Nanocrystalline TiO2 Research Articles

4,4′‐Diaminodiphenylsulfone; an efficient co‐additive in dye‐sensitized nanocrystalline TiO2 solar cells

The effect of 4,4′‐diaminodiphenylsulfone (DADPS) as a co‐additives in iodide/triiodide redox electrolyte on the performance of dye‐sensitized solar cell based on the 2‐cyano‐3‐(4‐(diphenylamino)phenyl)acrylic acid (TPA) and 2‐cyano‐3‐(2΄‐(5΄,10΄,15΄,20΄‐ tetraphenylporphyrinato Zinc (II)yl) acrylic acid (Zn‐1) dyes have been investigated. Compared withstandard electrolyte (0.1 M LiI, 0.05 M I2, 0.6 M 1‐butyl‐2,3‐dimethylimidazolium iodide (BDMII) and TBP (0.5, 1 M)), adding 0.5 M of DADPS, as a co‐additive, into the electrolyte system has caused increasing short current density (Jsc) and open‐circuit potential (Voc) consequently the energy conversion (η) improved. Electrochemical impedance results indicate adsorbing of DADPS on the titanium dioxide surface leads to an increase in the lifetime (τ). Adsorbing of DADPS on the semiconductor surface retards the interfacial charge recombination that has a beneficial effect on the Voc and Jsc. The results showed that amine groups of DADPS attach to the conduction band (CB) of TiO2 film and suppress the electron recombination process and as a result, it can be applied as a promising co‐additive in DSSCs.

Highly effective visible light-activated cobalt-doped TiO2 nanoparticles for antibacterial coatings against Campylobacter jejuni

Pure and cobalt-doped nanocrystalline TiO2 nanostructures, with different concentrations of cobalt (1, 2.5, 5, 10 mol%), were synthesized by a simple hydrothermal route and their antibacterial activity was tested. The corresponding structural and chemical properties of the as-synthesized nanoparticles clearly suggested the occurrence of lattice defects in TiO2 structure. The crystalline phases and particle-size study of the pure and doped TiO2 nanoparticles showed the formation of highly pure anatase phase with grain sizes ranging between 7 and 14 nm, where the functional groups and bond lengths were observed through Fourier transform infrared (FTIR) analysis. Raman spectroscopy analysis displayed the broadening of Raman peaks and a systematic frequency shifts with increase in cobalt concentration because of the reduced particle size. Moreover, UV–Vis spectroscopy indicated the visible light absorption of TiO2 with increase in the concentration of cobalt, which suggests decrease in the energy bandgap. Furthermore, these visible light-activated photocatalysts showed enhanced antibacterial activity in particular against notorious foodborne Gram negative pathogen i.e., Campylobacter jejuni. Moreover, these high energy photocatalysts were able to effectively kill waterborne Gram negative pathogen i.e., Vibrio cholerae as well as foodborne Gram positive pathogen i.e., Staphylococcus aureus. Therefore, we believe that these visible light-activated photocatalysts may be used as broad spectrum antimicrobial agents against groups of such pathogens impacting significantly human health and economy.

CdSe Quantum Dot Sensitized Molecular Photon Upconversion Solar Cells

Incorporating photon upconversion, via triplet–triplet annihilation (TTA-UC), directly into a solar cell is an intriguing strategy for harnessing sub-band gap photons and surpassing the Shockley–Queisser limit. A majority of TTA-UC solar cells to date rely on difficult to synthesize and expensive platinum and/or palladium porphyrin sensitizers. Here, we present, as far as we know, the first TTA-UC solar cell that integrates quantum dot (QD) sensitizers directly into the photocurrent generation mechanism. The photoanodes are composed of a nanocrystalline TiO2 substrate, 4,4′-(anthracene-9,10-diyl)bis(4,1-phenylene)diphosphonic acid (A) as the annihilator molecule, and CdSe QDs as the sensitizer in an inorganic–organic-inorganic layered architecture (TiO2-A-QD). The TiO2-A-QD devices generate a photocurrent that is more than 1.4 times the sum of its parts and does so via a TTA-UC mechanism as demonstrated by intensity dependence, IPCE, and spectroscopic measurements. The maximum efficiency onset threshold (...

