Catalytic Reduction Of AOCs And Azo Dye By Nanoscale Pd/Fe

Nano Zero-valent iron(nZVI)application as a novel technology for water pollution treatment had attracte increasing attention in recent years.Many pollutants would be efficiently removed by nZVI.However,nZVI need to be improved due to its shortages(it was inevitably oxidized in the process of reaction and particles were too small to recycle,etc).In this paper,EDTA was used to improve the reactivity of Pd/Fe nanoparticles.And the effects of EDTA concentration,initial pH,palladium loading,temperature,stirring rate and other factors on dechlorination of 2,4-Dichlorophenoxyacetic acid(2,4-D)and 2,4-Dichlorophenol(2,4-DCP)were studied.In addition,nano zero-valent iron particles were entrapped by Sodium Alginate(SA),then the SA-nZVI beads were used to catalytic reductive azo dye X3B.The concentration of SA,mass of nZVI,initial concentration of X3B,temperature,initial pH and other factors were investigated.High performance liquid chromatography(HPLC),Uv-vis spectrophotometer(UV-Vis),Scanning electron microscopy(SEM),Transmission electron microscope(TEM)and X-ray photoelectron spectroscopy(XPS)were employed to determine and analyze the degradation process of the target pollutant.Results can be summarized as follows:(1)Complexing agent EDTA could keep the reactivity of nZVI through the complexation with Fe2+ which generated by nZVI in the reaction process.And it also can remove the passivation layer on the surface of nZVI.(2)EDTA concentration,initial pH,palladium loading,temperature,stirring rate and concentration of pollutants were important factors of the dechlorination of 2,4-D and 2,4-DCP by Pd/Fe nanoparticles with EDTA.Higher concentration of EDTA,lower initial pH and higher palladium loading were conducive to the reductive dechlorination.25.0℃,nZVI dosage 1.0 g·L-1,Pd loading 0.5%,stirring rate 200 r·min-1,pH 7.1 and CEDTA 75.0 mmol·L-1 favored the 2,4-D removal.Under the suitable conditions,10.0 mg·L-1 2,4-D could be completely converted to PA after 50 mins.And the suitable experimental parameters for 2,4-DCP removal were:25.0℃,nZVI dosage 1.0 g·L-1,Pd loading 0.5%,stirring rate 200 r·min-1,pH 7.0 and CEDTA 25.0 mmol-L’1,within 110 min,the removal rate of 20.0 mg·L-1 2,4-DCP could reach to 94.6%.(3)nZVI was entrappd by SA and the SA-nZVI beads were used to catalytic reductive azo dyes.Immobilized nZVI could be recycled easier and avoid causing secondary pollution.(4)SA-nZVI beads could attain a high removal efficiency of X3B on the experimental conditions.2.0%SA,higher nZVI and initial pH were favorable for reaction process.The favorable experimental parameters for X3B removal were 25.0 ℃,SA concentration 2.0%,nanoscale Fe0 dosage 2.0 g·L-1,stirring rate 200 r·min-1 and pH 6.9,the removal rate of 25.0 mg·L-1 X3B could reach up to 90.7%。(5)Sodium alginate gel had no adsorption on X3B.The main mechanism for the removal of X3B by SA-nZVI beads was reduction reaction.Under the action of nZVI and[H]that generated by Fe-H2O corrosion in water,the chromophoric group(N=N)of X3B was broke.