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亮点
基于晶格失配的表面诱导分子对称性破缺
吴凯
2019, 35(6): 555-556  doi: 10.3866/PKU.WHXB201808032
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石墨烯/蓝宝石基底上无应力AlN的快速生长
唐智勇
2019, 35(6): 557-558  doi: 10.3866/PKU.WHXB201809010
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氮掺杂石墨炔用于氧还原反应
费慧龙, 段镶锋
2019, 35(6): 559-560  doi: 10.3866/PKU.WHXB201809016
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推荐
功能纳米碳点“照亮”应用征途
吴凯
2019, 35(6): 561-562  doi: 10.3866/PKU.WHXB201809022
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展望硼烯的化学合成
杨金龙
2019, 35(6): 563-564  doi: 10.3866/PKU.WHXB201809054
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综述
硼烯化学合成进展与展望
王琴, 薛珉敏, 张助华
2019, 35(6): 565-571  doi: 10.3866/PKU.WHXB201805080
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硼烯是由硼原子构成的单原子层厚的二维材料,具有丰富的化学和物理性质。本文集中介绍近年来硼烯在合成方面的理论与实验研究进展,重点分析基底、生长温度、生长前驱物等因素对硼成核选择性的影响,探讨能够促进硼烯成核的潜在方法。进一步将分析硼烯生长机制及理论研究方法,以此展望通过在基底上化学气相沉积合成硼烯的可能途径。本文旨在促进大面积、高质量硼烯样品的制备以推动硼烯的实际应用。
纳米碳点的制备与应用研究进展
胡超, 穆野, 李明宇, 邱介山
2019, 35(6): 572-590  doi: 10.3866/PKU.WHXB201806060
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纳米碳点是碳纳米材料家族的新成员,近年来在国内外受到广泛关注。与传统的荧光染料和半导体量子点发光材料相比,碳点不仅具有优异的光学性能及尺寸效应,且具有制备成本低廉、生物相容性好、易于官能化、能带结构可调等优势。本文在理清有关碳点概念的基础之上,介绍了碳点结构特征和制备策略,着重综述了纳米碳点在生物成像与诊疗、传感器件、催化、光电器件和能量存储领域的最新研究进展,探讨了碳点研究目前存在的问题及未来的发展方向。
Article
A Comparative Study of Ignition Delay of Cracked Kerosene/Air and Kerosene/Air over a Wide Temperature Range
Yijun WANG, Dexiang ZHANG, Zhongjun WAN, Ping LI, Changhua ZHANG
2019, 35(6): 591-597  doi: 10.3866/PKU.WHXB201806042
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Kerosene is an ideal endothermic hydrocarbon. Its pyrolysis plays a significant role in the thermal protection for high-speed aircraft. Before it reacts, kerosene experiences thermal decomposition in the heat exchanger and produces cracked products. Thus, to use cracked kerosene instead of pure kerosene, knowledge of their ignition properties is needed. In this study, ignition delay times of cracked kerosene/air and kerosene/air were measured in a heated shock tube at temperatures of 657–1333 K, an equivalence ratio of 1.0, and pressures of 1.01 × 105–10.10 × 105 Pa. Ignition delay time was defined as the time interval between the arrival of the reflected shock and the occurrence of the steepest rise of excited-state CH species (CH*) emission at the sidewall measurement location. Pure helium was used as the driver gas for high-temperature measurements in which test times needed to be shorter than 1.5 ms, and tailored mixtures of He/Ar were used when test times could reach up to 15 ms. Arrhenius-type formulas for the relationship between ignition delay time and ignition conditions (temperature and pressure) were obtained by correlating the measured high-temperature data of both fuels. The results reveal that the ignition delay times of both fuels are close, and an increase in the pressure or temperature causes a decrease in the ignition delay time in the high-temperature region (> 1000 K). Both fuels exhibit similar high-temperature ignition delay properties, because they have close pressure exponents (cracked kerosene: τignP-0.85; kerosene:τignP-0.83) and global activation energies (cracked kerosene: Ea = 143.37 kJ·mol-1; kerosene: Ea = 144.29 kJ·mol-1). However, in the low-temperature region (< 1000 K), ignition delay characteristics are quite different. For cracked kerosene/air, while the decrease in the temperature still results in an increase in the ignition delay time, the negative temperature coefficient (NTC) of ignition delay does not occur, and the low-temperature ignition data still can be correlated by an Arrhenius-type formula with a much smaller global activation energy compared to that at high temperatures. However, for kerosene/air, this NTC phenomenon was observed, and the Arrhenius-type formula fails to correlate its low-temperature ignition data. At temperatures ranging from 830 to 1000 K, the cracked kerosene ignites faster than the kerosene; at temperatures below 830 K, kerosene ignition delay times become much shorter than those of cracked kerosene. Surrogates for cracked kerosene and kerosene are proposed based on the H/C ratio and average molecular weight in order to simulate ignition delay times for cracked kerosene/air and kerosene/air. The simulation results are in fairly good agreement with current experimental data for the two fuels at high temperatures (> 1000 K). However, in the low-temperature NTC region, the results are in very good agreement with kerosene ignition delay data but disagree with cracked kerosene ignition delay data. The comparison between experimental data and model predictions indicates that refinement of the reaction mechanisms for cracked kerosene and kerosene is needed. These test results are helpful to understand ignition properties of cracked kerosene in developing regenerative cooling technology for high-speed aircraft.
Moisture-Responsive Behavior in the Azophenolic Ionic Liquid Solution Accompanied by a Naked-Eye Color Change
Mingguang PAN, Yongsheng ZHAO, Xiaoqin ZENG, Jianxin ZOU
2019, 35(6): 624-629  doi: 10.3866/PKU.WHXB201807035
