Preparation Of Calcium Alginate Coated Zero-valent Iron And Its Reduction/oxidation Synergistic Degradation Of Dyes

In this study,the zero-valent iron(ZVI)encapsulated by alginate beads(Fe0-ABs)was successfully prepared,and used for the Acid Red B(ARB)dye removal from solution.The ZVI was immobilized firmly on calcium alginate(CA)via complexation and liquid phase reduction.X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectroscopy(FTIR)and energy-dispersive X-ray spectroscopy(EDX)images showed that Fe0 particles were encapsulated and dispersed well in the alginate.N2 absorption-desorption(BET)and emission scanning electron microscope(SEM)were used to analyze the porous structure of Fe0-ABs.Degradation of Acid Red B from aquous solutions was achieved with synergetic reaction,which was capable of reduction with synthesized ZVI and oxidation with Fenton technology.In the reduction process,ARB solution was completely decolourized because of cleavage of azo bond(-N=N-)in the chromophore of an azo dye.Fe2+/3+ produced from ZVI during reduction played the key role to promote a subsequent Fenton reaction by its coupling with H2O2.The effects of Fe0-ABs dosage,pH and initial H2O2 concentration on ARB degradation were respectively evaluated.Meanwhile,the changes of pH and iron leakage during the reaction were also analyzed,and reused performance of Fe0-ABs was investigated.The results showed that release of Fe ions was low(<4.5%)because ZVI was immobilized firmly on supporter through cross-linked with carboxyl functional groups.The dye solution decolorization rate was 96%and mineralization rate was 74%after degradation.In order to explore the removal mechanism of ARB by Fe0-ABs,two blank adsorption experiments and three different reaction systems were designed,and Fe 2p spectra of ZVI before reaction,after reduction and after Fenton reaction were obtained by XPS characteriation.The comparison of different reaction systems suggested that TOC removal efficiency was enhanced by using ZVI as the pre-reduction.The results of blank adsorption experiments indicated that besides the reduction and oxidation,the sorption by Fe0-ABs was also responsible for the removal of ARB.The XPS spectra of Fe 2p showed that Fe0/Fe2+/Fe3+ on the carrier can all react with H2O2 to generate · OH during oxidation.