Polyurethane sponge modified by alginate and activated carbon with abilities of oil absorption, and selective cationic and anionic dyes clean-up

Abstract

In this study, compact disc-derived activated carbon black (D-ACB) was hybridized with sodium alginate to modify polyurethane (PU) sponges. After immersing the PU sponge in this suspension, it was crosslinked in the presence of CaCl2 to obtain PU@D-ACB/calcium alginate composite sponge (PU@D-ACB.CaA) so that after crosslinking, no leaching was observed. The hydrophobic nature of PU changed to superhydrophilic for treated PU, and the water contact angle decreased from 122° ± 11.8 to 0°. PU@D-ACB.CaA composite sponge showed higher mechanical properties (with a compressive strength of 1809 ± 1210 kPa and Young's modulus of 45 ± 7.1 kPa) in comparison to the neat PU (with a compressive strength of 2.84 ± 0.08 kPa and Young's modulus of 3.5 ± 0.71 kPa). The composite could absorb organic solvents and oil 8–21 times the sponge's weight, and it showed reusability properties as well. High removal yields (82% of methylene blue (MB), 97% of malachite green, and 54% of crystal violet) were attained for the composite sponge compared to the neat PU. The composite showed fast adsorption ability with 65% adsorbed MB within the first 15 min and equilibrium almost reached within 360 min, and 98% dye was removed. The outcomes presented that the linear form of Langmuir isotherm and nonlinear form of pseudo-second-order can better express MB adsorption on PU@D-ACB.CaA composite sponge. It showed the maximum adsorption capacity of 71.32 mg/g for the lower range and 386.49 mg/g for the higher range of concentrations. The composite could be reused for five cycles and even more, and the adsorption mechanisms on this sponge mostly contain physical interactions. Consequently, this study presents an economical and effective strategy for manufacturing an adsorbent containing recycled polymeric compact discs, efficiently eliminating dyes from wastewater.