Adsorption activity and selectivity of the surface of InP-CdS system semiconductors with respect to toxic microimpurities

The mechanism of and rules governing the interaction of carbon oxides (CO and CO₂) and ammonia with the surface of binary (InP and CdS) and quaternary ((InP) _x (CdS)_{1 ? x} ) InP-CdS system components were studied by piezoelectric quartz microweighing and IR and Raman spectroscopy. The results obtained, acid-base and other physicochemical adsorbent properties, and the electronic structure of adsorbate molecules led us to conclude that the adsorption of the gases at temperatures above 297 K was predominantly chemical in nature and largely occurred according to the donor-acceptor mechanism with the participation of coordination unsaturated “metallic” atoms. The adsorbabilities of the gases on the same adsorbent under equal conditions were different and increased in the series a(CO₂) → a(NH₃) → a(CO). The acid-base, adsorption, and optical properties of adsorbents changed in parallel, which was indicative of the same origin of active adsorption centers and surface biographical states. This also allowed the adsorption activity of a surface to be predicted from its acid-base properties and the volumetric properties of the initial binary compounds and elementary components. The behaviors of (InP) _x (CdS)_{1 ? x} solid solutions and binary system components (InP and CdS) had common and special features. Surface characteristic-composition diagrams were used to find the system component most active with respect to CO, which was the (InP)_0.95(CdS)_0.05 solid solution. It was used to create a high-sensitivity and selectivity sensor.     

Adsorption, electrophysical, and optical studies of the surface of solid solutions and the binary components of the InSb-ZnTe system

Piezoquartz microweighing, surface electroconductivity measurements, and IR and Raman spectroscopies were used to study the mechanism and regularities of the interaction of carbon monoxide, ammonia, and oxygen, gases of different electronic natures encountered in the environment and various technological processes, with the surface of solid solutions and the binary compounds of the InSb-ZnTe system. An analysis of the results with the use of the acid-base and other physicochemical characteristics of the adsorbents and of the electronic properties of the adsorbate molecules showed that the values of adsorption of the gases lie within α = 10⁻⁵−10⁻³ mol/m². It was demonstrated that, at temperatures above 293 K, the adsorption of CO and NH₃ occurs by the donor-acceptor mechanism, whereas oxygen is adsorbed through the ion-radical mechanism, with the predominant participation of coordinatively unsaturated metal atoms and vacancy defects, respectively. It was revealed that the acid-base, adsorption, electrophysical, and optical properties vary similarly with changing composition of the system, a behavior that suggests the same origin of adsorption sites and inherent surface states and makes it possible to predict the adsorption activity of a surface on the basis of its acid-base properties and the properties of the binary compounds and constituent elements. Similarities and distinctions in the behavior of (InSb) _x (ZnTe)_{1 − x} solid solutions and the binary compounds (InSb and ZnTe) were identified. Specific features of solid solutions, as multicomponent systems, are that adsorption on them is energetically more favorable, especially well pronounced in the acid-base characteristic-composition and adsorption characteristic-composition diagrams. Such diagrams made it possible to determine the solid solution most active with respect to ammonia, (InSb)_0.95(ZnTe)_0.05, which was used to make a selective high-sensitivity gas sensor.     

New catalysts and adsorbents on the basis of the InSb-CdTe semiconducting system

The acid-base properties of solid solutions and binary components of the InSb-CdTe system were studied by IR spectroscopy, pH isoelectric point measurements, and conductometric titration; adsorption properties with respect to CO, O₂, NO₂, NH₃, CO + O₂, and NO₂ + NH₃, by piezoquartz microweighing; and catalytic properties in the oxidation of carbon(II) oxide and reduction of nitrogen(IV) oxide with ammonia, by the pulsed and circulation flow methods. The nature, strength, and concentration of acid centers were determined. Changes in the concentration of acid centers under the action of gases (NO₂ and NH₃), gamma irradiation, and composition variations were estimated. The experimental dependences, thermodynamic and kinetic adsorption characteristics, the electrophysical, acid-base, and other physicochemical characteristics of the adsorbents, and adsorption characteristic-composition phase diagrams were analyzed taking into account the electronic nature of adsorbate molecules to determine the mechanism and characteristics of adsorption processes depending on the conditions of adsorption and the composition of the system. The results of adsorption studies were used to preliminarily determine the temperature regions of the occurrence and the mechanism of the reactions studied. A shock mechanism was suggested. Separate components (predominantly, solid solutions) of the InSb-CdTe system showed high catalytic activity at comparatively low temperatures. Along with behavior common to the system and its binary compounds (InSb and CdTe), solid solutions exhibited features characteristic of multi-component systems. These were the presence of extrema in the pH_iso-composition, adsorption characteristic-composition, and catalytic activity-composition diagrams. The use of these diagrams allowed us to discover system components most active with respect to the gases and reactions studied and create high-sensitivity and selective sensors and high-activity and selective catalysts on the basis of these components.     

