Surface-Enhanced Polyaniline/SiO2 Nanocomposite as a Robust Catalyst for One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-one Derivatives

A polyaniline/SiO2 nanocomposite catalyst was synthesized using a sol-gel and oxidative polymerization method. The material was analyzed using XRD, TEM, SEM–EDS, TG–DTA, FT-IR spectroscopy, BET surface area analysis, BJH pore size distribution and NH3-TPD. TEM images showed polyaniline nanofibers (21–23 nm in diameter, up to 500 nm in length) on spherical SiO2 particles (40–52 nm). XRD and SEM confirmed the expected composite structure. The BET surface area of the 10 wt % polyaniline/SiO2 catalyst was 75.34 m2/g, with an average pore diameter of 10.88 nm. Thermal analysis showed improved stability compared to pure polyaniline. NH3-TPD analysis revealed the presence of acidic sites with varying strengths. The catalytic performance was demonstrated in the Biginelli condensation reaction, producing 3,4-dihydropyrimidin-2(1H)-one derivatives with yields of 87–95% under reflux in ethanol within 2–2.5 h. The catalyst exhibited high activity, selectivity and recyclability, maintaining its performance over multiple cycles. This work highlights the potential of polyaniline/SiO2 nanocomposites as thermally stable, recyclable and efficient heterogeneous catalysts for sustainable organic synthesis.