K'Owino Isaac O, Omole Marcells A, Sadik Omowunmi A
Department of Chemistry, State University of New York at Binghamton, Binghamton, NY 13902, USA.
J Environ Monit. 2007 Jul;9(7):657-65. doi: 10.1039/b706225g. Epub 2007 May 24.
This work reports the feasibility of using Pd nanoparticles as innovative catalysts in the conversion of reducible contaminants from toxic to benign forms. Cr(VI) is a known carcinogen while the trivalent chromium salts are believed to be non-toxic. The ability of Pd nanoparticles to catalyze the rapid reduction of Cr(VI) to Cr(III) using reactive sulfur intermediates produced in situ was therefore studied. Using a microchamber set at 130 degrees C, the reduction mixture consists of palladium nanoparticles and sulfur (PdNPs/S), which generated highly reducing sulfur intermediates that effected the reduction of Cr(VI) to Cr(III) by 1st order reaction kinetics. UV-visible spectroscopy and cyclic voltammetry were employed to monitor the reduction process. The results showed that 99.8% of 400 microM Cr(VI) was reduced to Cr(III) by PdNPs/S in one hour compared to 2.1% by a control experiment consisting of sulfur only. The rate of Cr(VI) reduction was found to be dependent on temperature and pH and was greatly enhanced by the addition of PdNPs. Subsequent application of this approach in the reduction of Cr(VI) in soil and aqueous media was conducted. In contrast to the control experiments with and without PdNPs or sulfur, greater than 92% conversion rate was obtained in the presence of PdNPs/S within 1 hour. This represents over a 500-fold improvement in conversion rate compared to current microbial approaches. XPS analysis provided the confirmation regarding the oxidation states of Cr(VI), Cr(III) and the nature of the reactive intermediates. This work offers PdNPs/S as a new interface for the reduction of high oxidation state heavy metal pollutants.
这项工作报道了使用钯纳米颗粒作为创新催化剂将可还原污染物从有毒形式转化为良性形式的可行性。六价铬是一种已知的致癌物，而三价铬盐被认为是无毒的。因此，研究了钯纳米颗粒利用原位产生的活性硫中间体催化六价铬快速还原为三价铬的能力。在设置为130摄氏度的微室中，还原混合物由钯纳米颗粒和硫（PdNPs/S）组成，它们产生了高还原性的硫中间体，通过一级反应动力学实现了六价铬到三价铬的还原。采用紫外可见光谱和循环伏安法监测还原过程。结果表明，与仅含硫的对照实验中2.1%的还原率相比，在一小时内，400微摩尔的六价铬中有99.8%被PdNPs/S还原为三价铬。发现六价铬的还原速率取决于温度和pH值，并且通过添加钯纳米颗粒大大提高。随后将该方法应用于土壤和水介质中六价铬的还原。与有或没有钯纳米颗粒或硫的对照实验相比，在存在PdNPs/S的情况下，1小时内获得了大于92%的转化率。这代表与当前微生物方法相比转化率提高了500倍以上。XPS分析证实了六价铬、三价铬的氧化态以及活性中间体的性质。这项工作提供了PdNPs/S作为还原高氧化态重金属污染物的新界面。
