Molecular Design Strategy for Ordered Mesoporous Stoichiometric Metal Oxide

A molecular design strategy is used to construct ordered mesoporous Ti³⁺‐doped Li₄Ti₅O₁₂ nanocrystal frameworks (OM‐Ti³⁺‐Li₄Ti₅O₁₂) by the stoichiometric cationic coordination assembly process. Ti⁴⁺/Li⁺‐citrate chelate is designed as a new molecular precursor, in which the citrate can not only stoichiometrically coordinate Ti⁴⁺ with Li⁺ homogeneously at the atomic scale, but also interact strongly with the PEO segments in the Pluronic F127. These features make the co‐assembly and crystallization process more controllable, thus benefiting for the formation of the ordered mesostructures. The resultant OM‐Ti³⁺‐Li₄Ti₅O₁₂ shows excellent rate (143 mAh g^?1 at 30 C) and cycling performances (<0.005 % fading per cycle). This work could open a facile avenue to constructing stoichiometric ordered mesoporous oxides or minerals with highly crystalline frameworks.     

Novel synthesis of high-surface-area ordered mesoporous TiO2 with anatase framework for photocatalytic applications

Ordered mesoporous TiO₂ materials with an anatase frameworks have been synthesized by using a cationic surfactant cetyltrimethylammonium bromide (C₁₆TMABr) as a structure-directing agent and soluble peroxytitanates as Ti precursor through a self-assembly between the positive charged surfactant S⁺ and the negatively charged inorganic framework I^? (S⁺I^? type). The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO₂ materials indicates a hexagonal mesostructure. XRD and transmission electron microscopy results and nitrogen adsorption–desorption isotherms measurements indicate that the calcined mesoporous TiO₂ possesses an anatase crystalline framework having a maximum pore size of 6.9 nm and a maximum Brunauer–Emmett–Teller specific surface area of 284 m² g^?1. This ordered mesoporous anatase TiO₂ also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation.     

Surface Plasmon Resonance‐Enhanced Visible‐NIR‐Driven Photocatalytic and Photothermal Catalytic Performance by Ag/Mesoporous Black TiO2 Nanotube Heterojunctions

Ag/mesoporous black TiO₂ nanotubes heterojunctions (Ag‐MBTHs) were fabricated through a surface hydrogenation, wet‐impregnation and photoreduction strategy. The as‐prepared Ag‐MBTHs possess a relatively high specific surface area of ≈85 m² g^?1 and an average pore size of ≈13.2 nm. The Ag‐MBTHs with a narrow band gap of ≈2.63 eV extend the photoresponse from UV to the visible‐light and near‐infrared (NIR) region. They exhibit excellent visible‐NIR‐driven photothermal catalytic and photocatalytic performance for complete conversion of nitro aromatic compounds (100 %) and mineralization of highly toxic phenol (100 %). The enhancement can be attributed to the mesoporous hollow structures increasing the light multi‐refraction, the Ti³⁺ in frameworks and the surface plasmon resonance (SPR) effect of plasmonic Ag nanoparticles favoring light‐harvesting and spatial separation of photogenerated electron–hole pairs, which is confirmed by transient fluorescence. The fabrication of this SPR‐enhanced visible‐NIR‐driven Ag‐MBTHs catalyst may provide new insights for designing other high‐performance heterojunctions as photocatalytic and photothermal catalytic nanomaterials.     

Carbon‐Dot‐Sensitized,Nitrogen‐Doped TiO2 in Mesoporous Silica for Water Decontamination through Nonhydrophobic Enrichment–Degradation Mode

