TiO2 Samples Research Articles

Effect of Ce Doping on Catalytic Performance of Cu/TiO2 for CO Oxidation

CO is toxic and detrimental to human beings and the atmosphere. The presence of CO has become one of the important indicators for evaluating ambient air quality. Iron and steel sintering generate large amounts of flue gas emissions containing approximately 1% CO, which has become an important factor restricting the improvement of air quality in steel cities. The catalytic oxidation method is the simplest and most effective method for CO emission control. In this work, a series of CuxCey/TiO2 catalysts with different Ce doping levels were prepared by a one-step impregnation method and subsequently tested for catalytic CO oxidation. The Cu0.5Ce0.5/TiO2 sample has the best catalytic activity under the conditions of 1% CO and 10% H2O. The catalysts were next characterized by XRD, BET, TEM, H2-TPR, XPS and in-situ DRIFTS methods. The characterization results show that Ce doping promotes the dispersion of copper species on the catalyst surface and improve the redox performance of the catalyst. The results of in-situ experiments showed that both Cu/TiO2 and Cu0.5Ce0.5/TiO2 catalysts followed Mars and van Krevelen mechanism, and Ce doping enhanced the adsorption and activation of oxygen, thus improving the low-temperature reaction activity of the catalysts.

Structural, Photoluminescence and Electron Density Distribution Analysis of Rutile Phase TiO2

In this work, the mixed anatase and rutile phases of commercial TiO2 sample was purchased and converted to single rutile phase by sintering at 1000°C. Structural and spectroscopic analysis of the single phased rutile TiO2 were analyzed by PXRD, SEM, EDS, PL analysis, respectively. Rietveld profile refinement technique was performed to fit the observed and calculated PXRD profiles. Charge density distribution studies were used to determine the chemical bonding nature of Ti-O bond by maximum entropy method (MEM). From the MEM calculations, Ti-O bond exhibited covalent nature. PL measurements showed that the emission wavelength of rutile TiO2 at around 470 nm which may be due to band to band transitions of Ti and O atoms.

An investigation of the stirring duration effect on synthesized graphene oxide for dye-sensitized solar cells.

This study investigates the effects of stirring duration on the synthesis of graphene oxide (GO) using an improved Hummers’ method. Various samples are examined under different stirring durations (20, 40, 60, 72, and 80 h). The synthesized GO samples are evaluated through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The GO sample with 72 h stirring duration (GO72) has the highest d-spacing in the XRD results, highest atomic percentage of oxygen in EDX (49.57%), highest intensity of oxygen functional group in FTIR spectra, and highest intensity ratio in Raman analysis (ID/IG = 0.756). Results show that GO72 with continuous stirring has the highest degree of oxidation among other samples. Electrochemical impedance spectroscopy analysis shows that GO72–titanium dioxide (TiO2) exhibits smaller charge transfer resistance and higher electron lifetime compared with the TiO2-based photoanode. The GO72 sample incorporating TiO2 nanocomposites achieves 6.25% photoconversion efficiency, indicating an increase of more than twice than that of the mesoporous TiO2 sample. This condition is fully attributed to the efficient absorption rate of nanocomposites and the reduction of the recombination rate of TiO2 by GO in dye-sensitized solar cells.

Studying Structural and Optical Properties of TiO2–SnO2 Core–Shell Synthesized by Sol–Gel Route

AbstractHerein, the TiO2–SnO2 core–shell structures with the core‐to‐shell molar ratios of 5:0.5, 5:0.67, and 5:1 are synthesized by the sol–gel route, and then the structural and optical properties of the synthesized samples are investigated. In order to characterize the samples, the XRD, Raman, FESEM, and TEM techniques are used for their structural verification, while the UV–visible and photoluminescence spectra are used for their optical characterization. The XRD results obtained showed that the annealed TiO2 sample has an anatase tetragonal structure and that the core–shell samples contain the diffraction peaks of both the core TiO2 and the shell SnO2. The XRD results obtained are supported by Raman spectroscopy. The TEM images obtained show evidence of the formation of the composite (core–shell) nanostructure in the samples. The optical investigation shows that the band gaps of the core–shell samples are indirect, like the TiO2 core itself, and increase with an increase in the core‐to‐shell molar ratio. These results also show that the synthesized core–shell samples are suitable candidates for use in optoelectronic devices.

