Adsorption Capacity For Anionic Dyes Research Articles

Structure Characterization and Dye Adsorption Properties of Modified Fiber from Wheat Bran.

The fibers from four wheat varieties (FT, XW 26, XW 45, and KW 1701) were selected and chemically modified with NaOH, epichlorohydrin, and dimethylamine to improve the adsorption capacity for anionic dye. The structure of the fibers with or without modification was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectrometry. The modified products were studied from the aspects of adsorption capacities, adsorption kinetics, and thermodynamics to provide a reference for the utilization of wheat bran. By SEM, more porous and irregular structures were found on the modified fibers. The XRD results showed that the crystals from the original fibers were destroyed in the modification process. The changes in fibers' infrared spectra before and after modification suggested that quaternary ammonium salts were probably formed in the modification process. The maximum adsorption capacity of wheat bran fibers for Congo red within 120 min was 20 mg/g for the unmodified fiber (XW 26) and 93.46 mg/g for the modified one (XW 45). The adsorption kinetics of Congo red by modified wheat bran fiber was in accord with the pseudo-second-order kinetic model at 40 °C, 50 °C, and 60 °C, indicating that the adsorption process might be mainly dominated by chemisorption. The adsorption was more consistent with the Langmuir isothermal adsorption model, implying that this process was monolayer adsorption. The thermodynamic parameters suggested that the adsorption occurred spontaneously, and the temperature increase was favorable to the adsorption. As mentioned above, this study proved that the wheat bran fiber could possess good adsorption capacities for anion dye after chemical modification.

Facile synthesis and ultrastrong adsorption of a novel polyacrylamide-modified diatomite/cerium alginate hybrid aerogel for anionic dyes from aqueous environment

An eco-friendly cationic polyacrylamide (CPAM)-modified diatomite/Ce(III)-crosslinked sodium alginate hybrid aerogel (CPAM-Dia/Ce-SA) was synthesized successfully and characterized by SEM-EDS, XRD, FTIR, UV–Vis and XPS. Adsorption performance, interaction mechanism and reusability of CPAM-Dia/Ce-SA used for the removal of acid blue 113 (AB 113), acid blue 80 (AB 80), acid yellow 117 (AY 117), Congo red (CR) and Direct Green 6 (DG 6) anionic dyes from aqueous media were investigated in detail. The results demonstrate that CPAM-Dia/Ce-SA aerogel is macroscopic polymer hybrid spheres with a particle size of around 1.3 mm, unique undulating mountain-like surface and porous mesostructure, and exhibits outstanding adsorption capacity for anionic dyes and good reusability. The maximum adsorption amounts of AB 113, AB 80, AY 117, CR and DG 6 by CPAM-Dia/Ce-SA were 3008, 1208, 914, 1832 and 1232 mg/g at pH 2.0, 60 min contact time and 25 °C, and corresponding removal efficiency reached individually 97.5, 96.6, 99.7, 99.9 and 98.5 % respectively and were less affected by increasing pH up to 10.0. Dye adsorption behaviour and adsorption processes with spontaneous and exothermic nature were perfectly interpreted by the Langmuir and Pseudo-second-order rate models respectively. Physicochemical and multisite-H-bonding synergies promoted the ultrastrong biosorption of anionic dyes by CPAM-Dia/Ce-SA.

A sulfonate-functionalized covalent organic framework for record-high adsorption and effective separation of organic dyes

The emerging global water crisis necessitates the development of solid adsorbents for the removal of organic pollutants from wastewater. Herein, we develop an anionic sulfonate-functionalized covalent organic framework (COF), termed TpStb-SO3Na, by the Schiff-base condensation between 2,4,6-triformylphloroglucinol (Tp) and 4,4′-diaminostilbene-2,2′-disulfonic acid (Stb-SO3H) under solvothermal conditions in the presence of sodium acetate. Thanks to the dense sulfonate groups in the periodic one-dimensional channels, the negatively charged TpStb-SO3Na displayed rapid kinetics (average ∼ 99% uptake in merely 10 min) and ultrahigh adsorption capacities for multiple cationic dyes including methylene blue (MB, 1078 mg g−1), crystal violet (CV, 1861 mg g−1), malachite green (MG, 5857 mg g−1) and janus green B (JGB, 1339 mg g−1) at room temperature. Noteworthy, the adsorption capacities of TpStb-SO3Na toward CV, MG, and JGB were the record-high values among the documented COFs, metal–organic frameworks (MOFs), and other benchmark adsorbents. In addition, the adsorption behaviors of MB, CV, MG, and JGB on TpStb-SO3Na obeyed the pseudo-second-order adsorption kinetic model. On the contrary, TpStb-SO3Na presented low adsorption capacity for anionic dyes like methyl orange (MO) and fluorescein sodium (FS), rendering it a promising sorbent for the separation of cationic and anionic dyes based on charge difference. Furthermore, TpStb-SO3Na was easily regenerated and reused for five cycles with no obvious loss in its adsorption performance. This work uncovers the vast potential of anionic COFs for the effective removal of organic dye pollutants in wastewater.

