Surface Acid-base Properties Research Articles

Ethylbenzene to styrene over alkali doped TiO2-ZrO2 with CO2 as soft oxidant

Oxidative dehydrogenation of ethylbenzene (EB) to styrene monomer (SM) over alkali metal (Na, K) doped TiO2-ZrO2 (TZ) has been studied. The EB and CO2 conversions observed over alkali doped TZ are higher than that of non-doped TZ. The enhanced CO2 conversion compared with non-doped counterparts is attributed to improved basicity, formation of TiZrO4 phase with increased CO2 affinity and insertion of K or Na into the lattice which affects the binding energy of “O” in turn providing more labile oxygen species. Alkali doping also effected in fine tuning the surface acid base properties. Moreover, these K and Na doped binary metal oxides system showed high surface area of 256m2/g and 199m2/g respectively. There was a 10-fold increase in the CO2 conversions in case of the doped TZ compared to non-doped TZ increasing the stability of the catalyst by decreasing coking on the surface of the catalyst in spite of the high conversions.

Acid-Base and Photoinduced Processes on Magnesium-Containing Minerals and their Influence on the Troposphere Cleaning

Acid-base, adsorption and photosorption properties of microparticles surface of magnesium-containing compounds produced by dispersion of natural minerals after exposure to the air were studied. It was revealed that the reduction in predominant basicity of minerals surface in a range of periclase (MgO), brucite (Mg (OH)2) and magnesite (MgCO3) can be considered as a result of the presence of iron, silicon and magnesium oxide compounds. Quantum-chemical calculations made during the investigation, the decrease of pressure in the process of long-term contact of Freon 22 with the surface of MgO, irreversible character of adsorption and the absence of fluorine and chlorine-containing products in a gaseous phase give evidence of CFC destructive adsorption on the surface of magnesium oxide. The interaction of chlorine and fluorine derivatives of methane with the surface of aerosol particles from minerals in the darkness and under the influence of sunlight tropospheric radiation was studied. The evaluation of such interactions influence on the process of the Earth troposphere purification from carbon dioxide and dichlorofluoromethane during their adsorption and photosorption on the surface of precipitated aerosol was made.

Photocatalytic oxide films in the built environment

The possibility to increase human comfort in buildings is a powerful driving force for the introduction of new technology. Among other things our sense of comfort depends on air quality, temperature, lighting level, and the possibility of having visual contact between indoors and outdoors. Indeed there is an intimate connection between energy, comfort, and health issues in the built environment, leading to a need for intelligent building materials and green architecture. Photocatalytic materials can be applied as coatings, filters, and be embedded in building materials to provide self-cleaning, antibacterial, air cleaning, deodorizing, and water cleaning functions utilizing either solar light or artificial illumination sources – either already present in buildings, or by purposefully designed luminaries. Huge improvements in indoor comfort can thus be made, and also alleviate negative health effects associated with buildings, such as the sick-house syndrome. At the same time huge cost savings can be made by reducing maintenance costs. Photocatalytic oxides can be chemically modified by changing their acid-base surface properties, which can be used to overcome deactivation problems commonly encountered for TiO2 in air cleaning applications. In addition, the wetting properties of oxides can be tailored by surface chemical modifications and thus be made e.g. oleophobic and water repellent. Here we show results of surface acid modified TiO2 coatings on various substrates by means of photo-fixation of surface sulfate species by a method invented in our group. In particular, we show that such surface treatments of photocatalytic concrete made by mixing TiO2 nanoparticles in reactive concrete powders result in concrete surfaces with beneficial self-cleaning properties. We propose that such approaches are feasible for a number of applications in the built environment, including glass, tiles, sheet metals, plastics, etc.

ChemInform Abstract: Review on Modified N—TiO2 for Green Energy Applications under UV/Visible Light: Selected Results and Reaction Mechanisms.

AbstractReview: [426 refs.]

Ti,Zr]-pillared montmorillonite – A new quality with respect to Ti- and Zr-pillared clays

