Synthesis, characterisation and functionalisation of luminescent silica nanoparticles

The synthesis of highly monodispersed, homogeneous and stable luminescent silica nanoparticles, synthesized using a process based on the Stöber method is reported here. These particles have been functionalised with the ruthenium and europium complexes: bis (2,2??-bipyridine)-(5-aminophenanthroline) Ru bis (hexafluorophosphate), abbreviated to (Ru(bpy)₂(phen-5-NH₂)(PF₆)), and tris (dibenzoylmethane)-mono (5-aminophenanthroline) europium(III), abbreviated to (Eu:TDMAP). Both dyes have a free amino group available, facilitating the covalent conjugation of the dyes inside the silica matrix. Due to the covalent bond between the dyes and the silica, no dye leaching or nanoparticle diameter modification was observed. The generic and versatile nature of the synthesis process was demonstrated via the synthesis of both europium and ruthenium-functionalised nanoparticles. Following this, the main emphasis of the study was the characterisation of the luminescence of the ruthenium-functionalised silica nanoparticles, in particular, as a function of surface carboxyl or amino group functionalisation. It was demonstrated that the luminescence of the ruthenium dye is highly affected by the ionic environment at the surface of the nanoparticle, and that these effects can be counteracted by encapsulating the ruthenium-functionalised nanoparticles in a plain 15 nm silica layer. Moreover, the ruthenium-functionalised silica nanoparticles showed high relative brightness compared to the free dye in solution and efficient functionalisation with amino or carboxyl groups. Due to their ease of fabrication and attractive characteristics, the ruthenium-functionalised silica nanoparticles described here have the potential to be highly desirable fluorescent labels, particularly, for biological applications.     

Electrochemical and surface characterisation of carbon-film-coated piezoelectric quartz crystals

The electrochemical properties of carbon films, of thickness between 200 and 500 nm, sputter-coated on gold- and platinum-coated 6 MHz piezoelectric quartz crystal oscillators, as new electrode materials have been investigated. Comparative studies under the same experimental conditions were performed on bulk electrodes. Cyclic voltammetry was carried out in 0.1 M KCl electrolyte solution, and kinetic parameters of the model redox systems Fe(CN)₆^3−/4− and [Ru(NH₃)₆]^3+/2+ as well as the electroactive area of the electrodes were obtained. Atomic force microscopy was used in order to examine the surface morphology of the films, and the properties of the carbon films and the electrode-solution interface were studied by electrochemical impedance spectroscopy. The results obtained demonstrate the feasibility of the preparation and development of nanometer thick carbon film modified quartz crystals. Such modified crystals should open up new opportunities for the investigation of electrode processes at carbon electrodes and for the application of electrochemical sensing associated with the EQCM.     

Electrochemical and surface characterisation of gold nanoparticle decorated multi-walled carbon nanotubes

A novel type of gold nanoparticle/multi-walled carbon nanotube (AuNP/MWCNT) composite electrodes is presented. The electrochemical reduction of oxygen on these hybrid electrodes was studied using the rotating disk electrode (RDE) method. The AuNP/MWCNT nanocomposites were prepared by sputter deposition of gold in argon atmosphere on MWCNTs followed by heat-treatment of the catalyst at different temperatures. High-resolution scanning electron microscopy (HR-SEM), glancing incidence angle X-ray powder diffraction (GIXRD) and small-angle X-ray scattering (SAXS) techniques were employed to characterise the surface structure and morphology of catalyst materials. Au nanoparticles with diameter around 20 nm were dispersed at the tips and on the sidewalls of nanotubes. Electrochemical measurements were performed to demonstrate the electrocatalytic properties of the composite catalysts towards O₂ reduction in acid media. The successful preparation of AuNP/MWCNT nanocomposites by magnetron sputtering opens up the possibility of making an efficient dispersion of nanoparticles for electrocatalyst design.     