Functionalized PVA film with good adsorption capacity for anionic dye

AbstractThe dye‐water treatment by polyvinyl alcohol (PVA) is still a challenge as PVA is characterized by its strong affinity to water. Therefore, this study aims to fabricate a functional PVA film with good regeneration ability to remove anionic dyes from aqueous solution using polyamidoamine dendrimers (PAMAM) as a modifier and epichlorohydrin as a cross‐linker. Solution casting technique was applied to prepare the functionalized film. The adsorption efficiency of the film was evaluated by studying the effect of various parameters such as PAMAM loading (0, 12.5, 25, 50 wt%), initial dye concentration, film dose, solution pH, and adsorption time. The adsorption studies showed that with increasing PAMAM loading, the maximum adsorption capacity of the resulting film increased till it reached up to 73.8 mg/g by the PVA film with 50 wt% PAMAM. For understanding the nature of the adsorption process of the prepared film, the kinetics and isotherm analysis were studied. It was found that the mechanism of dye removal by the prepared film followed pseudo‐second‐order kinetic and Freundlich isotherm, respectively. The adsorption and regeneration studies indicated that this film has great potential to effectively remove anionic dye from wastewater.

Ionic liquid grafted polyethersulfone nanofibrous membrane as recyclable adsorbent with simultaneous dye, heavy metal removal and antibacterial property

In view of the harmfulness of the pollutants in wastewater to both human being and environment, it is urgent to develop a multifunctional polymer adsorbent that can remove dyes, heavy metals and bacteria simultaneously. Herein, ionic liquid (IL) grafted Polyethersulfone (PES) (PES-g-IL) nanofibrous membranes (NFMs) were prepared by combining radiation induced grafting method and electrospinning strategy. The adsorption behavior, antibacterial property as well as reusability were examined for the obtained NFMs. It was found that the PES-g-IL NFMs exhibited excellent adsorption ability for heavy metal ions and dyes as well as good recyclability. The adsorption capacity for anionic dyes Congo Red (CR) and heavy metal ions (Cd(II)) reached 120.3 and 187.3 mg/g, respectively. The adsorption mechanism of CR was proved to be the electrostatic interaction between the NFMs and CR, while the adsorption of Cd(II) was driven by the complex between the nitrogen atoms on the imidazolium ring of the grafted ionic liquid and Cd(II). According to the adsorption kinetics, the adsorption of CR and Cd(II) was well fitted by the pseudo-second-order kinetic equation, indicating that the adsorption process was controlled by multiple steps. By calculating the thermodynamic parameters, it is indicated that the adsorption of CR and Cd(II) was a spontaneous physical adsorption process. In addition, PES-g-IL NFMs had excellent antibacterial ability. The killing rate of E. coli. was close to 99%. Given the above advantages, the PES-g-IL NFMs showed great potential in wastewater treatment.

Functionalized waste cellulose with metal-organic-frameworks as the adsorbent with adjustable pore size: Ultralight, effective, and selective removal of organic dyes

In this work, we proposed a green and low-cost method to prepare novel waste cellulose/ZIF-67 composite aerogels as the adsorbent. These composites were fabricated by assembling ZIF-67 crystals into the three-dimension framework of cellulose aerogel derived from waste cigarettes. Due to the high specific surface area and electrostatic attraction, as-prepared waste cellulose/ZIF-67 aerogels had a high adsorption capacity for anionic dyes. The methyl orange was selectively adsorbed by waste cellulose/ZIF-67 compared to methyl blue. The maximum adsorption capacity for methyl orange reached to 134.36 ​mg ​g−1. Interestingly, this adsorption capacity can maintain above 80% after 5 cycles. Thus, as-prepared waste cellulose/ZIF-67 aerogels in this paper have an important potential application in waste water treatment as a selective adsorbent.

