Ti Oxide Surface Research Articles

Nucleation and growth mechanisms of ferrite on Mg–Ti–oxide surfaces: First-principles investigation

Fine and dispersed Mg–Ti–oxide inclusions, which act as heterogeneous nucleation sites for intragranular ferrite, have been acknowledged as an effective method for grain refinement. In this paper, the nucleation and growth mechanisms of ferrite on Mg–Ti-oxides surface were investigated through first-principles calculations and solid-state pressure bonding experiments. The calculated results show that the formation of cation vacancies is the limiting step for Mn solute atom absorption by Mg–Ti-oxides. As determined by the lower covalency and ionicity of the Mg–O bond compared to the Ti–O bond in Mg–Ti-oxides, Mn atoms will be efficiently absorbed by occupying the Mg vacancies. The experimental results demonstrate that MgTiO3 with the maximum Mn-depleted zone (MDZ) width is the most effective for ferrite nucleation, which is consistent with the calculation results. As a representative, the Fe(110)/MgTiO3(001) interface with the lowest planar disregistry (3.16%) was selected to analyze growth behaviors. Due to charge accumulation and variation, Fe atoms are more likely to gather on the Mg–O terminal MgTiO3(001) surface and form [(Mg–O)–Fe]-1 interfaces. Its adhesion work and interface energy are 1.74 and 2.46 J/m2, respectively. The present study illustrates the nucleation and growth mechanisms of ferrite on Mg–Ti-oxides, providing theoretical support for the application of Mg–Ti-oxide inclusions in oxide metallurgy.

Decontamination of Ti Oxide Surfaces by Using Ultraviolet Light: Hg-Vapor vs. LED-Based Irradiation.

C-range Ultraviolet (UVC) mercury (Hg)-vapor lamps have shown the successful decontamination of hydrocarbons and antimicrobial effects from titanium surfaces. This study focused on surface chemistry modifications of titanium dental implants by using two different light sources, Hg-vapor lamps and Light Emitting Diodes (LEDs), so as to compare the effectivity of both photofunctionalization technologies. Two different devices, a small Hg-vapor lamp (λ = 254 nm) and a pair of closely placed LEDs (λ = 278 nm), were used to irradiate the implants for 12 min. X-ray Photoelectron Spectroscopy (XPS) was employed to characterize the chemical composition of the surfaces, analysing the samples before and after the lighting treatment, performing a wide and narrow scan around the energy peaks of carbon, oxygen and titanium. XPS analysis showed a reduction in the concentration of surface hydrocarbons in both UVC technologies from around 26 to 23.4 C at.% (carbon atomic concentration). Besides, simultaneously, an increase in concentration of oxygen and titanium was observed. LED-based UVC photofunctionalization has been suggested to be as effective a method as Hg-vapor lamps to remove the hydrocarbons from the surface of titanium dental implants. Therefore, due to the increase in worldwide mercury limitations, LED-based technology could be a good alternative decontamination source.

Associations between zircon and Fe–Ti oxides in Hiltaba event magmatic rocks, South Australia: atomic- or pluton-scale processes?

