Surface Adsorption Properties Research Articles

Suppression of the NO2 interference by chromium addition in WO3-based ammonia sensors. Investigation of the structural properties and of the related sensing pathways

WO3 and Cr–WO3 powders were prepared by sol–gel process, with Cr:W atomic concentration ranging from 2% to 8.8%. WCl6 was used as W precursor and reacted with methanol in presence of acetyacetone as stabilizer. The required amount of Cr 2-ethylhexanoate was then added to the resulting solution, which was subsequently dried. The resulting powder was heat-treated at temperatures ranging from 200 to 700°C. With increasing the Cr concentration, the samples heat-treated at 500°C contained an increasing amount of the additional phase Cr2WO6, as evidenced by X-ray diffraction and Transmission Electron Microscopy. The sensing tests toward ammonia gas, from 50 to 500ppm showed that, up to 5% concentration, Cr addition lowered the best operating temperatures and/or enhanced the response with respect to pure WO3, then the response remarkably decayed. DFT modeling showed that Cr(III) incorporation was more favorable in interstitial position while Cr (VI) was more favored in substitutional configuration. In this case, highly acidic Cr sites are present, enhancing the adsorption of ammonia species and reactions not involving NO2 as by-product. Beyond 5% Cr concentration, Cr2WO6 formation extracts Cr from the WO3 structure, so decreasing the ammonia response. Moreover, the appearance of Cr2WO6 seems to deactivate the surface adsorption properties of the material.

A potential therapeutic system for Alzheimer’s disease using adsorbents with alkyl ligands for removal of blood amyloid β

Amyloid beta proteins (Aβ) in the brain are the main cause of Alzheimer's disease. Peripheral administration of Aβ-binding substances, which may act as a sink for Aβ from the brain, has been reported to reduce brain Aβ. We previously found C16-cellulose beads had high Aβ-removal activity in vitro. In this study, we investigated the optimum surface properties of adsorbents for removal of Aβ in vitro and in humans. Batch analysis was performed with porous cellulose beads or silica beads with or without 2-22 methylene groups. Aβ-removal activity of C16-cellulose beads increased with increasing alkyl chain length. In contrast, with cellulose the amount of Aβ removed by the silica beads decreased with increasing alkyl chain length. Cellulose beads with 16 or 22 methylene groups were best (over 99% removal) among all the beads tested (p≤0.01). The adsorbent surfaces were analyzed by near-infrared spectroscopy, which revealed that the optimum beads had a sufficiently hydrophobic surface with an appropriate amount of adsorbed water accessible on the surface. Aβ removal efficiency by C16-cellulose beads was investigated for 5 renal failure patients on hemodialysis, resulting in 51.1±6.6% for Aβ1-40 and 43.8±4.5% for Aβ1-42 (p≤0.01). In conclusion, cellulose beads with 16 or 22 methylene groups and an appropriate amount of adsorbed water were the optimum Aβ adsorbents. The device with C16-cellulose beads had high Aβ removal activity in humans. These adsorbents might be useful for Alzheimer's disease therapy.

Comparison on Pore Development of Activated Carbon Produced from Scrap Tire by Hydrochloric Acid and Sulfuric Acid

Two activated carbons employing Scrap Tire as precursor were produced by using two different activating agents, HCl and H2SO4 (fixed impregnation ratio 1:1). Both of activated carbons were allowed by single-step to get difference carbonized at 500, 600 and 700°C in a muffle furnace for 1 h. Activated carbons differed with the physical structure, chemical and adsorption properties which were derived from Scanning Electron Microscope, and N2 adsorption/desorption isotherms. Batched sorption studies were performed to compare the iodine and methylene blue adsorption properties of two carbons. The carbon materials obtained from sulfuric acid activation of 500°C has BET surface area as high as 1066.70 m2/g, Methylene blue adsorption and Iodine number of 288.90 and 590.50 mg/g, respectively. The surface area and adsorption properties of carbon produced using sulfuric acid activation were higher than that produced using hydrochloric acid activation. The results suggest the feasibility of the process from the point of view of both porous texture and adsorption yield.

