Preparation Of Al₂ O₃ Modified Pd/Fe/PVDF Catalytic Reductant For Dechlorination Of Chloroacetic Acid

Chloroacetic acid detected in chlorinated wate is a kind of less volatile halogenated organics. Zero-valent iron(ZVI) can catalytic dechlorinate chlorinated organic compounds (COCs), the dechlorination reaction rate can be increased with palladium coated on ZVI surface. Because of high surface area and reaction activity, Pd/Fe bimetallic system has higher dechlorination efficiency than iron. Pd/Fe bimetallic system was immobilized in carrier to retrieve Pd/Fe bimetallic nanoparticles and improve the dechlorination efficiency. The PVDF carrier surface modification and the self-made PVDF matrix modification was aim to immobilize Pd/Fe nanoparticles system for the dechlorination of chloroacetic acid in this study.Three kinds of surface modified PVDF carrier-immobilized Pd/Fe nanoparticles by hydrophilization method, in situ method and direct dip-coating method were studied. The result showed that: hydrophilization method and in situ method have no obvious difference in Fe loading and dechlorination efficiency, but was higher than direct dip-coating method.Adding different quantity (0%⁴%) nano Al₂O₃ particles into PVDF solution to prepare PVDF·Al₂O₃ organic-inorganic modified carrier. The best effect of PVDF·Al₂O₃ carrier is 2% Al₂O₃ adding, which studied by mechanical strength, contact angle and specific surface area. 2% PVDF·Al₂O₃ carrier dipped into different concentration cross-linking solution constituted with PAA, EG and FeSO₄·7H₂O to confirm the FeSO₄·7H₂O quantity in cross-linking solution. When cross-linking time is 15 minutes and FeSO₄·7H₂O content is 2.9%, Pd/Fe catalytic reductant in the PVDF·Al₂O₃ carrier have maximum loading and better disperse and Fe loading is 0.52 mg/cm2 by analyzing Fe loading and MCAA dechlorination efficiency.PVDF carrier, PVDF·Al₂O₃ modified carrier and Pd/Fe/PVDF·Al₂O₃ catalytic reductant were extensively characterized according to SEM, EDS, TEM, AFM and XRD to explicit the morphology and construct of modified PVDF matrix and identify the Pd/Fe particle shape and diameter, crystal structure, Pd content, and Pd/Fe loading evenness. The characterization showed that Pd/Fe/PVDF·Al₂O₃ catalytic reductant had smaller aggregation with good scattered tendency and were more evenly sized with a diameter in the range of 50^-150 nm, the crystal structure of iron was a regular -Fe0. The results show that PVDF·Al₂O₃ carrier has benign properties.Discussion the factor of chloroacetic acid dechlorination including Pd loading, Pd/Fe catalytic reductant quantity, initial concentration, Pd/Fe in different conservervation time, PVDF·Al₂O₃ using time. The results indicated that the dechlorination rate of chloroacetic acid by Pd/Fe/PVDF·Al₂O₃ increased with Pd loading increasing when Pd loading less than 0.511% and dechlorination rate decreased with Pd loading increasing when Pd loading more than 0.511%. Increasing Pd/Fe nanoparticles addition resulted in the increase of dechlorination efficiency. The dechlorination rate of chloroacetic acid decreased with high initial concentration. Fe loading and dechlorination rate of chloroacetic acid have no obvious change when Pd/Fe/PVDF·Al₂O₃ catalytic reductant long-term conserved in alcohol solution, which showed Pd/Fe/PVDF·Al₂O₃ catalytic reductant has good stabilization.Analysed the mechanism of PVDF·Al₂O₃ matrix modification and research the dechlorination kinetics of Pd/Fe/PVDF·Al₂O₃ catalytic dechloriantion of MCAA, DCAA, and TCAA. The results indicated that the chloroacetic acid dechlorination accorded with pseudo-first-order kinetics. Reaction rate constants of MCAA, DCAA, and TCAA were 0.0969min^-1, 0.1254 min^-1, 0.2859 min^-1, respectively.