Rapid Acceleration of Ferrous Iron/Peroxymonosulfate Oxidation of Organic Pollutants by Promoting Fe(III)/Fe(II) Cycle with Hydroxylamine

Abstract

The reaction between ferrous iron (Fe(II)) with peroxymonosulfate (PMS) generates reactive oxidants capable of degrading refractory organic contaminants. However, the slow transformation from ferric iron (Fe(III)) back to Fe(II) limits its widespread application. Here, we added hydroxylamine (HA), a common reducing agent, into Fe(II)/PMS process to accelerate the transformation from Fe(III) to Fe(II). With benzoic acid (BA) as probe compound, the addition of HA into Fe(II)/PMS process accelerated the degradation of BA rapidly in the pH range of 2.0-6.0 by accelerating the key reactions, including the redox cycle of Fe(III)/Fe(II) and the generation of reactive oxidants. Both sulfate radicals and hydroxyl radicals were considered as the primary reactive oxidants for the degradation of BA in HA/Fe(II)/PMS process with the experiments of electron spin resonance and alcohols quenching. Moreover, HA was gradually degraded to N2, N2O, NO2 (−), and NO3 (−), while the environmentally friendly gas of N2 was considered as its major end product in the process. The present study might provide a promising idea based on Fe(II)/PMS process for the rapid degradation of refractory organic contaminants in water treatment.

Efficient degradation of sulfamethoxazole by the Fe(II)/HSO5− process enhanced by hydroxylamine: Efficiency and mechanism

“…Therefore, HA and Fe(II) both should play a role in accelerating removal of SMX in the HA/Fe(II)/PMS process (Wu et al, 2015). The incomplete degradation of SMX in the HA/Fe(II)/PMS process might be due to the depletion of PMS (Zou et al, 2013). It should be pointed out that the HA/Fe(II)/PMS process exhibited an equivalent or even higher degradation efficiency of SMX, compared to reported catalytic PS oxidation processes (Table S1), e.g., Fe(II)/PS (Ji et al, 2014), thermo/PS (Ji et al, 2015), and Fe 0 /PS (Ghauch et al, 2013).…”

“…The variation tendency could be mainly attributed to the formation and increase of Fe(OH)2 with increasing solution pH. Fe(OH)2 has been demonstrated to be more active than Fe(II) iron to activate peroxide and PMS (Wells and Salam, 1968;Zou et al, 2013). The optimal initial pH range is 3.0 to 6.0 in the system for degradation of SMX (the final balanced range of pH from 2.9 to 3.7 as shown in Fig.…”

“…Then increasing HA concentration continuously from 0.4 to 1.0mM, the improvement on the removal of SMX was found to be insignificant. Authors (Chen et al, 2011;Zou et al, 2013) reported that HA could effectively promote the redox cycle of Fe(III) to Fe(II), improve the generation of reactive species and increase the removal of organic pollutants at pH 3.0. However, excess HA could quench the reactive species (e.g., SO4…”

“…Nonetheless, some intrinsic drawbacks of Fe(II)/PMS oxidation process have been gradually exposed. The slow conversion from Fe(III) back to Fe(II) is considered to be the major drawback of Fe(II)/PMS process (Zou et al, 2013). Chen et al (2011) reported that hydroxylamine (NH2OH, HA) could effectively accelerate the redox cycle of Fe(III) to Fe(II).…”

“…Chen et al (2011) reported that hydroxylamine (NH2OH, HA) could effectively accelerate the redox cycle of Fe(III) to Fe(II). Owing to the low rate constants with SO4 •- (Neta et al, 1988) and HO • (Buxton et al, 1988), protonated HA can improve the degradation of benzoic acid (Zou et al, 2013), trichloroethylene (Tan et al, 2012), diuron (Wu et al, 2015), and Orange G (Han et al, 2014), as well as reducing the dosage of Fe(II) in Fe(II)/PMS or Fe(II)/PS system. To the best of our knowledge, few literature reported the enhancement of HA on the capacity of Fe(II)/PMS process applied in the pollution remediation of antibiotics.…”