析气电极的传质过程研究

采用指示离子法研究了析气电极的传质过程。在Ｎｉ／ＫＯＨ体系中发现：ｌｇδ和ｌｇｉ的曲线斜率对于氢气泡为０．２８７，对于氧气泡则为０．５８３。用激光衍射法和激光多普勒法（ＬＤＡ）获得的气泡大小及气泡上升速度数据检测了析气电极传质过程的流体动力模型及渗透模型。结果表明，因析气效应产生的传质强化现象的机理一般不是单一的。     

电化学氢气制备耦合无机化学品电氧化的研究进展（英文）

电化学水裂解制备氢气因其固有的优势受到了广泛关注.然而,阳极氧气析出反应动力学缓慢、能耗高,极大地限制了其应用.与氧析出反应不同,一些无机化学品的电氧化无论是热力学还是动力学上都更易发生.因此,耦合氢气析出反应和无机化学品氧化在提高电化学制氢效率方面表现出巨大潜力.与氧气析出反应相比,无机化学品氧化可以显著降低过电位.同时,还可以在阳极去除污染物或制备高附加值化学品.本综合评述总结了电化学制备氢气耦合无机化学品电氧化方面的研究进展.首先,介绍并讨论一些具有代表性的无机化学替代品,如含氮的肼、一氧化氮以及含硫的硫化氢、二氧化硫等,其可以实现在很低的电压下制备氢气并且从根本上避免氧气的产生.另外,引入电化学中和能能够进一步降低电化学制备氢气电解槽的槽压,甚至可以实现在制备氢气的同时输出电力.最后,对该领域面临的挑战以及未来发展进行了展望.     

一含肉桂酸的单链Bola型两亲分子在有机溶剂中的光致二聚和聚集行为

制备了一种含肉桂酸基团的Bola型两亲分子HDC(4-(10-羟基癸氧基)-10-羟基癸氧基肉桂酸酯). 第一次观察到该分子在有机溶剂中经紫外光照发生光致二聚. 分离出来的二聚HDC在20%的乙醇/水混合溶剂中能形成球形的囊泡. 同时发现溶剂的介电常数大小与光致二聚过程密切相关, 介电常数的大小不仅关系到反应发生与否, 而且直接影响到反应的速率.     

锥形鼓泡浆液反应器内气含率和固含率轴向分布研究

在不同表观气体速度、淤浆浓度、静止液体高度和不同颗粒直径下考察了锥形鼓泡浆液反应器内气含率及固率轴向分布。由气泡聚并和破碎机理解释了气含率轴向分布规律;结合固体颗粒悬浮机理,利用沉降-扩散模型分析了操作条件影响固含率轴向分布的原因,回归出表征固含率轴向分布的特征参数——Peclet准数的数学关联式,并在相似操作条件下与园柱床内实验结果作了比较。     

预处理条件对Ag/SBA-15催化剂上甲苯催化氧化反应性能的影响

甲苯是一种典型的挥发性有机污染物.近年来,催化氧化法是一种广泛使用并具有开发潜力的有效去除挥发性有机污染物的方法,而贵金属催化剂一直是首选.介孔二氧化硅材料SBA-15具有规则孔道和较高的比表面积因而在催化领域中具有较大的应用潜力.本课题组已对一系列的SBA-15负载的纳米银催化剂的制备和低温催化氧化性能进行了研究,本文则通过研究不同预处理处理气氛对Ag/SBA-15催化剂结构以及甲苯催化氧化性能的系统研究,获得纳米银催化剂结构与甲苯催化氧化性能间的构效关系,对新催化剂的结构优化以及甲苯催化净化的低温催化剂开发具有重要的科学意义.研究表明,处理气氛明显影响了银物种和氧物种的状态,进而影响了催化剂的催化活性,先氧气(500℃)后氢气(300℃)处理的O500-H300催化剂对甲苯的反应活性明显优于在500℃氧气处理样品O500及氢气处理样品H500.由X-射线衍射和O2-程序升温脱附(TPD)可知,氧气500 oC处理使催化剂上形成大颗粒银粒子和氧化银粒子,以及大量次表层氧物种.氢气处理使催化剂形成较大的银粒子,由于未经过氧气处理,该催化剂上并没有次表层氧的生成.先氧气处理再氢气处理后催化剂上形成高分散的小粒径银粒子以及次表层氧物种,这表明低温氢气处理可以降低银粒子的尺寸并使催化剂上的银粒子得到再分散,同时不会影响次表层氧物种的形成.从催化剂的甲苯吸附和TPD实验中看出,大尺寸银粒子对甲苯具有较强的吸附性能,从而有利于甲苯在低温的催化氧化,但是在高温反应中没有优势;小尺寸银粒子虽然对甲苯的吸附能力不强,但是对分子氧有较好的吸附作用,进而增强自身与甲苯的相互作用,而且也促进了分子氧的活化,预处理中形成的次表层氧有效增强了甲苯和银粒子的相互作用,因此,先氧气后氢气处理的O500-H300样品在反应中显示出最好的甲苯催化活性.     

