Applied Mechanics and Materials Vol. 618

Abstract: Gold nanoparticles (AuNPs)/ZnFe₂O₄ nanocomposites were prepared by a colloidal deposition (CD) method. The as-prepared AuNPs/ZnFe₂O₄ nanocomposites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS). XRD results showed that the diffraction peaks of AuNPs gradually increased with the increase of AuNPs content. SEM observations revealed that the AuNPs were presented as regular nanoparticles on the ZnFe₂O₄ in all the composites. With the increase in Au content, the amount of AuNPs deposited on ZnFe₂O₄ surface increased. EDS element analysis indicated that the actual content of AuNPs in nanocomposites was consistent with its preset value before preparation by CD method. An active dye, Methyl Orange (MO), was employed as the target pollutant to evaluate the photocatalytic activity of AuNPs/ZnFe₂O₄ under UV irradiation. The photocatalytic evaluation showed that MO discoloration ratio could reach 72.17% when the nanocomposite with AuNPs content of 5 wt.% was used as the photocatalyst. Finally, the possible mechanism for the enhanced photocatalytic activity of ZnFe₂O₄ by AuNPs was proposed.

Abstract: The hydrophobic gold nanoparticles with monodispersity are synthesized by using n-butanol reduction in situ under the condition of alkali promotion in cetyltrimethylammonium bromide (CTAB)/n-butanol/n-heptane/HAuCl₄/NaOH(aq) W/O microemulsion at 30°C. The CTAB-stabilized gold nanoparticles are characterized by UV-vis, TEM , XRD and so on. The replacement of simple surfactant (CTAB ) with mixed surfactant CTAB/ octadecylamine can weaken the direction of CTAB to the growth of gold nanopartices and increase the monodispersity of gold nanoparticles. The effects of components of the microemulsion system on the shape, size and monodispersity of gold nanoparticles are also explored. The results show that the size of gold particles is changed by the amount of CTAB and C₁₈NH₂.

Abstract: As an innovative heterogeneous UV-Fenton catalyst nanocomposite, ferroferric oxide (Fe₃O₄) with inverse-spinel structure trapped by Multi-walled carbon nanotubes (MWCNTs) was successfully prepared by a facile and in-suit strategy in this study. The as-prepared products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). An active dye, Methyl Orange (MO) was employed as the target pollutant to evaluate the UV-Fenton efficiency of Fe₃O₄/MWCNTs nanocomposite. The effects of operating parameters, including solution pH, initial MO concentration, reaction temperature, initial H₂O₂ concentration and catalyst dosage on MO discoloration were detailedly investigated. Control experiments indicated Fe₃O₄/MWCNTs exhibited higher ability for MO discoloration than bare Fe₃O₄ under the same experimental conditions, which might be attributed to the synergetic effect between Fe₃O₄ and MWCNTs.

Abstract: Graphitic carbon nitride (g-C₃N₄) polymer material was synthesized via a simple approach by directly heating melamine as the precursor at 500°C. The phase composition, chemical functional groups, and surface morphology of the obtained product were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM), respectively. All the characterization results identified the formation of g-C₃N₄ with stack-layered structure. The absorption and photocatalytic performance of as-synthesized g-C₃N₄ for the discoloration of an active dye, Methylene Blue (MB), were proved to be excellent and control experiments inferred that adsorption and photocatalysis governed the MB discoloration under UV irradiation. The repeated experiments indicated that the obtained sample could be reused more than five times without loss of its absorption capacity and photocatalytic activity.

Abstract: SiO₂-coated phosphors of Ce_0.67Tb_0.33MgAl₁₁O₁₉ (CTMA) were prepared by the sol–gel method in order to enhance thermal stabilities. The phase structures, microstructures and luminescence properties were studied by the X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscope (TEM) and fluorescence spectrometer respectively. The emission intensity of SiO₂-coated Ce_0.67Tb_0.33MgAl₁₁O₁₉ phosphor was little lower than uncoated phosphor. After baked at 600°Cfor 6h, the coated CTMA showed good thermal stabilities. The luminance performance of SiO₂-coated phosphor is 93% compared with the unbaked CTMA, which is improved 10% in contrast to uncoated.

