Removal of Industrial Dyes from Aqueous Solution by Vanadium Pentoxide/Titanium Butyl-Oxide Hybrid Gel

Abstract

Industrial dye material is one of the most abundant pollutants of water worldwide. The dye effluent makes the aquatic system highly coloured and aesthetically unpleasant. They are also toxic and harmful to all forms of life. It is evidenced that the dye effluent are often mutagenic, teratogenic and carcinogenic. Thus, industrial dyes and colorants have emerged as a focus of environmental remediation efforts. Vanadium (V) pentoxide is the most stable oxide of vanadium. One of its hydrated form, vanadium oxide xerogel (VOX), has a unique structure, and is well studied for its intercalation properties. Its application in water treatment was limited because it forms a brown colloidal suspension when contact with water. A novel technique produces insoluble VOX by introducing titanium butyl-oxide to form a hybrid gel was discovered, and enabled VOX-based material in water treatment applications. In our previous study, the hybrid gel was found to be able to decolourise Rhodamine B, Methylene Blue and a small extent of Methyl Orange. This thesis presents an investigation of the decolourisation mechanism of dyes by the hybrid gel with detailed analysis of the interaction between the hybrid gel and the dye molecules. It was found that the hybrid gel has the ability to decolourise a range of industrial dyes. Analysis of the structure of dyes we tested showed that the cationic groups in the dye molecules were responsible for the interaction with the negatively charged hybrid gel surfaces. A sorption mechanism, predominantly driven by electrostatic forces, was proposed. Different decolourisation responses were observed in anionic dyes, and were attributed to their negatively charged ionic structure when dissociated. The microstructure of the dye-loaded hybrid gel was studied, and revealed an inner absorption mechanism. The microscopy analysis also discovered the heterogeneity of the novel hybrid gel; suggesting that VOX rich particles were the main dye absorbent and the hybrid gel’s dye absorption capacity could potentially be increased. Based on the electrostatic attraction mechanism proposed, complete desorption and improved absorption of selected dyes were successfully achieved by adjusting the pH of the dye solution with diluted hydrochloric acid and sodium hydroxide. These findings provide proof that the hybrid gel has the potential to absorb a wider range of dyes and to recover dyes from wastewater. The knowledge developed in this study assists with the development of this technique, which can be utilised as a waste water treatment technique and a water conservation measure that also has economic significance due to its dye recovery ability.