Carboxymethyl cellulose/poly(acrylic acid) interpenetrating polymer network hydrogels as multifunctional adsorbents

Interpenetrating polymer network (IPN) hydrogels were prepared by mixing carboxymethyl cellulose (CMC) solution and crosslinked poly(acrylic acid) (cPAA) single IPN hydrogel at mass ratios 100:0, 25:75, 50:50, 75:25 and 0:100 and subsequent crosslinking of CMC chains with citric acid, aimed towards the creation of full IPN hydrogels. The resulting CMC:cPAA hydrogels were freeze-dried for the determination of density, swelling degree, compressive modulus and thermal behavior. Morphological and structural parameters were determined by means of scanning electron microscopy, Fourier transform infrared spectroscopy in the attenuated total reflectance mode (FTIR-ATR) and X-ray microto-mography (CT) analyses. The efficiency of CMC: cPAA hydrogels as adsorbents for methylene blue (MB) dye at pH 7 and Cu2+ ions at pH 4.5 was systematically investigated at (24 +/- 1) degrees C and evaluated with Langmuir, Freundlich and Dubinin-Radushkevitch adsorption models and kinetic equations. The CMC: cPAA 50: 50 hydrogels were particularly interesting because they presented the highest compression modulus ( 141 +/- 3 kPa), swelling degree of 58 +/- 2 g(water)/g and maximum adsorption capacity (q(max)) for MB dye and Cu2+ ions as 613 mg g(-1) and 250 mg g(-1), respectively. The adsorption kinetics of MB and Cu2+ ions followed the pseudo-second order equation. Fitting with the intraparticle diffusion model showed that in both cases, the adsorbate molecules first diffuse rapidly from the medium to the adsorbent surface, and then in a second slower stage, they diffuse into the network macropores. The hydrogels could be recycled five times without losing efficiency.