Synthesis and bactericidal ability of Ag/TiO2 composite films deposited on titanium plate

In this study, we develop a bactericidal coating material for micro-implant, TiO₂ films with Ag deposited on were prepared on titanium plates by sol-gel process. Their anti-microbial properties were analyzed as a function of the annealed temperature using Escherichia coli as a benchmark microorganism. Ag nanoparticles deposited on TiO₂ film were of metallic nature and could grow to larger ones when the annealed temperature increased. The results indicated that the smaller size of Ag nanoparticles, the better bactericidal ability. On the other hand, the positive antibacterial effect of TiO₂ enhanced the bactericidal effect of Ag.     

Preparation and performance of photocatalytic TiO2 immobilized on palladium-doped carbon fibers

Pd-modified carbon fibers (CFs) are obtained by a facile oxidation-reduction method and then dip-coated in a sol-gel of titanium dioxide (TiO₂) to form supported TiO₂/Pd-CF photocatalysts. The morphology of the Pd-modified CFs and the amount Pd deposited are characterized by field emission scanning electron microscopy and atomic absorption spectrometry, respectively. X-ray diffraction is used to investigate the crystal structures of the TiO₂ photocatalyst. Acid orange II is used as a model contaminant to evaluate the photocatalytic properties of the photocatalyst under UV irradiation. TiO₂/Pd-CF exhibits higher catalytic activity than TiO₂/CF towards the degradation of acid orange II. Optimum photocatalytic performance and support properties are achieved when the Pd particle loading is about 10.8 mg/g.     

Influence of the heating temperature on the properties of nickel doped TiO2 films prepared by sol-gel method

Formation and properties of nickel doped TiO₂ films prepared by sol-gel method were studied using X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, and energy dispersive X-ray analysis. The results demonstrate that sizes of TiO₂ crystallites increase with increasing heating temperature. Also, at temperatures above 800 ° C diffusion of nickel onto the surfaces results in increased concentrations of nickel compounds on the surfaces. Similar to pure TiO₂ films the light-induced modification of hydrophilicity is observed also in the case of nickel doped TiO₂ films.     

Micro-structuring of TiO2 thin films by laser-assisted diffraction processing

Thin films of TiO₂ are deposited by magnetron sputtering on glass substrate and are irradiated by UV radiation using a KrF excimer laser (248 nm). These thin films are patterned with a razor blade placed on the way of the radiation just in front of the TiO₂ thin film. Just near the edge of the razor blade on the thin film, diffraction lines are observed, resulting in the ablation of the film. These patterns are characterized by optical microscopy, mechanical profilometry. Diffraction up to the 35th order is observed. The results are shown to be compatible with a model in which electronic excitation plays the major role.     

The effects of activated carbon supports on the structure and properties of TiO2 nanoparticles prepared by a sol-gel method

TiO₂-coated activated carbon (TiO₂/AC) composites and pure TiO₂ powders were prepared by a sol-gel method using tetrabutylorthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), X-ray photoelectron spectrum (XPS) and nitrogen absorption. The photoactivity of samples was evaluated by methylene blue (MB) degradation. The analysis results show that compared with pure TiO₂ powders, the spherical-shaped TiO₂ particles are well-dispersed in the AC matrix and the size of the resulting TiO₂ crystallites decreases to below 40 nm with increasing phase transformation temperature. The AC matrix creates anti-calcination effects and shows interfacial energy effects that control the growth of the TiO₂ particles, baffle the anatase to rutile phase transition, and cumber the TiO₂ particles to agglomerate. Compared with the surface areas of TiO₂ powders, the combination of TiO₂ and AC forms composites with high surface areas which are slightly affected by calcination temperature. By AC support, the photoactivity of TiO₂ is increased in MB photocatalytic course, possible because active carbon increases photocatalytic activity of TiO₂ particles by producing high concentration of organic compound near TiO₂, and small-size TiO₂ particles are well-dispersed on the surface of AC.     

Preparation of uniform TiO2 nanostructure film on 316L stainless steel by sol-gel dip coating

Sol was prepared by the mixing of tetra-η-butyle titanat, ethyl aceto acetate, and ethanol in an optimized condition. Polished 316L specimens were coated with the sol by dip-coating method. The influences of drying condition, withdrawal speed, calcination temperature, addition of dispersant, and pH of sol on TiO₂ nanostructure coating were investigated. Choosing of alcohol as drying atmosphere hindered the crack formation. The relation between coating thickness and withdrawal speed was evaluated. The optimum temperature to create a uniform distribution of nanoparticles of anatase was derived as 400 °C. Average roughness of coating was found about 10.61 nm by AFM analysis. Dispersant addition promoted formation of a uniform film as well as prevention of agglomeration. Acidic sol provided smaller particles than neutral sol.     

