Porous chitosan doped with graphene oxide as highly effective adsorbent for methyl orange and amido black 10B

Emerging Nanomaterials for Drinking Water Purification: A New Era of Water Treatment Technology

The applications of nanotechnology in the field of water treatment are rapidly expanding and have harvested significant attention from researchers, governments, and industries across the globe. This great interest stems from the numerous benefits, properties, and capabilities that nanotechnology offers in addressing the ever-growing challenges related to water quality, availability, and sustainability. This review paper extensively studies the applications of several nanomaterials including: graphene and its derivative-based adsorbents, CNTs, TiO2 NPs, ZnO NPs, Ag NPs, Fe NPs, and membrane-based nanomaterials in the purification of drinking water. This, it is hoped, will provide the water treatment sector with efficient materials that can be applied successfully in the water purification process to help in addressing the worldwide water scarcity issue.

HKUST-1 in-situ loaded ultrastable covalently crosslinked agarose aerogel with solvothermal for highly efficient removal of methylene blue

A new HKUST-1@covalently crosslinked agarose aerogel (HKUST-1@CCAGA) was synthesized for the highly effective elimination of Methylene Blue (MB). Firstly, the covalently crosslinked agarose aerogel (CCAGA) was obtained by hydrothermal crosslinking reaction with epichlorohydrin (ECH) as crosslinker, which remained stabilized under hydrothermal and solvothermal conditions. Then, HKUST-1 was made to bind to CCAGA by in situ solvothermal assays, and the HKUST-1 loading rate reached 47.4 % based on thermogravimetric data and calculated using the cross over method. Meanwhile, the SEM exhibited the complete 3D honeycomb structure of CCAGA, and HKUST-1 particles uniformly distributed on its layers. Additionally, the specific surface area of HKUST-1@CCAGA can reached 648.59 m2·g-1. The HKUST-1@CCAGA composite was utilized for MB removal, achieving a high adsorption capacity of 424.30 mg·g-1 at pH 8. The adsorption of MB was also maintained at 80 % after 5 cycles of the experiment. The composite aerogel exhibits good recyclability and has excellent adsorption capacity.

Chitosan-based aerogels: A new paradigm of advanced green materials for remediation of contaminated water

Chitosan (CS) aerogels are highly porous (∼99 %), exhibit ultralow density, and are excellent sorbents for removing ionic pollutants and oils/organic solvents from water. Their abundant hydroxyl and amino groups facilitate the adsorption of ionic pollutants through electrostatic interaction, complexation and chelation mechanisms. Selection of suitable surface wettability is the way to separate oils/organic solvents from water. This review summarizes the most recent developments in improving the adsorption performance, mechanical strength and regeneration of CS aerogels. The structure of the paper follows the extraction of chitosan, preparation and sorption characteristics of CS aerogels for heavy metal ions, organic dyes, and oils/organic solvents, sequentially. A detailed analysis of the parameters that influence the adsorption/absorption performance of CS aerogels is carried out and their effective control for improving the performance is suggested. The analysis of research outcomes of the recently published data came up with some interesting facts that the unidirectional pore structure and characteristics of the functional group of the aerogel and pH of the adsorbate have led to the enhanced adsorption performance of the CS aerogel. Finally, the excerpts of the literature survey highlighting the difficulties and potential of CS aerogels for water remediation are proposed.

C.I. Acid Black 1 transfer from dilute solution to perlite framework in organic waste management

Dyes, considered as toxic and persistent pollutants, must be removed from organic wastes prior to their composting and application in sustainable agriculture. Azo dyes, capable of altering the physicochemical properties of soil, are difficult to expel by conventional wastewater treatments. C.I. Acid Black 1 (AB 1), a sulfonated azo dye, inhibits nitrification and ammonification in the soil, lessens the nitrogen use efficacy in crop production and passes substantially unaltered through an activated sludge process. The retention of C.I. Acid Black 1 by raw and expanded perlite was investigated in order to examine the potential effectiveness of this aluminosilicate material toward organic waste cleanup. Dye adsorption proved spontaneous and endothermic in nature, increasing with temperature for both perlites. Expanded perlite having a more open structure exhibited a better performance compared to the raw material. Several of the most widely recognized two-parameter theoretical models, i.e., Langmuir, Freundlich, Temkin, Brunauer-Emmett-Teller (BET), Harkins-Jura, Halsey, Henderson, and Smith, were applied to reveal physicochemical features characterizing the adsorption. The Langmuir, Freundlich, Temkin, BET, Henderson, and Smith equations best fitted experimental data indicating that the adsorption of anionic dye on perlites is controlled by their surface, i.e., non-uniformity in structure and charge. This heterogeneity of surface is considered responsible for promoting specific dye adsorption areas creating dye "islands" with local dye supersaturations.