A density functional theory study on influence of 3d alloying elements on electrochemical properties of cobalt-base alloys

The paper systematically studies the impact of the 3d transition metals Ti, V, Cr, Mn, Fe, Ni and Cu on electrochemical stability of non-passivated cobalt-base alloys {0001} surface by evaluating the chemical potential and the electrode potential shift relative to pure cobalt metal using density functional theory calculations. Cr, Fe, Mn, and V are found to make the Co atoms more stable on the {0001} surfaces of the corresponding alloys compared to pure Co {0001} surfaces, whereas Ti, Ni, and Cu make Co atoms much less stable. Among all the considered alloying elements, chrome is the most beneficial to the stability enhancement of alloys. Furthermore, the effects of water and hydroxyl adsorption on the electrochemical stability are considered. It is found that the surface adsorption properties may be considerably modified by introducing the Cr atoms. Our results indicate that water or hydroxyl adsorption destabilizes both the Co–Cr alloy and pure Co surface. However, the Co–Cr alloy surface is still more stable than the pure Co surface in the presence of adsorbed water, while the pure Co surface is more stable than the Co–Cr alloy surface in the presence of adsorbed hydroxyl. Our calculation reveals that the electrochemical corrosion property of the Co–Cr alloy is insensitive to water adsorption and sensitive to hydroxyl adsorption in comparison with the pure Co metal.

Surface and aggregation properties of heterogemini surfactants containing quaternary ammonium and guanidine moiety

A novel gemini surfactant with nonidentical hydrophilic groups containing guanidine group and quaternary salt, N,N-dimethyl-N-[3-(N′,N′-dimethyl-N″-alkylguanidiumhydrochloride)propyl]-1-alkyl ammonium chloride (diCnGQ, where n represents hydrocarbon chain lengths of 8, 10, and 12) was successfully synthesized. The adsorption and aggregation properties of diCnGQ in aqueous solution have been investigated through surface tension, conductivity, steady-state fluorescence. The critical aggregation concentration (cac) obtained from different techniques showed fairly good agreement. Surface tension measurements have been used to derive surface adsorption properties such as adsorption efficiency and effectiveness (pC20 and cac/C20), the maximum surface excess concentration (Γmax) and minimum surface area permolecule (Amin) at the air–water interface. Temperature dependent conductivity measurements have been used to obtain the degree of counterion binding (β), and the thermodynamic parameters such as standard free energy (ΔGagg), enthalpy (ΔHagg), and entropy (ΔSagg) of aggregation. The aggregation number (Nagg) for diCnGQ has been derived by using the fluorescence quenching technique. As a comparison, the heterogemini surfactants showed a lower cac and higher efficiency in lowering the surface tension than the corresponding monomeric surfactants and their equimolar mixture.

Surface adsorption and micelle formation of imidazolium-based zwitterionic surface active ionic liquids in aqueous solution

A novel class of zwitterionic surface active ionic liquids (SAILs), N-alkyl-N′-carboxymethyl imidazolium inner salts ([NCn, N′CO2Im], n=10, 12, 14), was synthesized. Their aggregation behavior in aqueous solution was investigated by surface tension, isothermal titration calorimetry, and steady-state fluorescence. Compared with the reported imidazolium-based cationic SAILs, 1-alkyl-3-methylimidazolium bromide ([Cnmim]Br) and zwitterionic betaine surfactants, (CnH2n+1N(CH3)2CH2COO−), [NCn, N′CO2Im] exhibits significantly lower critical micelle concentration (cmc) and surface tension at cmc (γcmc) values. It is attributed to the incorporation of a deprotonated carboxylic group into the head group, which weakens the electrostatic repulsion between head groups and favors micellization. The micellar aggregation number of [NCn, N′CO2Im] is larger than that of [Cnmim]Br, while less than that of CnH2n+1N(CH3)2CH2COO−. Similar to the traditional zwitterionic surfactants, the surface activity and adsorption properties of [NC12, N′CO2Im] at air/water interface have a slight variation with temperature, pH, and ionic strength. This indicates that the present zwitterionic SAILs display the aggregation behavior much similar to zwitterionic surfactants, distinctly different from imidazolium-based cationic SAILs. Sets in low sensitivity to the environmental conditions, superior surface activity and unique physicochemical properties of ionic liquids, [NCn, N′CO2Im] can be exploited for utilizing as a potential substitute for conventional surfactants in certain fields.

