Titania Substrates Research Articles

Anchoring Modes of Ru-Based N719 Dye onto Titania Substrates

Anchoring Modes of Ru-Based N719 Dye onto Titania Substrates

Transparent TiO2 nanotubes supporting silver sulfide for photoelectrochemical water splitting.

Differences between photoelectrochemical and electrochemical activity were thoroughly investigated for the oxygen evolution reaction mediated by Ag2S deposited on two types of ordered titania substrates. Titanium dioxide nanotubes were fabricated by anodization of magnetron sputtered Ti films on ITO-coated glass substrates or directly from Ti foil. Further, Ag2S deposition on the nanotubes was carried out using successive ionic layer adsorption and reaction, known as SILAR, with 5, 25, and 45 cycles performed. Two types of nanotubes, one on transparent the other on non-transparent substrates were compared regarding their geometry, structure, optical, and electrochemical properties. It was demonstrated that the composite of Ag2S grown on transparent nanotubes exhibits higher catalytic activity compared to Ag2S grown on the nanotubes formed on Ti foil. The results showed that transparent nanotubes after modification with Ag2S by 25 SILAR cycles exhibit ca. 3 times higher photocurrent under visible light illumination than non-transparent ones treated with the same number of cycles. Furthermore, transparent nanotubes after 45 SILAR cycles of Ag2S exhibit enhanced activity towards oxygen evolution reaction with 9.3 mA cm-2 at 1.1 V vs. Ag/AgCl/0.1 M KCl which is six times higher than titania alone on Ti foil.

Functionalization of titania nanotubes surface with platinum(II) complexes

Functionalization of modern materials is one of the possibilities to make them better tailored for human needs. The paper describes a method of covering the titania nanotubes (TNTs) surfaces formed on Ti6Al4V (grade V) titanium alloy with four platinum(II) bimetallic complexes and cisplatin. The first step of the fabricated TNTs modification was their covering with (3-mercaptopropyl)triethoxysilane (MPTES) which plays a role of a bridge between the TNTs and platinum(II) coordination centres. The final application of platinum(II) dimethylformamide (DMF) solutions allowed to form a homogeneous layers of platinum(II) complexes bonded to the TNTs substrate by thiol sulphur atoms of MPTES without visible crystals of physically deposited complexes. The complexes were characterized with XRD, IR, Raman, 1H and 13C NMR spectroscopies, and thermal and elemental analyses. Characterization of titania substrates was done with IR, Raman, SEM, SEM/EDX, XRD, and XPS.

Dynamical properties of organo lead-halide perovskites and their interfaces to titania: insights from Density Functional Theory.

The vibrational density of states (VDOS), electronic structure and optical properties of bulk organo lead-halide perovskites, CH3NH3PbX3 (where X = Cl, I and Br), very promising and exciting candidate materials for solar-energy applications, have been studied by means of (hybrid) Density Functional Theory (DFT), with and without spin-orbit coupling, and equilibrium Born-Oppenheimer molecular dynamics (BOMD) in the constant-volume, isothermal (NVT) ensemble at 298 K. Particular emphasis has been directed towards the detailed characterisation of optimal hybrid-DFT strategies to reproduce faithfully the band gap, band structure and optical properties vis-à-vis both experiment and more computationally demanding GW calculations (i.e., those involving the single-particle Green's function, G, and the screened Coulomb interaction, W). The VDOS was found to feature intimate coupling between the lead and halide atoms, and was dominated by acoustic phonon modes – particularly so for chlorine, suggesting this as the more effective candidate material of the considered halides. Bulk optical properties were also determined. In view of promising ‘hybrid’ architectures of perovskites adsorbed on titania substrates, further simulations of lead iodide in contact with titania have been performed to assess thermal stability, as well as dynamical and structural properties of these systems. It was found that lattice strain led to some atomic layers in perovskite further from the interface adopting less crystal-like structure and less pronounced phonon spectra.

New details of assembling bioactive films from dispersions of amphiphilic molecules on titania surfaces.

