Two-step Chemical Method Research Articles

Photoanodes Consisting of Mesoporous Anatase TiO2 Beads with Various Sizes for High-Efficiency Flexible Dye-Sensitized Solar Cells

The synthesis and characterization of TiO2 beads and the use of them in the photoanodes of all-plastic flexible dye-sensitized solar cells (FDSCs) are reported. Pure anatase TiO2 beads having different sizes and characteristics were first made using a novel two-step chemical method under different conditions. Photoanodes consisting of the beads as scattering layers were then fabricated. The use of beads largely enhances the dye loading and gives highly effective light scattering, leading to improved light absorbance. The resulting cells were evaluated for the electron diffusion time, electron lifetime, charge collection efficiency, incident photon-to-electron conversion efficiency, electron injection efficiency, and IV characteristics. The pure anatase TiO2 beads, having low oxygen vacancy concentrations and directional attached grains, lead to more photoelectrons and enhance the electron diffusion, giving very short diffusion times. We have demonstrated for the first time that the use of beads, having diameters ranging from 250 to 750 nm, enhances the light-to-electricity conversion efficiency of FDSCs having plastic substrates by as much as 28%. The cell conversion efficiency is also enhanced from 4.3 to 5.5%.

Unveiling the Formation Pathway of Single Crystalline Porous Silicon Nanowires

Porous silicon nanowire is emerging as an interesting material system due to its unique combination of structural, chemical, electronic, and optical properties. To fully understand their formation mechanism is of great importance for controlling the fundamental physical properties and enabling potential applications. Here we present a systematic study to elucidate the mechanism responsible for the formation of porous silicon nanowires in a two-step silver-assisted electroless chemical etching method. It is shown that silicon nanowire arrays with various porosities can be prepared by varying multiple experimental parameters such as the resistivity of the starting silicon wafer, the concentration of oxidant (H(2)O(2)) and the amount of silver catalyst. Our study shows a consistent trend that the porosity increases with the increasing wafer conductivity (dopant concentration) and oxidant (H(2)O(2)) concentration. We further demonstrate that silver ions, formed by the oxidation of silver, can diffuse upwards and renucleate on the sidewalls of nanowires to initiate new etching pathways to produce a porous structure. The elucidation of this fundamental formation mechanism opens a rational pathway to the production of wafer-scale single crystalline porous silicon nanowires with tunable surface areas ranging from 370 to 30 m(2) g(-1) and can enable exciting opportunities in catalysis, energy harvesting, conversion, storage, as well as biomedical imaging and therapy.

Solution-based synthesis of SnO2 nanoparticle/CdS nanowire heterostructures

Heterostructures of SnO2 nanoparticles (NP)/CdS nanowires (NW) were successfully fabricated by a two-step chemical solution method. In the first step, CdS nanowires were synthesized by a simple solvothermal route. In the second step, SnO2 nanoparticles were grown on the surface of the CdS nanowires in a chemical solution of SnCl4·5H2O and anhydrous ethanol at 200 °C. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were adopted to characterize the as-prepared products. The possible formation mechanism of the SnO2 NP/CdS NW heterostructures has been phenomenologically discussed. The effects of reaction conditions, such as deposition reaction time, reaction temperature, and solvent were also studied.

Structure–property relationships for partially aliphatic polyimides

The structure–property relationship was studied for partially aliphatic polyimides containing alicyclic dianhydride and aromatic diamine unit. Rel-[1S,5R,6R]-3-oxabicyclo[3,2,1]octane-2,4-dione-6-spiro-3′-(tetrahydrofuran-2′,5′-dione) (DAn) was used as an unsymmetrical spiro dianhydride, and 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA) and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BOCA) were used as symmetrical non-spiro dianhydrides. The dianhydrides were polymerized with two aromatic diamines, 4,4′-oxydianiline (ODA) and 4,4′-(hexafluoroisopropylidene)dianiline (FDA), using a conventional two-step chemical imidization method. Structures of the PAl-PIs prepared were confirmed by 1H-NMR and FT-IR spectroscopy. Solubility of the polyimides was tested in various organic solvents. Thermal properties of the PAl-PIs were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). UV-visible spectroscopy was performed to evaluate the optical transparency of the polyimides. The effect of monomer structure on the properties was studied. The PAl-PIs prepared from DAn showed improved solubility, thermal properties, and transparency when compared with PAl-PIs derived from CPDA and BOCA. It is considered that the rigid, unsymmetrical spiro structure of DAn leads to rigidity, bulkiness, irregularity, and non-linearity of the polyimide chains, resulting in the enhanced properties of DAn polyimides. The molecular arrangement in the polyimides has also been studied by wide-angle X-ray diffraction (WAXD) and was correlated with the properties.

