Jinhua Ye

Direct splitting of water under visible light irradiation with an oxide semiconductor photocatalyst

The photocatalytic splitting of water into hydrogen and oxygen using solar energy is a potentially clean and renewable source for hydrogen fuel. The first photocatalysts suitable for water splitting, or for activating hydrogen production from carbohydrate compounds made by plants from water and carbon dioxide, were developed several decades ago. But these catalysts operate with ultraviolet light, which accounts for only 4% of the incoming solar energy and thus renders the overall process impractical. For this reason, considerable efforts have been invested in developing photocatalysts capable of using the less energetic but more abundant visible light, which accounts for about 43% of the incoming solar energy. However, systems that are sufficiently stable and efficient for practical use have not yet been realized. Here we show that doping of indium-tantalum-oxide with nickel yields a series of photocatalysts, In1-xNixTaO4 (x = 0–0.2), which induces direct splitting of water into stoichiometric amounts of oxygen and hydrogen under visible light irradiation with a quantum yield of about 0.66%. Our findings suggest that the use of solar energy for photocatalytic water splitting might provide a viable source for ‘clean’ hydrogen fuel, once the catalytic efficiency of the semiconductor system has been improved by increasing its surface area and suitable modifications of the surface sites.

Nano‐photocatalytic Materials: Possibilities and Challenges

Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.

An orthophosphate semiconductor with photooxidation properties under visible-light irradiation

The search for active semiconductor photocatalysts that directly split water under visible-light irradiation remains one of the most challenging tasks for solar-energy utilization. Over the past 30 years, the search for such materials has focused mainly on metal-ion substitution as in In(1-x)Ni(x)TaO(4) and (V-,Fe- or Mn-)TiO(2) (refs 7,8), non-metal-ion substitution as in TiO(2-x)N(x) and Sm(2)Ti(2)O(5)S(2) (refs 9,10) or solid-solution fabrication as in (Ga(1-x)Zn(x))(N(1-x)O(x)) and ZnS-CuInS(2)-AgInS(2) (refs 11,12). Here we report a new use of Ag(3)PO(4) semiconductor, which can harness visible light to oxidize water as well as decompose organic contaminants in aqueous solution. This suggests its potential as a photofunctional material for both water splitting and waste-water cleaning. More generally, it suggests the incorporation of p block elements and alkali or alkaline earth ions into a simple oxide of narrow bandgap as a strategy to design new photoelectrodes or photocatalysts.

Facet Effect of Single-Crystalline Ag3PO4 Sub-microcrystals on Photocatalytic Properties

We recently reported that Ag(3)PO(4) exhibits excellent photooxidative capabilities for O(2) evolution from water and organic dye decomposition under visible-light irradiation. However, very little is known about the shape and facet effects of Ag(3)PO(4) crystals on their photocatalytic properties. Herein we have developed a facile and general route for high-yield fabrication of single-crystalline Ag(3)PO(4) rhombic dodecahedrons with only {110} facets exposed and cubes bounded entirely by {100} facets. Moreover, studies of their photocatalytic performance have indicated that rhombic dodecahedrons exhibit much higher activities than cubes for the degradation of organic contaminants, which may be primarily ascribed to the higher surface energy of {110} facets (1.31 J/m(2)) than of {100} facets (1.12 J/m(2)).

MoS2/Graphene Cocatalyst for Efficient Photocatalytic H2 Evolution under Visible Light Irradiation

Exploiting noble-metal-free cocatalysts is of huge interest for photocatalytic water splitting using solar energy. Here we report a composite material consisting of CdS nanocrystals grown on the suface of a nanosized MoS2/graphene hybrid as a high-performance noble-metal-free photocatalyst for H2 evolution under visible light irradiation. Through the optimizing of each component proportion, the MoS2/G-CdS composite showed the highest photocatalytic H2 production activity when the content of the MoS2/graphene cocatalyst is 2.0 wt % and the molar ratio of MoS2 to graphene is 1:2. The photocatalytic H2 evolution activity of the proposed MoS2/G-CdS composite was tested and compared in Na2S-Na2SO3 solution and lactic acid solution. A 1.8 mmol/h H2 evolution rate in lactic acid solution corresponding to an AQE of 28.1% at 420 nm is not only higher than the case in Na2S-Na2SO3 solution of 1.2 mmol/h but also much higher than that of Pt/CdS in lactic acid solution. The relative mechanism has been investigated. It is believed that this kind of MoS2/G-CdS composite would have great potential as a promising photocatalyst with high efficiency and low cost for photocatalytic H2 evolution reaction.

