High thermoelectric figure of merit in rhombic porous carbon nitride nanoribbons

By performing extensive density functional theory calculations combined with non-equilibrium Green's function technique, we predict the rhombic porous carbon nitride nanoribbon (rPCNNR) and the vertical rPCNNR junction exhibiting high thermoelectric figure of merit (ZT) values of 0.57 and 2.1 at room temperature respectively. Theoretical results reveal that the ZT value of rPCNNR is significantly larger than that of armchair graphene nanoribbon with the almost same width (~0.035) due to the large Seebeck coefficients and the significantly decreased thermal conductance of rPCNNR, where the phonon states are blocked by the built-in porous structure and rhombic edge in rPCNNR. The ZT value is further enhanced to be 2.1 in the vertical rPCNNR junction, which is achieved by the synergy effect between the dramatically suppressed thermal conductance in in-plane direction due to the weak van der Waals interaction between two rPCNNRs, the almost unchanged Seebeck coefficients, and the good electron conductivity provided by the strong overlapping of delocalized VB- and CB-derived states in the scattering region. These presented findings highlight rPCNNR as a promising candidate in building flexible devices with high thermoelectric performance.     

Large thermoelectric figure of merit in hexagonal phase of 2D selenium and tellurium

We found a large thermoelectric figure of merit in the hexagonal phase of 2D selenium and tellurium from first-principles calculations. The hexagonal phase (α) is obtained from three atomic layers truncated along the [001] direction of trigonal Te and Se bulk in the equilibrium structure. We found the α-Se structure dynamically stable. The calculated electronic structures of α-Se and α-Te show interesting semiconductor character for both electronic and optoelectronic applications. Furthermore, the obtained elastic properties show that hexagonal tellurene is a softer material than selenene. The thermoelectric figure of merit for hexagonal 2D phase (∼1.0) is larger than those reported for the tetragonal 2D phase (∼0.75) of selenium and tellurium. Additionally, the computed electrical and phonon transport parameters indicate that selenene and tellurene are promising thermoelectric materials; both offer an alternative to recovering residual heat and transforming it into electricity.     

Nanostructures versus solid solutions: low lattice thermal conductivity and enhanced thermoelectric figure of merit in Pb9.6Sb0.2Te10-xSex bulk materials

The series of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compounds with different Se content (x) were prepared, and their structure was investigated at the atomic and nanosized regime level. Thermoelectric properties were measured in the temperature range from 300 to 700 K. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) series was designed after the refinement of the single-crystal structure of Pb(3.82)Sb(0.12)Te(4) (Pb(9.6)Sb(0.3)Te(10); S.G. Pmm) by substituting isoelectronically in anion positions Te by Se. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x)() compounds show significantly lower lattice thermal conductivity (kappa(L)) compared to the well-known PbTe(1)(-)(x)Se(x) solid solutions. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a kappa(L) value as low as 0.40 W/m.K was determined at 700 K. High-resolution transmission electron microscopy of several Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) samples showed widely distributed Sb-rich nanocrystals in the samples which is the key feature for the strong reduction of the lattice thermal conductivity. The reduction of kappa(L) results in a significantly enhanced thermoelectric figure of merit of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compared to the corresponding PbTe(1)(-)(x)Se(x) solid solution alloys. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a maximum figure of merit of ZT approximately 1.2 was obtained at approximately 650 K. This value is about 50% higher than that of the state-of-the-art n-type PbTe. The work provides experimental validation of the theoretical concept that embedded nanocrystals can promote strong scattering of acoustic phonons.     

High performance Na-doped PbTe-PbS thermoelectric materials: electronic density of states modification and shape-controlled nanostructures

Thermoelectric heat-to-power generation is an attractive option for robust and environmentally friendly renewable energy production. Historically, the performance of thermoelectric materials has been limited by low efficiencies, related to the thermoelectric figure-of-merit ZT. Nanostructuring thermoelectric materials have shown to enhance ZT primarily via increasing phonon scattering, beneficially reducing lattice thermal conductivity. Conversely, density-of-states (DOS) engineering has also enhanced electronic transport properties. However, successfully joining the two approaches has proved elusive. Herein, we report a thermoelectric materials system whereby we can control both nanostructure formations to effectively reduce thermal conductivity, while concurrently modifying the electronic structure to significantly enhance thermoelectric power factor. We report that the thermoelectric system PbTe-PbS 12% doped with 2% Na produces shape-controlled cubic PbS nanostructures, which help reduce lattice thermal conductivity, while altering the solubility of PbS within the PbTe matrix beneficially modifies the DOS that allow for enhancements in thermoelectric power factor. These concomitant and synergistic effects result in a maximum ZT for 2% Na-doped PbTe-PbS 12% of 1.8 at 800 K.     

