由于传统求解时间序列自回归(auto-regressive,AR)模型的最小二乘方法无法顾及设计矩阵误差,现有的AR模型迭代解法难以应用协方差传播率给出较为精确的精度评定公式。将块自助采样方法引入到AR模型精度评定研究中,并在其基础上借助Siev...由于传统求解时间序列自回归(auto-regressive,AR)模型的最小二乘方法无法顾及设计矩阵误差,现有的AR模型迭代解法难以应用协方差传播率给出较为精确的精度评定公式。将块自助采样方法引入到AR模型精度评定研究中,并在其基础上借助Sieve自助法的思想,定义了顾及设计矩阵误差AR模型精度评定的Sieve块自助采样方法。根据不同的分块准则和采样策略,给出了4种方法的重采样步骤。模拟实验结果表明,精度评定的Sieve块自助采样方法能够得到比最小二乘法、经典的AR模型迭代解法更加可靠的自回归系数标准差,具有更强的适用性。同时,北斗卫星精密钟差真实案例表明,所提出的Sieve移动块自助法、Sieve非重叠块自助法、Sieve圆形块自助法以及Sieve静止块自助法的均方根(root mean square,RMS)比总体最小二乘的RMS分别减小了70.25%、78.65%、70.89%和79.24%,进一步验证了所提算法的有效性和可靠性,为时间序列AR模型的精度评定问题提供了一种采样思路。展开更多
Carbon capture is an important strategy and is implemented to achieve the goals of CO_(2)reduction and carbon neutrality.As a high energy-efficient technology,membrane-based separation plays a crucial role in CO_(2)ca...Carbon capture is an important strategy and is implemented to achieve the goals of CO_(2)reduction and carbon neutrality.As a high energy-efficient technology,membrane-based separation plays a crucial role in CO_(2)capture.It is urgently needed for membrane-based CO_(2)capture to develop the high-performance membrane materials with high permeability,selectivity,and stability.Herein,ultrapermeable carbon molecular sieve(CMS)membranes are fabricated by py roly zing a finely-engineered benzoxazole-containing copolyimide precursor for efficient CO_(2)capture.The microstructure of CMS membrane has been optimized by initially engineering the precursor-chemistry and subsequently tuning the pyrolysis process.Deep insights into the structure-property relationship of CMSs are provided in detail by a combination of experimental characterization and molecular simulations.We demonstrate that the intrinsically high free volume environment of the precursor,coupled with the steric hindrance of thermostable contorted fragments,promotes the formation of loosely packed and ultramicroporous carbon structures within the resultant CMS membrane,thereby enabling efficient CO_(2)discrimination via size sieving and affinity.The membrane achieves an ultrahigh CO_(2)permeability,good selectivity,and excellent stability.After one month of long-term operation,the CO_(2)permeability in the mixed gas is maintained at 11,800 Barrer,with a CO_(2)/N_(2)selectivity exceeding 60.This study provides insights into the relationship between precursor-chemistry and CMS performance,and our ultrapermeable CMS membrane,which is scalable using thin film manufacturing,holds great potential for industrial CO_(2)capture.展开更多
In order to address challenges posed by the reduction in transistor size,researchers are concentrating on two-dimensional(2D)materials with high dielectric constants and large band gaps.Monoclinic ZrO_(2)(m-ZrO_(2))ha...In order to address challenges posed by the reduction in transistor size,researchers are concentrating on two-dimensional(2D)materials with high dielectric constants and large band gaps.Monoclinic ZrO_(2)(m-ZrO_(2))has emerged as a promising gate dielectric material due to its suitable dielectric constant,wide band gap,ideal valence-band offset,and good thermodynamic stability.However,current deposition methods face compatibility issues with 2D semiconductors,highlighting the need for high-quality dielectrics and interfaces.Here,high-quality 2D m-ZrO_(2)single crystals are successfully prepared using a onestep chemical vapor deposition(CVD)method,aided by 5A molecular sieves for oxygen supply.The prepared ZrO_(2)is utilized as a gate dielectric in the construction of MoS2 field-effect transistors(FETs)to investigate its electrical property.The FETs exhibit a high carrier mobility of up to 5.50 cm^(2)·V^(−1)·s^(−1),and a current switching ratio(Ion/off)of approximately 10^(4),which aligns with the current standards of logic circuits,indicating that ZrO_(2)has application value as a gate dielectric.The successful onestep preparation of single-crystal ZrO_(2)paves the way for the utilization of high-κgate dielectrics and creates favorable conditions for the development of high-performance semiconductor devices,offering new possibilities for transistor miniaturization.展开更多
Molecular sieve catalysts,owing to their unique chemical properties,are widely used as catalysts among various catalytic reactions.Abundant Br?nsted acid sites in molecular sieve catalysts usually enable active compon...Molecular sieve catalysts,owing to their unique chemical properties,are widely used as catalysts among various catalytic reactions.Abundant Br?nsted acid sites in molecular sieve catalysts usually enable active components to disperse well on the catalyst surface,and help to adsorb a large number of gas molecules to achieve maximum catalytic performance.Therefore,a variety of molecular sieve catalysts have been developed and used in the selective catalytic reduction of NO_(x)by NH_(3)(NH_(3)-SCR).For example,Cu molecular sieve catalysts such as Cu-SSZ-13 and Cu-SAPO-34 with wide temperature windows and stable structure are considered and applied as commercial catalysts for NO_(x)removal in diesel vehicles for a long time.Although molecular sieve catalysts possess many advantages,they still cannot avoid the serious deactivation caused by various factors in practical applications.In this review,reasons leading to the deactivation of molecular sieve catalysts for NO_(x)reduction in actual working conditions were concluded.The deactivation mechanisms of molecular sieve catalysts for NO_(x)reduction were analyzed and the corresponding anti-deactivation strategies were summarized.Finally,challenges and prospects of molecular sieve catalysts for NO_(x)reduction were also proposed.展开更多
