Effects of structures of pyrolyzed corrin,corrole and porphyrin on oxygen reduction reaction

The effects of the structures of various pyrolyzed cobalt-based macrocyclic compounds, which are pyrolyzed cobalt-corrin compounds (py-Co-Corrin/C), pyrolyzed cobalt-corrole compounds (py-Co-Corrole/C) and pyrolyzed cobalt-porphyrin compounds (py-Co-Porphyrin/C), on their activities in the oxygen reduction reaction (ORR) are studied. Following the pyrolysis, py-Co-Corrin/C has a higher ORR activity than py-Co-Corrole/C and py-Co-Porphyrin/C, which their electron-transfer numbers are 3.90, 3.87 and 3.37 at 0.3 V, respectively. According to the analysis of near edge X-ray absorption fine structure in N K-edge, only py-Co-Corrin/C has the Co–N₄ chelate and poly-aromatic hydrocarbons when pyrolyzed at high temperature. The X-ray absorption spectra reveal the oxidation states of central cobalt in cobalt-based macrocyclic compounds which are changed from high to low. Also, the atomic distances of cobalt to its neighbors vary among all of the samples. The experimental results suggest that the structure and the coordination of cobalt-based macrocyclic compounds strongly affect their ORR activities.     

Preparation of non-precious metal catalysts for PEMFC cathode from pyrolyzed vitamin B12

In this study, the effect of non-precious metal catalysts in the form of pyrolyzed Vitamin B12 that is supported by carbon black on oxygen reduction reaction (ORR) is examined. Pyrolysis was carried out at temperatures of 300 °C (py-B12/C-300), 500 °C (py-B12/C-500), 700 °C (py-B12/C-700) and 900 °C (py-B12/C-900) in an N₂-atmosphere. The ring-rotating disk electrode technique revealed that the electron-transfer numbers of py-B12/C-300, py-B12/C-500, py-B12/C-700 and py-B12/C-900 are 3.02, 3.42, 3.90 and 3.57, respectively: py-B12/C-700 exhibits near four-electron transfer. The X-ray absorption spectra demonstrate that during the pyrolysis, as the Co oxidation state of py-B12-700 is changed from Co(III) to Co(II), the Co coordination number changes from 6 to 4, suggesting that the structure is a square-planar Co–N₄ chelate. However, the Co–N₄ chelate is decomposed as the pyrolysis temperature increases to 900 °C, resulting in a loss of ORR activity. The H₂–O₂ PEMFC that uses py-B12/C-700 provides excellent performance, substantially outperforming py-CoTMPP/C.     

Two-stage thermally induced stable colloidal assemblies from PAAc/PNIPAAm/mPEG graft copolymer in water

A facile approach of forming stable polymeric complexes by the two-stage phase transition of the graft copolymer comprising poly(acrylic acid) (PAAc) as the backbone and poly(N-isopropylacrylamide) (PNIPAAm) and monomethoxy poly(ethylene glycol) (mPEG) as the grafts in water was illustrated. Rather loose and hydrated polymeric aggregates with a characteristic hydrophobic multicore structure, achieved by the first-stage thermally induced phase transition of PNIPAAm grafts, underwent the core structure rearrangement (including multicore fragmentation and fusion) upon the second-stage dehydration of mPEG grafts at 90 °C. This was followed by hydrogen-bond pairings of mPEG and PNIPAAm chain segments with unionized AAc residues acting as an effective protective shell against potential hydration of the hydrophobic inner cores during the annealing process. The polymer complexes thus obtained show surprisingly enhanced hydrophobicity of inner cores at 25 °C in water and excellent stability of the morphological structure in response to the temperature disturbance.     

Multi-scaled polymersomes from self-assembly of octadecanol-modified dextrans

Lipid-conjugated polysaccharide vesicles in nano- and micro-scale were developed from amphiphilic octadecanol-modified dextrans (OMD) prepared by partial esterification of dextran with activated octadecanol-carbamate imidazole in a well-controlled manner. The critical aggregation concentration (CAC) of OMD adducts in aqueous phase varies, depending mainly on their octadecanol contents. Through supramolecular assembly of the OMD adducts comprising either 17 or 28 mol% octadecanol residues with respect to the anhydroglucopyranose units by the partial solvent displacement technique with the initial water content of DMSO/H₂O solutions beyond a critical point, stable nano-scaled OMD assemblies were developed and characterized by the vesicle-like morphology. The dimension of polymersomes can be effectively controlled by the OMD composition as well as the initial water content. On the other hand, micro-scaled OMD polymersomes can be achieved by the double emulsion technique in a water/oil/water (w₁/o/w₂) manner. Both the contents of NaCl in aqueous solution as the w₁ phase and of DMSO in DMSO/CHCl₃ co-solvents as the organic phase, in which OMD was dissolved, are of great importance in controlling the polymersome morphology and size. These micro-scaled OMD polymersome walls are characterized by size-selective permeability capable of encapsulating large water-soluble cargoes while allowing transport of small polar species across the membrane, thereby rendering these unique colloidal particles of potential applications in biomedical technologies.     

