Rapid thermal melted TiO2 nano-particles into ZnO nano-rod and its application for dye sensitized solar cells

TiO₂ nano-particles with an anchored ZnO nano-rod structure were synthesized using the hydrothermal method to grow ZnO nano-rods and coated TiO₂ nano-particles on ZnO nano-rods using the rapid thermal annealing method on ITO conducting glass pre-coated with nano porous TiO₂ film. The XRD study showed that there was little difference in crystal composition for various types of TiO₂ nano-particles anchored to ZnO nano-rods. The as-prepared architecture was characterized using field-emission scanning electron microscopy (FE-SEM). Films with TiO₂ nano-particles anchored to ZnO nano-rods were used as electrode materials to fabricate dye sensitized solar cells (DSSCs). The best solar energy conversion efficiency of 2.397% was obtained by modified electrode material, under AM 1.5 illumination, achieved up to J_sc = 15.382 mA/cm², V_oc = 0.479 V and fill factor = 32.8%.     

Synthesis and electrochemical characterization of myoglobin-antibody protein immobilized self-assembled gold nanoparticles on ITO-glass plate

We report a protein immobilized self-assembled monolayer (SAM) of gold nanoparticles (GNPs) on indium-tin-oxide (ITO) coated glass plate. The protein-antibody, Mb-Ab, was covalently immobilized over the self-assembly of GNPs through a mixed SAM of 11-mercapto undecanoic acid (MUA) and 3-mercapto propionic acid (MPA) via carbodiimide coupling reaction using N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide (EDC) and N-hydroxy succinimide (NHS). The whole assembly was constructed on 0.25 cm² area of ITO-glass plate (Mb-Ab/MUA-MPA/GNPs/APTES/ITO-glass) and an impedimetric study was carried out for its application in myoglobin detection. This prototype assembly was characterized by scanning electron microscopy, atomic force microscopy and electrochemical techniques. The modified electrode showed an increased electron-transfer resistance on coupling with protein antigen, Mb-Ag, in the presence of a redox probe [Fe(CN)₆]^3−/4−. Its exhibits an electrochemical impedance response to protein myoglobin-antigen, Mb-Ag, concentration in a linear range from 0.01 μg to 1.65 μg mL⁻¹ with a lowest detection limit of 1.4 ng mL⁻¹.     

Electrical characterization of the polyaniline/p-silicon and polyaniline titanium dioxide tetradecyltrimethylammonium bromide /p-silicon heterojunctions

Au/PANI/p-Si/Al and Au/PANI TiO₂ TTAB/p-Si/Al heterojunctions have been fabricated by spin coating of soluble polyaniline (PANI) and PANI titanium dioxide (TiO₂) tetradecyltrimethylammonium bromide (TTAB) on the chemically cleaned p-Si substrates. The thicknesses of the polymeric films have been determined by a profilometer. The current-voltage (I-V) characteristics of the heterojunctions have been obtained in the temperature range of 98-258 K. These devices have showed the rectifying behavior such as diode. The I-V characteristics of the devices have been analyzed on the basis of the standard thermionic emission theory at low forward bias voltage regime. It has been shown that the values of ideality factor decrease while the values of barrier height increase with increasing temperature. This temperature dependence has been attributed to the presence of barrier inhomogeneities at the organic/inorganic semiconductor interface. Furthermore, analysis of the double logarithmic I-V plots at higher forward bias voltages at all temperatures indicates that transport through the organic thin film is explained by a space-charge-limited current process characterized by exponential distribution of traps within the band gap of the organic film. The total concentration of traps has been found to be 3.52 × 10¹⁴ cm^− 3 and 3.14 × 10¹⁵ cm^− 3 for PANI and PANI TiO₂ TTAB layer, respectively.     

