High-Performance Polyimides with Pendant Fluorenylidene Groups: Synthesis, Characterization and Adsorption Behaviour

Abstract

High-performance polyimides (HPIs) were synthesized using various aromatic dianhydrides and fluorenylidene containing diamine via two-step polycondensation method and used as an adsorbent for the removal of dyes (Methylene blue (MB) and Rhodamine-B (Rh-B)). Various functional moieties (–O–, –(CF3)2, –(CH3)2) were incorporated through synthesis in the HPIs back-bone using various aromatic dianhydrides, which enhance the adsorption capacity of adsorbent. The structure and functional groups of HPIs were confirmed by NMR and FT-IR analysis. The surface morphology of HPIs and dye adsorbed-HPIs were determined using SEM–EDX analysis. The solution dye concentration was examined using a UV/Visible spectrometer. Adsorption parameters such as solution pH, initial dye concentration, adsorbent dosage, contact time and temperature were optimised. The effect of contact time and initial dye concentration data were used to evaluate the adsorption kinetic and isotherm parameters respectively. Types and mechanism of the adsorption process were predicted using adsorption kinetics and isotherm parameters. Adsorption of dye onto HPIs followed pseudo second-order kinetic model which was confirmed by the adsorption kinetic result. The maximum monolayer adsorption capacity (qe) of HPIs was calculated. From thermodynamic study, ΔG°, ΔS° and ΔH° were calculated, which could predict the nature of the adsorption process with respect to temperature. Adsorbed-HPIs waste was converted into a PET-adsorbed-HPIs composite to reduce the hazardous solid waste and examined the dye leaching properties.