Hanjin Luo

Adsorption of hexavalent chromium from aqueous solutions by graphene modified with cetyltrimethylammonium bromide

In this study, cetyltrimethylammonium bromide was chosen to modify graphene, which was prepared using a modified Hummers method. The characteristics of graphene and modified graphene were characterized by X-ray diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. The effect factors including pH, contact time, temperature, and dosage on the adsorption properties of Cr(VI) onto graphene and modified graphene were investigated. Batch experiments were conducted to evaluate the adsorbance of Cr(VI) from aqueous solution using graphene and modified graphene as the adsorbent under different conditions. The results revealed that the optimal pH for the adsorption was about 2, and the best suitable temperature was at 293 K. The adsorption processes were rapid within the first 5 min and reached equilibrium in about 40 min. The adsorption kinetics fitted well with pseudo-second-order model. The adsorption capacity of Cr(VI) on modified graphene inferred from the Langmuir model was 21.57 mg/g at 293 K. The thermodynamic parameters indicated that the adsorption of Cr(VI) onto modified graphene was an exothermic and spontaneous process.

Synthesis of iron( iii )-based metal–organic framework/graphene oxide composites with increased photocatalytic performance for dye degradation

To improve the utilization efficiency of MOF catalysts, iron(III)-based metal–organic framework/graphene oxide composites were prepared by a facile method. The composites afforded fast degradation performance and high catalytic efficiency for degradation of methylene blue and rhodamine B under exposure to natural sunlight.

A novel modified graphene oxide/chitosan composite used as an adsorbent for Cr(VI) in aqueous solutions.

A novel adsorbent for removal of hexavalent chromium (Cr(VI)) from aqueous solutions has been successfully prepared by modifying graphene oxide/chitosan composite with disodium ethylenediaminetetraacetate (EDTA-2Na) (GEC). This modified composite was characterized by various technologies; including scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Batch adsorption experiments were carried out to evaluate the adsorption of Cr(VI) by GEC under different conditions. The results indicate that the adsorption of Cr(VI) on GEC was highly pH-dependent, with the highest adsorption capacity (86.17mg/g) occurring at pH 2. The kinetics of adsorption exhibited pseudo-second-order behavior. The adsorption data were well described by the Freundlich isotherm model. The adsorption capacity increased with increasing temperature. The calculated thermodynamic parameters indicate that the adsorption is a spontaneous, endothermic and feasible process. The further regeneration experiments showed the adsorption capacity of GEC for Cr(VI) decreased 5% after 7 times reuse, indicating the potential of the as-prepared material for practical application.

Fast adsorption of nickel ions by porous graphene oxide/sawdust composite and reuse for phenol degradation from aqueous solutions.

This work describes the preparation of an effective and low-cost porous graphene oxide/sawdust composite by a freeze-drying method. The composite exhibits a strong ability to adsorb nickel ions. The nickel ions adsorbed on graphene oxide/sawdust composite was reduced by sodium borohydride to generate a catalyst which was used in the degradation of phenol in water. The composite and the catalyst were characterized by XPS, FTIR, XRD and SEM. The adsorption of nickel ions by graphene oxide/sawdust composite was initially very fast and then slowly reached equilibrium in around 30 min. The adsorption of nickel ions by the composite could be well-described by the Freundlich isotherm model and the pseudo-second order kinetic model. The performance of the catalyst in phenol degradation was studied as a function of reaction time, dosage, temperature and initial pH. It was found that the catalyst optimally improved the degradation rate at pH 10 with a dose of 2 g/L in about 30 min. The results show that the degradation of phenol was an endothermic reaction and was a good fit to the Langmuir isotherm model.

Facile synthesis of magnetic Bi25FeO40/rGO catalyst with efficient photocatalytic performance for phenolic compounds under visible light

To improve the utilization efficiency of the Bi25FeO40 catalyst, Bi25FeO40-reduced graphene oxide (rGO) composite photo-catalysts were prepared by a facile hydrothermal method. The photocatalysts afforded fast degradation performance and high photocatalytic efficiency for degradation of phenol and p-chlorophenol under exposure to visible light irradiation.