Photo-Catalytic Nanometer Composite-Crystal TiO2 Powder Synthesized by Two-Step Method

TiCl4, ammonia, inorganic salts as raw material, nanometer composite-crystal TiO2 powders were synthesized by two-step chemical method. Precursors were crystallized with different phase and stable composite-crystal TiO2 with anatase and rutile phase was prepared at low temperature. Quantitative control of crystal phase was realized. Remarkable factors including reaction pH value, reaction time, which affected the phase content, microstructure, morphology were discussed. Applied experiments of photo-degradation organic dyes illuminated by sunshine showed higher photocatalytic activity of composite-crystal than that of pure anatase, pure rutile and mechanical mixture of both, nanometer composite-crystal TiO2 as photocatalyst.

Characterizations and thermal stability of soluble polyimide derived from novel unsymmetrical diamine monomers

Two kinds of novel aromatic, unsymmetrical diamines with ether–ketone group, 3-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone and 3-amino-4′-(4-aminophenoxy)-benzophenone, was successfully synthesized by two different synthetical routes and polymerized with various aromatic tetracarboxylic acid dianhydrides, including 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride, via a conventional two-step thermal or chemical imidization method to produce a series of fluorinated polyimides. The polyimides were characterized with solubility tests, viscosity measurements, mechanical properties tests, IR-FT, and thermogravimetric analysis. The polyimides had inherent viscosities of 0.54–0.77 dL/g and were easily dissolved in both polar, aprotic solvents and common, low-boiling-point solvents. The resulting strong and flexible polyimide films exhibited excellent thermal stability, with decomposition temperatures (at 10% weight loss) above 573 °C and glass-transition temperatures in the range of 222–251 °C. Moreover, the polymer films showed outstanding mechanical properties, with tensile strengths of 86.5–121.6 MPa, elongations at break of 9–16%, and initial moduli of 1.26–1.97 GPa. These outstanding combined features ensure that the polymers are desirable candidate materials for advanced applications.

Synthesis and characterization of fluorinated polyimides derived from novel unsymmetrical diamines

Two kinds of aromatic, unsymmetrical diamines with ether–ketone group, 3-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone and 4-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone, were successfully synthesized with two different synthetic routes. Then, they were polymerized with 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride to form a series of fluorinated polyimides via a conventional two-step thermal or chemical imidization method. The resulting polyimides were characterized by measuring their solubility, viscosity, mechanical properties, IR-FT, and thermal analysis. The results showed that the polyimides had inherent viscosities of 0.48–0.68 dl/g and were easily dissolved in bipolarity solvents and common, low-boiling point solvents. Meanwhile, the resulting strong and flexible polyimide films exhibited excellent thermal stability, e.g., decomposition temperatures (at 10% weight loss) are above 575 °C and glass-transition temperatures in the range of 218–242 °C. The polymer films also showed outstanding mechanical properties, such as tensile strengths of 86.5–132.8 MPa, elongations at break of 8–14%, and initial moduli of 1.32–1.97 GPa. These outstanding combined features ensure that the polymers are desirable candidate materials for advanced applications.

Synthesis and characterization of novel polyimides derived from 4-phenyl-2, 6-bis [3-(4-aminophenoxy)-phenyl]-pyridine diamine and aromatic dianhydrides

A new kind of pyridine-containing aromatic diamine monomer, 4-phenyl-2, 6-bis [3-(4-aminophenoxy)phenyl]-pyridine( m-PAPP),was synthesized by a modified Chichibabin reaction of benzaldehyde and a substituted acetophenone, 3-(4-nitrophenoxy)-acetophenone( m-NPAP), and a reduction of the resulting dinitro compound 4-phenyl-2, 6-bis[3-(4-nitrophenoxy)phenyl]-pyridine ( m-PNPP) with Pd/C and hydrazine monohydrate, successively. A series of novel aromatic polyimides were prepared from the diamine with various aromatic dianhydrides via a conventional two-step thermal or chemical imidization method. The inherent viscosities of the resulting poly (amic acid) precursors were 1.37–1.56 dL/g, and these polymers could be cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimides displayed higher solubility in polar solvents such as NMP, DMSO and m-cresol. The glass transition temperatures of these polymers were recorded at 180–264 °C. All of these novel polyimides held 10% weight loss at the temperature above 430 °C and left more than 50% residue even at 800 °C in air, as well as have outstanding mechanical properties with the tensile strengths of 91.6–114.1 MPa and elongations at breakage of 10.1–15.7%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous.

