Chitosan/Sn@C Composite Nanofiber Coatings for QCM-based Humidity Sensing

Sn nanoparticle–carbonized (Sn@C) nanofibers via electrospinning + calcination • Sn@C + chitosan (CS) ⇒ CS/Sn@C layers by spin coating • Layer tested for humidity sensing by quartz crystal microbalance (QCM) • High repeatability and reversibility; low humidity hysteresis • Combining structural integrity (Sn@C) + water adsorption sites (CS) SnCl₂·2H₂O was introduced into polyacrylonitrile (PAN) nanofibers through a simple electrospinning method, and composite Sn nanoparticle–carbonized (Sn@C) nanofibers were prepared by two-stage calcination. After dispersing different amounts of composite nanofibers in a 2.5   wt% chitosan (CS) solution via ultrasonication, a series of CS/Sn@C composite humidity-sensitive layers were spin-coated on quartz crystal microbalance (QCM) sensor surfaces. The morphology, structure, and composition of Sn@C nanofibers were analyzed by SEM, TEM, XPS, and BET. The diameter of Sn@C nanofibers was decreased from 180   nm to 95   nm upon decreasing the PAN content from 90% to 60%. The presence of metallic Sn nanoparticles, formed on the surface of Sn@C nanofibers, resulted in an increase in specific surface area from 5.1   m²·g⁻¹ to 106.5   m²·g⁻¹. Using an electrospinning solution with PAN:SnCl₂·2H₂O (8:2 w/w) and a Sn@C dispersion (0.05   mg/mL) in 2.5   wt% CS solution, a QCM sensor with a fitting correlation coefficient of 0.9998 was fabricated. The sensor parameters were optimized through QCM testing under varying conditions. The sensor demonstrated fast response/recovery times: <1.2   s (response)/50   s (recovery) in 11–33% RH and 67   s/37   s in 11–98% RH. Additionally, the CS/Sn@C-modified QCM sensor exhibited high repeatability, reversibility, and low humidity hysteresis. Download: Download high-res image (169KB) Download: Download full-size image