Zero-valent iron(ZVI),either as bulk-sized granules or colloidal nanoparticles,is the most important engineering material for in situ remediation of groundwater impacted by chlorinated solvents.In spite of iron's versatile utility in treating a broad range of reducible contaminants and its environmentally benign character,the intrinsic corrosion behavior of iron causes rapid surface passivation in groundwater environment.As a result,the degradation rates of target contaminants such as trichloroethylene(TCE)are slow in the absence of catalysts.