Correlation Between Tunable Oxygen Defects in TiO2 Nanoflower and Its Photocatalytic Performance for the Degradation of Organic Waste

Oxygen defects of nanoflower TiO2 photo-catalyst was fabricated at the presence of hydrogen at different temperatures (100–600∘C) and the concentrations of oxygen defects were firstly quantitatively analyzed by hydrogen programmed temperature reduction techniques (H2-TPR). Total oxygen defect concentration and surface oxygen defect concentration were consistent with XPS and EPR results, respectively. Even at the hydrogen thermal temperature of 600∘C, the shape of TiO2 was still kept as nanoflower structure as characterized by SEM. However, the rutile and anatase coexist in the composition of crystal phase when hydrogen reduction temperature of the TiO2 catalyst reached 400∘C to 600∘C as proved by Raman and XRD results. TiO2 sample with oxygen defects shows excellent photo-catalytic activity for degradation of Direct Blue 78(DB) regardless of ultraviolet light (the maximum degradation rate achieved within 100[Formula: see text]min was 93.27%) or visible light (the maximum degradation rate achieved within 100[Formula: see text]min was 88.25%). The photo-catalytic activity seems to be highly correlated with the surface oxygen defects of TiO2 catalyst. With surface oxygen-defect concentrations increase, the degradation ability on DB was significantly enhanced, while bulk oxygen defects had negligible effect on the photo-catalytic activity. The enhanced photo-catalytic performance of TiO2 with a fixed amount of oxygen defects was attributed to the strong capturing capability of the photo-generated electrons. In addition, the surface defects could also improve the photo-catalytic reaction efficiency.

Room-temperature synthesis of yellow TiO2 nanoparticles with enhanced photocatalytic properties

Anatase titanium dioxide (TiO2) nanoparticles have been successfully synthesized through a simple approach at low temperature. Particularly yellow TiO2 is well obtained at room temperature (25 °C). TiO2 samples are characterized by XRD, Raman, XPS, TEM, BET, UV–Vis, and Zeta Potential. The zeta potential value of TiO2 samples can be tuned from −26.8 to +13.6 mV by different reaction temperature. The yellow TiO2 has more oxygen vacancies and Ti3+ compared with other samples, which reduces the band gap from 3.1 to 2.9 eV and made the conduction band positively shift about 0.2 eV. Electrochemical impedance spectroscopy and Mott-Schottky plots reveal that the yellow TiO2 nanocrystals had higher carrier density and better conductivity for electron transfer. According to the XPS analysis, the Ti3+ content in different samples is 8.1%, 7.8%, 6%, 1%, and zero, respectively. The decomposition rate of Rhodamine B under UV light and visible light was 99.7% and 70.0%, and the NO removal efficiency in 5 min is 84.8% for yellow TiO2, respectively. The enhanced photocatalytic performance can be attributed to the presence of more oxygen vacancies in yellow TiO2 that can act as traps to reduce the recombination of e−/h+ pairs.

Optical characterization of photocatalytic copper doped thin films of anodized titanium

Titanium oxide is used in a myriad of applications such as in capacitors, insulation paints among others. It is a prime candidate for water splitting due to its photocatalytic properties. In this work, undoped TiO2 thin films were prepared by anodizing titanium foils cut into pieces measuring 60 mm by 20 mm. The specimens were anodized in an electrolyte consisting of 0.5 M H2SO4 and 0.075% wt HF at room temperature. The anodizing voltages ranged from 50 V to 100 V. Anion doping of copper in as anodized TiO2 was done electrochemically. The as anodized Ti foils were dipped in a 1 M Cu2SO4 solution. All samples were annealed at 450 °C for 3 h. Near-normal total reflectance was measured on as anodized and copper pigmented samples in the solar (300–2500 nm) wavelength range. Spectrophotometric reflectance data was analyzed to obtain the absorption coefficient and using the same to determine the band gap of the films. It was noted that the films exhibited reduced solar integrated reflectance for TiO2 samples prepared at lower anodic voltages of 50, 60 and 70 V. The copper pigmented, and annealed, TiO2 samples exhibited both direct and indirect energy band gaps in the ranges, 3.38–3.86 and 2.50–2.74, respectively. Further, annealing and copper doping of the films lead to increased absorption. The photocatalytic activity of the films was assessed by measuring the rate of degradation of 10ppm methylene blue in UV light source. Copper doped TiO2 exhibited enhanced photocatalytic performance in compared to pure TiO2. An increase in the anodization voltage caused subsequent increase in photocatalytic activity of films with 70 V as the optimum voltage above which photo degradation of methylene blue decreased.

