Michael Wörner - Academia.edu (original) (raw)
Papers by Michael Wörner
The goal of this work was the evaluation of the use of copper as suitable substrate for assessing... more The goal of this work was the evaluation of the use of copper as suitable substrate for assessing the trapping of a small metallic compound by immobilized myoglobin (myo). Our proposal was to demonstrate that disposable devices based in the use of this metal would be as interesting as more widely used gold ones and more suitable since the economical point of view, despite the well-known problem of copper dissolution and oxidation. For such reason copper electrodes covered with 2thiobarbituric acid (TBA) were tested as a platform to obtain myo modified electrodes with aptitude to trap a Ru complex present in a solution. The assembly process was followed using cyclic voltammetry, electrochemical impedance spectroscopy and contact angle measurements. Our results were consistent with the obtaining of a stable electrode of copper covered with a protein adsorbed onto TBA with reproducible behavior, pointing that copper could be a suitable material to develop electrochemical devices for biosensing. This stable Cu/TBA/myo electrode had enough sensitivity to detect the capture of a compound with low molecular weight and with low affinity for the protein, and, when immobilizing other biomolecules, it would sense the trapping of their specific target.
Polymers, 2021
Spherical, individual polymer nanoparticles with functional –SH groups were synthesized via aeros... more Spherical, individual polymer nanoparticles with functional –SH groups were synthesized via aerosol photopolymerization (APP) employing radically initiated thiol-ene chemistry. A series of various thiol and alkene monomer combinations were investigated based on di-, tri-, and tetrafunctional thiols with difunctional allyl and vinyl ethers, and di- and trifunctional acrylates. Only thiol and alkene monomer combinations able to build cross-linked poly(thio-ether) networks were compatible with APP, which requires fast polymerization of the generated droplet aerosol during the photoreactor passage within a residence time of half-minute. Higher monomer functionalities and equal overall stoichiometry of functional groups resulted in the best nanoparticles being spherical and individual, proven by scanning electron microscopy (SEM). The presence of reactive –SH groups in the synthesized nanoparticles as a basis for post-polymerization modifications was verified by Ellman’s test.
The Journal of Physical Chemistry B, 2001
Novel heterogeneous photocatalysts were developed which are able to transfer electrons from excit... more Novel heterogeneous photocatalysts were developed which are able to transfer electrons from excited Ru(II) donors within the zeolite framework to Co(III) acceptor complexes in the exterior. The materials were prepared and characterized by elemental analysis, electrochemical methods, diffuse reflectance, and raster and transmission electron microscopy. The catalysts consist of zeolite Y-encapsulated Ru(bpy) 3 2+ (bpy) 2,2′bipyridine) sensitizers in close proximity to TiO 2 nanoparticles on the same support. The photophysical properties of Ru(bpy) 3 2+ within the zeolite supercages were investigated at different loadings of Ru(bpy) 3 2+ and TiO 2. The photoexcited MLCT state of the zeolite-entrapped Ru(bpy) 3 2+ reacts via electron transfer with Co(dpphen) 3 3+ (dpphen) 4,7-diphenyl-1,10-phenanthroline) in the exterior of the zeolite particles. The relative quenching of Ru(bpy) 3 2+ by external Co(dpphen) 3 3+ increases as the TiO 2 content within the zeolite is increased, where electron transfer from Ru(bpy) 3 2+ complexes within the interior of the zeolite are able to transfer electrons to Co(dpphen) 3 3+. This observation indicates that electrons can be transported from the interior of the zeolite to the surface in the presence of an appropriate electron relay, such as TiO 2 nanoparticles.
Frontiers in Bioengineering and Biotechnology
Materials Science in Semiconductor Processing
RSC Adv.
A flame-free UV-mediated aerosol technology opens the way for the fabrication of organic–inorgani... more A flame-free UV-mediated aerosol technology opens the way for the fabrication of organic–inorganic powder products in a single operation and ambient temperature.
