MS-Environmental ChemistryCHEM-748 Functionalized Nanomaterials by Dr. ShamsaKanwal
Functionalized Nanomaterials The most important factor in determining quality of life in human society is the availability of pure, clean drinking water. Wars have been fought, and will continue to be fought, over access to and control of clean water. Drinking water has two major classes of contamination, biological contamination and chemical contamination.
Bacterial contamination can be dealt with by a number of well-established technologies (e.g., chlorination, ozone, UV), but chemical contamination is a somewhat more challenging target. • Organic contaminants, such as pesticides, agricultural chemicals, industrial solvents, and fuels can be removed by treatment with UV/ozone, activated carbon or plasma technologies. • Toxic heavy metals like mercury, lead and cadmium can be partially addressed by using traditional sorbent materials like alumina, but these materials bind metal ions non-specifically and can easily be saturated with harmless species like calcium, magnesium and zinc (which are actually nutrients, and don't need to be removed). • Another weakness of these traditional sorbent materials is that metal ion sorption to a ceramic oxide surface is an equilibrium process, meaning they can easily desorb back into the drinking water supply.
A chemically specific sorbent material, capable of permanently sequestering these toxic metal ions from groundwater, is needed. • Since we consume vast quantities of water every day, the kinetics of heavy metal sorption need to be fast, allowing for high throughput in the process stream. A high binding capacity for the target heavy metal is clearly of value. • In addition, as acceptable drinking water contamination limits get lower and lower, the need to make analytical methods more and more sensitive (and selective) is rapidly becoming of critical importance.
Nanostructured Materials There has been a great deal of developments in the synthesis of nanostructured materials recently, particularly in the area of surfactant templated synthesis of mesoporous ceramic materials. Synthetic methods have been developed to prepare these materials in a variety of morphologies (lamellar, cubic, hexagonal, etc.) with structural features ranging from about 20Å to as much as 300Å. A huge amount of surface area is condensed into a very small volume in these nanoporous ceramics, making them well suited for catalytic, sorbent and sensing applications. In addition, the rigid ceramic backbone precludes solvent swelling and allows facile diffusion throughout the entire porous matrix. The ceramic backbone is also structurally more robust than is a polymer-based ion exchange resin, so particle attrition is less of an issue.
Self-assembled monolayers The self-assembly of a monolayer onto a surface is the spontaneous aggregation of molecules into an ordered, organized array, one molecule thick. The self-assembly process is driven by the attractive forces between the molecules themselves (e.g., van der Waal's interactions, hydrogen bonding or dipole-dipole interactions), as well as the attractive forces between the molecule and interface (e.g., hydrogen bonding, acid/base interactions, etc.). There must be sufficient water on the interface to hydrolyze the silane. Only through the judicious choice of reaction conditions (i.e., solvent identity, water concentration, water location, and reaction temperature) can self-assembly take place, resulting in a dense, uniform coating of the surface.
By varying the chemical nature of the monolayer interface, it is possible to tailor the chemical affinity of the SAMMS materials for specific classes of target analytes. For example, thiol terminated SAMMS have been shown to have extremely high affinity for many forms of mercury (oxidized, organic, chelated, colloidal, etc.), as well as other "soft" heavy metals (e.g., Cd, Au, Ag, etc.). The kinetics of mercury sorption by thiol-SAMMS are extremely fast, with equilibrium generally be achieved in just a few minutes. In addition, thiol-SAMMS is the only known technology that is effective for mercury removal from hydrophobic oil phases (such as the contaminated vacuum pump oil at Savannah River). Installation of ligands analogous to the CMPO (octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide) extractants provides the SAMMS materials with excellent selectivity for lanthanides and actinides, even at low pH and high nitrate concentrations. Once again, selectivity is high and kinetics are rapid (minutes). Functionalizing the SAMMS surface with ferrocyanides creates a sorbent material that is highly effective, and selective, for cesium (radiocesium is one of the principal daughter nuclides resulting from actinide decay, and hence a key issue in nuclear waste clean-up).
Nanotechnology can help alleviate sustainability problems Climate change/Energy Water Infectious disease Food production Toxics/Pollution Nanotechnology Research Directions for Societal Needs in 2020 By Mihail C. Rao
Green Nano Processes Producing nanomaterials and products without harming the environment Incorporates the source reduction principles of environmentally benign chemistry and engineering and focuses on the processes of making nanomaterials without emitting harmful pollutants and using nanotechnology to make current processes greener Managing and designing nanomaterials and their production to minimize potential environmental, health, and safety risk t or human health
Nanotechnology promises exciting breakthroughs for sustainable future • A clean, sustainable world for all future generations • Abundant Clean energy from sun • Drinkable water for everyone around globe • Rapid poit of care medical diagnostics and treatment • Novel therapeutics-A cure for Cancer by 2020
Growing concerns about nanotechnology stem from new, unknown properties and manufacturing challenges • Will the products of nanotechnology ….be harmful to human health? ….pose risk to the environment? Numerous studies and reports suggest a need to address the hazards of these materials directly Lessons from GMOs- public acceptance as barrier to commercialization Will the manufacture of these products generate new hazarduous toxic waste streams? Hazardous reagents Toxic solvents and high solvent usage Low yield of materials
Applying Green Chemistry to nanomaterials and nanomanufacturing High Preformance Inexpensive More convenient Greener Green chemistry applied to nanoscience: Design nanomaterials that provide new properties and performance, but don't pose harm to human or environment. Manufacture complex nanomaterials efficiently, without using hazardous substances Assemble/interfacenanomaterials using bottom up approaches and self assembly to enhance performance and reduce waste
Use of Nanomaterials in Textiles • Products and purpose of using nanomaterials The textile industry is one of the most important consumer goods industries worldwide. Its mostly small and medium-sized enterprises produce textiles for various uses such as clothing, home textiles (such as bed and table linen, kitchen towels and cleaning rags), household textiles (such as curtains, furniture fabrics, textile floor coverings) and technical textiles (such as protective clothing, vehicle seat covers, tarps, tire fabrics, filter materials). In Germany, about 60 institutions and companies work in the field of nanotechnical textile processing (BMBF, 2011). There is already a rapidly growing number of textiles with dirt and water repellent or antimicrobial properties and UV protection offered in the market, and their product description states that they were produced using nanomaterials
Nanomaterials contained in textiles • The nanomaterials that are and soon will be used most frequently in textiles are: Silver, silicon dioxide, titanium dioxide, zinc oxide, aluminum (hydr)oxides, nanoclay (primarily montmorillonite), carbon nanotubes, carbon black. Copper, gold, iron (hydr)oxides, polypyrrol, and polyaniline are of secondary priority (Som et al., 2010) Few examples are • Moisture-absorbent - Titanium dioxide • Fire resistance - CNT Boroxosiloxan, Antimony ash • UV protection, protection from fading - Titanium dioxide (rutile), Zinc oxide
Stability of the nanomaterials in the textiles • The release of the nanomaterials from the textiles depends on the following parameters: • The integration site into the textile (e.g. into the sheath or core of the fiber, into the coating) • Type and strength of the bond between nanomaterials and textile fibers (e.g. a covalent bond) • Textile properties such as abrasion resistance and flexibility of the coating. --------------------------------------