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Title of Talk:
Simultaneous Environmental Monitoring and Purification Through Smart Particles

Abstract of Talk:
The University of Florida team has developed two multifunctional composite materials. The first composite material consists of a hard magnetic core, an intermediate silica layer and a photocatalytic titania shell (7.7 nm primary particle size). Figure 1 shows a TEM micrograph of the material (the region between the white arrows is the silica layer. The high surface area titania shell is responsible for photocatalytic oxidation of pollutants when illuminated by ultraviolet (UV) light. Under an external magnetic field as in the newly designed MAPR (Photocatalytically Agitated Magnetic Reactor), the composite can be magnetically fluidized, thus providing enhanced mixing with pollutants to be treated and enhanced exposure to UV light. The resultant advantage is improved pollutant destruction. An additional advantage is the retrieval of the material from the treated air or water media. The novel composite has been demonstrated to outperform the benchmark Degussa P25 in the destruction of phenol in laboratory tests.
The University of Florida team has also developed a silica-titania composite that possesses synergistic photocatalytic oxidation and adsorption. The nanostructured silica substrates provides high surface area while the nanosized titania particles are responsible for photocatalytic oxidation of pollutants. Excellent removal of elemental mercury vapor has been demonstrated. A unique feature of the novel composite is that the adsorption improves over time as shown in Figure 2. Based on the mechanisms identified, the team has developed a second generation of composite that has extraordinary mercury removal capability without the excitation of UV light.

Environmental Applications/Implications:
Photocatalytic TiO2 nanoparticles have been well recognized for its superior ability to oxidize pollutants. However, its separation from treated water has been a serious limitation. Unintentional release of nanoparticles into the environment also causes concerns due to their potential toxicity. Mass transfer limitation for TiO2 nanoparticles coated on tubes or beads is another constraint of the current TiO2 technology.
The multifunctional magnetic silica-titania composite material developed by the University of Florida has overcome these limitations and brings several advantages to the environment. Magnetic fluidization of the material allows its enhanced mixing with pollutants to be treated and enhanced exposure to light source. Pollutant destruction kinetics is improved, thus reducing the amount and energy required for pollutant treatment. Its movement can be well adjusted and confined to a prescribed space using a controlled magnetic field. Retrieval of the material from treated air or water media can also be accomplished easily by magnetic separation. By incorporating silica, photo-dissociation of the magnetic core, which commonly occurs to other magnetic materials, does not exist anymore. This prevents introduction of heavy metals into water and reduces unnecessary consumption of materials. In short, the magnetic silica-titania based nanotechnology enables us to improve environmental quality with less consumption of materials and energy.

In parallel developed is a nanostructured silica-titania composite that possesses synergistic photocatalytic oxidation and adsorption capabilities. The nanostructured silica provides high surface area for adsorbing pollutants as a concentrator while the nanosized TiO2 particles can photocatalytically oxidize pollutants. The synergistic combination allows reduced energy requirement since the light source only needs to be provided. This material has been successfully tested for removing elemental mercury vapor in air. The material changes its color as oxidized mercury accumulates on the material. The change of material color provides a convenient tool to identify the state of the material. The concentrated accumulation of oxidized mercury can be recycled by heat treatment or vacuum treatment. The recycle reduces demand of mercury from mining that is known to yield significant environmental damages. The silica-titania composite is regenerated in the meantime. The regeneration prolongs the lifetime of the material, thus reducing the required amount of material to be supplied. Furthermore, no hazardous waste is generated by this technology, which is in contrast to current carbon based technology. Hazardous waste disposal of mercury-loaded carbon is costly and may have long-term environmental impact. During the research, a unique feature of improved adsorption over time has been observed which has never been reported before. The mechanism of this feature has been identified, which leads to the development of a second generation of composite. The benefit of this new material is its independence from UV light, thus reducing the energy requirement.

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