Eco-friendly polyurethane composites with rice husk ash residue to remove petroleum hydrocarbons from aqueous media

Bio-based polyurethane foam sorbents were developed, incorporating different amounts of rice husk ash, 2, 8 and 20 wt% relative to the total mass of the polyols for the adsorption of diesel oil in single-phase and two-phase systems. The composites were characterized using scanning electron microscopy, microtomography, X-ray diffraction, infrared spectroscopy, thermogravimetry analysis and contact angle. In single-phase diesel oil systems, higher levels of ash incorporation (8 and 20%) increased the hydrocarbon removal capacity by up to 43% compared to pure polyurethane foam. Removals of up to 5.348 mg g⁻¹ were found for the composite with 8% ash and 5.518 mg g⁻¹ for the composite with 20%. In two-phase systems, varying the concentration of diesel oil from 10 g L⁻¹ to 150 g L⁻¹, there is a possibility that the lower contact angle of the composites may interfere with adsorption, as the composite with 2% ash tended to have a higher diesel oil sorption capacity. Sorption kinetics showed a high rate at contact times of around 8 min. The non-linear pseudo-second-order models fitted the observed sorption phenomena satisfactorily, with coefficients of determination greater than 0.90.