Effect of surface roughness of TiO2 films on short-circuit current density of photoelectrochemical cell of ITO/TiO2/PVC-LiClO4/graphite

This paper reports the effect of surface topography of titanium dioxide films on short-circuit current density of photoelectrochemical solar cell of ITO/TiO₂/PVC-LiCLO₄/graphite. The films were deposited onto ITO-covered glass substrate by screen-printing technique. The films were tempered at 300 °C, 350 °C, 400 °C, 450 °C and 500 °C for 30 min to burn out the organic parts and to achieve the films with porous structure. The surface roughness of the films were studied using scanning electron microscope (SEM). Current–voltage relationship of the devices were characterized in dark at room temperature and under illumination of 100 mW cm⁻² light from tungsten halogen lamp at 50 °C. The device utilising the TiO₂ film annealed at 400 °C produces the highest short-circuit current density and open-circuit voltage as it posses the smoothest surface topography with the electrolyte. The short-circuit current density and open-circuit voltage of the devices increase with the decreasing grain size of the TiO₂ films. The short-circuit current density and open-circuit voltage are 0.6 μA/cm² and 109 mV respectively.     

Preparation and photocatalytic properties of silver nanoparticles loaded on CNTs/TiO2 composite

In this study, new nanoscale photocatalyst based on silver and CNTs/TiO₂ was successfully prepared by photoreduction method. The prepared Ag-CNTs/TiO₂ was characterized by TEM, XRD and XPS. The photocatalytic activity was also evaluated by photocatalytic degradation of Reactive Brilliant Red X-3B dye. The results indicated that the photocatalytic efficiency of CNTs/TiO₂ increased in the presence of Ag nanoparticles and the photocatalysis reaction followed a first order kinetics. The kinetic constant of Ag-CNTs/TiO₂ for dye degradation was nearly 1.2 times than that of CNTs/TiO₂, which indicated decorating Ag nanoparticles on CNTs/TiO₂ could enhance the photocatalytic ability.     

Synthesis of TiN thin films by a new combined laser/sol-gel processing technique

In this work a novel method for synthesising TiN coatings is reported. A high-power diode laser at different powers and traverse speeds was applied to a mild steel substrate, coated with a slurry of titania sol-gel, urea and graphite. The reaction chemical thermodynamics was investigated to estimate the compositions, temperature range, and the required reaction enthalpy for producing TiN. A one-dimensional heat transfer model was used to optimise the processing parameters. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscope, and field emission gun scanning electron microscope which reveals deposition of very thin layer about 0.3 μm of pure TiN and the presence of sub-micron crystalline structure of TiN forming a metal matrix composite inter-layer with the substrate below the film which suggest a good metallurgically bonding with the substrate. Chemical composition was determined by energy dispersive X-ray analysis. The phases were identified by X-ray diffraction which confirms the synthesis of TiN film for all the samples. Results of nano-hardness measurements revealed a hardness value of the order of 22-27 GPa.     

Preparation, characterization and photocatalytic activity of the neodymium-doped TiO2 nanotubes

A series of Nd-TiO₂ powders have been prepared by the sol-gel technique with neodymium nitrate and tetra-n-butyl titanium as raw materials, and then Nd-TiO₂ nanotubes were fabricated by the hydrothermal method with a 10 mol l⁻¹ NaOH solution. The as-prepared Nd-TiO₂ nanotubes were characterized by TEM, XRD, DRS, and XPS, and their photocatalytic activity was also tested in the case of the degradation of methyl orange in water. TEM photograph showed that Nd-TiO₂ nanotubes were about 10-20 nm in diameter, with the lengths range from 100 to 300 nm. TiO₂ nanotubes contained anatase and rutile crystallites. However, 0.3% Nd-TiO₂ nanotubes contained anatase crystallites, and only little rutile crystallites, so it is shown that neodymium doping hindered the phase transformation from anatase into rutile. Nd doping increased the visible-light absorption ability of Nd-TiO₂ nanotubes, and a red shift for Nd-TiO₂ nanotubes appeared when compared to TiO₂ nanotubes. XPS analysis showed that two types of oxygen existed on the photocatalyst surface, including metal-O and hydroxyl group, and more hydroxyl group was on the surface of 2% Nd-TiO₂ nanotubes than on the surface of TiO₂ nanotubes. Nd doping enhanced the photocatalytic activities of Nd-TiO₂ nanotubes, and 0.3% Nd-TiO₂ nanotubes exhibited the highest photocatalytic activity.     

