Design of Stretchable and Conductive Self-Adhesive Hydrogels as Flexible Sensors by Guar-Gum-Enabled Dynamic Interactions.

The limited elasticity and inadequate bonding of hydrogels made from guar gum (GG) significantly hinder their widespread implementation in personalized wearable flexible electronics. In this study, we devise GG-based self-adhesive hydrogels by creating an interpenetrating network of GG cross-linked with acrylic, 4-vinylphenylboronic acid, and Ca2+. With the leverage of the dynamic interactions (hydrogen bonds, borate ester bonds, and coordination bonds) between -OH in GG and monomers, the hydrogel exhibits a high stretchability of 700%, superior mechanical stress of 110 kPa, and robust adherence to several substrates. The adhesion strength of 54 kPa on porcine skin is obtained. Furthermore, the self-adhesive hydrogel possesses stable conductivity, an elevated gauge factor (GF), and commendable durability. It can be affixed to the human body as a strain sensor to obtain precise monitoring of human movement behavior. Our research offers possibilities for the development of GG-based hydrogels and applications in wearable electronics and medical monitoring.

A Fluorescent Hydrogel with AIE Emission for Dehydration-Visualizable Wearable Sensors.

Hydrogel-based wearable sensors eventually experience dehydration, which negatively impacts their function, leading to decreased sensitivity. Monitoring the real-time water retention rate and sensing performance of wearable flexible sensors without dismantling them remains a significant difficulty. In this study, a molecule having aggregation-induced emission (AIE) properties in an aqueous environment has been developed and produced, which can combine with anionic guar gum and acrylic acid to create an AIE hydrogel. Wearable sensing electronic devices have the capability to track motion signals at various joints of the human body. Additionally, they can effectively and visually monitor dehydration status during extended periods of operation. The fluorescence intensity of the hydrogel is primarily influenced by the level of aggregation of luminous monomers inside the network. This level of aggregation is predominantly governed by the hydrogel's water retention rate. Hence, the extended duration of hydrogel dehydration can be manifested through alterations in their fluorescence characteristics, which are employed for strain sensing. This approach enables users to assess the water retention of hydrogels with greater efficiency, eliminating the requirement for disassembling them from the completed electrical gadget. In summary, the use of AIE-based fluorescent hydrogels will advance the progress of intelligent wearable electronics.

Bioinspired simultaneous regulation in fluorescence of AIEgen-embedded hydrogels.

The development of stimuli-responsive functional fluorescent hydrogels is of great significance for the realization of artificial intelligence. In the present work, we design and synthesize a stimulus-responsive hydrogel embedded with an aggregation-induced emission (AIE) monomer, in which the fluorescence brightness and intensity can be tuned. The hydrogel embedded with tetraphenylethene-grafted-poly[3-sulfopropyl methacrylate potassium salt] (TPE-PSPMA) as the functional element is prepared by the radical polymerization method. Among them, the TPE core exhibits adaptive fluorescence ability through the AIE effect, while the PSPMA chain provides tunable hydrophilic properties under an external stimulus. The effect of different cationic surfactants with different lengths of hydrophobic tails on the fluorescence properties of TPE-PSPMA in solution is systematically investigated. With cationic surfactants, such as cetyltrimethylammonium bromide (CTAB), the fluorescence intensity is gradually tuned from 1059 to 4623. And the fluorescence intensities increase with the growth of hydrophobic tails of surfactants, which results from hydrophobicity-induced electrostatic interactions among surfactants and polymer chains. Furthermore, an obvious tunable fluorescence feature of hydrogel copolymerized TPE-PSPMA is realized, resulting from the change of brightness and the dynamic increase of fluorescence intensity (from 1031 to 3138) for the hydrogel immersed in CTAB solution with different soaking times. Such a typical fluorescence-regulated behavior can be attributed to the AIE of the TPE-PSPMA chain and the electrostatic interaction between the surfactant and the anionic polymer chain. The designed TPE-PSPMA-based hydrogel is responsive to stimuli, inspiring the development of intelligent systems such as soft robots and smart wearables.

The construction of an artificial light-harvesting system with two-step sequential energy transfer based on supramolecular polymers.

An artificial light-harvesting system with two-step sequential energy transfer was constructed in aqueous media based on cyano-substituted p-phenylenevinylene derivative (PPTA) and bis-(p-sulfonatocalix[4]arenes) (BSC4) supramolecular polymers formed through host-guest interactions, in which two different fluorescent dyes, eosin Y (EY) and sulforhodamine (SR101), were employed as energy acceptors. The obtained artificial light-harvesting system can achieve an efficient two-step energy transfer process from PPTA-BSC4 to EY and then to SR101 with high energy-transfer efficiencies of up to 36.6% and 40.8%, respectively. More importantly, the harvested energy from the PPTA-BSC4 + EY + SR101 system can be used to promote the dehalogenation of α-bromoacetophenone with a yield of 89% in aqueous solution.

