Janusz W. Sobczak

Effect of calcium-ion implantation on the corrosion resistance and biocompatibility of titanium

This work presents data on the structure and corrosion resistance of titanium after calcium-ion implantation with a dose of 10(17) Ca+/cm2. The ion energy was 25 keV. Transmission electron microscopy was used to investigate the microstructure of the implanted layer. The chemical composition of the surface layer was examined by XPS and SIMS. The corrosion resistance was examined by electrochemical methods in a simulated body fluid (SBF) at a temperature of 37 degrees C. Biocompatibility tests in vitro were performed in a culture of human derived bone cells (HDBC) in direct contact with the materials tested. Both, the viability of the cells determined by an XTT assay and activity of the cells evaluated by alkaline phosphatase activity measurements in contact with implanted and non-implanted titanium samples were detected. The morphology of the cells spread on the surface of the materials examined was also observed. The results confirmed the biocompatibility of both calcium-ion-implanted and non-implanted titanium under the conditions of the experiment. As shown by TEM results, the surface layer formed during calcium-ion implantation was amorphous. The results of electrochemical examinations indicate that calcium-ion implantation increases the corrosion resistance, but only under stationary conditions; during anodic polarization the calcium-ion-implanted samples undergo pitting corrosion. The breakdown potential is high (2.7-3 V).

Effect of phosphorus-ion implantation on the corrosion resistance and biocompatibility of titanium

This work presents data on the structure and corrosion resistance of titanium after phosphorus-ion implantation with a dose of 10(17)P/cm2. The ion energy was 25keV. Transmission electron microscopy was used to investigate the microstructure of the implanted layer. The chemical composition of the surface layer was examined by X-ray photoelectron spectroscopy and secondary ion mass spectrometry. The corrosion resistance was examined by electrochemical methods in a simulated body fluid at a temperature of 37 C. Biocompatibility tests in vitro were performed in a culture of human derived bone cells in direct contact with the materials tested. Both, the viability of the cells determined by an XTT assay and activity of the cells evaluated by alkaline phosphatase activity measurements in contact with implanted and non-implanted titanium samples were detected. The morphology of the cells spread on the surface of the materials examined was also observed. The results confirmed the biocompatibility of both phosphorus-ion-implanted and non-implanted titanium under the conditions of the experiment. As shown by transmission electron microscope results, the surface layer formed during phosphorus-ion implantation was amorphous. The results of electrochemical examinations indicate that phosphorus-ion implantation increases the corrosion resistance after short-term as well as long-term exposures.

Hydrosilylation of phenylacetylene catalyzed by metal complex catalysts supported on polyamides containing a pyridine moiety

Abstract The hydrosilylation of phenylacetylene with triethoxysilane catalyzed by polymer-supported Rh(I) and Pt(II) complexes has been investigated. Polyamides having the 2,5- and 2,6-pyridine moiety in their repeat units were used as the catalysts supports. The effect of the support structure, the type of solvent used, the substrate ratio and catalyst concentration on reaction selectivity were studied. X-ray photoelectron spectroscopy (XPS) was used to characterize the polymer supports and the supported catalysts before and after use. It was found that the selectivity of the hydrosilylation can be controlled by the chemical structure of the polymer support. When the reaction was catalyzed by Rh(I) attached to the polyamide with a pyridine substituted in the 2,6 position, β( Z )-vinylsilane was formed as the major product. Use of the same catalyst supported on the polymer with the 2,5-pyridine resulted in a reversal of the stereoselectivity and β( E )-vinylsilane was the major product. These results have been correlated with the reaction mechanism and the electron density on the rhodium centres. The binding energy for the Rh3d 5/2 attached to the 2,6-py moiety was found to be lower by 1.03 eV than that for the Rh supported on the 2,5-py type polymer. Hydrosilylation using Pt(II) as the catalyst supported on the same series of polyamides proceeded in the usual manner of cis addition to give predominantly β( E )-vinyl product and the α-isomer. The only difference caused by the presence of the polymer support was the increased yield of α-product. Recycling tests demonstrated high stability of the supported catalysts during prolonged use.