Mesoporous silica synthesized from the cocondensation of tetraethoxysilane and silylated carbon dots containing an amide group has been adopted as the carrier for the in situ growth of TiO₂ through an impregnation–hydrothermal crystallization process. Benefitting from initial complexation between the titania precursor and carbon dot, highly dispersed anatase TiO₂ nanoparticles can be formed inside the mesoporous channel. The hybrid material possesses an ordered hexagonal mesostructure with p6mm symmetry, a high specific surface area (446.27 m² g^?1), large pore volume (0.57 cm³ g^?1), uniform pore size (5.11 nm), and a wide absorption band between λ=300 and 550 nm. TiO₂ nanocrystals are anchored to the carbon dot through Ti?O?N and Ti?O?C bonds, as revealed by X‐ray photoelectron spectroscopy. Moreover, the nitrogen doping of TiO₂ is also verified by the formation of the Ti?N bond. This composite shows excellent adsorption capabilities for 2,4‐dichlorophenol and acid orange 7, with an electron‐deficient aromatic ring, through electron donor–acceptor interactions between the carbon dot and organic compounds instead of the hydrophobic effect, as analyzed by the contact angle analysis. The composite can be photocatalytically recycled through visible‐light irradiation after adsorption. The narrowed band gap, as a result of nitrogen doping, and the photosensitization effect of carbon dots are revealed to be coresponsible for the visible‐light activity of TiO₂. The adsorption capacity does not suffer any clear losses after being recycled three times.     

Improvement of the Visible‐Light Photocatalytic Performance of TiO2 by Carbon Mesostructures

An improvement in the photodegradation performance for dyes due to interaction between carbon and titania in a self‐assembled mesoporous C? TiO₂ composite catalyst, even for the difficult degradation of azo dyes, is reported herein. The dye removal process involves adsorption of the dye from water by the mesoporous carbon–titania, followed by photodegradation on the separated dye‐loaded solid. Such adsorption–catalysis cycles can be carried out more than 80 times without discernible loss of photocatalytic activity or the anatase content of the composite. In each run, about 120 mg dye per g catalyst can be degraded. The mesoporous carbon–titania catalyst also exhibits a high capacity for converting methyl orange in aqueous solution under visible light. Characterization by XRD, TEM, and N₂ sorption techniques has revealed that the self‐assembled composite catalyst has an ordered mesostructure, uniform mesopores (4.3 nm), a large pore volume (0.30 cm³ g^?1), and a high surface area (348 m² g^?1). The pore walls are composed of amorphous carbon and anatase nanoparticles of size 4.2 nm, which are well dispersed and confined. X‐ray photoelectron spectroscopy (XPS), surface photovoltage spectroscopy (SPS), and UV/Vis absorption results indicate doping of carbon into the anatase lattice and a change in the bandgap of the semiconductor. The synergistic improvement in the composite catalyst can be attributed to the following features: (1) carbon doping of the anatase lattice modifies its bandgap and enhances its activity under visible light; (2) confinement within carbon pore walls prevents aggregation of tiny anatase nanoparticles, improving their activity and stability; (3) the mesopores provide a confined space for photocatalysis; and (4) the strong adsorption ability of porous carbon for organic substances ensures that large quantities can be processed and inhibits further diffusion of the adsorbed organic substances, thereby enhancing the mineralization on anatase.     

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.     

In Situ Preparation of a Ti3+ Self‐Doped TiO2 Film with Enhanced Activity as Photoanode by N2H4 Reduction

A new synthetic method to fabricate Ti³⁺‐modified, highly stable TiO₂ photoanodes for H₂O oxidation is reported. With Ti foil as both the conducting substrate and the Ti³⁺/Ti⁴⁺ source, one‐dimensional blue Ti³⁺/TiO₂ crystals were grown by a one‐step hydrothermal reaction. The concentration of Ti³⁺ was further tuned by N₂H₄ reduction, leading to a greater photoelectrocatalytic activity, as evidenced by a high photocurrent density of 0.64 mA cm^?2 at 1.0 V vs RHE under simulated AM 1.5 G illumination. Electron paramagnetic resonance and Mott–Schottky plots reveal that higher charge‐carrier density owing to N₂H₄ reduction contributes to the observed improvement. The generality of this synthesis method was demonstrated by its effectiveness in improving the performance of other types of photoanodes. By integrating the advantages of the 1D TiO₂ architecture with those of Ti³⁺ self‐doping, this work provides a versatile tool toward the fabrication of efficient TiO₂ photoanodes.     