Electrochemical investigations of stable cavitation from bubbles generated during reduction of water

Megasonic cleaning is traditionally used for removal of particles from wafer surfaces in semiconductor industry. With the advancement of technology node, the major challenge associated with megasonic cleaning is to be able to achieve high cleaning efficiency without causing damage to fragile features. In this paper, a method based on electrochemistry has been developed that allows controlled formation and growth of a hydrogen bubbles close to a solid surface immersed in an aqueous solution irradiated with ∼1 MHz sound field. It has been shown that significant microstreaming from resonating size bubble can be induced by proper choice of transducer duty cycle. This method has the potential to significantly improve the performance of megasonic cleaning technology through generation of local microstreaming, interfacial and pressure gradient forces in close vicinity of conductive surfaces on wafers without affecting the transient cavitation responsible for feature damage.     

Acoustic cavitation, bubble dynamics and sonoluminescence

Basic facts on the dynamics of bubbles in water are presented. Measurements on the free and forced radial oscillations of single spherical bubbles and their acoustic (shock waves) and optic (luminescence) emissions are given in photographic series and diagrams. Bubble cloud patterns and their dynamics and light emission in standing acoustic fields are discussed.     

Electrochemical characterisation of the Pt/YSZ interface exposed to a reactive gas phase

The Pt/yttria-stabilized cubic zirconia (YSZ) interface exposed to a reactive gas was characterised by solid electrolyte potentiometry and cyclic voltammetry. The catalytic reactions included total combustion of C₃H₈ and C₃H₆ to CO₂ and H₂O as well as NO reduction by C₃H₆ in the presence of O₂ under oxygen-rich and stoichiometric conditions. The solid electrolyte potentiometry as a function of the temperature in C₃H_x/O₂ (with x=6 or 8) reflected the catalytic properties of Pt for C₃H_x oxidation. In C₃H₆/NO/O₂, the reduction of NO was evidenced below 300 °C. The cyclic voltammetry evidenced the formation of an oxygen chemisorbed layer on the Pt surface under anodic potential. Propane had no effect on this chemisorbed layer, whereas propene weakened significantly the strength of this Pt–O bond. Addition of NO to C₃H₆/O₂ led to the disappearing of this chemisorbed layer. The use of solid electrolyte potentiometry in conjunction with cyclic voltammetry allowed us to determine the surface oxidation state of Pt during the catalytic reactions.     

Degradation of organic wastewater by hydrodynamic cavitation combined with acoustic cavitation

In this paper, the decomposition of Rhodamine B (RhB) by hydrodynamic cavitation (HC), acoustic cavitation (AC) and the combination of these individual methods (HAC) have been investigated. The degradation of 20 L RhB aqueous solution was carried out in a self-designed HAC reactor, where hydrodynamic cavitation and acoustic cavitation could take place in the same space simultaneously. The effects of initial concentration, inlet pressure, solution temperature and ultrasonic power were studied and discussed. Obvious synergies were found in the HAC process. The combined method achieved the best conversion, and the synergistic effect in HAC was even up to 119% with the ultrasonic power of 220 W in a treatment time of 30 min. The time-independent synergistic factor based on rate constant was introduced and the maximum value reached 40% in the HAC system. Besides, the hybrid HAC method showed great superiority in energy efficiency at lower ultrasonic power (88–176 W). Therefore, HAC technology can be visualized as a promising method for wastewater treatment with good scale-up possibilities.     