Investigation of resistive switching effect in nanocrystalline TiO2 thin film for neuromorphic system manufacturing

Effect of resistive switching in TiO2 thin film was investigated. It was shown, resistive switching from high resistance state (HRS) to low resistance state (LRS) has occurred at 3.2±0.2 V, and from LRS to HRS at -2.8±0.5 V. Endurance test shown that HRS decreased from 42.31±5.26 kΩ to 26.45±6.14 kΩ, LRS increased from 2.25±1.15 kΩ to 3.45±1.18 kΩ. HRS/LRS coefficient has decreased from 18.8 to 7.6. Time-stability of TiO2 surface charge was investigated. It was shown, that voltage decreased from 320±21 to 22±5 mV during 90 minutes and square side increased from 3.43±0.12 to 4.12±0.14 µm during 90 minutes. The results can be useful for neuromorphic systems manufacturing based on nanocrystalline TiO2 films.

Dimerization and low-dimensional magnetism in nanocrystalline TiO2 semiconductors doped by Fe and Co

The report is devoted to an analysis of the structural and magnetic state of the nanocrystalline diluted magnetic semiconductors based on TiO2 doped with Fe and Co atoms. Structural and magnetic characterization of samples was carried out using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR) spectroscopy, SQUID magnetometry, and the density functional theory (DFT) calculations. Analysis of the experimental data suggests the presence of non-interacting paramagnetic Fe3+ and Co2+ ions in the high-spin state and negative exchange interactions between them. The important conclusions is that the distribution of dopants in the TiO2 matrix, even at low concentrations of 3d-metal dopant (less than one percent), is not random, but the 3d ions localization and dimerization is observed both on the surface and in the nanoparticles core. Thus, in the paper the quantum mechanical model for describing the magnetic properties of TiO2:(Fe, Co) was suggested. The model operates only with two parameters: paramagnetic contribution of non-interacting 3d-ions and dimers having different exchange interactions between 3d magnetic carriers.

Effect of nano-crystalline TiO2 addition on reciprocating frictional behaviour of alumina ceramics

We report the effect of normal load and sliding frequency on the tribological performance of alumina ceramics in relation with nano-crystalline T iO2 addition. Tribological studies are conducted by reciprocating a silicon nitride ball on the prepared samples in dry condition in a linear reciprocating tribotester. Reciprocating friction tests are performed with sliding frequency of 15, 30, 45 and 60 Hz and at normal loads of 0.3, 0.5, 0.7 and 1.0 kg. The friction coefficient increases with increasing sliding frequency, normal load but decreases with nano titania addition. The coefficient of friction sharply increases at the level of sliding frequency from 30 Hz to 45 Hz. As the coefficient of friction gradually decreases with increase in T iO2 addition, it can be inferred that alumina ceramics with T iO2 addition upto 4 weight percent can be used as ceramic engine components, cutting tool inserts.

Features of the production and study of electrophysical characteristics (BeO + TiO2)-ceramics by impedance spectroscopy

The resulting electrically conductive two-component BeO ceramics with the addition of micro and nanocrystalline TiO 2 powder, which can be used as a material absorber of scattered microwave radiation in high-power electronic devices. The nature of the appearance of electrical conductivity and absorption of the microwave field in (BeO + TiO 2 )-ceramics has not been completely established. The impedance spectroscopy method was the first to investigate the electrical and dielectric characteristics of this ceramics in the frequency range from 100 Hz to 100 MHz, depending on the presence of a micro- and nanosized TiO 2 phase in the composition of BeO ceramics. It has been established that the static resistance of ceramics with the addition of a TiO 2 nanopowder is significantly reduced compared with the resistance of the original ceramics with TiO 2 micropowder. It is shown that the real and imaginary components of the dielectric constant of the studied ceramics increase to abnormally large values as the frequency of the effective electric field decreases, and in the high frequency range f ≥ 10 8 Hz, the process of dielectric relaxation begins, leading to an increase in the dielectric loss angle. The dielectric characteristics of ceramic samples are determined under blocking conditions for through conduction. The effect of TiO 2 micropowder additives on dielectric polarization processes with increasing frequency up to 12·10 9 Hz is considered. Ill. 8. Ref. 26.

