Single atom (Pd/Pt) supported on graphitic carbon nitride as efficient photocatalyst for visible-light reduction of carbon dioxide

Reducing carbon dioxide (CO2) to hydrocarbon fuel with solar energy is significant for high-density solar energy storage and carbon balance. In this work, single palladium/platinum (Pd/Pt) atoms supported on graphitic carbon nitride (g-C3N4), i.e. Pd/g-C3N4 and Pt/g-C3N4, acting as photocatalysts for CO2 reduction were investigated by density function theory (DFT) calcu-lations for the first time. During CO2 reduction, the individual metal atoms function as the active sites, while g-C3N4 provides the source of hydrogen (H*) from hydrogen evolution reaction. The complete, as-designed photocatalysts exhibit excellent activity in CO2 reduction. HCOOH is the preferred product of CO2 reduction on the Pd/g-C3N4 catalyst with a rate-determining barrier of 0.66 eV, while the Pt/g-C3N4 catalyst prefers to reduce CO2 to CH4 with a rate-determining barrier of 1.16 eV. In addition, depositing atom catalysts on g-C3N4 significantly enhances the visible light absorption, rendering them ideal for visible light reduction of CO2. Our findings open a new avenue of CO2 reduction for renewable energy supply.

New empirical expressions to correlate solubilities of solids in supercritical carbon dioxide

Supercritical processes are gaining importance in the last few years in the food, environmental and pharmaceutical product processing. The design of any supercritical process needs accurate experimental data on solubilities of solids in the supercritical fluids (SCFs). The empirical equations are quite successful in correlating the solubilities of solid compounds in SCF both in the presence and absence of cosolvents. In this work, existing solvate complex models are discussed and a new set of empirical equations is proposed. These equations correlate the solubilities of solids in supercritical carbon dioxide (both in the presence and absence of cosolvents) as a function of temperature, density of supercritical carbon dioxide and the mole fraction of cosolvent. The accuracy of the proposed models was evaluated by correlating 15 binary and 18 ternary systems. The proposed models provided the best overall correlations. (C) 2009 Elsevier BA/. All rights reserved.

Terahertz wave characteristics of a single-walled carbon nanotube containing a fluid flow using the nonlocal Timoshenko beam model

This paper presents the effect of nonlocal scaling parameter on the terahertz wave propagation in fluid filled single walled carbon nanotubes (SWCNTs). The SWCNT is modeled as a Timoshenko beam,including rotary inertia and transverse shear deformation by considering the nonlocal scale effects. A uniform fluid velocity of 1000 m/s is assumed. The analysis shows that, for a fluid filled SWCNT, the wavenumbers of flexural and shear waves will increase and the corresponding wave speeds will decrease as compared to an empty SWCNT. The nonlocal scale parameter introduces certain band gap region in both flexural and shear wave mode where no wave propagation occurs. This is manifested in the wavenumber plots as the region where the wavenumber tends to infinite (or wave speed tends to zero). The frequency at which this phenomenon occurs is called the ``escape frequency''. The effect of fluid density on the terahertz wave propagation in SWCNT is also studied and the analysis shows that as the fluid becomes denser, the wave speeds will decrease. The escape frequency decreases with increase in nonlocal scaling parameter, for both wave modes. We also show that the effect of fluid density and velocity are negligible on the escape frequencies of flexural and shear wave modes. (C) 2010 Elsevier B.V. All rights reserved.