Advanced processes for peroxymonosulfate(PMS)-based oxidation are efficient in eliminating toxic and refractory organic pol-lutants from sewage.The activation of electron-withdrawing HSO_(5)^(-)releases reactive speci...Advanced processes for peroxymonosulfate(PMS)-based oxidation are efficient in eliminating toxic and refractory organic pol-lutants from sewage.The activation of electron-withdrawing HSO_(5)^(-)releases reactive species,including sulfate radical(·SO_(4)^(-)),hydroxyl radical(·OH),superoxide radical(·O_(2)^(-)),and singlet oxygen(1O_(2)),which can induce the degradation of organic contaminants.In this work,we synthesized a variety of M-OMS-2 nanorods(M=Co,Ni,Cu,Fe)by doping Co^(2+),Ni^(2+),Cu^(2+),or Fe^(3+)into manganese oxide oc-tahedral molecular sieve(OMS-2)to efficiently remove sulfamethoxazole(SMX)via PMS activation.The catalytic performance of M-OMS-2 in SMX elimination via PMS activation was assessed.The nanorods obtained in decreasing order of SMX removal rate were Cu-OMS-2(96.40%),Co-OMS-2(88.00%),Ni-OMS-2(87.20%),Fe-OMS-2(35.00%),and OMS-2(33.50%).Then,the kinetics and struc-ture-activity relationship of the M-OMS-2 nanorods during the elimination of SMX were investigated.The feasible mechanism underly-ing SMX degradation by the Cu-OMS-2/PMS system was further investigated with a quenching experiment,high-resolution mass spec-troscopy,and electron paramagnetic resonance.Results showed that SMX degradation efficiency was enhanced in seawater and tap water,demonstrating the potential application of Cu-OMS-2/PMS system in sewage treatment.展开更多
Flue gas and coal bed methane are two important sources of greenhouse gases.Pressure swing adsorption process has a wide range of application in the field of gas separation,and the selection of adsorbent is crucial.In...Flue gas and coal bed methane are two important sources of greenhouse gases.Pressure swing adsorption process has a wide range of application in the field of gas separation,and the selection of adsorbent is crucial.In this regard,in order to assess the better adsorbent for separating CO_(2) from flue gas and CH_(4) from coal bed methane,adsorption isotherms of CO_(2),CH_(4) and N_(2) on activated carbon and carbon molecular sieve are measured at 303.15,318.15 and 333.15 K,and up to 250 kPa.The experimental data fit better with Langmuir 2 compared to Langmuir 3 and Langmuir-Freundlich models,and Clausius-Clapeyron equation was used to calculate the isosteric heat.Both the order of the adsorbed amount and the adsorption heat on the two adsorbents are CO_(2)>CH_(4)>N_(2).The adsorption kinetics are calculated by the pseudo-first kinetic model,and the order of adsorption rates on activated carbon is N_(2)-CH_(4)>CO_(2),while on carbon molecular sieve,it is CO_(2)-N_(2)>CH_(4).It is shown that relative molecular mass and adsorption heat are the primary effect on kinetics for activated carbon,while kinetic diameter is the main resistance factor for carbon molecular sieve.Moreover,the adsorption selectivity of CH_(4)/N_(2) and CO_(2)/N_(2) were estimated with the ideal adsorption solution theory,and carbon molecular sieve performed best at 318.15 K for both CO_(2) and CH_(4) separation.The study suggested that activated carbon is a better choice for separating flue gas and carbon molecular sieve can be a strong candidate for separating coal bed methane.展开更多
Mg-Li alloy is a lightweight hydrogen storage material with high hydrogen capacity,but its poor kinetics limited its practical applications.In this work,MCM-22 molecular sieve was added to Mg-Li alloy by friction stir...Mg-Li alloy is a lightweight hydrogen storage material with high hydrogen capacity,but its poor kinetics limited its practical applications.In this work,MCM-22 molecular sieve was added to Mg-Li alloy by friction stir processing(FSP)as the catalyst to enhance the kinetic properties of Mg-Li alloy(denoted as Mg-Li-MCM-22).The resulting Mg-Li-MCM-22 possesses the reversible hydrogen storage capacity of ca.6 wt.%and can release 5.62 wt.%hydrogen within 50 min at 623 K,showing improved kinetics.The Chou model and Johnson-Mehl-Avrami-Kolmogorov(JMAK)model calculations reveal that the lattice defects generated by FSP improve the kinetics of hydrogen adsorption/desorption.The pinning effect of MCM-22 particles produces more grain boundaries and dislocations,thus,increasing the diffusion rate of hydrogen atoms and providing more nucleation sites,therefore,reducing the dehydrogenation activation energy.This work provides a new strategy for the preparation of hydrogen storage materials.展开更多
Using coal gangue(CG)as raw material,a new type of all solid-waste-based 13-X molecular sieve material was controllably prepared by alkali fusion-hydrothermal method.The synthetic molecular sieve was used as a solid a...Using coal gangue(CG)as raw material,a new type of all solid-waste-based 13-X molecular sieve material was controllably prepared by alkali fusion-hydrothermal method.The synthetic molecular sieve was used as a solid adsorbent to treat Cd^(2+)-containing wastewater,and its adsorption behavior on Cd^(2+)in aqueous solution was studied and analyzed.The microstructure and morphology of the molecular sieve were investigated by X-ray diffraction(XRD),field emission scanning electron microscopy(FESEM)and specific surface area analyzer.The results show that the synthesized 13-X molecular sieve has higher Brunauer–Emmett–Teller(BET)specific surface area with higher crystallinity and higher adsorption capacity for the heavy metal Cd^(2+).The adsorption process of Cd^(2+)by molecular sieve conforms to the Langmuir isotherm adsorption equation and Lagergren pseudo-second-order rate equation.Combined with thermodynamic calculation,it can be concluded that the adsorption process is physically monolayer,spontaneous and exothermic.In this study,a low-cost and naturally available synthesis method of 13-X molecular sieve is reported.Combined with its adsorption mechanism for Cd^(2+),it provides a feasible and general method for removing heavy metal ions from coal gangue and also provides a new way for the utilization of coal gangue with high added value.展开更多
