β-Cyclodextrin hydroxypropyl methylcellulose hydrogels for bisphenol A adsorption

• DOI: 10.1016/j.molliq.2018.06.117
• Publication Date: 2018-07-02T09:04:31Z
• Authors: Ícaro F.T. de Souza; Denise F.S. Petri
• Keywords: Phenolphthalein

Abstract Crosslinking of βcyclodextrin (βCD) and hydroxypropyl methylcellulose (HPMC) was mediated by esterification with citric acid. The resulting networks presented high chemical stability in aqueous medium in the pH range from one to nine; pH > 10 led to the hydrolysis of ester bonds. The freeze-dried networks presented pores with size ranging from 10 μm to 200 μm. The amount of βCD bound to the HPMC network was estimated indirectly as 5.6 wt% with basis on the inclusion of phenolphthalein assay. Fourier transform infrared vibrational spectroscopy in the attenuated total reflectance mode evidenced the esterification between βCD, HPMC and citric acid molecules. HPMC and HPMC-βCD hydrogels presented similar swelling degrees for water of ~18 g per g of cryogel. The inclusion constant for the βCD-BPA complex was determined at 25 °C by 1H NMR spectroscopy and the Benesi-Hildebrand method as (100 ± 20) L mol−1. The adsorption kinetics of bisphenol A (BPA) on HPMC-βCD hydrogels fitted well to the pseudo-second order model, yielding rate constant of 0.00879 g mg−1 min−1, and to the intraparticle diffusion model. The latter revealed a two stage process: a fast one with diffusion rate of 1.185 mg g−1 min−0.5 related to the diffusion of BPA from bulk to hydrogel external area and a slower one related to the mass transport into the hydrogel internal area. The adsorption isotherms fitted well the Freundlich and Dubinin-Radushkevitch (D-R) models, the latter yielded maximum adsorption of 14.6 mg g−1 and mean adsorption energy E of 7.9 kJ mol−1. The hydrogels could be recycled five times without losing adsorption efficiency.