Fabrication and Conductive Mechanism Analysis of Stretchable Electrodes Based on PDMS-Ag Nanosheet Composite with Low Resistance, Stability, and Durability.

A flexible and stretchable electrode based on polydimethylsiloxane (PDMS)-Ag nanosheet composite with low resistance and stable properties has been investigated. Under the synergistic effect of the excellent flexibility and stretchability of PDMS and the excellent electrical conductivity of Ag nanosheets, the electrode possesses a resistivity as low as 4.28 Ωm, a low resistance variation in the 0-50% strain range, a stable electrical conductivity over 1000 cycles, and a rapid recovery ability after failure caused by destructive large stretching. Moreover, the conductive mechanism of the flexible electrode during stretching is explained by combining experimental tests, theoretical models of contact point-tunneling effect, and finite element simulation. This research provides a simple and effective solution for the structure design and material selection of flexible electrodes, and an analytical method for the conductive mechanism of stretchable electrodes, which has potential for applications in flexible electronic devices, smart sensing, wearable devices, and other fields.

MOF-derived AuNS/LDH with high adsorption ability for surface enhanced Raman spectroscopy detection.

The sensitivity of surface enhanced Raman spectroscopy (SERS) depends on the construction of "hot spots" and the number of analyte molecules adsorbed onto the substrates. Herein, we have constructed a kind of SERS substrate based on gold nanostars (Au NSs) coated with nickel-cobalt layered double hydroxide (LDH) using a zeolitic imidazolate skeleton as sacrificial template via nickel ions etching. LDH was used as the absorption medium for target molecules, and concurrently prevented Au NSs from agglomeration to improve stability and uniformity of the substrate. Meanwhile, encapsulated Au NSs were used as the enhancement medium for Raman detection. The porous LDH shell around the Au NSs promoted the target molecules to approach the Au NSs, which was certified by the experimental results of UV-Vis absorption and simulation analysis using the density functional theory. The detection of Rhodamine 6G solution with a concentration of 10-9 M was realized by the AuNS/LDH, and the relative standard deviation of Raman signals was less than 10%. Therefore, this work provides a new idea and a suitable structure to improve SERS signal intensity by introducing adsorption medium into the SERS substrate.

A flexible tissue-carbon nanocoil-carbon nanotube-based humidity sensor with high performance and durability.

A flexible humidity sensor based on a tissue-carbon nanocoil (CNC)-carbon nanotube (CNT) composite has been investigated. Taking advantage of the excellent water absorption of tissue and the electrical sensitivity of CNCs/CNTs to humidity, this humidity sensor obtains outstanding humidity sensing performance, including a wide sensing range of 10-90% RH, a maximum response value of 492% (ΔR/R0) at 90% RH, a maximum sensitivity of 6.16%/% RH, a good long-time stability of more than 7 days, a high humidity resolution accuracy of less than 1% RH and a fast response time of 275 ms. Furthermore, the sensor also exhibits robust bending (with a curvature of 0.322 cm-1) and folding (up to 500 times) durability, and after being made into a complex "thousand paper crane" shape it still provides stable humidity sensing performance. As a proof of concept, this humidity sensor demonstrates excellent responsivity to human breath monitoring, non-contact fingertip humidity detection, water boiling detection and air humidity monitoring, indicating great potential in the fields of wearable devices, weather forecasting systems and other intelligent humidity monitoring devices.

Novel Wearable Pyrothermoelectric Hybrid Generator for Solar Energy Harvesting.

Recently, wearable energy harvesting systems have been attracting great attention. As thermal energy is abundant in nature, developing wearable energy harvesters based on thermal energy conversion processes has been of particular interest. By integration of a high-efficient solar absorber, a pyroelectric film, and thermoelectric yarns, herein, we design a novel wearable solar-energy-driven pyrothermoelectric hybrid generator (PTEG). In contrast to those wearable pyroelectric generators and thermoelectric generators reported in previous works, our PTEG can enable effective energy harvesting from both dynamic temperature fluctuations and static temperature gradients. Under an illumination intensity of 1500 W/m2 (1.5 sun), the PTEG successfully charges two commercial capacitors to a sum voltage of 3.7 V in only 800 s, and the total energy is able to light up 73 LED light bulbs. The volumetric energy density over the two capacitors is calculated to be 67.8 µJ/cm3. The practical energy harvesting performance of the PTEG is further evaluated in the outdoor environment. The PTEG reported in this work not only demonstrates a rational structural design of high-efficient wearable energy harvesters but also paves a new pathway to integrate multiple energy conversion technologies for solar energy collection.

Surface modification of helical carbon nanocoil (CNC) with N-doped and Co-anchored carbon layer for efficient microwave absorption.

Surface modification and composition control for nanomaterials are effective strategies for designing high-performance microwave absorbing materials (MWAMs). Herein, we have successfully fabricated Co-anchored and N-doped carbon layers on the surfaces of helical carbon nanocoils (CNCs) by wet chemical and pyrolysis methods, denoted as Co@N-Carbon/CNCs. It is found that pure CNCs show a very good microwave absorption performance under a filling ratio of only 6%, which is attributed to the uniformly dispersed conductive network and the cross polarization induced by the unique chiral and spiral morphology. The coating of N-doped carbon layers on CNCs further enriches polarization losses and the uniform anchoring of Co nanoparticles in these layers generates magnetic losses, which enhance the absorption ability and improve the low frequency performance. As compared with the pure CNCs-filling samples, the optimized Co@N-Carbon/CNCs-2.4 enhances the absorption capacity in the lower frequency range under the same thickness, and realizes the decreased thickness from 3.2 to 2.8 mm in the same X band, as well as the decreased thickness from 2.2 to 1.9 mm in the Ku band. Resultantly, a specific effective absorption wave value of 22 GHz g-1 mm-1 has been achieved, which enlightens the synthesis of ultrathin and light high-performance MWAMs.

