Influence of long-term aqueous exposure on surface properties of plasma-sprayed oxides Cr2O3 and Cr2O3-25 wt% TiO2

The influence of water exposure on the surface properties of plasma-sprayed Cr(2)O(3) and Cr(2)O(3)-25 wt% TiO(2) was studied. It was shown that both plasma-sprayed materials contained Cr(VI) hydrous oxide phases, which dissolved rapidly at the beginning of water exposure. The dissolution continued slowly during the whole water exposure time. The Cr(VI) dissolution was accompanied by a rapid increase in surface IEP value. Both Cr(2)O(3) and Cr(2)O(3)-25 wt% TiO(2) showed similar dissolution, zeta potential, and surface oxidation states. Thus the addition of TiO(2) did not influence the surface properties of the plasma-sprayed Cr(2)O(3).     

Surface characterization of plasma sprayed oxide materials: estimation of surface acidity using mass titration

The aim of this study was to characterize the influence of plasma spraying on the point of zero charge (PZC) of Al2O3-, Cr2O3- and TiO2-based materials. PZC is one of the most important parameter, which describes the acidity of oxide material in aqueous environments. PZC values of several plasma sprayed oxides were determined using mass titration method. Studies were performed for initial spray powders and plasma sprayed coating materials. In addition, mass titration experiments were performed for water-washed and nonwashed samples. It was found that mass titration is a suitable method to estimate the surface acidity of relatively coarse sample powders. It was found for most of the studied materials that the limiting pH values (assumed to be close PZC) were close to those reported in literature for the PZC values of traditionally manufactured oxide materials. On the other hand, mass titration curves of some oxide samples showed unexpected deviation in curve shapes and limiting pH. These deviations were probably due to selective dissolution of sample contaminations or sample material.     

Al_2O_3包覆Ba_(0.6)Sr_(0.4)TiO_3复合粉体制备及表征

采用液相包覆法制备了Al2O3包覆的Ba0.6Sr0.4TiO3复合粉体。通过SEM,TEM,TG-DSC,XRD,XPS和ζ电位测试对包覆前后粉体的表面形貌、组织结构、等电点进行了测试和分析。结果表明:Al2O3以无定形结构成功的包覆在Ba0.6Sr0.4TiO3粉体表面,形成了Ba-O-Al、Sr-O-Al和Ti-O-Al键,Ba0.6Sr0.4TiO3颗粒的等电点由包覆前的pH=3.2增大至pH=8。     

Isoelectric point of fluorite by direct force measurements using atomic force microscopy

Interaction forces between a fluorite (CaF2) surface and colloidal silica were measured by atomic force microscopy (AFM) in 1 x 10(-3) M NaNO3 at different pH values. Forces between the silica colloid and fluorite flat were measured at a range of pH values above the isoelectric point (IEP) of silica so that the forces were mainly controlled by the fluorite surface charge. In this way, the IEP of the fluorite surface was deduced from AFM force curves at pH approximately 9.2. Experimental force versus separation distance curves were in good agreement with theoretical predictions based on long-range electrostatic interactions, allowing the potential of the fluorite surface to be estimated from the experimental force curves. AFM-deduced surface potentials were generally lower than the published zeta potentials obtained from electrokinetic methods for powdered samples. Differences in methodology, orientation of the fluorite, surface carbonation, and equilibration time all could have contributed to this difference.     

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.     

Effect of supporting surface layers on catalytic activities of gold nanoparticles in CO oxidation

The surfaces of fumed silica materials were modified with a surface sol-gel process for catalysis applications. This surface-modification approach allows not only a monolayer growth of TiO(2) or Al(2)O(3) but also a stepwise double-layer growth of TiO(2)/TiO(2), Al(2)O(3)/Al(2)O(3), TiO(2)/Al(2)O(3), or Al(2)O(3)/TiO(2) on the surfaces of the silica materials with a monolayer precision. XRD analyses revealed that the coated monolayers and double layers of TiO(2) and Al(2)O(3) were amorphous. Gold nanoparticles were successfully deposited on the above six surface-modified silica materials via a deposition-precipitation method. The catalytic activities of these six gold catalysts for CO oxidation are highly dependent on the structures of their surface monolayers or double layers. The gold catalyst supported on the silica material functionalized with a TiO(2) monolayer (Au/TiO(2)) is the most active in both as-synthesized and oxidized forms, while the gold catalyst supported on the silica material functionalized with an Al(2)O(3)/TiO(2) double layer (Au/Al(2)O(3)/TiO(2)/SiO(2)) is the most active in the reduced form among the six catalysts. Surprisingly, the gold catalyst supported on the silica material functionalized with a TiO(2)/Al(2)O(3) double layer (Au/TiO(2)/Al(2)O(3)/SiO(2)) has much less activity than Au/Al(2)O(3)/TiO(2)/SiO(2) under all various treatments, underscoring the sensitivity of the catalytic activity to the structure of the supporting surfaces.     