The Acid-Base Properties and Chemical Composition of the Surface of the InSb-ZnTe System

The acid-base properties and chemical composition of the surface of solid solutions and binary components of the InSb-ZnTe system were studied by the hydrolytic adsorption, nonaqueous conductometric titration, mechanochemistry, IR spectroscopy, and mass spectrometry methods. The strength, nature, and concentration of acid centers were determined. Changes in the concentration of acid centers caused by surface exposure to CO and changes in the composition of the system were also studied. The mechanism of acid-base interactions was established. The chemical composition of the surface of system components exposed to air included adsorbed H₂O molecules, OH⁻ groups, hydrocarbon and oxocarbon compounds, and the products of surface atom oxidation. After thermal treatment in a vacuum, the composition of the surface approached the stoichiometric composition. Original Russian Text ? I.A. Kirovskaya, E.G. Shubenkova, O.T. Timoshenko, T.N. Filatova, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 4, pp. 732–738.     

Comparative acid-base properties of the surface of components of the CdTe-ZnS system in series of substitutional solid solutions and their analogs

The acid-base properties of the surface of solid solutions and binary components of the CdTe-ZnS system are studied by hydrolytic adsorption, nonaqueous conductometric titration, mechanochemistry, IR spectroscopy, and Raman scattering spectroscopy. The strength, nature, and concentration of acid centers on the original surface and that exposed to CO are determined. The changes in acid-base properties in dependence on the composition of the system under investigation in the series of CdB₆, ZnB₆ analogs are studied.     

Molecular Organometallic Chemistry on Surfaces: Reactivity of Metal Carbonyls on Metal Oxides

Metal carbonyls react on metal oxide surfaces to give a wide range of structures analogous to those of known compounds. The reactions leading to formation of surface-bound metal carbonyls are explained by known molecular organometallic chemistry and the functional group chemistry of the surfaces. The reaction classes include formation of acid-base adducts as the oxygen of a carbonyl group donates an electron pair to a Lewis acidic center; nucleophilic attack at CO ligands by basic surface hydroxyl groups or O^2? ions; ion-pair formation by deprotonation of hydrido carbonyls to give carbonylate ions; interaction of bifunctional complexes with surface acid-base pair sites such as [Mg^2⊕O^2?]; and oxidative addition of surface hydroxyl groups to metal clusters. The reactions of surface-bound organometallic species include redox condensation and cluster formation on basic surfaces (paralleling the reactions in basic solution) as well as oxidation of mononuclear metal complexes and oxidative fragmentation of metal clusters by reaction with surface hydroxyl groups. Most supported metal carbonyls are unstable at high temperatures, but some, including osmium carbonyl cluster anions on the basic MgO surface, are strongly stabilized in the presence of CO and are precursors of catalysts for CO hydrogenation at 550 K.     

Adsorption properties of GaAs-CdS system

The adsorption properties of GaAs-CdS solid solutions and the constituent binary systems with respect to CO and NH₃ were studies by piezoquartz microweighing, temperature-programmed desorption, and IR spectroscopy. On the basis of an analysis of the measured α _p = f(T), α _T = f(p), and α _T = f(t) dependences, the thermodynamic and kinetic characteristics of adsorption, earlier obtained acid-base and other physicochemical characteristics of adsorbents, and the electronic properties of the adsorbate molecules, the mechanism and regularities of the adsorption processes at various conditions and compositions of the system were established. A comparison of the adsorption properties of the GaAs and CdS individual binary compounds with their (GaAs)_x(CdS)_1?x solutions, multicomponent systems, revealed common and distinctive features. Optimal compositions of adsorbents suitable for manufacturing primary transducers in sensors for medical and environmental purposes were determined.     