超声空化与超声医学

随着超声技术应用广泛而迅速的发展,整整一个世纪来,超声空化成了经久不衰的研究课题,特别近１０年来,超声空化成了多种学科的基础研究热点。本扼要地介绍了起声空化的最新研究进展,以及超声空化与超声医学发展的密切关系。     

Dynamics and measurement of cavitation bubble

Based on the introduction of international progress, our investigations on acoustic cavitation have been reported. Firstly we considered the cavity’s dynamics under the drive of the asymmetrical acoustic pressure. An aspheric dynamical model was proposed and a new stable and aspheric solution was found in numerical simulation of the theoretical framework of the aspheric model. Then, a dual Mie-scattering technique was developed to measure the cavity’s aspheric pulsation. A significant asynchronous pulsation signal between two Mie-scattering channels was caught in the case of large cavity driven by low acoustic pressure. As a direct deduction, we observed an evidence of cavity’s aspheric pulsation. Furthermore, we studied the dependency of the asynchronous pulsation signal on the various parameters, such as the amplitude and frequency of the driving acoustic pressure, and the surface tension, viscosity and gas concentration of the liquid. Finally, we introduced a new numeric imaging technique to measure the shapes of the periodic pulsation cavities. The time-resolution was in the order of 20 ns, one order of magnitude lower than that in the previous work, say, 200 ns.     

Fundamental problems of sonochemistry and cavitation

This paper discusses the problems of cavitation which are associated with sonochemistry. It is concluded that the hot-spot theory is not sufficient to accommodate all experimental data and the alternative is a new electrical theory of cavitation phenomena.     

Dependence of cavitation,chemical effect,and mechanical effect thresholds on ultrasonic frequency

Cavitation, chemical effect, and mechanical effect thresholds were investigated in wide frequency ranges from 22 to 4880 kHz. Each threshold was measured in terms of sound pressure at fundamental frequency. Broadband noise emitted from acoustic cavitation bubbles was detected by a hydrophone to determine the cavitation threshold. Potassium iodide oxidation caused by acoustic cavitation was used to quantify the chemical effect threshold. The ultrasonic erosion of aluminum foil was conducted to estimate the mechanical effect threshold. The cavitation, chemical effect, and mechanical effect thresholds increased with increasing frequency. The chemical effect threshold was close to the cavitation threshold for all frequencies. At low frequency below 98 kHz, the mechanical effect threshold was nearly equal to the cavitation threshold. However, the mechanical effect threshold was greatly higher than the cavitation threshold at high frequency. In addition, the thresholds of the second harmonic and the first ultraharmonic signals were measured to detect bubble occurrence. The threshold of the second harmonic approximated to the cavitation threshold below 1000 kHz. On the other hand, the threshold of the first ultraharmonic was higher than the cavitation threshold below 98 kHz and near to the cavitation threshold at high frequency.     

Possible photographic observations of ball lightning

Summary Using night sky time exposure photography with a 13 1/3 Hz chopping shutter, we have searched for ball and bead lightning. Both appear as a sequence of images which join a lightning stroke. Ball lightning events are recognized by the regular spacing of the ball images and by the nontangential way the image sequence joints the stroke channel. Our analysis indicates that two events are probably ball lightning and twenty-two events are bead lightning.

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Riassunto Usando un tempo di esposizione lungo adatto al cielo notturno con un otturatore che scatta ogni 13 1/3 Hz, abbiamo cercato fulmini globulari e a nervatura. Entrambi appaiono come una successione di immagini congiunte a un colpo di fulmine. I fulmini globulari si riconoscono dalla spaziatura regolare tra i globi e dal modo non tangenziale in cui la successione di immagini si inserisce nel canale del colpo. La nostra analisi indica che due eventi sono probabilmente fulmini globulari e ventidue sono fulmini a nervatura.

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Резюме Используя фотографирование ночного неба с временной экспозицией, определяемой 13 1/3 Гц фотоэлектрическим прерывателем, мы ищем события шаровых и четочных молний. Такие молнии появляются, как последовательность изображений, которые объединяются в светящиеся штрихи. События шаровых молний распознаются посредством правильного расположения шаровых изображений и некасательным путем посредовательность изображений объединяется в штриховой канал. Наш анализ указывает, что два события являются, вероятно, шаровыми молниями и двадцать два события являются четочными молниями.