Lee Chun-Chi, Doong Ruey-An
Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, 101, Section 2, Kuang Fu Road, Hsinchu 30013, Taiwan.
Environ Sci Technol. 2008 Jul 1;42(13):4752-7. doi: 10.1021/es071545x.
The combination of zerovalent metal with a catalytic second metal ion (bimetallic materials) to enhance the dechlorination efficiency and rate of chlorinated compounds has received much attention. Bimetallic materials not only enhance the dechlorination process but also alter the reduction pathway and product distribution. In this study, the efficiency and rate of tetrachloroethylene (PCE) dechlorination by metal-modified zerovalent silicon was investigated as a potential reductant for chlorinated hydrocarbons under anoxic conditions. The X-ray photoelectron spectroscopic (XPS) results showed that metal ions including Ni(II), Cu(II), and Fe(II) could be reduced to their zerovalent forms on the Si surface. The dechlorination of PCE obeyed the pseudo-first-order kinetics, and the pseudo-first-order rate constants (k(obs)) for PCE dechlorination followed the order Ni/Si > Fe/Si > Cu/Si. Addition of Cu(II) lowered the dechlorination efficiency and rate of PCE by Si, while the k(obs) values for PCE dechlorination in the presence of 0.1 mM Fe(II) and Ni(II) were 1.5-3.8 times higher than that by Si alone. In addition, the efficiency and rate of PCE dechlorination increased upon increasing the mass loading of Ni(II) ranging between 0.05 and 0.5 mM and then decreased when the Ni(II) loading was further increased to 1 mM. The scanning electron microscopic (SEM) images and electron probe microanalytical (EPMA) maps showed that the Ni nanoparticles deposited on the Si surface and aggregated to a large particle at 1 mM Ni(II), which clearly depicts that the Ni(II) loading of 0.5 mM is the optimal value to enhance the efficiency and rate of PCE dechlorination by Si. Also, the reaction pathways for PCE dechlorination changed from hydrogenolysis in the absence of Ni(II) to hydrodechlorination when Ni(II) concentrations were higher than 0.05 mM. Results obtained in this study reveal that the metal-deposited zerovalent silicon can serve as an environmentally friendly reductant for the enhanced degradation of chlorinated hydrocarbons for long-term performance.
零价金属与催化性二价金属离子(双金属材料)结合以提高氯代化合物的脱氯效率和速率已受到广泛关注。双金属材料不仅能增强脱氯过程,还会改变还原途径和产物分布。在本研究中,研究了金属改性零价硅作为缺氧条件下氯代烃潜在还原剂对四氯乙烯(PCE)的脱氯效率和速率。X射线光电子能谱(XPS)结果表明,包括Ni(II)、Cu(II)和Fe(II)在内的金属离子可在硅表面还原为零价形式。PCE的脱氯遵循准一级动力学,PCE脱氯的准一级速率常数(k(obs))遵循Ni/Si > Fe/Si > Cu/Si的顺序。添加Cu(II)会降低硅对PCE的脱氯效率和速率,而在存在0.1 mM Fe(II)和Ni(II)时,PCE脱氯的k(obs)值比单独使用硅时高1.5 - 3.8倍。此外,当Ni(II)质量负载在0.05至0.5 mM之间增加时,PCE脱氯的效率和速率增加,而当Ni(II)负载进一步增加到1 mM时则降低。扫描电子显微镜(SEM)图像和电子探针微分析(EPMA)图谱表明,沉积在硅表面的Ni纳米颗粒在1 mM Ni(II)时聚集形成大颗粒,这清楚地表明0.5 mM的Ni(II)负载是提高硅对PCE脱氯效率和速率的最佳值。而且,当Ni(II)浓度高于0.05 mM时,PCE脱氯的反应途径从无Ni(II)时的氢解变为加氢脱氯。本研究获得的结果表明,金属沉积的零价硅可作为一种环境友好的还原剂,用于长期增强氯代烃的降解。