Si/C nanocomposite anode materials by freeze-drying with enhanced electrochemical performance in lithium-ion batteries

The nanostructured Si/graphite composites embedded with the pyrolyzed polyethylene glycol was synthesized from coarse silicon and natural graphite by a facile and cost-effective approach. The Si/C nanocomposite showed the fluffy carbon-coated structure, which was confirmed by the SEM and TEM measurements. The as-obtained Si/C nanocomposite, employed as anode material in lithium-ion batteries, exhibited significantly enhanced rate capability and cycling stability. The improved electrochemical stability of the composite was evaluated by EIS and galvanostatically charge/discharge test. A reversible capacities as high as 85% and 91% of the initial charge capacities, could be maintained for the Si/C nanocomposite electrode after 40 cycles under the high current densities of 500 and 1,000?mA?g^?1, respectively. The relatively low cost and excellent electrochemical capability of the Si/C nanocomposite would well meet the challenge in rapid charge and discharge for large-size lithium-ion rechargeable batteries.     

用反相高效液相色谱法分离和测定丁烯二酸的顺反异构体

建立了分离和测定丁烯二酸的２个异构体－顺丁烯二酸和反丁烯二酸的反相高效液相色谱法。以Ｓｈｉｍ－ｐａｃｋ ＣＬＣ－ＯＤＳ柱为分析柱,以甲醇－水（体积比５：２）,用磷酸调至ｐＨ３．０）为流动相,流速０．７ｍＬ／ｍｉｎ,检测波长为２２０ｎｍ,外标法定量。顺、反丁烯二酸的检出限分别为０．１０和０．０７５ｍｇ／Ｌ（Ｓ／Ｎ＝２）;相对标准偏差分别为０．４７％和０．５４％（ｎ＝３）。二者的线性范围均为１０～６０     

Spinodal decomposition and nucleation and growth as a means to bulk nanostructured thermoelectrics: enhanced performance in Pb(1-x)Sn(x)Te-PbS

The solid-state transformation phenomena of spinodal decomposition and nucleation and growth are presented as tools to create nanostructured thermoelectric materials with very low thermal conductivity and greatly enhanced figure of merit. The systems (PbTe)(1-x)(PbS)(x) and (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) are not solid solutions but phase separate into PbTe-rich and PbS-rich regions to produce coherent nanoscale heterogeneities that severely depress the lattice thermal conductivity. For x > approximately 0.03 the materials are ordered on three submicrometer length scales. Transmission electron microscopy reveals both spinodal decomposition and nucleation and growth phenomena the relative magnitude of which varies with x. We show that the (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) system, despite its nanostructured nature, maintains a high electron mobility (>100 cm(2)/V x s at 700 K). At x approximately 0.08 the material achieves a very low room-temperature lattice thermal conductivity of approximately 0.4 W/m x K. This value is only 28% of the PbTe lattice thermal conductivity at room temperature. The inhibition of heat flow in this system is caused by nanostructure-induced acoustic impedance mismatch between the PbTe-rich and PbS-rich regions. As a result the thermoelectric properties of (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) at x = 0.04, 0.08, and 0.16 were found to be superior to those of PbTe by almost a factor of 2. The relative importance of the two observed modes of nanostructuring, spinodal decomposition and nucleation and growth, in suppressing the thermal conductivity was assessed in this work, and we can conclude that the latter mode seems more effective in doing so. The promise of such a system for high efficiency is highlighted by a ZT approximately 1.50 at 642 K for x approximately 0.08.     

Fabrication and performance of microencapsulated phase change materials with hybrid shell by in situ polymerization in Pickering emulsion

Microencapsulated phase change materials (MePCMs) using melamine–formaldehyde resin/SiO₂ as shell were investigated in this paper. Organically modified SiO₂ particles were employed to stabilize Pickering emulsion, and in situ polymerization of melamine and formaldehyde was carried out to form hybrid shell. The performances of resultant MePCMs with hybrid shell were investigated comparatively with the MePCMs with polymer shell. SiO₂ particles raise the microencapsulation efficiency by improving the stability of emulsion and providing a precipitation site for melamine–formaldehyde resin. Also, the mechanical strength, thermal reliability, and anti‐osmosis performance of MePCMs were improved significantly by SiO₂ particles in the shell. Our study shows that Pickering emulsion is a simple and robust template for MePCMs with polymer‐inorganic hybrid shell. Copyright © 2015 John Wiley & Sons, Ltd.     

