Improvement of the CO₂ Sensitivity: HPTS-Based Sensors along with Zn@SnO₂ and Sn@ZnO Additives

Fluorescent pH-sensitive indicator dye, 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS), has become known as a preferred alternative for continuous and accurate monitoring of dissolved and/or gaseous CO₂ in chemistry, medical, and biochemical research. The objective of this work is to enhance the HPTS dye's CO₂ sensitivity in the presence of Zn@SnO₂ and Sn@ZnO additive particles. Sol-gel synthesized metal oxide semiconductors (MOSs) were characterized using XRD, XPS, and SEM. The fluorophore dye and the MOS additives were embedded in the ethyl cellulose (EC) polymeric matrix to prepare the sensing thin films. The steady-state and decay kinetic measurements of the HPTS-based composites were obtained by PL spectroscopy for the concentration ranges of 0-100% p[CO₂]. As expected, the addition of MOSs improves the sensor characteristics, specifically its CO₂ sensing ability, linear response range, and relative signal change compared to the free form of HPTS. The CO₂ sensitivities of the HPTS-based thin films were found at 17.6, 23.2, and 40.9 for the undoped, Zn@SnO_2,-doped, and Sn@ZnO-doped forms of the HPTS, respectively. Additionally, the response and recovery times of the HPTS-based sensor agent with Sn@ZnO were measured as 10 and 460 s, respectively. The obtained results demonstrate that materials composed of HPTS with MOSs are potential candidates for CO₂ sensors.