Study on Young's modulus and microhardness of carbon nanotubes reinforced copper nanocomposite

Carbon nanotubes (CNTs) were discovered by Iijima in 1991 as the fourth form of carbon. Carbon nanotubes are the ultimate form of the carbon fibre because of its high Young's modulus in the order of 1 TPa, which is very useful for load transfer in nanocomposites. In the present work, CNT/Cu nanocomposites were fabricated by the powder metallurgy technique, and after extrusion of the nanocomposites, bright field transmission electron microscopic studies were carried out. From the transmission electron microscopic images obtained, a novel method of ascertaining the Young's modulus of multiwalled CNTs is worked out in the present paper, which turns out to be 0.94 TPa, which is consistent with experimental results. Furthermore, an attempt is made to investigate the microhardness of copper by reinforcing it with multiwalled CNTs. There is an increase in hardness by twofold in CNT/Cu nanocomposites as compared to pure Cu matrix. This is due to high relative density, even distribution of CNTs and proper bonding at CNT/Cu interfaces.

Studies on design, fabrication and reliability assessment of embedded passives on a high-density interconnect (HDI) organic substrate using a sequential build-up process

One of the foremost design considerations in microelectronics miniaturization is the use of embedded passives which provide practical solution. In a typical circuit, over 80 percent of the electronic components are passives such as resistors, inductors, and capacitors that could take up to almost 50 percent of the entire printed circuit board area. By integrating passive components within the substrate instead of being on the surface, embedded passives reduce the system real estate, eliminate the need for discrete and assembly, enhance electrical performance and reliability, and potentially reduce the overall cost. Moreover, it is lead free. Even with these advantages, embedded passive technology is at a relatively immature stage and more characterization and optimization are needed for practical applications leading to its commercialization.This paper presents an entire process from design and fabrication to electrical characterization and reliability test of embedded passives on multilayered microvia organic substrate. Two test vehicles focusing on resistors and capacitors have been designed and fabricated. Embedded capacitors in this study are made with polymer/ceramic nanocomposite (BaTiO3) material to take advantage of low processing temperature of polymers and relatively high dielectric constant of ceramics and the values of these capacitors range from 50 pF to 1.5 nF with capacitance per area of approximately 1.5 nF/cm(2). Limited high frequency measurement of these capacitors was performed. Furthermore, reliability assessments of thermal shock and temperature humidity tests based on JEDEC standards were carried out. Resistors used in this work have been of three types: 1) carbon ink based polymer thick film (PTF), 2) resistor foils with known sheet resistivities which are laminated to printed wiring board (PWB) during a sequential build-up (SBU) process and 3) thin-film resistor plating by electroless method. Realization of embedded resistors on conventional board-level high-loss epoxy (similar to 0.015 at 1 GHz) and proposed low-loss BCB dielectric (similar to 0.0008 at > 40 GHz) has been explored in this study. Ni-P and Ni-W-P alloys were plated using conventional electroless plating, and NiCr and NiCrAlSi foils were used for the foil transfer process. For the first time, Benzocyclobutene (BCB) has been proposed as a board level dielectric for advanced System-on-Package (SOP) module primarily due to its attractive low-loss (for RF application) and thin film (for high density wiring) properties.Although embedded passives are more reliable by eliminating solder joint interconnects, they also introduce other concerns such as cracks, delamination and component instability. More layers may be needed to accommodate the embedded passives, and various materials within the substrate may cause significant thermo -mechanical stress due to coefficient of thermal expansion (CTE) mismatch. In this work, numerical models of embedded capacitors have been developed to qualitatively examine the effects of process conditions and electrical performance due to thermo-mechanical deformations.Also, a prototype working product with the board level design including features of embedded resistors and capacitors are underway. Preliminary results of these are presented.

Terahertz Time Domain Spectroscopy to Detect Low-Frequency Vibrations of Double-Walled Carbon Nanotubes

We have measured the frequency-dependent real index of refraction and extinction coefficient (and hence the complex dielectric function) of a free-standing double-walled carbon nanotube film of thickness 200 nm by using terahertz time domain spectroscopy in the frequency range 0.1 to 2.5 THz. The real index of refraction and extinction coefficient have very high values of approximately 52 and 35, respectively, at 0.1 THz, which decrease at higher frequencies. Two low-frequency phonon modes of the carbon nanotubes at 0.45 and 0.75 THz were clearly observed for the first time in the real and imaginary parts of the complex dielectric function along with a broad resonance centred at around 1.45 THz, the latter being similar to that in single-walled carbon nanotubes assigned to electronic excitations. Our experiments bring out a possible application of double-walled carbon nanotube films as a neutral density filter in the THz range.

