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ChmL Module 2 Assessment (part2)
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- 1▪ Nanoparticles added to paints, for example, render them corrosion resistant and scratch-proof, and can even make them self-cleaning ▪ Slow down the rate of degradation due to UV exposurePaints and varnishes
- 2▪ Possible alternatives to problematic biocides ▪ Innovative new products in the areas of thermal insulation and self-cleaning surfaces ▪ HOWEVER, need to be proven to be safe in terms of human health and the environmentPaints and varnishes
- 3Because of their small size, nanoparticles have unique properties: ▪ Lower melting point, different colors, and greater reactivity than bulk materials ▪ Example: Gold nanoparticles are red and chemically reactive, whereas the bulk metal is yellow and inert.Nanoparticles
- 4Why nanoparticles have lower melting points and greater reactivity? ▪ Because a substantial percentage of the atoms in a nanoparticle are on the surface and are therefore bound less tightly than those within the bulk solid. ▪ Example: For a 5 nm particle, about 30% of atoms are on the surface.Nanoparticles
- 5Nanomaterials have a much greater surface area to volume ratio than their conventional forms, which can lead to greater chemical reactivity and affect their strength.A much larger relative surface per unit of mass
- 6At the nano scale, it is observed of induced changes in optical (photonic), electrical, electronic, mechanical, chemical, biological, rheological, structural or magnetic properties.New quantum effects
- 7have dimensions intermediate between those of individual atoms and bulk solids, they have intermediate electronic properties as well.Nanoparticles
- 8▪ Atoms and small molecule have discrete, quantized energy levels – electrons are confined to a very small volume ▪ Solid metals and semiconductors have broads of energy levels – electrons are delocalized throughout the entire crystal ▪ For solid nanoparticles, the spacing between energy levels increases as the size of the particle decreases.Nanoparticles
- 9The overall behavior of bulk crystalline materials changes when the dimensions are reduced to the nanoscale.Quantum effect
- 10➢ For 0-D nanomaterials, where all the dimensions are at the nanoscale, an electron is confined in 3-D space. No electron delocalization (freedom to move) occurs.Quantum effect
- 11For 1-D nanomaterials, electron confinement occurs in 2-D, whereas delocalization takes place along the long axis of the nanowire/rod/tube.Quantum effect
- 12For 2-D nanomaterials, the conduction electrons will be confined across the thickness but delocalized in the plane of the sheet.Quantum effect
- 13are semiconductor nanoparticles that are about 1-10 nm in diameter and contain only hundreds to tens of thousands of atoms.Quantum dots
- 14is irradiated with UV light, it emits visible light having a wavelength that depends on the size of the nanoparticle.Quantum dots
- 15For example: A 3 nm cadmium selenide (CdSe) particle emits green light at 520 nm, whereas a 5.5 nm CdSe particle emits red light at 620 nm.Quantum dots
- 16Color is due to electronic transitions.Quantum dots
- 17is irradiated with UV light, an electron is excited from the valence band to an energy level within the conduction band. ▪ Subsequently, the electron undergoes a transition from the bottom of the conduction band to the top of the valence band. ▪ This transition produces a visible photon having an energy roughly equal to the band gap. ▪ The smaller the particle, the larger the band gap and the greater the shift in the color of the emitted light from the red to the violet.Quantum dots
- 18Because of their distinctive optical properties, quantum dots may have numerous applications. As fluorescent probes or labels that allow simultaneous detection tracking and imaging in color of a number of biomolecules within a cell.Quantum dots
- 19➢ The modified quantum dots are thousands of times smaller than human cells and are able to penetrate cell membranes. ➢ The surface of quantum dots is modified by attaching an organic molecule that targets and bonds to a specific biomolecule, such as DNA or a protein. ➢ When they bond to a biomolecule and are irradiated with UV light, they serve as fluorescent probes, or labels, for the particular biomolecule.Quantum dots
- 20▪ Design and preparation of nanoparticles with high functionality, i.e. to fabricate nanomaterials which have the suitable properties for applications ▪ The fabrication of nanomaterials of tailored properties involves the control of size, shape, structure, composition and purity of their constituentsNanomaterials synthesis and processing
- 21To disassemble (break or dissociate) bulk solids into finer, nano-sized pieces“Top down” approach
- 22To assemble atoms or molecules together that leads to formation of clusters, that further come together to form self-assembled monolayers on the surface of substrate“Bottom up” approach
- 23Advantages ▪ Ultra-fine nanoparticles, nanoshells, nanotubes can be prepared ▪ Deposition parameters can be controlled ▪ Narrow size distribution is possible (1-20 nm) ▪ Cheaper techniqueBottom-Up
- 24Advantages ▪ Large scale production: deposition over a large substrate ▪ Chemical purificationTop-Down
- 25Disadvantages ▪ Broad size distributions (10-1000 nm) ▪ Varied particle shapes or geometry ▪ Control over deposition parameters is difficult to achieve ▪ Impurities: stresses, defects and imperfections get introducedTop-Down
- 26Disadvantages ▪ Large scale production is difficult ▪ Chemical purification of nanoparticles is requiredBottom-Up
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- Fichas sobre ChmL Module 2 Assessment (part2), creado por Cassy Rivera el 19/10/2024.
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