Systematic features of the variation in the crystal-chemical, electrical, and surface physicochemical properties of A X B8 − X materials on the energy of the inverse adsorption piezoelectric effect

Based on the generalization of experimental data on the structure, properties, adsorption and electrical properties of diamond-like semiconductors, the systematic features of variation in their crystalchemical, electrical, and surface (adsorption and electrical) properties depending on the energy of the reverse adsorption piezoelectric effect is established for the first time. It is noted that this energy coincides with the energy of formation and annihilation of point defects in solids, which is determined by the dilatometric and calorimetric methods. Empirical formulas for variation in the band gap, melting point, and microhardness depending on the energy density in oxygen are found for II–VI compounds. Based on the found systematic feature, the values of the microhardness for the semiconductor materials HgS, HgSe, and Cd0.12Hg0.88Te, which are lacking in published data, are found.

Higher methane storage at low pressure and room temperature in new easily scalable large-scale production activated carbon for static and vehicular applications

The methane adsorption properties of High Surface Activated Carbon (HSAC) samples were evaluated at room temperature (298K) and pressure up to 3.5MPa using a new optimized volumetric apparatus f-PcT (fast Pressure–concentration–Temperature) for accurate and reliable gas adsorption measurements. A comprehensive characterization of different activated carbon samples was carried out by means of helium picnometry for the skeletal density evaluation, by the Brunauer–Emmett–Teller (BET) method for the measurement of the surface area, by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) for topography and long-range order estimation, respectively.All the adsorption data were evaluated by Langmuir/Tóth isotherm model with a very high accuracy. Comparison with data available in the literature shows a good agreement in terms of maximum methane uptake on similar materials and an enhanced performance for the reversible adsorption at very low pressure. In fact, the probed HSAC samples show both higher methane storage values for pressure up to 1.5MPa and totally reversible methane uptake up to many cycles without any treatment in between. Furthermore, their adsorption properties are stable also after air exposure.These results represent the starting point for a real and efficient alternative method to the natural gas storage for static and/or automotive applications.

Role of proton ordering in adsorption preference of polar molecule on ice surface

Adsorption of polar monomers on ice surface, relevant to the physical/chemical reaction in ice clouds as well as growth of ice, remains an open issue partially due to the unusual surface characteristics with protons at the top layer of ice. Using first-principle calculations, we explore the adsorption properties of ice surface in terms of a surface proton order parameter, which characterizes the inhomogeneity of the dangling atoms on ice surface. We show that, due to an effective electric field created by dangling OH bonds and lone pairs of water molecules not only directly neighboring but also further away from the adsorbed polar molecule on the ice surface, the adsorption energy of polar monomer on ice surface exhibits large variance and a strong correlation with the proton order parameter of ice surface. Our results about the positive correlation between the inhomogeneity of ice surface and adsorption energies suggest that the physical/chemical reactions as well as the growth of ice may prefer to occur firstly on surfaces with larger proton order parameter.

Removal of internal caps during hydrothermal treatment of bamboo-like carbon nanotubes and application of tubes in phenol adsorption

Experimental data on the influence of the hydrothermal opening procedure conditions on the polarity, surface chemical composition and adsorption properties of multiwalled carbon nanotubes toward phenol are reported. The enthalpy of immersion measurements is reported, and it is shown that with the rise in burn-off, a progressive rise in nanotube surface polarity was observed. Using XPS data, the surface groups are identified. Moreover, by the analysis of HRTEM images and the values of enthalpy of immersion in benzene, it is shown that the removal of internal caps takes place mainly at higher burn-offs (larger than ca. 15%). Obtained series of nanotubes is tested in phenol adsorption, and calculated differential enthalpies of adsorption values are in the range of those determined for adsorption on graphite. Basing on obtained data, it is shown that the state of phenol in first layer is close to solid for adsorption on closed tubes and progressively approaches the state of supercooled liquid after tube opening and with the rise in burn-off.

Surface modification, characterization and adsorptive properties of a coconut activated carbon

A coconut activated carbon was modified using chemical methods. Different concentration of nitric acid oxidation of the conventional sample produced samples with weakly acidic functional groups. The oxidized samples were characterized by scanning electron micrograph, nitrogen absorption–desorption, Fourier transform infra red spectroscopy, Bothem method, pH titration, adsorption capacity of sodium and formaldehyde, and the adsorption mechanism of activated carbons was investigated. The results showed that BET surface area and pore volume of activated carbons were decreased after oxidization process, while acidic functional groups were increased. The surface morphology of oxidized carbons looked clean and eroded which was caused by oxidization of nitric acid. The oxidized carbons showed high adsorption capacity of sodium and formaldehyde, and chemical properties of activated carbon played an important role in adsorption of metal ions and organic pollutants.

