Tuning the Surface Structure of Nitrogen‐Doped TiO2 Nanofibres—An Effective Method to Enhance Photocatalytic Activities of Visible‐Light‐Driven Green Synthesis and Degradation

Nitrogen‐doped TiO₂ nanofibres of anatase and TiO₂(B) phases were synthesised by a reaction between titanate nanofibres of a layered structure and gaseous NH₃ at 400–700 °C, following a different mechanism than that for the direct nitrogen doping from TiO₂. The surface of the N‐doped TiO₂ nanofibres can be tuned by facial calcination in air to remove the surface‐bonded N species, whereas the core remains N doped. N‐Doped TiO₂ nanofibres, only after calcination in air, became effective photocatalysts for the decomposition of sulforhodamine B under visible‐light irradiation. The surface‐oxidised surface layer was proven to be very effective for organic molecule adsorption, and the activation of oxygen molecules, whereas the remaining N‐doped interior of the fibres strongly absorbed visible light, resulting in the generation of electrons and holes. The N‐doped nanofibres were also used as supports of gold nanoparticle (Au NP) photocatalysts for visible‐light‐driven hydroamination of phenylacetylene with aniline. Phenylacetylene was activated on the N‐doped surface of the nanofibres and aniline on the Au NPs. The Au NPs adsorbed on N‐doped TiO₂(B) nanofibres exhibited much better conversion (80 % of phenylacetylene) than when adsorbed on undoped fibres (46 %) at 40 °C and 95 % of the product is the desired imine. The surface N species can prevent the adsorption of O₂ that is unfavourable for the hydroamination reaction, and thus, improve the photocatalytic activity. Removal of the surface N species resulted in a sharp decrease of the photocatalytic activity. These photocatalysts are feasible for practical applications, because they can be easily dispersed into solution and separated from a liquid by filtration, sedimentation or centrifugation due to their fibril morphology.     

Synthesis and Studies of the Visible‐Light Photocatalytic Properties of Near‐Monodisperse Bi‐Doped TiO2 Nanospheres

Near‐monodisperse Bi‐doped anatase TiO₂ nanospheres with almost uniform diameters in the range of 117 to 87 nm were prepared simply by introducing different amounts of bismuth nitrate pentahydrate into the reaction system and subsequent calcinations. X‐ray diffraction, UV‐visible diffuse reflectance spectra, and X‐ray photoelectron spectroscopy confirm that the doped ions substitute some of the lattice titanium atoms, and furthermore, Bi³⁺ and Bi⁴⁺ ions coexist. All the Bi‐doped TiO₂ samples show much better photocatalytic activity than pure TiO₂ in the degradation of rhodamine B (RhB) under the irradiation of visible light (λ>420 nm), and, interestingly, it was found that the degradation mechanism is different from the conventional one, which has already been reported elsewhere. The detailed mechanism is discussed in this article.     

Tungsten and nitrogen co‐doped TiO2 nanobelts with significant visible light photoactivity

Tungsten and nitrogen co‐doped TiO₂ nanobelts (W/N‐TNBs) have been successfully synthesized via 1‐step hydrothermal method. The structure, morphology, and composition of prepared samples were characterized by X‐ray diffraction, scanning electron microscopy, and X‐ray photoelectron spectroscopy, respectively. The prominent phase of all as‐prepared samples is anatase crystal. For samples with N doping, new energy states can be introduced on top of O 2p states which reduced the band gap by 1.1 eV. The reduced band gap leads to efficient visible light activity. The 3%‐W/N‐TNBs were found to exhibit the highest activity. The photocatalytic performance of 3%‐W/N‐TNBs under visible light is about 4.8 times than that of pure TiO₂ nanobelts, which emphasizes the synergistic effect of W and N co‐doping for effectively inhibiting the recombination of photogenerated electrons and holes. In addition, our results testify the different redox potentials of the photoelectrons at different final states.     

The Critical Effect of Niobium Doping on the Formation of Mesostructured TiO2: Single‐Crystalline Ordered Mesoporous Nb‐TiO2 and Plate‐like Nb‐TiO2 with Ordered Mesoscale Dimples

Highly ordered mesoporous niobium‐doped TiO₂ with a single‐crystalline framework was prepared by using silica colloidal crystals with ca. 30 nm in diameter as templates. The preparation of colloidal crystals composed of uniform silica nanoparticles is a key to obtain highly ordered mesoporous Nb‐doped TiO₂. The XPS measurements of Nb‐doped TiO₂ showed the presence of Nb⁵⁺ and correspondingly Ti³⁺. With the increase in the amount of doped Nb, the crystalline phase of the product was converted from rutile into anatase, and the lattice spacings of both rutile and anatase phases increased. Surprisingly, the increase in the amount of Nb led to the formation of plate‐like TiO₂ with dimpled surfaces on one side, which was directly replicated from the surfaces of the colloidal silica crystals.     

