The effect of Sn dopant on crystal structure and photocatalytic behavior of nanostructured titania thin films

In this study, preparation of Sn doped (0–30 mol % Sn) TiO₂ dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of Sn content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission SEM (FE-SEM), and high resolution transmission electron microscopy (HR-TEM). Surface topography and surface chemical state of thin films were examined by atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). XRD patterns showed an increase in peak intensities of the rutile crystalline phase by increasing the Sn dopant. The prepared Sn-doped TiO₂ photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue solution under UV irradiation. The result shows that doping an appropriate amount of Sn can effectively improve the photo-catalytic activity of TiO₂ thin films, and the optimum dopant amount is found to be 15 mol%. The Sn⁴⁺ dopants substituted Ti⁴⁺ in the lattice of TiO₂ and increased surface oxygen vacancies and the surface hydroxyl groups. TEM results showed small increase in planar spacing (was detected by HR-TEM caused by Sn dopants in titania based crystals).     

Effect of annealing temperatures and of high content of the iron ion (Fe<Superscript>3+</Superscript>)-doping on transition anatase–rutile phase of nanocrystalline TiO<Subscript>2</Subscript> thin films prepared by sol–gel spin coating

Titanium dioxide doped with iron (III) was prepared by sol–gel Spin Coating method. The phase structures, morphologies, particle size of the doped TiO₂ have been characterized by X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectrophotometer. The XRD and Raman results show that the 10% Fe³⁺-doped TiO₂ thin films crystallize in anatase phase between 600 and 800 °C, and into the anatase–rutile phase at 1,000 °C, and further into the rutile phase when the content of Fe³⁺ increases (20%). The grain size calculated from XRD patterns shows that the crystallinity of the obtained anatase particles increased from 39.4 to 43.4 nm as the temperature of annealing increase, whereas the size of rutile crystallites increases, with increasing Fe³⁺ concentrations from 36.9 to 38.1 nm. The AFM surface morphology results confirmed that the particle size increases by increasing the annealing temperature and also with an increasing of Fe³⁺ content. The optical band gap (E _g) of the films was determined by the UV–Vis spectrophotometer. We have found that the optical band gap decreased with an increasing of annealing temperatures and also with an increasing of Fe³⁺ content.     

Dye degradation studies of Mo‐doped TiO2 thin films developed by reactive sputtering

TiO₂ thin films with various Mo concentrations have been deposited on glass and n‐type silicon (100) substrates by this radio‐frequency (RF) reactive magnetron sputtering at 400°C substrate temperature. The crystal structure, surface morphology, composition, and elemental oxidation states of the films have been analyzed by using X‐ray diffraction, field emission scanning electron microscopy, atomic force microscopy, and X‐ray photoelectron spectroscopy, respectively. Ultraviolet‐visible spectroscopy has been used to investigate the degradation, transmittance, and absorption properties of doped and undoped TiO₂ films. The photocatalytic degradation activity of the films was evaluated by using methylene blue under a light intensity of 100 mW cm⁻². The X‐ray diffraction patterns show the presence of anatase phase of TiO₂ in the developed films. X‐ray photoelectron spectroscopy studies have confirmed that Mo is present only as Mo⁶⁺ ions in all films. The Mo/TiO₂ band gap decreases from ~3.3 to 3.1 eV with increasing Mo dopant concentrations. Dye degradation of ~60% is observed in Mo/TiO₂ samples, which is much higher than that of pure TiO₂.     

Preparation and photoelectric properties of mesoporous ZnO films

Mesoporous ZnO films doped with Ti⁴⁺ (M-ZnO) have been prepared by doping process and sol–gel method. The films have mesoporous structures and consist of nano-crystalline phase, as evidenced from small angle X-ray diffraction and high resolution transmission electron microscopy. The wide angle X-ray diffraction of M-ZnO films confirms that M-ZnO has hexagonal wurtzite structure and ternary ZnTiO₃ phases. Ultraviolet–visible transmittance spectra, absorbance spectra and energy gaps of the films were measured. The Eg of M-ZnO is 3.25 eV. Photoluminescence intensity of M-ZnO centered at 380 nm increases obviously with the excitation power, which is due to the doping process and enhanced emission efficiency. M-ZnO thin films display a positive photovoltaic effect compared to mesoporous TiO₂ (M-TiO₂) films.     

