Enhanced reductive dechlorination of tetrachloroethene during reduction of cobalamin (III) by nano-mackinawite

► Adsorption and reduction of Co(III) occurred on nFeS surface. ► Co(III) was reduced to Co(II) by Fe2+. ► Co(II) formed complexation with S2− and Sn2−. ► S2−Co(II) and Sn2−Co(II) enhanced reductive dechlorination of PCE. ► PCE was transformed to acetylene and 1,3-butadine.