Mixed titanium–zirconium pillared montmorillonite [Ti,Zr]-PILC and reference Ti-PILC and Zr-PILC were synthesized and characterized with XRD, XRF, diffuse reflectance UV–Vis, XPS and Raman spectroscopies, thermal analysis, N2 adsorption/desorption at −196°C, NH3 TPD–MS, and FTIR monitored pyridine adsorption. Results indicate that pillars in [Ti,Zr]-PILC represent quasi-amorphous mixed Ti–Zr oxide, of short range order similar to that of a zirconium titanate phase. The size of intercalated mixed Ti–Zr cationic species is intermediate between that of Ti and Zr polycations. A new evidence is presented on the nature of pillars and their relationship to the clay sheets. It is demonstrated that in Ti-PILC material titanium sites present at the clay/pillar interface assume tetrahedral coordination, while in [Ti,Zr]-PILC they retain coordination number higher than 4. Textural studies suggest that mixed Ti–Zr-pillars are structurally better defined and more uniform than those formed upon intercalation of the Ti-pillaring sol, and resemble in this respect pillars derived from zirconium oligocations. Measurements of surface acidity prove that a new quality appears in the surface chemistry of oxide props present in [Ti,Zr]-PILC. Although, similarly as in the case of Ti-PILC and Zr-PILC references, the acidity is predominantly of the Lewis type, the [Ti,Zr]-PILC sample possesses a significant population of Lewis acid sites which are much stronger than those present in the reference materials. Results of this study show that uniqueness of structural, textural and surface acid–base properties of mixed titanium–zirconium pillared montmorillonite render this material very attractive from the point of view of potential applications in sorption and catalysis.

Formation of Dimethyl Carbonate on Nature Clay Supported Bimetallic Copper-Nickel Catalysts

Halloysite nanotubes supported Cu–Ni bimetallic catalysts were synthesized and applied to the direct formation of dimethyl carbonate (DMC) from methanol and CO2. Halloystite nanotubes (HNTs), K treated HNTs (KHNTs) and the synthesized catalysts were characterized by thermogravimetric and differential thermalgravimetric analysis (TG-DTA), temperature programmed reduction (TPR), X-ray photoelectron spectrum (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray powder diffraction (XRD), and temperature programmed desorption (TPD) techniques. The catalyst activities were evaluated in a continuous fixed-bed tubular microreactor under 1.2 MPa at 130 °C. The effects of the metal weight loadings on the catalytic performances and surface acid–base properties were studied. It was found that moderately acid–base balance on the catalysts surface were important for the DMC yield.

Surface Acid-Base Properties of Porous Prussian Blue Analogues

Surface acid-base properties of two compositions of porous Prussian blue analogues, Co3[Co(CN)6]2 and Zn3[Co(CN)6]2, are discussed from inverse gas chromatography data recorded in the 473–513 K temperature range. These compositions are representatives of the structural features, cubic (Co) and rhombohedral (Zn) unit cell, found in that family of porous coordination polymers. Chromatographic profiles at infinite dilution were recorded for neutral, acidic and basic probe molecules. For the cubic phase, with partially naked metal centers at the cavities surface, the material has acidic character (KA = 0� 32 and KB = 0� 12) but, for the rhombohedral one, a slightly basic behavior was found (KA = 0� 25 and KB = 0� 27) related to the electron density concentration on the N atom. In this structure the surface of the cavities is formed by N atoms from ZnN4 tetrahedra. These results herein discussed contribute to understand the acid-base interactions in Prussian blue analogues, including their performance in adsorption and separation of mixtures of gases and vapors by these porous solids.

Study of surface acid–base properties of natural clays and zeolites by the conversion of 2-methylbut-3-yn-2-ol

Surface acid–base properties of natural clays and non-clay minerals from Jordanian (J) and Russian (R) deposits as well as H-ZSM-5 were studied applying catalytic reaction of 2-methylbut-3-yn-2-ol (MBOH) conversion. Products of both acidic and basic pathways of the reaction were formed involving surface acid/basic sites of clay minerals. Specific conversions of MBOH decreased in the following order: kaolinite-R>hydromica-R>bentonite-J>red-kaolinite-J=palygorskite-R=H-ZSM-5>zeolite-J>white-kaolinite-J>diatomite-J, which fairly correlated with TPD-NH3 acidity assessment for a majority of samples. However, a contribution of basic sites to the reaction should be taken into account, especially for hydromica-R and kaolinite-R.The strength of acid sites of natural aluminosilicates was compared based on surface acidity and reaction product yields. After 116min of MBOH conversion, the strength of acid sites changed in the following order: kaolinite-R>palygorskite-R>bentonite-J>red- kaolinite-J>white-kaolinite-J>zeolite-J>diatomite-J>H-ZSM-5. At an early (17min) stage of the reaction, the strength of active sites for natural zeolite-J and H-ZSM-5 were comparable, while the latter underwent significant deactivation due to its microporous structure.The rise of activation temperature from 500°C to 700°C for montmorillonite containing sample increased the conversion of MBOH due to the formation of stronger or additional number of basic sites as a result of mineral dehydroxylation. Natural clay samples with a higher content of montmorillonite (30–80%) altered the acid–base properties of the surface and observed higher ability to convert MBOH over acid and basic pathways.