Journal of Nanoparticle Research, 2014
A continuous aerosol-based process is described for the encapsulation of nanoparticles with a thi... more A continuous aerosol-based process is described for the encapsulation of nanoparticles with a thin polymer shell. The process is essentially based on directed binary collisions between gas-borne core particles and liquid monomer droplets carrying opposite electrical charges, followed by photo-initiated polymerization. Once the two streams are mixed together, the process runs to completion on a time scale of about 2 min or less, required for coagulation and polymerization. Gold, silica, and sodium chloride nanoparticles were successfully coated by this technique with PHDDA [poly(hexanediol diacrylate)] and/ or crosslinked PMMA [poly(methyl methacrylate)]. It was found that all core materials as well as agglomerates were wettable at room temperature and that the spreading kinetics of the monomer were fast enough to cover the core particles uniformly within the time scale provided for coagulation. The shell thickness depends on the volume ratio between core particles and monomer droplets. This was demonstrated for a combination of monodisperse silica spheres (d = 241 nm) and polydisperse methyl methacrylate droplets, resulting in a theoretical shell thickness of 18 nm. There was very good agreement between measurements by TEM and electrical mobility spectroscopy. The results revealed that about 90 % or more of the core-shell structures were formed from 1:1 collisions between a core particle and a single monomer droplet.
Macromolecular Materials and Engineering, 2014
Colloid and Polymer Science, 2014
Water science and technology : a journal of the International Association on Water Pollution Research, 2004
Technical development work is presented, where the VUV photochemically induced oxidative degradat... more Technical development work is presented, where the VUV photochemically induced oxidative degradation is used: (i) for analytic purposes, and (ii) for small to medium scale (< 10 m2/d) waste water treatment processes or ultrapure water production. In the first case, small Xe-excimer radiation sources with an integrated reaction space designed for optimal conditions, as far as incident photon flux density, turbulence and concentration of dissolved molecular oxygen are concerned, have been built and tested. Under conditions of exhaustive oxidation and/or mineralization of pollutants in a continuous regime, they may be used for sample pre-treatment modules prior TOC, TOX and electrochemical trace metal analysis. Under conditions of partial oxidation or mineralization, the same lamp/reactor combination may be used for functionalization purposes prior to e.g. GC or HPLC analyses. In the second case, mass transfer limitations between the non-irradiated bulk volume and the irradiated vol...
Sustainable Energy and Environmental Technologies - Proceedings of the Third Asia-Pacific Conference, 2001
The Journal of Physical Chemistry A, 2002
The synthesis and photophysical properties of a ruthenium dyad (4) and triad (5) are reported. Bo... more The synthesis and photophysical properties of a ruthenium dyad (4) and triad (5) are reported. Both biomimetic systems are physical models for the photosynthetic reaction center. They consist of a ruthenium(II)-polypyridyl sensitizer featuring chemically attached 3,3′-dimethyl-4,4′-viologen and 4,4′-viologen electron acceptors. The binding of the chemically attached electron acceptors by the three structurally different crown ethers, DB 30 C 10 , BBO 5 O 5 , and AAO 5 O 5 , offers a remarkable tool for the enhancement of the lifetimes of the charge separated states (τ CS), up to a factor of 2 × 10 4. The drastic increase in the lifetimes observed can be explained by a decrease in the reorganization energy λ due to the presence of the crown ether units bound to the viologen acceptor.
The Journal of Physical Chemistry A, 1998
During the oxidative degradation of 2,4-dimethylaniline (2,4-xylidine) by means of the H 2 O 2 /U... more During the oxidative degradation of 2,4-dimethylaniline (2,4-xylidine) by means of the H 2 O 2 /UV method, a series of hydroxylated aromatic amines are formed, this result confirming the role of the hydroxyl radical as an initiator of the oxidative chain reaction. Thermal or ...
Synthesis, 2005
The synthesis of organic thiosulfates, up to 10 nm in length, which were tailored for generating ... more The synthesis of organic thiosulfates, up to 10 nm in length, which were tailored for generating artificial monomembranes on gold surfaces by electrochemically initiated deposition, was accomplished. (E)-3-(4-Hydroxyphenyl)acrylic acid (4-hydroxy cinnamic acid) was employed as aromatic head group and (C 10 H 20-On n (n = 1, 3, 5, 7) building blocks were attached. The synthetic procedure comprises a series of nucleophilic substitutions under carefully defined conditions. Extended purification is crucial for eliminating non-reacted starting materials.
