Eco-friendly QCM sensor based on biochar-functionalized nanofibers for rapid and selective detection of hydrogen...

Hydrogen chloride (HCl) is a colourless, highly corrosive gas exhibiting high solubility in water to form hydrochloric acid. It is widely used in industrial and research settings. Exposure to HCl gas can result in adverse health effects. Several sensing technologies to monitor HCl exposure have been developed including optochemical sensors, colorimetric detection and surface acoustic wave (SAW) devices. This method offers high sensitivity but are limited by complexity, high cost, or lack of portability. Owing to their compact form, real-time detection, and high sensitivity to mass changes at the nanogram scale, Quartz Crystal Microbalance (QCM) sensors offer a promising alternative.

This study presents the development of an eco-friendly HCl gas sensor based on a QCM system functionalized with polyvinyl acetate (PVAc) nanofibers and biochar derived from soybean dreg (okara). The sensor leverages the abundant functional groups in biochar, including amine, hydroxyl, and carbonyl groups, which enhances the adsorption of HCl molecules and improves the sensor's sensitivity. The QCM/PVAc NFs/ABAB sensor demonstrates a linear response to HCl concentrations in the range of 10-100 ppm, with a detection limit (LoD) of 2.75 ppm and a quantification limit (LoQ) of 8.34 ppm. It exhibits rapid response times (12 s) and high selectivity for HCl over other common laboratory acids. Stability tests conducted over a three-month period revealed that the sensor maintained consistent performance for two months. The adsorption of HCl onto the sensor was most accurately represented by the Freundlich and Harkin-Jura isotherm models.

These results suggested that the proposed sensor offered an environmentally sustainable and cost-effective solution for real-time HCl gas monitoring in industrial and laboratory environments, with potential for further optimization to improve long-term stability.