Tailoring the surface properties of materials for biomedical applications is important to avoid clinical complications. Forming thin layers of amphiphilic molecules with apolar regions that facilitate attractive intermolecular interactions, can be a suitable and versatile approach to achieve hydrophobic surface modification and provide functional antibacterial properties. Aiming to correlate layer structure and properties starting from film formation, octadecylphosphonic acid (ODPA) and dimethyloctadecyl (3-trimethoxysilylpropyl) ammonium chloride (DMOAP) layers were adsorbed onto smooth titania surfaces. Then the films were studied by atomic force microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS), and their interactions with aqueous environments were characterized by contact angle and zeta potential measurements. In addition, antibacterial assays were performed using E. coli and S. mutants to reveal the antibacterial properties effected by the surface modification. Immediately after sputter deposition, titania was hydrophilic; however, after air storage and adsorption of DMOAP or ODPA, an increase in the water contact angle was observed. XPS investigations after layer formation and after antibacterial tests revealed that the attachment of layers assembled from ODPA on titania substrates is considerably stronger and more stable than that observed for DMOAP films. Heat treatment strongly affects DMOAP layers. Furthermore, DMOAP layers are not stable under biological conditions.

Development of dense Al2O3–TiO2 ceramic composites by the glass-infiltration of porous substrates prepared from mechanical alloyed powders

In this work bio-composites were obtained by infiltrating porous alumina–titania (Al2O3–TiO2) substrates with a lanthania-rich (La2O3) glass. Al2O3–TiO2 substrates were fabricated using high-energy milled powder mixtures of two different compositions with molar ratios of 3:1 and 1:1, uniaxial compaction under 100 MPa and sintering at 1300 °C - 2 h or 1400 °C - 2 h. The high energy milling process of the powders resulted in homogeneous, extremely fine mixtures. For comparison, as-received Al2O3 and TiO2 powders were also mixed at a proportion of 3:1 and sintered at 1600 °C - 2 h. The sintered substrates presented α-Al2O3 and β-Al2TiO5 (aluminium titanate) as crystal phases and relative densities ranging between 65.5 ± 2% and 69.4 ± 1.2% of the theoretical density. These porous substrates were infiltrated with a lanthania containing glass at a temperature of 1140°C-2h. The resulting ceramic composites exhibited high density, varying between 94 to 99% of the theoretical density, Vickers hardness ranging between 895 ± 14 HV and 1036 ± 33 HV, fracture strength ranging between 218 ± 28 MPa and 254 ± 18 MPa and a fracture toughness (KC) higher than 2.6 MPam1/2. Phase analysis of the infiltrated substrates by X-ray diffraction indicated the decomposition of aluminium titanate into alumina and titania besides the formation of lanthanum borosilicate, LaBSiO5. In addition, all compositions studied presented non-cytotoxic behaviour and low chemical solubility, inferior to 75 μg/cm2.

Electrochemical and photoelectrochemical properties of the interface between titania nanotubes covered by conducting polymer in aqueous by conducting polymer in aqueous electrolytes – The effect of various geometry and electrolytes concentration

In the present work we show the impact of nanotubes (NTs) geometry of titania utilized as a substrate in organic-inorganic systems acting as a p-n junction on efficient conversion of radiation energy into electrochemical energy. The electrolytic bath composition and electrolysis conditions were controlled in order to obtain TiO2NTs of various geometry as a result of electrochemical oxidation of titanium foil. The electrode material was characterized using scanning electron microscopy, Raman and UV–vis spectroscopies in order to investigate their morphology, crystallinity and absorbance ability, respectively. According to SEM inspection, the electrolyte bath composition (water content) and duration of electrolysis significantly affects TiO2NTs morphology, namely the internal diameter and the layer thickness. The TiO2NTs electrode/electrolyte interface characterized using electrochemical impedance spectroscopy (EIS) exhibits varied impedance parameters depending on the outer K2SO4 electrolyte concentration (in the range of: 0.01–0.2 M) as the electric charge distribution at the interface is concentration dependent. The series of hydrogenated titania substrates were electrochemically modified by the conducting polymer: poly(3,4-ethylenedioxytiophene) doped with polystyrene sulphonate (pEDOT:PSS) thin film. The optimal geometry of titania was determined based on the photocurrent density recorded for the composite material (TiO2NTs/pEDOT:PSS). The most photoactive organic inorganic junction is composed of titania tubes of 2.5 µm length, the outer diameter equal to 205 nm giving the real surface area equal to 49.9 cm2 per 1 cm2.

