Urea-assisted one-step fabrication of a novel nitrogen-doped carbon fiber aerogel from cotton as metal-free catalyst in peroxymonosulfate activation for efficient degradation of carbamazepine

Nitrogen-doped carbon as metal-free catalysts exhibited exceptionally catalytic activities in environmental remediation fields. Herein, a novel nitrogen-doped carbon fiber aerogel (N-CFA), which was conveniently prepared using cotton and urea by a direct high temperature carbonization in one-step, was used to activate peroxymonosulfate (PMS) for the degradation of carbamazepine (CBZ) in water. Characterization results demonstrated that the key active sites (pyridinic N, pyrrolic N, and graphitic N) were formed in the process of nitrogen doping into the carbon fiber aerogel. More importantly, singlet oxygen (O-1(2)) instead of conventional (OH)-O-center dot and SO4 center dot- was suggested as the predominant reactive oxygen species (ROS) during N-CFA/PMS process based on the scavenger inhibition tests, and confirmed by molecular probe and liquid-phase electron paramagnetic resonance (EPR) experiments. It was speculated that nitrogen-containing functional groups played a key role in inducing the non-radical pathway. Moreover, CBZ degradation pathways mainly by O-1(2) were firstly proposed based on intermediates. The N-CFA/PMS system could achieve a CBZ degradation rate of 100% within 50 min, which was significantly higher than the catalytic effect of several carbon materials (ACF, GAC, and GO) and even higher than the catalytic effect of various metal-based catalysts including Co3O4, CuO, Fe3O4, and Fe2O3. It was also noted that the CBZ was removed with a satisfactory efficiency in different water matrices with inorganic anions (HCO3-, Cl-, H2PO4-, SO42-, and NO3-) and humic acid (HA). Thus, this study proposed a benign and highly efficient oxidation technology, which would exhibit wide potential for environmental restoration.