Mesoporous Carbon and Poly(3,4-ethylenedioxythiophene) Composite as Catalyst Support for Polymer Electrolyte Fuel Cells

In situ polymerization of 3,4-ethylenedioxythiophene with sol-gel-derived mesoporous carbon (MC) leading to a new composite and its subsequent impregnation with Pt nanoparticles for application in polymer electrolyte fuel cells (PEFCs) is reported. The composite exhibits good dispersion and utilization of platinum nanoparticles akin to other commonly used microporous carbon materials, such as carbon black. Pt-supported MC-poly(3,4-ethylenedioxythiophene) (PEDOT) composite also exhibits promising electrocatalytic activity toward oxygen reduction reaction, which is central to PEFCs. The PEFC with Pt-loaded MC-PEDOT support exhibits 75% of enhancement in its power density in relation to the PEFC with Pt-loaded pristine MC support while operating under identical conditions. It is conjectured that Pt-supported MC-PEDOT composite ameliorates PEFC performance/durability on repetitive potential cycling. (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3486172] All rights reserved.

Carbon recombination lines between 34.5 and 770 MHz toward Cassiopeia A

We present observations of low-frequency recombination lines of carbon toward Cas A near 34.5 MHz (n similar to 575) using the Gauribidanur radio telescope and near 560 MHz (n similar to 225) and 770 MHz (n similar to 205) using the NRAO 140 foot (43 m) telescope in Greenbank. We also present high angular resolution (1') observations of the C270 alpha line near 332 MHz using the Very Large Array in B-configuration. A high signal-to-noise ratio spectrum is obtained at 34.5 MHz, which clearly shows a Voigt profile with distinct Lorentzian wings, resulting from significant pressure and radiation broadening at such high quantum numbers. The emission lines detected near 332, 550, and 770 MHz, on the other hand, are narrow and essentially Doppler-broadened. The measured Lorentzian width at 34.5 MHz constrains the allowed combinations of radiation temperature, electron density, and electron temperature in the line-forming region. Radiation broadening at 34.5 MHz places a lower limit of 115 pc on the separation between Cas A and the line-forming clouds. Modeling the variation in the integrated line-to-continuum ratio with frequency indicates that the region is likely to be associated with the cold atomic hydrogen component of the interstellar medium, and the physical properties of this region are likely to be T-e = 75 K, n(e) = 0.02 cm(-3), T-R100 = 3200 K, and n(H) T-e = 10,000 cm(-3) K. Comparison of the distribution of the C270 alpha recombination line emission across Cas A with that of (CO)-C-12 and H I also supports the above conclusion.

Absolute Entropy and Energy of Carbon Dioxide Using the Two-Phase Thermodynamic Model

The two-phase thermodynamic (2PT) model is used to determine the absolute entropy and energy of carbon dioxide over a wide range of conditions from molecular dynamics trajectories. The 2PT method determines the thermodynamic properties by applying the proper statistical mechanical partition function to the normal modes of a fluid. The vibrational density of state (DoS), obtained from the Fourier transform of the velocity autocorrelation function, converges quickly, allowing the free energy, entropy, and other thermodynamic properties to be determined from short 20-ps MD trajectories. The anharmonic effects in the vibrations are accounted for by the broadening of the normal modes into bands from sampling the velocities over the trajectory. The low frequency diffusive modes, which lead to finite DoS at zero frequency, are accounted for by considering the DoS as a superposition of gas-phase and solid-phase components (two phases). The analytical decomposition of the DoS allows for an evaluation of properties contributed by different types of molecular motions. We show that this 2PT analysis leads to accurate predictions of entropy and energy of CO2 over a wide range of conditions (from the triple point to the critical point of both the vapor and the liquid phases along the saturation line). This allows the equation of state of CO2 to be determined, which is limited only by the accuracy of the force field. We also validated that the 2PT entropy agrees with that determined from thermodynamic integration, but 2PT requires only a fraction of the time. A complication for CO2 is that its equilibrium configuration is linear, which would have only two rotational modes, but during the dynamics it is never exactly linear, so that there is a third mode from rotational about the axis. In this work, we show how to treat such linear molecules in the 2PT framework.