Synthesis and characterization of soluble polyimides based on a new fluorinated diamine: 4-Phenyl-2,6-bis[3-(4′-amino-2′-trifluoromethyl-phenoxy) phenyl] pyridine

A new kind of pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[3-(4′-amino-2′-trifluoromethyl-phenoxy) phenyl] pyridine ( m-PAFP), was successfully synthesized by a modified Chichibabin reaction of 3-(4′-nitro-2′-trifluoro-methyl-phenoxy)-acetophenone with benzaldehyde, followed by a catalytic reduction. A series of fluorinated pyridine-bridged aromatic poly(ether-imide)s were prepared from the resulting diamine monomer with various aromatic dianhydrides via a conventional two-step thermal or chemical imidization method. The inherent viscosities values of these polyimides were in the range of 0.56–1.02 dL/g, and they could be cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimides displayed higher solubility in polar solvents such as NMP, DMSO and m-cresol. The polyimides had good thermal stability, with the glass transition temperatures ( T g) of 187–211 °C, the temperatures at 5% weight loss of 511–532 °C, and the residue at 800 °C in air was higher than 50%. These films also had dielectric constants of 2.64–2.74 at 10 MHz and low water uptake 0.53–0.66%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous. Moreover, the polymer films of these novel polyimides showed outstanding mechanical properties with the tensile strengths of 90.1–96.6 MPa, elongations at breakage of 8.9–10.7% and tensile modulus of 1.65–1.98 GPa.

The effect of powder properties on sintering, microstructure, mechanical strength and degradability of β-tricalcium phosphate/calcium silicate composite bioceramics

The effect of powder properties on sintering, microstructure, mechanical strength and degradability of β-tricalcium phosphate/Calcium silicate (β-Ca3(PO4)2/CaSiO3, β-TCP/CS) composite bioceramics was investigated. β-TCP/CS composite powders with a weight ratio of 50:50 were prepared by three different methods: mechanical milling method (TW-A), two-step chemical precipitation method (TW-B) and in situ chemical co-precipitation method (TW-C), and then the three composite powders were uniaxially compacted at 30 MPa, followed by cold isostatic pressing into rectangular-prism-shaped specimens under a pressure of 200 MPa for 15 min, and then sintered at 1150 °C for 5 h. The TW-B powders with less agglomerative morphologies and uniform nano-size particles attained 96.14% relative density (RD). A uniform microstructure with about 120 nm grains was observed. Whereas, the samples obtained from TW-A and TW-C powders only reached a RD of 63.08% and 78.86%, respectively. The bending strength of the samples fabricated from TW-B reached 125 MPa, which was more than 3.7 and 1.5 times higher as compared with that of samples obtained from TW-A and TW-C powders, respectively. Furthermore, the degradability of the samples fabricated from TW-B powders was obviously lower than that of the samples fabricated from TW-A and TW-C powders.

Evolution of Ni:B2O3 core-shell structure and magnetic properties on devitrification of amorphous NiB particles in air

The Ni:B2O3 nanoparticles have been synthesized by a novel two-step chemical reduction method, under ambient conditions and subsequent annealing in air. The evolution of this structure has been followed through a sequence of annealing treatments. Structural and magnetic investigations on as-prepared and annealed samples revealed that as-prepared samples are weakly magnetic and develop into spherical ferromagnetic entities with superior magnetic properties. The saturation magnetization (Ms∼42 emu/g) and coercivity (Hc∼482 Oe) at room temperature clearly suggest that the air annealed (500 °C) samples are protected from the oxidation due to formation of B2O3 protective layer. The magnetization results are consistent with the observed microstructural changes and satisfactorily explained on the basis of a core-shell model, where we consider each particle as a magnetically heterogeneous system consisting of a ferromagnetic core of Ni and nonmagnetic shell of B2O3. These results suggest that this kind of nanocomposite systems might have significant potential as a recording media.

