Graphene oxides and carbon nanotubes embedded in polyacrylonitrile-based carbon nanofibers used as electrodes for supercapacitor

This study investigates the use of graphene oxides (GOs) and carbon nanotubes (CNTs) embedded in polyacrylonitrile-based carbon nanofibers (GO–CNT/CNF) as electrodes for the supercapacitor. GO–CNT/CNF was prepared by electrospinning, and was subsequently stabilized and activated. The specific capacitance of GO–CNT/CNF is 120.5 F g⁻¹ in 0.5 M Na₂SO₄ electrolyte, which is higher than or comparable to the specific capacitances of carbon-based materials in neutral aqueous electrolyte, as prepared in this study. GO–CNT/CNF also exhibits a superior cycling stability, and 109% of the initial specific capacitance after 5000 cycles. The high capacitance of GO–CNT/CNF could be attributed to the edge planes and the functional groups of GO, the highly electrical conductivity of CNT, and the network structure of the electrode.     

Facile synthesis of flower-like nickel nanocrystals and properties

A solvo-hydrothermal synthesis approach for the preparation of a new type of flowerlike nickel nanostructure is reported. The as-synthesized flower-like nickel nanocrystallites were characterized by X-ray diffraction and scanning electron microscopy. The nickel flowers modified glassy carbon electrode can be prepared and used to detect methanol and ethanol in the solution. The results show that the nickel flowers give a very high activity for detecting the methanol and ethanol, which provide a new application of nickel flowers. Compared with that of bulk nickel, thus-prepared nickel flowers showed a much enhanced coercivity.     

Shape-controlled synthesis of Cu2O nano/microcrystals and their antibacterial activity

Uniform cuprous oxides with different morphologies have been successfully synthesized using polyvinylpyrrolidone (PVP) as a capping agent. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometer, Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy were employed to characterize the structure and morphology of cuprous oxides. It was found that the reaction conditions such as PVP, reducing agent and complexing agent played important roles in the formation of regular cuprous oxide crystals. In addition, their antibacterial activity against Bacillus subtilis (B. subtilis), Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) was also investigated by the Oxford cup method. Results suggested that cuprous oxides are selective in their antibacterial action. They display effective antibacterial activity against S. aureus, B. subtilis and P. aeruginosa. There is no bactericidal ability against E. coli in the tested concentration range, which indicates that E. coli may be a Cu(I)-tolerant bacterium.     

Size-controlled hydrothermal synthesis and electrochemical behavior of orthorhombic LiMnO2 nanorods

Large amount of uniform orthorhombic LiMnO₂ (o-LiMnO₂) nanorods was fabricated by a hydrothermal route in 180 °C using γ-MnOOH nanorods as precursors through an isomorphous ion exchange process. The size of as-obtained o-LiMnO₂ nanorods was determined by that of γ-MnOOH precursors, which could be deliberately controlled. The electrochemical performance of o-LiMnO₂ nanorods was characterized via galvanostatic tests, which suggested that the size of as-obtained products played an important role in their electrochemical performances.     

One-step synthesis of hydrophobic mesoporous silica and its application in nonylphenol adsorption

Highly CH₃-functionalized mesoporous silica with nearly spherical morphology was synthesized under acidic conditions by co-condensation of two different silica precursors polymethylhydrosiloxane (PMHS) and tetraethoxysilane (TEOS) in the presence of triblock copolymer P123 as template. XRD, N₂ adsorption–desorption, HRTEM, SEM and ²⁹Si MAS NMR were used to identify its highly-ordered mesopore array structure, nearly spherical particle morphology and CH₃ functionalization of the as-synthesized material. The resulting hydrophobic mesoporous silica possessed regular mesochannel arrays, indicating that the introduction of PMHS had little impact on the formation of an ordered mesostructure. Also, PMHS played an important role in morphology control and organic functionalization, ensuring nearly spherical particle morphology and high CH₃ functionalization degree of the obtained mesoporous silica material. As compared with pristine mesoporous silica SBA-15, the hydrophobic mesoporous silica showed the higher adsorption performance when they were used as adsorbents to remove organic pollutant nonylphenol at a very low concentration from aqueous solution.     

Chemical synthesis of self-assembled Ni nanoparticles and understanding of nonmagnetic layer inside their surface

To chemically synthesize mono-dispersed and self-assembled Ni nanoparticles, it was important to find the best combination of a Ni precursor and a ligand. Our Ni nanoparticles exhibited a face-centered cubic structure and superparamagnetism at room temperature. The value of saturation magnetization for our Ni nanoparticles was largely different from that of bulk Ni. Because of the relationship between the diameter and saturation magnetization per volume, the number of atoms composing the Ni nanoparticle was correlated with magnetization. This result indicated that a magnetic core/shell structure inside a Ni nanoparticle was produced. The nonmagnetic layer, as a magnetic shell of the core/shell structure, was created due to the low crystallinity of Ni nanoparticles and was composed of amorphous Ni‒O states. As a result, antiferromagnetic spins arrayed in the Ni‒O states were broken. Disordered spins were generated, which eventually decreased the total magnetization of the Ni nanoparticles.     