Hierarchical zeolites: enhanced utilisation of microporous crystals in catalysis by advances in materials design

The introduction of synthetic zeolites has led to a paradigm shift in catalysis, separations, and adsorption processes, due to their unique properties such as crystallinity, high-surface area, acidity, ion-exchange capacity, and shape-selective character. However, the sole presence of micropores in these materials often imposes intracrystalline diffusion limitations, rendering low utilisation of the zeolite active volume in catalysed reactions. This critical review examines recent advances in the rapidly evolving area of zeolites with improved accessibility and molecular transport. Strategies to enhance catalyst effectiveness essentially comprise the synthesis of zeolites with wide pores and/or with short diffusion length. Available approaches are reviewed according to the principle, versatility, effectiveness, and degree of reality for practical implementation, establishing a firm link between the properties of the resulting materials and the catalytic function. We particularly dwell on the exciting field of hierarchical zeolites, which couple in a single material the catalytic power of micropores and the facilitated access and improved transport consequence of a complementary mesopore network. The carbon templating and desilication routes as examples of bottom-up and top-down methods, respectively, are reviewed in more detail to illustrate the benefits of hierarchical zeolites. Despite encircling the zeolite field, this review stimulates intuition into the design of related porous solids (116 references).     

固相萃取-高效液相色谱法同时测定食品塑料包装材料中9种光稳定剂

建立了同时测定食品塑料包装材料中9种紫外光稳定剂含量的高效液相色谱方法。样品用甲醇-乙酸乙酯混合溶剂超声提取,经固相萃取小柱净化后,以ZORBAX SB-C18柱(250 mm×4.6 mm, 5 μm)为分离色谱柱,甲醇和水为流动相,梯度洗脱,以310 nm为检测波长进行定性、定量分析。该方法前处理简单、易操作,9种紫外光稳定剂分离效果良好。9种紫外光稳定剂在0.2～10 mg/L范围内呈良好的线性关系,线性相关系数大于0.999;方法检出限为0.05～0.1 mg/L;实际样品中的加标回收率为70.2%～89.0%,相对标准偏差为0.4%～4.5%。该方法简单、准确,能够满足食品塑料包装材料中紫外光稳定剂的检测要求。     

Photocatalysis of PbS quantum dots in a quantum dot-sensitized solar cell: photovoltaic performance and characteristics

PbS QDs have been synthesized by an in situ photocatalysis method using the photocatalytic activity of nanocrystalline TiO(2) films. Both the photovoltaic response and size of the synthesized PbS QDs were analyzed. Compared with the conventional synthesis route, this method is simpler and produces less waste.     

Rare-earth hexaborides nanostructures: Recent advances in materials, characterization and investigations of physical properties

Nanostructured rare-earth hexaborides (REB₆) are promising materials for photonic and electronic applications due to their unique characteristic. These include high melting point, hardness, chemical stability, low work function, low volatility at high temperatures, superconductivity, magnetic properties, efficiency, thermionic emission, and narrow band semiconductivity. This article focuses on recent developments regarding the synthesis, characterization, and applications of REB₆ nanostructures. We first summarize information regarding the classification and crystal chemistry of REB₆. Next, we examine the means by which researchers have successfully synthesized REB₆. We consider the structural properties and morphology of REB₆, and the growth mechanism involved in their fabrication. Finally, we offer suggestions for the use of REB₆ nanostructures in photonic and electronic applications, and identifying four areas for further research.     

Peptide/protein hybrid materials: enhanced control of structure and improved performance through conjugation of biological and synthetic polymers

The conjugation of peptides/proteins and synthetic polymers is a useful strategy to overcome some of the limitations related to the use of the individual components. This review will highlight two aspects: enhanced structural control at the nanometer level and improved performance, in particular with respect to biomedical applications. In the former case, peptide sequences are mainly used to mediate self-assembly of synthetic polymers. In the latter case, conjugation of an appropriate synthetic polymer to a pharmaceutically active peptide/protein can, for example, prevent premature enzymatic degradation and enhance blood circulation times, which is therapeutically advantageous.     

Superior lithium storage performance in MoO3 by synergistic effects:Oxygen vacancies and nanostructures

Molybdenum trioxide(MoO₃) has recently attracted wide attention as a typical conversion-type anode of Li-ion batteries(LIBs).Nevertheless,the inferior intrinsic conductivity and rapid capacity fading during charge/discharge process seriously limit large-scale commercial application of MoO₃.Herein,the density function theory(DFT) calculations show that electron-proton co-doping preferentially bonds symmetric oxygen to form unstable H_xMoO₃.When the-OH-gr...     