Spin Crossover in a Series of Non-Hofmann-Type Fe(II) Coordination Polymers Based on [Hg(SeCN)3]- or [Hg(SeCN)4]2- Building Blocks.

Self-assembly of [Hg(SeCN)4]2- tetrahedral building blocks, iron(II) ions, and a series of bis-monodentate pyridyl-type bridging ligands has afforded the new heterobimetallic HgII-FeII coordination polymers {Fe[Hg(SeCN)3]2(4,4'-bipy)2}n (1), {Fe[Hg(SeCN)4](tvp)}n (2), {Fe[Hg(SeCN)3]2(4,4'-azpy)2}n (3), {Fe[Hg(SeCN)4](4,4'-azpy)(MeOH)}n (4), {Fe[Hg(SeCN)4](3,3'-bipy)}n (5) and {Fe[Hg(SeCN)4](3,3'-azpy)}n (6) (4,4-bipy = 4,4'-bipyridine, tvp = trans-1,2-bis(4-pyridyl)ethylene, 4,4'-azpy = 4,4'-azobispyridine, 3,3-bipy = 3,3'-bipyridine, 3,3'-azpy = 3,3'-azobispyridine). Single-crystal X-ray analyses show that compounds 1 and 3 display a two-dimensional robust sheet structure made up of infinite linear [(FeL)n]2n+ (L = 4,4'-bipy or 4,4'-azpy) chains linked by in situ formed {[Hg(L)(SeCN)3]2}2- anionic dimeric bridges. Complexes 2 and 4-6 define three-dimensional networks with different topological structures, indicating, in combination with complexes 1 and 3, that the polarity, length, rigidity, and conformation of the bridging organic ligand play important roles in the structural nature of the products reported here. The magnetic properties of complexes 1 and 2 show the occurrence of temperature- and light-induced spin crossover (SCO) properties, while complexes 4-6 are in the high-spin state at all temperatures. The current results provide a new route for the design and synthesis of new SCO functional materials with non-Hofmann-type traditional structures.

TiO2/g-C3N4 photocatalyst for the purification of potassium butyl xanthate in mineral processing wastewater.

In the present work, TiO2-graphite-phase-carbon-nitride (TiO2/g-C3N4) was prepared through a hydrothermal method to obtain a new photocatalytic material. This material was characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray energy spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Solid-state UV-Vis diffuse reflectance spectrometry (UV-Vis-DRS) and electron paramagnetic resonance (EPR). The synthesized TiO2/g-C3N4 exhibited homogeneous morphology, in which TiO2 nanoparticles were uniformly distributed on the g-C3N4 nanosheets. Regarding its potential use as photocatalytic material in the treatment of mineral processing wastewater, 18% TiO2/g-C3N4 showed superior photodegradation performance than TiO2 and g-C3N4, to give 97.1% degradation rate under 100 min of simulated light irradiation. The experimental results showed that the successful incorporation of TiO2 on g-C3N4 nanosheets enhanced the spectral response range of TiO2/g-C3N4, and the photocatalytic activity was improved. In view of that, it can be considered that this kind of photocatalytic material has a good prospect in the treatment of mineral processing wastewater, which would have clearly environmental relevance.

The photophysical properties and imaging application of a new polarity-sensitive fluorescent probe.

A new excited-state intramolecular proton transfer (ESIPT) based and polarity-sensitive fluorescent probe M-HA was easily developed by conjugated connection of indole and 2'-hydroxyacetophenone through (E)-2-chloro-3-(hydroxymethylene)cyclohex-1-enecarbaldehyde. M-HA shows near-infrared fluorescence, high molar absorption coefficient and a large Stokes shift in various common solvents. In particular, M-HA exhibits red-shifted maximum emission wavelength, and extraordinarily high fluorescence intensity and quantum yield in high-polarity solvents. The theoretical calculation results indicate that the reduced electron-vibration coupling related to out-of-plane motions of benzene units in more polar solvents is mainly responsible for such unusual photophysical properties. For further application, M-HA was utilized to image live cells. The confocal fluorescence imaging results demonstrate that M-HA possesses excellent membrane permeability and can fluoresce brightly in the cytoplasm. Overall, M-HA, as a polarity-sensitive fluorescent probe, will serve as an excellent tool for quantitative determination of polarity in vitro and in-depth study of the polarity biology in physiopathology in future.

