期刊文献+
共找到4,371篇文章
< 1 2 219 >
每页显示 20 50 100
A Corpus-Driven Perspective on the Verb Valency Structure of Chinese EFL Learners:A Case Study of“Suggest”and“Advise”
1
作者 ZHENG Yiru ZHANG Le 《Sino-US English Teaching》 2024年第1期14-18,共5页
This paper investigates the verb valency structure of English that is used by English as Foreign Language(EFL)learners from a corpus-driven perspective.Specifically,it focuses on the usage of the verbs“suggest”and“... This paper investigates the verb valency structure of English that is used by English as Foreign Language(EFL)learners from a corpus-driven perspective.Specifically,it focuses on the usage of the verbs“suggest”and“advise”in a selected corpus.By analyzing a sample of written and spoken texts,this study attempts to investigate the similarities and differences in the patterns of verb valency between native English speakers and Chinese EFL learners.The findings of this research can contribute to a better understanding of the challenges faced by Chinese EFL learners in acquiring accurate verb valency structures and provide insights for language teachers in designing effective pedagogical approaches. 展开更多
关键词 valency structure vocabulary teaching synonym distinction CORPUS-DRIVEN
下载PDF
Morphology and valence state evolution of Cu:Unraveling the impact on nitric oxide electroreduction 被引量:1
2
作者 Ting Sun Fengyu Gao +4 位作者 Ya Wang Honghong Yi Qingjun Yu Shunzheng Zhao Xiaolong Tang 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2024年第4期276-286,共11页
Ammonia(NH3)serves as a critical component in the fertilizer industry and fume gas denitrification.However,the conventional NH3production process,namely the Haber-Bosch process,leads to considerable energy consumption... Ammonia(NH3)serves as a critical component in the fertilizer industry and fume gas denitrification.However,the conventional NH3production process,namely the Haber-Bosch process,leads to considerable energy consumption and waste gas emissions.To address this,electrocatalytic nitric oxide reduction reaction(NORR)has emerged as a promising strategy to bridge NH3consumption to NH3production,harnessing renewable electricity for a sustainable future.Copper(Cu)stands out as a prominent electrocatalyst for NO reduction,given its exceptional NH3yield and selectivity.However,a crucial aspect that remains insufficiently explored is the effects of morphology and valence states of Cu on the NORR performance.In this investigation,we synthesized CuO nanowires(CuO-NF)and Cu nanocubes(Cu-NF)as cathodes through an in situ growth method.Remarkably,CuO-NF exhibited an impressive NH3yield of 0.50±0.02 mg cm^(-2)h^(-1)at-0.6 V vs.reversible hydrogen electrode(RHE)with faradaic efficiency of29,68%±1,35%,surpassing that of Cu-NF(0.17±0.01 mg cm^(-2)h^(-1),16.18%±1.40%).Throughout the electroreduction process,secondary cubes were generated on the CuO-NF surface,preserving their nanosheet cluster morphology,sustained by an abundant supply of subsurface oxygen(s-O)even after an extended duration of 10 h,until s-O depletion ensued.Conversely,Cu-NF exhibited inadequate s-O content,leading to rapid crystal collapse within the same timeframe.The distinctive current-potential relationship,akin to a volcano-type curve,was attributed to distinct NO hydrogenation mechanisms.Further Tafel analysis revealed the exchange current density(i0)and standard heterogeneous rate constant(k0)for CuO-NF,yielding 3.44×10^(-6)A cm^(-2)and 3.77×10^(-6)cm^(-2)s^(-1)when NORR was driven by overpotentials.These findings revealed the potential of CuO-NF for NO reduction and provided insights into the intricate interplay between crystal morphology,valence states,and electrochemical performance. 展开更多
关键词 NORR Ammonia Synthesis COPPER MORPHOLOGY valence States Mechanism
下载PDF
Exotic compounds of monovalent calcium synthesized at high pressure OA
3
作者 Jun Kong Kaiyuan Shi +3 位作者 Artem R.Oganov Jiaqing Zhang Lei Su Xiao Dong 《Matter and Radiation at Extremes》 SCIE EI CSCD 2024年第6期105-113,共9页
