Co-doped TiO2 Nanocrystals Research Articles

Structural and optical properties of sol-gel synthesized TiO2 nanocrystals: Effect of Ni and Cr (co)doping

Nickel and chromium metal ions have been utilized to dope and co-dope titanium dioxide nanocrystals, thereby broadening the light absorption range of titania into the visible light spectrum. The doped and co-doped TiO2 nanocrystals were prepared using sol-gel techniques, with a varied doping concentration that extended from 0.25 to 10.0 wt%.These modified materials underwent comprehensive analysis using standard analytical tools such as X-ray diffraction, Raman spectroscopy, BET surface area measurement, Fourier transform infrared spectroscopy, UV–vis diffuse reflectance spectroscopy, and fluorescence spectroscopy. Powder XRD technique reveals that the modified catalyst majorly contains the anatase polymorph with the transition metal ion either substituting Ti or located as interstitials in the lattice of TiO2. Raman and UV–Vis absorption spectra of the doped and codoped catalyst a show λmax shift towards longer wavelength when in the metal ion concentration is increased from 0.25 to 10 wt%. FTIR patterns show the stretching and vibration patterns of hydroxyl radicals present in the nanocrystals. The BET surface areas of the doped and codoped TiO2 nanocrystals have substantially higher surface areas compared with that of the undoped TiO2. Electronic structural studies of the TiO2, (Ti,Cr)O2, (Ti,Ni)O2, and (Ti,Ni,Cr)O2 crystals using density functional theory indicated a reduction in the band gap width (Eg) of pure TiO2 when doped with transition metals. Specifically, the indirect bandgap values for Ni(10%), Cr(10%) and NiCr(5% + 5%) doping were 2.96, 2.83, and 2.7 eV, respectively. Furthermore, the photoluminescence intensity substantially decreased with the incorporation of transition metal ions in the TiO2 nanocrystals.

Sasol and UCT researchers collaborate on the use of commercial iron catalysts to convert hydrogen and CO2 into green jet fuel and chemicals

This study introduces a simple and fluorine free route to synthesize nitrogen and lanthanum co-doped TiO2 nanocrystals with exposed {0 0 1} facets through one-step hydrothermal method. The microstructure, chemical composition, and photocatalytic property of the co-doped TiO2 nanosheets were analyzed using XRD, FESEM, TEM, XPS and UV–vis. The experimental results indicated that N had been successfully doped into TiO2 lattice, while La was likely to form a binary nanocomposite with TiO2. The co-doped TiO2 nanosheets showed an additional visible light absorption band starting from 400 nm, which could improve the visible light photocatalytic activity of the sample. As the shape-controlling agent, DEA plays a crucial role in the formation of {0 0 1} facets. N and La co-doping could produce a synergistic effect. N doping can narrow the band gap of anatase TiO2 and increase the utilization efficiency of visible light, while La doping can enhance the separation efficiency of photo-induced electrons and holes. N and La co-doped TiO2 nanosheets exhibited higher visible light photocatalytic activity compared with P25, N doped TiO2 nanosheets and N, La co-doped TiO2 nanoparticles with the same doping concentration. In addition, N and La co-doped TiO2 nanosheets showed well recycling performance.

A review of scandium–hafnium doped TiO2 nanocrystals

TiO2 has a wide range of applications since it has the best photocatalytic activity. Its photocatalytic activity can be enhanced by doping with suitable elements. Hydrothermal method and sol–gel synthesis are mainly considered for the preparation of doped TiO2 nanoparticles. Modern characterization techniques are used to study the doped material. The main contribution of doping is enhanced photocatalytic activity by shifting the absorption edge towards the visible region. Here we had made a review on the synthesis procedure, characterization and photocatalytic activity of the Sc, Hf doped, and co-doped TiO2 nanocrystals.

La-Ce doped TiO2 nanocrystals: a review on synthesis, characterization and photocatalytic activity

Titanium dioxide (TiO2) is one of the best semiconductor photocatalysts due to its high stability, oxidative power, non-toxicity, low cost etc. But its photocatalytic activity is limited due to rapid recombination of photo-generated electron-hole pair, wide band gap and anatase to rutile phase transformation. These disadvantages can be eliminated by introducing dopants into the TiO2 nanocrystals. Sol-gel and hydrothermal methods can be used for the synthesis of doped and co-doped TiO2 nanocrystals. Advanced characterization techniques can be used for the study of phase structure, optical properties, thermal properties, surface area, morphological changes and photocatalytic activity of doped and co-doped TiO2 nanoparticles. Doping inhibits the anatase to rutile phase transformation and suppresses the recombination of photo-generated electron-hole pair which enhances the photocatalytic activity. Here we made a review on the synthesis, characterization and photocatalytic activity of La, Ce doped and co-doped TiO2 nanoparticles.