Effect of the structure of Ti-Sb-O catalysts on their acid-base properties,surface oxygen binding energy,and catalytic properties in propylene ammoxidation

The structure of Ti-Sb-O catalysts, namely, a solid solution of antimony ions in rutile-type TiO₂ and the titanium antimonate TiSb₂O₆, is characterized by X-ray diffraction, high-resolution electron microscopy, calorimetry, and IR spectroscopy. The structure effects on the acid-base properties and the surface oxygen binding energy are considered, as well as the correlation of these characteristics with the catalytic properties of the Ti-Sb-O system in propylene ammoxidation. The solid solution has a regular crystal structure. As a consequence, the surface has high concentrations of strong aprotic acid and strong basic sites and is characterized by a high surface oxygen binding energy. In the titanium antimonate structure, extended crystallographic shear defects cause a marked enrichment of the surface with antimony and, accordingly, an increase in the relative concentration of weak aprotic acid sites and a decrease in the surface oxygen binding energy. The changes of the structure and acid-base properties of the surface in passing from the solid solution to TiSb₂O₆ result in an increase in the acrylonitrile selectivity.     

Bimetallic Rh-Co/ZrO<Subscript>2</Subscript> catalysts for ethanol steam reforming into hydrogen-containing gas

The properties of supported bimetallic Rh-Co/ZrO₂ catalysts in ethanol steam reforming into hydrogen-containing gas were studied. The particles of Rh-Co solid solutions on the catalyst surface were prepared by the thermal decomposition of the double complex salt [Co(NH₃)₆][Rh(NO₂)₆] and the solid solution Na₃[RhCo(NO₂)₆]. It was found that the bimetallic Rh-Co/ZrO₂ catalysts exhibited high activity in the reaction of ethanol steam reforming. The equilibrium composition of reaction products was attained at 500–700°C and a reaction mixture space velocity of 10000 h⁻¹.     

Impurity and phase compositions of the surface of CdxHg1?xTe solid solutions

The results of our studies of the real surface impurity and phase compositions of Cd _x Hg_{1 − x} Te solid solutions and changes in the compositions induced by thermal evacuation and ion bombardment are presented. The impurity and phase compositions of the surface of CdHgTe solid solutions exposed to air included the gases and vapors (CO, O₂, H₂O) and hydrocarbons adsorbed from the atmosphere. Thermal vacuum treatment of the samples at 615 K led to surface purification from organic impurities, oxygen, water, and mercury microinclusions. The Cd _x Hg_{1 − x} Te sample surface was completely cleaned and its stoichiometric composition achieved by ion etching to a depth of 100 ?.     

Adsorption properties of CdS-CdTe system semiconductors

The adsorption of carbon(II) oxide and ammonia on nanofilms of solid solutions and binary compounds of the CdS-CdTe system is studied by means of piezoquartz microweighing, FTIR IR, and measuring electroconductivity. Allowing for the conditions and composition of semiconductor systems, we determine the mechanisms and principles of adsorption processes by analyzing the α _p = f(T), α _T = f(p), and α _T = f(t) experimental dependences; IR spectra; the thermodynamic and kinetic characteristics of adsorption; the acid-base, electrophysical, and other characteristics of adsorbents; the electron nature of adsorbate molecules; and the obtained acid-base characteristics: the composition and adsorption characteristics and composition state diagrams. Previous statements on the nature and retention of local active centers responsible for adsorption and catalytic processes upon changes in their habitus and composition (as components of systems of the A^IIIB^V-A^IIB^VI and A^IIB^VI-A^IIB^VI types) on the surface of diamond-like semiconductors are confirmed. Specific features of the behavior of (CdS) _x (CdTe)_{1 ? x} solid solutions are identified in addition to general features with binary compounds (CdS, CdTe), as is demonstrated by the presence of critical points on acid-base characteristics-composition and adsorption characteristics-composition diagrams. On the basis of these diagrams, the most active adsorbents (with respect to CO and NH₃) used in designing highly sensitive and selective sensors are identified.     

