Removal Of Pollutants From Water With Zero Valent Iron And The Mechanistic Insight

With the rapid development of industry, the earth’s ecological environment has been seriously damaged, especially the water pollution. Water is the source of life and the lifeblood of all things on earth. However, the serious water pollution brings great threat to human life. According to the survey, many residents and factories discharge plenty of sewage and industrial waste water into rivers everyday, which contain a lot of poisonous substances, such as synthetic pesticides and dyes. These pollutants decrease the water quality and have the serious influence to human life, industrial production and agricultural irrigation. Water pollution also increased the cost of water treatment, which is not favorable for the sustainable development. Therefore, it is of great importance to remove pollutants from wastewaters.Water pollution control is the important means of protecting the water environment. As the fourth element in nature, zero valent iron has been widely applied in wastewater treatment since 1990’s without causing secondary pollution. Therefore, this thesis aims to develop an efficient, low-cost and green water pollution control technology using environment friendly zero valent iron.1. We demonstrate that Fe@Fe2O3 core-shell nanowires can improve Fenton oxidation efficiency by two times with rhodamine B as a model pollutant at pH> 4. Active species trapping experiments revealed that the rhodamine B oxidation enhancement was attributed to molecular oxygen activation induced by Fe@Fe2O3 core-shell nanowires. The molecular oxygen activation process could generate superoxide radicals to assist iron core for the reduction of ferric ions to accelerate the Fe(Ⅲ)/Fe(Ⅱ) cycles, which favored the H2O2 decomposition to produce more hydroxyl radicals for the rhodamine B oxidation.2. Commercial Fe, with its surface covered with a layer of surface oxide, usually exhibits low activity for environmental remediation. Therefore, pretreating the commercial Fe0 aimed at removing the surface oxide layer is of considerable interests for practical use. In this paper, a non-aqueous microwave method was employed to improve the activity of commercial Fe0 employing ethylene glycol as solvent. Experimental results revealed that the thickness of the surface oxide layer could be significantly reduced with a concurrent generation of more surface adsorbed Fe due to the reduction of Fe3+(in the oxide layer) by ethylene glycol. As expected, the Cr(VI) removal efficiency of the treated commercial Fe0 at neutral pH increased by 51 times compared with the untreated one. Since the Cr(VI) removal efficiency in our case was positively correlated to the capacity of Fe0 core to deliver its free electrons as well as the Fe(Ⅱ) bound to its surface, the great enhanced removal of Cr(Ⅵ) efficiency could be attributed to the promoted electron transfer from the Fe° core to adsorbates and increased surface bound Fe(II).In summary, this article first systematically studied the influence of Fe@Fe2O3 core-shell nanowires on Fenton(Fe2+/H2O2) degradation of rhodamine B and then developed an effective strategy to eliminate the oxide layer for enhanced Cr(VI) removal. This study not only widens the application of zero valent iron on pollution control, but also deepens our understanding on the mechanism of aqueous pollutants removal with ZVI.