The Hiltaba Suite intrusive rocks and penecontemporaneous Gawler Range Volcanics (GRV) comprise the 1590 Ma Gawler silicic large igneous province in the Gawler Craton, South Australia. Zircon is principally associated with Fe–Ti oxides and clusters of touching crystals in these rocks, including in the Roxby Downs Granite (RDG), host of the Olympic Dam iron oxide–copper–gold deposit, and in other intrusive rocks that comprise the Olympic Province. There has been no explicit evaluation and explanation of potential origins published for concentrations of zircon with Fe–Ti oxides (herein zircon-rich clusters) found in these and similar rocks of western North America and elsewhere. Here we use U–Pb geochronology, mineral morphologies and compositions, and insights from surface chemistry and liquid-bound particle interaction studies to investigate zircon-rich clusters and provide a model for their formation. U–Pb geochronology does not reveal any concordant zircon populations older than ca 1590 Ma, so it is unlikely that there are significant xenocrystic zircon grains or that the zircons include significant inherited cores. The lack of pre-magmatic zircon, consistent intra-grain and inter-grain zircon compositional trends, the predominance of oscillatory zoned zircon with morphologies indicating growth from hot, evolved silicate melts, and the lack of evidence for zircon recrystallisation, indicates that zircon crystallised in the host GRV and RDG magmas. Variable zircon compositions within individual clusters does not support epitaxial nucleation of zircon on Fe–Ti oxides, but it is likely that some zircon grains grew from seed crystals formed by exsolution of Zr from Fe–Ti oxides. Aggregation of isolated, liquid-bound crystals is energetically favourable, and the grainsize discrepancy between larger crystals (Fe–Ti oxides, pyroxenes) and smaller accessory minerals (zircon, apatite) maximises the disparity in particle velocities and hence enhances the opportunities for collisions and adhesion between these crystals. We propose that zircon adheres to Fe–Ti oxides with greater ease and/or with greater bond strengths, than to other phases present in the parental magmas. It is possible that this association is related to interactions between zircon and Fe–Ti oxide surface sites with opposing charges, presuming the distance between phase surfaces is sufficiently small. The occurrence of small zircon grains within Fe–Ti oxides and both euhedral zircon and zircon with asymmetric growth zonation in contact with Fe–Ti oxides indicates that several processes are responsible for the high concentrations of zircon crystals in some Fe–Ti oxide clusters.Zircon is principally associated with Fe--Ti oxides in 1.59 Ga Gawler Range Volcanics (GRV) and Roxby Downs Granite (RDG)U–Pb geochronology does not reveal any concordant zircon populations older than ca 1590 MaZircon compositions and morphologies indicate that zircon crystallised in the host RDG and GRV magmas and suggest recharge, reheating and mixing occurred in these magmatic systemsSeed crystals, aggregation and surface chemical affinities contributed to the strong association of zircon and Fe–Ti oxides

Intrinsic Superhydrophilicity of Titania-Terminated Surfaces

The wettability of solid surfaces is of fundamental scientific interest and related to many diverse chemical and physical phenomena at the heart of practical technologies. In particular, the hydrophilicity of the photocatalytically active metal-oxide TiO2 has attracted considerable attention for many applications. However, the intrinsic hydrophilicity of Ti-oxide surfaces is not fully understood. In this work, we investigate the intrinsic hydrophilicity of Ti-oxide surfaces on the atomically stable (√13 × √13)-R33.7° SrTiO3 (001) surface. The surface has a TiOx double layer on a TiO2-terminated SrTiO3 (001) surface, which is available as a surface marker to assess the atomic-scale structural stability of the surface. Both experimental and theoretical results show that Ti-oxide surfaces are intrinsically superhydrophilic with a water contact angle of ∼0°. The results show that airborne surface contamination is the most significant factor affecting the wettability of titania surfaces, strongly supporting th...

Biomimetic anchors applied to the host-guest antifouling functionalization of titanium substrates

A biomimetic strategy was developed for the construction of antifouling titanium oxide (Ti(oxide)) surfaces based on host-guest interactions. Two catecholic derivatives, dopamine 4-(phenylazo)benzamide (AZODopa) and dopamine 1-adamantanecarboxamide (AdaDopa) were synthesized and immobilized onto the Ti(oxide) surfaces. The guest molecules-anchored Ti(oxide) surfaces were further functionalized with zwitterionic heptakis[6-deoxy-6-(N-3-sulfopropyl-N,N-dimethylammonium ethyl sulfanyl)]-β-cyclodextrin (SBCD) and hydrophilic β-CD polymer (CDP). The surface elemental compositions and hydrophobic/hydrophilic properties of the Ti(oxide) surfaces before and after modification were characterized by X-ray photoelectron spectroscopy (XPS) and static water contact angle measurements, respectively. The antifouling properties of the modified Ti(oxide) surfaces were evaluated by the protein adsorption and bacterial adhesion assays. The zwitterionic SBCD- and hydrophilic CDP-functionalized Ti(oxide) surfaces can reduce the adsorption of bovine plasma fibrinogen and adhesion of Escherichia coli, as compared to the pristine and guest molecules-anchored Ti(oxide) surfaces.

