Graphene oxides with different oxidation degrees for Co(II) ion pollution management

•A facile and cost-effective method to modify graphene oxide by ozone treatment.•The ozone treatment time affect the oxidation degrees and adsorption capacity for Co(II).•The microcosmic mechanism displayed that cobalt can complex with the oxygen-containing functional groups on GOs surfaces.•The modified graphene oxide can be conveniently used for further application.

Presented herein is a facile approach, which is easy, cost-effective, environmental benign without any secondary environmental pollution and no requirement for post purification, towards the synthesis of graphene oxides (GOs) with different oxidation degrees by ozone treatment. The synthesized GOs with controlled oxidation degrees can not only increase the quantity of oxygen-containing functional groups on GOs surfaces, but also decrease the sizes of GOs sheets to facilitate their dispersion abilities in aqueous solution, as revealed by characterization. The ozonized GOs were further applied as Co(II) adsorbents from aqueous solutions. The adsorption results showed that this adsorption processes was endothermic and spontaneous, and followed the pseudo-second-order kinetics and the Langmuir adsorption models. The microcosmic mechanism displayed that cobalt can complex with the oxygen-containing functional groups on GOs surfaces. As expected, increased adsorption capacities were observed by GOs with higher oxidation degrees.

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