Efficient and continuous removal of phenol by activating PMS via nitrogen doped carbon nanotube membrane in the structured fixed bed

Carbon nanotube (CNT/PSSF) and nitrogen doped carbon nanotube membrane (NCNT/PSSF) catalysts were prepared by vapor deposition on paper sintered stainless steel fiber support (PSSF). Firstly, the properties of the two catalysts were investigated by FE-SEM, TEM, XPS, Raman, TG, FT-IR and CO2-TPD. Subsequently, the ability of the two catalysts to activate peroxymonosulfonate (PMS) to degrade phenol in a structured fixed bed was compared and the free radical quenching experiment and EPR were employed to explore the reactive oxygen species in the reaction process. The catalytic results showed that NCNT/PSSF could convert more phenol with less metal leaching. Apart from the π electrons of the carbon nano-network itself and the carbonyl group at the edge, nitrogen doping endowed more active sites for graphite domain. Pyridine nitrogen acts as a Lewis base in which lone pair electrons drive the PMS to receive electrons and generate hydroxyl radicals and sulfate radicals. After the optimization of reaction conditions, NCNT/PSSF could maintain 100 % phenol conversion in 7 h, and the average TOC conversion reached 84.0 %. In addition, about 60 % phenol could still be mineralized after three cycles. The reason for the decline of catalytic effect was the enrichment of intermediate products induced by a long time of reaction and the reduction of sp2 carbon ratio, the increase of oxygen containing functional groups and the consumption of pyridine nitrogen under high oxidation environment. This study provides a new idea for the continuous and efficient removal of phenolic pollutants.