Synergistic Photocatalytic Reduction of Hexavalent Chromium Using Graphene Quantum Dots and Formic Acid Optimization and Kinetics

Abstract

Graphene Quantum Dots (GQDs) has garnered a significant deal of interest in environmental remediation, particularly for reducing hexavalent chromium [Cr (VI)] to trivalent chromium [Cr (III)]. This study focused on the photocatalytic process of Cr (VI) degradation using GQDs and Formic Acid (FA) under Uv-vis light. Batch experiments were conducted to observe the photocatalytic process of Cr (VI) degradation under Uv-vis light irradiation at varying concentrations of GQDs, FA, and Cr (VI) and different pH levels. The characterization of GQDs includes PL, XPS, XRD, and Raman Spectroscopy. This research revealed that combining GQDs and FA for the photocatalytic process of Cr (VI) reduction is possible. As expected, this system is more effective with lower concentrations of Cr (VI). When FA was introduced, the Cr (VI) degradation efficiency ratio increased. The GQDs/FA/Uv-vis system gave the highest degradation rate at 91.1% within 30 minutes. It was also observed that the optimum pH of the solution was 5.42, where the GQDs were quickly dissoluble. The photocatalytic reduction matched first-order reaction kinetics with a rate constant (k) of 0.1085 min⁻¹ and R² of 0.985. The primary radical in the degradation of Cr (VI) in the GQDs/FA/Uv-vis system was CO₂^•−. These findings highlight the potential of GQDs and FA as efficient catalysts for the photocatalytic reduction of Cr (VI) under Uv-vis light.