Highly Ordered Mesoporous Few‐Layer Graphene Frameworks Enabled by Fe3O4 Nanocrystal Superlattices

While great progress has been achieved in the synthesis of ordered mesoporous carbons in the past decade, it still remains a challenge to prepare highly graphitic frameworks with ordered mesoporosity and high surface area. Reported herein is a simple synthetic methodology, based on the conversion of self‐assembled superlattices of Fe₃O₄ nanocrystals, to fabricate highly ordered mesoporous graphene frameworks (MGFs) with ultrathin pore walls consisting of three to six stacking graphene layers. The MGFs possess face‐centered‐cubic symmetry with interconnected mesoporosity, tunable pore width, and high surface area. Because of their unique architectures and superior structural durability, the MGFs exhibit excellent cycling stability and rate performance when used as anode materials for lithium‐ion batteries, thus retaining a specific capacity of 520 mAh g^?1 at a current density of 300 mA g^?1 after 400 cycles.     

Hierarchical Activated Mesoporous Phenolic‐Resin‐Based Carbons for Supercapacitors

A series of hierarchical activated mesoporous carbons (AMCs) were prepared by the activation of highly ordered, body‐centered cubic mesoporous phenolic‐resin‐based carbon with KOH. The effect of the KOH/carbon‐weight ratio on the textural properties and capacitive performance of the AMCs was investigated in detail. An AMC prepared with a KOH/carbon‐weight ratio of 6:1 possessed the largest specific surface area (1118 m² g^?1), with retention of the ordered mesoporous structure, and exhibited the highest specific capacitance of 260 F g^?1 at a current density of 0.1 A g^?1 in 1 M H₂SO₄ aqueous electrolyte. This material also showed excellent rate capability (163 F g^?1 retained at 20 A g^?1) and good long‐term electrochemical stability. This superior capacitive performance could be attributed to a large specific surface area and an optimized micro‐mesopore structure, which not only increased the effective specific surface area for charge storage but also provided a favorable pathway for efficient ion transport.     

Sulfur and Ti3+ co‐Doping of TiO2 Nanotubes Enhance Photocatalytic H2 Evolution Without the Use of Any co‐catalyst

TiO₂ nanotubes were successfully co‐doped with sulfur and Ti³⁺ states using a facile annealing treatment in H₂/H₂S gas mixture. The obtained nanotubes were investigated for their photocatalytic performance and characterized by SEM, XRD, XPS, EPR, IPCE, IMPS and Mott‐Schottky measurements. The synthesized co‐doped TiO₂ nanotubes show an enhanced photocatalytic hydrogen production rate compared to tubes that were treated only in pure H₂ or H₂S atmosphere—this without the presence of any co‐catalyst. It was found that sulfur in co‐doped TiO₂ exists in the form of S^2? and a small quantity of S⁴⁺/S⁶⁺, which leads to a narrowing of the band gap. However, the enhanced absorption of light in the visible range is not the key reason for the improved photocatalytic performance. We ascribe the enhanced photocatalytic activity to a synergetic effect of S mid‐gap states and disordered Ti³⁺ defects that facilitate photo generated electron transfer.     

Probing the Electronic Structure and Photoactivation Process of Nitrogen‐Doped TiO2 Using DRS,PL, and EPR

The electronic structure and photoactivation process in N‐doped TiO₂ is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat‐ and photoinduced N‐doped TiO₂ catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti³⁺ states are formed to enhance the optical absorption in the visible‐light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N‐doped TiO₂, the DRS absorption and PL emission in the visible spectral region of 450–700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N_s^.), oxygen vacancies with one electron (V_o^.), and Ti³⁺ ions are produced with light irradiation and the intensity of N_s^. species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO₂ corresponding to the main absorption band at 410 nm of N‐doped TiO₂, but oxygen vacancies and Ti³⁺ states as defects contribute to the visible‐light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N‐doped TiO₂ is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen‐vacancy‐related defects leads to quenching of paramagnetic N_s^. species but they stabilize the active nitrogen species N_s^?.     

Reduced Graphene Oxide‐Supported TiO2 Fiber Bundles with Mesostructures as Anode Materials for Lithium‐Ion Batteries

Although the synthesis of mesoporous materials is well established, the preparation of TiO₂ fiber bundles with mesostructures, highly crystalline walls, and good thermal stability on the RGO nanosheets remains a challenge. Herein, a low‐cost and environmentally friendly hydrothermal route for the synthesis of RGO nanosheet‐supported anatase TiO₂ fiber bundles with dense mesostructures is used. These mesostructured TiO₂‐RGO materials are used for investigation of Li‐ion insertion properties, which show a reversible capacity of 235 mA h g^?1 at 200 mA g^?1 and 150 mA h g^?1 at 1000 mA g^?1 after 1000 cycles. The higher specific surface area of the new mesostructures and high conductive substrate (RGO nanosheets) result in excellent lithium storage performance, high‐rate performance, and strong cycling stability of the TiO₂‐RGO composites.     

