Zn-Al类水滑石零净电荷点及等电点研究

用非均相共沉淀法合成了系列Zn-Al类水滑石(HTlc)样品,研究发现A1／(Zn Al)摩尔比(x)在0．31～0．52范围内可得到纯类水滑石相．用电势滴定法和显微电泳法分别测定了5个纯Zn-Al HTic样品的零净电荷点(PZNC)和等电点(IEP),以考察结构电荷对PZNC和IEP的影响．研究发现随结构正电荷密度的增加,PZNC和IEP均降低;IEP高于PZNC,且随结构正电荷密度的降低,IEP与PZNC的差值也降低,表明IEP与PZNC的差异来自结构电荷的影响．结构正电荷对HTlc的IEP与PZNC相对大小的影响与高价阳离子特性吸附的影响一致．初步探讨了结构电荷对PZNC和IEP的影响机理．     

The Isoelectric Point and the Points of Zero Charge of Fe-Al-Mg Hydrotalcite-like Compounds

The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations.     

Influence of PZC (Point of Zero Charge) on the Static Adsorption of Anionic Surfactants on a Malaysian Sandstone

Static adsorption studies of two anionic surfactants produced in our lab are reported. The adsorption of surfactants on the rock samples was investigated with and without the presence of alkali. The point of zero charge (PZC) values were determined for the sandstone samples employing three titrimetric methods and it was found to be at pH 7.98. The relationship between the adsorption degree and pH value of brine below and above the PZC is discussed. It was found that at the pH of solution exceeds the PZC of the rock, the adsorption was 0.43 and 0.86mg/g of rock for the two surfactants. However, at pH values below PZC, the adsorption as high as 3.66 and 4.49mg/g for the two surfactants. The synthesized surfactants are found to be suitable for the EOR applications at pH values higher than the PZC of the rock sample.     

Effect of Discrete Macroion Charge Distributions on Electric Double Layer of a Spherical Macroion

The effect of replacing the conventional uniform macroion surface charge density with discrete macroion charge distributions on the structure of electric double layer (EDL) of a spherical macroion has been investigated by Monte Carlo (MC) simulations. Two discrete models have been investigated in addition to the central macroion charge: point charges localized on the macroion surface and finite-sized charges protruding into the solution. Both models have been studied with fixed and mobile macroion charges. The radial functions of local densities and electrostatic potential in EDL, are calculated and compared to the results obtained for the central macroion charge distribution. It is concluded that the model of charge distribution significantly affects the EDL structure close to the macroion, while the effect is much weaker at larger distances. With point charges localized on the macroion surface, counterions become stronger accumulated to the macroion, as a result the absolute values of surface potential ?₀ and zeta ξ potential are decreased. With protruding charges, the excluded volume effect dominates over the increased correlation ability; hence the counterions are less accumulated near the macroions and the absolute values of ?₀ and ξ potentials are increased.     

Mg-Al-NO_3层状双金属氢氧化物电性质研究

采用电泳法和电势滴定法测定出不同电解质（LiCl,NaCl和KCl）溶液中Mg-Al- NO_3层状双金属氢氧化物（Mg-Al-NO_3LDH）颗粒的ξ电位、等电点、永久电荷密 度以及零电荷点等电化学物理量，探讨了电解质、pH和样品化学组成对Mg-Al- NO_3LDH电性质的影响，研究发现一价阳离子Li~+,Na~+,K~+对Mg-Al-NO_3LDH颗粒 的等电点有影响，电荷点依次增大，而等电点依次降低。     

Point of zero charge/isoelectric point of exotic oxides: Tl2O3

The pristine point of zero charge of Tl(2)O(3) determined in the presence of NaNO(3) using the inert electrolyte titration method and confirmed by microelectrophoresis is at pH 7.9.     

Study on electric property at interface of positive sol of magnesium aluminum hydroxide

The isoelectric point (IEP) and zero point of charge (ZPC) of magnesium aluminumhydroxide were studied by electrophoresis method,potentiometric titration method,and elemental analysis.Results showed that the charge of magnesium aluminum hydroxide was composed of variable charge and permanent positive charge.Because of the permanent positive charge,the IEP and ZPC obtained were higher than calculated.The IEP decreased and ZPC increased as X increased.     

