Fabrication of carboxymethyl cellulose/graphene oxide/ZnO composite hydrogel for efficient removal of fuchsin dye from aqueous media

Hydrogels are hydrophilic, insoluble, and highly porous 3D networks capable of absorbing large amounts of water. This study aimed to develop a carboxymethyl cellulose/graphene oxide (CMC/GO) hydrogel, cross-linked with citric acid and modified with zinc oxide (ZnO) nanoparticles (CMC/GO/ZnO), synthesized via the sol-gel method. The formulated composite hydrogel samples were characterized by Fourier transmittance infrared spectroscopy (FTIR), scanning electron microscopy (SEM) analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermo-gravimetric analysis (TGA). The hydrogels were tested for the adsorption of basic fuchsin (BF) dye from the aqueous medium under various conditions, such as adsorbent dosage, contact time, pH, and temperature, using batch adsorption. The adsorption data best fit the Langmuir and Temkin models, with maximum adsorption capacity (qmax) of 172.41 mg/g for CMC/GO and 303.03 mg/g for CMC/GO/ZnO. Optimal adsorption occurred at pH = 6 and within 30 min. The process followed a pseudo-second-order kinetic model, and thermodynamic results indicated that the adsorption process is physical, endothermic and spontaneous. The COOH groups in the hydrogels enhanced affinity for cationic dyes through hydrogen bonding and electrostatic interactions. Thus, CMC/GO and CMC/GO/ZnO hydrogels are efficient and promising adsorbents for environmental remediation.

Enhanced dye sequestration with natural polysaccharides-based hydrogels: A review

Due to the expansion of industrial activities, the concentration of dyes in water has been increasing. The dire need to remove these pollutants from water has been heavily discussed. This study focuses on the reproducible and sustainable solution for wastewater treatment and dye annihilation challenges. Adsorption has been rated the most practical way of the several decolorization procedures due to its minimal initial investment, convenient utility, and high-performance caliber. Hydrogels, which are three-dimensional polymer networks, are notable because of their potential to regenerate, biodegrade, absorb bulky amounts of water, respond to stimuli, and have unique morphologies. Natural polysaccharide hydrogels are chosen over synthetic ones because they are robust, bioresorbable, non-toxic, and cheaply accessible. This study has covered six biopolymers, including chitosan, cellulose, pectin, sodium alginate, guar gum, and starch, consisting of their chemical architecture, origins, characteristics, and uses. The next part describes these polysaccharide-based hydrogels, including their manufacturing techniques, chemical alterations, and adsorption effectiveness. It is deeply evaluated how size and shape affect the adsorption rate, which has not been addressed in any prior research. To assist the readers in identifying areas for further research in this subject, limitations of these hydrogels and future views are provided in the conclusion.

Development of carboxymethyl cellulose-graphene oxide biobased composite for the removal of methylene blue cationic dye model contaminate from wastewater

Utilizing Glutaraldehyde crosslinked sodium carboxymethyl cellulose (CMC-GA) hydrogel and its nanographene oxide composite (CMC-GA-GOx), an effective carboxymethyl cellulose-graphene oxide biobased composites adsorbent was developed for the adsorption removal of methylene blue (MB) cationic dye contaminate from industrial wastewater. The CMC-GA-GOx composites developed were characterized using FTIR, RAMAN, TGA, SEM, and EDX analysis instruments. Through batch experiments, several variables affecting the removal of MB dye, including the biocomposites GO:CMC composition, adsorption time, pH and temperature, initial MB concentration, adsorbent dosage, and NaCl concentration, were investigated under different conditions. The maximum dye removal percentages ranged between 93 and 98%. They were obtained using biocomposites CMC-GA-GO102 with 20% GO weight percent, adsorption time 25 min, adsorption temperature 25 °C, MB concentrations 10-30 ppm, adsorption pH 7.0, and 0.2 g adsorbent dose. The experimental data of the adsorption process suit the Langmuir isotherm more closely with a maximal monolayer adsorption capacity of 76.92 mg/g. The adsorption process followed the kinetic model of pseudo-second order. The removal of MB was exothermic and spontaneous from a thermodynamic standpoint. In addition, thermodynamic results demonstrated that adsorption operates most effectively at low temperatures. Finally, the reusability of the developed CMC-GA-GO102 has been proved through 10 successive cycles where only 14% of the MB dye removal percentage was lost. These results suggest that the developed CMC-GA-GO102 composite may be an inexpensive and reusable adsorbent for removing organic cationic dyes from industrial wastewater.

