Mo-doped TiO2 Research Articles

A UV-stable Perovskite Solar Cell Based on Mo-doped TiO2 Interlayer

Mo-doped TiO2 interlayer increases the UV photostability of perovskite solar cells through the redox shuttle between Mo(VI) and Mo(V), which is actually a kind of Mo redox microbattery. These micro...

Application of Reverse Micelle Sol⁻Gel Synthesis for Bulk Doping and Heteroatoms Surface Enrichment in Mo-Doped TiO₂ Nanoparticles.

TiO2 nanoparticles containing 0.0, 1.0, 5.0, and 10.0 wt.% Mo were prepared by a reverse micelle template assisted sol–gel method allowing the dispersion of Mo atoms in the TiO2 matrix. Their textural and surface properties were characterized by means of X-ray powder diffraction, micro-Raman spectroscopy, N2 adsorption/desorption isotherms at −196 °C, energy dispersive X-ray analysis coupled to field emission scanning electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV–Vis spectroscopy, and ζ-potential measurement. The photocatalytic degradation of Rhodamine B (under visible light and low irradiance) in water was used as a test reaction as well. The ensemble of the obtained experimental results was analyzed in order to discover the actual state of Mo in the final materials, showing the occurrence of both bulk doping and Mo surface species, with progressive segregation of MoOx species occurring only at a higher Mo content.

Encapsulating Mo-Doped TiO2 Anatase in N-Doped Amorphous Carbon With Excellent Lithium Storage Performances

For improving the capability, cycling stability and rate capacity of anatase TiO2-based electrode, Mo-doped TiO2 anatase encapsulated in nitrogen-doped amorphous carbon (denoted for Mo-TiO2@NC) were synthesized through a facile hydrothermal method and followed by coating with polyaniline (PANI) and heating treatment. When tested as anode for lithium ion batteries, the Mo-TiO2@NC electrode showed initial discharge and charge capacities of 850.7 and 548.3 mAh g-1 at a current density of 85 mA g-1, respectively, with a remarkable discharge capacity maintained at 449.2 mAh g-1 after 100 cycles. Even at high current density of 850 mA g-1, a reversible capacity of 154 mAh g-1 after 200 cycles is obtained, displaying good rate capacity and long-term cycling stability. The outstanding electrochemical performance of Mo-TiO2@NC could be attributed to the synergistic effect of aliovalent ions doping and carbon coating.

Enhanced photocatalytic performance of nanostructured TiO2 thin films through combined effects of polymer conjugation and Mo-doping

Mo-doped TiO2 [≤ 0.20 wt% Mo; ≤ 0.10 mol% (metal basis)] with conjugated polyvinyl alcohol (TiO2/C-PVA) composite thin films was prepared by sol–gel dip coating on polished fused SiO2 substrates, followed by annealing at 180 °C for 4 h. These conditions were sufficient for solid solubility, despite the unusually low annealing temperature. The annealed thin films consisted of homogeneously distributed individual and slightly agglomerated anatase grains in a continuous C-PVA matrix characterized by the carbon double bond formed upon conjugation. The films exhibited drying shrinkage cracks, which increased consistently in extent with increasing Mo-doping concentration, effectively increasing the number of exposed TiO2 particles. Mo addition enhanced anatase nucleation, recrystallization, and growth at lower doping concentrations (up to ≤ 0.10 wt%), thereby increasing crystallinity. However, increasing doping levels (> 0.10 wt%) appeared to exceed the solubility limit, resulting in supersaturation and significant lattice destabilization. Mo-doping also caused the Ti2p XPS peaks to shift to lower binding energies and the Mo3d peaks to shift to higher binding energies. These data are consistent with thermodynamically unstable Ti4+ → Ti3+ conversion and thermodynamically stable Mo5+ → Mo6+ conversion, which are interpreted in terms of intervalence charge transfer (IVCT), in which charge compensation is achieved through majority Ti4+ → Ti3+ reduction plus Mo5+ → Mo6+ oxidation. Ti3+ concentration also reflects a direct correlation with the Mo-doping concentration and resultant IVCT within the Mo solubility limit and a reverse effect upon supersaturation. There is a correlation with the Eg but this can be attributed to recrystallization rather than a semiconducting effect. No effect of midgap state formation from enhancement of the $$ {\text{V}}_{\text{O}}^{ \cdot \cdot } $$ concentration is expected because IVCT is a redox effect only and dissolution of Mo5+ or Mo6+ would generate Ti vacancies. The methylene blue dye degradation data exhibited the same trend but at a significant level (90.6% degradation), thus indicating that the mechanism dominating the photocatalytic performance is the recrystallization of the anatase and/or the modification of the semiconducting properties induced by Mo-doping, as indicated by the trends in band gap.