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Room temperature ionic liquids (ILs) that can exhibit a colorimetric response to moisture in the air are rarely reported in the literature. In this study, an azophenolic IL solution exhibited a spontaneous a colorimetric response, driven by the formation of hydrogen bonding between the [PhN=NPhO] anion and moisture in the air. This phenomenon was clearly understood using ultraviolet-visible (UV-Vis) absorption spectroscopy, nuclear magnetic resonance (NMR) spectra, experimental data, and theoretical calculations. Specifically, in the UV-Vis absorption spectra, absorption around 455 nm decreased, while the band around 343 nm increased in the IL CHCl3 solution as time progressed; this was accompanied by a color change from orange to faint yellow. This spontaneous, self-responsive process was further observed using 1H NMR data. When the IL solution was placed with sufficient time, all the 1H NMR peaks of the azophenolic anion shifted downfield, but no new signals appeared in the upfield region. The reason for this was easily identified as the stimuli in the air, such as CO2 and moisture. When pure CO2 was bubbled through the IL CHCl3 solution, the solution color changed from its original orange to light orange, but could not change further to faint yellow, which ruled out CO2 gas as a stimulus. When a small amount of water was gradually added to the IL solution (MeCN solvent), the absorption band around 474 nm decreased, coupled with an increase in the absorption band around 347 nm. This was accompanied by a color change from orange to faint yellow, which was almost identical to the self-responsive process in CHCl3 and CCl4. Moreover, two cuvettes of IL CHCl3 solution were placed under relative humidities of 28% and 100%, respectively; the IL CHCl3 solution required a much longer time to exhibit a complete color change from orange to faint yellow under a lower relative humidity, demonstrating that moisture is the most likely stimulus triggering the self-responsive color change of the IL solution. As revealed by the Gaussian 09 program at the B3LYP/6-31++G(p, d) level, the distance between the oxygen atom on the azophenolic anion and the hydrogen atom on the H2O molecule was 0.174 nm, and the corresponding angle was 171.12°. Furthermore, the atomic dipole moment corrected Hirshfeld (ADCH) charge of the oxygen atom on the azophenolic anion was −0.52, and it increased to −0.62 after the azophenolic anion interacted with the H2O. Reduced density gradient analysis revealed that the spike corresponding to O∙∙∙H―O for the IL-H2O complex was located at around −0.04 a.u.. All the above data indicate that the presence of hydrogen bonding rendered the IL solution responsive to the moisture stimulus, and this response was accompanied by a color change that was visible to the naked eye. To the best of our knowledge, this is the first demonstration of a colorimetric change in an IL solution in response to moisture. We hope this work can help us to gain insight into some seemingly abnormal phenomena that occur during the research process.
论文
亮氨酸拉链型脂肽对脂质体温敏性调节的分子模拟
许谢君, 肖兴庆, 徐首红, 刘洪来
2019, 35(6): 598-606  doi: 10.3866/PKU.WHXB201806034
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含亮氨酸拉链型脂肽的温敏性脂质体被认为是抗癌药物的优良载体。亮氨酸拉链型脂肽的主要氨基酸残基序列为[VAQLEVK-VAQLESK-VSKLESK-VSSLESK],嵌入脂质体后可以有效改善脂质体的温敏性。本文首先采用隐式溶剂副本交换分子动力学方法,对N端修饰的亮氨酸拉链单链的折叠状态进行了模拟,得到了亮氨酸拉链单链的转变温度。并对包含该种新型亮氨酸拉链型脂肽的DPPC脂质体进行常规分子动力学模拟,研究了2种不同头基的亮氨酸拉链型脂肽(ALA,C3CO)二聚体嵌入后DPPC脂质体的相转变温度变化,证明了亮氨酸拉链型脂肽对于该脂质体温敏性的控制作用。利用这一规律,可以对亮氨酸拉链型脂肽进行优化改良,得到效果更佳的温敏脂质体,对于抗癌药物载体的开发有着重要的意义。
Ni/SiO2在甲烷部分氧化反应中的稳定性:W修饰的影响
连孟水, 王雅莉, 赵明全, 李倩倩, 翁维正, 夏文生, 万惠霖
2019, 35(6): 607-615  doi: 10.3866/PKU.WHXB201805054
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甲烷部分氧化制合成气反应(POM)是天然气、页岩气资源利用的重要途径之一,常用的Ni/SiO2催化剂在反应中易发生表面积炭而失活。为了解决这一问题,我们采用尿素沉淀法制备W修饰的Ni基催化剂,并考察其在POM反应中的稳定性和W的作用。结果表明,催化剂中适量W的存在可显著改善其POM反应稳定性。其原因为Ni-W作用修饰了Ni的化学态或其亲氧能力,从而改善了其表面抗积炭能力。此外,反应中催化剂表面形成的α-WC具有一定的抑制表面积炭形成的能力,且该α-WC具有良好的稳定性。
LaCoO3-TiO2纳米管阵列的构筑及可见光光催化性能
弓程, 向思弯, 张泽阳, 孙岚, 叶陈清, 林昌健
2019, 35(6): 616-623  doi: 10.3866/PKU.WHXB201805082
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TiO2纳米管阵列具有较高的光催化活性,但可见光吸收弱,限制了其太阳能利用和环境应用。窄带隙的钙钛矿(ABO3)型氧化物能够吸收大范围波段的可见光,且稳定性高,但光催化活性低。本文首先采用溶胶-凝胶法合成了LaCoO3纳米颗粒,然后利用电泳沉积技术将LaCoO3纳米颗粒修饰于TiO2纳米管阵列表面,构筑了LaCoO3-TiO2纳米管阵列。扫描电子显微镜(SEM)、透射电子显微镜(SEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)的表征结果显示溶胶-凝胶法合成的纳米颗粒为LaCoO3,其尺寸均匀,结晶度高,平均粒径约为100 nm。LaCoO3纳米颗粒与TiO2纳米管阵列之间的结合力好。紫外可见吸收光谱(DRS)显示,随着电泳沉积时间的延长,LaCoO3-TiO2纳米管阵列的吸收带边逐渐红移700 nm。可见光下光催化降解甲基橙(MO)的结果表明,电泳沉积15 min制得的LaCoO3-TiO2纳米管阵列对MO的光催化效率最高,其降解速率是相同条件下TiO2纳米管阵列的4倍。光致发光光谱和电化学阻抗谱证实LaCoO3纳米颗粒的负载有效地促进了光生电荷的分离和传输,可见光光催化活性明显增强。
基于金银合金薄膜的高灵敏度宽光谱表面等离子体共振成像传感器
梁爽, 高然, 张萌颖, 薛宁, 祁志美
2019, 35(6): 630-636  doi: 10.3866/PKU.WHXB201806082
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报道了一种基于金银合金薄膜的宽光谱表面等离子体共振成像(SPRI)传感器,该传感器能够对吸附在薄膜局部或整个表面上的生化分子进行原位定量检测,而且与常规的金膜SPRI传感器相比,检测成本更低,检测灵敏度更高。利用质量比1 : 1的金银合金溅射靶在玻璃基板上淀积了厚约50 nm的均匀的金银合金薄膜。利用实验室自制的Krestchmann结构多功能平台在不同入射角下测试了金银合金薄膜被纯水覆盖后的SPR光谱和SPR彩色图像。基于色相算法计算获得了每个SPR彩像的二维色相分布及其平均色相,从而使得宽光谱SPRI传感器能够利用平均色相作为灵敏度参数进行定量检测。实验确定了平均色相对溶液折射率(RI)变化和分子吸附最为敏感的光谱区间是595–610 nm之间。在这个窄光谱范围内,平均色相与共振波长呈线性关系,其斜率为Δhue/ΔλR = 7.52 nm-1,这意味着基于色相的RI灵敏度是基于共振波长的RI灵敏度的7.52倍,这一结论已被实验证明。将SPRI传感器的起始共振波长设定在色相敏感光谱区间内之后,实验测得基于色相的RI灵敏度为S = 29879 RIU-1,比在相同条件下测得的金膜SPRI的灵敏度高8倍。利用时间分辨宽光谱SPRI方法实时监测了牛血清白蛋白(BSA)分子在金银合金薄膜表面的非特异性吸附,从实验测得的平均色相随时间的变化曲线可知BSA吸附达到平衡所需时间约15 min。研究结果表明,基于金银合金薄膜的SPRI传感器具有动态定量检测蛋白质分子吸附过程的功能。
小尺寸金石墨纳米颗粒的合成与表征
刘芳, 张鲁凤, 董倩, 陈卓
2019, 35(6): 651-656  doi: 10.3866/PKU.WHXB201805037
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在表面增强拉曼光谱(SERS)的研究领域中,基于局域表面等离子体共振效应的等离子体SERS基底的制备成为过去几十年的研究热点。然而,通常开发的等离子体金属基底具有较差的稳定性和重现性。对于SERS而言,石墨烯类材料具有拉曼化学增强效应,除此之外,还具有分子富集、强的稳定性与荧光猝灭能力等优点,因此基于石墨金属复合纳米材料的SERS基底受到了研究人员的重视。我们利用化学气相沉积(CVD)法制备了小尺寸的金石墨核壳纳米颗粒(Au@G),其粒径约为17 nm。我们通过在Au NP上包覆介孔二氧化硅来控制Au@G的尺寸,同时还研究了包覆二氧化硅过程中,正硅酸乙酯(TEOS)的浓度对于石墨壳层形成的影响。结果表明当TEOS在一定浓度范围内,其浓度的降低有利于得到石墨化程度高的Au@G。进一步利用Au@G对结晶紫分子进行拉曼检测,也表明了Au@G具有较好的拉曼增强效果。这种小尺寸的Au@G在分子检测与细胞成像分析领域中具有广泛的应用潜力。
ARTICLE
Stabilization of the E/Z Configuration for Cyanostilbene-based Luminogens by Enhanced Charge Transfer Excited State
Yujie DONG, Chendong XU, Shizhao WANG, Weijun LI, Qingbao SONG, Cheng ZHANG
2019, 35(6): 637-643  doi: 10.3866/PKU.WHXB201807004
