Grafen Esaslı Yeşil Nanokompozitlerin Hazırlanması, Karakterizasyonu ve Çeşitli Uygulamalarda Kullanılması

Abstract

Graphene, a two-dimensional (2D) monoatomic thickness allotrope of carbon, has emerged as the exotic material of the 21st century and has become a rapidly rising star worldwide owing to its outstanding thermal, optical, electrical and mechanical properties. Thanks to its high crystalline nature and excellent physical properties, graphene and its derivatives are being studied with an increasing interest in science and engineering, particularly in materials science. In addition, a new polymer nanocomposite class has been obtained with the discovery of graphene due to its ability to be dispersed in various polymer matrices. In the study conducted within the scope of the thesis, using water as solvent, the eco-friendly “green" cellulose/graphene based nanocomposite films were prepared by a simple and low-cost solvent evaporation method. For this purpose, the original (nano) graphene used as reinforcement material is hydrophobic and commercially available. Cellulose-derived natural polymers, 2-hydroxyethyl cellulose (2-HEC), sodium carboxymethyl cellulose (Na-CMC) and hydroxypropyl methyl cellulose (HPMC), were used as the matrix phase. In the first step, the pristine graphene was modified with HCl and HNO3 to ensure its miscibility iv with cellulose matrices. Using these modified nanoplatelets as reinforcing phase, cellulose films were obtained. In the second stage of the study, boric acid (H3BO3) was used as a precursor to make heteroatom doping to the graphene and acid modified graphene samples were doped with boron atom. Cellulose nanocomposite films were prepared with boron doped acid modified graphene samples. Characterization studies were evaluated using different instrumental analysis methods, FT-IR, XRD, SEM-EDX, Raman Spectroscopy, TGA/DTG, DSC, Mechanical Testing and AFM. In the final stage of the study, the application area studies were performed for cellulose/graphene nanocomposite films using HNO3 modified- and H3BO3 doped HNO3 modified- graphene samples. In this context, controlled drug release tests using doxorubicin (DOXO)-a drug used in chemotherapy and electrical conductivity tests were performed by using a two-point probe conductivity system to investigate the electrical conductivity of nanocomposite films. Overall results show that the basic structure of graphene is preserved after HCl and HNO3 modification and also boron doping. In FT-IR, XRD and Raman spectroscopy results, it was observed that the hydrophilic properties of graphene were achieved by forming functional groups (hydroxyl group, –OH) at the edges of graphene layer by acid modification and boron atoms were substituted with tightly stacked carbon atoms in the lattice structure of graphene by boron doping. Morphology studies with SEM and AFM methods also confirmed the boron doped graphene. As a result of TGA/DTG, DSC and Mechanical Testing studies, it was observed that the nanocomposite films were obtained by the addition of HNO3 modified and heteroatom doped HNO3 modified graphene to cellulose matrices were more thermally stable and mechanically stronger than the pure cellulose film. Electrical conductivity tests have shown that acid modified and boron doped acid modified graphene contributes to the formation of conductive networks throughout the cellulose having non-conductive nature. Controlled drug release experiments are also promising for studies to be carried out in this area. In this study, natural polymers are used as matrices and hydrophobic pristine graphene is transformed to hydrophilic one with acid modification. Boron doping have changed the properties of acid modified graphene. The nanocomposite materials obtained in this thesis study have the potential to provide improvement in alternative application areas.