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<p>This work reports a dual-mode gas sensor based on vertically aligned TiO<sub>2</sub> nanotube arrays fabricated by electrochemical anodization in an HF-based electrolyte and integrated into a planar Ag/TiO<sub>2</sub>/Ti metal–insulator–metal architecture. After annealing at 450&#xa0;°C, the nanotubes crystallized in the anatase phase with uniform morphology, an inner diameter of 70–110&#xa0;nm, a wall thicknesses of 15–20&#xa0;nm, and abundant oxygen-vacancy defects, as confirmed by XRD and SEM analyses.The sensor simultaneously operates in resistive and capacitive modes during exposure to methanol, ethanol, 2-propanol, and acetone vapors in the 100–400 ppm range at room temperature, 100&#xa0;°C, and 200&#xa0;°C. Resistance decreases originate from redox reactions between VOC molecules and surface oxygen species, whereas capacitance increases result from dielectric polarization induced by polar molecule infiltration into the nanotube cavities. An Adsorption Dominance Factor (ADF = S<sub>R</sub>/S<sub>C</sub>) is developed to differentiate across adsorption mechanisms, categorizing them into chemisorption-dominated, physisorption-dominated, and mixed regimes. The temperature-dependent evolution of ADF indicates a transition from dielectric-controlled physisorption under ambient settings to charge-transfer-dominated chemisorption at higher temperatures, with ethanol exhibiting the most pronounced shift. Methanol demonstrates superior dual-mode performance, achieving resistive and capacitive responses of 76.31% and 3083.56% at 400 ppm and 200&#xa0;°C, respectively, due to its elevated polarity and effective surface oxidation. The integrated dual-mode sensing approach and ADF analysis provide mechanistic differentiation surpassing traditional single-channel sensors and establish a resilient framework for selective VOC detection.</p>

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Deciphering VOC adsorption mechanisms on TiO2 nanotubes: the adsorption dominance factor as a probe for surface interaction dynamics

  • 期刊论文

  • 发表日期：

    2026年3月26日

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  • Seddik Bouabida,
  • Liamine Kaba,
  • Sami Kahla,
  • Salima Benkara

摘要

This work reports a dual-mode gas sensor based on vertically aligned TiO2 nanotube arrays fabricated by electrochemical anodization in an HF-based electrolyte and integrated into a planar Ag/TiO2/Ti metal–insulator–metal architecture. After annealing at 450 °C, the nanotubes crystallized in the anatase phase with uniform morphology, an inner diameter of 70–110 nm, a wall thicknesses of 15–20 nm, and abundant oxygen-vacancy defects, as confirmed by XRD and SEM analyses.The sensor simultaneously operates in resistive and capacitive modes during exposure to methanol, ethanol, 2-propanol, and acetone vapors in the 100–400 ppm range at room temperature, 100 °C, and 200 °C. Resistance decreases originate from redox reactions between VOC molecules and surface oxygen species, whereas capacitance increases result from dielectric polarization induced by polar molecule infiltration into the nanotube cavities. An Adsorption Dominance Factor (ADF = SR/SC) is developed to differentiate across adsorption mechanisms, categorizing them into chemisorption-dominated, physisorption-dominated, and mixed regimes. The temperature-dependent evolution of ADF indicates a transition from dielectric-controlled physisorption under ambient settings to charge-transfer-dominated chemisorption at higher temperatures, with ethanol exhibiting the most pronounced shift. Methanol demonstrates superior dual-mode performance, achieving resistive and capacitive responses of 76.31% and 3083.56% at 400 ppm and 200 °C, respectively, due to its elevated polarity and effective surface oxidation. The integrated dual-mode sensing approach and ADF analysis provide mechanistic differentiation surpassing traditional single-channel sensors and establish a resilient framework for selective VOC detection.