Preface

Click on the DOI link to access the article (may not be free).Energy and environmental issues are of great concerns for the public and will keep increasing in the next few decades. The demand for clean energy sources in our current society also increases with large-scale economic developments and population growth. It is crucial to build clean energy systems

Synthesis and Variable Temperature Electrical Conductivity Studies of Highly Ordered TiO2 Nanotubes

Rafts of aligned, high aspect ratio TiO2 nanotubes were fabricated by an electrochemical anodization method and their axial electrical conductivities were determined over the temperature range 225-400 °C. Length, outer diameter and wall thickness of the nanotubes were approximately 60-80 µm, 160 nm and 30 nm, respectively. Transmission electron microscopy studies confirmed that the TiO2 nanotubes were initially amorphous, and became polycrystalline anatase after heat treatment attemperatures as low as 250 °C in air. The activation energy for conductivity over the temperature range 250 - 350 °C was found to be 0.87 eV. The conductivity values are comparable to those of nanocrystalline and nanoporous anatase thin films reported in literature.Engineering and Applied Science

Functionalization of Carbon Nanotube Yarn by Acid Treatment

Carbon nanotube (CNT) yarn was functionalized using sulfuric and nitric acid solutions in 3:1 volumetric ratio. Successful functionalization of CNT yarn with carboxyl and hydroxyl groups (e.g., COOH, COO–, OH, etc.) was confirmed by attenuated total reflectance spectroscopy. X-ray diffraction revealed no significant change to the atomic in-plane alignment in the CNTs; however, the coherent length along the diameter was significantly reduced during functionalization. A morphology change of wavy extensions protruding from the surface was observed after the functionalization treatment. The force required to fracture the yarn remained the same after the functionalization process; however, the linear density was increased (310%). The increase in linear density after functionalization reduced the tenacity. However, the resistivity density product of the CNT yarn was reduced significantly (234%) after functionalization

Electrical and Thermal Characterization of Electrospun PVP Nanocomposite Fibers

Polyvinylpyrrolidone (PVP) solutions incorporated with multiwall carbon nanotubes (MWCNTs) were electrospun at various weight percentages, and then the electrical resistance and some thermal properties of these nanocomposite fibers were determined using a high-accuracy electrical resistance measurement device. During the electrospinning process, system and process parameters, such as concentrations, applied voltage, tip-to-collector distance, and pump speeds, were optimized to receive the consistent nanocomposite fibers. When polymers are used in many industrial applications, they require high electrical and thermal conductivities. Most polymers exhibit low electrical conductivity values; however, in the presence of conductive inclusions, the electrical resistance of the MWCNT fibers was reduced from 50 MΩ to below 5 MΩ, which may be attributed to the higher electrical conductivities of these nanoscale inclusions and fewer voids under the applied loads. This study may open up new possibilities in the field for developing electrically conductive novel nanomaterials and devices for various scientific and technological applications

Effects of Hydrophobic Barrier Films on the Mechanical Properties of Fiber Reinforced Composites Immersed in Water

Click on the DOI link to access the article (may not be free).Fiber reinforced composites are subjected to a wide range of mechanical loads and environmental conditions, such as wind, high/low temperature, moisture, UV light and aggressive solvents. Compared to other structural materials, polymers can absorb more moisture and UV light from outside environment and lose their material properties (e.g., mechanical, electrical, surface and thermal) and thus the service life. In this study, hydrophobic barrier films including polyvinylfluoride (PVF) and polyether ether ketone (PEEK) were applied on the carbon, Kevlar, and glass fiber reinforced epoxy resin composites (laminate and sandwich structures), and then the effects of moisture absorption on those films were investigated in detail. The coupons were immersed in water for a number of days in order to determine the changes in mechanical properties of the composites. Three point bending tests were applied to the laminate composites, while four point bending tests were conducted on the Nomex sandwich structured composites. We found that moisture absorption could be eliminated by using these hydrophobic films. We found that PEEK film could be an alternative barrier film for the aircraft industry

Prevention of Surface Crack Formations on Polymeric Coatings Using Carbon Nanotubes

Click on the DOI link to access the article (may not be free).Polymeric coatings are frequently utilized for the protection of materials surface against UV light and other environmental factors (e.g., oxygen, pollutants and moistures) by many industries. However, the organic films have yet to be perfected and failures due to the degradation caused by the environmental factors are potential hazards. These hazards can cost the US economy billions of dollars and cause serious accidents. In order to minimize UV and other environmental factors on the polymeric coatings, new studies are focused on functional coating systems. In the present study, we have developed a nanocomposite coatings to reduce the crack formations and increase the life-time of the coatings. Different weight percentages (0%, 0.25%, 0.5%, 1% and 2%) of multi-wall carbon nanotubes (MWCNTs) were indvidually dispersed in the coating maetrials, and then sprayed on the surfaces of aircraft Al alloys. UV light and salt chamber tests were applied to the prepared coating samples. Optical microscopy and atomic force microscopy (AFM) studies showed that the micro and nanocrack formations on coatings were significanly lowered at higher MWCNT loadings (e.g., 2%). As a results, it is concluded that CNTs played a vital role in protecting of polymeric coatings against UV degradation and corrosion

Introduction to Green Nanostructured Photocatalysts

Recently, because of major concerns regarding fossil fuels, research in modern societies has focused on the utilization of alternative renewable energy sources in order to meet future energy demands. Solar energy is recognized as the primary source of renewable energy due to its year-round availability and its applications in various fields, such as heating, water splitting, and electricity generation using photocatalysts. The major drawbacks of solar energy conversion systems are their lower conversion efficiency, higher manufacturing and replacement costs, and health and environmental impacts of the materials employed. In order to eliminate such obstacles, many studies have focused on the energy and cost efficiency of solar cells (particularly dye-sensitized solar cells and thin-film solar cells), water-splitting devices, and CO2-capturing systems using various photocatalytic green nanomaterials, such as binary and ternary metal oxides, microorganisms (bacteria, algae, and viruses), and other catalysts and cocatalysts. These materials have been extensively studied because of their many advantages: chemical stability, tunable band gap structures, and abundance on Earth. In this book, we discuss the fundamentals of solar energy conversion, green synthesis approaches using these photocatalysts, the natural photosynthetic system, water splitting, CO2 capture, and organic and inorganic contaminant removal processes using photo-active green nanomaterials, as well as the theory behind these processes and standard measurements for comparisons. We also provide an update of recent developments in the field for the benefit of reader