Versatile Mesoporous Microblocks Prepared by Pattern-Induced Cracking of Colloidal Films

Mesoporous microparticles have the potential to be used in various fields, such as energy generation, sensing, and the environmental field. Recently, the process of making homogeneous microparticles in an economical and environmentally friendly way has gained much attention. Herein, rectangular mesoporous microblocks of various designs are produced by manipulating the fragmentation of colloidal films consisting of micropyramids while controlling the notch angles of pyramidal edges. During calcination of the colloidal films, cracks are generated in the valleys of micropyramids acting as notches, and the angle of notches can be controlled by the prepattern underneath the micropyramids. By changing the location of notches with sharp angles, the shape of microblocks can be controlled with excellent uniformity. After detaching the microblocks from substrates, mesoporous microparticles of various sizes with multiple functions are easily produced. This study demonstrates anti-counterfeiting functions by encoding the rotation angles of rectangular microblocks of various sizes. In addition, the mesoporous microparticles can be utilized for separating desired chemicals mixed with chemicals of different charges. The method of fabricating size-tunable functionalized mesoporous microblocks can be a platform technology to prepare special films and catalysts and for environmental applications.

Chitin nanofiber-coated biodegradable polymer microparticles via one-pot aqueous process

Tailoring the surface of biodegradable microparticles is important for various applications in the fields of cosmetics, biotechnology, and drug delivery. Chitin nanofibers (ChNFs) are one of the promising materials for surface tailoring owing to its functionality, such as biocompatibility and antibiotic properties. Here, we show biodegradable polymer microparticles densely coated with ChNFs. Cellulose acetate (CA) was used as the core material in this study, and ChNF coating was successfully carried out via a one-pot aqueous process. The average particle size of the ChNF-coated CA microparticles was approximately 6 μm, and the coating procedure had little effect on the size or shape of the original CA microparticles. The ChNF-coated CA microparticles comprised 0.2-0.4 wt% of the thin surface ChNF layers. Owing to the surface cationic ChNFs, the ζ-potential value of the ChNF-coated microparticles was +27.4 mV. The surface ChNF layer efficiently adsorbed anionic dye molecules, and repeatable adsorption/desorption behavior was exhibited owing to the coating stability of the surface ChNFs. The ChNF coating in this study was a facile aqueous process and was applicable to CA-based materials of various sizes and shapes. This versatility will open new possibilities for future biodegradable polymer materials that satisfy the increasing demand for sustainable development.

Ionic Liquid Cross-Linked High-Absorbent Polymer Hydrogels: Kinetics of Swelling and Dye Adsorption