It is well known that atoms of the same element in different valence states show very different chemical behaviors.Calcium is a typical divalent metal,sharing or losing both of its valence electrons when forming compo... It is well known that atoms of the same element in different valence states show very different chemical behaviors.Calcium is a typical divalent metal,sharing or losing both of its valence electrons when forming compounds.Attempts have been made to synthesize compounds of monovalent calcium ions for decades,but with very little success(e.g.,in clusters).Pressure can result in substantial changes in the properties of atoms and chemical bonding,creating an extensive variety of unique materials with special valence states.In this study,using the ab initio evolutionary algorithm USPEX,we search for stable calcium-chlorine(Ca-Cl)system compounds at pressures up to 100 GPa.Besides the expected compound CaCl_(2),we predict three new compounds with monovalent Ca to be stable at high pressures,namely,CaCl,Ca_(5)Cl_(6),and Ca_(3)Cl_(4).According to our calculations,CaCl is stable at pressures above 18 GPa and is predicted to undergo a transition from nonmagnetic Fm-3m-CaCl to ferromagnetic Pm-3m-CaCl at 40 GPa.Ca_(5)Cl_(6)and Ca_(3)Cl_(4)are stable at pressures above 37 and 73 GPa,with space groups P-1 and R-3,respectively.Following these predictions,we successfully synthesized Pm-3m-CaCl in laser-heated diamond anvil cell experiments.The emergence of the unusual valence state at high pressures reveals exciting opportunities for creating entirely new materials in sufficiently large quantities for a variety of potential applications. 展开更多
关键词 valent valencE entirely
下载PDF
Valence Bands Convergence in p-Type CoSb_(3) through Electronegative Fluorine Filling
4
作者 黄写格 李家良 +5 位作者 马浩钦 李昌隆 刘天乐 段波 翟鹏程 李国栋 《Chinese Physics Letters》 SCIE EI CAS CSCD 2024年第7期87-94,共8页
Band convergence is considered to be a strategy with clear benefits for thermoelectric performance,generally favoring the co-optimization of conductivity and Seebeck coefficients,and the conventional means include ele... Band convergence is considered to be a strategy with clear benefits for thermoelectric performance,generally favoring the co-optimization of conductivity and Seebeck coefficients,and the conventional means include elemental filling to regulate the band.However,the influence of the most electronegative fluorine on the CoSb_(3) band remains unclear.We carry out density-functional-theory calculations and show that the valence band maximum gradually shifts downward with the increase of fluorine filling,lastly the valence band maximum converges to the highly degenerated secondary valence bands in fluorine-filled skutterudites. 展开更多
关键词 valencE CONVERGENCE BANDS
下载PDF
Enhanced anomalous Hall effect in kagome magnet YbMn_(6)Sn_(6)with intermediate-valence ytterbium
5
作者 李龙飞 迟晟玮 +3 位作者 马文龙 郭凯臻 徐刚 贾爽 《Chinese Physics B》 SCIE EI CAS CSCD 2024年第5期43-50,共8页
We report on the magnetization and anomalous Hall effect(AHE)in the high-quality single crystals of the kagome magnet YbMn_(6)Sn_(6),where the spins of the Mn atoms in the kagome lattice order ferromagnetically and th... We report on the magnetization and anomalous Hall effect(AHE)in the high-quality single crystals of the kagome magnet YbMn_(6)Sn_(6),where the spins of the Mn atoms in the kagome lattice order ferromagnetically and the intermediate-valence Yb atoms are nonmagnetic.The intrinsic mechanism plays a crucial role in the AHE,leading to an enhanced anomalous Hall conductivity(AHC)compared with the other rare-earth RMn_(6)Sn_(6)compounds.Our band structure calculation reveals a strong hybridization between the 4f electrons of Yb and conduction electrons. 展开更多
关键词 anomalous Hall effect kagome magnet intermediate valence
下载PDF
Valence electron structures dependences of structural stability and properties of REX_(3)(RE=rare earth;X=In,Tl)and RE(In,Co)3 alloys
6
作者 Boyang Li Yongquan Guo +2 位作者 Yi-Chen Feng Xinze Wang Wei Liu 《Chinese Physics B》 SCIE EI CAS CSCD 2024年第11期331-339,共9页
Intermetallic compounds REIn3(RE=rare earth)have attracted much attention due to their unique characteristics:crystal field effect,Kondo effect,superconductivity,heavy fermion,and antiferromagnetism,and their cobalt d... Intermetallic compounds REIn3(RE=rare earth)have attracted much attention due to their unique characteristics:crystal field effect,Kondo effect,superconductivity,heavy fermion,and antiferromagnetism,and their cobalt diluted alloys exhibit the ferromagnetic half-metallic characteristics at room temperature.In this study,an empirical electron theory(EET)is employed to investigate systemically the valence electronic structure,the thermal and magnetic