Osseointegration of two different phosphate ion‐containing titanium oxide surfaces in rabbit cancellous bone

This study assessed the osseointegration of grit-blasted titanium (Ti) implants with a hydrophilic phosphate ion-incorporated oxide surface in rabbit cancellous bone, and compared its bone healing with commercially available phosphate-incorporated clinical implants obtained by micro-arc oxidation (TiUnite, TU implant). The hydrophilic phosphate-incorporated Ti surface (P implant) was produced by hydrothermal treatment on grit-blasted moderately rough-surfaced clinical implant. The TU surface was used as a control. The surface characteristics were evaluated by field emission-scanning electron microscopy, X-ray photoelectron spectroscopy, optical profilometry, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Thirty-two threaded implants with lengths of 10 and 3.3 mm diameter (16 P implants and 16 TU implants) were placed in the femoral condyles of 16 New Zealand White rabbits. Histomorphometric analysis, removal torque tests, and surface analysis of the torque-tested implants were performed 4 weeks after implantation. The P and TU implants displayed micro-rough surface features with similar Ra values at the micron-scale. ICP-AES analysis revealed that both the P and TU implants released phosphate ions into the solution. The torque-tested P and TU implants exhibited a considerable quantity of bone attached to the surface. The P implants exhibited significantly higher bone-implant contact percentages, both in terms of the all threads region and the total lateral length of implants compared with the TU implants (P < 0.01), but no statistical difference was found for the removal torque values. These results suggest that the phosphate-incorporated Ti oxide surface obtained by hydrothermal treatment achieves rapid osseointegration in cancellous bone by increasing the degree of bone-implant contact.

Surface characteristics and in vitro biocompatibility of a manganese-containing titanium oxide surface

This study investigated the surface characteristics and in vitro biocompatibility of a titanium (Ti) oxide layer incorporating the manganese ions (Mn) obtained by hydrothermal treatment with the expectation of utilizing potent integrin–ligand binding enhancement effect of Mn for future applications as an endosseous implant surface. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, optical profilometry and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The in vitro biocompatibility of the Mn-containing Ti oxide surface was evaluated in comparison with untreated bare Ti using a mouse calvaria-derived osteoblastic cell line (MC3T3-E1). The hydrothermal treatment produced a nanostructured Mn-incorporated Ti oxide layer approximately 0.6μm thick. ICP-AES analysis demonstrated that the Mn ions were released from the hydrothermally treated surface into the solution. Mn incorporation notably decreased cellular attachment, spreading, proliferation, alkaline phosphatase activity, and osteoblast phenotype gene expression compared with the bare Ti surface (p<0.05). The results indicate that the Mn-incorporation into the surface Ti oxide layer has no evident beneficial effects on osteoblastic cell function, but instead, actually impaired cell behavior.

Increased bone apposition on a titanium oxide surface incorporating phosphate and strontium

This study investigated the osteoconductivity of titanium (Ti) implants with a phosphate (P)- and strontium (Sr) ion-incorporated oxide surface, produced by hydrothermal treatment in the rabbit cortical and cancellous bone, for future biomedical applications as a biocompatible endosseous implant surface. The P- and Sr ion-incorporated Ti implants (P/Sr implant) were produced by hydrothermal treatment using a P- and Sr-containing solution. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy and optical profilometry. Forty screw implants (20 control and 20 experimental) were placed in the tibiae and femoral condyles of 10 New Zealand White rabbits. The surface in vivo osteoconductivity of the P/Sr implants was compared with micro-arc oxidized (TO) implants with surface calcium and P chemistry by histomorphometric analysis in the cortical and cancellous bone after 4 weeks of implantation. The P/Sr implants showed moderately rough surface features and had lower R(a) values than the TO implants. Histologically, more direct bone apposition was observed on the surface of the P/Sr implants. The P/Sr implants displayed significantly higher bone-to-implant contact percentages compared with the TO implant in both the tibiae and the femoral condyles (P<0.01). The results indicate that the hydrothermally produced P- and Sr ion-incorporated Ti oxide surface may be effective in improving implant osseointegration in both cortical and cancellous bone by increasing bone apposition, due to its surface properties combining micro-topography, P/Sr chemistry and superior wettability.