The Effect of Polyethylene Glycol (PEG) on TiO2 Thin Films via Sol-Gel Method

This research focus on the effect of polyethylene glycol (PEG) on TiO2 thin film. Sol-gel method is the best method which tends to be used due to its simplicity, good chemical homogeinity and high purity of the product. Titanium (IV) isopropoxide, isopropanol and acetic acid are the three different chemical which being used to make sol solution. The samples was then will annealed at three different temperature which are 400 °C, 500 °C and 600 °C to observed the phase composition of TiO2 added PEG thin film and pure TiO2 by using x-ray diffraction (XRD) analysis and the structural surface by using scanning electron microscope (SEM) analysis. The XRD analysis show the anatase phase present for the sample of pure TiO2 thin film and rutile phase present for the sample of TiO2 added PEG thin film. The micrograph of SEM show that with the addition of PEG at high temperature will give the analysis of flaky large cracked which is not separated to each other on the surface coating. Meanwhile, pure TiO2 give the result of irregular shape structure of the film.

Visible light photocatalytic activity of metal (Mo/V/W) doped porous TiO2 coating fabricated on Cp-Ti by plasma electrolytic oxidation

Photocatalytic degradation under visible light region acquired a wide interest in the field of wastewater treatment. In this study, the transition metal ion (Mo/V/W) doped TiO2 layer was developed on commercially pure titanium (Cp-Ti), by plasma electrolytic oxidation (PEO), as an immobilized photocatalytic surface for textile wastewater treatment application. The effect of transition metal ion (Mo/V/W) doping on TiO2 coating phase composition, surface morphology, corrosion, wettability, bandgap, charge separation and electron-hole recombination rate are investigated. The phase analysis of coatings showed that the dopants suppressed the formation of the rutile. The doped TiO2 samples exhibited higher surface porosity and active surface area, thereby enhancing the photocatalytic activity. Among the doped titanium oxides, W doped TiO2 exhibited superior charge separation with 95% degradation and 71% mineralisation of methylene blue dye under visible light irradiation for 180 min. This could be attributed to the synergistic effect of lower bandgap, high charge separation, and low electron-hole recombination rate. The present research positively demonstrated an efficient, visible light driven immobilized photo catalyst surface by a simple PEO process as a promising photocatalytic system in the quest for the development of low cost and sustainable process for textile wastewater treatment application.

Elementary steps and site requirements in formic acid dehydration reactions on anatase and rutile TiO2 surfaces

Mechanistic details of HCOOH decomposition routes provide valuable insights into reactions involving bound formates as intermediates or spectators; these routes are also widely used as a probe of the acid-base properties of oxide surfaces. The identity and kinetic relevance of bound intermediates, transition states, and elementary steps are reported here for HCOOH dehydration on anatase and rutile TiO2 surfaces through complementary kinetic, isotopic, spectroscopic and theoretical assessments. Five-coordinate exposed Ti5c centers are saturated with bidentate formates (*HCOO*) at catalytic conditions (423–463 K; 0.1–3 kPa HCOOH), as evident from infrared spectra collected during catalysis and the amounts of HCOOH and CO evolved upon heating the TiO2 samples containing pre-adsorbed HCOOH-derived species. These *HCOO* species are inactive but form a stable “surface template” that contains stochiometric protons onto which HCOOH binds molecularly (HCOOH-H*) to form a coexisting adlayer. H2O elimination from HCOOH-H* is the sole kinetically-relevant step. DFT-derived barriers show that this step involves its reaction with Ti5c-O2c that acts as a Lewis acid-base pair. Such route, in turn, requires the access of HCOOH-H* to a Ti5c center, which is made available through a momentary reprotonation of a *HCOO*. This step is much less facile on rutile than on anatase due to stronger acid strength of its Ti5c centers that binds *HCOO* species more strongly and its shorter Ti5c-Ti5c distances that induce greater repulsions between co-adsorbed HCOOH* formed upon reprotonation step. These differences account for low dehydration reactivity of rutile at these temperatures. This mechanistic interpretation is in full accord with DFT-derived barriers, binding energies, and kinetic isotope effects that quantitatively agree with the values from regressed kinetic and thermodynamic parameters, with in-situ infrared spectra that identify HCOOH-H* species as the sole reactive intermediates, and with the differences in turnover rates between anatase and rutile catalysts. These dehydration routes are also consistent with the surface chemistry expected for Lewis acid-base pairs on stoichiometry TiO2 surfaces without requiring the presence or involvement of reduced centers or titanols in the catalytic cycle. The reaction routes described in this work show how strongly-bound species, evident in presence and unreactive nature from in-situ infrared spectra, provide an organic “permanent” template for reactions of weakly-bound species that are often invisible in spectroscopy.

