A polymer gel-gated flexible transistor based on chitosan physically cross-linked films for hydrogen sulfide gas sensing

A flexible field-effect transistor with a chitosan ion gel-gate design was developed as a gas sensor, utilizing chitosan, 1,3-propanediol, and graphene to detect and eliminate hydrogen sulfide (H₂S). Adding 1,3-propanediol after the complete dissolution of chitosan in acetic acid yielded a novel, physically cross-linked chitosan conductive polymer gel. Due to the presence of −OH groups in 1,3-propanediol, gelation occurs through an increase in the degree of hydrogen bonding between the polymer chains and 1,3-propanediol, forming a rubbery network. The increase in the hydrogen bonding network, as shown in the FTIR spectra, not only enhances the mechanical strength of the polymer gel but also promotes proton conduction through proton hopping (Grotthuss mechanism), thereby enhancing electrical conductivity. The optimum conductivity of the film is depicted at a 5 % (v/v) concentration of 1,3-propanediol. The chitosan physically cross-linked films exhibited the best sensing performance at a 0.5 ppm H₂S concentration. The gas sensor sensitivity, response and recovery time of chitosan film are 3.87 %, 23 s, and 17 s, respectively. Additionally, the ion gels were successfully applied to organic thin-film transistors as highly capacitive gate dielectrics. The flexible chitosan ion gel-gated transistors with graphene have carrier mobilities as high as µ_hole = −9400 cm²V⁻¹s⁻¹. The sensitivity of this gel-gated transistor is 42.96 mV/ppm for various H₂S concentrations, ranging from 10 ppm to 0.5 ppm.