强碱性介质对硫化银膜表面的腐蚀与测硫条件的选择

硫化银膜构成的硫/银离子选择电极可用于硫和银等的分析,其电极性能已有一些研究。由于S~(2-)要水解,人们采用增加溶液碱度的办法促进S~(2-)离子的生成,以期提高电极检测硫的灵敏度,但仅能实测10~(-5)M〔S~(2-)〕。而该电极可响应的硫离子活度是10~(-25)M。我们初步研究了产生这种差别的原因,进而拟定了痕量硫的测试条件。主要仪器、试剂与实验方法仪器:PZ-8型直流数字电压表;pHS-2型酸度计;681型磁搅拌器;Neophot-2型显     

钛基二氧化铅电极上氯析出过程的研究

用极化曲线法研究了钛基二氧化铅电极(β-PbO_2)在NaCl溶液中的阳极析氯过程。结果表明,反应速度与Cl~-离子浓度成正比,H~ 离子通过OH~-离子的竞争吸附对析氯过程起促进作用。电极转速对阳极极化曲线没有影响,说明扩散过程不起控制作用。稳态动力学数据指出,氯的析出机理符合电化学放电规律,速度控制步骤为:MCl~-_(adi)→MCl~-_(adi e)。     

离子选择电极的发展

离子选择电极是一种根据物理化学原理直接测量分析组分的新工具,也可以这样来定义:离子选择电极是一种以电位法来测量溶液中某一特殊离子活度的指示电极。最早的pH玻璃电极就是离子选择电极的一种。我们知道溶液是具有生命活力的有机体的组成部分,而且又非常辽阔地布满于地球表面,所以这一工具的出世,对溶液化学的影响甚大,有人把它与光学上的激光相比。离子选择电极对其他技术较难以测量的离子,例如Na~ 、K~ 、Ca~(2 )、F~-、SO_4~(2-)、S~(2-)、NO_3~-、ClO_4~-等,具有特别效验,它的灵敏度常常低于1ppb,选择比普通在10~5以上,此外还有其他一些相     

硫电极法测定H_2S离解常数的研究

测定平衡常数多采用电导法、冻点法或反应速率法等。用离子选择电极测定平衡常数或离解常数多集中研究各种氟络合物。用硫电极测定平衡常数的工作仅见到测SnS_3~(2-)的平衡常数。我们在对硫电极研究的基础上,用pH玻璃电极测定溶液的pH值,用pS电极测定不同pH值溶液中的[S~(2-)]浓度,根据H_2S在溶液中的平衡理论及硫电极在溶液中的响应特性,找到一种推算H_2S离解常数的途径。     

钛基导电氧化物电极上氧的阳极析出动力学与机理研究

本文通过在碱溶液中Ti/RuO_2+TiO_2(A)和Ti/SnO_2+CuCo_2O_4(B)电极上氧阳极析出动力学的对比研究, 表明这两类电极上氧的极化曲线均有两Tafel区。低极化区的Tafel斜率为0.039V(简称b_1区); 高极化区为0.120V(简称b_2区)。在A电极上b_1区i～a_W·a_(OH~-); b_2区i～a_W(浓碱溶液)或i～a_(OH)~(0.1～0.5)(稀碱溶液),在B电极上b_1区i～a_(OH~-); b_2区i～a_(OH~-)~(0.39)(浓碱溶液);或i～a_(OH~-)(稀碱溶液), 实验结果表明, 虽然这两类电极上氧阳极析出过程都由第二电子转移步骤控制, 但其机理不同, 前者是由水分子参加, 控制步骤为RuO_2·OH_(ads)+H_2O ~(rds)→ RuO(OH)~+_3+e后者则为 (SOH)~(n+)_(ads) ~(rds)→ (SOH)~((n+1)+)_(ads)+e它们与PbO_2、Pt和低碳钢上机理有些不同~[1,2]。     

离子选择电极测定烟气中碘

烟气通过冲击式吸收管,碘被管中水吸收。加KMnO_4氧化S~(2-)、加锌还原Hg~(2-)以消除S~(2-)、Hg~(2+)的干扰。在柠檬酸钠-柠檬酸介质中,pH4.5—5.5进行离子选择电极测定。本法可测定0.006碘μg/L。     

n型碲化镉单晶光电化学电池的研究 Ⅱ.金属离子修饰与光电化学催化

n-CdTe单晶表面用H_2PtCl_6或RuCl_3溶液浸渍,显著提高了电池的效率及稳定性.除选择金属离子种类外,电极预处理及浸渍时间对修饰作用也有很大影响.固体表面分析表明,在PtCl_6~(2-)溶液中短时间浸渍的电极表面上有大量铂岛,能减少表面缺陷并催化界面反应.在RuCl_3溶液中浸渍,将可使Ru~(3+)离子吸附于电极表面,有利于光电化学反应.PdCl_2溶液浸渍或长时间PtCl_6~(2-)溶液处理均得到不利的结果.     

