Zhenfeng Bian

Solvothermally controllable synthesis of anatase TiO2 nanocrystals with dominant {001} facets and enhanced photocatalytic activity

A new non-hydrolytic approach was developed to synthesize anatase TiO2 nanocrystals with dominant {001} facets by solvothermal alcoholysis of TiF4, which was relatively green since the direct use of HF was avoided and less HF released from alcoholysis. These TiO2 nanocrystals displayed uniform shape and could be easily controlled owing to the smooth alcoholysis process. Using tert-butanol as the initial alcohol source, the total surface area was 103 m2 g−1 with small crystal sizes around 23 nm. By changing different alcohols, both the percentage of exposed {001} facets and the particle size could be adjusted. The results show that alcohols play important roles in the present strategy (1) oxygen donor to provide mild condition for crystal growth and (2) assistant agent to stabilize F species for dominant {001} facets. In further application, the absolute surface area of the {001} facets, instead of total surface area, has become the most important factor for influencing the activity of TiO2 crystals under photocatalytic selective oxidation of toluene to benzaldehyde.

Pseudocapacitive Sodium Storage in Mesoporous Single-Crystal-like TiO2–Graphene Nanocomposite Enables High-Performance Sodium-Ion Capacitors

Sodium-ion capacitors can potentially combine the virtues of high power capability of conventional electrochemical capacitors and high energy density of batteries. However, the lack of high-performance electrode materials has been the major challenge of sodium-based energy storage devices. In this work, we report a microwave-assisted synthesis of single-crystal-like anatase TiO2 mesocages anchored on graphene as a sodium storage material. The architecture of the nanocomposite results in pseudocapacitive charge storage behavior with fast kinetics, high reversibility, and negligible degradation to the micro/nanostructure. The nanocomposite delivers a high capacity of 268 mAh g-1 at 0.2 C, which remains 126 mAh g-1 at 10 C for over 18 000 cycles. Coupling with a carbon-based cathode, a full cell of sodium-ion capacitor successfully demonstrates a high energy density of 64.2 Wh kg-1 at 56.3 W kg-1 and 25.8 Wh kg-1 at 1357 W kg-1, as well as an ultralong lifespan of 10 000 cycles with over 90% of capacity retention.

Single-Crystal-like Titania Mesocages†

Titania represents the most widely used oxide semiconductor for photocatalysts and photovoltaics, and its performance is heavily governed by its surface area and the exposed crystal planes. To date, however, as-made TiO2 samples have been limited to the single crystals with low surface area or porous polycrystals exposing their less-active planes. We report herein the synthesis of high-surface-area, singlecrystal-like anatase with controlled mesoporous network and preferential exposure of the highly active (001) planes. This simple solution-growth method is readily extendable to the synthesis of other mesoporous single crystals beyond TiO2, providing a new class of materials for catalysis, energy storage and conversion, and other applications. The photocatalytic activity of TiO2 is generally dependent on its crystallography. For example, the (001) planes of anatase are much more active than the (101) planes, which are the most commonly observed and thermodynamically more stable crystalline planes in the anatase form. Significant effort has therefore been devoted to synthesize TiO2 crystals with preferential (001) plane exposure. As well as crystallographic control, equally important is building networks of pores within the crystals to increase the surface area and provide pore-dependent activity and selectivity. To date, although a large number of porous TiO2 have been made using sol–gel and softor hard-templating approaches, 8, 21,23–25] the current materials are limited to porous TiO2 with amorphous or polycrystalline frameworks that exhibit low photocatalytic activity and charge-transport capability. Herein, using a method of crystal oriented growth, we report the synthesis of highly active mesoporous, singlecrystal-like TiO2 (mesocages) with both preferential (001) plane exposure and controllable mesoporous networks. As illustrated in Figure 1, we started with precursor solutions containing SO4 2 ; solvothermal reactions generate TiO2 building crystals of which the (001) planes are preferably

Multitemplates for the Hierarchical Synthesis of Diverse Inorganic Materials

Described here is a new and highly general strategy for multiple-template (multitemplate) patterning. This process is significant because it allows us to create various unusual shapes such as solid spheres, yolk-shell spheres, flowerlike particles, and structured nanocomponents. Alcoholysis of the metal-organic precursors with mixtures of glycerol and various amounts of ethanol followed by calcination yields oxides. The glycerol plays the dual role of hierarchically assembling the metal-organic composites and stabilizing the structures during the subsequent conversions. Furthermore, we demonstrate for the first time that these metal-organic composites can be converted into oxides, nitrides, and highly graphitized carbon nanostructures. We show that these yolk-shell structures display superior photocatalytic activity and electrochemical properties.