The use of polymer gels for the removal of toxic chemicals from wastewater is an important area in terms of both academic and industrial research. This work presents a simple approach to the fabrication of chemically cross-linked cationic hydrogel adsorbents using designed ionic liquid-based cross-linkers and their successful use in the removal of organic dyes. Two different ionic liquid cross-linkers, [VIm-4VBC][Cl] (ILA)/[DMAEMA-4VBC][Cl] (ILB), are synthesized by the simple nucleophilic substitution reaction of 4-vinylbenzyl chloride (4VBC) separately with 1-vinylimidazole (VIm) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). Cross-linked poly(acrylamide) (CPAam) and poly(2-hydroxyethyl methacrylate) (CPHEMA) hydrogels are then prepared from the corresponding monomers and as-synthesized cross-linkers (ILA and ILB) by free radical polymerization in the presence of a redox initiator combining ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED). The dried CPAam and CPHEMA xerogels exhibit macroporous morphology and high thermal stability. The hydrogel samples exhibit high swelling behavior, and the diffusion of water molecules into the hydrogels follows pseudo-Fickian kinetics. The cationic cross-linking sites in the hydrogel networks allow preferable binding with anionic dyes, and these dye uptake capacities are determined using different model anionic dyes via UV-vis spectroscopy. The dye adsorption onto these hydrogels follows a pseudo-second-order kinetic model. The adsorption mechanism is also analyzed by employing intraparticle diffusion and Boyd kinetic models. The relationship between the maximum equilibrium adsorption capacity (q_m) of the hydrogels for eosin B (EB) dye and the equilibrium EB concentration can be better described by Langmuir and Freundlich isotherm models, and the estimated q_m using the Langmuir isotherm can reach more than 100 mg g^-1. The cross-linked hydrogels can be easily regenerated and have a recycling efficiency of >80% for up to three consecutive dye adsorption-desorption cycles, which is promising for their use in wastewater treatment.

Facile fabrication of a broad-spectrum starch/poly(α-l-lysine) hydrogel adsorbent with thermal/pH-sensitive IPN structure through simultaneous dual-click strategy

A thermal/pH-sensitive interpenetrating network (IPN) hydrogel was prepared facilely from starch and poly(α-l-lysine) through amino-anhydride and azide-alkyne double-click reactions in one pot. The synthesized polymers and hydrogels were systematically characterized using different analytical techniques such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rheometer. The preparation conditions of the IPN hydrogel were optimized via one-factor experiments. Experimental results indicated the IPN hydrogel possessed pH and temperature sensitivity. Effect of different parameters (pH, contact time, adsorbent dosage, initial concentration, ionic strength, and temperature) on adsorption behavior were investigated in monocomponent system with cationic methylene blue (MB) and anionic Eosin Y (EY) as model pollutants. The results indicated that the adsorption process of the IPN hydrogel for MB and EY followed pseudo-second-order kinetics. The adsorption data for MB and EY fitted well with the Langmuir isotherm model, indicating monolayer chemisorption. The good adsorption performance was due to various active functional groups (-COOH, -OH, -NH₂, etc.) in the IPN hydrogel. The strategy described here opens up a new way for preparing IPN hydrogel. The as-prepared hydrogel exhibits potential application and bright prospects as an adsorbent in wastewater treatment.

Decoration of sodium carboxymethylcellulose gel microspheres with modified lignin to enhanced methylene blue removal

The introduction of active groups from biomass is currently the most promising alternative method for increasing the adsorption effect of dyes. In this study, modified aminated lignin (MAL) rich in phenolic hydroxyl and amine groups was prepared by amination and catalytic grafting. The factors influencing the modification conditions of the content of amine and phenolic hydroxyl groups were explored. Chemical structural analysis results confirmed that MAL was successfully prepared using a two-step method. The content of phenolic hydroxyl groups in MAL significantly increased to 1.46 mmol/g. MAL/sodium carboxymethylcellulose (NaCMC) gel microspheres (MCGM) with enhanced methylene blue (MB) adsorption capacity owing to the formation of a composite with MAL were synthesized by a sol-gel process followed by freeze-drying and using multivalent cations Al³⁺ as cross-linking agents. In addition, the effects of the MAL to NaCMC mass ratio, time, concentration, and pH on the adsorption of MB were explored. Benefiting from a sufficient number of active sites, MCGM exhibited an ultrahigh adsorption capacity for MB removal, and the maximum adsorption capacity was 118.30 mg/g. These results demonstrated the potential of MCGM for wastewater treatment applications.

