Promoting effect of nitration modification on activated carbon in the catalytic ozonation of oxalic acid

A commercial activated carbon (AC) was modified with a nitration or amination method, and the effects of textural and chemical properties on the ability of the AC samples to destroy oxalic acid (OA) using ozone was investigated in this work. The degradation rates of OA on the nitrated and aminated AC samples increased by 38.5% and 9.6%, respectively. The adsorption capacity of the AC sample was not enhanced after modification, but the decomposition rate of ozone in solution increased. The surface area of AC significantly decreased after nitration because the entrance of micropores and some larger pores were blocked by the modified functional groups. In addition, the surface area was recovered when the nitrated AC was further aminated. We demonstrated that the enhancement in the catalytic activity was primarily caused by the differences in surface chemistry. The pHpzcvalues and Boehm titration results showed that nitration increased the acidity of the AC, while more basic groups were grafted after amination. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) results confirmed that–NO2 and acid oxygenated groups were simultaneously grafted onto AC during nitration. Meanwhile, the –NO2 group was completely reduced to NH2 and the carboxylic groups were partially reduced during amination. The basic groups (NH2 and possible pyrone groups) enhanced the catalytic activity of the aminated AC sample, and the increased activity of the nitrated AC material was mainly due to the acid oxygenated surface groups