Enhanced photocurrent of nitrogen-doped TiO2 film for dye-sensitized solar cells

Nitrogen (n)-doped titanium dioxide (TiO₂) was prepared with varying doping extent by a general sol–gel process with a pure TiO₂ film as the control sample. The n-doped-2 electrode showed the maximum conversion efficiency with an open-circuit voltage (V_oc) of 0.726 V, a photocurrent (J_sc) of 10.52 mA cm^?2, a fill factor of 63.6%, and an efficiency of 4.86%, compared to 0.751 V, 7.4 mA cm^?2, 67.1%, and 3.73%, respectively, for the undoped (u-doped) TiO₂ electrode. The approximate 23% enhancement in the conversion efficiency of the n-doped-2 TiO₂ electrode-based dye-sensitized solar cells (DSSCs) was mostly ascribed to the increase of light absorption in the near-vis absorbance and partially to the morphological characteristics of the n-doped TiO₂ film. Additionally, the doping type of nitrogen in the TiO₂ lattice was closely studied using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The relation between the doping type and the electron behavior in the DSSCs was also examined.     

Preparation and properties of sliver and nitrogen co-doped TiO2 photocatalyst

TiO₂ photocatalysts co-doped with different content of Ag and N were prepared by sol–gel method combined with microwave chemical method. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), ultraviolet–visible diffuse reflectance spectrum (UV–vis) and photo-luminescence emission spectrum (PL). The photocatalytic activity was investigated by photocatalytic degradation of methylene blue (MB) under irradiation of fluorescent lamp. The results indicate that Ag and N co-doping can restrain the increase of grain size, broaden the absorption spectrum to visible light region, and inhibit the recombination of the photo-generated electron–hole pairs. Moreover, the photocatalytic activity of Ag–N–TiO₂ in MB degradation is remarkable improved. The degradation rate of the sample with Ag:TiO₂ = 0.05 at%, N:TiO₂ = 18.50 wt% in 5 h is 93.44%, which is much higher than that of Degussa P25 (39.40%).     

Preparation and optical properties of iron-modified titanium dioxide obtained by sol–gel method

In this paper twelve TiO₂:Fe powders prepared by sol–gel method were analyzed being into consideration the kind of iron compound applied. As a precursor titanium (IV) isopropoxide (TIPO) was used, while as source of iron Fe(NO₃)₃ or FeCl₃ were tested. Fe doped TiO₂ was obtained using two methods of synthesis, where different amount of iron was added (1, 5 or 10% w/w). The size of obtained TiO₂:Fe particles depends on the iron compound applied and was found in the range 80–300 nm as it was confirmed by SEM technique. TiO₂:Fe particles were additionally investigated by dynamic light scattering (DLS) method. Additionally, for the TiO₂:Fe particles UV–vis absorption and the zeta potential were analyzed. Selected powders were additionally investigated by magnetic force microscopy (MFM) and X-ray diffraction techniques. Photocatalytic ability of Fe doped TiO₂ powders was evaluated by means of cholesteryl hemisuccinate (CHOL) degradation experiment conducted under the 30 min irradiation of simulated solar light.     

The effect of calcination conditions on the morphology,the architecture and the photo-electrical properties of TiO2 nanotube arrays

Highly ordered TiO₂ nanotube arrays were successfully prepared by electrochemical anodization in a formamide-based electrolyte containing 0.5 wt.% NH₄F and 2 vol.% H₂O. The effects of the calcining temperature, the calcining time and the heating rate on the formation of the TiO₂ nanotube arrays were investigated in detail. The morphological changes and phase transformations of the TiO₂ nanotubes were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It was found that the calcining temperature and the calcining time determined the crystal phase, while the heating rate was only beneficial to altering the crystallinity. UV–vis diffuse reflectance spectroscopy was used to examine changes in the band gap energy. For applications to dye sensitized solar cells, a maximum conversion efficiency was achieved at 500 °C for 2 h with a heating rate of 10 °C/min, which is attributed to the highly crystalline anatase and the lower surface defect concentrations of the nanotubes. The optimum calcination conditions help to retard the electron recombination and allow higher dye absorption capacities, thereby increasing V_oc and J_sc.     