Recent Advances in Nanocellulose Aerogels for Efficient Heavy Metal and Dye Removal

Water pollution is a significant environmental issue that has emerged because of industrial and economic growth. Human activities such as industrial, agricultural, and technological practices have increased the levels of pollutants in the environment, causing harm to both the environment and public health. Dyes and heavy metals are major contributors to water pollution. Organic dyes are a major concern because of their stability in water and their potential to absorb sunlight, increasing the temperature and disrupting the ecological balance. The presence of heavy metals in the production of textile dyes adds to the toxicity of the wastewater. Heavy metals are a global issue that can harm both human health and the environment and are mainly caused by urbanization and industrialization. To address this issue, researchers have focused on developing effective water treatment procedures, including adsorption, precipitation, and filtration. Among these methods, adsorption is a simple, efficient, and cheap method for removing organic dyes from water. Aerogels have shown potential as a promising adsorbent material because of their low density, high porosity, high surface area, low thermal and electrical conductivity, and ability to respond to external stimuli. Biomaterials such as cellulose, starch, chitosan, chitin, carrageenan, and graphene have been extensively studied for the production of sustainable aerogels for water treatment. Cellulose, which is abundant in nature, has received significant attention in recent years. This review highlights the potential of cellulose-based aerogels as a sustainable and efficient material for removing dyes and heavy metals from water during the treatment process.

Recent advances in cellulose microgels: Preparations and functionalized applications

Microgels are soft, deformable, permeable, and stimuli-responsive microscopic polymeric particles that are now emerging as prospective multifunctional soft materials for delivery systems, interface stabilization, cell cultures and tissue engineering. Cellulose microgels are emerging biopolymeric microgels with unique characteristics such as abound hydroxyl structure, admirable designability, multiscale pore network and excellent biocompatibility. This review summarizes the fabrication strategies for microgel, then highlights the fabrication routes for cellulose microgels, and finally elaborates cellulose microgels' bright application prospects with unique characteristics in the fields of controlled release, interface stabilization, coating, purification, nutrition/drug delivery, and bio-fabrication. The challenges to be addressed for further applications and considerable scope for development in future of cellulose microgels are also discussed.

Graphene oxide modified with carboxymethyl cellulose for high adsorption capacities towards Nd(III) and Ce(III) from aqueous solutions

This work addresses a simple method to functionalize graphene oxide with sodium carboxymethyl cellulose using tetraethyl orthosilicate as a linker for rapid and significant removal of Nd(III) and Ce(III) from aqueous solutions. The prepared composite (GO–CMC) was characterized by different techniques to confirm the modification and adsorption process. The sorption performance of the GO–CMC was evaluated using Nd(III) and Ce(III) as absorbent materials. The experimental results demonstrated that the sorption process was excellently fitted by the pseudo-second-order kinetic model. The adsorption results were also analyzed by different isotherm models. According to the Langmuir isotherm model, the experimental sorption capacities at pH 3.0 was 661.21 and 436.55 mg/g for Nd(III) and Ce(III), respectively. The thermodynamic results indicated that the sorption process of the two examined metal ions was endothermic and spontaneous. The regenerated GO–CMC composite has a similar removal percentage to the original composite. These results confirmed that the prepared composite (GO–CMC) could be used as an effective adsorbent for Nd(III) and Ce(III) from certain multielement solutions.

Microgels based on 0D-3D carbon materials: Synthetic techniques, properties, applications, and challenges

Microgels are three-dimensional (3D) colloidal hydrogel particles with outstanding features such as biocompatibility, good mechanical properties, tunable sizes from submicrometer to tens of nanometers, and large surface areas. Because of these unique qualities, microgels have been widely used in various applications. Carbon-based materials (CMs) with various dimensions (0-3D) have recently been investigated as promising candidates for the design and fabrication of microgels because of their large surface area, excellent conductivity, unique chemical stability, and low cost. Here, we provide a critical review of the specific characteristics of CMs that are being incorporated into microgels, as well as the state-of-the art applications of CM-microgels in pollutant adsorption and photodegradation, H₂ evoluation, CO₂ capture, soil conditioners, water retention, drug delivery, cell encapsulation, and tissue engineering. Advanced preparation techniques for CM-microgel systems are also summarized and discussed. Finally, challenges related to the low colloidal stability of CM-microgels and development strategies are examined. This review shows that CM-microgels have the potential to be widely used in various practical applications.

