Bio-inspired N,S-doped siligraphenes as novel metal-free catalysts for removal of dyes in the dark

Abstract

Bio-inspired porous Siligraphene (graphene-like SiC) catalyst and its N and N,S-doped SiC variants were synthesized via a low-temperature magnesiothermic method using natural precursors. The synthesized SiC catalysts were tested for the removal of anionic azo dyes (Congo red, Methyl orange, and Methyl red) in the dark. Si atoms in the siligraphene structure are more positive than C atoms due to the electronegativity of the latter. In doped structure, insertion of N and S atoms can further increase the positive charge of Si atoms and improve adsorption of oxygen and of the above anionic dyes on the surface of SiC. Thus, the catalytic activity of doped SiC for degradation of the dyes increased. A mechanism is proposed where O2 molecules chemisorb onto the surface of SiC, OO bond length elongates, oxygen bond dissociates and radicals are produced. Quenching experiments show that •O2– and •OH radicals are the main reactive species in this process. Doping of nitrogen and sulfur in the presence of Si atoms in siligraphene structure has been shown to improve its capacity for dye removal compared to the corresponding carbon catalysts. Moreover, the SiC catalysts display good stability so that their performance did not significantly decrease even in continuous operation.