Poly(acrylic acid-co-2-acrylamido-2-methyl-1-propanesulfonic acid)-grafted chitosan hydrogels for effective adsorption and photocatalytic degradation of dyes

As a result of the growth of industrialization and urbanization, the water ecosystem is contaminated by various pollutants, including heavy metal ions and dyes. The use of low-cost and environmentally friendly dye adsorbents has been investigated. A hydrogel was fabricated via graft polymerization of acrylic acid (AA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) onto chitosan. The hydrogel was used as a dye adsorbent and support for a zinc oxide (ZnO) powder photocatalyst. The adsorption capacity of the bare hydrogel was greater towards cationic dyes than anionic dyes. Grafting P(AA-co-AMPS) exhibited a 23-time increase in adsorption capacity towards crystal violet (CV) compared to pristine chitosan. The effect of the AA-AMPS molar ratio on CV adsorption was studied. A hydrogel with an AA-AMPS ratio of 10 : 1 had the highest adsorption capacity towards CV in water, removing 91% of the dye in 12 h. The maximum adsorption capacity was 2023 mg g-1. The adsorption kinetics and isotherm were described by the pseudo-second-order model and the Langmuir model, respectively. ZnO particles were in situ synthesized within the 10 : 1 hydrogel to facilitate the recovery of the photocatalyst. The ZnO hydrogel composite could remove 95% and 92% of CV from solutions on the 1st and 2nd cycle, respectively. In addition, the hydrogel composite containing only 8.7 wt% of ZnO particles effectively degraded adsorbed CV under sunlight and could be reused without requiring a chemical regeneration or photocatalyst recovery procedure. This hydrogel composite is an effective dual-functional material for the adsorption and photodegradation of dye pollutants in wastewater.

Flexible fabrication chitosan-polyamidoamine aerogels by one-step method for efficient adsorption and separation of anionic dyes

Chitosan in situ grown polyamidoamine (CTS-Gx PAMAM (x = 0, 1, 2, 3)) aerogels were fabricated by a facile one-step freeze-drying method, with glutaraldehyde serving as a crosslinker. The three-dimensional skeletal structure of aerogel provided numerous adsorption sites and accelerated the effective mass transfer of pollutants. The adsorption kinetics and isotherm studies of the two anionic dyes were consistent with the pseudo-second-order and Langmuir models, indicating that the removal of rose bengal (RB) and sunset yellow (SY) was a monolayer chemisorption process. The maximum adsorption capacity of RB and SY reached 370.28 mg/g and 343.31 mg/g, respectively. After five adsorption-desorption cycles, the adsorption capacities of the two anionic dyes reached 81.10% and 84.06% of the initial adsorption capacities, respectively. The major mechanism between the aerogels and dyes was systematically investigated based on using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy analyses, confirming that electrostatic interaction, hydrogen bonding and van der Waals interactions were the main driving forces for the superior adsorption performance. Furthermore, the CTS-G2 PAMAM aerogel exhibited good filtration and separation performance. Overall, the novel aerogel adsorbent possesses excellent theoretical guidance and practical application potential for the purification of anionic dyes.

Carbon nanomaterial-based membranes in solid-phase extraction

Carbon nanomaterials (CNMs) have some excellent properties that make them ideal candidates as sorbents for solid-phase extraction (SPE). However, practical difficulties related to their handling (dispersion in the atmosphere, bundling phenomena, reduced adsorption capability, sorbent loss in cartridge/column format, etc.) have hindered their direct use for conventional SPE modes. Therefore, researchers working in the field of extraction science have looked for new solutions to avoid the above-mentioned problems. One of these is the design of CNM-based membranes. These devices can be of two different types: membranes that are exclusively composed of CNMs (i.e. buckypaper and graphene oxide paper) and polysaccharide membranes containing dispersed CNMs. A membrane can be used either as a filter, operating under flow-through mode, or as a rotating device, operating under the action of magnetic stirring. In both cases, the main advantages arising from the use of membranes are excellent results in terms of transport rates, adsorption capability, high throughput, and ease of employment. This review covers the preparation/synthesis procedures of such membranes and their potential in SPE applications, highlighting benefits and shortcomings in comparison with conventional SPE materials (especially, microparticles carbonaceous sorbents) and devices. Further challenges and expected improvements are addressed too.

Micro-mechanism insights into the adsorption of anionic dyes using quaternary ammonium-functionalised chitosan aerogels

The development of adsorbents with outstanding adsorption capacities, wide versatility, and excellent recyclability for the removal of organic dyes remains a challenge. In this study, a quaternised chitosan-based aerogel (QCSA) was fabricated via a facile method to effectively treat concomitant anionic dyes. Porous QCSA with high hydrophilicity, nontoxicity, excellent thermal stability, and sustainability exhibits adsorption properties superior to most previously reported adsorbents. The equilibrium adsorption capacities for Congo red, Sunset yellow, and Methyl orange were 1259.6, 550.2, and 607.5 mg/g, respectively. Notably, the spent QCSA exhibits excellent cyclic performance. The multilayer adsorption, external-internal mass transfer resistance, and adsorption on the active site models were employed to enable a more accurate description of the dynamic characteristics, confirming that double-layer chemisorption was the dominant process. A quantitative analysis of the electrostatic potential and the independent gradient model further verified that electrostatic interactions, hydrogen bonding, and van der Waals forces led to the highly efficient adsorption of dye molecules. Therefore, the eco-friendly and recyclable QCSA is a promising adsorbent for trapping anionic dyes from aquatic systems.