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The E/Z isomerization reaction is found extensively in most organic molecules containing double bond unit. This limits their practical application as luminescent materials partly, especially under photoirradiation. Therefore, it is important to obtain E/Z isomers with stable configuration in the excited state after photoirradiation. It is well known that cyanostilbene and its analogues play an important role in the development of organic opto/electronic materials. The substituted cyano group on C=C double bonds has strong electron-withdrawing ability and large steric hindrance, which benefits the formation of donor-acceptor (D-A) structures and formation of intramolecular charge transfer. In our previous work, we reported a triphenylamine-cyanostilbene molecule (TPNCF) formed by modifying the cyanostilbene structure with triphenylamine, which maintained a stable E/Z configuration as a film and in high polar solvents. According to solvatochromism mechanisms and the results of theoretical calculations, we proposed that the charge transfer (CT) excited state between the triphenylamine donor and cyanostilbene acceptor groups induced the stable configuration of the E- and Z- isomers under photoirradiation. Under irradiation, the E/Z isomerization process occurring at a higher energy locally excited (LE) state was suppressed by a rapid internal conversion process from the LE to CT state. This work inspired us to provide a universal and effective molecular design strategy by modifying D-A substituents on double bonds that can successfully stabilize E/Z isomers. To further confirm that the CT excited state induced stable E- and Z- isomers in the cyanostilbene structure under photoirradiation, we designed and synthesized a donor-acceptor phenoxazine-cyanostilbene molecule (PZNCF) and successfully characterized its two E/Z isomers. In comparison with the reported TPNCF molecule, the in-situ NMR and UV spectra of E- and Z- isomers of PZNCF demonstrated that the E/Z isomerization rate became slower under photoirradiation, which indicated that the stronger electron-donating group of phenoxazine substituted in the cyanostilbene structure induced a more stable E/Z isomer configuration in its excited state. DFT calculations and photophysical results indicated that a stronger CT state was generated in both E- and Z- isomers of PZNCF. This further confirmed our hypothesized mechanism where the stable E/Z configuration can be obtained under photoirradiation by forming a suitable donor-acceptor structure to suppress the E/Z isomerization reaction in the LE state by a rapid internal crossing process from the LE to CT state. This molecular design strategy is of great significance to organic photochemistry and photoelectronics for molecules with double bond units.
Self-Conversion from ZnO Nanorod Arrays to Tubular Structures and Their Applications in Nanoencapsulated Phase-Change Materials
Yingjie FENG, Jinping WANG, Lili LIU, Xidong WANG
2019, 35(6): 644-650  doi: 10.3866/PKU.WHXB201805068
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In the emerging field of nanoscience, tubular structures have been attracting remarkable interest due to their well-defined geometry, high specific area, and exceptional physical and chemical properties. Among them, oriented ZnO tubular arrays are regarded as promising candidates for various applications such as optoelectronics, solar cells, sensors, field emission, piezoelectrics, and catalysis. Although template-directed and selective dissolution synthesizing strategies are commonly used to prepare ZnO nanotubes, repeatability and large scale preparation are still challenging. In this study, ZnO nanotube arrays were controllably prepared by tuning the hydrothermal parameters, without the use of any additives. The mechanism underlying the self-conversion of ZnO nanorods to nanotubes was comprehensively studied based on the surface energy theory. It has been proved that the metastable top surface of the ZnO nanorods dissolves preferentially to reach a stable state during the hydrothermal growth. The specific surface energy of different crystal faces of ZnO nanorods was calculated using molecular dynamics simulation. The top surface of the ZnO nanorod, the Zn-terminated [0001] face, demonstrated much higher surface free energy than did the lateral faces, which indicated that the self-dissolution of top face (002) is energetically favorable. The self-conversion behavior of ZnO nanorod arrays with different diameters was specifically investigated by adjusting the initial precursor concentration, density of the crystal seed layers, and growth time. The dissolution-crystallization equilibrium concentration, determined by crystal surface energy, was found to be a key factor for the formation of the tubular structure. Notably, the critical equilibrium conditions for the self-conversion of ZnO nanorods to nanotubes, including zinc ion concentration and pH, have been identified by studying parameters corresponding to the dissolution-crystallization equilibrium for the metastable top surface of the ZnO nanorods. The preparation of the ZnO nanotube arrays was successfully accelerated and simplified via two-step procedure: (1) preparation of ZnO nanorod arrays and (2) self-conversion of ZnO nanorods to nanotubes. The preparation method based on the self-conversion mechanism from rods to tubes for polar oxides is simpler and more easily controllable as compared to the reported methods involving variety of additives. Because of the advantages of adaptability to a wide range of substrates, excellent conducting properties, and filling ability, the prepared ZnO nanotube array films were used in encapsulating phase-change materials. The encapsulated phase-change material exhibited excellent heat storage/release properties and heat conductivities. This indicates the potential application of precision devices for temperature control.