DFT and surface-enhanced Raman scattering study of tryptophan–silver complex

Surface-enhanced Raman scattering (SERS) study of tryptophan was carried out in silver hydrosol. The surface adsorption properties of tryptophan were investigated due to its biological importance. Tryptophan is an essential amino acid needed for the normal growth in infants and for nitrogen balance in adults. DFT calculations using B3LYP functional with LANL2DZ basis set was carried out to support the experimental Raman and SERS data. The strong enhancement of 1343cm−1 band, assigned to the CO2 sym. stretching vibration in the SERS spectrum along with a red shift of 63cm−1, manifests that chemical mechanism contributes to the SERS activity. Moreover, the observed features in the SERS spectrum as well as theoretical calculations infer that tryptophan is chemisorbed to the silver surface directly through the oxygen and nitrogen atoms of the carboxylate and amino groups with an edge-on orientation with the indole ring lying nearly perpendicular to the silver surface. The SERS enhancement factors for various Raman vibrations of tryptophan were found to be of the order of 105–106.

Environmental Implications of Nanoparticle Aging in the Processing and Fate of Copper-Based Nanomaterials

Copper nanomaterials are being used in a large number of commercial products because these materials exhibit unique optical, magnetic, and electronic properties. Metallic copper nanoparticles, which often have a thin surface oxide layer, can age in the ambient environment and become even more oxidized over time. These aged nanoparticles will then have different properties compared to the original nanoparticles. In this study, we have characterized three different types of copper-based nanoparticle (NP) samples designated as Cu(new) NPs, Cu(aged) NPs, and CuO NPs that differ in the level of oxidation. The solution phase behavior of these three copper-based nanoparticle samples is investigated as a function of pH and in the presence and absence of two common, complexing organic acids, citric and oxalic acid. The behavior of these three copper-based NP types shows interesting differences. In particular, Cu(aged) NPs exhibit unique chemistry including oxide phases that form and surface adsorption properties. Overall, the current study provides some insights into the impacts of nanoparticle aging and how the physicochemical characteristics and reactivity of nanomaterials can change upon aging.

Adsorption properties of surface of carbon materials at extremely low coverages

Adsorption properties of blacks and their graphitized analogues were examined by the inverse gas chromatography at extremely low surface coverage.

J056035 バイオ燃料利用燃料電池燃料極反応に関する理論解析

Ethanol and other biofuels will play an important role in realizing the sustainable energy system in the future. The direct use of such fuels in fuel cell is one of the promising options to realize high-efficiency utilization. In this study, we focus on ethanol oxidation in alkaline environment as a first step to tackle the electrooxidation of biofuels in fuel cells. Gold is selected as a catalyst alternative to platinum. The surface states of gold catalyst and catalytic reaction process in alkaline environment are studied. Surface adsorption properties are first studied to find out that the gold surface is fully covered by O or OH. No reaction barrier for the initial step is obtained from the analysis of reaction over OH-covered surface. The formation of acetic acid as next step is then studied to have a small barrier over OH-covered surface. Reaction mechanisms will be discussed on the basis of calculation results.

Cyclodextrin functionalized magnetic iron oxide nanocrystals: a host-carrier for magnetic separation of non-polar molecules and arsenic from aqueous media

A single-step magnetic separation procedure that can remove both organic pollutants and arsenic from contaminated water is clearly a desirable goal. Here we show that water dispersible magnetite nanoparticles prepared by anchoring carboxymethyl-β-cyclodextrin (CMCD) cavities to the surface of magnetic nanoparticles are suitable host carriers for such a process. Monodisperse, 10 nm, spherical magnetite, Fe3O4, nanocrystals were prepared by the thermal decomposition of FeOOH. Trace amounts of antiferromagnet, FeO, present in the particles provides an exchange bias field that results in a high superparamagnetic blocking temperature and appreciable magnetization values that facilitate easy separation of the nanocrystals from aqueous dispersions on application of modest magnetic fields. We show here that small molecules like naphthalene and naphthol can be removed from aqueous media by forming inclusion complexes with the anchored cavities of the CMCD-Fe3O4 nanocrystals followed by separation of the nanocrystals by application of a magnetic field. The adsorption properties of the iron oxide surface towards As ions are unaffected by the CMCD capping so it too can be simultaneously removed in the separation process. The CMCD-Fe3O4 nanocrystals provide a versatile platform for magnetic separation with potential applications in water remediation.