Corrigendum to “Decontamination of chemical warfare agents by Zn2+ and Ge4+ co-doped TiO2 nanocrystals at sub-zero temperatures: A solid-state NMR and GC study” [Chem. Phys. Lett. 707 (2018) 31–39

Corrigendum to “Decontamination of chemical warfare agents by Zn2+ and Ge4+ co-doped TiO2 nanocrystals at sub-zero temperatures: A solid-state NMR and GC study” [Chem. Phys. Lett. 707 (2018) 31–39

Synthesis and characterization of Nb-La co-doped TiO2 nanoparticles by sol-gel process for dye-sensitized solar cells

One of the main challenges of the current photovoltaic systems is improving the performance of the dye-sensitized solar cells (DSSCs). The deliberate insertion of impurity ions into the TiO2 crystal lattice as an electron transporting material in DSSCs might be an effective method for improving the electronic properties of TiO2, which leads to enhancing the photovoltaic efficiency. Recently, co-doping has become a promising strategy that can be used for effective tuning of the electronic properties. In the present study, this method was applied as a novel approach to synthesize Lanthanum-Niobium(La,Nb)-codoped TiO2 nanocrystals via the Pechini sol-gel technique. According to the results, the x-ray diffraction investigation approved the anatase phase formation of (Nb-La)-codoped TiO2 nanoparticles. In addition, the field-emission scanning electron microscopy (FESEM) showed the nanoparticles were semi-spherical and approximately 30 nm in size. The photovoltaic parameters of the assembled dye-sensitized solar cells were tested via current density-voltage measurement, exhibiting an enhancement through introducing 2% mol Nb-La ions into the TiO2 crystal lattice. The electrochemical impedance spectroscopy showed that the charge transfer process occurred faster at the FTO/TiO2 interface, which was attributed to the reduction of charge recombination and enhanced electron conductivity.

Observation of Optical Band-Gap Narrowing and Enhanced Magnetic Moment in Co-Doped Sol–Gel-Derived Anatase TiO2 Nanocrystals

The magnetic behavior of TiO2 and doped TiO2 nanocrystals has been a challenge due to the unambiguous nature of defects present in oxide semiconductors. Here, a simple, low-temperature sol–gel method is developed for the synthesis of low-dimensional and highly efficient stable anatase TiO2 nanocrystals. The X-ray powder diffraction pattern and Raman spectra confirm the formation of a single-phase anatase structure of TiO2. High-resolution transmission electron microscopy studies reveal the crystalline nature of the sol–gel-derived nanocrystals. The increase in lattice parameters together with the shifting and broadening of the most intense Eg(1) mode in micro-Raman spectra of Co-doped TiO2 nanocrystals indicate the incorporation of Co in TiO2. Shifting of the absorption edge to the visible region in UV–visible spectra indicates narrowing of the band gap due to Co incorporation in TiO2. X-ray photoelectron spectra confirm the presence of Co2+ and Co3+ in Co-doped TiO2 samples. Oxygen vacancy defects lead t...

Effects of calcination temperature and Li+ ions doping on structure and upconversion luminescence properties of TiO2:Ho3+-Yb3+ nanocrystals

Ho3+-Yb3+ co-doped and Ho3+-Yb3+-Li+ tri-doped TiO2 nanocrystals were prepared using the sol-gel method. Effects of the calcination temperature and Li+ ions doping on the structure and upconversion luminescence properties of Ho3+-Yb3+ co-doped TiO2 nanocrystals were investigated. The upconversion luminescence of nanocrystals was enhanced with the reduction of the crystal lattice symmetry and the crystallinity improvement of the matrix, which were facilitated by the calcination temperature change and Li+ ions doping. The lowest lattice symmetry and the best crystallinity of the matrix resulted in the maximum luminescence intensity.

Enhanced up-conversion red light emission from rare earth titanium oxide nanocrystals with pyrochlore phase

A facile sol-gel method combined with the post-annealing process has been used to synthesize Yb3+/Er3+ co-doped TiO2 nanocrystals. It is found that the high Yb3+ concentrations can promote the formation of TiO2 nanocrystals with pyrochlore phase. An intense up-conversion (UC) red light emission (658 nm) has been achieved under 980 nm laser excitation, which is enhanced by 108 folds compared with the reference sample. Both the luminescence intensity and the red-to-green emission intensity ratio are dependent of the annealing temperature, which can be explained as the distribution of rare-earth ions and phase change of TiO2 nanocrystals.