Structural and optical characterization of sol–gel derived boron doped Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanostructured films

Pure and boron (B) doped iron oxide (Fe₂O₃) nanostructured thin films were prepared by sol–gel spin coating method. The effects of B (0.1, 0.2, 0.5 and 1 %) content on the crystallinity and morphological properties of Fe₂O₃ films were investigated by X-ray diffractometer and atomic force microscopy. X-ray diffraction patterns revealed that the Fe₂O₃ films have a rhombohedral crystalline phase of α-Fe₂O₃ phase (hematite) with nanostructure and their crystallite size (D) is changed from 27 ± 2 to 45 ± 5 nm with B dopant content. The minimum crystallite size value of 27 ± 2 nm was obtained for 0.2 % B doped Fe₂O₃ film. Carrying out UV–VIS absorption study for both doped and undoped films at room temperature, it was realized that allowed optical transitions may be direct or indirect transitions. The direct and indirect energy gap values for pure Fe₂O₃ were obtained to be 2.07 and 1.95 eV, respectively. The optical band gap value of the films was changed with 0.1 % B doping to reach 1.86 eV for direct band gap and 1.66 eV in case of indirect band gap.     

Sonophotocatalytic activity of methyl orange over Fe(III)/TiO2

TiO₂ doped with Fe³⁺ was prepared by an impregnation technique and its sonophotocatalytic activity over methyl orange (MO) was investigated. The Fe/TiO₂ surface presented red shift to longer wavelength, resulting in a lower energy band gap. Fe loading of 0.1 wt% on TiO₂ provided the optimum degradation. The MO degradation rate constant under sonophotocatalytic conditions was 2.5 times higher than under photocatalytic conditions.     

The magnetic polaron modulated luminescence bands of organic-inorganic hybrid ferroelectric anti-perovskite (C3H9N)3Cd2Cl7 doped with Mn2+

Recently, the excellent optical properties of organic-inorganic hybrid metal halides have attracted much attention in the optoelectronic field. However, their complicated preparation processes seriously influence their properties and applications. In this work, we developed a series of organic-inorganic hybrid metal halides (C₃H₉N)₃Cd₂Cl₇:x%Mn²⁺ with an antiperovskite structure with ferroelectrics in an early report, giving tunable emissions contemporarily with different manganese (Mn)²⁺ concentrations via a simple mechanochemical method. Meanwhile, their single crystals were also grown by a slow thermal evaporation method. The as-grown products with Mn dopants exhibited diluted magnetic semiconductor behavior and varied emission profiles by different excitation wavelengths, which could be modified by the heat treatment. All the emission bands come from the different magnetic polarons with enhanced electron-phonon coupling or self-trapped exciton formation. Ferromagnetic coupling Mn–Mn pairs or clusters in the doped lattice favor the magnetic polaron and red emission at room temperature and even give much stronger emission above room temperature. The excitonic magnetic polaron and local excitonic magnetic polaron were detected at about 309 nm and 398 nm, respectively, with Mn doping. Without Mn²⁺ dopant, the weak emission band at about 398 nm can also be detected from an intrinsically bound exciton or confined exciton from the amine incorporated metal chlorides. This Mn-doped anti-perovskite Cd halides may find applications in the solid display and lighting, as well as the magneto-optical devices.     

