Fan Zuo

Self-Doped Ti3+ Enhanced Photocatalyst for Hydrogen Production under Visible Light

Through a facile one-step combustion method, partially reduced TiO(2) has been synthesized. Electron paramagnetic resonance (EPR) spectra confirm the presence of Ti(3+) in the bulk of an as-prepared sample. The UV-vis spectra show that the Ti(3+) here extends the photoresponse of TiO(2) from the UV to the visible light region, which leads to high visible-light photocatalytic activity for the generation of hydrogen gas from water. It is worth noting that the Ti(3+) sites in the sample are highly stable in air or water under irradiation and the photocatalyst can be repeatedly used without degradation in the activity.

Pore Space Partition and Charge Separation in Cage-within-Cage Indium−Organic Frameworks with High CO2 Uptake

The integration of negatively charged single-metal building blocks {In(CO2)4} and positively charged trimeric clusters {In3O} leads to three unique cage-within-cage-based porous materials, which exhibit not only high hydrothermal, thermal, and photochemical stability but also attractive structural features contributing to a very high CO2 uptake capacity of up to 119.8 L/L at 273 K and 1 atm.

Active facets on titanium(III)-doped TiO2: an effective strategy to improve the visible-light photocatalytic activity.

The properties and applications of materials are significantly controlled by their physical characteristics, such as size, shape, and structural state. Many processes are governed by interface reactions by which the surface energy and reactivity depend on the spatial configuration, coordination, and structural state of surface atoms and molecules. For crystals, this dependence is directly related to the expression of specific crystallographic faces, which exhibit different surface structures and atomic configurations. These differences explain why some applications, such as molecular adsorption and desorption, gas sensing, drug molecule delivery and release, and heterogeneous catalysis are highly sensitive to the surface atomic structures. Recent progress in the engineering of crystal morphology has included the synthesis of polyhedral silver nanocrystals by the polyol method, the epitaxially seeded growth of highly faceted Pt-Pd nanocrystals, and the controlled overgrowth of Pd-Au core–shell structures enclosed by {111} facets. Apart from these metallic nanocrystals, binary or ternary compounds with preferentially developed facets have also been reported. The facet effect is an important factor for heterogeneous photocatalysts, because surface atom arrangement and coordination intrinsically determine the adsorption of reactant molecules, surface transfer between photoexcited electrons and reactant molecules, and desorption of product molecules. This phenomenon has been well studied in TiO2 photocatalysts. TiO2 is one of the most extensively studied photocatalysts owing to its abundance, nontoxicity, and stability. However, for practical applications, pure TiO2 is not a good candidate because it is only active under ultraviolet (UV) irradiation owing to the band gap of 3.2 eV for the anatase phase. Therefore, band-gap engineering is required to use TiO2 as a water-splitting catalyst under visible-light irradiation. Reduced TiO2 (TiO2 x), containing Ti or O vacancies, has been reported to show visible-light absorption. Various strategies have been applied to synthesize reduced TiO2, such as heating under vacuum [8] or reducing gas, laser irradiation, and high-energy particle bombardment (electrons or Ar ions). A big challenge for the application of reduced TiO2 is that the surface oxygen defects are highly unstable in air owing to the susceptibility of Ti toward oxidation by O2. [13] Recently, we reported a facile one-step combustion method to synthesize partially reduced TiO2. [14] The presence of Ti in the sample extends the photoresponse of TiO2 from the UV to the visible light region, which leads to high visible-light photocatalytic activity for the generation of hydrogen gas from water. However, in the rapid and harsh combustion process, there is very limited control over the crystallization process, which results in the irregularly shaped products. Herein we report the development of a simple solution method to grow non-stoichiometric rutile TiO2 crystals with desired facets. The incorporation of Ti, which extends the light absorption from the UV into the visible range, along with the development of facets with high reactivity, results in a material exhibiting greatly enhanced photocatalytic H2 production activity relative to the combustion product we reported before. Powder X-ray diffraction analysis (Figure 1a) shows that the sample of as-produced TiO2 (sample S1) has rutile structure. All of the diffraction peaks can be assigned to

Synthesis and Photocatalytic Properties of a New Heteropolyoxoniobate Compound: K10[Nb2O2(H2O)2][SiNb12O40]·12H2O

The synthesis and photocatalytic properties of a heteropolyoxoniobate, K(10)[Nb(2)O(2)(H(2)O)(2)][SiNb(12)O(40)]·12H(2)O (1), are reported, revealing an important role of Zr(4+) additives in the crystallization. Compound 1 exhibits overall photocatalytic water splitting activity, and its photocatalytic activity is significantly higher than that of Na(10)[Nb(2)O(2)][SiNb(12)O(40)]·xH(2)O (2). Fluorescence lifetime measurements suggest that the enhanced photocatalytic activity of 1 likely results from a larger yield of longer-lived charge trapping states in 1 due to the coordination of one water molecule to the bridging Nb(5+), leading to highly unsymmetrical seven-coordinated Nb(5+) sites.

