Sulfur and Nitrogen Co-Doped Graphene for Metal-Free Catalytic Oxidation Reactions

Abstract

Sulfur and nitrogen co‐doped reduced graphene oxide (rGO) is synthesized by a facile method and demonstrated remarkably enhanced activities in metal‐free activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol. Based on first‐order kinetic model, S–N co‐doped rGO (SNG) presents an apparent reaction rate constant of 0.043 ± 0.002 min−1, which is 86.6, 22.8, 19.7, and 4.5‐fold as high as that over graphene oxide (GO), rGO, S‐doped rGO (S‐rGO), and N‐doped rGO (N‐rGO), respectively. A variety of characterization techniques and density functional theory calculations are employed to investigate the synergistic effect of sulfur and nitrogen co‐doping. Co‐doping of rGO at an optimal sulfur loading can effectively break the inertness of carbon systems, activate the sp2‐hybridized carbon lattice and facilitate the electron transfer from covalent graphene sheets for PMS activation. Moreover, both electron paramagnetic resonance (EPR) spectroscopy and classical quenching tests are employed to investigate the generation and evolution of reactive radicals on the SNG sample for phenol catalytic oxidation. This study presents a novel metal‐free catalyst for green remediation of organic pollutants in water.

A Library of Doped-Graphene Images via Transmission Electron Microscopy

“…During this co-doping process, many O-functional groups would be removed to achieve a higher reducibility, leading to powerful π-π stacking in graphene planes. XRD and X-ray photoelectron spectroscopy (XPS) data also confirmed the changes in the chemical compositions and surface functional groups [34]. Consequently, the S-N co-doped graphene would be a high-performance metal-free catalyst for sustainable environmental remediation.…”

“…In particular, co-doping through the mixture of two or three metal elements with electronegativity could produce a novel electron distribution resulted in a synergistic effect [86]. Recently, S and N co-doping incorporated into graphene sheet was demonstrated by Duan et al to enhance the metal-free activation of peroxymonosulfate (PMS) for the catalytic oxidation of phenol [34]. Co-doping with S highly upgraded the catalytic efficiency of Ndoped graphene (NG) [34].…”

“…Recently, S and N co-doping incorporated into graphene sheet was demonstrated by Duan et al to enhance the metal-free activation of peroxymonosulfate (PMS) for the catalytic oxidation of phenol [34]. Co-doping with S highly upgraded the catalytic efficiency of Ndoped graphene (NG) [34]. The morphology and structure of GO and S-N co-doped rGO (SNG) were obtained from TEM images (Figure 7a) [34].…”

“…Co-doping with S highly upgraded the catalytic efficiency of N-doped graphene (NG) [34]. The morphology and structure of GO and S-N co-doped rGO (SNG) were obtained from TEM images (Figure 7a) [34]. The difference from the smooth surface of GO, silk-like wrinkled flakes, and several stacked layers was observed on SNG ( Figure 7a).…”

“…In the disoriented features of graphene, TEM image also revealed the stacked aggregates of SNG with wrinkled graphene sheets ( Figure 7a) and the SAED spot rings can be assigned to the hexagonal carbon lattice structure of graphite planes (inset of Figure 7a). The interlayer spacing was reduced from 0.83 nm (GO) to 0.34 nm (SNG) [34]. During this co-doping process, many O-functional groups would be removed to achieve a higher reducibility, leading to powerful π-π stacking in graphene planes.…”