Recycling, taking advantage of waste is an imperative need. Hence, scientists seek how to make the most of them. This was the idea that led several experts to investigate what could be done with the surrounding 100 million tons of rice husk waste generated each year in the world when separating the grain. A team of Japanese researchers has developed a way to recycle rice hulls to create the first silicon quantum dot (QD) LED light.. A finding that has garnered unanimous applause from the scientific community.
This novel method transforms agricultural waste into state-of-the-art light-emitting diodes in an economical and environmentally friendly wayas revealed by the research team, belonging to the Center for Natural Sciences for Basic Research and Development of the University of Hiroshima in the journal ‘ACS Sustainable Chemistry & Engineering’ of the American Chemical Society.
“The toxicity of nanomaterials and environmental concerns inspired us to develop a scalable method to fabricate quantum dots with a positive environmental impact,” the researchers note in their report. Rice milling remains are “an excellent source of high-quality silica (silicon dioxide, SiO2) and value-added silicon (Si) powders.” 20% of the weight of this waste is silicon dioxide, they highlight.
The study authors explain that they synthesized silicon dioxide, porous silicon, and silicon quantum dots from rice hulls, using a conventional chemical synthesis method and investigated the structure, optical and optoelectric properties. The extraction yields of SiO2 and silica powders from rice husks are 100 and 86%, respectively. The final product results in an orange-red electroluminescence.
“Given the typical quantum dots often involve toxic material, such as cadmium, lead or other heavy metals, environmental concerns have been frequently discussed when using nanomaterials. Our proposed process and manufacturing method for QDs minimize these concerns,” explained Ken-ichi Saitow, lead author of the study and professor of chemistry at Hiroshima University.
Since porous silicon was discovered in the 1950s, scientists have explored its uses for applications in lithium-ion batteries, luminescent materials, biomedical sensors, and drug delivery systems. Silicon, non-toxic and abundant in nature, has photoluminescent propertiesderived from their microscopic (quantum-sized) dot structures that serve as semiconductors.
Aware of the environmental concerns surrounding current QDs due to the toxicity of the nanomaterials used and their impact on the environment, researchers set out to find a new method of manufacturing quantum dots that would have a positive environmental impact. They found the solution in rice husks.
The researchers used a combination of milling, heat treatments, and chemical etching to process the silica from the rice husk. First, they ground the husks and extracted silica powders by burning the organic compounds in the ground husks.
Second, they heated the resulting silica powder in an electric furnace to obtain silica powder through a reduction reaction. Third, the product was a purified silica powder that was further reduced to three-nanometer size by chemical etching.
The surface of the powder was then chemically treated and finally the silica quantum dots were produced, luminescent in the orange-red range with a High luminescence efficiency of more than 20%.
An “attractive alternative”
“This is the first research to develop an LED from waste rice hulls,” said Saitow. He added that the fact that silicon is non-toxic makes it a “Attractive Alternative” to Current Semiconductor Quantum Dots Available Today, Developing “Environmentally Friendly” QD LEDs from Natural Productshe indicated.
“By synthesizing high-yield silica quantum dots from rich shells and dispersing them in organic solvents, it is possible that one day these processes could be implemented on a large scalelike other high-performance chemical processes,” said Saitow.
The research team has already announced its next steps, which include developing higher-efficiency luminescence in silica quantum dots and LEDs. Also explore the possibility of producing silica quantum dot LEDs other than red-orange they just created.
Looking to the future, scientists believe that the method they have developed could be applied to other plants, such as sugar cane, bamboo, wheat, barley or grasses, which contain silicon dioxide. These natural products and their waste could also have the potential to be transformed into non-toxic optoelectronic devices.
The scientists said they would like to see the commercialization of their eco-friendly approach to creating luminescent devices from rice husk waste.
Reference report: https://pubs.acs.org/doi/10.1021/acssuschemeng.1c04985