A starch based sustainable bio-hybrid composite for surface assimilation of methylene blue: preparation, characterization, and adsorption study

Abstract

Water pollution is a serious problem as it destroys food sources and contaminates drinking water and thus poses a significant challenge to the development of eco-friendly wastewater treatment methodologies. In the present work, biodegradable and naturally available polymer (starch) and halloysite nanotube (HNT) composite flakes were prepared using a facile route of solution casting to treat polluted water containing methylene blue. X-ray diffraction, scanning electron microscopy, Fourier transform-infrared spectroscopy, thermogravimetry, surface analysis, pore size measurements, and point of zero charge determination were used to study the composite flakes. The optimum conditions for the adsorption of methylene blue onto the composite flakes were achieved using 0.15 g of adsorbent after 30 min of contact time with 99.5% efficiency. No pH modifications were required to complete the adsorption process. The correlation coefficient (R²) values showed that the Langmuir isotherm model and pseudo second order kinetics provided a superior fit for adsorption relative to other tested models. The maximum monolayer adsorption capacity found was 604 mg g⁻¹ for the physisorption uptake of methylene blue dye. Additionally, the impact of temperature was investigated, which showed improved adsorption with increasing temperature. The free energy of adsorption was favorable with a positive enthalpy (58.35 kJ mol⁻¹) and entropy change (0.192 kJ mol⁻¹ K⁻¹). Further, the regeneration studies confirmed the starch–HNT adsorbent to be an excellent system for treating methylene blue containing wastewater with negligible loss of efficiency after six successive sorption–desorption cycles. The starch–HNT duo proposed in this work can serve as a vital and efficient strategy to remove dyes from wastewater compared to reported methodologies.