Franz Grieser

Combined advanced oxidation processes for the synergistic degradation of ibuprofen in aqueous environments.

Ibuprofen (IBP) is a widely used analgesic and anti-inflammatory drug and has been found as a pollutant in aqueous environments. The sonolytic, photocatalytic and sonophotocatalytic degradations of IBP in the presence of homogeneous (Fe(3+)) and heterogeneous photocatalysts (TiO(2)) were studied. When compared with sonolysis and photocatalysis, a higher degradation rate was observed for sonophotocatalysis in the presence of TiO(2) or Fe(3+) and also a slight synergistic enhancement was found with a synergy index of 1.3 and 1.6, respectively. Even though TiO(2) sonophotocatalysis showed an additive process effect in the mineralization, a significant synergy effect was observed for the sonophotocatalysis in the presence of Fe(3+). This might be due to the formation of photoactive complexes between Fe(3+) and IBP degradation products, such as carboxylic acids. High performance liquid chromatography (HPLC) and electrospray ionisation mass spectrometry (ESMS) techniques were employed for the identification of the degradation intermediates. The sonication of IBP led to the formation of its mono- and di-hydroxylated intermediates. Apart from the hydroxylated intermediates, products formed due to the oxidation of propanoic acid and isobutyl substituents of IBP were also observed.

The characterization of ag sols by electron microscopy, optical absorption, and electrophoresis

Abstract Several differently prepared silver sols and a gold sol were examined using electron microscopy optical absorption and microelectrophoresis techniques. The effects of 4-dimethyl-amino-pyridine and pyridine addition to the sols were also studied. In all cases of amine adsorption onto the sol particles, an accompanying decrease in the magnitude of the electrophoretic mobility of the particles was observed, and a long wavelength (>500 nm) absorption band was formed. The solution species responsible for these changes is an aggregate composed of the primary sol.

Ultrasonic synthesis of stable, functional lysozyme microbubbles.

High-intensity ultrasound induces emulsification and cross-linking of protein molecules in aqueous medium. The stability and the functionality of the resultant protein-coated microbubbles are crucial in many of their applications. For example, the stability of drug-loaded microbubbles should be sufficiently long enough, in vivo, so that they can be ruptured only at specific sites for release of the drugs. In this study, we report the synthesis of stable and functional microbubbles, coated with chemically reduced lysozyme, using high-intensity ultrasound in aqueous solution. In the absence of chemical reduction, stable microbubbles were not produced with native lysozyme, indicating the importance of free -SH functional groups for protein cross-linking. The degree of cross-linking between lysozyme molecules was controlled by manipulating both the extent of chemical reduction of the intramolecular disulfide bonds and sonication time. The lysozyme-coated microbubbles are stable for several months and retain the enzymatic (antimicrobial) activity of lysozyme. The layer-by-layer (LbL) deposition of polyelectrolytes onto the protein-shell air-core template has been used as a versatile procedure to modify the surface properties of the microbubbles, indicating the possibility of adsorbing potential drugs and/or biolabels on the surface of these microbubbles for therapeutic and diagnostic applications.

Room temperature phosphorescence of aromatic hydrocarbons in aqueous micellar solutions

Abstract The phosphoresence spectra of several simple arenas, pyrene, naphthalene, biphenyl and their brominated derivatives have been observed in aqueous micellar solutions at room temperature. The success of these experiments is due to the protective screening of the arene triplet state by solubilization in the micelles. Impurities in the aqueous phase are thus excluded from the excited arene. Small traces of oxygen efficiently remove the phosphorescence as oxygen readily penetrates into the micelle to quench the arene triplet. Hydrophilic quenchers such as Cu 2+ and Tl + also reduce the lifetime of the phosphorescence. In anionic micelles these quenchers are located at the surface of the micelle and efficient quenching take place at the lipid water interface. Cupric ions reduce the lifetime and yield of phosphorescence, while Tl + ions reduce the lifetime but also enhance the rate of emission of the phosphorescence via heavy atom spin orbit coupling. The technique and data are relevant to the measurement of kinetic parameters in micelles and membranes.

Synthesis and electronic properties of semiconductor nanoparticles/quantum dots

This review examines recent work on the synthesis, characterisation and potential applications of semiconductor nanoparticles (quantum dots). Recent advances in single quatum dot spectroscopy is also reviewed.

