Results 1 - 10 of 1022
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[en] This paper investigates the influence of the cell compression of a PEM water electrolysis cell. A small single cell is therefore electrochemically analyzed by means of polarization behavior and impedance spectroscopy throughout a range of currents (0.01 A cm−2 to 2.0 A cm−2) at two temperatures ( and ) and eight compressions (0.77 MPa–3.45 MPa). Additionally, a computational model is utilized to support the analysis. The main findings are that cell compression has a positive effect on overall cell performance due to decreased contact resistances, but is subject to optimization. In this case, no signs of severe mass transport problems due to crushed transport layers are visible in either polarization curves or impedance plots, even at high currents. However, a Tafel plot analysis revealed more than one slope throughout the current range. The change in the Tafel slope is therefore discussed and connected to the electrochemical reaction or an ohmic contribution from a non-electrode component.
[en] Nanoparticle-mediated histotripsy (NMH) is an ultrasound treatment strategy that combines acoustically sensitive nanoparticles with histotripsy. Previous NMH studies using perfluorocarbon (PFC) nanodroplets (ND’s), ∼200 nm in diameter, demonstrated that NMH can selectively generate cavitation by reducing the cavitation threshold from ∼25–30 MPa to ∼10–15 MPa. Recent studies have also shown that cavitation nucleation in NMH is directly caused by the incident negative pressure (p-) exposed to the PFC, as predicted by classical nucleation theory (CNT), suggesting that the NMH cavitation threshold is dependent on the total volume of PFC present in the focal region. In this study, we investigate the use of a newly developed NMH nanoparticle synthesized using an inclusion complex of methylated β-cyclodextrin and perfluorohexane (PFH). These ‘nanocones’ (NCs) have advantages compared to previously used ND’s due to their smaller size (∼50 nm), simple synthesis method, higher stability and information of definite PFH amount carried by the NC. To test the hypothesis that NCs can reduce the NMH cavitation threshold similar to ND’s, and that the NMH cavitation threshold is dependent upon the total PFH concentration, tissue phantoms containing concentrations of NCs ranging from 10−5 to 10−10 (ml PFH/ml water) were exposed to single cycle ultrasound pulses using a 500 kHz focused transducer where high speed imaging captured cavitation data. Results showed that NCs significantly reduced the histotripsy cavitation threshold to 11.0 MPa for a concentration of 10−5 (ml PFH/ml water), with the threshold increasing at lower concentrations. Finally, the ability of NCs to be used for effective NMH ablation was demonstrated in tissue phantoms containing red blood cells (RBCs). Overall, the results of the study support our hypotheses that NCs can be used for effective NMH therapy and that NC concentration has a predictable threshold-reducing effect. (paper)
[en] Highlights: • Response surface method is applied to trace the fading path of photochromic film. • The effects on the decoloration rate of photochromic film are explored. • Quantum chemical calculation offers quantitative insight into the photochromism. Response surface method is applied here to trace the photochromic path and explore the substituent and β-cyclodextrin effects on the decoloration of the spiropyran/β-cyclodextrin polymer (SP/CDP) complex. Calculations support the ultraviolet/visible experimental results, suggesting that introducing an electron-withdrawing group to the benzopyryl moiety of SPs favors an enhancement in their decoloration, whereas replacing the benzopyryl with a naphthopyryl moiety obstructs their decoloration. CDP complexation weakens the C1O bond of the closed SP form and enhances the polar zwitterionic structure in the open photomerocynine form. However, the electron-withdrawing group strengthens the interaction of benzopyryl SPs with CDP, thereby hindering their decoloration.