In vitro biocompatibility of magnesium-incorporated submicro-porous titanium oxide surface produced by hydrothermal treatment

This study investigated the surface characteristics and in vitro biocompatibility of titanium (Ti) oxide surface incorporating magnesium ions (Mg), produced by hydrothermal treatment using an alkaline Mg-containing solution, for future biomedical applications. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and optical profilometry. Mouse calvaria-derived osteoblastic cell (MC3T3-E1) attachment, spreading, proliferation, alkaline phosphatase (ALP) activity, and osteoblastic gene expression on Mg-containing surfaces were compared with untreated Ti surfaces. Hydrothermal treatment resulted in Mg-incorporated Ti oxide layer with submicro-porous surface structures approximately 2 μm in thickness. ICP-AES analysis revealed Mg ions release from treated surfaces into the solution. The Mg-incorporated surface displayed significantly increased cellular attachment and ALP activity compared with untreated surface ( p < 0.05), and supported better cell spreading. Real-time polymerase chain reaction analysis showed notably higher mRNA expression of the osteoblast transcription factor genes (Dlx5, Runx2) and the osteoblast phenotype genes (ALP, bone sialoprotein and osteocalcin) in cells grown on the Mg-incorporated surfaces than untreated surfaces. These results demonstrate that the Mg-incorporated submicro-porous Ti oxide surface produced by hydrothermal treatment may improve implant osseointegration by enhancing the attachment, spreading and differentiation of osteoblastic cells.

Osteoblast response to magnesium ion‐incorporated nanoporous titanium oxide surfaces

This study investigated the surface characteristics and in vitro osteoconductivity of a titanium (Ti) surface incorporated with the magnesium ions (Mg) produced by hydrothermal treatment for future application as an endosseous implant surface. Mg-incorporated Ti oxide surfaces were produced by hydrothermal treatment using Mg-containing solution on two different microstructured surfaces--abraded minimally rough (Ma) or grit-blasted moderately rough (RBM) samples. The surface characteristics were evaluated using scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, optical profilometry, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). MC3T3-E1 pre-osteoblast cell attachment, proliferation, alkaline phosphatase (ALP) activity, and quantitative analysis of osteoblastic gene expression on Ma, RBM, Mg-incorporated Ma (Mg), and Mg-incorporated grit-blasted (RBM/Mg) Ti surfaces were evaluated. Hydrothermal treatment produced an Mg-incorporated Ti oxide layer with nanoporous surface structures. Mg-incorporated surfaces showed surface morphologies and surface roughness values almost identical to those of untreated smooth or micro-rough surfaces at the micron scale. ICP-AES analysis showed Mg ions released from treated surfaces into the solution. Mg incorporation significantly increased cellular attachment (P=0 at 0.5 h, P=0.01 at 1 h) on smooth surfaces, but no differences were found on micro-rough surfaces. Mg incorporation further increased ALP activity in cells grown on both smooth and micro-rough surfaces at 7 and 14 days of culture (P=0). Real-time polymerase chain reaction analysis showed higher mRNA expressions of the osteoblast transcription factor gene (Dlx5), various integrins, and the osteoblast phenotype genes (ALP, bone sialoprotein and osteocalcin) in cells grown on micro-rough (RBM) and Mg-incorporated (Mg and RBM/Mg) surfaces than those on Ma surfaces. Mg incorporation further increased the mRNA expressions of key osteoblast genes and integrins (α1, α2, α5, and β1) in cells grown on both the smooth and the micro-rough surfaces. These results indicate that an Mg-incorporated nanoporous Ti oxide surface produced by hydrothermal treatment may improve implant bone healing by enhancing the attachment and differentiation of osteoblastic cells.