离子液体在CO_2电还原反应过程中的催化作用与机理研究

在1-丁基3-甲基咪唑三氟甲基磺酸盐([Bnlim][CF_3SO_3])/碳酸丙烯酯(PC)溶液中,采用循环伏安曲线、交流阻抗谱及阻抗模拟方法,研究了CO_2在Au上发生电还原反应的速率控制步骤与离子液体的催化作用.结果表明,在CO_2电还原反应过程中,吸附态CO_2经单电子还原生成CO_2~-自由基是速率控制步骤.由于离子液体的催化作用,CO_2在[Bmim][CF_3SO_3]/PC溶液中电还原的过电位比在四丁基三氟甲基磺酸铵([Bu_4N][CF_3SO_3])/PC溶液中降低了239 mV.交流阻抗测试结果表明,离子液体中的阳离子[Bmim]~+吸附在Au电极表面,形成离子液体吸附层,吸附态的CO_2分子经单电子还原后生成CO_2~·-)自由基,与周围离子液体发生相互作用,形成中间体[Bmim-CO_2]_(ad),降低了CO_2~(·-)的能量状态,使得CO_2电还原反应的过电位大幅度降低.     

Pt电极上乙醛吸附及氧化的现场FTIR反射吸收光谱电化学研究

本文用现场FTIR反射吸收光谱法和循环伏安法研究了Pt电极上HCl, H2SO4水溶液中乙醛的吸附及氧化过程。实验结果表明, 0.3至1.0V(vs. SCE)电势范围内乙醛主要以式I吸附于电极表面上, 并发生了生成乙酸的电化学反应, 产物乙酸可能以式II吸附。对于H2SO4水溶液中, 上述电势范围内电极表面上还检测出硫酸根离子与乙醛和乙酸的竞争吸附。     

氢氧化钠溶液和氢氧化钠-氯化钠混合溶液中铂电极上氧还原反应的研究

采用带环旋转圆盘电极,研究了铂电极在不同浓度NaOH与NaOH-NaCl混合溶液中的氧阴极还原,发现C_(OH)~-及C(?)~-均影响液相中间产物进一步反应的动力学.观察到的差别一部份可用高pH溶液中H_2O_2的离解来解释,同时阴、阳离子特性吸附的影响也不容忽视.OH~-对H_2O_2的阴极还原有明显抑阻,而Cl~-则能部分减弱这一效应.在含有NaOH的溶液中均观察到I_DN/I_(R-ω~(-1/2))在高转速区与直线偏离,我们试用中间产物的覆盖度以定性地解释这种现象.     

Synthesis of uniform anatase TiO2 nanoparticles by the gel-sol method 2. Adsorption of OH- Ions to Ti(OH)4 gel and TiO2 particles

The pH value in the gel-sol system for the preparation of uniform anatase TiO2 nanoparticles, as a decisive factor for controlling the size and shape of the final product, was found to be significantly changed during the formation process of the anatase TiO2 particles from a condensed Ti(OH)4 gel. The dramatic evolution of pH with the progress of the synthetic process has clearly been explained in terms of the adsorption and desorption of a hydroxide ion (OH-) ora proton (H+) on the solids transforming with time. The adsorption and desorption of OH- or H+ were enhanced by the presence of an inert electrolyte such as NaClO4, as explained by its shielding effect on the electrical interactions between the electrically charged precipitates and free OH- and H+ ions. The electrolyte also hampered the phase transformation of Ti(OH)4 precipitate to anatase TiO2. This effect of electrolytes was explained in terms of the inhibited nucleation of anatase TiO2 by enhanced adsorption of OH- ions toTiO2 embryos. The points of zero charge (PZC) of the amorphous Ti(OH)4 precipitate and the anatase TiO2 particles at 25 degrees C were obtained from the change in pH associated with the adsorption and desorption of OH- or H+, i.e., 4.6 for Ti(OH)4 precipitate and 6.0 for anatase TiO2 in the presence of 0.1 mol dm(-3) NaClO4. The PZCof the Ti(OH)4 precipitate measured at 25 degrees C after additional aging at 100 degrees C for 30 min was shifted to 4.1, owing to the promoted adsorption of OH-.     

