A DFT Study of Thiophene Adsorption on the Rh（111） Surfaces

Thiophene adsorption on the Rh(111) surfaces has been investigated by density functional theory.The results show that the adsorption at the hollow and bridge sites is the most stable.The molecular plane of the thiophene ring is distorted,the C=C bond is stretched to 1.448  and the C-C bond is shortened to 1.390.The C-H bonds tilt 22～42oaway from the surface.The calculated adsorption geometries are in reasonable agreement with population analysis and density of states.The thiophene molecule obtains 0.74 electrons,reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal.The reaction paths and transition states for desulfurization of the molecule have been investigated.The bridge adsorption structure of thiophene leads to a thiol via an activated reaction with an energetic barrier of 0.30 eV.This second step is slightly difficult,and dissociation into a C4H4 fragment and a sulfur atom is possible,with an energetic barrier of 0.40 eV.     

Two-parameter stochastic resonance in a model of electrochemical oxidation of formic acid on Pt

Stochastic resonance (SR) is shown in a two-parameter system, a model of electrochemical oxidation of formic acid on Pt. The driving current and the saturation coverage for carbon monoxide are two control parameters in this model. Modulation of an excitable focal stable state close to a Hopf bifurcation by a weak periodic signal in one parameter and noise in the other parameter is found to give rise to SR. The results indicate that the noise can enlarge a weak periodic signal and lead the system to be ordered. The scenario and novel aspects of SR in this system are discussed.     

Chemical Reactions and Kinetics of the Carbon Monoxide Coupling in the Presence of Hydrogen

The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence.     

Purification and Characterization of Cold-active α-Amylase Excreted by A Strain of Marine Cold-adaptive Penicillia

The filamentous fungi from the Huanghai sea sludge were screened according to their ability to produce cold-active α-amylase. The strain with the highest amylase activity was identified as Penicilllum species. The α-amylase purified by ammonium sulphate precipitation and column chromatography on DEAE-sepharose and sephadex G-100 shows a molecular weight of about 55000 and a pl of 4. 38. The enzyme is stable in a pH range of 5.5—8.0 and has a maximum activity at pH 6.0. Compared with the α-amylase from mesophiles and thermophiles, the cold-active enzyme shows a high enzyme activity at lower temperatures and a high sensitivity at temperatures higher than 50℃. The optimal temperature is 40℃ and the activity decreases dramatically at temperatures above 50℃. Ca^2 shows a significant effect on maintaining the structure and the activity of the enzyme. EDTA and Cu^2 are its inhibitors. The products from the hydrolysis of soluble starch with the cold-active enzyme are maltose and other oligosaccharides.     

Purification and Characterization of Cold-active α-Amylase Excreted by A Strain of Marine Cold-adaptive Penicillia

The filamentous fungi from the Huanghai sea sludge were screened according to their ability to produce cold-active α-amylase. The strain with the highest amylase activity was identified as Penicillium species. The α-amylase purified by ammonium sulphate precipitation and column chromatography on DEAE-sepharose and sephadex G-100 shows a molecular weight of about 55000 and a pI of 4.38. The enzyme is stable in a pH range of 5.5-8.0 and has a maximum activity at pH 6.0. Compared with the α-amylase from mesophiles and thermophiles, the cold-active enzyme shows a high enzyme activity at lower temperatures and a high sensitivity at temperatures higher than 50 ℃. The optimal temperature is 40 ℃ and the activity decreases dramatically at temperatures above 50 ℃. Ca2 shows a significant effect on maintaining the structure and the activity of the enzyme. EDTA and Cu2 are its inhibitors. The products from the hydrolysis of soluble starch with the cold-active enzyme are maltose and other oligosaccharides.     

Calculations of heat of solvation by a simple electrostatic approach to molecular interactions

An extremely simple formula to estimate the heat of formation of complexes between anion and a polar molecule or between highly polar systems is presented.The formula is entirelyelectrostatic and the expression used is verified by means of perturbation theory.This formula is test-ed for several ion-molecule and molecule-molecule pairs.It is also applied to estimate the heat ofhydration of simple salts.     

Popularising Chemistry in Secondary Schools——through the development of Scientific and Technological Literacy for All

While chemistry is popular for children of primary school age,its popularity drops dramatically in secondary schools,A potential solution to address this is to recognise the need for greater relevance-relevance to the curriculum,to the needs of society and,in the eyes of the students.The paper tries to puts forward a rethink of the philosophy for school chemistry education,based on the underlying belief that chemistry education is an integral part of education.The target is labelled scientific and technological literacy for all (STL),STL rejects the notion that chemistry is taught solely to acquire tha abilities to be a scientist and supports the vision of a single curriculum goal,applicable to all students.Besides being a philosophy,STL is also a teaching approach.This approach is to initiate the teaching of chemistry topics,starting from a carefully chosen society perspective and to introduce the conceptual learning on a need-to-know basis.A limitatioin is the professional development of teachers,Suggestion for overcoming this involve workshop on materials development.Aconcern is expressed in cases where teachers make use of ready-made teaching materials(a common practice),without first gaining an understanding and an appreciation of the intended philosophy related to these materials.     

