Ordered arrays of Au-nanobowls loaded with Ag-nanoparticles as effective SERS substrates for rapid detection of PCBs.

Large-scale hexagonally close-packed arrays of Au-nanobowls (Au-NBs) with tens of Ag-nanoparticles (Ag-NPs) dispersed in each bowl (denoted as Ag-NPs@Au-NB arrays) are achieved and utilized as effective surface-enhanced Raman scattering (SERS) substrates. The field enhancement benefiting from the special particle-in-cavity geometrical structure as well as the high density of SERS hot spots located in the sub-10 nm gaps between adjacent Ag-NPs and at the particle-cavity junctions all together contribute to the high SERS activity of the Ag-NPs@Au-NB arrays; meanwhile the ordered morphological features of the Ag-NPs@Au-NB arrays guarantee uniformity and reproducibility of the SERS signals. By modifying the Ag-NPs@Au-NB arrays with mono-6-thio-ß-cyclodextrin, the SERS detection sensitivity to 3,3('),4,4(')-tetrachlorobiphenyl (PCB-77, one congener of polychlorinated biphenyls (PCBs, kinds of persistent organic pollutants which represent a global environmental hazard)) can be further improved and a low concentration down to 5 × 10(-7) M can still be examined, showing promising potential for application in rapid detection of trace-level PCBs in the environment.

Insights into the highly efficient SPR enhanced photodegradation of tetracycline by Bi/Bi2MoO6 composites.

A Bi/Bi2MoO6 nanocomposite is fabricated utilizing a simple one-pot solvothermal method, which shows great photodegradation ability to tetracycline (TC). The effect of Bi0 nanoparticles on the photodegradation of TC was investigated, and it is ascribed to the surface plasmonic resonance (SPR) effect. The light energy could be strongly absorbed by the Bi0 nanoparticles, and then transferred to the adjacent Bi2MoO6, to enhance the photocatalytic performance. The results of the sacrifice experiment and quantitative analysis of active radicals showed that the photoelectrons could react with soluble O2 and ·OH to form ·O2-, which finally dominates in the process of photocatalytic degradation of TC. This work proposed a way to construct a highly efficient photocatalyst based on SPR effect, which has great application potential in environmental treatment.

Solid-solutioned homojunction nanoplates with disordered lattice: a promising approach toward "phonon glass electron crystal" thermoelectric materials.

The concept of "phonon glass electron crystal" (PGEC) was proposed in the mid-1990s to maximize the ZT value for thermoelectric materials, based on its combined advantages of low thermal conductivity as in a glass but high electricity as in a well-ordered crystal. Although a great amount of research in complex materials systems for achieving this concept has been done, a perfect "PGEC" material has not been acquired yet. Herein, we first put forward a solid-solutioned homojunction in high temperature phase with disordered lattice, which possesses both high electrical conductivity and low thermal conductivity, as an effective way to optimize the low/mid-temperature thermoelectric property. As an example, nonambient cubic phase AgBiSe(2) was successfully stabilized to room temperature through the formation of a solid solution by Sb incorporation for the first time, and furthermore, in situ formed homojunctions on the surface of solid-solutioned nanoplates were also first achieved through a simple colloidal method. A significant enhancement of thermoelectric performance at low/mid-temperature was realized through synergistical regulation on electronic and thermal transport. As a result, compared to that of original AgBiSe(2) (ZT = 0.03 at 550 K), the ZT value of AgBi(0.5)Sb(0.5)Se(2) was increased to 0.51 at 550 K by the formation of a solid solution, and then further increased to 1.07 at 550 K by the formation of solid-solutioned homojunction.

Half-metallic ferromagnetism in synthetic Co9Se8 nanosheets with atomic thickness.

Controlling the synthesis of atomic-thick nanosheets of nonlayered materials is extremely challenging because of the lack of an intrinsic driving force for anisotropic growth of two-dimensional (2D) structures. In that case, control of the anisotropy such as oriented attachment of small building blocks during the reaction process will be an effective way to achieve 2D nanosheets. Those atomic-thick nanosheets possess novel electronic structures and physical properties compared with the corresponding bulk samples. Here we report Co(9)Se(8) single-crystalline nanosheets with atomic thickness and unique lamellar stacking formed by 2D oriented attachment. The atomic-thick Co(9)Se(8) nanosheets were found to exhibit intrinsic half-metallic ferromagnetism, as supported by both our experimental measurements and theoretical calculations. This work will not only open a new door in the search for new half-metallic ferromagnetic systems but also pave a practical way to design ultrathin, transparent, and flexible paperlike spintronic devices.

