Activation of persulfate and H2O2 by using attapulgite-supported sulfide nanoscale zero-valent iron for degradation of p-nitrophenol: a comparative study

Highly reactive oxidizing species such as sulfate and hydroxyl radicals have been widely used in oxidative degradation of various organic pollutants. In this paper, attapulgite supported sulfide modified nanoscale zero-valent iron (APT/S-nZVI) was synthesized and utilized to activate persulfate (Ps) and hydrogen peroxide (H2O2) for removal of p-nitrophenol (PNP), respectively. The effects of main factors (such as S/Fe molar ratio, oxidant concentration, initial PNP concentration, pH, temperature and others) on the removal of PNP in different systems were investigated. The results showed that the APT/S-nZVI/H2O2 system had stronger removal efficiency and faster reaction rate for PNP than that of the APT/S-nZVI/Ps system under the same fitting conditions, but the APT/S-nZVI/Ps system was efficient over a wide pH range of 3-9, while the efficient pH in the APT/S-nZVI/H2O2 system was confined to just 3. Among them, dosage of oxidant, pH value and temperature significantly influenced the PNP removal performance by APT/S-nZVI/H2O2, while the influence of the molar ratio of S/Fe and the initial concentration of PNP on the PNP removal performance of APT/S-nZVI/Ps system is more obvious. The factors that affect the PNP removal performance are different in two systems due to the different free radicals generated by Fe2+ activated Ps and H2O2. The underlying mechanism and degradation products of APT/S-nZVI in activating Ps and H2O2 were elucidated through UV-Vis spectra and gas chromatography-mass spectrometry. In addition, the effect of different inorganic ions on the degradation of PNP in the two systems was investigated, and the result showed that the common anions certain inhibitory effect on PNP removal, but the degradation of PNP remained above 97%. The study demonstrated that both APT/S-nZVI/Ps and APT/S-nZVI/H2O2 system can efficiently remove PNP, but which system is more suitable for the practical application should be according to the requirements of removal and circumstance conditions.