Enhanced sensitivity of fluorescence-based optical CO₂ sensor by using HPTS/Chitosan/ZnO/GO/polymethyl methacrylate composites

This study was deeply focused on developing a novel gaseous CO₂ sensor based on the emission-based response of HPTS in polymethyl methacrylate/chitosan/ZnO/GO composites. HPTS is a well-known fluorescent dye that possesses a decreasing luminescence intensity at 520 nm to CO₂. The ion-pair form of the HPTS was used in different composites either in thin film and fiber form. Chitosan has received important attention due to its structural characteristics such as being biocompatible, biodegradable, cost-effective, non-toxic polymer, and its suitability for gas storage. It is a biopolymer having amine-rich groups which is appropriate especially for CO₂ adsorption purposes. Thus, we have employed chitosan and/or zinc oxide/graphene oxide for the first time either in solid or dissolved forms in the concerned polymethyl methacrylate based matrices for enhancing CO₂ sensitivity. The best results were obtained for the optimum concentration of chitosan containing thin film sensor slides which exhibited 75 times higher sensitivity than the ones which do not contain any chitosan. The addition of ZnO/GO composite revealed a 14% enhancement in the sensor response and it facilitated the fiber sensor formation by electrospinning process due to its increasing effect of electrical conductivity.The HPTS/Chitosan/ZnO/GO/polymethyl methacrylate sensing composites were stable for long periods that no significant changes in the fluorescence intensity and sensor characteristics were observed over 20 months.