Adsorption on a surface with varying properties

We propose a self-consistent model taking into account the variations in adsorption properties of an adsorbent surface in the process of adsorption–desorption of gas particles on it. We introduce a dimensionless coupling parameter equal to the normalized adsorption-induced activation energy for desorption due to the substrate deformation caused by the adsorption-induced force. Bistability of the system of noninteracting adparticles is established in the case when the coupling parameter is greater than a critical value and the gas concentration belongs to a certain interval. We show that the adsorption isotherms obtained within the framework of the proposed model essentially differ from the Langmuir isotherms and we show that the Zeldovich hysteresis is possible. The kinetics of the surface coverage is analyzed in detail in the overdamped approximation. We show the possibility of a ‘quasi-stationary’ state of the system due to variations in adsorption properties of the surface in adsorption–desorption.

Aggregation Behavior of Amino Acid Ionic Liquid Surfactants in Aqueous Media

Self-aggregation of amino acid ionic liquid surfactants (AAILSs) in aqueous solution has been investigated through surface tension, conductivity, steady-state fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The critical aggregation concentration (cac) of AAILSs obtained from different techniques showed fairly good agreement. Surface tension measurements have been used to derive surface adsorption properties such as adsorption efficiency (pC(20), effectiveness of surface tension reduction (Π(cac)), and minimum surface area per molecule (A(min)) at the air-water interface. Temperature-dependent conductivity measurements have been used to obtain the degree of counterion binding (β), and the thermodynamic parameters such as standard free energy (ΔG(agg)(0)), enthalpy (ΔH(agg)(0)), and entropy (ΔS(agg)(0)) of aggregation. The aggregation number (N(agg)) for various AAILSs has been derived by using the fluorescence quenching technique. Size of the aggregates has been obtained from DLS and TEM measurements. The aggregation properties of AAILSs have been analyzed as a function of structure of amino acids and compared with those of analogous ionic liquids (ILs) and conventional ionic surfactants. Surface activity of the AAILSs has been found superior to that of analogous ILs and conventional ionic surfactants of the same alkyl chain length.

Adsorption properties of immobilized metal nanoparticles

The adsorption properties of the original TiO2, MgO, and SiO2 surfaces and those modified with nanoscale gold and nickel particles are studied using the dynamic sorption in a range of low coverages. N-alkanes (C6–C9) and adsorbate molecules with different donor and acceptor properties were taken as the reference compounds. Differential molar heats of adsorption of the adsorbates (Qν) are determined from the experimental retention data and, in the case of polar adsorbates, contributions from the dispersion and specific interactions to Qν are found. Donor and acceptor characteristics of the original and modified oxide surfaces are estimated. The immobilization of gold and nickel nanoparticles is shown to result in the formation of less active donor (KD) and acceptor (KA) sites compared to those on the original substrate surfaces. Changes in the surface chemistry and adsorption properties of Au/SiO2 composites compared to the original substrate are less pronounced than in the case of Au,Ni/TiO2 and Au,Ni/MgO composites.

Mapping the Surface Adsorption Forces of Nanomaterials in Biological Systems

The biological surface adsorption index (BSAI) is a novel approach to characterize surface adsorption energy of nanomaterials that is the primary force behind nanoparticle aggregation, protein corona formation, and other complex interactions of nanomaterials within biological systems. Five quantitative nanodescriptors were obtained to represent the surface adsorption forces (hydrophobicity, hydrogen bond, polarity/polarizability, and lone-pair electrons) of the nanomaterial interaction with biological components. We have mapped the surface adsorption forces over 16 different nanomaterials. When the five-dimensional information of the nanodescriptors was reduced to two dimensions, the 16 nanomaterials were classified into distinct clusters according their surface adsorption properties. BSAI nanodescriptors are intrinsic properties of nanomaterials useful for quantitative structure-activity relationship (QSAR) model development. This is the first success in quantitative characterization of the surface adsorption forces of nanomaterials in biological conditions, which could open a quantitative avenue in predictive nanomedicine development, risk assessment, and safety evaluation of nanomaterials.