Novel one-step fabrication of highly ordered Mo-doped TiO2 nanotubes arrays with enhanced visible light catalytic activity

Doping with transition metals has been established as a promising approach for extending the absorption spectrum of TiO2 to the visible light region for enhancing its photocatalytic (PC) activity under visible light illumination. In this work, highly ordered Mo-doped TiO2 nanotubes arrays (Mo-TNTs) were fabricated by a facile in situ anodization of Ti in ethylene glycol/fluoride electrolyte using sodium molybdate as the molybdenum source. The doping levels (0.13–1.51 at.%) of Mo were conveniently adjusted by varying the initial concentrations of sodium molybdate and ammonium fluoride in the electrolyte. Various characterizations were performed to investigate the morphologies, crystal phases, elements’ valence states of the as-prepared samples. Results indicated that Mo6+ ions were successfully introduced into the lattice of anatase TiO2, forming isostructural substitution of Ti4+. Compared with undoped TNTs, the Mo-TNTs exhibited the obvious extension of absorption spectra to the visible light region, higher photoelectric conversion efficiency and lower recombination of photogenerated carriers. Meanwhile, their photoelectrochemical properties were also significantly affected by the doping level of Mo. Of all samples, 6Mo-TNTs (0.82 at.% Mo) showed the best photoelectrochemical performance and highest PC activity under visible light. This was mainly attributed to the synergetic contributions of the enhanced visible light absorption and suppressed recombination.

Synthesis of Mo-doped TiO2/reduced graphene oxide nanocomposite for photoelectrocatalytic applications

This study was carried out with the goal of lowering the band gap and electron recombination of the titanium dioxide through doping with Mo, and hybridizing with reduced graphene oxide, respectively, for photoelectrocatalytic applications. Mo with various atomic percentages (0.5, 1, 2, and 3 at%) was doped with TiO2 using the mechanical alloying technique. The results of the ultraviolet diffuse reflectance spectroscopy analysis revealed that the TiO2 doped with 1 at% Mo possessed the lowest band gap energy. Also, to further improve the photoelectrocatalytic efficiency, the 1 at% Mo-doped TiO2 powder was hybridized with the reduced graphene oxide (RGO) through UV-assisted photocatalytic reduction of the graphene oxide. The XRD, FESEM, EDX, and FTIR analyses were implemented for characterization of the TiO2, 1 at% Mo-doped TiO2, and 1 at% Mo-doped TiO2/RGO powders. The superior integration of the TiO2 and RGO was achieved as a result of the photocatalytic reduction method. After coating the powders on the fluorine-doped tin oxide (FTO) glass using the doctor blade technique, linear sweep voltammetry, amperometry, and electrochemical impedance spectroscopy tests were used to study the photoelectrocatalytic behavior of the samples. The results of the electrochemical tests showed that the photoelectrocatalytic activity of the TiO2 was significantly enhanced as doped with Mo, and hybridized with the RGO. The mechanisms affecting the photoelectrocatalytic response in the Mo-doped TiO2/RGO composite are discussed, as well.

Postillumination Activity in a Single-Phase Photocatalyst of Mo-Doped TiO2 Nanotube Array from Its Photocatalytic “Memory”

Several composite photocatalysts with photocatalytic “memory” effect had recently been developed, which could possess postillumination activity for an extended period of time in the dark for many potential applications. Here, a single-phase photocatalyst of Mo-doped TiO2 nanotube array was developed for the first time with the postillumination photocatalytic memory effect, which could eliminate the requirement of building composite photocatalysts with heterojunctions and largely broaden the material selection for this interesting photocatalytic memory effect. Because of the proper electronic band gap structure and variable valences of Mo dopants, photogenerated electrons could transfer from TiO2 to Mo dopants and be trapped there by reducing Mo6+ to Mo5+ under UV irradiation. When UV irradiation was switched off, these trapped electrons could be released from Mo dopants and react with O2 through the two-electron O2 reduction process to produce H2O2 in the dark. Thus, Mo-doped TiO2 nanotube array could remain active in the dark as demonstrated by its effective disinfection of Escherichia coli cells when UV irradiation was turned off. This work demonstrated that photocatalysts with postillumination photocatalytic memory effect were not limited to composite photocatalysts with heterojunctions. Various single-phase photocatalysts could also possess this interesting photocatalytic memory effect through doping metal elements with variable valences.