In order to comprehend the applicability of microwave irradiation for recovering coalbed methane,it is necessary to evaluate the microwave irradiation-induced alterations in coals with varying levels of metamorphism.I...In order to comprehend the applicability of microwave irradiation for recovering coalbed methane,it is necessary to evaluate the microwave irradiation-induced alterations in coals with varying levels of metamorphism.In this work,the carbon molecular sieve combined with KMnO_(4)oxidation was selected to fabricate carbon molecular sieve with diverse oxidation degrees,which can serve as model substances toward coals.Afterwards,the microwave irradiation dependences of pores,functional groups,and highpressure methane adsorption characteristics of model substances were studied.The results indicated that microwave irradiation causes rearrangement of oxygen-containing functional groups,which could block the micropores with a size of 0.40-0.60 nm in carbon molecular sieve;meanwhile,naphthalene and phenanthrene generated by macro-molecular structure pyrolysis due to microwave irradiation could block the micropores with a size of 0.70-0.90 nm.These alterations in micropore structure weaken the saturated methane adsorption capacity of oxidized carbon molecular sieve by 2.91%-23.28%,suggesting that microwave irradiation could promote methane desorption.Moreover,the increased mesopores found for oxidized carbon molecular sieve after microwave irradiation could benefit CH4 diffusion.In summary,the oxidized carbon molecular sieve can act as model substances toward coals with different ranks.Additionally,microwave irradiation is a promising technology to enhance coalbed methane recovery.展开更多
Zinc metal anodes are gaining popularity in aqueous electrochemical energy storage systems for their high safety,cost-effectiveness,and high capacity.However,the service life of zinc metal anodes is severely constrain...Zinc metal anodes are gaining popularity in aqueous electrochemical energy storage systems for their high safety,cost-effectiveness,and high capacity.However,the service life of zinc metal anodes is severely constrained by critical challenges,including dendrites,water-induced hydrogen evolution,and passivation.In this study,a protective two-dimensional metal–organic framework interphase is in situ constructed on the zinc anode surface with a novel gel vapor deposition method.The ultrathin interphase layer(~1μm)is made of layer-stacking 2D nanosheets with angstrom-level pores of around 2.1Å,which serves as an ion sieve to reject large solvent–ion pairs while homogenizes the transport of partially desolvated zinc ions,contributing to a uniform and highly reversible zinc deposition.With the shielding of the interphase layer,an ultra-stable zinc plating/stripping is achieved in symmetric cells with cycling over 1000 h at 0.5 mA cm−2 and~700 h at 1 mA cm^(−2),far exceeding that of the bare zinc anodes(250 and 70 h).Furthermore,as a proof-of-concept demonstration,the full cell paired with MnO_(2) cathode demonstrates improved rate performances and stable cycling(1200 cycles at 1 A g−1).This work provides fresh insights into interphase design to promote the performance of zinc metal anodes.展开更多
Hammer mill is widely used in the feed processing industry.During its operation,the material is thrown against the inner wall of the sieve after being broken by the hammer.Limited by the annular structure sieve,the gr...Hammer mill is widely used in the feed processing industry.During its operation,the material is thrown against the inner wall of the sieve after being broken by the hammer.Limited by the annular structure sieve,the grinded material tends to produce a"air-material circulation layer"on the inner wall of the sieve,leading to problems such as low grinding efficiency and high grinding energy consumption.Considering the disruptive characteristics of the special profile structure of a pigeon's wing on the airflow field,we extract the geometric characteristics of the coupling element and optimize the related structural parameters.Based on the principles of bionics,a new wing sieve is then designed,and its efficient grinding mechanism is studied.Compared to the commercial sieve,the experimental results indicate the bio-inspired sieve can significantly improve the material productivity and grinding quality.展开更多
The ultrastructures of the root protophleom sieve element at different developmental stages of Arabidopsis thaliana L. were investigated using the technique of high pressure freezing and freeze substitution fixing spe...The ultrastructures of the root protophleom sieve element at different developmental stages of Arabidopsis thaliana L. were investigated using the technique of high pressure freezing and freeze substitution fixing specimen. The results show that in the development of the sieve elements, the nuclei undergo typical characteristics of the programmed cell death (PCD): the nuclear envelopes form emboli, the chromatin condenses and aggregates towards the nuclear envelope, which degrades and fully disappears later. Before the nucleus degradation, neither the nuclear envelope undulation, nucleus lobe nor marked dilation (or bleb) of perinuclear space could be observed. In the cytoplasm of the mature sieve element, there are starch-like granules separately sheathed with a layer of membrane and usually with mitochondria around. These gnanules seem to provide substrates to mitochondria in their function. Small vacuoles originate from endoplasmic reticulum (ER), and no bigger vacuole was found.展开更多