Photoluminescence properties of RE-activated Na3GdP2O8 (RE = Tb, Dy, Eu, Sm) under VUV excitation

RE³⁺-activated monoclinic Na₃GdP₂O₈ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) phosphors have been synthesized by a solid-state reaction method. Their photoluminescence properties in the vacuum ultraviolet (VUV) region were investigated. By analyzing their excitation spectra, the host-related absorption band was determined to be around 166 nm. The f-d transition bands and the charge transfer bands for Na₃GdP₂O₈:RE³⁺ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) were assigned and corroborated. For the sample Na₃GdP₂O₈:5%Tb³⁺, the strong bands at around 202 and 221 nm are assigned to the 4f-5d spin-allowed transitions and the weak band at 266 nm is related to the spin-forbidden transition of Tb³⁺. For Na₃GdP₂O₈:5%Dy³⁺, the broad band at 176 nm could be related to the f-d transitions of Dy³⁺ and the O²⁻ → Dy³⁺ charge transfer band (CTB) besides the host-related absorption. In the excitation spectrum of Eu³⁺ doped sample, the O²⁻ → Eu³⁺ CTB is observed to be at 245 nm. For the Sm³⁺ doped sample, the O²⁻ → Sm³⁺ CTB is not distinguished obviously and is overlapped with the host-related absorption band.     

Enhancement of titania by doping rare earth for photodegradation of organic dye (Direct Blue)

Lanthanide ions (La³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, and Yb³⁺)/doped TiO₂ nanoparticles were successfully synthesized by sol–gel method. Their photocatalytic activities were evaluated using Direct Blue dye (DB53) as a decomposition objective. The structural features of TiO₂ and lanthanide ions/TiO₂ were investigated by XRD, SEM, UV-diffuse reflectance, and nitrogen adsorption measurements. Our findings indicated that XRD data characteristic anatase phase reflections and also XRD analysis showed that lanthanides phase was not observed on Lanthanide ions/TiO₂. The results indicated that Gd³⁺/TiO₂ has the lowest bandgap and particle size and also the highest surface area and pore volume (V_p) as well. Lanthanide ions can enhance the photocatalytic activity of TiO₂ to some extent as compared with pure TiO₂ and it was found that Gd³⁺/TiO₂ is the most effective photocatalyst. The photocatalytic tests indicate that at the optimum conditions; illumination time 40 min, pH ∼4, 0.3 g/L photocatalyst loading and 100 ppm DB53; the dye removal efficiency was 100%. Details of the synthesis procedure and results of the characterization studies of the produced lanthanide ions/TiO₂ are presented in this paper.     

Surface treatment of TiO2 films for dye-sensitized solar cells using atmospheric-pressure non-equilibrium DC pulse discharge plasma jet

In this paper, we report the utilization of the DC pulse discharge plasma jet technique as a means for the preparation of titanium oxide (TiO₂) films on fluorine dope tin oxide (FTO) coated glass substrates used for dye-sensitized solar cells (DSCs). The TiO₂ film made on these experimental bases exhibited the BET specific surface area of 95 m²/g, the pore volume of 0.3 cm²/g and the TEM particle size of ∼25 nm. The DSCs made by the TiO₂ film exhibited an energy conversion efficiency of 5.7% at 100 mW/cm² light intensity. Consequently, we believe that the optimization between the specific surface area and photocurrent density of TiO₂ film was achieved by the plasma surface treatment which also contributed to the improvement of energy conversion efficiency of DSCs.     

The gas sensitivity of nano TiO2-SnO2 film doped with Cd(II) ion

The nanocomposite oxide (0.2TiO₂-0.8SnO₂) doped with Cd²⁺ powder have been prepared and characterized by XRD and their gas-sensing sensitivity were characterized using gas sensing measurement. Experimental results show that, bicomponent nano anatase TiO₂ and rutile SnO₂ particulate thick film doped with Cd²⁺ behaves with good sensitivity to formaldehyde gas of 200 ppm in the air, and the optimum sensing temperature was reduced from 360 °C to 320 °C compared with the undoped Cd²⁺ thick film. The gas sensing thick films doped with Cd²⁺ also show good selectivity to formaldehyde among benzene, toluene, xylene and ammonia as disturbed gas and could be effectively used as an indoor formaldehyde sensor.     