测定裸大麦中生育酚和生育三烯酚的正相高效液相色谱法

建立了同时测定裸大麦中α_、β_、δ_生育酚和α_、γ_、δ_生育三烯酚以及γ_生育酚 +β_生育三烯酚含量的正相高效液相色谱法;采用国产YWG_SiO2 柱 (250mm×4mmID ,5μm) ,V 正己烷∶V 异丙醇=99∶1体系为流动相 ,流速为1.2mL/min,荧光检测器检测 ,激发波长290nm ,发射波长330nm,并采用正交设计法优化样品的皂化工艺。     

Evaluation of chromatographic performance of various packing materials having different structural characteristics as stationary phase for fast high performance liquid chromatography by new moment equations

Chromatographic performance of various separation media having different structural characteristics as the stationary phase for fast HPLC was quantitatively evaluated by using the new moment equations recently developed with considering the shape and porous structure of the packing materials. Four types of separation media, i.e., full-porous, partially porous (pellicular or shell) type, and non-porous spherical particles and full-porous cylindrical fiber, were chosen as examples. The moment equations were used for predicting the chromatographic behaviors of benzene under hypothetical RPLC conditions. The overall performance of the four types of packing materials as the separation media for fast HPLC was compared with each other from the viewpoint of the peak capacity, which depends on both the retention equilibrium and the mass transfer kinetics. It seems that the full-porous cylindrical fiber and the pellicular type spherical particle are more preferable than the others, i.e., the full-porous and non-porous spherical particles. Now we can use the new moment equations for the quantitative prediction of the chromatographic behaviors of the various packing materials on the basis of a related experimental information and for the evaluation of their performance from various chromatographic points of view. The new moment equations are effective not only for the detailed analyses of chromatographic behaviors but also for the preliminarily evaluation of new types of separation media for fast HPLC.     

多壁碳纳米管固相萃取-高效液相色谱-串联质谱法测定食品接触材料中双酚-二环氧甘油醚的迁移量

建立了测定食品接触材料中6种双酚-二环氧甘油醚(双酚A二缩水甘油醚(BADGE)及其衍生物双酚A(2,3-二羟丙基)甘油醚(BADGE•H2O)、双酚A(3-氯-2-羟丙基)甘油醚(BADGE•HCl)、双酚A(3-氯-2-羟丙基)(2,3-二羟丙基)醚(BADGE•H2O•HCl)和双酚F二缩水甘油醚(BFDGE)及其衍生物双酚F双(3-氯-2-羟丙基)甘油醚(BFDGE•2HCl))迁移到食品中的迁移量的高效液相色谱-串联质谱法(HPLC-MS/MS)。样品以叔丁基甲醚(MTBE)为提取溶剂,超声提取,提取液经多壁碳纳米管(MWCNTs)固相萃取(SPE)柱富集、净化。以COSMOSIL C18为分析柱,流动相为0.1%甲酸的5 mmol/L醋酸铵溶液和甲醇。6种双酚-二环氧甘油醚在1.0～100 μg/L范围内线性关系良好(r2＞0.9991)。在3个添加水平下,6种目标化合物的回收率范围为78.6%～89.9%,相对标准偏差小于10%。方法检出限范围为0.5～1.5 μg/L。该方法操作简单,灵敏度高,可应用于食品接触材料中双酚-二环氧甘油醚迁移量的快速检测。     

高效液相色谱法测定食品接触材料中苯酚和4-叔丁基苯酚迁移量

提出了食品接触材料在水、3％(质量分数)乙酸溶液、乙醇(1+9)溶液、异辛烷4种食品模拟物中苯酚、4-叔丁基苯酚迁移量的高效液相色谱测定方法.不同种类的食品模拟物采用不同的样品前处理方法提取后,用Diamonsil C18色谱柱为固定相,甲醇-水为流动相梯度洗脱,以激发波长220 nm、发射波长312nm的荧光检测器进...     

Dynamics of a surface phase transition as monitored by in situ second harmonic generation

The dynamics of the (2 x 2)-3CO <--> dilute phase transition involving CO adsorbed on Pt(111) microfacets has been monitored in situ in a CO-saturated acidic electrolyte using potential step-second harmonic generation techniques. Apparent time constants derived strictly from the optical data were found to be orders of magnitude slower for the forward process as compared to those of the reverse process. This behavior is consistent with the activated nature of CO electrooxidation, which requires the presence of a neighboring adsorbed oxygenated species, for example, hydroxyl, for the process to ensue.