Colorimetric cotton sensors fabricated by ultraviolet photografting for acidic gas detection: optimization and characterization

Detection of acidic gases such as HCl in industrial settings is essential for safeguarding the environment and human health. In particular, halochromic-dye-based colorimetric textile sensors—which are cost-effective, flexible systems that can enable visual detection—show promise for HCl gas detection. However, their limited dyeability and wash fastness on cotton fibers restrict their practical utility. Nevertheless, these issues can potentially be resolved through UV-induced photografting, which can help generate covalent bonds between the halochromic dye and cotton fibers. Therefore, in the present study, two graftable rhodamine dyes were synthesized by incorporating radical-sensitive vinyl or styrene groups into a pH-sensitive rhodamine derivative. Subsequently, textile sensors were fabricated by UV-induced photografting, which was optimized by probing the effects of the UV energy, comonomer, pH, photoinitiator, co-initiator, and dye concentration on sensing efficiency. The HCl gas detection performance, durability, and reusability of the sensors were investigated thereafter. The sensors exhibited high detection rates, distinct color changes upon HCl exposure, even at low concentrations (< 100 ppm), as well as remarkable washability and reusability. Furthermore, the sensors were integrated with an RGB sensor to accurately detect color changes under low-light conditions. Overall, this study demonstrates the feasibility of adopting UV-induced photografting to prepare textile sensors that can improve safety in industrial settings.