Showing papers by "Wuhan University of Technology published in 2012"

Graphene-based semiconductor photocatalysts

Abstract: Graphene, a single layer of graphite, possesses a unique two-dimensional structure, high conductivity, superior electron mobility and extremely high specific surface area, and can be produced on a large scale at low cost. Thus, it has been regarded as an important component for making various functional composite materials. Especially, graphene-based semiconductor photocatalysts have attracted extensive attention because of their usefulness in environmental and energy applications. This critical review summarizes the recent progress in the design and fabrication of graphene-based semiconductor photocatalysts via various strategies including in situ growth, solution mixing, hydrothermal and/or solvothermal methods. Furthermore, the photocatalytic properties of the resulting graphene-based composite systems are also discussed in relation to the environmental and energy applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation and photocatalytic disinfection. This critical review ends with a summary and some perspectives on the challenges and new directions in this emerging area of research (158 references).

Synergetic Effect of MoS2 and Graphene as Cocatalysts for Enhanced Photocatalytic H2 Production Activity of TiO2 Nanoparticles

Abstract: The production of H2 by photocatalytic water splitting has attracted a lot attention as a clean and renewable solar H2 generation system. Despite tremendous efforts, the present great challenge in materials science is to develop highly active photocatalysts for splitting of water at low cost. Here we report a new composite material consisting of TiO2 nanocrystals grown in the presence of a layered MoS2/graphene hybrid as a high-performance photocatalyst for H2 evolution. This composite material was prepared by a two-step simple hydrothermal process using sodium molybdate, thiourea, and graphene oxide as precursors of the MoS2/graphene hybrid and tetrabutylorthotitanate as the titanium precursor. Even without a noble-metal cocatalyst, the TiO2/MoS2/graphene composite reaches a high H2 production rate of 165.3 μmol h–1 when the content of the MoS2/graphene cocatalyst is 0.5 wt % and the content of graphene in this cocatalyst is 5.0 wt %, and the apparent quantum efficiency reaches 9.7% at 365 nm. This unusu...

Convergence of conduction bands as a means of enhancing thermoelectric performance of n-type Mg2Si(1-x)Sn(x) solid solutions.

Abstract: Mg(2)Si and Mg(2)Sn are indirect band gap semiconductors with two low-lying conduction bands (the lower mass and higher mass bands) that have their respective band edges reversed in the two compounds. Consequently, for some composition x, Mg(2)Si(1-x)Sn(x) solid solutions must display a convergence in energy of the two conduction bands. Since Mg(2)Si(1-x)Sn(x) solid solutions are among the most prospective of the novel thermoelectric materials, we aim on exploring the influence of such a band convergence (valley degeneracy) on the Seebeck coefficient and thermoelectric properties in a series of Mg(2)Si(1-x)Sn(x) solid solutions uniformly doped with Sb. Transport measurements carried out from 4 to 800 K reveal a progressively increasing Seebeck coefficient that peaks at x=0.7. At this concentration the thermoelectric figure of merit ZT reaches exceptionally large values of 1.3 near 700 K. Our first principles calculations confirm that at the Sn content x≈0.7 the two conduction bands coincide in energy. We explain the high Seebeck coefficient and ZT values as originating from an enhanced density-of-states effective mass brought about by the increased valley degeneracy as the two conduction bands cross over. We corroborate the increase in the density-of-states effective mass by measurements of the low temperature specific heat. The research suggests that striving to achieve band degeneracy by means of compositional variations is an effective strategy for enhancing the thermoelectric properties of these materials.