Enhanced osteoblast response to hydrophilic strontium and/or phosphate ions‐incorporated titanium oxide surfaces

This study investigated the surface characteristics and in vitro biocompatibility of titanium (Ti) surfaces incorporated with strontium ions (Sr) and/or phosphate ions (P) produced by hydrothermal treatment for future applications as endosseous implant surfaces. Sr and/or P-incorporated Ti oxide surfaces were produced by hydrothermal treatment. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, contact angle and surface energy measurements, inductively coupled plasma atomic emission spectroscopy, and profilometry. MC3T3-E1 pre-osteoblast cell attachment, morphology of spread cells, viability, and quantitative analysis of osteoblastic gene expression on grit-blasted microrough (RBM), P-incorporated (P), and P- and Sr-incorporated (SrP) Ti surfaces were evaluated. Microstructured P and SrP surfaces showed significantly higher wettability and surface energy compared with RBM surfaces (P<0.01). After immersion in Hank's balanced salt solution, considerable apatite deposition was observed on the P and SrP surfaces. Sr incorporation significantly increased cellular attachment and viability compared with other surfaces (P<0.05). Real-time polymerase chain reaction analysis showed markedly higher mRNA expressions of the osteoblast transcription factor gene (Runx2) and the osteoblast phenotype genes (alkaline phosphatase, osteopontin, bone sialoprotein, and osteocalcin) in cells grown on the P and SrP surfaces compared with those on the RBM surface. These results demonstrate that Sr- and P-incorporated Ti oxide surfaces may improve implant bone healing by enhancing attachment, viability, and differentiation of osteoblastic cells.

Assessment of novel chemical strategies for covalent attachment of adhesive peptides to rough titanium surfaces: XPS analysis and biological evaluation

Bioactive molecules have been proposed to promote beneficial interactions at bone-implant interfaces for enhancing integration. The main objective of this study was to develop novel methods to functionalize oxidized titanium surfaces by the covalent immobilization of bioactive peptides, through selective reaction involving single functional groups. In the first protocol, an aminoalkylsilane was covalently linked to the Ti oxide layer, followed by covalent binding of glutaric anhydride to the free NH(2) groups. The carboxylic group of glutaric anhydride was used to condense the free N-terminal group of the side-chain protected peptide sequence. Finally, the surface was treated with trifluoroacetic acid to deprotect side-chain groups. In the second protocol, the peptide was directly anchored to the Ti oxide surface via UV activation of an arylazide peptide analogue. X-ray photoelectron spectroscopy analyses confirmed that modifications induced onto surface composition were in agreement with the reactions performed. The peptide density of each biomimetic surface was determined on the basis of radiolabeling and XPS derived reaction yields. The in vitro cellular response of the biomimetic surfaces was evaluated using a primary human osteoblast cell model. Cell adhesion, proliferation, differentiation, and mineralization were examined at initial-, short-, and long-time periods. In was shown that the biomimetic surface obtained through photoprobe-marked analogue that combines an easily-performed modification provides a favorable surface for an enhanced cellular response.

Bone response to endosseous titanium implants surface‐modified by blasting and chemical treatment: A histomorphometric study in the rabbit femur

This study evaluated the effects of the addition of oxide structure with submicron-scale porous morphology on the periimplant bone response around titanium (Ti) implants with microroughened surfaces. Hydroxyapatite-blasted Ti implants with (experimental) and without (control) a porous oxide structure produced by chemical treatment were investigated in a rabbit femur model. Surface characterizations and in vivo bone response at 4 and 8 weeks after implantation were compared. The experimental implants had submicron-scale porous surface structure consisted of anatase and rutile phase, and the original R(a) values produced by blasting were preserved. The histomorphometric evaluation demonstrated statistically significantly increased bone-to-implant contact (BIC) for experimental implants, both in the three best consecutive threads (p < 0.01) and all threads (p < 0.05) at 4 weeks. There was no remarkable difference in the BIC% or bone area percentage between the two groups at 8 weeks. The porous Ti oxide surface enhanced periimplant bone formation around the Ti implants with microroughened surfaces at the early healing stage. Based on the results of this study, the addition of crystalline Ti oxide surface with submicron-sized porous morphology produced by chemical treatment may be an effective approach for enhancing the osseointegration of Ti implants with microroughened surfaces by increasing early bone-implant contact.

