Efficiency and active sites of the synergetic sorption and photocatalysis in Cr(vi) decontamination on a 3D oxidized graphene ribbon framework

Abstract

The synergetic effect of sorption and photocatalysis for metal sequestration promises unique advantages in environmental remediation; however, the mechanism, especially with regard to the photocatalytic sites, is still ambiguous in carbon catalysts. Here, a metal-free three-dimensional carbon framework, named P-OGR, was fabricated via the assembly of oxidized graphene ribbons (OGRs) and polyacrylamide (PA). In the dark, the sorption capacity of Cr(VI) on P-OGR achieved 338.2 mg g⁻¹ within 2 min. In sunlight for 5 days, P-OGR could immobilize and photo-reduce 687.8 mg g⁻¹ of Cr(VI) into Cr₂O₃ nanospheres. The active sites on P-OGR were explored via modeling experiments. In the sorption, –NH₃⁺ was the best site due to the electrostatic attraction with Cr(VI) anions. Hydroxyls, followed by carboxyl groups, enabled weak hydrogen bonding to capture Cr(VI). During the photocatalysis, the activities of the catalytic sites were evaluated as follows: carboxyl > hydroxyl > ketone > aldehyde, which were consistent with their Lewis acidities.