Dechlorination Of Haloacetic Acid By Nanoscale Pd/Fe Bimetallic System

Iron plays an important role in reducing chlorinated organics for its efficiency and convenience. Nanoscale Pd/Fe bimetallic particles and membrane stabilized nanoscale Pd/Fe bimetallic particles were used to enhance dechlorination efficiency of iron.Nanoscale Pd/Fe bimetallic particles were prepared by chemical deposition method. Membrane stabilized Pd/Fe bimetallic particles(hybrid membrane) were prepared by dip-coating method. Systematic work on nanoscale Pd/Fe bimetallic particles and membrane stabilized Pd/Fe bimetallic particles were conducted in this study.Particle shape, size, crystal structure, Pd to Fe ratio(PFR) and specific surface area of nanoscale Pd/Fe bimetallic particles were studied by transmission electronic microscopy(TEM), scanning electron microscope(SEM), X-ray diffraction(XRD), X-ray fluorescence(XRF), enengy distribution spectra(EDS) and Brunauer-Emmett-Teller-nitrogen(BET) method. Iron element in nanoscale Pd/Fe bimetallic particles prepared in this study existed mainly asα-Fe0. The diameter and specific surface area of nanoscale Pd/Fe bimetallic particles were 30-50 nm and 51m2/g, respectively.Nanoscale Pd/Fe bimetallic particles were used to dechlorinate monochloroacetic acid(MCAA). Dechlorination of MCAA with different reducts was studied. Effect of dose and PFR of nanoscale Pd/Fe bimetallic particles on dechlorination of MCAA was detected. Data showed that dechlorination efficiency(DE) of MCAA with nanoscale Pd/Fe bimetallic particles were 6.9 times and 0.7 times larger than that with reductive Fe and nanoscale Fe, respectively. When the amount of nanoscale Pd/Fe bimetallic particles were 10 g/L and PFR was 0.083%, DE of MCAA was the best.Nanoscale Pd/Fe bimetallic particles were used to dechlorinate trichloroacetic acid(TCAA). More than 90% of TCAA were dechlorinated to dichloroacetic acid(DCAA) during the first 1 min of reaction. DCAA were dechlorinated completely to MCAA after 30 min and the concentration of MCAA in solution appeared a decrease trend after the increase.Surface morphology and PFR of hybrid membrane were studied by inductively coupled plasma atomic emission spectrometer(ICP-AES) and SEM. It was found that metrical PFR of hybrid membrane was lower than theoretical PFR. Nanoscale Pd/Fe bimetallic particles stabilized in HCPF hybrid membrane congregated less than that in HPF, CPF and PF hybrid membranes.Four kinds of hybrid membranes were used to dechlorinate TCAA. It was found that modified reaction rate constant of HCPF hybrid membrane was 2.1, 4.2 and 7.8 times as large as that of HPF hybrid membrane, CPF hybrid membrane and PF hybrid membrane, respectively.HCPF hybrid membrane was used to dechlorinate TCAA. Effect of PFR of nanoscale Pd/Fe bimetallic particles stabilized in the hybrid membrane, dose of hybrid membrane, stability of hybrid membrane, H2O amount in solution and initial TCAA concentration on dechlorination of TCAA were detected. Data showed that dechlorination efficiency of TCAA could be the best when PFR was 0.534% and dose of nanoscale bimetallic particles stabilized in hybrid membrane was more than 5.08 mg. HCPF hybrid membrane could dechlorinate TCAA with the same dechlorination efficiency during the fist 4 repetition times. H2O plays an important role in dechlorination, and dechlorination of TCAA did not occur without H2O. Dechlorination effect of TCAA decreased as the initial concentration increased.