Ultrastructural changes in the sieve element and dense cells of nectariferous tissue during the development of floral nectary in Arabidopsis thaliana L. were investigated with transmission electron microscopy. Samples...Ultrastructural changes in the sieve element and dense cells of nectariferous tissue during the development of floral nectary in Arabidopsis thaliana L. were investigated with transmission electron microscopy. Samples were prepared with high pressure freezing and freeze substitution techniques. The ultrastructure of dense cell was similar to that of sieve element at its early developmental stage. With the concurrent agglutination of chromatin in the nucleus, the abnormal location of organelles and the high density of cytoplasm, the ultrastructural characteristics in die dense cells of the nectariferous tissue and in the sieve element are matched with those of the programmed cell death in animal and plant reported in recent years. The disorganization of nucleus and most organelles in the differentiation of sieve elements and dense cells is closely associated with the transportation and modification of pre-nectar and the transference of nectar. This suggests that the cytological changes in sieve element and nectariferous tissue are closely associated with the nectary functional activities.展开更多
A mathematical model for simulating concentric-bed and other components of molecular sieve oxygen concentrator is established. In the model, the binary Langmuir equilibrium adsorption equation is adopted to describe t...A mathematical model for simulating concentric-bed and other components of molecular sieve oxygen concentrator is established. In the model, the binary Langmuir equilibrium adsorption equation is adopted to describe the adsorption performance of the adsorbent, the linear driving force (LDF) model is used to describe the mass transfer rate, and the thermal effect during adsorption is considered. The finite difference method is used in simulation and comparison. Numerical results have a reasonable agreement with the experimental research.展开更多
Vapor liquid solid three phase equilibria of ethanol water 4A molecular sieve system are studied experimentally and theoritically. It is proved that the addition of adsorbent does not chang...Vapor liquid solid three phase equilibria of ethanol water 4A molecular sieve system are studied experimentally and theoritically. It is proved that the addition of adsorbent does not change the equilibrium relation between vapor and bulk liquid phase. A calculation procedure is proposed to predict vapor liquid solid (adsorbent) three phase euquilibria.展开更多
Silicoaluminophosphate（SAPO） molecular sieves doped with cobalt（Co-SAPO-5） were synthesized hydrothermally with different concentrations of Co.Each sample was characterized by X-ray diffraction,N2 adsorption-desor...Silicoaluminophosphate（SAPO） molecular sieves doped with cobalt（Co-SAPO-5） were synthesized hydrothermally with different concentrations of Co.Each sample was characterized by X-ray diffraction,N2 adsorption-desorption,scanning electron microscopy,ultraviolet-visible spectroscopy,temperature-programmed desorption of NH3（NH3-TPD）,and infrared spectrascopy of adsorbed pyridine（Py-IR）.The results showed that Co was highly dispersed in the Co-SAPO-5 samples.In addition,a part of the Co content had been incorporated into the SAPO-5 framework,while the remainder existed on the surface as extra-framework Co.The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample.However,the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample.As the concentration of Co increased,the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface.NH3-TPD and Py-IR results revealed that the amount of Br（？）nsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample.These values were also higher for samples with higher Co content.The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen.When Co was added to the SAPO-5 catalyst,the catalytic activity of the Co-SAPO-5 catalysts improved.In addition,the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased.However,with a high conversion of cyclohexane（6.30%）,the total selectivity of cyclohexanone（K） and cyclohexanol（A） decreased sharply.The K/A ratio ranged from 1.15 to 2.47.The effects of reaction conditions（i.e.,reaction temperature,reaction time,initial oxygen pressure,and the catalyst amount） on the performance of the Co-SAPO-5 catalysts have also been measured.Furthermore,the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.展开更多
Mineralogical characterization applied to mineral processing is now widespread. The first step for a mineralogi- cal characterization study is usually size fractionation. Preparation of polished sections is done on si...Mineralogical characterization applied to mineral processing is now widespread. The first step for a mineralogi- cal characterization study is usually size fractionation. Preparation of polished sections is done on size fractions to reduce complications in making representative cross sections of particles with large size differences. A sample is commonly fractionated into five or six size intervals. The drawback of this procedure is that it makes liberation studies more expensive, because one sample actually produces five or six sub-samples that need to be studied, i.e. one from each size interval. Thus to reduce cost of liberation studies, it would be desirable to study the un-sized sample. This paper provides a comparative liberation study of a set of samples both using size fractions and using the un-sized samples. The samples studied are the feed, the concentrate and the tails of a lead rougher flotation circuit. The results consistently show significant differences between the sized and the un-sized samples. Nevertheless, the results indicate that un-corrected liberation data from un-sized samples can be used for comparative studies that involve several related samples. Thus, it is possible to improve (or further understand) a concentrator circuit by using mineralogical data from un-sized samples around such circuit.展开更多
This paper introduces a method of sieve which can be to calculate the number of residues of the integers 1,2,...,2a sifted by n paiwise coprime numbers.
