Abstract: In this work, studies of the doping effects on the electronic and structural properties of graphene were performed. Calculations have been done within the periodic density functional theory (DFT) as implemented in PWscf code of the Quantum Espresso Package. Graphene layers have been modeled using the 4x4 periodic supercells. The doping is explored considering phosphorus (P), aluminum (Al) and silicon (Si) heteroatoms. One heteroatom per supercell was considered. Electronic structure results show that the pristine graphene has a linear dispersion at high symmetry K point and zero gap. Band structure of graphene doped with Al atoms exhibit a metal behavior since a valence band crosses the Fermi level. Graphene doped with P also presents a metal behavior but in this case a conduction band crosses the Fermi level. In addition, when the dopant is Si the band structure shows a semiconductor behavior with a 0.3 eV gap. In all cases, the zero gap energy characteristic of graphene was changed by dopant heteroatom. The Dirac lineal dispersion relation is preserved only in the pristine graphene.
Abstract: Abstract. This study focuses on detailed investigation of solvent effects on controlling photophysical properties of poly [2-methoxy,5-(2’-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) nanoparticles prepared by using reprecipitation techniques. In this work, the MEH-PPV polymer is dissolved in various solvents, including chlorobenzene (CRB), toluene (TOL) and pyridine (PYR). The polymers in solutions adopt different conformations (i.e. collapsed or extended coils), depending on local polymer-solvent interactions. The differences of chain conformations cause the variations of chain packing within the nanoparticles. The majority of nanoparticles exhibit diameter of about 65-70 nm. The photophysical properties of MEH-PPV nanoparticles varied with type of solvents. The absorption spectra of nanoparticles exhibit a broad pattern with a long red tail at about 550 nm, indicating the formation of inter-and/or intrachain aggregates within the nanoparticles. However, the nanoparticle from TOL system shows blueshift of λmax, corresponding to the decrease of conjugation length due to the existence of collapsed coil. The photoluminescence (PL) spectra of MEH-PPV nanoparticles show consistent result with the shift of λmax to about 590 nm and vibronic shoulder at about 640 nm. The PL patterns vary with the type of solvents. In addition, the PL patterns depend on the variations of excitation wavelengths. These discrepancies indicated the variation of chain conformation and degree of aggregation within the nanoparticles. Our results demonstrate the simple method to prepare the conjugated polymer nanoparticle with different photophysical properties by changing solvents.
Abstract: Cooper doped SrAl2O4:xCu powders were synthesized by combustion method. The doping concentrations were x= 0.1%, 0.3%, 0.5%, and 1.0 at.%. X-ray diffraction patterns indicate that all Cu doped/undoped powders has monoclinic phase. Also, TEM images show that the size of the nanoparticles decreases as the content of Cu increases. The photocatalytic degradation of Congo red (CR) was studied by monitoring intensity of its characteristic absorbance band centered at 494 nm. The best result was obtained with the 0.1% Cu doped sample, since it degraded 100% of CR after 120 minutes under sunlight excitation. Hence, our results suggest that SrAl2O4:xCu powders could be suitable candidates for photocatalytic degradation of dye pollutants under sunlight.
Abstract: In this study, the effects of cyclic voltammetry (CV) has been modeled with Rule-based mamdani-type fuzzy (RBMTF), by using experimental data for proton exchange membrane fuel cell with PVA/AG. In the system developed, RBMTF apply input parameters are CV, scan rate and time, output parameters are current density and voltage. 12300 values for experimental study also obtained with RBMTF. Membership functions (MFs) are the building blocks of fuzzy set theory, i.e., fuzziness in a fuzzy set is determined by its MF. Accordingly, the shapes of MFs are important for a particular problem since they effect on a fuzzy inference system. They may have different shapes like triangular, trapezoidal, Gaussian, etc. When the results obtained from RBMTF and statistical analyses of experimental data have been compared, it has been determined that the two groups of data are coherent, and that there is not a significant difference between them. As a result, this study indicates that RBMTF with different membership functions can be safely used for CV.
Abstract: Formation of the Ti3(Al,Sn)C2 solid solutions was studied by combustion synthesis from elemental powder compacts with Al4C3 and TiC additions. Combustion temperatures of 1590–1700 °C and flame-front speeds of 14.2–18.8 mm/s were measured for the Al4C3-added samples. Due to the dilution effect of TiC, the combustion temperature and flame velocity were significantly reduced to 1220–1280 °C and 7.1–9.6 mm/s, respectively, for the TiC-adopted samples. The XRD analysis indicated that MAX solid solutions Ti3(Al1–xSnx)C2 with x = 0.2, 0.4, and 0.6 were produced from the Al4C3-adopted samples. Because of the low reaction temperature, the extent of Sn substitution for Al in Ti3(Al1–ySny)C2 was narrowed down to y = 0.4 for the TiC-containing samples. The as-synthesized Ti3(Al,Sn)C2 grains were plate-like and closely stacked into a laminated microstructure.