Solar light-assisted photocatalytic degradation of methylene blue with Mo/TiO2: a comparison with Cr- and Ni-doped TiO2

Highly active Cr-doped, Ni-doped and Mo-doped TiO2 photocatalysts were synthesized by a sol–gel method. The synthesized catalysts were characterized by UV–DRS, BET, XRD, FE-SEM–EDS, TEM and XPS. Metal doping decreased the band gap of TiO2 to 2.83 eV for Mo-doped TiO2 and Ni-doped TiO2. The activity of the synthesized photocatalysts was evaluated by studying the degradation of MB as a model pollutant under both UV and solar irradiation. The Mo/TiO2 catalyst achieved 98% degradation under solar light within 120 min. The activity of the catalysts was in the order Ni-doped TiO2 7 and followed pseudo-first order kinetics. Degradation by-products were analyzed on HR-LCMS and a mechanism is proposed.

Nano-sized Mo- and Nb-doped TiO2 as anode materials for high energy and high power hybrid Li-ion capacitors

Nano-sized Mo-doped titania (Mo0.1Ti0.9O2) and Nb-doped titania (Nb0.25Ti0.75O2) were directly synthesized via a continuous hydrothermal flow synthesis process. Materials characterization was conducted using physical techniques such as transmission electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, Brunauer–Emmett–Teller specific surface area measurements and energy dispersive x-ray spectroscopy. Hybrid Li-ion supercapacitors were made with either a Mo-doped or Nb-doped TiO2 negative electrode material and an activated carbon (AC) positive electrode. Cells were evaluated using electrochemical testing (cyclic voltammetry, constant charge discharge cycling). The hybrid Li-ion capacitors showed good energy densities at moderate power densities. When cycled in the potential window 0.5–3.0 V, the Mo0.1Ti0.9O2/AC hybrid supercapacitor showed the highest energy densities of 51 Wh kg−1 at a power of 180 W kg−1 with energy densities rapidly declining with increasing applied specific current. In comparison, the Nb0.25Ti0.75O2/AC hybrid supercapacitor maintained its energy density of 45 Wh kg−1 at 180 W kg−1 better, showing 36 Wh g−1 at 3200 W kg−1, which is a very promising mix of high energy and power densities. Reducing the voltage window to the range 1.0–3.0 V led to an increase in power density, with the Mo0.1Ti0.9O2/AC hybrid supercapacitor giving energy densities of 12 Wh kg−1 and 2.5 Wh kg−1 at power densities of 6700 W kg−1 and 14 000 W kg−1, respectively.

Enhanced photoelectric property of Mo-C codoped TiO2 films deposited by RF magnetron cosputtering

Mo-C codoped TiO2 films were prepared by RF magnetron cosputtering. Ultraviolet-visible spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray Analysis and X-Ray Diffraction were used to study the influences of codoping on energy gap, surface morphology, valence states of elements, ions content and crystal structure, respectively. The concentration of photogenerated carriers was measured by studying photocurrent density, while catalytic property was evaluated by observing degradation rate of methylene blue under visible light. A Mo-doped TiO2 film, whose content of Mo had been optimized in advance, was prepared and later used for subsequent comparisons with codoped samples. The result indicates that Mo-C codoping could curtail the energy gap and shift the absorption edge toward visible range. Under the illumination of visible light, codoped TiO2 films give rise to stronger photocurrent due to smaller band gaps. It is also found that Mo, C codoping results in a porous surface, whose area declines gradually with increasing carbon content. Carbon and Molybdenum doses were delicately optimized. Under the illumination of visible light, sample doped with 9.78at% carbon and 0.36at% Mo presents the strongest photocurrent which is about 8 times larger than undoped TiO2 films, and about 6 times larger than samples doped with Mo only.

W and Mo doped TiO2: Synthesis, characterization and photocatalytic activity

W-doped TiO2 and Mo-doped TiO2 photocatalysts were synthesized by EISA method and were characterized by different techniques. The photoactivity of these materials was evaluated by the degradation of 4-chlorophenol without oxygen supply. The catalysts exhibited only anatase crystalline phase and high specific surface areas of about 179m2g−1. The amount of dopant cations in TiO2 was a key parameter to increase the photoactivity. The results obtained show that with low dopant concentrations the degradation is improved, and this can be attributed to an increase in the lifetime of the photogenerated charges due to that dopant cations may easily trap electrons decreasing the recombination rate. Doped photocatalysts degraded 95% of 4CP, three times faster than Degussa P25. 69% reduction of total organic carbon (TOC) content was achieved by 1wt.% W-doping.

