Ultra-exclusive Selectivity for the Detection of Formaldehyde in Laser-induced ZnO Mesh Sensor with Few-nanometer Pores

Abstract

Formaldehyde is classified as a Group 1 biological agent that is "carcinogenic to humans." A gas sensor can be developed as a chemiresistive device with rapid response, outstanding sensitivity, reproducibility, and excellent selectivity for the detection of formaldehyde, providing a crucial pathway to protect human health in formaldehyde-rich environments. To this end, we designed a formaldehyde gas sensor that demonstrates ultra-exclusive selectivity, including a superior sensing response of 6682.8 at 10 ppm formaldehyde and 1687.6 for the optimized sensor with reasonable response (2.96 s) and recovery (46.2 s) times, based on a ZnO mesh structure. The sensor was fabricated using a rapid 1-minute CO₂ laser process, forming a ZnO precursor into a mesh structure with few nanometer-sized pores between ZnO crystal domains. The small kinetic size (2.43 Å) and large dipole moment (2.30 D) of formaldehyde allow for effective adsorption and good permeability within these pores, providing exceptional selectivity. Other gases such as acetone, styrene, and CO₂ showed significantly lower responses, confirming the sensor’s selectivity for formaldehyde. Oxygen vacancies, which increased with laser power (up to 38% at 4 W), played a crucial role in enhancing the interaction between formaldehyde and the ZnO surface, contributing to the sensor's high sensitivity and efficiency. Additionally, the sensor exhibited excellent long-term stability, with only a 15% reduction in response over 7 weeks of continuous operation at 400°C. The sensor also showed a linear correlation (R² = 0.999) across a range of formaldehyde concentrations (0.01 ppm to 10 ppm), with a low detection limit (LOD) of ~0.1 ppm, making it suitable for detecting even trace amounts of formaldehyde. This ultra-exclusive formaldehyde gas sensor design offers a promising strategy for air quality monitoring in both indoor and outdoor environments, with significant potential for public health protection.