Degradation of Aqueous Carbon Tetrachloride by Nanoscale Copper Particles Supported on a Cation-Resin
Date Issued
2005
Date
2005
Author(s)
lin, Chin-Jung
DOI
zh-TW
Abstract
The use of zero valent metal as a reductant of organohalides has been extensively investigated over the last 15 years. The disappearance of contaminants is attributed to a corrosion-like process, in which the metal donates electron to reduce target pollutants, accompanied by the dissociation of water. Early investigations have gained insight concerning the mechanism and kinetics of the electron transfer process through batch and column experiments. The degradation of carbon tetrachloride by iron, the most commonly used reactive material, yields chlorinated intermediates at a level of 60-80% of the degraded carbon tetrachloride for lack of a stronglyπbond formed between carbon tetrachloride and d-orbit. Thus, not only reaction rate but also chlorinated intermediates yields attracts interesting.
Nanoscale zerovalent copper supported on a cation resin was successfully synthesized to enhance the removal of carbon tetrachloride (CCl4) from contaminated water. The use of the cation resin as a support prevents the reduction of surface area due to agglomeration of nanoscale zero valent copper particles. Moreover, the cation resin recycles the copper ions resulting from the reaction between CCl4 and Cu0 by simultaneous ion exchange.
The decline in the amount of CCl4 in aqueous solution results from the combined effects of degradation by nanoscale zero valent copper and sorption by the cation resin; thus the amount of CCl4 both in aqueous solution and sorbed onto the resin were measured. The orders of degradation reaction (Na) with respect to aqueous CCl4 concentration were 0.94 and 0.91 for 0.2 and 0.5g Cu0/resin loading per vial, respectively (both values were close to unity). Reducing the size of a Cu0 particle on the resin to approximately close to 10 nm would sharply increase kSA by a factor of 112-125.The pseudo-first-order rate constant normalized by the surface-area and the mass concentration of nanoscale zero valent copper (kSA) was 2.1 0.1 L h-1 m-2, approximately twenty times that of commercial powdered zero valent copper (0.04 mm). Due to the exchange between Cu2+ and the strongly acidic ions (H+ or Na+), the pH was between 3 and 4 in unbuffered solution and Cu2+ at the concentration of less than 0.1 mg L-1 was measured after the dechlorination reaction.
Bimetallic particles are extremely interesting in accelerating the dechlorination of chlorinated organics. Four noble metals (Pd, Pt, Ru and Au), separately deposited onto the copper surface through a spontaneous redox process, promoted the CCl4 dechlorination rate, and the catalytic activity of the noble metal followed the order of Pd>> Ru> Pt> Au. This order was found to be dependent on the concentrations of adsorbed atomic hydrogen, indicating that the initial reaction was cathodically controlled.
Resin as a support extends the choice of zero valent metals and provides easy emplacement and replacement. Both exchange current density and the number of free electron successful elucidate the selectivity of single-electron and two-electron transfer. Nano-metal/resin would facilitate the development of a process that could be designed for convenient emplacement and regeneration of porous reductive medium.
Subjects
零價金屬
四氯化碳
還原脫氯反應
奈米
zero valent metal
carbon tetrachloride
reductive dechlorination reaction
nanoscale
Type
thesis
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