properties of REX_(3) and their cobalt diluted alloys for revealing the mechanism of physical properties.The calculated bond length,melting point,and magnetic moment match the experimental ones very well.The study reveals that structural stability and physical properties of REX_(3) and their cobalt dilute alloys are strongly related to their valence electron structures.It is suggested that the structural stability and cohesive energy depend upon the covalent electron,the melting point is modulated by covalent electron pair,and the magnetic moment is originated from 3d magnetic electron.The ferromagnetic characteristics of Co-diluted REIn3 alloys is originated from the introduction of strong ferromagnetic Co atom,but,a competition is caused between the electron transition from valence electron to magnetic electron on d orbit and its reversal electron transformation with increasing the content of cobalt,which results in the formations of diluted magnetic Gd(In,Co)3 alloy with minor amount of cobalt and strong magnetic Nd(In,Co)3 alloy with doping more Co atoms. 展开更多
关键词 REX_(3) cobalt dilute alloy valence electron structures empirical electron theory MOMENT
下载PDF
Coherence of the Even-Odd Rule with an Effective-Valence Isoelectronicity Rule for Chemical Structural Formulas: Application to Known and Unknown Single-Covalent-Bonded Compounds 被引量:5
7
作者 Geoffroy Auvert 《Open Journal of Physical Chemistry》 2014年第3期126-133,共8页
Ions or molecules are said to be isoelectronic if they are composed of different elements but have the same number of electrons, the same number of covalent bonds and the same structure. This criterion is unfortunatel... Ions or molecules are said to be isoelectronic if they are composed of different elements but have the same number of electrons, the same number of covalent bonds and the same structure. This criterion is unfortunately not sufficient to ensure that a chemical structure is a valid chemical compound. In a previous article, a procedure has been described to draw 2D valid structural formulas: the even-odd rule. This rule has been applied first to single-bonded molecules then to single-charged single-bonded ions. It covers hypovalent, hypervalent or classic Lewis’ octet compounds. The funding principle of the even-odd rule is that each atom of the compound possesses an outer-shell filled only with pairs of electrons. The application of this rule guarantees validity of any single-covalent-bond chemical structure. In the present paper, this even-odd rule and its electron-pair criterion are checked for coherence with an effective-valence isoelectronic rule using numerous known compounds having single-covalent-bond connections. The test addresses Lewis’ octet ions or molecules as well as hypovalent and hypervalent compounds. The article concludes that the even-odd rule and the effective-valence isoelectronicity rule are coherent for known single-covalent-bond chemical compounds. 展开更多
关键词 Isoelectronicity EFFECTIVE valencE MOLECULE Ion Even-Odd RULE Structural Formula COvalent Bond
下载PDF
The Influence of Bond Valence on Bond Covalency in RMn_2O_5 (R=La, Pr, Nd, Sin, Eu) 被引量:1
8
作者 Zhi Jian WU Si Yuan ZHANG(Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022) 《Chinese Chemical Letters》 SCIE CAS CSCD 1999年第1期91-94,共4页
The relationship between bond valence and bond covalency in RMn2O5 (R = La, Pr, Nd.Sm, Eu) has been investigated by a semiempirical method. This method is the generalization of thedielectric description theory of Phil... The relationship between bond valence and bond covalency in RMn2O5 (R = La, Pr, Nd.Sm, Eu) has been investigated by a semiempirical method. This method is the generalization of thedielectric description theory of Phillips. Van Vechten, Levine and Tanaka scheme. The resultsindicate that larger valences usually result in higher bond covalencies, in good agreement with thepoint that the excess charge in the bonding region is the origin of formation of bond covalency.Other factors, such as oxidation state of elements, only make a small contribution to bondcovalency. 展开更多
关键词 Bond valence bond covalency semiempirical method RMn_2O_5
下载PDF
High valence metals engineering strategies of Fe/Co/Ni-based catalysts for boosted OER electrocatalysis 被引量:6
9
作者 Lu Li Xianjun Cao +6 位作者 Juanjuan Huo Junpeng Qu Weihua Chen Chuntai Liu Yufei Zhao Hao Liu Guoxiu Wang 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2023年第1期195-213,I0006,共20页
