Maziar Ghazinejad

Synthesis of a Pillared Graphene Nanostructure: A Counterpart of Three-Dimensional Carbon Architectures

Graphene is a single sheet of carbon atoms with outstanding electrical and physical properties and is being exploited for applications in electronics, sensors, photovoltaics, and energy storage. A novel 3D architecture called a pillared graphene nanostructure (PGN) is a combination of two allotropes of carbon, including graphene and carbon nanotubes. A one-step chemical vapor deposition process for large-area PGN fabrication via a combination of surface catalysis and in situ vapor-liquid-solid mechanisms is described. A process by which PGN layers can be transferred onto arbitrary substrates while keeping the 3D architecture intact is also described. Single and multilayer stacked PGNs are envisioned for future ultralarge and tunable surface-area applications in hydrogen storage and supercapacitors.

Centimeter-scale high resolution metrology of entire CVD grown graphene sheets

A high-throughput metrology method for measuring the thickness and uniformity of entire large-area chemical vapor deposition-grown graphene sheets on arbitrary substrates is demonstrated. This method utilizes the quenching of fluorescence by graphene via resonant energy transfer to increase the visibility of graphene on a glass substrate. Fluorescence quenching is visualized by spin-coating a solution of polymer mixed with fluorescent dye onto the graphene then viewing the sample under a fluorescence microscope. A large-area fluorescence montage image of the dyed graphene sample is collected and processed to identify the graphene and indicate the graphene layer thickness throughout the entire graphene sample. Using this metrology method, the effect of different transfer techniques on the quality of the graphene sheet is studied. It is shown that small-area characterization is insufficient to truly evaluate the effect of the transfer technique on the graphene sample. The results indicate that introducing a drop of acetone or liquid poly(methyl methacrylate) (PMMA) on top of the transfer PMMA layer before soaking the graphene sample in acetone improves the quality of the graphene dramatically over immediately soaking the graphene in acetone. This work introduces a new method for graphene quantification that can quickly and easily identify graphene layers in a large area on arbitrary substrates. This metrology technique is well suited for many industrial applications due to its repeatability and flexibility.

Tuning Electron Transport in Graphene-Based Field-Effect Devices using Block Co-polymers

Graphene possesses many remarkable properties and shows promise as the future material for building nanoelectronic devices. For many applications such as graphene-based field-effect transistors (GFET), it is essential to control or modulate the electronic properties by means of doping. Using spatially controlled plasma-assisted CF(4) doping, the Dirac point shift of a GFET covered with a polycrystalline PS-P4VP block co-polymer (BCP) [poly(styrene-b-4-vinylpyridine)] having a cylindrical morphology can be controlled. By changing the chemical component of the microdomain (P4VP) and the major domain (PS) with the CF(4) plasma technique, the doping effect is demonstrated. This work provides a methodology where the Dirac point can be controlled via the different sensitivities of the PS and P4VP components of the BCP subjected to plasma processing.

Fabrication and characterization of polycaprolactone-graphene powder electrospun nanofibers

Porous fibrous membranes having multiple scales geometries and tailored properties have become attractive microfabrication materials in recent years. Due to the feasibility of incorporating graphene in electrospun nanofibres and the growing interest on these nanomaterials, the present paper focuses on the electrospinning of Poly (ε-Caprolactone) (PCL) solutions in the presence of different amounts of Graphene platelets. Electrospinning is a process whereby ultrafine fibers are formed in a high-voltage electrostatic field. The morphological appearance, fiber diameter, and structure of PCL nanofibers produced by the electrospinning process were studied in the presence of different concentration of graphene. Moreover, the effect of a successful incorporation of graphene nanosheets into PCL polymer nanofibers was analyzed. Scanning electron microscope micrographs of the electrospun fibers showed that the average fiber diameter increases in the presence of graphene. Furthermore, the intrinsic properties developed due to the interactions of graphene and PCL improved the mechanical properties of the nanofibers. The results reveal the effect of various graphene concentrations on PCL and the strong interfacial interactions between the graphene platelets phase and the polymer matrix. The functional complexity of the electrospun fibers provides significant advantages over other techniques and shows the promise of these fibers for many applications including air/water filters, sensors, organic solar cells, smart textiles, biocompatible scaffolds for tissue engineering and load-bearing applications. Optimizing deposition efficiency, however, is a necessary milestone for the widespread use of this technique.

Nitrogen-Rich Polyacrylonitrile-Based Graphitic Carbons for Hydrogen Peroxide Sensing

Catalytic substrate, which is devoid of expensive noble metals and enzymes for hydrogen peroxide (H2O2), reduction reactions can be obtained via nitrogen doping of graphite. Here, we report a facile fabrication method for obtaining such nitrogen doped graphitized carbon using polyacrylonitrile (PAN) mats and its use in H2O2 sensing. A high degree of graphitization was obtained with a mechanical treatment of the PAN fibers embedded with carbon nanotubes (CNT) prior to the pyrolysis step. The electrochemical testing showed a limit of detection (LOD) 0.609 µM and sensitivity of 2.54 µA cm−2 mM−1. The promising sensing performance of the developed carbon electrodes can be attributed to the presence of high content of pyridinic and graphitic nitrogens in the pyrolytic carbons, as confirmed by X-ray photoelectron spectroscopy. The reported results suggest that, despite their simple fabrication, the hydrogen peroxide sensors developed from pyrolytic carbon nanofibers are comparable with their sophisticated nitrogen-doped graphene counterparts.

