This paper investigated ultraviolet A light-emitting diode (UVA-LED) irradiation to activate Fe­(VI) for the degradation of micropollutants (e.g., sulfamethoxazole (SMX), enrofloxacin, and trimethoprim). UVA-LED/Fe­(VI) could significantly promote the degradation of micropollutants, with rates that were 2.6–7.2-fold faster than for Fe­(VI) alone. Comparatively, UVA-LED alone hardly degraded selected micropollutants. The degradation performance was further evaluated in SMX degradation via different wavelengths (365–405 nm), light intensity, and pH. Increased wavelengths led to linearly decreased SMX degradation rates because Fe­(VI) has a lower molar absorption coefficient at higher wavelengths. Higher light intensity caused faster SMX degradation, owing to the enhanced level of reactive species by stronger photolysis of Fe­(VI). Significantly, SMX degradation was gradually suppressed from pH 7.0 to 9.0 due to the changing speciation of Fe­(VI). Scavenging and probing experiments for identifying oxidative species indicated that high-valent iron species (Fe­(V)/Fe­(IV)) were responsible for the enhanced degradation. A kinetic model involving target compound (TC) degradation by Fe­(VI), Fe­(V), and Fe­(IV) was employed to fit the TC degradation kinetics by UVA-LED/Fe­(VI). The fitted results revealed that Fe­(IV) and Fe­(V) primarily contributed to TC degradation in this system. In addition, transformation products of SMX degradation by Fe­(VI) and UVA-LED/Fe­(VI) were identified and the possible pathways included hydroxylation, self-coupling, bond cleavage, and oxidation reactions. Removal of SMX in real water also showed remarkable promotion by UVA-LED/Fe­(VI). Overall, these findings could shed light on the understanding and application of UVA-LED/Fe­(VI) for eliminating micropollutants in water treatments.

Stimuli-responsive materials activated by a pair of molecular or ionic species are of interest in the design of chemical logic gates and signal amplification schemes. There are relatively few materials whose coactivated response has been well-characterized. Here, we demonstrate a specific ion coactivation (SICA) effect at the interfaces of transient polymer solids and liquid solutions. We found that depolymerization of the transient polymer, cyclic poly(phthalaldehyde) (cPPA), exhibited a SICA effect when the cPPA core-shell microcapsules were suspended in ion-containing acidic methanol solutions. Significant acceleration in cPPA depolymerization rate is triggered by the combination of acid and ion coactivators. Intriguingly, the SICA effect is related to the Hofmeister behavior. The SICA effect is primarily determined by anions, and cations exhibit a secondary effect that modulates the coactivation strength. Based on these observations, we developed cPPA programmable microcapsules whose payload release rates depend on the composition and concentration of the salt/acidic-methanol solutions.

We reported here a new platform of supramolecular hydrogels cross-linked by the cooperation of metal-ligand coordination and hydrophobic interaction. A salicylaldehyde benzoyl hydrazone-terminal poly(ethylene glycol) (2SBH-PEG) was synthesized and formed small micelles in an aqueous environment. Addition of Ni connected the low-molecular-weight 2SBH-PEG into a metallopolymer via metal-ligand coordination and led to micelle aggregation, resulting in gelation due to the enhancement of hydrophobic interaction. The forming hydrogel, Ni-PEGel, exhibited rapid self-healing ability and reversible pH-responsive property. Because of the containing metal coordination bond, it was also sensitive to the strong competing ligands, such as ethylenediaminetetraacetic acid (EDTA) and pyridine. In addition, Ni-PEGel showed colorimetric changes when exposed to biogenic amine (BA) vapor. The color development of Ni-PEGel toward BAs makes it a good candidate in monitoring food spoilage.

Hydrogel strain sensors with extreme temperature tolerance have recently gained great attention. However, the sensing ability of these hydrogel strain sensors changes with temperature, resulting in the variety of output signals that causes signal distortion. In this study, double-network hydrogels comprising SiO 2 nanoparticles composed of polyacrylamide and phytic aciddoped polypyrrole were prepared and applied on strain sensors with a wide sensing range, high adhesiveness, and invariable strain sensitivity under flame and cold environments. The hydrogels had stable conductivity, excellent adhesive strength of up to 79.7 kPa on various substrates, and high elongation of up to 1896% at subzero temperature and after heating. They also exhibited effective flame retardancy with low surface temperature (71.2 °C) after 1200 s of heating (200 °C) and antifreezing properties at a low temperature of −20 °C. Remarkably, even under cold temperature and heat treatment, the hydrogel-based strain sensor displayed consistent sensing behaviors in detecting human motions with a broad strain range (up to 500%) and steady gauge factor (GF, ∼2.90). Therefore, this work paves the way for the applications of hydrogel sensors in robotic skin, human−mechanical interfaces, and health monitoring devices under harsh operating environments.

Aiming at the problem that the reported smart optical metallohydrogels were limited with poor mechanical properties, we reported here a novel smart optical metallohydrogel (Al-hydrogel) with excellent elongation, shape-memory ability, self-healing property, and controllable fluorescence intensity. The Al-hydrogel was obtained by the HHPMA–Al3+ and carboxylate–Al3+ coordination after one-pot micellar copolymerization of acrylic acid (AAc), acrylamide (AAm), and hydrophobic arylhydrazone-based ligand (HHPMA). This hydrogel was able to extend up to 5000% of its original length without fracture. Its emission intensity was tunable by OH–/H+ or Zn2+/AAc and increased by 500% with 0.1 M OH– or Zn2+. Its tunable fluorescence enabled us to repeatedly pattern it. A reversible system consisting of Fe3+/H+, was implemented to control the shape of the Al-hydrogel, endowing the Al-hydrogel with shape-memory ability. This highly stretchable and multifunctional Al-hydrogel has potential applications in information transmission, wearable devices, and flexible sensors.