In response to the serious problem of trace pollutants in the natural environment, photocatalytic degradation technology has become an effective solution for trace pollutant removal. Defective carbon nitride (g-C3Nx ) materials have attracted much attention because of their superior visible light absorption properties. In this study, the Co3O4/ZnO@MG-C3Nx visible photocatalyst was prepared by mixing the magnetic MG-C3Nx material as the precursor CoZn-ZIF with different ratio of Co to Zn, and then calcinated at 900 oC. The structure, morphology and composition of the prepared photocatalyst were characterized by means of XRD, SEM, TEM, TGA and BET, to verify the successful preparation of the catalyst. It follows that the catalyst with the optimal ratio of Co∶Zn = 5∶1 possessed the excellent visible light catalytic activity, and the degradation rate of methylene blue (MB) reached 95.4% within 150 min. The catalytic efficiency of this catalyst was 4.77 and 2.2 times higher than that of G-C3N4 and Co3O4/ZnO, respectively. It was shown that the formation of a large number of nitrogen defects on the surface of G-C3Nx after alkali activation was conducive to accelerating the capture of photogenerated electrons, and the promotion of synergistic interaction between the metal active sites led to an obvious acceleration of the photogenerated electron-hole separation and migration, which in turn enhanced the photocatalytic activity. The main active species were verified to be 1O2 and ·OH by the active species capture experiments. In conclusion, the catalyst has excellent visible light absorption performance, stability and recyclability, and has a broad application prospect.
A series of alkali-modified HZSM-5 zeolite were prepared via chemical treatment of the parent HZSM-5 with NaOH solution of different concentrations. And then, as solid acid, the alkali-modified HZSM-5 was physically mixed with commercial Cu-ZnO-Al2O3 to obtain bifunctional catalysts of HZSM-5 zeolite/Cu-ZnO-Al2O3 for steam reforming of dimethyl ether (SRD) reaction. The products were systematically characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), N2 adsorption-desorption at low temperature, and NH3 temperature-programmed desorption (NH3-TPD) techniques. The results showed that the acidity and structure of the HZSM-5 could be effectively adjusted by altering the concentration of NaOH, and then affecting the SRD performance of the corresponding bifunctional catalyst. The bifunctional catalyst composed of the HZSM-5-0.4 treated by 0.4 mol/L NaOH and Cu-ZnO-Al2O3 exhibited the best SRD performance, i.e., the initial dimethyl ether conversion and H2 yield reached 100% and 93% under the conditions of reaction temperature 350 oC, pressure 0.1 MPa, space velocity 3000 mL/(g·h), respectively, and dimethyl ether conversion and H2 yield remained basically constant in 10 h, indicating that the catalyst had better stability.
In order to fabricate epoxy resin composite coating with superior long-term anti-corrosive properties, graphene oxide (GO) and cerium dioxide (CeO2) nanoparticles were covalently modified with (3-Aminopropyl) triethoxysilane and 3-Glycidyloxypropyltrimethoxysilane, respectively. Subsequently, CeO2 nanoparticles were anchored on the surface of GO through the reaction between -NH2 and -C-O-C-, obtaining CeO2-GO hybrid materials. Afterwards, the composite coating (CeO2-GO)/EP was prepared via incorporating the prepared hybrid material with epoxy resin matrix. While the prepared CeO2-GO hybrid materials and the composite coating (CeO2-GO/E) P were characterized by means of FT-IR, XPS and SEM. The SEM images of the coating fracture morphology show that the CeO2-GO hybrid material was uniformly dispersed in epoxy resin matrix. The results of water absorption and friction wear test manifest that the water absorption and friction coefficient of CeO2-GO/EP coating are significantly lower than that of the pure epoxy resin coating. The potentiodynamic polarization curve and EIS test results indicate that the coating (CeO2-GO/EP) with addition of 1.0%CeO2-GO/EP has the lowest Icorr value (8.42 × 10-13 A·cm-2) and the higher Ecorr value (-65 mV). After being immersed in 3.5% (mass fraction) NaCl solution for 60 d, the CeO2-GO/EP coatings with mass fraction of 0.5%, 1.0%, 1.5% and 2.0% CeO2-GO still presented |Z|0.01 Hz values 7.88 × 109, 4.97 × 109, 5.26 × 109 and 7.41 × 109 Ω·cm2, respectively. It is 1000 times of the pure epoxy resin coating |Z|0.01 Hz value 6.56 × 106 Ω·cm2. According to the various performance test results, the long-term anti-corrosion performance of CeO2-GO/EP coatings may be ascribed to the dual active/passive anti-corrosion mechanism.