Preparation of immunomagnetic nanoparticles and their application in the separation of mouse CD34 hematopoietic stem cells

The magnetic nanoparticles with a diameter of about 60 nm were synthesized by coprecipitation from ferrous and ferric iron solutions and coated with silica. Then the nanoparticles were modified with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS) in order to immobilize anti-CD34⁺ monoclonal antibodies to the surface of modified magnetic particles. The results of transmission electron microscope (TEM) and Fourier transformed infrared (FT-IR) indicated that the nanoparticles were successfully prepared. Scanning electron microscope (SEM) photo confirmed that the mouse CD34⁺ cells (cells expressing CD34) were separated by the immunomagnetic nanoparticles. The viability of the separated cells was studied by hematopoietic colony-forming assay, the result of which showed that the target cells still had an ability of proliferation and differentiation. The application of the separated CD34⁺ cells was in testing the pharmacological effect of three samples isolated from enzyme-digested traditional Chinese medicine Colla corii asini.     

Electrocatalytic oxidation of methanol on Pt catalyst supported on nitrogen-doped graphene induced by hydrazine reduction

Hydrazine is often used to reduce graphene oxide (GO) to produce graphene. Recent observations suggested that when hydrazine is used to reduce GO, the resulting reduced graphene actually contains certain amounts of nitrogen dopants, which may influence the properties of the obtained material, and in some cases may be deployed for beneficial advantage. In this work, we prepared graphene oxide by the chemical oxidation method, then used either hydrazine or sodium borohydride (as a control) to reduce the graphene oxide to graphene and to explore the nature of the nitrogen functionalities introduced by hydrazine reduction. Pt nanoparticles were then deposited on the nitrogen doped (hydrazine-reduced) and undoped (control) graphene substrates, and the morphology, structure, and electrocatalytic methanol oxidation activity were characterized and evaluated. The results show that the nitrogen functional groups introduced into the graphene by hydrazine reduction greatly improve the electrocatalytic activity of the underlying Pt nanoparticles towards the methanol oxidation reaction.     

Controllable synthesis of layered Co–Ni hydroxide hierarchical structures for high-performance hybrid supercapacitors

A facile solvothermal method is developed for synthesizing layered Co–Ni hydroxide hierarchical structures by using hexamethylenetetramine (HMT) as alkaline reagent. The electrochemical measurements reveal that the specific capacitances of layered bimetallic (Co–Ni) hydroxides are generally superior to those of layered monometallic (Co, Ni) hydroxides. The as-prepared Co_0.5Ni_0.5 hydroxide hierarchical structures possesses the highest specific capacitance of 1767 F g⁻¹ at a galvanic current density of 1 A g⁻¹ and an outstanding specific capacitance retention of 87% after 1000 cycles. In comparison with the dispersed nanosheets of Co–Ni hydroxide, layered hydroxide hierarchical structures show much superior electrochemical performance. This study provides a promising method to construct hierarchical structures with controllable transition-metal compositions for enhancing the electrochemical performance in hybrid supercapacitors.     

Complexed sol-gel synthesis of improved Pt-Ru-Os-based anode electro-catalysts for direct methanol fuel cells

A high specific surface area (SSA) Pt-Ru-Os-based anode catalyst synthesized by a novel complexed sol-gel (CSG) process shows better catalytic activity in comparison to pure equi-atomic compositions of Pt-Ru anode catalysts synthesized by similar sol-gel processes. A homogeneous amorphous gel was successfully synthesized by complexing platinum(II) acetylacetonate, ruthenium(III) acetylacetonate and osmium(III) chloride with tetramethylammonium hydroxide (TMAH) used as a complexing agent. Phase-pure Pt(Ru,Os) and Pt(Ru) solid solutions possessing high specific surface area (∼110-120 m²/g) were successfully synthesized by controlled removal of carbonaceous species present in the as-prepared precursor generated from the CSG process. This has been successfully achieved by precise thermal treatments of the precursor using controlled oxidizing atmospheres. Results indicate that the nano-crystalline Pt(Ru,Os) solid solution of nominal composition 50 at%-Pt-40 at% Ru-10 at% Os possesses good chemical homogeneity, and reveals excellent catalytic activity, thus demonstrating the potential of the novel CSG process for synthesizing high-performance Pt-Ru-Os-based catalysts for direct methanol fuel cells.     