Characterization and activity of visible-light-driven TiO2 photocatalyst codoped with nitrogen and cerium

Nitrogen and cerium codoped TiO₂ photocatalysts were prepared by a modified sol-gel process with doping precursors of cerium nitrate and urea, and characterized by X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray photoelectron spectra (XPS) and ultraviolet-visible light diffuse reflectance spectra (UV-vis DRS). Results indicate that anatase TiO₂ is the dominant crystalline type in as-prepared samples, and CeO₂ crystallites appear as the doping ratio of Ce/Ti reaches to 3.0 at%. The TiO₂ starts to transform from amorphous phase to anatase at 987.1 K during calcination, according to the TG-DSC curves. The XPS show that three major metal ions of Ce³⁺, Ce⁴⁺, Ti⁴⁺ and one minor metal ion of Ti³⁺ coexist on the surface. The codoped TiO₂ exhibits significant absorption within the range of 400-500 nm compared to the non-doped and only nitrogen-doped TiO₂. The enhanced photocatalytic activity of the codoped TiO₂ is demonstrated through degradation of methyl orange under visible light irradiation.     

Review on Undoped/Doped TiO2 Nanomaterial; Synthesis and Photocatalytic and Antimicrobial Activity

This review covers the various synthetic methods of doped and undoped TiO₂ nanomaterials, ranging from single‐doped and co‐doped to multidoped with transition‐metal ions, rare earth metal ions, and other metals and nonmetals ions. The effects of doping on the physiochemical propertiesas well as the photocatalytic and antimicrobial activities of TiO₂ nanomaterial are discussed. The results from the literature show that doping of TiO₂ shifts the absorption edge to the visible region as a result of the decrease in the bandgap due to the formation of new energy levels in the bandgap. The dopent also acts as a trapping center for electrons and holes, thereby reducing the recombination rate of charge carriers and increasing the photocatalytic and antimicrobial activity of TiO₂ nanomaterials. All multidoped TiO₂ nanomaterials show higher activity than their undoped, single‐doped, and co‐doped counterparts.     

Photocatalytic Activity of TiO2 Nanofibers with Doped La Prepared by Electrospinning Method

La‐TiO₂ nanofibers are prepared by a sol‐gel assisted electrospinning method. The structure and morphology of La‐TiO₂ nanofibers are characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis shows that the weight percentage of anatase and rutile in the 1.5 mol% La‐TiO₂ nanofibers calcined at 600 °C is about 8:2, which is similar to P‐25. The XRD data of La‐TiO₂ nanofibers with different La content shows that La³⁺ dopant has a great inhibition on TiO₂ phase transformation. The photocatalytic activity of the as‐prepared La‐TiO₂ nanofibers is evaluated by photocatalytic decolorization of Methylene Blue (MB) aqueous solution. The results show that the 1.5 mol% La‐TiO₂ nanofibers calcined at 600 °C exhibit high photocatalytic activity, indicating that 600 °C and 1.5 mol% are the appropriate calcination temperature and optimal molar ratio of La to Ti, respectively.     

Synthesis of Bi-doped TiO2 Nanotubes and Enhanced Photocatalytic Activity for Hydrogen Evolution from Glycerol Solution

Bi‐doped TiO₂ nanotubes with variable Bi/Ti ratios were synthesized by hydrothermal treatment in 10 mol·L^?1 NaOH (aq.) through using Bi‐doped TiO₂ particles derived from conventional sol‐gel method as starting materials. The effects of Bi content on the morphology, textural properties, photo absorption and photocatalytic activity of TiO₂ nanotubes were investigated. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) observations of the obtained samples revealed the formation of titanate nanotube structure doped with Bi, which exists as a higher oxidation state than Bi³⁺. Bi‐doping TiO₂ nanotubes exhibited an extension of light absorption into the visible region and improved photocatalytic activities for hydrogen production from a glycerol/water mixed solution as compared with pure TiO₂ nanotubes. There was an optimal Bi‐doped content for the photocatalytic hydrogen production, and high content of Bi would retard the phase transition of titanate to anatase and result in morphology change from nanotube to nanobelt, which in turn decreases the photocatlytic activity for hydrogen evolution.     

