Green-synthesized Co-doped ZnO/cellulose hydrogel nanocomposites for high-efficiency photocatalytic degradation of methylene blue

Abstract

The development of sustainable, highly efficient photocatalysts for wastewater treatment remains a significant scientific and technical challenge. Here, we present a cobalt-doped zinc oxide/cellulose hydrogel nanocomposite (Co-ZnO HNC), produced from sawdust cellulose, which serves as a multifunctional and sustainable photocatalyst for the degradation of methylene blue. Cobalt-doped zinc oxide nanoparticles were uniformly integrated into a cellulose hydrogel matrix via radical polymerization, resulting in a hierarchically structured composite with improved surface functionality and light absorption efficiency. Morphological and structural analyses confirmed the formation of crystalline, cobalt-doped ZnO (Co-ZnO) with an average crystal size of approximately 6.2 nm, homogeneously distributed within the hydrogel matrix. Optical analyses revealed a significant redshift, attributable to bandgap modulation and enhanced charge separation. The photocatalytic activity was thoroughly investigated under UV light by varying pH, catalyst quantity, and dye concentration. Under optimal conditions, the Co-ZnOHNC achieved a metal oxide degradation of 97.9% after 120 min, surpassing both pure ZnO and undoped hydrogel alternatives. This improved performance is attributed to the synergistic interactions between the Co-induced defect states and the porous structure of the hydrogel. These interactions facilitate charge transport, inhibit electron-hole recombination, and enable mass transport. The study illustrates a sustainable approach to converting lignocellulose waste into high-performance photocatalysts and highlights the significant potential of cellulose-based metal oxide hydrogel composites for advanced wastewater treatment processes.