Gas sensors play an indispensable role in industrial, personal safety and environmental protection, and have been widely investigated by researchers. In some cases, the sensitivity of a two-dimensional material sensor can be enhanced by generating vacancies or applying an external electric field. Similar results can be achieved using Janus 2D materials, which have an inherent electric field and are good candidates for high-sensitivity gas sensors. In this study, the electronic and transport properties of Janus group-Ⅲ chalcogenide monolayers(Ga_2SSe, In_2SSe) were investigated for detecting CO_2 and NO_2 using first-principles calculations. For several parameters that affect the performance of gas sensors, such as adsorption distances, adsorption energies,charge transfers and density of states(DOS), a detailed comparison of Janus group-Ⅲ chalcogenide monolayers has been provided with their pristine systems, Janus group-Ⅲ chalcogenide monolayers(Ga_2SSe, In_2SSe) have high selectivity. It was mainly ascribed to the built-in electric field caused by the out-of-plane asymmetric structure of Janus monolayer which enhances the dipole-dipole interaction between the polar gas molecule and the 2D materials. And the variation of transmission spectra of the Janus group-Ⅲ chalcogenide monolayer before and after adsorbing molecules further proves the feasibility of this kind of material as a high-sensitivity gas sensor.
WANG XinZhi;LIU Dan;CHENG Gong;HUANG YuDong;HE YuRong
来源期刊：Science China(Technological Sciences)
年/卷/期：2020 / 63 / 08
The rapid cleanup of heavy crude oil spills is challenging due to the poor mobility of highly viscous oil. Traditional absorption strategies involve heating oils to a relatively high temperature to reduce their viscosity, but this method is expensive. Herein, a solar-heated reduced graphene oxide(rGO)-wrapped melamine sponge(MS) was proposed to rapidly absorb oil. The prepared rGO-MS exhibited good hydrophobicity and oleophilicity and could be used for the rapid cleanup of oil spills from water. In addition, the excellent photothermal conversion effect of rGO enabled the rGO-MS composite to achieve a solar energy absorption efficiency of 91%. Due to the localized solar energy collection and wetting properties of rGO-MS, viscous oil near the contact region was effectively heated, enabling rapid heavy oil recovery under solar light illumination. This proposed solar heating-assisted viscous oil sorbent has great promise for use in heavy oil spill cleanups in the future.
Numerical simulation has become a useful approach to explore the complex physical and chemical process inside the supercritical water(SCW) fluidized bed reactor. Due to the drastic and non-linear variation of water properties near pseudocritical point, the flow field and drag coefficient of SCW flow past a cold particle are considerably different from that of conventional flow. Therefore, in this work, particle-resolved numerical investigation is conducted to study the flow field and drag characteristics under the influence of the special water properties variation. Through varying the enthalpy corresponding to the particle surface temperature, which will be called the particle surface enthalpy for short, in a wide range, it realizes the study under different properties variation tendencies. The simulated results demonstrate that the variations of drag coefficient versus Reynolds number(Re) and particle surface enthalpy are in good regularity when taking the freestream temperature as reference temperature. The drag coefficient is enhanced greatly at high enthalpy difference between particle surface and inflow, and the enhancement is mainly contributed by that of the frictional drag coefficient. Moreover, the drag coefficient variations under different pressures are in good agreement when cases are set with the same inflow and particle surface enthalpies, respectively.By fitting the simulated results, a new drag coefficient correlation is developed for Re range of 10–200 with consideration of the influence of the special properties variation. The fitting quality is good that the maximum deviation between the new correlation and simulated data is 13.92%, and the mean deviation is 3.67%.
The optical properties of polymethyl methacrylate(PMMA) with varying degrees of artificial scratches have been studied with the aim of reproducing the change of visibility of an aircraft's PMMA optical windows after being damaged in their service environment. A novel maintenance method that can perfectly restore the optical property of PMMA has been identified and employed in the repair of the scratches that are formed on the surface of PMMA. This convenient and low-cost method entails polishing PMMA with different types of sandpaper to remove the scratches, and then spin-coating the repair solution in order to restore the optical properties of PMMA. The effect of this repair mechanism and parameters of the repair process were studied.The results indicated that the optical performance of PMMA is closely related to the mesh size of sandpaper, and improper parameter selection destroys the general effect of the repair. When the number of sandpaper mesh is low, the size of the abrasive particle is relatively larger, which can cause deeper friction marks on the surface of PMMA optical windows. Surface treatment using 5000 mesh sandpaper lowers surface roughness(R——a=0.566 nm), and optical transmittance in visible range can be restored to more than 88%.
The electrical characteristics of laminar propane flame during head-on quenching were investigated experimentally and computationally. A variable small electric field was applied between the burner and the quenching plate, which recorded flame current as a function of the height of the quenching plate, for both polarities, different premixed-air volume, and quenching plate materials. More detailed information of flame, such as the distribution of OH radical and main charged species(H_3O~+ and e~-)were obtained by using numerical simulation. The results showed that during the head-on quenching, the resistance of the propane flame is on the order of 10~8Ω, the flame current increases with the increase of the premixed-air volume, and the effect of the quenching plate materials on the flame current is negligible. In addition, it is found that the direction of the electric field has a significant influence on the flame current, indicating the "rectifier" characteristics of the flame. Moreover, it is interestingly found that the trend of flame current for burner-(burner is negative) is more consistent with the trend of the maximum OH mole concentration than for burner+(burner is positive), which indicates that the trend of flame current for burner-can more accurately reflect the combustion state during head-on quenching. And it would be a better choice to use burner as the negative electrode when diagnosing the combustion state with an applied electric field.