Copper modified Ti3+ self-doped TiO2 photocatalyst for highly efficient photodisinfection of five agricultural pathogenic fungus

In this study, Ti3+ self-doped TiO2 decorated with metallic copper photocatalyst (marked as Cu/Ti3+-TiO2) was successfully prepared by a novel method. The ESR (Electron Spin Resonance) analysis indicated that the synthesized sample contained Ti3+. The TEM (transmission electron microscopy) images showed that the TiO2 nanoparticles were modified with nano copper. The as-synthesized photocatalyst was found to exhibit markedly enhanced photocatalytic inactivation of E. coli under visible light irradiation compared with pure TiO2, especially in the case of the 10% Cu/Ti3+-TiO2 sample. The photodisinfection effect of the 10% Cu/Ti3+-TiO2 sample was further confirmed using five agricultural pathogenic fungal spores. The photocatalytic inactivation effect against F. graminearum and Botryosphaeria dothidea spores was certified by fluorescent staining of CFDA-AM (the acetoxymethyl ester of the esterase substrate 5-carboxyfluorescein diacetate)/PI (Propidium Iodide). In addition, fluorescent staining by H2DCFDA demonstrated that the intracellular ROS (reactive oxygen species) of the F. graminearum macroconidia was increased after treatment by the photocatalysis.

Structural studies and photocatalytic properties of Mn and Zn co-doping on TiO2 prepared by single step sonochemical method

Titanium dioxide nanoparticles dual doped with zinc and manganese were prepared by the single step of sonochemical method using the sonicator with 20 kHz and 750 W for 30 min. Phase structure analysis results showed that the pure anatase phase was detected for all prepared samples. TEM analysis reveals the nanosized structure with uniformity of nanoparticles. The calculated bandgap energies change to be below the typical band gap energy of bare TiO2 and single doped sample suggesting high ability to harvest visible light. X-ray absorption spectroscopy was conducted to investigate the electronics structure and to study the local structure of prepared samples. XANES results confirmed the existence of Ti4+ ions in all prepared samples with anatase crystal structure. EXAFS analysis indicates the Ti4+ site was substituted by Mn and Zn dopant ions. The photocatalytic performance was evaluated by degradation of Rhodamine B dye solution under visible light irradiation. The results revealed that the dually Mn–Zn doped TiO2 sample exhibited excellent photocatalytic activity comparing to single doped and pure TiO2. The complete degradation of dye was achieved at optimum condition of 1 mol%-Zn and 2 mol%-Mn molar ratio. The highest photodegradation rate constant was found to be 0.0238 min−1, which is 10 times greater than pure-TiO2 samples.

