBT adsorption in the acidic pH range (2-5) due to strong electrostatic and chemical interactions. The kinetic and isotherm results were well demonstrated by pseudo-second order, Freundlich, and Redlich Peterson models. The maximum adsorption capacity of biocomposite was 876.2 mg/g achieved within 45 min. The spectroscopic analyses imply that the high removal of EBT by biocomposite is mainly governed by electrostatic attraction, hydrogen bonding, and chemical/metal complexation mechanisms. The biocomposite maintained high EBT removal after six successive adsorption cycles and excellent dye adsorption in the different water matrices. The results suggest that tailoring biochar properties with layered double hydroxide and CNC is a promising way for the enhanced removal of dye contaminants from wastewater.

Behavior and mechanism of the adsorption of lead by an eco-friendly porous double-network hydrogel derived from keratin

In this study, a novel eco-friendly porous double-network keratin/polyacrylic acid (keratin-PAA) hydrogel was prepared using the one-pot method to improve the adsorption performance of the hydrogel toward Pb(II). The obtained porous keratin-PAA hydrogel was then characterized using nitrogen adsorption-desorption isotherms, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The interaction mechanism of Pb(II) and the keratin-PAA hydrogel was further investigated using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results showed that keratin-PAA hydrogel was successfully synthesized, with a specific surface area of 49.35 m²/g and a uniform pore distribution of 6.20 nm. The synthesized keratin-PAA hydrogel only took 6 min to adsorb nearly 70% of Pb(II) from the solution because of the interconnected porous network. The keratin-PAA hydrogel also showed a maximal adsorption amount of 234.6 mg/g, and satisfactory selectivity toward Pb(II). The adsorption kinetics of the keratin-PAA hydrogel binding to Pb(II) could be better described by the pseudo-second-order model, whereas the adsorption isotherms could be fitted using the Langmuir equation; this suggested that chemisorption was the main rate-limiting step. The XPS and FT-IR analysis results indicated that the sulfur-, nitrogen- and oxygen-containing groups in the keratin-PAA hydrogel were the main binding sites for Pb(II). In real aqueous samples, the keratin-PAA hydrogel could remove 93-104% of Pb(II). It is clear that the keratin-PAA hydrogel is an outstanding adsorbent material for the removal of Pb(II) from aqueous samples.

Simultaneous adsorption for cationic and anionic dyes using chitosan/electrospun sodium alginate nanofiber composite sponges

The coexistence of anionic and cationic dyes in dye wastewater has highlighted a great necessity to develop amphoteric adsorbents for their simultaneous removal. Herein, an amphoteric composite sponge was successfully fabricated by combining chitosan with electrospun sodium alginate nanofiber using lyophilization in acetic acid/water/dioxane mixed solvents, which owned the abundant functional groups and superior microstructure of interconnected pores and nanoscale fibers, beneficial for the adsorption capacity improvement. The optimum adsorption capacities for Acid Blue-113 and Rhodamine B were 926.2 ± 25.7 mg/g and 695.4 ± 17.0 mg/g, respectively, much higher than that of the controlled sample prepared with chitosan and non-spinning sodium alginate in traditional acetic acid/water solvents. Meanwhile, the sponge provided with the superior adsorption performance under various pH environment and cyclic adsorption. Importantly, it had considerable simultaneous adsorption capacity for binary system containing anionic and cationic dyes. Overall, the chitosan/electrospun sodium alginate nanofiber composite sponge shows potential for complex wastewater treatment.

Preparation of Magnetic Composite Polyaniline/Fe3O4−Hydrotalcite and Performance in Removal of Methyl Orange

Magnetic composite fabricated from polyaniline and Fe3O4-hydrotalcite (Pan/MHT) was successfully applicated for removal of methyl orange (MO) from wastewater. The structure and properties of Pan/MHT were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer, and Brunauer-Emmett-Teller adsorption isotherm. Adsorption kinetic results indicated that the adsorption process followed pseudosecond-order kinetic model ( $R^2=0.999$ ), MO adsorption onto Pan/MHT was well described by Freundlich isotherm ( $R^2=0.994$ ), and the MO adsorption capacity of 2 Pan/MHT obtained the highest with $Q_e=156.25\text{mg}/\text{g}$ . Batch adsorption experiments were carried out using magnetic composite with the effects of initial MO concentration, solution pH, and adsorbent dosage. The results revealed that the magnetic Pan/MHT exhibited efficient adsorption of MO in the aqueous solution as a result of the affinity for organic dyes, microporous structure, and suitable surface area for adsorption (15,460 m2/g). The superparamagnetic behavior of Pan/MHT (with $H_c=18.56\text{Oe}$ , $M_s=23.38\times {10}^{-3}\text{emu}/\text{g}$ , and $M_r=0.91\times {10}^{-3}\text{emu}/\text{g}$ ) helps that it could be separated from the solution and performs as an economical and alternative adsorbent to removal and degrade azo dye from wastewater. Pan/MHT was also investigated to reuse after desorption of MO in 0.1 M HCl, and the results show that 2 Pan/MHT can be reused for 4 cycles with $Q_e=79.66\text{mg}/\text{g}.$