Electrocatalysis for the oxygen evolution reactions(OER)has attracted much attention due to its important role in water splitting and rechargeable metal-air batteries.Therefore,designing highly efficient and low-cost ... Electrocatalysis for the oxygen evolution reactions(OER)has attracted much attention due to its important role in water splitting and rechargeable metal-air batteries.Therefore,designing highly efficient and low-cost catalysts for OER process is essential as the conventional catalysts still rely on precious metals.Transition metal-based compounds have been widely investigated as active OER catalysts,and renewed interest in the high valence metals engineered compounds has been achieved for superior catalytic activity and stability.However,an in-depth understanding of the construction strategies and induced effects for the high valence metals engineered catalysts is still lacking and desired.In this review,we have summarized the construction strategies of high valence metals as dopants or formed heterostructures with the iron/cobalt/nickel(Fe/Co/Ni)-based catalysts.Then the induced effects on Fe/Co/Ni-based catalysts by incorporating high valence metals,e.g.,accelerating the surface reconstruction,forming amorphous structure,generating vacancies/defects,and acting as stabilizers,are highlighted.The impacts of high valence metals on OER performance are elucidated based on different elements,including molybdenum(Mo),tungsten(W),cerium(Ce),vanadium(V),chromium(Cr),manganese(Mn),niobium(Nb),zirconium(Zr).The correlations of construction strategies,induced effects,catalytic activity and OER reaction pathways are elaborated.Finally,the remaining challenges for further enhancements of OER performance induced by high valence metals are presented. 展开更多
关键词 High valence metals Construction strategies Induced effect Oxygen evolution reactions
下载PDF
Interface and M^(3+)/M^(2+)Valence Dual-Engineering on Nickel Cobalt Sulfoselenide/Black Phosphorus Heterostructure for Efficient Water Splitting Electrocatalysis 被引量:2
10
作者 Tingting Liang Syama Lenus +5 位作者 Yaoda Liu Ya Chen Thangavel Sakthivel Fuyi Chen Fei Ma Zhengfei Dai 《Energy & Environmental Materials》 SCIE EI CAS CSCD 2023年第2期165-174,共10页
The catalyst innovation that aims at noble-metal-free substitutes is one key aspect for future sustainable hydrogen energy deployment.In this paper,a nickel cobalt sulfoselenide/black phosphorus heterostructure(NiCoSe... The catalyst innovation that aims at noble-metal-free substitutes is one key aspect for future sustainable hydrogen energy deployment.In this paper,a nickel cobalt sulfoselenide/black phosphorus heterostructure(NiCoSe|S/BP)was fabricated to realize the highly active and durable water electrolysis through interface and valence dual-engineering.The NiCoSe|S/BP nanostructure was constructed by in-situ growing NiCo hydroxide nanosheet arrays on few-layer BP and subsequently one-step sulfoselenization by SeS2.Besides the conductive merit of BP substrate,holes in p-type BP are capable of oxidizing the Co^(2+)to high-valence and electron-accepting Co^(3+),benefiting the oxygen evolution reaction(OER).Meanwhile,Ni^(3+)/Ni^(2+)ratio in the heterostructure is reduced to maintain the electrical neutrality,which corresponds to the increased electron-donating character for boosting hydrogen evolution reaction(HER).As for HER and OER,the heterostructured NiCoSe|S/BP electrocatalyst exhibits small overpotentials of 172 and 285 mV at 10 mA cm^(-2)(η_(10))in alkaline media,respectively.And overall water splitting has been achieved at a low cell potential of 1.67 V at η_(10) with high stability.Molecular sensing and density functional theory(DFT)calculations are further proposed for understanding the rate-determine steps and enhanced catalytic mechanism.The investigation presents a deep-seated perception for the electrocatalytic performance enhancement of BP-based heterostructure. 展开更多
关键词 black phosphorus interface engineering metal sulfoselenide overall water splitting valence regulation
下载PDF
Novel ternary metals-based telluride electrocatalyst with synergistic effects of high valence non-3d metal and oxophilic Te for pH-universal hydrogen evolution reaction 被引量:2
11