Potential of zero total charge of platinum single crystals: A local approach to stepped surfaces vicinal to Pt(111)

The electrochemical behavior of platinum single-crystal electrodes is revisited, with special emphasis on the determination of the potential of zero charge. We show that the measure of the charge displaced during CO adsorption allows the determination of the potential of zero total charge (PZTC). The estimation of the potential of zero free charge (PZFC) is discussed, with different degrees of approximation. The application of this methodology to the study of the PZTC of platinum stepped surfaces vicinal to Pt(111) reveals a marked decrease of the PZTC due to the introduction of surface steps. This effect is interpreted as the result of the existence of markedly smaller surface potentials localized on step sites. The importance of considering local aspects of the interface is emphasized with the use of N₂O reduction as a sensitive probe to the local structure of the surface. It is proposed that the different local maxima observed in the absolute value of the reduction current correspond to the local values of PZTC. It is shown that there is, in general, good agreement between the overall PZTC, obtained from the CO displacement, and that calculated from the local values inferred from the N₂O reduction. Further insight is obtained with the application of the laser-induced temperature jump method. This technique is useful to calculate the potential of maximum entropy of the double-layer formation. The resulting value of this potential for Pt(111) is discussed in the light of the PZFC value obtained from different approaches. For stepped surfaces vicinal to Pt(111), two local maxima in the entropy of the double layer are observed that are close to the local PZTC values estimated from the N₂O reduction. This result suggests the existence of cooperative effects in the organization of the water dipoles close to the electrode surface. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1275–1292. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Temperature effects on the point of zero charge and isoelectric point of a red soil rich in kaolinite and iron minerals

The effects of temperature (373–1373 K) on the point of zero charge (PZC) and isoelectric point (IEP) of a red soil rich in kaolinite and iron minerals were studied. PZC values of the soil treated at 373 and 573 K indicated the presence of iron oxide. The soil calcined between 773 and 1173 K shows a PZC almost coincident with the respective values of kaolinite. At 1373 K, the PZC of the soil is nearer to the value of iron oxide. In the entire temperature range studied the PZC values were lower than the IEP values. An approach of PZC and IEP values was observed after a partial removal of iron oxide by the dithionite-citrate-bicarbonate (DCB) method. The analyses of the PZC and IEP values, of electron probe micro analysis (EPMA) data and of specific surface areas evidence a specific adsorption of iron oxide on kaolinite. Finally, the dissolution sequence of iron and aluminium contained in soil was determined using hydrochloric acid.     

An impedance study of Ir(210) in HCl solutions

In the Ir(210)/aqueous HCl solution system the “hydrogen adsorption region” is due to the combined process of hydrogen and chloride ion adsorption. We demonstrate that by using impedance spectroscopy the rates of, and charges associated with, hydrogen and chloride adsorption rates can be determined separately. Published in Elektrokhimiya in Russian, 2009, Vol. 45, No. 1, pp. 32–41. Dedicated to the 100th anniversary of B.V. Ershler. The text was submitted by authors in English.     

Intrinsic Surface Reaction Constant in 1-pK Model of Mg-Fe Hydrotalcite-like Compounds

The relationship among intrinsic surface reaction constant (K) in 1-pK model, point of zero net charge (PZNC) and structural charge density (σst) for amphoteric solid with structural charges was established in order to investigate the effect of σst on pK. The theoretical analysis based on 1-pK model indicates that the independent PZNC of electrolyte concentration (c) exists for amphoteric solid with structural charges. A common intersection point (CIP) should appear on the acid-base titration curves at different c, and the pH at the CIP is pHPZNC. The pK can be expressed as pK=-pHPZNC log[(1 2αPZNC)/(1-2αPZNC)], where αPZNC≡σst/eNANs, in which e is the elementary charge, NA the Avogadro‘s constant and Ns the total density of surface sites. For solids without structural charges, pK=-pHPZNC. The pK values of hydrotalcite-like compounds (HTlc) with general formula of [Mg1-xFex(OH)2](Cl,OH)x were evaluated. With increasing x, the pK increases, which can be explained based on the affinity of metal cations for H^- or OH^- and the electrostatic interaction between charging surface and H^- or OH^-.     

Formal Mathematical Analysis of the Existence of the Common Intersection Point in Relation to Determining the Parameters Describing Ion Adsorption at the Oxide/Electrolyte Interface: Comparison of the Triple and Four-Layer Models

For most oxide/electrolyte systems potentiometric titration curves measured for different ionic strengths have a Common Intersection Point (CIP) which corresponds to the Point of Zero Charge (PZC). However, there are systems where a CIP exists but the surface charge at this point does not equal zero (PZC CIP). In this paper theoretical analysis of the systems in which the PZC and CIP do not coincide is presented. It is based on the well-known 2-pK surface charging approach and Triple Layer Model (TLM) as well as the Four Layer Model (FLM) of the electric double layer. The appropriate mathematical criterion for CIP existence was applied with detailed derivations, both for TLM and FLM. Having determined in this manner the parameter values, one can draw proper conclusions about the features of oxide/electrolyte adsorption systems, in which PZC and CIP do not coincide. The values of adsorption parameters are found by fitting simultaneously the obtained theoretical expressions to both of the experimental titration isotherms, and to the individual isotherms of electrolyte cation adsorption measured using radiometric methods.     