Simultaneous removal of aqueous same ionic type heavy metals and dyes by a magnetic chitosan/polyethyleneimine embedded hydrophobic sodium alginate composite: Performance, interaction and mechanism

Heavy metals and azo dyes caused huge harm to the aqueous system and human health. A magnetic chitosan/polyethyleneimine embedded hydrophobic sodium alginate composite (MCPS) was designed and prepared to simultaneously remove aqueous same ionic type heavy metals and azo dyes. In mono-polluted system, the optimal pH for Cr(VI), MO (methyl orange), Cu(Ⅱ) and MB (methylene blue) were 3, 2, 6 and 12 with a saturated adsorption capacity of 87.53, 66.41, 351.03 and 286.54 mg/g, respectively. Pseudo-second-order was suitable to describe the adsorption kinetics of them and the adsorption isotherms were more consistent with the Langmuir isotherm model being a spontaneous, endothermic, and entropy-increasing process. In binary-polluted system, MCPS possessed simultaneous adsorption for Cr (Ⅵ)-MO and Cu(Ⅱ)-MB pollutants at their optimal pH, in addition, whether in anionic or cationic solution, the removal of heavy metals were promoted with the add of azo dyes but the removal of azo dyes were suppressed with the add of heavy metals. Both Cr (Ⅵ)-MO and Cu(Ⅱ)-MB pollutants could be effectively adsorbed and desorbed from MCPS by changing the pH of the aqueous solution to realize recyclability. Lastly, removal mechanism was revealed in detail by FT-IR, EDS and XPS.

Bioaerogels, the emerging technology for wastewater treatment: A comprehensive review on synthesis, properties and applications

Over the past decade use of aerogels has received much attention as an emerging technology for wastewater treatment. However, production of aerogels is not environment-friendly. Owing to its excellent properties such as porosity, three-dimensional structure, being amenable to chemical modifications, it is imperative to devise strategies for their improved production and use. Bioaerogels are non-toxic and most of their precursor compounds are biomass-derived. This review aims to present a comprehensive report on survey of existing literature published on the use of bioaerogels for removal of all major categories of water contaminants, namely, heavy metals, industrial dyes, oil, organic compounds and pharmaceuticals. It also gives critical analysis of the lacunae in the existing knowledge such as lack of studies on domestic sewage, emerging pollutants, toxicity of raw materials and adequate disposal of used adsorbents. Proposals of overcoming the limitations in the applicability of bioaerogels, like combining constructed wetlands with use of bioaerogels, among others have been discussed. In this review, emphasis has been given on production of bioaerogels, with an aim to underscore the potential of valorization of biomass waste to develop novel materials for wastewater treatment in an effort towards creating a circular and green economy.

Effect of additional Fe2+ salt on electrocoagulation process for the degradation of methyl orange dye: An optimization and kinetic study

The wastewater generated from textile industries is highly colored and contains dyes including azo dyes, which are toxic to human and water-living organisms. The treatment of these azo dyes using conventional treatment techniques is challenging due to their recalcitrant properties. In the current study, the effect of additional Fe²⁺ on electrocoagulation (EC) using Fe electrodes has been studied for the removal of methyl orange (MO) azo dye. pH between 4-5 was found to be optimum for EC and treatment efficiency decreased with increasing dye concentrations. With the addition of Fe²⁺ salt, dye removal for a certain concentration was increased with the increase of current density and Fe²⁺ up to a certain limit and after that, the removal efficiency decreased. The COD, color and dye removals were 88.5%, 93.1% and 100%, respectively, for EC of 200 mg.L⁻¹ dye solution using only 0.20 mmol.L⁻¹ Fe²⁺ for 0.40 mA cm⁻² current density, whereas for EC, the respective removal efficiencies were 76.7%, 63.4% and 82.4% for 32 min. The respective operating cost for EC was $768 kg⁻¹ removed dye ($0.342 m⁻³), whereas, for EC with additional Fe²⁺ salt, it was $350 kg⁻¹ removed dye ($0.189 m⁻³). The kinetic results revealed that the first-order kinetic model was fitted best for EC, whereas the second-order kinetic model was best fitted for Fe²⁺ added EC. For real textile wastewater, 57.6% COD removal was obtained for 0.15 mmol.L⁻¹ Fe²⁺ added EC compared to 27.8% COD removal for EC for 32 min. Based on the study we can conclude that Fe²⁺ assisted EC can be used for effective treatment of textile wastewater containing toxic compounds like azo dyes.

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EC represents limiting treatment performance for higher contaminant concentrations.

