Grafen aerojel sentezlenmesi ve uygulamaları

Three-dimensional (3D) graphene-based aerogels with well-defined interconnected porous networks are one of the lightest materials in the world. Thanks to their excellent properties, which include large surface area, controllable porous structure and functionalizable surface properties, they have not only electronic transmission capability but also unique features of interconnected networks and can be embedded in different materials. Also, graphene aerogels (GAs) have fascinating properties such as low density, low thermal conductivity, high adsorption capacity, high mechanical strength, and electrical conductivity. Due to these features, they attract the attention of various research areas. Up to now, many synthesis methods have been used to produce GAs, which differ in performance and structure. This thesis is devoted to the synthesis of GA via one step hydrothermal treatment of graphene oxide (GO) solutions based on modified Hummer's method and the fabrication of different strain sensors based on these produced GAs for its applications. To achieve this, GO and reduced graphene oxide (rGO) solutions are synthesized as precursors to produce the high surface area GAs (~700 m2/g) with the support of supercritical CO2 (scCO2) drying. Obtained GAs are used to construct GA based hybrid materials for the fabrication of strain sensors as its applications. Strain sensors are very attractive tools for structural health monitoring applications and intelligent management. Especially, flexible piezotronics strain sensors provide high sensitivity and fast response times which make them an ideal candidate for these applications. Therefore, the nanostructured architectures have become very attractive but challenging in the recent years. Various designs have been developed using different piezoelectric materials, yet most applications use ZnO nanomaterials due to their unique advantages such as biocompatibility and optical properties. However, these nanowires require a compatible host material that includes ZnO electronically and permits them a flexible movement. To satisfy this need, ZnO nanowires (ZnO-NWs) are constantly embedded in various materials to build flexible strain sensors. In this thesis, we develop a technique to produce a flexible piezotronics strain sensor based on ZnO-NWs embedded in the synthesized GA substrates, since GAs provide excellent receiving substrate properties, which in turn helps to maintain ZnO piezoelectric properties under any conditions. Moreover, this defined strain sensor is fabricated with chemical vapor deposition (CVD) grown ZnO-NWs film on the synthesized GA substrate. Strain sensing, both static and dynamic loading, is demonstrated to show that GAs are promising candidates as a host material due to their remarkable properties. Additionally, the I-V characteristic of the sensor shows high sensitivity owing to the desirable piezotronics properties, piezo potential modulated changes in Schottky barrier height (SBH), under both static and dynamic loads. A good gauge factor (GF) of as high as 120 has been demonstrated, which is almost 50 % higher than GF for any ZnO/Carbon based strain sensor. Besides, numerous efforts are made to develop wearable devices through the utilization of nanomaterials, including nanowires, carbon nanotubes, and twodimensional (2D) materials. Particularly, graphene has been extensively studied for wearable applications thanks to its excellent electrical and mechanical properties. Especially, the focus is on the 3D graphene-based sensor architectures such as conductive foam, nano-papers, etc. However, all geometries still confront some obstacles with conformal integration and sensitivity. Hence, a novel method to create GA based strain sensors which can effectively extract information from involuntary human motion is demonstrated in this thesis. GAs were uniquely strengthened with carbon nanotubes (CNTs) to produce 3D hybrid frameworks. These provide stretchable characteristics, which is desirable since the conductive pathways are often maintained under high strain or stress conditions. Maintaining the conductive pathways is extremely important to supply reliable information, yet it is one of the challenges in strain sensor design. However, combination of GA and CNTs provides a superb framework for reliable data gathering and their material functionalization properties provide great opportunity to supply sensitive sensors. During this study, a strain sensor was prepared from highly functionalized GA by reconstruction with CNTs and dispersing technique, which is straightforward, low cost, and scalable.