Preparation of 2D Materials with Small Scale Multiphase Flows

Official URL: https://risc01.sabanciuniv.edu/record=b2583864_(Table of contents)

Tremendous research efforts have recently focused on the synthesis of graphene from graphitic materials, while environmental issues, scalability, and cost are some of the major challenges to be surmounted. Liquid phase exfoliation (LPE) of graphene is one of the principal methods for this synthesis. Nevertheless, sufficient information about the mechanisms of exfoliation has yet to emerge. Here, a microreactor based on the hydrodynamic cavitation (HC) on a chip concept is introduced to exfoliate graphite in a totally green process which involves only natural graphite flakes and water. The present sustainable reactor system was found to exfoliate thick and large graphite particles to nano-sized sheets (⁓ 1.2 nm) with a lateral size of ⁓ 500 nm to 5 μm. Besides the application of hydrodynamic cavitation for 2D material synthesis, in the second part of this thesis we tried to fabricate a filter/membrane for separating of gas or some component of liquid media with the use of electrospinning method. Electrospinning is an electrohydrodynamic process involving a polymeric droplet and slim charged liquid jet. The polymer solution is subjected to a high potential electric field. The high voltage enables the production of continuously long fibers on a collector surface. In this thesis, the effects of major parameters on the electrospun fibers were extensively investigated. Optimum conditions for electrospinning were obtained on the surface of a collector, and the diameter of resulting fibers, through SEM (Scanning Electron Microscopy) investigations, was determined. The optimum values for concentration, applied voltage, the distance between the tip of needle and collector, and flow rate determined to be 10 wt.%, 12 kV, 20 cm, and 0.6 ml.h-1, respectively. Afterwards, the hydrophilicity of fibers was modified by adding different poly (ethylene glycol) (PEG) concentrations (20, 30, and 40 wt.%) to the polymeric solution. The contact angle analysis revealed that the poly (methyl methacrylate) (PMMA) and 30 wt.% PEG fabricated fibrous mat exhibited a better wettability and lower hydrophobicity compared to pure PMMA electrospun mats. In the next step, silica NPs (nanoparticles) were introduced to the polymeric solution of electrospinning in the form of an IPA (isopropanol)-based collide solution. The dispersed solution-based addition of silica NPs prevented the aggregation state of NPs in the nanofibers. The addition of silica nanoparticles also changed the thermal and mechanical properties of the ternary composite, which were analyzed in TGA (thermogravimetric analysis) and tensile tests. These results highlight that the hybrid composite leads to a promising new electrospun mat for filtration and bioengineering applications.