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0.20 mmol.L⁻¹ Fe²⁺ salt enhances the EC treatment performance of MO dye to 100%.

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EC followed first-order kinetic model, whereas Fe²⁺ added EC followed second-order kinetic model.

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Operating cost was reduced to $0.327 m⁻³ from $0.598 m⁻³ for EC with additional Fe²⁺.

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58% COD was removed for 0.15 mmol.L⁻¹ Fe²⁺ added EC for real textile wastewater.

Adsorption of methylene blue by Nicandra physaloides(L.) Gaertn seed gum/graphene oxide aerogel

In this study, a novel composite aerogel of Nicandra physaloides(L.) Gaertn seed, gum/graphene oxide (NPG/GO), was prepared by using a vacuum freeze drying method for methylene blue (MB) adsorption. The techniques, including Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), were adopted for studying the structure and surface characteristics of NPG/GO, with thermogravimetric analysis (TGA) being adopted for testing thermal properties. The effects of pH value, initial dye concentration, temperature and adsorbent dosage on adsorption performance were elaborately analysed. The adsorption kinetic studies showed that the process of adsorption follows Langmuir isotherm and a pseudo-second-order kinetic model. When the mass ratio of NPG to GO was 1.25:1, the adsorption capacity was the highest. According to Langmuir isotherm, the maximum adsorption capacity of 408.16 mg/g was higher than that of NPG. The specific surface area and average pore diameter of NPG/GO was measured as 2.70 m²/g and 4.8 nm, respectively. Thermodynamic analysis revealed that the adsorption process of methylene blue on NPG/GO was a spontaneous and endothermic process. In general, the prepared nanocomposites were excellent candidates for adsorption and removal process because of simple synthesis, low cost, high efficiency, non-toxicity, environment protection and degradability.

Chitosan- and Alginate-Based Hydrogels for the Adsorption of Anionic and Cationic Dyes from Water

Novel hydrogel systems based on polyacrylamide/chitosan (PAAM/chitosan) or polyacrylic acid/alginate (PAA/alginate) were prepared, characterized, and applied to reduce the concentrations of dyes in water. These hydrogels were synthetized via a semi-interpenetrating polymer network (semi-IPN) and then characterized by Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), and their swelling capacities in water were measured. In the adsorption experiments, methylene blue (MB) was used as a cationic dye, and methyl orange (MO) was used as an anionic dye. The study was carried out using a successive batch method for the dye absorption process and an equilibrium system to investigate the adsorption of MO on PAAM/chitosan hydrogels and MB on PAA/alginate in separate experiments. The results showed that the target hydrogels were synthetized with high yield (more than 90%). The chemical structure of the hydrogels was corroborated by FTIR, and their high thermal stability was verified by TGA. The absorption of the MO dye was higher at pH 3.0 using PAAM/chitosan, and it had the ability to remove 43% of MO within 10 min using 0.05 g of hydrogel. The presence of interfering salts resulted in a 20–60% decrease in the absorption of MO. On the other hand, the absorption of the MB dye was higher at pH 8.5 using PAA/alginate, and it had the ability to remove 96% of MB within 10 min using 0.05 g of hydrogel, and its removal capacity was stable for interfering salts.

Adsorptive removal of organic dyes via porous materials for wastewater treatment in recent decades: A review on species, mechanisms and perspectives

Organic dyes, a type of high toxic and carcinogenic chemicals that present severe threats to human and aquatic life, are the most commonly seen organic pollutants in wastewater of industries such as textile, rubber, cosmetic industry etc. Various techniques for the removal of dyes are compared in this review. Adsorption has proven to be a facile and promising approach for the removal of dyes in wastewater. This work focuses on the latest development of various porous materials for the adsorption of organic dyes. The characteristics, functionalization and modification of different porous materials are also presented. Furthermore, adsorption behaviors and mechanism of these adsorbents in the adsorption of organic dyes are critically reviewed. Finally, challenges and opportunities for future research in the development of novel materials for the highly efficient removal of dyes are proposed.

Graphene-Based Materials Immobilized within Chitosan: Applications as Adsorbents for the Removal of Aquatic Pollutants

Graphene and its derivatives, especially graphene oxide (GO), are attracting considerable interest in the fabrication of new adsorbents that have the potential to remove various pollutants that have escaped into the aquatic environment. Herein, the development of GO/chitosan (GO/CS) composites as adsorbent materials is described and reviewed. This combination is interesting as the addition of graphene to chitosan enhances its mechanical properties, while the chitosan hydrogel serves as an immobilization matrix for graphene. Following a brief description of both graphene and chitosan as independent adsorbent materials, the emerging GO/CS composites are introduced. The additional materials that have been added to the GO/CS composites, including magnetic iron oxides, chelating agents, cyclodextrins, additional adsorbents and polymeric blends, are then described and discussed. The performance of these materials in the removal of heavy metal ions, dyes and other organic molecules are discussed followed by the introduction of strategies employed in the regeneration of the GO/CS adsorbents. It is clear that, while some challenges exist, including cost, regeneration and selectivity in the adsorption process, the GO/CS composites are emerging as promising adsorbent materials.

