Dangguo Gong

Nitrogen-doped TiO2 nanotube array films with enhanced photocatalytic activity under various light sources

Highly ordered nitrogen-doped titanium dioxide (N-doped TiO(2)) nanotube array films with enhanced photocatalytic activity were fabricated by electrochemical anodization, followed by a wet immersion and annealing post-treatment. The morphology, structure and composition of the N-doped TiO(2) nanotube array films were investigated by FESEM, XPS, UV-vis and XRD. The effect of annealing temperature on the morphology, structures, photoelectrochemical property and photo-absorption of the N-doped TiO(2) nanotube array films was investigated. Liquid chromatography and mass spectrometry were applied to the analysis of the intermediates coming from the photocatalytic degradation of MO. The experimental results showed that there were four primary intermediates existing in the photocatalytic reaction. Compared with the pure TiO(2) nanotube array film, the N-doped TiO(2) nanotubes exhibited higher photocatalytic activity in degradating methyl orange into non-toxic inorganic products under both UV and simulated sunlight irradiation.

Titanate and titania nanostructured materials for environmental and energy applications: a review

Nanosized TiO2-based materials with unique structural and functional properties have already led to breakthroughs in various applications including photocatalysis, adsorption, lithium-ion batteries, etc. In this review, we present the state-of-the-art development of fabrication strategies of titanate/titania nanostructures and their corresponding environmental and energy applications. First, the structural features of titanate and titania and their correlation are explained in great detail. After which, recent research efforts on the development of multi-dimensional titanate materials are summarized. Following that, the applications of titanate/titania nanomaterials in the fields of adsorbents, photocatalysis, lithium-ion batteries, photovoltaics, electrochromic devices, self-cleaning and oil–water separation are reviewed. Finally, the future perspectives for the nanostructured titanate and titania are discussed. Continuous development in this area is essential to endow TiO2-based materials with advanced functionality and improved performance for practical applications.

Synthesis of Nanostructured Silver/Silver Halides on Titanate Surfaces and Their Visible-Light Photocatalytic Performance

Dense and uniform silver halides AgX (X = Cl, Br, I) nanoparticles were successfully fabricated on layered titanate nanowired honeycomb (TNHC) thin films. The growth of AgX nanocrystals was carried out through two steps. Firstly, ion-exchange was employed to incorporate Ag(+) ions into the interlayer of the titanate nanowires. Secondly, hydrogen halide (HX) solution was rapidly injected onto the ion-exchanged silver TNHC surface to generate nanosized AgX particles on TNHC films. The effect of the reaction time, solution pH, and concentration of halide anions on the morphology of the AgX photocatalysts has been studied. Followed by light-irradiation, the optimized Ag/AgX thin films exhibited excellent degradation performance under visible light because of localized surface plasmon resonance effect.

Hierarchical layered titanate microspherulite: formation by electrochemical spark discharge spallation and application in aqueous pollutant treatment

An ultrafast and template-free method to synthesize three-dimensional (3D) hierarchical layered titanate microspherulite (TMS) particles with high surface area is reported. The synthesis makes use of an electrochemical spark discharge spallation (ESDS) process, during which a fast anodic reaction on the titanium surface creates a layer of titanium dioxide that instantly breaks down by the applied electrical field into the solution in the form of titanium oxide particles. The spalled particles readily react with the heated NaOH electrolyte to form the titanate particles. A typical as-prepared TMS with a diameter of 0.4∼1.5 μm is synthesized by ESDS of Ti foils in 10 M NaOH solution under an applied current density of 0.5 A cm−2, leading to a reaction yield of approximately 0.10∼0.15 g per square centimetre of exposed Ti foil within 20 min. After hydrogen ion exchange, the surface area can reach as high as ∼406 m2 g−1. On the Ti surface, a crystalline rutile TiO2 nanosheet structure is formed, which is attributed to the local exothermic heat caused by the spark discharge. A formation mechanism of the TMS is discussed based on field emission scanning electron microscopy (FESEM), a transmission electron microscopy (TEM) study and Raman scattering spectroscopy analysis. The as-prepared TMS shows excellent adsorption performance compared with a titanate micro-particle (TMP), nanowire (TNW) and nanotube (TNT) when methylene blue (MB) and PbII ions are used as representative organic and inorganic pollutants. The mechanism of adsorption has also been discussed.

