Effect of Molecular Structure in Chlorinated Organic Compounds on Zero-valent Copper Degradation Mechanism Based on SEM-EDS and GC-MS Techniques

Abstract

Zero-valent copper, even cheap, is rarely used in hydrodechlorination (such as chlorinated aromatic hydrocarbons), because Cu has poor catalytical dechlorination activity and complex reaction mechanisms. In this study, Cu-Fe and Cu-Ni alloys were prepared by mechanical ball-milling, and the effect of micro-environment for the chlorophenol (4-CP) dechlorination behavior of Cu was studied in order to investigate the effect of organic chlorine molecular structure on Cu dechlorination. Two reaction mechanisms were examined for low-cost copper during dechlorination. SEM-EDS and GC-MS analyses show that the structure of organic chlorine and Cu metal environment could directly affect the mechanism. In the Cu-Fe system, Cu follows the classic catalytic hydrodechlorination mechanism and the degradation product 4-CP is phenol. But in the Cu-Ni system, nickel metal does not play a catalytic hydrogenation of action, the degraded product for 4-CP by Cu-Ni alloy is cyclohexanone. Copper acts as hydrogen-metal and shows a strong reducing activity by direct electron transfer. 4-CP degradation for Zero-valent copper was up to 70%, while only 34% for Cu-Fe system. These differences concluded that the aromatic ring was a direct electron transfer for Cu. Zero-valent copper can degrade 4-CP and phenol with high chemical stability, but cannot degrade aliphatic chlorinated organics (e.g., monochloroacetic acid and dichloroacetic acid) with relatively poor chemical stability. In conclusion, dechlorination mechanism for zero-valent copper is not traditional catalytic hydrodechlorination, but the direct electron transfer reduction mechanism which is affected by target molecule structure.

Keywords

• chlorinated organic compounds
• zero-valent copper
• copper alloy
• degradation mechanism
• mechanical ball milling
• scanning electron microscopy-energy-dispersive spectrometry (sem-eds)
• gas chromatography-mass spectrometry (gc-ms)