Chitosan based antibacterial composite materials for leather industry: a review

Abstract

Chitosan is an amorphous translucent substance with a structural unit similar to the polysaccharide structure of the extracellular matrix, It has good antibacterial, biocompatible, and degradable properties. It has important application value in leather, water treatment, medicine, food and other fields, so chitosan and its modified products have received widespread attention. This article reviewed the preparation methods of chitosan-based antibacterial composites in recent years, including chitosan/collagen, chitosan/graphene, chitosan/tannic acid, and chitosan/polyethylene glycol composite materials, elaborates their modification methods and antibacterial mechanism were reviewed in detail, and its applications in the leather industry as antibacterial auxiliaries and water treatment antibacterial adsorption materials were discussed. Finally, the future development and challenges of chitosan-based composite materials in the leather industry were forecasted.

Graphical abstract

Design of PAMAM grafted chitosan dendrimers biosorbent for removal of anionic dyes: Adsorption isotherms, kinetics and thermodynamics studies

PAMAM grafted chitosan as biocompatible adsorbent was synthesized through Michael addition of methyl acrylate followed by amidation of ethylenediamine on the chitosan backbone. Then, the adsorption capacity of bioadsorbents were assessed by employing two anionic dyes. The adsorption experiments were carried out using a batch adsorption system. The influence of various operational variables such as different PAMAM generations, pH, adsorbent dosage, contact time, initial dye concentration and temperature on the maximum adsorption capacity (q_m) were investigated. The adsorbent consists of second generation of PAMAM (CS-PAMAM G2) demonstrated high removal efficiency for both dyes. The maximum adsorption capacity of CS-PAMAM G2 for Congo Red at certain operational conditions was 559.3 mg/g; while the maximum adsorption capacity for Amido Black 10B at certain operational conditions was 489.8 mg/g; which revealed endothermic and exothermic nature of adsorption process for Congo Red and Amido Black 10B, respectively. These results were then well confirmed by thermodynamics studies. Also, kinetic studies showed that the dye adsorption process followed a pseudo-second-order kinetic model. Moreover, among various applied isotherms, the experimental data were well-fitted by Sips model. Consequently, CS-PAMAM G2 showed superior potential for the removal of dyes from aqueous phase.

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.

HKUST-1 modified ultrastability cellulose/chitosan composite aerogel for highly efficient removal of methylene blue

A novel composite HKUST-1/cellulose/chitosan aerogel (HKUST-1/CCSA) as an efficient adsorbent with hierarchical pores was prepared through a facile in situ growth way combining covalent cross-linking, vacuum freeze-drying, and solvothermal methods. By incorporating with cellulose (CE), covalently cross-linked cellulose (CE)/chitosan (CS) composite aerogel exhibits good stability, maintaining fine morphology and structures in acidic solutions under solvothermal conditions. Meantime, a high content of CS is beneficial to enhancing the growth of HKUST-1. Finally, the mass loading ratio of HKUST-1 is as high as 42.54 % in HKUST-1/CCSA. The BET specific surface area of HKUST-1/CCSA reaches 457.75 m² g^-1, which is much larger than that of CCSA (9.74 m² g^-1). HKUST-1/CCSA was applied to remove methylene blue with high adsorption capacity (526.3 mg g^-1) and good recycling capability. This strategy can provide an effective and facile pathway to prepare ultra-stable polysaccharide-based composite aerogel with high specific surface area and hierarchical pores, branching out more applications in pollutant treatment fields.

Preparation of Chitosan-Graphene Oxide Composite Aerogel by Hydrothermal Method and Its Adsorption Property of Methyl Orange

Graphene based aerogel has become one of the most likely functional adsorption materials that is applicable to purify various contaminated water sources, such as dye wastewater, because of its high porosity, structural stability, large specific surface area, and high adsorption capacity. In this study, chitosan and graphene oxide were first selected as the matrix to prepare the composite hydrogel through the hydrothermal method, which was further frozen and dried to obtain the target aerogel. The microscopic structures and adsorption capacity of the composite aerogel were then characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and N₂ (nitrogen) physical adsorption and desorption tests. The results show that the specific surface area of the composite aerogel was reached at 297.431 m²/g, which is higher than that of graphene oxide aerogel and chitosan aerogel. The aperture was reduced to about 3 nm. The adsorption rate of the composite aerogel for the methyl orange solution was as high as 97.2% at pH = 1, and the adsorption capacity was 48.6 mg/g. The adsorption process of the composite aerogel satisfies the Langmuir equation and can be described by the second-order adsorption kinetics. In addition, it is worth noting that this composite aerogel can provide a striking adsorption characteristic on methyl orange due to the combining effects from massive amino groups on chitosan and the structural conjugation of graphene oxide.