![Research paper thumbnail of Chiral modified electrodes. Part 2. Marcus behaviour and high enantioselectivity in the photoelectrochemistry at a polymeric [Ru(4-methyl-4′-vinyl-2,2′-bipyridine)3]2+ electrode](https://attachments.academia-assets.com/66913933/thumbnails/1.jpg)
](Physical Chemistry Chemical Physics, 2000
Part 2.¤ Marcus behaviour and high enantioselectivity in the photoelectrochemistry at a polymeric... more Part 2.¤ Marcus behaviour and high enantioselectivity in the photoelectrochemistry at a polymeric [ Ru(4-methyl-4º-vinyl-2,2º-bipyridine) 3 ] 2' electrode
Photochemical & Photobiological Sciences, 2012
The hydrogen peroxide production upon vacuum ultraviolet (VUV) irradiation of water is reviewed, ... more The hydrogen peroxide production upon vacuum ultraviolet (VUV) irradiation of water is reviewed, because published results from the last 10 years lead to conflicting mechanistic interpretations. This work confirms that in pure water, hydrogen peroxide is only produced in the presence of molecular oxygen. Mechanistic schemes explain these findings and confirm earlier statements that recombination of hydroxyl radicals is kinetically disfavoured. In agreement with other recent publications, this work confirms that enhanced hydrogen peroxide production takes place upon VUV irradiation of aqueous solutions of organic compounds. For these investigations, methanol was chosen as an organic model compound. During photolyses, hydrogen peroxide, dissolved molecular oxygen, pH-value of the reaction system, methanol and its products of oxidative degradation were analyzed, and kinetic studies were undertaken to explain the evolution of the concentrations of these components.
Photochemical & Photobiological Sciences, 2008
... Komandorska 118/120, 53-345, Wroclaw, Poland. E-mail: Monika.Zahorodna@ae.wroc. pl. b Lehrstu... more ... Komandorska 118/120, 53-345, Wroclaw, Poland. E-mail: Monika.Zahorodna@ae.wroc. pl. b Lehrstuhl für Umweltmesstechnik, Engler-Bunte Institut, Universität Karlsruhe, 76128, Karlsruhe, Germany. E-mail: Andre.Braun@ciw.uni-karlsruhe.de. ...
Photochemical & Photobiological Sciences, 2006
Vacuum-ultraviolet (VUV) irradiation (k exc : 172 ± 12 nm) of polystyrene films in the presence o... more Vacuum-ultraviolet (VUV) irradiation (k exc : 172 ± 12 nm) of polystyrene films in the presence of oxygen produced not only oxidatively functionalized surfaces, but generated also morphological changes. Whereas OH-and C=O-functionalized surfaces might be used for e.g. secondary functionalization, enhanced aggregation or printing, processes leading to morphological changes open new possibilities of microstructurization. Series of experiments made under different experimental conditions brought evidence of two different reaction pathways: introduction of OH-and C=O-groups at the polystyrene pathways is mainly due to the reaction of reactive oxygen species (hydroxyl radicals, atomic oxygen, ozone) produced in the gas phase between the VUV-radiation source and the substrate. However, oxidative fragmentation leading to morphological changes, oxidation products of low molecular weight and eventually to mineralization of the organic substrate is initiated by electronic excitation of the polymer leading to CC bond homolysis and to a complex oxidation manifold after trapping of the C-centred radicals by molecular oxygen. The pathways of oxidative functionalization or fragmentation could be differentiated by FTIR-ATR analysis of irradiated polystyrene surfaces before and after washing with acetonitrile and microscopic fluorescence analysis of the surfaces secondarily functionalized with the N,N,N-tridodecyl-triaza-triangulenium (TATA) cation. Ozonization of the polystyrene leads to oxidative functionalization of the polymer surface but cannot initiate the fragmentation of the polymer backbone. Oxidative fragmentation is initiated by electronic excitation of the polymer (contact-mode AFM analysis), and evidence of the generation of intermediate C-centred radicals is given e.g. by experiments in the absence of oxygen leading to cross-linking (solubility effects, optical microscopy, friction-mode AFM) and disproportionation (fluorescence).
