Preparation of hyper-cross-linked hydroxylated polystyrene for adsorptive removal of methylene blue

A series of hydroxylated polystyrene (PS-OH) resins were prepared from macroporous poly(styrene-co-divinylbenzene) by nitration, reductive amination, diazotation and hydrolysis in sequence, and then a series of hyper-cross-linked hydroxylated polystyrene (HCPS-OH) resins were successfully prepared from the PS-OH resins by the Friedel-Crafts post-cross-linking using dichloromethane as an external cross-linker. Benefiting from the synthetic protocol, the HCPS-OH resins showed better adsorption performance for methylene blue in aqueous solution as compared with the corresponding PS-OH resins. HCPS-OH-4, one of the fabricated HCPS-OH resins which had the hydroxyl content of 5.0 mmol g^-1 and BET specific surface area of 69.0 m² g^-1, showed the highest adsorption capacity and selectivity for methylene blue. Higher temperature, higher pH, and higher ionic strength were beneficial to adsorption of methylene blue from aqueous solution. HCPS-OH-4 could be regenerated by treatment with 1.0 M HCl methanol solution and deionized water sequentially. Moreover, HCPS-OH-4 retained good adsorption performance for methylene blue even after 5 cycles of adsorption and regeneration, which implied that it was a good candidate for adsorptive removal of methylene blue dye in waste water.