Magnetic graphene/chitosan nanocomposite: A promising nano-adsorbent for the removal of 2-naphthol from aqueous solution and their kinetic studies

In this study, magnetic/graphene/chitosan nanocomposite (MGCH) is prepared through facile solvothermal process and employed as an adsorbent for the removal of 2-naphthol from aqueous solution. The physico-chemical characteristic results of FESEM, Raman, FTIR, XRD and VSM confirms that the MGCH nanocomposite is effectively prepared. The FESEM and EDS analysis reveals that the high density of spherical-like Fe₃O₄ nanoparticles and chitosan are successfully assembled on the surfaces of the graphene sheets. VSM result of MGCH composite exhibited higher saturation magnetization of 46.5 emu g^-1 and lower coercivity (H_c) of 50 O_e. This result discloses that MGCH possesses enough response required for the separation from aqueous solution. The batch mode adsorption studies demonstrates that MGCH based adsorbent showed almost 99.8% adsorption of 2-naphthol with a maximum adsorption capacity of 169.49 mg g^-1 at pH 2. Moreover, the kinetic studies of the samples are performed by fitting adsorption models to ensure the nature of the adsorption system. This work proves that MGCH nanocomposite can be used as high-performance adsorbent for removing of phenolic pollutants from contaminated wastewater.

Facile synthesis of a BCN nanofiber and its ultrafast adsorption performance

Boron carbonitride (BCN) nanofibers with rapid and efficient adsorption performance were prepared by electrospinning technology. TEM, XRD, XPS and N₂ adsorption–desorption isotherms were performed to study the microstructure of the nanofibers. The results showed that the BCN fibers synthesized at 1000 °C (BCN-1000) have good crystallinity and high specific surface areas (403 m² g⁻¹). BCN-1000 nanofibers adsorb 70% of amino black 10B (AB-10B) within 10 minutes and reach adsorption equilibrium within 60 minutes. Compared with previous reports, it is found that the adsorption rate of BCN-1000 nanofibers to amino black (AB-10B) is much higher than that of other adsorbents. And BCN nanofibers exhibit a large adsorption capacity (625 mg g⁻¹). In addition, the process of AB-10B adsorption on BCN nanofibers was systematically investigated, which was in accordance with the pseudo-second-order kinetics model and Langmuir isotherm model.

Boron carbonitride (BCN) nanofibers with rapid and efficient adsorption performance were prepared by electrospinning technology.

Facile synthesis of laccase mimic Cu/H3BTC MOF for efficient dye degradation and detection of phenolic pollutants

Herein, we report an effectual method for designing a novel form of nanozyme laccase mimic namely Cu/H3BTC, using copper ions and 1,3,5-benzene tricarboxylic acid (1,3,5-H3BTC). This Cu-based metal-organic framework (MOF) was synthesized through a simple procedure of mixing of two usual reagents at room temperature. Amido Black 10B (AB-10B) was chosen as a model dye for degradation consequences. Results showed that Cu/H3BTC MOF revealed significantly higher catalytic efficacy under certain conditions like high pH, extreme temperature and high salt conditions and it has long-term storage stability, which can lead to a significant decline in catalytic activity of laccase. In addition, the degradation of AB-10B was up to 60% after ten cycles, showing good recyclability of Cu/H3BTC MOF. The UV-visible spectral changes clearly showed that Cu/H3BTC MOF is an effective laccase mimic for the degradation of azo dye AB-10B, which was degraded more easily within the time duration of 60 min. The Cu/H3BTC MOF also possessed fundamental activities like laccase with regard to oxidation of the phenolic compounds. Moreover, a technique for the quantitative detection of epinephrine by Cu/H3BTC MOF was established. These findings help to understand the laccase-like reactivity and provide a basis for the future design and application of metal-based catalysts.

Novel cellulose/montmorillonite mesoporous composite beads for dye removal in single and binary systems

Fine aminated cellulose/montmorillonite mesoporous composite beads (ACeMt) were prepared as green-based adsorbent via a novel approach utilizing ultra-fine calcium carbonate as a pore-forming agent to increase the porosity and specific surface area of ACeMt. The resulting bioadsorbent was characterized by means of SEM, FTIR and BET analysis and used for dye removal. Adsorption experimental data were fitted with various isotherm and kinetic models. The results indicated that chemical adsorption was the rate-limiting step. The maximum adsorption capacities of ACeMt, better described by Langmuir model, were much higher than those of conventional adsorbents, particularly for the removal of Auramine O dye (up to 1336.2 mg/g at 55 °C). The adsorptions at equilibrium were better correlated with Redlich-Peterson model and uncompetitive Langmuir isotherm model in single and binary system, respectively. Overall, ACeMt is a promising bioadsorbent and highly efficient in the removal of dyes for water clarification.