Dynamic interactions between microbubbles in water

The interaction between moving bubbles, vapor voids in liquid, can arguably represent the simplest dynamical system in continuum mechanics as only a liquid and its vapor phase are involved. Surprisingly, and perhaps because of the ephemeral nature of bubbles, there has been no direct measurement of the time-dependent force between colliding bubbles which probes the effects of surface deformations and hydrodynamic flow on length scales down to nanometers. Using ultrasonically generated microbubbles (∼100 μm size) that have been accurately positioned in an atomic force microscope, we have made direct measurements of the force between two bubbles in water under controlled collision conditions that are similar to Brownian particles in solution. The experimental results together with detailed modeling reveal the nature of hydrodynamic boundary conditions at the air/water interface, the importance of the coupling of hydrodynamic flow, attractive van der Waals–Lifshitz forces, and bubble deformation in determining the conditions and mechanisms that lead to bubble coalescence. The observed behavior differs from intuitions gained from previous studies conducted using rigid particles. These direct force measurements reveal no specific ion effects at high ionic strengths or any special role of thermal fluctuations in film thickness in triggering the onset of bubble coalescence.

A single spectroscopic probe for the determination of both the interfacial solvent properties and electrostatic surface potential of model lipid membranes

2,6-Diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenoxide, ET(30), has been investigated in order to ascertain its suitability as a probe for both the effective interfacial dielectric constant (Iµeff) and the electrostatic surface potential (ψ0) of model lipid membranes in aqueous solution. This work establishes that the solvatochromic visible absorption band for ET(30) can be used to provide a good estimate of the Iµeff for cationic micelles. It is also shown that the acid–base dissociation of ET(30) can be utilized to obtain a quantitative measure of the ψ0 in the case of cationic micelles. There are problems and uncertainties associated with the use of ET(30) in aqueous solutions of other types of charged self-assembled surfactant aggregates, and these are discussed.

Degradation of orange-G by advanced oxidation processes

The degradation and mineralization of orange-G (OG) in aqueous solutions by means of ultrasound irradiation at a frequency of 213kHz and its combination with a heterogeneous photocatalyst (TiO(2)) were investigated. The effects of various operational parameters such as, the concentration of the dye and solution pH on the degradation efficiency were studied. The degradation of the dye followed first-order like kinetics under the conditions examined. The sonolytic degradation of OG was relatively higher at pH 5.8 than that at pH 12. However, an alkaline pH was favoured for the photocatalytic degradation of OG using TiO(2). Total organic carbon (TOC) measurements were also carried out in order to evaluate the mineralization efficiency of OG using sonolysis, photocatalysis and sonophotocatalysis. The hybrid technique of sonophotocatalytic degradation was compared with the individual techniques of photocatalysis and sonolysis. A simple additive effect was observed during the sonophotocatalytic oxidation of OG using TiO(2) indicating that the combined treatment offers no synergistic enhancement. TOC results also support the additive effect in the dual treatment process.

Measurement and analysis of forces in bubble and droplet systems using AFM

The use of atomic force microscopy to measure and understand the interactions between deformable colloids - particularly bubbles and drops - has grown to prominence over the last decade. Insight into surface and structural forces, hydrodynamic drainage and coalescence events has been obtained, aiding in the understanding of emulsions, foams and other soft matter systems. This article provides information on experimental techniques and considerations unique to performing such measurements. The theoretical modelling frameworks which have proven crucial to quantitative analysis are presented briefly, along with a summary of the most significant results from drop and bubble AFM measurements. The advantages and limitations of such measurements are noted in the context of other experimental force measurement techniques.

Ultrasound assisted photocatalytic degradation of diclofenac in an aqueous environment.

Diclofenac (DF) is an anti-inflammatory drug found in aqueous environments as a pollutant due to its widespread use. The sonolytic, photocatalytic and sonophotocatalytic degradation of DF using three photocatalysts (TiO(2), ZnO and Fe-ZnO) were studied. The degradation of DF followed first-order like kinetics. The sonophotocatalytic degradation using TiO(2) under UV-vis radiation showed a slight synergistic enhancement in the degradation of the parent compound, whereas a detrimental effect was observed for the mineralization process. In the case of Fe-ZnO, both degradation and mineralization showed near additive effects. A number of degradation products were identified.