Preparation of silver nanowires coated with TiO2 using chemical binder and their applications as photoanodes in dye sensitized solar cell

In this study, the core–shell structured Ag@TiO₂ wire was prepared for application to dye-sensitized solar cell (DSSC). The Ag nanowire, having an excellent electrical conductivity, was synthesized by using the facile microwave-assisted polyol reduction process. The diameter and length of Ag wires were 40–50 nm and 20–30 μm, respectively, and the face-centered cubic silver crystal structure was obtained. In the presence of 2-mercaptoethanol as a chemical binder, the entire surface of Ag wire was coated with the TiO₂ shell, which has thickness of 20 nm, through solvothermal method. The crystalline structure of TiO₂ shell was the anatase phase possessing an advantage to achieve the high efficiency in DSSC. The core–shell structured Ag@TiO₂ wire exhibited the high thermal stability. The high conversion efficiency (5.56%) in fabricated device with Ag@TiO₂ electrode, which is about 10% higher than reference cell, was achieved by enhancement of short-current density (J_sc) value. The core–shell structured Ag@TiO₂ wire could effectively reduce the charge recombination through the contribution to electron shortcut for improvement in the electron transfer rate and lifetime.     

A novel ammonia-assisted method for the direct synthesis of Mn3O4 nanoparticles at room temperature and their catalytic activity during the rapid degradation of azo dyes

In this study, we prepared trimanganese tetroxide nanoparticles from MnCl₂ solution in an ammonia atmosphere using a new surfactant-free method at room temperature. We analyzed and characterized the effects of different processing conditions, such as the concentrations of manganese and the ammonia source, as well as the reaction time, on the structure, purity, and morphology of the products using powder X-ray diffraction (XRD), scanning electron microscopy, and Fourier transformation infrared spectroscopy (FTIR) techniques. The XRD and FTIR analyses confirmed that the prepared products comprised single phase Mn₃O₄. At room temperature, the paramagnetic characteristics were also verified by vibrating sample magnetometry. Furthermore, we tested the catalytic activity of the nanoparticles during the degradation of methyl orange and Congo red, which are organic pollutants. Our experiments demonstrated the rapid color removal and reduction in the chemical oxygen demand (>70% and >50% within 10 min, respectively) using aqueous solutions of azo dyes.     

Drastic change in shape of tetragonal TeO2 nanowires and their application to transparent chemical gas sensors

We have synthesized one-dimensional structures of tellurium dioxide (TeO₂) by heating of tellurium powders. Their morphology was drastically changed as the growth temperature increased in the range of 400-500 °C, in which high-temperature process facilitated the thickening of the stem nanowires, as well as the growth of secondary branches on the stems. The obtained TeO₂ products were crystalline with tetragonal structure. The TeO₂ nanowire film exhibited a high transmission rate of about 73%. We have investigated the NO₂ sensing properties of the as-fabricated TeO₂ nanowires, in which a linear relationship between sensitivity and the NO₂ gas concentration was observed. Thus, the TeO₂ nanowires demonstrated their potential application to transparent chemical sensors.     

Hexamethylenetetramine assisted hydrothermal synthesis of BiPO4 and its electrochemical properties for supercapacitors

The well defined microstructures of BiPO₄ were successfully synthesized by the facile hexamethylenetetramine (HMT) assisted hydrothermal method. The low temperature monoclinic BiPO₄ structure with space group P2₁/n, were obtained from X-ray diffraction (XRD) for the pristine and HMT-assisted BiPO₄ with 1, 3, 5 and 10 mmole concentration. A transformation from low temperature monazite-type phase to the high temperature SbPO₄-type phase of BiPO₄ was observed at the 10 mmole concentration. There was a variation in the morphology from polyhedron to octahedra-like and finally into cube shape upon an increase in concentration of HMT. The role of reaction time in the morphology of BiPO₄ particles was investigated. The selected area electron diffraction (SAED) pattern elucidated the ordered dot pattern and the calculated d-spacing revealed the formation of BiPO₄. An increased specific capacitance of HMT assisted materials (202 F/g) compared with pristine BiPO₄ (89 F/g) at 5 mA/cm² was observed upon morphological variation due to HMT addition.     

Facile synthesis of α-MnO2 nanorods for high-performance alkaline batteries

Single-crystalline α-MnO₂ nanorods have been successfully synthesized by a novel hydrothermal method based on the redox reactions between the permanganate anion MnO₄^- and H₂O in mixture containing KMnO₄ and HNO₃. The products have been characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectrum (FT-IR) and Brunauer-Emmett-Teller (BET). The results prove that the grain size of α-MnO₂ nanorods with the surface area ∼95.2 m² g⁻¹ is homogeneous with diameters ranging from 10 to 20 nm. The electrochemical property of the material shows that compared with the commercial electrolytic manganese dioxide (EMD), the discharge capacity of the as-prepared α-MnO₂ nanorods is increased by 70.4%, 104.1% and 135.7% at different constant currents of 50, 250 and 500 mA g⁻¹, respectively.     

