ABSTRACT
Doping heteroatom in phosphor can effectively improve luminescent properties, which has attracted great attention recently. GdAlO3 phosphors (GAP) doped with Er3+/Yb3+/Tm3+ were prepared via the co-precipitation method. Upon 980 nm excitation, strong blue, green, and red up-conversion (UC) emissions centered at 476, 524, 546, and 659 nm were observed, which could be successfully combined to form pure white light. It was found that changing the doping concentration of Er3+ and Yb3+ ions, the calcination temperature of the precursor, the laser power of the excitation light source, and doping Li+ could systematically adjust red/green/blue colors of GdAlO3:Er3+/Yb3+/Tm3+ phosphors to optimize the white emitting luminescence. When the Er3+ doping concentration of the phosphors increased, each color distribution successfully moved, making the maximum shift of the CIE coordinate. Finally, the influence of each factor on adjusting the UC white light performance and its mechanism were explored.
ABSTRACT
According to the need of sustainable development, solid catalysts are critical materials for green biodiesel production. In this study, a hydrothermal method was used to develop a reusable and highly active Fe-BTC and UiO-66 metal-organic framework encapsulated Zr-doped polyoxometalate nano-hybrid catalysts (ZrSiW/Fe-BTC and ZrSiW/UiO-66) for the acid-catalyzed esterification of oleic acid with methanol. The structural and compositional characterization of the synthesized catalysts were characterized using various techniques such as Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), nitrogen adsorption-desorption, scanning electron microscopy (SEM), and thermogravimetric (TG) and temperature programmed desorption (NH3-TPD) analysis. The as-prepared ZrSiW/UiO-66 had excellent catalytic activity in the esterification of oleic acid with methanol, higher than that of ZrSiW/Fe-BTC catalyst, owing to the fact that ZrSiW/UiO-66 nano-hybrids have high acidity, large specific surface area and pore volumes, and relatively large average pore sizes. Furthermore, the reusability and stability of nano-hybrids were also evaluated, and it was found that the stability of ZrSiW/UiO-66 catalyst was better.
ABSTRACT
Metal-organic frameworks (MOFs) have been shown to be promising candidates in the recent decades for the immobilization of guest active species due to their diversified structures, porosity, and high surface area. In this study, silicotungstic acid (HSiW) encapsulated UiO-66 has been successfully synthesized by one-pot synthesis strategy. The synthesized composite (HSiW-UiO-66) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), nitrogen adsorption-desorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric (TG) techniques, and the HSiW-UiO-66 was also employed as a solid acidic catalyst for the synthesis of biodiesel by esterification of lauric acid with methanol. The results revealed that the HSiW-UiO-66 composite had better textural properties (such as large BET surface area (758.3 m2 g-1), large pore volume (0.438 cm3 g-1), and smaller particle size (about 50-200 nm)), good thermal stability, and high catalytic activity. In addition, the effect of the esterification process parameters on biodiesel production was analyzed using single factor experimental method combined with response surface methodology (RSM); a high conversion of 80.5% with single factor optimization and 92.8% with RSM was obtained. More importantly, the conversion of lauric acid decreased from 80.5% to just 70.2% when the catalyst had been reused six times, which exhibited that the catalyst had excellent reusability. The high activity of HSiW-UiO-66 benefited from low activation energy of 27.5 kJ mol-1. This work thus offers an underlying application for green biodiesel obtained from free fatty acids esterification or pre-esterification of low-cost oils with high acid value.
ABSTRACT
We carried out density functional theory simulations to examine the stability and CO oxidation activity of single Cu atoms supported on CeO2 (111). Both the strong binding energy and high activation energy for Cu single atom diffusion indicate a high stability of the Cu1 /CeO2 single-atom catalyst. Electronic structure analysis verifies the formation of Cu+ cation due to electron transfer. The frequency analysis further corroborates that the experimentally observed IR bands around 2114-2130â cm-1 of CO adsorption at the boundary of Cu/CeO2 correspond to Cu+ -carbonyl species. Cu1 /CeO2 single-atom catalyst displays a promising catalytic activity for CO oxidation via Mars van Krevelen mechanism.