Dimethylsulfoxide-Dependent Environments for Fabricating Graphene Hydrogels for High-Performance Supercapacitor.

In present work, reduced graphene oxide hydrogels (DRGHs) with three-dimensional (3D) porous structures are prepared through chemical reduction method by using dimethylsulfoxide (DMSO) as reductants in alkaline environment of ammonia. The reduction of graphene oxide (GO) into DRGHs was confirmed by X-ray powder diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). The field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) of DRGHs exhibited 3D structures with well-defined porous networks crosslinking of graphene sheets, which is beneficial to be promising electrode materials for supercapacitors. Moreover, the obtained DRGHs exhibited different electrochemical performance in supercapacitors with adding different amounts of DMSO. With increasing the dosage of the reductants, the DRGHs revealed better specific capacitances. DRGHs showed excellent capacitive performance with a very high specific capacitance up to 313.6, 323.6 and 348.0 F g-1 for DRGHs-1, DRGHs-2 and DRGHs-3 at 0.2 A g-1, respectively. It also showed that the electrode based on DRGHs has good stability and high reversibility in the charge/discharge cycling test.

Three Dimensional Nitrogen-Doped and Nitrogen, Sulfur-Codoped Graphene Hydrogels for Electrode Materials in Supercapacitors.

In present work, reduced graphene oxide hydrogels (RGOHs) with three-dimensional (3D) porous structure are prepared through chemical reduction method by using aminourea (NRGOHs) and aminothiourea (NSRGOHs) as reductants. The as-prepared RGOHs are considered not only as promising electrode materials for supercapacitors, but also the doping of nitrogen (aminourea, NRGOHs) or nitrogen/sulfur (aminothiourea, NSRGOHs) can improve electrochemical performance through faradaic pseudocapacitance. The optimized samples have been prepared by controlling the mass ratios of graphene oxide (GO) to aminourea or aminothiourea to be 1:1, 1:2 and 1:5, respectively. With adding different amounts of aminourea or aminothiourea, the obtained RGOHs exhibited different electrochemical performance in supercapacitors. With increasing the dosage of the reductants, the RGOHs revealed better specific capacitances. Moreover, NSRGOHs with nitrogen, sulfur-codoping exhibited better capacitance performance than that of NRGOHs with only nitrogen-doping. NSRGOHs showed excellent capacitive performance with a very high specific capacitance up to 232.2, 323.3 and 345.6 F g-1 at 0.2 A g-1, while NRGOHs showed capacitive performance with specific capacitance up to 220.6, 306.5 and 332.7 F g-1 at 0.2 A g-1. This provides a strategy to improve the capacitive properties of RGOHs significantly by controlling different doping the materials.

The novel PEI-modified biochars and their application for the efficient elimination of Cr(VI) from aqueous solutions.

In this study, the polyethyleneimine (PEI) was grafted onto the biochars from chestnut shells and nori via the cross-linking reaction. Scanning electron microscopy, transmission electron microscopy and Fourier transferred infrared spectroscopy analysis indicated that the PEI was successfully grafted on the surface of biochars. The PEI modified and pristine biochars were used as adsorbents to remove Cr(VI) from aqueous solutions as a function of pH, ionic strength, contact time and initial concentrations of Cr(VI) through batch technique. The strongly pH-dependent and ionic strength-independent of Cr(VI) sorption indicated that the sorption was mainly dominated by electrostatic interaction and inner-sphere surface complexation. The maximum sorption capacities of PEI modified chestnut shell and nori biochars were 141.42 and 222.84 mg/g, respectively, which were significantly higher than those of pristine biochars. The PEI grafted onto the biochars significantly enhanced Cr(VI) sorption capacity because PEI, which contains volumes of amine/imine groups, provided an excellent platform for Cr(VI) ions removal. In addition, the sorption-desorption experimental results indicated that the PEI modified biochars possessed a stable and recyclable performance. All these results manifested that the PEI modified biochars could be applied as environmentally friendly and efficient adsorbents for the removal of Cr(VI) from wastewater.

Three-Dimensional Reduced Graphene Hydrogels Using Various Carbohydrates for High Performance Supercapacitors.