Fabrication,characterization and comparison of DSSC using anatase TiO2 synthesized by various methods

In this study, anatase TiO₂ nanoparticles were synthesized by three techniques, namely, sol–gel, acid-base co-catalyst and room temperature colloidal methods. The synthesized materials were characterized by X-ray diffraction, scanning electron microscopy, pore diameter, pore volume and surface area. The dye-sensitized solar cells were fabricated using the synthesized materials and characterized for incident photon to current conversion efficiency, photocurrent density to photo voltage measurement and electrochemical impedance analysis. Among the studied materials, TiO₂ synthesized by sol–gel method displayed highest photon to current conversion of 76.8% and a maximum solar cell efficiency of 7.85% with J_sc of 14.75 mA/cm², V_oc of 0.76 V and FF of 0.7. This is the first study to report a high power conversion efficiency of DSSC using a sol–gel synthesized titania and its comparison with other two synthesized materials. The high power conversion efficiency of the solar cell using TiO₂ synthesized by sol–gel method is attributed to its characteristic properties such high surface area, larger pore diameter and larger pore volume and highest dye loading capacity.     

Reduced graphene oxide-based photocatalysts containing Ag nanoparticles on a TiO2 nanotube array

A simple one-step electrochemical deposition method was demonstrated to fabricate reduced graphene oxide/Ag nanoparticle co-decorated TiO₂ nanotube arrays (RGO/Ag–TiO₂NTs) photocatalyst in this study. The structures and properties of these photocatalysts were characterized using scanning electron microscope, X-ray diffraction, UV–Vis diffuse reflection spectra, and photoluminescence. By taking the advantages of TiO₂, graphene, and Ag nanoparticles (AgNPs), RGO/Ag–TiO₂NTs showed a greatly improved photocatalytic activity compared with the bare TiO₂NTs, Ag–TiO₂NTs or RGO–TiO₂NTs. The deposited RGO and AgNPs not only reduce the recombination of photogenerated electrons and holes, but also increase the surface area of the catalyst. Both photocatalytic performance and adsorptivity of the catalyst have been improved. The ternary photocatalyst exhibited over 93 % removal efficiency of typical herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) under simulated solar light irradiation with good stability and easy recovery, which justifies the photocatalytic system, a promising application for herbicide or other organic pollutant removal from water.     

Synthesis and characterization of rice grains like Nitrogen-doped TiO2 nanostructures by electrospinning–photocatalysis

Rice grain-shaped Nitrogen-doped titanium dioxide (N–TiO₂) nano/mesostructures were fabricated through a combination of sol–gel and electrospinning methods. As-spun nanofibers were continuous and upon thermal treatment at 500° C for 1 h in air, the continuous fibers break into rice grain-shaped TiO₂ nanostructures of average diameter 50–80 nm. The nanostructures were characterized by spectroscopy, microscopy and powder X-ray diffraction. The rice grains consist of spherical particles of average diameter of ~ 18 nm and with N doping, their average diameters decrease from ~ 18 to ~ 12 nm. The presence of N in the TiO₂ lattice was confirmed by X-ray photoelectron spectroscopy (XPS). The band-gap of TiO₂ reduced from 3.19 eV to 2.83 eV upon increasing doping level of N from 0% to 5% (w/w), respectively. The N–TiO₂ rice grains showed an enhanced UV light-assisted photocatalysis compared to pure TiO₂ in the photodegradation of Alizarin Red S dye, an industrially important anthraquinone dye.     

Fabrication of partially crystalline TiO2 nanotube arrays using 1, 2-propanediol electrolytes and application in dye-sensitized solar cells

We report the fabrication of self-organized partial crystalline TiO₂ nanotube arrays in 1, 2-propanediol containing fluoride ion. The influence of anodization parameters including NH₄F concentration, water content, anodization voltage and time on the morphology, diameter and length of TiO₂ nanotube were investigated in detail. The prepared TiO₂ nanotube has diameter in 30–120 nm and length in 0.6–3 μm. TiO₂ nanotube arrays are used as photoanode for the application in dye-sensitized solar cell and the photovoltaic performance of 1.91% is achieved with a TiO₂ nanotube sample of 2.2 μm in length combining with N719 dye, and the corresponding photovoltaic parameters of 3.6 mA cm^?2 in short circuit photocurrent density, 840 mV in open circuit potential, and 63.2% in fill factor.     