Structural Engineering of Hierarchical Aerogels Comprised of Multi-dimensional Gradient Carbon Nanoarchitectures for Highly Efficient Microwave Absorption.

Recently, multilevel structural carbon aerogels are deemed as attractive candidates for microwave absorbing materials. Nevertheless, excessive stack and agglomeration for low-dimension carbon nanomaterials inducing impedance mismatch are significant challenges. Herein, the delicate "3D helix-2D sheet-1D fiber-0D dot" hierarchical aerogels have been successfully synthesized, for the first time, by sequential processes of hydrothermal self-assembly and in-situ chemical vapor deposition method. Particularly, the graphene sheets are uniformly intercalated by 3D helical carbon nanocoils, which give a feasible solution to the mentioned problem and endows the as-obtained aerogel with abundant porous structures and better dielectric properties. Moreover, by adjusting the content of 0D core-shell structured particles and the parameters for growth of the 1D carbon nanofibers, tunable electromagnetic properties and excellent impedance matching are achieved, which plays a vital role in the microwave absorption performance. As expected, the optimized aerogels harvest excellent performance, including broad effective bandwidth and strong reflection loss at low filling ratio and thin thickness. This work gives valuable guidance and inspiration for the design of hierarchical materials comprised of dimensional gradient structures, which holds great application potential for electromagnetic wave attenuation.

Tip-to-tip assembly of urchin-like Au nanostar at water-oil interface for surface-enhanced Raman spectroscopy detection.

Au Nanostar (NS) monolayer as a surface enhanced Raman scattering (SERS) substrate has been synthesized by self-assembly at a water-oil interface. It is confirmed from the experiment and simulation results that the Au NS monolayer includes lots of "hot spots" at or between the tips of the Au NSs, enhancing the local electromagnetic fields and giving rise to strong SERS signals sequentially. The limit of detection is determined to be down to 4.2 × 10-12 M for rhodamine 6G. Furthermore, the Au NS monolayer can detect multiple molecules, including thiabendazole, methylene blue, 4-mercaptobenzoic acid, and p-amino thiophenol, indicating that the SERS substrate composed of Au NS monolayer has potential applications in analytical chemistry, food safety, and environmental safety.

Reduced holey graphene oxide film and carbon nanotubes sandwich structure as a binder-free electrode material for supercapcitor.

A novel carbon nanotubes (CNTs) and reduced holey graphene oxide film (RHGOF) sandwich structure has been fabricated to enhance its electrochemical properties. CNTs are grown by a catalyst assisted chemical vapor deposition technique, interpenetrated between the RHGOF layers. A RHGOF/CNTs hybrid film is used as a binder-free supercapacitor electrode. The grown CNTs in the graphene layers structure act as spacers and bridges to increase the counductivity of RHGOF, while the grown CNTs on the surfaces of the graphene contribute to increase the specific surface area of RHGOF. The results demonstrate that the synthesized porous, flexible and binder free hybrid electrode has advantages of higher ion diffusion rate, longer diffusion length and larger ion accessible surface area as compared to the pristine graphene which results in an extra ordinary galvanostatic charge-discharge specific capacitance of 557 F/g at a current density of 0.5 A/g, with excellent rate capabilities and superior cyclic stabilities.

Growth of Carbon Nanocoils by Porous α-Fe2O3/SnO2 Catalyst and Its Buckypaper for High Efficient Adsorption.

High-purity (99%) carbon nanocoils (CNCs) have been synthesized by using porous α-Fe2O3/SnO2 catalyst. The yield of CNCs reaches 9,098% after a 6 h growth. This value is much higher than the previously reported data, indicating that this method is promising to synthesize high-purity CNCs on a large scale. It is considered that an appropriate proportion of Fe and Sn, proper particle size distribution, and a loose-porous aggregate structure of the catalyst are the key points to the high-purity growth of CNCs. Benefiting from the high-purity preparation, a CNC Buckypaper was successfully prepared and the electrical, mechanical, and electrochemical properties were investigated comprehensively. Furthermore, as one of the practical applications, the CNC Buckypaper was successfully utilized as an efficient adsorbent for the removal of methylene blue dye from wastewater with an adsorption efficiency of 90.9%. This study provides a facile and economical route for preparing high-purity CNCs, which is suitable for large-quantity production. Furthermore, the fabrication of macroscopic CNC Buckypaper provides promising alternative of adsorbent or other practical applications.

Sensitivity-Tunable Strain Sensors Based on Carbon Nanotube@Carbon Nanocoil Hybrid Networks.

A novel vanelike nanostructure based on the hybridization of carbon nanotubes and carbon nanocoils has been fabricated by a two-step chemical vapor deposition method. A flexible and sensitive strain sensor is prepared by coupling this hybrid structure with polydimethylsiloxane. By regulating the density and length of carbon nanotubes, the gauge factor and strain range of the sensors are tuned from 4.5 to 70 and 9 to 260%, respectively. These sensors exhibit high reliability and stability in a more than 10 000-cycle test and have a prompt response time of less than 37 ms. Owing to the tunable properties, these sensors show great potential in monitoring both subtle and large-scale displacements, which can meet the diverse demands of human motion monitoring.