Pore structure evolution and adsorption behaviors of porous poly (vinyl alcohol) hydrogel prepared using Na2SO4 and CaCO3 as porogens

In this work, porous poly (vinyl alcohol) (PVA) hydrogels with different pore sizes were fabricated using inorganic non-metallic porogens by an environmentally friendly method, providing a potential solution for the field of wastewater treatment. PVA hydrogels have gained much attention in the field of wastewater treatment due to their excellent adsorption performance and porous network structure. However, the employment of inorganic non-metallic salts as porogens for PVA hydrogels has received limited attention so far. In this study, porous PVA hydrogels were prepared by freeze-thawing and freeze-drying with sodium sulfate (Na 2 SO 4 ) and calcium carbonate (CaCO 3 ) as porogens. PVA-Na exhibited denser network structure with the concentration of Na 2 SO 4 solution increased, and the tensile stress was enhanced by about 45 times. Meanwhile, the tensile stress of PVA-Ca was improved significantly from 0.06 to 1.67 MPa, and the network structure became looser after adding CaCO 3 . Moreover, a comprehensive investigation was conducted on the adsorption performance of porous PVA hydrogel for Congo red (CR). Finally, five adsorption models were fitted to investigate the adsorption mechanism of porous PVA hydrogels, in which the maximum adsorption capacity of CR by PVA-Na-0.5 was predicted to be 215 mg/g by the Langmuir isothermal model fitting. Highlights The structure of PVA hydrogels was adjusted by Na 2 SO 4 and CaCO 3 , respectively. The tensile stress of PVA-Na with dense network structure increased 45 times. Compared to PVA-FD, swelling equilibrium time of PVA-Na reduced from 24 to 6 h. Equilibrium swelling rate of PVA-Ca declined by half in comparison to PVA-FD. Langmuir isothermal model predicted q max of 215 mg/g for CR by PVA-Na-0.5.