Decontamination of Chemical Warfare Agents by Zn2+ and Ge4+ co-doped TiO2 nanocrystals at sub-zero temperatures: A solid-state NMR and GC study

Using solid-state NMR spectroscopy (SSNMR) and gas chromatography (GC) we studied the sub-zero temperature decontamination performance of Chemical Warfare Agents (sulphur mustard (HD), soman (GD) and S-2-(diisopropylamino)ethyl O-ethyl methylphosphonothiolate (VX)) and their simulants (2-chloroethyl ethyl sulphide (2-CEES) and dimethyl methylphosphonate (DMMP)) on a novel nanoparticulate Zn2+ and Ge4+ co-doped titanium dioxide (Zn-Ge-TiO2) material. To discover further progress toward the practice use of the powdered catalyst and improve its low-temperature disinfection, a novel suspension decontaminant was prepared successively by suspending Zn-Ge-TiO2 in hydrofluoroether (HFE). By means of a variety of characterization methods such as XRD, BET, BJH, SEM and TEM, the evolution of structure and properties across Zn2+ and Ge4+doping were systematically studied. Our data show that Zn (5.28 wt%)-Ge (1.48 wt%)-TiO2 exhibited the best photocatalytic performance. Versus undoped TiO2, the sample has unchanged crystal structure (anatase) and decreased average pore diameter (2.86 nm), accompanied with increased specific surface area (424.9 m2/g), crystallite size (5.8 nm) and pore volume (0.29 cm3/g). Under simulated sunlight irradiation at −30 °C, after a reaction time of 120 min, the degradation efficiency of HD, GD and VX on the suspension composed of Zn (5.28 wt%)-Ge (1.48 wt%)-TiO2 and HFE-458 (HCF2CF2CH2OCF2CF2H) were all over 99.95%. This indicated that the suspension will have a promising prospect of application in CWAs decontamination under the sub-zero environment.

Synthesis and characterization of visible-light-active mesoporous titania by doping Ni and N

Ultrafine TiO2 nanoparticles with a narrow size distribution were designed for extending the light absorption wavelength from ultraviolet to visible light with the increased photocatalytic activity. The mesoporous spherical TiO2 nanoparticles and the Ni doped TiO2 nanoparticles were prepared by sol–gel method, with the Ni molar fraction ranged from 0.5, 1, 2, 3, 4 to 5%. Samples were calcined at 550 °C to form crystallized TiO2 and eliminate organic impurities. The Ni and N co-doped TiO2 nanocrystals were prepared by heating Ni doped TiO2 powders in NH3 flow at 650 °C. All the doped titania nanocrystals are well crystallized anatase with a tetragonal structure. 0.5% Ni–TiO2 exhibited optimum photocatalytic activity for MB degradation under UV-light irradiation, which was about twice compared to that of the blank TiO2. The visible light photocatalytic activity of 5% Ni/N-TiO2 was remarkably raised up to 4 times by contrast with the blank TiO2 while the photocatalytic activity of N-TiO2 only increased to 2 times compared to that of the blank TiO2.

Trans-Regime Structural Transition of (In3+ + Nb5+) Co-Doped Anatase TiO2 Nanocrystals under High Pressure

Chemical co-doping and high pressure reactions have been broadly used to synthesize novel materials or to tune the physicochemical properties of traditional materials. Here, we take In3+ and Nb5+ ions co-doped anatase TiO2 nanocrystals as an example and report that a combination of both a chemical and a high pressure reaction route is more powerful for the preparation of metastable polymorphs. It is experimentally demonstrated that In3+ and Nb5+ co-doping significantly changes the high-pressure reaction behaviors of anatase TiO2 nanocrystals (<10 nm) and leads to their trans-regime structural transition in terms of in situ Raman analysis, from an anatase to a baddeleyite-like phase under compressive pressures and then to an α-PbO2-like structure under decompressive pressures. This abnormal phase transition is attributed to a defect-induced heterogeneous nucleation mechanism. Furthermore, the stiffness of co-doped TiO2 nanocrystals is significantly enhanced due to the synergistic effects of co-dopants. Thi...

