Production Of Intermediate Species Research Articles

Photocatalytic degradation of cefixime using visible light-driven Z-scheme ZnO nanorod/Zn2TiO4/GO heterostructure

ZnO nanorod along with a Zn2TiO4/GO heterostructure with enhanced charge transfer capability was synthesized by a facile sol-gel method. FT-IR, XRD, XPS, TEM, SEM, EDX, UV–Vis DRS, photocurrent response and PL analyses were applied to characterize the as-prepared photocatalysts. To investigate the photocatalytic activity of the composite, Cefixime (CEF) removal under visible light was evaluated. The ZnO nanorod/Zn2TiO4/GO, including 65 wt% ZnO and 3 wt% graphene oxide, showed the highest CEF degradation and was selected as the optimal ternary composite. Reduction of electron-hole pair recombination rate, successful interfacial charge transfers, and more visible light reception in the Z-scheme system were the important reasons for improving the photocatalytic properties of ZnO nanorod/Zn2TiO4/GO. Effective operating parameters in the CEF photocatalytic removal process were optimized employing the response surface method and were as follows: photocatalyst dosage = 0.88 g/L, pH = 5, radiation time = 115 min, and CEF concentration = 10 ppm. The photocatalytic degradation% of CEF and total organic carbon (TOC) removal% under the optimal conditions were 71.4 and 57.5%, respectively, for the three-component composite indicating the production of intermediate species during the process. This photocatalytic reaction confirmed the first-order kinetic and using the ZnO nanorod/Zn2TiO4/GO composite was able to improve the reaction rate by about 2.7 and 6.2 times more than ZnO nanorod/Zn2TiO4 and ZnO, respectively. The effects of radiation intensity and temperature were investigated and 175 W/m2 and 35 °C were obtained as optimum values. Eventually, according to the trapping test, h+, superoxide radical, and hydroxyl radical are the most effective active species in this photocatalytic reaction, respectively.

Electron swarm properties and nanosecond-pulsed discharge characteristics in partially oxidized fuel:air mixtures

Electron swarm parameters were calculated in partially oxidized H2:air and CH4:air mixtures for various gas temperatures and reduced electric fields. Comparison of the calculated results with previous calculations for H2:O2 and hydrocarbon:O2 mixtures showed that the addition of N2 does not greatly affect the electron properties in partially oxidized combustion mixtures. In particular, the production of H2O during fuel oxidation caused a sharp decrease in the mean electron energy and electron drift velocity for low (<60 Td) reduced electric fields, whereas the mean attachment coefficient increased with H2O formation. Partial fuel oxidation led to an increase in the critical reduced electric field corresponding to the balance between electron-impact ionization and electron attachment because of a decreased effective detachment coefficient and enhanced attachment coefficient. The calculated transport and rate coefficients were applied for simulating plasma properties during fuel oxidation in H2:air mixtures excited by a high-voltage nanosecond repetitively pulsed discharge. It was shown in the zero-dimensional approximation that the reduced electric field corresponding to the peak energy input was close to the critical electric field and enhanced when fuel was oxidized. It follows from the calculated results that the variation of the electron transport coefficients with increasing fuel oxidation can lead to the development of the thermocurrent instability in the discharge plasma generated in combustible mixtures. The production of intermediate species does not influence the electron swarm parameters and the critical electric field. However, these intermediate species can affect the positive ion composition in the plasma and change the rate of its decay.

Electrochemical Study of Platinum-Ruthenium-Copper Trimetallic Nanostructures for Methanol Oxidation