Adsorption of Direct Blue 78 Using Chitosan and Cyclodextrins as Adsorbents

The dyeing industry is one of the most polluting in the world. The adsorption of dyes by polymeric matrixes can be used to minimize the discharge of dyes into the environment. In the present study, chitosan-NaOH and β-cyclodextrin-epichlorohydrin polymers were used to remove the dye Direct Blue 78 from a wastewater model. To understand the adsorption behavior of Direct Blue 78 onto the polymers, adsorption rate and maximum adsorption capacity were calculated using kinetic tests and isotherm curves respectively. The kinetic data and mechanism of the adsorption process were analyzed by three models and the equilibrium data by three adsorption isotherms; also the different thermodynamic parameters were calculated. Results showed that the adsorption process follows pseudo-second-order kinetics in both polymers and the Langmuir isotherm best-fitted data for chitosan-NaOH polymer and the Freundlich isotherm for the β-CDs-EPI polymer. The adsorption process is exothermic in both cases and spontaneous for the β-CDs-EPI polymer to a certain temperature and not spontaneous for the chitosan-NaOH polymer and β-CDs-EPI polymer at higher temperatures. The complementary action of an advanced oxidation process eliminated >99% of the dye from water. The coupled process seems to be suitable for reducing the environmental impact of the dyeing industry.

Environmental application of three-dimensional graphene materials as adsorbents for dyes and heavy metals: Review on ice-templating method and adsorption mechanisms

The remediation of wastewater requires treatment technologies which are robust, efficient, simple to operate and affordable such as adsorption. Lately, three-dimensional (3D) graphene based materials have attracted significant attention as effective adsorbents for wastewater treatment. The intrinsic properties of 3D graphene structure such as large surface area and interconnected porous structure can facilitate the transport of pollutants into the 3D network and provide abundant active sites for trapping the pollutants. For the synthesis of 3D graphene structure, ice-templating is commonly practiced due to its facile steps, cost effectiveness and high scalability potential. This review covers the ice-templating fabrication technique for 3D graphene based materials and their application as adsorbents in eliminating dyes and heavy metals from aqueous media. The assembly mechanisms of the ice-templating fsynthesis are comprehensively discussed. Further discussion on the fundamental principles, critical process parameters and characteristics of ice-templated 3D graphene structures is also included. A thorough review on the mechanisms for batch adsorption of dyes and heavy metals is presented based on the structures and properties of the 3D graphene materials. The review further evaluates the dynamic adsorption in packed columns and the regeneration of 3D graphene based materials.

Advances in the applications of graphene adsorbents: from water treatment to soil remediation

Graphene, a novel carbon allotrope, is single-layered graphite with honeycomb lattice. Its unique structure endows graphene many outstanding physical/chemical properties and a large surface area, which are beneficial to its applications in many areas. The potential applications of graphene in pollution remediation are adsorption, membrane separation, catalysis, environmental analysis, and so on. The adsorption efficiency of graphene adsorbents largely depends on its surface area, porous structure, oxygen-containing groups and other functional groups, adsorption conditions, and also the properties of adsorbates. With appropriate modifications, graphene materials are mostly efficient adsorbents for organic pollutants (e.g. dyes, pesticides, and oils) and inorganic pollutants (e.g. metal ions, nonmetal ions, and gas). Since our first report of graphene adsorbents in 2010, plenty of studies have been dedicated to developing various graphene adsorbents and to evaluating their performance in treating contaminated water. Recently, there is a growing trend in graphene adsorbents that could be applied in soil remediation, where the situation is much more complicated than in aqueous systems. Herein, we review the design of graphene adsorbents for water treatment and analyze their potential in soil remediation. Several suggestions to accelerate the research on graphene-based soil remediation technology are proposed.

Bentonite Modified by Allylamine Polymer for Adsorption of Amido Black 10B

The main object of this work is to remove Amido black 10B using a new type of bentonite-based adsorbent with cationic groups by the modification of polyallyl amines between the interlayers of bentonite. Fourier transform infrared, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy were used to characterize the functionalized bentonite. A series of batch adsorption experiments were performed. The maximum adsorption amount was 144.08 mg g⁻¹ when the pH was 2 and the contact time was 120 min. In addition, the equilibrium isotherm data were analyzed using Langmuir and Freundlich isotherm models, while only the Langmuir model could provide a high correlation. Therefore, this study provided a new functionalized bentonite as a low-cost adsorbent for dye removal from water.

Ice-templated graphene oxide/chitosan aerogel as an effective adsorbent for sequestration of metanil yellow dye

Graphene oxide/chitosan aerogel (GOCA) was prepared by a facile ice-templating technique without using any cross-linking reagent for metanil yellow dye sequestration. The adsorption performance of GOCA was investigated by varying the adsorbent mass, shaking speed, initial pH, contact time, concentration and temperature. The combined effects of adsorption parameters and the optimum conditions for dye removal were determined by response surface methodology. GOCA exhibited large removal efficiencies (91.5-96.4%) over a wide pH range (3-8) and a high adsorption capacity of 430.99 mg/g at 8 mg adsorbent mass, 400 mg/L concentration, 35.19 min contact time and 175 rpm shaking speed. The adsorption equilibrium was best represented by the Langmuir model. GOCA could be easily separated after adsorption and regenerated for re-use in 5 adsorption-desorption cycles thereby maintaining 80% of its adsorption capability. The relatively high adsorption and regeneration capabilities of GOCA render it an attractive adsorbent for treatment of azo dye-polluted water.