Adsorption Capacity of Smectite Clay and Its Thermal and Chemical Modification for Two Anionic Dyes: Comparative Study

The present research evaluates the influence of modification of smectite clay (BC) on its adsorption capacity of anionic dyes from aqueous solutions. Thermal (BC 250), acidic (BC H2SO4), and alkaline (BC NaOH) modification of clay was carried out. The clays were characterized by X-ray powder diffraction, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Adsorption of dyes was investigated by batch experiments at room temperature (23 ± 2 °C), a wide range of initial dye concentrations (1–1000 mg/dm3), and an adsorbent dose of 50 g. All modifications increased the clay’s adsorption capacity for Reactive Red 198, in the order BC H2SO4 > BC NaOH > BC 250 > BC; it was 10.32, 5.06, 3.32, and 2.92 mg/g, respectively. Acid and thermal modification of the clay increased its adsorption capacity for Acid Red 18, in the series BC H2SO4 > BC 250 > BC > BC NaOH; it was 3.07, 2.66, 2.16, and 1.28 mg/g, respectively. The experimental data were analyzed by Freundlich, Langmuir, Dubinin–Radushkevich, and Sips isotherms, using nonlinear regression. The experimental data best fitted the Sips isotherm. Taking into account the structure of the adsorbent and adsorbates and the results obtained, it can be concluded that the dyes were probably bound through chemisorption, by forming hydrogen bonds between Si–OH and Al–OH groups in the clay and –NH, –NH2, and –OH groups in the dyes. From the results obtained, it can be concluded that smectite clay is a promising material for dye adsorption.

A novel surface-active monomer decorating a self-floating adsorbent with high pH adaptability for anionic dyes: π-π stacking

It remains a challenge to remove anionic dyes under alkaline conditions. In this study, we studied the pH independent adsorption of anionic dyes on a surface-active cationic monomer, benzyl(methacryloyloxyethyl)dimethylammonium chloride (BMDAC), which was used to decorate a self-floating adsorbent, BDSA. To compare the pH adaptability, a traditional cationic monomer, methacrylatoethyl trimethyl ammonium chloride (MTAC), which is similar to BMDAC in terms of its structure but does not contain aromatic groups, was used instead of BMDAC to prepare another adsorbent, MDSA. Through comparison of characterization and adsorption experiments, we found that BDSA could maintain a high dye-removal efficiency under different pH conditions. The AG25 removal rate was above 90% in the pH range of 2–10. In addition, BDSA showed outstanding recovery and reutilization performance; its adsorption capacity remained above 80% after five cycles of use. The π-π stacking between the benzyl group in BDSA and the aromatic ring in the dye molecule was found to enhance the adsorption interaction, which was confirmed by theoretical calculations. With its excellent adsorption capacity for anionic dyes, high pH adaptability, easy separation ability and good reusability, BDSA is an ideal candidate for dye wastewater treatment.

Enhanced adsorption removal performance of UiO-66 by rational hybridization with nanodiamond

Abstract In the present work, a series of nanohybrids based on UiO-66 as a physicochemical stable metal-organic framework (MOF) and different amounts of thermally oxidized nanodiamond (OND) (0.5–10 wt%) were synthesized and used as adsorbents for anionic (methyl red, MR, and methyl orange, MO) and cationic (malachite green, MG, and methylene blue, MB) dyes from contaminated water in single and binary dye solutions. The single adsorbents and their nanohybrids were characterized by FESEM, FTIR, XRD,TGA, BET, and zeta potential measurements. The experimental adsorption results displayed that the synthesized nanohybrids presented higher adsorption capacity for anionic dyes compared to cationic dyes in both single and binary dye solutions. It was deduced that the electrostatic interactions and hydrogen bonding between anionic dye molecules and adsorbents were the main mechanisms for selective adsorption of these dyes onto synthesized nanohybrids. Additionally, the results suggested that the maximum improvement in dye adsorption was achieved at certain concentration of OND in the nanohybrid, e.g. at 3 wt% OND named OND-UiO-3, which was associated to its microstructure. OND-UiO-3 nanoparticles displayed an increase of 532% in MR adsorption capacity and a four-order-of-magnitude increase, in removal rate compared to parent UiO-66 nanoparticle.