Preparation of aminofunctionalized TiO2 surfaces by binding of organophosphates

Titanium dioxide (TiO₂) powder was chemically modified with 2-aminoethyl dihydrogen phosphate (AEPH₂) and with 2-aminoethyl hydrogen ammonium phosphate (AEPHNH₄) in order to achieve an aminofunctionalized high-surface-area TiO₂ carrier suitable for more complex functionalizing. AEPH₂ was found to form the monoammonium salt AEPHNH₄ with ammonium ion rather than the diammonium salt AEP(NH₄)₂. The AEPHNH₄ was thoroughly characterized by various techniques and compared with AEPH₂. Bonding of AEPH₂ and AEPHNH₄ with TiO₂ powder was studied. According to the ³¹P NMR and elemental analysis results, AEPH₂ and AEPHNH₄ form covalent chelate bidentate bonds between the phosphate group and the TiO₂, while the amino groups remain accessible, creating uniform aminofunctionalized TiO₂ surface fully occupied by AEP groups. Amount of AEP groups on TiO₂ was limited to 1.5 wt-%.     

Novel synthesis and electrophoretic response of low density TiO-TiO2-carbon black composite

Novel low density TiO-TiO₂-carbon black composite was synthesized, which involved the deposition of inorganic coating on the surface of core-shell latex particles and subsequent removal of latex particles by calcination in high-purity nitrogen. The morphology and interior structure were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The images exhibited the composite had spherical shape and smooth surface, and the interior structure was hollow or porous. X-ray diffraction peaks (XRD) were mostly in agreement with the standard diffraction patterns of rutile TiO₂. In addition, the observed peaks at 2θ of 43.5°, 50.6° and 74.4° can be indexed to (1 1 1), (2 0 0) and (2 2 0) planes of cubic phase TiO. The X-ray photoelectron spectroscopy (XPS) results indicated that composite consisted of carbon black, TiO and TiO₂. The apparent density of the composite was suitable to 1.62 g cm⁻³, due to density matching with suspending media. Glutin-arabic gum microcapsules containing TiO-TiO₂-carbon black composite electrophoretic liquid were prepared via complex coacervation. The particles in the microcapsules showed excellent electrophoretic mobility under a DC field.     

Preparation of continuous TiO2 fibers by sol-gel method and its photocatalytic degradation on formaldehyde

The continuous TiO₂ fibers were prepared by sol-gel method using the tetrabutyl orthotitanate as the precursor. The sol-formation process is studied by FT-IR spectroscopy. The synthesized continuous TiO₂ fibers were characterized using SEM, HRTEM and XRD. Results demonstrate that the titanate sol has good spinnability when R ≤ 2 (R = H₂O:Ti(OC₄H₉)₄, molar ratio). The fibers have the length of several meters and the diameter of about 30 μm. The fibers are a radial close-packed product of nano-particles with high crystallinity. The continuous TiO₂ fibers are co-crystal including anatase phase and rutile phase. The formaldehyde degradation ratio of continuous TiO₂ fiber was 98.6%.     

Composite SiO2/TiO2 and amine polymer/TiO2 nanoparticles produced using plasma-enhanced chemical vapor deposition

Plasma-enhanced chemical vapor deposition was used to conformally coat commercial TiO₂ nanoparticles to create nanocomposite materials. Hexamethyldisiloxane (HMDSO)/O₂ plasmas were used to deposit SiO₂ or SiO_xC_yH_z films, depending on the oxidant concentration; and hexylamine (HexAm) plasmas were used to deposit amorphous amine-containing polymeric films on the TiO₂ nanoparticles. The composite materials were analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). These analyses reveal film composition on the nanoparticles was virtually identical to that deposited on flat substrates and that the films deposit a conformal coating on the nanoparticles. The performance of the nanocomposite materials was evaluated using UV-vis spectroscopy to determine the dispersion characteristics of both SiO_x and HexAm coated TiO₂ materials. Notably, the coated materials stay suspended longer in distilled water than the uncoated materials for all deposited films.     

Dynamics of water adsorption on TiO2 monitored by work function spectroscopy

Water adsorption dynamics on two TiO₂ (1 1 0) rutile surfaces at room temperature has been investigated using the work function (WF) change as a function of time. The first surface was prepared in a standard way using sputtering/annealing cycles, whereas the second one was long term annealed at 620 K in moderate vacuum conditions (the residual gas pressure of about 1 × 10⁻⁷ mbar) and cleaned afterwards. The WF change show striking difference as compared to those obtained for highly reduced TiO₂ (1 1 0) rutile or the (2 × 1) reconstructed surfaces. For the first kind of surface we show that the observed adsorption dynamics can be qualitatively explained by the present understanding of the water adsorption on non-reconstructed TiO₂ (1 1 0) rutile surface according to which the bridging oxygen vacancies and Ti rows are the main adsorption sites. Although generally similar to the former results, water adsorption dynamics on the second kind of the surface has an additional feature that can be only explained by a new adsorption site, which we suggest to be due to (2 × 1) reconstructed regions coexisting with the non-reconstructed TiO₂ (1 1 0) surface.     

