Reductive Dechlorination of Carbon Tetrachloride and Tetrachloroethylene by Zerovalent Silicon−Iron Reductants

Abstract

Reductive dechlorination of carbon tetrachloride (CT) and tetrachloroethylene (PCE) by zerovalent silicon (ZVS, Si0) and the combination of Si0 with metal iron (Fe0) was investigated as potential reductants for chlorinated hydrocarbons. The X-ray photoelectron spectroscopy (XPS) was used to identify the surface characteristics of Si0. CT and PCE can be completely degraded via sequential reductive dechlorination to form lesser chlorinated homologues by Si0. Productions of chloroform (CF) and trichloroethylene (TCE) accounted for 80% of CT and 65% of PCE dechlorination, respectively. The degradation of CT and PCE by Si0 at pH 8.3 followed pseudo-first-order kinetics, and the normalized surface rate constants (k(sa)) were 0.288 and 0.003 L m(-2) h(-1), respectively, which react more efficiently than zerovalent iron in CT and PCE dechlorination. A linear relationship was also established between pH and the k(sa) value. The XPS results showed that the hydrogenated silicon surface and silicon oxides on the silicon surface were removed during the dechlorination processes, thus providing a relatively clean silicon surface for dechlorination reactions. The combination of zerovalent silicon with iron influences both the dechlorination rate and the distribution of products. Sequential reductive dechlorination was still the main reaction for CT dechlorination by Si0/Fe0, while reductive dechlorination and beta-elimination were the dominant reaction pathways for PCE dechlorination with ethane and ethene as the major end products. Also, the combination of silicon and iron constitutes a buffer system to maintain the pH at a stable value. A 0.3 unit of pH changed upon increasing the amount of Fe by a factor of 35 was observed, depicting that Si0 serves as a pH buffer in Si0/Fe0 system during dechlorination processes.

Effects of transition metal and sulfide on the reductive dechlorination of carbon tetrachloride and 1,1,1-trichloroethane by FeS

“…Based on the measurement of CT and its products, the total carbon mass balance was about 50% at the end of reaction. Many studies have reported that CT was mainly transformed to CF through hydrogenolysis pathway by iron-bearing soil minerals and that the extent of CF production was dependent on the type of soil minerals [20][21][22][23]. In the experimental results reported by Zwank et al, the portions of CF formation during the reductive dechlorination of 10 M CT by mackinawite, goethite, magnetite, lepidocrocite, hematite, and siderite were 55%, 33%, 80%, 14%, 17%, and 33%, respectively [23].…”

Enhanced dechlorination of 2,4-dichlorophenol by recoverable Ni/Fe–Fe 3 O 4 nanocomposites

“…Most of the CPs are listed as priority pollutants by the USEPA (Cheng et al, 2007;Ma et al, 2014). Reductive dechlorination is an effective method to detoxify these contaminants and has been widely investigated Doong et al, 2003;Yan et al, 2010;Xu and Gao, 2007;Zhu et al, 2010).…”

“…In recent years, double-metal-catalyzed dechlorination materials have been developed, which greatly improve the dechlorination efficiency, and have been used to remediate water and soil contaminated by chlorinated pollutants, such as chlorinated hydrocarbons, chlorophenols, chlorobenzenes, polychlorinated biphenyls and other polychlorinated aromatics (Jovanovic et al, 2015;Liu et al, 2014;Wei et al, 2014;Yang et al, 2014). In these bimetallic materials, Fe, as a metal with low standard redox potential, is an electron donor and hydrogen donor to reduce the chlorinated organic compounds (Doong et al, 2003;Zhu et al, 2010), while the second metal (Ni, Pd, Cu, or Ag) with high standard redox potential, promotes the reactivity via hydrogenation and accelerating corrosion (DeVor et al, 2008;Nie et al, 2013;Wei et al, 2006;Zhang et al, 2009;Zhu et al, 2010), acting as a catalyst and accelerator. Among these materials, Pd/Fe has attracted a great deal of attention thanks to the low cost of Fe and excellent hydrogenation activity of Pd (Wei et al, 2006;Yan et al, 2010), but the cost of Pd greatly restricts the wide application of Pd/Fe catalysts.…”

Analysis of dechlorination kinetics of chlorinated aliphatic hydrocarbons by Fe(II) in cement slurries

“…One of main mechanisms to treat CAHs under anaerobic environment is a reductive dechlorination. Reductive dechlorination of various CAHs such as tetrachloroethylene (PCE), trichloroethylene (TCE), 1,1,1-trichloroethane (1,1,1-TCA) and carbon tetrachloride (CT) can be achieved by various natural or synthesized reductants including zero-valent iron [2][3][4], ferrous iron [5], iron-oxides (e.g. goethite, hematite and magnetite) [6][7][8][9][10][11][12][13][14], iron hydroxides (green rust) [15][16][17][18], iron sulfide (FeS) [19][20][21], pyrite (FeS 2 ) [9,22] and iron-phyllosilicates [23].…”