A new method to prepare high-surface-area N-TiO2/activated carbon

A new method, combining impregnation and vapor-hydrolysis, was developed to prepare hybrid photocatalyst: nitrogen doped TiO₂ coated activated carbon (N-TiO₂/AC). The activated carbon (AC) was impregnated into titanium tetraethoxide/urea/methanol solution, and then the impregnated AC powder was kept in water vapor at 90 °C for 3 h for hydrolysis. Then it was calcinated to fabricate N-TiO₂/AC. Transmission electron microscopy (TEM) results showed that the nitrogen doped TiO₂ (N-TiO₂) in the as-synthesized hybrid was anatase TiO₂ powder with 10-20 nm in grain size, and the bandgap was about 3.08 eV. Moreover, the hybrid photocatalyst (8 wt.% N-TiO₂) had high specific surface area that was up to 1321 m²/g. The hybrid photocatalyst is expected to have high photocatalytic performance with visible irradiation.     

Studying trivalent/bivalent metal ion doped TiO2 as p-TiO2 in bipolar heterojunction devices

Trivalent/bivalent metal ions doped TiO₂ thin films (M_xTi_1−xO₂, M = Cr³⁺, Fe³⁺, Ni²⁺, Co²⁺, Mn²⁺ and x = 0.01, 0.05, 0.1, 0.15, 0.2) were deposited on Indium–tin oxide (ITO) coated glass substrates by spin coating technique. X-ray photoelectron spectroscopy (XPS) showed Ti⁴⁺ oxidation state of the Ti2p band in the doped p-TiO₂. The homogenous M_xTi_1−xO₂ was used to support n-ZnO thin films with thickness ∼40–80 nm and vertically aligned n-ZnO nanorods (NR) with length ∼300 nm and 1.5 μm. Current (I)–voltage (V) characteristics for the Ag/n-ZnO/M_xTi_1−xO₂/ITO/glass assembly showed rectifying behavior with small turn-on voltages (V₀) < 1 V. The ideality factor (η) and the resistances in both forward and reverse bias were calculated. The temperature dependence performance of these bipolar devices was performed and variation of the parameters with temperature was studied.     

Effect of TiO2-SiO2 sol-gel coating on the cpTi-porcelain bond strength

The effects of TiO₂-SiO₂ sol-gel coating with different firing temperatures (300 °C, 500 °C, and 750 °C) on the cpTi-porcelain bond strength were investigated in the present study. Prior to applying the low-fusing dental titanium porcelain, the phase, surface morphology, surface roughness and static water contact angle of the intermediate layer were evaluated. The cpTi-porcelain bond strength was measured using the three-point flexure test according to ISO 9693 standard. Statistical analyses were made using one-way ANOVA and Dunnett-t test. Significantly higher bond strength of TiO₂-SiO₂/750 °C (specimens coated with TiO₂-SiO₂ sol-gel coating and fired at 750 °C for 1 h) when compared to the control group was observed (p < 0.05). No rutile phase was found in all the tested specimens coated with TiO₂-SiO₂ sol-gel coating. The surface morphology of the intermediate layer was apparently different with different firing temperatures. It was found that the static water contact angle of TiO₂-SiO₂/750 °C significantly decreased (p < 0.05). However, no markedly different R_a of TiO₂-SiO₂/500 °C and TiO₂-SiO₂/750 °C in comparison to that of the control group was observed (p > 0.05). The results show that the TiO₂-SiO₂ sol-gel coating fired at 750 °C for 1 h can notably improve the cpTi-porcelain bond strength and may be suitable for clinical use.     

Substitution site and photoluminescence spectra of Eu-substituted SrTiO3 prepared by Pechini method

Eu³⁺-substituted SrTiO₃ (Sr_1 − xEu_xTiO₃) without second phase has been successfully prepared by Pechini method. X-ray diffraction patterns have suggested that solid-solubility limit would be 1-2 mol% due to large ionic radius difference between Eu³⁺ and Sr²⁺. Photoluminescence spectra of Sr_1 − xEu_xTiO₃ have shown the intense ⁵D₀-⁷F₁ transition higher than ⁵D₀-⁷F₂ transition, which indicates that Eu³⁺ was substituted for Sr²⁺ site.     

