Applications of NPs

What is a catalyst

speed up, lower temp or lower pressure of a reaction without being damaged (permanently) or consumed in the process

Why are NPs good catalysts

surface area, novel nanoscale surface properties; but catalytic activity can be site blocking (eg solid C deposits)

Gold as a catalyst

only works when <4nm; increased surface atom mobility increases reactivity; CO-CO2 oxidation; VOC oxidation; NOx reduction; used in H2 purification, catalytic converters and waste/pollutant breakdown;

Ceria NPs as a catalyst

tune growth conditions to change shape; O vacancies and high activity nano-facets most important in catalytic activity

Ceria NP applications

solid C and CO oxidation; car exhausts; co-catalyst support for other metal NPs; enhanced by alloying with Zr, Co or rare earths

Why is Ceria a good catalyst

rapidly switch between 3+ and 4+ without fluorite structure breakdown by accomodation O vacancies; gives ionic conductivity, O storage and release, and electrochemical interaction

What is used in a catalytic converter

Pt, Pd (palladium), Rh (rhodium) often mounted on alumina/ceria particles

Platinum group metals as catalysts

increase combustion efficiency at low T; used in car exhaust

Transition metal NPs

ammonia synthesis; hydrogen from methane; cracking of CC bonds in hydrocarbons; making CNTs from hydrocarbons

What are the two types of support that platinum group metals can be mounted on

non functional: large A/V, stable at high T, porosity enables gas flow; functional: electron transfer to oxide substrate, can tune NP activity or act as bi-catalyst

Key properties and uses of TiO2 NPs

UV blocking, photocatalysis, paints (white), food additives, coatings, antimicrobial

NPs in sunscreen

needs to absorb UV but pass visible light; smaller NPs shift absorption edge more blue; smaller NPs scatter light less; need good dispersion to be effective

TiO2 for photocatalysis

is a SC so absorbs light generating e/h pairs which react with oxygen or water producing reactive species which break down pollution molecules

TiO2 in environmental uses

reactive species break down organic matter good for dirt on self cleaning windows, pollution molecules and killing bacteria and viruses

Concerns about TiO2

potenitally biotoxic, can penetrate deep into skin, photocatalysis effects can damage skin cells

How are NPs used in fuel cells

Pt accelerates redox reaction; use of NPs reduces amount of Pt required

How are NPs used in solar cells

used in QDSSCs in place of dye; metal NPs used for absorption and surface plasmon resonance

How are NPs used in batteries

anode: Si NPs or nanorods, nanocarbons; cathode; Si has highest Li storage capacity but unusable in bulk due to cyclic failure

Advantages of NPs in batteries

less cyclic strain when loading Li into structure; shorter distance to move ions from particle centre to electrolyte; more freedom of shape design

Disadvantages of NPs in batteries

More SEI, complex manufacturing and recycling

Biomedical applications of NPs

consumer health: sunscreens, cleaning, cosmetics; medical: drug delivery, dental care, biosensors, bioimaging agents

How are silver NPs used

Ag+ damage bacterial membrane, DNA/proteins; used in wound dressings, disinfection and as anti-odour agents

Disadvantages of using Ag NP

toxicity to body cells, Ag can accumulate in organs and skin, post usage environmental concern

How and why are hydroxyapatite (HA) NPs used

calcium phosphate making largest volume fraction in bone; used in pastes/gels to fill gaps in bones: stimulates cell intergrowth; enamel/teeth restoration