Noble Metal-Free Reduced Graphene Oxide-ZnxCd1–xS Nanocomposite with Enhanced Solar Photocatalytic H2-Production Performance

Abstract: Design and preparation of efficient artificial photosynthetic systems for harvesting solar energy by production of hydrogen from water splitting is of great importance from both theoretical and practical viewpoints. ZnS-based solid solutions have been fully proved to be an efficient visible-light driven photocatalysts, however, the H2-production rate observed for these solid solutions is far from exciting and sometimes an expensive Pt cocatalyst is still needed in order to achieve higher quantum efficiency. Here, for the first time we report the high solar photocatalytic H2-production activity over the noble metal-free reduced graphene oxide (RGO)-ZnxCd1–xS nanocomposite prepared by a facile coprecipitation-hydrothermal reduction strategy. The optimized RGO-Zn0.8Cd0.2S photocatalyst has a high H2-production rate of 1824 μmol h–1 g–1 at the RGO content of 0.25 wt % and the apparent quantum efficiency of 23.4% at 420 nm (the energy conversion efficiency is ca. 0.36% at simulated one-sun (AM 1.5G) illuminati...

Hierarchically Structured Porous Materials for Energy Conversion and Storage

Abstract: Materials with hierarchical porosity and structures have been heavily involved in newly developed energy storage and conversion systems. Because of meticulous design and ingenious hierarchical structuration of porosities through the mimicking of natural systems, hierarchically structured porous materials can provide large surface areas for reaction, interfacial transport, or dispersion of active sites at different length scales of pores and shorten diffusion paths or reduce diffusion effect. By the incorporation of macroporosity in materials, light harvesting can be enhanced, showing the importance of macrochannels in light related systems such as photocatalysis and photovoltaics. A state-of-the-art review of the applications of hierarchically structured porous materials in energy conversion and storage is presented. Their involvement in energy conversion such as in photosynthesis, photocatalytic H 2 production, photocatalysis, or in dye sensitized solar cells (DSSCs) and fuel cells (FCs) is discussed. Energy storage technologies such as Li-ions batteries, supercapacitors, hydrogen storage, and solar thermal storage developed based on hierarchically porous materials are then discussed. The links between the hierarchically porous structures and their performances in energy conversion and storage presented can promote the design of the novel structures with advanced properties.

Preparation, properties and applications of polysaccharide nanocrystals in advanced functional nanomaterials: a review

Abstract: Intensive exploration and research in the past few decades on polysaccharide nanocrystals, the highly crystalline nanoscale materials derived from natural resources, mainly focused originally on their use as a reinforcing nanophase in nanocomposites. However, these investigations have led to the emergence of more diverse potential applications exploiting the functionality of these nanomaterials. Based on the construction strategies of functional nanomaterials, this article critically and comprehensively reviews the emerging polysaccharide nanocrystal-based functional nanomaterials with special applications, such as biomedical materials, biomimetic optical nanomaterials, bio-inspired mechanically adaptive nanomaterials, permselective nanostructured membranes, template for synthesizing inorganic nanoparticles, polymer electrolytes, emulsion nano-stabilizer and decontamination of organic pollutants. We focus on the preparation, unique properties and performances of the different polysaccharide nanocrystal materials. At the same time, the advantages, physicochemical properties and chemical modifications of polysaccharide nanocrystals are also comparatively discussed in view of materials development. Finally, the perspective and current challenges of polysaccharide nanocrystals in future functional nanomaterials are outlined.

Surface plasmon resonance-mediated photocatalysis by noble metal-based composites under visible light

Abstract: Harvesting abundant and renewable sunlight in energy production and environmental remediation is an emerging research topic. Indeed, research on solar-driven heterogeneous photocatalysis based on surface plasmon resonance has seen rapid growth and potentially opens a technologically promising avenue that can benefit the sustainable development of global energy and the environment. This review briefly summarizes recent advances in the synthesis and photocatalytic properties of plasmonic composites (e.g., hybrid structures) formed by noble metal (e.g., gold, silver) nanoparticles dispersed on a variety of substrates that are composed of metal oxides, silver halides, graphene oxide, among others. Brief introduction of surface plasmon resonance and the synthesis of noble metal-based composites are given, followed by highlighting diverse applications of plasmonic photocatalysts in mineralization of organic pollutants, organic synthesis and water splitting. Insights into surface plasmon resonance-mediated photocatalysis not only impact the basic science of heterogeneous photocatalysis, but generate new concepts guiding practical technologies such as wastewater treatment, air purification, selective oxidation reactions, selective reduction reactions, and solar-to-hydrogen energy conversion in an energy efficient and environmentally benign approach. This review ends with a summary and perspectives.

