Enhanced Nitrogen Dioxide Sensing via Titanium Dioxide Nanotube Decorated with Cobalt Nanoparticles

Abstract

Cobalt-modulated sensitivity of titanium dioxide nanotube arrays (TNTAs) has been systematically investigated for nitrogen dioxide (NO₂) detection. This study highlights the utilization of cobalt-decorated titanium dioxide nanotubes (Co-TNTAs) as robust and efficient sensors for NO_2, addressing the critical need for accurate detection of NO₂ gas with significant environmental and public health implications. In addition, titanium dioxide nanotubes are particularly advantageous in gas sensing due to their facile fabrication, broad availability, and remarkable surface reactivity, which collectively enhance their gas sensing performance. In this work, bare TNTAs were prepared via anodization, followed by electrochemical deposition of cobalt at varying salt concentrations to produce Co-TNTAs. Comprehensive characterization was performed to correlate material properties with sensing behavior: X-ray diffraction (XRD) confirmed phase structure and crystallite size, field emission scanning electron microscopy (FE-SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) revealed morphological and compositional features, and UV–Vis diffuse reflectance spectroscopy (DRS) provided insights into optical absorption and band gap variation. The optimized Co-TNTAs (with 0.2 M cobalt concentration) demonstrated impressive NO₂ sensitivity, reaching 87.43% at 100 ppm NO₂ and an operating temperature of 150°C. Notably, both TNTAs and Co-TNTAs also exhibited excellent response and sensitivity even at ambient temperatures, highlighting their suitability for real-world applications where low temperatures are preferred. These findings highlight the significant role of cobalt modification in enhancing gas sensing functionality and establish Co-TNTAs as promising candidates for next-generation NO₂ sensors that combine high sensitivity, low operating temperature, and structural tunability.