亮点
同分异构的胶体硫化镉半导体幻数团簇的可逆转化
刘忠范
2019, 35(5): 451-452  doi: 10.3866/PKU.WHXB201807016
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异原子占据Ag原子簇的中心核用于催化CO2生成碳碳键的反应
侯文华
2019, 35(5): 453-454  doi: 10.3866/PKU.WHXB201807017
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基于Au@PPy核壳结构纳米粒子自组装阵列的可程序化负微分电阻效应研究
韩布兴
2019, 35(5): 455-456  doi: 10.3866/PKU.WHXB201807063
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摘要:
当期推荐
弛豫时间分布法分解固体氧化物燃料电池电化学阻抗谱
庄林
2019, 35(5): 457-458  doi: 10.3866/PKU.WHXB201807065
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摘要:
电荷驱动水中氧化物纳米颗粒自组装的原位透射电子显微镜研究
吴凯
2019, 35(5): 459-460  doi: 10.3866/PKU.WHXB201807077
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摘要:
综述
有机太阳能电池中基于苝二酰亚胺结构小分子受体进展
邓祎华, 彭爱东, 吴筱曦, 陈华杰, 黄辉
2019, 35(5): 461-471  doi: 10.3866/PKU.WHXB201806073
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摘要:
最近几年,有机太阳能电池中的非富勒烯小分子受体研究引起了人们的兴趣。其中,苝二酰亚胺(PDI)类分子因具有良好的电子传输能力,较强的电子亲和力,稳定的光、热、化学性能以及化学结构的可设计性带来的性能可调控性而得到广泛的关注。本文总结了近三年来在体异质结有机太阳能电池应用方面PDI小分子受体的研究进展,重点关注了PDI分子结构对其性能的影响,希望为以后PDI类受体分子的设计思路起到一定的启发作用。
碳基非贵金属氧还原电催化剂的活性位结构研究进展
杨晓冬, 陈驰, 周志有, 孙世刚
2019, 35(5): 472-485  doi: 10.3866/PKU.WHXB201806131
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摘要:
以热解型Fe/N/C为代表的碳基非贵金属材料被认为是当前最具潜力替代铂的非贵金属氧还原催化剂,其综合性能的进一步突破,对于推动质子交换膜燃料电池商业化应用具有重要意义。对热解型Fe/N/C催化剂活性位结构的深入认识是实现催化剂高活性位密度和高稳定性理性设计的关键。本文总结了热解型Fe/N/C活性位的研究进展,重点介绍了非晶态铁氮配位活性中心、氮掺杂和碳缺陷三类活性位构型。由于热解型Fe/N/C是非均相的,结构非常复杂,导致在活性位认识上还存在诸多争议,本文总结阐述了活性位结构的不同观点。最后,我们展望了Fe/N/C催化剂活性位研究的未来方向。
论文
正十二烷高温机理简化及验证
卢海涛, 刘富强, 王于蓝, 王成冬, 范雄杰, 刘存喜, 徐纲
2019, 35(5): 486-495  doi: 10.3866/PKU.WHXB201806081
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摘要:
由于详细化学反应机理在模拟燃烧室燃烧时,计算量极大,很难被广泛运用。为了满足工程设计要求,采用替代燃料的简化机理进行计算不失为一种行之有效的方法。本文基于误差传播的直接关系图法和敏感性分析法对正十二烷180组分1962步高温机理(温度大于1100 K)进行简化,获得40组分234步化学反应机理。在温度为1100–1650 K,压力为0.1–4 MPa条件下,采用简化机理及详细机理对不同当量比、压力下着火延迟时间进行模拟,模拟结果与实验数据吻合得较好。通过对不同压力及温度下火焰传播速度进行模拟,验证了简化机理能够正确地反映正十二烷的燃烧特性。利用C12H26/OH/H2O/CO2等重要组分随时间变化的数据,验证了简化机理能够准确描述燃烧过程反应物消耗、基团变化、生成物产生的过程,并表明该机理具有较高的模拟精度。利用该简化机理对本生灯进行数值分析,结果表明该机理能够准确地反映火焰区温度和组分浓度的变化。紧凑的正十二烷高温简化机理不仅能够正确体现其物理化学特性,而且能够用于三维数值模拟,具有较高的工程运用价值和应用前景。
固体氧化物燃料电池电化学阻抗谱差异化研究方法和分解
施王影, 贾川, 张永亮, 吕泽伟, 韩敏芳
2019, 35(5): 509-516  doi: 10.3866/PKU.WHXB201806071
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摘要:
电化学阻抗谱技术(EIS)在固体氧化物燃料电池(SOFC)中已获得广泛应用。在EIS分析过程中,研究者能够清楚地获得燃料电池内部因纯离子(电子)导电引起的欧姆电阻和因电化学过程、扩散作用引起的极化阻抗的大小,但是对于极化阻抗的构成缺乏进一步解析。本文选用传统的Ni-YSZ阳极支撑电池,通过改变测试温度、阳极运行气氛和阴极运行气氛,设计了一套完整的阻抗差异分析(ADIS)实验。并基于弛豫时间分布法(DRT)和阻抗差异分析法,系统地分析并解释了阻抗谱中各频率段对应阻抗的物理或(电)化学含义,将该类型电池阻抗谱以6个RQ并联电路予以拟合,为之后燃料电池性能稳定性的研究奠定基础。
原位透射电子显微镜观察电荷驱动的氧化物纳米颗粒水中自组装
赵喆, 卢岳, 张振华, 隋曼龄
2019, 35(5): 539-545  doi: 10.3866/PKU.WHXB201806012
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摘要:
以四氧化三钴Co3O4纳米棒为研究对象,我们利用液体环境透射电子显微镜,原位观察了四氧化三钴纳米棒在水中的自组装过程。研究发现在电子束辐照的水环境下,四氧化三钴纳米棒的晶面存在互补式自组装现象。随着纳米棒之间的距离越来越近,纳米棒之间的相对运动速率逐渐增加,纳米棒之间的相互作用力逐渐增加。通过进一步分析纳米棒的形貌发现,纳米棒的暴露晶面大多数为{100}、{110}以及{111}晶面,而Co3O4属于极性氧化物,这些晶面往往会带有一定的电荷。在液体环境下,正是由于这些易暴露面都带有不同大小的电荷,在晶面电荷的驱动下,电荷属性相反的四氧化三钴纳米棒会互相吸引,形貌结构上进行互补,实现快速驱动的纳米棒之间自组装。
ARTICLE
Perylenediimide: Phosphonium-Based Binary Blended Small-Molecule Cathode Interlayer for Efficient Fullerene-Free Polymer Solar Cells with Open Circuit Voltage to 1.0 V
Monika GUPTA, Dong YAN, Fugang SHEN, Jianzhong XU, Chuanlang ZHAN
2019, 35(5): 496-502  doi: 10.3866/PKU.WHXB201805101
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摘要:
The fabrication of high-efficiency organic solar cells requires a cathode interlayer (CIF) having multiple properties such as forming an ohmic contact with the active layer, high electron conductivity, low-density traps, and hole blocking. These roles can be more completely fulfilled by using a suitable binary blended CIF rather than a single molecule based CIF. In this article, we present the roles by using binary blended PDINO (amino N-oxide perylene diimide) and QPhPBr (tetraphenylphosphonium bromide) as the CIF to fabricate fullerene-free polymer solar cells (PSCs) with PBDB-T:IDTBR, a new donor: acceptor combination, as the active layer. The high-lying lowest unoccupied molecular orbital of the acceptor and the low-lying highest occupied molecular orbital (HOMO) of the polymer with small driving force (the donor-acceptor HOMO-HOMO energy offset, ∆HOMO) for the hole transfer, both result in a high open circuit voltage (Voc). Moreover, our strategy to insert a dual mixed solution of CIF over the blended active layer better facilitates the role, which significantly improves charge extraction and collection, leading to the high Voc, short-circuit current density (Jsc), and fill factor (FF) observed in comparison to a single CIF material. It was observed that the power conversion efficiency (PCE) increases to 8.27%, with a high Voc of 1.0 V, using a binary mixture of CBL. Such tremendous improvements in Voc using well known polymer donors have not been reported till date in binary solar cell systems. This idea demonstrates that the minimum energy loss because of the small ∆HOMO of the D-A combination and the use of a dual mixed layer of CBL together present the future prospects of non-fullerene photovoltaic devices for researchers.