Poly(2-oxazoline)s as Polymer Therapeutics

Abstract: Poly(2-oxazoline)s (POx) are currently discussed as an upcoming platform for biomaterials design and especially for polymer therapeutics. POx meets several requirements needed for the development of next-generation polymer therapeutics such as biocompatibility, high modulation of solubility, variation of size, architecture as well as chemical functionality. Although in the early 1990s first and promising POx-based systems were presented but the field lay dormant for almost two decades. Only very recently, POx based polymer therapeutics came back into the focus of very intensive research. In this review, we give an overview on the chemistry and physicochemical properties of POx and summarize the research of POx-protein conjugates, POx-drug conjugates, POx-based polyplexes and POx micelles for drug delivery.

Hierarchically structured zeolites: synthesis, mass transport properties and applications

Abstract: Zeolites with hierarchically porous structures have garnered much attention due to their highly attractive properties. Hierarchically structured zeolites integrate at least two levels of porosity and present the advantages associated with each level of porosity, from selectivity to mass transport. They are categorized into three distinctly different types according to their hierarchical porosities: mesostructured zeolites, macrostructured zeolites, and micro–meso–macroporous structured zeolites. Most importantly, hierarchically structured zeolites offer an effective solution to the mass transport problem associated with conventional zeolites in catalysed reactions because they combine the catalytic features of micropores and the improved accessibility and increased molecular transport related to the addition of several porosities within a single body. In recent years, many strategies have been successfully developed to synthesize hierarchically structured zeolitic materials. This feature article thoroughly summarizes recent developments that have been achieved in the field of hierarchically structured zeolites, with the main focus on the synthesis strategies that are available, with examples given from the literature. Available approaches are reviewed for the preparation of micro–mesoporous structured zeolites, micro–macroporous structured zeolites and micro–meso–macroporous structured zeolites. Furthermore, the enhanced mass transport properties of hierarchically structured zeolites, featuring additional larger pores in addition to the crystalline micropores, have also been described. The significant improvement in catalytic properties in a range of important reactions resulting from enhanced mass transport properties have also been discussed through several representative cases. It is the intent of this work to stimulate intuition into the optimal design of related hierarchically organized zeolites with desired characteristics.

Enhanced photocatalytic activity of hierarchical macro/mesoporous TiO2–graphene composites for photodegradation of acetone in air

Abstract: Graphene, a single layer of graphite, possesses a unique two-dimensional structure, high conductivity, superior electron mobility and extremely high specific surface area, and can be obtained on a large scale at low cost. Thus, it has been regarded as an excellent catalyst support. Recently, graphene-based semiconductor photocatalysts have attracted more attention due to their enhanced photocatalytic activity. In this work, hierarchical macro/mesoporpous TiO2–graphene composites with low loadings (0–0.2 wt.%) of graphene were first produced by a simple one-step hydrothermal method using tetrabutyl titanate as the titanium precursor. The prepared composite samples presented enhanced photocatalytic activity in photodegradation of acetone in air. Graphene content exhibited an obvious influence on photocatalytic activity and the optimal graphene addition content was determined. At the optimal graphene concentration (0.05 wt.%), the prepared composites showed the highest photocatalytic activity, exceeding that of pure TiO2 and Degussa P-25 by a factor of 1.7 and 1.6, respectively. The enhanced photocatalytic activity is due to graphene as an excellent electron acceptor and transporter, thus reducing the recombination of charge carriers and enhancing the photocatalytic activity. The transient photocurrent response experiment further confirmed the transfer of photogenerated electrons from TiO2 to graphene and the suggested mechanism.

Hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 nanowires with ultrahigh capacity for Li-air batteries

Abstract: Lithium-air batteries have captured worldwide attention due to their highest energy density among the chemical batteries. To provide continuous oxygen channels, here, we synthesized hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 (LSCO) nanowires. We tested the intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity in both aqueous electrolytes and nonaqueous electrolytes via rotating disk electrode (RDE) measurements and demonstrated that the hierarchical mesoporous LSCO nanowires are high-performance catalysts for the ORR with low peak-up potential and high limiting diffusion current. Furthermore, we fabricated Li-air batteries on the basis of hierarchical mesoporous LSCO nanowires and nonaqueous electrolytes, which exhibited ultrahigh capacity, ca. over 11,000 mAh⋅g –1, one order of magnitude higher than that of LSCO nanoparticles. Besides, the possible reaction mechanism is proposed to explain the catalytic activity of the LSCO mesoporous nanowire.

Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds.

Abstract: Half-Heusler (HH) alloys have attracted considerable interest as promising thermoelectric (TE) materials in the temperature range around 700 K and above, which is close to the temperature range of most industrial waste heat sources. The past few years have seen nanostructuing play an important role in significantly enhancing the TE performance of several HH alloys. In this article, we briefly review the recent progress and advances in these HH nanocomposites. We begin by presenting the structure of HH alloys and the different strategies that have been utilized for improving the TE properties of HH alloys. Next, we review the details of HH nanocomposites as obtained by different techniques. Finally, the review closes by highlighting several promising strategies for further research directions in these very promising TE materials.

Facet-Mediated Photodegradation of Organic Dye over Hematite Architectures by Visible Light

Abstract: Structure–reactivity correlations are a central theme in heterogeneous catalysis. In general, the crystallographic surface structure of a catalyst is determined by its exposed facets, and the enclosed facets of a particle-like catalyst in turn determine its geometric shape as well as catalytic properties. Tuning the shape of catalysts, therefore, is essential in developing new catalysts and modifying existing ones with desirable reactivity, selectivity, and stability. Indeed, great advances have been achieved on model catalysts, and insights into the structure–reactivity correlations are crucial not only for our understanding of catalytic processes, but also for generating new concepts to guide the rational design of practical catalysts. In recent years, significant attention has been directed towards using solar-driven photocatalysts to degrade aqueous organic pollutants (for example, azo dyes). In view of being naturally abundant and environmentally benign, iron oxides show great promise. Among iron oxides, hematite (aFe2O3) is the most thermodynamically stable semiconductor (Eg = 2.1–2.2 eV) that can absorb visible light, that is, a substantial fraction of the solar spectrum. a-Fe2O3 has a wide range of applications, such as light-induced