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

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Sensing

Background:

• Precise decoration of bimetallic nanocrystals (NCs) with uniform size and composition on metal oxide (MOX) surfaces is vital for high-performance gas sensors.
• Metal oxide semiconductor (MOS) gas sensors require enhanced sensitivity and selectivity for detecting volatile organic compounds (VOCs).

Purpose of the Study:

• To synthesize homogeneous gold-palladium (Au@Pd) bimetallic NCs on TiO2 nanohelices (NHs) for advanced MOX gas sensors.
• To investigate the impact of uniform Au@Pd NC decoration on toluene (C7H8) sensing performance, selectivity, and mechanism.

Main Methods:

• Seed-mediated sequential reduction of Au and Pd on TiO2 NHs to form homogeneous Au@Pd bimetallic NCs.
• Fabrication and characterization of MOX-based gas sensors using the decorated TiO2 NHs matrix.
• Gas sensing performance evaluation (response, recovery, selectivity) towards toluene and other VOCs at various temperatures.
• Density functional theory (DFT) calculations and mechanistic experiments to elucidate the sensing mechanism.

Main Results:

• The optimized Au@Pd NCs (Au:Pd = 55:45) on TiO2 NHs exhibited an outstanding response (Ra/Rg ≈ 130,000) to 100 ppm toluene at 200 °C.
• Achieved rapid response and recovery times of 69 s and 4 s, respectively, for toluene detection.
• Demonstrated superior selectivity, with a 1008-fold higher response to toluene compared to acetone.
• DFT calculations and experiments confirmed the generation of toluene-selective catalytic sites on Au@Pd NCs facilitating complete oxidation.

Conclusions:

• Homogeneous Au@Pd bimetallic NCs uniformly integrated on a porous TiO2 NHs matrix significantly enhance gas sensor sensitivity and selectivity.
• The optimized Au@Pd NCs facilitate oxygen spillover and electronic sensitization, leading to exceptional toluene sensing performance.
• This approach offers a promising pathway for developing highly selective and sensitive MOX-based gas sensors for advanced applications.