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[Display omitted] • A metal ion-induced strategy to construct a multifunctional hydrogel. • This strategy utilizes Au-induced luminescence, Zn2+-induced shape memory, and Hg2+-induced fluorescence quenching. • This hydrogel exhibited fluorescence, shape memory effect and ionic conductivity properties. • Simple and versatile construction of three-dimensional encryption platforms and detection of Hg2+. • Information is written by Hg2+ and protected by Zn2+ fixing the shape, which is read under shape recovery and UV irradiation. Information security has long been a focal point of research. However, the development of cryptographic hydrogels endowed with both high security and multifunctionality remains a challenge. Herein, we reported a method to construct multifunctional hydrogels using a metal ion-induced strategy. Leveraging Au- induced luminescence, Zn2+- induced shape memory, and Hg2+- induced fluorescence quenching, our method engendered a suite of distinctive properties, including fluorescence, shape memory effects, and ionic conductivity. Tunable fluorescence was utilized for detecting Hg2+ with a detection limit as low as 0.0007 μmol/L. Additionally, a successful design of a multilevel information encryption platform, ranging from 2D to 3D, was achieved by combining the aforementioned properties. The information written using Hg2+ as ink can be protected by the fixed shape of Zn2+, and the encrypted information can only be read under the conditions of shape recovery and UV irradiation. This simple yet effective strategy demonstrates a promising future for the application of this hydrogel in information encryption. [ABSTRACT FROM AUTHOR]

Inspired by "disappear after reading", a time-modulated encryption hydrogel was synthesized by carboxymethyl cellulose with carbon quantum dots. Carboxymethyl cellulose in this system stabilized carbon quantum dots, which ensured the whole hydrogel worked well. The encryption/decryption of information depended on pH adjustment, application of EDTA and Cr (VI). Furthermore, an in-depth analysis of the fluorescence change mechanism uncovered that fluorescence quenching was potentially influenced by internal filtering effects and static quenching, which involved the amino, carboxyl, and hydroxyl groups present within the hydrogel. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel wood-derived nanocellulose hydrogel with gold nanoclusters was prepared. • This hydrogel simultaneously has effective adsorption and detection abilities. • Maximum sorption capacity of this hydrogel for Hg(II) ion reached 234.4 mg/g. • The hydrogel had sensitive detection ability with the detection limit of 0.09 μg/L. • Electrostatic, metallophilic and complexation interactions worked for sorption. A wood-derived nanocellulose hydrogel (WNH) with gold nanoclusters (Au NCs) was prepared by in situ multistep reactions, which was used as an effective adsorbent for the adsorption of mercury ion (Hg2+) and a solid-state fluorescent probe for detecting Hg2+. The WNH's morphology, chemical structure and optical properties were investigated. The adsorption performance of WNH towards the Hg2+ ion was studied, indicating that the sorption data were well fitted by Langmuir and pseudo-second-order models with a maximum sorption capacity of 234.4 mg/g. The detection performance of WNH towards the Hg2+ ion was also investigated, showing excellent selectivity and sensitivity to Hg2+ with a detection limit of 0.09 μg/L. The 3D porous structure created by wood-derived nanocellulose increased adsorption and detection, according to the mechanism analysis. Furthermore, a cost analysis was performed for WNH and commercial activated carbon, and the results showed that WNH was the economically viable option for Hg2+ sorption. This research could pave the way for a low-cost, multi-functional and environmentally friendly mercury adsorbent. [ABSTRACT FROM AUTHOR]

• A hydrogel with excellent sorption and sensing abilities for Cr(VI) was synthesized. • Carbon dots wrapped into this hydrogel provided a rapid visual response to Cr(VI). • Carbon dots facilitated amino group-induced aggregation of Cr(VI). • The mechanism of Cr(VI) sorption and sensing for this hydrogel was determined. To effectively detect and remove environmentally hazardous Cr(VI), a novel 3D porous fluorescent hydrogel was synthesised using amino-modified carbon dots and cellulose nanofibers. The synthesised fluorescent hydrogel was characterized to determine its morphology, crystalline structure, chemical composition and optical property using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, UV–vis absorption spectroscopy and photoluminescence spectroscopy. The sorption properties of the synthesised fluorescent hydrogel were further analyzed. The maximum sorption capacity for Cr(VI) reached 534.4 mg/g, the adsorption isotherm was well fitted using Langmuir model, and the adsorption kinetics were well fitted using a pseudo-second-order model. The sensing ability of the synthesized hydrogel for Cr(VI) was also determined. Furthermore, the mechanism of Cr(VI) sorption and sensing was determined. Accordingly, this novel 3D porous fluorescent hydrogel was identified to be a promising sorbent with advantages of excellent sorption and sensing abilities for environmentally hazardous Cr(VI). [ABSTRACT FROM AUTHOR]