water splitting, solar cells, lithium ion batteries, and biotechnology. Most studies to date have been carried out on powder substrates in which particle shapes are inherently not welldefined, making it difficult to explore the structure–reactivity correlations. While the vast majority of studies on the impact of particle shape on photocatalytic reactivity are limited to titanium dioxide (TiO2), [18–27] far less information is available regarding the shape effects on other photocatalysts, including iron oxides. In this regard, systematic studies on heterogeneous photo-Fenton catalysis, a technologically promising process in wastewater treatment, by iron-bearing nanocatalysts with particular shapes are still lacking. 29] Over the past decade, size, shape, and architecture control of low-dimensional nanomaterials (for example, nanodots, nanorods, and nanosheets) with unusual properties has seen rapid growth. For example, in one-dimensional (1D) anisotropic nanostructures, it is possible to enhance the photoreactivity by tuning the direction and path of photogenerated charge carriers through quantum confinement while minimizing the e –h recombination. Herein, we investigate visible-light-induced photodegradation of model dye rhodamine B (RhB) in the presence of hydrogen peroxide (H2O2) over hematite architectures, namely 1D nanorods, 2D nanoplates, and 3D nanocubes. Herein we use “architectures” to describe hematite nanostructures that can be assembled by nano-building units by oriented attachment. 36, 39] To the best of our knowledge, this is the first study to investigate heterogeneous photo-Fenton catalysis by nanocatalysts with well-defined architectures. The detailed synthesis of a-Fe2O3 architectures [39–42] is described in the Experimental Section and the Supporting Information. The structure, stoichiometry, and oxidation state of the as-prepared a-Fe2O3 architectures were characterized using X-ray diffraction (XRD; Supporting Information, Figure S1a), micro-Raman (Supporting Information, Figure S1b), and high-resolution X-ray photoelectron spectroscopy (XPS; Supporting Information, Figure S1c,d), and results demonstrate that all samples are pure a-Fe2O3 with a rhombohedral hexagonal phase (space group R3̄c). The morphology and crystallinity of as-prepared a-Fe2O3 architectures were analyzed using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). A TEM image for 2D nanoplates is shown in Figure 1a. All of the nanoplates display a well-defined hexagonal shape. Based on a SEM (Supporting Information, Figure S2a) and TEM analysis (Figure 1 a; Supporting Information, Figure S2b), the width and thickness of the plates is determined to be (208.5 27.3) and (14.6 2.6) nm, respectively. A representative HRTEM image (Figure 1 b) and fast Fourier transforms (FFT; inset in Figure 1b) show the lattice fringe to be 0.25 nm, which is consistent with (110), ( 120), and ( 210) planes, respectively. Thus, the resulting basal plane is (001). Vertically aligned plates that are frequently observed (Supporting Information, Figure S2b,c) are wedgeshaped and the lateral facets are ascribed to {102}. A TEM [*] X. M. Zhou, J. Y. Lan, Prof. G. Liu, Prof. K. Deng, Prof. Y. L. Yang, Prof. G. J. Nie, Prof. L. J. Zhi National Center for Nanoscience and Technology Beijing, 100190 (China) E-mail: liug@nanoctr.cn zhilj@nanoctr.cn