预处理条件对Ag/SBA-15催化剂上甲苯催化氧化反应性能的影响（英文）

甲苯是一种典型的挥发性有机污染物.近年来,催化氧化法是一种广泛使用并具有开发潜力的有效去除挥发性有机污染物的方法,而贵金属催化剂一直是首选.介孔二氧化硅材料SBA-15具有规则孔道和较高的比表面积因而在催化领域中具有较大的应用潜力.本课题组已对一系列的SBA-15负载的纳米银催化剂的制备和低温催化氧化性能进行了研究,本文则通过研究不同预处理处理气氛对Ag/SBA-15催化剂结构以及甲苯催化氧化性能的系统研究,获得纳米银催化剂结构与甲苯催化氧化性能间的构效关系,对新催化剂的结构优化以及甲苯催化净化的低温催化剂开发具有重要的科学意义.研究表明,处理气氛明显影响了银物种和氧物种的状态,进而影响了催化剂的催化活性,先氧气(500°C)后氢气(300°C)处理的O500-H300催化剂对甲苯的反应活性明显优于在500°C氧气处理样品O500及氢气处理样品H500.由X-射线衍射和O2-程序升温脱附(TPD)可知,氧气500 oC处理使催化剂上形成大颗粒银粒子和氧化银粒子,以及大量次表层氧物种.氢气处理使催化剂形成较大的银粒子,由于未经过氧气处理,该催化剂上并没有次表层氧的生成.先氧气处理再氢气处理后催化剂上形成高分散的小粒径银粒子以及次表层氧物种,这表明低温氢气处理可以降低银粒子的尺寸并使催化剂上的银粒子得到再分散,同时不会影响次表层氧物种的形成.从催化剂的甲苯吸附和TPD实验中看出,大尺寸银粒子对甲苯具有较强的吸附性能,从而有利于甲苯在低温的催化氧化,但是在高温反应中没有优势;小尺寸银粒子虽然对甲苯的吸附能力不强,但是对分子氧有较好的吸附作用,进而增强自身与甲苯的相互作用,而且也促进了分子氧的活化,预处理中形成的次表层氧有效增强了甲苯和银粒子的相互作用,因此,先氧气后氢气处理的O500-H300样品在反应中显示出最好的甲苯催化活性.     