Controlled synthesis of germanium nanowires and nanotubes with variable morphologies and sizes.

We report on the controlled growth of germanium (Ge) nanostructures in the form of both nanowire (NW) and nanotube (NT) with ultrahigh aspect ratios and variable diameters. The nanostructures are grown inside a porous anodic aluminum oxide (AAO) template by low-temperature chemical vapor deposition (CVD) assisted by an electrodeposited metal nanorod catalyst. Depending on the choice of catalytic metals (Au, Ni, Cu, Co) and germane (GeH(4)) concentration during CVD, either Ge NWs or NTs can be synthesized at low growth temperatures (310-370 °C). Furthermore, Ge NWs and NTs with two or more branches can be grown from the same stem while using AAO with branched channels as templates. Transmission electron microscopy studies show that NWs are single crystalline and that branches grow epitaxially from the stem of NWs with a crystalline direction independent of diameter. As-grown NTs are amorphous but can crystallize via postannealing at 400 °C in Ar/H(2) atmosphere, with a wall thickness controllable between 6 and 18 nm in the CVD process. The yield and quality of the NTs are critically dependent on the choice of the catalyst, where Ni appears the best choice for Ge NT growth among Ni, Cu, Co, and Au. The synthesis of structurally uniform and morphologically versatile Ge nanostructures may open up new opportunities for integrated Ge-nanostructure-based nanocircuits, nanodevices, and nanosystems.

Revealing the truncated conical geometry of nanochannels in anodic aluminium oxide membranes.

Anodic aluminium oxide (AAO) membranes with self-ordered nanochannels have become promising candidates for applications in the aspects such as structural coloration, photonic crystals, upconversion luminescence and nanofluidic transport. Also, self-ordered AAO membranes have been extensively used for the fabrication of functional nanostructures such as nanowires, nanotubes, nanoparticles, nanorods and nanopillars. Geometries of nanochannels are crucial for the applications of AAO membranes as well as controlling growth (e.g., nucleation, direction and morphology) and in applications (e.g., optics, magnetics, thermoelectrics, biology, medicine, sensing, and energy conversion and storage) of the functional nanostructures fabricated via AAO template-based methods. However, observation of whole nanochannels with nanometer-resolution in thick AAO membranes remains a fundamental challenge, and the nanochannel geometry has not yet been sufficiently elucidated. Here, for the first time, we use depth-profiling transmission electron microscopy to reveal the truncated conical geometry of whole nanochannels of 70 µm in length. Such shape nonuniformity of the nanochannels leads to different reflectance properties of the different depths of the nanochannels along their long axis for one AAO membrane, which suggests that the nonuniformity result in some effects on applications of the nanostructures. Furthermore, we introduce a shape factor to evaluate the shape nonuniformity and demonstrate that the nonuniformity can be remarkably removed by an effective etching method based on a temperature gradient regime.

Prototype of a porous ZnO SPV-based sensor for PCB detection at room temperature under visible light illumination.

To detect polychlorinated biphenyls (PCBs), a prototype of a porous ZnO sensor based on the surface photovoltage (SPV) mechanism working under visible light illumination at room temperature has been presented. The SPV of the porous ZnO sensor can be remarkably reduced under visible light illumination after PCB adsorption, and the reduction of amplitude is proportional to the population of adsorbed PCB molecules. We propose that the reduction of SPV response is due to trapping of the electrons in the surface states by the adsorbed PCBs. The lower detection limits of this new prototype sensor reach at least 2.2 micromol/L for PCB29 and 1.1 micromol/L for PCB101, respectively. So, it demonstrates great potential for practical application in trace detection of PCBs.

Porous biochar modified with polyethyleneimine (PEI) for effective enrichment of U(VI) in aqueous solution.