How many lithium ions can be inserted onto fused C6 aromatic ring systems

Abstract: A fundamental and persistent problem in the study of carbonbased electrode materials for lithium ion batteries is the question of how many lithium ions can be inserted onto a C6 aromatic ring. Although different empirical models of Lix/C6 (x< 3) have been proposed, the question remains unresolved. Herein we employ 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), an aromatic compound containing a naphthalene ring system (fused C6 aromatic rings), to demonstrate that each carbon in a C6 ring can accept a Li ion to form a Li6/C6 additive complex through a reversible electrochemical lithium addition reaction. This process results in Li ion insertion capacities of up to nearly 2000 mAhg , depending on the exact molecular structure. This value is several times higher than any other organic electrode material previously reported and can be fully released under certain conditions. Our experiments and theoretical calculations indicate that the anhydride groups on the sides of the aromatic system are crucial for this process, which provides a promising strategy for the design of novel high-performance organic electrode materials. Organic molecules are intriguing candidates for electrode materials for use in rechargeable Li ion batteries. The application of such species has aroused much interest recently, owing to the obvious advantages of such a system: no need for rare metals, low safety risks compared to transition metal oxides, and design flexibility at the molecular level. However, organic molecules are usually considered to possess relatively poor specific energies and cycling properties, as compared to those of inorganic materials, and these factors greatly limit their practical application. Recently, studies on aromatic carbonyl derivatives showed that organic materials can possess outstanding electrochemical performance comparable to, or even superior to, inorganic materials. Furthermore, the wide diversity of organic redox systems, as well as the excellent flexibility in their molecular design, suggest even greater prospects for these materials, and this has inspired the exploration of new organic Li ion insertion systems with improved performance. Aromatic C6 rings are the basic structural units of graphite and other carbon-based electrode materials, which are the most commonly used anodes in commercial Li ion batteries owing to their high electric conductivity and low cost. It has traditionally been believed that each C6 ring can accept one Li ion to form an intercalated Li/C6 complex, giving a relatively low theoretical capacity of 372 mAhg . Recently, studies on graphene, nanographene, and their derivatives reveal that, through the reduction of size and dimensionality, these materials exhibit unique electric and electrochemical properties superior to those of conventional graphitic materials; thus, these materials are currently a hot research topic. In studies of electrode materials for Li ion batteries, these derivatives also exhibit high reversible capacities of up to almost twice the theoretical value of graphite, although the detailed mechanism is still unclear. This leads to a fundamental question in the study of carbonbased electrode materials: How many Li ions can actually be inserted onto each C6 aromatic ring? Multi-ring aromatics (for example, naphthalene, NTCDA, perylene, etc.) and their derivatives have planar C6 ring structures similar to graphene or nanographene. NTCDA is a typical example; it has a naphthalene-like ring structure consisting of two C6 rings fused together along with two cyclic anhydride groups (Figure 1a). NTCDA is a well-known organic semiconductor with good crystallinity and has been extensively studied for use in molecular electric devices. It provides an ideal model to study Li ion insertion onto C6 rings owing to the minimal number of C6 rings it possesses, which guarantees the necessary insolubility of the electrode materials in the commonly used electrolyte solution (ethylene carbonate/dimethyl carbonate/LiPF6) for Li ion batteries. NTCDA also possesses the necessary degree of conductivity for electron transport among molecules. We investigated the electrochemical Li ion insertion/deinsertion properties of NTCDA using model test cells with Li metal as the counter electrode. The working electrode consisted of NTCDA, acetylene black (AB), and polytetrafluoroethylene binders in a weight ratio of about 60:35:5. The cells were initially cycled by discharging (Li ion insertion) and charging (Li ion deinsertion) repeatedly in a potential range of 0.001–3.0 V vs. Li/Li at a moderate current rate of 100 mAg . Figure 1b shows selected discharge/charge curves (the 1st, 2nd, 3rd, and 8th cycles) for NTCDA. Figure 1c shows the corresponding discharge and charge capacities of NTCDA versus the cycle number. The first discharge and charge capacities are 1273 and 724 mAhg , respectively, showing a coulombic efficiency [*] X. Han, G. Qing, T. Sun State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology Wuhan, 430070 (China) E-mail: suntaolei@iccas.ac.cn

Enhanced visible-light photocatalytic activity of Bi2WO6 nanoparticles by Ag2O cocatalyst

Abstract: Cocatalyst modification is an efficient strategy to improve the photocatalytic efficiency of photocatalysts by promoting the effective separation of photogenerated electrons and holes. However, most of the cocatalysts are restricted to noble metals (e.g., Ag, Au, Pt) and seldom investigation has been focused on their oxides. In this study, Ag 2 O cocatalyst was coated on the surface of Bi 2 WO 6 nanoparticles by an impregnation method followed by a low-temperature treatment (100–350 °C) and their photocatalytic performance was evaluated by the photocatalytic decolorization of methyl orange solution under visible-light irradiation. It was found that after the surface coating of Ag 2 O, the obtained Ag 2 O/Bi 2 WO 6 composites exhibited an obvious higher photocatalytic activity than the unmodified Bi 2 WO 6 nanoparticles and N-doped TiO 2 . Owing to the photosensitive property of pure Ag 2 O phase, the Ag–Ag 2 O composite easily formed during the decomposition process of organic substances under visible-light irradiation. On the bases of experimental result and band structure analysis, an Ag–Ag 2 O cocatalyst-enhanced photocatalytic mechanism is proposed; namely, the Ag–Ag 2 O cocatalyst possibly reduces oxygen via a multi-electron transfer mechanism. The present results suggest that Ag–Ag 2 O can act as a new and effective cocatalyst for the enhanced photocatalytic performance of photocatalysts, which provides a new approach for the design and development of high-performance visible-light photocatalysts.

