Milling of rice to separate the grain from the husk produces approximately 100 million tons of rice bran waste globally each year. Scientists searching for a scalable method for making quantum dots have developed a way to recycle rice bran to make the first silicon quantum dot (QD) LED light. Their new method turns agricultural waste into state-of-the-art light-emitting diodes in a low-cost, eco-friendly way.
The research team from Hiroshima University’s Natural Science Center for Basic Research and Development published their findings on January 28, 2022, in the Journal of the American Chemical Society. ACS Sustainable Chemistry and Engineering,
“Since typical QDs often include toxic substances such as cadmium, lead, or other heavy metals, environmental concerns are often discussed when using nanomaterials. Our proposed process and fabrication method for QDs reduce these concerns. ,” said Ken-ichi Saito, lead study author and professor of chemistry at Hiroshima University.
Since porous silicon (Si) was discovered in the 1950s, scientists have explored its use in applications in lithium-ion batteries, luminescent materials, biomedical sensors, and drug delivery systems. Non-toxic and found abundantly in nature, Si possesses photoluminescence properties, which result from its microscopic (quantum-sized) dot structures that act as semiconductors.
Aware of the environmental concerns surrounding current quantum dots, researchers set out to find a new method for making quantum dots that have a positive environmental impact. It turns out that uncooked rice bran is an excellent source of high purity silica (SiO.)2) and value-added C powder.
The team used a combination of milling, heat treatment, and chemical etching to process rice bran silica: First, they milled the rice bran and extracted the silica (SiOO).2) Powdered by burning the organic compounds of ground rice bran. Second, they heated the resulting silica powder in an electric furnace to obtain the Si powder via a reduction reaction. Third, the product was a pure Si powder that was reduced to 3 nanometers in size by chemical etching. Finally, its surface was chemically functionalized for high chemical stability and high dispersion in solvent, with 3 nm crystalline particles with a high luminescence efficiency of more than 20% for SiQDs luminescent in the orange-red range. was produced.
“This is the first research to develop an LED from waste rice bran,” Saito said, adding that the non-toxic quality of silicon makes them an attractive alternative to the semiconductor quantum dots available today.
“The current method becomes a great method for developing environmentally friendly quantum dot LEDs from natural products,” he said.
The LEDs were assembled as a series of physical layers. An indium-tin-oxide (ITO) glass substrate was the LED anode; It is a good conductor of electricity while being sufficiently transparent to emit light. Additional layers were spin-coated onto the ITO glass, including the SiQDs layer. The material was capped with an aluminum film cathode.
The chemical synthesis method developed by the team has allowed them to evaluate the optical and optoelectrical properties of SiQD light-emitting diodes, including the structure, synthesis yields, and properties of SiO.2 and Si powder and SiQDs.
“By synthesizing high-yield SiQDs from rich husks and dispersing them in organic solvents, it is possible that one day these processes could be applied on a large scale like other high-yield chemical processes,” Saito said.
The team’s next steps include developing high-efficiency luminescence in SiQDs and LEDs. They will also explore the possibility of producing SiQD LEDs other than the orange-red ones they have just made. Looking ahead, the scientists suggest that the method they developed could be applied to other plants, such as sugarcane bamboo, wheat, barley, or grasses, which contain SiO.2, These natural products and their wastes have the potential to be converted into non-toxic optoelectronic devices. Ultimately, scientists would like to see the commercialization of this eco-friendly approach to making luminescent devices out of rice bran waste.
Other members of the Hiroshima University research team include Honoka Ueda, Shiho Terada and Taisei Ono.
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Shiho Terada et al, Orange-Red Si Quantum Dot LEDs from Recycled Rice Bran, ACS Sustainable Chemistry and Engineering (2022). DOI: 10.1021/acssuschemeng.1c04985
Provided by Hiroshima University
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