TiO₂ Nanohelices Decorated with Homogeneous Au-Core Pd-Shell Nanocatalysts for Selective Toluene Gas Detection

The precise decoration of bimetallic nanocrystals (NCs) with uniform size and homogeneous composition on metal oxide (MOX) surfaces is crucial for developing highly sensitive and selective MOX-based gas sensors. In this study, MOX-based gas sensors are present decorated with homogeneous Au-Pd bimetallic (Au@Pd) NCs synthesized via seed-mediated sequential reduction of Au and Pd on an array of TiO₂ nanohelices (NHs) matrix. Due to the uniform composition, size, and dispersion of the bimetallic NCs, the sensor exhibits outstanding toluene (C₇H₈) sensing performance. The optimized Au@Pd NC composition (Au:Pd = 55:45) facilitates chemisorbed oxygen spillover and electronic sensitization, achieving an exceptionally high response (R_a/R_g) of ≈130 000 and rapid response/recovery (69 s/4 s) toward 100 ppm of C₇H₈ at 200 °C. Furthermore, the homogeneity of Au@Pd NCs enhances selectivity by providing controlled active sites, yielding a 1008-fold higher response to toluene compared to acetone. Density functional theory calculations and mechanistic experiments reveal that Au@Pd NCs generate toluene-selective catalytic sites that enable complete oxidation. The findings demonstrate that homogeneous core-shell bimetallic NCs can be uniformly integrated on a highly porous MOXs-based gas sensing matrix, enabling exceptional selectivity and sensitivity for advanced gas sensor applications.