Sol–gel preparation and photocatalytic performance of TiO2/SrAl2O4: Eu2+, Dy3+ toward the oxidation of gaseous benzene

It has been found that the photocatalytic activity of TiO₂ toward the decomposition of gaseous benzene can be greatly enhanced by loading TiO₂ on the surface of SrAl₂O₄: Eu²⁺, Dy³⁺ using sol–gel technology. The prepared photocatalyst was characterized by BET, XRD, and XPS analyses. XRD results reveal that the peaks of titania in either rutile or anatase form are not detected by XRD in the 2θ region from 20° to 50°. The binding energy values of Ti 2p of pure TiO₂ are 458.90 and 464.60 eV, while for TiO₂/SrAl₂O₄: Eu²⁺, Dy³⁺, the binding energy values of Ti 2p are 458.50 and 464.20 eV. The results indicate that the optimum loading of TiO₂ is 1 wt% and TiO₂/SrAl₂O₄: Eu²⁺, Dy³⁺ (1 wt%) demonstrates 1.4 times the photocatalytic activity of that of pure TiO₂, but the underlying mechanism of SrAl₂O₄: Eu²⁺, Dy³⁺ in the photocatalytic reaction remains to be unraveled.     

Magnetic,optical and electrical properties of Mn-doped CuCrO<Subscript>2</Subscript> thin films prepared by chemical solution deposition method

CuCrO₂ and CuCrO₂:Mn thin films were prepared on sapphire substrates by chemical solution deposition method. The effects of the annealing temperatures and Mn concentration on the structural, electrical and optical properties were investigated. The X-ray diffraction measurement was used to confirm the c-axis orientation of CuCrO₂ and CuCrO₂:Mn thin films. The maximum transmittances of the films in the visible region are about 65% with direct band gaps of 3.25 eV. All films showed the p-type conduction and semiconductor behavior. The electrical conductivity decreases rapidly with the increase of Mn content, the maximum of the electrical conductivity of 1.35 × 10⁻² S cm⁻¹ is CuCrO₂ film deposited at 600 °C temperature in 10⁻³ Torr vacuum, which is about four orders of magnitude higher than that of the Mn-doped CuCrO₂ thin film. The energy band of the samples is constructed based on the grain-boundary scattering in order to investigate the conduction mechanism. Moreover, the samples exhibit a clear ferromagnetism, which was likely ascribed to originating from the double-exchange interaction between the Mn³⁺ and Cr³⁺ ions.     

Influence of Mn incorporation on the structural and optical properties of sol gel derived ZnO film

Undoped and manganese doped ZnO (ZnO:Mn) films were prepared by sol gel method using spin coating technique. The effect of Mn incorporation on the structural and optical properties of the ZnO film has been investigated. The crystalline structure and orientation of the films have been investigated by using their X-ray diffraction spectra. The films exhibit a polycrystalline structure. Mn incorporation led to substantial changes in the structural characteristics of the ZnO film. The scanning electron microscopy (SEM) images of the films showed that the surface morphology of the ZnO film was affected by the Mn incorporation. The transparency of the ZnO film decreased with the Mn incorporation. The optical band gap and Urbach energy values of the ZnO and ZnO:Mn films were found to be 3.22, 3.19 eV and 0.10, 0.23 eV, respectively. The optical constants of these films, such as refractive index, extinction coefficient and optical dielectric constants were determined using transmittance and reflectance spectra. The refractive index dispersion curve of the films obeys the single oscillator model with dispersion parameters. The oscillator energy, E _o , and dispersion energy, E _d, of the films were determined 5.30 and 16.26 eV for ZnO film and 5.80 and 12.14 eV for ZnO:Mn film, respectively.     

