Synthesis and characterization of poly(vinyl alcohol-g-acrylamide)/SiO2@ZnO photocatalytic hydrogel composite for removal and degradation of methylene blue

Poly(vinyl alcohol)-g-polyacrylamide (PVA-g-PAM) hydrogel was synthesized using free radical polymerization with an n,n'-methylenebis acrylamide crosslinker to create an interconnected porous structure. ZnO nanoparticles were functionalized by a sol-gel process with a thin layer of SiO2, introducing silanol groups to form silane-bridges on and within the PVA-g-PAM hydrogel. Scanning electron microscopy and thermogravimetric analysis confirmed that 3 wt% of SiO2@ZnO nanoparticles were directly attached to the surface of the hydrogel. This hydrogel composite exhibited water absorbency of similar to 8000% and 96% removal of methylene blue (MB) within 24 h. The adsorption studies of the PVA-g-PAM/SiO2@ZnO hydrogel composite were well fitted to the Langmuir isotherm and pseudo-second-order model with a maximum adsorption capacity of 757 mg/g. Upon exposure to UV radiation, the hydrogel composite could decompose adsorbed MB at the rate of 0.1019 h(-)(1). The SiO2@ZnO surface-coating also improved degradation of the polymers. This hydrogel composite would advance a closed loop dye removal and wastewater treatment system with easy sample handling and separation. It combined the adsorption capacity of a superadsorbent and the dye degradation rate of an effective photocatalyst. This material is a promising low-cost development that could eliminate secondary pollution from wastewater treatment processes.