One step method of structure engineering porous graphitic carbon nitride for efficient visible-light photocatalytic reduction of Cr(Ⅵ)

Porous g-C3N4 nanosheets (PCN) were prepared by the nickel-assisted one-step thermal polymerization method.Hydrogen (H2) which was produced by the reaction between nickel (Ni) foam and ammonia (NH3) defined the structure and properties of PCN.During the formation of PCN,the participation of H2 not only enhanced the spacing between layers but also boosted the specific surface area that more active sites were exposed.Additionally,H2 promoted pores formation in the nanosheets,which was beneficial to the transfer of photons through lamellar structure and improved the absorption efficiency of visible light.Remarkably,the obtained PCN possessed better Cr(Ⅵ) photocatalytic reduction efficiency than pure g-C3N4.The reaction rate constant (k) of PCN (0.013 min-1) was approximately twice that of bare g-C3N4 (0.007 min-1).Furthermore,the effects of original pH and concentration of Cr(Ⅵ)-containing solution on removal efficiency of Cr(Ⅵ) were explored.A possible photocatalytic mechanism was proposed based on the experiments of radical scavengers and photoelectrochemical characterizations.     

置换过程的电化学和工艺分析

本文对置换过程进行了简要的电化学分析，并较详细地讨论了影响置换过程的各工艺因素．     

一种新型MMC并联双端口子模块及其三阶段故障电流阻断机理

为使模块化多电平换流器(modular multilevel converter,?MMC)具备直流故障自清除能力和电容电压均衡能力,提出了一种新型并联双端口子模块：钳位双全桥子模块(clamp double full bridge submodule,?CD-FBSM)。该子模块器件成本和运行损耗较低,正常工作时相邻子模块之间具有多种协同运行模式,通过特有的并联模式可提高电容电压均衡度。故障闭锁时,模块内部电容并联、模块之间电容串联且反向接入电路,能够可靠阻断故障电流并均衡电容电压,有利于系统快速重启。此外,提出了三阶段故障电流阻断机理分析方法,对CD-FBSM的故障电流阻断过程进行了研究。通过Matlab/Simulink的仿真结果表明,所提子模块电容电压均衡度较高,可快速阻断故障电流,且故障电流阻断过程与理论分析一致。     

A high efficiency multi-module parallel RF inverter system for plasma induced hydrogen

Hydrogen energy plays an important role in achieving carbon neutralization, and plasma induced hydrogen is an effective production method. One challenge is how to guarantee high efficiency operation with wide power output range of the RF inverter system used to generate the plasma. In this paper, a multi-module parallel topology of a high-frequency inverter is analyzed, in which the power combining network can maintain the soft switching characteristics of the inverter modules. A control method of "ON/OFF + phase shift" is adopted to broaden the output power range of the inverter. The equivalent impedances of different modules are analyzed in detail. A four-module 13.56 MHz high-frequency inverter prototype is built and tested. The results show that the inverter can operate at high efficiency and wide output power range with efficiency improved by at least 5% compared with the traditional parameter design method without considering the effect of paralleled modules.     

Mechanism and Inhibition of Grain Coarsening of Al-Mg-Si Alloy in Hot Forming

A high-Ti 6061 alloy was rolled with strains up to 0.8-2.0 and at 350-550 ℃. Microstructures that developed during deformation and subsequent solution heat treatment (SHT) were observed by using optical and transmission electron microscopy. Microstructure evolution during SHT depends mainly on the initial rolling temperature, and it was found that the higher this temperature is, the coarser the grains are. After rolling at 400 ℃, well-defined cells and subgrains were formed, which induced further sites for recrystallization nucleation during subsequent SHT. The recrystallization mechanism was found to be subgrain rotation, with a final grain size smaller than 200 μm. Increasing the rolling temperature to 500 ℃ results in a low density of dislocations distributed uniformly in the deformed matrix and fewer nucleation sites during subsequent SHT. The recrystallization mechanism is grain boundary bulging, while the final grain size approaches several millimeters. Finally, a hot forming process of high-Ti 6061 alloy for inhibiting grain coarsening was proposed, and verified by experiments.     

Bonding strength of graded anti-corrosive coatings of fluoroethylenepropylene （FEP）/polyphenylene sulfide （PPS）

Fluororesin-based anti-corrosive coatings including graded FEP/PPS were prepared on carbon steel by melt powder coating, the bonding strength of all coating systems was determined by the pull-off test. It is found that the poor adhesion of fluororesin coatings to metallic substrates is improved obviously by the graded coating structure of FEP/PPS, and the bonding strength reaches up to 11.8 MPa for the five-layer system. Examination by electron probe microanalysis （EPMA） verifies that the distribution of main components is graded in the five-layer system, which is responsible for the enhancement of the interfacial bonding.     

