Preparation and characterization of graphene oxide/O-carboxymethyl chitosan (GO/CMC) composite and its unsymmetrical dimethylhydrazine (UDMH) adsorption performance from wastewater

The removal of unsymmetrical dimethylhydrazine (UDMH) has long been a concern because of its harmful effect on the environment and humans. This study aimed to prepare a novel graphene oxide/O-carboxymethyl chitosan (GO/CMC) composite adsorbent using the solution-blending method for the removal of UDMH from wastewater. The prepared GO/CMC was systematically characterized by Fourier-transform infrared, Raman, scanning electronic microscopy, transmission electron microscopy, thermogravimetric, and zeta potential analyses. The effects of initial pH, temperature, adsorbent dosage, initial concentration, contact time, and recyclability on the UDMH adsorption behaviour of GO/CMC were studied. The adsorption kinetics was consistent with the pseudo-second-order kinetics model, and the adsorption process was mainly controlled by chemisorption. Adsorption isotherms indicated that the adsorption of UDMH by GO/CMC followed the Langmuir adsorption isotherm. The adsorption mechanisms were mainly electrostatic attraction, hydrogen bonding, and surface complexation. Furthermore, GO/CMC composites can be used as a renewable and eco-friendly adsorbent for the removal of UDMH wastewater. The designed GO/CMC composites exhibited a relatively satisfactory recyclability and removal efficiency after five adsorption-desorption cycles.

A Weed-Derived Hierarchical Porous Carbon with a Large Specific Surface Area for Efficient Dye and Antibiotic Removal

Adsorption is an economical and efficient method for wastewater treatment, and its advantages are closely related to adsorbents. Herein, the Abutilon theophrasti medicus calyx (AC) was used as the precursor for producing the porous carbon adsorbent (PCAC). PCAC was prepared through carbonization and chemical activation. The product activated by potassium hydroxide exhibited a larger specific surface area, more mesopores, and a higher adsorption capacity than the product activated by sodium hydroxide. PCAC was used for adsorbing rhodamine B (RhB) and chloramphenicol (CAP) from water. Three adsorption kinetic models (the pseudo-first-order, pseudo-second-order, and intra-particle diffusion models), four adsorption isotherm models (the Langmuir, Freundlich, Sips, and Redlich–Peterson models), and thermodynamic equations were used to investigate adsorption processes. The pseudo-second kinetic and Sips isotherm models fit the experimental data well. The adsorption mechanism and the reusability of PCAC were also investigated. PCAC exhibited a large specific surface area. The maximum adsorption capacities (1883.3 mg g⁻¹ for RhB and 1375.3 mg g⁻¹ for CAP) of PCAC are higher than most adsorbents. Additionally, in the fixed bed experiments, PCAC exhibited good performance for the removal of RhB. These results indicated that PCAC was an adsorbent with the advantages of low-cost, a large specific surface area, and high performance.

Adsorptive removal of Rhodamine B dye from aqueous solution by using graphene-based nickel nanocomposite

In this work, reduced graphene oxide-nickel (RGO–Ni) nanocomposite is synthesized. X-ray diffraction (XRD), scanning electron microscopy (SEM) and SEM–EDS (Energy Dispersive X-Ray Spectroscopy) are used to study the crystalline nature, morphology and elemental composition of the RGO–Ni nanocomposite, respectively. As synthesized RGO–Ni nanocomposite is used to develop selective adsorptive removal of Rhodamine B (RhB) dye from the aqueous solution. The experiments have been performed to investigate RhB uptake via RGO–Ni nanocomposites which include, contact time (60 min), initial dye concentration (50 mg/100 ml), adsorbent dosage (0.5 mg) and pH 8 of dye solution. The equilibrium concentration is determined by using different models namely, Freundlich, Langmuir and Tempkin. Langmuir isotherm has been fitted well. Langmuir and Tempkin equations are determined to have good agreement with the correlation coefficient data. The kinetic study concluded that RhB dye adsorption follows with the pseudo-second-order kinetic model. Further, adsorption mechanism of RGO–Ni is proposed which involves three steps. The synthesized adsorbent is compared with the other adsorbents in the literature and indicates that RGO–Ni nanocomposite used in this study shown better results for a particular adsorption capacity than polymeric, natural and synthetic bioadsorbents. The regeneration and reusability experiments suggest RGO–Ni nanocomposite can be used for many numbers of times for purification/adsorption.

