Changhao Liang

Catalytic growth and photoluminescence properties of semiconductor single-crystal ZnS nanowires

Abstract Semiconductor single-crystal ZnS nanowires have been successfully synthesized in bulk quantities by a new, simple and low cost process based on thermal evaporation of ZnS powders onto a silicon substrate with the presence of Au catalyst. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) observations show that the ZnS nanowires have diameters about 30–60 nm and lengths up to several tens micrometers. The growth of ZnS nanowires is controlled by the conventional vapor–liquid–solid (VLS) mechanism. And the photoluminescence (PL) properties of these synthesized single-crystal ZnS nanowires have been presented in this Letter.

Chemical‐Template Synthesis of Micro/Nanoscale Magnesium Silicate Hollow Spheres for Waste‐Water Treatment

Micro/nanoscale magnesium silicate hollow spheres were synthesized by using silica colloidal spheres as a chemical template in one pot. The hollow spherical structure, consisting of well-separated nanoscale units, was microscale as a whole and could be easily handled in solution. The as-synthesized magnesium silicate hollow spheres with large specific surface area showed availability for the removal of organic and heavy-metal ions efficiently from waste water. Importantly, the micro/nanoscale magnesium silicate hollow spheres that had adsorbed organic pollutants could be regenerated by calcination and used repeatedly in pollutant removal. Magnesium silicate hollow spheres synthesized by a scaled-up chemical template method may have potential applications in removing cationic dyes and heavy-metal ions from waste water.

Mass production of micro/nanostructured porous ZnO plates and their strong structurally enhanced and selective adsorption performance for environmental remediation

A facile route was presented for mass fabrication of porous ZnO nanoplates, with a yield of >94%, based on a solvothermal method, using ethylene glycol as the morphology director, and subsequent annealing process. The as-prepared ZnO nanoplates are composed of two terminal non-polar planes with several microns in the planar dimensions and 10–15 nm in thickness. The nanoplates are porous with a pore diameter of 5–20 nm and a high specific surface area (147 m2 g−1). Importantly, such ZnO nanoplates show strong and selective adsorption to cationic contaminants. Especially, they can very efficiently adsorb heavy metal cations in aqueous solution, and have an unsaturated adsorption capacity of more than 1600 mg g−1 for Cu(II) ions, exhibiting a strong, structurally enhanced adsorption performance. The adsorption isotherm is subject to the Freundlich equation, in contrast to that of the commercial ZnO nanopowders, which follows a Langmuir isotherm model. This work not only demonstrates the possibility and validity of the porous ZnO nanoplates as promising adsorbents for contaminant-removal and environmental remediation, but also gives insight into understanding the adsorptive behavior of porous ZnO plates.

Defect-Mediated Formation of Ag Cluster-Doped TiO2 Nanoparticles for Efficient Photodegradation of Pentachlorophenol

A novel strategy was designed to prepare Ag cluster-doped TiO(2) nanoparticles (Ag/TiO(2) NPs) without addition of any chemical reducing agent and/or organic additive. A defect-rich TiO(x) species was generated by laser ablation in liquid (LAL) of a Ti target. The silver ions could be reduced and deposited on the surface of TiO(2) NPs through the removal of oxygen vacancies and defects; the TiO(x) species evolved into anatase NPs in a hydrothermal treatment process. The derived Ag/TiO(2) NPs are approximately 25 nm in size, with narrow size distribution. The Ag clusters are highly dispersed inside TiO(2) and less than 3 nm in size. The doped amount can be tuned by changing the concentration of Ag(+) ions. The as-synthesized Ag/TiO(2) NPs display improved photocatalytic efficiency toward pentachlorophenol (PCP) degradation.

Fabrication and photoluminescence of ordered GaN nanowire arrays

Large-scale of crystalline GaN nanowires (diameter∼50u200anm) have been fabricated through chemical-vapor deposition in the nanochannels of the anodic alumina template. X-ray diffraction and selected area electron diffraction pattern investigations indicate that the nanowires are single crystal with hexagonal wurtzite structure. A typical scanning electron microscopy image and the energy dispersive x-ray spectroscopy results indicate that indium nanoparticles only act as catalyst in GaN nanowires growth. At room temperature, photoluminescence spectrum of the GaN nanowire arrays shows a visible broadband with three peaks, which are located at about 363, 442, and 544 nm. The light emission may be attributed to GaN band-edge emission, the existence of defects or surface states, and the interaction between the ordered GaN nanowires and anodic alumina membrane. The growth mechanism of crystalline GaN nanowires is discussed. The method makes it possible to synthesize other nitride nanowire arrays.