Direct methanol fuel cells commonly utilize platinum based catalysts due to their efficiency for methanol oxidation (MOR). Platinum based electrocatalysts are limited by intermediates adsorbing onto the electrocatalyst’s surface.1 Methanol oxidation forms multiple intermediate species, which are integral in generating electrons that drive the fuel cell.2 The production of intermediate species can also slow down reaction kinetics, while specific intermediate species can strongly adsorb onto active sites along the platinum catalyst surface reducing the number of MOR reactive sites. In order to remove the adsorbed intermediates, the MOR onset potential will shift to a more oxidizing potential.1These limitations can be addressed by developing a durable electrocatalyst that resists CO poisoning, maintains efficiency for MOR, and reduces the onset potential of methanol oxidation. An electrocatalyst comprised of nanomaterials could address some of these limitations, due to their synthetically tunable properties. Nanomaterials can be tailored to possess the ideal composition, morphology, and surface roughness for the catalysis of specific reactions. Previous studies have shown that Pt-based nanomaterials are efficient electrocatalysts, and their activity can be attributed to energetically favorable surface facets, as well as synergistic properties of alloys, specifically electronic and geometric effects.3 Geometric effects allow for the contraction or expansion of the nanomaterial’s crystal lattice, altering its electrochemical activity for a specific fuel.4 Electronic effects occur when the center d-band shifts, weakening the bond to the adsorbed species. In the case of MOR, the oxidation of CO would become more energetically favorable.1 These effects improve the resistance of intermediate poisoning, as well as the activity of the electrocatalyst by freeing more reactive sites. These effects can also influence the activity of pair sites in platinum alloyed nanomaterials, through the bifunctional mechanism.1 , 3 , 5 Previous work by our group investigated the effect of anisotropic alloyed nanostructures electrochemical activity, which demonstrated that the platinum-copper nanodendrites can enhance the MOR activity, while maintaining the dendritic morphology of the nanostructures.1 Current research focuses on the development of multimetallic nanostructures with various morphologies, surface roughness, as well as investigating each nanomaterial’s electrocatalytic activity. Multimetallic nanostructures are formed by first synthesizing copper nanomaterials. Then platinum and ruthenium precursor salts can alloy and co-reduce onto the vertices and edges of the copper nanomaterials, through galvanic replacement and co-reduction mechanisms. The morphology, porosity, surface roughness, and composition of these ruthenium-platinum-copper nanomaterials can be synthetically tailored. Platinum and ruthenium were chosen as secondary alloying metals with copper due to their binding energy for species such as –CO, -OH.6 During the synthetic process pair sites between Pt, Cu, and Ru will form, which could improve resistance towards intermediate poisoning and activity for MOR. The activity of these supportless electrocatalysts will be evaluated by cyclic voltammetry and chronoamperometry. The electrochemical surface area, the charging double layer capacitance, surface diffusion, the efficiency for MOR, and the resistance for CO for each electrocatalyst will be evaluated. Additionally, the morphological and electrochemical durability of each multimetallic nanomaterial in electrolyte and analyte will also be studied in this work. As previously discussed the pair site can affect the electrocatalytic activity for MOR; this work will also study the influence of the nanomaterial's copper core on the electrocatalytic properties. 1. Chen, A.; Holt-Hindle, P., Platinum-Based Nanostructured Materials: Synthesis, Properties, and Applications. Chemical Reviews 2010, 110(6), 3767-3804. 2. Cohen, J. L.; Volpe, D. J.; Abruna, H. D., Electrochemical determination of activation energies for methanol oxidation on polycrystalline platinum in acidic and alkaline electrolytes. Physical Chemistry Chemical Physics 2007, 9(1), 49-77. 3. Lee, H.-Y.; Vogel, W.; Chu, P. P.-J., Nanostructure and Surface Composition of Pt and Ru Binary Catalysts on Polyaniline-Functionalized Carbon Nanotubes. Langmuir 2011, 27(23), 14654-14661. 4. Wang, J. X.; Ma, C.; Choi, Y.; Su, D.; Zhu, Y.; Liu, P.; Si, R.; Vukmirovic, M. B.; Zhang, Y.; Adzic, R. R., Kirkendall Effect and Lattice Contraction in Nanocatalysts: A New Strategy to Enhance Sustainable Activity. Journal of the American Chemical Society 2011, 133(34), 13551-13557. 5. Sun, X.; Li, D.; Ding, Y.; Zhu, W.; Guo, S.; Wang, Z. L.; Sun, S., Core/Shell Au/CuPt Nanoparticles and Their Dual Electrocatalysis for Both Reduction and Oxidation Reactions. Journal of the American Chemical Society 2014, 136(15), 5745-5749. 6. Rossmeisl, J.; Ferrin, P.; Tritsaris, G. A.; Nilekar, A. U.; Koh, S.; Bae, S. E.; Brankovic, S. R.; Strasser, P.; Mavrikakis, M., Bifunctional anode catalysts for direct methanol fuel cells. Energy & Environmental Science 2012, 5 (8), 8335-8342.

Enhancing the low temperature oxidation performance over a Pt and a Pt–Pd diesel oxidation catalyst

The influence of hydrogen over platinum and combined platinum–palladium diesel oxidation catalysts were investigated on the oxidation kinetics of CO, HC and NO. Although H2 has been reported to have a positive effect on CO and HC oxidation as well as NO2 formation over platinum catalysts, there is still uncertainty whether this is due to the temperature rise caused by H2 oxidation or the result of a change in the reaction kinetics of CO, HC and NO oxidation by the production of intermediate species. The results have showed smaller H2 concentrations are more effective in improving the catalyst light-off temperature as well as promoting NO oxidation over both platinum and platinum–palladium catalysts. It is suggested that these benefits are a result of not only the exothermic reactions which in turn increase the local catalyst temperature but also H2 increasing the rate of reactions and the species accessibility to the catalyst active sites thus further CO, HC and NO oxidation can occur at lower catalyst temperatures.