Double Layer at the Pt(111)–Aqueous Electrolyte Interface: Potential of Zero Charge and Anomalous Gouy–Chapman Screening

We report, for the first time, the observation of a Gouy–Chapman capacitance minimum at the potential of zero charge of the Pt(111)‐aqueous perchlorate electrolyte interface. The potential of zero charge of 0.3 V vs. NHE agrees very well with earlier values obtained by different methods. The observation of the potential of zero charge of this interface requires a specific pH (pH 4) and anomalously low electrolyte concentrations (<10^?3 m ). By comparison to gold and mercury double‐layer data, we conclude that the diffuse double layer structure at the Pt(111)‐electrolyte interface deviates significantly from the Gouy–Chapman theory in the sense that the electrostatic screening is much better than predicted by purely electrostatic mean‐field Poisson–Boltzmann theory.     

The relation between the potential of zero charge and work function for <Emphasis Type="Italic">sp</Emphasis>-metals

It is shown that for numerous sp-metals there exists no unified work function (W _e) dependence of the potential of zero charge E _{q = 0} and the potential drop characterizing the metal lyophilic behavior Δ _M ^Hg E _chem) _{q = 0}. The reason is that the metal work function is by no means the only factor affecting the value of E _{q = 0}. The quantities E _{q = 0} and (Δ _M ^Hg E _chem) _{q = 0} depend also on the distance of the solvent dipoles’ closest approach to metal surfaces (d _ms) in the absence of the metal-solvent chemisorption interaction. When the metal-solvent chemisorption interaction is involved, this distance affects the degree of overlapping of the metal’s acceptor levels and the upper occupied donor levels in the solvent molecules. To reliably investigate the effect of any of these factors on E _{q = 0}, the other one should be fixed up. It is shown, by example of Ga-, Bi-Gaand Sn-Ga-electrodes, as well as Pb-Ga-, In-Ga-, and Cd-Ga-electrodes demonstrating very close values of the “electrochemical work function” that the metal-solvent chemisorption interaction becomes stronger with the decreasing of d _ms. The influence of this factor is intensified with the increasing of the solvent’s donor number DN. The W _e dependence of E _{q = 0} and (Δ _M ^Hg E _chem) _{q = 0} can be traced by example of metals with nearly equal d _ms values, e.g., Tl-Ga, In-Ga, and Ga. In all studied solvents, the deviation of E _{q = 0} from W _e increased in the series Tl-Ga < In-Ga < Ga, that is, with the increasing of the metal’s work function in vacuum. The effect is intensified with the increasing of the solvent’s DN. The obtained results agree with the concept of donor-acceptor nature of the metal-solvent chemisorption interaction.     

Interfacial Study of Nickel-Modified Pt(111) Surfaces in Phosphate-Containing Solutions: Effect on the Hydrogen Evolution Reaction

The surface modification of electrodes attracts great interest in electrocatalysis. It has often been observed that deposition of foreign adatoms on the surface of an electrode can originate a significant enhancement in the catalytic activity. For example, it has been reported that nickel deposits on Pt surfaces improve the rate of the hydrogen evolution reaction (HER, Nature Energy 2017, 2, 17031). During the deposition process of such metal adlayers, the pH and the nature of the ions in the electrolyte play an important role. Phosphate species are typically used to prepare buffer solutions in a wide range of pH. Therefore, electrolytes containing phosphate species are used in a large number of applications. However, the effect of phosphate on platinum surface modification with nickel deposits has not been studied yet. In this work, new data about the interaction of phosphate with nickel adatoms deposited on Pt(111) at pH 5 is investigated using cyclic voltammetry and infrared spectroscopy. The results show that, when nickel is in solution, the phosphate ions are adsorbed at lower potentials than in the absence of nickel. In addition, Laser-Induced Temperature Jump Technique demonstrates that nickel facilitates the adsorption of phosphate because of a shift of the potential of zero charge (pzc) toward negative potentials. This increases the magnitude of the positive electric field on the electrode surface, at a given potential E>pzc, facilitating the adsorption of anions. CO displacement technique has been also employed to obtain additional information about co-adsorbed phosphate on nickel adlayers. Finally, the HER has been studied at pH 5 in the presence of nickel, with and without phosphate in the bulk solution.     

