Activation of peroxydisulfate by biogenic nanocomposites of reduced graphene oxide and goethite for non-radical selective oxidation of organic contaminants: Production of singlet oxygen and direct electron transfer

Composites of carbon nanomaterials and nanosized iron oxides have been extensively investigated as efficient catalysts for H2O2 decomposition in advanced oxidation. However, little is known about their catalytic activity and mechanism in peroxydisulfate (PDS) activation. In this study, reduced graphene oxide (rGO) and goethite (Gt) nanocomposites (Gt-rGO) with different rGO contents were biologically prepared and their abilities of activating PDS for elimination of organic pollutants were investigated. In 4 h, 97.5% of sulfanilamide (SA, 20 μM) was efficiently degraded in the Gt-rGO/PDS system. The pseudo-first-order rate constant of SA degradation in the Gt-rGO/PDS system (0.682 h−1) was 6.3, 22.7, and 25.3 folds higher than those in the control rGO/PDS, Gt/PDS, and PDS systems, respectively. The nanocomposites maintained high stability and exhibited excellent catalytic effects on SA degradation over four continuous cycles. Quenching experiments and electron spin resonance results verified that singlet oxygen was generated in the Gt-rGO/PDS system. Additionally, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemical experiments demonstrated that Gt-rGO acting as mediator directly accelerated electron transfer between organic pollutants and PDS. Based on the non-radical oxidation mechanism, a selective reactivity of the Gt-rGO/PDS system toward organic pollutants possessing different ionization potentials was shown. Biogenic C-Fe nanocomposites prepared under growing conditions present new potentials for efficient activation of persulfates and effective removal of SA and other organic pollutants.