文摘由于传统求解时间序列自回归(auto-regressive,AR)模型的最小二乘方法无法顾及设计矩阵误差,现有的AR模型迭代解法难以应用协方差传播率给出较为精确的精度评定公式。将块自助采样方法引入到AR模型精度评定研究中,并在其基础上借助Sieve自助法的思想,定义了顾及设计矩阵误差AR模型精度评定的Sieve块自助采样方法。根据不同的分块准则和采样策略,给出了4种方法的重采样步骤。模拟实验结果表明,精度评定的Sieve块自助采样方法能够得到比最小二乘法、经典的AR模型迭代解法更加可靠的自回归系数标准差,具有更强的适用性。同时,北斗卫星精密钟差真实案例表明,所提出的Sieve移动块自助法、Sieve非重叠块自助法、Sieve圆形块自助法以及Sieve静止块自助法的均方根(root mean square,RMS)比总体最小二乘的RMS分别减小了70.25%、78.65%、70.89%和79.24%,进一步验证了所提算法的有效性和可靠性,为时间序列AR模型的精度评定问题提供了一种采样思路。
基金financial support from the National Key R&D Program of China(2021YFB3801200)the National Natural Science Foundation of China(22278051,22178044,22308043)CNPC Innovation Found(2022DQ02-0608)。
文摘Carbon capture is an important strategy and is implemented to achieve the goals of CO_(2)reduction and carbon neutrality.As a high energy-efficient technology,membrane-based separation plays a crucial role in CO_(2)capture.It is urgently needed for membrane-based CO_(2)capture to develop the high-performance membrane materials with high permeability,selectivity,and stability.Herein,ultrapermeable carbon molecular sieve(CMS)membranes are fabricated by py roly zing a finely-engineered benzoxazole-containing copolyimide precursor for efficient CO_(2)capture.The microstructure of CMS membrane has been optimized by initially engineering the precursor-chemistry and subsequently tuning the pyrolysis process.Deep insights into the structure-property relationship of CMSs are provided in detail by a combination of experimental characterization and molecular simulations.We demonstrate that the intrinsically high free volume environment of the precursor,coupled with the steric hindrance of thermostable contorted fragments,promotes the formation of loosely packed and ultramicroporous carbon structures within the resultant CMS membrane,thereby enabling efficient CO_(2)discrimination via size sieving and affinity.The membrane achieves an ultrahigh CO_(2)permeability,good selectivity,and excellent stability.After one month of long-term operation,the CO_(2)permeability in the mixed gas is maintained at 11,800 Barrer,with a CO_(2)/N_(2)selectivity exceeding 60.This study provides insights into the relationship between precursor-chemistry and CMS performance,and our ultrapermeable CMS membrane,which is scalable using thin film manufacturing,holds great potential for industrial CO_(2)capture.
基金support from the National Natural Science Foundation of China(No.21975067)Shenzhen Science and Technology Program(No.JCYJ20220530160407016).
文摘In order to address challenges posed by the reduction in transistor size,researchers are concentrating on two-dimensional(2D)materials with high dielectric constants and large band gaps.Monoclinic ZrO_(2)(m-ZrO_(2))has emerged as a promising gate dielectric material due to its suitable dielectric constant,wide band gap,ideal valence-band offset,and good thermodynamic stability.However,current deposition methods face compatibility issues with 2D semiconductors,highlighting the need for high-quality dielectrics and interfaces.Here,high-quality 2D m-ZrO_(2)single crystals are successfully prepared using a onestep chemical vapor deposition(CVD)method,aided by 5A molecular sieves for oxygen supply.The prepared ZrO_(2)is utilized as a gate dielectric in the construction of MoS2 field-effect transistors(FETs)to investigate its electrical property.The FETs exhibit a high carrier mobility of up to 5.50 cm^(2)·V^(−1)·s^(−1),and a current switching ratio(Ion/off)of approximately 10^(4),which aligns with the current standards of logic circuits,indicating that ZrO_(2)has application value as a gate dielectric.The successful onestep preparation of single-crystal ZrO_(2)paves the way for the utilization of high-κgate dielectrics and creates favorable conditions for the development of high-performance semiconductor devices,offering new possibilities for transistor miniaturization.
基金the support from the National Natural Science Foundation of China(No.22125604)the Chenguang Program supported by Shanghai Education Development Foundation and Shanghai Municipal Education Commission(No.22Z00354)。
文摘Molecular sieve catalysts,owing to their unique chemical properties,are widely used as catalysts among various catalytic reactions.Abundant Br?nsted acid sites in molecular sieve catalysts usually enable active components to disperse well on the catalyst surface,and help to adsorb a large number of gas molecules to achieve maximum catalytic performance.Therefore,a variety of molecular sieve catalysts have been developed and used in the selective catalytic reduction of NO_(x)by NH_(3)(NH_(3)-SCR).For example,Cu molecular sieve catalysts such as Cu-SSZ-13 and Cu-SAPO-34 with wide temperature windows and stable structure are considered and applied as commercial catalysts for NO_(x)removal in diesel vehicles for a long time.Although molecular sieve catalysts possess many advantages,they still cannot avoid the serious deactivation caused by various factors in practical applications.In this review,reasons leading to the deactivation of molecular sieve catalysts for NO_(x)reduction in actual working conditions were concluded.The deactivation mechanisms of molecular sieve catalysts for NO_(x)reduction were analyzed and the corresponding anti-deactivation strategies were summarized.Finally,challenges and prospects of molecular sieve catalysts for NO_(x)reduction were also proposed.
