Search

Doping can greatly reduce the lattice thermal conductivity of thermoelectric materials, which is considered as one of the effective ways to improve the thermoelectric properties of thermoelectric materials. First of all, we use the simple and environmentally friendly solution thermal method combined with the tube furnace sintering technology to explore the optimal temperature of sintering Cu2S in the tube furnace. When the sintering temperature reaches 700 °C, we get the thermoelectric value of 0.21. Subsequently, Cu2S thermoelectric materials doped with xmol%Sn (x = 0.5, 1, 3, 5) were prepared and the optimal concentration of Sn was explored. The Sn atom replaces the Cu atom with a smaller radius, greatly reducing the thermal conductivity of the matrix material. In the sample doped with 1%Sn, the total thermal conductivity reaches 0.31 WK−1 m−1, which is 22.5% lower than that of the pure phase sample. In addition, above 623 K, the conductivity of samples doped with 1%Sn is better than that of intrinsic samples, indicating that Sn doping can optimize the conductivity of Cu2S to a certain extent. At 773 K, the ZT of Cu2S + 1 mol%Sn can reach 0.51. 132% higher than undoped Cu2S.This provides a new idea for the preparation and commercial application of Cu–S based thermoelectric materials. [ABSTRACT FROM AUTHOR]

As consumer electronics and industrial control systems continue to evolve, the operating temperature range of capacitors is gradually increasing. Barium titanate-based ceramic capacitors are widely used in the field of high dielectrics, so temperature-stable barium titanate-based dielectric materials have been a hot research topic in the field of dielectric ceramics. The construction of a core–shell structure by unequal doping is an effective way to obtain temperature-stable dielectric materials. At the same time, this structure retains part of the highly dielectric tetragonal phase, and materials with overall high dielectric constants can be obtained. In this work, we prepared BaTiO3-xNaNbO3-0.002Gd2O3 (x = 1.0–6.0 mol%) as well as BaTiO3-0.05NaNbO3-yGd2O3 (y = 0–0.30 mol%) dielectric ceramics. On the basis of high-electronic-bandgap NaNbO3-modified BaTiO3 dielectric ceramics, a core–shell structure with a larger proportion of core phase was obtained by further doping the amphiphilic rare-earth oxide Gd2O3. By designing this core–shell structure, the temperature stability range of capacitors can be expanded. At a doping level of 5.0 mol% NaNbO3 and 0.20 mol% Gd2O3, the room temperature dielectric constant εr = 4266 and dielectric loss tan δ = 0.95% conforms to the X8R standard (from −55 °C to 150 °C, TCC < ±15%); volume resistivity ρv = 10,200 GΩ·cm and breakdown strength Eb = 13.5 kV/mm is attained in BaTiO3-based ceramics. The system has excellent dielectric and insulating properties; it provides a new solution for temperature-stable dielectric ceramics. [ABSTRACT FROM AUTHOR]

In this article, density functional theory (DFT) was applied to research the structures of γ-Fe2O3 and MFe2O4 (M=Co, Cu, Zn) and to optimize the adsorption models of gases such as CO and NO onto the catalysts. Additionally, the study analyzed the CO oxidation reaction on MFe2O4 (M=Co, Cu, Zn) and the selective catalytic reduction (SCR) reaction of CO + NO in CuFe2O4 and ZnFe2O4. Results showed that CO can effectively adsorb on the reactive substrates, reacting with lattice oxygen to produce CO2 and oxygen vacancies during the CO oxidation process. γ-Fe2O3 (001) required an energy of 0.95 eV to complete the reaction, while CuFe2O4 (100) needed only 0.33 eV, offering better selectivity. In the reaction of CO + NO on CuFe2O4 and ZnFe2O4, NO adsorbed on the surface with double oxygen vacancy to form N2O2 intermediate, then reacted to produce N2 and fill the oxygen vacancy. CuFe2O4 and ZnFe2O4 required energy barriers of 0.68 eV and 0.73 eV, respectively, demonstrating the feasibility of the CO-SCR reaction on the catalyst surface. Further exploration of the reaction in an oxygen-enriched environment found that O2 can inhibit the CO-SCR reaction. The study reveals that MFe2O4 (M=Co, Cu, Zn) catalysts can improve the catalytic activity of the CO oxidation reaction and CO-SCR reaction, with CuFe2O4 exhibiting the best selectivity and catalytic activity. What's more, this study also provides insights for the simultaneous removal of CO and NO. [ABSTRACT FROM AUTHOR]