Nitridated mesoporous Li4Ti5O12 spheres for high-rate lithium-ion batteries anode material

Nitridated mesoporous Li₄Ti₅O₁₂ spheres were synthesized by a simple ammonia treatment of Li₄Ti₅O₁₂ derived from mesoporous TiO₂ particles and lithium acetate dihydrate via a solid state reaction in the presence of polyethylene glycol 20000. The carbonization of polyethylene glycol could effectively restrict the growth of primary particles, which was favorable for lithium ions diffusing into the nanosized TiO₂ lattice during the solid state reaction to form a pure phase Li₄Ti₅O₁₂. After a subsequent thermal nitridation treatment, a high conductive thin TiO _x N _y layer was in situ constructed on the surface of the primary nanoparticles. As a result, the nitridated mesoporous Li₄Ti₅O₁₂ structure, possessing shorter lithium-ion diffusion path and better electrical conductivity, displays significantly improved rate capability. The discharge capacity reaches 138 mAh?g^?1 at 10 C rate and 120 mAh?g^?1 at 20 C rate in the voltage range of 1–3 V.     

Mesoporous Spherical Li4Ti5O12 as High‐Performance Anodes for Lithium‐Ion Batteries

Porous microspherical Li₄Ti₅O₁₂ aggregates (LTO‐PSA) can be successfully prepared by using porous spherical TiO₂ as a titanium source and lithium acetate as a lithium source followed by calcinations. The synthesized LTO‐PSA possess outstanding morphology, with nanosized, porous, and spherical distributions, that allow good electrochemical performances, including high reversible capacity, good cycling stability, and impressive rate capacity, to be achieved. The specific capacity of the LTO‐PSA at 30 C is as high as 141 mA h g^?1, whereas that of normal Li₄Ti₅O₁₂ powders prepared by a sol–gel method can only achieve 100 mA h g^?1. This improved rate performance can be ascribed to small Li₄Ti₅O₁₂ nanocrystallites, a three‐dimensional mesoporous structure, and enhanced ionic conductivity.     

Direct synthesis of Nd3+ doped mesoporous TiO2 and investigation of its photocatalytic performance

Nd³⁺ doped mesoporous TiO₂ samples with different molar ratio of Nd/Ti were synthesized by a sol?Cgel method. The textural and optical properties of the samples were systematical characterized by X-ray diffraction, transmission electron microscopy, N₂ adsorption?Cdesorption isotherms, Fourier transform infrared spectroscopy and UV?CVisible absorbance spectroscopy. It was revealed that Nd³⁺ doping inhibited the phase transformation from anatase to rutile after calcination, and the mesoporous structure of doped samples was still retained with the increase of Nd/Ti molar ratio. The surface area of the samples varied from 137 to 210 m²g^?1 and the average pore size of them ranged between 5.7 and 8.2?nm. The photocatalytic activities of all the samples were evaluated by degradation methyl orange (MO) in aqueous solution as a model reaction under UV light irradiation. The results showed that the doped samples demonstrated a higher photocatalytic activity than the mesoporous TiO₂, and the 3?mol% Nd³⁺ doped mesoporous TiO₂ exhibited the best photocatalytic performance. Meanwhile, a promotion effect of the H₂O₂ added was verified in the degradation of MO.     

后处理法合成高热稳定性的中孔Ti-P-Al材料

 以阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为模板剂,采用水热合成法制备了中孔氧化钛原粉,再采用磷酸和氯化铝溶液依次对中孔氧化钛原粉进行后处理,得到了具有高热稳定性的中孔Ti-P-Al材料. 通过粉末X射线衍射、透射电子显微镜和氮物理吸附等方法对样品进行了表征. 结果表明,反应凝胶组成对样品的中孔结构有较大的影响,当反应凝胶配比为Ti(SO4)2∶CTAB∶H2O=1∶0.54∶430, 温度为363 K, 处理时间为10～20 min时,所得的TiO2原粉具有较规整的中孔结构. 此样品经过0.25 mol/L的磷酸处理后有序性有较大程度的提高. 将磷酸处理过的样品进一步用氯化铝溶液处理,得到了中孔结构的Ti-P-Al材料,此材料经过873 K焙烧后仍具有典型的中孔特征,其比表面积为 382 m2/g, 孔径为3.13 nm.     