基金supported by the National Natural Science Foundation of China(Nos.21972073,22136003,22206188,and 21805166).
文摘Advanced processes for peroxymonosulfate(PMS)-based oxidation are efficient in eliminating toxic and refractory organic pol-lutants from sewage.The activation of electron-withdrawing HSO_(5)^(-)releases reactive species,including sulfate radical(·SO_(4)^(-)),hydroxyl radical(·OH),superoxide radical(·O_(2)^(-)),and singlet oxygen(1O_(2)),which can induce the degradation of organic contaminants.In this work,we synthesized a variety of M-OMS-2 nanorods(M=Co,Ni,Cu,Fe)by doping Co^(2+),Ni^(2+),Cu^(2+),or Fe^(3+)into manganese oxide oc-tahedral molecular sieve(OMS-2)to efficiently remove sulfamethoxazole(SMX)via PMS activation.The catalytic performance of M-OMS-2 in SMX elimination via PMS activation was assessed.The nanorods obtained in decreasing order of SMX removal rate were Cu-OMS-2(96.40%),Co-OMS-2(88.00%),Ni-OMS-2(87.20%),Fe-OMS-2(35.00%),and OMS-2(33.50%).Then,the kinetics and struc-ture-activity relationship of the M-OMS-2 nanorods during the elimination of SMX were investigated.The feasible mechanism underly-ing SMX degradation by the Cu-OMS-2/PMS system was further investigated with a quenching experiment,high-resolution mass spec-troscopy,and electron paramagnetic resonance.Results showed that SMX degradation efficiency was enhanced in seawater and tap water,demonstrating the potential application of Cu-OMS-2/PMS system in sewage treatment.
基金supported by the renewable energy and hydrogen projects in National Key Research and Development Plan of China(2019YFB1505000).
文摘Flue gas and coal bed methane are two important sources of greenhouse gases.Pressure swing adsorption process has a wide range of application in the field of gas separation,and the selection of adsorbent is crucial.In this regard,in order to assess the better adsorbent for separating CO_(2) from flue gas and CH_(4) from coal bed methane,adsorption isotherms of CO_(2),CH_(4) and N_(2) on activated carbon and carbon molecular sieve are measured at 303.15,318.15 and 333.15 K,and up to 250 kPa.The experimental data fit better with Langmuir 2 compared to Langmuir 3 and Langmuir-Freundlich models,and Clausius-Clapeyron equation was used to calculate the isosteric heat.Both the order of the adsorbed amount and the adsorption heat on the two adsorbents are CO_(2)>CH_(4)>N_(2).The adsorption kinetics are calculated by the pseudo-first kinetic model,and the order of adsorption rates on activated carbon is N_(2)-CH_(4)>CO_(2),while on carbon molecular sieve,it is CO_(2)-N_(2)>CH_(4).It is shown that relative molecular mass and adsorption heat are the primary effect on kinetics for activated carbon,while kinetic diameter is the main resistance factor for carbon molecular sieve.Moreover,the adsorption selectivity of CH_(4)/N_(2) and CO_(2)/N_(2) were estimated with the ideal adsorption solution theory,and carbon molecular sieve performed best at 318.15 K for both CO_(2) and CH_(4) separation.The study suggested that activated carbon is a better choice for separating flue gas and carbon molecular sieve can be a strong candidate for separating coal bed methane.
基金Fundamental Research Funds for Central Universities(No.2022CDJKYJH028)National Natural Science Foundation of China(No.52271091)Chongqing Special Key Project of Technology Innovation and Application Development,China(No.cstc2019jscx-dxwtBX0016).
文摘Mg-Li alloy is a lightweight hydrogen storage material with high hydrogen capacity,but its poor kinetics limited its practical applications.In this work,MCM-22 molecular sieve was added to Mg-Li alloy by friction stir processing(FSP)as the catalyst to enhance the kinetic properties of Mg-Li alloy(denoted as Mg-Li-MCM-22).The resulting Mg-Li-MCM-22 possesses the reversible hydrogen storage capacity of ca.6 wt.%and can release 5.62 wt.%hydrogen within 50 min at 623 K,showing improved kinetics.The Chou model and Johnson-Mehl-Avrami-Kolmogorov(JMAK)model calculations reveal that the lattice defects generated by FSP improve the kinetics of hydrogen adsorption/desorption.The pinning effect of MCM-22 particles produces more grain boundaries and dislocations,thus,increasing the diffusion rate of hydrogen atoms and providing more nucleation sites,therefore,reducing the dehydrogenation activation energy.This work provides a new strategy for the preparation of hydrogen storage materials.