Photochemical & Photobiological Sciences, 2009
Aerosols of submicron polystyrene particles were oxidized by either vacuum-ultraviolet (VUV) irra... more Aerosols of submicron polystyrene particles were oxidized by either vacuum-ultraviolet (VUV) irradiation in the presence of molecular oxygen (O 2) and/or by ozone (O 3). Different degrees of oxidation and oxidative degradation were reached by VUV-photolysis depending on radiant energy, O 2 and H 2 O concentrations in the bulk gas mixture as well as on particle diameter. The same functionalization was obtained by exposing the aerosol to O 3 , however, oxidation, in particular oxidative degradation, was less efficient. The evolution of hydroxyl and carbonyl functions introduced was quantified by ATR-FTIR spectroscopy of filtered particles, and oxidative degradation of the polymer particles was confirmed by determining size and number of aerosol particles before and after oxidation. Efficiency analyses are based on the results of an O 3 actinometry and on an evaluation of the rate of absorbed photons by the aerosol particles in function of their size.
Journal of Physics: Conference Series, 2011
Nanostructures with long-term stability at the surface of gold electrodes are generated by recons... more Nanostructures with long-term stability at the surface of gold electrodes are generated by reconstituting the porin MspA from Mycobacterium smegmatis into a specially designed monolayer of long-chain lipid surfactant on gold. Tailored surface coverage of gold electrodes with long-chain surfactants is achieved by electrochemically assisted deposition of organic thiosulfates (Bunte salts). The subsequent reconstitution of the octamericpore MspA is guided by its extraordinary self-assembling properties. Importantly, electrochemical reduction of copper(II) yields copper nanoparticles within the MspA nanopores. Electrochemical impedance spectroscopy, reflection electron microscopy, and atomic force microscopy (AFM) show that: 1) the MspA pores within the self-assembled monolayer (SAM) are monodisperse and electrochemically active, 2) MspA reconstitutes in SAMs and with a 10-nm thickness, 3) AFM is a suitable method to detect pores within SAMs, and 4) the electrochemical reduction of Cu 2 + to Cu 0 under overpotential conditions starts within the MspA pores.
The goal of this work was the evaluation of the use of copper as suitable substrate for assessing... more The goal of this work was the evaluation of the use of copper as suitable substrate for assessing the trapping of a small metallic compound by immobilized myoglobin (myo). Our proposal was to demonstrate that disposable devices based in the use of this metal would be as interesting as more widely used gold ones and more suitable since the economical point of view, despite the well-known problem of copper dissolution and oxidation. For such reason copper electrodes covered with 2thiobarbituric acid (TBA) were tested as a platform to obtain myo modified electrodes with aptitude to trap a Ru complex present in a solution. The assembly process was followed using cyclic voltammetry, electrochemical impedance spectroscopy and contact angle measurements. Our results were consistent with the obtaining of a stable electrode of copper covered with a protein adsorbed onto TBA with reproducible behavior, pointing that copper could be a suitable material to develop electrochemical devices for biosensing. This stable Cu/TBA/myo electrode had enough sensitivity to detect the capture of a compound with low molecular weight and with low affinity for the protein, and, when immobilizing other biomolecules, it would sense the trapping of their specific target.
Polymers, 2021
Spherical, individual polymer nanoparticles with functional –SH groups were synthesized via aeros... more Spherical, individual polymer nanoparticles with functional –SH groups were synthesized via aerosol photopolymerization (APP) employing radically initiated thiol-ene chemistry. A series of various thiol and alkene monomer combinations were investigated based on di-, tri-, and tetrafunctional thiols with difunctional allyl and vinyl ethers, and di- and trifunctional acrylates. Only thiol and alkene monomer combinations able to build cross-linked poly(thio-ether) networks were compatible with APP, which requires fast polymerization of the generated droplet aerosol during the photoreactor passage within a residence time of half-minute. Higher monomer functionalities and equal overall stoichiometry of functional groups resulted in the best nanoparticles being spherical and individual, proven by scanning electron microscopy (SEM). The presence of reactive –SH groups in the synthesized nanoparticles as a basis for post-polymerization modifications was verified by Ellman’s test.
