Phosphorus-doped carbon fibers as an efficient metal-free bifunctional catalyst for removing sulfamethoxazole and chromium (VI).

Developing an efficient and metal-free bifunctional catalyst for the simultaneous degradation of antibiotic and reduction of Cr (VI) has been regarded as increasingly attractive yet challenging objectives in the environmental catalysis field. Herein, phosphorus-doped carbon fibers (P-CFs) was innovatively prepared by doping and calcination methods, characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Sulfamethoxazole (SMX) as the target contaminant was selected to evaluate the catalytic activity of P-CFs in PMS activation, over 90% SMX removal and 82.75% mineralization were high-efficiently achieved in the P-CFs/peroxymonosulfate (PMS) system. Particularly, P-CFs/PMS system exhibited a superior catalytic oxidation performance over a wide pH range (3.5-9.5) and even in the complicated water matrix. Surprisingly, the presence of humic acid (HA) in the P-CFs/PMS system could achieve about 2 times enhancement on SMX removal, different from most reports about the inhibition of HA in PMS activation. More importantly, Brunauer-Emmett-Teller (BET) method and XPS analysis revealed that the highly toxic Cr (VI) could be reduced to Cr (III) by P-CFs. Furthermore, electron spin resonance (ESR) combined with various trapping agents demonstrated that SO4•-, •OH and 1O2. were generated and participated in the SMX degradation, while the free electron in P-CFs played a main role in Cr (VI) reduction. This finding not only provided a high-efficiency strategy in the treatment of wastewaters containing organic contaminants and heavy metals Cr (VI), but might open new insights into an innovative metal-free catalyst in environment remediation.