铝和水反应实验的改进

从铝的电极电势可知,理论上铝能和水反应产生氢气;同时,汞齐化的铝片在潮湿的空气中可与氧气发生反应。基于以上原理,笔者改进并设计了铝和水反应的连续实验。     

聚联乙炔囊泡负载的Bola型两亲分子识别三聚氰胺过程中Chaotrope促进型显色机制及热力学

用聚联乙炔囊泡为载体,将bola型两亲分子1,12-二乳清酸十二胺盐(DDO)对三聚氰胺的分子识别作用用肉眼可见的颜色变化显示出来.通过比较不同碳链长度的聚联乙炔囊泡对分子识别过程的反映,发现二十三烷基-2.4-二炔酸(TCDA)囊泡的显色灵敏度较高.研究表明,TCDA肉眼可见的颜色变化来自于DDO与三聚氰胺多重氢键的形成以及溶液环境中水结构的变化.为了更好地理解显色机理,用差示扫描量热(DSC)仪详细研究了分子识别过程中聚联乙炔囊泡的相变行为及热力学参数.结果表明:TCDA囊泡和带有识别分子的DDO/TCDA囊泡在三聚氰胺存在下,相变温度Tm均向高温方向移动,并且,随三聚氰胺浓度的增加,Tm值逐渐增大直至囊泡瓦解;但是Tm值的变化没有与囊泡变色必然关联,仅仅DDO/TCDA囊泡具有变色现象,而且,只有当三聚氰胺的浓度超过分子识别氢键形成所需理论量时,肉眼才能可见明显的由蓝到红的颜色变化.为了理解溶液中过量的三聚氰胺对囊泡变色的作用,选用蔗糖和尿素作为典型的水结构促进剂和水结构破坏剂(chaotrope),详细研究了它们对聚联乙炔囊泡反映分子识别过程中相变温度的影响及显色规律.结果表明,过量的三聚氰胺在溶液中起到类似尿素水结构破坏剂的作用.这种作用和分子识别过程中多重氢键的形成对聚联乙炔囊泡的变色缺一不可.本研究首次揭示了由水结构破坏剂参与的聚联乙炔囊泡变色机理,有助于理解共轭聚合物热相变过程中的Hofmeister效应.     

电场下离子型聚合物复合囊泡结构变化的分子动力学模拟

利用粗粒化分子动力学模拟研究了电场作用下离子型聚合物复合囊泡形变与破裂的过程.定量分析了囊泡破裂过程中的结构变化,包括囊泡的形变程度、破裂速度、组分分布以及破裂后的结构.研究表明,电场强度较弱时,囊泡表面所吸附的聚电解质首先脱落,囊泡由球形结构转变为椭球结构.随着电场强度增大,离聚物的离子侧基发生重新排布,囊泡表面电荷的有序结构被破坏,导致囊泡的结构无法维持而破裂,囊泡塌缩,分裂形成离聚物团簇,并进一步破裂为小尺寸的离聚物聚集体,均匀分散于溶液中.本文利用分子动力学模拟明确了电场中离子型高分子复合囊泡破裂过程的分子机理,为药物释放技术的优化及发展提供了理论支持.     

第二配位层的氧化还原活性二茂铁促使铁卟啉在氧存在下发生质子还原

采用洁净、可持续的替代能源以解决化石燃料的过度消耗及因其燃烧而导致的日益加剧的全球变暖问题已经成为当务之急.其中,如何实现在大气含氧条件下的析氢反应成为需要攻克的重大挑战.氧还原在热力学上比质子还原更容易进行,并且氧气部分还原时通常产生活性氧物种,致使催化剂失活.因此,需要开发在氧气存在情况下能够有效还原质子的催化剂.本文设计了一种四苯基铁卟啉分子,该分子通过三氮唑将四个二茂铁连接在苯基邻位,并证明该催化剂能够在有氧气的情况下高效还原质子,产生氢气.作为铁卟啉类化合物催化质子还原的活性物种,Fe(0)发生质子还原比发生O2还原的动力学速率快得多,从而为氧气存在下的选择性质子还原奠定了基础.     

A dual electrolyte H2/O2 planar membraneless microchannel fuel cell system with open circuit potentials in excess of 1.4 V

A dual electrolyte H2/O2 fuel cell system employing a planar microfluidic membraneless fuel cell has been investigated and compared to single electrolyte H2/O2 systems under analogous conditions. The fuel is H2 dissolved in 0.1 M KOH (pH 13), and the oxidant is O2 dissolved in 0.1 M H2SO4 (pH 0.9), comprising a system with a calculated thermodynamic potential of 1.943 V (when 1 M H2 and O2 concentrations are assumed). This value is well above the calculated thermodynamic maximum of 1.229 V for an acid, or alkaline, single electrolyte H2/O2 fuel cell. Experimentally, open-circuit potentials in excess of 1.4 V have been achieved with the dual electrolyte system. This is a 500 mV increase in the open circuit potentials observed for single electrolyte H2/O2 systems also studied. The dual electrolyte fuel cell system shows power generation of 0.6 mW/cm2 from a single device, which is nearly 0.25 mW/cm2)greater than the values obtained for single electrolyte H2/O2 fuel cell systems studied. Microchannels of varying dimensions have been employed to study both the single and dual electrolyte H2/O2 systems. Channel thickness variation and the flow rate dependences of power generation are also addressed.     

