NanoparticlesT
Nanoparticle — a particle with a diameter in the range of 1–100 nm (nanometres). 1 nm = 1 × 10⁻⁹ m. Nanoparticles are only slightly larger than individual atoms and molecules.
Nanoscience — the study of nanoparticles and how they can be used.
| Scale | Typical size |
|---|---|
| Atom | ~0.1 nm = 1 × 10⁻¹⁰ m |
| Small molecule | ~0.5–2 nm |
| Nanoparticle | 1–100 nm = 1 × 10⁻⁹ – 1 × 10⁻⁷ m |
| Fine particles (PM2.5) | 100–2 500 nm (1 × 10⁻⁷ – 2.5 × 10⁻⁶ m) |
| Coarse particles (PM10) — dust | 2 500–10 000 nm (2.5 × 10⁻⁶ – 1 × 10⁻⁵ m) |
| Human hair | ~70 000 nm (70 µm) |
The SI prefixes on a logarithmic scale of size — each step down is ten times smaller.
Surface Area to Volume Ratio
As a particle gets smaller, its surface area to volume ratio increases dramatically. A nanoparticle has a very large surface area relative to its volume, compared to the same material as a large lump. For a cube, every time the side length decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10.
Chemical reactions happen at surfaces. A nanoparticle exposes a much greater proportion of its atoms at the surface than a larger particle made of the same material. More surface atoms = more reaction sites = reactions happen much faster.
This is why nanoparticles are so effective as catalysts — a tiny mass of nanoparticles can catalyse a reaction that would need far more of the same material in bulk form.
Changed Properties
Nanoparticles can have very different properties from the same material in bulk (large-scale) form. This is mainly because of their very high surface area to volume ratio. Examples:
- Gold nanoparticles appear red or purple rather than gold, depending on their size.
- Titanium dioxide nanoparticles are transparent (unlike bulk TiO2, which is white) — used in sun creams.
- Some materials become much more reactive, stronger, or conductive at the nanoscale.
Beyond the syllabus (useful context): you are not required to recall these specific materials or their individual properties — only the general principle that a high surface-area-to-volume ratio can give nanoparticles different properties, together with the application areas named below.
Uses of Nanoparticles
| Application | Material | Reason nanoparticles are used |
|---|---|---|
| Sun creams | Titanium dioxide (TiO2) | Absorbs UV radiation. Nanoparticles are transparent on skin (unlike bulk TiO2 which is white and opaque). |
| Catalysts | Various metals (e.g. platinum) | Very high surface area dramatically increases the rate of reaction. |
| Medical drug delivery | Various | Nanoparticles can cross cell membranes and deliver drugs directly to target cells (e.g. cancer cells). Buckminster fullerene can store medicines in its hollow centre. |
| Electronics / sensors | Carbon nanotubes, graphene | Tiny size enables microscale circuitry; high conductivity; sensitive detection of small amounts of substances. |
| Stronger materials | Carbon nanotubes | Incredibly strong and lightweight — reinforcing composites for sports equipment and aerospace. |
| Deodorants | Silver nanoparticles | Silver nanoparticles are antibacterial; they kill bacteria on the skin that cause body odour. The high surface area makes them effective at low concentrations. |
| Other antibacterial products | Silver nanoparticles | Silver is antibacterial; nanoparticles increase the surface area in contact with bacteria — used in wound dressings, socks, and food packaging. |
Risks of Nanoparticles
The use of nanoparticles raises concerns because little is yet known about their long-term effects on human health and the environment. Scientists treat nanoparticles cautiously because:
- Their very small size means they can penetrate cell membranes and potentially damage cells from the inside.
- Some nanoparticles may be toxic to living organisms.
- Very small particles might cross the blood-brain barrier, potentially affecting the nervous system.
- If released into the environment, nanoparticles could act as nanopollutants, with unpredictable effects on ecosystems.
- They can speed up biological reactions in unpredictable ways.
AQA questions on nanoparticles often ask you to evaluate their use. Always acknowledge both the benefits and the risks. A complete answer mentions the high surface area to volume ratio (benefit: faster reactions / more effective catalysts), and acknowledges that their long-term health and environmental effects are not yet fully understood (risk). Avoid writing as though nanoparticles are either entirely safe or entirely dangerous.
🧪 Exam-style questions
What is the approximate number of atoms in a nanoparticle?Tick (✓) one box.
Nanoparticles of some elements can be used as catalysts. Which element is most likely to be used as a catalyst?Use the periodic table. Tick (✓) one box.