Chitosan – TiO2 Nanocomposite Films for Efficient Decolourisation of Sulphur Black Dye under Dark Conditions

Abstract

ABSTRACT Sulphur dyes are a class of dyes known for their low cost and excellent fastness to light and wash. But, excess amounts of unused dyes, electrolytes and sulphide contents were found to cause serious hazards to health and environment. This work reports the synthesis of cost-effective, non-toxic, environment-friendly chitosan (CS) and chitosan-TiO2 (5 wt% (CST-5), 10 wt% (CST-10) and 15 wt% (CST-15)) polymer nanocomposite films by the facile solution casting method. CS and CST polymer nanocomposite films were tested for the decolourisation of sulphur black dye. The structural analysis of the synthesised films using X-ray Diffraction (XRD) displayed the semi-crystalline peaks of chitosan and the anatase phase of TiO2 with tetragonal-bcc structure. The morphological analysis using Atomic Force Microscopy (AFM) revealed that TiO2 had dispersed uniformly into the polymer matrix. UV–Vis DRS and PL revealed the wide indirect band gap energy and charge transfer characteristics, respectively, of the polymer nanocomposite films. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) studies revealed the various bonds, functional groups and elemental properties of CS and TiO2-loaded CS films. Sulphur black dye decolourisation studies conducted under dark conditions at room temperature and atmospheric pressure revealed that CST-5 nanocomposite film exhibited an excellent decolourisation efficiency of 87.6% within 12 min of contact with the sulphur black dye solution. This swift and enhanced decolourisation was due to the synergistic effects of adsorption by chitosan and catalytic wet air oxidation (CWAO) by the catalyst TiO2. These nanocomposite films are potential materials for the treatment of wastewater and decolourisation of various toxic dyes.