Facile synthesis of metal-organic frameworks embedded in interconnected macroporous polymer as a dual acid-base bifunctional catalyst for efficient conversion of cellulose to 5-hydroxymethylfurfural

5-Hydroxymethylfurfural (5-HMF), as a key platform compound for the conversion of biomass to various biomass-derived chemicals and biofuels, has been attracted extensive attention. In this research, using Pickering high internal phase emulsions (Pickering HIPEs) as template and functional metal-organic frameworks (MOFs, UiO-66-SO₃H and UiO-66-NH₂)/Tween 85 as co-stabilizers to synthesis the dual acid-base bifunctional macroporous polymer catalyst by one-pot process, which has excellent catalytic activity in the cascade reaction of converting cellulose to 5-HMF. The effects of the emulsion parameters including the amount of surfactant (ranging from 0.5% to 2.0% (mass)), the internal phase volume fraction (ranging from 75% to 90%) and the acid/base Pickering particles mass ratio (ranging from 0:6 to 6:0) on the morphology and catalytic performance of solid catalyst were systematically researched. The results of catalytic experiments suggested that the connected large pore size of catalyst can effectively improve the cellulose conversion, and the synergistic effect of acid and base active sites can effectively improve the 5-HMF yield. The highest 5-HMF yield, about 40.5%, can be obtained by using polymer/MOFs composite as catalyst (Poly-P12, the pore size of (53.3 ±11.3) μm, the acid density of 1.99 mmol·g^-1 and the base density of 1.13 mol·g^-1) under the optimal reaction conditions (130 ℃, 3 h). Herein, the polymer/MOFs composite with open-cell structure was prepared by the Pickering HIPEs templating method, which provided a favorable experimental basis and theoretical reference for achieving efficient production of high added-value product from abundant biomass.     

Wear Resistance of CO2 Corrosion Product Scale Formed at High Temperature

 To investigate the correlation between structure characteristics and wear resistance of CO2 corrosion product scales at high temperature and high pressure, an autoclave was used to prepare CO2 corrosion product scales on N80 steel in carbon dioxide corrosion environment. The correlation between wear resistance of the scales and many other factors, such as temperature, pressure, morphology, structure, velocity of fluid medium, sand grain size, and so on, was comparatively analyzed by a self assembled wear device, and the scale morphologies before or after being worn were observed by scanning electron microscope (SEM). And then the surface grain size and thickness of scale were measured. The results showed that the cross section of the corrosion scale was of a double layer structure, the outer layer of which was composed of regular crystals, whereas the inner layer was a thin scale of fine grains. The outer grain size and thickness of scale varied with temperature, and the initial wear loss was consistent with the surface grain size; at the same time, the total wear loss corresponded to the thickness of scale. Compared to wear resistance in different depths of the scale, it was found that the structure of scale was a double layer structure in cross section, and the wear resistance of inner layer was better than that of the outer layer; the closer the scale to the matrix, the greater was the wear resistance of scale; and the larger the size or the higher the rotary speed of solid grain in multiphase flowing medium, the more was the wear loss of scale.     

Iterative Phase Noise Suppression for Full-Duplex Communication Systems

Oscillator phase noise is one of the bottlenecks that limits the self-interference(SI) cancellation capability of full-duplex systems. In this paper,we propose a method for the suppression of common phase error(CPE) and intercarrier interference(ICI)induced by the phase noise in full-duplex orthogonal frequency division multiplexing(OFDM) systems.First, we regard the effect of CPE as a portion of the SI channel and perform estimation, reconstruction and elimination in the time domain. Then, the ...     

Postsynthesis of hierarchical core/shell ZSM-5 as an efficient catalyst in ketalation and acetalization reactions

Hierarchical core/shell Zeolite Socony Mobil-five (ZSM-5) zeolite was hydrothermally postsythesized in the solution of NaOH and diammonium surfactant via a dissolution-reassembly strategy. The silica and alumina species were firstly dissolved partially from the bulky ZSM-5 crystals and then were in situ reassembled into the MFI-type nanosheets with the structure-directing effect of diammonium surfactant, attaching to the out-surface of ZSM-5 core crystals. The mesopores thus were generated in both the core and shell part, giving rise to a micropore/mesopore composite material. The micropore volume and the acidity of the resultant hybrid were well-preserved during this in situ recrystallization process. Possessing the multiple mesopores and enlarged external surface area, the core/shell ZSM-5 zeolite exhibited higher activity in the ketalation and acetalization reactions involving bulky molecules in comparison to the pristine ZSM-5.