Characterization of Ultra Fine Solids（BS） in Athabasca Bitumen

The ultra fine (＜200 nm) inorganic solids (BS) were separated from bitumen which was washed by toluene and centrifugated at 2000 rpm. The result of PAS FTIR and image of TEM showed that the structure of BS particles was smiliar to that of kaolinite clay. On the surface of BS, both toluene insoluble organic matter and structural OH group are detected at the same time.The surface characteristics imparted a bi-wettable nature to the BS. As a result, the BS is able to stabilize fine water emulsion in the bitumen phase. The organic matter associated with BS is a possible factor of the fouling on catalyst and equipment.     

Investigation on the Performance of Supported Molybdenum Carbide for the Partial Oxidation of Methane

The performance of uspported and unsupported molybdenum carbide for the partial oxidation of methane (POM) to syngas was investgated.An evaluation of the catalysts indicates that bulk molybdenum carbied has a higher methane conversion during the initial stage but a lower selectivity to CO and H2/CO ratio in the products.The rapid deactivation of the catalyst is also a significant problem.However,the supported molybdenum carbide catalyst shows a much higher methane conversion,increased selectivity and significantly improved catalytic stability.The characterization by XRD and BET specific area measurements depict an improved dispersion of molybdenum carbide when using alumina as a carrier.The bulk or the supported molybdenum carbide exists in the β-Mo2C phase,while it is transformed into molybdenum dioxide postcatalysis which is an improtant cause of molybdenum carbide deactivation.     

The Evaluation of Two-Dimensional Madelung Constant For NaCl Crystal Structure

The following documentation is an evaluation of the two-dimensional Madelung constant for the NaCl structure. The infinite series for the structure is formulted asThe first term in the formula converges to 41n2. The series after K =2 in the second term is put together with the third term and a constant- 4/ 2 is left. The combination of the third term and the series after K=2 in the second term is assumed to be 8 Sn. The converging series Sn can be solved on a computer. The seven significant figures of the two-dimensional Madelung constant for the NaCl structure is then determined as 1. 615558.     

SiO2/聚乙二醇非牛顿流体流变性能研究

利用应力控制流变仪考察了SiO₂/聚乙二醇分散体系稳态和动态的流变性能. 实验结果表明, 该体系具有剪切变稀和可逆的剪切增稠现象. 稳态应力实验中, 当应力较小时, 体系具有剪切变稀现象, 而在剪切应力(σ)大于临界剪切应力(σ_c^s, σ_c^s=9.99 Pa)后, 体系粘度急剧增大. 在动态实验中, 剪切应力小于临界剪切应力(σ_c^o, σ_c^o=15.85 Pa)时, 储能模量G′减小, 耗能模量G″与复合粘度η*基本不变, 但σ＞15.85 Pa后, G′、G″及η*同步增大, 且在所研究的应力范围内, G″均大于G′. 同时还考察了测试频率、分散相含量以及分散介质平均分子量的差别对流变性的影响. σ_c^o随测试频率的增大而变大; SiO₂质量分数越大, σ_c^o基本不变, 但增稠现象变得更明显; 与平均分子量小的PEG200体系相比, 平均分子量大的PEG400体系, σ_c^o并未发生改变, 但在增稠之前体系的粘度较低, 增稠之后体系粘度增大的幅度较大.     

利用强度调制光电流/光电压谱研究碳点/KOH电解液界面的动力学行为

通过强度调制光电流谱(IMPS)和强度调制光电压谱(IMVS)技术研究在光电分解水制氢体系中碳点光阳极与KOH电解液界面的动力学行为。结果表明,光强在30–90 m W·cm~(-2)范围内,界面的电子传输时间(τ_d)、电子寿命(τ_n)、电子扩散系数(D_n)、电子扩散长度(L_n)均没有变化;当光强增加到110和130 m W·cm~(-2)时,τ_d和τ_n延长,而D_n减小。实验表明,不同于Ti O_2/电解液等界面,碳点光电极/电解液界面中碳点电极存在的缺陷少,因此电子主要以无陷阱限制扩散方式传输为主。且在30–130 m W·cm~(-2)的光强范围内,与τ_d和τ_n相关的载流子收集效率(η_(cc))相近。     