The role of titania in supported Mo, CoMo, NiMo, and NiW hydrodesulfurization catalysts: analysis of past and new evidences

Previous results and new evidence on the role of titania in supported hydrodesulfurization catalysts are analyzed in order to construct a rational explanation for the different findings in Ti-containing HDS catalysts. Some of the important findings follow. The preparation method of Al–Ti oxide supports is important to catalytic activity. It is not the total amount of Ti but the Ti oxide surface structures that is relevant. TiO 2 is an electronic promoter in HDS catalysts. Ti 3+ species formed under HDS reaction conditions act as electron donors. These electrons can be easily transferred, through the conduction band of the support, and be injected to the Mo 3d conduction band. This causes a weakening of the Mo S bonds and helps the creation of more CUS. The addition of TiO 2 to the surface of alumina eliminates the most reactive surface hydroxyl groups and avoids the formation of tetrahedral Mo oxide species, causing an increase of well-sulfided active phase and hence in catalytic activity. This effect, although significant, is less important than the electronic promotion of Mo by Ti. TiO 2-containing catalysts are well suited for deep HDS because they facilitate the formation of a greater number of CUS in MoS 2 (or WS 2), favoring the hydrogenation–hydrodesulfurization route of transformation of 4,6-DMDBT.

Quantitative assessment of the response of primary derived human osteoblasts and macrophages to a range of nanotopography surfaces in a single culture model in vitro

The effect of nanotopography on a range of Ti oxide surfaces was determined. Flat Ti, 3%, 19%, 30% and 43% topography densities of 110 nm high hemispherical protrusions were cultured in contact with primary derived human macrophages and osteoblasts in single culture models. Prior to introduction of the test substrate the phenotype and optimum conditions for in vitro cell culture were established. The cellular response was investigated and quantified by assessments of cytoskeletal development and orientation, viable cell adhesion, cytokine production and release and RT-PCR analysis of osteogenic markers. The tested nanotopographies did not have a statistically significant effect on viable cell adhesion and subsequent cytoskeletal formation. Surface chemistry was the dominant factor as established via incorporation of a tissue culture polystyrene, TCPS, control. The topography surfaces induced a release of chemotactic macrophage activation agents at 1 day in conjunction with stress fibre formation and a subsequent fibronectin network formation. Osteoblasts migrated away from the topography surfaces to the exposed TCPS within the wells during the 7-day period.

Effect of Ti-capping thickness on the formation of an oxide-interlayer-mediated-epitaxial CoSi2 film by ex situ annealing

A modified oxide mediated epitaxy process using a single deposition and ex situ annealing by Ti capping has been suggested in this study. It has been shown that in the case of pure Co on SiOx-covered Si, the reaction between Co and Si did not occur up to 800 °C during ex situ annealing. However, Co silicidation occurred in the case of Ti-capped Co on SiOx-covered Si. The crystalline nature of CoSi2 formed in this case strongly depends on the Ti capping thickness. When a thin Ti capping layer of thickness less than 5 nm was used, Ti oxidation occurred nonuniformly, and the morphology of the surface Ti oxide layer was very rough. This caused an exposure of Co to the oxygen in the ambient, resulting in the formation of polycrystalline CoSi2 due to the suppressed Co diffusion towards the Si substrate. In the case of Ti capping thickness being more than 10 nm, however, a uniform Ti oxide surface layer, which blocks the incoming oxygen retarding Co diffusion, was formed, and it led to uniform Co diffusion into the Si substrate, resulting in epitaxial CoSi2.

Ex situ formation of oxide-interlayer-mediated-epitaxial CoSi2 film using Ti capping

A modified oxide mediated epitaxy process using a single deposition and ex situ annealing by Ti capping has been developed in this study. With pure Co on Shiraki oxide, the reaction between Co and Si did not occur even at 800 °C during ex situ annealing, because of the adsorption of oxygen on the Co film. However, when the pure Co on the Shiraki oxide was capped by Ti, a uniform Ti oxide surface layer was formed during the initial stage of annealing, which had a role to eliminate the adsorption of oxygen on the Co film. It led to uniform Co diffusion into the Si substrate through the Shiraki oxide, resulting in epitaxial CoSi2. A good channeling χmin value of 18% comparable to that of the Ti/Co bilayer system was measured in the epitaxial CoSi2 formed from this modified oxide mediated epitaxy process.

