This work reveals influence of electrospinning of polyacrylonitrile-N,N-dimethylformamide solution of different concentrations on nanofiber web color parameters, molecular structure, and heat stability. It is found that fiber diameters depend on concentration through the power law relationship; however, the medium concentration-based web is characterized by a green-yellow hue, representative of the chromophore color; while, the solvent-rich and solvent-poor solution-based webs give rise to Stokes shifts and ultraviolet-blue emission bands, attributed to fluorescence. The chromophore structure, present in the neat powder, undergoes changes as a result of electrospinning reflected by the enamine-to-ketonitrile conversion and the fraction of C@N conjugation. Blue-shifting of the C@N conjugation is indicative of a reduction of the pelectron system, which is coincident with the decreased color saturation value but observed only in the nanofibers prepared from the medium concentration solution. A decrease in the glass transition and an increase in cyclization temperatures also support these findings.
Summary
Electrospun TiO2 nanofibers incorporated with graphene and C60 nanoparticles at 0, 1, 2, 4, and 8 wt.% were produced using poly (vinyle acetate), dimetylfomamide, and titanium (IV) isopropoxide. The resultant nanofibers were heat treated at 300 °C for 2 hrs in a standard oven to remove all the organic parts of the nanofibers, and then further heated up to 500 °C in Ar for additional 12 hrs to crystallize the TiO2 nanofibers. For the graphene and C60 containing nanofibers, two steps annealing at 300 °C (air) and 500 °C (Ar) were conducted to eliminate the decomposition processes of the graphene and C60 in the TiO2 nanofibers. SEM, TEM and XRD studies were conducted on the samples. The results showed that graphene and C60 were well integrated in the nanofiber structures. The TiO2 nanofibers with the inclusions were mixed in a solution to form a paste, which was then applied on a conductive glass after the TiCl4 solution treatments to make various dye sensitized solar cells (DSSCs). This technique enables creation of solar cells with variable thicknesses of 7 µm to 45 µm. The effects of the manufacturing technique, thickness of the paste, different percentages of graphene and C60 nanoparticles on overall efficiency of the solar cell were studied in detail. The test studies indicated that in the presence of graphene and C60, the DSSC efficiency increased more than 50%. The present study may guide some of the scientists and engineers to tailor the energy band gap structures of the semiconductor materials for different industrial applications, including DSSCs, as well as water splitting, catalyst, Li‐ion batteries, and fuel cells.
Nanoparticles of ZnO doped with 6 at.% Mn were produced by a sol-gel method. X-ray diffraction confirms the hexagonal structure as that of the parent compound ZnO, and high-resolution electron transmission microscopy reveals a single-crystallite lattice. Magnetic measurements using a superconducting quantum interference device indicate that about one half of the Mn2+ions follow Curie's law for paramagnetism. The remaining Mn2+ions exhibit a weak ferromagnetic character, which might be induced through canted antiferromagnetic interactions.
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