A New Approach for Photocorrosion Inhibition of Ag2CO3 Photocatalyst with Highly Visible-Light-Responsive Reactivity

Abstract: A novel visible-light-responsive photocatalyst Ag2CO3 was prepared by a facile precipitation reaction between NaHCO3 and AgNO3. The as-prepared samples showed relatively high photocatalytic activity toward rhodamine B (RhB) degradation in aqueous solution. The observed photoreactivity on Ag2CO3 was attributed to the synergetic effects of small band gap, great oxidation potential of photogenerated holes, and high separation efficiency of photogenerated electrons and holes. Nevertheless, Ag2CO3 was unstable under visible light due to the photocorrosion resulting from metallic silver formation. The photocorrosion of Ag2CO3 can be efficiently inhibited by adding AgNO3 in the photocatalytic reaction system owing to the lower electrode potential of Ag/AgNO3 than that of Ag/Ag2CO3. Our results shed new light on the photocatalytic activity as well as photocorrosion mechanism of silver-containing compounds and inhibit the method of photocorrosion.

UV- and Visible-Light Photocatalytic Activity of Simultaneously Deposited and Doped Ag/Ag(I)-TiO2 Photocatalyst

Abstract: Ag modification has been demonstrated to be an efficient strategy to improve the photocatalytic performance of TiO2 photocatalysts. However, the previous studies about the Ag modification are only restricted to the surface loading of metallic Ag or Ag(I) doping, investigations have seldom been focused on the simultaneously deposited and doped Ag/Ag(I)-TiO2 photocatalyst. In this study, Ag/Ag(I)-TiO2 photocatalyst was prepared by a facile impregnated method in combination with a calcination process (450 °C) and the photocatalytic activity was evaluated by the photocatalytic decomposition of methyl orange and phenol solutions under both UV- and visible-light irradiation, respectively. It was found that Ag(I) doping resulted in the formation of an isolated energy level of Ag 4d in the band gap of TiO2. On the basis of band-structure analysis of Ag/Ag(I)-TiO2 photocatalyst, a possible photocatalytic mechanism was proposed to account for the different UV- and visible-light photocatalytic activities. Under visi...

One-pot pyridine-assisted synthesis of visible-light-driven photocatalyst Ag/Ag3PO4

Abstract: A highly efficient and stable Ag/Ag3PO4 photocatalyst was prepared by a facile one-pot hydrothermal method assisted by pyridine. Pyridine played two important roles in the synthesis: it could work as a coordination agent role of Ag+ and act as reductant for reduce partial Ag+ to metallic Ag. The influences of pyridine amount, reaction temperature and pH value on the content of Ag in the composite were investigated. The diffuse reflectance spectra (DRS) indicated that the Ag/Ag3PO4 had strong absorption in UV and visible light regions. The photocatalytic activity of the composite was evaluated by the degradation of methyl orange (MO) and phenol under visible light irradiation. The experimental results indicated that the Ag/Ag3PO4 showed highly efficient and stable photocatalytic activity under visible light irradiation. It was considered that the excellent performance resulted from the surface plasmon resonance of Ag nanoparticles and a large negative charge of PO43− ion.

Enhanced photovoltaic performance of dye-sensitized solar cells based on TiO2 nanosheets/graphene composite films

Abstract: Dye-sensitized solar cells (DSSCs) based on TiO2 nanosheets (TiO2-NSs)/graphene nanocomposite films were fabricated, and the effects of graphene on the microstructures and photoelectric conversion performance of the as-fabricated DSSC were investigated. The graphene loading clearly influences the textural properties (including specific surface areas, porosity and pore volume) and the optical absorption properties. Moreover, the charge transfer and transport versus the charge trapping and recombination is also affected by the graphene loading. As a consequence, the photoelectric conversion efficiency of the TiO2-NSs/graphene nanocomposite film electrodes can be improved to a great extent upon graphene loading, dependent on the loading amount of graphene. A moderate amount of graphene ( 0.75 wt%) largely lowered the DSSC performance. Higher graphene loading not only impaired the crystallinity of the TiO2-NSs, but also shielded the light adsorption of the dyes and reduced the number of photogenerated electrons.

