CeO2–ZrO2 (CZO) nanoparticles (NPs) have applications in many catalytic reactions, such as methane dry reforming, due to their oxygen cycling ability. Ni doping has been shown to improve the catalytic activity and produces active sites for the decomposition of methane. In this work, Ni:CZO NPs were synthesized via a two-step co-precipitation/molten salt synthesis to compare Ni distribution, oxygen vacancy concentration, and catalytic activity relative to a reference state-of-the-art catalyst prepared by a sol–gel-adsorptive deposition technique. To better understand the dispersion of Ni and oxygen vacancy formation in these materials, the Ni concentration, position, and reaction time were varied in the synthesis. X-ray diffraction (XRD) measurements show a homogeneous, cubic phase with little to no segregation of Ni/NiO. Catalytic activity measurements, performed via a differential scanning calorimetry (DSC)/thermogravimetric analysis (TGA) method, displayed a 5-fold increase in the activity per surface area with an order of magnitude decrease in the coking rate for the particles synthesized by the molten salt method. Additionally, this approach resulted in an order of magnitude increase in oxygen vacancies, which is attributed to the high dispersion of Ni2+ ions in the NP core. This ability of controlling the oxygen vacancies in the lattice is expected to impact other such systems, which utilize the substrate redox cyclability to drive conversion via, e.g., a Mars–van Krevelen mechanism.
Transition-metal (TM)-doped solids are one of the most extensively studied compounds in the fields of catalysis, magnetism, solar cells, etc., due to their tunable optoelectronic properties that stem from TM energy-level hybridization. In this work, the hybridization of the Ni–O bond in TiO2:Ni films was controlled in a stable, reversible manner via surface functionalization with polarized molecules. The Ni-doped TiO2 surface was functionalized with para-benzoic acid groups to modify the electron density distribution within the film. The dopant distribution and elemental composition at the interface are probed via high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy mapping. The effect of the surface modification on the dopant, Ni2+, is studied via surface-sensitive electronic characterization techniques, such as X-ray photoelectron spectroscopy and soft X-ray absorption spectroscopy (XAS). The electron density in the valence orbitals of the dopant was observed to be a function of the dipole moment of the para-substituted benzoic acid. The resulting XAS spectra of the Ni2+ after surface modification of TiO2:Ni films were modeled (CTM4XAS) and indicated ligand-dependent symmetry breaking around the Ni2+ at the functionalized interface. Therefore, the modified electron density at the interface due to the polarized molecules is observed to impact the hybridization of the TM dopant energy levels in solid hosts. This phenomenon of adaptive dopant hybridization in a solid host (TiO2) can be exploited to obtain tunable optical responses from TM-doped inorganic phosphors, which have an impact in various fields, such as luminescent displays, solar cells, sensors, telecommunications, counterfeit technologies, and biodetection.
Crystallization of Sr1−xNbO3−δ nanoparticles using the low-pressure wet-chemical method.
Y 2 Zr 2 O 7 (YZO) is widely used as a host material for luminescent centers because of its high stability and the ability to accommodate anion defects. In this work, the effects of Ce and Tb doping on the photoluminescence (PL) properties of YZO nanoparticles (NPs) are studied in detail to correlate the emission intensity with the dopant concentration. Herein, a two-step synthesis method of coprecipitation and molten salt was employed to prepare the YZO:Tb,Ce NPs. The single doped YZO:Tb (2 mol %) NPs shows a strong Tb 3+ emission. However, after codoping with Ce ions, the Tb 3+ emission is quenched instead of the expected sensitization. To identify the mechanism of quenching (oxidation state/local symmetry), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) were performed. The Ce 4+ ions were observed to drive further oxidation of Tb to a nonluminescent +4 oxidation state. Alternatively, Eu 3+ was employed to probe local symmetry changes upon Ce doping. The asymmetry ratio of the magnetic and electronic transitions indicates that the Ce dopant also pushes the system into a higher symmetry, resulting in two separate quenching mechanisms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.