Orientation control (horizontal and vertical) of TiO2 single-crystalline nanowire arrays for high-performance gas sensing: a surface supersaturation-driven approach

Abstract

In the field of advanced functional nanoarrays, the development of one-dimensional (1D) single-crystalline nanoarrays (SCNAs) with highly orientated alignment is of paramount significance owing to their essential roles in batteries, catalysis, and sensing applications. However, tuning SCNAs to ensure a uniform orientation is extremely challenging. Herein, a surface supersaturation-driven hydrothermal growth approach that could successfully modulate the growth directions of TiO₂ nanowires is proposed. By precisely tuning the concentrations of the crystal seed solution, a series of highly aligned TiO₂ SCNAs was obtained, which was grown horizontally (TiO2-H-NAs) or vertically (TiO2-V-NAs) on sapphire. Compared with TiO₂-V-NAs, TiO₂-H-NAs displayed better sensing performance towards ethanol at room temperature, which represents one of the highest responses among various other material categories, including metal oxide semiconductors, metal–organic frameworks, 2D materials and polymers. Demonstrating their practical utility, TiO₂-H-NAs showcased an obvious response value (288%) in an exhalation breath testing after wine consumption, underscoring their potential in real-time monitoring applications. This study offers a promising pathway to overcome the synthetic challenges and unlock the full potential of 1D nanowires for various chemical applications.