In present work, three-dimensional (3D) reduced graphene hydrogels (RGHs) are prepared through an efficient and facile strategy by employing three types of carbohydrates (glucose, fructose and sucrose) as reducing agents in aqueous solution of graphene oxide (GO) with ammonia. The formation of RGHs could be confirmed by X-ray powder diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The structures and porosity were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and N2 sorption experiments. Benefiting from the abundant porous architectures as fast ionic channels for electrochemical energy storage, the prepared RGHs exhibited a high specific capacitance up to 153.5, 145.0 and 150.3 F g−1 at 0.3 A g−1 for FRGHs (fructose), GRGHs (glucose) and SRGHs (sucrose), which can be maintained for 61.4, 61.5 and 46.9% as the discharging current density was increased up to 20 A g−1. Moreover, it also showed that the electrode based on RGHs has good electrochemical stability and high degree of reversibility in the charge/discharge cycling test.

Conformation-Controlled Diplatinum(II)-Ferrocene Dyads to Achieve Long-Lived Charge-Separated States.

Square-planar polypyridyl platinum(II) complexes possess a rich range of structural and spectroscopic properties that are ideal for designing artificial photosynthetic centers. Taking advantage of the directionality in the charge-transfer excitation from the metal to the polypyridyl ligand, we describe here diplatinum(II)-ferrocene dyads, open-butterfly-like dyad 1 and closed-butterfly-like dyad 2, which were designed to understand the conformation and orientation effects to prolong the lifetime of charge-separated state. In contrast to the open-butterfly-like dyad 1, the closed-butterfly-like dyad 2 shows three-times long lifetime of charge separated state upon photoexcitation, demonstrating that the orientation in the rigid structure of dyad 2 is a very important issue to achieve long-lived charge separated state.

Dual-responsive vesicles formed by an amphiphile containing two tetrathiafulvalene units in aqueous solution.

The first example of tetrathiafulvalene (TTF)-based vesicle fabricated in water solution with 1 vol.% tetrahydrofuran that could be prevented by chemical oxidant Fe(ClO4)3 or electron-deficient cyclobis(paraquat-p-phenylene) tetracation cyclophane (CBPQT(4+)) is described.

Breaking aziridines to construct morpholines with a gold(i)-catalyzed tandem ring-opening and cycloisomerization reaction.

A convenient synthetic method for the construction of morpholine derivatives from easily available aziridines and propargyl alcohols has been successfully developed. A tandem nucleophilic ring-opening of aziridine/6-exo-dig cyclization/double bond isomerization sequence was achieved by using a single gold(i) catalyst under mild conditions. The gold(i) catalyst served as a π acid and also a σ acid to realize the dual activation of both reactants in this reaction. The obtained unsaturated morpholine products could be easily hydrogenated to achieve target morpholine derivatives with good diastereoselectivities in high yields.

Highly sensitive and selective fluoride ion sensors based on microcantilevers modified with hydrogels.

We have developed two microcantilever sensors, one modified with chitosan/gelatin hydrogels doped with CH3(OCH2CH2)3OTBDPS and another modified with chitosan-OTBDPS/gelatin hydrogels, for the sensitive and selective detection of fluoride ions (F-) in aqueous solution. Upon exposure to F-, the microcantilevers underwent bending deflection due to the cleavage of Si-O bond on reacting with F- in the hydrogel. The results show that the maximum bending deflections are proportional to the concentrations of F-, and the limits of detection are 10(-8) M and 10(-9) M for the two microcantilevers, respectively. Other ions, such as Cl-, Br-, NO3-, H2PO4-, HSO4-, and AcO- have little effect on the deflection of the microcantilevers. The results show that the microcantilever may be used for in situ quantitative detection of F- in an aqueous solution and the mechanism of the bending are discussed.

Switchover from singlet oxygen to superoxide radical through a photoinduced two-step sequential energy transfer process.

The competitive nature of type II photosensitizers in the transfer of excitation energy for the generation of singlet oxygen (1O2) presents significant challenges in the design of type I photosensitizers to produce the superoxide anion radical (O2˙-). In this study, we present an efficient method for the direct transformation of type II photosensitizers into type I photosensitizers through the implementation of an artificial light-harvesting system (ALHSs) involving a two-step sequential energy transfer process. The designed supramolecular complex (DNPY-SBE-ß-CD) not only has the ability to generate 1O2 as type II photosensitizers, but also demonstrates remarkable fluorescence properties in aqueous solution, which renders it an efficient energy donor for the development of type I photosensitizers ALHSs, thereby enabling the efficient generation of O2˙-. Meanwhile, to ascertain the capability and practicality of this method, two organic reactions were conducted, namely the photooxidation reaction of thioanisole and oxidative hydroxylation of arylboronic acids, both of which display a high level of efficiency and exhibit significant catalytic performance. This work provides an efficient method for turning type II photosensitizers into type I photosensitizers by a two-step sequential energy transfer procedure.

