SnO2 encapsulated in alginate matrix: Evaluation and optimization of bioinspired nanoadsorbents for azo dye removal

Synthesized SnO2 NPs demonstrate potential capacity to adsorb toxic azo dye. Powder X-ray diffraction and SEM imaging confirmed the rutile phase and spherical morphology of SnO2 NPs. Average particle size has been confirmed to be approximately 3 nm through TEM analysis. Adsorption capacity is attributed to the high surface and presence of oxygen vacancy confirmed through BET and XPS, respectively. To mitigate the leaching of NPs in treated water, the encapsulation of NPs in sodium alginate (SA) has been proposed as an environmentally friendly, biocompatible, and economic solution. This study specifically focuses on investigating the parameters for the encapsulation of NPs within a sodium alginate matrix using CaCl2 as cross-linker, including effect of physical shape of encapsulation, effect of sodium alginate and CaCl2 concentration on the encapsulation efficiency and overall adsorption efficiency. Experimental results indicated that the physical form of encapsulation, such as spherical, wire-like, or irregular shape maintained consistent adsorption efficiency, which indicates its versatility. For effective encapsulation of NPs and adsorption, SA and CaCl2 concentration are suggested to be within the range of 0.2-0.3 g and > 0.5 M, respectively..