Bandgap Modulation of Dithienonaphthalene-Based Small-Molecule Acceptors for Nonfullerene Organic Solar Cells
Meiqi ZHANG, Yunlong MA, Qingdong ZHENG
2019, 35(5): 503-508  doi: 10.3866/PKU.WHXB201805151
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摘要:
By using photovoltaic technology, ambient solar light can be directly converted to electricity. The photovoltaic technology has been regarded as one of the most important and promising strategies to resolve the worldwide energy and pollution problems. As one type of photovoltaic technology, polymer solar cells have attracted increasing interest due to their advantages of solution processing capability, low-cost, feasibility to be fabricated on flexible substrates etc. Not until a few years ago, the fullerene derivatives had been dominated the organic photovoltaic field as the most promising acceptor materials for polymer solar cells. However, fullerene-based polymer solar cells have a power conversion efficiency bottleneck due to the relatively fixed energy levels as well as the fixed bandgaps of fullerene derivatives. Therefore, researchers started to develop nonfullerene acceptors which can be used as alternatives to replace the traditional fullerene derivatives. Compared to the fullerene derivatives, nonfullerene acceptors offer several advantages such as stronger light absorption, tunable bandgaps and frontier molecular orbital energy levels. For nonfullerene acceptors, a ladder-type fused ring is usually used as the central core which is an essential building block to tailor the bandgaps and energy levels. Although many fused ring systems have been explored for efficient nonfullerene acceptors, ladder-type angular-shape dithienonaphthalene is seldom reported as the donor unit for nonfullerene acceptors. Furthermore, the impact of thiophene bridge on the optical and photovoltaic properties of the dithienonaphthalene-based nonfullerene acceptors has never been reported. In this context, we report on the design and synthesis of a dithienonaphthalene-based small-molecule acceptor which contains thiophene bridges in between the acceptor terminals and the fused-ring donor core. Compared to the dithienonaphthalene-based small-molecule without the thiophene bridges, the resulting acceptor (DTNIT) exhibits a reduced bandgap of 1.52 eV which makes it more suitable to be blended with the benchmark large bandgap copolymer, poly[(2, 6-(4, 8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1, 2-b: 4, 5-b']dithiophene))-alt-(5, 5-(1', 3'-di-2-thienyl-5', 7'-bis(2-ethylhexyl)benzo[1', 2'-c:4', 5'-c']dithiophene-4, 8-dione)] (PBDB-T). The reduced band-gap of the resulting nonfullerene acceptor can be attributed to its extended π-conjugation in comparison with the dithienonaphthalene-based acceptor without the thiophene bridges. Inverted polymer solar cells with a device configuration of indium tin oxide/ZnO/PBDB-T:DTNIT/MoO3/Ag were fabricated and characterized. Polymer solar cells based on PBDB-T:DTNIT showed an open circuit voltage of 0.91 V, an enhanced short circuit current of 14.42 mA∙cm−2, and a moderate PCE of 7.05% which is comparable to the PCE of 7.12% for the inverted device based on PBDB-T:PC71BM. Our results not only provide a method to synthesize efficient nonfullerene acceptors with reduced bandgaps, but also offer a bandgap modulation strategy for nonfullerene acceptors.
Effect of Ink Solvents on Low-Pt Loading Proton Exchange Membrane Fuel Cell Performance
Wenhui CHEN, Shengli CHEN
2019, 35(5): 517-522  doi: 10.3866/PKU.WHXB201806011
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Owing to the scarcity of platinum, it is of high importance to develop electrodes with low platinum metal loading and to thereby improve the utilization of Pt for the commercialization of proton-exchange membrane fuel cells (PEMFCs). In comparison to conventional high-platinum electrodes, the thickness of the catalyst layer (CL) is thinner and the interatomic Pt spacing is larger for the low-Pt loading electrodes. The distribution of electrolyte ionomer and the electrode morphology, which are strongly influenced by the solvents used in the fabrication process, are therefore increasingly important factors for achieving high performance in the membrane electrode assembly (MEA). In this work, different solvents with various dielectric constants and evaporation rates were used to prepare the inks for low-Pt loading cathode (0.1 mg·cm-2) fabrication. First, the inks were fabricated by dispersing the catalyst and ionomer in different solvents which were then coated onto carbon paper to prepare the gas diffusion electrodes. The anode and cathode electrodes were then hot-pressed together with the Nafion membrane to produce the MEAs. The results showed a mixture of isopropanol-water (4:1) yielded the best-performing MEA during the single-cell tests compared to the other solvents tested. In order to elucidate the relationship between the performance of MEAs and the