Mo-doped Gray Anatase TiO2: Lattice Expansion for Enhanced Sodium Storage

Gray-colored Mo6+-doped anatase TiO2 is prepared uniformly with particle size of 10–20nm, and is firstly employed as anode material in sodium-ion batteries (SIBs), presenting excellent electrochemical performances. It delivered reversible specific capacities of 231.8mAhg−1 at 0.1C (33.5mAg−1) after 100 cycles and 108.3mAhg−1 at 5C (1.68Ag−1), comparing to 170.5mAhg−1 at 0.1C and only 41.7mAhg−1 at 5C for the bare TiO2. The improved electrochemical performances might be beneficial from the doping of Mo6+, which can effectively enhance the conductivity of TiO2 resulting from induced conduction band electrons, interstitial oxygen defects and vacancies. In addition, the doping can also lead to the lattice expansion, which can facilitate the diffusion of Na+. In combination with natural abundance and environmental benignity, Mo6+-doped TiO2 can be expected to be utilized as an anode material for enhanced sodium storage.

Interplay between Molybdenum Dopant and Oxygen Vacancies in a TiO2 Support Enhances the Oxygen Reduction Reaction

In this study, molybdenum doping of anatase TiO2, used as a Pt catalyst support, both augments resistance against the carbon corrosion that commonly occurs in oxygen reduction reaction (ORR) Pt/C catalysts and promotes the generation of oxygen vacancies that allow better electron transfer from the nanosupport to Pt, thereby facilitating the oxygen dissociation reaction. The effects of the oxygen vacancies within the Mo-doped TiO2 nanosupport on ORR activity and stability are investigated both experimentally and by density functional theory analysis. The mass activity of Pt-supported molybdenum-doped anatase TiO2 is shown to be 9.1 times higher than that of a commercial standard Pt/C catalyst after hydrogen reduction. The oxide-supported nanocatalysts also show improved stability against Pt sintering under during cycling, because of strong metal–support interactions.

Magnetic properties of Mo–N co-doped TiO2 anatase nanotubes films

In this paper, the un-doped, Mo doped, N doped and Mo–N co-doped TiO2 nanotubes (TNTs) films were prepared by a two-step anodic oxidation method. The paper mainly investigated the origin of room temperature (RT) magnetic properties of all the samples. X-ray diffraction studies showed that the impurity of magnetic Mo atoms or N atoms were doped into anatase TiO2 lattices. It is revealed by the results of X-ray photoelectron spectroscopy and photoluminescence spectra that oxygen vacancies (Vos) exist. For all the samples the values of the saturation magnetizations (Ms) are in the order of Mo–N co-doped TiO2 > Mo-doped TiO2 > N-doped TiO2 > un-doped TiO2. Thus, the the Mo–N co-doped film achieved the highest RT Ms. The enhancement of the Ms origins from the cooperationg of the doping Vo, Mo and N. This progress provides some clues for the increase the saturation magnetization in TiO2-based dilute magnetic semiconductors at RT. The experiment results indicate that the Vos play a crucial role in RT ferromagnetic properties for TNTs films.

Synthesis of Mo-doped TiO2 nanowires/reduced graphene oxide composites with enhanced photodegradation performance under visible light irradiation

Mo-doped TiO2 nanowires/reduced graphene oxide composites with improved visible-light photocatalytic activity were first synthesized, the photocatalytic mechanism was also discussed.

Molybdenum-doped and anatase/rutile mixed-phase TiO2 nanotube photoelectrode for high photoelectrochemical performance

Molybdenum-doped TiO2 nanotube arrays (Mo-doped TiO2 NTs) photoelectrodes with anatase/rutile mixed phase are successfully fabricated via two-step anodization of titanium followed by a hydrothermal doping treatment process. The Mo-doped TiO2 NT material shows higher photocurrent density and enhanced incident photon to current conversion efficiency (IPCE) compared with the pristine TiO2 NTs for photoelectrochemical (PEC) water-splitting. The improvement of PEC response results from not only the increasing of oxygen vacancies and reducing of the recombination of photoexcited charges by Mo-doping, but also the new formed heterojunctions of anatase/rutile mixed-phase by hydrothermal treatment. Moreover, the Mo-doped TiO2 NTs show high stability and obvious visible absorption with considerable photocurrent density under visible light (λ > 420 nm).

