RESUMEN
The low photoluminescence quantum yield of Bi3+-doped lead halide perovskite nanocrystals (NCs) is a big challenge to the scientific community. This makes them a weak candidate in the optoelectronics field in spite of their better stability than the pure lead analogue. Herein, the reason behind this reduction of quantum yield in hybrid mixed lead-bismuth bromide (MPBBr) NC is investigated and proposed to be due to ultrafast trapping transfer in the core of the NC, and not due to the surface trap states. Further, we have successfully boosted the quantum yield of MPBBr NC from 9% to 64% by passivating the deep traps within the crystal core by monovalent potassium ion doping. The stability of the developed Bi3+/K+-doped lead halide perovskite NC was found to be extremely high in atmospheric conditions, and this property is sustained up to 100 °C.
RESUMEN
Nanocrystalline CoFe2O4 and Co0.5M0.5Fe2O4 (M = Mn, Ni, and Zn) ferrites were prepared by the solution combustion method using oxalyl dihydrazide as a fuel. These materials were characterized by several physicochemical techniques. X-ray diffraction (XRD) patterns indicate the cubic spinel structure of these ferrites. Field emission scanning electron microscopy (FESEM) images demonstrate the microporous nature of the materials because of the large amount of gas production during their synthesis. High resolution transmission electron microscopy (HRTEM) images show lattice fringes corresponding to the {220} and {311} planes of the spinel structure. Fourier transform infrared (FTIR) spectra exhibit absorption bands around the 500-600 cm-1 wavenumber region which are related to metal-oxygen bonds with tetrahedral coordination. Symmetric and asymmetric stretching and symmetric bending modes associated with tetrahedral and octahedral cations present in the spinel structures have been assessed by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) studies demonstrate the presence of Co2+, Mn2+, Ni2+, Zn2+, and Fe3+ in tetrahedral and octahedral coordinations in these ferrites. Co0.5Zn0.5Fe2O4 is observed to show the highest saturation magnetization among all these materials. The dielectric measurements reveal that the dielectric constant and loss values decrease with an increase in frequency and the ac conductivity increases at higher frequencies due to mobilization of the charge carriers.
RESUMEN
An ultra-slow crystal growth over a period of 24â h of a newly synthesized CH3 NH3 Pb1/2 Bi1/3 I3 perovskite (MPBI) nanocrystal in non-polar toluene medium is reported here. From several spectroscopic techniques as well as from TEM analysis we found that the size of nanocrystals changes continuously with time, in spite of being capped by the ligands. Using a single molecular spectroscopic technique, we also found that this size change is not due to the stacking of nanocrystals but due to crystal growth. The notable temperature dependence and reversible nature of the nanocrystals growth is explained by the dynamic nature of the capping. The observed temperature-dependent ultra-slow growth is believed to be a pragmatic step towards controlling the size of perovskite NC in a systematic manner.
RESUMEN
Dry reforming of methane was carried out over La2-2xRu2xO3 (x = 0.005, 0.01). Substitution of just 0.5 atom% of Ru in La2O3 enhanced the activity by 20 times in terms of conversion when compared to the activity exhibited by La2O3. The oxygen storage capacity of the Ru doped sample was considerably higher than undoped La2O3, which resulted in higher conversions of CH4 and CO2. The measured conversion of CH4 and CO2 was 72 and 80%, respectively, at 850 °C. The same was merely 4% with La2O3 under the same experimental conditions. DRIFTS studies demonstrated the role of a specific type of carbonates in promoting the activity of the catalyst. DFT calculations provided the rationale behind the selection of the Ru-in-La2O3 methane dry reforming catalyst. The surface structures of the pure and Ru-substituted compounds were determined, corroborating the experimental observation of enhanced oxygen storage capacity on Ru substitution. Different active surface oxygen species were identified and their roles in improving reducibilities and improving reactivities were established. The experimentally observed surface carbonate species were also identified using calculations. The combined experiment + calculation approach proved ionic Ru in La2-2xRu2xO3 to be a novel and efficient dry reforming catalyst.