Degradation of aqueous 2,4,4′-Trihydroxybenzophenone by persulfate activated with nitrogen doped carbonaceous materials and the formation of dimer products

In this work, we systematically investigated the persulfate (PS) activation potential of a series of nitrogen doped carbonaceous materials for the degradation of 2,4,4′-trihydroxybenzophenone (2,4,4′-HBP), an additive in polyvinyl acetate films and personal care products. Nitrogen originating from urea, NH4NO3, indole and polyaniline was doped into carbonaceous materials, including hydroxylated multi-walled carbon nanotubes (CNT-OH), large-inner thin-walled carboxylated carbon nanotubes (CNT-COOH) and graphite oxide (GO), to examine the catalytic effect. The NH4NO3-CNT-OH catalyst, which showed the best catalytic performance in 2,4,4′-HBP removal, was characterized by SEM, TEM, FT-IR, Raman, BET surface area, XRD and XPS, and pyrrolic nitrogen was found to play a highly important role in the activation of PS. Under the conditions of [2,4,4′-HBP]0: [PS]0 = 1: 500, T = 25 °C, pH0 = 7.0, concentration of catalyst = 100 mg L−1, 43.48 μM 2,4,4′-HBP was completely removed in 2 h. According to electron paramagnetic resonance (EPR) spectra and radical quenching experiments, hydroxyl and sulfate radicals on the surface of the catalyst contributed to the substrate oxidation. Cleavage of C-C bridge bond, hydroxylation and polymerization were mainly involved in the oxidation process, leading to the formation of 10 intermediates (e.g., dimers), as detected by the MS/MS spectra. To the best of our knowledge, this report is the first to describe the transformation mechanism of 2,4,4′-HBP in nitrogen doped carbonaceous materials catalyzed PS system.