Numerical solutions for nonlinear partial differential equations arising from modelling dye-sensitized solar cells

Dye-sensitized solar cells have generated diverse research directions, which include a mathematical model based on the diffusion of electrons in the conduction band of a nano-porous semiconductor (traditionally TiO\(_2\)). We solve the nonlinear diffusion equation under its boundary conditions, as stated by Anta et al. [J. Phys. Chem. B 110 (2006) pp 5372--5378]. We employ a standard finite difference method, a fourth order finite difference method scheme and a Runge--Kutta scheme. We calculate errors and evaluate the utility of each scheme as it applies to this boundary value problem. 
 
 References J. A. Anta, F. Casanueva, and G. Oskam. A numerical model for charge transport and recombination in dye-sensitized solar cells. J. Phys. Chem. B, 110(11):5372–5378, 2006. doi:10.1021/jp056493h. F. Cao, G. Oskam, G. J. Meyer, and P. C. Searson. Electron transport in porous nanocrystalline TiO\(_2\) photoelectrochemical cells. J. Phys. Chem., 100(42):17021–17027, 1996. doi:10.1021/jp9616573. A. J. Frank, N. Kopidakis, and J. van de Lagemaat. Electrons in nanostructured TiO\(_2\) solar cells: transport, recombination and photovoltaic properties. Coordin. Chem. Rev., 248:1165–1179, 2004. doi:10.1016/j.ccr.2004.03.015. Y. Gacemi, A. Cheknane, and H. S. Hilal. Simulation and modelling of charge transport in dye-sensitized solar cells based on carbon nano-tube electrodes. Phys. Scripta, 87(3):035703–035714, 2013. doi:10.1088/0031-8949/87/03/035703. B. O'Regan and M. Gratzel. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO\(_2\) films. Nature, 353:737–740, 1991. doi:10.1038/353737a0. S. Sodergren, A. Hagfeldt, J. Olsson, and S. Lindquist. Theoretical models for the action spectrum and the current-voltage characteristics of microporous semiconductor films in photoelectrochemical cells. J. Phys. Chem., 98:5552–5556, 1994. doi:10.1021/j100072a023.

Metalorganic-aerosol-deposited Au nanoparticles for the characterization of ultrathin films by surface-enhanced Raman spectroscopy

An alternative approach for ultrathin film characterization by means of Surface-Enhanced Raman Spectroscopy was realized and applied to the characterization of nanocrystalline TiO2 films. The vacuum-free metalorganic aerosol deposition (MAD) technique was used to grow gold nanoparticles onto the surface of thin TiO2 films. An averaged enhancement factor of 107, as well as the characterization of a 3 nm thin film, was accomplished. Since the thin film acts as a substrate itself, this technique can be used for the characterization of a variety of solid thin film materials. Furthermore, MAD-based nanoparticle growth can be of special interest for oxide films due to the high oxygen partial pressure and the constant oxygen flow during the deposition.

Comparative study of Ag, Sn or Zn doped TiO2 thin films for photocatalytic degradation of methylene blue and methyl orange

Nanocrystalline titania (TiO2) films with high optical transmittance and appropriate type and level of metal dopants offer promise for use in photocatalysis and environmental remediation purposes. In this study, a facile, cost-efficient sol-gel reflux synthesis route was devised to obtain smooth, nanocrystalline anatase TiO2 thin films doped with silver (Ag), tin (Sn) or zinc (Zn) with up to 5 mole percent. The microstructure, surface morphology and phase composition were determined using scanning electron microscope, atomic force microscope and x-ray diffraction techniques. The films were found to be nanocrystalline with average crystallite size of the order of ∼11 nm. Upon Ag or Sn doping, the films became superhydrophilic due to generation of surface defects and enhanced absorption via incident light scattering. The low extinction coefficient confirmed low surface roughness and uniform dispersion of the metal dopants into the TiO2 lattice. There was a decrease in the refractive index values of the Zn-doped films. The band gap values, as computed using Tauc plots, indicated a maximum reduction from 3.66 eV for the updoped TiO2 to 3.25 eV for Ag-doped TiO2 film. When assessed for photocatalytic degradation of methylene blue (MB) and methyl orange (MO), all the films were found to follow pseudo first-order kinetics in accordance with the Langmuir-Hinshelwood model. The apparent rate constant values were found to increase by 2 to 3 fold (4.30 × 10−3 s–1 for MB; 5.34 × 10−3 s–1 for MO) upon doping with 5 mole percent ZnO, presumably due to dual role of Zn as a reductant causing Ti3+ formation and a stabilizer of the oxygen vacancies.

