Sulfonated and gamma-irradiated waste expanded polystyrene with iron oxide nanoparticles, for removal of indigo carmine dye in textile wastewater

In this work, waste expanded polystyrene (WEPS) was irradiated with gamma rays, ranging doses from 100 kGy to 1,000 kGy. After irradiation, the WEPS had decrease on its glass transition temperature (Tg), as consequence of the scissions of its polymer chains. Then, the irradiated WEPS was sulfonated, and its degree of sulfonation (DS) was measured. The highest DS value, 46.6%, was obtained for an irradiation dose of 200 kGy. The sulfonated and irradiated polystyrene (denominated as iS-WEPS), was used as a support of iron oxide nanoparticles. Such composite system was denominated (FeO-NPs + iS-WEPS). The results show nanoparticle sizes of 31.5 nm containing 21.97% iron oxide. The composites followed a pseudo-second order model, with a maximum adsorption capacity of 20 mg/g, and an equilibrium time of 30 min, according to the Langmuir model. Moreover, the optimal conditions followed by the Fenton process were: pH = 3.2, H2O2 concentration = 0.32 mM/L, composite concentration (FeO-NPs + iS-WEPS) = 2 g/L, and a reaction time 20 min. Finally, 99% removal of indigo carmine dye was achieved, and a reduction of 83% of COD in textile wastewater.