Sustainable synthesis of graphene-based adsorbent using date syrup

Here we demonstrate, a facile in-situ strategy for the synthesis of environmentally benign and scalable graphene sand hybrid using date syrup as a sustainable carbon source through pyrolysis at 750 °C. Raman and SEM images revealed that the as-prepared date syrup-based graphene sand hybrid (D-GSH) had imperfections with macroporous 2-D graphene sheet-like structures stacked on the inorganic sand support. The applicability of the D-GSH for decontaminating the water from cationic (Methyl Violet, MV) and anionic (Congo Red, CR) dye and heavy metals (Pb2+ and Cd2+) was tested. Batch experiments demonstrated that D-GSH showcased exceptional capability for both dye and heavy metals removal with fast adsorption following pseudo-second-order kinetics. The adsorption capacities for MV, Pb2+, and Cd2+ were respectively 2564, 781 and 793 mg/g at 25 °C, the highest capacity graphene-based adsorbent reported in the literature to date. In addition, D-GSH also exhibited high adsorption capacity for anionic dye, CR (333 mg g−1) and good recyclability (3 cycles) for all the contaminants. The thermodynamic studies further confirmed that the adsorption of all contaminants was thermodynamically feasible, spontaneous and endothermic with ∆H° of 48.38, 89.10, 16.89 and 14.73 kJ/mol for MV, CR, Pb2+ and Cd2+, respectively. Thus, utilization of a simple one-step strategy to produce graphenic sand hybrid using date syrup helped in developing a cost-effective and environmentally friendly dye and heavy metal scavenger that can be used as a one-step solution for water decontamination.

Positively-charged polyethersulfone nanofibrous membranes for bacteria and anionic dyes removal

Given the complexity of pollutants in wastewater, development of facile and effective multifunctional materials, which can not only kill bacteria but also remove dyes from wastewater, is in high demand. Herein, a facile strategy for the preparation of positively-charged nanofibrous membranes (NFMs) is reported via the combination of electrospinning and in-situ cross-linked polymerization of poly ([2-(methacryloyloxy)-ethyl] trimethyl ammonium chloride) (PMETAC) in poly (ether sulfone) (PES) solution. The quaternary ammonium salt polymer of PMETAC enabled the NFMs with positive charge to kill bacteria and remove anionic dyes. The antibacterial tests including agar plate counting and live/dead staining indicate that the NFMs show strong antibacterial ability with bacterial killing ratios of nearly 99% for both Escherichia coli and Staphylococcus aureus, as well as remarkable recyclability towards killing bacteria. The dyes adsorption experiments show that the NFMs exhibit high adsorption capacity for anionic dyes up to 208 mg g−1 for Congo Red (CR) and good reusability toward CR. Impressively, the membrane adsorption column test indicates that the CR dye removal ratio is up to 100% for the first time, and that is still as high as 96.5% for the third time with a fresh dye solution. Given the above advantages, such fascinating NFMs may provide new perspectives in the exploitation of multifunctional membrane materials for complex water remediation.

Acid-salt treated CoAl layered double hydroxide nanosheets with enhanced adsorption capacity of methyl orange dye

In this study, the ultra-thin CoAl layered double hydroxide (LDH) nanosheets with Cl− intercalation were prepared by a hydrothermal method following acid-salt treatment. The morphology, structure and composition information of CoAl LDHs were identified by a variety of characterization methods including SEM, XRD, XPS, FT-IR, and BET. The effects of initial adsorbent concentration, pH, competitive anions, and temperature were also measured. The fitted adsorption curves are matched well with Langmuir isotherm model and pseudo-second-order kinetic model, suggesting that the removal of methyl orange (MO) is governed by monolayer heterogeneous adsorption and chemical adsorption, respectively. The measurements of adsorption capacity at various temperatures revealed that the adsorption process is spontaneous. Co-existing anions have different negative effects on the adsorption capacity. The Co4Al1-Cl LDH adsorbent shows the maximum experimental and theoretical adsorption capacity of 801.08 and 827.50 mg g−1 (pH = 7 and T = 293 K), respectively. An adsorption mechanism called “ion exchange and expansion-extrusion” is proposed to explain the change of interlayer spacing. These results indicate that a novel avenue for designing LDH-type adsorbent has been proposed with excellent adsorption capacity for anionic dyes like MO.