Synthesis,Structure, and Photoluminescence Properties of Novel KBaSc2(PO4)3:Ce3+/Eu2+/Tb3+ Phosphors for White‐Light‐Emitting Diodes

A series of novel KBaSc₂(PO₄)₃:Ce³⁺/Eu²⁺/Tb³⁺phosphors are prepared using a solid‐state reaction. X‐ray diffraction analysis and Rietveld structure refinement are used to check the phase purity and crystal structure of the prepared samples. Ce³⁺‐ and Eu²⁺‐doped phosphors both have broad excitation and emission bands, owing to the spin‐ and orbital‐allowed electron transition between the 4f and 5d energy levels. By co‐doping the KBaSc₂(PO₄)₃:Eu²⁺ and KBaSc₂(PO₄)₃:Ce³⁺ phosphors with Tb³⁺ ions, tunable colors from blue to green can be obtained. The critical distance between the Eu²⁺ and Tb³⁺ ions is calculated by a concentration quenching method and the energy‐transfer mechanism for Eu²⁺→Tb³⁺ is studied by utilizing the Inokuti–Hirayama model. In addition, the quantum efficiencies of the prepared samples are measured. The results indicate that KBaSc₂(PO₄)₃:Eu²⁺,Tb³⁺ and KBaSc₂(PO₄)₃:Ce³⁺,Tb³⁺ phosphors might have potential applications in UV‐excited white‐light‐emitting diodes.     

Photocatalytic degradation of organic compounds in aqueous systems by Fe and Ho codoped TiO<Subscript>2</Subscript>

Undoped, single-doped, and codoped TiO₂ nanoparticles were prepared by the sol-gel method and characterized with X-ray diffraction (XRD), the Brunauer-Emmett-Teller (BET)-specific surface area (S_BET), UV-Vis absorption spectra (UV-Vis), and X-ray photoelectron spectroscopy (XPS). Their photocatalytic activity was evaluated by methyl orange (MO) degradation in an aqueous suspension under UV or simulated solar light illumination. XRD showed that all samples calcined at 600°C preserved the anatase structure, and doping inhibited the increase of crystallite size. The BET result revealed that doping improved the surface area of TiO₂. UV-Vis indicated that Fe³⁺-doping broadened the absorption profile of TiO₂. XPS demonstrated that doping was advantageous to absorb more surface hydroxyl groups or chemisorbed water molecules. Photocatalytic degradation showed that the photocatalytic activity of TiO₂ codoped with Fe³⁺ and Ho³⁺ ions was markedly improved. This was ascribed to the fact that there was a cooperative action in the two doped elements. Fe³⁺-doping broadens the absorption profile, improves photo utilization of TiO₂, and then generates more electronhole pairs. Ho³⁺-doping restrains the increase in grain size and retards the recombination of photo-generated electrons and holes.     

New Insights into the Band‐Gap Narrowing of (N,P)‐Codoped TiO2 from Hybrid Density Functional Theory Calculations

The electronic properties of anatase‐TiO₂ codoped by N and P at different concentrations have been investigated via generalized Kohn–Sham theory with the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional for exchange‐correlation in the context of density functional theory. At high doping concentrations, we find that the high photocatalytic activity of (N, P)‐codoped anatase TiO₂ vis‐à‐vis the N‐monodoped case can be rationalized by a double‐hole‐mediated coupling mechanism [Yin et al., Phys. Rev. Lett. 2011, 106, 066801] via the formation of an effective N? P bond. On the other hand, Ti³⁺ and Ti⁴⁺ ions’ spin double‐exchange results in more substantial gap narrowing for larger separations between N and P atoms. At low doping concentrations, double‐hole‐coupling is dominant, regardless of the N? P distance.     

