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Green Chemistry and Nanotechnology
The unique physical and chemical properties of nanomaterials, such as different conductivity, optical sensitivity, and reactivity, originate mainly from factors such as small size, surface structure, chemical composition, shape, solubility, or aggregation. These varied properties are attractive for use in a variety of technologies. Consequently, nanomaterials are becoming widely used in applications from cosmetics to semiconductors. Nanotechnology development and production presents a unique opportunity to offer a more sustainable approach to protect public health and the environment.
Nano-catalysts and Their Applications
Magnetic nanoparticles are important due to their easy recovery from the reaction mixture by the use of an external magnetic field. We have designed novel magnetically recoverable heterogeneous asymmetric catalyst systems supported on Fe3O4 nanoparticles. Such catalysts can find applications in various asymmetric C-C bond formation reactions, asymmetric hydrogenations, and asymmetric cycloaddition reactions. Water-splitting and the generation of H2 as a clean fuel would be ideally studied via the use of reusable and recyclable benign nano-catalysts. Additional utility may be in highly sensitive sensors, water purification, membrane systems, the adsorption of heavy metals, and antibacterial coatings. Additional applications for nano-catalysts may be as catalysts to destroy noxious and toxic gases in automobile catalytic converters and in power generation systems that burn gasoline and coal.
Mercury Removal and ‘Deep’ Desulfurization
Magnetically separable and visible light-activated nano-catalysts, carbon, nitrogen and sulfur-doped TiO2, have been used to convert biomass-derived acids to useful platform chemicals. Two US patents have been issued following the successful adaptation and use of nano-catalysts to capture elemental mercury from coal-fired power plants (#7,858,061) and in the ‘deep’ desulfurization of transportation fuels (#8,029,662).
Novel Eco-friendly Synthesis of Nanomaterials and Nanocomposites
Our results have shown that vitamins B1, B2 or C, or related naturally occurring and benign materials such as polyphenols from tea, from coffee or from wine waste can function both as reducing and capping agents. These agents provide an extremely simple, one-pot, greener method to synthesize bulk quantities of nanomaterials in water without the need for large amounts of insoluble templates. We have extended our unconventional microwave route to make these nanostructures via the spontaneous reduction of gold, silver, platinum, and palladium nanostructures with sugar solutions. A newer form of carbon-doped porous titania, which was prepared using dextrose, can be useful for the visible light-induced photodegradation of pollutants.
We extended the work to produce nitrogen and sulfur-doped titania that is not only active in visible light but also can be regenerated and recycled. We use a facile microwave method that accomplishes the cross-linking reaction of polyvinyl alcohol with metallic and bimetallic systems. For the first time, we accomplished a single-step bulk synthesis of leucoemealdine polyaniline nanofibers without the need of a reducing agent, template, or seed at room temperature. The polyaniline nanofibers can reduce metal salts to generate novel nanocomposites. These nanocomposites exhibit high thermal stability with broad decomposition temperatures, which could lead to a myriad of applications such as energy storage systems, catalysis, fuel cell membranes, and nanodevices.
Sustainable Nanomaterials and Their Applications in Green Environmental Remediation
A range of natural phenolic compounds and biodegradable in situ chemical oxidation protocols have been explored for the remediation of contaminants using nanoparticles. Our green chemistry approach to safely synthesizing these nano-metals coats or caps them with antioxidants to make the particles less toxic, time-released and safer. Two US patents have been issued on iron nanomaterials produced using polymers (#7,963,720) and plant/fruit/tea extracts (# 8,057,682), which are licensed by VeruTEK Technologies.
Cooperative Research and Development Agreements are in place with entities ranging from universities to small businesses. VeruTEK Technologies, a leading green environmental remediation company, is involved with our group in the development of green nanomaterials-based sustainable approaches to environmental cleanup worldwide.
Selected Recent Publications
Highly Active and Magnetically Retrievable Nanoferrite-DOPA-Copper Catalyst for the Coupling of Thiophenols with Aryl Halides.
R. B. Nasir Baig, R. S. Varma: Chem. Commun., 48, 2582-2584(2012).
Microwave-Assisted Green Synthesis of Silver Nanostructures
M. N. Nadagouda, T. Speth and R.S. Varma: Acc. Chem. Res., 44, 469-478 (2011).
Green Chemistry by Nano-Catalysis.
V. Polshettiwar, R.S. Varma: Green Chem., 12, 743-754 (2010).
Self-Assembly of Metal Oxides into Three-Dimensional Nanostructures: Synthesis and Application in Catalysis.
V. Polshettiwar, B. Baruwati, R.S. Varma: ACS Nano, 3, 728 (2009).
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