Modification of Karaya gum by graft copolymerization for effective removal of anionic dyes

ABSTRACTA graft copolymer gel based on the ‘Karaya gum’ has been made by grafting Karaya gum (KG) with 2-(methacryloyloxyethyl)trimethylammonium chloride (METAC) via microwave irradiation technique. The swelling of the gel appeared to be a second-order kinetic process following Fickian diffusion. The material exhibited significant adsorption capacity for anionic dyes, namely, indigo carmine, methyl orange, Remazol brilliant blue R and Direct Black 38 from aqueous solution. The pseudo-first-order kinetic model and Freundlich isotherm models provided good correlation with the dye adsorption data on KG-g-PMETAC. Thermodynamic studies revealed the adsorption process to be endothermic in all cases.

Influence of dextran hydrogel characteristics on adsorption capacity for anionic dyes

A series of cationic amphiphilic dextran hydrogels with pendent N, N-dimethyl-N-alkyl-N-(2-hydroxypropyl) ammonium chloride pendent groups was obtained with various molar ratios hydrophilic (alkyl = C2)/hydrophobic groups (alkyl = C12 or C16), total content in amino groups (50–68 mol%) and water swelling capacity (3–15 g water/g dry gel). Adsorption capacity for anionic dyes (Methyl Orange and Rose Bengal) was studied as a function of hydrogel characteristics. Adsorption kinetics was mainly influenced by swelling porosity and dye molecular weight. Equilibrium data showed that the maximum sorption capacity was strongly dependent on hydrophobic segment content, which enhanced the affinity dye-gel (increased Langmuir constant KL) and contribution of ion-exchange to adsorption mechanism, and significantly decreased the maximum uptake of Rose Bengal. The hydrophilic highly swollen hydrogel had the best adsorption capacity for Rose Bengal (1700 mg/g) at 25 °C, and more hydrophobic gels could adsorb 830–900 mg Methyl Orange/g, irrespective of the medium temperature.

Sulfonated Hollow Covalent Organic Polymer: Highly‐Selective Adsorption toward Cationic Organic Dyes over Anionic Ones in Aqueous Solution

AbstractA sulfonated hollow covalent organic polymer (sh‐COP‐P) was prepared by post sulfonation of hollow covalent organic polymer (h‐COP‐P) synthesized through poly‐condensation of tetrabiphenylporphyrin (TBPP). In comparison with h‐COP‐P, sh‐COP‐P exhibits significantly enhanced adsorption capacity of organic cationic dyes in aqueous solutions accompanied with notably reduced adsorption capacity of anionic dyes. This gives sh‐COP‐P a satisfactory performance in selectively separating cationic organic dyes from anionic ones, mainly attributed to the electrostatic interaction between polymer backbone and the guest molecules.

Design and preparation of a cellulose-based adsorbent modified by imidazolium ionic liquid functional groups and their studies on anionic dye adsorption

Adsorption of dyes via strong interactions between modified cellulose paper and dyes is an economical, effective, and sustainable method for treating wastewater. In this work, using multiple interactions with dye molecules, an imidazolium ionic liquid modified cellulose adsorbent (CCP-Im) was prepared and used to treat anionic dye wastewater effectively. Zeta potential tests and Gaussian simulations revealed the strong interactions between CCP-Im and anionic dye molecules. Under optimum adsorption conditions, CCP-Im has good adsorption capacity for anionic dyes, and the maximum adsorption capacities of xylenol orange and Congo red could reach 1169 and 563 mg g−1, which were 3.1 and 3.5 times, respectively, higher than the values of the original cellulose paper. The Freundlich and Scatchard models for isothermal study demonstrated the adsorption process of CCP-Im toward anionic dyes occurred on a heterogeneous surface via multilayer sorption, and the kinetics revealed that a Pseudo-second-order model described the adsorption process well, indicating the adsorption was controlled by the mechanism of chemical adsorption. Therefore, preparation of this bioadsorbent would be useful for environmental protection and development of sustainable resources.

Adsorption Removal of Multiple Dyes Using Biogenic Selenium Nanoparticles from an Escherichia coli Strain Overexpressed Selenite Reductase CsrF.

Selenite reductase CsrF overexpressed Escherichia coli was used as a microbial factory to produce Se(0) nanoparticles (Bio-SeNPs). The Bio-SeNPs were characterized by transmission electronic microscopy, element mapping, scanning electron microscopy, energy-dispersive X-ray spectrographs, Zeta-potential, dynamic light scattering, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. The results indicated that Bio-SeNPs are irregular spheres with diameters from 60 to105 nm and mainly consist of Se(0), proteins and lipids. Furthermore, it exhibited maximum adsorption capacity for anionic dye (congo red) at acidic pH and cationic dyes (safranine T and methylene blue) at alkaline pH. To gain more insight, adsorption kinetics, adsorption isotherms and adsorption thermodynamics studies were carried out. These results showed that the adsorption capacities of congo red, safranine T and methylene blue were 1577.7, 1911.0 and 1792.2 mg/g, respectively. These adsorption processes were spontaneous and primarily physical reactions. In addition, Bio-SeNPs can be effectively reused by 200 mmol/L NaCl. To the best of our knowledge, this is the first report of adsorption removal dyes by Bio-SeNPs. The adsorption capacities of Bio-SeNPs for congo red, safranine T and methylene blue were 6.8%, 25.2% and 49.0% higher than that for traditional bio-based materials, respectively.

