그라핀 특성 연구와 응용

Abstract

Graphene is a new synthetic allotrope of carbon which has high intrinsic electrical conductivity, large theoretical specific surface area, high mechanical strength, and high chemical stability. It has potential applications in electronic/spintronic devices, touch panels, gas/biosensors, solar cells, removal of hazardous materials, and fast DNA sequencing. Although graphene exfoliated by scotch tape shows superior properties to that fabricated by other methods, chemical vapour deposition (CVD) and chemically exfoliated graphene (graphene oxdie or reduced graphene oxide) have become a major manufacturing process for application in technological area. Thus, characterization of two types of graphene became important. The systematic study of line defects and convenient visualization method of graphene surface are introduced in chapter 2 and chapter 3. Although CVD is the most promising technique for industrial-scale fabrication of graphene, diverse defects are formed due to multiple seeds and differential thermal expansion coefficients. Among these defects, line defects are of utmost importance, because even a single line defect can form two separated grains. The electrical and mechanical properties of graphene largely depend on line defects and grain sizes. Generally, there are two types of line defects: wrinkles and grain boundaries (GBs). More specifically, there are two types of GBs: stitched, overlapped. Wrinkles are also categorized into two types: standing collapsed wrinkle, and folded wrinkle. In two chapter, characterization of four types of line defects and easy visualization method of grain boundaries of graphene are explained. As one of application using high surface area of graphene, N-doped porous carbon via chemical activation of polypyrrole/graphene composites using potassium hydroxide solution for CO2 absorption application are introduced in chapter 3. Ruoff’s group reported synthesis of porous carbon with a BET (Brunauer–Emmett–Teller) surface area of~3100 m2 g-1 via chemical activation of graphene, enabling supercapacitors with high energy storagecapacity. This is related with high surface area of graphene and can be applied to graphene oxide/polymer composite for enhancing gas absorption properties. In chapter 2, the grain boundaries of CVDgraphene were visualized by chemical oxidation methods. Highly adhesive properties of graphene grain boundaries to permanganate lead to a very quick, easy and convenient method to visualize the grainboundaries simply using an optical microscope, which would be vital to improve specific properties of graphene In chapter 3, the surface information of CVD graphene was thoroughly studied by thermal evaporation of gold adatom. Although line defects such as grain boundaries (GBs) and wrinkles are unavoidable in graphene, difficulties in identification preclude studying their impact on electronic and mechanical properties. As previous methods focus on a single type of line defect, simultaneous measurements of both GBs and wrinkles with detailed structural information have not been reported. Effective visualization of both line defects was introduced by controlled gold deposition. Upon depositing gold on graphene, single lines and double lines of gold nanoparticles (NPs) are formed along GBsand wrinkles, respectively. Moreover, it is possible to analyze whether a GB is stitched or overlapped, whether a wrinkle is standing or folded, and the width of the standing collapsed wrinkle. Theoretical calculations show that the characteristic morphology of gold NPs is due to distinct binding energies of line defects, which are correlated to disrupting diffusion of NPs. Our approach could be further exploited to investigate the defect structures of other two-dimensional materials In chapter4, reduced graphene oxide and polymer composite (N-doped porous carbon) was introduced as CO2 absorption material. N-doped porous carbon produced via chemical activation of polypyrrole functionalizedgraphene sheets shows selective adsorption of CO2 (4.3 mmol g-1) over N2 (0.27 mmol g-1) at 298 K. The potential for large scale production and facile regeneration makes this material useful for industrial applications.