Synthesis of nanosized amorphous and nanocrystalline TiO2 for photochemical oxidation of methomyl insecticide in aqueous media

AbstractAqueous solution loaded with methomyl insecticide is photocatalytically treated upon UV radiation and TiO2 in a green sustainable oxidation technique. TiO2 is a highly promising photocatalytic oxidation method, whereas the main findings is increasing the surface area for maximizing the treatment efficiency. Herein, TiO2 was synthesized via sonochemical hydrolysis technique and amorphous TiO2 (TM100) was obtained. Further, annealing of amorphous TiO2 at 500 ºC resulting in anatase phase TiO2 (TN500). The phase structure of the both samples was confirmed by high‐resolution transmission electron microscope (HR‐TEM). The results revealed that the materials exhibited high methomyl removal efficiency due to its nanostructure nature. The optimum TM100 and TN500 for the treatment were 40 and 20 mg/L and resulted in 99.5 and 100% methomyl removal, respectively. Furthermore, pH and H2O2 effect were studied. Additionally, high correlation was attained between empirical and modelled values with a second‐order kinetic model for the two processes.

Features of the Preparation and Study of Electrophysical Characteristics (BeO+TiO2)-Ceramics by Impedance Spectroscopy

An electrically conducting two-component BeO-ceramic with the addition of micro- and nano-crystalline TiO2 powder is prepared that can be used as a material for scattered microwave radiation absorption in high-power electronic devices. The nature of the occurrence of electrical conductivity and absorption of the microwave field in (BeO + TiO2)-ceramics is not completely established. Impedance spectroscopy is used for the first time to investigate the electrical and dielectric characteristics of this ceramic in the frequency range from 100 Hz to 100 MHz in relation to presence of micro- and nano-sized TiO2 phase within the BeO ceramic composition. It is established that the static resistance of ceramics with addition of a TiO2 nanopowder is significantly reduced compared with the resistance of original ceramic with TiO2 micropowder. It is shown that real and imaginary components of the dielectric constant of the ceramic studied increase to abnormally large values with a reduction in frequency of the effective electric field, and in the high frequency range f ≥ 108 Hz the process of dielectric relaxation commences leading to an increase in dielectric loss angle. Dielectric properties of ceramic samples are determined under blocking conditions for through conduction. The effect of TiO2 micropowder additions on dielectric polarization processes with frequency increasing up to 12 × 109 Hz is considered.

Comparative Study of Thin-Film-Based Planar and Vertical Devices Towards Isopropyl Alcohol Sensing

The influence of the electrode position in devices based on nanocrystalline TiO2 thin film for sensing of isopropyl alcohol has been investigated. Two types of device structure, viz. planar and vertical, with similar dimensions (length and width) were fabricated, employing Al metal electrodes. Both sensors were tested in the concentration range from 20 ppm to 400 ppm in the temperature range of 50°C to 200°C. The comparative study revealed that both sensors (planar and vertical) exhibited an optimum operating temperature of 150°C, with an optimum response of 77% and 33.08%, respectively. The response time and recovery time were found to be faster for the vertical device compared with its planar counterpart. The dissimilar sensor response of the planar and vertical devices can be understood based on the surface states and interface kinetics of the TiO2 sensing layer. An electrical model describing the modulation of the barrier height, the effect of grain boundaries (GBs), and carrier trapping at interface states at GBs was applied to understand the response time and recovery time.

Screening Doping Strategies To Mitigate Electron Trapping at Anatase TiO2 Surfaces.

