Advancement of Ag–Graphene Based Nanocomposites: An Overview of Synthesis and Its Applications

Graphene has been employed as an excellent support for metal nanomaterials because of its unique structural and physicochemical properties. Silver nanoparticles (AgNPs) with exceptional properties have received considerable attention in various fields; however, particle aggregation limits its application. Therefore, the combination of AgNPs and graphene based nanocomposites (Ag–graphene based nanocomposites) has been widely explored to improve their properties and applications. Excitingly, enhanced antimicrobial, catalytic, and surface enhanced Raman scattering properties are obtained after their combination. In order to have a comprehensive knowledge of these nanocomposites, this Review highlights the chemical and biological synthesis of Ag–graphene nanocomposites. In particular, their applications as antimicrobial agents, catalysts, and sensors in biomedicine, agricultural protection, and environmental remediation and detection are covered. Meanwhile, the factors that influence the synthesis and applications are also briefly discussed. Furthermore, several important issues on the challenges and new directions are also provided for further development of these nanocomposites.     

Recent Progress in Graphene‐Based Noble‐Metal Nanocomposites for Electrocatalytic Applications

The fast industrialization process has led to global challenges in the energy crisis and environmental pollution, which might be solved with clean and renewable energy. Highly efficient electrochemical systems for clean‐energy collection require high‐performance electrocatalysts, including Au, Pt, Pd, Ru, etc. Graphene, a single‐layer 2D carbon nanosheet, possesses many intriguing properties, and has attracted tremendous research attention. Specifically, graphene and graphene derivatives have been utilized as templates for the synthesis of various noble‐metal nanocomposites, showing excellent performance in electrocatalytic‐energy‐conversion applications, such as the hydrogen evolution reaction and CO₂ reduction. Herein, the recent progress in graphene‐based noble‐metal nanocomposites is summarized, focusing on their synthetic methods and electrocatalytic applications. Furthermore, some personal insights on the challenges and possible future work in this research field are proposed.     

Bioinspired Graphene‐Based Nanocomposites and Their Application in Flexible Energy Devices

Graphene is the strongest and stiffest material ever identified and the best electrical conductor known to date, making it an ideal candidate for constructing nanocomposites used in flexible energy devices. However, it remains a great challenge to assemble graphene nanosheets into macro‐sized high‐performance nanocomposites in practical applications of flexible energy devices using traditional approaches. Nacre, the gold standard for biomimicry, provides an excellent example and guideline for assembling two‐dimensional nanosheets into high‐performance nanocomposites. This review summarizes recent research on the bioinspired graphene‐based nanocomposites (BGBNs), and discusses different bioinspired assembly strategies for constructing integrated high‐strength and ‐toughness graphene‐based nanocomposites through various synergistic effects. Fundamental properties of graphene‐based nanocomposites, such as strength, toughness, and electrical conductivities, are highlighted. Applications of the BGBNs in flexible energy devices, as well as potential challenges, are addressed. Inspired from the past work done by the community a roadmap for the future of the BGBNs in flexible energy device applications is depicted.     

Interphase Induced Dynamic Self‐Stiffening in Graphene‐Based Polydimethylsiloxane Nanocomposites

The ability to rearrange microstructures and self‐stiffen in response to dynamic external mechanical stimuli is critical for biological tissues to adapt to the environment. While for most synthetic materials, subjecting to repeated mechanical stress lower than their yield point would lead to structural failure. Here, it is reported that the graphene‐based polydimethylsiloxane (PDMS) nanocomposite, a chemically and physically cross‐linked system, exhibits an increase in the storage modulus under low‐frequency, low‐amplitude dynamic compressive loading. Cross‐linking density statistics and molecular dynamics calculations show that the dynamic self‐stiffening could be attributed to the increase in physical cross‐linking density, resulted from the re‐alignment and re‐orientation of polymer chains along the surface of nano‐fillers that constitute an interphase. Consequently, the interfacial interaction between PDMS‐nano‐fillers and the mobility of polymer chain, which depend on the degree of chemical cross‐linking and temperature, are important factors defining the observed performance of self‐stiffening. The understanding of the dynamic self‐stiffening mechanism lays the ground for the future development of adaptive structural materials and bio‐compatible, load‐bearing materials for tissue engineering applications.     

