IIT team finds carbon ‘flowers’ excelling at turning light to heat

Subject :Science and Tech

Section: AWARENESS IN IT

Context:

Researchers at IIT Bombay have synthesized particles that absorb three frequencies of sunlight and convert it to heat with an efficiency of 87%. These particles can be coated on surfaces to heat homes and sterilize surfaces in hospitals. The researchers have applied for a patent.

Details:

Researchers heated a special form of silicon dust called DFNS (for dendritic fibrous nanosilica) in a furnace. Once heated, they introduced acetylene gas into the chamber. The white powder turned black – a sign that carbon had been deposited on the DFNS.
Then they collected the black powder and treated it with a strong chemical that dissolved the DFNS away, leaving carbon particles behind.
The structure of the silicon particles – 50-1,200 nanometers in size – resembled spikes arranged around a sphere. With the silicon filling taken away, what was left behind were little carbon beads whose surfaces were pocked with cone-shaped pits. In effect, the beads were spherical nanostructures composed of carbon cones.

Nanoflorets:

When looking through a microscope, these particles appears like tiny marigold flowers, made only of carbon. They called the material carbon nanoflorets.
These nanoflorets could absorb sunlight at many frequencies and convert it to heat with an unprecedented efficiency.
The nanoflorets also didn’t easily dissipate the heat generated into the environment, making the material a good candidate to heat other materials, like water, using solar energy.
It can be coated on paper, metal, and terracotta clay.

Two different techniques:

In 2018, another identical structure was reported that was dubbed “carbon nanospheres with wrinkled cages”. It was developed using formaldehyde-phenol polymerisation chemistry.
But nanoflorets differed in the techniques used to deposit carbon on the DFNS template (although this didn’t affect the characteristics of the product). It is developed using chemical vapour deposition (CVD).
- In CVD, volatile compounds like acetylene are used to deposit a thin carbon film on the silicon-dust template.

‘Blacker than black’:

The nanoflorets was extremely black in colour, which means it is a good absorber of light.
The nanoflorets converted the light energy they absorbed into thermal energy – a process called solar-thermal conversion – with a remarkable efficiency of 87%, which is highest among known materials.

Unusual properties:

Its high efficiency comes from three properties:
- The nanoflorets absorb three frequencies in sunlight – infrared, visible light, and ultraviolet. Other common materials for solar-thermal conversion, like photovoltaic materials used in solar panels, absorb only visible and ultraviolet light.
- As light falls on the material, the carbon cones ensure that very little is reflected back. Instead, most light is reflected internally.
- It does not lose trapped heat into the environment.

Source: TH