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。     

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.     

Studies on Zero Point of Charge and Permanent Charge Density of Mg-Fe Hydrotalcite-like Compounds

The theoretical analysis on the zero point of charge (ZPC) and charge density of colloidal particle possessing permanent charges indicates that ZPC determined directly by means of potentiometric titration (PT) should be zero point of net charge (ZPNC) and the permanent charge density (σ_P) can be obtained from the adsorption amount of H⁺ and OH^-(Γ_OH--Γ_H+) at ZPNC. ZPNC does not change with the electrolyte concentration while the zero point of variable charge (ZPVC) changes with the electrolyte concentration. When σ_P is zero, ZPNC equals to ZPVC, and only under this condition is ZPC measured directly by PT equal to ZPVC. The relationship between ZPNC, ZNVC, σ_P, the variable charge density (σ_V)5 or the total net surface charge density (σ_T) with pH or electrolyte concentration is derived.     

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.     

氢氧化铝镁钠米颗粒的零电荷点及电荷密度研究

探讨了电位滴定(PT)法测定的零电荷点的物理意义, 认为是零净电荷点(ZPNC)。并对零净电荷点pH(pHZPNC), 零可变电荷点pH(pHZPVC), 永久电荷密度(σP), 可变电荷密度(σV)和净电荷密度(σT)之间的关系进行了理论分析。用PT法测定了氢氧化铝镁纳米颗粒的pHZPNC和σP, 探讨了电解质浓度和pH对各电化学性质的影响规律。另外, 还考察了CO3^2^-对PT法测定结果的影响。     

Synthesis and characterization of goethite and goethite-hematite composite: experimental study and literature survey

Aging of synthetic goethite at 140 degrees C overnight leads to a composite material in which hematite is detectable by M?ssbauer spectroscopy, but X-ray diffraction does not reveal any hematite peaks. The pristine point of zero charge (PZC) of synthetic goethite was found at pH 9.4 as the common intersection point of potentiometric titration curves at different ionic strengths and the isoelectric point (IEP). For the goethite-hematite composite, the common intersection point (pH 9.4), and the IEP (pH 8.8) do not match. The electrokinetic potential of goethite at ionic strengths up to 1 mol dm(-3) was determined. Unlike metal oxides, for which the electrokinetic potential is reversed to positive over the entire pH range at sufficiently high ionic strength, the IEP of goethite is rather insensitive to the ionic strength. A literature survey of published PZC/IEP values of iron oxides and hydroxides indicated that the average PZC/IEP does not depend on the degree of hydration (oxide or hydroxide). Our material showed a higher PZC and IEP than most published results. The present results confirm the allegation that electroacoustic measurements produce a higher IEP than the average IEP obtained by means of classical electrokinetic methods.     

Studies on intrinsic ionization constants of Fe-Al-Mg hydrotalcite-like compounds

The theoretical analysis of the intrinsic ionization constant (K(a2)(int)) of Fe-Al-Mg hydrotalcite-like compounds (HTlc) possessing permanent charges was first performed using the double extrapolation method proposed by James et al. The theoretical permanent charge density (sigma(p,T)) of the HTlc sample was calculated from the crystal structure of HTlc, and the influence of sigma(p,T) on the K(a2)(int) was also examined. From the experimental results, these conclusions can be obtained: the zero point of the charge (pH(ZPC)) of Fe-Al-Mg HTlc increases with decreased Fe3+ content and increases with increased Mg2+ in the HTlc. The pK(a2)(int) of Fe-Al-Mg HTlc also increases with decreased Fe3+ and increased Mg2+ content in the sample; furthermore, the pK(a2)(int) of Fe-Al-Mg HTlc increases with decreased sigma(p,T).     

Measurements and theoretical interpretation of points of zero charge/potential of BSA protein