solvents, the structure and the surface morphology of the CL and the distribution of Nafion ionomer in the CL was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A comparison of the SEM and TEM images of representative samples indicated that the best performing electrode had a much improved homogeneity in the surface morphology as well as the dispersion of catalyst and ionomer. This was because of the moderate evaporation rate and better dispersion, caused by the increased hydrogen bonding and high dielectric constant, respectively. The results from dynamic light scattering (DLS) showed that the size of the catalyst and ionomer aggregates are influenced by the solvents. It is suggested that larger aggregates might help the formation of holes in the CL for gas diffusion and water removal, with the optimum size found to be around 400–800 nm. In conclusion, the MEA fabricated from the isopropanol-water solvent exhibited a significantly increased power density (1.79 W·cm-2), and the utilization of Pt was increased to approximately 0.047 mg·W-1, which is among the best-performing fuel cells reported to date.
Molybdenum Carbide Prepared by a Salt Sealing Approach as an Electrocatalyst for Enhanced Hydrogen Evolution Reaction
Zhou LIN, Linfan SHEN, Ximing QU, Junming ZHANG, Yanxia JIANG, Shigang SUN
2019, 35(5): 523-530  doi: 10.3866/PKU.WHXB201806191
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摘要:
Molybdenum carbide is regarded as an excellent substitute for Pt-based catalysts in the hydrogen evolution reaction (HER), owing to its low cost, superior catalytic performance, and long-term stability. In this work, salt-sealed molybdenum carbide was prepared using sodium molybdate and 2, 6-diaminopyridine as the reactive raw materials, followed by continuous salt sealing and calcination of the precursor under an inert atmosphere. The morphology, composition and structure of salt-sealed molybdenum carbide were determined by scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results indicate that salt-sealed molybdenum carbide has irregular morphology and includes nanoparticles and nanorods. A comparison of the TEM images of Mo2C with salt sealing (Mo2C/SS) and Mo2C without salt sealing (Mo2C) indicates that Mo2C/SS exhibits a smaller particle size. This suggests that salt sealing can efficiently avoid particle aggregation. The Brunauer-Emmett- Teller (BET) specific surface area of the catalysts was obtained from nitrogen adsorption/desorption isotherms. The increase in BET surface area from 2.55 to 8.14 m2·g−1 after salt sealing provides evidence for the formation of pores in the product. The results of XRD, EDS and XPS analyses show that Mo2C/SS has an orthorhombic crystal structure with molybdenum oxides on the surface, which may originate from surface oxidation. Considering the results of XPS and the turnover frequency (TOF) calculation, we can conclude that the formation of pores via salt sealing contributes to the exposure of more active sites, while simultaneously enlarging the contact area with oxygen. Therefore, higher molybdenum oxide content is generated on the surface, resulting in a lower proportion of active centers (molybdenum carbides) on the catalyst surface. Furthermore, the pseudocapacitance generated by the faradaic reaction of molybdenum oxides is superimposed on the double-layer capacitance of Mo2C catalysts, which increases the double layer capacitance. Since the effect of pseudo-capacitance on Mo2C/SS is more significant, the TOF number declines after salt sealing. Compared with Mo2C, Mo2C/SS exhibits three features that promote HER mass activity: (1) the generation of large quantities of pores via salt sealing leads to an increase in the BET surface area and exposure of more active sites, which is beneficial for improving HER performance; (2) the porous structure and enlarged surface area pave the way for effective mass and charge transfer; (3) the decrease of the Tafel slope from 145 to 88 mV·dec−1. In summary, salt-sealed Mo2C exhibited enhanced HER activity with an overpotential of 175 mV to achieve a current density of 10 mA·cm−2. The Tafel slope for HER on salt-sealed Mo2C is 88 mV·dec−1. This can be considered as the proof of the Volmer-Heyrovsky mechanism with electrochemical desorption as the rate-determining step.
Reactivities of VO1–4+ Toward n-CmH2m+2 (m = 3, 5, 7) as Functions of Oxygen Content and Carbon Chain Length
Yue ZHAO, Jiatong CUI, Jichuang HU, Jiabi MA
2019, 35(5): 531-538  doi: 10.3866/PKU.WHXB201805231