基金This study was financially supported by the National Natural Science Foundation of China(No.52172099)the Basic Research Plan of Natural Science of Shaanxi Province(No.2020JQ-754)+3 种基金the Key Innovation Team of Shaanxi Province(No.2014KCT-04)the Excellent Youth Science and Technology Fund Project of Xi'an University of Science and Technology(Grant No.6310221009)the Excellent Youth Science and Technology Fund Project of Xi'an University of Science and Technology(Grant No.6310221009)the Special Project of Shaanxi Province(No.19JK0490)and the Study on Preparation and Properties of New Solid-Wastebased Cementitious Materials(No.6000190120).
文摘Using coal gangue(CG)as raw material,a new type of all solid-waste-based 13-X molecular sieve material was controllably prepared by alkali fusion-hydrothermal method.The synthetic molecular sieve was used as a solid adsorbent to treat Cd^(2+)-containing wastewater,and its adsorption behavior on Cd^(2+)in aqueous solution was studied and analyzed.The microstructure and morphology of the molecular sieve were investigated by X-ray diffraction(XRD),field emission scanning electron microscopy(FESEM)and specific surface area analyzer.The results show that the synthesized 13-X molecular sieve has higher Brunauer–Emmett–Teller(BET)specific surface area with higher crystallinity and higher adsorption capacity for the heavy metal Cd^(2+).The adsorption process of Cd^(2+)by molecular sieve conforms to the Langmuir isotherm adsorption equation and Lagergren pseudo-second-order rate equation.Combined with thermodynamic calculation,it can be concluded that the adsorption process is physically monolayer,spontaneous and exothermic.In this study,a low-cost and naturally available synthesis method of 13-X molecular sieve is reported.Combined with its adsorption mechanism for Cd^(2+),it provides a feasible and general method for removing heavy metal ions from coal gangue and also provides a new way for the utilization of coal gangue with high added value.
基金supported by the National Natural Science Foundation of China(42272202 and 52264001)the Yunnan Fundamental Research Projects(202201AT070144)+1 种基金the Yunnan Ten Thousand Talents Plan Young&Elite Talents Project(YNWRQNBJ-2019-164)Training Programmes of Innovation and Entrepreneurship for Undergraduates of Yunnan Province(S202210674128).
文摘In order to comprehend the applicability of microwave irradiation for recovering coalbed methane,it is necessary to evaluate the microwave irradiation-induced alterations in coals with varying levels of metamorphism.In this work,the carbon molecular sieve combined with KMnO_(4)oxidation was selected to fabricate carbon molecular sieve with diverse oxidation degrees,which can serve as model substances toward coals.Afterwards,the microwave irradiation dependences of pores,functional groups,and highpressure methane adsorption characteristics of model substances were studied.The results indicated that microwave irradiation causes rearrangement of oxygen-containing functional groups,which could block the micropores with a size of 0.40-0.60 nm in carbon molecular sieve;meanwhile,naphthalene and phenanthrene generated by macro-molecular structure pyrolysis due to microwave irradiation could block the micropores with a size of 0.70-0.90 nm.These alterations in micropore structure weaken the saturated methane adsorption capacity of oxidized carbon molecular sieve by 2.91%-23.28%,suggesting that microwave irradiation could promote methane desorption.Moreover,the increased mesopores found for oxidized carbon molecular sieve after microwave irradiation could benefit CH4 diffusion.In summary,the oxidized carbon molecular sieve can act as model substances toward coals with different ranks.Additionally,microwave irradiation is a promising technology to enhance coalbed methane recovery.
基金supported by the grants from the Research Grants Council of the Hong Kong Special Administrative Region,China(Project No.C5031-20)the Guangdong Major Project of Basic and Applied Basic Research(2023B0303000002).
文摘Zinc metal anodes are gaining popularity in aqueous electrochemical energy storage systems for their high safety,cost-effectiveness,and high capacity.However,the service life of zinc metal anodes is severely constrained by critical challenges,including dendrites,water-induced hydrogen evolution,and passivation.In this study,a protective two-dimensional metal–organic framework interphase is in situ constructed on the zinc anode surface with a novel gel vapor deposition method.The ultrathin interphase layer(~1μm)is made of layer-stacking 2D nanosheets with angstrom-level pores of around 2.1Å,which serves as an ion sieve to reject large solvent–ion pairs while homogenizes the transport of partially desolvated zinc ions,contributing to a uniform and highly reversible zinc deposition.With the shielding of the interphase layer,an ultra-stable zinc plating/stripping is achieved in symmetric cells with cycling over 1000 h at 0.5 mA cm−2 and~700 h at 1 mA cm^(−2),far exceeding that of the bare zinc anodes(250 and 70 h).Furthermore,as a proof-of-concept demonstration,the full cell paired with MnO_(2) cathode demonstrates improved rate performances and stable cycling(1200 cycles at 1 A g−1).This work provides fresh insights into interphase design to promote the performance of zinc metal anodes.
基金supported by Fundamental Research Funds for the Central Universities(Grant No.2682021ZTPY067)Sichuan Science and Technology Program(Grant NO:2021YFG0194).
