Energy and environmental issues, such as fossil fuel shortage and climate change are global challenges that need to be addressed. Research and innovation in sustainable energy-related functional materials, produced by environmentally benign technologies, will play a critical role in meeting these challenges.In this sense, energy, environment, and materials constitute a trinomial combination of special relevance for the sustainable development of our society. Aerosol science and technology is an enabling discipline that can address these issues effectively. These gas phase techniques are widely recognized as being capable of producing a variety of novel materials with controlled functionality for energy and environmental applications. Fundamental principles of aerosol processing of materials are briefly described. Specific examples of advanced functional materials development by using aerosol processes are demonstrated, such as photocatalysts for carbon dioxide photoreduction and thin films for gas sensing. By deeply understanding the particle formation mechanisms inside the process, the aerosol technology can be used for development of advanced functional materials for various applications, such as catalysts, electrodes, phosphors, sensors, drug carriers, biomarkers, and cancer tracers.
Characteristics of pulsed wire discharge (PWD) for preparation of nanosized powders is described in this review paper. Firstly, principle of the high energy conversion efficiency is explained. Secondly, the high speed photographs of plasma and prepared grains in the PWD processes with various conditions are presented. Finally, a grain size determining factor is proposed and validity of the equation derived assuming ideal gas and Brownian motion is discussed using the obtained volumes of plasma and median diameters of the grains.
Plasma spray physical vapor deposition (PS-PVD) is inherently a high throughput processing and its characteristic rapid condensation of high temperature vapor offers to produce Si nanoparticles from metallurgical grade Si powders that are feasible for the negative electrode of lithium ion batteries. Structuring the high-ordered nanocomposite Si particles is further anticipated by a control of co condensation of high temperature alloy vapor in a single continuous processing. The guiding principle of the nanocomposite particle formation in PS-PVD and their structural characteristics as well as the potential as the negative electrode of the lithium ion batteries are reviewed.
Thermal plasma generated in radio-frequency (RF) induction torch has extremely high temperatures (about 10,000 K) and can easily produce reactive species. And, compared with direct arc current torch, the volume of RF induction plasma is relatively large and the residence/reaction time is long due to its comparatively low plasma-gas velocity. Its very large high-temperature field can completely vaporize a large amount of raw materials even with high melting/boiling points. In addition, rapid quenching (105–107 K/s) takes place in the tail of the plasma flame region. Thus, effective formation of nanoparticles is simultaneously achieved by nucleation and condensation in a highly supersaturated state. These characteristics of the plasma give unique reaction fields for the producing of various kinds and large quantities of nanoparticles. This paper introduces the synthesis of various nanoparticles by RF plasma method and its applications.
Iron (Fe) is an essential element for marine phytoplankton growth. Long-range transport of atmospheric aerosols from the continent and subsequent deposition is an important process to supply Fe to the ocean. The mixing states with water-soluble materials are the significant factor for the dry and wet depositions of aerosol particles. In this study, we focused on water-insoluble Fe-containing particles and clarified the mixing states with water-soluble materials. We collected aerosol particles on the R/V Hakuho Maru in the mid-latitude over the North Pacific Ocean. Collected particles were analyzed using a transmission electron microscopy with a water dialysis method and an energy-dispersive X-ray (EDX) analysis. Particles larger than 0.5 μm in diameter during a dust event and no dust events (maritime and continental sample) were analyzed. The number fractions of water-insoluble material containing particles to total analyzed particles were 10% (maritime), 20% (continental) and 30% (dust event), respectively. Most of water-insoluble materials were mixed with water-soluble materials. Based on EDX analyses of water-insoluble materials in analyzed 3 samples, water-insoluble Fe-containing particles were found with other mineral components (Si or Al) and the number fractions of Fe-containing particles to total analyzed particles were 2% (maritime), 2% (continental) and 8% (dust events), respectively.
Degradation of volatile organic compound (VOC) gas by ultrasonic mist was investigated using a batch reactor under various experimental conditions. The experiments were conducted with or without hydrogen peroxide (H2O2) under 254 nm of UV irradiation. In the techniques with H2O2, VOC gas was removed by adsorption or reaction with OH radicals generated from H2O2 on the mist surface or inside it. Since 100% of toluene gas could be removed under all conditions by the adsorption or reaction with OH radicals on the mist surface, we evaluated the reactivity under the various experimental conditions by their reaction rates. The removal rate of toluene under UV/H2O2/mist condition was faster than that under UV/pure water/mist condition. Therefore, it is evident that H2O2 plays an important role in the generation of OH radicals and removal of gaseous VOC. Furthermore, in cases of 200 kHz of high frequency ultrasonic irradiation for the continuous generation of H2O2, sufficient removal rates were obtained not only under 200 kHz/UV/pure water/mist condition but also under 200 kHz/pure water/mist condition. Therefore, the results indicate that 200 kHz of ultrasound irradiation has a capability of continuous supply of H2O2, and a direct reaction with toluene by creating reactive cavities.
An inertial filter (INF) sampler can collect ultrafine particles (UFP) uniformly onto a 47 mmφ quartz filter with a low pressure drop (20–30 kPa) at 40 L/min. However, gas adsorption may influence chemical composition of UFP as a positive artifact during sampling period owing to very low mass concentration of UFP. In this study, we evaluated organic gas adsorption onto the quartz filter settled in the INF sampler during collection of atmospheric UFP in summer and winter to elucidate the influence of seasonal temperature and relative humidity. The filter samples collected by the INF sampler were analyzed for organic carbon (OC), elemental carbon (EC) by a thermal/optical carbon analyzer following the IMPROVE method. As a result, the artifacts of OC ranged from 33.0±11.7% in summer to 27.8±12.0% in winter, a large difference in the OC concentration was not observed between the seasons. The artifacts for each OC fraction showed that OC1 and OC4 were almost not adsorbed onto the filter but OC2 and OC3 were adsorbed about 40%, indicating that high boiling point components were adsorbed onto the filter at the high flow rate condition. From these results, it was thought that the gas adsorption was relatively low for the mass concentration of UFP and the INF sampler can be a useful device for UFP collection.
This review has touched on the applications of Electrodynamic Balance (EDB) in mass transfer and heterogeneous reaction of droplet. The EDB was adapted to establish the unsteady flow around the droplet by oscillating a 1-Dodecanol droplet by AC electric field. The enhancement of mass transfer was examined from the evaporation rate of single oscillating droplet. Desulfurization reactions of a levitated single Na2CO3 droplet were followed by the EDB coupled with a Raman spectroscopy. The mechanism of heterogeneous reaction was discussed from the changes in mass and Raman spectra of the levitated particle. These examples have been demonstrated that EDB was a powerful tool for the kinetic studies of aerosol.