Ultrasound-assisted bottom-up synthesis of Ni-graphene hybrid composites and their excellent rhodamine B removal properties

In this paper, a facile one-pot bottom-up approach has been developed for the rapid preparation (≤5 min) of graphene nanostructures and Ni-graphene hybrid composites. Under the aid of ultrasonic irradiation, the graphene nanostructures were prepared via reducing hexachloro-benzene(C₆Cl₆) with sodium (Na) in non-polar organic solvent n-tetradecane (C₁₄H₃₀). On the basis of this route, the Ni-graphene hybrid composites were easily synthesized by adding Ni nanoparticles (NPs) into reaction system. The whole reaction was carried out at low temperature (100-120 °C) and in air atmosphere. Despite the absence of nitrogen protection, the result from surface analysis still shows a relatively high C/O ratio (10:1). The effect of the Ni NPs content and size on the specific surface area (SSA) of the products is also investigated. The synthesized samples exhibit large SSA, which is significantly affected by the Ni NPs content rather than their size. The adsorption performances of the samples are evaluated for the removal of organic dyes such as rhodamine B (RhB) from aqueous solutions. The testing results show great adsorption capacity (q_max = 963.04 mg g^-1), rapid adsorption rate (~99.88%, 2 min), high adsorption efficiency (>99.7%) and good chemical stability in a wide pH range (3-13), high salt tolerance (>80 mg mL^-1), and good recyclability (>99.5%, 20 cycles).

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.

A nanocomposite consisting of silica-coated magnetite and phenyl-functionalized graphene oxide for extraction of polycyclic aromatic hydrocarbon from aqueous matrices

In this study, graphene oxide was covalently immobilized on silica-coated magnetite and then modified with 2-phenylethylamine to give a nanocomposite of type Fe₃O₄@SiO₂@GO-PEA that can be applied to the magnetic solid-phase extraction of polycyclic aromatic hydrocarbons (PAHs) from water samples. The resulting microspheres (Fe₃O₄@SiO₂@GO-PEA) were characterized by Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), CHNS elemental analysis, and vibrating sample magnetometry (VSM) techniques. The adsorbent possesses the magnetic properties of Fe₃O₄ nanoparticles that allow them easily to be separated by an external magnetic field. They also have the high specific surface area of graphene oxide which improves adsorption capacity. Desorption conditions, extraction time, amount of adsorbent, salt concentration, and pH were investigated and optimized. Following desorption, the PAHs were quantified by gas chromatography with flame ionization detection (GC-FID). The limits of detection (at an S/N ratio of 3) were achieved from 0.005 to 0.1μg/L with regression coefficients (R²) higher than 0.9954. The relative standard deviations (RSDs) were below 5.8% (intraday) and 6.2% (inter-day), respectively. The method was successfully applied to the analysis of PAHs in environmental water samples where it showed recoveries in the range between 71.7% and 106.7% (with RSDs of 1.6% to 8.4%, for n=3). The results indicated that the Fe₃O₄@SiO₂@GO-PEA microspheres had a great promise to extraction of PAHs from different water samples.

Selective removal of cationic micro-pollutants using disulfide-linked network structures

Micropollutants are found in all water sources, even after thorough treatments that include membrane filtration. We have developed swellable di-sulfide covalent organic polymers (COPs) with great affinity towards cationic textile micropollutants.

