Chanchana Thanachayanont

Heavy-metal ion sensors using chitosan-capped gold nanoparticles

Abstract We report a novel strategy for using gold nanoparticles capped with chitosan for sensing ions of heavy metals. Acidic anions (glutamate ions in our case) are expected to cap the nanoparticle surfaces similar to conventional methods of stabilization of gold nanoparticles by citrate ions. The polycationic nature of chitosan enables attachment of the polymer to the negatively charged gold nanoparticle surfaces through electrostatic interactions. Use of chitosan serves dual purpose of providing sufficient steric hindrance ensuring stability of the colloid and also to functionalize the nanoparticles for use as sensors. The well-documented chelating properties of chitosan and the sensitivity of the optical properties of gold nanoparticles to agglomeration have been employed to detect low concentrations of heavy metals ions (Zn2+ and Cu2+) in water. A comparison of the optical absorption spectra of the colloidal suspension before and after exposure to metal ions is a good indicator of the concentration of the heavy metal ions.

Luminescent nanoparticles of Mn doped ZnS passivated with sodium hexametaphosphate

Abstract We report the synthesis of luminescent nanoparticles of manganese doped zinc sulfide (ZnS:Mn2+) with an emission peak at around 590 nm. Nanoparticles of ZnS:Mn2+ are prepared by a co-precipitation reaction from homogenous solutions of zinc and manganese salts. Based on Ostwald ripening and surface passivation, we discuss a mechanism for the formation of ZnS:Mn2+ nanoparticles. The reaction proceeds with the nucleation of ZnS crystals, which are immediately passivated by the anions in the solution. This in turn attracts cations including zinc and manganese which contribute to the growth of the crystal. These nanoparticles are sterically stabilized using polyphosphates of sodium namely sodium tripolyphosphate (STTP) and sodium hexametaphosphate (SHMP). The nanoparticles consist of particles of 60–80 nm in diameter, each containing primary crystallites that was estimated from the X-ray diffraction patterns to be at around 2.2 nm.

Growth of ZnO nanowires on nonwoven polyethylene fibers

Abstract We report the growth of ZnO nanowires on nonwoven polyethylene fibers using a simple hydrothermal method at a temperature below the boiling point of water. The ZnO nanowires were grown from seed ZnO nanoparticles affixed onto the fibers. The seed ZnO nanoparticles, with diameters of about 6–7 nm, were synthesized in isopropanol by reducing zinc acetate hydrate with sodium hydroxide. The growth process was carried out in a sealed chemical bath containing an equimolar solution of zinc nitrate hexahydrate and hexamethylene tetramine at a temperature of 95 °C over a period of up to 20 h. The thickness and length of the nanowires can be controlled by using different concentrations of the starting reactants and growth durations. A 0.5 mM chemical bath yielded nanowires with an average diameter of around 50 nm, while a 25 mM bath resulted in wires with a thickness of up to about 1 μm. The length of the wires depends both on the concentration of the precursor solution as well as the growth duration, and in 20 h, nanowires as long as 10 μm can be grown. The nonwoven mesh of polyethylene fibers covered with ZnO nanowires can be used for novel applications such as water treatment by degrading pollutants by photocatalysis. Photocatalysis tests carried out on standard test contaminants revealed that the polyethylene fibers with ZnO nanowires grown on them could accelerate the photocatalytic degradation process by a factor of 3.

Growth of Zinc Oxide Nanowires and Nanobelts for Gas Sensing Applications

Zinc Oxide (ZnO) is a very useful as a solid state gas sensor material. In chemical sensing the surface and interface interactions between the analyte molecules and the sensing material is all but important that is read through the changes in electrical conductance. In that sense, nano-objects with a large surface atom/bulk atom ratio, like nanoparticles and nanowires, are potentially the best chemical sensors. The mechanism envisioned involves the adsorption (and eventually diffusion) of the analyte molecule at the surface that induces a change in the electrical resistance of the nano-object. The most convenient way to measure changes in electrical resistance in such devices is to obtain the specific material as nanowires or as connected nanoparticles. Here, we will discuss about a low-temperature wet-chemical process of synthesizing ZnO nanoparticles, nanowires and nanobelts for application as gas sensors.

Electrical and optical properties of p-type CuFe1-xSnxO2 (x = 0.03, 0.05) delafossite-oxide

The CuFe1-xSnxO2 (x = 0.03, 0.05) delafossite samples have been synthesized by a solid-state reaction to investigate electrical and optical properties of the transparent conducting oxide materials. Crystal structure was characterized by XRD. The electrical conductivity and Seebeck coefficient were measured in the high temperature range of 300 to 960 K, while the Hall coefficient, XPS, and UV-VIS-NIR spectra were analyzed at room temperature. The XRD peaks of the samples indicate the delafossite structure phase, and the XPS spectra reveal the stable Sn2+-doping state. The Seebeck and Hall coefficient display a positive sign indicating the p-type conducting oxide. The optical allowed direct gap is 3.45 eV as a visible-transparent material. The activation energies for polaron hopping between Sn2+ sites and Fe3+ sites of 36 and 32 meV are obtained from the samples having x = 0.03 and 0.05, respectively. The CuFe1-xSnxO2 delafossite oxide compounds, of which the Fe3+ sites in the CuFeO2 are substituted by the Sn2+ ions, are p-type transparent conducting oxide materials. The activation energy is found to decrease with an increased in Sn content.

