Colloidal activated carbon as a highly efficient bifunctional catalyst for phenol degradation.

A preparation of colloidal activated carbon (CAC) for phenol remediation from groundwater was introduced. The CAC prepared by a simple pulverization technique was an excellent metal-free catalyst for persulfate (PS) activation due to high contact surface area. The removal efficiency of phenol in the PS/CAC system (~100%) was higher than that in the PS/activated carbon (AC) system (90.1%) and was superior to the conventional PS/Fe system (27.9%) within 30 min. The phenol removal reaction occurred both in bulk solution and at the surface of the CAC, as confirmed by Langmuir-Hinshelwood (L-H) kinetic model fitting, FT-IR, and electron spin resonance (ESR) analyses. The downsizing of particle size from AC to CAC played a critical role in the radical oxidation mechanism by leading to the formation of predominant superoxide radical (O) species in the PS/CAC system. Anions NO, SO, and Cl slightly inhibited the phenol removal efficiency, whereas CO, HCO and PO3 did not. Ferulic acid (CHO) was detected as an organic byproduct of phenol oxidation. The use of CAC as a metal-free bifunctional catalyst has an important implication in the PS activation for phenol degradation in groundwater.