A synergistic enhancement strategy for mechanical and conductive properties of hydrogels with dual ionically cross-linked κ-carrageenan/poly(sodium acrylate-co-acrylamide) network.

Applying conductive hydrogels in electronic skin, health monitoring, and wearable devices has aroused great research interest. Yet, it remains a significant challenge to prepare conductive hydrogels simultaneously with superior mechanical, self-recovery, and conductivity performance. Herein, a dual ionically cross-linked double network (DN) hydrogel is fabricated based on K+ and Fe3+ ion cross-linked κ-carrageenan (κ-CG) and Fe3+ ion cross-linked poly(sodium acrylate-co-acrylamide) P(AANa-co-AM). Benefiting from the abundance of hydrogen bonds and metal coordination bonds, the conductive hydrogel has excellent mechanical properties (fracture strain up to 1420 %, fracture stress up to 2.30 MPa, and toughness up to 20.63 MJ/m3) and good self-recovery performance (the recovery rate of the toughness can reach 85 % after waiting for 1 h). Meanwhile, due to the introduction of dual metal ions of K+ and Fe3+, the ionic conductivity of conductive hydrogel is up to 1.42 S/m. Furthermore, the hydrogel strain sensor has good sensitivity with a gauge factor (GF) of 2.41 (0-100 %). It can be a wearable sensor that monitors different human motions, such as sit-ups. This work offers a new synergistic strategy for designing a hydrogel strain sensor with high mechanical, self-recovery, and conductive properties.

Linearly Manipulating Color Emission via Anion Exchange Technology for High Performance Amplified Spontaneous Emission of Perovskites.

The most attractive advantages of all-inorganic cesium lead halide perovskites are their optical gain over broad spectral ranges through the visible spectrum, so are well suited to use in tunable lasers or broadband amplifiers. Most reported anion exchange reactions face a challenge to achieve the desired halogen-variable perovskites due to rapid and uncontrollable reactions and difficulty to synthesize directly. In this study, a simple vapor/solid anion exchange strategy is demonstrated for controlling the reaction process and realizing a wide range tuning of band gap and amplified spontaneous emission (ASE) wavelength, which exhibits a temperature-dependent anion exchange rate. By optimizing the reaction temperature at 90 °C, the ASE wavelength can be linearly manipulated by just controlling the reaction time. A clear quantitative relationship between ASE peak position and reaction time is achieved. Compares with the CsPbClBr2 film obtained via the liquid phase anion exchange method, the fabricated perovskite films obtained by vapor/solid anion exchange technology exhibit superior film quality and enhanced ASE performance. This work may have applications in the future using facile and controllable techniques to develop high-quality full-color visible lasers.

High-performance self-powered integrated system of pressure sensor and supercapacitor based on Cu@Cu2O/graphitic carbon layered porous structure.

With the rapid development of human-machine technology, self-powered pressure sensor integrated systems have been extensively studied. However, there are only a few reports on such multifunctional devices using a single active material. In this work, we report a flexible integrated system, which consists of flexible pressure sensors and supercapacitors. Both of the devices were fabricated based on layered porous Cu@Cu2O/graphitic carbon (Cu@Cu2O/GC) composites, which were obtained by a one-step simple polymer heat treatment method. Due to the discontinuous conductive paths and effective stress concentration relief in the composite, the pressure sensor shows a high sensitivity of 90 kPa-1 in a wide working range of 0-150 kPa, a fast response time of 90 ms, and a detection limit of 2.4 Pa. Moreover, the layered porous structure Cu@Cu2O/GC can not only maintain the integrity of the electrode material, but also promote the diffusion of electrons, enabling super capacitors to obtain excellent electrochemical performance. The specific capacitance of the super capacitor is 17.8 mF cm-2. More importantly, the flexible self-powered integrated system could be directly attached to the human body to detect human motions, showing its great potential application in wearable devices.

Integrated Sensing and Warning Multifunctional Devices Based on the Combined Mechanical and Thermal Effect of Porous Graphene.

Wearable devices with integrated alarm functions play a vital role in daily life and can help people prevent potential hazards. Although many wearable sensors have been extensively studied and proposed to monitor various physiological signals, most of them are needed to integrate with the external alarm elements to realize warning, such as light-emitting diodes and buzzers, resulting in the system complexity and poor flexibility. In this paper, an integrated sensing and warning multifunctional device based on the mechanical and thermal effect of porous graphene is proposed on a bilayer asymmetrical pattern of laser-induced graphene (LIG). Compared with the strain sensor with nonpatterned LIG, the mechanical performance is greatly improved with the highest gauge factor value of up to 950 for the strain sensor with mesh-patterned LIG. On the contrary, the heating performance of the heater with nonpatterned LIG is better than that with mesh-patterned LIG. Combining the performance differences of different LIG patterns, the integrated wearable device with a bilayer asymmetrical LIG pattern is demonstrated. It can generate enough heating energy to warn the person when the detected signal meets the threshold condition measured in real time by the ultrasensitive strain sensor. This work will provide a new way to construct an integrated wearable device for realizing multifunctional applications. This integrated multifunctional device shows great potential toward the applications in healthcare monitoring and timely warning.

An investigation of the positive effects of doping an Al atom on the adsorption of CO2 on BN nanosheets: a DFT study.

Nowadays, climate problems caused by greenhouse gases are becoming more and more serious. Motivated by reducing carbon dioxide emissions from fossil fuel power generation, scientists are devoting themselves to developing novel materials or technologies for capturing carbon dioxide. Nanostructure materials, which show great potential for this application, have come to the attention of scientists. Herein, the effects of doping an aluminum atom (replacing one boron atom by one aluminum one) on the adsorption of carbon dioxide on boron nitride nanosheets are theoretically investigated through computational analysis based on density functional theory. The results show that the binding between oxygen and aluminum atoms, which comes from classical Lewis base (CO2)-Lewis acid (Al) interactions, can provide a considerable gain to the mutual effect between the carbon dioxide molecule and the doped substrate. Compared with pristine boron nitride nanosheets, the adsorption energy value of the carbon dioxide molecule is markedly increased to 0.4784 eV (about 2.5-fold) after the doping process, which is in the range of the ideal adsorption energy of 0.415-0.829 eV. More importantly, the essence of physisorption signifies that carbon dioxide can be released by means of specific physical desorption, and, sequentially, this is more conducive for achieving reversible adsorption.

A Plasmonic Temperature-Sensing Structure Based on Dual Laterally Side-Coupled Hexagonal Cavities.

A plasmonic temperature-sensing structure, based on a metal-insulator-metal (MIM) waveguide with dual side-coupled hexagonal cavities, is proposed and numerically investigated by using the finite-difference time-domain (FDTD) method in this paper. The numerical simulation results show that a resonance dip appears in the transmission spectrum. Moreover, the full width of half maximum (FWHM) of the resonance dip can be narrowed down, and the extinction ratio can reach a maximum value by tuning the coupling distance between the waveguide and two cavities. Based on a linear relationship between the resonance dip and environment temperature, the temperature-sensing characteristics are discussed. The temperature sensitivity is influenced by the side length and the coupling distance. Furthermore, for the first time, two concepts-optical spectrum interference (OSI) and misjudge rate (MR)-are introduced to study the temperature-sensing resolution based on spectral interrogation. This work has some significance in the design of nanoscale optical sensors with high temperature sensitivity and a high sensing resolution.