The nature of interactions on copolymer of ethylene with a vynilacetate-metal interface

Surface energetic and acid-base properties of coatings based on copolymers of ethylene with vinylacetate are studied. It is shown, that acid-base interactions have determining role in adhesion interaction on the interface with metal.

Influence of acid-base properties of oxides surface on their reactivity towards epoxy compounds

Acid-base properties of surface of aluminum, iron, and silicon oxides have been studied by pK spectroscopy. γ-Al2O3 and γ-AlO(OH) have been found the most reactive modifiers for epoxy oligomers, due to the presence of active surface groups with pK1 ≈ 4, capable of chemical interaction with the matrix.

Microwave synthesis of a photocatalytically active SnO-based material

Tin(II) oxide nanopowder has been prepared through microwave processing of an ammoniacal Sn6O4(OH)4 suspension, and the effect of synthesis duration on the surface morphology, acid-base properties, and photocatalytic activity of the SnO has been examined. The results demonstrate that the surface morphology plays a key role in determining the photocatalytic activity of powder SnO for methyl orange photo-degradation.

The negative effect of ceria on the propene selectivity for isopropanol decomposition over phosphated and phosphate-free ceria/alumina catalysts

Consequences of loading level of ceria (5, 10 and 20-wt%) on the structural, textural and surface acid–base properties as well as the impacts on catalytic activity towards isopropanol decomposition on pure and phosphated alumina is described. The obtained results indicated that composites mainly kept γ–alumina structure and the addition of ceria and/or phosphate has no effect on the bulk structure of alumina. Textural characteristics show that the phosphated composites have higher surface area than phosphate free samples. Pyridine adsorption as followed by FTIR indicated the presence of Lewis acid sites with different strengths. Moreover, results of gas phase decomposition of isopropanol show a systematic inhibition in propene selectivity based on ceria ratio.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-619) contains supplementary material, which is available to authorized users.

Study of the effect of the acid-base surface properties of ZnO, Fe2O3 and ZnFe2O4 oxides on their gas sensitivity to ethanol vapor

Binary (ZnO, Fe2O3) and ternary (ZnFe2O4) gas-sensitive oxide materials are synthesized, and the correlation between their sensitivity to ethanol vapor and the functional chemical composition of the surface is studied by X-ray photoelectron spectroscopy and by the technique of the adsorption of acid-base indicators. It is found that the sensitivity to ethanol increases with increasing content of Bronsted acid sites with the acidity index pKa ≈ 2.5 and with increasing percentage of surface oxygen involved in OH/CO3/C-O groups. This interrelation is attributed to the specific features of interaction between ethanol molecules and hydroxyl groups on the surface of the oxides.

Assessment of the changes in the cellulosic surface of micro and nano banana fibres due to saponin treatment

The effect of saponin on the surface properties of banana fibres was studied by Inverse Gas Chromatography (IGC). Parameters including the dispersive component of the surface energy, surface heterogeneity, surface area, as well as acid–base surface properties were determined for saponin modified banana micro and nanofibres. These parameters show a more extensive saponin coating on the nanofibres with a network formation which is explained by the higher reactivity of nanofibres due to the higher surface energy, specific interaction and higher surface area presented by the nanofibres. The energetic profile indicates that both micro and nanofibres coated with saponin interact with the same, or similar, energy active sites. Saponin treatment reduces considerably the surface area of the fibres, with the consequent decrease in the monolayer capacity. The interaction with the polar probes clearly indicates that saponin treatment creates new polar active sites for specific interactions in both samples. However, the treatment increases predominately the basicity of the fibre surface with more relevance to the nanofibres. This behaviour will lead to better polymer/fibre interaction during composite preparation.

Application of the Surface Complexation Model to the Biosorption of Cu(II) and Pb(II) Ions onto Pseudomonas Pseudoalcaligenes Biomass

In this study, a potentiometric titration was performed to investigate the surface acid-base properties of Pseudomonas pseudoalcaligenes isolated from activated sludge. Batch sorption as a function of pH was performed to explain the sorption behaviour of Cu(II) and Pb(II) ions onto the bacterial surface. The surface complexation approach in the frame of constant capacitance model was applied to determine the deprotonation constants, site concentrations and metal stability constants for the important surface-functional groups on the biomass. The optimized results showed that the three discrete sites-three pK(a)s model, involving three distinct types of functional groups, namely, carboxyl, phosphate and hydroxyl, could actually fit the protonation of the bacterial functional groups, with average pK(a) values of 4.18, 6.31 and 9.18, and site concentrations of 0.526, 0.525 and 0.478 mmol/g, respectively. The two sites model provided the best fit for the biosorption of Cu(II) and Pb(II) ions onto the biomass by forming complexes with carboxyl and phosphate surface sites, with average log stability constants of 5.95 and 6.94 for Cu(II), and 6.64 and 8.08 for Pb(II), respectively. These results suggested that the surface complexation model yielded the accurate prediction for the biosorption behaviour of Cu(II) and Pb(II) ions on the bacterial biomass and the affinity of P. pseudoalcaligenes biomass for the adsorption of Cu(II) and Pb(II) ions was high enough to remove the metal ions from water.