Synthesis and characterization of novel InVO<Subscript>4</Subscript>–TiO<Subscript>2</Subscript> thin films using the low temperature sol

The InVO₄ sol was obtained by a mild hydrothermal treatment (the precursor precipitation solution at 423 K, for 4 h). Novel visible-light activated photocatalytic InVO₄–TiO₂ thin films were synthesized through a sol–gel dipping method from the composite sol, which was obtained by mixing the low temperature InVO₄ sol and TiO₂ sol. The photocatalytic activities of the new InVO₄–TiO₂ thin films under visible light irradiation were investigated by the photocatalytic discoloration of methyl orange aqueous solution. The thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV–Vis absorption spectroscopy (UV–Vis). The results revealed that the InVO₄ doped thin films enhanced the methyl orange degradation rate under visible light irradiation, 3.0 wt% InVO₄–TiO₂ thin films reaching 80.1% after irradiated for 15 h.     

Synthesis of TiO<Subscript>2</Subscript> using different hydrolysis catalysts and doped with Zn for efficient degradation of aqueous phase pollutants under UV light

In this work, various TiO₂ and TiO₂ doped with 0.1, 1.0, and 5.0 mol% of Zn were prepared by the sol–gel method varying different hydrolysis catalysts (HNO₃, OHAc, H₃PO₄) in order to be used as photocatalysts for environmental applications. The X-ray diffraction results showed that the different TiO₂ samples have presented the anatase as main phase, However, the acid nature has played an important role in the superficial and optical properties. The N-physisortion analysis has revealed that the specific surface area of calcined TiO₂ samples prepared using H₃PO₄, HOAc, and HNO₃ was 245, 100, and 90 m² g⁻¹, respectively, while the spectroscopic UV analysis, the band gap energy has shifted by 3.3–3.0 eV. In order to improve the optical properties of TiO₂, the last preparation was doped with different zinc concentrations. The result showed that, as the Zn concentration increase by 0.1–5.0 mol%, the surface area increased from 90 to 120 m² g⁻¹. Nevertheless, the E _g returned from 3.0 to 3.32. The SEM analyses have not revealed important morphological changes between no doped and doped materials. The catalytic activity of the composite was studied on the photocatalytic degradation of 2,4-Dichlorophenoxyacetic acid (2,4-D) and the activity results showed that small Zn concentrations decrease the t _1/2 in 28 min.     

Photocatalytic Reduction of Greenhouse Gas CO2 to Fuel

Sun is the Earth’s ultimate and inexhaustible energy source. One of the best routes to remedy the CO₂ problem is to convert it to valuable hydrocarbons using solar energy. In this study, CO₂ was photocatalytically reduced to produce methanol, methane and ethylene in a steady-state optical-fiber reactor under artificial light and real sunlight irradiation. The photocatalyst was dip-coated on the optical fibers that enable the light to transmit and spread uniformly inside the reactor. The optical-fiber photoreactor, comprised of nearly 120 photocatalyst-coated fibers, was designed and assembled. The XRD spectra indicated the anatase phase for all photocatalysts. It is found that the methanol yield increased with UV light intensity. A maximum methanol yield of 4.12 μmole/g-cat h is obtained when 1.0 wt% Ag/TiO₂ photocatalyst was used under a light intensity of 10 W/cm². When mixed oxide, TiO₂–SiO₂, is doped with Cu and Fe metals, the resulting photocatalysts show substantial difference in hydrocarbon production as well as product selectivity. Methane and ethylene were produced on Cu–Fe loaded TiO₂–SiO₂ photocatalyst. Since dye-sensitized Cu–Fe/P25 photocatalyst can fully harvest the light energy of 400–800 nm from sunlight, its photoactivity was significantly enhanced. Finally, CO₂ photoreduction was studied by in situ IR spectroscopy and possible mechanism for the photoreaction was proposed.     