A DMFC with Methanol-Tolerant-Carbon-Supported-Pt-Pd-Alloy Cathode

Methanol-tolerant Pt-Pd alloy catalysts supported on to carbon with varying Pt:Pd atomic ratios of 1:1, 2:1 and 3:1 are prepared by a novel wet-chemical method and characterized using powder XRD, XPS, FESEM, EDAX and TEM techniques. The optimum atomic weight ratio for Pt to Pd in the carbon-supported alloy catalyst as established by linear-sweep voltammetry (LSV) and cell polarization studies is found to be 2:1. A direct methanol fuel cell (DMFC) employing carbon-supported Pt-Pd (2:1) alloy (Pt-Pd/C) catalyst as the cathode catalyst delivers a peak-power density of 115 mW/cm(2) at 70 degrees C as compared to peak-power density of 60 mW/cm(2) obtained with the DMFC employing carbon-supported Pt (Pt/C) catalyst operating under similar conditions. In the literature, DMFCs operating with Pt-TiO2 (2:1)/C and Pt-Au (2:1)/C methanol-tolerant cathodes are reported to exhibit maximum ORR activity among the group of these methanol-tolerant cathodes with varying catalysts compositions. Accordingly, the present study also provides an effective route to design methanol-tolerant-oxygen-reduction catalysts for DMFCs. (C) 2011 The Electrochemical Society. DOI: 10.1149/1.3596542] All rights reserved.

Effect of packing density and adsorption parameters on the throughput of a thermal compressor

Vapour adsorption refrigeration systems (VAdS) have the advantage of scalability over a wide range of capacities ranging from a few watts to several kilowatts. In the first instance, the design of a system requires the characteristics of the adsorbate-adsorbent pair. Invariably, the void volume in the adsorbent reduces the throughput of the thermal compressor in a manner similar to the clearance volume in a reciprocating compressor. This paper presents a study of the activated carbon +HFC-134a (1,1,1,2-tetrafluoroethane) system as a possible pair for a typical refrigeration application. The aim of this study is to unfold the nexus between the adsorption parameters, achievable packing densities of charcoal and throughput of a thermal compressor. It is shown that for a thermal compressor, the adsorbent should not only have a high surface area, but should also be able to provide a high packing density. Given the adsorption characteristics of an adsorbent-adsorbate pair and the operating conditions, this paper discloses a method for the calculation of the minimum packing density necessary for an effective throughput of a thermal compressor. (C) 2002 Elsevier Science Ltd. All rights reserved.

Electrochemical tuning and mechanical resilience of single-wall carbon nanotubes

Single-wall carbon nanotubes (SWNTs) are fascinating systems exhibiting many novel physical properties. In this paper, we give a brief review of the structural, electronic, vibrational, and mechanical properties of carbon nanotubes. In situ resonance Raman scattering of SWNTs investigated under electrochemical biasing demonstrates that the intensity of the radial breathing mode varies significantly in a nonmonotonic manner as a function of the cathodic bias voltage, but does not change appreciably under anodic bias. These results can be quantitatively understood in terms of the changes in the energy gaps between the 1 D van Hove singularities in the electron density of states, arising possibly due to the alterations in the overlap integral of pi bonds between the p-orbitals of the adjacent carbon atoms. In the second part of this paper, we review our high-pressure X-ray diffraction results, which show that the triangular lattice of the carbon nanotube bundles continues to persist up to similar to10 GPa. The lattice is seen to relax just before the phase transformation, which is observed at similar to10 GPa. Further, our results display the reversibility of the 2D lattice symmetry even after compression up to 13 GPa well beyond the 5 GPa value observed recently. These experimental results explicitly validate the predicted remarkable mechanical resilience of the nanotubes.