WO3/TiO2 composite coatings: Structural, optical and photocatalytic properties

WO3/TiO2 and TiO2 coatings were prepared on titania substrates using facile and cost-effective plasma electrolytic oxidation process. The coatings were characterized by X-ray diffraction, scanning electron microscopy, Raman, UV⿿vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. With increasing duration of PEO process, the monoclinic WO3 phase became dominant and new monoclinic WO2.96 phase appeared. The optical absorption edge in the WO3/TiO2 samples, enriched with WO3/WO2.96 phase, was shifted to the visible region. The photocatalytic efficiency of WO3/TiO2 and pure TiO2 samples was evaluated by performing the photodegradation experiments in an aqueous solution of Rhodamine 6G and Mordant Blue 9 under the visible and UV light. The WO3/TiO2 catalysts are much more efficient than pure TiO2 under visible light and slightly better under UV light. The improvement of photocatalytic activity in the visible region is attributed to better light absorption, higher adsorption affinity and increased charge separation efficiency.

Ru-bis(pyridine)pyrazolate (bpp)-Based Water-Oxidation Catalysts Anchored on TiO2: The Importance of the Nature and Position of the Anchoring Group.

Three distinct functionalisation strategies have been applied to the in,in-[{Ru(II)(trpy)}2(μ-bpp)(H2O)2](3+) (trpy=2,2':6',2''-terpyridine, bpp=bis(pyridine)pyrazolate) water-oxidation catalyst framework to form new derivatives that can adsorb onto titania substrates. Modifications included the addition of sulfonate, carboxylate, and phosphonate anchoring groups to the terpyridine and bis(pyridyl)pyrazolate ligands. The complexes were characterised in solution by using 1D NMR, 2D NMR, and UV/Vis spectroscopic analysis and electrochemical techniques. The complexes were then anchored on TiO2-coated fluorinated tin oxide (FTO) films, and the reactivity of these new materials as water-oxidation catalysts was tested electrochemically through controlled-potential electrolysis (CPE) with oxygen evolution detected by headspace analysis with a Clark electrode. The results obtained highlight the importance of the catalyst orientation with respect to the titania surface in regard to its capacity to catalytically oxidize water to dioxygen.

Ex-situ sensitization of ordered TiO2 nanotubes with CdS quantum dots

Ordered titania nanotubes (pore diameter≈90nm and wall thickness≈10nm) were obtained by the anodization technique and used for the ex-situ deposition of cadmium sulfide quantum dots (CdS QDs) via simple immersion of titania substrates in the CdS colloid. The colloidal dispersion of CdS nanoparticles in water was obtained in the presence of the bifunctional ligand, mercapto silane, which binds to the surface of CdS providing stability to the colloid and preventing further growth of the synthesized nanoparticles. The blue-shift of the optical absorption indicated that the CdS nanoparticles were of quantum dot size. Using the effective mass model, the average particle size was calculated to be 5.4nm. Transmission electron microscopy provided the verification for the estimated size of the nanoparticles, which was followed by performing selected area electron diffraction to determine the mixed phase (cubic and hexagonal) of the synthesized CdS QDs. Scanning electron microscopy and reflectance spectroscopy were employed to characterize the nanostructures consisting of TiO2 nanotubes with different loadings of CdS QDs (after 24h and 72h immersion). It was demonstrated that mercapto silane efficiently binds CdS QDs onto TiO2 nanotubes enabling visible-light response of the obtained nanocomposites.

