Nanoparticles & Surface Properties

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CognitoNanoparticles — properties and uses

Key facts & methods

What are nanoparticles?

Nanoparticles: particles with dimensions between 1 and 100 nanometres (nm).
1 nm = 1 × 10⁻⁹ m. Compare: atom ~0.1 nm; bacterium ~1000 nm; human hair ~80,000 nm.
Nanoparticles contain a few hundred to a few thousand atoms.
They behave differently from the same material in bulk form — due to their very high surface area to volume ratio.
Examples: gold nanoparticles (red, not gold-coloured), titanium dioxide nanoparticles (transparent sunscreen).

Surface area to volume ratio

As particle size decreases, the surface area to volume ratio increases dramatically.
This is why nanoparticles are so reactive — more surface atoms exposed per unit mass.
Bulk gold is unreactive (used in jewellery). Gold nanoparticles are reactive and can act as catalysts.
Surface area to volume ratio = total surface area ÷ volume.
For a cube of side n: SA = 6n², V = n³, ratio = 6/n. Smaller n → bigger ratio.

Applications of nanoparticles

Medicine: drug delivery — nanoparticles carry drugs directly to tumour cells (targeted therapy).
Sunscreens: titanium dioxide nanoparticles block UV more effectively and are transparent.
Catalysts: high surface area makes them more effective catalysts.
Antibacterial: silver nanoparticles in wound dressings and clothing (e.g. socks).
Electronics: nanoscale transistors, conductive inks.

Potential risks

Nanoparticles are so small they can pass through cell membranes and enter the body.
May accumulate in cells and organs — potential toxicity not fully understood.
Could enter food chains and have unexpected environmental effects.
Regulation is difficult because effects may take years to manifest.
Risk vs benefit must be weighed: sunscreen nanoparticles probably safer than skin cancer risk from UV.

Exam questions — 4 questions · 10 marks · AQA 8462 style

1 markNanoparticle sizeAQA 8462 style

What is the size range of nanoparticles?

A 1 to 100 micrometres (μm)

B 1 to 100 nanometres (nm)

C 1 to 100 millimetres (mm)

D 1 to 100 picometres (pm)

3 marksSurface area to volume ratioAQA 8462 style

Explain why a catalyst made from nanoparticles is more effective than the same mass of catalyst as a solid block. (3 marks)

Hint: Key concept: surface area to volume ratio. More surface exposed → more active sites → more collisions → faster reaction.

+30 XP

1 markNanoparticle applicationAQA 8462 style

Why are silver nanoparticles used in medical dressings rather than bulk silver?

A Nanoparticles are cheaper to produce than bulk silver

B Nanoparticles have a much higher surface area to volume ratio, making them more effective antibacterial agents

C Bulk silver is toxic to the human body

D Nanoparticles are transparent and do not change the appearance of the dressing

3 marksRisk assessmentAQA 8462 style

Titanium dioxide nanoparticles are added to sunscreens. Give TWO benefits and ONE potential risk of this application. (3 marks)