Adsorption and photocatalytic decomposition of amino acids in TiO2 photocatalytic systems

The adsorption and photodecomposition of seven kinds of amino acids on a TiO2 surface were investigated by zeta potential measurements and 1H NMR spectroscopy in TiO2 aqueous suspension systems. The decomposition rates increased in the order of Phe < Ala < Asp < Trp < Asn < His < Ser. For Phe, Trp, Asn, His, and Ser, the isoelectric point (IEP) of TiO2 shifted to a lower pH with increasing decomposition rates upon adsorption on TiO2, suggesting that the effective adsorption and photocatalytic sites for these amino acids should be the basic terminal OH on the solid surface. Since the amino acids that decomposed faster than the others contain -OH (Ser), -NH (Trp, His), or -NH2 (Asn) in their side chain, they are considered to interact with the basic terminal OH groups more preferably by the side chain and are vulnerable to photocatalytic oxidation. On the other hand, Ala interacts with the acidic bridged OH on TiO2 to cause an IEP shift to a higher pH. The correlation of the surface hydroxyl groups with the photocatalysis of amino acids was verified by the use of calcined TiO2 without surface hydroxyl groups.     

Adsorption of human serum albumin (HSA) onto colloidal TiO2 particles, Part I

The adsorption of human serum albumin (HSA) onto colloidal TiO2 (P25 Degussa) particles was studied in NaCl electrolyte at different solution pH and ionic strength. The HSA-TiO2 interactions were studied using adsorption isotherms and the electrokinetic properties of HSA-covered TiO2 particles were monitored by electrophoretic mobility measurements. The adsorption behavior shows a remarkable dependence of the maximum coverage degree on pH and was almost independent of the ionic strength. Other characteristic features such as maximum adsorption values at the protein isoelectric point (IEP approximately 4.7) and low-affinity isotherms that showed surface saturation even under unfavorable electrostatic conditions (at pH values far away from the HSA IEP and TiO2 PZC) were observed. Structural and electrostatic effects can explain the diminution of HSA adsorption under these conditions, assuming that protein molecules behave as soft particles. Adsorption reactions are discussed, taking into account acid-base functional groups of the protein and the surface oxide in different pH ranges, considering various types of interactions.     

Dispersion of TiN in aqueous media

The dispersion of TiN powders in aqueous media was studied through XPS, zeta potential, adsorption, sedimentation, and rheology measurements. XPS showed that there are TiO2, TiN, and TiOxNy sites on the TiN particle surface. In the absence of dispersant, the isoelectric point (pH(IEP)) of the TiN particles was at pH 2.2. Based on the surface properties of TiN particles, a cationic polymer, polyethylene imine (PEI), was selected as a dispersant. In the presence of PEI, the pH(IEP) shifted from pH 2.2 to pH 11.10. It was evidenced that TiN slurries could be stabilized around pH 9.50 with 1-2 wt% PEI as dispersant. Subsequently, TiN slurries with solid content as high as 57 vol% were developed and exhibited dilatant rheological behavior at high shear rate. The results showed that PEI is an effective dispersant for TiN in aqueous media.     

