(Nanowerk Spotlight) A black cotton T-shirt absorbs about 85% of visible light. The darkest paints can capture about 95%. But researchers have now created materials so black they absorb 99.7% of all light that hits them – making them appear as almost perfect voids to human eyes.
These “super-black” materials are essential for modern technology. Space telescopes use them to absorb stray light that would otherwise blur images of distant stars. Solar panels need them to capture as much energy as possible. Thermal cameras rely on them to detect tiny differences in heat. But until now, making super-black materials required complex manufacturing processes and only worked with carbon-based materials.
Previous attempts focused on growing microscopic forests of carbon nanotubes. While effective, this approach was expensive, limited to carbon, and required harsh manufacturing conditions like extreme heat and toxic chemicals.
Chinese researchers have now discovered a simpler way to create super-black materials that works with over 100 different types of light-absorbing particles, from metals like platinum and gold to semiconductors like copper oxide and titanium carbide. Their method, published in Advanced Materials (“Suspending Light-Absorbing Nanoparticles in Silica Aerogel Enables Numerous Superblacks”), uses a transparent foam-like material called silica aerogel as a scaffold to hold tiny particles perfectly spaced apart.
Schematic illustration of the design and fabrication of superblacks. a) Light transmitting to various LNs-based architectures with different configurations including stacked together, dispersed in the solid dense matrix, sparsely arrayed in the pattern, and suspended in the air, leading to light absorbance with different degrees. b) A novel universal strategy to create numerous superblacks by suspending Ti3C2 MXene or other 99 species of LNs in the ultra-low reflective silica aerogel with ultra-high light transparency. (Image: Reprinted with permission by Wiley-VCH Verlag)
Think of aerogel as frozen smoke – it’s 99% empty space but maintains its shape. The researchers made their aerogel from silica particles about 10,000 times thinner than a human hair. This structure is so fine that light passes through it almost as easily as through air. The challenge lies in achieving uniform suspension of the nanoparticles throughout this delicate structure – a process requiring precise control of conditions like temperature and mixing speed.
The aerogel keeps the particles suspended and separated, like insects trapped in amber. When light enters this structure, it bounces between the particles until they absorb it completely. The method needs surprisingly few particles – as little as one particle for every 20,000 parts of aerogel. This efficiency surpasses previous super-black materials, which typically required much higher concentrations of light-absorbing materials.
By combining different types of nanoparticles, researchers demonstrated they could create materials with multiple useful properties. For example, mixing magnetic iron oxide particles with light-absorbing carbon creates a super-black material that responds to magnets. Adding titanium dioxide particles produces versions that break down pollutants in water when exposed to sunlight. The researchers estimate that mixing and matching different nanoparticles could theoretically yield billions of unique combinations, each with its own set of properties.
These new materials solve problems that plagued previous super-black materials. They withstand temperatures up to 600 °C without losing their light-absorbing properties – hot enough to melt lead. They can be squeezed and compressed without breaking. Some versions repel water, making them self-cleaning and suitable for outdoor use.
In solar heating tests, the materials converted sunlight to heat so efficiently they could evaporate water three times faster than conventional solar heating. This suggests applications in water purification systems for regions lacking clean drinking water. Spacecraft could use these materials as coatings to better regulate temperature by absorbing or reflecting sunlight. Telescope manufacturers could create more sensitive instruments for studying distant galaxies.
The manufacturing process works at room temperature using standard lab equipment, making it more practical than previous methods requiring specialized conditions. However, scaling up production while maintaining uniform particle distribution remains a technical challenge researchers are working to solve.
Beyond their impressive blackness, these materials open new possibilities in optical and solar technology. They could improve solar panel efficiency by capturing more light energy. Thermal imaging systems could detect smaller temperature differences. The ability to combine super-black properties with features like magnetism or chemical reactivity creates opportunities for entirely new technologies.
The breakthrough demonstrates how rethinking a problem’s approach can lead to elegant solutions. Instead of building complex nanostructures, these researchers simply suspended light-absorbing particles in transparent scaffolds. This straightforward idea, combined with unprecedented versatility in material choice, may transform how we harness and control light in applications from solar energy to space exploration.
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