Removal of methylene blue from wastewater using ternary nanocomposite aerogel systems: Carboxymethyl cellulose grafted by polyacrylic acid and decorated with graphene oxide

In this study, environmentally-friendly nanocomposite hydrogels were fabricated. These hydrogels consisted of semi-interpenetrating networks of carboxymethyl cellulose (CMC) molecules grafted to polyacrylic acid (PAA), as an eco-friendly and non-toxic polymer with numerous carboxyl and hydroxyl functional groups, which were reinforced with different levels of graphene oxide particles (0.5, 1.5 or 3% wt). Field-emission electron scanning microscopy (FESEM) images indicated that the pore size of the nanocomposites decreased with increasing graphic oxide concentration. The presence of the graphic oxide increased the storage modulus and thermal stability of the nanocomposite hydrogels. The hydrogels had an adsorption capacity of 138 mg/g of a model cationic dye pollutant (methylene blue) after 250 min. Moreover, a reusability test showed that the adsorption capacity remained at around 90% after 9 cycles. Density functional theory (DFT) simulations suggested that the adsorption of methylene blue was mainly a result of π-π bonds, hydrogen bonds, and electrostatic interactions with graphene oxide. Our results indicated that the nanocomposite hydrogels fabricated in this study may be eco-friendly, stable, efficient, and reusable adsorbents for ionic pollutants in wastewater treatment.

A Novel Additive Manufacturing Method of Cellulose Gel

Screen-additive manufacturing (SAM) is a potential method for producing small intricate parts without waste generation, offering minimal production cost. A wide range of materials, including gels, can be shaped using this method. A gel material is composed of a three-dimensional cross-linked polymer or colloidal network immersed in a fluid, known as hydrogel when its main constituent fluid is water. Hydrogels are capable of absorbing and retaining large amounts of water. Cellulose gel is among the materials that can form hydrogels and, as shown in this work, has the required properties to be directly SAM, including shear thinning and formation of post-shearing gel structure. In this study, we present the developed method of SAM for the fabrication of complex-shaped cellulose gel and examine whether successive printing layers can be completed without delamination. In addition, we evaluated cellulose SAM without the need for support material. Design of Experiments (DoE) was applied to optimize the SAM settings for printing the novel cellulose-based gel structure. The optimum print settings were then used to print a periodic structure with micro features and without the need for support material.

Preparation and characterization of carboxymethylcellulose based citric acid cross-linked magnetic aerogel as an efficient dye adsorbent

A low-cost, collectable, and efficient material is essential for adsorbing water pollution, such as dyes and heavy metal ions pollution. In this work, we proposed a novel strategy for the preparation of an efficient and collectable magnetic aerogel as adsorbent for dye. The magnetic aerogels were prepared from sodium carboxymethylcellulose (CMC) hydrogel using citric acid (CA) as the crosslinker, followed by vacuum freeze-drying technique to obtain aerogels. The effects of magnetic Fe₃O₄ nanoparticle contents on the adsorption properties of the aerogels were investigated. The results show that the as-prepared magnetic composite aerogels exhibit porous structure and display good adsorption and collectable performance for methylene blue (MB) in water with the removal rate of 97.5% in 6 h. The maximum compress strength and absorption capacity of the magnetic aerogel with 1 wt% Fe₃O₄ nanoparticle loading for MB is 0.13 MPa and 83.6 mg/g, respectively. Aerogels with Fe₃O₄ nanoparticles exhibited magnetism which enables the aerogels to easily collect. This excellent structure stability and collectability guarantees long-term integrity and floatability of the magnetic aerogels in water.

