The aerosol processing of materials has attracted increasing attention because of its rapid synthesis and simplicity for scaling up as compared to the traditional liquid or solid methods. In this article, aerosol processing of nanoscale adsorbents and catalysts for air pollution control applications is reviewed. Special focuses are on the synthesis and application of nano-materials developed in our research group, with mesoporous spherical-silica particles (MSPs) and nitrogen-doped TiO2 (N-TiO2) photocatalysts as examples. The MSPs possess high surface area, pore volume and uniform pore size distribution in the nano-scale, thus they are suitable to serve as adsorbents or catalysts supports. And the N-TiO2 particles are effective photocatalysts under visible light irradiation. The synthesis parameters for producing MSPs via aerosol-assisted evaporation induced self assembly (EISA) method and for producing N-TiO2 via atmospheric pressure plasma enhanced nanoparticle synthesis (APPENS) process were investigated. The characteristics of MSPs and N-TiO2 for either adsorbing or destructing the volatile organic compounds (VOCs) were discussed. Their effectiveness was also compared with adsorbents or photocatalysts made by non-aerosol processes.
Several methods for physical vapor deposition of polymer thin films have been reviewed with an emphasis on its application to organic light-emitting devices. Codepositon method of two bifunctional monomers can produce such films as polyimide, polyurea, polyurethane, and π-conjugated polymers. Radical polymerization of single monomer can be achieved by electron-assisted vapor deposition of vinyl and acryl monomers. Surface-initiated deposition polymerization combines a self-assembled monolayer with the vapor deposition to grow polymer thin films that are chemically bound to the substrate surface. Patterned polymer thin films can be prepared by depositing photosensitive films consisting of functional monomers and photoinitiators. These methods are capable of preparing nanometer-thick polymer thin films and their multilayers, and are suitable for device fabrication. It was shown that the lifetime of organic light-emitting device can be extended by using the vapor deposition polymerization.
With the fabrication and processing of films produced by conventional liquid-phase deposition methods, the obtained film porosities are often limited due to the need of post-deposition heat treatment steps. This may lead to collapse of microstructures and detrimentally affect the open morphology of porous films. A novel alternative production method therefore is single-step, gas-phase aerosol deposition. This method has been shown to produce films with estimated porosities of up to 98 %, validated in numerical simulations. The key to synthesize highly porous films through this approach is the successful generation of nanoparticle aggregates, ensuring high specific surface area. Particle production is to be assisted by thermophoretic deposition for loose packings while maintaining a cooled substrate to hinder possible film sintering. Highly porous films have found challenging applications e.g. in gas sensing, and as a consequence, much work has focused on characterizing porous film properties and understanding the diffusion and gas transport through porous structures.
Spray dry technique is one of the useful tools and is widely used for preparing pharmaceutical dosage forms and manufacturing pharmaceutical excipients. Spray drying of particles adds functions to the raw particles, e.g., flowability and compressibility. Other advantages of spray drying technique are to encapsulate drug in polymer matrix (microcapsule) and prepare the composite particle by a simple process. Microcapsule shows the controlled release properties. In developing the drug delivery system, nano-drug carriers are paid recent attention. The spray dry technique can produce composite of nano-drug carrier and sugar alcohol in powder state. When the nano-composite powder is administered, the nano-drug carrier can promptly dissolve by the dissolution of sugar alcohol. The spray drying technique will be used more widely and more frequently in the future as a tool for hybridization of drug with functional materials so as to develop effective drug delivery systems.
The versatility of the pulmonary delivery route has encouraged recent research efforts to deliver a plethora of materials through the lungs, including pharmaceutical drugs, proteins, peptides, and DNA, for systemic circulations in the form of dry-powder aerosols. Therapeutic agents delivered through the pulmonary route are typically targeted to the lung alveolar region, which presents a large surface area for rapid absorptions into the systemic circulation. As a result of the rapid advances in nanotechnology, the use of inhaled nanoparticles as therapeutic carriers has become a subject of very active research. This review article covers the various methods to prepare micron-size dry-powder aerosols of nanoparticle aggregates intended for inhaled delivery by means of spray drying, spray-freeze-drying, and controlled precipitation. The selection of the preparation method, as well as the adjuvants and excipients used to convert nanoparticulate suspensions into the dry-powder form, depends on the physicochemical properties of the therapeutic agents and their encapsulation materials. An effective deposition of the therapeutic nanoparticles in the targeted lung region is achieved by creating nano-aggregate aerosols with appropriate aerodynamic diameters.
Filter sampling was conducted at the summit of Mt. Fuji to observe microphysical properties of Asian dust in the free troposphere. In order to avoid influence of local mineral dust elevated from near the summit, the filter sampling was conducted only during the nighttime from 0:00 to 6:00. Volume-size distribution of water-insoluble aerosol particles was measured by using a Coulter Multisizer. The samples with the minimum local influence showed the size distributions with the mode diameters of 3.1 and 4.5 μm. These mode diameters correspond to those measured on the ground during Asian dust event. Therefore, the measured water-insoluble aerosol particles were of background Asian dust in the free troposphere. In addition, a narrow size distribution with a mode diameter of 1.8 μm which could be the contribution of inorganic ash spheres also appeared. The measurement of sample which was separated by wind direction and speed during 2006 summer showed the mode diameter of around 5-6 μm, which would be of the mineral dust elevated from near the summit. For proper observation of mineral dust (water-insoluble particle) in the free troposphere, it is required to adopt the sampling time from 0:00 till sunrise.
We investigated the effect of environmental temperature on the counting efficiency of condensation particle counters (CPCs) by using a temperature-controlled chamber. The CPCs studied were TSI models 3010D and 3790, which were designed for automobile exhaust particle measurement with the nominal lower size detection limit (d50) of 23 nm. A set of counting efficiency measurements were conducted for particle sizes of 23, 41 and 55 nm at a temperature between 21 and 29°C. As a result, the counting efficiency of CPC 3010D showed linear temperature dependence for the particle size of 23 nm with the proportionality factor of -0.62 %/°C. Weaker temperature dependence was observed for particle sizes of 41 and 55 nm. On the contrary, the counting efficiency of CPC 3790 was not affected by the temperature for any particle sizes studied. Subsequently, the counting efficiency of CPC 3790 at 23 nm was repeatedly measured by changing the environmental temperature at the rate of about 15°C/h. We observed, at most, about 2 % reduction in the counting efficiency although there was a large scatter in the counting efficiency. These results suggest that we should control the environmental temperature for the calibration of CPC 3010D but there is no need for CPC 3790. However, since our experiments did not totally rule out the possibility of CPC counting efficiency dependence on rapid change in environmental temperature, use of a constant temperature chamber is recommended even for the calibration of CPC 3790.