Highly compressible and macro-porous hydrogels via the synergy of cryogelation and double-network for efficient removal of Cr(VI).

Mechanically robust and macro-porous hydrogels are urgently required for the dynamic removal of heavy metals in wastewater purification field. Herein, a novel microfibrillated cellulose/polyethyleneimine hydrogel (MFC/PEI-CD) with high compressibility and macro-porous structures was fabricated via the synergy of cryogelation and double-network for Cr(VI) adsorption from wastewater. MFCs were pre-cross-linked by bis(vinyl sulfonyl)methane (BVSM) and then formed double-network hydrogels with PEIs and glutaraldehyde below freezing. The SEM showed that the MFC/PEI-CD possessed interconnected macropores with an average pore diameter of 52 μm. Mechanical tests indicated a high compressive stress of 116.4 kPa at 80 % strain, which was 4 times higher than the corresponding MFC/PEI with a single-network. The Cr(VI) adsorption performance of MFC/PEI-CDs was systematically investigated under different parameters. Kinetic studies indicated that the adsorption process was well described by the pseudo-second-order model. Isothermal adsorption behaviors accorded well with Langmuir model with the maximum adsorption capacity of 545.1 mg/g, which was superior to most adsorption materials. More importantly, the MFC/PEI-CD was applied to dynamically adsorb Cr(VI) with the treatment volume of 2070 mL/g. Therefore, this work demonstrates that the synergy of cryogelation and double-network is a novel method for preparing macro-porous and robust materials with promising heavy metal removal from wastewater.