气相SiO2在不同pH值介质中的分散特性

以激光动态光散射法考察了气相SiO2在不同pH值的H2SO4和NaOH介质中的分散平均水化粒径与表面Zeta电位及二者间的关系。 Zeta电位数据表明，气相SiO2在水中分散的表面硅羟基的等电点(IEP)和滴定终点(TE)的pH值分别为pH(IEP)=2.09和pH(TE)=7.47，利用滴定终点pH (TE)给出了一种简单的气相SiO2表面Si-OH浓度的测定方法。 分散相粒径数据显示，在等电点和滴定终点之间，气相SiO2在水中的分散粒子的粒径能够稳定在230 nm附近；在H2SO4介质中，当pH＜pH(IEP)时，随着H2SO4浓度的增大，体系中的分散粒子发生聚结而使表观粒径增大；在NaOH介质中，当pH＞pH(TE)时，随着NaOH浓度的增大，分散相的表观水化粒径降低，表明NaOH的加入有利于气相SiO2的分散。     

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。     

Titania-silver and alumina-silver composite nanoparticles: novel, versatile synthesis, reaction mechanism and potential antimicrobial application

Titania-silver (TiO(2)-Ag) and alumina-silver (Al(2)O(3)-Ag) composite nanoparticles were synthesised by a simple, reproducible, wet chemical method under ambient conditions. The surface of the oxides was modified with oleic acid, which acted as an intermediate between the oxide surface and the silver nanoparticles. The resulting composite nanoparticles were thoroughly characterised by XRD, TEM, XPS, FTIR and TGA to elucidate the mode of assembly of Ag nanoparticles on the oxide surfaces. Epoxy nanocomposites were formulated with TiO(2)-Ag and Al(2)O(3)-Ag to examine potential applications for the composite nanoparticles. Preliminary results from disc diffusion assays against Escherichia coli DH5α and Staphylococcus epidermidis NCIMB 12721 suggest that these TiO(2)-Ag and Al(2)O(3)-Ag composite nanoparticles have potential as antimicrobial materials.     

TiO2／Al2O3负载量对气相酯交换合成碳酸甲丙酯的影响

采用XRD、N2 physical adsorption、XPS、NH3-TPD和吡啶吸附IR等技术,对碳酸二甲酯和丙醇气固相合成碳酸甲丙酯的TiO2/Al2O3催化剂进行了表征.实验结果表明,TiO2/Al2O3表面的Lewis酸中心是反应的催化活性位,酸性主要来源于Al2O3,TiO2起修饰作用,有利于选择性生成碳酸甲丙酯.随着Ti负载量的增加,TiO2在Al2O3表面由高度分散状态向晶态转变,其比表面积逐渐降低,但是TiO2/Al2O3的表面酸性质没有受到显著影响,L酸量先是增加,而后略有下降.当Ti负载量为5%时,DMC的转化率及MPC的选择性分别达到54.3%和88.1%.     

The adsorption and reaction of a titanate coupling reagent on the surfaces of different nanoparticles in supercritical CO2

The adsorption and reaction in supercritical CO2 of the titanate coupling reagent NDZ-201 on the surfaces of seven metal oxide particles, SiO2, Al2O3, ZrO2, TiO2 (anatase), TiO2 (rutile), Fe2O3, and Fe3O4, was investigated. FTIR and TG analysis indicated that the adsorption and reaction were different on different particle surfaces. On SiO2 and Al2O3 particles, there was a chemical reaction of the titanate coupling reagent on the surfaces. On the surfaces of ZrO2 and TiO2 (anatase) particles, there were two kinds of adsorption, weak and strong adsorption. On the surfaces of TiO2 (rutile), Fe2O3, and Fe3O4 particles, there was only weak adsorption. The acidity or basicity of the OH groups on the particle surface was the key factor that determined if a surface reaction occurred. When the OH groups were acidic, the titanate coupling reagent reacted with these, but otherwise, there was no reaction. The surface density of OH groups on the original particles and the amount of titanate coupling reagent adsorbed and reacted were estimated from TG analysis. The reactivity of the surface OH groups of Al2O3 particles was higher than that of the SiO2 particles.     

X射线荧光光谱法测定黏土中的主次组分

采用熔融玻璃片制样,选用标准样品,以经验α系数和散射线内标法校正元素谱线重叠干扰和基体效应,使用ZSX Primus Ⅱ X射线荧光光谱仪对黏土样品中的Al₂O₃、SiO₂、Fe₂O₃、CaO、MgO、K₂O、Na₂O、MnO、P₂O₅、TiO₂、Cu、Cr等组分进行测定,分析结果与标准值和化学值相吻合,12次测定的相对标准偏差小于10%.     

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).     