Structural,morphological, optical and dielectric properties of M3+/PVA/PEG SPE Films (M = La,Y, Fe or Ir)

Low band gap polymer complexes are promising due to its flexibility, and exhibiting electronic and optical properties of inorganic semiconductors. The effect of PEG on the physical properties of PVA was evaluated. Then, blend (PVA: PEG = 50:50) doped with rare earth (La or Y) and transition metal (Fe or Ir) chlorides to obtain solid polymer electrolyte films. XRD shows that adding PEG to PVA results in a new peak, 2θ = 23^o with increased intensity as PEG ratio increases. However, doping with La³⁺, Fe³⁺ or Ir³⁺ eliminate this peak and decrease the crystallinity. SEM exhibits significant changes in the morphology of films. FTIR confirms miscibility between PVA & PEG and the complexation of the salts. The optical band gap (E_g) of PVA ~ 5.37 eV, decreased slightly by blending with PEG. While it decreased significantly to 2.64 eV and 2.78 eV after doping with Fe³⁺ or Ir³⁺. There are a consistency between E_g values obtained by Tauc's model and that obtained from the optical dielectric loss. The dielectric constant and loss, in temperature range 303–405 K & frequency range 1.0 kHz ‐ 5.0 MHz, indicate one or two relaxation peak(s) depending on the film composition. Accordingly, conduction mechanism varied between correlated barrier hopping and large polaron tunneling. The DC conductivity was strongly depend on the dielectric loss. The transition metal salts appear to be more effective than the rare earth ones in increasing σ_ac of films to higher values that candidates them in semiconductors industry.     

Photothermal and photocatalytic processes on TiO2 based materials prepared by sol-gel method

In the present work, Fe³⁺ doped TiO₂ coatings on glass substrates were prepared by dip-coating from a sol-gel solution. The influence of the dopant concentration on the structure, optical, photocatalytic and photothermal properties of the films was studied. The results obtained have shown a strong correlation between the catalytic properties and the amount of iron dopant and the temperature of the thermal treatment.     

Effect of dopant concentration on photocatalytic activity of TiO2 film doped by Mn non-uniformly

The thin films of TiO₂ doped by Mn non-uniformly were prepared by sol-gel method under process control. In our preceding study, we investigated in detail, the effect of doping mode on the photocatalytic activity of TiO₂ films showing that Mn non-uniform doping can greatly enhance the activity. In this study we looked at the effect of doping concentration on the photocatalytic activity of the TiO₂ films. In this paper, the thin films were characterized by UV-vis spectrophotometer and electrochemical workstation. The activity of the photocatalyst was also evaluated by photocatalytic degradation rate of aqueous methyl orange under UV radiation. The results illustrate that the TiO₂ thin film doped by Mn non-uniformly at the optimal dopant concentration (0.7 at %) is of the highest activity, and on the contrary, the activity of those doped uniformly is decreased. As a comparison, in 80 min, the degradation rate of methyl orange is 62 %, 12 % and 34 % for Mn non-uniform doping film (0.7 at %), the uniform doping film (0.7 at %) and pure titanium dioxide film, respectively. We have seen that, for the doping and the pure TiO₂ films, the stronger signals of open circuit potential and transient photocurrent, the better photocatalytic activity. We also discusse the effect of dopant concentration on the photocatalytic activity of the TiO₂ films in terms of effective separation of the photon-generated carriers in the semiconductor.     

Characterization and optical properties of mechanochemically synthesized molybdenum-doped rutile nanoparticles and their electronic structure studies by density functional theory

The optical and electronic properties of molybdenum (Mo) doped rutile TiO₂ prepared by the mechanochemical method were studied both experimentally and using density functional theory (DFT). The synthesized nanoparticles were characterized by XRD, TEM, EDS-MAP, and XPS. The XRD results showed the successful incorporation of Mo in the rutile crystal lattice. High-resolution TEM images illustrated a decreasing trend in the (110) d-spacing for samples doped up to 3 at%. The shift toward higher binding energies in the XPS spectra was due to the higher oxidization tendencies of Mo⁵⁺ and Mo⁶⁺ substituted in Ti⁴⁺ sites. The optical behavior of samples was examined by UV–Vis and photoluminescence spectroscopy. The bandgap energy value of rutile was reduced from 3.0 eV to 2.4 eV by 2 at% Mo doping. The DFT calculations showed a reduction of bandgap energy value of rutile to 2.35 eV with 2 at% Mo, which is in harmony with the experimental results. The creation of energy states below the conduction band because of Mo doping was identified as the reason for reducing the bandgap energy and photoluminescence emission of rutile.     

