Characterization of adsorbed arsenate on amorphous and nano crystalline MgFe-layered double hydroxides

Abstract

This article investigated sorption of toxic and carcinogenic arsenate (AsO4 (3-)) ions on positively charged surface of amorphous and nano crystalline MgFe-layered double hydroxides (LDHs). Based on Brunauer-Emmett-Teller (BET) and Transmission Electron Microscopy (TEM), average size, and specific surface area of nano crystalline MgFe-LDHs, which was about range of about 50-200 nm and 90.2 m(2)/g, was lower and higher when compared to them of amorphous MgFe-LDHs, respectively. In addition, X-ray diffraction (XRD) peak and point of zero charge (PZC) of crystalline MgFe-LDHs was higher intensity and same, respectively, when compared to that of nano crystalline FeMg-LDHs. Adsorption rate of arsenate on amorphous MgFe-LDHs was a little faster when compared to that of nano crystalline MgFe-LDHs. In addition, as pH decreased, adsorption amount of arsenate on amorphous MgFe-LDHs increased significantly when compared to that of nano crystalline MgFe-LDHs. These results indicate that mechanism of arsenate in two materials was significantly different. We investigate sorption characteristic at pH 5, based on XRD and Fourier-transformed infrared (FTIR). In amorphous MgFe-LDHs, ferric arsenate precipitate was formed on surface of amorphous MgFe-LDHs and constituted the predominant surface arsenate. However, in nano crystalline MgFe-LDHs, arsenate was dominantly sorbed as a "non-surface-complexed" As-O bond on surface and anion exchange in interlayer.