Zero-valent aluminum for reductive removal of aqueous pollutants over a wide pH range: Performance and mechanism especially at near-neutral pH. (15th October 2017)

• Record Type: Journal Article
• Authors: Yang, Shiying; Zheng, Di; Ren, Tengfei; Zhang, Yixuan; Xin, Jia
• Is Part Of: Water research. Volume 123(2017)
• Page Start: 704
• Page End: 714
• Publication Date: 2017-10-15
• Subjects: Zero-valent aluminum -- Near-neutral pH -- Reductive removal -- Surface film -- Reaction mechanism -- Nitrobenzene; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2017.07.013
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Zero-valent aluminum (ZVAl) draws much attention due to its strong reducibility. However, under neutral pH conditions, the reduction ability of ZVAl for pollutant removal has still been suspected because of the formed compact surface film of Al-(hydr)oxide. In this study, unmodified ZVAl was employed to reductively remove aqueous pollutants over a wide pH range, and its performance and mechanism, especially at near-neutral pH, were systematically studied for the first time. Results demonstrated that ZVAl had a wide range of pH applicability from 2 to 12, even in neutral environment. Typical nitro compound nitrobenzene (NB), typical azo dye acid orange 7 (AO7), and typical inorganic heavy metal ion Cr(VI) can be effectively removed at initial pH 7. Based on the changes of pH, ORP, DO, Al ions and TOC of the reaction solution, and the determination of reduction products of NB by UV–Vis and GC-MS, we found that NB removal by ZVAl can be primarily attributed to the reduction role. NB was reduced to nitrosobenzene firstly, and to aniline finally. Meanwhile, the adsorption phenomenon existed in this system. Next, the surface reaction mechanism was deeply revealed through the characterization of ZVAl particles before and after reaction by SEM-EDS, TEM, HRTEM, XRD, and XPS. It was found that ZVAl powders with core/shell structure participated in the redox reaction, and that ZVAl core was corroded, generating Al-(hydr)oxide. ZVAl surface oxide film was not directly removed, instead of a rougher one. Finally, the proposed reductive mechanism of aqueous pollutants by ZVAl was speculated from the angle of electronic competition. In water environment, O2, H2 O and pollutants, with a clear competitive relationship, can capture electrons released from ZVAl. When pollutant's opportunities for getting electrons are enhanced, efficiently reductive reactions for pollutant removal can take place, even at near-neutral pH. In a word, ZVAl is a promising material to remove aqueous pollutants over a wide pH range, even in neutral environment, which exhibits its great potential as an effective and environment-friendly agent for pollutant removal from water. Graphical abstract: Image 1 Highlights: ZVAl has a wide range of pH applicability (2–12), even at neutral pH. Nitrobenzene, acid orange 7 and Cr(VI) can be reduced by ZVAl at initial pH 7. The removal of NB by ZVAl was primarily attributed to the reduction. NB is firstly reduced to nitrosobenzene, and via a further reduction, forms aniline. The surface reaction mechanism of ZVAl particles is deeply revealed.