Polyacrylonitrile ferrous chloride composite porous nanofibers and their strong Cr-removal performance

A simple and effective route is presented for the fabrication of polyacrylonitrile (PAN)/ferrous chloride (FeCl2) composite porous nanofibers based on electrospinning technology. The obtained composite nanofibers are amorphous and nanoporous in structure, and 100–300 nm in diameter and 10 m2 g−1 in specific surface area. Importantly, such PAN/FeCl2 porous nanofibers have exhibited excellent performance for Cr-removal from a Cr2O72−-containing solution in one step. The Cr-removal capability is more than 110 mg Cr/g FeCl2, which is much higher than the previously reported values of the other nanomaterials, as Cr(VI)-removal adsorbents, in addition to the easier separation from solution. This was attributed to the formation of weak coordination bonds PAN⋯Fe(II) in the nanofibers. The coordination bonds on the pore walls and surface not only adsorb the Cr(VI) but also reduce it to Cr(III), alleviating the Cr-induced toxicity. In contrast, the pure PAN nanofibers can not remove Cr, the mixture of PAN nanofibers with FeCl2 powder, and the PAN/FeCl2 cast films only induce insignificant Cr-removal. This study provides an effective route for the development of new environmental remediation materials. The PAN/FeCl2 composite nanofibers could be a good candidate for efficient Cr-removal from wastewater and for the deep-purification of pollutant water.

A Versatile Method for Controlled Synthesis of Porous Hollow Spheres

A versatile method was developed to synthesize nickel silicate, silica, and silica-nickel composite porous hollow spheres by using silica spheres as templates. In the preparation, silica spheres were treated with a mixture of NiSO(4)·6H(2)O and NH(3)·H(2)O. The nickel-based ingredient reacted with the silica to form a shell while the alkaline solution could remove the silica core, thus forming the nickel silicate hollow spheres. After these spheres were further treated with hydrogen in reduction or with HCl in etching, they became silica-nickel hollow spheres or silica hollow spheres, respectively. The sizes of these hollow spheres depended on the concentration of the precursor. Our investigation also found that their surface properties or magnetic properties could be tailored by adjusting the fabrication parameters.

Template-induced synthesis of hierarchical SiO2@γ-AlOOH spheres and their application in Cr(VI) removal

Hierarchical structured SiO(2)@gamma-AlOOH spheres were fabricated in one step by using silica colloidal spheres as a template. Scanning electron microscopy and transmission electron microscopy investigation showed that the shell is composed of large amounts of nanoscale gamma-AlOOH lamellas. The growth mechanism was proposed as silica template-induced heterogeneous deposition of gamma-AlOOH lamellas. The adsorption properties of hierarchical SiO(2)@gamma-AlOOH spheres annealed at different temperatures were investigated through the removal test of Cr(VI) ions in model wastewater, and the nanostructures annealed at 400 degrees C showed good adsorption capability of Cr(VI) ions.

Highly Dispersed Ultrafine Pt Nanoparticles on Reduced Graphene Oxide Nanosheets: In Situ Sacrificial Template Synthesis and Superior Electrocatalytic Performance for Methanol Oxidation.

We report a simple and environmentally friendly route to prepare platinum/reduced graphene oxide (Pt/rGO) nanocomposites (NCs) with highly reactive MnOx colloids as reducing agents and sacrificial templates. The colloids are obtained by laser ablation of a metallic Mn target in graphene oxide (GO)-containing solution. Structural and morphological investigations of the as-prepared NCs revealed that ultrafine Pt nanoparticles (NPs) with an average size of 1.8 (±0.6) nm are uniformly dispersed on the surfaces of rGO nanosheets. Compared with commercial Pt/C catalysts, Pt/rGO NCs with highly electrochemically active surface areas show remarkably improved catalytic activity and durability toward methanol oxidation. All of these superior characteristics can be attributed to the small particle size and uniform distribution of the Pt NPs, as well as the excellent electrical conductivity and stability of the rGO catalyst support. These findings suggest that Pt/rGO electrocatalysts are promising candidate materials for practical use in fuel cells.

In situ self-assembly synthesis and photocatalytic performance of hierarchical Bi0.5Na0.5TiO3 micro/nanostructures

A novel hierarchical Bi0.5Na0.5TiO3 (BNT) micro/nanostructure was synthesized viain situself-assembly of BNT nanocrystals under hydrothermal conditions. Each spheric flower-like BNT micro/nanostructure is composed of nanosheetsca. 100 nm in width, 300 nm in length and 10 nm in thickness. The self-assembly growth process of hierarchical BNT micro/nanostructures from BNT nanocrystals was investigated by changing the reaction time, the molar ratio of precursors and NaOH concentration. From time-dependent morphology evolution, a two-step growth mechanism was proposed to explain the growth of the hierarchical BNT micro/nanostructure. Importantly, such structured BNT shows better photocatalytic performance in the photodegradation of methyl orange than that of the powders of spheric and cubic structured BNT. The intrinsic structure of BNT may contribute to its higher surface-to-volume ratio and stability against overdue aggregation. This study not only gives insights into the hierarchical growth behavior of BNT complex micro/nanoarchitectures, but also provides an efficient route for enhancing the photocatalytic performance of BNT.