The points of zero charge/potential of proteins depend not only on pH but also on how they are measured. They depend also on background salt solution type and concentration. The protein isoelectric point (IEP) is determined by electrokinetical measurements, whereas the isoionic point (IIP) is determined by potentiometric titrations. Here we use potentiometric titration and zeta potential (ζ) measurements at different NaCl concentrations to study systematically the effect of ionic strength on the IEP and IIP of bovine serum albumin (BSA) aqueous solutions. It is found that high ionic strengths produce a shift of both points toward lower (IEP) and higher (IIP) pH values. This result was already reported more than 60 years ago. At that time, the only available theory was the purely electrostatic Debye-Hu?ckel theory. It was not able to predict the opposite trends of IIP and IEP with ionic strength increase. Here, we extend that theory to admit both electrostatic and nonelectrostatic (NES) dispersion interactions. The use of a modified Poisson-Boltzmann equation for a simple model system (a charge regulated spherical colloidal particle in NaCl salt solutions), that includes these ion specific interactions, allows us to explain the opposite trends observed for isoelectric point (zero zeta potential) and isoionic point (zero protein charge) of BSA. At higher concentrations, an excess of the anion (with stronger NES interactions than the cation) is adsorbed at the surface due to an attractive ionic NES potential. This makes the potential relatively more negative. Consequently, the IEP is pushed toward lower pH. But the charge regulation condition means that the surface charge becomes relatively more positive as the surface potential becomes more negative. Consequently, the IIP (measuring charge) shifts toward higher pH as concentration increases, in the opposite direction from the IEP (measuring potential).     

Charging and aggregation of latex particles by oppositely charged dendrimers

Poly(amidoamine) (PAMAM) dendrimers were shown to adsorb strongly on negatively charged latex particles, and their effect on the particle charge and aggregation behavior was investigated by light scattering and electrophoretic mobility measurements. Time-resolved simultaneous static and dynamic light scattering was used to measure absolute aggregation rate constants. With increasing dendrimer dose, the overall charge could be tuned from negative to positive values through the isoelectric point (IEP). The aggregation is fast near the IEP and slows down further away. With decreasing ionic strength, the region of fast aggregation narrows and the dependence of the aggregation rate on the dendrimer dose is more pronounced. Surface charge heterogeneities become important for higher dendrimer generations. They widen the fast aggregation region, reduce the dependence of the aggregation rate on the dendrimer dose, and lead to an acceleration of the rate in the fast aggregation regime near the IEP. The ratio of the dendrimer charge and the particle charge exceeds the stoichiometric ratio of unity substantially and further increases with increasing generation. The tentative interpretation of such superstoichiometric charge neutralization involves coadsorption of anions and the finite thickness of the adsorbed dendrimer layer.     

Charging and stability of anionic latex particles in the presence of linear poly(ethylene imine)

Charging properties and colloidal stability of negatively charged polystyrene latex particles were investigated in the presence of linear poly(ethylene imine) (LPEI) of different molecular masses by electrophoresis and dynamic light scattering (DLS). Electrophoretic mobility measurements illustrate that LPEI strongly adsorbs on these particles leading to charge neutralization at isoelectric point (IEP) and charge reversal. Time-resolved DLS experiments indicate that the aggregation of the latex particles is rapid near the IEP and slows down away from this point. Surprisingly, the colloidal stability does not depend on the molecular mass, which indicates that the adsorbed LPEI layer is rather homogeneous.     

The effect of humic acid adsorption on pH-dependent surface charging and aggregation of magnetite nanoparticles

The pH-dependent adsorption of humic acid (HA) on magnetite and its effect on the surface charging and the aggregation of oxide particles were investigated. HA was extracted from brown coal. Synthetic magnetite was prepared by alkaline hydrolysis of iron(II) and iron(III) salts. The pH-dependent particle charge and aggregation, and coagulation kinetics at pH approximately 4 were measured by laser Doppler electrophoresis and dynamic light scattering. The charge of pure magnetite reverses from positive to negative at pH approximately 8, which may consider as isoelectric point (IEP). Near this pH, large aggregates form, while stable sols exist further from it. In the presence of increasing HA loading, the IEP shifts to lower pH, then at higher loading, magnetite becomes negatively charged even at low pHs, which indicate the neutralization and gradual recharging positive charges on surface. In acidic region, the trace HA amounts are adsorbed on magnetite surface as oppositely charged patches, systems become highly unstable due to heterocoagulation. Above the adsorption saturation, however, the nanoparticles are stabilized in a way of combined steric and electrostatic effects. The HA coated magnetite particles form stable colloidal dispersion, particle aggregation does not occur in a wide range of pH and salt tolerance is enhanced.     

