De-Kun Ma

From Hollow Olive-Shaped BiVO4 to n−p Core−Shell BiVO4@Bi2O3 Microspheres: Controlled Synthesis and Enhanced Visible-Light-Responsive Photocatalytic Properties

In this study, hollow olive-shaped BiVO(4) and n-p core-shell BiVO(4)@Bi(2)O(3) microspheres were synthesized by a novel sodium bis(2-ethylhexyl)sulfosuccinate (AOT)-assisted mixed solvothermal route and a thermal solution of NaOH etching process under hydrothermal conditions for the first time, respectively. The as-obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, Brunauer-Emmett-Teller surface area, and UV-vis diffuse-reflectance spectroscopy in detail. The influence of AOT and solvent ratios on the final products was studied. On the basis of SEM observations and XRD analyses of the samples synthesized at different reaction stages, the formation mechanism of hollow olive-shaped BiVO(4) microspheres was proposed. The photocatalytic activities of hollow olive-shaped BiVO(4) and core-shell BiVO(4)@Bi(2)O(3) microspheres were evaluated on the degradation of rhodamine B under visible-light irradiation (λ > 400 nm). The results indicated that core-shell BiVO(4)@Bi(2)O(3) exhibited much higher photocatalytic activities than pure olive-shaped BiVO(4). The mechanism of enhanced photocatalytic activity of core-shell BiVO(4)@Bi(2)O(3) microspheres was discussed on the basis of the calculated energy band positions as well. The present study provides a new strategy to enhancing the photocatalytic activity of visible-light-responsive Bi-based photocatalysts by p-n heterojunction.

One-pot synthesis of N-doped carbon dots with tunable luminescence properties

N-Doped carbon dots synthesized by a one-pot solvothermal route displayed tunable luminescence due to different N contents. They could be directly applied in the imaging of peritoneal macrophages of mice. This study provides a new method to tune the luminescence of carbon-based materials through non-metal doping.

Controlled synthesis of olive-shaped Bi2S3/BiVO4 microspheres through a limited chemical conversion route and enhanced visible-light-responding photocatalytic activity

Well-defined olive-shaped Bi(2)S(3)/BiVO(4) microspheres were synthesized through a limited chemical conversion route (LCCR), where olive-shaped BiVO(4) microspheres and thioacetamide (TAA) were used as precursors and sulfur source, respectively. The as-synthesized products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission microscope (HRTEM), X-ray photoelectron spectra (XPS), UV-visible diffuse-reflectance spectroscopy (UV-vis DRS), and photoluminescence (PL) spectra in detail. Compared with pure BiVO(4) microspheres and Bi(2)S(3) nanorods, the Bi(2)S(3)/BiVO(4) products showed obviously enhanced photocatalytic activity for the degradation of rhodamine B (Rh B) in aqueous solution under visible-light irradiation (λ > 400 nm). In addition, the Bi(2)S(3)/BiVO(4) composite microspheres showed good visible-light-driven photocatalytic activity for the degradation of refractory oxytetracycline (OTC) as well. On the basis of UV-vis DRS, the calculated energy band positions, and PL spectra, the mechanism of enhanced photocatalytic activity of Bi(2)S(3)/BiVO(4) was proposed. The present study provides a new strategy to design composite materials with enhanced photocatalytic performance.

Various Bismuth Oxyiodide Hierarchical Architectures: Alcohothermal-Controlled Synthesis, Photocatalytic Activities, and Adsorption Capabilities for Phosphate in Water

Controllable synthesis of morphology and composition of functional material through a similar method is very necessary to understand the related properties. In this study, we report a facile solvothermal route to synthesize a series of bismuth oxyiodide compounds, including BiOI, Bi7O9I3, and Bi4O5I2 hierarchical microspheres, under relatively mild conditions through only adjusting the types of alcohols. It was found that the viscosity of alcohol played key roles in determining the morphologies and compositions of the final products. UV-visible diffuse-reflectance spectra and theoretic calculations indicated that bismuth oxyiodides with different ratios of Bi:O:I clearly possessed different light absorption and energy band structures. As a result, the as-synthesized BiOI, Bi7O9I3, and Bi4O5I2 hierarchical microspheres displayed morphology- and composition-dependent photocatalytic activities for the degradation of rhodamine B (RhB) and colorless phenol under visible-light irradiation. On the basis of experimental results, the difference of photocatalytic activity of these bismuth oxyiodide compounds was discussed. Furthermore, hierarchical bismuth oxyiodide microspheres were also evaluated as adsorbents for removing phosphate from aqueous solution. The results showed that Bi7O9I3 and Bi4O5I2 hierarchical microspheres had good adsorption capabilities for phosphate in water because of their larger surface areas and hierarchical porous structures.

Size control of Au@Cu2O octahedra for excellent photocatalytic performance

Due to its intrinsic structure and characteristics, small size and monodispersity, control of single-crystalline Cu2O polyhedra in aqueous media is a challenge, which is important to overcome to achieve enhanced photocatalytic activity. Here, we use heterogeneous nucleation, rather than homogeneous nucleation, of Cu2O with gold nanorods as seeds to realize subsequent uniform crystal growth. We obtained nearly monodisperse octahedral Au@Cu2O nanocrystals with single-crystalline shells, which are distinct from the pentagonal column-shaped structures previously described. Due to the fact that one Au@Cu2O holds only one Au nanorod, two formulas were deduced for convenient size control of the Cu2O shell. The formulas were calculated by adjusting the amount of Au rods that are relatively quantified. The formula also allows the size of the final product to be predicted when a given amount of gold seeds are employed. The experimental results agree well with the calculated data. The result of larger surface area and improved charge separation from core-shell interaction, made five samples of different sizes exhibit excellent photocatalytic activity toward MO degradation. The synthetic strategy reported here provides a clue to monodispersity and size control of core-shell nanocrystals, which is useful in developing new catalysts with better performance that are urgently needed in the fields of both science and technology.