Transition metals Fe3+, Ni2+ modified titanium dioxide (TiO2) film sensors fabricated by CPT method to sense some toxic environmental pollutant gases

The present investigation deals synthesis of undoped TiO₂, Ni²⁺ doped TiO₂, and Fe³⁺ doped TiO₂ nanoparticles by low-cost co-precipitation (CPT) method. The thick film sensors of all the fabricated modified TiO₂ nanoparticles were designed by a screen printing strategy. The prepared thick film sensors were characterized by various sophisticated techniques. The structural parameters of undoped TiO₂ and modified TiO₂ film sensors were characterized by X-Ray Diffraction (XRD) which confirmed anatase phase of TiO₂ lattice. The surface morphological properties of all the prepared materials were confirmed by means of scanning electron microscope (SEM). The energy dispersive spectroscopy (EDS) confirms the elemental composition of all the prepared materials. High-Resolution Transmission Electron Microscopy (HR-TEM) was utilized to investigate the crystal lattice of fabricated TiO₂ material. The HR-TEM results revealed the anatase phase crystal morphology of prepared material. The prepared TiO₂ materials were also characterized by means of X-Ray photoelectron spectroscopy (XPS) to confirm the surface doping, specific biding energies, chemical states and elemental composition of modified TiO₂ materials. The Brunauer–Emmett–Teller (BET) study was carried to investigate the specific surface area of all the prepared sensors. The Fe³⁺ doped TiO₂ sensor found with enhanced surface area (83.10 ​m²/g) in comparison to Ni²⁺ doped TiO₂ and bare TiO₂ (67.34 ​m²/g). All the prepared materials were investigated for gas sensing characteristics. The NO₂, SO₂, and CO₂ gases were investigated for all the prepared sensors. The reusability test confirms that the Fe³⁺ doped TiO₂ is reproducible and stable sensor for long time repeated sensing of SO₂ and NO₂ vapors. Importantly, Fe³⁺ doped TiO₂ sensor showed rapid response and recovery towards SO₂ and NO₂ vapors.     

Enhanced and suppressed effects of ionic liquid on the photocatalytic activity of TiO2

The effects of a room temperature ionic liquid, 1-butyl-3-methylimidazolium terafluoroborate ([Bmim]BF₄), on the photocatalytic performance of Degussa P25 TiO₂ were investigated. Also, the photocatalysis mechanism was systematically analyzed by conducting different reactive radical trapping experiments. The results showed that photogenerated electrons were the main reactive species involved in the photocatalytic degradation of methyl orange (MO), while ?OH radicals and photogenerated holes played an important role in the photocatalytic decomposition of rhodamine B (RhB). The addition of ionic liquid (IL) could slightly enhance the photocatalytic degradation rate of MO because adsorption of [Bmim]⁺ ions on the TiO₂ surface not only enhanced traping and transfer of photogenerated electrons, but also facilitated adsorption of negatively charged MO. On the contrary, IL suppressed the degradation rate of RhB because [Bmim]⁺ on the TiO₂ surface not only hindered the access of positively charged RhB to TiO₂, but also restricted the diffusion of positively charged holes to the TiO₂/solution interface.     

Photodegradation of Rhodamine B on Sulfur Doped ZnO/TiO2 Nanocomposite Photocatalyst under Visible-light Irradiation

Sulfur doped ZnO/TiO₂ nanocomposite photocatalysts were synthesized by a facile sol‐gel method. The structure and properties of catalysts were characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), UV‐vis diffusive reflectance spectroscopy (DRS) and N₂ desorption‐adsorption isotherm. The XRD study showed that TiO₂ was anatase phase and there was no obvious difference in crystal composition of various S‐ZnO/TiO₂. The XPS study showed that the Zn element exists as ZnO and S atoms form SO^2?₄. The prepared samples had mesoporosity revealed by N₂ desorption‐adsorption isotherm result. The degradation of Rhodamine B dye under visible light irradiation was chosen as probe reaction to evaluate the photocatalytic activity of the ZnO/TiO₂ nanocomposite. The commercial TiO₂ photocatalyst (Degussa P25) was taken as standard photocatalyst to contrast the prepared different photocatalyst in current work. The improvement of the photocatalytic activity of S‐ZnO/TiO₂ composite photocatalyst can be attributed to the suitable energetic positions between ZnO and TiO₂, the acidity site caused by sulfur doping and the enlargement of the specific area. S‐3.0ZnO/TiO₂ exhibited the highest photocatalytic activity under visible light irradiation after Zn amount was optimized, which was 2.6 times higher than P25.     

Photocatalytic Activity of High Aspect Ratio TiO2 Nanorods

In this article, TiO₂ nanorods (aspect ratio >20) were prepared through a polyol process and doped with metal ions (Cu²⁺, Ni²⁺, Fe³⁺, and Cr³⁺). Compared with TiO₂ nanoparticles, the TiO₂ nanorods displayed relatively higher photocatalytic activity for the degradation of copper sulfophthalocyanine. Moreover, the photocatalytic activity was greatly enhanced when the metal ions were doped in the TiO₂ nanorods.     