Microstructural impact of anodic coatings on the electrochemical chlorine evolution reaction

Sol-gel Ru(0.3)Sn(0.7)O(2) electrode coatings with crack-free and mud-crack surface morphology deposited onto a Ti-substrate are prepared for a comparative investigation of the microstructural effect on the electrochemical activity for Cl(2) production and the Cl(2) bubble evolution behaviour. For comparison, a state-of-the-art mud-crack commercial Ru(0.3)Ti(0.7)O(2) coating is used. The compact coating is potentially durable over a long term compared to the mud-crack coating due to the reduced penetration of the electrolyte. Ti L-edge X-ray absorption spectroscopy confirms that a TiO(x) interlayer is formed between the mud-crack Ru(0.3)Sn(0.7)O(2) coating and the underlying Ti-substrate due to the attack of the electrolyte. Meanwhile, the compact coating shows enhanced activity in comparison to the commercial coating, benefiting from the nanoparticle-nanoporosity architecture. The dependence of the overall electrode polarization behaviour on the local activity and the bubble evolution behaviour for the Ru(0.3)Sn(0.7)O(2) coatings with different surface microstructure are evaluated by means of scanning electrochemical microscopy and microscopic bubble imaging.     

Self-assembly of Yttrium-containing lacunary polyoxotungstate macroanions in solution with controllable supramolecular structure size by pH or solvent content

The self-assembly and the formation of "Blackberry" type supramolecular structures for a type of Yttrium-containing polyoxometalate (K 15Na 6(H 3O) 9[(PY 2W 10O 38) 4(W 3O 14)].9H 2O, or {P 4Y 8W 43}) macroanions is characterized by using static and dynamic light scattering techniques. {P 4Y 8W 43} macroions are found to form hollow, spherical, single-layer "blackberry" structures in water and water-acetone mixed solvents. Very interestingly, the blackberry size can be accurately controlled by either changing acetone content in water-acetone mixed solvents, or by changing solution pH in aqueous solution. The blackberry size increases with decreasing pH (lower charge density) or higher acetone content in the mixed solvent (lower dielectric constant) and the blackberry size can change in responding to the change of external conditions. This indicates that the {P 4Y 8W 43} macroanions possess the properties of both "strong electrolyte type" and "weak electrolyte type" macroions, as we outlined previously. This is due to the special chemical feature of such clusters, which can be treated as Na 2HPO 4-type electrolytes in solution. The kinetics of the blackberry formation can be controlled by temperature.     

Redox-induced solid-solid phase transformation of TCNQ microcrystals into semiconducting Ni[TCNQ]2(H2O)2 nanowire (flowerlike) architectures: a combined voltammetric, spectroscopic, and microscopic study

