Efficient bis(indoyl)methanes synthesis enabled by SnO2/SiO2 nanocomposite

This study focuses on the synthesis of SnO₂/SiO₂ nanocomposite materials using sol-gel method and investigates their role in the synthesis of bis(indoyl)methanes via the Friedel–Craft alkylation route. The results, based on TON and TOF, show that 15 wt % SnO₂/SiO₂ exhibits high production efficiency and greater stability, with yields reaching 91–93% within 80–93 min. The prepared catalysts were characterized using various analytical techniques. The XRD revealed a crystalline size of 25.05 nm. The TEM analysis indicated a reduced particle size of about 25–30 nm. The SEM reflected the porous nature of the material and EDS showed the constituent elements Sn, O and Si with 3.65, 54.93, and 41.44 atomic %, respectively. FT-IR identified the composite framework with bands at 3408, 1620, 1093, 806 and 631 cm⁻¹. The NH₃-TPD indicated the presence of both Lewis acidic and Bronsted acidic sites in the composite materials. The BET method revealed a specific surface area and average pore diameter of 331.5814 m²/g. The developed method offers several advantages, such as a simple workup procedure, high yield, nontoxicity, cleanliness, and the ability to recycle and reuse the catalytic materials three times without loss in catalytic activity. These findings demonstrate the potential of SnO₂/SiO₂ nanocomposites as efficient and environmentally friendly catalysts for the synthesizing bis(indoyl)methane derivatives.