Highly Stable and Dispersive Silver Nanoparticle–Graphene Composites by a Simple and Low‐Energy‐Consuming Approach and Their Antimicrobial Activity

A simple and low‐energy‐consuming approach to synthesize highly stable and dispersive silver nanoparticle–graphene (AgNP–GE) nanocomposites has been developed, in which the stability and dispersivity of the composites are varied greatly with the pH value and temperature of the reaction. The results demonstrate that the optimal reaction conditions are pH 11 at room temperature for 70 min. As‐synthesized composites display excellent antimicrobial activity, and can completely inhibit the growth of Escherichia coli cells at a concentration of 20 mg L^?1 (20 ppm). After treatment with 10 ppm AgNP–GE composites, the cells are killed completely within 3 h. The unique structure imparts such good antimicrobial properties to the composites. Firstly, the sheetlike AgNP–GE tends to be adsorbed and accumulated onto the surface of cells, which can change the permeability and enhance the antimicrobial activity. Secondly, Ag⁺ released from AgNPs can act on the cells effectively and fully, thereby resulting in cell death.     

A Bioinspired Interface Design for Improving the Strength and Electrical Conductivity of Graphene‐Based Fibers

Graphene‐based fibers (GBFs) are attractive for next‐generation wearable electronics due to their potentially high mechanical strength, superior flexibility, and excellent electrical and thermal conductivity. Many efforts have been devoted to improving these properties of GBFs in the past few years. However, fabricating GBFs with high strength and electrical conductivity simultaneously remains as a great challenge. Herein, inspired by nacre‐like multilevel structural design, an interface‐reinforced method is developed to improve both the mechanical property and electrical conductivity of the GBFs by introducing polydopamine‐derived N‐doped carbon species as resistance enhancers, binding agents, and conductive connection “bridges.” Remarkably, both the tensile strength and electrical conductivity of the obtained GBFs are significantly improved to ≈724 MPa and ≈6.6 × 10⁴ S m^?1, respectively, demonstrating great superiority compared to previously reported similar GBFs. These outstanding integrated performances of the GBFs provide it with great application potential in the fields of flexible and wearable microdevices such as sensors, actuators, supercapacitors, and batteries.     

氧化锌插层蒙脱土纳米复合材料的制备及其光催化活性

采用一种简便的方法制备了氧化锌插层蒙脱土纳米复合材料。首先将蒙脱土充分充水后进行冷冻,具有层状结构的蒙脱土充水后会发生膨胀,部分从块状的蒙脱土上剥离形成超薄的片层结构。然后通过可控的水热过程使氧化锌纳米粒子进入蒙脱土层间或覆盖于表面。结果表明,直径1~3 nm 的纳米氧化锌会插层于蒙脱土的层间,而直径达10~25 nm的纳米氧化锌则会镶嵌在蒙脱土表面。该纳米复合材料对模拟污染物甲基橙具有优异的光催化性能。     

Graphene‐Based Electrodes

Graphene, the thinnest two dimensional carbon material, has become the subject of intensive investigation in various research fields because of its remarkable electronic, mechanical, optical and thermal properties. Graphene‐based electrodes, fabricated from mechanically cleaved graphene, chemical vapor deposition (CVD) grown graphene, or massively produced graphene derivatives from bulk graphite, have been applied in a broad range of applications, such as in light emitting diodes, touch screens, field‐effect transistors, solar cells, supercapacitors, batteries, and sensors. In this Review, after a short introduction to the properties and synthetic methods of graphene and its derivatives, we will discuss the importance of graphene‐based electrodes, their fabrication techniques, and application areas.     

Graphene‐Based Nafion Nanocomposite Membranes: Enhanced Proton Transport and Water Retention by Novel Organo‐functionalized Graphene Oxide Nanosheets

Novel nanostructured organo‐modified layered materials based on graphene oxide carrying various hydrophilic functional groups (‐NH₂, ‐OH, ‐SO₃H) are prepared and tested as nanofillers for the creation of innovative graphene‐based Nafion nanocomposites. The hybrid membranes are characterized by a combination of analytical techniques, which show that highly homogeneous exfoliated nanocomposites are created. The pulsed field gradient NMR technique is used to measure the water self‐diffusion coefficients. Remarkable behavior at temperatures up to 140 °C is observed for some composite membranes, thereby verifying the exceptional water retention property of these materials. Dynamic mechanical analysis shows that hybrid membranes are much stiffer and can withstand higher temperatures than pure Nafion.