The facile solid-solid phase transformation of TCNQ microcrystals into semiconducting and magnetic Ni[TCNQ]2(H2O)2 nanowire (flowerlike) architectures is achieved by reduction of TCNQ-modified electrodes in the presence of Ni2+(aq)-containing electrolytes. Voltammetric probing revealed that the chemically reversible TCNQ/Ni[TCNQ]2(H2O)2 conversion process is essentially independent of electrode material and the identity of nickel counteranion but is significantly dependent on scan rate, Ni2+(aq) electrolyte concentration, and the method of solid TCNQ immobilization (drop casting or mechanical attachment). Data analyzed from cyclic voltammetric and double-potential step chronoamperometric experiments are consistent with formation of the Ni[TCNQ]2(H2O)2 complex via a rate-determining nucleation/growth process that involves incorporation of Ni2+(aq) ions into the reduced TCNQ crystal lattice at the triple phase TCNQ|electrode|electrolyte interface. The reoxidation process, which includes the conversion of solid Ni[TCNQ]2(H2O)2 back to TCNQ0 crystals, is also controlled by nucleation/growth kinetics. The overall redox process associated with this chemically reversible solid-solid transformation, therefore, is described by the equation: TCNQ0(S) + 2e- + Ni2+(aq)+ 2 H2O <==> {Ni[TCNQ]2(H2O)2}(S). SEM monitoring of the changes that accompany the TCNQ/Ni[TCNQ]2(H2O)2 transformation revealed that the morphology and crystal size of electrochemically generated Ni[TCNQ]2(H2O)2 are substantially different from those of parent TCNQ crystals. Importantly, the morphology of Ni[TCNQ]2(H2O)2 can be selectively manipulated to produce either 1-D/2-D nanowires or 3-D flowerlike architectures via careful control over the experimental parameters used to accomplish the solid-solid phase interconversion process.     

Relationship between the bubble temperature and main oxidant created inside an air bubble under ultrasound

Numerical simulations of nonequilibrium chemical reactions in a pulsating air bubble have been performed for various ultrasonic frequencies (20 kHz, 100 kHz, 300 kHz, and 1 MHz) and pressure amplitudes (up to 10 bars). The results of the numerical simulations have indicated that the main oxidant is OH radical inside a nearly vaporous or vaporous bubble which is defined as a bubble with higher molar fraction of water vapor than 0.5 at the end of the bubble collapse. Inside a gaseous bubble which is defined as a bubble with much lower vapor fraction than 0.5, the main oxidant is H2O2 when the bubble temperature at the end of the bubble collapse is in the range of 4000-6500 K and O atom when it is above 6500 K. From the interior of a gaseous bubble, an appreciable amount of OH radical also dissolves into the liquid. When the bubble temperature at the end of the bubble collapse is higher than 7000 K, oxidants are strongly consumed inside a bubble by oxidizing nitrogen and the main chemical products inside a bubble are HNO2, NO, and HNO3.     

Theoretical study of single-bubble sonochemistry

Numerical simulations of bubble oscillations in liquid water irradiated by an ultrasonic wave are performed under the experimental condition for single-bubble sonochemistry reported by Didenko and Suslick [Nature (London) 418, 394 (2002)]. The calculated number of OH radicals dissolving into the surrounding liquid from the interior of the bubble agrees sufficiently with the experimental data. OH radicals created inside a bubble at the end of the bubble collapse gradually dissolve into the surrounding liquid during the contraction phase of an ultrasonic wave although about 30% of the total amount of OH radicals that dissolve into the liquid in one acoustic cycle dissolve in 0.1 micros at around the end of the collapse. The calculated results have indicated that the oxidant produced by a bubble is not only OH radical but also O atom and H2O2. It is suggested that an appreciable amount of O atom is produced by bubbles inside a standing-wave-type sonochemical reactor filled with water in which oxygen is dissolved as in the case of air.     

MAA修饰ZnO量子点及其发光特性

以ZnAc2·2H2O为原料,在乙醇中通过70℃回流4h,得到ZnO前驱物,与LiOH·H2O反应,制备出ZnO.采用巯基乙酸(mercaptoacetic acid,MAA)对所合成的ZnO进行表面修饰,修饰后的产物经SEM和XRD表征,证明获得了物相单一、近似球状、粒径为4.6nm的ZnO量子点.借助紫外-可见和荧光分析,研究了MAA对该量子点的修饰效果,探讨了设置条件下ZnO的发光机理和性质.发现该实验体系之所以产生荧光表面缺陷发射峰消失和激子发射峰明显增加的光学现象,是因为MAA有效地覆盖了ZnO的表面缺陷,并稳定包裹住ZnO粒子.同时还研究了MAA加量、温度、电解质对修饰产物发光性能的影响,发现经MAA修饰后的ZnO量子点具有较强的荧光发光性能、良好的长期陈放稳定性,以及一定的抗电解质影响能力.研究结果对ZnO量子点应用于生物分析具有重要参考价值.     

