TiO2 Host Lattice Research Articles

Structural, optical, and electrical characteristics of anatase titanium dioxide tailored by doping of nitrogen and copper ions

Pure anatase TiO2 nanoparticles and its mono–doped and co–doped derivatives [i.e. (TiN0.007O1.993); (Ti0.998Cu0.002O2); (Ti0.998Cu0.002N0.007O1.993)] were prepared by sol–gel auto–combustion technique. Further, the effects of copper (Cu) and nitrogen (N) dopants have been investigated on structural, optical and dielectric properties of nanostructured TiO2 using X–ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy and dielectric spectroscopy measurement respectively. The Rietveld refinement analysis of XRD data and Raman spectra revealed that all the synthesized samples have pure anatase phase having tetragonal structure with space group of I41/amd. The pure anatase phase of doped samples illustrate the substitution of Cu ions at Ti4+ sites and N ions at O2− sites in the TiO2 host lattice. The crystallite size of TiO2 and its derivatives has been observed in the range of 11–14 nm. The band gap of TiO2 reduced from 3.2 to 1.9 eV with mono–doping and co–doping of the N and Cu in TiO2 lattice as confirmed by UV–Vis spectroscopy. This red–shift might be occur due to the possible formation of N–2p and Cu–3d localized levels (mono–doping case), and the creation of isolated intermediate states (co–doping case). The dielectric spectroscopy was carried out to investigate the electrical properties in details and explained in terms of structural and intrinsic ionic behaviour of different dopants. The detected band gap energies in N/Cu mono–doped and co–doped anatase TiO2 fall within the visible spectrum, rendering them suitable for harnessing solar energy in photocatalysis and photovoltaic applications.

Enhanced Alkaline Hydrogen Evolution on Gd1.0/Ndx (x = 0.5, 1.0, 3.0, and 6.0%)-Doped TiO2 Bimetallic Electrocatalysts

The work reports a facile synthesis of high thermally stable nanocrystalline anatase TiO2 nanoparticles (NPs) doped with different atomic concentrations (0.5, 1.0, 3.0, and 6.0%) of Gd3+ and Nd3+ ions by a template-free and one-step solvothermal process, using titanium(IV) butoxide as a titanium precursor and dimethyl sulfoxide (DMSO) as a solvent. The structure and morphology of the Gd3+, Nd3+, and 0.5%Gd3+-0.5%Nd3+/doped TiO2 NPs have been characterized by using various analytical techniques. The Gd3+/ and Nd3+/TiO2 molar ratios were found to have a pronounced impact on the crystalline structure, size, and morphology of TiO2 NPs. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies revealed the proper substitution of Ti4+ by Gd3+ and Nd3+ ions in the TiO2 host lattice. The as-prepared Gdx/TiO2, Ndx/TiO2, and Gd1.0/Ndx/TiO2 bimetallic NPs, x = 0.5, 1.0, 3.0, and 6%, have been investigated as electrocatalysts for hydrogen evolution reaction (HER) in 1.0 M KOH solution using a variety of electrochemical techniques. At any doping percentage, the Gd1.0/Ndx/TiO2 bimetallic NPs showed higher HER catalytic performance than their corresponding counterparts, i.e., Gdx/TiO2 and Ndx/TiO2. Upon increasing the Nd content from 0.5 to 6.0%, the HER catalytic performance of the Gd1.0/Ndx/TiO2 bimetallic NPs was generally enhanced. Among the studied materials, the bimetallic Gd1.0/Nd6.0/TiO2 NPs emerged as the most promising catalyst with an onset potential of −22 mV vs. RHE, a Tafel slope of 109 mV dec−1, and an exchange current density of 0.72 mA cm−2. Such HER electrochemical kinetic parameters are close to those recorded by the commercial Pt/C (onset potential: −15 mV, Tafel slope: 106 mV dec−1, and exchange current density: 0.80 mA cm−2), and also comparable with those measured by the most active electrocatalysts reported in the literature. The synergistic interaction of Gd and Nd is thought to be the major cause of the bimetallic catalyst’s activity.