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Vanadium oxides are one of the most important heterogeneous catalysts that are widely used to oxidize hydrocarbon molecules into value-added chemicals. In order to reveal the mechanisms and the nature of active sites, numerous experimental and theoretical studies have been reported on the reactivities of gas-phase vanadium oxide clusters toward small molecules. However, there has been very limited research on the chemical reactivity changes associated with the oxygen contents of vanadium oxides and the carbon chain lengths of alkanes. In this work, the reactions of vanadium oxide ions VO1−4+ with alkanes (n-CmH2m+2, m = 3, 5, 7) were systematically investigated by time-of-flight mass spectrometry and the reactions of VO1−3+ with pentane were further studied by density functional theory calculations. Experimental results show that in the reactions of VO+, VO3+, and VO4+ with n-C5H12, in addition to the major adsorption processes, the activation of the C―H and C―C bonds of n-C5H12 was observed. The activation of both the bonds was observed experimentally during the reaction of VO2+ with n-C5H12 with large branching ratios. Among the vanadium oxide cations studied, VO2+ shows the strongest oxidizability and the generation of lighter alkanes and alkenes dominates the reactions; VO+ is more reactive than VO3+. VO4+ pocesses only one η2-O2 unit. Due to the weak bond between VO2+ and η2-O2, the η2-O2 unit is released in VO4+/n-C5H12 system leading to the formation of VO2+; thus VO4+ cations reflect some reactivity of VO2+. Although the oxidation states in the vanadium oxide clusters increase from +Ⅲ in VO+ to +Ⅴ in VO2+ and +Ⅳ in VO3+, the reactivity does not gradually increase. Moreover, the reactivity of the mononuclear vanadium oxide cations also does not exhibit a gradually increasing trend with the increase in oxygen content. Based on the observed reactivity trend, the adsorption channels gradually become weak as the carbon chain lengths increase; meanwhile, the dehydrogenation and C―C bond activation channels gradually become obvious and some oxygen transfer products appear. Therefore, much lighter fragments of alkanes/alkenes will be obtained if linear alkanes with more carbon atoms were reacted with VO1−4+. The theoretical results are generally consistent with those obtained from the experiments. The various reaction channels and versatile reactivity of the mononuclear vanadium oxide cations investigated in this study not only offer new insights into gas-phase reactions but also shed light on the processes occurring on the surfaces of the corresponding condensed-phase catalysts.
Single-Molecule Study on the Folding of OmpT in Tween-20 Micelles
Peixuan BU, Chenhui HE, Xinsheng ZHAO
2019, 35(5): 546-554  doi: 10.3866/PKU.WHXB201806072
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摘要:
The cell envelope of gram-negative bacteria consists of the outer membrane (OM), inner membrane (IM), and periplasm. The β-barrel outer membrane proteins (OMPs) embedded in the OM perform diverse and significant functions such as signaling, transporting, and proteolysis. The OMPs of gram-negative bacteria share similar folding pathways with that of mitochondria and chloroplasts. Therefore, the study of the OMP folding mechanism not only provides insights into antimicrobial drug design but also helps elucidate mitochondrial and chloroplast biogenesis. Most knowledge about OMP folding was obtained from ensemble experiments where OMPs were usually at micromolar concentrations and prone to aggregate, which is different from the physiological environment in the cells. Unlike ensemble techniques, single-molecule detection (SMD) can measure OMPs from nano- to picomolar concentrations and prevent aggregation. In this work, we investigated the folding of OmpT, one of the OMPs, in Tween-20 and n-dodecyl β-d-maltopyranoside (DDM) micelles by SMD. We prepared monodisperse OmpT and observed both unfolded and folded OmpT in Tween-20 and DDM micelles under different urea concentrations by single-molecule fluorescence resonance energy transfer (FRET). The folded OmpT in Tween-20 is structurally similar to the native OmpT folded in DDM but exhibits weaker resistance to urea. In contrast, OmpA barely folds and OmpC hardly folds in Tween-20 micelles. We confirmed that folded OmpT forms complexes with detergent micelles and estimated the number of bound Tween-20 and DDM molecules per OmpT by fluorescence correlation spectroscopy. We compared the enzymatic activity of OmpT folded in two detergents with a fluorescent peptide as substrate, and found that the folded form of OmpT in Tween-20 possesses weaker enzymatic activity than that in DDM. We also investigated the folding properties of OmpT, OmpA, and OmpC in the presence of the β-barrel assembly machine (BAM) complex. OmpT folds efficiently in liposome even without the BAM complex; OmpA only folds with the help of the BAM complex; and OmpC does not fold with or without the BAM complex. Based on the comparison of the folding of OmpT, OmpA, and OmpC in detergent micelles and in the presence of the BAM complex, we propose that OmpT has stronger folding tendency than OmpA and OmpC, which supports the idea that the exact role of the BAM complex is dependent on the distinct folding properties of individual OMPs. Since Tween-20 is a widely used reagent to block nonspecific adsorption in SMD experiments, our results also remind people to exercise caution to prevent possible wrong interpretations caused by the interaction between proteins and Tween-20.