Catalytic hydrogenation of alkadienes and alkynes by palladium catalysts supported on heterocyclic polyamides

The catalytic behavior of palladium supported on polyamides having a pyridine moiety has been studied in the liquid phase hydrogenation of alkadienes and alkynes at 25°C and 1 atm pressure. The palladium centre was introduced into the polyamides of formula Figure options Download full-size image Download as PowerPoint slide with n=2 and 6, by ligand exchange using PdCl2(PhCN)2. The resulting precursor catalysts, which were activated in an hydrogen atmosphere, selectively reduced alkadienes and alkynes to monoenes and alkenes, respectively. The reaction stopped after 1 molar equivalent of hydrogen had been consumed. The effects of solvent polarity and of support structure has also been investigated. Several techniques have been used to characterize these palladium catalytic systems. The type of interaction between palladium and pyridine modified polyamides was studied by using low molecular weight model compound and IR spectroscopy. X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) were used to characterize the palladium catalysts before and after use. It can be concluded from these results that both matrix functional groups i.e. Npy and OCO act as coordination sites for the palladium centre and mixed valence state species are formed, giving a selective palladium catalyst. Evaluation of the stability of the supported palladium catalyst was tested in eleven successive runs involving 4300 catalytic cycles: neither loss of activity nor selectivity was found.

Spectroscopic studies of polyaniline protonation with poly(alkylene phosphates)

Abstract Polyaniline doped with poly(alkylene phosphates) has been studied by Fourier transform infra-red, X-ray photoelectron and ultraviolet/visible spectroscopies. The protonation of the polymer was indicated by the appearance of infra-red modes characteristic of polyaniline salts and by the bands typical of polyphosphates at ca. 1000 cm−1. X-ray photoelectron spectra showed a decrease in the concentration of imine groups as well as the co-existence of ionized and unionized phosphates independent of the doping level. The influence of the protonation method on the obtained product was observed.

Mechanistic studies of the electrochemical polymerization of C60 in the presence of dioxygen or C60O

Electropolymerization of C60 in the presence of dioxygen, in a mixture of acetonitrile and toluene (1 : 4, v : v) containing tetra(alkyl)ammonium perchlorate, was investigated by multi-scan cyclic voltammetry and piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance. The fullerene was readily electropolymerized if the O2 to C60 concentration ratio in solution exceeded 1 : 10 and the applied potential reached values where electro-reduction of dioxygen to superoxide, O2˙−, and C60 to C602− occurred. The redox activity of the polymer was determined by cyclic voltammetry for solutions with different tetra-(alkyl)ammonium perchlorates used as supporting electrolytes. The film conductivity was higher the smaller the size of the cation in the supporting electrolyte. The C60 electropolymerization in the presence of dioxygen was suppressed when a spin trapping agent, N-tert-butyl-α-(4-nitrophenyl)nitrone that could intercept superoxide, was present. The fullerene was also electropolymerized in the presence of small amounts of the epoxide, C60O, in the absence of dioxygen. We postulate that the C60 electropolymerization in the presence of O2 proceeds via the initial nucleophilic attack of superoxide on C60 to form a C60O2˙− radical anion, which then interacts with another molecule of C60 to produce C60O and C60O˙−. Under further electro-reduction, these intermediates serve to initiate polymerization of C60 through the formation of C60O2−, as determined earlier in studies of the electropolymerization of C60O itself.

Structure and properties of C60–Pd films formed by electroreduction of C60 and palladium(II) acetate trimer: evidence for the presence of palladium nanoparticles