Mesoporous Sn@TiO2 nanostructures as excellent adsorbent for Ba ions in aqueous solution

Efficient adsorption of Ba ions was achieved using Sn@TiO2 nanocomposite generated by ultrasonication process with subsequent calcination at 300 °C. X-ray diffraction, nitrogen adsorption-desorption isotherm, X-ray photoelectron spectroscopy, Fourier transformer infra-red, and scanning/transmission electron microscopy analyses were performed to probe the structural and textural features of the adsorbent powder. The XPS, FTIR, and EDX analyses confirmed the Sn doping into TiO2 host lattice. Some interesting features, including the increase of crystallite size and lattice parameters, were attained due to the successful Sn incorporation into the TiO2 host, as indicated further by XRD analysis. The sorption results fitted the Langmuir isotherm model and the kinetic data complied with the pseudo-second-order kinetics. The adsorption process improved markedly above the pHzc due to the electrostatic attraction between the negatively charged Sn@TiO2 particles’ surface and the positively charged Ba ions. The achieved high-performance mesoporous Sn@TiO2 nanostructures for the adsorption of Ba2+ could be potentially utilized to remove other toxic metal cations.

Photocatalytic Degradation of Organic Pollutants by Using Nanocrystalline Boron‐doped TiO2 Catalysts

AbstractIn this work, bare or mixed environmentally non‐benign organic pollutants have been decontaminated using boron‐doped TiO2 nanoparticles (B@TiO2). B@TiO2 nanoparticles (NPs) with varying content of boron (0.0 to 7.0 mol %) are synthesized using sol‐gel method. These NPs are characterized by using different tools. XRD reveals the high crystalline nature with formation of anatase phase and also shows slight increase in crystallite size with increase in boron content in TiO2 host lattice. The optical shift towards higher wavelength increases with increase of boron doping and hence corresponding decrease in optical band gap of doped NPs is confirmed. FTIR and TGA studies reveal the increase of surface hydroxylation of NPs with increase in dopant content. B@TiO2 samples have been used for the photocatalytic degradation of bisphenol A, rhodamine B, methylene blue, methyl orange and mixture of these three dyes under sunlight illumination. 7.0 mol % B@TiO2 has shown the best activity than other prepared samples. Rate of degradation of mixed dyes using 7.0 mol % B@TiO2 is about seven times higher to that of bare TiO2 and also shown higher rate than other doped samples.

Effect of Nitrogen Doping on Photocatalytic Activity of TiO2

Nitrogen doped TiO2 nanoparticles (N-doped TiO2) in different mol percentage (2-6 mol%) of nitrogen with anatase phase, have been prepared by using EDTA-glycol method. Samples were characterized by various physico-chemical techniques. Physico-chemical characterization revealed that crystallite size, surface hydroxylation, and tuning of optical band gap towards visible region of catalyst increases with increase in dopant concentration upto 4.0 mol% in TiO2 host lattice. Thereafter, the samples were used to photocatalytic degradation of the organic dye methylene blue (MB) under sunlight irradiation directly. The progress of photodegradation reaction was monitored by UV-visible spectroscopy. During photocatalytic reaction, the effect of calcination temperature, amount of catalyst, initial concentration of dye and the effect of pH on the rate of degradation reaction was also studied. It is clearly shown that N doping in TiO2 results in the enhancement of the degradation ability of MB in UV-visible light.

A remarkable improvement in photocatalytic activity of titanium dioxide nanoparticles through samarium doping synthesized by hydrothermal technique for water treatment

The aim of the present work is to investigate the influence of Samarium ions doping in the TiO2 host lattice and the contribution to the optical properties of this semiconductor. The X-ray diffraction pattern shows the formation of anatase phase TiO2 nanoparticles of average sizes 7.8 nm, 7.21 nm and 6.1 nm for both pure and 1 wt% and 4 wt% of Sm3+ doped samples respectivity. Energy Dispersive X-ray (EDX) spectroscopy confirms the presence of Sm ions within the Sm substituted TiO2 nanoparticles. These results suggest that, Pure and doped TiO2 samples confirm anatase phase of good crystallinity with smaller crystallite size. UV–visible spectra display stronger absorption in the visible region. The photocatalytic experiments are investigated by the removal of rhodamine B under UV light. Compared to the other two photocatalysts, the results shows that 4 wt% of Sm3+ doped TiO2 exposes the highest photocatalytic performance.