The Journal of Physical Chemistry B, 2001
Novel heterogeneous photocatalysts were developed which are able to transfer electrons from excit... more Novel heterogeneous photocatalysts were developed which are able to transfer electrons from excited Ru(II) donors within the zeolite framework to Co(III) acceptor complexes in the exterior. The materials were prepared and characterized by elemental analysis, electrochemical methods, diffuse reflectance, and raster and transmission electron microscopy. The catalysts consist of zeolite Y-encapsulated Ru(bpy) 3 2+ (bpy) 2,2′bipyridine) sensitizers in close proximity to TiO 2 nanoparticles on the same support. The photophysical properties of Ru(bpy) 3 2+ within the zeolite supercages were investigated at different loadings of Ru(bpy) 3 2+ and TiO 2. The photoexcited MLCT state of the zeolite-entrapped Ru(bpy) 3 2+ reacts via electron transfer with Co(dpphen) 3 3+ (dpphen) 4,7-diphenyl-1,10-phenanthroline) in the exterior of the zeolite particles. The relative quenching of Ru(bpy) 3 2+ by external Co(dpphen) 3 3+ increases as the TiO 2 content within the zeolite is increased, where electron transfer from Ru(bpy) 3 2+ complexes within the interior of the zeolite are able to transfer electrons to Co(dpphen) 3 3+. This observation indicates that electrons can be transported from the interior of the zeolite to the surface in the presence of an appropriate electron relay, such as TiO 2 nanoparticles.
Frontiers in Bioengineering and Biotechnology
Materials Science in Semiconductor Processing
RSC Adv.
A flame-free UV-mediated aerosol technology opens the way for the fabrication of organic–inorgani... more A flame-free UV-mediated aerosol technology opens the way for the fabrication of organic–inorganic powder products in a single operation and ambient temperature.
Journal of Nanoparticle Research, 2014
A continuous aerosol-based process is described for the encapsulation of nanoparticles with a thi... more A continuous aerosol-based process is described for the encapsulation of nanoparticles with a thin polymer shell. The process is essentially based on directed binary collisions between gas-borne core particles and liquid monomer droplets carrying opposite electrical charges, followed by photo-initiated polymerization. Once the two streams are mixed together, the process runs to completion on a time scale of about 2 min or less, required for coagulation and polymerization. Gold, silica, and sodium chloride nanoparticles were successfully coated by this technique with PHDDA [poly(hexanediol diacrylate)] and/ or crosslinked PMMA [poly(methyl methacrylate)]. It was found that all core materials as well as agglomerates were wettable at room temperature and that the spreading kinetics of the monomer were fast enough to cover the core particles uniformly within the time scale provided for coagulation. The shell thickness depends on the volume ratio between core particles and monomer droplets. This was demonstrated for a combination of monodisperse silica spheres (d = 241 nm) and polydisperse methyl methacrylate droplets, resulting in a theoretical shell thickness of 18 nm. There was very good agreement between measurements by TEM and electrical mobility spectroscopy. The results revealed that about 90 % or more of the core-shell structures were formed from 1:1 collisions between a core particle and a single monomer droplet.
Macromolecular Materials and Engineering, 2014
Colloid and Polymer Science, 2014
Water science and technology : a journal of the International Association on Water Pollution Research, 2004
Technical development work is presented, where the VUV photochemically induced oxidative degradat... more Technical development work is presented, where the VUV photochemically induced oxidative degradation is used: (i) for analytic purposes, and (ii) for small to medium scale (< 10 m2/d) waste water treatment processes or ultrapure water production. In the first case, small Xe-excimer radiation sources with an integrated reaction space designed for optimal conditions, as far as incident photon flux density, turbulence and concentration of dissolved molecular oxygen are concerned, have been built and tested. Under conditions of exhaustive oxidation and/or mineralization of pollutants in a continuous regime, they may be used for sample pre-treatment modules prior TOC, TOX and electrochemical trace metal analysis. Under conditions of partial oxidation or mineralization, the same lamp/reactor combination may be used for functionalization purposes prior to e.g. GC or HPLC analyses. In the second case, mass transfer limitations between the non-irradiated bulk volume and the irradiated vol...