Existence of oriented ion-hydroxide clusters in concentrated aqueous NaCl solution at pH 13

We probe the local electronic structure at solvated Na+ ions in 1 M aqueous NaCl solutions as a function of pH. A dramatic change in the Na+ white line intensity in X-ray absorption is observed for high pH values, reflecting a changing local electronic structure at the Na+ ions when OH- is present. Given the relative abundance of sodium and hydroxide ions, we conclude that one OH- affects at least 2.4+/-0.6 Na+ ions in an electronically noticeable way at pH 13. From the experimental data we infer that spatially extended clusters or networks incorporating Na+ and OH- can exist in the electrolyte solution. The experimental data are complemented by molecular dynamics simulations, which indicate the presence of structured clusters incorporating Na+, OH-, and solvent molecules.     

Effects of pH and ionic strength on the stability of nanobubbles in aqueous solutions of alpha-cyclodextrin

Formation of stable nanobubbles in aqueous solutions of water-soluble organic molecules is a spontaneous process. Using a combination of laser light scattering (LLS) and zeta-potential measurements, we investigated the effects of salt concentration and pH on their stability in alpha-cyclodextrin (alpha-CD) aqueous solutions. Our results reveal that the nanobubbles are unstable in solution with a higher ionic strength, just like colloidal particles in an aqueous dispersion, but become more stable in alkaline solutions. The zeta-potential measurement shows that the nanobubbles are negatively charged with an electric double layer, presumably due to adsorption of negative OH- ions at the gas/water interface. It is this double layer that plays a critical dual role in the formation of stable nanobubbles in aqueous solutions of water-soluble organic molecules, namely, it not only provides a repulsive force to prevent interbubble aggregation and coalescence but also reduces the surface tension at the gas/water interface to decrease the internal pressure inside each bubble.     

锌电极在氢氧化钾溶液中阳极惰化时的表面相变的研究

本文试图进一步从动力学方面证明恒电位下的锌电极在KOH溶液中阳极惰化时,阳极溶解电流随时间而缓慢下降是由于“表面相变”所引起。用恒电位法测取了锌电极在不同浓度的KOH溶液中电流对时间的曲线。实验结果与推导的动力学方程式相符,表明在恒电位惰化条件下,锌电极表面上最初形成的[Zn(OH)_2]_(ad)在OH~-参预下徐缓地转变为较不易溶的[ZnO]_(ad),因而导致阳极溶解电流的下降。这一表面相变过程可表示如下:     

Nature of the aqueous hydroxide ion probed by X-ray absorption spectroscopy

X-ray absorption spectra of aqueous 4 and 6 M potassium hydroxide solutions have been measured near the oxygen K edge. Upon addition of KOH to water, a new spectral feature (532.5 eV) emerges at energies well below the liquid water pre-edge feature (535 eV) and is attributed to OH- ions. In addition to spectral changes explicitly due to absorption by solvated OH- ions, calculated XA spectra indicate that first-solvation-shell water molecules exhibit an absorption spectrum that is unique from that of bulk liquid water. It is suggested that this spectral change results primarily from direct electronic perturbation of the unoccupied molecular orbitals of first-shell water molecules and only secondarily from geometric distortion of the local hydrogen bond network within the first hydration shell. Both the experimental and the calculated XA spectra indicate that the nature of the interaction between the OH- ion and the solvating water molecules is fundamentally different than the corresponding interactions of aqueous halide anions with respect to this direct orbital distortion. Analysis of the Mulliken charge populations suggests that the origin of this difference is a disparity in the charge asymmetry between the hydrogen atoms of the solvating water molecules. The charge asymmetry is induced both by electric field effects due to the presence of the anion and by charge transfer from the respective ions. The computational results also indicate that the OH- ion exists with a predominately "hyper-coordinated" solvation shell and that the OH- ion does not readily donate hydrogen bonds to the surrounding water molecules.     