Synergistics of Cr(III) doping in TiO2/MWCNTs nanocomposites: Their enhanced physicochemical properties in relation to photovoltaic studies

In the present investigation, optoelectronic modifications of the TiO2 host lattice through insertion of Cr(III) (0.5–3.0 mol.%) as a dopant and thereafter its composites with MWCNTs prepared using single step in-situ sol-gel route and its photovoltaic performance of the hybrids was investigated using Ru(II) based sensitizer. The physicochemical properties (viz. structural, opto-electrical, morphological and charge transfer behavior) of the ternary Cr@TiO2/MWCNTs NCs are compared with the TiO2/MWCNTs NC through various spectroscopic (XRD, Raman, UV–Visible DRS, XPS, FT-IR, PL, TRPL and EIS measurements) and microscopic (HR-TEM with SAED) analysis. TRPL and EIS studies reveals that, average life time of the electrons in the excited state increases and interfacial charge transfer resistance decreases after the insertion of Cr(III) ion into the TiO2 host lattice. After the detailed physicochemical investigations, binder free NCs were deposited on the F:SnO2 (FTO) by doctor-blade technique using DMF and CH3CN solvents and then anchored with N719 dye. Finally, sensitized photoelectrode sandwiched with Pt-counter electrode for making the sandwich dye sensitized solar cells (DSSCs) and photovoltaic performance of the assembled devices was measured under AM 1.5 solar simulator for I-V and IPCE measurements. The Cr.0.010@Ti0.990C NCs based DSSCs shows highest photovoltaic conversion efficiency up to η = 7.69% which is 20% (η = 6.18%) higher to that of undoped TiO2/MWCNTs based DSSCs.

Strategies for Tuning Optoelectronic Properties of TiO2 Nanomaterials for Solar Photovoltaic Studies

Third generation solar cells are mainly focusing on the use of nanomaterials as host components for solar-to-electrical conversions. Among the various nanomaterials, TiO2 is one of the most promising candidates used in solar devices due to their remarkable structural and opto-electrical properties. However, bare TiO2 nanomaterials have the various constraints in efficient solar energy conversions. In the present research endeavors, TiO2 nanomaterials have been modified with the different strategies such as dyad anchoring, dye-quantum dot sensitization, composites of carbon nanostructures with sensitizers, metal ion doping with sensitizers so as to tune its optoelectronic properties for efficient solar energy harvesting. In addition, the interconnectivity between the various components and their optoelectronic properties of modified TiO2 for solar energy conversions have been studied in detail. In the dyad system, a supramolecular ruthenium(II)phthalocyanine··peryleneimide (RuPc···PI) has been anchored on the surfaces of TiO2 and thereafter these TiO2-dyad sensitized solar cells have assembled in a bottom-up fashion. Upon photo-irradiation at air-mass (AM) 1.5, the dyad-based solar devices convert solar light to electricity of 2.1%; which is higher than that of individual dyes. In next strategies, the synthesized CdS quantum dots (QDs) have connected electrostatically to the surfaces of TiO2 nanoparticles (NPs) and thereafter, this binary hybrid heterojunction is further self-assembled physically with N719 dye to form ternary TiO2 NPs-CdS QDs-N719 photoelectrodes. These co-sensitization devices reported the solar energy conversion efficiency (η) up to 2.35 %. In addition, anatase TiO2 NPs is anchored on the surface of functionalized carbon nanostructures (MWCNTs or RGO); which is further sensitized with Ru(II) dyes for solar devices having efficiency reached to 6.21%. In another modification, Cr(III) as well as Mo(VI) ions are inserted into TiO2 host lattice and then their composites with CNs are further sensitized for boosting the solar energy conversions and reached up to 7.69 % of efficiency. Figure 1

Direct Z-scheme of Cu2O/TiO2 enhanced self-cleaning, antibacterial activity, and UV protection of cotton fiber under sunlight

This work presents a modified solvothermal process for a facile synthesis of high thermally stable nanocrystalline anatase TiO2 NPs doped with Cu2O NPs. A Z-scheme mechanism was used to account for the enhanced photocatalytic activity exhibited by these materials. Also, the nanocomposite was impregnated in cotton fabric to obtain a modified fiber with high thermal stability, self-cleaning, enhanced UV protection, and antibacterial activity. The as-prepared nanomaterials and the coated fabric were characterized by various physicochemical techniques such as XRD, EDXRF, TGA, TEM, HRTEM, and SEM. The Cu2O/TiO2 molar ratio in the nanocomposite was found to possess a pronounced impact on the crystalline structure, size and morphology of TiO2 NPs. The XRD revealed proper substitutions of the few Ti4+ sites by Cu2+ ions in TiO2 host lattice. Optical measurements showed that the plasmonic peak of the Cu2O/TiO2 nanocomposite was affected by the copper-doping concentration, enhancing self-cleaning of Cu2O/TiO2 under direct sunlight. The TiO2/fiber self-cleaning efficiency (12 h for MB removal) was increased by the in situ growing of Cu2O (5.5 h). Antibacterial activity studies revealed high potential activity of Cu2O/TiO2 against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli, Kleissella pneumonia, Saccharomyces sp.) bacteria. The promising photocatalytic and biocidal activity of our synthesized Cu2O/TiO2 nanocomposites was ascribed to the reactive oxygen species generated by the Z-scheme mechanism under direct Sunlight.

