Eco-friendly nanocomposite SA/Al2O3/Ag2Mo2O7 microbeads for fast and sustainable photo-induced adsorption of methylene blue dye from industrial wastewater

Abstract

Abstract The increasing release of hazardous synthetic dye waste poses a serious threat to the environmental and human health. In this study, a novel ternary nanocomposite was designed as an innovative photo-responsive adsorbent by embedding poly silver molybdate (Ag 2 Mo 2 O 7 ) and alumina nanoparticles (Al 2 O 3 ) into a sodium alginate (SA) polymeric matrix. Designed to efficiently eliminate methylene blue (MB) dye from contaminated water and overcome the separation bottleneck of traditional powdered materials. The SA/Al 2 O 3 /Ag 2 Mo 2 O 7 microbeads were synthesized via a facile and eco-friendly ionotropic gelation method. Structural and morphological characterization of the prepared nanocomposite was authenticated via X-ray diffraction (XRD) and transmission electron microscopy (TEM), confirmed the successful formation of the ternary nanocomposite with particle size ranging from 10 to 12 nm. The incorporation of Ag 2 Mo 2 O 7 and Al 2 O 3 within the alginate polymer matrix significantly enhanced the photo-induced adsorption performance compared to bulk sodium alginate (SA) microbeads. Notably, 1.2 g/L of the microbeads achieved a remarkable 91.78% removal efficiency for methylene blue (MB) dye (77.5 mg/g) within just 40 min under visible light irradiation. In comparison, the nanocomposite demonstrates a significantly higher elimination compared to individual Ag 2 Mo 2 O 7 and Al 2 O 3 , which exhibited only 60.69% and 56.89%, respectively. Kinetic studies revealed that the removal process obeyed the pseudo-second-order model, while the equilibrium data closely followed the Freundlich isotherm. Thermodynamic parameters confirmed that the photo-induced adsorption process is spontaneous and endothermic. Furthermore, the reusability of the SA/Al 2 O 3 /Ag 2 Mo 2 O 7 microbeads was tested through five adsorption–desorption cycles, consistently removing more than 73.89% of MB dye. These results demonstrate the practical application of this photo-responsive nanocomposite as an easily recoverable and efficient solution for eliminating toxic cationic dyes from industrial wastewater.