Organic–inorganic hybrid materials designed by controlled radical polymerization and mediated using commercial dual functional organophosphorous coupling agents

Hybrid materials that are composed of a polymeric material interfaced with an inorganic, metal oxide material have been a rapidly expanding research area in the last few decades. However, interfacial regions remain an important area of focus, and as such hybrid materials do not always possess a very robust or stable interface. Tailor-made interfacial molecules have been successfully reported but material scientists wishing to develop composite interfacial materials would favorably use commercial solutions. Our study shows how we can leverage a commercially available organophosphonic acid group that is coupled with a 2-bromo isobutyrate initiator for surface initiated atom transfer radical polymerization (SI-ATRP) for use as a strong interfacial molecule. We illustrate this mechanism with both nanoparticles of titania and flat titania substrates used as the grafting support and polymerization anchoring points. We demonstrate that the size of the organophosphonic acid initiator, specifically the carbon spacer between the reactive groups, controls the stability of the molecule. The actual covalent linkage between the phosphonic acid group and the titania surface while also leaving the ATRP initiating group able to start the polymerization, is confirmed via31P solid state NMR spectroscopy, liquid 1H NMR spectroscopy XPS, DLS and SEM.

Control on titania nanostructure by combining block copolymer assisted sol–gel synthesis with rapid flux solvent atmosphere treatment

A method is developed for rapid preparation of titania substrates using a sol–gel preparation route in combination with an amphiphilic block copolymer (BCP) template, acting as structure directing agent. The method consists in performing the spin coating of an initial solutions of BCP and titania species in a controlled atmosphere using a flux of solvent vapors (Rapid-Flux-Solvent-Atmosphere, RFSA method). The method is demonstrated in the case of thin films of polystyrene-b-poly(oxyethylene) BCP (PS-PEO) with cylindrical morphology of PEO domains in the PS matrix, characterized by the selective inclusion of titanium species inside the PEO cylinders. Upon removal of the organic matrix by heat treatment at 600°C, titania substrates of different morphology are obtained depending on the concentration of titania precursor and processing conditions. The method allows preventing the negative effect of hydrolysis and condensation reactions of Ti species and titania substrates with morphology reminiscent of that one achieved in the hybrid nanostructured thin films are obtained. The RFSA method is simple, direct, and it is of particular interest for systems that require a short processing time to eliminate the solvent and to obtain regular nanostructured thin-films over large area. Merit figures such as the degree of hexagonal order and the degree of coverage of the surface with titania motifs are identified to characterize the hybrid composites and titania substrates.

Insights into meso-structured photoanodes based on titanium oxide thin film with high dye adsorption ability

In this work, the absorption of N719 dye on titania films with significantly different morphologies has been investigated. By changing the synthetic approach, we have prepared sol–gel titania films with a flat surface (TiSG), mesoporous films with an ordered porous structure (TiMS) and a reference film from commercial titania P25 using the well-known doctor-blade technique (TiDB). The surface roughness and grain size distribution of titania films has been explored by atomic force microscopy. The effectiveness of the various type of titania films to absorb the N719 dye has been investigated by UV–vis spectroscopy, whereas the dye-titania interaction was examined by Raman spectroscopy. Further information on the structural and morphological properties of titania films were obtained by small angle X-ray diffraction and scanning electron microscopy. Both sol–gel and mesoporous titania films were deposited by spin-coating the solution of titania precursor, which produces films of about 300nm, much thinner than those afforded by the doctor-blade technique (∼6.8μm). When the thickness of TiMS film was increased up to 1μm, the absorbance of dye-sensitized titania became also higher, reaching levels similar to those of the reference N719-TiDB film in spite of its lower thickness. Our findings show that the morphological properties of titania substrates affect their ability to adsorb the N719 dye and, in particular, it was observed an enhanced dye adsorption onto meso-structured titania. N719 absorbance normalized to titania film thickness reveals that both the roughness and porosity of titania promote the dye adsorption. The much higher ability of meso-structured photoanodes to adsorb the dye can be attributed to the ordered and highly porous structure of TiMS. The photocurrent–voltage measurements of TiMS and TiDB dye sensitized films with similar thickness (∼500nm) have shown the superiority of N719-TiMS thus suggesting the key role of the mesoporous structure.