PS-b-PAA嵌段共聚物修饰的智能表面的制备及其响应行为的研究

利用原子转移自由基聚合(ATRP), 再经水解后得到了嵌段共聚物聚苯乙烯-b-聚丙烯酸(PS-b-PAA), 接枝到硅烷偶联剂γ-(2,3环氧丙氧)丙基三甲氧基硅烷[γ-(2,3-glycidoxypropyl)trimethoxysilane, GPS]修饰的Si表面得到了对溶剂具有响应性的智能表面, 并通过凝胶渗透色谱(GPC)、傅立叶变换红外光谱(FTIR)、核磁共振(¹H NMR)和原子力显微镜(AFM)等测试手段对产物进行了表征. 然后, 通过接触角测试研究了所得智能表面对不同溶剂的响应行为. 结果显示, PS-b-PAA接枝表面的润湿性与接枝共聚物的组成及表面处理的溶剂性质有关. 在相同的溶剂处理条件下, 共聚物中PS/PAA比值越小, 表面亲水性越大; 乙醇和碱性溶液处理后的表面呈亲水状态, 甲苯和酸性水溶液处理后的表面又切换到疏水状态, 同时其表面的酸碱响应行为具有非常稳定的可逆性.     

The Effects of Beating,Web Forming and Sizing on the Surface Energy of <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> Kraft Fibres Evaluated by Inverse Gas Chromatography

In this work attention has been focused on the effects of papermaking beating, web forming and sizing operations on the physical/chemical surface properties of bleached Eucalyptus globulus kraft fibres. Inverse gas chromatography (IGC) was used to determine the dispersive component of surface tension (γ_s^d) as well as the acidic/basic character (according to the Lewis concept) of the solid surfaces (pulp fibres and pulp handsheets). The results have shown that the main effect of beating is to increase the fibre's Lewis acidic character. Web forming caused a strong decrease in γ_s^d and significant increments in the adhesion works of both acidic and basic probes, lowering the ratio between the two. Nevertheless, the surface of handsheets still exhibited a dominant acidic character. The sizing operation did not change the dispersive component of the surface tension significantly but decreased the difference between the adhesion works of the acidic and basic probes, rendering the handsheet surface less Lewis acidic and more Lewis basic. Thus, although internal sizing is expected to strongly influence liquid spreading at the paper surface and liquid penetration of the fibre's network, it is concluded that beating and web forming lead to important changes in the surface energetic properties of the Eucalyptus globulus kraft fibres.     

ZrO_2负载Pt催化巴豆醛选择性加氢

以高比表面积ZrO2为载体,采用浸渍法制备了负载型Pt催化剂,应用于常压下气相巴豆醛加氢反应,考察了Pt负载量和H2还原温度等对巴豆醛选择性加氢性能的影响.实验结果表明,Pt负载量(质量分数)为3%的3Pt/ZrO2催化剂经500℃还原后,具有较高的巴豆醛选择性加氢性能:巴豆醛转化率为27%,巴豆醇的选择性为55%.X射线粉末衍射(XRD)分析,CO化学吸附,NH3程序升温脱附(NH3-TPD)表征结果表明Pt/ZrO2催化剂上Lewis强酸中心和适宜的Pt颗粒(约为8nm)有利于巴豆醛选择性加氢生成巴豆醇.     

Study of the Acid-Base Properties of sio2-Supported Nimoo4 Catalysts by Temperature-Programmeddesorption. Effect of the Active Phase Content

The acid-base properties of a series of SiO₂-supported NiMoO₄ catalysts were investigated by temperature-programmed desorption of NH₃ and CO₂. Results show that supported catalysts with ca. one monolayer of the active phase are less acidic than the unsupported stoichiometric NiMoO₄.     

Optimization of Active Sites via Crystal Phase,Composition, and Morphology for Efficient Low-Iridium Oxygen Evolution Catalysts

Reducing the amount of iridium in oxygen evolution electrocatalysts without compromising their catalytic performances is one of the major requirements in proton-exchange-membrane water electrolyzers. Herein, with the help of theoretical studies, we show that anatase-type TiO₂-IrO₂ solid solutions possess more active iridium catalytic sites for the oxygen evolution reaction (OER) than IrO₂, the benchmark OER catalyst. Note that the same is not observed for their rutile-type counterparts. However, owing to their thermodynamic metastability, anatase-type TiO₂-IrO₂ solid solutions are generally hard to synthesize. Our theoretical studies demonstrate that such catalytically active anatase-type solid-solution phases can be created in situ on the surfaces of readily available SrTiO₃-SrIrO₃ solid solutions during electrocatalysis in acidic solution as the solution can etch away Sr atoms. We experimentally show this with porous SrTiO₃-SrIrO₃ solid-solution nanotubes synthesized by a facile synthetic route that contain 56 % less iridium than IrO₂ yet show an order of magnitude higher apparent catalytic activity for OER in acidic solution.     

