In today s lecture, we will cover:

Transcription

1 In today s lecture, we will cover: Metal and Metal oxide Nanoparticles Semiconductor Nanocrystals Carbon Nanotubes 1

2 Week 2: Nanoparticles Goals for this section Develop an understanding of the physical properties that are affected when a particle is in the nano size regime: optical, melting point, electronic, etc. Look at the production and application of metal, metal oxide, and semiconductor nanoparticles Understand the theory behind the properties of carbon nanotubes 2

3 Definitions Nanoparticle: a material with all three dimensions in the nanoscale regime (1-100 nm). Can be spherical or other shapes. Nanocrystals: crystalline nanoparticles Quantum Dots: semiconductor nanocrystals with fluorescent properties. Ag Au

4 Why do nanoparticles behave they Greater surface area way they do? The surface is where reactions can happen Spatial confinement (a.k.a. quantum effects) are the unusual properties of a nanomaterial that are only observed once the diameter of the particle is of a certain size. These effects manifest themselves in different differently depending on the material material material. 4

5 Unusual properties of nano Enhanced mechanical strength Change in fluorescence and colour Change in magnetic properties 5

6 Metal Nanoparticles Gold nanoparticles for sensing and therapy Silver nanoparticles for antibacterial properties 6

7 How are they made? Gold and silver nanoparticles can be prepared by reducing (adding electrons) to a metal ion Synthesis video 7

8 What is special about them at the nanoscale? Localized surface plasmon resonance explains why the colour of the nanoparticles change with size (when the particles are nano)

9 Size-dependent colour changes in metal nanoparticles Electrons on metal nanoparticles are affected by light energy in the visible larger particles interact with light of longer wavelength 9

10 How can this be useful? Gold nanoparticle-based visual sensors If nanoparticles can be aggregated then they will change colour because they will be larger and will interact with a different wavelength of light Image: nanowerk.com

11 Applications: Antibacterial uses of Ag nanoparticles Silver ion released from the nanoparticle is thought to be the active agent that kills bacteria Greater surface area useful for interacting with bacteria Nanoparticle form a way to package the agent Image:102theavenue.wordpress.com Video: silver nano and health 11

12 Applications: Gold nanoparticles for therapy Gold nanoparticles can serve as biocompatible carriers for drug delivery Image: Medgadget.com Animation for gold nano delivery 12

13 Metal oxide nanoparticles: Titania Titanium dioxide nanoparticles are prepared by bottom up chemical methods 13

14 Applications: Sunscreen Titanium dioxide nanoparticles will absorb/scatter UV but not visible less chalky appearance Image: Antaria 14

15 Metal Oxide Nanoparticles: Iron Oxide Magnetite (iron oxide) nanoparticles for ferrofluids 15

16 Iron Oxide nanoparticles: Ferrofluids Liquid of nanoscale ferromagnetic particles (e.g. magnetite) in a carrier fluid Invented in 1963 by NASA as an additive for liquid rocket fuel in order to move the fuel where there is no gravity to guide the flow. Ferrofluids in motion Image: ForceField 16

17 How are they made? Ferrofluid synthesis Magnetite (Fe 3 O 4 ) needs to be synthesized in colloidal form and suspended in solution with a surfactant. Image: chobotix.cz 17

18 What makes them special? 18

19 Superparamagnetism and Ferrofluids Ferromagnetics that have a single domain are very susceptible to magnetic fields and become superparamagnetic These particles are greatly influenced by a magnetic field but have no magnetic memory The patterns in the fluid are a result of an imposed magnetic field

20 Applications of ferrofluids Seals: creates a liquid o-ring around a rotating shaft due to a magnetic field 20

21 Applications of ferrofluids Audio speakers: holds the voice coil and diaphragm steady without causing friction that can distort the sound Image: Ferrotec Inc. Image: Sony 21

22 Medical applications of ferrofluids? Magnetic nanoparticles are also being applied in medical imaging, such as MRI, as contrast agents. In the future, they may be used for delivering drugs within the body or as drugs themselves for hyperthermia. Image: magnetmicrosphere.com Image: trialx.com Hyperthermia video 22

23 Quantum dots: Semiconductor Nanocrystals Small crystals of semiconductors either single element (e.g. Si) or multi-element (e.g. CdSe) Semiconductors do not conduct electricity as well as metals because of their Band Gap 23

24 Changing the Band Gap Bulk semiconductors have band gaps that are in the energy range of the infrared (heat) If an electron is excited across the band gap by absorbing energy (with light for example), it can give that energy back in the form of infrared light or heat.

25 Bigger gap for smaller QDs Source: 2nm Increasing size 6nm 25

26 How are they made? Synthesis video Chemical precursors decompose at very high temperatures to form nuclei that grow into small crystals 26

27 Applications: Displays, TVs, and Lighting Quantum dots can take one energy of light and convert it to multiple colours useful for many applications: Quantum dot LED Companies include QD vision and Nanoco Applications: Quantum dot TVs; Quantum dot lighting 27

28 Quantum dot applications (cont d) Solar cells use semiconductors to convert light energy into electrons Quantum dots can convert light efficiently into electrons Video: Solar cell applications Image: Nano-reviews.net 28

29 Diamond Forms of carbon compared

30 Graphite Forms of carbon compared

31 Graphene, fullerene, and carbon nanotubes Image:

32 Definitions Single-Walled Carbon Nanotube (SWNT): Nanostructure conceptualized as a one atom thick graphene sheet wrapped into a seamless cylinder. Multi-Walled Carbon Nanotube (MWNT): Nanostructure consisting of multiple rolled layers (concentric tubes) of graphene. 32

33 SWNT Structure Conceptualized by wrapping a one-atomthick layer of graphene) into a seamless cylinder. How the graphene sheet is wrapped is represented by a pair of indices (n,m) called the chiral vector. The integers n and m denote the number of unit vectors along two directions in the honeycomb lattice of graphene. If m = 0, the nanotubes are called "zigzag". If n = m, the nanotubes are called "armchair". Otherwise, they are called "chiral".

34 The Chiral Vector The chiral vector defines the circumference of the nanotube. Depending on the chiral vector, the tubes can be conducting, semiconducting, or insulating. Armchair (n = m) tubes are always conducting.

35 10, 10 SWNT

36 10,5 SWNT

37 Carbon nanotubes have amazing properties 200 stronger than steel with half the density of aluminum 5 more electrical conductivity and at least 1000 more current capacity than copper 15 more thermal conductivity than copper

38 Strength relates to intramolecular and intermolecular bonds sp 2 bonds in carbon nanotubes are very strong High surface area in between the individual carbon nanotubes allows for strong Van der Waals bonds

39 Electrical conductivity depends on how the tube is rolled up The conduction and valence band of a graphene sheet come into contact (i.e. exhibit metallic conduction) at six points corresponding to the carbon atoms. Thus, any cut in the graphene structure (to make a tube) that passes through those points will make a metallic-conducting nanotube. Avouris, P. Chem. Phys , 429, and references therein. Image:

40 Conductivity The rule for an (n,m) conducting tube is: n m = 3i where i is a whole number including 0. Image:

41 Bottom up synthesis of carbon nanotubes Needs three components: 1) Active catalyst 2) Source of carbon 3) Lots of energy! Tip growth: catalyst particle leads growth (typical for MWCNTs) Base growth: nanotube extrudes from catalyst particle (typical for SWCNTs)

42 Real Time CNT Growth (tip growth)

43 Synthesis and thread preparation videos

44 Applications in Space (Optical and Elevator!) Space (elevator): Space (optical) :

45 Other applications and companies Artificial muscles: Companies: