L-glutamic acid-functionalized graphene oxide with characteristic of anti-stacking towards efficient adsorption-reduction removal of Cr(VI)

Hexavalent chromium (Cr(VI)) pollution in aquatic environments has triggered constant worries. As one of the popular adsorbents, graphene oxide (GO) still confronts shortcomings in the Cr(VI) removal, including easy aggregation, limited adsorption amounts, monotonous type of functional groups, constant negative charge and unable valence conversion. Herein, L-glutamic acid (L-Glu) was utilized for GO functionalization through the solvothermal method to fabricate L-Glu/GO with the trait of anti-stacking for overcoming the above-mentioned drawbacks. Results proved that L-Glu/GO possessed the relatively large specific surface area and average pore diameters, various functional groups and variable surface charges. The as-prepared L-Glu/GO exhibited satisfying adsorption amounts with the changeable acid environment, adsorbent dosages and initial Cr(VI) concentrations. Besides, Cr(VI) adsorption process conformed to the pseudo-second-order kinetic model and the Langmuir isotherm model with q m for Cr(Ⅵ) of 71.12 mg·g –1 , almost 27 times higher than that of GO (2.64 mg·g –1 ) in pH = 2. The adsorption thermodynamics result portrayed the adsorption process was a spontaneous endothermic process. Additionally, L-Glu/GO possessed excellent reusability with q e of Cr(Ⅵ) of 57.19 mg·g –1 after five cycles, with the economic cost of ¥0.498·g –1 . More importantly, Cr(VI) was changed into Cr(III) during adsorption to accomplish the toxicity elimination due to existence of amine groups from L-Glu. On the whole, pore filling, anion-π interaction, electrostatic interactions, adsorption-reduction and coordination interaction jointly contributed to the Cr(VI) adsorption. This work provided the strategy for effectively enhancing the Cr(VI) adsorption capacity of GO and deepened the adsorption mechanism towards hazardous metal ions elimination.