Modification in structural,optical, morphological,and electrical properties of zinc oxide (ZnO) nanoparticles (NPs) by metal (Ni,Co) dopants for electronic device applications

In the present work, Zinc Oxide (ZnO) nanoparticles (NPs) were synthesized by the chemical co-precipitation method using Zinc Chloride as the initial chemical, while Nickel and Cobalt chloride as dopants. Phase identification of metal (Ni, Co) doped Zinc Oxide nanoparticles (NPs) was observed using x-ray diffraction (XRD). The small lattice distortion or phase changes appeared due to shifting of diffraction angles peaks towards larger angle in ZnO are corresponded to metal (Ni, Co) dopant. The average crystallite size appears to decrement in NP size from 7.67 nm to 6.52 nm and 5.35 nm to 5.17 nm with increasing 5 % to 80 % of metal (Ni, Co) dopant respectively. The optical characteristics, including the absorption spectra of the prepared sample were observed through UV–Vis spectroscopy, Meanwhile SEM confirmed the observation of composition change in specimen with metal (Ni, Co) dopant concentration. The bandgap value was also found decrement 5.23 eV to 5.05 eV with increment of metal (Ni, Co) dopant concentration. The functional groups were measured by Fourier transformation infrared spectroscopy (FTIR). FTIR peaks found the metal (Ni, Co) doped ZnO with the vibration mode of (Zn²⁺ –O^2?) ions due to the increment of dopant concentrations. Furthermore, electrical results show the ohmic behavior of prepared samples. These findings indicate the possibility of tuning optical, structural and electrical properties of metal (Ni, Co) doped ZnO with various dopant concentrations of Nickel and will have great potential to find application in optoelectronic devices.     

Photocatalytic degradation of methyl orange on arrayed porous iron-doped anatase TiO2

Arrayed porous iron-doped TiO₂ was prepared by sol–gel with polystyrene spheres as template and used as photocatalyst for the degradation of methyl orange. The structure and performances of the prepared photocatalyst were characterized with X-ray diffractometer, inductively coupled plasma-atomic emission spectrometer, scanning electron microscope, UV-visible spectrometer, and methyl orange degradation tests. It is found that the iron dopant does not change the crystal phase of TiO₂ but affects its lattice constant, optical absorption, electronic conductivity, charge-transfer resistance, and activity toward the degradation of methyl orange. The sample doped with 0.01 wt.% Fe (based on Ti) and with smaller pore size exhibits the better photocatalytic activity. The degradation rate of methyl orange on the sample with a pore size of 190 nm is 2.3 times that on the undoped sample with the same pore size.     

Correlation between structural and optical properties of TiO<Subscript>2</Subscript>:ZnO thin films prepared by sol–gel method

We have studied structural and optical properties of thin films of TiO₂, doped with 5% ZnO and deposited on glass substrate (by the sol–gel method). Dip-coated thin films have been examined at different annealing temperatures (350–450 °C) and for various layer thicknesses (89–289 nm). Refractive index, porosity and energy band gap were calculated from the measured transmittance spectrum. The values of the index of refraction are in the range of 1.97–2.44, the porosity is in the range of 0.07–0.46 and the energy band gap is in the range of 3.32–3.43. The coefficient of transmission varies from 50 to 90%. In the case of the powder of TiO₂, doped with 5% ZnO, and aged for 3 months in ambient temperature, we have noticed the formation of the anatase phase (tetragonal structure with 20.23 nm grains). However, the undoped TiO₂ exhibits an amorphous phase. After heat treatments of thin films, titanium oxide starts to crystallize at the annealing temperature 350 °C. The obtained structures are anatase and brookite. The calculated grain size, depending on the annealing temperature and the layer thickness, is in the range of 8.61–29.48 nm.