Ultrasonically enhanced dye removal using conducting polymer functionalised ZnO nanocomposite at near neutral pH: kinetic study, isotherm modelling and adsorbent cost analysis

Abstract

ABSTRACT Alarming increase in water pollution due to the disposal of industrial wastewater loaded with toxic dye has become one of the serious environmental problems since last few decades. Thus in recent years, development of highly functionalised novel composite materials for dye loaded wastewater remediation has become an important area of research. In this study, a conducting polymer (polyaniline) functionalised ZnO nanocomposite (PAn/ZnO-PNC) was synthesised and investigated its adsorptive behaviour for the removal of an anionic dye Eriochrome Black T (EBT) under ultrasonic irradiation. The synthesised PAn/ZnO-PNC was characterised by various analytical techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) surface area analysis. Experimental results demonstrated that after the functionalization of ZnO with polyaniline the adsorption capacity of PAn/ZnO-PNC improves as compared to pure polyaniline as well as pure ZnO nanoparticles. In addition to that, adsorption of EBT dye with PAn/ZnO-PNC could yield to lesser solution pH dependency as compared to pure ZnO nanoparticles and the optimum solution pH was fixed at 6.0 for EBT dye adsorption using PAn/ZnO-PNC. The adsorption mechanism between EBT dye and PAn/ZnO-PNC can be explained by electrostatic attraction, hydrogen bonding, and stronger π-π interaction bond between nanocomposite and dye molecules. The adsorption kinetic data were well fitted with the pseudo-second-order kinetic model which designates chemisorption between EBT dye molecules and PAn/ZnO-PNC. Isotherm study explores that EBT dye adsorption onto PAn/ZnO-PNC follows the Langmuir isotherm model with a maximum monolayer capacity of 108.69 mg/g. Performance evaluation study explores that sono-assisted adsorption was much superior to conventional magnetic stirring and batch stirring aided adsorption techniques. Cost analysis of synthesised PAn/ZnO-PNC revealed that the preparation cost of the composite is ~65$/kg.