Tailoring the microstructure and mechanical properties of arrays of aligned multiwall carbon nanotubes by utilizing different hydrogen concentrations during synthesis

We synthesize vertically aligned arrays of carbon nanotubes (CNTs) in a chemical vapor deposition system with floating catalyst, using different concentrations of hydrogen in the gas feedstock. We report the effect of different hydrogen concentrations on the microstructure and mechanical properties of the resulting material. We show that a lower hydrogen concentration during synthesis results in the growth of stiffer CNT arrays with higher average bulk density. A lower hydrogen concentration also leads to the synthesis of CNT arrays that can reach higher peak stress at maximum compressive strain, and dissipate a larger amount of energy during compression. The individual CNTs in the arrays synthesized with a lower hydrogen concentration have, on average, larger outer diameters (associated with the growth of CNTs with a larger number of walls), but present a less uniform diameter distribution. The overall heights of the arrays and their strain recovery after compression have been found to be independent of the hydrogen concentration during growth. (C) 2011 Elsevier Ltd. All rights reserved.

Solubilities of resorcinol and pyrocatechol and their mixture in supercritical carbon dioxide

The equilibrium solubilities of dihydroxy benzene isomers (resorcinol and pyrocatechol) and its mixture were experimentally determined at different temperatures (308, 318, 328, and 338 K) in the pressure range of 9.8-16.2 MPa. In the ternary system, the solubilities of pyrocatechol increased while the solubilities of resorcinol decreased relative to their binary solubilities. A new association model was developed based on the concept of formation of solvate complex molecules to correlate the solubility of the solid for mixed solids in supercritical carbon dioxide (SCCO(2)). The model equation relates the solubility of solute in terms of the cosolute composition, temperature, pressure and density of SCCO(2). The proposed model correlated the solubilities of sixteen solid systems taken from the literature and current experimental data with an average absolute relative deviation (AARD) of around 4%. (C) 2011 Elsevier B.V. All rights reserved.

Poly(lactic-co-glycolic acid): Carbon nanofiber composites for myocardial tissue engineering applications

The objective of the present in vitro research was to investigate cardiac tissue cell functions (specifically cardiomyocytes and neurons) on poly(lactic-co-glycolic acid) (PLGA) (50:50 wt.%)-carbon nanofiber (CNF) composites to ascertain their potential for myocardial tissue engineering applications. CNF were added to biodegradable PLGA to increase the conductivity and cytocompatibility of pure PLGA. For this reason, different PLGA:CNF ratios (100:0, 75:25, 50:50,25:75, and 0:100 wt.%) were used and the conductivity as well as cytocompatibility of cardiomyocytes and neurons were assessed. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy analysis characterized the microstructure, chemistry, and crystallinity of the materials of interest to this study. The results show that PLGA:CNF materials are conductive and that the conductivity increases as greater amounts of CNF are added to PLGA, from OS m(-1) for pure PLGA (100:0 wt.%) to 5.5 x 10(-3) S m(-1) for pure CNF (0:100 wt.%). The results also indicate that cardiomyocyte density increases with greater amounts of CNF in PLGA (up to 25:75 wt.% PLGA:CNF) for up to 5 days. For neurons a similar trend to cardiomyocytes was observed, indicating that these conductive materials promoted the adhesion and proliferation of two cell types important for myocardial tissue engineering applications. This study thus provides, for the first time, an alternative conductive scaffold using nanotechnology which should be further explored for cardiovascular applications. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.