Rapid-flux-solvent-atmosphere method for tailoring the morphology of titania substrates over a large area via direct self-assembly of block copolymers

A fast method for the preparation of block-copolymer-based hybrid composite nanostructures and titania substrates well oriented over a large area, is illustrated.

Generic Process for Highly Stable Metallic Nanoparticle-Semiconductor Heterostructures via Click Chemistry for Electro/Photocatalytic Applications

Metallic nanoparticles (MNP) are utilized as electrocatalysts, cocatalysts, and photon absorbers in heterostructures that harvest solar energy. In such systems, the interface formed should be stable over a wide range of pH values and electrolytes. Many current nonthermal processing strategies rely on physical interactions to bind the MNP to the semiconductor. In this work, we demonstrate a generic chemical approach for fabricating highly stable electrochemically/photocatalytically active monolayers and tailored multilayered nanoparticle structures using azide/alkyne-modified Au, TiO2, and SiO2 nanoparticles on alkyne/azide-modified silicon, indium tin oxide, titania, stainless steel, and glass substrates via click chemistry. The stability, electrical, electrochemical, and photocatalytic properties of the interface are shown via electrochemical water splitting, methanol oxidation, and photocatalytic degradation of Rhodamine B (RhB) dye. The results suggest that the proposed approach can be extended for the large-scale fabrication of highly stable heterostructure materials for electrochemical and photoelectrocatalytic devices.

Stable Protein Device Platform Based on Pyridine Dicarboxylic Acid-Bound Cubic-Nanostructured Mesoporous Titania Films

Here we shortly report a protein device platform that is extremely stable in a buffer condition similar to human bodies. The protein device platform was fabricated by covalently attaching cytochrome c (cyt c) protein molecules to organic coupler molecules (pyridine dicarboxylic acid, PDA) that were already covalently bound to an electron-transporting substrate. A cubic nanostructured mesoporous titania film was chosen as an electron-transporting substrate because of its large-sized cubic holes (∼7 nm) and highly crystalline cubic titania walls (∼0.4 nm lattice). Binding of PDA molecules to the mesoporous titania surface was achieved by esterification reaction between carboxylic acid groups (PDA) and hydroxyl groups (titania) in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) mediator, whereas the immobilization of cyt c to the PDA coupler was carried out by the EDC-mediated amidation reaction between carboxylic acid groups (PDA) and amine groups (cyt c). Results showed that the 2,4-position isomer among several PDAs exhibited the highest oxidation and reduction peak currents. The cyt c-immobilized PDA-bound titania substrates showed stable and durable electrochemical performances upon continuous current-voltage cycling for 240 times (the final current change was less than 3%) and could detect superoxide that is a core indicator for various diseases including cancers.

Titania nanotube porosity controls dissolution rate of sputter deposited calcium phosphate (CaP) thin film coatings

Calcium phosphate (CaP) coatings are of continuing significant interest due to their ability to directly promote bone cell differentiation. Whereas sputter deposited CaP coatings have much to offer in this regard, in the as-deposited state they are inherently amorphous and readily undergo rapid dissolution. This behaviour severely limits their ability to support bone cell adhesion and the subsequent events of proliferation and/or differentiation without subsequent processing such as thermal annealing. Removal of the need for this additional processing step would significantly increase their utility. This paper reports a study of the use of nano-porous titania substrates to directly control the rate of dissolution of thin amorphous as-deposited CaP sputter coatings. Titania nanotubes with different pore sizes were prepared by electrochemical anodization of titanium foils and sputter coated with CaP. Dissolution studies were performed on the as-deposited CaP layers in cell culture media for periods of up to 21 days. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the potential of the nanotubes to prolong the rate of loss of CaP over the entire 21 day period as compared to coatings prepared on flat polished titanium surfaces, which dissolved completely in less than 48 h. The CaP coated titania nanotube surfaces showed high levels of osteoblast attachment and proliferation with no signs of cell death. Alkaline phosphatase (ALP) activity measurements at 21 days indicated that the highest levels of osteoblast differentiation occurred on CaP thin films deposited onto titania nanotubes with an average pore size of 30 ± 7.5 nm and tube length of 1.3 ± 0.2 μm. These results indicate that prolonged availability of the as-deposited sputtered CaP can be provided for by use of a substrate surface comprising titania nanotubes. Moreover, nanotube pore size and tube length affect the rate of CaP dissolution and attendant cell behaviour thereon.