Sustainable Energy and Environmental Technologies - Proceedings of the Third Asia-Pacific Conference, 2001
The Journal of Physical Chemistry A, 2002
The synthesis and photophysical properties of a ruthenium dyad (4) and triad (5) are reported. Bo... more The synthesis and photophysical properties of a ruthenium dyad (4) and triad (5) are reported. Both biomimetic systems are physical models for the photosynthetic reaction center. They consist of a ruthenium(II)-polypyridyl sensitizer featuring chemically attached 3,3′-dimethyl-4,4′-viologen and 4,4′-viologen electron acceptors. The binding of the chemically attached electron acceptors by the three structurally different crown ethers, DB 30 C 10 , BBO 5 O 5 , and AAO 5 O 5 , offers a remarkable tool for the enhancement of the lifetimes of the charge separated states (τ CS), up to a factor of 2 × 10 4. The drastic increase in the lifetimes observed can be explained by a decrease in the reorganization energy λ due to the presence of the crown ether units bound to the viologen acceptor.
The Journal of Physical Chemistry A, 1998
During the oxidative degradation of 2,4-dimethylaniline (2,4-xylidine) by means of the H 2 O 2 /U... more During the oxidative degradation of 2,4-dimethylaniline (2,4-xylidine) by means of the H 2 O 2 /UV method, a series of hydroxylated aromatic amines are formed, this result confirming the role of the hydroxyl radical as an initiator of the oxidative chain reaction. Thermal or ...
Synthesis, 2005
The synthesis of organic thiosulfates, up to 10 nm in length, which were tailored for generating ... more The synthesis of organic thiosulfates, up to 10 nm in length, which were tailored for generating artificial monomembranes on gold surfaces by electrochemically initiated deposition, was accomplished. (E)-3-(4-Hydroxyphenyl)acrylic acid (4-hydroxy cinnamic acid) was employed as aromatic head group and (C 10 H 20-On n (n = 1, 3, 5, 7) building blocks were attached. The synthetic procedure comprises a series of nucleophilic substitutions under carefully defined conditions. Extended purification is crucial for eliminating non-reacted starting materials.
Physical Chemistry Chemical Physics, 2000
Part 2.¤ Marcus behaviour and high enantioselectivity in the photoelectrochemistry at a polymeric... more Part 2.¤ Marcus behaviour and high enantioselectivity in the photoelectrochemistry at a polymeric [ Ru(4-methyl-4º-vinyl-2,2º-bipyridine) 3 ] 2' electrode
Photochemical & Photobiological Sciences, 2012
The hydrogen peroxide production upon vacuum ultraviolet (VUV) irradiation of water is reviewed, ... more The hydrogen peroxide production upon vacuum ultraviolet (VUV) irradiation of water is reviewed, because published results from the last 10 years lead to conflicting mechanistic interpretations. This work confirms that in pure water, hydrogen peroxide is only produced in the presence of molecular oxygen. Mechanistic schemes explain these findings and confirm earlier statements that recombination of hydroxyl radicals is kinetically disfavoured. In agreement with other recent publications, this work confirms that enhanced hydrogen peroxide production takes place upon VUV irradiation of aqueous solutions of organic compounds. For these investigations, methanol was chosen as an organic model compound. During photolyses, hydrogen peroxide, dissolved molecular oxygen, pH-value of the reaction system, methanol and its products of oxidative degradation were analyzed, and kinetic studies were undertaken to explain the evolution of the concentrations of these components.
Photochemical & Photobiological Sciences, 2008
... Komandorska 118/120, 53-345, Wroclaw, Poland. E-mail: Monika.Zahorodna@ae.wroc. pl. b Lehrstu... more ... Komandorska 118/120, 53-345, Wroclaw, Poland. E-mail: Monika.Zahorodna@ae.wroc. pl. b Lehrstuhl für Umweltmesstechnik, Engler-Bunte Institut, Universität Karlsruhe, 76128, Karlsruhe, Germany. E-mail: Andre.Braun@ciw.uni-karlsruhe.de. ...
