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Nanoparticles- sizes, uses and potential dangers

Imagine materials so tiny they behave in completely unexpected ways, well this describes the world of nanochemistry. Nanochemistry is the study of structures between 1 and 100 nanometres in size. A nanometre (1nm) is one billionth of a metre (1x10^-9m). Normally in a science lab you would be used to working with volumes of liquids of around 50 to 100 ml or masses of substances around 5-100 grams so really these nanoparticles are on a completely different scale to the everyday or bulk materials we are used to dealing with.

Nanochemistry is different from "normal chemistry", these tiny nano objects have different properties from the bulk materials we are normally used to using in everyday life. Nanoparticles are much much smaller than normal everyday particles we are used to dealing with. To give you an idea of just how small nanoparticles are consider that a human hair has a diameter of about 0.08mm or 80 000 nm.

Particulate matter

Image show sthe risks associated with PM10 and PM2.5 particles

Image shows the effects of PM10 particles such as pollen on the respiratory system.

Image shows the problem of PM10 particles in construction sites.

Particulate Matter or simply PM is a term used to describe tiny solid particles and liquid droplets suspended in the air. These tiny particles vary greatly in size, shape, and composition and can be made of many different chemicals from a variety of sources. For air quality monitoring and health concerns they are often categorised by their size, for example small course particles are often referred to as PM₁₀ particles, where the number 10 refers to their size in micrometres (µm); where a micrometre is one millionth of metre ( 1 x10^-6) in size. These course PM₁₀ particles often come from sources such as:

Crushing or grinding operations e.g. from the work on construction sites and from quarrying.

Household Dust and dust from roads and fields is also a source of these PM₁₀ small particles.

Pollen from trees and plants also has a diameter in the range of 10 to 100 micrometres (µm) though this can vary considerably depending on the particular pollen grains.

Mould spores from fungi.

Air pollution, health and PM particles

PM₁₀ particles are easily inhalable and they can irritate your eyes, nose, and throat. They can also affect the lungs and heart, especially in people with existing respiratory or cardiovascular conditions. However, these PM₁₀ particles unlikely to be able to penetrate deeply into your lungs due to their size and because PM₁₀ particles are more likely to be deposited in the upper airways (nose, throat, and larger bronchi) where the body has mechanisms like cilia and mucus to trap and remove them. Smaller and more dangerous particles are PM_2.5 particles. These small particles have diameters of about 2.5 micrometers (µm) or smaller, that is they are about 4 times smaller than the PM₁₀ particles.

These PM_2.5 particles are produced by a number of different sources such as the burning of fuels such as petrol and diesel in cars, lorries and buses as well as many industrial processes. They are also found in the fumes released by the burning of coal in power stations and log burners in homes, other sources of burning at home including the burning of candles, incense, and tobacco products will release PM_2.5 particles into the air. Even cooking especially frying foods at high temperatures in the kitchen can release these small particles into the air. Since these particles are much smaller than the PM₁₀ particles they are considered much more dangerous to our health simply because being smaller they are able to travel much deeper into the lungs and they may even enter the bloodstream leading to potentially serious respiratory and cardiovascular problems including increased risks of heart attacks and strokes. So when air quality is measured the levels of both PM₁₀ and PM_2.5 particles are closely monitored to provide details of any potential health risks. The table below shows the relative sizes of several PM sized particles and nanoparticles.

Particle	Diameter
hydrogen atom	1 x 10^-10 m or 0.1nm
fine particles (also called PM_2.5)	1x10^-7 to 2.5x10^-6m
course particles (also called PM₁₀ or simply dust particles	These particles have diameters in the range 1 x 10^-5-2.5 x 10^-6m
Nanoparticles	These particles have diameters in the range 1 x 10^-9-1 x 10^-7m (1-100nm)

Dangers from nanoparticles

Image shows the dangers of inhaling small airbourne particles and nanoparticles into the lungs The table above shows that nanoparticles are considerably smaller than PM₁₀ and PM_2.5 particles. When nanoparticles are released into the air, they can potentially pose health risks that share some similarities with PM_2.5 particles, in that they can easily be inhaled deeply into the lungs, reaching the alveoli where gas exchange occurs; they can then enter the bloodstream which can result in cadiovascular disease and contribute to issues such as heart attacks and strokes.

Crossing the biological barriers in the body

Due to their extremely small size (1-100 nm), nanoparticles have the potential to cross many of the biological barriers in the human body much more easily than larger particles as PM₁₀ particles. This includes the lung-blood barrier and potentially even the blood-brain barrier which would allow nanoparticles to pass from the bloodstream into the various cells present in the brain. The small size of nanoparticles may even allow them to cross the placenta which is a biological barrier present between pregnant women and their unborn baby.

Crossing many of these biological barriers in the body could ultimately lead to many unwanted effects on various organs and organ systems within the body. Nanoparticles can be taken up by cells more readily than larger particles and once inside cells, they may interfere with cellular processes, damage DNA and cause other toxic effects. However more research is needed on the risks associated with nanoparticles and their long terms effects on the human body. Therefore through, careful and continual monitoring and research into the sources and health effects of airborne nanoparticles are crucial to ensure that any potential risks are identified and counter-measures are put in place to control and eliminate these risks.

Safety concerns

Nanotechnology is a new and fast growing area of research and development with many promising new advances in electronics and materials products being produced as a result of this new and advancing technology. However many of the long term harmful side-effects of nanoparticles are not fully known. Some scientists are worried about the possible side-effects of these tiny particles; these include: Images shows the effects of nanoparticles on the bacteria present in aquatic systems, the nanoparticles can kill essential bacteria.