The structure and chemical and acid-base state of the surface of solid solutions and binary components in the InSb-CdS system

The surface physicochemical properties, including microstructure, chemical composition, and acid-base surface properties, of solid solutions and binary components in the InSb-CdS system obtained for the first time were studied. Films of all the components had a polycrystalline structure with a nonuniform character of the distribution of crystallites, which associated into agglomerates. The chemistry of the surface was mainly determined by adsorbed H₂O and CO₂ molecules, OH⁻ groups, and, to a lesser extent, oxygen and hydrogen carbon compounds. The strength, concentration, and nature of acid centers were determined. Coordination-unsaturated In and Cd atoms, adsorbed water molecules, and OH-groups were responsible for acid-basic centers. Changes in the acid-base properties of the surface of InSb-CdS system components caused by composition variations were studied. They correlated with the “specific conductivity-composition” dependence, reflected the special features of donor-acceptor interactions in solid solutions, and could be used to predict adsorption-catalytic properties.     

Cleaning of pyrolytic hexagonal boron nitride surfaces

Hexagonal boron nitride (h‐BN) has recently garnered significant interest as a substrate and dielectric for two‐dimensional materials and devices based on graphene or transition metal dichalcogenides such as molybdenum disulfide (MoS₂). As substrate surface impurities and defects can negatively impact the structure and properties of two‐dimensional materials, h‐BN surface preparation and cleaning are a critical consideration. In this regard, we have utilized X‐ray photoelectron spectroscopy to investigate the influence of several ex situ wet chemical and in situ thermal desorption cleaning procedures on pyrolytic h‐BN surfaces. Of the various wet chemistries investigated, a 10 : 1 buffered HF solution was found to produce surfaces with the lowest amount of oxygen and carbon contamination. Ultraviolet/ozone oxidation was found to be the most effective ex situ treatment for reducing carbon contamination. Annealing at 1050 °C in vacuum or 10^?5 Torr NH₃ was found to further reduce oxygen and carbon contamination to the XPS detection limits. Copyright © 2015 John Wiley & Sons, Ltd.     

Ion-exchange properties of silica gel with covalently bonded histidine

The ion-exchange and acid-base properties of Silasorb 600 (10 μm) with immobilized histidine (His-SiO₂) were investigated. The acid-base properties of the sorbent were estimated from the dependence sof the retention of organic acids and bases on the eluent pH. The effect of various organic modifiers (benzoic, citric, oxalic, and sulfuric acids) and the eluent pH on the retention of inorganic ions was studied. It was shown that His-SiO₂ exhibits anion-exchange properties in acidic and weakly acidic media at pH < 5.7. Eight anions were separated under optimal conditions on a 150 × 4.6-mm column in 21 min using a 5 mM oxialic acid solution as an eluent.     

Correlation Between the Surface Acid-base Nature of Solid Metal Oxides and Temperature of CaSO4 Decomposition

By means of the combined use of scanning electron microscopy+energy dispersive spectrometry(SEM+EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetry (TG), the thermal decomposition of gypsum and gypsum bonded investment used for casting jewellery products has been studied in order to gain a further insight into the origin of the gas porosity in gold-based alloys produced via lost wax casting. The occurrence of the defect is related to the thermal decomposition of CaSO₄ that constitutes with silica the investment material and the decomposition of which takes place at a temperature very close to the casting temperature of some typical gold alloys. The decrease of the thermal decomposition temperature of gypsum is induced by the presence of silica and is related to the surface acid-base interaction between SiO₂ and CaSO₄. On the base of these results, the solid state thermal decomposition of calcium sulphate in the presence of other metal oxides characterised by different acid-base nature has been investigated and a correlation between the surface acid-base properties measured as isoelectric point of the solid surface (IEPS) and via XPS analysis and the temperature of CaSO₄ thermal decomposition is observed. This revised version was published online in July 2006 with corrections to the Cover Date.