Rare earth ion modification has been widely used to improve the electrical properties of ferro/piezoelectric materials. In this work, Lu3+ doped lead-free ferroelectric ceramics of 0.67BiFe1 - x Lu x O3-0.33BaTiO3 (BF-BT-xLu, x = 0, 0.005, 0.008, 0.010, 0.012, 0.015, 0.020, 0.030) were prepared by using a conventional high-temperature solid-state reaction method. The results of XRD powder diffraction showed that the introduction of Lu3+ ions did not cause significant change of the crystal structure for the Lu3+ doped lead-free ferroelectric ceramics, and of which all the components of ceramics are retained in the morphotropic phase boundary (MPB) region, where tetragonal and rhombohedral perovskite structures coexisted. Microscopic morphology analysis shows that all ceramics were well sintered and have high relative density. By analyzing and comparing the changes in iron ion valence and oxygen vacancies, it can be determined that the incorporation of appropriate amount of Lu3+ ions can effectively hinder the transformation of Fe3+ ions to Fe2+ ions, thereby reducing the leakage current in the BF-BT-xLu ceramics, therewith, improving its electrical performance. Pure BF-BT exhibits P-E hysteresis loops of typical ferroelectrics, with remnant polarization (Pr) = 26.47 μC/cm2, coercive field (Ec) = 30.45 kV/cm. After moderate Lu3+ modification, the ferroelectric properties of the BF-BT system were improved, with Pr = 28.66 μC/cm2, Ec = 28.12 kV/cm for the BF-BT-0.015Lu. By 80 kV/cm at room temperature, the electric field-strain S of BF-BT-0.01Lu is 0.328%, and the high-field piezoelectric coefficient d33* is 410 pm/V. The present study expands the application of rare earth ions in the field of ferroelectric materials and provides an example for further designing high-performance BF-BT lead-free ferroelectrics.
The corrosion behavior of oil well tubing P110 steel in environments of different oil-water mixing ratios (0.5:9.5, 1:9, 2:8, quality ratios) in the presence of sulfate-reducing bacteria (SRB) and iron-oxidizing bacteria (IOB) were investigated via biological culture technology, weightlessness measurement, surface analysis and electrochemical testing. The results showed that the corrosion rate of P110 steel is maximum (0.2787 ± 0.0042) at an oil-water ratio of 2:8, while the steel is suffered from heavy corrosion in environments of different oil-water ratio. This is due to that the increase in oil content may lead to an increase in the carbon source, which is in favor of the formation corrosive substances and the growth of bacteria in the solution. After adding ternary compound biocides, the corrosion rate of P110 steel in environments of different oil-water ratio were significantly reduced, especially for the corrosion test in environment of the oil-water ratio of 2:8 for different times, its bactericidal rate of SRB and IOB were above 93% and 85%, respectively with corrosion inhibition rate between 38.08% and 64.11%. In fact, the best inhibition effect was achieved by adding the compounded biocides after 3 d of corrosion, indicating that the effect of compounded biocides on slowing down the corrosion of mixed bacteria of P110 steel was extremely significant; this is due to the addition of compound biocides, which containing D-tyrosine can lead to the existing biofilm dispersion, shedding, while changing the cell structure, destroys the concentration environment, and dimethyl sulfoxide as a synergistic penetrant, can accelerate the Tetrakis hydroxymethyl phosphonium sulfate (THPS) into the biofilm, the synergistic effect of the components in the compound biocides accelerates the process of killing the mixed bacteria, inhibiting the P110 steel corrosion.