Bubble coalescence during acoustic cavitation in aqueous electrolyte solutions

Bubble coalescence behavior in aqueous electrolyte (MgSO(4), NaCl, KCl, HCl, H(2)SO(4)) solutions exposed to an ultrasound field (213 kHz) has been examined. The extent of coalescence was found to be dependent on electrolyte type and concentration, and could be directly linked to the amount of solubilized gas (He, Ar, air) in solution for the conditions used. No evidence of specific ion effects in acoustic bubble coalescence was found. The results have been compared with several previous coalescence studies on bubbles in aqueous electrolyte and aliphatic alcohol solutions in the absence of an ultrasound field. It is concluded that the impedance of bubble coalescence by electrolytes observed in a number of studies is the result of dynamic processes involving several key steps. First, ions (or more likely, ion-pairs) are required to adsorb at the gas/solution interface, a process that takes longer than 0.5 ms and probably fractions of a second. At a sufficient interfacial loading (estimated to be less than 1-2% monolayer coverage) of the adsorbed species, the hydrodynamic boundary condition at the bubble/solution interface switches from tangentially mobile (with zero shear stress) to tangentially immobile, commensurate with that of a solid-liquid interface. This condition is the result of spatially nonuniform coverage of the surface by solute molecules and the ensuing generation of surface tension gradients. This change reduces the film drainage rate between interacting bubbles, thereby reducing the relative rate of bubble coalescence. We have identified this point of immobilization of tangential interfacial fluid flow with the "critical transition concentration" that has been widely observed for electrolytes and nonelectrolytes. We also present arguments to support the speculation that in aqueous electrolyte solutions the adsorbed surface species responsible for the immobilization of the interface is an ion-pair complex.     

The influence of membrane electrode assembly water content on the performance of a polymer electrolyte membrane fuel cell as investigated by 1H NMR microscopy

The relation between the performance of a self-humidifying H(2)/O(2) polymer electrolyte membrane fuel cell and the amount and distribution of water as observed using (1)H NMR microscopy was investigated. The integrated (1)H NMR image signal intensity (proportional to water content) from the region of the polymer electrolyte membrane between the catalyst layers was found to correlate well with the power output of the fuel cell. Several examples are provided which demonstrate the sensitivity of the (1)H NMR image intensity to the operating conditions of the fuel cell. Changes in the O(2)(g) flow rate cause predictable trends in both the power density and the image intensity. Higher power densities, achieved by decreasing the resistance of the external circuit, were found to increase the water in the PEM. An observed plateau of both the power density and the integrated (1)H NMR image signal intensity from the membrane electrode assembly and subsequent decline of the power density is postulated to result from the accumulation of H(2)O(l) in the gas diffusion layer and cathode flow field. The potential of using (1)H NMR microscopy to obtain the absolute water content of the polymer electrolyte membrane is discussed and several recommendations for future research are provided.     

Reactions in the rechargeable lithium-O2 battery with alkyl carbonate electrolytes

The nonaqueous rechargeable lithium-O(2) battery containing an alkyl carbonate electrolyte discharges by formation of C(3)H(6)(OCO(2)Li)(2), Li(2)CO(3), HCO(2)Li, CH(3)CO(2)Li, CO(2), and H(2)O at the cathode, due to electrolyte decomposition. Charging involves oxidation of C(3)H(6)(OCO(2)Li)(2), Li(2)CO(3), HCO(2)Li, CH(3)CO(2)Li accompanied by CO(2) and H(2)O evolution. Mechanisms are proposed for the reactions on discharge and charge. The different pathways for discharge and charge are consistent with the widely observed voltage gap in Li-O(2) cells. Oxidation of C(3)H(6)(OCO(2)Li)(2) involves terminal carbonate groups leaving behind the OC(3)H(6)O moiety that reacts to form a thick gel on the Li anode. Li(2)CO(3), HCO(2)Li, CH(3)CO(2)Li, and C(3)H(6)(OCO(2)Li)(2) accumulate in the cathode on cycling correlating with capacity fading and cell failure. The latter is compounded by continuous consumption of the electrolyte on each discharge.