Applications of chitin and chitosan based biomaterials for the adsorptive removal of textile dyes from water - A comprehensive review

The presence of pollutants in the water bodies deteriorate the water quality and make it unfit for use. From an environmental perspective, it is essential to develop new technologies for the wastewater treatment and recycling of dye contaminated water. The surface modified chitin and chitosan biopolymeric composites based adsorbents, have an important role in the toxic organic dyes from removal wastewater. The surface modification of biopolymers with various organics and inorganics produces more active sites at the surface of the adsorbent, which enhances dye and adsorbent interaction more reliable. Herein, the work brought in the thought of the application of various chitin and chitosan composites in wastewater remediation and suggested the versatility in composites for the development of rapid, selective and effective removal processes for the detoxification of a variety of organic dyes. It further emphasizes the existing obstruction and impending prediction for the deprivation of dyes via adsorption techniques.

Recent developments in polysaccharide-based electrospun nanofibers for environmental applications

Electrospinning has become an inevitable approach to produce nanofibrous structures for diverse environmental applications. Polysaccharides, due to their variety of types, biobased origins, and eco-friendly, and renewable nature are wonderful materials for the said purpose. The present review discusses the electrospinning process, the parameters involved in the formation of electrospun nanofibers in general, and the polysaccharides in specific. The selection of materials to be electrospun depends on the processing conditions and properties deemed desirable for specific applications. Thereby, the conditions to electrospun polysaccharides-based nanofibers have been focused on for possible environmental applications including air filtration, water treatment, antimicrobial treatment, environmental sensing, and so forth. The polysaccharide-based electrospun membranes, for instance, due to their active adsorption sites could find significant potential for contaminants removal from the aqueous systems. The study also gives some recommendations to overcome any shortcomings faced during the electrospinning and environmental applications of polysaccharide-based matrices.

Crystal violet dye sorption over acrylamide/graphene oxide bonded sodium alginate nanocomposite hydrogel

The synthesis of acrylamide bonded sodium alginate (AM-SA) hydrogel and acrylamide/graphene oxide bonded sodium alginate (AM-GO-SA) nanocomposite hydrogel was successfully performed using the free radical method. The AM-SA and AM-GO-SA hydrogels were applied as composited adsorbents in crystal violet (CV) dye removal. The adsorption process experiments were performed discontinuously and the acquired data showed that the efficiency is more dependent on pH than other factors. The C-O, CO, and CC groups were detected in the produced hydrogels. The amount of surface area was computed to be 44.689 m²/g, 0.0392 m²/g, and 6.983 m²/g for GO, AM-SA, and AM-GO-SA nanocomposite hydrogel, respectively. The results showed that the experimental data follow the Redlich-Peterson isotherm model. Also, the maximum adsorption capacity of monolayer for CV dye adsorption was determined using AM-SA hydrogel and AM-GO-SA nanocomposite hydrogel 62.07 mg/g and 100.30 mg/g, respectively. In addition, the parameters R_L, n, and E showed that the processes of adsorption of CV dye using both types of adsorbents are physical and desirable. Thermodynamically, the CV elimination was exothermic and spontaneous. Besides, thermodynamic results showed that the adsorption process is better proceeding at low temperatures. The experimental data followed a pseudo- second- order (PSO) kinetic model. Also, the Elovich model showed that AM-GO-SA nanocomposite hydrogel has more ability to absorb CV dye. Therefore, according to the obtained results, it can be stated that the produced hydrogels are efficient and viable composited adsorbent in removing CV dye from aqueous solution.

Chitosan-based hybrid materials for adsorptive removal of dyes and underlying interaction mechanisms

Environmental pollution by dyes molecules has become a subject of intensive research in recent years due to their hazardous effects on human health, organisms, and animals. Effective treatment and removal of dye molecules from the environmental matrices and water sources are of supreme concern. The deployment of cheap, safe, green, sustainable, and eco-friendly materials to remove these pollutants from water is the main challenge during the last decades. Chitosan and its derivatives/composites, as a cheap, easily available, and environmentally friendly sorbent, have attracted increasing attention for the removal of dye molecules. This review article focuses on the application of chitosan and chitosan-based smart adsorbents for the removal of dyes. Recent methods for the preparation of chitosan-based composites and their application in the removal of dyes are discussed. Moreover, the possible mechanisms for the interaction of chitosan and chitosan-based adsorbents with dyes molecules were evaluated. Finally, future prospects of using chitosan as an adsorbent for the removal of dye molecules are directed.