Synthesis of Mesoporous Wall‐Structured TiO2 on Reduced Graphene Oxide Nanosheets with High Rate Performance for Lithium‐Ion Batteries

Mesoporous wall‐structured TiO₂ on reduced graphene oxide (RGO) nanosheets were successfully fabricated through a simple hydrothermal process without any surfactants and annealed at 400 °C for 2 h under argon. The obtained mesoporous structured TiO₂–RGO composites had a high surface area (99 0307 m² g^?1) and exhibited excellent electrochemical cycling (a reversible capacity of 260 mAh g^?1 at 1.2 C and 180 mAh g^?1 at 5 C after 400 cycles), demonstrating it to be a promising method for the development of high‐performance Li‐ion batteries.     

Highly Crystalline Mesoporous C60 with Ordered Pores: A Class of Nanomaterials for Energy Applications

Highly ordered mesoporous C₆₀ with a well‐ordered porous structure and a high crystallinity is prepared through the nanohard templating method using a saturated solution of C₆₀ in 1‐chloronaphthalene (51 mg mL^?1) as a C₆₀ precursor and SBA‐15 as a hard template. The high solubility of C₆₀ in 1‐chloronaphthalene helps not only to encapsulate a huge amount of the C₆₀ into the mesopores of the template but also supports the oligomerization of C₆₀ and the formation of crystalline walls made of C₆₀. The obtained mesoporous C₆₀ exhibits a rod‐shaped morphology, a high specific surface area (680 m² g^?1), tuneable pores, and a highly crystalline wall structure. This exciting ordered mesoporous C₆₀ offers high supercapacitive performance and a high selectivity to H₂O₂ production and methanol tolerance for ORR. This simple strategy could be adopted to make a series of mesoporous fullerenes with different structures and carbon atoms as a new class of energy materials.     

Highly Ordered Mesoporous Tungsten Oxides with a Large Pore Size and Crystalline Framework for H2S Sensing

An ordered mesoporous WO₃ material with a highly crystalline framework was synthesized by using amphiphilic poly(ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) diblock copolymers as a structure‐directing agent through a solvent‐evaporation‐induced self‐assembly method combined with a simple template‐carbonization strategy. The obtained mesoporous WO₃ materials have a large uniform mesopore size (ca. 10.9 nm) and a high surface area (ca. 121 m² g^?1). The mesoporous WO₃‐based H₂S gas sensor shows an excellent performance for H₂S sensing at low concentration (0.25 ppm) with fast response (2 s) and recovery (38 s). The high mesoporosity and continuous crystalline framework are responsible for the excellent performance in H₂S sensing.     

Highly Efficient Low‐Temperature Plasma‐Assisted Modification of TiO2 Nanosheets with Exposed {001} Facets for Enhanced Visible‐Light Photocatalytic Activity

Anatase TiO₂ nanosheets with exposed {001} facets have been controllably modified under non‐thermal dielectric barrier discharge (DBD) plasma with various working gas, including Ar, H₂, and NH₃. The obtained TiO₂ nanosheets possess a unique crystalline core/amorphous shell structure (TiO₂@TiO_2?x), which exhibit the improved visible and near‐infrared light absorption. The types of dopants (oxygen vacancy/surface Ti³⁺/substituted N) in oxygen‐deficient TiO₂ can be tuned by controlling the working gases during plasma discharge. Both surface Ti³⁺ and substituted N were doped into the lattice of TiO₂ through NH₃ plasma discharge, whereas the oxygen vacancy or Ti³⁺ (along with the oxygen vacancy) was obtained after Ar or H₂ plasma treatment. The TiO₂@TiO_2?x from NH₃ plasma with a green color shows the highest photocatalytic activity under visible‐light irradiation compared with the products from Ar plasma or H₂ plasma due to the synergistic effect of reduction and simultaneous nitridation in the NH₃ plasma.