Selective dye adsorption by pH modulation on chemically modified nanopolyaniline by N-grafting of maleic acid

Abstract

Dyes are potential pollutants in water due to their non-degradable nature and stability toward oxidizing agents and light. Among all the techniques available for the removal of dyes, the adsorption method is attracting the interest of researchers worldwide owing to its advantages, for instance, inexpensiveness, high efficiency and ease of synthesis. In this work, the emeraldine base form of polyaniline (EBPANI) was used as a nucleophile to synthesize polyaniline grafted maleic acid (PANI-g-MA) adsorbent, which was used to adsorb dyes selectively from wastewater upon modulation of the pH. The prepared grafted polymer was analysed using characterization techniques including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. PANI-g-MA demonstrated the adsorption of cationic and anionic dyes selectively at different pH values owing to the availability of different charges. The maximum adoption capacity for methylene blue (MB) dyes was found to be 181.81 mg g⁻¹. The adsorption parameters, such as adsorbent dose, pH, temperature, initial dye concentration and contact time, along with the kinetics and thermodynamic parameters (ΔG°, ΔH°, ΔS°), were evaluated for potential application in the real world. The Langmuir isotherm model is best suited to explain this adsorption process. This type of adsorption follows pseudo-second-order kinetics.