关键词: 碳黑, 金属酞菁, 高价铁氧活性种, 降解, 有机污染物

Abstract: The rapid development of industry, the intensification of urbanization and the growth of population make human's increath demand for clean freshwater resources year by year, but at the same time, human production and domestic wastewater was discharged into the environment, resulting in the scarce freshwater resources. Organic pollutants such as drugs, personal care products, are present at extremely low concentrations from ng/L to μg/L in water, but they can cause immeasurable damage to the environment and living organisms, it causes harm to the human body ultimately. So more and more researchers pay attention to the recycling of wastewater which comes from daily life, agricultural or industrial production.
In order to respond to the “dual carbon”strategic objectives, it is necessary to efficiently degrade and remove organic pollutants in water to achieve sustainable development. Biological enzymes have high catalytic activity and strong selectivity to substrates, we can use them to catalyze degradation of organic pollutants. However, the direct extraction of enzymes from organisms will bring high extraction cost, the change of the application environment of enzymes will significantly reduce their catalytic activity. So we designed an environmentally friendly bionic catalyst called peroxide mimicking enzyme which can catalyze the degradation of organic pollutants in water efficiently. In peroxide mimicking enzyme, iron hexadecachlorophthalocyanine (FePcCl16) worked as the active site, pyridine group (Py) acted as the fifth ligand, carbon black (CB) served as a protein skeleton. Inspired by the principle of peroxidase metabolizing drugs, we constructed the environmentally-friendly bionic catalytic system which used peroxide simulation enzyme as catalys, hydrogen peroxide as oxidant to catalyze the oxidative degradation of dexamethasone (DXMS). The results showed that the bionic catalytic system maintained high efficiency and stable degradation rate of DXMS in the range of temperature from 25℃ to 65℃，it showed that the simulated enzyme catalyst was not sensitive to temperature. The degradation rate of DXMS was 100% in 60 min in acid or neutral conditions. It can be seen that the catalytic system was better than that of Fenton system. At the same time, the catalytic system did not change the degradation rate of organic pollutants in the presence of inorganic salts, and the degradation rate of DXMS still reached 100%, indicated that the catalytic system still had a good catalytic oxidation degradation efficiency in complex water environment. However, the degradation rate of DXMS was reduced by 28% due to the rapid decomposition of H2O2 under alkaline conditions. Surprisingly, we found that the catalytic system had excellent recycling performance, the degradation rate of DXMS was still 95% after 6 cycles of use. By adding isopropyl alcohol (IPA) and p-benzoquinone (p-BQ) into the system as trapping agents of hydroxyl radical(·OH) and superoxide radical (O2▪-) respectively, electron spin resonance (EPR) detection of ⸱OH and O2▪- captured by 5,5-Dimethyl-1-pyrroline N-oxide (DMPO), gas chromatography-mass spectrometry (GC-MS) for the detection of dimethyl sulfone (DMSO) oxidation product confirmed that the main active species of DXMS in the catalytic system were high-valent iron oxo (Fe (IV)=O) active sites, followed by ⸱OH.
Degradation path analysis showed that the first path of DXMS degradation began with the dehydrogenation of C8 and C14, then hydroxylation, the second path of DXMS degradation started with the removal of HF at C8 and C9, then hydroxylation or demethylation at C19. After 60min, all the intermediate products generated small molecule organic acid (succinic acid) or mineralization. The construction of the bionic catalytic system provided a new perspective for sewage treatment.

Key words: carbon black, metal phthalocyanine, high-valent iron-oxo active species, degradation, organic pollutant