Visible light-induced degradation of antibiotic ciprofloxacin over Fe–N–TiO2 mesoporous photocatalyst with anatase/rutile/brookite nanocrystal mixture

Titanium dioxide photocatalysts co-modified with iron and nitrogen (Fe–N–TiO2) were produced via hydrothermal method using iron(III) nitrate nonahydrate and urea as iron and nitrogen sources, respectively. The effects of different dopant concentrations were investigated. The modified TiO2 catalysts were characterized for phase composition, surface morphology, specific surface area, degree of doping, charge states and bandgap energy combining various techniques. The results showed that controlled iron and nitrogen concentrations significantly altered the physicochemical properties of the catalysts. The photocatalysts displayed the anatase/rutile/brookite crystal phase mixture. The rutile and brookite phase contents increased with increasing iron content. On the other hand, increasing nitrogen content inhibited the formation of rutile and brookite phases and the catalysts displayed predominantly the anatase phase. High iron and low nitrogen contents led to the highest BET surface areas. The surface morphology changed from nanorice to spherical shape with increasing iron content. The bandgap energy of all Fe–N–TiO2 samples was in the range 2.7–3.1 eV, being lower than that of undoped TiO2 and pure anatase phase. Nitrogen was incorporated into the TiO2 lattice on interstitial positions (Ti–O–N). The iron, substituting some Ti4+ in the lattice was presented in Fe2+ and Fe3+ oxidation state, as confirmed by XANES measurements. The photocatalytic degradation of antibiotic ciprofloxacin was performed under visible light using a LED illumination source and nearly 70 % of the antibiotic was removed in 6 h by using the most active sample (2.5 %N–1.5 %Fe). As verified by photoluminescence results, the iron and nitrogen dopants synergistically enhanced the charge separation, since they promoted the formation of the different TiO2 phases.

Study on thermochromic-emissivity performance of Mn doped TiO2 under temperature fluctuations

In this work, Mn doped TiO2 powders were synthesized directly by a solid state reaction route. Thermal treatment of the samples was carried out in air at temperatures from 800 °C to 1200 °C. Mn doped TiO2 powders have been structurally characterized by XRD, SEM and XPS, which indicates that as-prepared samples have the rutile phase structure and Mn ions are +2 and +3 state in rutile TiO2 after thermal treating at 800 °C −1200 °C. The band gap for Mn doped TiO2 powders was measured by UV–Vis absorption spectra, and these results found that the band gap shown a decreasing trend from 3.14 eV to 1.70 eV with the annealing temperature increasing. The reversible thermochromic phenomenon is attributed to the electrons in color centers absorbing the visible light. Variable emissivity property is connected with the morphology, electrical resistivity as well as lattice vibration of Mn doped TiO2 samples. The results demonstrated that heat treatment is a powerful avenue to improve the thermochromic-emissivity performance for Mn doped TiO2 materials.

Catalytic and photocatalytic oxidation of diphenyl sulphide to diphenyl sulfoxide over titanium dioxide doped with vanadium, zinc, and tin.

Samples of TiO2 (P25) doped with zinc, tin, and vanadium, thermally treated at 550 °C for 6 h, were tested as catalysts and photocatalysts for the oxidation of diphenyl sulphide to diphenyl sulfoxide and sulfone, using hydrogen peroxide as an oxidation agent. Thermal treatment of pure TiO2 and its vanadium-doped forms resulted in a decrease of anatase and an increase of rutile content. The opposite effect was observed for TiO2 doped with zinc or tin, where thermal treatment resulted in the rutile to anatase phase transition. The role of V, Zn, and Sn admixtures as TiO2 phase-composition controllers was postulated. The catalytic and photocatalytic activity was found to be influenced more by the rutile and anatase contents of the samples than the presence of admixtures. The rutile-containing samples, TiO2 and V-TiO2, presented much better activity in the catalytic oxidation of diphenyl sulphide compared with the catalysts that only contained the anatase phase, Sn-TiO2 and Zn-TiO2. The reaction efficiency was significantly improved under UV radiation. In this case, the best photocatalytic activity was found for calcined TiO2, containing both anatase and rutile components. An increase in rutile content, observed in the vanadium-doped TiO2, decreased the efficiency of the photocatalytic diphenyl sulphide oxidation. Thus, the presence of both anatase and rutile phases, with their favourable contributions, typical for P25, is necessary for the effective oxidation of Ph2S to Ph2SO. Moreover, it was shown that for the second oxidation stage, Ph2SO to Ph2SO2, the presence of the rutile phase is very important.