Nanocrystalline anatase titanium dioxide is an efficient electron transport material for solar cells and photocatalysts. However, low-coordinated Ti cations at surfaces introduce low-lying Ti 3d states that can trap electrons, reducing charge mobility. Here, a number of dopants (V, Sb, Sn, Zr, and Hf) are examined to replace these low-coordinated Ti cations and reduce electron trapping in anatase crystals. V, Sb, and Sn dopants act as electron traps, while Zr and Hf dopants are found to prevent electron trapping. We also show that alkali metal dopants can be used to fill surface traps by donating electrons into the 3d states of low-coordinated Ti ions. These results provide practical guidance on the optimization of charge mobility in nanocrystalline TiO2 by doping.

The sensitization effect and microscopic essence of different additives on the electronic structure of nanocrystalline TiO2 in dye-sensitized solar cell

The reliable periodic density functional theory calculations have been carried out to investigate the diverse sensitization effects of five different additives, Guanidinium thiocyanate (GNCS), 3-Methoxypropionitrile (MPN), N-Butylbenzimidazole (NBB), N-Methylbenzimidazole (NMB) and 4-tert-butylpyridine (TBP), on the electronic structures of TiO2 anatase (1 0 1), (1 0 0) and (0 0 1) surfaces in vacuum and acetonitrile conditions, respectively. The complex microscopic essence of sensitization effect induced by additive can be revealed successfully by an in-depth interpretation on the inherent relations of the open-circuit photovoltage with fundamental electronic properties, i.e. Fermi energy, molecular orbital, dipole moment, electrostatic potential and work function. There is an explicit inverse correlation between the change of energy gap (E△(LUMO-HOMO)) and Fermi energy shift (E△Fermi) through the comparison among different additives adsorption under the same conditions of surface and solvent, namely, the smaller E△(LUMO-HOMO) corresponds to the bigger E△Fermi. The more positive E△Fermi (i.e. negative potential shift) results in the higher open-circuit photovoltage of dye-sensitized solar cells. Moreover, the E△(LUMO-HOMO) is in the order TiO2 (1 0 1) < (1 0 0) < (0 0 1) for every additive adsorption, exactly opposite to the order of surface stability. Total dipole moment is more suitable than its component normal to the TiO2 surface for measuring the sensitization performances of different species of additives. The smaller work function contributes to the bigger E△Fermi of the sensitized nanocrystalline TiO2. The influences of acetonitrile on the sensitization performances of five additives are diversified, better for MPN, NBB and NMB, general for GNCS, and the worst for TBP.

Structural, optical properties and photocatalytic activity of Fe3+ doped TiO2 thin films deposited by sol-gel spin coating

Nanocrystalline TiO2: Fe3+ films were deposited using a simple spin coating technique. The effect of Fe3+ on spectroscopic features and photocatalytic activity of films were studied using X-ray diffractometer (XRD), scanning electron microscope (SEM), Energy dispersive X-ray (EDX), high-resolution transmission electron microscope (HR-TEM), Raman spectrometer, UV–Vis and fluorescence spectrophotometer. The XRD of all the TiO2: Fe3+ films exhibits a decrease in the crystallite size with an increase in Fe3+ concentration. The Fe3+ doped TiO2 nanocrystals exhibited a high specific surface area. The HR-TEM images of 1% and 7% Fe doped TiO2 thin films confirmed the average particle size is about 14 and 8 nm respectively. The Raman modes of vibrations present in the TiO2:Fe3+ films also confirms the formation of the anatase phase. The optical bandgap energy of titania decreases from 3.32 to 2.57 eV. The luminescent emission intensity of TiO2: Fe3+ films decreased compare to pure titania film. Moreover, the photocatalytic activity (PCA) of TiO2:x%Fe3+ (x = 0, 1, 3, 5, 7 and 10) catalysts were determined by the decomposition of methylene blue (MB) under irradiation of visible light. The observed results revealed that the optimized Fe3+ doped TiO2 film displayed high PCA. The enhancement of PCA of the films is due to the effect of Fe doping.