This study focuses on the design, characterization and testing of a novel anorthite based glass-ceramic solder for joining dense Si_3N_4 and porous Si_3N_4 ceramic. It was found that the glass solder possesses a favorable wetting ability on two ceramic surfaces.Additionally, the influence of crystallization treatment on the microstructure and shear strength of joints was investigated. The results showed that CaAl_2 Si_2O_8 was the main product in the seam. After crystallization treatment, the crystallinitiy of the seam and shear strength of joints were improved obviously. The shear strength of joints after crystallization was 52 MPa at room temperature, and it increased to 59 MPa at 850℃. Finally, the joining mechanism of the dense Si_3N_4/glass-ceramic/porous Si_3N_4 bonded joints was proposed. Intergranular diffusion of elements was identified as the main mechanism of bonding in the interface of dense Si_3N_4/glass-ceramic. In the porous Si_3N_4 side, the bonding was achieved by infiltration that was controlled by capillarity and resistance of the viscous forces.
LI Yang;YANG Jian;ZHAN ZhaoYao;WU Jumiati;LI Hai;ZHEN Liang;HE QiYuan;XU ChengYan
来源期刊：Science China(Technological Sciences)
年/卷/期：2020 / 63 / 08
Lateral hetero-junctions are considered as potential candidate for building blocks in modern electronics and optoelectronics,however, the construction of which remains a challenge. In this work, by using a laser-assisted manufacture technique,WSe_2/WO_(3-x) hetero-junction and monolayer/trilayer WSe_2 homo-junction with Schottky diode like behavior are fabricated, both of which present competitive performance for photodetection and power generation in a wide range of wavelengths from ultraviolet to infrared, with maximum photoresponsivity of 10 A/W, external quantum efficiency of 14%, and power conversion efficiency of 1.3%. Combined with Kelvin probe microscopy and electrical transport measurements, it is demonstrated that the barrier-induced built-in electric field at WSe_2/WO_(3-x) interface, and the energy band discontinuities at the monolayer/trilayer WSe_2 interface facilitate the separation of photo-generated electron-hole pairs. Our work provides a solid step towards the controllable construction of lateral junctions by laser-assisted manufacture for exploiting van der Waals materials-based novel electronic and optoelectronic applications.
A periodically-poled LiNbO_3(PPLN) crystal features space-dependent second-order nonlinear coefficients, which is one of the most important materials to effectively control nonlinear optical interactions through quasi-phase matching(QPM). By using electri
CO_2 geological sequestration in a depleted shale gas reservoir is a promising method to address the global energy crisis as well as to reduce greenhouse gas emissions. Though improvements have been achieved by many researchers, the carbon sequestration and enhanced gas recovery(CS-EGR) in shale formations is still in a preliminary stage. The current research status of CO_2 sequestration in shale gas reservoirs with potential EGR is systematically and critically addressed in the paper. In addition, some original findings are also presented in this paper. This paper will shed light on the technology development that addresses the dual problem of energy crisis and environmental degradation.
YU Liang;WANG Wen Yu;WANG Si Xu;FENG Yuan;QIAN Yong;LU Xing Cai
来源期刊：Science China(Technological Sciences)
年/卷/期：2020 / 63 / 05
N-hexadecane is a potential candidate of diesel surrogate fuels and is also the largest linear alkane(n-alkanes) with known chemical kinetic models. The objective of this study is to investigate the autoignition characteristics of n-hexadecane in the lowto-intermediate temperature region and to validate the existing kinetic models. In this study, the ignition delay times(IDTs) of nhexadecane were measured using a heated rapid compression machine(RCM) at two pressures of 7 and 10 bar, and over equivalence ratios ranging from 0.5 to 1.3. Two-stage ignition characteristic and the negative temperature coefficient(NTC)behavior of total ignition delay time were experimentally captured. This study paid special attention to the influence of pressure,equivalence ratio, and oxygen content on the IDTs of n-hexadecane. It is observed that both the total IDTs and the first-stage IDTs decrease with the rise of those parameters. It is worth noting that the first-stage IDT is found to show a greater dependence on temperature but a weaker dependence on other parameters compared to the total IDT. The observed IDT dependence in the lowtemperature region(LTR) were quantitatively described by ignition delay time correlations. The newly measured IDTs were then validated against two kinetic models(LLNL and CRECK). Simulation results show that both models underpredict the first-stage IDT but generally capture the temperature dependence. The CRECK model well predicts the total IDTs of n-hexadecane while the LLNL model significantly underpredicts the total IDTs at most investigated conditions. To the best of our knowledge, this study is the first investigation on n-hexadecane autoignition under low-to-intermediate temperatures, which deepens the understanding of large n-alkane oxidation and contributes to the improvement of the existing kinetic models.