N, La Co-Doped TiO2 for Use in Low-Temperature-Based Dye-Sensitized Solar Cells

In this survey, N, La co-doped TiO2 nanocrystals are synthesized through simple sol–gel method. Results reveal that both elements of N and La are introduced successfully into the structure of TiO2 and exist as the form of La (Ti–O–La) bonds, N (N–Ti–O) bonds and N (Ti–O–N) bonds by several characterization analysis, thereby resulting in the formation of new impurity energy level between the forbidden bands, and great enhancement of light absorption ability in visible light region. These resulting samples are fabricated for low-temperature-based dye-sensitized solar cells (DSSCs), and the highest temperature of the whole process is 120°C. EIS, Bode plot and I-V analysis are employed to measure photovoltaic performance of DSSCs. The photoelectric conversion efficiency (η) of DSSCs with co-doped TiO2 materials as the photoanode is 5.33%, and when compared to pure TiO2-based cell (4.02%), the η is increased by 32.6%.

Exploring the effect of boron and tantalum codoping on the enhanced photocatalytic activity of TiO2

Aiming to improve the photocatalytic activity, boron and tantalum co-doped TiO2 nanocrystals were prepared by a sol–gel method. Pure and doped titania samples were characterized by X-ray diffraction (XRD) measurements, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy. The results revealed that all the samples have highly crystalline anatase structure, and no any other second phase was observed. It is found that the incorporation of dopants inhibits the growth of TiO2 nanocrystal. Moreover, XPS observations showed that Ta are in the form of Ta5+ while the majority of B species are present at interstitial sites. Finally, photocatalytic activities of all the samples were evaluated by degradation of methylene blue (MB) solutions under simulated solar light irradiation. Ta-doped and (B, Ta)-codoped catalysts exhibit enhanced photocatalytic activities in comparison with pure TiO2, with the codoped sample exhibiting the best photodegradation performance. This indicates that B and Ta co-doping is an effective way to improve photocatalytic performance of TiO2. The catalytic activity of B-doped TiO2 becomes slightly worse than pure TiO2 nanocrystals, which is plausible due to increased charge carrier recombination centers induced by incorporation of boron species.

One-step hydrothermal method to prepare nitrogen and lanthanum co-doped TiO2 nanocrystals with exposed {0 0 1} facets and study on their photocatalytic activities in visible light

The photocatalytic activity of TiO2 can be mainly improved from three approaches: (1) enhancing the separation efficiency of photoelectrons and holes, (2) enhancing surface energy, and (3) increasing availability of visible light. Here, we report a one-step method to obtain nitrogen and lanthanum co-doped TiO2 nanosheets with dominant {001} facets through a hydrothermal process, using TBOT, triethylamine and LaCl3·nH2O as precursor and sources of N, La respectively in HF–HNO3 mixed aqueous solution, and the samples were characterized by XRD, SEM, TEM, XPS, UV-DRS and BET analyses. The XRD and XPS results confirmed that N was doped into the lattice of anatase TiO2, while La was not. N acts as an O–Ti–N structure or interstitial N and La exists as LaF3 in TiO2 nanosheets. The SEM and TEM results show that the percentage of {001} facets in the as-synthesized N,La–TiO2 nanosheets is estimated to be about 75% on average at RF=1.0. N,La–TiO2 nanosheets can absorb visible light due to the red shift in the absorption edges, and compared with N–TiO2 nanosheets, N and La co-doping can further strengthen the absorption of visible light. N,La–TiO2 nanosheets exhibited higher photocatalytic activity for photodegradation of Rh B under visible light than pure TiO2, N–TiO2, La–TiO2 nanosheets and N,La–TiO2 nanoparticles. N and La co-doping could produce a synergistic effect. The N doping narrowed the band gap of TiO2, while the La doping could improve the separation efficiency of photoelectrons and holes. In addition, the La doping could enhance the adsorption property of photocatalyst for organic pollutants.

A fluorine free method to synthesize nitrogen and lanthanum co-doped TiO2 nanocrystals with exposed {0 0 1} facets for enhancing visible-light photocatalytic activity

This study introduces a simple and fluorine free route to synthesize nitrogen and lanthanum co-doped TiO2 nanocrystals with exposed {001} facets through one-step hydrothermal method. The microstructure, chemical composition, and photocatalytic property of the co-doped TiO2 nanosheets were analyzed using XRD, FESEM, TEM, XPS and UV–vis. The experimental results indicated that N had been successfully doped into TiO2 lattice, while La was likely to form a binary nanocomposite with TiO2. The co-doped TiO2 nanosheets showed an additional visible light absorption band starting from 400nm, which could improve the visible light photocatalytic activity of the sample. As the shape-controlling agent, DEA plays a crucial role in the formation of {001} facets. N and La co-doping could produce a synergistic effect. N doping can narrow the band gap of anatase TiO2 and increase the utilization efficiency of visible light, while La doping can enhance the separation efficiency of photo-induced electrons and holes. N and La co-doped TiO2 nanosheets exhibited higher visible light photocatalytic activity compared with P25, N doped TiO2 nanosheets and N, La co-doped TiO2 nanoparticles with the same doping concentration. In addition, N and La co-doped TiO2 nanosheets showed well recycling performance.

