Zeta Potential of Nanobubbles Generated by Ultrasonication in Aqueous Alkyl Polyglycoside Solutions.
A simple and convenient method to measure microelectrophoretic mobilities was proposed to determine the zeta potential of nanobubbles generated by ultrasonication. Bubbles in pure water solutions and in aqueous solutions of alkyl polyglycoside (AG) with different alkyl chain lengths and degrees of polymerization in the head group were sonicated with a palladium-coated electrode designed specially by the manufacturer. The zeta potentials of bubbles with ordinary cationic and ionic surfactants are consistent with others' previous results. The average size of the bubbles generated by sonication is in the range of 300 to 500 nm. The zeta potentials of bubbles in both pure water and AG solutions at all pH values are negative. As the chain length of AG increases, zeta potentials significantly decrease at high pH. For nonionic AG, a possible charging mechanism based on known mechanisms is suggested to explain the negative charge, known to be unusual. Even with a very high concentration of H(+) ions in solution the bubbles are charged negatively because the interface is covered with slightly acidic alcohol groups of AGs. At high pH, the less polar the surfactant, the more negative the charge, since nonpolar surfactant molecules induce the adsorption of OH(-) ions, rather than H(+) ions that prefer hydration by water molecules. Copyright 2000 Academic Press.
Electrokinetic potentials at the gas-aqueous interface by spinning cylinder electrophoresis
The natural buoyancy of gas bubbles has hampered conventional electrokinetic methods of evaluating charge at the gas-liquid interface.In this study, bubbles are held by centripetal force at the centre of a horizontal, rotating cylinder filled completely with liquid. Migration of the bubble along the axis of the cylinder can be achieved by applying a gravity force or an electrophoretic force.An expression for the drag coefficient has been developed and used to calculate surface charge densities and electrokinetic potentials. In the presence of potassium chloride, anionic and non-ionic surfactants, the electrokinetic potentials were negative (∼2–5 mV) at the air-aqueous interface. A cationic surfactant rendered the zeta potential positive.A knowledge of the air-aqueous interfacial rheology is desirable if the drag coefficient, and consequently the zeta potential, at all types of gas-liquid interfaces is to be evaluated.
An Ultrasensitive Analytical Method Based on Chemiluminescence Sensing Electrochemical Parallel Catalytic Reaction Event
An ultrasensitive electrochemiluminescence (ECL) method on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed for improving ECL analytical characteristics using vanadate(V) as a representative. Vanadate(V) could be electrochemically reduced to generate vanadate(II) which could be chemically oxidized by potassium periodate to regenerate vanadate(V) and give parallel catalytic wave effect. Then, the reduced product of potassium periodate could react with butyl-rhodamine B to emit a sensitive chemiluminescence signal. The chemiluminescence intensity was correlative with vanadate(V) concentration. The investigation on the electrochemical reaction rate constant (k0) confirmed that the speed of electrochemical reaction was faster than that of the subsequent chemiluminescence reaction. The possibility of the combination of electrochemical parallel catalytic reaction with chemiluminescence signal sensing was proved. The similar ECL behaviors could be observed at zirconia nanowires-Nafion modified electrode. Because of the separation and enrichment effect of the modified electrode on vanadate(V), the selectivity and sensitivity was further improved greatly. Based on these findings, a new concept on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed and an ultrasensitive ECL method for the determination of vanadate(V) was developed at zirconia nanowires-Nafion modified electrode. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of vanadate(V) in the range of 2.0×10−12 mol/L–2.0×10−10 mol/L. The detection limit was 8.0×10−13 mol/L, which was more than 6 orders of magnitude lower than that observed by electrochemical current transduction for electrochemical parallel catalytic reaction at zirconia nanowires-Nafion modified electrode.