Ultrafast adsorption and selective desorption of aqueous aromatic dyes by graphene sheets modified by graphene quantum dots

Graphene modified by graphene quantum dots (GQDs) has been employed to remove toxic organic dyes. An excellent removal capacity (497 mg g(-1)) and record-breaking adsorption rate (475 mg g(-1) min(-1) at 20 °C) were demonstrated for Rhodamine B. The enhancement in performance by nearly a factor of three compared to that of graphene was ascribed to the greatly increased accessible surface area of graphene in aqueous solution as well as the increase in surface charges with the modification with GQDs. Besides, this unique adsorption behavior of the modified graphene was expanded to other typical toxic aqueous aromatic dyes such as Evans Blue, Methyl Orange, Malachite Green and Rose Bengal. What is more, a unique desorption behavior of dyes was first observed when employing different solvents, which enabled the GQD-modified graphene to be exploited for selective extraction of dyes and recycling of the adsorbent. The adsorption and desorption mechanism were further investigated. Combining high removal capacity, rapid adsorption kinetics, good recyclability and unique selective desorption, GQD-modified graphene has potential applications in both water purification and separation of aromatic dyes.

Macroporous three-dimensional graphene oxide foams for dye adsorption and antibacterial applications

Applicability of graphene oxide foams in water remediation.

Reduction of graphene oxide/alginate composite hydrogels for enhanced adsorption of hydrophobic compounds

Carbon-based materials, consisting of graphene oxide (GO) or reduced GO (rGO), possess unique abilities to interact with various molecules. In particular, rGO materials hold great promise for adsorption and delivery applications of hydrophobic molecules. However, conventional production and/or usage of rGO in aqueous solution often causes severe aggregation due to its low water solubility and thus difficulties in handling and applications. In our study, to prevent the severe aggregation of GO during reduction and to achieve a high adsorption capacity with hydrophobic compounds, GO/alginate composite hydrogels were first prepared and then reduced in an aqueous ascorbic acid solution at 37 °C. Adsorption studies with a model hydrophobic substance, rhodamine B, revealed that the reduced composite hydrogels are more highly absorbent than the unreduced hydrogels. In addition, the adsorption properties of the composite hydrogels, which are consequences of hydrophobic and ionic interactions, could be modulated by controlling the degree of reduction for the adsorption of different molecules. The composite hydrogels embedding rGO can be very useful in applications related to drug delivery, waste treatment, and biosensing.

Microbial preparation of magnetite/reduced graphene oxide nanocomposites for the removal of organic dyes from aqueous solutions

Magnetite/rGO nanocomposites synthesized by microbial cells can function as effective dye adsorbents and be regenerated through a Fenton-like reaction.

Removal and recycling of ppm levels of methylene blue from an aqueous solution with graphene oxide

Methylene blue (several ppm) could be efficiently collected and easily recycled by graphene oxide from solution via simple adsorption process.

Porous graphene materials for water remediation

Water remediation has been a critical issue over the past decades due to the expansion of wastewater discharge to the environment. Currently, a variety of functional materials have been successfully prepared for water remediation applications. Among them, graphene is an attractive candidate due to its high specific surface area, tunable surface behavior, and high strength. This Concept paper summarizes the design strategy of porous graphene materials and their applications in water remediation, such as the cleanup of oil, removal of heavy metal ions, and elimination of water soluble organic contaminants. The progress made so far will guide further development in structure design strategy of porous materials based on graphene and exploration of such materials in environmental remediation.

Mesoporous graphite nanoflakes via ionothermal carbonization of fructose and their use in dye removal

The ionothermal synthesis of oligo-layer graphene-type nanoflakes from fructose in the iron-containing ionic liquid 1-butyl-3-methylimidazolium tetrachloridoferrate (III), [Bmim][FeCl₄] serving as solvent, catalyst, and template for product formation is presented.

Facile synthesis of magnetic nanocomposites of cellulose@ultrasmall iron oxide nanoparticles for water treatment

We report a facile in situ approach to synthesize magnetic nanocomposites of cellulose@ultrasmall iron oxide nanoparticles by co-precipitation using ionic liquid as co-solvent for cellulose and iron salt.