Facile physical entrapment of halochromic dye via UV-photografting for the fabrication of colorimetric cotton sensors to detect toxic ammonia gas

Textile-based halochromic gas sensors are useful for detecting volatile organic compounds (VOCs) such as ammonia, because they undergo changes that are distinguishable to the naked eye. Herein, we report the UV photografting system we developed for the fabrication of halochromic cotton sensors with reduced amounts of salt, resources, and effluents. First, 4-hydroxycoumarin-based dye (HD) was synthesized as a halochromic indicator, where after the synthesized dye, monomer, and photoinitiators were introduced to a dye bath to fabricate the UV photografting system. This system was produced by grafting monomers on a fiber surface under UV light irradiation to formulate a polymer network that entraps dye molecules. A series of different monomer concentrations and photoinitiators were introduced to the dye bath. Subsequently, the dyeability and gas detection performance of the fabricated cotton sensors were evaluated. In addition, fastness and reusability tests were performed to ensure the fabricated cotton sensors were durable and sustainable. The dyeability of the fabricated cotton sensors increased as the monomer concentration increased and the color change upon exposure to ammonia gas followed the same tendency. The fabricated cotton sensor prepared with the highest monomer concentration underwent a distinctive color change upon exposure to ammonia gas for 300 s (ΔE > 15). Furthermore, the cotton sensor exhibited remarkable durability to washing (wash fastness level: 5, ΔE maintenance rate after washing: ∼85 %) and rubbing (rubbing fastness level: 4/5, ΔE maintenance rate after rubbing: ∼95 %). Reusability testing of the fabricated cotton sensors showed that the halochromic property was retained after repeated washing (10 cycles). The results confirmed that the UV-induced photografting performance had been optimized and suggested that UV-induced photografting offered an eco-friendly alternative to conventional dyeing for the fabrication of halochromic textile sensors.