Role of surface functional groups of hydrogels in metal adsorption: From performance to mechanism

Hydrogels have been studied quite intensively in recent decades regarding whether their metal adsorption abilities may be modified or even enhanced via functionalization (i.e., functionalizing the surfaces of hydrogels with specific functional groups). Studies have found that functionalizing hydrogels can in fact give them higher adsorptive power. This enhanced adsorptive performance is articulated in this paper through critically reviewing more than 120 research articles in such terms as the various techniques of synthesizing functionalized hydrogels, the roles that specific functional groups play on adsorption performance, selectivity, reusability, as well as on adsorption mechanism. Moreover, this critical review offers insight into future designs of functionalized hydrogels with specific metal adsorption capabilities.

Cellulose-Based Hydrogels for Wastewater Treatment: A Concise Review

Finding affordable and environment-friendly options to decontaminate wastewater generated with heavy metals and dyes to prevent the depletion of accessible freshwater resources is one of the indispensable challenges of the 21st century. Adsorption is yet to be the most effective and low-cost wastewater treatment method used for the removal of pollutants from wastewater, while naturally derived adsorbent materials have garnered tremendous attention. One promising example of such adsorbents is hydrogels (HGs), which constitute a three-dimensional polymeric network of hydrophilic groups that is highly capable of adsorbing a large quantity of metal ions and dyes from wastewater. Although HGs can also be prepared from synthetic polymers, natural polymers have improved environmental benignity. Recently, cellulose-based hydrogels (CBHs) have been extensively studied owing to their high abundance, biodegradability, non-toxicity, and excellent adsorption capacity. This review emphasizes different CBH adsorbents in the context of dyes and heavy metals removal from wastewater following diverse synthesis techniques and adsorption mechanisms. This study also summarizes various process parameters necessary to optimize adsorption capacity followed by future research directions.

Bio-mass derived functionalized graphene aerogel: a sustainable approach for the removal of multiple organic dyes and their mixtures

Herein, fabrication of a functionalized graphene aerogel (f-GA) from a biomass (pear fruit)-derived graphene aerogel (GA) is described. f-GA is showing better adsorption capacity towards CV, MB and RhB dyes than GA and activated charcoal.

Fabrication of UiO-66/MIL-101(Fe) binary MOF/carboxylated-GO composite for adsorptive removal of methylene blue dye from aqueous solutions

This study provides a novel composite as an efficient adsorbent of cationic methylene blue dye. UiO-66/MIL-101(Fe) binary metal organic framework (MOF) was fabricated using a solvothermal technique. Additionally, the developed binary MOF was modified with carboxylated graphene oxide (GOCOOH) using a post-synthetic technique. The as-fabricated UiO-66/MIL-101(Fe)-GOCOOH composite was analyzed by FTIR, XRD, SEM, BET, TGA, XPS and zeta potential analysis. The adsorption performance of UiO-66/MIL-101(Fe)-GOCOOH composite was examined for its aptitude to adsorb cationic MB dye using a batch technique. The obtained data revealed that, the developed UiO-66/MIL-101(Fe)-GOCOOH composite exhibited higher adsorption capacity compared to UiO-66/MIL-101(Fe) binary MOF. Adsorption isotherms and kinetic studies revealed that MB dye adsorption onto UiO-66/MIL-101(Fe)-GOCOOH composite fitted a Langmuir isotherm model (q m = 448.71 mg g-1) and both pseudo 1st order and pseudo 2nd order kinetic models. An intra-particle diffusion model showed that the adsorption process occurs through three steps. Besides, thermodynamic data reflected that the adsorption of MB onto UiO-66/MIL-101(Fe)-GOCOOH composite is an endothermic and spontaneous process and the adsorption involves both physisorption and chemisorption interactions. The as-fabricated UiO-66/MIL-101(Fe)-GOCOOH composite exhibited good reusability and can be considered as a promising reusable adsorbent for the treatment of dye-containing industrial effluents with high efficiency.

Graphene/waste-newspaper cellulose composite aerogels with selective adsorption of organic dyes: preparation, characterization, and adsorption mechanism

Waste-newspaper cellulose/graphene composite aerogels were facilely synthesized via the sol–gel and freeze-drying processes for dye wastewater treatment.