作者 Seunghwan Jo Wenxiang Liu +5 位作者 Yanan Yue Ki Hoon Shin Keon Beom Lee Hyeonggeun Choi Bo Hou Jung Inn Sohn 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2023年第5期736-743,I0015,共9页
Electrocatalyst designs based on oxophilic foreign atoms are considered a promising approach for developing efficient pH-universal hydrogen evolution reaction(HER)electrocatalysts by overcoming the sluggish alkaline H... Electrocatalyst designs based on oxophilic foreign atoms are considered a promising approach for developing efficient pH-universal hydrogen evolution reaction(HER)electrocatalysts by overcoming the sluggish alkaline HER kinetics.Here,we design ternary transition metals-based nickel telluride(Mo WNi Te)catalysts consisting of high valence non-3d Mo and W metals and oxophilic Te as a first demonstration of non-precious heterogeneous electrocatalysts following the bifunctional mechanism.The Mo WNi Te showed excellent HER catalytic performance with overpotentials of 72,125,and 182 mV to reach the current densities of 10,100,and 1000 mA cm^(-2),respectively,and the corresponding Tafel slope of 47,52,and 58 mV dec-1in alkaline media,which is much superior to commercial Pt/C.Additionally,the HER performance of Mo WNi Te is well maintained up to 3000 h at the current density of 100 mA cm^(-2).It is further demonstrated that the Mo WNi Te exhibits remarkable HER activities with an overpotential of 45 mV(31 mV)and Tafel slope of 60 mV dec-1(34 mV dec-1)at 10 mA cm^(-2)in neutral(acid)media.The superior HER performance of Mo WNi Te is attributed to the electronic structure modulation,inducing highly active low valence states by the incorporation of high valence non-3d transition metals.It is also attributed to the oxophilic effect of Te,accelerating water dissociation kinetics through a bifunctional catalytic mechanism in alkaline media.Density functional theory calculations further reveal that such synergistic effects lead to reduced free energy for an efficient water dissociation process,resulting in remarkable HER catalytic performances within universal pH environments. 展开更多
关键词 Telluride catalyst Oxophilic effect High valence non-3d metal Bifunctional mechanism pH-universal hydrogen evolution reaction
下载PDF
Valence Stabilization of Polyvalent Uranium Ions in Presence of Some Organic Additives during Extended Gamma Irradiation of Their Aqueous Acidic Solutions
12
作者 M. F. Barakat M. M. Abdelhamid 《World Journal of Nuclear Science and Technology》 2015年第3期157-168,共12页
In gamma irradiated aqueous acidic uranium solutions, tetravalent uranium ions are easily oxidized while U(VI) ions remain unchanged. In general, valence change of polyvalent metallic ions during chemical reprocessing... In gamma irradiated aqueous acidic uranium solutions, tetravalent uranium ions are easily oxidized while U(VI) ions remain unchanged. In general, valence change of polyvalent metallic ions during chemical reprocessing of spent nuclear fuel solutions can lead to undesirable effects under the influence of the existing gamma radiations. Consequently, studies on valence stabilization of Uranium ions during chemical treatment in strong gamma irradiation fields seem to be highly interesting. It has been reported before that some organic compounds proved to be effective in stabilizing the valence of Fe(II) ions during extended gamma irradiation of their acidic solutions. In the present work, valence stabilization of Uranium ions in acidic solutions in presence of different classes of organic compounds has been studied. The results showed that in case of U(IV), methanol or formic acid are capable of providing about 80% protection while ethanol or acetaldehyde can provide about 70% protection. Propanol has the least protective effect i.e. about 54%. On using U(VI) instead of U(IV) in the irradiated solutions, the uranium ions were reduced and the formed U(IV) was protected as follows: formic acid or methanol can provide 69% or 63% protection respectively while ethanol, acetaldehyde or propanol can provide 50%, 35% and 24% respectively. In any case, protection exists as long as the organic additives were not completely consumed. 展开更多
关键词 valencE STABILIZATION Uranium(IV) Ions RADIOLYSIS Protective Effect COMPETITIVE Reactions
下载PDF
Valency Increasing in South Ethio-Semitic
13
作者 Tsige Yohannes Zeleke 《宏观语言学》 2022年第1期111-131,共21页
