SnO2 Encapsulated in Alginate Matrix: Evaluation and Optimization of Bioinspired Nanoadsorbents for Azo Dye Removal

Synthesized SnO₂ nanoparticles (NPs) demonstrate potential capacity to adsorb toxic azo Congo red dye. The formation of rutile phase SnO₂ NPs was confirmed using Powder X-ray diffraction and spherical morphology was corroborated through SEM imaging. TEM analysis confirms average particle size of SnO₂ NPs is nearly 3 nm. High azo dye removal efficiency is attributed to large surface area and presence of oxygen vacancies which were substantiated through BET and XPS analysis, respectively. To mitigate the leaching of NPs in treated water, NPs are encapsulated in sodium alginate (SA) matrix, which is 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. This work investigates the effect of physical shape of encapsulation, effect of SA and cross-linker (CaCl₂) concentration on the feasibility of NP encapsulation 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.