Effect of Silver Nanoparticle Size on Efficiency Enhancement of Dye-Sensitized Solar Cells

Titanium dioxide/silver (TiO2/Ag) composite films were prepared by incorporating Ag in pores of mesoporous TiO2 films using a photoreduction method. The Ag nanoparticle sizes were in a range of 4.36–38.56 nm. The TiO2/Ag composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The TiO2 and TiO2/Ag composite films were then sensitized by immersing in a 0.3 mM N719 dye solution and fabricated for conventional dye-sensitized solar cells (DSCs). J-V characteristics of the TiO2/Ag DSCs showed that the Ag nanoparticle size of 19.16 nm resulted in the short circuit current density and efficiency of 8.12 mA/cm2 and 4.76%.

Fullerene Functionalized Polystyrene: Synthesis, Characterizations, and Application in Bulk Heterojunction Polymer Solar Cells

Fullerene functionalized polystyrene (PSFu) with a variety of fullerene (C60) contents was synthesized and characterized. The best PSFu was selected on the basis of solubility and band gap energy for application studies. Feasibility for using PSFu as a replacement of C60 in bulk heterojunction (BHJ) polymer solar cells was explored. Performance of the BHJ cells containing PSFu was comparable to that of the cells containing neat C60, irrespective of the acceptor/donor weight ratios, even the actual amount of C60 in PSFu molecules was (about 5 times) lower than that of the neat C60.

ZnS:Mn2+ Phosphors Capped with Chitosan

We report on the synthesis of Nanophosphors of Zinc sulphide using a novel capping agent, ‘chitosan’. Water based wet chemical reactions to obtain stable colloids have been done that does not involve any organic solvents. The resultant nanoparticles approximately 30 nm in size, consisting of 3-5 nm crystallites, show a marked improvement in PL compared to other capping agents generally used to passivate the unsaturated defects on the nanoparticle surfaces, showing orange-red color (590 nm) of luminescence even in broad daylight when illuminated with a low power UV source. The high luminescence efficiency renders these nanophosphors ideal for applications in FEDs and quantum cryptography. The presence of biocompatible capping agent, chitosan, makes it a suitable for bio-labels (markers).

Poly(3-hexyl thiophene)-b-Fullerene Functionalized Polystyrene Copolymers (P3HT-b-PSFu) as Compatibilizer in P3HT/Phenyl-C61-butyric Acid Methyl Ester (PCBM) Solar Cells

Poly(3-hexyl thiophene)-fullerene functionalized polystyrene block copolymers (P3HT-b-PSFu) with a variety of block lengths and compositions were synthesized by reacting P3HT macroinitiator with styrene and chloromethyl styrene via an atom transfer radical polymerization. After that, the prepared copolymers were reacted with C60 via an atom transfer radical addition to obtain P3HT-b-PSFu. Chemical structures and molecular weights of the products were characterized by1H-NMR, FTIR, and GPC, respectively. Next, the various P3HT-b-PSFu copolymers were added to P3HT/PCBM bulk heterojunction (BHJ) polymer solar cell. It was found that efficiency increased from 0.52% to the maximum value of 1.23%, after adding the copolymers.

Effects of Substrate Temperature and Vacuum Annealing on Properties of ITO Films Prepared by Radio-Frquency Magnetron Sputtering

Indium tin oxide (ITO) films were prepared by rf magnetron sputtering under two conditions: (i) at substrate temperature Ts from room temperature (RT) to 350° C, (ii) with additional post-annealing in vacuum at 400° C for 30 min in comparison of their crystalline structures, and electrical-optical properties of the films deposited. From the experimental results, it is found that, under the first condition, the crystalline structures and the electrical-optical properties of the films are improved with the increasing Ts. Under the other condition, i.e. with the additional post-annealing, the films exhibit higher degree of crystallinities and better electrical-optical properties. Under the two deposition conditions, inter-relation between electrical-optical properties and the crystalline structure is observed clearly. However, even under the same annealing condition, it is observed that improved properties of the films are different, depending on their deposition temperatures, which implies that an initial stage of the ITO film before annealing is an important factor for the films properties improved after annealing. The resistivity of 2.33 × 10−4 Ω·cm can be achieved at Ts of 350° C after annealing.