Photochemical & Photobiological Sciences, 2006
Vacuum-ultraviolet (VUV) irradiation (k exc : 172 ± 12 nm) of polystyrene films in the presence o... more Vacuum-ultraviolet (VUV) irradiation (k exc : 172 ± 12 nm) of polystyrene films in the presence of oxygen produced not only oxidatively functionalized surfaces, but generated also morphological changes. Whereas OH-and C=O-functionalized surfaces might be used for e.g. secondary functionalization, enhanced aggregation or printing, processes leading to morphological changes open new possibilities of microstructurization. Series of experiments made under different experimental conditions brought evidence of two different reaction pathways: introduction of OH-and C=O-groups at the polystyrene pathways is mainly due to the reaction of reactive oxygen species (hydroxyl radicals, atomic oxygen, ozone) produced in the gas phase between the VUV-radiation source and the substrate. However, oxidative fragmentation leading to morphological changes, oxidation products of low molecular weight and eventually to mineralization of the organic substrate is initiated by electronic excitation of the polymer leading to CC bond homolysis and to a complex oxidation manifold after trapping of the C-centred radicals by molecular oxygen. The pathways of oxidative functionalization or fragmentation could be differentiated by FTIR-ATR analysis of irradiated polystyrene surfaces before and after washing with acetonitrile and microscopic fluorescence analysis of the surfaces secondarily functionalized with the N,N,N-tridodecyl-triaza-triangulenium (TATA) cation. Ozonization of the polystyrene leads to oxidative functionalization of the polymer surface but cannot initiate the fragmentation of the polymer backbone. Oxidative fragmentation is initiated by electronic excitation of the polymer (contact-mode AFM analysis), and evidence of the generation of intermediate C-centred radicals is given e.g. by experiments in the absence of oxygen leading to cross-linking (solubility effects, optical microscopy, friction-mode AFM) and disproportionation (fluorescence).
Photochemical & Photobiological Sciences, 2009
Aerosols of submicron polystyrene particles were oxidized by either vacuum-ultraviolet (VUV) irra... more Aerosols of submicron polystyrene particles were oxidized by either vacuum-ultraviolet (VUV) irradiation in the presence of molecular oxygen (O 2) and/or by ozone (O 3). Different degrees of oxidation and oxidative degradation were reached by VUV-photolysis depending on radiant energy, O 2 and H 2 O concentrations in the bulk gas mixture as well as on particle diameter. The same functionalization was obtained by exposing the aerosol to O 3 , however, oxidation, in particular oxidative degradation, was less efficient. The evolution of hydroxyl and carbonyl functions introduced was quantified by ATR-FTIR spectroscopy of filtered particles, and oxidative degradation of the polymer particles was confirmed by determining size and number of aerosol particles before and after oxidation. Efficiency analyses are based on the results of an O 3 actinometry and on an evaluation of the rate of absorbed photons by the aerosol particles in function of their size.
Journal of Physics: Conference Series, 2011
Nanostructures with long-term stability at the surface of gold electrodes are generated by recons... more Nanostructures with long-term stability at the surface of gold electrodes are generated by reconstituting the porin MspA from Mycobacterium smegmatis into a specially designed monolayer of long-chain lipid surfactant on gold. Tailored surface coverage of gold electrodes with long-chain surfactants is achieved by electrochemically assisted deposition of organic thiosulfates (Bunte salts). The subsequent reconstitution of the octamericpore MspA is guided by its extraordinary self-assembling properties. Importantly, electrochemical reduction of copper(II) yields copper nanoparticles within the MspA nanopores. Electrochemical impedance spectroscopy, reflection electron microscopy, and atomic force microscopy (AFM) show that: 1) the MspA pores within the self-assembled monolayer (SAM) are monodisperse and electrochemically active, 2) MspA reconstitutes in SAMs and with a 10-nm thickness, 3) AFM is a suitable method to detect pores within SAMs, and 4) the electrochemical reduction of Cu 2 + to Cu 0 under overpotential conditions starts within the MspA pores.