Smart Textile: Electrohydrodynamic Jet Printing of Ionic Liquid-Functionalized Cu₃(HHTP)₂ Metal–Organic Frameworks for Gas-Sensing Applications

Abstract

This study presents the development and characterization of a smart textile gas sensor based on the integration of ionic liquid (IL)-functionalized Cu₃(HHTP)₂ metal-organic frameworks (MOFs), using electrohydrodynamic jet (e-jet) printing. The sensor was designed for the detection of nitric oxide (NO) gas, a critical target in various environmental and safety applications. Cu₃(HHTP)₂ MOFs were synthesized and subsequently functionalized with 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM⁺ Otf^-) ionic liquid to enhance their chemiresistive performance toward NO gas. The functionalized MOF was then e-jet printed onto electrospun polylactic acid (PLA) substrates to fabricate smart textile sensors. The IL-functionalized Cu₃(HHTP)₂ sensors demonstrated a 582× increase in conductivity compared to previously reported MOF-based sensors. Additionally, IL functionalization enhanced sensor sensitivity, with a response increasing from less than 5% in pristine MOF@PLA sensors to approximately 570% at 100 ppm of NO gas. Performance was systematically evaluated across NO concentrations ranging from 5 to 300 ppm, achieving a theoretical limit of detection of 3.7 ppm. The sensors exhibited partial reversibility and retained functionality over extended periods and under humid conditions. Comprehensive analyses using SEM, EDX, FTIR, and XRD were performed to assess the crystallinity of MOF deposits and elucidate the sensing mechanism. These findings highlight the potential of e-jet printing of IL-functionalized MOFs for the development of advanced, flexible gas sensors with applications in both civilian and military settings and implications for personal protective wearable technologies.