Contaminant Degradation by •OH during Sediment Oxygenation: Dependence on Fe(II) Species

Abstract

It has been documented that contaminants could be degraded by hydroxyl radicals (•OH) produced upon oxygenation of Fe­(II)-bearing sediments. However, the dependence of contaminant degradation on sediment characteristics, particularly Fe­(II) species, remains elusive. Here we assessed the impact of the abundance of Fe­(II) species in sediments on contaminant degradation by •OH during oxygenation. Three natural sediments with different Fe­(II) contents and species were oxygenated. During 10 h oxygenation of 200 g/L sediment suspension, 2 mg/L phenol was negligibly degraded for sandbeach sediment (Fe­(II): 9.11 mg/g), but was degraded by 41% and 52% for lakeshore (Fe­(II): 9.81 mg/g) and farmland (Fe­(II): 19.05 mg/g) sediments, respectively. •OH produced from Fe­(II) oxygenation was the key reactive oxidant. Sequential extractions, X-ray diffraction, Mössbauer, and X-ray absorption spectroscopy suggest that surface-adsorbed Fe­(II) and mineral structural Fe­(II) contributed predominantly to •OH production and phenol degradation. Control experiments with specific Fe­(II) species and coordination structure analysis collectively suggest the likely rule that Fe­(II) oxidation rate and its competition for •OH increase with the increase in electron-donating ability of the atoms (i.e., O) complexed to Fe­(II), while the •OH yield decreases accordingly. The Fe­(II) species with a moderate oxidation rate and •OH yield is most favorable for contaminant degradation.

Review: Clay-Modified Electrodes in Heterogeneous Electro-Fenton Process for Degradation of Organic Compounds: The Potential of Structural Fe(III) as Catalytic Sites

“…The authors compared the electron transfer rate parameters calculated with a predictive model to experimental parameters available in the literature and concluded that the hydrolysis of hexaquo Fe(II) ions in basic pH favored the inner-sphere mechanism while fully coordinated Fe(II) ion in acid pH favored electron transfer to O 2 using the outer-sphere mechanism. However, Xie et al [63] complemented observations from Rosso and Morgan [65] as well as Hug and Leupin [64] proposing that the electron density of Fe(II) also influenced which mechanism the electron transfer reaction is compelled to proceed at near neutral pH. As for the relative performance of kaolinite and montmorillonite, Xie et al predicted that the ligands ≡Al(III)Oand ≡Fe(III)Oshould attribute greater reactivity to surface-adsorbed Fe(II) in montmorillonite than only ≡Al(III)Oin kaolinite.…”

“…As for the relative performance of kaolinite and montmorillonite, Xie et al predicted that the ligands ≡Al(III)Oand ≡Fe(III)Oshould attribute greater reactivity to surface-adsorbed Fe(II) in montmorillonite than only ≡Al(III)Oin kaolinite. The authors interpreted their experimental observations for kaolinite and montmorillonite arguing that the interaction of surface-adsorbed Fe(II) with octahedral Fe(III) in montmorillonite stabilized Fe(II) against oxidation being responsible for the slower oxidation rates observed for farmland sediment [63].…”

“…Recently, Xie et al investigated the role of Fe(II) species within different subsurface sediments in the generation of •OH radicals after 10 h of oxygenation for degradation of phenol in order to uncover the fate of contaminants in the subsurface-layers of soil perturbed with O 2 [63]. In their study, the performance in phenol degradation, the concentration of •OH radicals and the extent of oxidation was evaluated for each of the Fe(II) species within the natural sediments that were original from beach sand, lakeshore and farmland soil.…”

“…The authors discussed this experimental observation following the reasoning previously described but applied to Fe(II) coordinated with different ligands within the structure. The authors stated that the balance of electron poor (≡Si(IV)O-) and rich (≡HO-) ligands coordinated to structural Fe(II) in montmorillonite was responsible for superior performance of this mineral in comparison to iron oxide and other clay minerals [63]. This study was considered of great importance since it firstly introduced a parallel between the electron density of structural or surface-adsorbed Fe(II) and their reactivity towards oxidation and thus reduction of O 2 .…”

Resistance and induction of viable but non culturable states (VBNC) during inactivation of E. coli and Klebsiella pneumoniae by addition of H2O2 to natural well water under simulated solar irradiation

“…Precisely, Xie et al, have argued that ferrous ions released from inosilicates and iron(hydr)oxides naturally present in natural well water samples by mechanical mixing could react with molecular oxygen generating ferric ions and O 2 −• radicals ( Eq. ( 2) ) ( Xie et al, 2020 ). These latter can undergo further disproportion reactions leading to the generation of H 2 O 2 ( Eq.…”