文摘Hammer mill is widely used in the feed processing industry.During its operation,the material is thrown against the inner wall of the sieve after being broken by the hammer.Limited by the annular structure sieve,the grinded material tends to produce a"air-material circulation layer"on the inner wall of the sieve,leading to problems such as low grinding efficiency and high grinding energy consumption.Considering the disruptive characteristics of the special profile structure of a pigeon's wing on the airflow field,we extract the geometric characteristics of the coupling element and optimize the related structural parameters.Based on the principles of bionics,a new wing sieve is then designed,and its efficient grinding mechanism is studied.Compared to the commercial sieve,the experimental results indicate the bio-inspired sieve can significantly improve the material productivity and grinding quality.
文摘The ultrastructures of the root protophleom sieve element at different developmental stages of Arabidopsis thaliana L. were investigated using the technique of high pressure freezing and freeze substitution fixing specimen. The results show that in the development of the sieve elements, the nuclei undergo typical characteristics of the programmed cell death (PCD): the nuclear envelopes form emboli, the chromatin condenses and aggregates towards the nuclear envelope, which degrades and fully disappears later. Before the nucleus degradation, neither the nuclear envelope undulation, nucleus lobe nor marked dilation (or bleb) of perinuclear space could be observed. In the cytoplasm of the mature sieve element, there are starch-like granules separately sheathed with a layer of membrane and usually with mitochondria around. These gnanules seem to provide substrates to mitochondria in their function. Small vacuoles originate from endoplasmic reticulum (ER), and no bigger vacuole was found.
文摘Ultrastructural changes in the sieve element and dense cells of nectariferous tissue during the development of floral nectary in Arabidopsis thaliana L. were investigated with transmission electron microscopy. Samples were prepared with high pressure freezing and freeze substitution techniques. The ultrastructure of dense cell was similar to that of sieve element at its early developmental stage. With the concurrent agglutination of chromatin in the nucleus, the abnormal location of organelles and the high density of cytoplasm, the ultrastructural characteristics in die dense cells of the nectariferous tissue and in the sieve element are matched with those of the programmed cell death in animal and plant reported in recent years. The disorganization of nucleus and most organelles in the differentiation of sieve elements and dense cells is closely associated with the transportation and modification of pre-nectar and the transference of nectar. This suggests that the cytological changes in sieve element and nectariferous tissue are closely associated with the nectary functional activities.
文摘A mathematical model for simulating concentric-bed and other components of molecular sieve oxygen concentrator is established. In the model, the binary Langmuir equilibrium adsorption equation is adopted to describe the adsorption performance of the adsorbent, the linear driving force (LDF) model is used to describe the mass transfer rate, and the thermal effect during adsorption is considered. The finite difference method is used in simulation and comparison. Numerical results have a reasonable agreement with the experimental research.
文摘Vapor liquid solid three phase equilibria of ethanol water 4A molecular sieve system are studied experimentally and theoritically. It is proved that the addition of adsorbent does not change the equilibrium relation between vapor and bulk liquid phase. A calculation procedure is proposed to predict vapor liquid solid (adsorbent) three phase euquilibria.
基金supported by the National Basic Research Program of China(2010CB732300)the National Natural Science Foundation of China(21103048)~~
文摘Silicoaluminophosphate（SAPO） molecular sieves doped with cobalt（Co-SAPO-5） were synthesized hydrothermally with different concentrations of Co.Each sample was characterized by X-ray diffraction,N2 adsorption-desorption,scanning electron microscopy,ultraviolet-visible spectroscopy,temperature-programmed desorption of NH3（NH3-TPD）,and infrared spectrascopy of adsorbed pyridine（Py-IR）.The results showed that Co was highly dispersed in the Co-SAPO-5 samples.In addition,a part of the Co content had been incorporated into the SAPO-5 framework,while the remainder existed on the surface as extra-framework Co.The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample.However,the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample.As the concentration of Co increased,the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface.NH3-TPD and Py-IR results revealed that the amount of Br（？）nsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample.These values were also higher for samples with higher Co content.The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen.When Co was added to the SAPO-5 catalyst,the catalytic activity of the Co-SAPO-5 catalysts improved.In addition,the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased.However,with a high conversion of cyclohexane（6.30%）,the total selectivity of cyclohexanone（K） and cyclohexanol（A） decreased sharply.The K/A ratio ranged from 1.15 to 2.47.The effects of reaction conditions（i.e.,reaction temperature,reaction time,initial oxygen pressure,and the catalyst amount） on the performance of the Co-SAPO-5 catalysts have also been measured.Furthermore,the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.
文摘Mineralogical characterization applied to mineral processing is now widespread. The first step for a mineralogi- cal characterization study is usually size fractionation. Preparation of polished sections is done on size fractions to reduce complications in making representative cross sections of particles with large size differences. A sample is commonly fractionated into five or six size intervals. The drawback of this procedure is that it makes liberation studies more expensive, because one sample actually produces five or six sub-samples that need to be studied, i.e. one from each size interval. Thus to reduce cost of liberation studies, it would be desirable to study the un-sized sample. This paper provides a comparative liberation study of a set of samples both using size fractions and using the un-sized samples. The samples studied are the feed, the concentrate and the tails of a lead rougher flotation circuit. The results consistently show significant differences between the sized and the un-sized samples. Nevertheless, the results indicate that un-corrected liberation data from un-sized samples can be used for comparative studies that involve several related samples. Thus, it is possible to improve (or further understand) a concentrator circuit by using mineralogical data from un-sized samples around such circuit.
文摘This paper introduces a method of sieve which can be to calculate the number of residues of the integers 1,2,...,2a sifted by n paiwise coprime numbers.