Effect of samarium (Sm3+) doping on structural, optical properties and photocatalytic activity of titanium dioxide nanoparticles

ABSTRACTThe current work reports the hydrothermal preparation of pure TiO2 and Sm3+ ion-doped TiO2 nanoparticles and the influence of samarium ion doping in the TiO2 host lattice. The as-synthesized both pure and Sm3+-doped TiO2 nano samples were extensively characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDX) and UV–VIS spectroscopy. XRD pattern reveals the crystalline size and phase of the nanoparticles and the formation of spherical morphology was confirmed by HR-TEM observation. The incorporation of Sm in TiO2 is confirmed by EDX. The optical properties of TiO2 and Sm3+:TiO2 nanoparticles have been studied using diffuse reflectance spectroscopy analysis. The addition of the dopant ion markedly increases the bandgap from 3.39 to 3.46 eV. The photocatalytic activity of the crystalline as-synthesized nanoparticles was examined for the degradation of Rhodamine B induced by UV irradiation and the degradation efficiency is also reported.

Sunlight-assisted photocatalytic degradation of textile effluent and Rhodamine B by using iodine doped TiO2 nanoparticles

Abstract Iodine-doped TiO2 nanoparticles (I@TiO2 NPs), in different mol percentage (mol%) of iodine with anatase phase only, have been prepared by using simple sol-gel method. Samples were characterized by various physico-chemical techniques. Physico-chemical characterization revealed that crystallite size, surface hydroxylation, and tuning of optical band gap towards visible region of composites increases with increase in dopant concentration upto 7.0 mol% in TiO2 host lattice. Thereafter, the samples were used to photocatalytic degradation of textile effluent (TE) as well as Rhodamine B (RhB) under sunlight irradiation directly. The progress of photodegradation reaction was monitored by UV–visible spectroscopy. The chemical oxygen demand (COD) of TE samples was evaluated before and after photocatalytic studies. During photocatalytic reaction, the effect of pH and amount of catalyst on the rate of degradation reaction was also studied. It is clearly shown that I@TiO2 particles result in the enhancement of the degradation ability of RhB as well as TE in sunlight.

Effect of Cr3+ concentration on structural and optical properties of TiO2:Cr3+ anatase and rutile phases

TiO2 powders doped with different amounts of Cr3+ions (from 0 to 10 mol%) have been prepared by hydrothermal technique. TiO2:Cr3+ powders were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, diffuse reflection, absorption, photoluminescence and photoluminescence excitation spectra. The results showed that the Cr3+ dopant concentrations did not affect on the lattice constants of TiO2 crystal, but affected on shift and broadening of the Raman modes for both anatase and rutile phases. The band gap of both the anatase and rutile TiO2 host lattice was strongly decreased with increasing Cr3+ dopant concentration. The photoluminescence spectra of TiO2:Cr3+ anatase phase exhibited a weak narrow peak (the so-called R-line) at 698 nm, meanwhile those of TiO2:Cr3+ rutile phase consisted of a very intense narrow zero-phonon R-line at 695 nm assigned to the 2E(2G) → 4A2(4F) transition of Cr3+ ions in strong octahedral field and its phonon-sidebands. In particular, in the PL spectrum of TiO2:Cr3+ rutile phase is also observed an abroad emission band centered at 813 nm assigned to the 4T2(4F) → 4A2(4F) transition of ions Cr3+ in weak octahedral field.