Oxygen vacancies enhance photocatalytic removal of NO over an N-doped TiO2 catalyst

The proposed process of photocatalytically oxidizing NO into NO3− over N–TiO2 samples under visible light irradiation.

Effect of Sulfur Doped Nanotitania for Degradation of Remazol Yellow and Phenol

Nanocrystalline TiO2 and sulfur-doped TiO2 were synthesized using the sol-gel method. Tween-80, titanium tetraisopropoxide (TTIP), and sulfuric acid were employed as raw materials for the synthesis of TiO2. All the synthesized samples were heated for 3 h at 500 ºC. Each cell parameter of the prepared samples was explored by employing the Rietveld refinement of X-ray diffraction (XRD) patterns. For sulfur-doped TiO2 and TiO2 samples, considerable differences were observed in their cell parameters. Under ultraviolet (UV) irradiation, the phenol and remazol yellow (RY) photodegradation of the sintered samples was analyzed. Physical properties were studied using Brunauer-Emmett-Teller (BET) and transmission electron microscopy (TEM) analyzes to measure the surface area. The XRD results confirmed that except nano-anatase, no other phase was present in any sample. The particle size range is 10-15 nm. BET surface results showed that doping concentrations influenced the surface area. On the samples with a larger surface area, photodegradation is superior, which coincides with a higher doping concentration.

Surface tension of liquid Ti with adsorbed oxygen and a simple associate model for its prediction

Surface tensions of electromagnetically levitated liquid Ti-samples were measured under the influence of oxygen. For this purpose, Ti-O samples were prepared by adding different amounts of TiO2 powder to pure Ti. The surface tension was found to strongly depend on the bulk oxygen mole fraction determined by chemical analysis. The results could be described by a simple model presented in the present work. In this model the Butler equation is applied and the formation of TiO2 – associates are taken into account. Non-ideal interactions ΔH≠0 between titanium and the associates also need to be taken into account. Good agreement with the experimental data is evident and also with a different model developed earlier by us.

Evaluation of phototoxic and cytotoxic potential of TiO2 nanosheets in a 3D reconstructed human skin model

Despite a continuous increase of commercial products containing nanoparticles, only few materials are currently used in such large amounts, forms and sizes as titanium dioxide - TiO2. Besides its use in cosmetics, food industry and biomedicine, TiO2 nanoparticles (NPs) are also used as highly efficient photocatalysts due to their unique ability to convert complex organic materials to carbon dioxide, water and simple mineral acids via complex radical and electron transfer reactions. The main objective of the current project was to assess the potential dermal effect (phototoxicity and skin toxicity) of TiO2 nanosheets (TIG-800) synthesized from the lyophilized aqueous colloids of peroxo-titanic acid by high-temperature treatment. The effect was examined on reconstructed human skin model EpiDerm in the test pre-validated by ECVAM and adopted into the ICH S10 guidelines for the preclinical photo-safety assessment of drugs. In addition, two further commercial samples of nanocrystalline TiO2, namely Aeroxide P25 and Eusolex T-2000, and six benchmark materials from pre-validation studies were tested. None of the TiO2 NPs tested in the study caused acute phototoxicity or cytotoxicity in the reconstructed 3D tissues up to the highest concentration tested. The prediction of photo-irritation potency for the benchmark chemicals was comparable to previous studies. For some of the tested materials, we identified reasons for false negative results or variability in previously published datasets by improved dosing, conditions of irradiation, and choice of suitable solvents. The method proved its suitability for photo-irritation assessment of topically applied materials.

Homogeneous annealing of TiO2, ZrO2 and ITO sol-gel layers with CO2 laser

Laser annealed sol-gel layers have the potential to replace the furnace process and expand the field of applications for selective annealed sol-gel coatings. In this study laser annealed TiO2, ZrO2 and ITO layers on glasses are investigated. Processing parameters of the CO2-laser system such as scanning speed, line overlap, laser power and focal spot are evaluated to generate sufficient thermal energy for densification. The ITO annealing process results in a sheet resistance comparable with the furnace annealed samples. Microscope images of the TiO2 and ZrO2 samples show a homogeneous layer morphology. XRD images exhibit crystalline tetragonal ZrO2 as seen in thermally annealed layers.