A high performance dye-sensitized solar cell with a novel nanocomposite film of PtNP/MWCNT on the counter electrode

An imide-functionalized material, poly(oxyethylene)-segmented polymer, was synthesized from the reaction of poly(oxyethylene) diamine of 2000 g mol(-1) M(w) and 4,4'-oxydiphthalic anhydride and used to disperse hybrid nanomaterials of platinum nanoparticles and multi-wall carbon nanotubes (PtNP/MWCNT). The composite material was spin-coated into film and further prepared as the counter electrode (PtNP/MWCNT-CE) for a dye-sensitized solar cell (DSSC). The short-circuit current density (J(SC)) and power-conversion efficiency (eta) of the DSSC with PtNP/MWCNT-CE were found to be 18.01 +/- 0.91 mA cm(-2) and 8.00 +/- 0.23%, respectively, while the corresponding values were 14.62 +/- 0.19 mA cm(-2) and 6.92 +/- 0.07% for a DSSC with a bare platinum counter electrode (Pt-CE). The presence and distribution of PtNP/MWCNT on the CE were characterized by using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The attachment of PtNPs on MWCNTs was observed by transmission electron microscopy (TEM). Cyclic voltammetry (CV), incident-photo-to-current efficiency (IPCE) and electrochemical impedance spectra (EIS) were correlated to explain the efficacy of this nanocomposite system

Sudden switch of generalized Lieb-Robinson velocity in a transverse field Ising spin chain

The Lieb-Robinson theorem states that the speed at which the correlations between two distant nodes in a spin network can be built through local interactions has an upper bound, which is called the Lieb-Robinson velocity. Our central aim is to demonstrate how to observe the Lieb-Robinson velocity in an Ising spin chain with a strong transverse field. We adopt and compare four correlation measures for characterizing different types of correlations, which include correlation function, mutual information, quantum discord, and entanglement of formation. We prove that one of correlation functions shows a special behavior depending on the parity of the spin number. All the information-theoretical correlation measures demonstrate the existence of the Lieb-Robinson velocity. In particular, we find that there is a sudden switch of the Lieb-Robinson speed with the increasing of the number of spin

Tandem synthesis of silver nanoparticles and nanorods in the presence of poly(oxyethylene)-amidoacid template

Sequential formation of silver nanoparticles (AgNPs) and nanorods from the reduction of AgNO(3) was affected by a poly(oxyethylene)-amidoacid (POE-amidoacid) in aqueous solution. The requisite POE-amidoacid, consisting of -(CH(2)CH(2)O)(n)- segments with amide and carboxyl groups, was simply prepared via amidation with trimellitic anhydride of a poly(oxyethylene)-monoamine (POE-amine) of molecular weight (M(w)) similar to 2000 g/mol. The POE-amidoacid afforded AgNPs as small as 5 nm in diameter, which gradually (over a period of months) self-assembled into nanorods that were 10-15 nm in width and 30-50 nm in length. The hierarchical formation of Ag species occurred only at ambient temperature, but Ag aggregates formed above 50 degrees C. The process could be monitored by UV absorption at 420 and 380 nm for AgNPs and nanorods, respectively, and by transmission electron microscopy (TEM) for the nanorods. Fourier transform infrared (FTIR) and tapping-mode atomic force microscopy (TM-AFM) analyses revealed that the structurally tailored POE-amidoacid was indeed multifunctional: it reduced Ag(+), stabilized the obtained Ag(0) species, and served as a template for the tandem formation of AgNPs and nanorods. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved

Two new secoiridoid glycosides from Gentiana algida.

Two new acylated secoiridoid glycosides were isolated from the aqueous acetone extract of the whole herb of Gentiana algida. The structures of these new products were established by spectral and chemical methods as 6'-(2,3-dihydroxybenzoyl)sweroside and 6'-(2,3-dihydroxybenzoyl)swertiamarin, respectively

The disruption of bacterial membrane integrity through ROS generation induced by nanohybrids of silver and clay

Nanohybrids, synthesized via silver nitrate reduction in the presence of silicate clay, exhibit a high potency against bacterial growth. The plate-like clay, due to its anionic surface charges and a large surface area, serves as the support for the formation of silver nanoparticles (AgNPs) similar to 30 nm in diameter. The nano-hybrid consisting of Ag/silicate at a 7/93 weight ratio inhibited the growth of dermal pathogens including Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa and Streptococcus pyrogens, as well as the methicillin- and oxacillin-resistant S. aureus (MRSA and ORSA). Scanning electron microscope revealed that these nanohybrids were adherent on the surface of individual bacteria. The thin silicate plates provide a surface for immobilizing AgNPs in one highly concentrated area but prevent them from entering the cell membrane. Subsequent cytotoxicity studies indicated that surface contact with the reduced AgNPs on clay is sufficient to initiate cell death. This toxicity is related to a loss in membrane integrity due to reactive oxygen species (ROS) generation. The hybridization of AgNPs on clay surface is viable for generating a new class of nanohybrids exhibiting mild cytotoxicity but high efficacy for battling drug-resistant bacteria. (C) 2009 Elsevier Ltd. All rights reserved