Abstract
Pd/Fe-modified carbon paper (Pd/Fe-C) electrode was prepared from PdCl2 and FeSO4 via electrodeposition onto carbon paper. It was observed that the diameters of electrodeposited Pd/Fe particles were around 20nm with a uniform distribution on carbon paper, which is smaller than Pd/Fe particles of impregnated and calcined electrode. The electrodeposited Pd/Fe-C electrode exhibited higher activity in dechlorination of chloroacetic acids than impregnated and calcined electrode. Under optimal experiment conditions of Pd:Fe molar ratio of 2:1 at −1.5V (vs SCE), 95% of trichloroacetic acid (TCAA) with the initial concentration of 500μg/L was removed within 20min at pH 3. The dechlorination of chloroacetic acids followed the order of TCAA>dichloroacetic acid (DCAA)>monochloroacetic acid (MCAA). MCAA cannot be dechlorinated at C and Fe-C electrodes via direct reduction. However, a part of chloroacetic acids was directly dechlorinated to acetic acid at Pd-C and Pd/Fe-C electrodes via indirect reduction. The Pd(0) and Pd(II) species were detected by X-ray photoelectron spectroscopy. Compared with the individual Pd-C electrode, in situ formation of Fe(0) decreased the interface impedance as observed by electrochemical impedance spectroscopy analysis. In conclusion, the presence of Pd(0) nanoparticles played a significant role in forming atomic H* to realize indirect reduction process which could achieve the complete dechlorination of chloroacetic acids.
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