Elias K. Stefanakos

Synthesis, characterization, and applications of ZnO nanowires

ZnO nanowires (or nanorods) have been widely studied due to their unique material properties and remarkable performance in electronics, optics, and photonics. Recently, photocatalytic applications of ZnO nanowires are of increased interest in environmental protection applications. This paper presents a review of the current research of ZnO nanowires (or nanorods) with special focus on photocatalysis. We have reviewed the semiconducting photocatalysts and discussed a variety of synthesis methods of ZnO nanowires and their corresponding effectiveness in photocatalysis. We have also presented the characterization of ZnO nanowires from the literature and from our own measurements. Finally, a wide range of uses of ZnO nanowires in various applications is highlighted in this paper.

Nanomaterials for Hydrogen Storage Applications: A Review

Nanomaterials have attracted great interest in recent years because of the unusual mechanical, electrical, electronic, optical, magnetic and surface properties. The high surface/volume ratio of these materials has significant implications with respect to energy storage. Both the high surface area and the opportunity for nanomaterial consolidation are key attributes of this new class of materials for hydrogen storage devices. Nanostructured systems including carbon nanotubes, nano-magnesium based hydrides, complex hydride/carbon nanocomposites, boron nitride nanotubes, nanotubes, alanates, polymer nanocomposites, and metal organic frameworks are considered to be potential candidates for storing large quantities of hydrogen. Recent investigations have shown that nanoscale materials may offer advantages if certain physical and chemical effects related to the nanoscale can be used efficiently. The present review focuses the application of nanostructured materials for storing atomic or molecular hydrogen. The synergistic effects of nanocrystalinity and nanocatalyst doping on the metal or complex hydrides for improving the thermodynamics and hydrogen reaction kinetics are discussed. In addition, various carbonaceous nanomaterials and novel sorbent systems (e.g. carbon nanotubes, fullerenes, nanofibers, polyaniline nanospheres and metal organic frameworks etc.) and their hydrogen storage characteristics are outlined.

Rectenna developments for solar energy collection

The rectenna concept for solar energy collection rests on the dual wave/photon nature of light. The recent developments in nanotechnology and manufacturing led to the re-examination of the rectenna concept for solar energy collection. Two fundamental physical limitations, skin effect resistance and very low voltage per antenna element, were identified for the rectenna system. This paper reports on research efforts to identify the problems through experimentation at lower frequencies and simulation at the light frequencies and has identified possible design solutions to some of the problems.

Visible light photocatalysis via CdS/TiO 2 nanocomposite materials

Nanostructured colloidal semiconductors with heterogeneous photocatalytic behavior have drawn considerable attention over the past few years. This is due to their large surface area, high redox potential of the photogenerated charge carriers, and selective reduction/oxidation of different classes of organic compounds. In the present paper, we have carried out a systematic synthesis of nanostructured CdS-TiO2 via reverse micelle process. The structural and microstructural characterizations of the as-prepared CdSTiO 2 nanocomposites are determined using XRD and SEM-EDS techniques. The visible light assisted photocatalytic performance is monitored by means of degradation of phenol in water suspension.

Direct DC-DC electric vehicle charging with a grid connected photovoltaic system

The Electric Vehicle/Photovoltaic Demonstration and Evaluation Program being conducted at the University of South Florida (USF) includes a 20 kW (peak) photovoltaic (PV) system in which PV panels form the roof of a 12 bay carport. A 6 kW (peak) segment of the PV system can be simultaneously distributed between computer controlled direct DC-DC charging and power grid interconnection. The DC-DC charger (DC-DAS) controls the charging current of a battery pack with minimal power waste, by computer control of current flow direction of each of four source circuits. It demonstrates superior efficiency, dependability and safety for DC-DC charging over DC-AC-DC charging and has greater control over the last 20% of charge than traditional PV DC-DC chargers.

Measurements of Peltier cooling at a Ga‐GaAs interface using a liquid‐phase epitaxy system

The Peltier coefficient of n‐type GaAs was measured by passing an electrical current through the GaAs‐Ga solid‐liquid interface in a vertical liquid‐phase epitaxy (LPE) system. Application of a steady‐state heat‐transfer analysis yielded values for the Peltier coefficient of 0.141 to 0.203 V in the 530–830 °C temperature range. From the study of measurements of Peltier cooling as a function of GaAs substrate thickness, current amplitude, and system geometry, it was concluded that effective utilization of Peltier cooling depends greatly on specimen thickness, doping, and furnace temperature, especially in LPE applications.

Organic Fluids in a Supercritical Rankine Cycle for Low Temperature Power Generation

This paper presents a performance analysis of a supercritical organic Rankine cycle (SORC) with various working fluids with thermal energy provided from a geothermal energy source. In the present study, a number of pure fluids (R23, R32, R125, R143a, R134a, R218, and R170) are analyzed to identify the most suitable fluids for different operating conditions. The source temperature is varied between 125 C and 200 C, to study its effect on the efficiency of the cycle for fixed and variable pressure ratios. The energy and exergy efficiencies for each working fluid are obtained and the optimum fluid is selected. It is found that thermal efficiencies as high as 21% can be obtained with 200 C source temperature and 10 C cooling water temperature considered in this study. For medium source temperatures (125 150 C), thermal efficiencies higher than 12% are obtained.

A review of self-assembled monolayers as potential terahertz frequency tunnel diodes

AbstractIn this review, we describe the principles of the tunnel junction, self-assembled monolayer (SAM) application techniques, experimental testbed fabrication, and characterization of the films and devices. In addition, techniques for directed application, removal, and functionalization of the monolayers are discussed. Bottom-up fabrication techniques have seen increased attention because of their versatility and ease of use. These films see mechanical uses as surface modifiers and micro-scale lubricants. Advances in nanowatt electronics and ultra-low power sensors have opened up an energy harvesting niche for solutions which would have proven ineffective just some years ago. The focus of this study is the two-terminal junction which has potential applications in THz rectification for energy harvesting, medical imaging, and defense sensing. The quantum theory of operation behind these devices is touched on briefly—describing tunneling through the organic monolayers. Commentary on trends in research and potential future work are presented as well.

A novel nitrogen rich porous aromatic framework for hydrogen and carbon dioxide storage

A nitrogen rich, p-phenylenediamine based, porous aromatic framework (NPAF) with 1790 m2 g−1 BET surface area has been synthesized by using a Yamamoto coupling technique. The NPAF has shown a hydrogen uptake of 1.87 and 0.33 wt% at 77 K per 1 atm and 298 K per 80 bar, respectively. The CO2 uptake and selectivity of the NPAF at 273 K per 1 atm is 3.64 mmol g−1 and 48, respectively.

Synthesis and characterization of photocatalytic TiO 2 -ZnFe 2 O 4 nanoparticles

A new coprecipitation/hydrolysis synthesis route is used to create a TiO2-ZnFe2O4 nanocomposite that is directed towards extending the photoresponse of TiO2 from UV to visible wavelengths (> 400 nm). The effect of TiO2s accelerated anatase-rutile phase transformation due to the presence of the coupled ZnFe2O4 narrow-bandgap semiconductor is evaluated. The transformations dependence on pH, calcinations temperature, particle size, and ZnFe2O4 concentration has been analyzed using XRD, SEM, and UV-visible spectrometry. The requirements for retaining the highly photoactive anatase phase present in a ZnFe2O4 nanocomposite are outlined. The visible-light-activated photocatalytic activity of the TiO2-ZnFe2O4 nanocomposites has been compared to an Aldrich TiO2 reference catalyst, using a solar-simulated photoreactor for the degradation of phenol.