Highly efficient nitrogen-doped carbon nanotubes coated on paper-like sintered stainless steel fibers as metal-free structured catalyst for phenol degradation

Abstract

Three types of carbon nanotubes coated on paper-like sintered stainless steel fibers (PSSF) were synthesized and applied for continuous catalytic wet hydrogen peroxide oxidation (CWPO) of phenol. The novel metal-free nitrogen-doped carbon nanotube-coated PSSF catalyst (N-CNTs/PSSF) was designed by direct chemical vapor deposition using melamine as solid precursor for the first time, and CNTs/PSSF and Fe2O3-deposited CNTs/PSSF (Fe-CNTs/PSSF) catalysts were synthesized for comparison. Characterization results showed that all the catalysts exhibited three-dimensional networks structure, with nanotubes wrapping on the stainless steel fibers successfully, and the N-CNTs showed distinct irregular corrugated morphology with nitrogen-doping level about 5.18 at.%. CWPO of phenol revealed that the N-CNTs/PSSF catalyst achieved favorable catalytic activity and highest stability during 100-h reaction (phenol and TOC conversions reached about 90% and 50%, respectively), while phenol conversions of CNTs/PSSF and Fe-CNTs/PSSF catalysts decreased over time to 72% and 58%, respectively. The N-CNTs/PSSF catalyst also showed the lowest Fe weight loss ratio (about 2.44 wt%) among the three catalysts. The favorable catalytic results of N-CNTs/PSSF can be ascribed to the synergistic effects of the strong affinity toward polar molecules of N-CNTs, as well as the enhancement in contact efficiency associated with three-dimensional networks structure of the PSSF.