Metal affinity-carboxymethyl cellulose functionalized magnetic graphene composite for highly selective isolation of histidine-rich proteins

A metal affinity-carboxymethyl cellulose functionalized magnetic graphene, namely MGCI-Cu composite, was prepared by successive modifications of graphene oxide nanosheets with magnetic nanoparticles, carboxymethyl cellulose (CMC), iminodiacetic acid (IDA) and then chelated with copper ions. The successful modifications of the graphene surface were demonstrated by various characterizations, and a high density of 6.17 μmol m^-2 for metal affinity groups was obtained. The composite exhibited high adsorption selectivity toward histidine-rich proteins. The adsorption was governed by strong metal affinity binding force between hisitidine residues of proteins and immobilized Cu²⁺ ions of MGCI-Cu composite. In particular, highly selective isolation of hemoglobin (Hb) was achieved in 0.2 mol L^-1 phosphate buffer at pH 8. The adsorption capacity of Hb significantly increased to 769 mg g^-1 in comparison to that of 435 mg g^-1 on metal affinity modified magnetic graphene composite (MGI-Cu) without CMC modification. The adsorbed Hb molecules were recovered with a carbonate buffer (0.2 mol L^-1 pH 10) containing 0.5 mol L^-1 imidazole. MGCI-Cu composite displayed favorable reusability for at least four times after regeneration of the composite by edetic acid (EDTA) and Cu²⁺ solution. The practical applications demonstrated that MGCI-Cu composite could highly selectively isolate Hb from human whole blood and polyhistidine-tagged recombinant protein from Escherichia coli (E. coli) lysate.

Sorption of methyl orange from aqueous solution by protonated amine modified hydrochar

The protonated amine modified hydrochar (PAMH) was synthesized by etherification, amination and protonated reaction with hydrochar, which was enriched with abundant protonated amine for methyl orange (MO) removal. PAMH was characterized by elemental analysis, scanning electron microscopy, nitrogen adsorption-desorption measurement, zeta potential and Fourier transform infrared. The sorption of MO from aqueous solution by PAMH was investigated by batch experiments. The results showed that sorption of MO was significantly influenced by the initial concentration of MO, temperature, contact time and ionic strength, while hardly affected by pH values ranging from 4 to 11. The pseudo-second-order and Langmuir equations were able to depict sorption kinetics and sorption isotherms, respectively. Thermodynamic analysis indicated that the sorption behavior was thermopositive and spontaneous. The maximum theoretical uptake computed by the Langmuir equation was 909.09 mg·g^-1 at 303 K, which suggested that PAMH was an effective sorbent to eliminate anionic dye from aqueous solution.

Hexavalent chromium ion and methyl orange dye uptake via a silk protein sericin-chitosan conjugate

Sericin, a protein waste product of the silk industry, was crosslinked with chitosan, and a chitosan-sericin conjugate (CS) was prepared, characterized and used to remove hexavalent chromium (Cr(vi)) ions and methyl orange (MO) dye from aqueous solutions. The CS was shown to effectively remove Cr(vi) ions and MO dye at maximum adsorption capacities (Langmuir) of 139 mg g-1 for Cr(vi) ions and 385 mg g-1 for MO dye. Moreover, the adsorption of both Cr(vi) ions and MO dye was highly pH dependent and varied under different experimental conditions. Cr(vi) ion and MO dye uptake by the CS was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry analysis. Additionally, XPS analysis of the Cr(vi)-loaded CS revealed that Cr(vi) was reduced to the less toxic Cr(iii). The CS was shown not only to be highly amenable to regeneration, but also to be able to effectively remove MO dye and Cr(vi) ions from a binary mixture.

Simple fabrication of Chitosan/Graphene nanoplates composite spheres for efficient adsorption of acid dyes from aqueous solution

A facile method for the fabrication of crosslinked chitosan/graphene nanoplates composite sphere (CS/GNPs) was presented. The obtained samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS) and thermogravimetric analysis (TGA). The adsorption activities of CS/GNPs for methyl orange (MO) and acid red 1 (AR1) were evaluated such as the effect of pH and GNPs content, as well as adsorption kinetics and isotherms. In view of practical, the reusability of CS/GNPs was also tested. The resulting adsorption capacity for MO is 230.91mgg^-1 and 132.94mgg^-1 for AR1, respectively. After saturated adsorption, CS/GNPs can be efficiently regenerated and reused with little uptake loss. Therefore, CS/GNPs is the apromising adsorbent with non-toxic, efficient, low-cost and easy to prepare for the dye removal.