Experimental design in the electrodeposition process of porous composite Ni–P + TiO2 coatings

In this paper, an environmentally friendly electroplating process of the composite Ni–P + TiO₂ coatings was developed. Such coatings were prepared by in situ codeposition of Ni–P with TiO₂ powder (anatase) on a polycrystalline copper substrate from the nickel-plating bath in which titanium dioxide particles were held in suspension. The codeposition was carried out under galvanostatic conditions on a rotating disc electrode. To optimize the production conditions of the Ni–P coatings modified with TiO₂ by the method of mathematical statistics, the Hartley's polyselective quasi D optimum plan of experiments was used. The relationship between the percentage content in the electrodeposited composite Ni–P + TiO₂ coatings (z) and the electrodeposition parameters like cathodic current density (j_dep), bath temperature (T) as well as content of TiO₂ powder suspended in the galvanic bath (c), has been described by the adequate cubic polynomial equation and illustrated graphically. Based on the Hartley's plan it can be stated that the maximal TiO₂ content of 28.7 at.% in the Ni–P + TiO₂ coating can be obtained for the following optimal parameters of the electrodeposition process: j_dep = 0.05 A cm⁻², c = 99 g dm⁻³ and T = 40 °C. The chemical and physical characteristics of the coating obtained under such optimum conditions, have been presented. The deposit exhibits the presence of TiO₂ particles embedded into the amorphous Ni–P matrix. It has been ascertained that embedding of TiO₂ powder to the amorphous Ni–P matrix leads to the production of deposits with large surface area. Such electrochemical codeposition method may be a good alternative in the field of porous composite coatings used in gas evolution.     

(Eu-Nb)-codoped TiO2 nanopowders synthesized via Ar/O2 radio frequency thermal plasma oxidation processing: Phase composition and photoluminescence properties through energy transfer

(Eu³⁺-Nb⁵⁺)-codoped TiO₂ nanopowders have been prepared by Ar/O₂ radio frequency (RF) thermal plasma oxidizing liquid precursor mists, with various addition contents of dopants (molar ratio of Eu³⁺:Nb⁵⁺ = 1:1). Characterizations have been performed by the combined studies of XRD, TEM, Raman spectra, UV-vis spectroscopy, and excitation and PL spectra. The plasma-generated nanopowders mainly consist of anatase and rutile polymorphs. Doping Nb⁵⁺ cannot have appreciable influence on Eu³⁺ solubility (0.5 at.%) in the TiO₂ host lattice, but can significantly inhibit the increase of rutile weight fraction for TiO₂. 617 nm PL intensity at 350 nm indirect excitation through energy transfer is considerably weaker than that at 467 nm direct excitation, indicating that a defect state level in the TiO₂ host lattice might be lowered below the excited state of Eu³⁺ by doping Nb⁵⁺, which is conceivable from a relatively large amount of oxygen deficiencies yielded in the TiO₂ host lattice.     

Fabrication of TiO2 nanostructured films by spray deposition with high photocatalytic activity of methylene blue

TiO₂ films were successfully deposited onto hot quartz substrates by airbrush spraying using an aqueous dispersion. The films consisting of cubic or cauliflower-shaped structures expressed higher photodegradation efficiencies of methylene blue than those with prism-, flower- or fan-blade-shaped morphology due to the difference in the optical band gap energy. The photodegradation obeyed the pseudo-first-order Langmuir-Hinshelwood kinetic model with apparent rate constants ranging from 3.95 × 10^− 3 to 19.38 × 10^− 3 min^− 1 based on the film surface morphology.     

Fabrication of highly conductive Ta-doped SnO2 polycrystalline films on glass using seed-layer technique by pulse laser deposition

We discuss the fabrication of highly conductive Ta-doped SnO₂ (Sn_1 − xTa_xO₂; TTO) thin films on glass by pulse laser deposition. On the basis of the comparison of X-ray diffraction patterns and resistivity (ρ) values between epitaxial films and polycrystalline films deposited on bare glass, we proposed the use of seed-layers for improving the conductivity of the TTO polycrystalline films. We investigated the use of rutile TiO₂ and NbO₂ as seed-layers; these are isostructural materials of SnO_2, which are expected to promote epitaxial-like growth of the TTO films. The films prepared on the 10-nm-thick seed-layers exhibited preferential growth of the TTO (110) plane. The TTO film with x = 0.05 on rutile TiO₂ exhibited ρ  = 3.5 × 10^− 4 Ω cm, which is similar to those of the epitaxial films grown on Al₂O₃ (0001).     