Evaluating the electrochemical capacitance of surface-charged nanoparticle oxide coatings

While transition metal oxides have been thoroughly investigated as coatings for electrochemical capacitors due to their pseudocapacitance, little work has been done investigating other oxide coatings. There exists a whole class of nanoporous oxides typically synthesized by sol-gel chemistry techniques that have very high differential capacitance. This high differential capacitance has been attributed to the surface potential of these materials and the close approach of counterions near the surface of these oxides. This study focuses on investigating the electrochemical capacitance of non-transition metal oxide nanoparticle coatings when deposited on supporting electrodes. Here, we show that, by adding coatings of SiO(2), AlOOH, TiO(2), and ZrO(2) nanoparticles to graphite support electrodes, we can increase the electrochemical capacitance. We also show that the measured electrochemical capacitance of these oxide-coated electrodes directly relates to the electrophoretic mobility of these materials with the lowest values in capacitance occurring at or near the respective isoelectric pH (pH(IEP)) of each oxide.     

TiO2-Al2O3作为Mo催化剂担体的研究

Tio。－AI。oa二元氧化物的制备at艺大体可分为两种．一种是利用液相浸渍或气相沉积方法将Tio。担载在AI。0。上，使Tio。主要覆盖在AI。0。表面上［‘－1另一种是通过Ti盐和AI盐混合溶液共沉淀方法使Tio。和AI。0。均匀混合在一起【‘－’1．不同的制备工艺对Tio。－AI。03的表面结构和表面性质有很大影响问．我们曾报导用TICly蒸气化学气相沉积方法制备出了D02在1川2O3表面呈现十分均匀分布的DoZ一周。03复合氧化物担体＊’1．本文进一步考察D0。在周。0。表面的沉积对川。0。孔结构的影响，以及Ti02－A1203作为加氢精制MO催…     

桑色素修饰的纳米TiO_2分离富集铬和铝

建立了在表面活性剂十二烷基硫酸钠(SLS)的活化作用下,桑色素修饰的纳米TiO2分离富集,电感耦合等离子体原子发射光谱(ICP-AES)测定Cr3+和A l3+的新方法。考察了溶液pH、洗脱条件和干扰离子等因素对分析物分离富集的影响。结果表明,在pH 3.0时,Cr3+和A l3+可被桑色素修饰的纳米TiO2定量富集,吸附的金属离子可用1.5 mL 0.50 mol/L HC l溶液完全洗脱。在优化的实验条件下,纳米TiO2-桑色素对Cr3+和A l3+的吸附容量分别为9.69 mg/g和12.76 mg/g。本法对Cr3+和A l3+的检出限(3σ)分别为:0.21和0.49 ng/mL,相对标准偏差(RSD)分别为2.2%和1.6%(n=11,C=50 ng/mL)。本法应用于藏药和扇贝标准样品(GBW 10024)中Cr3+和A l3+的测定,测定值与标准值基本吻合,分析结果满意。     

Termination and water adsorption at the alpha-Al2O3 (012)-aqueous solution interface

Understanding the interaction of water with metal oxide surfaces is important to a diverse array of fields and is essential to the interpretation of surface charging and ion adsorption behavior. High-resolution specular X-ray reflectivity was used to determine the termination of and water adsorption on the alpha-Al2O3 (012)-aqueous solution interface. Interference features in the reflectivity data were used to identify the likely termination, consisting of a full Al2O3 layer plus an additional oxygen layer that completes the coordination shell of the upper aluminum site. This was further investigated through a model-independent inversion of the data using an error correction algorithm, which also revealed that there are two sites of adsorbed water above the surface. Characteristics of these two water sites were quantified through a model-dependent structural refinement, which also revealed additional layering in the interfacial water that gradually decays toward disordered bulk water away from the surface. Although the termination observed in this study differs from that assumed in past studies of surface charging, the density of key surface functional groups is unchanged, and thus, predictions of surface charging behavior are unchanged. As the pH(pzc) of this surface has yet to be modeled accurately, a full 3-dimensional surface structural analysis based on the termination observed in this study is needed so that the effects of surface functional group bond length changes on the pK(a) values can be incorporated. Consideration of the termination and sites of water adsorption suggest that singly coordinated oxygen groups will be the primary sites of ion adsorption on this surface.