Possible lung damage by breathing in these nanoparticles. Pollutants from cars and factories release small particles into the air which cause damage to the lungs, as outlined above using PM₁₀ and PM_2.5 particles. It is likely that nanoparticles will be even more of a problem than these particles due to their small size e.g. carbon nanotubes have a similar shape to asbestos fibres and they have been shown to cause extensive damage to the lungs in rats.

Nanoparticles can pass through many of the biological barriers in the body such as the skin, lungs and the digestive system where they can cause damage to living cells e.g. some anti-aging creams contain fullerenes and these are potentially toxic if they penetrate the skin.

The release of nanoparticles into the water, air or soil can cause environmental problems e.g. nanoparticles with anti-bacterial properties can enter the water system and kill bacteria in many ecosystems and even kill essential bacteria such as those in found in sewage treatment works. Other nanoparticles can stick to air pollutants and be transported vast distances, these nanoparticles could have toxic effect on many living organisms and this could result in widespread global damage to many natural environments and ecosystems.

Quick-check

Match the name of the particle with its size.

PM10

PM2.5

Nanoparticle

1–100 nm

Up to 10 µm

2.5 µm or less

Surface area to volume ratio- the advantage of being small

Nanoparticles have different properties from the everyday bulk materials that we use due to their very high surface area to volume ratio. Consider the following example to further illustrate the point, this shows how to calculate the surface area of the two cubes shown below and it then compares the surface area of the large and small cubes to their volume:

Boxes of various sizes to show relationship of surface area to volume

Calculating the surface area of each cube

Each of the cubes or boxes in the image has 6 faces; a front, back, top, bottom and left and right faces.
The surface area of the front face of the large cube is found by simply multiplying the breadth (10cm) and height (10cm) of the cube together, which is simply 100cm².
Similarly:
The surface area of the front face of the small cube is simply 1cm².
Now both the large cube and the small cube have 6 faces. So the total surface area of each box or cube is:
Total surface area of the large box= 6 x 100cm² = 600cm²
And
Total surface area of the small box= 6 x 1cm² = 6cm²

Calculating the volume of each cube

Now the volume of each cube can simply be found by using the formula:
Volume = length x breadth x height

So the volume of the large box will simply be = 10cm x 10cm x 10cm = 1000cm³
And
The volume of the small cube will simply be = 1cm x 1cm x 1cm = 1cm³

Calculating the surfac area and volume of various sized cubes

Since the volume of the small cube is 1cm³ and the volume of the large cube is 1000cm³ then 1000 small cubes will fit inside the large cube. Now the total surface area of the small cube was 6cm², so the total surface area of 1000 small cubes will be 6000cm², however the total surface area of the large cube was only 1000cm²; so we can see that if we were to break or smash the large cube into 1000 smaller cubes the this would greatly increases the total surface area. Many of the unique uses and properties of nanoparticles are directly linked to their very large surface area to volume ratio.

Gold and platinum two unreactive and yet reactive metals!

Image shows use of metal nanoparticles in a catalytic converter.

As an example of the "power of being small" and having a large surface area to volume ratio consider the use of two very unreactive metals such as gold and platinum as catalysts. These two metals are perhaps best known for their use in expensive jewellery and also for the fact that they are chemically unreactive metals.

Despite the fact that platinum is a very unreactive metal it is found in catalytic converters fitted in car exhaust system where it helps in the oxidation of many harmful pollutants including the toxic gas carbon monoxide (CO), which is oxidised into the less harmful gas carbon dioxide (CO₂) by the catalytic converter.

In a catalytic converter, the platinum (Pt) is in the form of platinum nanoparticles which are typically in the size range of 2 to 10 nanometres. The large surface area of the platinum nanoparticles provides many active sites where the carbon monoxide (CO) and oxygen (O₂) gas molecules can be adsorbed onto the surface of the platinum nanoparticles which coat the surface of an inert and highly porous ceramic material with a honeycomb structure inside the catalytic converter; as shown in the image opposite. This honeycomb structure also provides a large surface area for the nanoparticles to be stuck onto and ensures they are not all clumped or stuck together in large lumps with small surface area to volume ratios.

So the very small size of the platinum and other metal nanoparticles in the catalytic converter honeycomb structure is crucial because it maximizes the surface area to volume ratio and allows the conversion of the harmful gases such as carbon monoxide (CO) into the less harmful carbon dioxide gas CO₂.

Key points

Images summarises the properties of nanoparticles

Nanochemistry studies structures at the 1-100 nanometre scale, which are vastly smaller in scale and size than the everyday materials we handle; nanoparticles exhibit different properties from these everyday bulk materials due to their large surface area to volume ratio.

Particulate Matter (PM) describes tiny airborne particles, categorised by size such as PM₁₀ (larger, up to 10 µm) and PM_2.5 (finer, up to 2.5 µm), both of which pose health risks upon inhalation.

PM₁₀ particle sources include crushing, dust, pollen, and mould spores, these particles mainly irritate the upper airways.

PM_2.5 particles are produced by combustion (vehicles, industry, burning fuels) and can penetrate more deeply into the lungs and bloodstream than PM₁₀ particles causing serious health issues.

Nanoparticles are significantly smaller than PM₁₀ and PM_2.5, potentially allowing them to cross biological barriers (lung-blood, blood-brain, placenta) and cause damage to the cells in the body.

The large surface area to volume ratio of nanoparticles gives them unique properties, for example the use of metals such as platinum nanoparticles as catalysts in catalytic converters to oxidise harmful gases like carbon monoxide.

Potential safety concerns exist regarding nanoparticles, including potential lung damage (similar to asbestos), penetration of biological barriers (like skin), and environmental risks (harming bacteria, long-distance transport of pollutants).