Photocatalytic degradation of different chromophoric dyes in aqueous phase using La and Mo doped TiO2 hybrid carbon spheres

La and Mo-doped TiO2 coated carbon spheres have been synthesized using the hydrothermal method. The prepared materials were characterized by standard analytical techniques, X-ray diffraction (XRD), UV–Vis spectrophotometry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and Raman spectroscopy. The XRD and Raman spectroscopic analysis showed that the particles are in anatase phase. The EDX and SEM images showed that La/Mo-doped TiO2 are present on the surface of the carbon spheres. The photocatalytic activity of the synthesized particles were tested by studying the degradation of three different chromophoric dyes, i.e., Acid Yellow 29 (azo dye), Coomassie Brilliant Blue G250 (triphenylmethane dye) and Acid Green 25 (anthraquinone dye) as a function of time on irradiation in aqueous suspension. TiO2 particle with dopant concentration of 2.0% La and 1.5% Mo showed the highest photocatalytic activity as compared to the other dopant concentrations for the degradation of all the dyes under investigation.

Mo-doped TiO2 with enhanced visible light photocatalytic activity: a combined experimental and theoretical study.

In this paper, the effects of Mo doping on the geometrical, electronic, optical, and photocatalytic properties of TiO2 have been investigated theoretically and experimentally. The density functional theory based calculations show that Mo doping creates impurity states (Mo 4d) below the conduction band of TiO2 and the Fermi level is pinned inside the conduction band verifying n-type doping nature of the Mo in TiO2, which enhances its visible light absorption. Anatase TiO2 particles with Mo contents of 0.08, 0.1, 0.5, 1.0, 1.5 and, 2.0 at.% were synthesized by hydrothermal method without any post heat treatment for crystallization. Experiment results show that Mo ions have been successfully doped into the TiO2 lattice. The morphology of TiO2 particles is nearly spherical and the grain size is uniformly distributed as about 10 nm. Synthesized sample with 0.1 at.% Mo doping concentration shows the best visible light photocatalytic activity due to the reduced band gap and improved electron-hole pairs separation. However, the photocatalytic activity of the sample with 2.0 at.% Mo is relatively low although its visible light absorption is the best among the samples. The enhanced recombination of electron-hole pairs caused by the excessive Mo doping concentration may account for it.

Photocatalytic TiO2 and Doped TiO2 Coatings to Improve the Hygiene of Surfaces Used in Food and Beverage Processing—A Study of the Physical and Chemical Resistance of the Coatings

TiO2 coatings deposited using reactive magnetron sputtering and spray coating methods, as well as Ag- and Mo-doped TiO2 coatings were investigated as self-cleaning surfaces for beverage processing. The mechanical resistance and retention of the photocatalytic properties of the coatings were investigated over a three-month period in three separate breweries. TiO2 coatings deposited using reactive magnetron sputtering showed better mechanical durability than the spray coated surfaces, whilst the spray-deposited coating showed enhanced retention of photocatalytic properties. The presence of Ag and Mo dopants improved the photocatalytic properties of TiO2 as well as the retention of these properties. The spray-coated TiO2 was the only coating which showed light-induced hydrophilicity, which was retained in the coatings surviving the process conditions.

Electrical and Optical Properties of Nickel- and Molybdenum-Doped Titanium Dioxide Nanoparticle: Improved Performance in Dye-Sensitized Solar Cells

Nanocrystalline undoped and doped TiO2 particles with different concentrations of nickel and molybdenum (1-7%) was synthesized using the hydrothermal method followed by characterization using standard analytical techniques such as x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis spectroscopy. The XRD analysis shows no change in crystal structure of TiO2 after doping with different concentration of Ni and Mo which indicates the single phase polycrystalline material. The SEM analysis shows the partial crystalline nature of undoped and doped TiO2 and TEM analysis shows the particle size were in the range of 7-11 nm for Ni and 9-13 nm for Mo-doped TiO2. The electrical and photovoltaic properties of the undoped and newly synthesized Ni- and Mo-doped TiO2 were studied. The a.c. analysis shows that the dielectric constant e′ and dielectric loss tan δ decreases with increase in frequency and become independent at higher frequency ranges. The dielectric property decreases with increase in dopant concentration which provides the valuable information about conduction process. At low frequency, the mechanism of a.c. conductivity was found to be same as that of d.c. conduction. As the frequency increases, the magnitude of complex impedance decreases indicating the increase in a.c conductivity. It was observed that the impedance increases with the corresponding increase in the dopant concentration. Under simulated solar illumination with an optimum content of Ni and Mo involves in TiO2, the amount of dye absorption increases resulting in the gradual increase in photovoltaic current and hence improvement in the cell efficiency of dye-sensitized solar cell (DSSC) from 6.23 to 6.72% and 6.23 to 7.16% by increasing the dopant concentration of Ni and Mo from 0 to 5%, respectively, was achieved.