Graphene quantum dots on stainless-steel nanotubes for enhanced photocatalytic degradation of phenanthrene under visible light.

A novel nanocomposite of stainless-steel nanotubes with graphene quantum dots (SSNT@GQD) was synthesized to degrade phenanthrene photocatalytically under visible light. Photocatalytic performance of bare stainless-steel nanotubes (SSNT) is not satisfactory due to the fast recombination of photoinduced electron-hole pairs. This phenomenon was effectively overcome by inclusion of GQDs and addition of persulfate as an external electron acceptor to improve charge separation. The pseudo-first-order rate constant of phenanthrene degradation by SSNT@GQD with persulfate under visible light was 0.0211 ± 0.0006 min, about 42 times higher than that of persulfate and visible light, 0.0005 ± 0.0000 min. Effects of different water quality parameters were investigated, including levels of initial pH, natural organic matters, bicarbonate, and chloride. Sulfate radicals, superoxide radicals, and photo-generated holes were the key reactive species in this photocatalytic process. Based on the analysis of intermediates using purge and trap-GC-MS, possible photocatalytic degradation pathways of phenanthrene in this process were proposed. The SSNT@GQD showed high figure of merit (99.5 without persulfate and 78.7 with persulfate) and quantum yield (1.56 × 10 molecules photon without persulfate and 4.64 × 10 molecules photon with persulfate), indicating that this material has excellent potential for practical photocatalysis applications.