Ultrafast Synthesis of Layered Titanate Microspherulite Particles by Electrochemical Spark Discharge Spallation

Recently, a new hydrothermal approach to fabricate titanate materials has attracted much attention. These layered titanate nanomaterials show excellent abilities in ion-exchange, absorption, photoelectronicity, and so on. To satisfy the requirement of different applications, there has been a drastic increase in research to develop new approaches to produce different types of semiconductor oxide nanostructures, especially titanium-based oxides. Up to now, the synthesis of 1D and 2D nanotitanate has been widely investigated with many interesting properties reported. For example, 1D titanate nanotubes, nanowires, nanorods, and 2D titanate nanosheets have been synthesized by hydrothermal, high-temperature oxidation, molten-salt synthesis, and exfoliation methods. Among which hydrothermal synthesis is most widely used. Recent investigations have demonstrated that 3D hierarchical nanostructures could improve the performance of the material in catalysis, biomedical, energy conversion, and water-treatment applications, among others, due to the superior properties derived from the high specific surface area and porous structure. However, it is still challenging to produce 3D hierarchically complex shapes of titanate over multiple scales and the synthetic method is usually not straightforward. Until now, the general approach for preparing hierarchical titanate structures involved the use of sacrificial templates, such as zinc oxide nanotemplate. Alternatively, the template-free methods for generating hierarchical titanates typically employ bottom-up methods, such as reacting agar gel containing a solution of titanium precursor in NH4OH, [5b] two-stage growth through an H2O2-enhanced oxidation process, [5c] twostep synthesis combining hydrolysis and hydrothermal treatment, the chimie douce route by heating TiO2 powder in 15m NaOH solution at reflux, and self-assembly by treating TiCl4 precursor in ethylenediamine at high temperaACHTUNGTRENNUNGtures.[5f] These approaches either take multiple steps or require a long time to ensure complete reaction, for example, the time taken for the reaction between agar gel with Ti precursor and NH4OH is one week. [5b] A simple, fast, and inexpensive method to form 3D hierarchical nanostructures is still lacking and will be of great interest. It is known that a TiO2 porous layer can be formed on a Ti foil surface by mild anodic oxidation in fluoride-containing solutions, rapid breakdown anodization in chloride-/perchlorate-containing electrolytes, or a plasma electrolytic oxidation method. However, to the best of our knowledge, there are no reports using these techniques to generate the titanate materials in powder form, which is traditionally prepared by hydrothermal method. Herein, we report a onestep, template-free method (electrochemical spark discharge spallation) to quickly fabricate layered titanate hierarchical microspherulites (TMSs) with a large surface area (406 mg ) by carefully adjusting the applied electrical spark parameters in the experimental setup (Figure S1 in the Supporting Information). The formation principle of the layered titanate is different from the formation of the TiO2 nanostructures, which include two important steps. First, an ultrahigh anodic reaction oxidizes the Ti surface layer and the formed oxide is immediately broken down by the applied electrical field into the solution in the form of small precipitates. This spallation of the oxide particle is driven by the continuously discharged sparks that simultaneously heat [a] Y. Tang, Dr. Y. Lai, D. Gong, Prof. Z. Dong, Prof. Z. Chen School of Materials Science and Engineering Nanyang Technological University, 50 Nanyang Avenue 639798 (Singapore) Fax: (+65)6790-9081 E-mail : zldong@ntu.edu.sg aszchen@ntu.edu.sg [b] Dr. Y. Lai State Key Laboratory of Physical Chemistry of Solid Surfaces College of Chemistry and Chemical Engineering Xiamen University, Xiamen, 361005 (China) [c] K.-H. Goh, Prof. T.-T. Lim School of Civil and Environmental Engineering Nanyang Technological University, 50 Nanyang Avenue 639798 (Singapore) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000330.

Dual-Phase Titanate/Anatase with Nitrogen Doping for Enhanced Degradation of Organic Dye under Visible Light

The need for environmental remediation processes on a large scale is becoming ever more urgent, especially in anticipation of the increasing demand (and potential shortage) of potable water supplies for a growing world population. Among the armory of advanced oxidation technologies (AOTs), photocatalytic (solar-light-driven) processes are particularly attractive, and photocatalysts have a well-demonstrated potential to mineralize harmful organic substances in air and water and even to act as regenerable adsorbents for toxic heavy metal ions, some of these being recovered as photodeposited metals. [1] Although anatase TiO2 remains the most popular photocatalyst due to high catalytic activity and chemical stability, there are some drawbacks associated with it. The activity is confined to UV-light stimulation, representing just a few percent of the solar-power spectrum. In this respect, much research has been done in modifying the bandgap of the material to extend the absorption into the visible-light region. [2] In addition, the adsorptive properties of TiO2 are not ideal either. [3] Since photoreactions take place at or near the catalyst surface, surface adsorption is critical for efficient interfacial charge transfer to and from the target molecules. In contrast, titanate materials have recently been identified as superior adsorbents for, for example, organic dyes and heavy metal ions. [4] The crystal structure consists of layers of TiO6 octahedra in edge connectivity with protons or alkali metal ions localized between the layers. [5] Various one-dimensional structures, including nano

Correction: Titanate and titania nanostructured materials for environmental and energy applications: a review

Correction for ‘Titanate and titania nanostructured materials for environmental and energy applications: a review’ by Yanyan Zhang et al., RSC Adv., 2015, 5, 79479–79510.