Improving catalytic degradation of organic pollutants through highly efficient non-radical peroxymonosulfate activation using interlayer-expanded mesoporous nitrogen-doped graphene

Nitrogen-doped graphene (N-rGO) has shown great potential for activation of peroxymonosulfate (PMS), yet the catalytic reaction rate was rather limited due to concealment of active sites caused by agglomeration of graphene sheets. In this study, SiO2 nanoparticles were introduced to modulate the structure of N-rGO to form an interlayer-expanded mesoporous SiO2@N-rGO. Compared to N-rGO with a 2D structure, the nitrogen contents of SiO2@N-rGO were at the same level, yet the graphene sheets were cracked and the interlayers were expanded due to the intercalation of SiO2 nanoparticles, and a wide range of slit-like pores (1.8 nm to 70 nm) were formed. As a result, the degradation efficiencies of phenol and humic acid (HA) in 10 min were increased by 150 % and 240 %, respectively. This was attributed primarily to the synergistic effect of the electron-enriched nitrogen sites which functioned as active sites for PMS activation and the interlayer-expanded mesoporous structure, thanking to which that more active sites were exposed and the internal diffusion was also improved. Quenching experiment, electron paramagnetic resonance and linear sweep voltammetry tests suggested that phenol and HA were degraded mainly through the non-radical pathway, in which the singlet oxygen (O-1(2)) was the key reactive species. This study provides a simple method to fabricate an efficient graphene-based catalyst for PMS activation, and will be useful for further development of persulfate-based advanced oxidation process.