Defect-controlled growth of ZnO nanostructures using its different zinc precursors and their application for effective photodegradation

Various zinc precursors, such as zinc acetate, zinc nitrate, zinc sulfate, and zinc chloride, have been used to control the formation of zinc oxide (ZnO) nanostructures onto aluminum substrate by chemical means. FESEM images of the ZnO nanostructures showed the formation of different morphologies, such as flakes, nanowalls, nanopetals, and nanodisks, when the nanostructures were synthesized using zinc acetate, zinc nitrate, zinc sulfate, and zinc chloride precursors, respectively. The TEM image of disk-like ZnO nanostructures formed using zinc chloride as a precursor revealed hexagonally shaped particles with an average diameter of 0.5 μm. Room-temperature photoluminescence (PL) spectra revealed a large quantity of surface oxygen defects in ZnO nanodisks grown from zinc chloride compared with those using other precursors. Furthermore, the ZnO nanostructures were evaluated for photocatalytic activity under ultraviolet (UV) light illumination. Nanostructures having a disk-like shape exhibited the highest photocatalytic performance (k = 0.027 min⁻¹) for all the ZnO nanostructures studied. Improved photocatalytic activity of ZnO nanodisks was attributed to their large specific surface area (4.83 m² g⁻¹), surface oxygen defects, and super-hydrophilic nature of their surface, which is particularly suitable for dye adsorption.     

Solvothermal synthesis and characterization of CdSe nanocrystals with controllable phase and morphology

Zinc blende (ZB) CdSe hollow nanospheres were solvothermally synthesized from the reaction of Cd(NO₃)₂·4H₂O with a homogeneously secondary Se source, which was first prepared by dissolving Se powder in the mixture of ethanol and oleic acid at 205 °C. As Se power directly reacted with Cd(NO₃)₂·4H₂O in the above mixed solvents, wurtzite (W) CdSe solid nanoparticles were produced. Time-dependent experiments suggested that the formation of CdSe hollow nanospheres was attributed to an inside-out Ostwald ripening process. The influences of reaction time, temperature and ethanol/oleic acid volume ratio on the morphology, phase and size of the hollow nanospheres were also studied. Infrared (IR) spectroscopy investigations revealed that oleic acid with long alkene chains behaved as a reducing agent to reduce Se powder to Se²⁻ in the synthesis. Photoluminescence (PL) measurements showed that the ZB CdSe hollow nanospheres presented an obvious blue-shifted emission by 42 nm, and the W CdSe solid nanoparticles exhibited a band gap emission of bulk counterpart.     

Effect of aluminium doping and annealing on structural and optical properties of cerium oxide nanocrystals

Nanocrystalline fluorite-like structures of Ce_1−xAl_xO_2−δ compounds were prepared by the chemical precipitation method using cerium chloride and aluminium chloride as precursors. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS). The effects of aluminium doping concentration and annealing on particle size, lattice parameter and band gap energies were investigated. The particle size of Al-doped CeO₂ samples were found to decrease with Al concentration and it increases from 6 to 20 nm as annealing temperature increases to 900 °C.     

Effect of iron doping and annealing on structural and optical properties of cerium oxide nanocrystals

Nanocrystalline fluorite-like structures of Ce_1−xFe_xO_2−δ compounds were prepared by chemical precipitation method using cerium chloride and iron chloride as precursors. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS). The effects of iron doping concentration and annealing on particle size, lattice parameter and band gap energies were investigated. The particle size of Fe-doped CeO₂ samples were found to decrease with iron concentration and it increases from 9 to 26 nm as annealing temperature increases to 900 °C.     

Facile preparation of mesoporous titanium nitride microspheres as novel adsorbent for trace Cd2+ removal from aqueous solution

A simple and facile route is developed for the preparation of mesoporous titanium nitride (TiN) microspheres with a large surface area and a highly porous structure. This method involves the preparation of an amorphous precursor via a solvothermal reaction and subsequent short-time nitridation process to mesoporous TiN. X-ray diffraction and X-ray photoelectron spectroscopy analyses confirm the composition of the resultant sample. The mesoporous structure of the as-prepared TiN sample has been studied by nitrogen adsorption/desorption measurement. The surface area obtained by the Brunauer–Emmett–Teller method is 50.6 m² g⁻¹ and the pore sizes are in the range of 2.0–4.0 nm. In addition, the obtained sample is evaluated as a new sorbent for Cd²⁺ removal. Experimental parameters such as solution pH, contact time and concentration of adsorbate are optimized. The maximum adsorption capacity for Cd²⁺ removal is found to be 12.40 mg g⁻¹ and it is a potentially attractive adsorbent for Cd²⁺ removal from aqueous solution.