C, Volume 2, Issue 1 (March 2016) – 8 articles

Pt-Sn supported on reduced graphene oxide (Pt-Sn/rGO) was synthesized and characterized by SEM, EDX, and XRD. The catalytic activity of Pt-Sn/rGO was tested for the solvent free liquid phase oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone, also called KA oil, under mild reaction conditions. The products were analyzed gravimetrically, by UV spectrophotometer, and GC equipped with FID. The catalyst was found to be fairly active as well as selective for the desired products. The experimental data was analyzed by Freundlich, Temkin, and Langmuir adsorption isotherms. The L-H model was found to give a better fit of the data. The catalyst was fully recyclable and truly heterogeneous. Full article

A comparative study of the removal of Pb²⁺ ions and Cr³⁺ ions was conducted to determine the efficiency of carbon nanotubes (CNTs) produced using microwave heating as an adsorbent in removing heavy metal ions from waste water. Optimization of parameters such as adsorbent dosage, pH value, agitation speed, and agitation time was done using the Design Expert software version 6.0. The statistical analysis revealed that optimized conditions for the highest removal for Pb²⁺ are at pH 4.0, CNTs dosage of 0.09 g, agitation time and speed of 50 min and 150 rpm respectively. Meanwhile, the highest removal Cr³⁺ ions was observed at pH 8.0, CNTs dosage of 0.09 g, agitation time and speed of 60 min and 150 rpm respectively. For the initial concentration of 2 mg/L, the removal efficiency of Pb²⁺ ions and Cr³⁺ ions were 99.9% and 95.5% respectively. The maximum adsorption capacities of both Pb²⁺ ions and Cr³⁺ ions onto the CNT were 15.34 mg/g for Pb²⁺ ions and 24.45 mg/g for Cr³⁺ ions. Besides that, the Langmuir and Freundlich constants for the removal of Pb²⁺ ions were 0.073 and 1.438 L/mg while 0.071 and 1.317 L/mg for Cr³⁺ ions. The statistical analysis proved that the removal of Pb²⁺ ions and Cr³⁺ ions fits the Langmuir and Freundlich isotherm models, and both models obeyed the pseudo-second-order. Full article

Single-walled carbon nanotubes (SWCNTs) dispersed in aqueous media have many potential applications in chemistry, biology and medicine. To disperse SWCNTs into aqueous media, it is often necessary to modify the surface of SWCNTs by either covalent or noncovalent methods. As a result of this modification, the properties of SWCNTs may be profoundly influenced by the nature of the surface modification. Here, by using SWCNTs dispersed with single-stranded DNA of different lengths, we show that the kinetics of SWCNTs’ aggregation in aqueous media is strongly dependent on the status of the overall surface charge. SWCNTs with a greater number of surface charges showed faster aggregation. The difference in the rate of aggregation can differ by more than ten-fold among different conditions tested. AFM imaging of the discrete time points along the aggregation process suggests that aggregation starts with the formation of microfilaments, which can further grow to form bigger aggregates. The formation of bigger aggregates also renders it more difficult to redisperse them back into the aqueous media. The concentration of counterions required to trigger SWCNT aggregation also shows a dependence on the concentration of KCl in the aqueous solution, which supports that electrostatic interactions instead of van der Waals interactions dominate the interactions among these individually-dispersed SWCNTs in aqueous media. Full article

The polymerization of CO₂ by Lewis basic moieties has been recently proposed to account for the high adsorption ability of N and S-doped porous carbon materials formed from the pyrolysis of sulfur or nitrogen containing polymers in the presence of KOH. Ab initio calculations performed on the ideal CO₂ tetramer complex LB-(CO₂)₄ (LB = NH₃, H₂O, H₂S) showed no propensity for stabilization. A weak association is observed using Lewis acid species bound to oxygen (LA = H⁺, AlF₃, AlH₃, B₄O₆); however, the combination of a Lewis acid and base does allow for the formation of polymerized CO₂ (i.e., LB-C(O)O-[C(O)O]_n-C(O)O-LA). While the presence of acid moieties in porous carbon is well known, and borate species are experimentally observed in KOH activated porous carbon materials, the low stability of the oligomers calculated herein, is insufficient to explain the reported poly-CO₂. Full article