The present paper focuses on a descriptive method of valency-increasing devices in five South Ethio-Semitic languages(Amharic,Harari,Kɨstane,Məsqan,and Endəgaɲ).The five languages were selected for two reasons.The fir... The present paper focuses on a descriptive method of valency-increasing devices in five South Ethio-Semitic languages(Amharic,Harari,Kɨstane,Məsqan,and Endəgaɲ).The five languages were selected for two reasons.The first reason is that conducting a valency study on all South Ethio-Semitic languages would have been impossible.With limited resources and time,it will prove difficult to cover all languages.The second reason is that,except for Amharic,these languages are known for being the least studied.Most of them even lack sufficient recording and description.So this research needs to choose the representative language in each branch.As a result,no explicit theoretical framework is followed;data analysis is guided solely by a descriptive perspective.The study’s data was gathered by consulting native speakers via elicitation.Valency has been considered as both a semantic and syntactic notion.As a semantic notion,it is used to refer to the participants in an event;as a syntactic notion,it is used to indicate the number of arguments in a construction.There are different types of transitivity classes of verbs in the South Ethio-Semitic Language,which is spoken in Ethiopia:intransitive,transitive,and ditransitive.Apart from these,there are verbs that can be used both intransitively and transitively.The facts that provide clear evidence for grammatical relations in South Ethio-Semitic languages are crucial to the study of the concept of valency-increasing devices.As is the case in many languages,South Ethio-Semitic languages possess morphosyntactic means through which the valency of verbs can be adjusted.The application of these morphosyntactic processes decreases or increases the valency of verbs.This article looks at valency-increasing devices in Causative and Applicative South Ethio-Semitic languages. 展开更多
关键词 applicative CAUSATIVE INTRANSITIVE SESL TRANSITIVE valency
下载PDF
Electrochemical Study on the Change in Valency of Niobium Oxide in the MnO-SiO_2-Nb_2O_5 System
14
作者 Tan Zanlin Wei Shoukun University of Science and Technology Beijing 《Rare Metals》 SCIE EI CAS CSCD 1990年第1期1-4,共4页
Change in valency of Nb-oxide in MnO-SiO_2-Nb_2O_5 system was studied with the electrochemical method using ZrO_2 as the solid electrolyte.Thermodynamic analysis has shown that the only possible reaction that could ta... Change in valency of Nb-oxide in MnO-SiO_2-Nb_2O_5 system was studied with the electrochemical method using ZrO_2 as the solid electrolyte.Thermodynamic analysis has shown that the only possible reaction that could take place at the working elec- trode is:2(Nb_2O_5)=2(Nb_2O_4)+O_2 with the a_0 values experimentally evaluated,values of a Nb_2O:/a Nb_2O:were calculated and isoactivity-ratio curves drawn in MnO-SiO_2-Nb_2O_5 triangles at 1418 and 1585K.The simultaneous existence of tetra-and penta-valent Nb mineral constituents in industrial Nb-bearing slags was thus verified experimentally. 展开更多
关键词 Electrochemical Study on the Change in valency of Niobium Oxide in the MnO-SiO2-Nb2O5 System SIO MNO
下载PDF
SYNTHESIS AND CHARACTERIZATION OF MONOVALENT AND MIXED-VALENCE COMPLEXES OF COPPER WITH 2-THIOURACIL
15
作者 周小寅 《Journal of China Textile University(English Edition)》 EI CAS 1996年第2期29-33,共5页
Five polynuclear monovalent and mixed-valence complexes of copper with 2-thiouracil were synthesized. They were characterized by the molar conductivity, electromc spectra, infrared spectroscopy, thermogravimetric and ... Five polynuclear monovalent and mixed-valence complexes of copper with 2-thiouracil were synthesized. They were characterized by the molar conductivity, electromc spectra, infrared spectroscopy, thermogravimetric and magnetic susceptibility measurements. Their coordination properties and tentative structures were discussed. 展开更多
关键词 2-throuracil COPPER COMPLEX POLYNUCLEAR COMPLEX MIXED-valencE COMPLEX
下载PDF
SPECTRAL VARIATION AND CHARACTERISTICS OF LOW VALENCY RARE EARTH IONS IN COMPLEX OXIDESⅢ.EFFECT OF THE CRYSTAL ENVIRONMENT AND CHEMICAL FACTORS ON LUMINESCENCE PROPERTIES OF EUROPIUM (Ⅱ) ION
16
作者 孙家跃 石春山 李有谟 《Journal of Rare Earths》 SCIE EI CAS CSCD 1990年第2期110-116,共7页