Colloidal behavior of aluminum oxide nanoparticles as affected by pH and natural organic matter

The colloidal behavior of aluminum oxide nanoparticles (NPs) was investigated as a function of pH and in the presence of two structurally different humic acids (HAs), Aldrich HA (AHA) and the seventh HA fraction extracted from Amherst peat soil (HA7). Dynamic light scattering (DLS) and atomic force microscopy (AFM) were employed to determine the colloidal behavior of the NPs. Influence of pH and HAs on the surface charges of the NPs was determined. zeta-Potential data clearly showed that the surface charge of the NPs decreased with increasing pH and reached the point of zero charge (ZPC) at pH 7.9. Surface charge of the NPs also decreased with the addition of HAs. The NPs tend to aggregate as the pH of the suspension approaches ZPC, where van der Waals attraction forces dominate over electrostatic repulsion. However, the NP colloidal suspension was stable in the pHs far from ZPC. Colloidal stability was strongly enhanced in the presence of HAs at the pH of ZPC or above it, but in acidic conditions NPs showed strong aggregation in the presence of HAs. AFM imaging revealed the presence of long-chain fractions in HA7, which entangled with the NPs to form large aggregates. The association of HA with the NP surface can be assumed to follow a two-step process, possibly the polar fractions of the HA7 sorbed on the NP surface followed by entanglement with the long-chain fractions. Thus, our study demonstrated that the hydrophobic nature of the HA molecules strongly influenced the aggregation of colloidal NPs, possibly through their conformational behavior in a particular solution condition. Therefore, various organic matter samples will result in different colloidal behavior of NPs, subsequently their environmental fate and transport.     

Study of the adsorption of F(ab')2 onto polystyrene latex beads

An experimental investigation on the adsorption of F(ab')₂ from rabbit IgG onto polystyrene (PS) latex beads is described. All adsorption isotherms were of high affinity and showed well-defined plateaus. Maximum protein adsorption was found around the average isoelectric point (IEP) of the dissolved protein. According to the findings, the F(ab')₂ adsorption on the polystyrene surface is strongly irreversible with respect to ionic strength changes. The pH changes, however, exert a certain effect on the adsorption-desorption process of F(ab')₂ on negatively charged polystyrene surfaces. In order to determine the role played by the electrostatic forces in the F(ab')₂ adsorption onto negatively charged latex particles, an electrokinetic study of the protein-latex complexes has also been carried out. The isoelectric pH of the F(ab')₂-PS complexes is always smaller than the IEP of the dissolved F(ab')₂, indicating that the PS surface charge must partly compensate the positive charge on the protein. Finally, a comprehensive study on the colloidal stability of the sensitized latex beads was performed.     

The Isoelectric Point of an Exotic Oxide: Tellurium (IV) Oxide

The pH-dependent surface charging of tellurium (IV) oxide has been studied. The isoelectric point (IEP) of tellurium (IV) oxide was determined by microelectrophoresis in various 1-1 electrolytes over a concentration range of 0.001–0.1 M. In all electrolytes studied and irrespective of their concentration the zeta potential of TeO₂ was negative over the pH range 3–12. In other words the IEP of TeO₂ is at pH below 3 (if any). TeO₂ specifically adsorbs ionic surfactants, and their presence strongly affects the zeta potential. In contrast the effect of multivalent inorganic ions on the zeta potential of TeO₂ is rather insignificant (no shift in the IEP). In this respect TeO₂ is very different from metal oxides.     

Electroacoustic isoelectric point determinations of bauxite refinery residues: different neutralization techniques and minor mineral effects

Bauxite refinery residue (BRR) is a highly caustic, iron hydroxide-rich byproduct from alumina production. Some chemical treatments of BRR reduce soluble alkalinity and lower residue pH (to values <10) and generate a modified BRR (MBRR). MBRR has excellent acid neutralizing (ANC) and trace-metal adsorption capacities, making it particularly useful in environmental remediation. However, soluble ANC makes standard acid-base isoelectric point (IEP) determination difficult. Consequently, the IEP of a BRR and five MBRR derivatives (sulfuric acid-, carbon dioxide-, seawater-, a hybrid neutralization, i.e, partial CO(2) neutralization followed by seawater, and an activated-seawater-neutralized MBRR) were determined using electroacoustic techniques. Residues showed three significantly different groups of IEPs (p < 0.05) based around the neutralization used. Where the primary mineral assemblage is effectively unchanged, the IEPs were not significantly different from BRR (pH 6.6-6.9). However, neutralizations generating neoformational minerals (alkalinity precipitation) significantly increased the IEP to pH 8.1, whereas activation (a removal of some primary mineralogy) significantly lowered the IEP to pH 6.2. Moreover, surface charging curves show that surfaces remain in the ±30 mV surface charge instability range, which provides an explanation as to why MBRRs remove trace metals and oxyanions over a broad pH range, often simultaneously. Importantly, this work shows that minor mineral components in complex mineral systems may have a disproportionate effect on the observable bulk IEP. Furthermore, this work shows the appropriateness of electroacoustic techniques in investigating samples with significant soluble mineral components (e.g., ANC).     