Ordered mesoporous TiO2 with exposed (001) facets and enhanced activity in photocatalytic selective oxidation of alcohols

Single-crystal TiO2 with 2D and 3D ordered mesoporous structures and exposed (001) facets were synthesized by SBA-15 or KIT-6 templated alcoholysis of TiOSO4 under solvothermal conditions. In the liquid phase photocatalytic selective oxidation of alcohols to aldehydes under UV-light irradiation, the single-crystal TiO2 exhibited much higher activity than the polycrystalline TiO2, since the high crystallization degree favored the transfer of photoelectrons, which might reduce their rate of recombination with holes. Meanwhile, the TiO2 with ordered mesopores showed higher activity than that with disordered mesopores, and the 3D ordered mesoporous channels were more favorable for photocatalytic oxidation than the 2D ordered mesoporous channels, which could be attributed to both the enhanced light harvesting resulting from the multiple light reflections in the pore channels, and the facilitated diffusion and adsorption of the reactant molecules. Also, the exposed (001) facets favored the photocatalytic oxidation due to its high surface energy and increased oxygen vacancies, which reduced the photocharge recombination rate by capturing photoelectrons.

Aerosol-spraying synthesis of SiO2/TiO2 nanocomposites and conversion to porous TiO2 and single-crystalline TiOF2.

Single-crystalline TiOF2 was prepared by HF-etching the SiO2/TiO2 nanocomposite obtained via aerosol-spraying, which exhibited high activity and durability in visible-light driven photocatalysis.

Plant uptake-assisted round-the-clock photocatalysis for complete purification of aquaculture wastewater using sunlight.

A novel reactor equipped with solar batteries, Bi2O3/TiO2 film photocatalyst, and celery plant was designed and used for purification of aquaculture wastewater. The Bi2O3/TiO2 film photocatalyst started photocatalytic degradation of organonitrogen compounds under irradiation of sunlight. Meanwhile, the solar batteries absorbed and converted excess sunlight into electric energy and then started UV lamps at night, leading to round-the-clock photocatalysis. Subsequently, the inorganic nitrogen species including NH4(+), NO2(-), and NO3(-) resulting from photocatalytic degradation of the organonitrogen compounds could subsequently be uptaken by the celery plant as the fertilizer to reduce the secondary pollution. It was found that, after 24 h circulation, both organonitrogen compounds and NO2(-) species were completely removed, while NH4(+) and NO3(-) contents also decreased by 30% and 50%, respectively. The reactor could be used repetitively, showing a good potential in practical application.

Mesoporous TiN Microspheres with Hierarchical Chambers and Enhanced Visible Light-Driven Hydrogen Evolution

Mesoporous titanium nitride (TiN) microspheres with tunable chamber structures were synthesized through NH3 nitridation of organotitania obtained via solvothermal alcoholysis. Owing to high content of organic species in organotitania, which stabilized the original structure and also promoted the nitridation at low temperature, TiN duplicated the solid, yolk-shell, and hollow chambers of organotitania in NH3 nitridation and also formed the mesoporous structure after removing organic species. During visible light-induced photocatalytic water splitting, the yolk-shell TiN demonstrated a higher H2 evolution efficiency than the solid, hollow, and crushed TiN; the yolk-shell TiN obtained through N2 nitridation; and other semiconductor photocatalysts reported so far without the aid of noble metals. This could be attributed mainly to the narrow energy band gap for absorbing visible light, high surface area, and excellent electrical conductivity, which facilitated light harvesting, reactant adsorption, and photoelectron-hole separation to suppress their recombination. Moreover, it could be easily recycled and thus used repetitively.

Synthesis of well ordered crystalline TiO2 photocatalyst with enhanced stability and photoactivity

Mesoporous TiO 2 was successfully synthesized using a modified evaporation induced self-assembly (EISA) method. We find that doping proper La 2 O 3 , mesoporous TiO 2 can enhance the thermal stability and also enhance its photocatalytic activity.

Enhanced Photocatalytic Degradation Performance by Fluid-Induced Piezoelectric Field

The introduction of a piezoelectric field has been proven a promising method to enhance photocatalytic activity by preventing photoelectron-hole recombination. However, the formation of a piezoelectric field requires additional mechanical force or high-frequency ultrasonic baths, which limits its potential application on industrial scale. Therefore, it is of great practical significance to design the catalyst that can harvest the discrete energy such as the fluid mechanical energy to form the electric field. Herein, PZT/TiO2 catalyst with a core-shell configuration was prepared by a simple coating method. By collecting the mechanical energy of water, an internal piezoelectric field was induced. Under 800 rpm stirring, transient photocurrent measured on PZT/TiO2 electrode is about 1.7 times higher than that of 400 rpm. Correspondingly, the photocatalytic degradation rate and mineralization efficiency of RhB, BPA, phenol, p-chlorophenol much improved, showing the promoting effect of piezoelectric field generated directly from harvesting the discrete fluid mechanical energy.