Removal of para-nitrochlorobenzene from aqueous solution on surfactant-modified nanoscale zero-valent iron/graphene nanocomposites

This study demonstrated a remarkably simple and efficient method for the synthesis of nanoscale zero-valent iron (NZVI)/graphene (GN) nanocomposites. In order to prevent the agglomeration and restack of nanocomposites, chemical functionalization of nanocomposites with cetyltrimethylammonium bromide was proposed. The adsorption performance of surfactant-modified NZVI/GN nanocomposites was evaluated for the removal of para-nitrochlorobenzene (p-NCB) from aqueous solutions. The characteristics of nanocomposites were characterized by X-ray diffraction, BET surface area, Fourier transform infrared spectrum, thermogravimetric analysis and scanning electron microscopy. The effect factors including initial solution pH, contact time, reaction temperature, dosage, initial concentration of humic acid (HA) on the adsorption property of p-NCB onto surfactant-modified nanocomposites were investigated. The adsorption kinetics fitted well with pseudo-second-order model. The adsorption capacity of p-NCB on surfactant-modified nanocomposites inferred from the Langmuir model was 105.15 mg/g at 293 K. The thermodynamic parameters indicated that the adsorption of p-NCB onto surfactant-modified nanocomposites was an exothermic and spontaneous process. HA had a strong suppression effect on p-NCB uptake in the adsorption experiment.

Efficient Removal of Congo Red from Aqueous Solutions by Surfactant-Modified Hydroxo Aluminum/Graphene Composites

Different surfactant-modified hydroxo aluminum/graphene nanocomposites were synthesized and used for the adsorptive decolorization of Congo red from aqueous solution. Nanocomposites were prepared by the intercalation of hydroxo aluminum/graphene oxide with three different surfactants, followed by reduction using sodium borohydride. Batch experiments were conducted to evaluate the adsorbance from aqueous solution using different adsorbents under different conditions. The results showed that the maximum adsorption capacity can reach 497.51 mg/g, 398.4 mg/g, and 352.1 mg/g on different adsorbents at pH 3 and 323 K. The as-prepared adsorbents all had good reusability, and the optimal eluent buffer is ethanol, NaOH and HCl for different adsorbents. The adsorption kinetics fitted well with a pseudo-second-order model. Adsorption data were found to fit well with the Freundlich model. The thermodynamic analysis indicated that these adsorptions were endothermic and spontaneous in nature.

Pd nanoparticles supported on MIL-101/reduced graphene oxide photocatalyst: an efficient and recyclable photocatalyst for triphenylmethane dye degradation.

To improve the photocatalytic efficiency of chromium-based metal−organic framework (MIL-101) photocatalyst, Pd nanoparticles and reduced graphene oxide were used to modify the MIL-101 via a facile method. The resulting novel photocatalyst was characterized by UV–vis diffuse reflectance spectra (DRS), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was indicated that the photocatalyst afforded high photocatalytic efficiency for degradation of two triphenylmethane dyes, brilliant green and acid fuchsin, under exposure to visible light irradiation. Cyclic experiments demonstrated that the photocatalyst showed good reusability and stability for the dye degradation.

Synthesis of graphene/SiO 2 @polypyrrole nanocomposites and their application for Cr(VI) removal in aqueous solution

A novel hybrid nanocomposite, polypyrrole nanoparticles (PPy) anchored on the graphene/silica nanosheets with the high specific surface area (polypyrrole-graphene/silica, GS-PPy), was synthesized by a facile in situ polymerization and shows great potential to remove hexavalent chromium [Cr(VI)] in aqueous solutions. Characterizations by XRD, TEM, SEM, BET, FT-IR and XPS, have confirmed that the PPy nanoparticles were well-distributed on the surface of GS nanosheets. The effects of pH, contact time, the concentration of Cr(VI), temperature, coexisting ions and the number of adsorption-desorption cycles were studied. The maximum adsorption capacity of the GS-PPy for Cr(VI) was 429.2u202fmgu202fg-1 at 298u202fKu202fat pH 2, which was much higher than PPy nanoparticles and other related materials. The adsorption data fitted to the pseudo-second-order model and Langmuir isotherm model. The removal mechanism involved in electrostatic attraction, ion exchange and reduction process that partial adsorbed Cr(VI) was reduced to Cr(III). And Cr(III) was still retained on the surface of GS-PPy. The GS-PPy nanocomposite will be a potential candidate for the removal of Cr(VI) from the industrial waste water.