Simultaneous Removal of Graphene Oxide and Chromium(VI) on the Rare Earth Doped Titanium Dioxide Coated Carbon Sphere Composites

The potential coexistence of toxic metals and graphene oxide (GO) in the natural environment threatens human health. Herein, rare earth doped titanium dioxide coated carbon sphere composites (C@La-TiO2 and C@Ce-TiO2) were synthesized for the simultaneous removal of GO and Cr(VI) from wastewater. The results showed that a relatively high concentration of NaCl was beneficial to the binding of GO, whereas it was adverse to Cr(VI) removal. The removal capacity of C@La-TiO2 reached 383.3 mg/g for GO and 50.5 mg/g for Cr(VI) at pH 5.0. The adsorption process of GO and Cr(VI) on the composites was spontaneous and endothermic. Interestingly, the removal capacity of Cr(VI) on the composites increased significantly in the presence of GO, which was ascribed to the simultaneous adsorption of GO and Cr(VI) on composites and surface adsorbed GO for Cr(VI). However, in the presence of Cr(VI), the GO removal on the composites decreased prominently due to the competitive adsorption between GO and Cr(VI) on the composite surfaces. The interaction of GO was mainly dominated by electrostatic attraction and hydrogen bonding, whereas the removal of Cr(VI) was mainly attributed to outer-sphere surface complexation and electrostatic attraction. The findings can provide new insights into the simultaneous elimination of GO and heavy metal ions in natural aquatic environmental pollution cleanup.