The catalytic performance of cobalt–chromium spinel NH3-SCR can be enhanced by Mn-doped and Mn–Ti co-doped catalysts; however, there is insufficient understanding of the underlying reaction mechanism. Our work is based on a first-principles computational approach of density functional theory to calculate the optimized configurations of CoAl2O4(100) both before as well as after being Mn-doped and Mn–Ti co-doped. We also simulated the adsorption behavior of gas molecules such as NH3 and NO on the catalyst before and after doping. The optimized configurations and the associated energy distributions for the NH3 dehydrogenation and SCR reactions on Mn0.1Co0.9Al2O4 and Mn0.1Co0.9Ti0.1Al1.9O4 catalysts have undergone a thorough investigation. Our findings demonstrate that the introduction of Mn-doping and Mn–Ti co-doping can enhance the adsorption capacity of gas molecules, such as NH3 and NO, on CoAl2O4 catalysts while significantly reducing the energy barriers for NH3 dehydrogenation and SCR reactions. The performance of Mn–Ti co-doping surpasses that of Mn-doping. Furthermore, we conducted an investigation into the adsorption of H2O and SO2 on the doped catalysts, revealing that Mn–Ti co-doping effectively enhances the water and sulfur resistance properties of the catalysts. Our study is anticipated to serve as a crucial theoretical guide for the development, preparation, and modification of cobalt–aluminum spinel catalysts. [ABSTRACT FROM AUTHOR]

Copper-based photocatalysts have attracted much attention because of their great prospects in photochemical conversion. However, the preparation of highly stable copper-based photocatalysts is a challenge. In this study, copper nanoparticles (Cu NPs) wrapped in graphitized polyacrylonitrile (g-PAN) were prepared by a two-step sintering method. Even if Cu@g-PAN is placed in the air for one month, the Cu NPs were still not oxidized. Furthermore, we succeeded in further introducing graphitized carbon nitride (g-C3N4) into the g-PAN shell structure, which was confirmed using a Scanning Transmission Electron Microscope (STEM), FT-IR, and UV-Vis absorption spectra. Cu@g-PAN/g-C3N4 can degrade 88.61% of methylene blue (MB) in one hour, showing a higher catalytic activity than Ag@g-PAN/g-C3N4 (55.18%). XPS and Auger electron spectroscopy tests of catalyzed Cu@g-PAN/g-C3N4 show that Cu is not oxidized. We have proposed a possible mechanism for charge separation and transformation in the Cu@g-PAN/g-C3N4 composites to explain the enhanced photocatalytic performance. This work provides a new method to protect Cu NPs and demonstrates the prospect of rational design of copper-based photocatalysts with high stability and efficiency. [ABSTRACT FROM AUTHOR]

Experimental evidence shows that CuFe 2 O 4 exhibits excellent catalytic performance in the SCR reaction. However, there is a lack of in-depth research on its specific reaction mechanism. Our study begins by computing the adsorption model of molecules like NH 3 and then goes on to examine the SCR reaction mechanism of NH 3 on CuFe 2 O 4 before and after Zn doping. The results indicate that NH 3 is chemically adsorbed (-1.26 eV) on the surface and has a strong interaction with the substrate. Importantly, Zn doping provides more favorable reactive sites for NH 3 molecules. Subsequent investigation into the NH 3 dehydrogenation and SCR reaction processes showed that incorporating Zn can greatly decrease the energy barrier of the most critical step in the reaction (0.58 eV). Additionally, the study also assesses the feasibility of the reaction of adsorbed NO with surface active O atoms to form NO 2 (barrier 0.86 eV). Lastly, the sulfur resistance of the catalyst before and after doping is calculated and analyzed, and it is found that Zn doping effectively improves the sulfur resistance. Our study provides valuable theoretical guidance for the development of ferrite spinel and doping modification.

The photocatalytic enhancement of sliver-based metals compounded with semiconductor materials has been demonstrated. However, there are relatively few studies on the effect of particle size in the system on photocatalytic performance. In this paper, silver nanoparticles of two different sizes, 25 and 50 nm, were prepared by a wet chemical method and subsequently sintered to obtain a photocatalyst with a core-shell structure. The photocatalyst Ag@TiO 2 -50/150 prepared in this study has a hydrogen evolution rate as high as 4538.90 μmol·g -1 ·h -1 . It is interesting to find that when the ratio of silver core size to composite size is 1:3, the hydrogen yield is almost not affected by the silver core diameter, and the hydrogen production rate is basically the same. In addition, the rate of hydrogen precipitation in air for 9 months was still more than 9 times those of previous studies. This provides a new idea for the study of the oxidation resistance and stability of photocatalysts.