[en] Since the discovery of polyphthalocyanines (PPCs) in late 1950s, numerous attempts have been made to synthesize this 2D polymer by different approaches. Interestingly, the reported IR, Raman and UV-vis spectra of PPCs show drastic variation depending on the synthesis conditions. In this work, we show that the spectral data obtained in some works should be assigned not to the target polymer, but rather to octacyano phthalocyanine (OCP), which is an early step of the reaction. We discuss the spectral signatures of the well-polymerized and monomeric PCs based on reliable experimental data and support the spectral assignments with DFT calculations. (paper)
[en] In this paper, we report a novel method for constructing a soluble organic nanotube supported catalyst system based on single-molecule templating of core–shell bottlebrush copolymers. Various organic or metal catalysts, such as sodium prop-2-yne-1-sulfonate (SPS), 1-(2-(prop-2-yn-1-yloxy)ethyl)-1H-imidazole (PEI) and Pd(OAc)_2 were anchored onto the tube walls to functionalize the organic nanotubes via copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Depending on the ‘confined effect’ and the accessible cavity microenvironments of tubular structures, the organic nanotube catalysts showed high catalytic efficiency and site-isolation features. We believe that the soluble organic nanotubes will be very useful for the development of high performance catalyst systems due to their high stability of support, facile functionalization and attractive textural properties. (paper)
[en] Highlights: • Dimethoxycurcumin (DMC). • Oxidation process and kinetics for DMC. • Electrochemical behavior over a platinum electrode. • DFT calculations. Dimethoxycurcumin (DMC) ((1E,6E)-1-(3,4-dimethoxycyclohexyl)-7-(3,4-dimethoxyphenyl) hepta-1,6- diene-3,5-dione) is a natural polyphenolic compound that appears together with curcumin in turmeric. Both molecules have wide range biological activities as antioxidant, anti-inflammatory and anti-carcinogenic agent. To evaluate the oxidation process and kinetics for DMC, the rate constant, electron transfer and diffusion coefficients for the electrochemical oxidation were determined. Therefore, its electrochemical behavior over a platinum electrode in anhydrous media was investigated. Furthermore, DFT calculations were performed to give a rational explanation to the obtained results. All the results support the fact that the central CH2 group is the most reactive against an oxidation process.
[en] We investigate oxygen reduction in alkaline solution with the focus on gold and silver electrodes. On the basis of theoretical considerations we propose a detailed mechanism, which we support by explicit calculations. In accordance with previous suggestions we conclude that the first step is an outer-sphere electron transfer to the oxygen molecule. The breaking of he oxygen-oxygen bond involves adsorption of OH on the electrode surface. This is much stronger on Au(100) than on Au(111), which explains why the former is a better catalyst.
[en] Huge quantities of waste cooking oils are produced all over the world every day, especially in the developed countries with 0.5 million ton per year waste cooking oil are being generated in Malaysia alone. Such large amount of waste cooking oil production can create disposal problems and contamination to water and land resources if not disposed properly. The use of waste cooking oil as feedstock for bio diesel production will not only avoid the competition of the same oil resources for food and fuel but will also overcome the waste cooking oil disposal problems. However, waste cooking oil has high acid value, thus would require the oil to undergo esterification with an acid catalyst prior to transesterification with a base catalyst. Therefore, in this study, bifunctional catalyst supports were developed for one-step esterification-transesterification of waste cooking oil by varying the CeO2 loading on γ-Al2O3. The bifunctional supports were then impregnated with 5 wt % Mo and characterized using N2 adsorption-desorption isotherm to determine the surface area of the catalysts while temperature programmed desorption with NH3 and CO2 as adsorbents were used to determine the acidity and basicity of the catalysts. Results show that the γ-Al2O3-CeO2 supported Mo catalysts are active for the one-step esterification-transesterification of waste cooking oil to produce bio diesel with the Mo/ γ-Al2O3-20 wt% CeO2 as the most active catalyst. Optimization of process parameters for the production of bio diesel from waste cooking oil in the presence of this catalyst show that 81.1 % bio diesel yield was produced at 110 degree Celsius with catalyst loading of 7 wt %, agitation speed of 600 rpm, methanol to oil ratio of 30:1 and reaction period of 270 minutes. (author)