Critical roles of low-molecular-weight organic acid in enhancing hydroxyl radical production by ferrous oxidation on γ-Al2O3 mineral surface.

Recognizing the pervasive presence of alumina minerals and low-molecular-weight organic acids (LMWOAs) in the environment, this study addressed the gap in the interaction mechanisms within the ternary system involving these two components and Fe(II). Specifically, the impacts of LMWOAs on hydroxyl radicals (•OH) production and iron species transformation during Fe(II) oxidation on γ-Al2O3 mineral surface were examined. Results demonstrated that adding 0.5 mM oxalate (OA) or citrate (CA) to the γ-Al2O3/Fe(II) system (28.1 µM) significantly enhanced •OH production by 1.9-fold (51.9 µM) and 1.3-fold (36.2 µM), respectively, whereas succinate (SA) exhibited limited effect (30.7 µM). Raising OA concentration to 5 mM further promoted •OH yield to 125.0 µM after 24 h. Deeper analysis revealed that CA facilitated the dissolution of adsorbed Fe(II) and its subsequent oxygenation by O2 through both one- and two-electron transfer mechanisms, whereas OA enhanced the adsorption of dissolved Fe(II) and more efficient two-electron transfer for H2O2 production. Additionally, LMWOAs presence favored the formation of iron minerals with poor crystallinity like ferrihydrite and lepidocrocite rather than well-crystallized forms such as goethite. The distinct impacts of various LMWOAs on Fe(II) oxidation and •OH generation underscore their unique roles in the redox processes at mineral surface, consequently modulating the environmental fate of prototypical pollutants like phenol.

Speciation and bioaccessibility of arsenic in rice under different cooking methods and its implication in risk assessment.

Numerous studies have studied the health risk assessment of human exposure to As or bioaccessible As via rice intake; however, the bioaccessibility of different As species in rice is seldom reported. In the present study, 31 rice samples were collected from markets or individual growers to investigate the speciation and bioaccessibility of As. Five different species (AsIII, AsV, DMA, MMA, and AsB) were detected in rice samples from different regions, among which AsIII accounted for the largest proportion (62.95% in average), followed by DMA and AsV. In addition, the cooking method could facilitate the release of As from rice into gastric and intestinal juice, and subsequently increase the bioaccessibility of As. The bioaccessibility of inorganic As in cooked rice ranged from 71.83 to 100%, and that of organic As ranged from 31.69 to 61.04%. Non-carcinogenic and carcinogenic risk assessment of children and adults exposure to As via rice intake considering the bioaccessibility of cooked rice was carried out. The target hazard quotient (THQ) of iAs and total As for children ranged from 0.21 to 1.61 and 0.48 to 2.26, respectively, while those for adults ranged from 0.12 to 0.88 and 0.26 to 1.23, respectively. Incremental lifetime cancer risk (ILCR) for children and adults ranged from 9.57 [Formula: see text] 10-5 to 7.25 [Formula: see text] 10-4 and 5.21 [Formula: see text] 10-5 to 3.95 [Formula: see text] 10-4, respectively. The results of risk assessment indicated that children would face a higher health risk than adults when they took the same type of rice as their staple food.

Critical roles of sulfidation solvent in controlling surface properties and the dechlorination reactivity of S-nZVI.

Sulfidation of nanoscale zero-valent iron (nZVI) has been frequently applied to enhance its reactivity, selectivity, and electron utilization efficiency. However, sulfidation of nZVI is generally carried out in aqueous solution, and formation of passivated iron (hydro)oxide species on the surface of S-nZVI due to the reaction between nZVI and water is inevitable. To mitigate this issue, sulfidation of nZVI with hydrogen sulfide dissolved in absolute ethanol was developed. The properties of the resultant S-nZVI, denoted as S-nZVI-H2S-Ethanol, were compared with S-nZVIs prepared through sulfidation of nZVI with aqueous hydrogen sulfide (S-nZVI-H2S-Water) and aqueous sodium sulfide (S-nZVI-Na2S-Water). S-nZVI-H2S-Ethanol shows increased BET specific surface, reduced susceptibility to incidental oxidation, increased reduction potential, decreased electron-transfer resistance, and improved reactivity toward the reduction of trichloroethylene, compared with S-nZVI-Na2S-Water and S-nZVI-H2S-Water. The results highlight the critical roles of sulfidation solvent in controlling the structure, the physicochemical and electrochemical properties, and the dechlorination reactivity of S-nZVI. In addition, these findings offer fundamental mechanistic insights into the sulfidation processes of nZVI by sulfides, suggesting that solvent-iron (hydro)oxide and sulfide-iron (hydro)oxide interactions at the solvent/nZVI interface play key roles in regulating the sulfidation of nZVI and the properties of S-nZVI.