In this paper,the influence of crystal-field on the Luminescence properties of Eu^(2+) in complex oxides are studied theoretically by using purely electrostatic model,the dependence of the 4f^65d levels on Eu-O bond d... In this paper,the influence of crystal-field on the Luminescence properties of Eu^(2+) in complex oxides are studied theoretically by using purely electrostatic model,the dependence of the 4f^65d levels on Eu-O bond distance is given.Quantum chemistry calculation shows that the splitting extent of 4f^65d energy band in cubic or in octahedral fields will be inversely proportional to R^5,where R is the distance of Eu^(2+) to oxygen ligand.The value of R affects slightly the location of the centre of 4f^65d energy band.According to the exper- imental spectrum data,we have discussed the influence of the host chemical composition,the replaced sites of Eu^(2+) and degree of covalency of Eu-O bond on luminescence properties of Eu^(2+).Some regularity of fluorescence spectrum was observed. In alkali-alkaline earth-phosphates,the splitting extent of 4f^65d band (△E) becomes smaller as the Eu-O bond distance (R) increases.In Na_(3-x)(PO_4)_(1-x)(SO_4)_x and Na_(2-x)CaSi_(1-x)P_xO_4 hosts,d-d emission peak of Eu^(2+) will shift to shorter wavelength with the increase of x's value. The crystal structure data show that Eu^(2+) in K_2Mg_2(SO_4)_3 is affected more strongly by crystal-field and covalancy than in KMgF_3,so K_2Mg_2(SO_4)_3:Eu^(2+) emits blue light (E_(em)~m=400nm) and KMgF_3:Eu^(2+) produces ultraviolet fluorescence. 展开更多
关键词 Eu SPECTRAL VARIATION AND CHARACTERISTICS OF LOW valency RARE EARTH IONS IN COMPLEX OXIDES EFFECT OF THE CRYSTAL ENVIRONMENT AND CHEMICAL FACTORS ON LUMINESCENCE PROPERTIES OF EUROPIUM ION
下载PDF
Alternative lead-free mixed-valence double perovskites for high-efficiency photovoltaic applications
17
作者 Wenbo Li Yuheng Li +1 位作者 Zilong Zhang Peng Gao 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2023年第9期347-353,共7页
Lead-based organic-inorganic hybrid perovskites have exhibited great potential in photovoltaics,achieving power conversion efficiencies(PCEs) exceeding 25%.However,the toxicity of lead and the instability of these mat... Lead-based organic-inorganic hybrid perovskites have exhibited great potential in photovoltaics,achieving power conversion efficiencies(PCEs) exceeding 25%.However,the toxicity of lead and the instability of these materials under moist conditions pose significant barriers to large-scale production.To overcome these limitations,researchers have proposed mixed-valence double perovskites,where Cs_(2)Au~ⅠAu~ⅢI_6 is a particularly effective absorber due to its suitable band gap and high absorptance efficiency.To further extend the scope of these lead-free materials,we varied the trivalent gold ion and halogen anion in Cs_(2)Au~ⅠAu~ⅢI_6,resulting in 18 new structures with unique properties.Further,using first-principles calculations and elimination criteria,we identified four materials with ideal band gaps,small effective carrier mass,and strong anisotropic optical properties.According to theoretical modeling,Cs_(2)AuSbCl_6,Cs_(2)AuInCl_6,and Cs_(2)AuBiCl_6 are potential candidates for solar cell absorbers,with a spectroscopic limited maximum efficiency(SLME) of approximately 30% in a 0.25 μm-thick film.These three compounds have not been previously reported,and therefore,our work provides new insights into potential materials for solar energy conversion.We aim for this theoretical exploration of novel perovskites to guide future experiments and accelerate the development of high-performance photovoltaic devices. 展开更多
关键词 Mixed valence double perovskite Theoretical calculation Electronic configuration Photovoltaic performance
下载PDF
Valence state effect of Cu on photocatalytic CO_(2)reduction
18
作者 Fangxu Dai Mingming Zhang +2 位作者 Zhenjiang Li Jun Xing Lei Wang 《Materials Reports(Energy)》 EI 2023年第4期39-45,共7页