Rapid synthesis of homogeneous MnO2/multi-wall carbon nanotubes nanostructure and its electrochemical capacitive behavior

A homogeneous composite of MnO₂/multi-wall carbon nanotubes (MnO₂/MWCNTs) was rapidly and efficiently synthesized by a redox reaction of MnO₄⁻ and Mn²⁺ on the MWCNTs under ultrasonic irradiation. The structure and morphology of the obtained MnO₂ and MnO₂/MWCNTs composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. Electrochemical investigation indicated that the maximum specific capacitance of the MnO₂/MWCNTs composite, measured by galvanostatic charge-discharge test, was 315 F g^− 1, compared to the pristine MnO₂ (192 F g^− 1) and MWCNTs electrode (25 F g^− 1), showing the synergistic effect of MWCNTs and MnO₂. The homogeneous hybrid nanostructure and the good conductivity of MWCNTs were considered to be responsible for its preferable electrochemical performances.     

A yellow-emitting Ca3Si2O7: Eu phosphor for white LEDs

A series of yellow-emitting phosphors based on a silicate host matrix, Ca_3 − xSi₂O₇: xEu²⁺, was prepared by solid-state reaction method. The structure and photoluminescent properties of the phosphors were investigated. The XRD results show that the Eu²⁺ substitution of Ca²⁺ does not change the structure of Ca₃Si₂O₇ host and there is no impurity phase for x < 0.12. The SEM images display that phosphors aggregate obviously and the shape of the phosphor particle is irregular. The EDX results reveal that the phosphors consist of Ca, Si, O, Eu and the concentration of these elements is close to the stoichiometric composition. The Ca_3 − xSi₂O₇: xEu²⁺ phosphors can be excited at a wavelength of 300-490 nm, which is suitable for the emission band of near ultraviolet or blue light-emitting-diode (LED) chips. The phosphors exhibit a broad emission region from 520 to 650 nm and the emission peak centered at 568 nm. In addition, the shape and the position of the emission peak are not influenced by the Eu²⁺ concentration and excitation wavelength. The phosphor for x = 0.045 has the strongest excitation and emission intensity, and the Ca_3 − xSi₂O₇: xEu²⁺ phosphors can be used as candidates for the white LEDs.     

Enhanced thermoelectric properties of NaCo2O4 by adding ZnO

The primary phase present in the as-sintered Na(Co_1 − xZn_x)₂O₄ (0 ≤ x ≤ 0.1) bodies was the solid solution of the constituent oxides with a bronze-type layered structure. The electrical conductivity of the Na(Co_1 − xZn_x)₂O₄ samples significantly increased with an increase in ZnO content. The sign of the Seebeck coefficient for all samples was positive over the whole temperature range (723-1073 K), i.e., p-type conduction. The power factor of Na(Co_0.95Zn_0.05)₂O₄ showed an outstanding power factor (1.7 × 10^− 3Wm^− 1 K^− 2) at 1073 K. The power factor was above four times superior to that of ZnO-free NaCo₂O₄ (0.4 × 10^− 3Wm^− 1 K^− 2). This originates from an unusually large Seebeck coefficient (415 μVK^− 1) accompanied with high conductivity (127Ω^− 1 cm^− 1) at 1073 K.     

Influence of cobalt ion implantation on optical properties of titanium dioxide thin films

Nano-crystalline TiO₂ thin films were synthesized by using sol-gel and spin-coating techniques on glass substrates for photo-catalytic applications. Prior to deposition, a TiO₂ colloidal suspension was synthesized by microwave-induced thermal hydrolysis of the titanium tetrachloride aqueous solution. In this study, the deposited TiO₂ coating with a grain size of 13 ± 2 nm was uniform without aggregation. Co ion implantation into the as-calcined TiO₂ thin films was conducted with fluences of 1 × 10¹⁵-1 × 10¹⁶ doses/cm² at 40 keV. In addition to the emission of TiO₂, the photoluminescence study showed the presence of another Co-related optical center at 405 nm in the Co-implanted TiO₂ thin films. Due to the strong capability of forming impurity compounds between the energetic cobalt ions and TiO₂, the photoluminescence emission and UV-Vis absorption efficiencies were improved.