Chemical Heterogeneity of Metal Oxide Surfaces as Studied by Inverse Gas Chromatography at Finite Concentrations

A method for the calculation of the heterogeneous solid surface distribution function on the adsorption (free adsorption) energy as the sum of two uniform functions and on parameters describing the donor–acceptor and dispersive properties of the adsorption sites direct from chromatographic peaks as measured by inverse gas chromatography of ‘test ’ adsorbates at finite concentrations has been proposed. Average parameters reflecting the donor–acceptor properties of the adsorption sites and the dispersive component of the free surface energy in the monolayer region for the individual and mixed Si, Ti and Al pyrogenic oxide surfaces were determined using this method from the adsorption data for 18 ‘test ’ compounds possessing different donor–acceptor and polarizable properties.

Protein adsorption from seawater onto solid substrata, I. Influences of substratum surface properties and protein concentration

To model non-specific protein adsorption in seawater, partitioning of the plant enzyme, ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO), from seawater onto a variety of materials (Ti, Cu, Fe, PTFE [Teflon], Polycarbonate, Pyrex) was examined as functions of time and bulk concentration. Protein film thicknesses on titanium and copper varied temporally over 24 h in a laminar flow regime, increasing rapidly in the first hour on both metals and continuing to increase slowly on Ti but decreasing on Cu in the subsequent 15–23 h. Films also varied spatially from 0 to 28 nm on Ti and from 20 to 160 nm on Cu. Desorption kinetics of protein monolayers bound to Ti oxide surfaces were twice as rapid as those bound to Cu oxides. Proteins in overlying layer(s) of multilayered films, bound only to other proteins, desorbed more rapidly than molecules bound to metal oxide surfaces, irrespective of the type of substratum. Isothermic adsorption studies of 3H-RuBisCO indicated that surface concentrations were best described as a first-order function ( Γ = KC 1/ 0 n) of bulk protein concentration, C 0, which was varied from 0.001 to 1050μg cm −3. Surface films varied in thickness from submono- to multilayer coverage. Each substratum material exhibited significantly different binding capacities ( K) and adsorption intensities (1/ n) and at moderate bulk protein concentrations (10μg cm −3) yielded an overall ranking of adsorption equilibria as follows: Pyrex < PTFE < Ti < PC < Cu < Fe. While the chemical composition of the substratum surfaces varied widely among the six materials tested, the initial critical surface tensions (CST) of these surfaces accounted for 87% of the variance observed in adsorption intensity, 1/ n, (excluding Pyrex). In seawater, bulk concentration and substratum CST were shown to be critical in determining rates of non-specific protein adsorption and desorption as well as partitioning equilibria. Results illustrate the complexity of protein adsorption in seawater indicative of multilayered, heterogeneous adsorption at the surface.

Cyclic voltammetry studies of copper and nickel hexacyanoferrate immobilized on a silica gel surface coated with titanium(IV) oxide

The cyclic voltammetric behavior of copper and nickel hexacyanoferrate complexes immobilized on a silica gel surface coated with Ti(IV) oxide indicated good chemical stability for the copper complex film and that the nickel film undergoes a structural change with time. The potential of the redox reaction Ti +{M[Fe III(CN) 6]} − + C + e − → Ti +{CM[Fe II(CN) 6]} − (M = Cu 2+, Ni 2+; C = K +, NH 4 +, Na +, Li +; Ti denotes Ti(IV) oxide substrate on a silica gel surface) is dependent on the degree of reticulation and the affinity of C to the transition metal hexacyanoferrate solid film. The cyclic voltammetry waves in Li + and Na + as the supporting electrolyte were broadened for Ti{Cu[Fe II/III(CN) 6]}, suggesting that the diffusion of these cations through the zeolitic cavity of the surface complex was hindered because of their larger hydrated ionic radii compared with those of K + and NH 4 +. The Ti{Ni[Fe II/III(CN) 6]} cyclic voltammetry waves depend on the capacity of the electroactive species on the Ti(IV) oxide surface to interact with the cationic species of the supporting electrolyte.