一个新颖的三核镍配合物[Ni3(C13H9N2O)5(CH3OH)(CH3CH2OH)]Cl的合成、晶体结构及性质研究

在甲醇-乙醇混合溶剂中, 含有N, O给体的二齿配体2-(2-羟苯基)苯并咪唑与NiCl2•6H2O在常温下反应合成得到标题化合物, 采用元素分析、红外光谱、紫外光谱、热分析以及X射线单晶衍射法对其进行了组成和结构表征. 结果表明该化合物为三斜晶系, 空间群P-1, 晶胞参数: a＝1.2046(2) nm, b＝1.4891(3) nm, c＝2.1342(4) nm, α＝96.787(3)°, β＝104.862(3)°, γ＝99.993(3)°, V＝3.5904(12) nm3, Z＝2, Dc＝1.349 g/cm3, F(000)＝1516, GOF＝1.008, R1＝0.0583, wR2＝0.1455 [I＞2σ(I)]. 在标题化合物的晶体结构中, 晶体学不对称的三个配位中心Ni(II)原子配位环境各不相同, 五个配体提供的五个氧配位基中有四个起着桥联的作用, 形成了一个新颖的V型金属簇状化合物. 变温磁化率研究表明标题化合物在整体上表现为弱的反铁磁性耦合作用.     

OXIDATION OF α-METHYL OR α-METHYLENE GROUPS IN CARBONYL COMPOUNDS WITH AMMONIUM CHLOROCHROMATE

This paper reports a new method for oxidizing the α-methyl orα-methylene groups in carbonyl compounds into 1,2-dicarbonyl compoundsby ammonium chlorochromate(ACC).     

Ag/Ag2WO4等离子体共振催化剂可见光催化还原CO2

转化CO₂为有机组分是缓解全球变暖和保障持续能源供给的有效方法之一.采用简易的离子交换结合水合肼还原法制备了一系列不同晶相Ag₂WO₄载银(Ag/Ag₂WO₄)的等离子共振光催化剂,并用X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜-能量色散X射线光谱(SEM-EDS)、紫外-可见(UV-Vis)吸收光谱和比表面积测试对催化剂进行了表征.较之Ag₂WO₄, Ag/Ag₂WO₄在可见光催化还原CO₂生成CH₄时显示了明显提高的量子产率(QY)、能量投入产出比(EROEI)、转换数(TON),就Ag/α-Ag₂WO₄, Ag/β-Ag₂WO₄和Ag/γ-Ag₂WO₄而言,最佳催化剂为Ag/β-Ag₂WO₄,其实际最佳Ag:Ag₂WO₄摩尔比为4:96,该催化剂还原CO₂为CH₄的QY、EROEI、TON和拟一级反应速率常数分别为0.145%、0.067%、9.61和1.96×10^-6 min^-1.此外,制备的等离子共振Ag/Ag₂WO₄光催化剂在可见光辐照下进行循环反应仍能保持稳定性.局域表面等离子共振效应是强化Ag/Ag₂WO₄光催化剂活性和稳定性的主要原因.     

χ-Fe_5C_2：结构，合成与催化性质调控

铁碳化物,特别是χ-Fe_5C_2,因在多个不同领域的应用长期以来受到研究者的密切关注。事实上,χ-Fe_5C_2已经被认定为铁基费托合成催化剂的活性相。除了作为催化剂外,χ-Fe_5C_2在电化学、磁成像和治疗等方面也有应用价值。自发现以来,人们对χ-Fe_5C_2的结构、稳定性、催化性能等物理化学性质开展了研究。χ-Fe_5C_2的C2/c结构在上世纪60年代初次得到解析,但是受限于样品中常常混合其他氧化铁和碳化铁,在结构方面还存在争议。研究者仍致力于结合先进表征技术和理论方法,利用高纯度的样品来建立更加准确的模型。作为一种亚稳态结构,传统合成方法很难制备高纯度的χ-Fe_5C_2。经过对合成方法的不断探索,物相单一和尺寸形貌可控的合成已经实现。多种铁和碳的前驱体可以用来合成χ-Fe_5C_2,而固-固、固-气和固-液相的碳化过程均能够用来制备不同粒度和形貌的χ-Fe_5C_2。合成方法方面的成果来了对χ-Fe_5C_2物相形成机理的新认识。利用原位表征方法,研究者已经揭示了气固相和液固相制备过程中物相形成的一些细节。无定形的Fe-C复合物的形成与晶化有可能是关键步骤。在新的制备方法基础上,出现了多种调控χ-Fe_5C_2催化活性的新手段。低钴含量的有钴纳米粒子和χ-Fe_5C_2组成的复合体具有非常高的低温费托合成活性。通过第二组分的修饰后可以使χ-Fe_5C_2突破传统的费托合成反应的局限,成为制备低碳烯烃、长链α烯烃、芳烃和含氧化物的新型催化剂。在这篇综述中,我们将回顾自上世纪中期以来对χ-Fe_5C_2物相的研究成果,聚焦于对结构解析,制备方法,生成机制以及在催化性能调控等方面的进展。我们总结了一系列用于制备χ-Fe_5C_2的方法以及控制催化性质的路径。合成方法的突破是更好认识χ-Fe_5C_2物理化学的关键。     

