Controllable synthesis of ortho-hexagonal ZnAl-LDHs nanosheets for high-performance room-temperature ethanol gas sensing

Layered double hydroxides (LDHs) have attracted considerable attention in gas sensing applications due to their highly tunable chemical composition and unique two-dimensional layered architecture. In this study, a series of ZnAl-LDHs with varying Zn/Al molar ratios were synthesized via a facile hydrothermal method, and their ethanol sensing performance at room temperature was systematically evaluated. The influence of composition on the structural, morphological, and electronic properties of the materials was thoroughly investigated using a suite of characterization techniques, including XRD, FTIR, SEM, TEM, BET, XPS, PL, and EPR. Among the synthesized samples, the Zn/Al = 2 : 1 composition (denoted as ZA2.1) exhibited the highest sensing performance, achieving a 60% response ((R_g - R_a)/R_g × 100%) to 100 ppm ethanol at room temperature, with a rapid response time of 33 s and a recovery time of 4 s. This sample also demonstrated excellent selectivity and long-term stability. The enhanced sensing behavior is attributed to the synergistic effect between the optimized oxygen vacancy concentration (controlled by the Zn/Al molar ratio) and the efficient gas diffusion promoted by the orthorhombic hexagonal nanosheet morphology. The defect and nanostructure of ZnAl-LDHs can be regulated through composition engineering, providing a promising strategy for the development of high-performance room-temperature gas sensors.