One of the major challenges of metal-air batteries is the impeded oxygen reduction reaction (ORR) during discharge occurring at the gas diffusion electrode (GDE) of the battery. Due to the impeded ORR, high overpotentials emerge and result in a loss of energy efficiency. In order to improve the latter, suitable catalysts have to be employed. Transition metal oxides like manganese oxides (e.g., MnO₂, Mn₂O₃, Mn₃O₄, Mn₅O₈, MnOOH) [1,2] are known as good and inexpensive materials for the ORR in alkaline media. A drawback of manganese oxide catalysts is the poor electrical conductivity. Hence, the approach presented in this work aims to enhance the catalytic activity of Mn₃O₄ and γ–MnO₂ by the incorporation of conductive carbon material into the pure manganese oxide. The resulting hybrid catalysts are prepared either by impregnation of Super C 65, Vulcan XC 72, and Kuraray YP 50F via a sol-gel technique employing a MnO₂ precursor sol or by direct precipitation of Mn₃O₄ or γ–MnO₂ particles in the presence of the carbon materials mentioned above. Investigations by rotating disc electrode (RDE) show a noticeably higher catalytic activity of the hybrid catalysts than for the pure materials. For verification of the results measured by RDE, screen printed GDEs are prepared and tested in Zn-air full cells. Full article

Carbon nanotube yarns have extraordinary mechanical, electrical and thermal properties that make them attractive for high-performance and multifunctional composite materials. They also exhibit a unique piezoresistive response when subjected to mechanical strain. This characteristic is of interest for sensing applications including strain measurement and damage detection when integrated in polymeric and composite materials. Thus, there is a need to understand the coupled mechanical and electrical behavior of the carbon nanotube yarns to fully comprehend the entire scope of their sensing applications. Of particular interest are their characteristics when used as piezoresistive strain sensors in structures that are subjected to dynamic loading including fatigue and impact, or quasi-static cyclic loading. This paper presents a study about the presence of hysteresis and other time-dependent effects in carbon nanotube yarns during quasi-static cyclic uniaxial tensile loading. By simultaneously measuring the resistance, the load and the displacement histories, any direct correlations between the mechanical and electrical characteristics of the carbon nanotube yarns are investigated including the effect of strain level, strain rate, and stress relaxation. It was observed that all these effects play a significant role in the piezoresistive response of the carbon nanotube yarns. In particular, a low strain rate appears to bring out a unique piezoresistive response that is not observed at higher strain rates. The underlying phenomena determining the piezoresistive responses are hypothesized and discussed in the context of strain rate and maximum strain level. Full article

We analyzed the electronic structures of carbon-doped hexagonal boron nitride, focusing on the comparison with the corresponding π-conjugate hydrocarbon molecules and odd-number substitution by first principle calculation. The band gaps are about the half that of the HOMO-LUMO gaps of corresponding hydrocarbons, except for the cis-butadiene structure in which aromatic hexagonal ring formation is important. Odd number doping makes metallic materials with very different work functions, depending upon the difference in B and N numbers, and has an expected application as electrodes for flexible devices. Full article

Acceleration effects of heat flow are included in the law of heat conduction by eliminating the acceleration term between the equation of motion for a spinless electron and the Boltzmann equipartition energy theorem differentiated with respect to time. The resulting law of heat conduction is a capite ad calcem in temperature as given in Equations (17), (19) and (20). (q_z/k)_z = -(δT/δz) - 1/v_h(δT/δt). Evaluation of use of this equation using the entropy production term reveals that as long as the flux, q, and the temperature accumulation both have the same signs, the law does not violate the second law of thermodynamics. For systems that obey the first law of thermodynamics, this is the case. σ == q/T²(q/k + 1/v_h • q(δT/δt)). In the chemical potential Stokes-Einstein formulation, when acceleration of the molecule is accounted for, a law of diffusion a capite ad calcem concentration results. In cartesian one-dimensional heat conduction in semi-infinite coordinates, the governing equation for temperature or concentration was solved for by the method of Laplace transforms. The results are in terms of the modified Bessel composite function in space and time of the first order and first kind. This is when τ > X. X > τ the solution is in terms of the Bessel composite function in space and time of the first order and first kind. The wave temperature is a decaying exponential in time when X = τ. An approximate expression for dimensionless temperature was obtained by expanding the binomial series in the exponent in the Laplace domain and after neglecting fourth- and higher-order terms before inversion from the Laplace domain. The Fourier model, the damped wave model and the a capite ad calcem in temperature/concentration model solutions are compared side by side in the form of a graph. The a capite ad calcem model solution is seen to undergo the convex to concave transition sooner than the damped wave model. The results of the a capite ad calcem temperature model for distances further from the surface are closer to the Fourier model solution. Full article