编委会

发布时间:


《物理化学学报》第4届编委会

(按拼音排序)

名誉主编

唐有祺

北京大学

顾问编委

包信和

中国科学院大连化学物理研究所

段雪

北京化工大学

付贤智

福州大学

侯建国

中国科学技术大学

黄维

南京工业大学

LIEBER Charles M.

Harvard University

田中群

厦门大学

万立骏

中国科学院化学研究所

吴云东

北京大学

谢晓亮

Harvard University, 北京大学

杨伟涛

 Duke University

姚建年

中国科学院化学研究所

赵新生

北京大学

主编

刘忠范

北京大学

副主编

韩布兴

中国科学院化学研究所

刘鸣华

国家纳米科学中心

申文杰

中国科学院大连化学物理研究所

吴凯

北京大学

杨金龙

中国科学技术大学

庄林

武汉大学

迟力峰

苏州大学

编委

曹勇

复旦大学

陈经广

University of Delaware

陈军

南开大学

崔屹

Stanford University

邓风

中国科学院武汉物理与数学研究所

邓友全

中国科学院兰州化学物理研究所

樊卫斌

中国科学院山西煤炭化学研究所

房喻

陕西师范大学

付红兵

中国科学院化学研究所

傅强

中国科学院大连化学物理研究所

高毅勤

北京大学

郭林

北京航空航天大学

郝京诚

山东大学

侯文华

南京大学

金荣超

Carnegie Mellon University

来鲁华

北京大学

李朝军

McGill University

李隽

清华大学

李象远

四川大学

梁万珍

厦门大学

刘海超

北京大学

刘洪来

华东理工大学

刘述斌

University of North Carolina

刘义

武汉大学

刘志敏

中国科学院化学研究所

罗小民

中国科学院上海药物研究所

马晶

南京大学

孟庆波

中国科学院物理研究所

邵翔

中国科学技术大学

孙俊奇

吉林大学

谭蔚泓

湖南大学

唐智勇

国家纳米科学中心

王键吉

河南师范大学

王鹏

中国科学院长春应用化学研究所

王心晨

福州大学

王永锋

北京大学

魏子栋

重庆大学

翁羽翔

中国科学院物理研究所

吴鹏

华东师范大学

夏永姚

复旦大学

许国勤

National University of Singapore

杨俊林

国家自然科学基金委员会

余家国

武汉理工大学

尉志武

清华大学

占肖卫

北京大学

张东辉

中国科学院大连化学物理研究所

张浩力

兰州大学

张锦

北京大学

章俊良

上海交通大学

周永贵

中国科学院大连化学物理研究所

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发布时间: 2018-05-02


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发布日期:2009-06-24 浏览: