Biocompatible and Biodegradable 3D Graphene/Collagen Fiber Hybrids for High-Performance Conductive Networks and Sensors.

Polymer-based flexible conductive materials are crucial for wearable electronics, electronic skin, and other smart materials. However, their development and commercial applications have been hampered by the lack of strain tolerance in the conductive network, poor bonding with polymers, discomfort during wear, and a lack of biocompatibility. This study utilized oil-tanned leather with a natural network structure, high toughness, and high tensile deformation recovery as a structural template. A graphene (Gr) conductive network was then constructed on the collagen network of the leather, with coordination cross-linking between Gr and collagen fibers through aluminum ions (Al3+). A new flexible conductive material (Al-GL) was then constructed. Molecular dynamics simulations and experimental validation revealed the existence of physical adsorption, hydrogen bonding adsorption, and ligand bonding between Al3+, Gr, and collagen fibers. Although we established that the binding sites between Al3+ and collagen fibers were primarily on carboxyl groups (-COOH), the mechanism of chemical bonding between Gr and collagen fibers remains unclear. The Al-GL composite exhibited a high shrinkage temperature (67.4 °C) and low electrical resistance (16.1 kΩ·sq-1), as well as good softness (9.33 mN), biocompatibility, biodegradability (<60 h), and air and moisture permeability. Furthermore, the incorporation of Al3+ resulted in a heightened Gr binding strength on Al-GL, and the resistance remained comparable following 1 h of water washing. The Al-GL sensor prepared by WPU encapsulation not only demonstrated highly sensitive responses to diverse motion signals of the human body but also retained a certain degree of response to external mechanical effects underwater. Additionally, the Al-GL-based triboelectric nanogenerator (Al-GL TENG) exhibited distinct response signals to different materials. The Al-GL prepared by the one-pot method proposed in this study offers a novel approach to combining functional nanofillers and substrate materials, providing a theoretical foundation for collagen fiber-based flexible conductive materials.

Ultra-thin freestanding graphene films for efficient thermal insulation and electromagnetic interference shielding.

The preparation of freestanding graphene films by convenient and environmentally friendly preparation methods is still the focus of attention in various industrial fields. Here, we first select electrical conductivity, yield and defectivity as evaluation indicators and systematically explore the factors affecting the preparation of high-performance graphene by electrochemical exfoliation, then further post-process it under volume-limited conditions by microwave reduction. Finally, we obtained a self-supporting graphene film with an irregular interlayer structure but excellent performance. It is found that the electrolyte is ammonium sulfate, the concentration is 0.2 M, the voltage is 8 V, and the pH is 11, which were the optimal conditions for preparing low-oxidation graphene. The square resistance of the EG was 1.6 Ω sq-1, and the yield could be 65%. In addition, electrical conductivity and joule heat were significantly improved after microwave post-processing, especially its electromagnetic shielding performance with a shielding coefficient of 53 dB able to be achieved. At the same time, the thermal conductivity is as low as 0.05 W m-1 K-1. The mechanism for the improvement of electromagnetic shielding performance is that (1) microwave reduction effectively enhances the conductivity of the graphene sheet overlapping network; (2) the gas generated by the instantaneous high temperature causes a large number of void structures between the graphene layers, and the irregular interlayer stacking structure makes the reflective surface more disordered, thereby prolonging the reflection path of electromagnetic waves among layers. In summary, this simple and environmentally friendly preparation strategy has good practical application prospects for graphene film products in flexible wearables, intelligent electronic devices, and electromagnetic wave protection.

Synthesis and application of a novel polyurethane nanoemulsion bearing coumarin derivative as a "turn-on" fluorescence sensor toward Hg2.

A novel polyurethane (PU-co-HCCA) nanoemulsion bearing coumarin derivative (HCCA) was synthesized as a "turn-on" fluorescent probe and used to modify filter paper, and its sensing properties were investigated. Results showed that PU-co-HCCA nanoemulsion exhibited high selectivity and excellent sensitivity toward Hg2+ over other metal ions, and possessed excellent fluorescence quantum yields of 0.976, ppb-levels detection limits of 1.61 ppb and large Stokes shifts of 101 nm. Meanwhile, as an application example of as-prepared PU-co-HCCA nanoemulsion, a Hg2+ test paper was prepared by modifying filter paper with PU-co-HCCA nanoemulsion, and results indicated that the test paper is portable and convenient and has a wide working pH range. We believe that the PU-co-HCCA nanoemulsion and the modified filter paper can provide a new design principle for the application of fluorescence sensors for metal ions including Hg2+.

Improving stability and separation performance of graphene oxide/graphene nanofiltration membranes by adjusting the laminated regularity of stacking-sheets.

The laminated graphene oxide (GO) membranes are promising alternatives in the field of nanofiltration due to their unique stacked interlayer structure and controllable molecular transport channels. However, it is still challenging to obtain satisfactory physical stability and separation performance to meet its practical application. In this study, a novel GO/Gr (graphene) nanofiltration membrane with high stability was engineered by post-hot-pressure treatment, following forward pressure filtration. The impact of GO/Gr loading ratio of the composites nanofiltration membranes for the permeability, selectivity, hydrophilicity and physical stability was investigated. The GO/Gr nanofiltration membranes exhibited high stability and separation performance because of the enhanced regularity and smoothness of the overall stacking layers. It was demonstrated that the satisfactory permeability (12.8-20 L·m-2·h-1) of GO/Gr nanofiltration membranes could be achieved. Compared with the pure GO membranes, GO/Gr-0.5 membranes exhibited a higher Na2SO4, NaCl, MgCl2, and MgSO4 rejection rate of approximately 78.3%, 51.2%, 34.5% and 32.6%, respectively. Meanwhile, the rejection rate (99.5%, 99.9%, 97.3% and 98.6%) of composite membranes for Methylene blue, Congo red, Rhodamine B and Methyl orange could be achieved. This facile way reveals the potential of stacked GO/Gr membranes in developing GO-based nanofiltration membranes.

Self-Healing, Solvent-Free, Anti-Corrosion Coating Based on Skin-like Polyurethane/Carbon Nanotubes Composites with Real-Time Damage Monitoring.

Self-healing anti-corrosion materials are widely regarded as a promising long-term corrosion protection strategy, and this is even more significant if the damage can be monitored in real-time and consequently repaired. Inspired by the hierarchical structure of human skin, self-healing, solvent-free polyurethane/carbon nanotubes composites (SFPUHE-HTF-CNTs) with a skin-like bilayer structure were constructed. The SFPUHE-HTF-CNTs were composed of two layers, namely, a hydrophobic solvent-free polyurethane (SFPUHE-HTF) containing disulfide bonds and fluorinated polysiloxane chain segments consisting of a self-healing layer and CNTs with good electrical conductivity consisting of a corrosion protection layer, which also allowed for the real-time monitoring of damage. The results of corrosion protection experiments indicated that the SFPUHE-HTF-CNTs had a low corrosion current density (8.94 × 10-9 A·cm-2), a positive corrosion potential (-0.38 V), and a high impedance modulus (|Z| = 4.79 × 105 Ω·cm2). The impedance modulus could still reach 4.54 × 104 Ω·cm2 after self-healing, showing excellent self-healing properties for anti-corrosion protection. Synchronously, the SFPUHE-HTF-CNTs exhibited a satisfactory damage sensing performance, enabling the real-time monitoring of fractures at different sizes. This work realized the effective combination of self-healing with corrosion protection and damage detection functions through a bionic design, and revealed the green, and low-cost preparation of advanced composites, which have the advantage of scale production.

Mechanical Properties and Wear Resistance of Sulfonated Graphene/Waterborne Polyurethane Composites Prepared by In Situ Method.

In order to improve the dispensability of graphene oxide (GO) in waterborne polyurethane (WPU), sulfonated graphene (SGO) with superior dispersity was prepared by modifying graphene oxide with sodium 2-chloroethane sulfonate to introduce hydrophilic sulfonic groups into the structure. SGO/WPU composites were prepared using isophorone diisocyanate (IPDI), polytetramethylene ether glycol (PTMEG 2000), dimethylolpropionic acid (DMPA) and SGO as raw materials. The influence of SGO content on composite properties were investigated. The structure and morphology of SGO and SGO/WPU composites were characterized by infrared spectroscopy, X-ray diffractometry and transmission electron microscopy etc. Their mechanical properties and wear resistance were analyzed as well. The experimental results showed that SGO was successfully grafted onto polyurethane macromolecule by an in situ method and, with the introduction of sulfonic groups, the interfacial compatibility of GO and PU was improved significantly so that SGO evenly dispersed into WPU. The SGO that was grafted onto WPU macromolecules exhibited layered morphology with nanometers in the WPU matrix. With increasing SGO content, the tensile strength and the wear resistance of the film increased, but the addition of more than 0.8 wt % SGO yielded unfavorable results. When the added amount of SGO was 0.8 wt % of WPU, the tensile strength of the composite film was 46.53% higher than that of the blank group, and the wear resistance of the film was remarkably improved, which was due to a strong interaction between the SGO and WPU phases. Thus, the conclusion can be drawn that appropriate amount of SGO addition can enhance the mechanical properties of SGO/WPU composite film.

An Environmentally Friendly Approach for the Fabrication of Conductive Superhydrophobic Coatings with Sandwich-Like Structures.

A large amount of research has been devoted to developing novel superhydrophobic coatings. However, it is still a great challenge to pursuean environmentally friendly method that leads to superhydrophobic coatings. Herein, we demonstrate for the first time, an environmentally friendly method for the preparation of conductive superhydrophobic coatings with sandwich-like structures by using aminoethylaminopropyl polydimethylsiloxane modified waterborne polyurethane (SiWPU) and N-octadecylamine functionalized multi-wall carbon nanotubes. These environmentally friendly coatings with the sheet resistance of 1.1 ± 0.1 kΩ/sq exhibit a high apparent contact angle of 158.1° ± 2° and a low sliding angle below 1°. The influence of the surface texture before and after heat treatment on the wetting properties is discussed. In addition, the coatings can be electrically heated by 3~113 °C with a voltage of 12~72 V, and thus, can be used for deicing. Furthermore, the resulting coatings demonstrate good performance of wear resistance and ultraviolet resistance, which will have broad application potential in harsh environments.

Hot water-repellent and mechanically durable superhydrophobic mesh for oil/water separation.

The leakage of oil or organic pollutants into the ocean arouses a global catastrophe. The superhydrophobic materials have offered a new idea for the efficient, thorough and automated oil/water separation. However, most of such materials lose superhydrophobicity when exposed to hot water (e.g. >55 °C). In this study, a hot water-repellent superhydrophobic mesh used for oil/water separation was prepared with one-step spray of modified polyurethane and hydrophobic silica nanoparticles on the copper mesh. The as-prepared superhydrophobic mesh could be applied as the effective materials for the separation of oil/water mixture with a temperature up to 100 °C. In addition, the obtained mesh could selectively remove a wide range of organic solvents from water with high absorption capacity and good recyclability. Moreover, the as-prepared superhydrophobic mesh shows excellent mechanical durability, which makes it a promising material for practical oil/water separation.