Recycled polypropylene/chitosan-fly ash composites for adsorptive removal of Rhodamine B from water

Abstract Novel composite adsorbents were fabricated using recycled polypropylene (PP), chitosan (CS) and fly ash (FA) for the efficient removal of Rhodamine B (RhB) dye from water. A single screw extruder was used to fabricate the PP composites with varied chitosan and fly ash content. The composites were characterized using Fourier transform-infrared (FTIR) spectrometer, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Water uptake and surface charge of the composites were also determined. The results showed that chitosan and fly ash were successfully embedded in the composites. SEM showed good distribution and dispersion of FA on PP polymer surface. The maximum recorded water uptake was 39% and all the composites were negatively charged after the pH of 6.2. Further, the study systematically investigated the adsorption efficiency of the composites under different pH levels, initial dye concentrations, and contact times. The adsorption kinetics were analysed using pseudo-first-order and pseudo-second-order models with the latter providing a better fit to the experimental data. The adsorption isotherms were evaluated, revealing that the Freundlich model best described the adsorption process, indicating multilayer adsorption on a heterogeneous surface. The best performing composite which had highest loading of chitosan and fly ash recorded 100% removal efficiency on the first adsorption–desorption cycle and 96.94% after the fifth cycle, highlighting the potential reusability of the adsorbent. The study revealed that loading CS and FA in the PP polymer matrix leads to high efficiency in removal of RhB from water. Furthermore, it demonstrated that waste materials, recycled PP and FA, may be useful in water treatment.