Fluorine ions-mediated morphology control of anatase TiO2 with enhanced photocatalytic activity

Abstract: This review briefly summarizes recent advances in fluorine ions-mediated morphology control of anatase TiO2 in the forms of nanotube arrays, nanosheets with high-energy facets, and hollow spheres. The correlations between the enhanced photocatalytic activity and structural and morphological modifications of anatase TiO2 by fluorine ions are addressed.

Visible-Light Photocatalytic Activity and Deactivation Mechanism of Ag3PO4 Spherical Particles

Abstract: Ag(3)PO(4) spherical particles were synthesized by a facile precipitation method using silver nitrate and Na(2) HPO(4) as precursors. The as-prepared samples had a high photocatalytic activity toward Rhodamine B (RhB) degradation under visible-light illumination. With increasing recycling times the photocatalytic activity first increased and then decreased. Based on systematic characterization of particles by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis absorption spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), a possible mechanism responsible for the improvement and subsequent decline of the photocatalytic performance of Ag(3)PO(4) is proposed. Ag(3)PO(4) spherical particles recycled for four times showed the highest photocatalytic activity because, according to our mechanism, Ag nanoparticles deposited on Ag(3)PO(4) acted as electron trapping centers to prevent photogenerated electron-hole pairs from recombination. A further increase in the recycle times decreases the photocatalytic activity owing to the shielding effect by Ag layers on the surface of Ag(3)PO(4). The results presented herein shed new light on the photostability of Ag(3) PO(4) spherical particles and are potentially applicable to other photocatalytically active composites.

One-Dimensional Metal Oxide Nanotubes, Nanowires, Nanoribbons, and Nanorods: Synthesis, Characterizations, Properties and Applications

Abstract: One dimensional nanomaterials have attracted much attention from academia and industry. A large series of devices have been created on the basis of 1D nanomaterials. Their applications have changed and will continuously change our daily life. In this paper, we will present a comprehensive review on the synthesis, structure characterization, properties and actual and future potential applications of one dimensional nanomaterials. Due to the large number of review papers on Carbon and ZnO nanomaterials, we will focus only on one dimensional nanostructures based on other important metal oxides than ZnO based 1D nanomaterials. Different general synthesis strategies have firstly been presented. A series of very promising and representative 1D metal oxide nanaomaterials, their synthesis and properties, will then be discussed. The applications of these 1D metal oxide nanomaterials in catalysis, photocatalysis, electrocatalysis, in sensors development, in solar cells, in field effect transistor development, in Li...

Unique photocatalytic oxidation reactivity and selectivity of TiO2–graphene nanocomposites

Abstract: Mesoporous TiO2–graphene nanocomposites are fabricated in high yield via two successive steps: (1) hydrothermal hydrolysis of Ti(SO4)2 in an acidic suspension of graphene oxide to gain TiO2–graphene oxide nanocomposites; (2) UV-assisted photocatalytic reduction of graphene oxide to get the TiO2–graphene nanocomposites. The anatase TiO2 nanocrystals with a crystallite size of 10–20 nm are densely packed and supported on meshy graphene sheets with close interfacial contacts, which is confirmed by transmission electron microscopy (TEM) together with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Although a low graphene loading (0–2 wt%) slightly influences the textural properties (including the crystallite size, specific surface areas, and pore volume etc.), the incorporation of graphene in TiO2–graphene nanocomposites greatly increases the adsorption capacity towards azo dyes such as MO and MB, which is possibly associated with their unique surface properties. Significantly, the incorporated graphene exerts combined effects on the adsorption and charge transfer dynamics in TiO2–graphene nanocomposites, which together endow them with good photocatalytic reactivity and tunable photocatalytic selectivity in decomposing MO and MB in aqueous solution.