Graphitizing Non-graphitizable Carbons by Stress-induced Routes

Graphitic carbons’ unique attributes have attracted worldwide interest towards their development and application. Carbon pyrolysis is a widespread method for synthesizing carbon materials. However, our understanding of the factors that cause differences in graphitization of various pyrolyzed carbon precursors is inadequate. We demonstrate how electro-mechanical aspects of the synthesis process influence molecular alignment in a polymer precursor to enhance its graphitization. Electrohydrodynamic forces are applied via electrospinning to unwind and orient the molecular chains of a non-graphitizing carbon precursor, polyacrylonitrile. Subsequently, exerting mechanical stresses further enhances the molecular alignment of the polymer chains during the formative crosslinking phase. The stabilized polymer precursor is then pyrolyzed at 1000 °C and characterized to evaluate its graphitization. The final carbon exhibits a uniformly graphitized structure, abundant in edge planes, which translates into its electrochemical kinetics. The results highlight the significance of physical synthesis conditions in defining the structure and properties of pyrolytic carbons.

Fluorescence quenching metrology of graphene

We investigate the application of fluorescence quenching microscopy (FQM) for visual characterization of graphene quality, number of layers and uniformity over its landscape. The method relies on the fact that pristine, modified and multi-layer graphene regions quench fluorescence with different rates. Steady-state and time-resolved emission spectroscopy are used to comparatively characterize the photophysical behavior of pristine graphene relative to unquenched dye on bare substrate. The results demonstrate that with premeditated choice of Fluorescence dye, the interaction between fluorophores and graphene provides valuable tools for identifying the chemical structure and thickness of graphene. Fluorescence quenching metrology can be implemented as the basis for a microscopy based metrology for 2D materials.

Thermoeconomic Optimization of Gas Turbine Combined Heat and Power System in a Paper Mill

Located in the South of Iran, Jiroft Paper Mill Company requires an integrated combined heat and power plant, which can provide 50 MW of electric power and 100 ton/hr saturated steam at 13 bars, to produce paper from an adjacent eucalyptus forest. The plant is comprised of a gas turbine, air compressor, combustion chamber, and air preheater as well as a heat recovery steam generator (HRSG). The design Parameters of the plant were chosen as: compressor pressure ratio (rc ), compressor isentropic efficiency (ηAC ), gas turbine isentropic efficiency (ηT ), combustion chamber inlet temperature (T3 ), and turbine inlet temperature (T4 ). In order to optimally find the design parameters a thermoeconomic approach has been followed. An objective function representing the total cost of the plant in terms of dollar per second, was defined as the sum of the operating cost related to the fuel consumption, and the capital investment which stands for equipment purchase and maintenance costs and the cost, corresponding to the exergy destruction in various components. Subsequently, different parts of the objective function have been expressed in terms of decision variables. Finally, the optimal values of decision variables were obtained by minimizing the objective function using sequential quadratic programming (SQP). The influence of changes in the demanded power and steam on the design parameters have been also studied for 40, 50, 60, and 70 MW of net power output, and 100, 120, 150, ton/hr of saturated steam mass flow rate.Copyright

Rapid Iodine Sensing on Mechanically Treated Carbon Nanofibers

In this work, we report on a rapid, efficient electrochemical iodine sensor based on mechanically treated carbon nanofiber (MCNF) electrodes. The electrode’s highly graphitic content, unique microstructure, and the presence of nitrogen heteroatoms in its atomic lattice contribute to increased heterogeneous electron transfer and improved kinetics compared to conventional pyrolytic carbons. The electrode demonstrates selectivity for iodide ions in the presence of both interfering agents and high salt concentrations. The sensor exhibits clinically relevant limits of detection of 0.59 µM and 1.41 µM, in 1X PBS and synthetic urine, respectively, and a wide dynamic range between 5 µM and 700 µM. These results illustrate the advantages of the material’s unique electrochemical properties for iodide sensing, in addition to its simple, inexpensive fabrication. The reported iodine sensor eliminates the need for specimen processing, revealing its aptitude for applications in point-of-care diagnostics.

Manufacturing Carbon Nanofiber Electrodes with Embedded Metallic Nanoparticles using Block Copolymers Templates

Owing to its superb thermal and electrical attributes, as well as electrochemical stability, carbon is emerging as an attractive material for fabrication of many bioelectrochemical devices such as biosensors and biofuel cells. However, carbon’s inert nature makes it difficult to functionalize with biocatalysts; often requiring harsh chemical treatment, such as nitric acid oxidation, to attach reactive amines and carboxylic acids to its surface. Recent studies, however, points toward a self-assembly approach for fabricating well organized layers of carbon loaded with arrays of metallic nanoparticles patterned by block-copolymers (BCP) templates. Herein, we demonstrate an effective method for developing carbon nanofibers meshes embedded with metal nanoparticles, by incorporating a BCP self-assembly approach into our C-MEMS fabrication technique. The main phase of this hybrid method includes electrospinning metal salt-loaded BCP into nanofiber meshes, and subsequently reducing the metal salts into metal nanoparticles prior to pyrolysis. This cost-effective process will pave the way for fabricating scalable advanced 3-D carbon electrodes that can be applied to biosensors and biofuel cells devices.