Inorganic nanowires with ultrathin diameters below the magic size (i.e., less than 2 nm) and even one unit cell size, have attracted much research attention in the past few years owing to their unique chemical and physical properties. [1][2][3][4][5][6][7][8][9] As an important semiconductor material, tungsten oxide (WO 3Àx ) nanowires and nanorods have attracted considerable attention because of their wide applications in gas sensors, electrochromic windows, optical devices, and photocatalysts. [10][11][12][13] In particular, monoclinic W 18 O 49 is of great interest owing to its unusual defect structure and promising properties in the nanometer regime. [14,15] Early on, Park and co-workers reported the synthesis of W 18 O 49 nanorods with a diameter of 4 nm by decomposing [W(CO) 6 ] in Me 3 NO 2 ·2 H 2 O and oleylamine.[16] Subsequently, Niederberger and co-workers synthesized hybrid W 18 O 49 / organic nanowires with a very thin diameter of 1.3 nm by a bioligand-assisted method.[17] Recently, Tremel and coworkers prepared W 18 O 49 nanorods with a diameter of 2 nm by decomposing tungsten ethoxide in a mixture of oleic acid and trioctyl amine.[18] Although good control over nanocrystal dimensions can be realized in these methods, removal of the surfactants or organic residues from the nanowire surface requires multiple washing steps. For fundamental investigations on the ultrathin oxide nanowire itself, as well as for technological applications (such as sensing and catalysis), the presence of residues on the nanowire surface from the synthesis may be a significant drawback.Herein, we report the preparation of ultrathin W 18 O 49 nanowires that are efficient in the photochemical reduction of carbon dioxide by visible light. The ultrathin W 18 O 49 nanowires were prepared by a very simple one-pot solution-phase method (see the experimental section in the Supporting Information). In a typical procedure, WCl 6 was dissolved in ethanol, and the clear yellow solution was transferred to a teflon-lined stainless-steel autoclave and heated at 180 8C for 24 h. A blue flocculent precipitate was collected, washed, dried in air, and obtained in a yield of approximately 100 %. The product is insoluble in water and in acid (HCl, pH 0), and has a high specific surface area.W 18 O 49 is a monoclinic structure type (P2 m) with lattice parameters of a = 18.318, b = 3.782, and c = 14.028 . Monoclinic W 18 O 49 has a distorted ReO 3 structure in which cornersharing distorted and tilt WO 6 octahedra are connected in the a-, b-, and c-direction, thereby forming a three-dimensional structure (inset in Figure 1 a). The X-ray diffraction (XRD) pattern of our sample demonstrates that the sample consists of monoclinic-phase W 18 O 49 (Figure 1 a). The narrow (010) and (020) peaks strongly suggest that the possible crystal growth direction of the sample is [010], since the close-packed planes of the monoclinic W 18 O 49 crystal are {010}, which will be further demonstrated by the direct observation of the highresolution transmission electr...

A strategy of reaction-environment modulation was employed to change the surface property of a semiconductor photocatalyst to enhance its photocatalytic performance. Surface alkalinization induced by a high alkalinity of the solution environment significantly shifted the surface energy band of a SrTiO(3) photocatalyst to a more negative level, supplying a strong potential for H(2)O reduction and consequently promoting the photocatalytic efficiency of H(2) evolution. This mechanism is also applicable for visible-light-sensitive La,Cr-codoped SrTiO(3) photocatalyst, which hence, could achieve a high apparent quantum efficiency of 25.6% for H(2) evolution in CH(3)OH aqueous solution containing 5 M NaOH at an incident wavelength of 425 ± 12 nm.

The development of precious-metal-free electrocatalysts with high-efficiency for hydrogen evolution reaction (HER) at all pHs is of great interest for the development of electrochemical overall splitting technologies. Despite that intense efforts have been made to developing cost-effective electrocatalysts toward HER under both acidic and alkaline electrolytes with high efficiency, electrocatalysts with remarkable performance in neutral media are rare. Herein, N atoms doped Co2P nanorod arrays grown on carbon cloth (N–Co2P/CC) have been successfully synthesized and further used as efficient electrocatalysts for HER at all pH values. Specially, the N–Co2P/CC exhibits an overpotential of 42 mV at the current density of 10 mA cm –2 with long-term stability in 1.0 M PBS (phosphate-buffered solution), which is comparable to the benchmark Pt/CC. Density functional theory (DFT) calculations suggest nitrogen doping could tailor the electronic structure of Co2P, leading to optimized adsorption free energies of water (ΔG *H2O) and hydrogen (ΔG *H), facilitating hydrogen generation through the Volmer–Heyrovsky mechanism.

Cubic and orthorhombic NaNbO 3 were fabricated to study the effects of crystal structure and electronic structure on the photocatalytic activities in detail. The samples were characterized by X-ray diffraction, field emission transmission electron microscopy, high-resolution transmission electron microscopy, UV−visible absorption spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activities of the two phases of NaNbO 3 have been assessed by H 2 evolution from aqueous methanol solution and CO 2 photoreduction in gas phase. The photocatalytic H 2 evolution and CO 2 reduction activities over cubic NaNbO 3 were nearly twice of those over orthorhombic NaNbO 3 . The first-principles calculation reveals that the higher activity over cubic NaNbO 3 can be attributed to its unique electronic structure, which is beneficial for electron excitation and transfer. ■ INTRODUCTIONAs the fossil fuels have limitations in availability, a new source that can provide abundant and maintainable energy must be developed.1,2 For the past decades, photocatalysis has been developed as a candidate that can supply a renewable, unlimited, and environmentally friendly energy source to solve the energy crisis.3,4 The investigations on photocatalytic reaction mechanisms, 5−7 energy-band structure engineering (including the optimization of crystal structure and the modulation of band energy levels), 8−10 and morphology control 11−15 have been carried out to enhance the photocatalytic efficiency. Generally, to study the relationship between crystal structure and electronic structure is helpful to understand the process of photogenerated carrier excitation and transfer. Up to now, the relevant studies have been performed on the TiO 2 , CdS, BiVO 4 , and AgGaO 2 with different crystal structures. 16−19 Among intensively studied photocatalysts, the materials with perovskite and multilayered perovskite structures have received considerable attention.20−24 However, the report about the influence of crystallographic symmetry on photogenerated carrier excitation and transfer in the perovskite-structured photocatalysts is still limited. NaNbO 3 is nontoxic, highly stable, and with a typical perovskite structure and thus attracts extensive attention in the field of photocatalysis. Many investigations have proved that NaNbO 3 is a high-efficient photocatalyst for H 2 generation.25−29 Under the irradiation of high-pressure mercury lamp, H 2 O can be reduced into H 2 with quite high efficiency over NaNbO 3 nanoparticles.29 Nanofiber-structured NaNbO 3 was also verified to be useful to slit pure water and reduce CO 2 to CH 4 . 30 Moreover, NaNbO 3 normally belongs to the orthorhombic system at room temperature and exhibits an unusual complex sequence of temperature-, pressure-, and particle-size-driven phase transitions. 31−35 When the temperature ranges from room temperature to 1000 K, there are several other phases of NaNbO 3 existing, such as tetragonal and cubic structures. 36 All of them, cubic, tetragonal, and orthorhomb...