Facile synthesis of rhombic dodecahedral AgX/Ag3PO4 (X = Cl, Br, I) heterocrystals with enhanced photocatalytic properties and stabilities

Herein, we have developed a facile and general method for the high-yield fabrication of AgX/Ag(3)PO(4) (X = Cl, Br, I) core-shell heterostructures with an unusual rhombic dodecahedral morphology, which exhibit much higher photocatalytic activities, structural stabilities and photoelectric properties than pure Ag(3)PO(4) crystals in environment and energy applications.

Non-covalent doping of graphitic carbon nitride polymer with graphene: controlled electronic structure and enhanced optoelectronic conversion

By union of graphitic carbon nitride polymer with reduced graphene oxide (rGO, ≤1 wt%) via π–π stacking interaction, the band structure of carbon nitride could be well modulated. As a result, a significant increase of photocurrent was observed (e.g., when biased at 0.4 V vs.Ag/AgCl, the anodic photocurrent became 300% higher after doping). Not merely interesting in itself, graphene was also used as a general dopant for semiconductors in band-structure engineering.

Ultrathin W18O49 Nanowires with Diameters below 1 nm: Synthesis, Near‐Infrared Absorption, Photoluminescence, and Photochemical Reduction of Carbon Dioxide

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. As an important semiconductor material, tungsten oxide (WO3 x) nanowires and nanorods have attracted considerable attention because of their wide applications in gas sensors, electrochromic windows, optical devices, and photocatalysts. In particular, monoclinic W18O49 is of great interest owing to its unusual defect structure and promising properties in the nanometer regime. Early on, Park and co-workers reported the synthesis of W18O49 nanorods with a diameter of 4 nm by decomposing [W(CO)6] in Me3NO2·2 H2O and oleylamine. [16] Subsequently, Niederberger and co-workers synthesized hybrid W18O49/ organic nanowires with a very thin diameter of 1.3 nm by a bioligand-assisted method. Recently, Tremel and coworkers prepared W18O49 nanorods with a diameter of 2 nm by decomposing tungsten ethoxide in a mixture of oleic acid and trioctyl amine. 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 W18O49 nanowires that are efficient in the photochemical reduction of carbon dioxide by visible light. The ultrathin W18O49 nanowires were prepared by a very simple one-pot solution-phase method (see the experimental section in the Supporting Information). In a typical procedure, WCl6 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. W18O49 is a monoclinic structure type (P2 m) with lattice parameters of a = 18.318, b = 3.782, and c = 14.028 . Monoclinic W18O49 has a distorted ReO3 structure in which cornersharing distorted and tilt WO6 octahedra are connected in the a-, b-, and c-direction, thereby forming a three-dimensional structure (inset in Figure 1a). The X-ray diffraction (XRD) pattern of our sample demonstrates that the sample consists of monoclinic-phase W18O49 (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 W18O49 crystal are {010}, which will be further demonstrated by the direct observation of the highresolution transmission electron microscopy (HRTEM) image (see below). Energy-dispersive X-ray spectroscopy (EDS) confirms that the sample only contains W and O elements (Figure 1b). Furthermore, the Fourier transform infrared (FTIR) spectrum exhibits the clear surface of our sample (Figure S1 in the Supporting Information). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the as-synthesized sample is composed of nanowires with large aspect ratio and lengths of up to several micrometers (Figure 1c, d). Interestingly, higher-magnification TEM images (Figure 1e and Figures S2 and S3 in the Supporting Information) clearly reveal that the nanowires shown in Figure 1d are composed of a lot of individual, thinner nanowires. The diameter of the thinner nanowires is only about 0.9 nm. The HRTEM image and corresponding fast Fourier transform (FFT) pattern demonstrate that the ultrathin nanowires are crystalline and grow along [010] direction (Figure 1 f and Figure S4 in the Supporting Information). A comparison of the unit cell of W18O49 projected along the [010] direction with the typical diameter of the nanowires of 0.9 nm (red circle) allows [*] Dr. G. C. Xi, Dr. S. X. Ouyang, P. Li, Prof. J. H. Ye International Center for Materials Nanoarchitectonics (WPIMANA), and Environmental Remediation Materials Unit National Institute for Materials Science (NIMS) 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan) E-mail: jinhua.ye@nims.go.jp

A Room‐Temperature Reactive‐Template Route to Mesoporous ZnGa2O4 with Improved Photocatalytic Activity in Reduction of CO2