Effect of Inorganic Ions on Oleate Adsorption at a Nigerian Hematite–Water Interface

Using “pure” natural hematite selected from a high silica Nigerian hematitic ore, oleate adsorption densities at the hematite–water interface were determined in the presence of various inorganic ions (anions and cations) of different charges and at varying concentrations. Adsorption density was determined using electrical conductivity measurements. The specific surface area of the hematite particles was determined using the method of adsorption of paranitrophenol in aqueous solution. Inorganic ions in solution depressed oleate adsorption at the aqueous hematite surface. The charge of the ion proved to be the dominant factor determining the depression of oleate adsorption. Ionic strength also was an influence, up to a limiting value at which monolayer oleate coverage of the hematite surface occurred. The inorganic ions in solution are considered to function through nonspecific adsorption in the diffuse region of the electric double layer.     

The use of the pH at the point of zero charge for characterizing the properties of oxide hydroxides

The modern theoretical views on the point of zero charge of the oxide hydroxide surface are considered. Methods for determination of the pH of the point of zero charge and the use of this value to characterize the properties of oxide hydroxides are described. Examples of using the pH of the point of zero charge in studies of oxide anodes and amorphous oxide hydroxide sorbents are presented. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1029–1035, June, 1999.     

An Analysis of the Interactions of BSA with an Anion-Exchange Surface Under Linear and Non-Linear Conditions

The interactions of BSA with an anion-exchange adsorbent have been studied to aid in the understanding of protein adsorption in ion-exchange chromatography. Linear chromatography, flow microcalorimetry and isotherm measurements were used to analyze adsorption energetics in the linear and overloaded regions of the equilibrium isotherm. The effects of salt type, salt and protein concentration, and temperature are reported. It was observed that under all conditions studied the adsorption process was entropically driven. This was contrary to expectations, since at the pH selected ion exchange is expected to dominate. A major driving force for the adsorption of BSA on the anion exchanger was concluded to be the increase in entropy from the release of water due to interactions between hydrophobic regions on the protein and adsorbent. The data further suggest that the conformational entropy change accompanying protein adsorption on the ion exchanger may also be significant.     

东北草甸棕壤的零电荷点和界面酸-碱反应特征平衡常数

分别采用电势滴定(Potentiometric titration)法, 质量滴定(Mass titration)法和惰性电解质滴定(Inert electrolyte titration)法测定了荷结构负电荷的东北草甸棕壤的零净电荷点(PZNC), 研究表明荷结构负电荷的土壤依然存在与电解质浓度无关的零净电荷点, 三种方法的实验结果分别为2.9, 5.0和3.3. 相比较而言, 电势滴定法和惰性电解质滴定法的结果相近, 而质量滴定法的结果偏高. 对文献中推算表面质子活性位密度(N_s)的方法进行了改进, 得到东北草甸棕壤样品的N_s为2.5 mmol•g^－1. 根据实验测定的pH_PZNC, N_s和结构电荷密度(σ_st)值直接计算得出东北草甸棕壤样品的界面反应特征平衡常数即1-pK模型中的pK, 2-pK模型中pK_a1^int和pK_a2^int, 分别为3.37, 2.42和4.32, 与文献报道的沉积物和蒙脱土的值相吻合.     

Ultrathin Silicon Oxide Film-Induced Enhancement of Charge Separation and Transport of Nanostructured Titanium(IV) Oxide Photoelectrode

The development of nanostructured semiconductor electrodes represented by a mesoporous TiO₂ nanocrystalline (mp-TiO₂) film is currently bringing great progresses in photoelectrochemical (PEC) devices for solar-to-electricity and solar-to-chemical conversion. Two serious losses can occur in PEC devices: 1) recombination between the conduction band (CB) electrons and valence band (VB) holes in the bulk and at the surface and 2) back reaction or electron trapping by oxidant in the electrolyte solution during transport to the electron-collecting electrode. Thus, the major challenge in common with the nanostructured semiconductor photoanodes is to achieve efficient charge separation and electron transport. In this study, an ultrathin SiO_x layer was formed on both the external and the internal surface of mp-TiO₂ using an original chemisorption-calcination technique employing 1,3,5,7-tetramethyltetrasiloxane as a starting material. The SiO_x surface modification of the mp-TiO₂ photoanode drastically prolongs the mean lifetime of CB-electrons in TiO₂ because of enhanced charge separation and electron transport by the negative charge applied in aqueous electrolyte solution. We have demonstrated that the performance of a one-compartment H₂O₂-photofuel cell using mp-TiO₂ as the photoanode is greatly boosted by the surface modification with the SiO_x layer. We anticipate that this methodology is widely applicable to nanostructured metal oxide semiconductor electrodes, contributing to the improvement in the performance of PEC devices.