Growth and Photocatalytic Activity of Dendrite-like ZnO@Ag Heterostructure Nanocrystals

Dendrite-like ZnO@Ag heterostructure nanocrystals are designed and fabricated by a facial two-step chemical method in a large scale. The heterostructure nanocrystals are composed of single crystal Ag nanowires as trunks and highly dense (0001) oriented ZnO nanorods as branches. ZnO nanorods with diameters of about 50−400 nm are vertically grown on the six lateral surfaces of the Ag nanowires. Ultrathin ZnO nanowires or nanotubes with a diameter of less than 30 nm are decorated on the ZnO nanorods. The photocatalysis test shows that the ZnO@Ag heterostructures exhibit a higher photocatalytic activity than the pure ZnO nanorods, thereby implying that the Ag/ZnO interfaces promote the separation of photogenerated electron−hole pairs and enhance the photocatalytic activity.

Solution-Based Synthesis of a CdS Nanoparticle/ZnO Nanowire Heterostructure Array

CdS nanoparticle (NP)/ZnO nanowire (NW) heterostructure arrays were fabricated by a two-step chemical solution deposition method. First, vertically aligned ZnO nanowire arrays were grown on a substrate from Zn(NO3)2 (10 mM) and an aqueous ammonia (pH ∼ 11) solution at 95 °C for 6 h. Then, CdS nanoparticles were deposited on the ZnO nanowire array in a chemical bath containing CdSO4, thiourea, and an aqueous ammonia solution (molar ratio of 1:5:500) at 60 °C. The effects of deposition reaction conditions, such as solution concentrations and deposition time, were investigated. Synthesized CdS NP/ZnO NW heterostructures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM), and their optical absorption property was measured by light absorbance spectrometry. As the solution concentrations and deposition time increased, the sizes and density of CdS nanoparticles on the surfaces of ZnO nanowires increased and the visible-light absorption ca...

Fabrication of ZnO/CdS core/shell nanowire arrays for efficient solar energy conversion

ZnO/CdS core/shell nanowire heterostructure arrays are fabricated by a two-step chemical solution method for use in semiconductor-sensitized photoelectrochemical cells (PECs). The successive ion layer adsorption and reaction (SILAR) shows a remarkable controllability of CdS shell thickness, which affects visible-light absorption properties and PEC performances of the heterostructures. The cell has a high short-circuit photocurrent density of 7.23 mA/cm2 with a power conversion efficiency of 3.53% under AM 1.5G illumination at 100 mW/cm2. These results demonstrate that the ZnO/CdS core/shell heterostructure nanowire arrays can provide a facile and compatible frame for the potential applications in nanowire-based solar cells.

Tapered Optical Fibers Designed for Surface Plasmon Resonance Phase Matching

Combining a modified two-step chemical etch method with equations to predict etch parameters and photon-plasmon phase-matching resulted in single-mode tapered optical fibers (TOFs) to optimize electromagnetic field enhancement. The phase-matching equation was used to identify the angle of incidence near the TOF cutoff radius at which surface plasmon resonance (SPR) is maximized. The axisymmetric Young-Laplace equation was used to predict the angle of incidence from the fabrication of a TOF via chemical etching. An optimal cone angle of 20.0 degrees , angles of incidence averaging (81.6 +/- 1.9) degrees , and tip diameters of (80.0 +/- 14.1) nm were achieved through a two-step etching process. These TOF characteristics maximize SPR excitation and field enhancement. The refractive index for optimized SPR excitation in the fabricated TOFs at a wavelength of 650 nm was found to be 1.343.

Synthesis and properties of soluble fluorinated poly(ether imide)s with different pendant groups

Two types of new fluorinated diamine monomer, [1,4-(4-amino-2-trifluoromethyl-phenoxy)-2-(3′-trifluoromethylphenyl) benzene (III)] and [1,4-(4-amino-2-trifluoromethyl-phenoxy)-2-(3′-methylphenyl) benzene (IV)] were synthesized and polymerized with aromatic dianhydrides. A series of soluble poly(ether imide)s (PEIs) were prepared from the diamines and dianhydrides by two-step chemical imidization methods. Experimental results indicated that all the PEIs had glass transition temperature between 230°C and 247°C, the temperature at 5% weight loss between 527°C and 598°C under nitrogen. The membranes hand tensile strengths in the range of 74–101MPa, tensile modulus in the range of 1.9–2.6GPa, and elongation at break from 20 to 28%. The cast membranes also exhibited high optical transparency, with a UV–vis absorption edge of 354–406nm. Moreover, these PEIs membranes possessed low dielectric constants of 2.63–3.20 (at 1MHz) and low water uptakes (<0.75wt%).

