Synthesis and Characterisation of Penta-Bismuth Hepta-Oxide Nitrate, Bi₅O₇NO₃, as a New Adsorbent for Methyl Orange Removal from an Aqueous Solution

Abstract

This paper presents the synthesis of penta-bismuth hepta-oxide nitrate, Bi₅O₇NO₃, via the chemical precipitation method. After calcination, the precipitate was characterised by several methods, which included X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, BET surface area and pH drift method to determine the pH of point of zero charge (pH_pzc). The study results revealed that Bi₅O₇NO₃ had an orthorhombic crystal structure, a surface area of 1.6 m2 g-1 and a point of zero charge at pH 9.7. The chemical state of Bi₅O₇NO₃ indicated the presence of three oxidation states of bismuth centre. Furthermore, the decolourization ability of Bi₅O₇NO₃ to remove the azo dye was also evaluated. Although it had lower surface area, the removal efficiency was extremely good. This finding suggests that Bi₅O₇NO₃ could be used as a promising adsorbent for azo dye removal. The XPS spectra showed that the accumulation of dye onto Bi₅O₇NO₃ could be due to the anion exchange process, suggesting the birth of a new anion exchanger for azo dye removal.