The composition, surface morphology, structure, and electrochemical properties of thin solid films of the polymer, C60–Pd, were studied by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and energy dispersive X-ray fluorescence (EDXRF) as well as being examined by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) with selective area diffraction (SAD) and by cyclic voltammetry (CV), respectively. The C60–Pd films were deposited onto Au or Pt electrodes by electroreductive co-polymerization of C60 and the palladium(II) acetate trimer, [Pd(ac)2]3, in a mixed acetonitrile–toluene (4∶1, v/v) solution of 0.1 M tetra(n-butyl)ammonium perchlorate under multicyclic voltammetry or potentiostatic conditions. The structure and composition of the C60–Pd films were dependent on the relative concentration of the polymer precursors, i.e., C60 and [Pd(ac)2]3, in the solution for electropolymerization. That is, in films grown in solutions with a high [Pd(ac)2]3∶C60 ratio, (–C60–Pd–)n polymeric chains were separated by the Pd nanoclusters. These films were relatively smooth and uniform. In contrast, films electropolymerized in solutions with a low [Pd(ac)2]3∶C60 ratio were rough, porous and much less uniform. The presence of the Pd nanoclusters in the C60–Pd film influenced the electrode processes of probing redox species dissolved in solution. That is, electro-oxidation of an N,N,N′,N′-tetramethyl-1,4-phenylenediamine (TMPDA) electrochemical redox probe was partially inhibited at the electrode coated by the C60–Pd film with a relatively low Pd nanocluster content. In contrast, electro-oxidation of TMPDA was effectively mediated by the C60–Pd film containing appreciable amounts of dispersed Pd nanoclusters.

Effect of plasma electrolytic oxidation in the solutions containing Ca, P, Si, Na on the properties of titanium†

The surface layers were formed on titanium by plasma electrolytic oxidation (PEO) in the solutions which contain various amounts of Na(2)SiO(3)x5H(2)O, Na(3)PO(4) x12H(2)O and Ca(CH(3)COO)(2) xH(2)O. The layers were characterized using a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and an X-ray diffractometer (XRD). The titanium/oxide surface layer interface was analyzed by X-ray photoelectron spectroscopy (XPS). The adhesive strength of the oxide layers was evaluated by the scratch-test. The bioactivity of the surface was determined by soaking in a simulated body fluid (SBF) for 7 and 30 days. The corrosion resistance was determined by electrochemical methods after 13, 181, and 733 h exposure in SBF at a temperature of 37°C. The oxide layers obtained were rough and porous and enriched with Ca, P, Si, and Na and their properties depended on the concentration of the components of the electrolyte. The results of the electrochemical examinations, after a 13 h exposure in SBF, show that the surface modification by PEO improves the corrosion resistance of titanium and it is not degraded after a long-term exposure in SBF. The electrochemical impedance spectroscopy (EIS) results indicate that the surface layers have a complex structure.

Thiol–Yne Click Reactions on Alkynyl–Dopamine‐Modified Reduced Graphene Oxide

The large-scale preparation of graphene is of great importance due to its potential applications in various fields. We report herein a simple method for the simultaneous exfoliation and reduction of graphene oxide (GO) to reduced GO (rGO) by using alkynyl-terminated dopamine as the reducing agent. The reaction was performed under mild conditions to yield rGO functionalized with the dopamine derivative. The chemical reactivity of the alkynyl function was demonstrated by post-functionalization with two thiolated precursors, namely 6-(ferrocenyl)hexanethiol and 1H,1H,2H,2H-perfluorodecanethiol. X-ray photoelectron spectroscopy, UV/Vis spectrophotometry, Raman spectroscopy, conductivity measurements, and cyclic voltammetry were used to characterize the resulting surfaces.

XANES investigations of Pd-doped polyaniline

Polyaniline doped with palladium (PANI-Pd) demonstrated a particular catalytic activity and selectivity in reaction of the hydrogenation of the triple C-C bond. Pd K-edge X-ray absorption near edge structure (XANES) studies were performed for PANI-Pd and several palladium compounds like PdCl 2 , (NH 4 ) 2 PdCl 4 , Pd(NH 3 ) 4 Cl 2 , (NH 4 ) 2 PdCl 6 , K 2 PdCl 4 , [(C 3 H 5 )PdCl] 2 , PdCl 2 (CH 3 CN) 2 and PdO. The measurements were carried out in transmission mode at the station Xl in HASYLAB. Chemical shifts of Pd K edge for PANI-Pd and other palladium compounds were evaluated. The experimental XANES spectra were compared with the theoretical XANES spectrum calculated for PdCl 2 by applying the FEFF8 program. It was found that the Pd K edge XANES spectrum for PANI-Pd was similar to that for ammonium tetrachloropalladate (NH 4 ) 2 PdCl 4 . Our results indicated that in the PANI-Pd catalyst the tetrachloropalladate ion [PdCl 4 ] -2 is coordinated to the amine part of the polymer chain and is responsible for specific catalytic properties.