Effect of the Preparation Procedure on the Morphology of Thin TiO2 Films and Their Device Performance in Small-Molecule Bilayer Hybrid Solar Cells

Flat titanium dioxide films, to be used as the acceptor layer in bilayer hybrid solar cell devices, were prepared by spray-pyrolysis and by spin-casting. Both preparation methods resulted in anatase titania films with similar optical and electronic properties but considerably different film morphologies. Spray pyrolysis resulted in dense TiO₂ films grown onto and affected by the surface roughness of the underlying conducting glass substrates. The spin-casting preparation procedure resulted in nanoporous titania films. Hybrid solar cell devices with varying layer thickness of the small-molecule semiconducting dye TDCV-TPA were investigated. Devices built with spray-pyrolyzed titania substrates yielded conversion efficiencies up to 0.47%. Spin-cast titania substrates exhibited short circuits for thin dye layer thickness. For thicker dye layers the performance of these devices was up to 0.6% due to the higher interfacial area for charge separation of these nanoporous TiO₂ substrates.

Synthesis of Highly Ordered Crystalline Wurtzite (ZnO) Membrane for Selenium-Chromium Separation

Pure ZnO and composite ZnO-CeO2 coated thin films on titania substrates were prepared using a chelating sol-gel method under controlled conditions to be used in the separation and/or rejection of Se(IV) and Cr(VI). XRD and SEM studies confirmed the formation of highly ordered arrays of crystalline wurtzite microstructure with mixed orientation. An increase in average particle size of the prepared membranes from 1.25 to 3 µm with increasing CeO2 percent was observed indicating the vital role of CeO2 as secondary phase in improving the crystallinity of the coated films formed. Detailed study of the separation performance of the selected membranes toward Se(IV)-Cr(VI) was studied. A high separation performance for the different membranes prepared was observed toward Se(IV) with respect to Cr(VI). The polar characteristic of ZnO thin films played an essential role in Se(IV) separation. However, a high permeation flow of Cr(VI) through the membranes was governed by the capillary pressure induced within the porous structure of the membranes.

Observation of Structure‐Sensitive Decomposition of Cp(allyl)Pd on Pd Nanodots Formed by MOCVD

AbstractThe decomposition kinetics of the organometallic precursor cyclopentadienyl‐allyl‐Pd [Cp(allyl)Pd] on silica and titania substrates (as well as previously deposited Pd) are investigated by continuous metal‐organic (MO)CVD under atmospheric pressure. The substrate particles are freshly generated in an aerosol process with well‐defined and known densities of surface OH groups, and then coated immediately in a second reactor. Time‐resolved data on size and number density of deposited Pd nanodots on the carrier particles are obtained by electron microscopy and used as a means to infer the decomposition kinetics. It is found that decomposition proceeds very rapidly for a few seconds, both by proton‐initiated decomposition on surface OH groups and by autocatalysis, until the Pd nanodots have grown to a size of about 2 nm, where autocatalysis comes to a standstill, regardless of precursor concentration, residence time in the CVD reactor, or decomposition temperature. Proton‐initiated decomposition on OH groups continues to depend measurably on these process parameters in terms of the number density of Pd dots, even after autocatalysis has stopped. Our observations indicate that autocatalysis is structure‐sensitive.