Development of lightweight, flexible, and high-efficiency electromagnetic shielding films is urgently required for practical application for wearable devices, thin-film electronics, and miniaturized equipment. In order to significantly enhance the electrical conductivity and electromagnetic shielding effectiveness (EMI SE) of carbon fiber felts (CFFs), MXene nanosheets were well dispersed in ethanol aqueous solutions and then spray-deposited onto CFF surfaces to fabricate MXene@CFF composite films. The effect of MXene deposition on the micromorphology, electrical conductivity and EMI SE of the composite films was investigated in detail. The results showed that the incorporation of MXene could significantly improve the EMI shielding performance. The surface electrical resistivity of the composite films with 2.37% (mass fraction) MXene decreased from 9.3 Ω/sq to 2.7 Ω/sq, while the EMI SE in the range of 8.2~12.4 GHz (X-band) increased to 57.9 dB, increasing by 27.8% in comparison with that of the bare CFFs. This performance improvement may mainly be attributed to the enhanced electrical conductivity of MXene-coated CFFs, the hierarchical porous structure, and the increased multiple reflection and absorption at multi-component interfaces.
In order to improve the corrosion resistance of galvanized fasteners, it is necessary to develop a silane conversion film with good storage stability and high corrosion resistance. Herein, a high performance composite silane conversion film was prepared on electroplated Zn surface with amino-silane KH550 and epoxy-silane KH560 as raw materials. The effect of ratios the two silanes on the storage stability of the conversion liquid and the corrosion resistance of the conversion film were studied. The prepared composite silane conversion liquid and composite silane conversion film were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), infrared spectroscopy (IR), neutral salt spray test, polarization curve test, long-term storage test, binding force test and pencil hardness test, in terms of the relevant storage stability, surface morphology, composition, mechanical properties and corrosion etc. The results show that when the ratio of KH550 to KH560 is 5∶5, the composite silane conversion film has the best performance, its storage stability reaches 180 d. After 72 h of neutral salt spray test, no white rust was produced in the coating. The corrosion current density and polarization resistance of the composite conversion film reach 4.229 × 10-9 A·cm-2 and 5.443 × 105 Ω·cm2, respectively. It provides theoretical and application support for the further development of corrosion prevention of galvanized fasteners.
5083 Al-alloy with high strength, good corrosion resistance and thermal stability, is widely used in welding manufacturing. In this paper, by setting the same welding heat input, the welded joints of 5083-H111 Al-alloy sheets were prepared by gas metal arc welding techniques with the applying either pulsed direct current or constant direct current, respectively. Then the effect of welding techniques on the formation, microstructure and mechanical properties of welded joints were studied via metalloscopy, material mechanics testing machine, microhardness tester, and scanning electron microscope with EDS. The results indicate that the pulsed GMAW welds are smoother with better appearance, indicating that the arc pulses can partially inhibit the porosity formation of the weld joints. The area of columnar crystals formed in the Pulsed GMAW welds is larger, indicating that the temperature gradient of the molten pool is larger during pulsed arc welding. The mechanical properties of the weld joints were similar for the two current modes, which presented the joint strengths about 288~303 MPa corresponding to 90% that of the base metal. Fractures of the tensile samples occur in the weld metal, and the fracture surfaces reveal dimples. The decrease of weld strength is attributed to the presence of coarse grains and porosity.
Ni-nano-Al2O3/micro-Diamond composite coating was prepared by electrodeposition on 9310 carburizing steel. The morphology, microstructure, composition of the composite coating were characterized by XRD and SEM, while its bond strength, tensile properties and wear resistance were also tested. Ni-Al2O3/Diamond composite coating is dense and continuous. The average bonding strength between the coating and the substrate is higher than 55.2 MPa. The wear rate of the composite coating is reduced by 43.8% compared with the 9310 carburizing steel and reduced by 76.4% compared with the Ni-Al2O3 composite coating. Wear mechanism of the composite coating was abrasive wear and adhesive wear by analyzing wear tracks.