Adhesion of polymers: New approaches to determination of surface properties of metals

Determination of the acid-base properties of metal surfaces used as substrates in adhesive compounds was performed by a two-liquid method. It was shown that the suggested method provides a possibility of scientifically grounded selection of a substrate for creating adhesive polymeric-adhesive-metal compounds with a high level of interphase acid-base interaction.

Sustainable production of acrolein: catalytic performance of hydrated tantalum oxides for gas-phase dehydration of glycerol

A series of tantalum oxide samples (Ta2O5-T) were prepared by varying the calcination temperature T in the range of 110–700 °C of a highly hydrated precursor (Ta2O5·2.1H2O), which was obtained from a hetero-phase reaction between tantalum pentachloride and aqueous ammonia. These Ta2O5-T samples were characterized by TG/DTA, XPS, nitrogen adsorption, XRD, and UV-Raman, and were employed to catalyze the gas-phase dehydration of glycerol (GL) to produce acrolein (AC) at around 315 °C. n-Butylamine titration using Hammett indicators, NH3- and CO2-TPD, and IR of adsorbed pyridine were measured to assess the surface acid–base properties of the catalysts. The Ta2O5-350 catalyst, which was in a hydrated amorphous state and showed no basicity but a maximum strong acidity at −8.2 < H0 ≤ −3.0 (H0 being the Hammett acidity function) prior to the reaction, was identified among all Ta2O5-T samples as the best performing catalyst in terms of AC selectivity and GL consumption rate. The AC selectivity increased with increasing the fractional strong acidity at −8.2 < H0 ≤ −3.0 but the catalytic GL consumption rate increased with increasing the number of strong acid sites on the catalyst prior to the reaction. The partly (Ta2O5-600) and fully (Ta2O5-700) crystallized samples showed almost no strong acidity but they exhibited some basicity in the CO2-TPD experiments; their much lower AC selectivity (<40 mol%) as compared with that on Ta2O5-350 (75 mol%) indicated that surface basicity was detrimental to the AC selectivity. The best performing Ta2O5-350 catalyst also showed after activation in the initial hours of the reaction a good catalytic stability in long term reactions, regardless of the reaction temperature (305–340 °C) and GHSVGL (80–400 h−1).

Degradation of GD and VX over Oxides Mixing with Bleaching Powder

Nanosize oxides with acidic or basic sites could neutralize the droplets of chemical warfare agents. Refined bleaching powder was added to increase the reactivity of the nanosize oxides for degradation of GD(3,3-dimethyl-2-butyl methylphophonofluoridate or Soman) and VX(O-ehtyl S-2-(diisopropylamino)ethyl methyl-phosphonothioate). It was found that all the studied decontaminant powders exhibited room-temperature reactivity for GD and VX droplets which depends on their surface acid–base property. Decontaminant powders with basicity like nanosize MgO have the best activity towards GD and the degradation rate was improved obviously for N-MgO due to the adding of refined bleaching powder. However, surface acidity was very important for neutralizing VX over the decontaminant powders.

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.

Solvothermal Synthesis and Catalytic Properties of Nanocrystalline ZnFe2−xAlxO4 (x = 0, 1, 2) Spinels in Aniline Methylation

ZnFe2−xAlxO4 (x = 0, 1, 2) spinels were obtained by microwave-assisted solvothermal method using 1,4-butanediol as reaction medium. The results of XRD and HRTEM studies have indicated higher nanocrystallinity of aluminium containing spinels, and N2 adsorption–desorption measurements have revealed their enhanced textural properties, in particular much higher specific surface areas. NH3-TPD method and cyclohexanol test have shown the variation of surface acid–base properties with the changes in the spinel composition. All studied spinels were active in aniline methylation and proved to be selective for N-methylation leading to N-methylaniline and N,N-dimethylaniline. The main advantage of aluminium containing spinels is that N-alkylation with methanol is possible at significantly lower temperature (200–260 °C) when pure zinc ferrite is almost inactive.