Conjugates of poly(ferrocenyldimethylsilane) (PFDMS) with Ac-(GA)(2)-OH, Ac-A(4)-OH, Ac-G(4)-OH and Ac-V(4)-OH have been prepared by reaction of the tetrapeptide units with the amino-terminated metallopolymer. The number average degree of polymerisation (DP(n)) of the PFDMS was approximately 20 and comparable materials with shorter (DP(n) ≈ 10) and/or amorphous chains have been prepared by the same procedure. Poly(ferrocenylethylmethylsilane) (PFEMS) was employed for the latter purpose. All conjugates were characterised by GPC, MALDI-TOF MS, NMR and IR spectroscopy. With the exception of Ac-V(4)-PFDMS(20), all materials exhibited some anti-parallel β-sheet structure in the solid state. The self-assembly of the conjugates was studied in toluene by DLS. The vast majority of the materials, irrespective of peptide sequence or chain crystallinity, afforded fibres consisting of a peptidic core surrounded by a PFS corona. These fibres were found in the form of cross-linked networks by TEM and AFM. The accessibility of the chemically reducing PFS corona has been demonstrated by the localised formation of silver nanoparticles on the surface of the fibres.
We investigated the crystalline phase and electronic structure of perovskite-type La1-xSrxMnO3 (0.0 ≤ x ≤ 1.0) (LSMx) catalysts synthesized via the citric sol-gel route, for H2O2 reduction. The resulting materials were characterized by XRD, XANES, TR-XANES, and TPO and, after calcination, consisted of cubic perovskite for 0.0 ≤ x ≤ 0.8 and hexagonal perovskite for x = 1.0. Mn species in the precalcined catalysts were oxidized to Mn(3+) for x = 0.0 to 0.6 and to Mn(2+) for x = 0.8 and 1.0. After calcination, Mn species were present in a mixed oxidation state of Mn(3+)/Mn(4+), while Sr(2+) and La(3+) were not altered. TR-XANES and TPO showed that Mn species were oxidized at 210-220 °C and formed active perovskites LSM0.4 and LSM0.0 at 580 °C and 640 °C. This shows that Sr doping can reduce the oxidation temperature of LSMx with 0.2 ≤ x ≤ 0.4. However, the concentration of Mn(4+) in LSMx is increased which is useful for enhancing their catalytic activity and stability. When tested in an alkaline electrolyte, LSM0.6 containing the optimum Mn(4+)/Mn(3+) ratio promoted the formation of hydroxyl via the oxygen intercalation reaction and exhibited low polarization resistance and the highest catalytic activity for H2O2 reduction.
Silica has been used as reinforcing filler in natural rubber for a period of time as it results in excellent properties for NR vulcanizes. Rice husk ash (RHA), bagasse ash (BA), and oil palm ash (OPA) obtained from agricultural wastes are mainly composed of silica in the percentage of 80.00%, 57.33%, and 40.20% by weight, respectively. The effect of these fillers on cure characteristics and mechanical properties of natural rubber materials at fixed silica content at 35 parts per hundred of rubber (phr) were investigated. The results indicated that ashes showed greater cure time compared to that of the silica. The incorporation of ashes into natural rubber gradually improved compression set but significantly decreased tensile strength, elongation at break, and resilience. Moreover, young's modulus increased, while hardness showed no significant change with the addition of ashes. Overall results indicated that ashes could be used as cheaper fillers for natural rubber materials where improved mechanical properties were not critical.
PdCoNi nanocomposites supported on graphene (PdCoNi/G) have been obtained from chemical reduction of metal catalysts and graphite oxide (GO) with a strong reducing agent, followed by calcination at high temperature under N2 condition, and used for electrooxidation of methanol in direct methanol fuel cell. The morphologies and structural properties of electrocatalysts were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). X-ray spectroscopy techniques (X-ray photoelectron spectroscopy XPS) was used to investigate the chemical state of the synthesized catalysts. The results of Pd XPS spectra showed the metallic Pd and PdO phases for precalcined and calcined PdCoNi/G nanocomposite, respectively. The X-ray measurement of Co and Ni displayed the various metallic oxides in synthesized electrocatalysts. For electrochemical analysis, cyclic voltammetry (CV) and chronoamperometry (CA) indicated that the PdCoNi/G nanocomposites enhanced the methanol oxidation, compared to the lower activity in the calcined electrocatalysts.
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