Characterization of oxide layers on Ti6Al4V and titanium by streaming potential and streaming current measurements

Titanium and titanium alloys (e.g. Ti6Al4V) are increasingly used as medical implant materials in a wide variety of applications. So far, many surface properties of the passive layer considered to explain interactions with biological tissues are deduced from those of the crystalline phases of titanium dioxide (anatase, rutile, brookite), but do not necessarily correspond to those of naturally formed amorphous passive layers. We report on streaming potential and streaming current measurements on oxide layers on Ti6Al4V and Ti, carried out using a microslit electrokinetic set-up (MES) and a commercial electrokinetic analyzer (EKA, PAAR). Passive and anodic oxide layers on Ti6Al4V, as well as passive layers on titanium sputtered on glass, were investigated in this study. Isoelectric points (IEP) of ≈4.4 were found for all oxide layers. The IEP of the air-formed passive layer on Ti6Al4V did not depend on the KCl concentration. Hence, it was concluded that IEP is here identical to the point of zero charge (pzc). Controversially, the charge formation process seems to depend on the chloride ion concentration in the neutral and basic pH region.     

铝阳极氧化多孔膜层的界面电性能研究

采用电渗方法研究了经硫酸溶液氧化并利用逆向电解方法剥离后的铝阳极氧化多孔膜层的ζ电位与溶液ｐＨ的关系．结果表明：该多孔膜层在１．０×１０－２ｍｏｌ／ＬＫＣｌ溶液中的ｐＨ等电点（ｐＨＩＥＰ）＝９．２０,２．００＜ｐＨ＜９．２０,ζ＞０,多孔膜荷正电;９．２０＜ｐＨ＜１１．００,ζ＜０,多孔膜荷负电．     

Adsorbed anthranilic acid molecules cause charge reversal of nonionic micelles

The effect of anthranilic acid, an aromatic amino acid, on the structural characteristics of nonionic micelles of Triton X-100 at different pH values was investigated by light scattering and small-angle neutron scattering (SANS) measurements. The scattered light intensity decreases as pH is increased or decreased on either side of the isoelectric point (IEP = 3.4) of the amino acid. Analysis of the SANS data using a sticky hard-sphere model shows that the micelles are oblate ellipsoids with an axial ratio of approximately 2.3. No significant change could be observed in the size of the micelles with a change in the pH, while the stickiness parameter (tau), which is related to the interaction potential (u(0)) increases on either side of the IEP. As tau increases, u(o) becomes less negative, indicating a decrease in the attractive interaction between nonionic micelles. This can be explained in terms of the changes in the surface charge of the micelles resulting from a shift in the acid-base equilibrium of the adsorbed amino acid. The variation of the intermicellar interaction as calculated from the stickiness parameter is consistent with the picture of reversal of charge of amino acids with pH. This is further supported by the observed variation of the cloud point of the solutions at different pH values. The change in the interparticle interaction is also reflected in the diffusion coefficient of the micelles measured by dynamic light scattering.     

Study of a Solvated Adsorbed Gelatin Layer Using a Modified Force Microscope

The interaction energies between gelatin-coated surfaces at various electrolyte and pH conditions are reported. The surfaces are of glass and are negatively charged under all conditions used here. Gelatin is a polyampholyte, with an isoelectric pH (IEP) of approximately 4.9. At low pH the gelatin molecules have a net positive charge, and thus the polyampholyte tends to adsorb with a relatively flat conformation. As the pH is increased the strong attractive interaction between the surface and the polyampholyte decreases as more negative charges and then fewer positive charges appear on the polyampholyte, and so the gelatin extends away from the surface. On changing electrolyte concentrations after adsorption no effect was seen at the IEP, but the layer was observed to swell at more alkaline pHs. This is consistent with the net minimum charge situation on the polymer under these conditions. Changing the adsorption conditions was seen to have an effect, and this is attributed to the different affinities of the gelatin chain to the surface depending on the solution chemistry. Results obtained when the gelatin was initially adsorbed on one surface or two were similar, suggesting that the gelatin transfers rapidly from one surface to another. The importance of adsorption conditions as well as current conditions is discussed. Copyright 1999 Academic Press.     

两性高分子的溶液性质

两性高分子是分子链上同时含有正负电荷基团的一类高聚物、具有独特的溶液性质。本文就两性高分子等电点的构象状态、影响等电点的因素、两性高分子的溶解性以及高分子结构和组成、ｐＨ、溶液离子强度、混合溶剂、温度对流体力学行为的影响进行了综述。