This study investigated the modification of moso bamboo biochar with polyethyleneimine (PEI) for the efficient enrichment of U(VI) in aqueous solution. The alkali/acid treated biochars with amine groups (PEI-alkali-biochar or PEI-acid-biochar) were characterized by SEM, BET, TGA, FTIR and XPS. The effects of contact time, U(VI) concentration, pH and ionic strength on U(VI) adsorption by PEI-alkali/acid-biochar were studied. U(VI) adsorption process on PEI-alkali/acid-biochar obeys pseudo-second-order model. Intraparticle diffusion model was used to investigate the controlled factors of the adsorption process. The fitting of Langmuir model gives the maximum adsorption capacities of 212.7 mg/g for PEI-alkali-biochar and 185.6 mg/g for PEI-acid-biochar, which are almost 9-10 times higher than that of pristine biochar (20.1 mg/g). The thermodynamic parameters illustrate that U(VI) adsorption on PEI-alkali/acid-biochar is an exothermic and spontaneous process. The FTIR and XPS analyses imply that U(VI) adsorption by PEI-alkali/acid-biochar is mainly controlled by complexation between U(VI) and amine groups. PEI-alkali/acid-biochar could be considered as a low-cost and outstanding material for U(VI) removal from radionuclide wastewater in practical application.

K2Ti6O13 hybridized graphene oxide: Effective enhancement in photodegradation of RhB and photoreduction of U(VI).

The environmental pollutions by organic pollutants and radionuclides have aroused great concern. Developing highly efficient elimination methods becomes an imperious demand. In this study, a nanocomposite of K2Ti6O13 (KTO) nanobelts hybridized graphene oxide (GO) nanosheets (GO/KTO) was used to photodegrade RhB (dye) and photoreduce U(VI) (radionuclide), which was synthesized by a facile hydrothermal method. The adsorption capacity and the slope (k) of the curve -ln(C/C) versus time in photodegradation of RhB by GO/KTO were higher than that by GO and KTO. In the presence of different free radical scavengers, superoxide radical (·O2-) was found to play the most significant role in the reaction. The XPS experiment indicates U(VI) was successfully photoreduced to less toxic U(IV). The pH dependent photocatalytic experiments on RhB and U(VI) both showed the best performance at neutral pH value (from pH 6 to pH 8). To investigate the reason for the enhanced photocatalysis of GO/KTO, the morphology/microstructure, optical and photo-electrochemical properties were examined. The enhanced abilities of separation of photo electrons and holes and the adsorption of GO/KTO were ascribed to the structure of KTO nanobelts laying on the surface of GO nanosheets, which may maximize the contacting area between KTO and GO, and thus greatly reduce the surface related oxygen defects to enhance the electron interface transfer between KTO and GO and decrease the recombination efficiency of electrons and holes. These results showed the GO/KTO has great application potential in environmental treatment of organic pollutants and high valent heavy/radionuclide ions at neutral condition.

Determining E1 and E2 values for yttrium aluminum garnet ceramics using the Duane-Hunt limit.

A major challenge when performing scanning electron microscopy and X-ray analysis on many ceramic materials is their electrical insulation properties, which leads to buildup of the surface charge and reduced contrast in the secondary electron image. A new procedure was established to quantitatively determine the neutral state values, E1 and E2 , of yttrium aluminum garnet (YAG) ceramics using the Duane-Hunt limit (EDHL ) of Bremsstrahlung, in order to eliminate this charge effect. Thirty-eight EDHL values were linearly fitted with the last portion of X-ray spectra acquired under the incident energy, E0 , from 0.35 to 5.0 kV. According to the distribution of EDHL , two piecewise linear fitting was first employed with a breakpoint of 1.0 kV. Consequently, two intersection points of 0.54 and 2.48 kV, which correspond to E1 and E2 for YAG ceramics, were directly determined using a theoretical curve (EDHL = E0 ). As a result, the high-resolution images of the YAG ceramic grain structure were successfully obtained using the calculated E1 and E2 values.

Improved production of polysaccharides in Ganoderma lingzhi mycelia by plasma mutagenesis and rapid screening of mutated strains through infrared spectroscopy.