Mesoporous materials are of scientific and technological interest due to their potential applications in various areas. Over the past two decades, significant effort has been devoted to the synthesis of mesoporous materials. For instance, mesoporous silica and phosphate metal oxides have been synthesized and applied widely in many industrial processes. However, little progress has been made in the synthesis of mesoporous metal oxides containing more than one type of metal. To date, a limited number of routes including evaporation-induced self-assembly (EISA) and nonaqueous solvent methods have been developed to synthesize multimetallic mesoporous materials such as Pb3Nb4O13, [3] Bi20TiO32, [4] SrTiO3, MgTa2O6, CoxTi1 xO2 x, [5] and Ce1 xZrxO2. [6] In these routes, introducing surfactant molecules or a template is a general method used to construct the mesostructures. Challenges in using the template method to synthesize multimetallic mesoporous materials are uncontrolled phase separation in the multicomponent reactions and poor thermal and chemical stability of the resulting mesoporous structure. Maintaining the complete mesostructure during removal of the template by heating or chemical treatment is a key process for obtaining the expected mesostructures, and increases the uncertainty in a given synthetic route. In addition, to obtain a crystalline mesoporous material, high-temperature heat treatment is usually required for crystallization of the product. However, this process probably induces collapse of mesostructures. Recently, we developed a synthetic route to mesoporous multimetal oxides that uses the inorganic starting reactants directly as pore makers which aid in building the mesoporous structures of multimetal oxides and improve the thermal stability of the resulting mesostructure. However, in these reported synthetic routes, postcrystallization and introducing or removing an exotemplate are usually needed. In recent years, a route that does not require template removal, which was named “reactive hard templating”, was developed to synthesize porous TiN/carbon composite materials. In this route, the template consists of nanostructures of porous graphitic C3N4, which thermally decomposes completely during formation of porous TiN. This route provides a means to overcome the problems associated with synthesizing multimetal mesoporous materials. A simplified soft-chemistry route based on a reactive template is expected to allow synthesis to proceed at room temperature without requiring the introduction or removal of a template. Here we report a novel direct method for preparing mesoporous ZnGa2O4 with a wormhole framework by an ion-exchange reaction at room temperature involving a mesoporous NaGaO2 colloid precursor. The method does not require any additional processes and can be extended to prepare other porous materials, such as CoGa2O4 and NiGa2O4. The X-ray diffraction (XRD) pattern of NaGaO2 powder, which can be indexed as the orthorhombic phase (JCPDS 762151), is presented in Figure 1. Scanning electron microscopy (SEM) revealed that the powder particles are irregular in shape with little agglomeration, and most of the particles are larger than 500 nm in diameter (see Supporting Information). The as-prepared NaGaO2 powder can be dispersed in water to form a suspension. When the NaGaO2 suspension is illuminated with a 532 nm laser, a Tyndall effect is observed, that is, the suspension behaves as a colloid (see Supporting Information). Multimodal measurements of particle size distribution by dynamic light scattering show that the NaGaO2 colloidal particles exhibit two peak distributions: 20 % of the particles have an average size of 70 nm, and 80 % an average size of 335 nm. Most particulate or macroscopic materials in contact with a liquid acquire an electric charge on their surfaces. The zeta potential is an important and useful indicator of this charge that can be used to predict the stability of colloidal suspensions. The zeta potential of NaGaO2 colloidal particles is 21.57 mV (pH 6). This is lower than the critical zeta potential of 30 mV for maintaining colloid stability in an aqueous system, that is, the colloidal particles are slightly [*] S. C. Yan, J. Gao, M. Yang, X. X. Fan, L. J. Wan, Prof. Y. Zhou, Prof. Z. G. Zou Ecomaterials and Renewable Energy Research Center National Laboratory of Solid State Microstructures, Nanjing University, 22 Hankou Road, Nanjing 210093 (China) E-mail: zgzou@nju.edu.cn

Efficient photocatalytic decomposition of acetaldehyde over a solid-solution perovskite (Ag0.75Sr0.25)(Nb0.75Ti0.25)O3 under visible-light irradiation.

A green chemistry process for environmental purification is realized on a novel visible-light-active photocatalyst (Ag0.75Sr0.25)(Nb0.75Ti0.25)O3. This mixed valent solid-solution perovskite with a modulated electronic structure possesses a strong oxidative potential for efficient photocatalytic decomposition of acetaldehyde into CO2 at ambient temperature.