Sulfo-functional 3D porous cellulose/graphene oxide composites for highly efficient removal of methylene blue and tetracycline from water

Cellulose/graphene oxide (CG) porous composites with 3D network structure were prepared via a solution mixing-regeneration and freeze-drying process. The CG aerogels were functionalized with 1,4-butane sultone under mild reaction conditions to achieve sulfated composite aerogels (SCGs), in which the sulfo groups were simultaneously introduced onto GO and cellulose components. The adsorption ability of SCG aerogel was greatly enhanced compared with CG aerogels. The fitting results of adsorption models suggested the monolayer adsorption and chemisorptive characteristics with the maximal uptake capacity as high as 421.9 mg/g for methylene blue (MB) and 163.4 mg/g for tetracycline (TC). The adsorption mechanism was also studied in detail. For the simulated wastewater containing MB and TC, the novel SCG adsorbent exhibited a removal efficiency of 99%. Furthermore, its adsorption capacity was not apparently deteriorated after seven cycles for MB and ten cycles for TC while the original structural integrity was almost maintained. Herein, this recyclable and reusable adsorbent exhibited the potential application on the removal of MB and TC from water.

Novel magnetic polysaccharide/graphene oxide @Fe3O4 gel beads for adsorbing heavy metal ions

As a kind of potential absorbent, polysaccharide materials are limited due to weak stability, low absorption and recovery rate. Herein, a novel composite adsorbent - the magnetic composite gel beads (CMC/SA/graphene oxide@Fe₃O₄) were prepared by combining carboxymethyl chitosan (CMC), sodium alginate (SA) with graphene oxide@Fe₃O₄, and then utilized for the adsorption of Cu²⁺, Cd²⁺ and Pb²⁺ from the wastewater. The physicochemical property of CMC/SA/graphene oxide@Fe₃O₄ beads were characterized in detail. The CMC/SA/graphene oxide@Fe₃O₄ magnetic gel beads could separate easily from the wastewater and showed a higher stability due to the addition of graphene oxide@Fe₃O₄. The adsorption experiments show that the adsorption of Cu²⁺, Cd²⁺ and Pb²⁺ on the magnetic gel bead was well fitted with pseudo-second-order model and Langmuir isotherm model, and the maximum adsorption capacity of Cu²⁺, Cd²⁺ and Pb²⁺ reached 55.96, 86.28 and 189.04 mg/g, respectively. Moreover, the magnetic gel beads had selective adsorption toward Pb²⁺. In addition, the magnetic gel beads still obtained 90% of the adsorption rates after five cycles, and showed good adsorption efficiency in the simulated real environment. This work proves that the CMC/SA/graphene oxide@Fe₃O₄ magnetic gel beads as the adsorbents have promising potential in wastewater treatment.

Three-dimensional graphene-based adsorbents in sewage disposal: a review

A kind of graphene functional materials based on three-dimensional (3D) porous structure is a new star for environmental application in the past decades because it not only inherits the perfect carbon crystal structure of two-dimensional (2D) graphene sheets but also exhibits several advantages such as extremely low density, high porosity, and big surface area, all which enable diverse contaminants to easily access and diffuse into 3D networks, and make these materials ideal adsorbents with superior adsorptivity and recyclability. This review aims to summarize the recent progress in constructing 3D graphene-based adsorbents (3DGBAs) with two hybrid systems such as graphene/polymers and graphene/inorganic nanomaterials, and to provide a fundamental understanding of synthetic methods for interconnecting these nanostructures, structure-property relationships, and extensive applications in environmental protection towards adsorption of heavy metals, dyes, oils, and organic pollutants. Furthermore, we make a forecast on the future development opportunities and technical challenges, which is hoped to make an inspiration for the researchers to exploit a new family of graphene-based adsorption materials. Graphical abstract ᅟ.