One-Step Synthesis of Anatase Nanocrystalline TiO2 at a Low Temperature for High Photocatalytic Performance

One-Step Synthesis of Anatase Nanocrystalline TiO2 at a Low Temperature for High Photocatalytic Performance

Stability of the oxidized form of RuLL′(NCS)2 dyes in acetonitrile in the presence of water and pyridines – Why the dye-sensitized solar cell electrolyte should be dry

The detrimental effect of electrolyte water contamination on the light-soaking lifetime of Dye-sensitized Solar Cells (DSCs) prepared with RuLL′(NCS)2 dyes and N-additives like 4-tert-butylpyridine (TBP) is not well understood. A new explanation is presented based on investigation of the stability of the ruthenium(III) complexes Ru(bipy)2(NCS)2+ (1+) and RuLL′(NCS)2+ (L = 4,4′-dicarboxy-2,2′-bipyridine, L′= 4,4′-nonyl-2,2′-bipyridine) (Z907+) in acetonitrile in the presence of water and pyridines covering a large variation in basicity. 1+ reacts with small amounts of water in the acetonitrile containing a pyridine base (X) according to the overall reaction: 6Ru(bipy)2(NCS)2+ + 4H2O + 8X → 5Ru(bipy)2(NCS)2 + Ru(bipy)2(NCS)(CN) + SO42− + 8XH+. The reaction mechanism of 1+ (and Z907+) is proposed to be initiated by an attack of OH− giving Ru(bipy)2(NCS)(NCS-OH). The stronger the base the faster the reaction. Extrapolating the life time of Z907+ to a typical TBP concentration of 0.5 M in the DSC gives a degradation rate around 7 s−1. Z907+ bound to a layer of nano crystalline TiO2 surface reacted fast too, when inserted in an acetonitrile solution containing 4-tert-butylpyridine. In a “wet” electrolyte, containing more than 500 mM of water the light-soaking lifetime of a DSC prepared with Z907 is predicted to be about 10 days at out-door light soaking conditions, whereas trace amounts of water (<25 mM) in a “dry” electrolyte is used up by consumption of only 10% of the Z907 in a typical DSC. Therefore, the DSC is expected to have a long light-soaking lifetime with a “dry” electrolyte.

Preparation and Characterization of Nanocrystalline TiO2 on Microsericite for High-Efficiency Photo-Energy Conversion of Methanol to Hydrogen

TiO2 and TiO2/sericite photocatalysts were successfully synthesized via the sol-gel method by adding a varying amount of acetic acid. The effect of acetic acid on TiO2 and TiO2/sericite photocatalysts was studied. The crystallite size, surface morphology, chemical composition, specific surface area, surficial functional groups, and light absorbance of the prepared photocatalysts were revealed by the analysis of X-ray diffraction (XRD), scanning electron microscope-energy dispersive spectrometry (SEM-EDS), nitrogen adsorption-desorption isotherms by using BET theory (Brunauer–Emmett–Teller), Fourier-transform infrared spectroscopy (FTIR), and UV-Vis absorption spectrometry. Photo-energy conversion of methanol to hydrogen was also conducted over the prepared photocatalysts. The best hydrogen production was achieved by using the TiO2/sericite photocatalyst to give a hydrogen production rate of 1424 μmol/g·h in 6 h of UV-light irradiation.

Effect of annealing temperature on structural, morphological and optical properties of nanocrystalline TiO2 thin films synthesized by sol–gel dip coating method

TiO2 is one of the common materials used for solar cells, diodes, different types of gas sensors, optoelectronic devices, etc., TiO2 is widely used in photovoltaic devices due to interesting optical and electrical properties. In this work, nanocrystalline TiO2 thin films have been prepared by sol gel dip coating method. X-ray diffraction pattern showed the formation of anatase phase of TiO2. The scanning electron microscopy (SEM) is used for analysis of morphology. The energy dispersive X-ray spectroscopy (EDX) analysis confirmed that Ti and O elements are present in the sample. The FT-IR spectrum revealed the strong presence of TiO2. Photoluminescence (PL) and UV–Vis spectroscopy was used for investigation of TiO2 optical properties.