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With widespread utilization of graphene oxides (GO) in industry, it is ineluctably discharged into environment and has been found to be toxic to cells and animals. Effective techniques and functional materials are necessary for the elimination of GO from wastewater. In this work, the GO was removed by the magnetic Fe3O4/MgAl-layered double hydroxide (MLDH) and its oxide (MLDO) from aqueous solution. The effects of dosage, time and solution pH on the removal capacity of the MLDH and MLDO was carried out in detail through batch experiments. The results showed that the MLDH and MLDO can remove GO from aqueous solution quickly and efficiently. The maximum adsorption capacities were 82.4 mg/g of MLDH and 86.7 mg/g of MLDO. The pseudo-second-order equation was well accorded with the adsorption kinetic data. The isothermal data followed the Langmuir and Freundlich models. The interaction mechanisms of GO were ascribed to the surface complexation and electrostatic attraction by using zeta potential determination and XRD spectra. Moreover, the MLDH and MLDO after adsorbing GO can be separated in 10 s by a magnet. The short adsorption time, excellent removal capacity and extremely fast solid-liquid separation indicated that the MLDH and MLDO were potential magnetic adsorbents to remove the GO nanoparticles in aqueous system.

Phosphorylated magnetic chitosan composite (P-MCS) was successfully synthesized and applied to adsorb Pb(II) and Cd(II) from aqueous solutions. The as-prepared P-MCS composite was characterized by EDS, SEM, FTIR, XRD, XPS and zeta potential analysis. Factors affecting adsorption including adsorbent dose, pH value and contact time were optimized to improve the adsorption performance. The adsorption isotherm and kinetic model could well conform to Langmuir model and pseudo-second-order kinetic model. The as-prepared adsorbent exhibited good adsorption capacities for Pb(II) (151.06 mg g−1) and Cd(II) (71.53 mg g−1) from Langmuir isotherm. Besides, spectroscopic analysis after adsorption including FTIR and XPS were also performed to further reveal the adsorption mechanism. The results indicated that surface complexation and ion exchange between functional groups and metal ions played an important role in adsorption process. Thermodynamic studies (∆G 0, ∆S > 0) implied that the adsorption process is an endothermic and spontaneous reaction. Furthermore, the excellent magnetic separation and regeneration performance indicated the feasibility of using P-MCS composite for Pb(II)/Cd(II)-bearing wastewater remediation.

Adsorption of four acid dyes onto cetyltrimethyl ammonium bromide (CTMAB) modified organobentonite from aqueous solution was studied, and effects of the parameters like adsorbent dosage, solution pH, contact time and dye concentration were investigated. The adsorption onto CTMAB-Bent attained equilibrium quickly within 10 min for Acid Blue 93 (AB93), Acid Turquoise Blue A (ATBA), Acid Golden Yellow G (AGYG) and 50 min for Acid Blue 25 (AB25). The adsorption capacity decreased slightly along with the increasing solution pH of 7.0. Four adsorption kinetics equations (pseudo-first-order, pseudo-second-order, intraparticle diffusion and Elovich) were employed to evaluate experimental kinetics data. The rates of the acid dyes adsorption conformed to the pseudo-second-order equation well. The adsorption equilibrium data were analyzed with six models. Both linear and nonlinear regression methods were implemented to calculate isotherm parameters, and the nonlinear regression was more favorable. Regarding to the results of nonlinear analysis, the most applicable adsorption isotherm models were found to be Freundlich, Langmuir, Radke–Prausnitz, Fritz–Schlunder, and Sips equations. The removal ratios of the acid dyes by CTMAB-Bent were all above 88% at the experimental conditions, suggesting that CTMAB-Bent was an excellent adsorbent for acid dyes removal from aqueous solution.

Hydroxy-aluminum pillared bentonite (Al-Bent) was prepared and characterized in this work, and its dye adsorption capacity was comparatively studied in batch experiments. Results of characterization revealed that because of the intercalation of hydroxy-aluminum polyoxycations, a significant increase of interlayer basal spacing, BET surface area and total pore volume was beneficial to dyes' adsorption. The sodium bentonite had a higher adsorption affinity for Basic Fuchsin (BF) and Basic Green (BG) than Acid Turquoise Blue A (ATBA). After pillaring, the adsorption capacity of the three dyes increased and the rise of pH changed insignificantly with solution from 2 to 8. The pseudo-second-order kinetic model provided the best correlation of the experimental data (R2 > 0.99). Henry and Freundlich models both described the adsorption isotherm data well. The adsorption capacity of Al-Bent for the three dyes, especially the basic dyes BF and BG, was high over a wide range of aqueous concentrations and followed the order of BG > BF > ATBA.

In this study, a novel, amino-functionalized magnetic composite of CoFe2O4-chitosan-graphene (MCGS) had been successfully synthesized. The crystal phase, surface morphology and structure of the MCGS were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential measurement, and Brunauer–Emmett–Teller (BET) surface area. The adsorptive characteristics of the MCGS which was intended for removal of Hg(II) from aqueous solutions were deeply studied. The results showed that the adsorption efficiency increased with the increasing of pH and reached the highest point at pH 7.0. The Hg(II) adsorption kinetics on MCGS was consistent with the pseudo second-order process. Langmuir and Freundlich isotherm models were employed to analyze the experimental data, and the Langmuir model was fitted better with a maximum adsorption capacity of 361.0 mg/g at pH 7.0 and 323 K. Thermodynamic studies illustrated that the adsorption process was endothermic and spontaneous.

Magnetic cobalt ferrite (CoFe 2 O 4 )-reduced graphene oxide (rGO) nanocomposites (CoFe 2 O 4 -rGO) were developed as an adsorbent to remove Pb(II) and Hg(II) from aqueous solution. The CoFe 2 O 4 -rGO was prepared by a facile approach and characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area and Zeta potential measurement. In this work, contact time, adsorbent dose, and solution pH temperature were optimized. The sorption kinetics and isotherm model fitting studies, demonstrated that data fit well to pseudo-second order kinetics and Langmuir isotherm models. The highest adsorption equilibrium for Pb(II) were 299.4 mg/g at pH of 5.3 and 25 °C; while for Hg(II) were 157.9 mg/g at pH of 4.6 and 25 °C. Due to magnetic property, CoFe 2 O 4 -rGO could be simply recovered from water by magnetic separations at low magnetic field within 2 min.