Photocatalytic selective oxidation of toluene under encapsulated air conditions.

Benzaldehydes are indispensable building blocks in chemistry. However, the selective oxidation of toluene to benzaldehyde remains an ongoing challenge due to the low oxidation potential of benzaldehyde compared to toluene. We report herein a mild protocol that combines hydrogen atom transfer (HAT) with encapsulated air conditions and suitable catalyst loading for selective oxidation of toluene with high selectivity as well as good functional-group tolerance and a broad substrate scope for the synthesis of various high-value aromatic aldehydes. Moreover, the compatibility of this reaction with toluene derivatives of bioactive molecules further demonstrated the practicality of this approach. Mechanism studies have demonstrated that the collaboration between the oxygen quantity and the HAT catalytic system has a major impact on the high selectivity of the reaction. This study not only showcases the effectiveness of HAT strategies toward selective oxidation of toluene to benzaldehyde, but also provides an approach to controlling the selectivity of HAT reactions.

A supramolecular photosensitizer based on triphenylamine and pyrazine with aggregation-induced emission properties for high-efficiency photooxidation reactions.

Recently, there has been a great interest in the study of photocatalysts (PCs) and photosensitizers (PSs) in the field of organic photocatalysis. In the present study, a pure organic thermally activated delayed fluorescence (TADF) molecule 4,4'-(12-(pyridin-4-yl)dibenzo[f,h]pyrido[2,3-b]quinoxaline-3,6-diyl)bis(N,N-diphenylaniline) (DPQ-TPA) was designed and synthesized, which not only have excellent TADF property and small energy splitting (ΔEST), but also can self-assembly in water to form cross-linked nanoparticles with exceptional aggregation-induced emission (AIE) characteristics. DPQ-TPA exhibits excellent remarkable selectivity and notably enhances the production capacity of reactive oxygen species (ROS), particularly 1O2, which was employed as a highly effective photocatalyst in the photooxidation reaction of phosphine and hydroazobenzenes under blue light irradiation with high yields up to 94% and 91%, respectively. This work expands the potential application of (donor-acceptor) D-A type AIE-TADF molecules in photocatalytic organic transformations through supramolecular self-assembly.

Superoxide radical generator based on triphenylamine-based supramolecular organic framework for green light photocatalysis.

Supramolecular organic frameworks (SOFs) mostly require high-energy purple or blue light for photocatalytic reactions, while highly abundant and low-energy light systems have rarely been explored. Therefore, it is necessary to construct 2D SOFs for low-energy light-induced photocatalysis. This study describes the design and synthesis of a water-soluble two-dimensional (2D) supramolecular organic framework (TP-SOF) using the host-guest interaction between a triphenylamine derivative (TP-3Py) and cucurbit[8]uril (CB[8]). The formation of the 2D SOF can be attributed to the synergistic impact resulting from the orientated head-to-tail superposition mode between the vinylpyridine arms of TP-3Py and CB[8], which results in a significant redshift in the UV-vis absorption spectrum, especially displaying a strong absorption band in the green light region. The monomeric TP-3Py can effectively produce singlet oxygen (1O2) and realize the photocatalytic oxidation of thioanisole in the aqueous solution. In comparison to monomeric TP-3Py, the confinement effect of CB[8] results in a notable enhancement in the production efficiency of superoxide anion radicals (O2•-), exhibiting promising prospects in the field of photocatalytic oxidation reaction, which facilitates the application of TP-SOF as a very efficient photosensitizer for the promotion of the oxidative hydroxylation of arylboronic acids under green light in the aqueous solution, giving a high yield of 91%. The present study not only presents a compelling illustration of photocatalysis utilizing a 2D SOF derived from triphenylamine, but also unveils promising avenues for the photocatalytic oxidation of SOF employing low-energy light systems.

Visible-light-mediated direct C3 alkylation of quinoxalin-2(1H)-ones using alkanes.

Due to the high C-H bond dissociation energy of alkanes, the utilization of alkanes as alkyl radical precursors for C-H functionalization of heteroarenes is synthetically captivating but practically challenging, especially under metal- and photocatalyst-free conditions. We report herein a mild and practical visible-light-mediated method for C-H alkylation of quinoxalin-2(1H)-ones using trifluoroacetic acid as a hydrogen atom transfer reagent and air as an oxidant. This mild protocol was performed under metal- and photocatalyst-free circumstances and presented good functional-group tolerance as well as a broad substrate scope.