Mimicking Zeolite to Its Core: Porous Sodalite Cages as Hangers for Pendant Trimeric M3(OH) Clusters (M = Mg, Mn, Co, Ni, Cd)

A new class of zeolite-type porous materials in which 3D frameworks are covalently functionalized with crystallographically ordered pendant metal clusters have been synthesized. This work demonstrates a new paradigm for and the feasibility of functionalizing zeolite-type frameworks through the conversion of extraframework sites in mineral zeolites into part of the framework for occupation by dangling metal clusters in metal-organic frameworks.

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

A new synthetic method to fabricate Ti(3+)-modified, highly stable TiO2 photoanodes for H2O oxidation is reported. With Ti foil as both the conducting substrate and the Ti(3+)/Ti(4+) source, one-dimensional blue Ti(3+)/TiO2 crystals were grown by a one-step hydrothermal reaction. The concentration of Ti(3+) 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 Ti(3+) self-doping, this work provides a versatile tool toward the fabrication of efficient TiO2 photoanodes.

Cooperative Assembly of Three‐Ring‐Based Zeolite‐Type Metal–Organic Frameworks and Johnson‐Type Dodecahedra

Two birds with one stone One synthetic strategy led to the preparation of both 3-ring-based zeolite-type metal-organic frameworks (NPO-type) and Johnson-type metal-organic polyhedra. The strategy is based on the cooperative assembly of 4-connected indium nodes with two symmetry-complementary ligands (one serves to generate 3-rings and the other crosslinks 3-rings). Photocatalytic H2 production experiments demonstrated these NPO-zeolite compounds behave as semiconductors and exhibit photocatalytic activity for the generation of dihydrogen from water under ultraviolet irradiation.

Hard template synthesis of crystalline mesoporous anatase TiO2 for photocatalytic hydrogen evolution

Mesoporous crystalline anatase TiO2 has been synthesized by using the nanocasting method with mesoporous silica KIT-6 as the hard template and titanium alkoxide as the precursor. Three key synthetic parameters play important roles in the formation of crystalline porous materials. These are precursor/template ratios, calcination temperatures and immersion time (in 2 M NaOH to remove template). The synthesized materials are characterized with powder X-ray diffraction (XRD), N2 adsorption–desorption isotherm analysis and energy-dispersive X-ray spectroscopy (EDX) elemental analysis. Owing to the template confinement effect, mesoporous anatase TiO2 instead of rutile phase was obtained at the calcination temperature of 750 °C. Materials with a surface area as high as 207 m2 g−1 have been obtained. The photocatalytic activities of the as-prepared mesoporous TiO2 were studied with a loading of 0.5% Pt. The materials with higher surface areas showed higher H2 evolution activities. The H2 evolution activity of the mesoporous anatase sample prepared under optimal conditions was 5.5 times higher than that of bulk anatase TiO2. The work represents a step forward in the development of highly efficient photocatalysts based on crystalline high surface area porous materials and our results indicate that the hard template method may be an effective method to achieve this goal.

Facile Synthesis of Thermal‐ and Photostable Titania with Paramagnetic Oxygen Vacancies for Visible‐Light Photocatalysis

A novel dopant-free TiO(2) photocatalyst (V(o)(.)-TiO(2)), which is self-modified by a large number of paramagnetic (single-electron-trapped) oxygen vacancies, was prepared by calcining a mixture of a porous amorphous TiO(2) precursor, imidazole, and hydrochloric acid at elevated temperature (450 °C) in air. Control experiments demonstrate that the porous TiO(2) precursor, imidazole, and hydrochloric acid are all necessary for the formation of V(o)(.)-TiO(2). Although the synthesis of V(o)(.)-TiO(2) originates from such a multicomponent system, this synthetic approach is facile, controllable, and reproducible. X-ray diffraction, XPS, and EPR spectroscopy reveal that the V(o)(.)-TiO(2) material with a high crystallinity embodies a mass of paramagnetic oxygen vacancies, and is free of other dopant species such as nitrogen and carbon. UV/Vis diffuse-reflectance spectroscopy and photoelectrochemical measurement demonstrate that V(o)(.)-TiO(2) is a stable visible-light-responsive material with photogenerated charge separation efficiency higher than N-TiO(2) and P25 under visible-light irradiation. The V(o)(.)-TiO(2) material exhibits not only satisfactory thermal- and photostability, but also superior photocatalytic activity for H(2) evolution (115 μmol h(-1) g(-1)) from water with methanol as sacrificial reagent under visible light (λ>400 nm) irradiation. Furthermore, the effects of reaction temperature, ratio of starting materials (imidazole:TiO(2) precursor) and calcination time on the photocatalytic activity and the microstructure of V(o)(.)-TiO(2) were elucidated.

Boron Carbides as Efficient, Metal-Free, Visible-Light-Responsive Photocatalysts†

Solar-powered photocatalytic and photoelectrochemical(PEC) water splitting provide two promising strategies toproduce hydrogen for future energy needs. Currently, mostphotocatalytic or PEC water-splitting materials are based ontransition metal oxide, (oxy)nitride, or (oxy)sulfide semi-conductors with suitable band gaps and band positions.