Effects of cellulose/salicylaldehyde thiosemicarbazone complexes on PVA based hydrogels: Portable, reusable, and high-precision luminescence sensing of Cu2+

Highlights: • Fluorescent polyvinyl alcohol-borax (PB) hydrogel sensors are prepared to detect Cu²⁺. • TEMPO-oxidized cellulose nanofibers/salicylaldehyde thiosemicarbazone is added to PB matrix. • The resultant hydrogels are thermally reversible, which reduces the deviations in the detection. • The resultant hydrogels possess good mechanical and antibacterial properties. • The hydrogels exhibit excellent fluorescence performance even after 10 reuse cycles. Novel portable, high-precision, and reusable fluorescent polyvinyl alcohol (PVA)-borax hydrogel sensors were prepared to detect Cu²⁺ in aqueous environment. A TEMPO-oxidized cellulose nanofibers/salicylaldehyde thiosemicarbazone (TOCN/ST) complex was further incorporated into the PVA-borax matrix. The in situ polymerization of TOCN/ST complex enhanced the mechanical properties of the hydrogels and improved the accuracy of detection. The resultant hydrogels were thermo reversible, and it converted to the liquid state during heating, which could greatly reduce the deviations caused in the detection of solid sensors. After cooling, the hydrogel could transform into the solid condition, which was easily portable. The sensor induced a significant luminescence quenching to the Cu²⁺ at 485 nm, with a detection limit of 0.086 μM. In the presence of ethylenediaminetetraacetic acid disodium, Cu²⁺ were tightly seized, causing the liberation of TOCN/ST complex and thus, a reversible "ON-OFF-ON" fluorescence behavior was displayed. The fluorescence intensity was maintained at 82 % after 10 uses, and the mechanical strength was maintained at 85 % after 3 uses. The anti-bacterial activity test also confirmed the TOCN/ST complex was extremely potent in suppressing the growth and reproduction of Escherichia coli. The proposed hydrogel provides a new insight into the detection of Cu²⁺ in aqueous environments.