As a traditional Chinese medicine, Ganoderma lingzhi has attracted increasing attention for both scientific research and medical application. In this work, in order to improve the production of polysaccharides from an original wide-type (WT) strain (named "RWY-0") of Ganoderma lingzhi, we applied atmospheric-pressure dielectric barrier discharge (DBD) nonthermal plasma to the protoplasts of RWY-0 for mutagenesis treatment. Through a randomly amplified polymorphic DNA (RAPD) assay, at least 10 mutagenic strains were confirmed. They also showed different mycelium characteristics in terms of shape, color, size and biomass in liquid fermentation. The mutant strains were examined by infrared spectroscopy, and based on the established near-infrared (NIR) quantification model, the polysaccharide contents in these mutants were quantitatively evaluated. As a result, we found that the Ganoderma polysaccharide contents in some of the mutant strains were significantly changed compared with that of the original WT strain. The polysaccharide content of RWY-1 G. lingzhi was considerably higher than that of the WT strain, with an increase of 25.6%. Thus, this preliminary work demonstrates the extension of the plasma mutagenesis application in acquiring polysaccharide-enhanced Ganoderma lingzhi mutants and shows the usefulness of NIR spectroscopy in the rapid screening of mutagenic strains for other important ingredients.

SiO2 nanowires growing on hexagonally arranged circular patterns surrounded by TiO2 films.

An effective approach has been demonstrated for the synthesis of novel composite architectures, SiO2 nanowires (NWs) growing on hexagonally arranged circular patterns surrounded by TiO2 films on Si substrate. First, a solution-dipping template strategy is used to create TiO2 films with hexagonally arranged pores on Au-coated Si substrate, resulting in hexagonally arranged circular patterns of catalysts surrounded by TiO2 films. Then the patterned catalysts guide the growth of SiO2 NWs with the original TiO2 films preserved, realizing the composite structures. Such composite architectures combine the photoluminescence (PL) properties of the two components, and also present more favorable PL property, laying a foundation for future advanced nano-optoelectronic devices.

Quantitative analysis of martensite and bainite microstructures using electron backscatter diffraction.

In the present work, ultra-high-strength steels with multiphase microstructures containing martensite and bainite were prepared by controlling the cooling rate. A new approach was proposed for quantitatively statistical phase analysis using electron backscatter diffraction (EBSD) based on the band contrast which correlates to the quality and intensity of the diffraction patterns. This approach takes advantage of the inherently greater lattice imperfections of martensite, such as dislocations and low-angle grain boundaries, relative to that of bainite. These can reduce the intensity and quality of the EBSD patterns of martensite, which decrease the band contrast. Thus, combined with morphological observations, Gaussian two-peak fitting was employed to analyze the band contrast profile and confirm the ranges of band contrast for the two phases. The volume fractions of bainite and martensite in different samples were determined successfully. In addition, the results show that increased cooling rates improve the proportion of martensite and the ratio of martensite to bainite. Microsc. Res. Tech. 79:814-819, 2016. © 2016 Wiley Periodicals, Inc.

Nanocontainers made of various materials with tunable shape and size.

Nanocontainers have great potentials in targeted drug delivery and nanospace-confined reactions. However, the previous synthetic approaches exhibited limited control over the morphology, size and materials of the nanocontainers, which are crucial in practical applications. Here, we present a synthetic approach to multi-segment linear-shaped nanopores with pre-designed morphologies inside anodic aluminium oxide (AAO), by tailoring the anodizing duration after a rational increase of the applied anodizing voltage and the number of voltage increase during Al foil anodization. Then, we achieve nanocontainers with designed morphologies, such as nanofunnels, nanobottles, nano-separating-funnels and nanodroppers, with tunable sizes and diverse materials of carbon, silicon, germanium, hafnium oxide, silica and nickel/carbon magnetic composite, by depositing a thin layer of materials on the inner walls of the pre-designed AAO nanopores. The strategy has far-reaching implications in the designing and large-scale fabrication of nanocontainers, opening up new opportunities in nanotechnology applications.

Synthesis of nitrogen-doped porous carbon nanofibers as an efficient electrode material for supercapacitors.

Supercapacitors (also known as ultracapacitors) are considered to be the most promising approach to meet the pressing requirements of energy storage. Supercapacitive electrode materials, which are closely related to the high-efficiency storage of energy, have provoked more interest. Herein, we present a high-capacity supercapacitor material based on the nitrogen-doped porous carbon nanofibers synthesized by carbonization of macroscopic-scale carbonaceous nanofibers (CNFs) coated with polypyrrole (CNFs@polypyrrole) at an appropriate temperature. The composite nanofibers exhibit a reversible specific capacitance of 202.0 F g(-1) at the current density of 1.0 A g(-1) in 6.0 mol L(-1) aqueous KOH electrolyte, meanwhile maintaining a high-class capacitance retention capability and a maximum power density of 89.57 kW kg(-1). This kind of nitrogen-doped carbon nanofiber represents an alternative promising candidate for an efficient electrode material for supercapacitors.