Construction of polycationic film coated cotton and new inductive effect to remove water-soluble dyes in water

In order to realize the high efficient purification of dyeing waste-water, we designed the construction of the polycationic film coated on cotton. We firstly detected that the crystallization spaces of natural cotton could be decreased by triethanolamine pretreatment, so that the cationic reagent:3-chloro-2-hydroxypropylmethyldiallylammonium chloride (CMDA) could be grafted more efficiently, in turn forming the higher cationic degrees of grafting cotton (G-cotton). Subsequently, a copolymerization of another cationic monomer: dimethyldiallylammonium chloride (DMAC) with the cationic CMDA units in G-cotton was carried out, to obtain the polycationic film coated cotton (PF-cotton). Under equal conditions, the G-cotton adsorption capacity of anionic dyes was 15.70 times of that of activated carbon, while the PF-cotton adsorption capacity was near to that of G-cotton, but the average adsorption rate of PF-cotton was 2.8 times of that of G-cotton, indicating that the obtained PF-cotton was very suitable to purify the dyeing waste-water. Moreover, the PF-cotton had a wide range of application universal, e.g., enlarged use, adsorbing different dye solutions and simulated dyeing waste-water, being a filtering filler, and recycling utilization. In addition, we also detected that a new inductive effect occurred in the process of PF-cotton adsorption, playing an important role in speeding up the adsorption.

Enhanced adsorption removal of anionic dyes via a facile preparation of amino-functionalized magnetic silica.

A novel amino-functionalized magnetic silica (Fe3O4@SiO2-NH2) was easily prepared via a one-step method integrating the immobilization of 3-aminopropyltriethoxysilane with a sol-gel process of tetraethyl orthosilicate into a single process. This showed significant improvement in the adsorption capacity of anionic dyes. The product (Fe3O4@SiO2-NH2) was characterized with scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectrometry, zeta potential and vibrating sample magnetometry. The adsorption performance of Fe3O4@SiO2-NH2 was then tested by removing acid orange 10 (AO10) and reactive black 5 (RB5) from the aqueous solutions under various experimental conditions including initial solution pH, initial dye concentrations, reaction time and temperature. The results indicated that the maximum adsorption capacity of AO10 and RB5 on Fe3O4@SiO2-NH2 was 621.9 and 919.1 mg g-1 at pH 2, respectively. The sorption isotherms fit the Langmuir model nicely. Similarly, the sorption kinetic data were better fitted into the pseudo-second order kinetic model than the pseudo-first order model. In addition, the thermodynamic data demonstrated that the adsorption process was endothermic, spontaneous and physical. Furthermore, Fe3O4@SiO2-NH2 could be easily separated from aqueous solutions by an external magnetic field, and the preparation was reproducible.

One-step approach for the synthesis of CoFe2O4@rGO core-shell nanocomposites as efficient adsorbent for removal of organic pollutants.

CoFe2O4-reduced graphene oxide nanocomposites (CFG) have been successfully synthesized via one-step solvothermal method. The prepared CFG are characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FESEM), vibrating sample magnetometer and so on. The FESEM results show that CFG have uniform core-shell structure with an average diameter of about 75 nm and the thickness of the outer graphene shell is about 15-20 nm. The mass ratio of CoFe2O4 to graphene oxide is a key factor affecting the formation of core-shell hybrids. CFG display much higher adsorption capacity for anionic dyes than cationic dyes owing to the favorable electrostatic interaction. The adsorption capacity for methyl orange is observed as high as 263 mg g-1 at 298 K, and the adsorption isotherms follow the Langmuir model. Furthermore, the specific saturation magnetization (Ms) of CFG is 32.8 emu g-1, and the as-synthesized nanocomposites can be easily separated by external magnetic field after adsorption. The results suggest that CFG have great potential for the practical industrial wastewater treatment.