Novel Method of Hydroxyapatite Coating on Titanium Using Chemical Deposition

The aim of this study was to deposit an adherent apatite coating on titanium substrate using a two-step chemical deposition method. First, titanium substrates were immersed in an acidic solution containing calcium and phosphate ions, resulting in the deposition of a monetite (CaHPO4) coating. Second, the monetite crystals were converted to apatite by hydrolysis in NaOH solution. Composition and morphology of the initial and final coatings were identified using X-ray diffraction (XRD), Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS). The final coating was porous and the apatite crystals were agglomerated and followed the outline of the large monetite crystals. The average tensile bond of the coating was 5.2 MPa and cohesion failures were observed more frequently than adhesion failures. The coating adhesion measured using scratch test was 13.1N. In conclusion, this study showed the potential of a two-step chemical deposition method for depositing an adherent coating of apatite at low temperatures.

Synthesis and characterization of soluble polyimides derived from a novel unsymmetrical diamine monomer: 1,4-(2′,4″-diaminodiphenoxy)benzene

A new aromatic unsymmetrical diamine monomer, 1,4-(2′,4″-diaminodiphenoxy)benzene (OAPB), was successfully synthesized in three steps using hydroquinone as starting material and polymerized with various aromatic tetracarboxylic acid dianhydrides, including 4,4′-oxydiphthalic anhydride (ODPA), 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride (6FDA) and pyromellitic dianhydride (PMDA) via the conventional two-step thermal or chemical imidization method to produce a series of the unsymmetrical aromatic polyimides. The polyimides were characterized by solubility tests, viscosity measurements, IR, 1H NMR, and 13C NMR spectroscopy, X-ray diffraction studies, and thermogravimetric analysis. The polyimides obtained had inherent viscosities ranged of 0.38–0.58 dL/g, and were easily dissolved in common organic solvents. The resulting strong and flexible PI films exhibited excellent thermal stability with the decomposition temperature (at 5% weight loss) of above 505 °C and the glass transition temperature in the range of 230–299 °C. Moreover, the polymer films showed outstanding mechanical properties with the tensile strengths of 41.4–108.5 MPa, elongation at breaks of 5–9% and initial moduli of 1.15–1.68 GPa.

Synthesis of a new siloxane-containing diamine and related polyimide

A novel siloxane-containing diamine, bis[4-( p-aminophenoxy)phenoxy]dimethylsilane (APPMS), was successfully synthesized in three steps using hydroquinone as starting material, which was reacted with 4,4′-oxydiphthalic anhydride (ODPA) via a conventional two-step thermal or chemical imidization method to produce a new siloxane-containing polyimide. The resulting polyimide exhibited excellent solubility, and film-forming capability.

Chemical Fractionation of Ellements in Airborne Particulate Matter: Primary Results on PM10 and PM2.5 Samples in the Lazio Region (Central Italy)

This paper describes how a two-step chemical fractionation method that allows the determination of 17 elements in airborne particulate matter, has been applied to a monitoring campaign of PM10 and PM2.5 in the Lazio region (Italy). This method involved an extraction in a pH buffered aqueous solution followed by a microwave-assisted acid digestion of the residue. With respect to the determination of the total elemental contents, the evaluation of a soluble fraction provides more reliable information on the presence and of the destiny of heavy metals in the environment. Furthermore, the pH buffered extraction conditions chosen, rendered the results independent of the intrinsic acidity of the collected samples and, although the chemical fractionation has a purely operational function, it facilitates the study of the relationship between the distribution of solubility and the different emission sources. Results are discussed in relation to the different concentration and the different degrees of solubility of the elements observed in two sampling sites; one in an urban and one in a rural environment. Since in-parallel sampling of PM2.5 and PM10 were performed in both sites, the influence of particle size is also discussed. Behaviour of some tracers deriving from both vehicular traffic, with particular attention to re-suspended road dusts, and naturally generated particulate matter, such as marine aerosol and Saharian dust, are discussed.