Development of multifunctional hydrogel composite based on poly(vinyl alcohol-g-acrylamide) for removal and photocatalytic degradation of organic dyes

Abstract

Polyacrylamide (PAM) was grafted onto biodegradable polymer: poly(vinyl alcohol) (PVA). The grafted polymer was simultaneously crosslinked with N,N′-methylene-bis-acrylamide to yield a 3-dimensional network structure. PVA-g-PAM hydrogel containing 50 wt% of PAM showed 6400% water absorbency and adsorbed both cationic and anionic dyes. The adsorption data were consistent with the pseudo-second-order model and the Freundlich isotherm, indicating multilayer adsorption controlled by chemisorption. The maximum adsorption capacities for methylene blue, crystal violet, and congo red were 703 mg/g, 863 mg/g, and 174 mg/g, respectively. ZnO photocatalyst particles were coated with SiO2 and the surface of the hydrogel was functionalized with the synthesized particles. The content of particles in the composite increased from 18% to 24% when the thickness of the SiO2 layer was increased. Under UV irradiation for 16 h, up to 90% of adsorbed dye was degraded. Compared with TiO2-hydrogel composites, the composite with ZnO particles showed higher degradation percentage and faster rate of degradation. Dye removal efficiency and photocatalytic degradation persisted for 5 cycles of use. The composite showed antibacterial activities against S. aureus and E. coli and underwent biodegradation in soil. This work produced a photocatalytic biodegradable super-adsorbent multifunctional material for wastewater treatment that did not produce secondary toxic waste.