Coulometrische argentometrie : Quantitative bestimmung von chlor-, brom- und jodionen

By electrolytic oxidation of various metal anodes, metal ions can be quantitatively introduced into solution. This process can be used for coulometric determination of anions forming insoluble salts with metal ions.Semimicro and micro determinations of chloride, bromide and iodide ions with electrolytically generated silver ions have been performed at constant current and by a simple apparatus. The end-points have been determined with adsorption indicators, i.e. with dichloro(R)fluorescein for chlorides and eosin for bromides and iodides. The lower concentration limit of applicability of this method depends on the sensitivity of the end-point determination method used.The developed method of coulometric argentometry presents a new possibility for coulometric standardization of volumetric solutions, in conformity with our earlier proposals, as well as a further support for the introduction of the coulomb as a primary standard in all analytical chemistry.     

氢氧根离子在TiO2薄膜电极上的吸附行为和光氧化动力学

在醇的水溶液中，应用电化学方法研究了OH－在TiO2薄膜电极上的吸附行为和光氧化动力学.实验结果表明，OH－在TiO2表面的吸附模型符合Langmuir等温吸附方程式，其光氧化动力学行为能用Langmuir-Hinshelwood动力学方程来描述.在光强足够大时，光电流和OH－在TiO2表面的吸附浓度成正比，这表明，光生空穴仅氧化吸附于TiO2表面的OH－，同时吸附的水分子则不能被氧化.在醇浓度足够高的溶液中，自由基OH•和电子之间的复合反应几乎不发生，这时整个光氧化反应的速控步骤是光生自由基OH•的生成.     

Identification of hydrolysis products of FeCl3.6H2O by ESI-MS

The hydrolysis reactions of FeCl3 in 0.1 mM aqueous solutions were monitored by electrospray ionisation time-of-flight mass spectrometry (ESI-ToF-MS). In contrast to the other ionisation techniques, electrospray ionisation provides information on the composition of the elemental cores even in water and salt cluster ions. Therefore, the technique facilitates detection of the bonding of the chloride ions in the oxo-hydroxo-iron cores. A variety of mononuclear and polynuclear iron-oxohydroxo-chloride complexes were characterised from the cationic and anionic mass spectra of iron(III) solutions. Oxidation and reduction reactions of iron, as well as competition between OH- and Cl- ions within one iron core, were also observed.     

Investigation of the electrokinetic properties of paraffin suspension. 2. In cationic and anionic surfactant solutions

Electrical phenomena at nonionogenic hydrophobic surfaces (solid or liquid) in water, electrolyte, and/or surfactant solutions still attract research. In part 1 of this paper we described the electrokinetic behavior of paraffin wax suspension in water and electrolyte solutions (NaCl or LaCl3). On the basis of the latest data of water structure near hydrophobic surfaces it was concluded that immobilized water dipoles at the interface can play an essential role in the zeta potential formation. In this paper were investigated the zeta potentials of paraffin wax in cationic surfactants cetyltrimethylammonium bromide, C16H33(CH3)3NBr, and octadecyltrimethylammonium chloride, C18H37(CH3)3NCl, and anionic surfactant sodium dodecyl sulfate, C12H25SO4Na. Also changes in wettability of the paraffin surface due to the surfactant's adsorption were studied via wetting contact angle measurements and calculation of the surface free energy. It was concluded that at a low surfactant concentration (10(-6) M) the water dipole structure still contributes to the zeta potential, but at a higher one the zeta potential is determined by the surfactant molecules' adsorption. A special role of OH- ions is also clearly seen. Moreover, a functional relationship was found between the surface free energy of the surfactant-covered paraffin surface and the zeta potential.     

Adsorption of sodium dodecyl sulfate onto clathrate hydrates in the presence of salt

This work presents the effect of NaCl on the adsorption of sodium dodecyl sulfate (SDS) at the cyclopentane (CP) hydrate-water interface. The adsorption isotherms and the SDS solubility in NaCl solutions are obtained using liquid-liquid titrations. The solubility data are determined at typical hydrate forming temperatures (274-287K) to ensure that the adsorption isotherms are obtained within SDS solubility limits in NaCl solutions. The isotherms show L-S (Langmuir-Step) type behaviors with 1mM and 10mM NaCl solutions while L type isotherm is determined for 25mM NaCl solutions due to the low SDS solubility in this salt concentration. Zeta potentials of CP hydrate particles in the aqueous solutions support the shape of the adsorption isotherm with the 1mM NaCl solution. The 1mM NaCl case shows the highest SDS adsorption amount among the cases with 0mM, 10mM, and 25mM NaCl solutions. In this case, the competition for adsorption between Cl(-) and DS(-) is not as strong compared to the 10 and 25mM NaCl cases and the presence of Na(+) ions may reduce the repulsion between DS(-) ions, which results in a higher adsorption of DS(-) ions and enhanced enclathration.