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We discovered that chemically reduced graphene oxide, with an I(D)/I(G) >1.4 (defective to graphite) can effectively activate peroxymonosulfate (PMS) to produce active sulfate radicals. The produced sulfate radicals (SO(4)(•-)) are powerful oxidizing species with a high oxidative potential (2.5-3.1 vs 2.7 V of hydroxyl radicals), and can effectively decompose various aqueous contaminants. Graphene demonstrated a higher activity than several carbon allotropes, such as activated carbon (AC), graphite powder (GP), graphene oxide (GO), and multiwall carbon nanotube (MWCNT). Kinetic study of graphene catalyzed activation of PMS was carried out. It was shown that graphene catalysis is superior to that on transition metal oxide (Co(3)O(4)) in degradation of phenol, 2,4-dichlorophenol (DCP) and a dye (methylene blue, MB) in water, therefore providing a novel strategy for environmental remediation.

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Pollution of air, water and soil is a worldwide issue for the eco-environment and human society.Removal of various pollutants including inorganic and organic compounds from the environment is a big challenge. Adsorption techniques are usually simple and work effectively. However, the adsorption capacities of materials depend on their porous structure and surface properties. Graphene oxide and graphene are new carbonaceous nanomaterials. Graphene has a large theoretical specific surface area and graphene oxide has functional groups, indicating their potential for the adsorption processes. In the past few years, many investigations have been focused on the applications of graphene or composites in removal of pollutants from air and water. In this paper, we will review recent advances in graphene-related nanomaterials for adsorptive treatment of environmental pollution. Graphene oxide possesses several functional groups and strong acidity, exhibiting high adsorption for basic compounds and cations while graphene shows hydrophobic surface and presents high adsorption to chemicals due to strong π-π interaction. Modification of graphene oxide or graphene with metal oxides or organics can produce various nanocomposites, enhancing adsorption capacity and separation efficiency. Activation of graphene into porous carbonaceous material will be a promising way to further enhance adsorption capacity.

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The kinetics and mechanism of methylene blue adsorption onto raw pine cone biomass (Pinus radiata) was investigated under various physicochemical parameters. The extent of the methylene blue dye adsorption increased with increases in initial dye concentration, contact time and solution pH but decreases with the amount of adsorbent, salt concentration and temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process followed pseudo-second-order kinetics among various kinetic models tested. The different kinetic parameters including rate constant, half-adsorption time and diffusion coefficient are determined at different physicochemical conditions. Equilibrium data were best represented by Langmuir isotherm among Langmuir and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 109.89 mg/g at 30°C. The value of separation factor, R L , from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. Thermodynamic parameters such as standard Gibbs free energy (ΔG 0 ), standard enthalpy (ΔH 0 ), standard entropy (ΔS 0 ) and the activation energy (A) were calculated. A single-stage batch absorber design for the methylene blue adsorption onto pine cone biomass has been presented based on the Langmuir isotherm model equation. Nomenclature AActivation energy of adsorption (kJ/mol) C f Final metal ion concentration, ppm (mg/l) C 0 Initial metal ion concentration, ppm (mg/l) C t Metal ion concentration at time t, ppm (mg/l) D Diffusion coefficient (cm 2 /s) ΔG 0 Gibbs free energy change (kJ/mole) ΔH 0 Enthalpy change (kJ/mole) ΔS 0 Entropy change (J/k mole) k 1 Pseudo-first-order rate constant (min −1 ) k 2 Pseudo-second-order rate constant (mg/g min) K f Freundlich adsorption constant (mg/g) K idIntra-particle rate constant [(mg/g) min 0.5 ] MMass of adsorbent per unit volume (g l −1 ) m Amount of adsorbent added (g) n Freundlich constant q Amount of adsorbate per gram of adsorbent (mg/g) q e Amount of adsorbate per gram of adsorbent at equilibrium, (mg/g) q tAmount of adsorbate per gram of adsorbent at any time, t q m Equilibrium adsorption capacity using model q max Maximum adsorption capacity (mg/g) R 2Linear correlation coefficient Water Air Soil Pollut (2011) 218:499-515