Ag nanoparticle decorated nanoporous ZnO microrods and their enhanced photocatalytic activities.

Nanostructured Ag nanoparticles (Ag-NPs)/nanoporous ZnO micrometer-rods (n-ZnO MRs) have been synthesized by a two-step method. The n-ZnO MRs was initially prepared by solvothermal-assisted heat treatment. The rods had the diameter ranged from 90 to 150 nm and length between 0.5 and 3 µm. They were found to be porous and were composited of ZnO nanopartiles with size of about 20 nm. In the second stage, Ag-NPs with a diameter of 20-50 nm were anchored onto the surface of the as-prepared n-ZnO MRs by a photoreduction method. The Ag-NPs/n-ZnO MRs were evaluated for their ability to degrade methylene blue (MB) solution under visible to ultraviolet (UV) light irradiation. The rate of degradation of the as-prepared Ag-NPs/n-ZnO MRs was more than twice and nearly 5.6 times faster than that of using bare n-ZnO MRs under the UV and solar light irradiation, respectively. The formation of Schottky barriers in the regions between the Ag-NPs and n-ZnO MRs had improved the charge separation and consequently enhanced the efficiency of the degradation process. Moreover, the as-prepared hybrid structure exhibited high photostability, and 98% of degradation efficiency could be maintained even after being used five times. This endurance was attributed to the retardation of photocorrosion of ZnO as a result of the low concentration of surface defects in the as-prepared n-ZnO MRs. It also minimized the surface defects of the as-prepared n-ZnO MRs and consequently further inhibited the photocorrosion of ZnO when the deposited Ag-NPs were much more inclined to combine with the chemisorbed oxygen.

Nanochannel-directed growth of multi-segment nanowire heterojunctions of metallic Au(1-x)Ge(x) and semiconducting Ge.

We report on the synthesis of multi-segment nanowire (NW) junctions of Au(1-x)Ge(x) and Ge inside the nanochannels of porous anodic aluminum oxide template. The one-dimensional heterostructures are grown with a low-temperature chemical vapor deposition process, assisted by electrodeposited Au nanowires (AuNWs). The Au-catalyzed vapor-liquid-solid growth process occurs simultaneously in multiple locations along the nanochannel, which leads to multi-segment Au(1-x)Ge(x)/Ge heterojunctions. The structures of the as-grown hybrid NWs, analyzed by using transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping, show clear compositional modulation with variable modulation period and controllable junction numbers. Remarkably, both GeNW and Au(1-x)Ge(x)NW segments are single crystalline with abrupt interfaces and good crystallographic coherences. The electronic and transport properties of individual NW junctions are measured by using a multi-probe scanning tunneling microscope, which confirms the semiconducting nature of Ge segments and the metallic behavior of Au(1-x)Ge(x) segments, respectively. The high yield of multiple segment NW junctions of a metal-semiconductor can facilitate the applications in nanoelectronics and optoelectronics that harness multiple functionalities of heterointerfaces.

Crystalline silicon nanotubes and their connections with gold nanowires in both linear and branched topologies.

Silicon, being in the same group in the periodic table as carbon, plays a key role in modern semiconductor industry. However, unlike carbon nanotube (NT), progress remains relatively slow in silicon NT (SiNT) and SiNT-based heteroarchitectures, which would be the fundamental building blocks of various nanoscale circuits, devices, and systems. Here, we report the synthesis of linear and branched crystalline SiNTs via porous anodic aluminum oxide (AAO) self-catalyzed growth and postannealing, and the connection of crystalline SiNTs and gold nanowires (AuNWs) via a combinatorial process of electrodepositing AuNWs with predesired length and location in the channels of the AAO template and subsequent AAO self-catalyzed and postannealing growth of SiNTs in the remaining empty channels adjacent to the AuNWs. Using the approach, a large variety of two-segment AuNW/SiNT and three-segment SiNT/AuNW/SiNT heteronanostructures with both linear and branched topologies have been achieved, paving the way for the rational design and fabrication of SiNT-based nanocircuits, nanodevices, and multifunctional nanosystems in the future.