Design and development of electronic- and micro-structures for multi-functional working electrodes in dye-sensitized solar cells

This paper outlines a new strategy to optimize the performance of electrodes in dye-sensitized solar cells (DSSCs), through the engineering of electronic structures in conjunction with the micro-structures of the devices. We propose a simple hydrolysis method for the fabrication of a family of quasi-core–shell TiO₂ (hydrolysis)/PbS composites for working electrodes. Measurements confirm a shift in absorption from the UV to visible range. We also measured cell performance, including short-circuit photocurrent, open-circuit photovoltage, and the power conversion efficiency (η) of DSSCs. The obtained η of DSSC (6.05%) with a TiO₂ (P-25)/TiO₂ (hydrolysis) + 0.005 M PbS electrode is substantially higher than that of the conventional DSSC (5.11%) with a TiO₂ (P-25) electrode, due to improved p–n junctions, light-scattering, and light absorption. Finally, the shell of TiO₂ (hydrolysis) protected the core of PbS from the corrosive effects of electrolytes, thereby prolonging the life span of the DSSC. This novel approach to electrode design could lead to advances in DSSC as well as other energy applications including photo-catalysis technology.     

Visible-light absorption and photocatalytic activity of Cr-doped TiO2 nanocrystal films

Chromium doped titanium dioxide (TiO₂) nanocrystal films with various doping concentration have been successfully prepared by a sol–gel dip-coating process. These films have been characterized by XRD, XPS, AFM, and UV–vis absorption spectroscopy. It is found that Cr doping can effectively reduce the transition temperature of anatase to rutile phase as well as the grain size. The absorption edges of TiO₂ thin films shift towards longer wavelengths (i.e. red shifted) from 375 nm to about 800 nm with increasing Cr concentration, which greatly enhances TiO₂ nano-materials on the absorption of solar spectrum. The appearance of UV–vis absorption features in the visible region can be ascribed to the newly formed energy levels such as Cr 2p level and oxygen vacancy state between the valence and the conduction bands in the TiO₂ band structure. The enhancement of the photocatalytic properties is observed for Cr-doped TiO₂ thin film.     

Effect of SiO2 nanoparticles on the phase transformation of TiO2 in micron-sized porous TiO2–SiO2 mixed particles

Spherical and nanoporous TiO₂ and TiO₂–SiO₂ mixed micro-particles with four different compositions (20/80, 50/50, 80/20, 90/10 in weight ratio of TiO₂/SiO₂) were prepared by spray drying method from colloidal mixtures of amorphous silica and anatase titania nanoparticles. The as-prepared particles were heat-treated at 900 °C for 0.5–5 h. The TiO₂ and TiO₂–SiO₂ particles were spherical in shape and the average particle diameter was about 1 μm. The anatase mass fraction and the specific surface area of TiO₂–SiO₂ (50 wt.% SiO₂) mixed particles were kept to 61.5% and 30.6%, respectively, of their initial values after 5 h heat-treatment whereas these values of TiO₂ particles were rapidly decreased to 13.0% and 1.2% of their initial values, respectively, within 30 min after heat-treatment. And the anatase mass fraction and specific surface area increased as SiO₂ content in the TiO₂–SiO₂ mixed particles increased.     

RBS,XRR and optical reflectivity measurements of Ti–TiO2 thin films deposited by magnetron sputtering

Single-, bi- and tri-layered films of Ti–TiO₂ system were deposited by d.c. pulsed magnetron sputtering from metallic Ti target in an inert Ar or reactive Ar + O₂ atmosphere. The nominal thickness of each layer was 50 nm. The chemical composition and its depth profile were determined by Rutherford backscattering spectroscopy (RBS). Crystallographic structure was analysed by means of X-ray diffraction (XRD) at glancing incidence. X-ray reflectometry (XRR) was used as a complementary method for the film thickness and density evaluation. Modelling of the optical reflectivity spectra of Ti–TiO₂ thin films deposited onto Si(1 1 1) substrates provided an independent estimate of the layer thickness. The combined analysis of RBS, XRR and reflectivity spectra indicated the real thickness of each layer less than 50 nm with TiO₂ film density slightly lower than the corresponding bulk value. Scanning Electron Microscopy (SEM) cross-sectional images revealed the columnar growth of TiO₂ layers. Thickness estimated directly from SEM studies was found to be in a good agreement with the results of RBS, XRR and reflectivity spectra.     