AN INVESTIGATION ON THE INTERACTION MECHANISM OF β-CAROTENE WITH HALOGEN ATOM PRODUCED IN HALOBENZENE BY UV IRRADIATION

ESR measurements using spin trapping technique werecarried out for β-carotene-halobenzene system under UV lightirradiation.The ESR spectra observed in the presence andin the absence of β-carotene are markedly different.Thepossible scheme of β-carotene interacting with halogen atomwas proposed.     

质子化g-C3N4/β-SiC复合材料的制备及光催化降解茜素红性能

分别采用热解法和溶胶-凝胶-碳热还原法合成了石墨相氮化碳(g-C₃N₄)和纳米级碳化硅(β-SiC), 通过浸渍-热处理法将两者复合并通过浓盐酸质子化, 分别制备了g-C₃N₄/β-SiC和质子化g-C₃N₄/β-SiC(P-g-C₃N₄/β-SiC)复合光催化剂. 利用X射线衍射(XRD)、 扫描电子显微镜(SEM)、 高分辨透射电子显微镜(HRTEM)、 傅里叶变换红外光谱(FTIR)、 X射线光电子能谱(XPS)、 紫外-可见漫反射光谱(UV-Vis-DRS)和光致发光光谱(PL)等对样品进行了表征. 结果表明, P-g-C₃N₄/β-SiC复合材料的比表面积增大, 光生电子-空穴对的复合几率降低, 光催化性能明显提高. 在光催化降解染料茜素红(ARS)研究中, 样品的可见光催化活性顺序为P-g-C₃N₄/β-SiC>g-C₃N₄/β-SiC>P-g-C₃N₄>g-C₃N₄>β-SiC. 其中P-g-C₃N₄/β-SiC在60 min内对ARS的降解效率高达99.9%, 符合准一阶动力学模型, 速率常数为0.0967 min ^-1, 且循环使用9次后, 光催化降解效率仍保持97.5%以上.     

g-CN体系的准粒子能带结构和光学特性

利用多体格林函数理论,本文研究了二维CN体系(包括triazine和tri-s-triazine)的激发态特性。通过GW方法,我们计算了准粒子的能量。考虑电子-空穴相互作用,通过求解Bethe-Salpeter方程,我们获得了激发态能量和光谱。我们发现,在这两种CN体系的价带中,σ轨道和π轨道之间的交换作用非常强烈。由于占据的σ轨道和π轨道之间的准粒子修正量非常不同,因此,为了得到准确的带隙值和光谱,我们需要对这两种轨道开展精确的GW计算。与单层的CN体系相比,双层结构中层与层之间的范德华相互作用使带隙值降低了0.6 eV,而光吸收谱红移了0.2 eV,这是由于双层结构具有更小的激子束缚能。我们计算的吸收峰的位置与实验结果符合很好。实验中的吸收峰主要是由深能级的π轨道到π^*轨道的跃迁形成的。π→π^*跃迁和σ→π^*跃迁之间的耦合能够在长波长范围产生弱的吸收尾巴,如果调整入射光的极化方向,由σ→π^*跃迁产生的高强度的吸收峰将会在更低能量处出现。     

基于完全活性空间自洽场的杂化多组态密度泛函方法λ-DFCAS

提出了一种杂化多组态密度泛函新方法——λ-DFCAS. 在λ-DFCAS方法中, 电子相关能被分为静态和动态相关能. 静态相关能由多组态波函数方法完全活性空间自洽场(CASSCF)得到, 而动态相关能由密度泛函理论方法描述. 两种相关能的杂化比例由一个可调节的参数λ控制. 参数λ的取值取决于分子体系的多组态特性, 在0~1之间变化, 从而使得λ-DFCAS可以应用于各种强相关分子体系. 该方法能够以与CASSCF相当的计算代价获得接近完全活性空间二阶微扰(CASPT2)的计算精度, 并具备了大小一致性.