Tannin as a porogenic agent in the synthesis of silica by an acid-catalyzed sol-gel process

This study investigates the use of Acacia mearnsii tannin as a natural porogenic agent in the sol-gel synthesis of silica xerogels. Silica samples were synthesized under acid-catalyzed conditions with varying tannin concentrations (0–5000 mg), and characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), small-angle X-ray scattering (SAXS), N 2 sorption isotherms, and fractal dimension analysis. Results revealed that tannin significantly influenced the morphology, porosity, and surface structure of the xerogels, promoting the formation of mesopores at higher concentrations—without the use of conventional surfactants. The surface roughness and complexity of the pore network were quantitatively assessed through the FHH model, enabling determination of fractal dimensions in both micro- and mesopore regimes. The optimized mesoporous material was further tested for methylene blue (MB) adsorption, achieving >81% removal efficiency at 800 mg/L, with kinetic behavior well-described by the Elovich model, indicating chemisorption. These findings highlight a sustainable and efficient strategy to engineer mesoporous silica with tailored structural features and high adsorption performance, offering promising applications in water treatment and beyond. • Acid-catalyzed sol-gel forms mesoporous silica without surfactants; • Acacia tannin templates 4 nm pores in silica structure; • Tannin can reduce silica shrinkage during gelation.