IIT Bombay's Marigold Like NCF Comes As A Break-Through In Heat Absorption Materials (Image: iitb.ac.in)
IIT Bombay has designed and developed a Marigold-like nanostructured material that can absorb the highest heat of the sun. The study, which has been conducted by Prof. C. Subramaniam from the Department of Chemistry at IIT Bombay, works with the fundamental form of energy – the heat energy, which is the essential form of life. This breakthrough material has been named as nanostructured hard-carbon florets or NCF and this allows heat to be absorbed and stored with above 87 percent efficiency, which in turn brings in many applications for this invention.
The material, NCF, demonstrates unprecedented solar-thermal conversion. In his study, prof. Subramanium says, “this is particularly relevant for heating spaces located in cold climatic conditions that receive abundant sunshine such as Leh and Ladakh.” The NCF absorbs above 97 percent of the ultraviolet, visible, and infrared rays of sunlight and efficiently converts this into thermal energy. The uses of NCF are many. The heat produced using NCF can be transferred to air or water for practical uses. Using this, a room temperature can be raised by 60 degrees Celsius and can be used to provide a smoke free heating solution.
The NCF’s can be used in water heaters as an inexpensive alternative when compared to the present market thermal heating materials. NCF’s components, which are made of carbon, and their environmentally friendly nature make it an apt choice for heating applications. Dr. Ananya Shah, the lead author of the study, says, “Conventional coatings and materials for solar-thermal conversion are based on chromium (Cr) or nickel (Ni) films. While anodised chromium is a heavy metal and toxic to the environment, both Cr and Ni-films exhibit solar-thermal conversion efficiencies ranging anywhere between 60-70%. In fact, the best commercial ones in the market operate at 70% solar-thermal conversion efficiencies.” NCF material can be used as a coating in vacuum jackets, and it would work very well as a solar heat absorber and is less challenging to maintain.
Materials would need two contrasting characteristics in the conversion of solar energy into usable heat. Firstly, photon thermalisation – the ability to convert light or photons into heat and the ability to hold this without giving way to thermal conductivity and radiation and secondly, the retaining capacity of heat without giving way to thermal conductivity and radiation. NCF works on both of these fronts well; it has high photon thermalisation and is low on phonon conductivity.
The NCF is made of interconnected tiny carbon cones, resembling marigold. This unique structure allows both characteristics to seep through. Prof. Subramaniam explains that “NCF has ordered structure in short-range (shorter lengths) and disordered structure in long-range (longer distances). So, when light energy is absorbed by NCF, this short-range ordering causes strong phonon activation (oscillations in the ordered lattice). Anything that has strong phonons should also help in conducting the energy away. However, in NCF, the long-range disorder acts to scatter these phonon-waves. Therefore, the phonon thermal conductivity is low.”
The production of these materials is done through a technique called chemical vapour deposition, in which carbon is deposited onto a substrate of amorphous dendritic fibrous nanosilica (DFNS) to form the NCF, the IIT release said. The NCF’s advantage also lies in its processability. The materials to produce NCF’s are easily available, and the process to make them is easily scalable, thus making it commercially inexpensive. It can be coated on any surface with low maintenance and application cost. Prof. Subramanium says, “we have shown that the coating is possible over surfaces such as paper, elastomer, metal and terracotta clay.”
Applications, apart from solar thermal conversion and room and space heating, include using them on copper for heating air and converting water into vapour with the highest recorded efficiency of 186 percent. Solar vapour conversion is an essential process for the purification of water. “One metre square of NCF coatings converts 5 litres of water in an hour, that is at least 5 times better than commercial solar stills.” When it comes to efficiency in sun’s energy conversion, NCF’s have outperformed very other options.
The pioneering work of Prof Subramanium has been supported by the Swarna Jayanti Fellowship of the Department of Science and Technology, India. The team has come up with a company at the Society for Innovation and Entrepreneurship (SINE) at IIT Bombay to commercialise the various potentials of NCFs. The focus would be on the development and manufacturing of products to water and space heating.
The team has been the recipient of several awards, such as the Vishwakarma Prize for Engineering for invention, 2021 at IIT Gandhinagar and several awards for the carbon-zero product at IIT Madras. Prof. Subramaniam concluded, saying that he strongly believes that “NCF has the potential to change the solar-thermal energy market in India and lead the way in decarbonization.”