High stability of oxidation of methanol catalyzed by Pt supported by oxygen-incorporated bamboo-shaped CNTs grown directly on carbon cloth

Bamboo-shaped CNTs in which oxygen was incorporated were directly grown on carbon cloth (O-BCNT-CC) by microwave plasma-enhanced chemical vapor deposition. Mixed precursors CH₄/H₂/N₂/O₂ were introduced during the growth process. For comparison, bamboo-shaped CNTs without incorporated oxygen were prepared herein (BCNT-CC). Then, platinum catalysts were prepared on the as-grown O-BCNT-CC (Pt/O-BCNT-CC) and the as-grown BCNT-CC (Pt/BCNT-CC). According to TEM-EELS oxygen mapping, O atoms were uniformly distributed on the O-BCNT surface. Methanol oxidation was performed using Pt/O-BCNT-CC and Pt/BCNT-CC in 1 M methanol and 1 M sulfuric acid by cyclic voltammetry. In the initial cycle, the peak current density of Pt/O-BCNT-CC was almost equal to that of Pt/BCNT, indicating that both had nearly equal activities in the beginning. After 300 cycles, the peak current of Pt/BCNT-CC was reduced to half of the initial peak current owing to platinum-poisoning; however, the peak current of Pt/O-BCNT-CC decayed less. In Pt/O-BCNT-CC, the oxygen-containing functional groups affect the orientation index of crystalline Pt, providing a means of oxidizing methanol and stabilizing Pt catalysts for the long-term.     

Using dynamic pixel value mapping method to construct visible and reversible image watermarking scheme

A reversible and visible image watermarking scheme extracts a visibly embedded binary watermark image and recovers the original cover image. This paper presents a reversible and visible image watermarking scheme that embeds visible watermarks into a part of the cover image, called the embedded region R, and embeds required binary strings into the whole image through the conventional difference-expansion method. The size of the embedded visible watermark is determined by the coefficient k; a large k value leads to a large embedded region for the visible watermark. The embedded region R is first segmented to non-overlapped k×k blocks, and each block is related to one bit of the watermark image. For those blocks that are related to the logo bits of the watermark image, these k×k blocks are adjusted by the proposed dynamic pixel value mapping method for highly visual detection. The binary bit string S, composed of the binary watermark image and LSB bits of the logo watermark bits’ corresponding k×k blocks, is embedded into the cover image using the conventional difference-expansion method. Experimental results show that the watermark is clearly embedded into the embedded region R and that the distortion of the reversible embedding is limited.     

Air stable organic complementary inverter with high and balance noise margin based on polymer/metal oxide hybrid gate dielectrics

This study demonstrates an ambient air operated organic complementary inverter composed of a pentacene p-channel and a N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide n-channel organic thin-film transistor (TFT) fabricating at room temperature. The gate dielectric is an ultrathin polystyrene-co-methyl methacrylate (PS-r-PMMA)-modified hafnium oxide hybrid layer. Grafting the PS-r-PMMA passivates the surface defects. The transistors exhibit balanced performance, including threshold voltage, on/off current ratio, and field effect mobility. Similar channel dimensions for both types of TFT can be designed for the inverter construction. The inverter operates well below 6 V. The switching voltage is approximately V_dd/2 with a high noise margin (87% of theoretical value), which is suitable for flexible logic applications.     

Synthesis and characterization of amphiphilic graft copolymers with poly(ethylene glycol) and cholesterol side chains

Amphiphilic graft copolymers comprising monomeric units of methoxy poly(ethylene glycol) (mPEG)-acrylate, 2-hydroxyethyl methacrylate (HEMA)–cholesterol conjugates and HEMA were synthesized and their properties characterized. The value of the critical micelle concentration (CMC) for these copolymers is linearly proportional to the ratio of the number of mPEG–acrylates to that of the HEMA–cholesterol conjugates per macromolecule (N_PEG/N_c), which is the most important parameter which influences the formation of polymeric micelles. The latter show excellent colloidal stability and their sizes decrease with increasing CMC. Based on the quenching of pyrene fluorescence, the relatively high levels of the loading capacity of pyrene are attributed to the elevated hydrophobicity of the micelle core. The loading capacity of pyrene decreases with increasing CMC. The weight-average partition coefficient for pyrene in polymeric micelles increases with increasing polymer concentration because more micelles are available for accommodating pyrene. Copyright © 2004 Society of Chemical Industry     

FTIR-ATR measurements of the ionization extent of acrylic acid within copolymerized methacrylated dextran/acrylic acid networks and its relation with pH/salt concentration-induced equilibrium swelling

In this study, dextran hydrogels were obtained by free radical copolymerization of methacrylated dextran with acrylic acid (AAc) in aqueous solution. The fractions of dissociation of AAc units within hydrogel in response to changes in pH and ionic strength of external aqueous solution were determined by FTIR-ATR spectroscopy. The influence of small ion concentration within hydrogel on the dissociation constant of AAc follows the Debye-Hückel behavior. Based on the results from the FTIR-ATR measurements, the total ion concentration difference inside and outside the hydrogel was determined according to the Donnan equilibrium theory, taking account of the counterion condensation effect quantitatively. The swelling response of hydrogels to changes in external pH and ionic strength was governed mainly by the ionic osmotic pressure due to the accumulation of diffusible ions within hydrogels. The energy balance between the osmotic and elastic retractile responses indicates the non-Gaussian behavior of elastically effective subchains with increasing swelling.