Overcoming barriers to the remediation of carbon tetrachloride through manipulation of competing reaction mechanisms

Overcoming barriers to the remediation of CCl₄ through manipulation of competing reaction mechanisms were studied. The product-branching ratio depended on the nature of the reducing surface as well as the composition of the aqueous phase. The presence in solution of readily available H donors could affect the product-distribution ratio. Isopropanol increased the amount of CCl₄ degraded by the one-electron pathway under photochemical stimulation. Manipulation of solution pH also affected product distribution. With sorbed Fe(II) systems, increasing the pH above 6 enhanced the amount and density of Fe(II) sorbed and this, in turn, increased both the overall rate and the proportion of reactant following the two-electron pathway. Similar enhancement at high pH was observed for photochemical degradation of CCl₄ at TiO₂ surfaces and attributed to the base-catalyzed hydrolysis of the dichlorocarbene. At pH of ≥ 8.5, however, hydrolysis of Fe(II) led increasingly to its oxidation by water and precipitation of mixed-valence green-rust phases in which the Fe(II) density was less and the dichlorocarbene pathway was less favored.