Abstract: The structures and magnetic properties of monolayer and bilayer of transitional metallo-porphine (MP) species (M = Mn, Fe, Co, Ni, Cu) on the Ag (111) substrate are investigated by DFT based first-principle method. The MP monolayer has a distortion about 10° towards the substrate due to strong interaction between adsorbed molecule and substrate. The molecule-substrate interaction could quench the magnetic moment of the adsorbed molecule. For MP bilayer adsorption on the Ag (111), the top layer remains its planar structure and magnetic moment due to the screening of substrate effects by bottom layer, meanwhile the bottom layer has strong structural distortions and obvious variations of magnetic moment.

Abstract: To investigate the influence of the ball grinding time on the particle sizes of the negative ion powder and the release ability of negative ions for dental applications. Ethanol as a dispersant , steel ball as grinding media, the negative ion powder was grinded (4h, 8h, 12h, 16h, 22h) through the ultrasonic dispersion and ball milling and high-speed mixing process. Its crystal pattern, particle size and surface morphology were characterized by XRD, dynamic laser scattering instrument, SEM. The number of negative ion in different grinding time was tested by 3010-pro negative ion tester. With the increasing of the milling time, particle size of negative ion powder was gradually decreasing, after 22h, the particle size was 232nm, which was consistent with the results of electron microscope, but the number of negative ions was not significantly changed. Therefore, optimum utilization of the ultrasonic dispersion and ball milling and high-speed mixing technologies is necessary to most efficiently achieve stable dispersions with the target particle size characteristics.

Abstract: Results of studies of humic substances in the quality of natural polymeric modifier for the coated palladium catalysts are presented in the paper, along with synthesis of new catalysts based on palladium – potassium humate, fixed on various inorganic carriers and their catalytic properties are studied. The catalysts may be placed in the following order according to activity: Pd-PHum/B-094 > Pd-PHum/Shungit (Sht), proc.1%КОН > Pd-PHum/Sht >> Pd-PHum/SiO₂. More active and optimal are the catalysts of 0,8% Pd – Potassium’s Humat (1%)/B-94 and 0,8% Pd/Shungit 1% КОН.

Abstract: In the course of study the optimal conditions of conduction of the process are found. Optimal temperature for preparation of motor oils from chark chemical tar is 400 °С. On the increase of temperature from 350 °С to 400 °С the yield of liquid products on Mo-containing catalyst increases from 47,1 mass. % to 65.2 mass. % compared to the yield of liquid products obtained without the catalyst. The yield of gasoil fraction constitutes 15 mass. %. Optimal quantity of catalyst for preparation of liquid products from the tar is 0,05 mass. %. According to the results of study the catalytic effect of synthesized from emulsion catalyst appears at low concentration of molybdenum (0,05 mass.%). But the double increase of concentration of molybdenum weakly affects the improvement of indicators of the process.

Abstract: In order to improve the corrosion resistance of electro-less Ni-P-PTFE composite coating, electro-less Ni-P-PTFE composite coatings were prepared on 45# carbon steels specimen with addition of rare element cerium (Ce). Surface morphology of the coatings was observed by scanning electron microscope (SEM). Effect of cerium concentration on PTFE content of the coatings was investigated. The results indicated that properly added cerium into the bath increases the PTFE content of the coatings, decrease the corrosion rate, made the corrosion resistance improved of the coatings. And effect of cerium concentration on corrosion resistance of the composite coatings was evaluated by immersion test with 3.5% NaCl and 5% NaOH solutions respectively. With the rare element cerium concentration exceeding, the corrosion rate gradually increase. At the cerium concentration was 0.01 g.L^-1, the corrosion rate of coating in the solutions were lowest, at 0.00186 mg·cm^-2·h^-1 and 0.00109 mg·cm^-2· h^-1. But with the cerium concentration go on increasing, the corrosion resistance of the coatings then decreases.