Oxidative removal of 4-nitrophenol using activated carbon fiber and hydrogen peroxide to enhance reactivity of metallophthalocyanine

We have developed a novel heterogeneous metallophthalocyanine catalyst, Co-TDTAPc–ACF, by immobilizing cobalt tetra(2,4-dichloro-1,3,5-triazine)aminophthalocyanine (Co-TDTAPc) on activated carbon fiber (ACF) covalently. The oxidative removal of 4-nitrophenol (4-NP) in the Co-TDTAPc–ACF/H2O2 system, based on phase transfer catalytic oxidation, was investigated in aqueous solution by ultra-performance liquid chromatography (UPLC). The results indicated that 4-NP could be removed efficiently by catalytic oxidation in the presence of Co-TDTAPc–ACF and H2O2. In addition, the removal of total organic carbon of 4-NP accounted for about 90% in 300 min of reaction. Gas chromatography/mass spectrometry (GC–MS) analysis showed that the residue products were mainly small molecular compounds such as maleic acid and succinic acid, etc. This system exhibited high catalytic activity across a wide pH and temperature range. Importantly, compared with homogeneous Co-TDTAPc used alone, the introduction of ACF contributed specifically to the activity enhancement of Co-TDTAPc. Controlled experiments showed that the presence of 2-propanol, as hydroxyl radicals scavenger, has little influence on 4-NP oxidation. The further result of electron paramagnetic resonance (EPR) spin-trap experiments indicated that free radicals did not dominate the reaction in our system. This paper discusses a possible catalytic oxidation mechanism of the Co-TDTAPc–ACF/H2O2 system. Repetitive tests showed that Co-TDTAPc–ACF can maintain high catalytic activity over several cycles, and it has a better regeneration capability under mild conditions. We conclude that phase transfer catalytic oxidation has proven itself to be a feasible approach which may be potentially applied to the elimination of widely existing pollutants.