New Zero Valent Iron-based Nanocomposites: Preparation And Adsorption Performance For Arsenic

In recent years,with the development of society,heavy metal pollution has become a hot social issue that should be solved.The use of nanomaterials for environmental pollutants has become new pollution control methods.Compared with traditional adsorbent materials,nanoscale zero-valent iron(nZVI)possess the advantage of small particle size,large surface area and high surface reactivity,which have been utilized in the treatment of environment heavy metal pollution.However,nZVI is easy to agglomeration and oxidation,leading to decrease its chemical reactivity in the practical application.Therefore,in orer to improve the dispersion and stability of nanoscale zero-valent iron,it is necessary to modify the iron nanoparticles.In this paper,zero valent iron-based nanocomposites were prepared by liquid-phase chemical reduction method and characterized by scanning electron microscope(SEM),energy dispersive X-ray spectrometry(EDS)with image mapping,transmission electron microscopy(TEM),X-ray diffraction(XRD)and nitrogen adsorption-desorption measurements.The study had been conducted to investigate the effects of contact time,solution pH,initial concentration and coexisting ions on the adsorption of arsenic by these nanocomposites.In order to investigated the mechanism adsorption model of iron-based nanocomposite material for removal of arsenic.Fourier transform infrared(FTIR)and X-ray photoelectron spectroscopy(XPS)analysis were used to demonstrate the adsorption mechanism.The main research results of this work were made as follows:1.The iron nanoparticles were dispersed uniformly in the cellulose@nZVI and the average grain sizes of nZVI were in the range of 40-80 nm.The cellulose@nZVI could be easily separated from solutions through the external magnetic field and it demonstrated better treatment performance for As(III)removal at pH 6-9.Arsenic adsorption was followed the pseudo-second order kinetic model and Langmuir isotherm model.The effects of two competitive anions,such as SiO32-and PO43-,did show obvious changes for As(III)adsorption.FTIR analysis indicated that the hydroxyl groups on the surface of cellulose @nZVI played an important role in arsenic adsorption,while XPS studies further demonstrated that there were As(III)and As(V)on the surface of cellulose@nZVI and As(III)occurred oxidation in the process of adsorption.2.Ni/Fe bimetallic nanoparticles were prepared by liquid-phase chemical reduction method.The average particle size of Ni/Fe NPs was around 40 to 60 nm and it demonstrated better treatment performance for As(III)and As(V)removal at pH 4 and 5,respectively.Arsenic adsorption was followed the pseudo-second order kinetic model and Langmuir isotherm model.The maximum adsorption capacities of As(III)and As(V)were 65.40 mg g-1 and 113.89 mg g-1,respectively.In the coexisting anions,SiO32-and PO43-showed significant effect on the adsorption of arsenic.Combined with FTIR and XPS characterization,it was proved that the hydroxyl groups on the surface of Ni/Fe NPs were involved in arsenic adsorption.As(III)and As(V)were adsorbed on the surface of Ni/Fe NPs.XPS studies demonstrated that arsenic removal on the surface of Ni/Fe NPs was a synergistic adsorption and redox process.3.A ‘house-of-cards' structure was shaped by stacking of the montmorillonite interlayers that formed in the supported core-shell structured iron nanoparticles,it was conducive to make nZVI well dispersed and stabilized.The Fe@Fe2O3/MMT demonstrated better treatment performance for arsenic removal at pH 3.Arsenic adsorption was followed the pseudo-second order kinetic model and Langmuir isotherm model.Combined with FTIR and XPS characterization,it was proved that there were a large number of hydroxyl groups on the surface of Fe@Fe2O3/MMT.As(III)was oxidated to As(V)by oxidizing intermediate that formed from corrosion of nZVI in solution,which was accompanied by the oxidation process,while As(V)occured only adsorption process.Adsorption of As(III)and As(V)through forming monodentate and bidentate surface complexes were on the surface of MMT-nZVI between As(III)/As(V)and hydroxyl group.