Preparation and Characterization of Bismuth Doped TiO2 Thin Films

A series of Bismuth-doped titanium oxide (Bi-doped TiO₂) thin films on glass substrates have been prepared by sol-gel dip coating process. The prepared catalysts were characterized by XRD and XPS. The photocatlytic activity of the thin film catalysts was evaluated through the photodegradation of aqueous methyl orange under UV illumination. The experiments demonstrated that the Bi-doped TiO₂ prepared was anatase phase. The doped bismuth was in the 3⁺ oxidation state. The presence of Bi significantly enhanced the photocatalytic activity of TiO₂ films. At calcination temperature of 500°C, with doping concentration of 2 wt %, Bi-doped TiO₂ thin film showed the highest photocatalyic activity.     

Zr离子掺杂TiO2可见光催化剂光催化活性的研究

本文采用溶胶-凝胶法制备了Zr离子掺杂TiO₂光催化剂。光催化降解对氯苯酚实验表明,Zr离子掺杂浓度为10%时活性最高,其紫外光、可见光催化活性分别是纯TiO₂的1.5倍和4倍。利用XRD、Raman、XPS、UV-Vis DRS、PL等技术对样品进行了表征,结果表明：Zr离子以取代式掺杂方式进入TiO₂晶格,在TiO₂导带下方形成掺杂能级,增强了可见光响应,促进了光生载流子的分离,此外Zr离子掺杂在催化剂表面引入大量表面缺陷,增加了表面羟基物种,从而使得Zr离子掺杂TiO₂光催化剂的紫外、可见光催化活性显著提高。     

First‐principles calculation of electronic structure of V‐doped anatase TiO2

The energetic and electronic structures of V‐doped anatase TiO₂ have been investigated systematically by the GGA+U approach, including replacement of Ti by V in the absence and presence of oxygen vacancies and the presence of an interstitial site. It was found that V should exist as a V⁴⁺ ion in the replacement of Ti in the anatase lattice, the electron transitions of which to the conduction band from V 3d states are responsible for the experimentally observed visible light absorption. The influence of V dopant concentration on the electronic and magnetic properties is also discussed, such as the influence of the U value in systems containing oxygen vacancies and spin flip phenomena for interstitial V‐doping.     

Enhanced Photoreversible Color Switching of Redox Dyes Catalyzed by Barium‐Doped TiO2 Nanocrystals

Colloidal barium‐doped TiO₂ nanocrystals have been developed that enable the highly reversible light‐responsive color switching of redox dyes with excellent cycling performance and high switching rates. Oxygen vacancies resulting from the Ba doping serve as effective sacrificial electron donors (SEDs) to scavenge the holes photogenerated in TiO₂ nanocrystals under UV irradiation and subsequently promote the reduction of methylene blue to its colorless leuco form. Effective color switching can therefore be realized without relying on external SEDs, thus greatly increasing the number of switching cycles. Ba doping can also accelerate the recoloration under visible‐light irradiation by shifting the absorption edge of TiO₂ nanocrystals to a shorter wavelength. Such a system can be further casted into a solid film to produce a rewritable paper on which letters and patters can be repeatedly printed using UV light and then erased by heating; this process can be repeated for many cycles and does not require additional inks.     

Methanol Conversion into Dimethyl Ether on the Anatase TiO2(001) Surface

Exploring reactions of methanol on TiO₂ surfaces is of great importance in both C1 chemistry and photocatalysis. Reported herein is a combined experimental and theoretical calculation study of methanol adsorption and reaction on a mineral anatase TiO₂(001)‐(1×4) surface. The methanol‐to‐dimethyl ether (DME) reaction was unambiguously identified to occur by the dehydration coupling of methoxy species at the fourfold‐coordinated Ti⁴⁺ sites (Ti_4c), and for the first time confirms the predicted higher reactivity of this facet compared to other reported TiO₂ facets. Surface chemistry of methanol on the anatase TiO₂(001)‐(1×4) surface is seldom affected by co‐chemisorbed water. These results not only greatly deepen the fundamental understanding of elementary surface reactions of methanol on TiO₂ surfaces but also show that TiO₂ with a high density of Ti_4c sites is a potentially active and selective catalyst for the important methanol‐to‐DME reaction.