Copper(Cu)is extensively employed in photocatalytic CO_(2)reduction reactions for the production of high-value products.The valence state of transition metals plays a pivotal role in influencing the catalytic process.... Copper(Cu)is extensively employed in photocatalytic CO_(2)reduction reactions for the production of high-value products.The valence state of transition metals plays a pivotal role in influencing the catalytic process.However,due to the complex valence state changes of Cu in the CO_(2)reduction reaction,research on its valence state effect is lacking.The current work is to prepare a series of TiO_(2)/CuX with stable Cu valence composition using different copper halides(CuX and CuX_(2),X=Br or Cl)as precursors.The results show that the CuBr_(2)loading leads to Cu^(+)/Cu^(2+) mixed cocatalyst and exhibits the highest activity for CO_(2)photoreduction.The CH4 evolution rate of the TiO_(2)/CuBr_(2)catalyst is as high as 100.59μmol h^(-1)g^(-1),which is 6.6 times that of pristine TiO_(2).The CH4 selectivity reaches 77%.The enhanced catalytic activity and selectivity can be ascribed to the efficient surface adsorption,activation,excellent carrier separation,and transfer ofCu^(+)/Cu^(2+) mixed cocatalyst.Our findings provide a reference for designing highly active Cu-based photocatalysts. 展开更多
关键词 valence state CU PHOTOCATALYTIC CO_(2)reduction
下载PDF
Integrating the valence theory and the norm activation theory to understand consumers’ e-waste recycling intention
19
作者 Hong Thi Thu Nguyen 《Chinese Journal of Population,Resources and Environment》 2023年第1期26-36,共11页
Electrical and electronic waste(e-waste)is a growing challenge,matching the widespread boom in the use of information and communication technology.Opposite to an alarming increasing amount of e-waste,a low rate of con... Electrical and electronic waste(e-waste)is a growing challenge,matching the widespread boom in the use of information and communication technology.Opposite to an alarming increasing amount of e-waste,a low rate of consumer engagement in ensuring the proper disposal of such materials intensifies the pressure on the exist‐ing e-waste crisis.To deal with this thorny problem,it is of great interest to grasp consumers’disposal and re‐cycling behavioral intentions.Therefore,this study attempts to understand complementary perspectives around consumers’e-waste recycling intention based on the integration of the valence theory and the norm activation theory.Four data mining models using classification and prediction-based algorithms,namely Chi squared automatic interaction detector(CHAID),Neural network,Discriminant analysis,and Quick,unbiased,efficient statistical tree(QUEST),were employed to analyze a set of the 398 data collected in Vietnam.The re‐sults revealed that the social support value is by far the most critical predictor,followed by the utilitarian value,task difficulty,and monetary risk.It is also noteworthy that the awareness of consequences,education background,the ascription of responsibility,and age were also ranked as critical affecting factors.The lowest influential predictors found in this study were income and gender.In addition,a comparison was made in terms of the classification performance of the four utilized data mining techniques.Based on several evalua‐tion measurements(confusion matrix,accuracy,precision,recall,specificity,F-measure,ROC curve,and AUC),the aggregated results suggested that CHAID and Neural network performed the best.The findings of this research are expected to assist policymakers and future researchers in updating all information surround‐ing consumer behavioral intention-related topics focusing on e-waste.Furthermore,the adoption of data min‐ing algorithms for prediction is another insight of this study,which may shed the light on data mining applica‐tions in such environmental studies in the future. 展开更多
关键词 CHAID Discriminant analysis E-waste recycling intention Neural network Norm activation theory QUEST Sustainable development goals valence theory
下载PDF
零价铁活化过硫酸盐降解土壤中邻苯二甲酸酯
20
作者 李海峰 刘河疆 +4 位作者 郭文博 苏含明 刘志刚 马兴旺 刘国宏 《环境科学与技术》 CAS CSCD 北大核心 2024年第7期156-165,共10页
为了探究零价铁(ZVI)活化过硫酸盐(PS)对土壤邻苯二甲酸二(2-乙基己基)酯(DEHP)的降解效率、最优降解条件及对土壤性质的影响,该文通过单因素实验和正交实验,研究初始pH值、水土比、PS浓度、ZVI添加量、反应时间对DEHP降解效率的影响,... 为了探究零价铁(ZVI)活化过硫酸盐(PS)对土壤邻苯二甲酸二(2-乙基己基)酯(DEHP)的降解效率、最优降解条件及对土壤性质的影响,该文通过单因素实验和正交实验,研究初始pH值、水土比、PS浓度、ZVI添加量、反应时间对DEHP降解效率的影响,同时探讨了氧化体系对土壤理化性质和速效养分的影响。结果表明,5个因素对DEHP降解率的影响程度依次为PS>初始pH>ZVI添加量>水土比>反应时间。当初始pH为3、水土比4∶1、PS浓度为1 mmol/g、ZVI添加量为0.5 mmol/g、反应80 min时DEHP降解率在75.12%~80%之间,降解效果最佳。ZVI/PS氧化体系对土壤性质影响较大,随着PS浓度增加,土壤pH、土壤有机质含量呈现不同程度的降低,土壤电导率和氧化还原电位呈递增趋势。当同时加入PS和ZVI时,速效氮含量显著增大;单独向土壤溶液中添加ZVI或PS均使土壤速效磷含量显著增高,当土壤溶液中同时添加PS和ZVI后,速效磷含量急剧下降;而当ZVI或PS的浓度比≥1时,速效钾含量急剧下降,降幅达到76%。在实际修复PAEs污染土壤时要充分评估氧化剂添加量对土壤性质的影响,该研究可为ZVI活化PS去除土壤环境介质中的DEHP提供了理论和实践依据。 展开更多
关键词 零价铁 过硫酸盐 土壤 邻苯二甲酸二(2-乙基己基)酯 降解效率
下载PDF
上一页 1 2 219 下一页 到第
使用帮助 返回顶部