A Versatile Strategy for Shish-Kebab-like Multi-heterostructured Chalcogenides and Enhanced Photocatalytic Hydrogen Evolution.

A series of multi-heterostructured metal chalcogenides (CdS-Te, NiS/CdS-Te, and MoS2/CdS-Te) with a surprising shish-kebab-like structure have been synthesized via a one-step microwave-assisted pyrolysis of dithiocarbamate precursors in ethylene glycol. Subsequently, CdS-Te composites were exploited as a self-sacrificial template to craft various CdS-Te@(Pt, Pd) multi-heterostructures. Highly uniform dispersion and intimate interactions between CdS and multicomponent cocatalysts, together with improved separation of photogenerated carriers due to the presence of Te nanotubes (NTs) and trace CdTe, enable CdS-based heterostructured photocatalysts to exhibit greatly enhanced efficiency and stability in the photocatalytic production of H2. Thorough morphological characterizations revealed that the growth of metal sulfide/Te heterostructures originates from the growth of Te tubes, which is likely governed by diffusion-limited depletion of the Te precursor and the dissolution-crystallization process of Te seeds followed by the formation of metal sulfide kebabs.

One-dimensional hexagonal-phase NaYF4: Controlled synthesis, self-assembly, and morphology-dependent up-conversion luminescence properties

One-dimensional (1D) hexagonal-phase NaYF4 with various morphologies including nanowires, nanowire bundles, submicrorods, and hexagonal microprisms have been selectively synthesized via a facile complexing reagent-surfactant-assisted hydrothermal route. The effects of reaction temperature, the amount of SDBS (sodium dodecylbenzenesulfonate) and citric acid, and the sorts of surfactants and complexing reagents on the morphology, size, and crystal phase purity of the as-synthesized products have been investigated in detail. By choosing NaYF4 nanowire as a candidate, its formation mechanism was proposed on the basis of XRD analysis and SEM observation of the products at the different reaction time periods. The studies on the up-conversion emission of hexagonal-phase Yb3+, Er3+ ions-codoped NaYF4 including nanowires, submicrorods, and hexagonal microprisms showed that the optical properties of the as-synthesized materials are morphology-dependent. It was found that NaYF4 : Yb, Er nanowires had the highest ratios between the intensities of green and red band emission whereas hexagonal NaYF4 : Yb, Er microprisms had the lowest ones. The synthesis of hexagonal-phase NaYF4 with controllable size and morphology, optical properties, together with the realization of self-assembly of NaYF4 nanowires reported in this work will be useful for further applications in the fabrication of optoelectronic nanodevices.

Synthesis, characterization and optical properties of flower-like tellurium

Tellurium (Te) with a flower-like superstructure has been successfully synthesized through a low temperature biphasic solvothermal reaction utilizing diethyldithiocarbamato tellurium (IV) (TDEC) as Te source and 2,2′-dithiodibenzoic acid (DTBA) as a reducing agent. Characterizations by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), energy dispersive X-ray spectroscopy (EDS), selected-area electron diffraction (SAED) show that the as-prepared product consists of well-aligned needle-like t-Te nanorods growing radically from the core. These nanorods have a diameter ranging from tens to hundreds of nanometers and a length of several micrometers, and the Raman spectra are greatly affected by their diameter. Fluorescence measurement reveals that the t-Te superstructures produce blue–violet emission.

An unusual zinc substrate-induced self-construction route to various hierarchical architectures of hydrated tungsten oxide

A novel active zinc substrate-induced sequential self-construction method is presented for the fabrication of hydrated WO(3) hierarchical octahedrons, flakes, lanterns, and arresting sandwiched double-layer nanorods arrays architectures for the first time. Photocatalytic activity and gas sensing properties of the as-obtained various WO(3).0.33H(2)O architectures were studied as well.

Concave Bi2WO6 nanoplates with oxygen vacancies achieving enhanced electrocatalytic oxygen evolution in near-neutral water

Developing highly efficient and inexpensive oxygen evolution reaction (OER) electrocatalysts in near-neutral water is of paramount importance for many practical applications. Herein, we report that Bi2WO6 concave nanoplates (CNPs) with oxygen vacancies enable the electrocatalytic OER under neutral conditions with high activity and good durability. To the best of our knowledge, this is the first example on W-based electrocatalysts containing no first-row transition metal or precious metal elements for the OER in near-neutral water. Experimental results and first-principles calculations revealed that the presence of oxygen vacancies in Bi2WO6 CNPs could significantly decrease the charge-transfer resistance and adsorption barrier of H2O molecules in the process of electrochemistry, thus benefiting the improvement of OER activity. The fabrication of concave surfaces with high energy facets could further enhance the OER activity of the Bi2WO6 NP electrocatalysts. As a result, the synergistic effect of oxygen vacancies and concave surfaces led to impressive performance of Bi2WO6 CNPs for the OER, which is comparable to the best electrocatalysts among known inorganic non-precious metal compounds. The present strategy on the combination of defect and crystal facet engineering could open a new avenue to design new and highly efficient OER electrocatalysts.