Preparation Of Modified Pd/Fe Nanoparticles For 2,4-dichlorophenol Removal From Wastewater

Chlorophenols(CPs)have been still considering as a particular group of priority organic pollutants due to their biological activities,phytotoxicity and ability to accumulate in animal tissues.Once released into both the ground and surface waters,CPs will produce disagreeable taste to drinking water and even cause a considerable negative effect on human's health.In recent years,the amendment of CPs with nanoscale zero valent iron(nZVI)particles or their bimetallic counterparts have been attracting extensive research in nanotechnology.Unfortunately,it is the van der Waals interactions between particles,magnetic interactions and their high surface energy that make the freshly prepared nanoparticles(NPs)easily aggregated and oxidized.With the aim of overcoming the aforementioned drawbacks,polyacrylic acid(PAA),cetyltrimethylammonium bromide(CTAB)and poly(methylmethacrylate)(PMMA)were employed to modify Pd/Fe bimetallic NPs for 2,4-dichlorophenol(2,4-DCP)dechlorination.PAA,CTAB and PMMA modified Pd/Fe bimetallic NPs were prepared by the liquid phase and coprecipitation method.The morphology,particle shape,size,crystal structure and BET surface areas of the resulted Pd/Fe bimetallic NPs were studied by field emission scanning electron microscope(FE-SEM),transmission electron microscope(TEM),x-ray diffractometer(XRD)and BET.The results indicated that,compared to unmodified Pd/Fe bimetallic NPs,modifying Pd/Fe bimetallic NPs with PAA,CTAB and PMMA was an ideal alternative to enhance the dispersion and the ability to resist oxidation of NPs.The modified Pd/Fe bimetallic NPs showed roughly spherical shape with varying sizes in the range of 50?90 nm and arranged with each other in a much more ordered dendritic structure.The crystal structure of the modified Pd/Fe bimetallic NPs was bcc ?-Fe0.Catalytic dechlorination of 2,4-DCP using the resulted Pd/Fe bimetallic NPs were investigated and compared.Degradation results showed that the catalytic dechlorination efficiency of 2,4-DCP with Pd/Fe NPs modified with PAA,CTAB and PMMA respectively increased by 13%?38%,42%?49%and 42%?56%within a given reaction period of 30 min in comparison with unmodified Pd/Fe NPs,But the role of volume ratio of PAA to water,weight ratio of PMMA to anisole and volume ratio of water to ethanol in determining the properties of Pd/Fe NPs was not remarkable.Studies on the kinetics of 2,4-DCP reacted with Pd/Fe NPs in our cases implied that their behaviors didn't match the first-or pseudo-first-order kinetics:because the presence of oxidation phases on the surface of unmodified Pd/Fe NPs and the modifiers on the surface of NPs could influence the diffusion of 2,4-DCP onto reactive sites,thus affecting the whole degradation process.So,an innovatively revised kinetics was proposed in the study.Effects of NPs addition,initial concentration of target pollutant,initial pH value of reaction solution on the catalytic dechlorination properties of 2,4-DCP by modified Pd/Fe bimetallic NPs were systematically studied.The results suggested that the removal efficiency of 2,4-DCP increased with the increased NPs addition,and decreased with the increased initial 2,4-DCP concentration.when the initial pH value was 8,dechlorination efficiencies of 2,4-DCP by PAA,CTAB and PMMA modified Pd/Fe bimetallic NPs all reached a maximum.As for the initial pH ranged from 5 to 7,dechlorination efficiencies of 2,4-DCP decreased with the increased initial pH value in the case of PAA and CTAB modified Pd/Fe bimetallic NPs,but increased with the increased initial pH value in the case of PMMA modified Pd/Fe bimetallic NPs.In addition,alkaline condition(pH=9)would produce unfavorable effect on catalytic dechlorination of 2,4-DCP by PAA,CTAB and PMMA modified Pd/Fe bimetallic NPs.