STM imaging of a model surface of Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2 dye-sensitized TiO2 photoelectrodes

A TiO₂(1 1 0)-(1 × 1) surface was prepared in an ultra-high vacuum, transported in laboratory air, and observed with a scanning tunneling microscope (STM) operated in a vacuum of 10⁻⁴ Pa. Empty state images showed atomically flat terraces separated by single-height steps, on which 5-fold-coordinated surface Ti atoms were observed as spots arranged in a rectangular lattice. The Ru(4,4′-dicarboxy-2,2′-bipyridine)₂(NCS)₂ (N3) dye was adsorbed on the TiO₂ surface by immersing the TiO₂ wafer into an acetonitrile solution of the dye. In the empty state images, individual N3 molecules were observed as oval particles protruding by 0.6 nm from the TiO₂ surface. The oval shape elongated to the [1  0] directions was attributed to electron tunneling from tip to unoccupied states localized at the two carboxyl groups bound to the TiO₂ surface.     

Excimer laser processing as a tool for photocatalytic design of sol-gel TiO2 thin films

Nanostructured sol-gel TiO₂ thin films spin coated on silicate glass plates are subjected to excimer (KrF^*) pulsed laser irradiation in order to tailor their structure and photocatalytic properties. The surface morphology of virgin and laser-processed films are followed applying electron optical imaging and atomic force microscopy. The evolution of the surface roughness and pore formation are shown to be accompanied by optical absorption edge shift to infrared wavelength range. Conventional X-ray diffraction analysis and high-resolution transmission electron imaging are applied in order to obtain information on the phase composition. Co-existence of amorphous and anatase TiO₂ phases in nonirradiated sol-gel films is found. It is established that after laser processing the most intense XRD anatase peak is shifted to lower 2θ range. The analysis of high-resolution transmission electron images of film profiles evidences for the laser induced phase transitions. Formation of rutile and brookite TiO₂ accompanied by evolution of oxygen deficient Ti_nO_2n−1 phases are identified in the subsurface region. The contribution of laser processing for increasing the photocatalytic efficiency of laser-modified films toward the oxidation of methylene blue water solution is demonstrated. The results obtained reveal a novel-processing route for designing sol-gel titania films with improved photocatalytical activity.     

Synthesis and characterization of TiO2 thin films coated on metal substrate

Nanostructured titanium dioxide (TiO₂) thin films have been prepared on metal substrates using a facile layer-by-layer dip-coating method. The phase structure and morphologies of preparing samples were characterized by means of X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The results confirm that films are highly crystalline anatase TiO₂ and free from other phases of titanium dioxide. Scanning electron microscopy (SEM) shows that the nanoparticles are sintered together to form a compact structure. The electrical properties of samples were investigated by cutternt-voltage analysis, the result indicates that a rectifying junction between the nanocrystalline TiO₂ film and metal substrate was formed. The photoelectrochemical characteristics recorded under 1.5 AM illumination indicates that the as-fabricated thin film electrode possesses the highest photocurrent density at 450 °C, which is 1.75 mA/cm² at 0 V vs. Ag/AgCl.     

Electronic exchanges between adsorbed Ni atoms and TiO2(1 1 0) surface evidenced by resonant photoemission

Nickel was deposited on stoichiometric TiO₂(1 1 0) surface in the 0.02–2.1 equivalent monolayer (eqML) range and analyzed by means of photoemission and resonant photoemission. In the case of very low coverage (lower than 0.1 eqML), deposited nickel reacts with the surface through an electronic transfer from nickel atoms towards titanium ions. This exchange caused the filling of unoccupied Ti3d states leading to the increase of a peak in the TiO₂ band gap. These states can be better characterized through resonant photoemission experiments at the Ti 3p → 3d absorption edge: for very low coverage, these states in the TiO₂ band gap have resonant behavior of Ti3d electrons rather than Ni3d ones, confirming the filling of Ti3d states and thus electron transfer between nickel and titanium. For coverage higher than 0.14 eqML, nickel peaks (both Ni3p core level and valence band) should be related to the presence of metallic nickel in small clusters.