Hydrothermal Synthesis of Ultra-Light Coal-Based Graphene Oxide Aerogel for Efficient Removal of Dyes from Aqueous Solutions

A novel carboxymethyl cellulose (CMC)-supported graphene oxide aerogel (CGOA) was fabricated from a cost-effective and abundant bituminous coal by a mild hydrothermal process and freeze-drying treatment. Such an aerogel has cross-linked graphene oxide layers supported by CMC, and therefore, displays high mechanical strength while having ultra-low density (8.257 mg·cm-3). The CGOA has a 3D interconnected porous structure, beneficial graphene framework defects and abundant oxygen-containing functional groups, which offer favorable diffusion channels and effective adsorption sites for the transport and adsorption of dye molecules. The adsorption performance of rhodamine B by an optimized CGOA shows a maximum monolayer adsorption capacity of 312.50 mg·g-1, as determined by Langmuir isotherm parameters. This CGOA exhibited a better adsorption efficiency (99.99%) in alkaline solution, and satisfactory stability (90.60%) after three cycles. In addition, adsorption experiments on various dyes have revealed that CGOA have better adsorption capacities for cationic dyes than anionic dyes.

In situ formation of catalytically active graphene in ethylene photo-epoxidation

Ethylene epoxidation is used to produce 2 × 10⁷ ton per year of ethylene oxide, a major feedstock for commodity chemicals and plastics. While high pressures and temperatures are required for the reaction, plasmonic photoexcitation of the Ag catalyst enables epoxidation at near-ambient conditions. Here, we use surface-enhanced Raman scattering to monitor the plasmon excitation-assisted reaction on individual sites of a Ag nanoparticle catalyst. We uncover an unconventional mechanism, wherein the primary step is the photosynthesis of graphene on the Ag surface. Epoxidation of ethylene is then promoted by this photogenerated graphene. Density functional theory simulations point to edge defects on the graphene as the sites for epoxidation. Guided by this insight, we synthesize a composite graphene/Ag/α-Al₂O₃ catalyst, which accomplishes ethylene photo-epoxidation under ambient conditions at which the conventional Ag/α-Al₂O₃ catalyst shows negligible activity. Our finding of in situ photogeneration of catalytically active graphene may apply to other photocatalytic hydrocarbon transformations.

Self-Assembled TEMPO Cellulose Nanofibers: Graphene Oxide-Based Biohybrids for Water Purification

Nanocellulose, graphene oxide (GO), and their combinations there off have attracted great attention for the application of water purification recently because of their unique adsorption capacity, mechanical characteristics, coordination with transition metal ions, surface charge density, and so on. In the current study, (2,2,6,6-tetramethylpiperidine-1-oxylradical) (TEMPO)-mediated oxidized cellulose nanofibers (TOCNF) and GO sheets or graphene oxide nanocolloid (nanoGO) biohybrids were prepared by vacuum filtration method to obtain self-assembled adsorbents and membranes for water purification. The porous biohybrid structure, studied using advanced microscopy techniques, revealed a unique networking and self-assembling of TOCNF, GO, and nanoGO, driven by the morphology of the GO phase and stabilized by the intermolecular H-bonding between carboxyl groups and hydroxyl groups. The biohybrids exhibited a promising adsorption capacity toward Cu(II) due to TOCNF and formed a unique "arrested state" in water because of ionic cross-linking between adsorbed Cu(II) and the negatively charged TOCNF and GO phase. The mechanical performance of the freestanding biohybrid membranes investigated using PeakForce Quantative NanoMechanics characterization confirmed the enhanced modulus of the hybrid membrane compared to that of the TOCNF membrane. Besides, the TOCNF+nanoGO membrane shows unique hydrolytic stability and recyclability even under several cycles of adsorption and desorption and strong sonication. This study shows that TOCNF and nanoGO hybrids can generate new water-cleaning membranes with synergistic properties because of their high adsorption capacity, flexibility, hydrolytic stability, and mechanical robustness.