Synthesis,structure, and optical properties of Au–TiO2 composite thin films

Titanium dioxide (TiO₂) films with varying concentrations of gold particles were synthesized using pulsed DC magnetron sputtering, with the intent to develop infrared reflecting films for use on cars and planes to reduce solar heat load. Under our deposition conditions, the films are smooth (RMS roughness on the order of 1.0–2.0 nm) and consist of rutile TiO₂ with embedded gold. The average gold particle diameter on the sample surface was found to change from 60 to 200 nm as the volume fraction of gold in the films increased from 1.9 to 4.3% (3.5 to 7.9 mol% Au). The maximum reflectance of these films in the infrared region (800–2500 nm) is > 50%, compared with 30% for pure TiO₂. The Maxwell–Garnett equation does not model the reflectance data very well, due to the relatively large gold particle size. Instead, by assuming that the contribution of gold particles to the reflectance response is proportional to their projected areal fraction in an effective medium approximation, we were able to fit the observed reflectance data quite well.     

Influence of TiO2 dimension and graphene oxide content on the self-cleaning activity of methylene blue-stained photocatalytic films

In the present study, TiO₂ and graphene oxide (GO)/TiO₂ composite films were simply fabricated by hot-plate spray coating technique. The influences of TiO₂ dimension and GO content on the self-cleaning activity of methylene blue (MB)-stained films were investigated. The matrix of anatase TiO₂ quasi-cubic and octahedral particles in diameter of 6–9 nm (ST film) degraded 80% stained dye, much higher than those either in bigger size (30–50 nm) or in flower morphology due to the nano effect. Moreover, the photocatalytic performance of such nanostructured film was strongly enhanced by the combination with GO sheets. Increasing GO content led to significant enhancement in film transmittance and MB adsorptivity. In the aspect of the self-cleaning activity for MB, the addition of GO up to 1 wt.% showed higher efficiency but excess content led to similar performance in comparison with pure TiO₂ film.     

Microstructural evolution and optical properties of TiO2 synthesized by eggshell membrane templating for DSSCs application

This article presents the bio-inspired synthesis of TiO₂ using eggshell membranes (ESM) as a biotemplate on which the crystals of TiO₂ are nucleated and grown. The microstructure, phase transformations and optical behavior were studied with the objective of understanding the effects of the thermal treatment on the properties of the TiO₂ powder for application in dye sensitized solar cells (DSSC). The technique used for the mimetization of the ESM consists of submerging the biotemplate in an alcoholic solution of TiCl₄ and thermal treating the samples at 600, 700 and 800 °C. Thermal analysis (DTA and TGA) was used to investigate the thermal decomposition of the membranes. X-ray diffraction (XRD) studies revealed the phase evolution and the average crystal sizes. Scanning and transition electron microscopy (SEM and TEM, respectively) were used to investigate the morphology of the obtained powders. UV–vis diffuse reflectance was used to investigate the optical properties. The porosity was also evaluated using a BET instrument. The results indicated that the best features for DSSC application were presented by the sample that was thermally treated at 600 °C. This is reflected in the good replication of the morphology of the used biotemplate, with a nanocrystalline anatase phase (average crystal size 15.82 nm), high surface area (64.8 m²/g), mesoporous structure (average pore size of 26.31 Å) and large band gap (3.31 eV).     

Al2TiO5–Al2O3–TiO2 nanocomposite: Structure,mechanical property and bioactivity studies

Novel biomaterials are of prime importance in tissue engineering. Here, we developed novel nanostructured Al₂TiO₅–Al₂O₃–TiO₂ composite as a biomaterial for bone repair. Initially, nanocrystalline Al₂O₃–TiO₂ composite powder was synthesized by a sol–gel process. The powder was cold compacted and sintered at 1300–1500 °C to develop nanostructured Al₂TiO₅–Al₂O₃–TiO₂ composite. Nano features were retained in the sintered structures while the grains showed irregular morphology. The grain-growth and microcracking were prominent at higher sintering temperatures. X-ray diffraction peak intensity of β-Al₂TiO₅ increased with increasing temperature. β-Al₂TiO₅ content increased from 91.67% at 1300 °C to 98.83% at 1500 °C, according to Rietveld refinement. The density of β-Al₂TiO₅ sintered at 1300 °C, 1400 °C and 1500 °C were computed to be 3.668 g cm^?3, 3.685 g cm^?3 and 3.664 g cm^?3, respectively.Nanocrystalline grains enhanced the flexural strength. The highest flexural strength of 43.2 MPa was achieved. Bioactivity and biomechanical properties were assessed in simulated body fluid. Electron microscopy confirmed the formation of apatite crystals on the surface of the nanocomposite. Spectroscopic analysis established the presence of Ca and P ions in the crystals. Results throw light on biocompatibility and bioactivity of β-Al₂TiO₅ phase, which has not been reported previously.     