Structural and photocatalytic studies of hydrothermally synthesized Mn2+–TiO2 nanoparticles under UV and visible light irradiation

Pure TiO2 and Mn2+–TiO2 nanoparticles have been prepared by simple hydrothermal method with different Mn2+ concentrations. Obtained samples were analysed to determine it’s structural, optical, morphological and compositional properties using x-ray diffraction, UV-DRS, Raman, photoluminescence, XPS, TEM and EDS analysis. The EDS micrograph confirms the existence of Mn2+ atoms in TiO2 matrix with 0.86, 1.60 and 1.90 wt%. The crystallite size as well as band gap decreases with increase in Mn2+ concentration. The average particle size obtained from TEM was found 8–11 nm which is in good agreement with XRD results. Raman bands at 640, 518 and 398 cm−1 further confirmed pure phase anatase in all samples. XPS shows the proper substitutions of few sites of Ti4+ ions by Mn2+ ions in the TiO2 host lattice. The intensity of PL spectra for Mn2+–TiO2 shows a gradual decrease in the peak intensity with increasing Mn2+ concentration in TiO2, it implies lower electron-hole recombination rate as Mn2+ ions increases. The obtained samples were further studied for its photocatalytic activities using malachite green dye under UV light and visible light.

Structure and high photocatalytic activity of (N, Ta)-doped TiO2 nanoparticles

A hydrothermal method was used to prepare three nano-crystalline samples of TiO2 (S1), N-doped TiO2 (S2), and (N, Ta)-codoped TiO2 (S3) with average crystallite sizes (D) of 13–25 nm. X-ray diffraction studies confirmed a single phase of the samples with a tetragonal/anatase structure. A slight increase in the lattice parameters was observed when N and/or Ta dopants were doped into the TiO2 host lattice. Detailed analyses of extended X-ray absorption spectra indicated that N- and/or Ta-doping into TiO2 nanoparticles influenced the co-ordination number and radial distance (R) of Ti ions in the anatase structure. Concerning their absorption spectra, (N, Ta)-doping narrowed the band gap (Eg) of TiO2 from 3.03 eV for S1 through 2.94 eV for S2 to 2.85 eV for S3. Such results revealed the applicability of these nanoparticles in the photocatalytic field working in the ultraviolet (UV)-visible region. Among these, photocatalytic activity of S3 was the strongest. By using S3 as a catalyst powder, the degradation efficiency of methylene blue solution was about 99% and 93% after irradiation of UV-visible light for 75 min and visible-light for 180 min, respectively.

Effect on the stabilization of the anatase phase and luminescent properties of samarium-doped TiO2 nanocrystals prepared by microwave irradiation

The structural and luminescent properties of TiO2 and TiO2:Sm3+ powder, synthesized by microwave irradiation using benzyl alcohol as solvent, were studied over an annealing range of 200–1000 °C. Structural and luminescent characterization was carried out by XRD, TEM, HRTEM, HRSEM and PL. Pure synthesized TiO2 presents similar structural characteristics to other methods and its transformation from the anatase to the rutile phase occurs between 600 and 800 °C. It was determined that the anatase phase of TiO2 is stabilized when doped with Sm3+, even at temperatures up to 1000 °C. Crystal growth of TiO2:Sm3+ powder is very slow, measuring 5 nm at 200 °C and 29 nm at 800 °C. It was observed that the particles consist of nano-sized crystals for all working conditions. Microwave irradiation technic allowed the successful incorporation of Sm3+ ions into the TiO2 host lattice, so it is reasonable to conclude that Sm3+ ions distorted octahedron of TiO6 to replace Ti4+ ions. TiO2:Sm3+ nanocrystals show emission of Sm3+ ion in the visible wavelength region. The visible photoluminescence correspond to transitions from the excited 4G5/2 level to the 6H11/2, 9/2, 7/2, 5/2 levels, respectively. The results of spectroscopic measurements of luminescence excitation, imply that Sm3+ emissions, are due to indirect excitation of the Sm3+ ions through an energy transference process from electron-hole pairs generated in the TiO2 host. The increased emission intensity is directly related with high crystallinity obtained by annealing treatment.

Low-temperature fabrication of brown TiO2 with enhanced photocatalytic activities under visible light.

Here we report a facile one-step low-temperature solution-based method to treat native TiO2 with NaH. The NaH treatment effectively induces the Ti(iii) species and oxygen vacancies into the TiO2 host lattice, and enables the absorption edge of TiO2 to be conveniently adjusted from the UV region to the red end of the visible spectrum.