A Review on Polymer Nanocomposites and Their Effective Applications in Membranes and Adsorbents for Water Treatment and Gas Separation

Globally, environmental challenges have been recognised as a matter of concern. Among these challenges are the reduced availability and quality of drinking water, and greenhouse gases that give rise to change in climate by entrapping heat, which result in respirational illness from smog and air pollution. Globally, the rate of demand for the use of freshwater has outgrown the rate of population increase; as the rapid growth in town and cities place a huge pressure on neighbouring water resources. Besides, the rapid growth in anthropogenic activities, such as the generation of energy and its conveyance, release carbon dioxide and other greenhouse gases, warming the planet. Polymer nanocomposite has played a significant role in finding solutions to current environmental problems. It has found interest due to its high potential for the reduction of gas emission, and elimination of pollutants, heavy metals, dyes, and oil in wastewater. The revolution of integrating developed novel nanomaterials such as nanoparticles, carbon nanotubes, nanofibers and activated carbon, in polymers, have instigated revitalizing and favourable inventive nanotechnologies for the treatment of wastewater and gas separation. This review discusses the effective employment of polymer nanocomposites for environmental utilizations. Polymer nanocomposite membranes for wastewater treatment and gas separation were reviewed together with their mechanisms. The use of polymer nanocomposites as an adsorbent for toxic metals ions removal and an adsorbent for dye removal were also discussed, together with the mechanism of the adsorption process. Patents in the utilization of innovative polymeric nanocomposite membranes for environmental utilizations were discussed.

Recent Developments in Chitosan-Based Adsorbents for the Removal of Pollutants from Aqueous Environments

The quality of water is continuously under threat as increasing concentrations of pollutants escape into the aquatic environment. However, these issues can be alleviated by adsorbing pollutants onto adsorbents. Chitosan and its composites are attracting considerable interest as environmentally acceptable adsorbents and have the potential to remove many of these contaminants. In this review the development of chitosan-based adsorbents is described and discussed. Following a short introduction to the extraction of chitin from seafood wastes, followed by its conversion to chitosan, the properties of chitosan are described. Then, the emerging chitosan/carbon-based materials, including magnetic chitosan and chitosan combined with graphene oxide, carbon nanotubes, biochar, and activated carbon and also chitosan-silica composites are introduced. The applications of these materials in the removal of various heavy metal ions, including Cr(VI), Pb(II), Cd(II), Cu(II), and different cationic and anionic dyes, phenol and other organic molecules, such as antibiotics, are reviewed, compared and discussed. Adsorption isotherms and adsorption kinetics are then highlighted and followed by details on the mechanisms of adsorption and the role of the chitosan and the carbon or silica supports. Based on the reviewed papers, it is clear, that while some challenges remain, chitosan-based materials are emerging as promising adsorbents.

Application of cellulose nanocrystals prepared from agricultural wastes for synthesis of starch-based hydrogel nanocomposites: Efficient and selective nanoadsorbent for removal of cationic dyes from water

A novel and bio-based hydrogel nanocomposite were developed using reinforcement of starch grafted copolymers of 2-acrylamido-2methyl propane sulfonate and acrylic acid (starch-g-(AMPS-co-AA)) hydrogel with magnetite-functionalized cellulose nanocrystals (MCNCs). The MCNCs-hydrogel was utilized as a proficient and environmentally benign nanoadsorbent for removal of cationic dyes with great capacity and selectivity. Sugar-beet pulp (SBP) was exploited for CNCs production through acid hydrolysis of enzymatic-mediated SBP. Fe₃O₄ nanoparticles were anchored on CNCs to synthesize MCNCs as the nanofiller of MCNCs/starch-g-(AMPS-co-AA) hydrogel. The synthesis of CNCs, MCNCs and hydrogel nanocomposite were confirmed using FESEM, FTIR, VSM and TGA analyses. Hydrogel nanocomposite showed excellent and reusable capacity for specific adsorption of cationic dyes. The effects of nanoadsorbent dosage, time, pH, dye initial concentration, and temperature on the adsorption were scrutinized for two model cationic dyes (crystal violet (CV) and methylene blue (MB). Adsorption capacities for CV and MB were 2500.0 mg/g and 1428.6 mg/g, respectively.

A review on the synthesis of graft copolymers of chitosan and their potential applications

Chitosan is an antimicrobial, biodegradable and biocompatible natural polymer, commercially derived from the partial deacetylation of chitin. Currently modified chitosan has occupied a major part of scientific research. Modified chitosan has excellent biotic characteristics like biodegradation, antibacterial, immunological, metal-binding and metal adsorption capacity and wound-healing ability. Chitosan is an excellent candidate for drug delivery, food packaging and wastewater treatment and is also used as a supporting object for cell culture, gene delivery and tissue engineering. Modification of pure chitosan via grafting improves the native properties of chitosan. Chitosan grafted copolymers exhibit high significance and are extensively used in numerous fields. In this review, modifications of chitosan through several graft copolymerization techniques such as free radical, radiation, and enzymatic were reported and the properties of grafted chitosan were discussed. This review also discussed the applications of grafted chitosan in the fields of drug delivery, food packaging, antimicrobial, and metal adsorption as well as dye removal.