F, Ca co-doped TiO2 nanocrystals with enhanced photocatalytic activity.

F, Ca co-doped TiO2 was synthesized by a facile one-step hydrothermal method. After doping with F, electrons can be simultaneously excited from valence band to the F doping energy level. The smaller crystal size caused by doping with Ca can exhibit more powerful redox ability and the efficient separation of photogenerated hole-electron pairs. Therefore, F, Ca co-doped TiO2 exhibited enhanced photocatalytic activity.

Enhanced visible-light activity of F-N co-doped TiO2 nanocrystals via nonmetal impurity, Ti3+ ions and oxygen vacancies

A visible light active F-N co-doped TiO2 photocatalysts with varying molar ratio of TiO2/NH4F were successfully prepared using an effective yet simple ethanol–water solvothermal method. The photocatalytic activities of the prepared catalysts were tested for the degradation of methylene blue (MB) under visible light irradiation. Superior photocatalytic activity relative to that of undoped TiO2 was observed on the F-N co-doped catalyst with TiO2:NH4F molar ratio of 1.0. Based on the characterization results including FT-IR, XRD, Raman analysis, UV–vis DRS, XPS and ESR, the F and N dopants were effectively incorporated into the anatase TiO2 lattice, and resulted in a decrease in the energy gap, especially for the TONF-2 sample, which shows two optical absorption edge at 2.32eV and 2.99eV, respectively. The ESR data showed that the presence of fluorine and nitrogen in the lattice induces the formation of reduced Ti3+ centers and oxygen vacancies. In addition, the surface O2− radicals were also detected by ESR analysis, which together with OH radicals are responsible for the MB solution decoloration under visible light. According to the experimental results, it is believed that the enhanced visible light activity arises from the synergistic effect of F-N co-doping, the presence of Ti3+ centers and oxygen vacancies, and thus possible mechanism for both visible light absorption and charge separation were proposed.

The synthesis of nitrogen/sulfur co-doped TiO2 nanocrystals with a high specific surface area and a high percentage of {001} facets and their enhanced visible-light photocatalytic performance.

Nitrogen/sulfur co-doped anatase TiO2 nanocrystals with a high specific surface area and a high percentage of {001} facets were synthesized by a solvent-thermal process followed by the calcination with thiourea at an optimum heat treatment temperature. Under current experimental conditions, the optimum heat treatment temperature was found at 300°C, which successfully introduced nitrogen and sulfur dopants into the anatase lattice to replace a small portion of oxygen atoms while preserving the geometry of these anatase TiO2 nanocrystals to maintain a high percentage of {001} facets. These nitrogen/sulfur co-doped anatase TiO2 nanocrystals demonstrated a largely enhanced light absorption in the whole visible-light range and exhibited much higher photocatalytic performance than both P25 TiO2 nanoparticles and anatase TiO2 nanocrystals with a high percentage of {001} facets under visible-light illumination.

Iron–sulfur codoped TiO2 anatase nano-materials: UV and sunlight activity for toluene degradation

Iron and sulfur single- and co-doped TiO2 nanocrystals were prepared and characterized by a multitechnique approach. The presence of sulfur affected drastically the crystal size of anatase as well as other morphological characteristics such as BET surface area, pore volume and pore size. Significant differences were also detected on the isolated OH species concentration as a function of sulfur content. On the contrary, X-ray absorption spectroscopy (XAFS) showed that sulfur did not alter substantially the structural and electronic properties of Fe on TiO2. The photocatalytic activity of the synthesized TiO2 powders was studied in the gas-phase oxidation of toluene. The trials showed that the co-doped S/Fe-TiO2 nanomaterials have enhanced photo-activity compared to the reference single-doped Fe-TiO2 under both sunlight and UV-light irradiation. This is not however the case if compared with the single S-doped materials. Sulfur additionally modifies the selectivity of toluene photo-oxidation toward partial oxidation products. The partial vs. total oxidation yield ratio increased with increasing S content in both co-doped S/Fe-TiO2 or single-doped S-TiO2 series and was attributed to differences in surface properties related to both S-containing and OH entities.