Enhanced visible light photocatalytic activity of Cr3+-doped anatase TiO2 nanoparticles synthesized by sol–gel method

The photocatalytic degradation of methylene blue (MB) has been investigated under visible light irradiation with an incandescent light bulb using chromium doped TiO2 nanoparticles. Cr–TiO2 photocatalysts were successfully synthesized by sol–gel method at room temperature and characterized by X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), Raman spectroscopy, Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy. The band gap energy of the nanoparticles were estimated using UV–Vis DRS technique. With increasing Cr3+ cations content into TiO2 host lattice, the optical absorption band tuned in the visible region. XRD and TEM results reveal uniform and crystalline anatase TiO2 nanoparticles. The photodegradation of MB indicated that the photocatalytic activity of pure TiO2 nanoparticles increased with increasing Cr3+ cations concentration.

Synthesis, characterization and photocatalytic behavior of Ag doped TiO2 thin film

In this study, structure, microstructure, optical properties and photocatalytic degradation of Rhodamine B (RhB) have been investigated in an aqueous heterogeneous media containing pure and Ag doped TiO2 nanostructures thin films which were prepared by a simple sol–gel route. Thermal analysis demonstrated that Ag content decreased the temperature of anatase-to-rutile phase transformation. X-ray diffraction analysis confirmed that the prepared nanostructures crystallize within anatase-type structure and that the dopant Ag ions were not fully incorporated within TiO2 host lattice, meanwhile both the refractive index and optical band gap were affected by Ag concentration. The photodegradation of Rhodamine B under UV-C radiation by using pure and Ag-doped TiO2 nanostructures showed that Ag played an important role in a significant improvement of the photodegradation efficiency and that the optimum content of Ag ions was found to be 0.5% molar ratio.

Effect of Cr\(^{3+}\) Concentration and Heat-treating Temperature on Structural Property of Cr\(^{3+}\)- doped TiO\(_2\) Nanowires Synthesized by Hydrothermal Method

Anatase Ti1-xCrxO2 nanowires with Cr3+ dopant contents ranging from x = 0 to 0.1 have been successfully synthesized by hydrothermal method. The nanowires were prepared from anatase titanium dioxide powder (TiO2), chrome nitrate (Cr(NO3)3), and sodium hydroxide (NaOH). The effect of the Cr3+ concentration and heat-treating temperature on structure, morphology of the synthesized Ti1-xCrxO2 samples has been studied by X-ray diffraction, scanning electron microscopy and Raman scattering. At low heat-treating temperature (≤ 600 oC), the samples exhibited anatase phase and in the Raman spectra of samples with x ≥ 0.01 exhibited a new series peak at 120, 236, 250, 292, 362, 430, 467 and 550 cm-1, which were assigned to the localized vibrational modes related to the complexes containing Cr3+ ion. But at high heat-treating temperature (1100 oC), the samples exhibited rutile phase, in the Raman spectra the above-mentioned peak series did not appear, instead of this, only observed shifting and broadening of characteristic Raman modes (Eg and M) for rutile TiO2 with increasing Cr3+ dopant content, which proves that the Cr3+ ions have replaced the Ti4+ ions in the rutile TiO2 host lattice. The lattice constants of both the rutile and anatase TiO2 crystallites have been hardly affected by Cr3+ ions dopant contents.

Photocatalytic activities of europium (III) and niobium (V) co-doped TiO2 nanopowders synthesized in Ar/O2 radio-frequency thermal plasmas

Europium (III) and niobium (V) co-doped TiO2 nanopowders were synthesized in Ar/O2 radio-frequency thermal plasmas by pyrolyzing aqueous precursors that contained various concentrations of Eu3+/(Eu3++Nb5++Ti4+)=0–0.5at.% and Nb5+/(Eu3++Nb5++Ti4+)=0–1.0at.%. Phase identification was performed by X-ray diffraction (XRD), particle morphology was observed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), and UV–vis absorption spectra were determined by UV–vis spectroscopy. The photocatalytic activities under UV and visible light irradiations were both evaluated by bleaching 20μM of a methyl orange aqueous solution. All the resulting powders had a phase composition of anatase (30–66nm crystalline size) (major phase: ∼80% mass proportion) and rutile (56–94nm crystalline size) polymorphs, with a relatively wide particle size distribution from several nanometers (faceted crystallites) to ∼100nm (spherical particles). The photocatalytic activities dominated by oxygen defects in the TiO2 host lattice for the powders prepared with identical doping concentrations of Eu3+ and Nb5+ were both superior under UV and visible light irradiations over those obtained with different doping amounts. More interestingly, the co-doped powder exhibited an improved photocatalytic performance under 600–700nm visible light illumination than the Eu3+-doped TiO2 and P25 commercial powders.