Abstract
This study is aimed to prevent the agglomeration of Pd/Fe bimetallic nanoparticles and thus improve the efficiency toward degradation and dechlorination of chlorinated organic contaminants. A mesoporous silica with a primary pore diameter of 8.3 nm and a specific surface area of 688 m2/g was prepared and used as the host of Pd/Fe nanoparticles. The Pd/Fe nanoparticles were deposited onto or into the mesoporous silica by reduction of ferrous ion and hexachloropalladate ion in aqueous phase. Batch degradation and dechlorination reactions of trichloroethylene were conducted with initial trichloroethylene concentration of 23.7 mg/L, iron loading of 203 or 1.91 × 103 mg/L and silica loading of 8.10 g/L at 25 °C. Concentration of trichloroethylene occurs on the supported Pd/Fe nanoparticles, with trichloroethylene degrading to 56% and 59% in 30 min on the supported Pd/Fe nanoparticles with weight percentage of palladium to iron at 0.075% and 0.10% respectively. The supported Pd/Fe nanoparticles exhibit better dechlorination activity. When the supported Pd/Fe nanoparticles with a weight percentage of palladium to iron of 0.10% were loaded much less than the bare counterpart, the yield of ethylene plus ethane in 10 h on them was comparable, i.e., 19% vs. 21%. This study offers a future approach to efficiently combine the reactivity of supported Pd/Fe nanoparticles and the adsorption ability of mesoporous silica.
Highlights
Bimetallic iron nanoparticles such as palladium/iron (Pd/Fe) and nickel-iron (Ni-Fe) nanoparticles have been proven to be effective in transforming chlorinated organic contaminants in groundwater or wastewater into innocuous or biodegradable compounds [1,2,3,4,5,6]
Since pore-expanding step was introduced into the preparation of mesoporous silica and the aging step was carried out at ambient pressure, non-crystalline morphology with ununiform pore size was obtained
The primary diameter of 8.3 nm is smaller than that obtained by Schmidt-Winkel et al [20]
Summary
Bimetallic iron nanoparticles such as palladium/iron (Pd/Fe) and nickel-iron (Ni-Fe) nanoparticles have been proven to be effective in transforming chlorinated organic contaminants in groundwater or wastewater into innocuous or biodegradable compounds [1,2,3,4,5,6]. Catalytic dechlorination of aqueous trichloroethylene by Pd/Fe nanoparticles can be expressed by Equation (1). If n equals 4, trichloroethylene is converted into ethane; if n equals 3, ethylene is produced. Iron mediates the reductive dechlorination providing electrons, water donates hydrogen, and palladium acts as a catalyst initiating the reaction. Pd/Fe nanoparticles tend to agglomerate due to high surface energy and magnetic attraction, decreasing the specific surface area and lowering dechlorination activity.
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