Application of ionic liquid–TiO2 nanoparticle modified carbon paste electrode for the voltammetric determination of benserazide in biological samples

An ionic liquid–TiO₂ nanoparticle modified carbon paste electrode (IL–TiO₂/CPE) was used as a fast and sensitive tool for the investigation of the electrochemical oxidation of benserazide using voltammetry. This modified electrode has been fabricated using hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) as a binder. The modified electrode offers a considerable improvement in voltammetric sensitivity toward benserazide, compared to the bare electrode. Using differential pulse voltammetry (DPV), the electrocatalytic oxidation peak current of benserazide shows a linear calibration curve in the range of 1.0–600 μmol L^? 1 benserazide. The limit of detection was equal to 0.4 μmol L^? 1. The relative standard deviation (RSD%) for eight successive assays of 10 μmol L^? 1 benserazide was 1.1%. Finally, the proposed method was successfully applied to the determination of benserazide in real samples such as blood serum and urine.     

Mechanical alloying and sintering of nanostructured TiO2 reinforced copper composite and its characterization

Mechanical alloying is a suitable method for producing copper based composites. Cu–TiO₂ composite was fabricated using high energy ball milling and conventional consolidation. Ball milling was performed at different milling durations (0–24 h) to investigate the effects of the milling time on the formation and properties of produced nanostructured Cu–TiO₂ composites. The amount of the TiO₂ in the final composition of the composite assumed to be 0, 1, 3, 5 and 7 wt%. The milled composite powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy to investigate the effects of the milling time on the formation of the composite and its properties. Also hardness, density and electrical conductivity of the sintered specimen were measured. High energy ball milling causes a high density of defects in the powders. Thus the Cu crystallite size decreases, generally to less than 50 nm. The maximum hardness value (105 HV) of the sintered compacts belongs to Cu–5 wt%TiO₂ which has been milled for 12 h.     

Grafting of nano-TiO2 onto flax fibers and the enhancement of the mechanical properties of the flax fiber and flax fiber/epoxy composite

In this article, a flax fiber yarn was grafted with nanometer sized TiO₂, and the effects on the tensile and bonding properties of the single fibers and unidirectional fiber reinforced epoxy plates were studied. The flax fiber yarn was grafted with nanometer sized TiO₂ through immersion in nano-TiO₂/KH560 suspensions under sonification. The measured grafting content of the nano-TiO₂ ranged from 0.89 wt.% to 7.14 wt.%, dependent on the suspension concentration. With the optimized nano-TiO₂ grafting content (∼2.34 wt.%), the tensile strength of the flax fibers and the interfacial shear strength to an epoxy resin were enhanced by 23.1% and 40.5%, respectively. The formation of Si–O–Ti and C–O–Si bonds and the presence of the nano-TiO₂ particles on the fiber surfaces contributed to the property enhancements. Unidirectional flax fiber reinforced epoxy composite (V_f = 35.4%) plates prepared manually showed significantly enhanced flexural properties with the grafting of nano-TiO₂.     

Effects of TiO2 nanoparticles addition on microstructure,microhardness and tensile properties of Sn–3.0Ag–0.5Cu–xTiO2 composite solder

The effects of TiO₂ nanoparticles addition on the microstructure, microhardness, and tensile properties of Sn–3.0 wt.%Ag–0.5 wt.%Cu–x wt.%TiO₂ (x = 0, 0.05, 0.1, and 0.6) composite solders were systematically investigated. Scanning electron microscope (SEM) was used to observe the microstructural evolution of the composite solders, measure the size of the Ag₃Sn grains, and estimate the spacing between the Ag₃Sn grains in the solder matrix. Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD) were used to identify the phases of eutectic areas in the composite solder matrix. Results show that both the average size of Ag₃Sn grains and the spacing between the Ag₃Sn grains decrease significantly, which might owe to the strong adsorption effect and high surface free energy of the TiO₂ nanoparticles. The microhardness is improved by 37% compared with TiO₂-free noncomposite solder as the weight percentage of TiO₂ nanoparticles is 0.1 wt.%. The improvement is due to the microstructural change of the composite solders, which is in good agreement with the prediction of the classic theory of dispersion strengthening. Tensile tests reveal that the TiO₂-containg composite solder alloys have higher ultimate tensile strength (UTS) than TiO₂-free noncomposite solder alloy due to solid solution hardening. UTS of solder alloys have a logarithmic increase relation with strain rate ranging from 10⁻³ s⁻¹ to 10⁻¹ s⁻¹ and decreases with an increase of test temperatures ranging from 25 °C to 125 °C.