Environmentally friendly LEDs created using rice husks

This new method transforms agricultural waste into state-of-the-art light-emitting diodes in a low-cost, environmentally friendly way.

Milling rice to separate the grain from the husks typically produces about 100 million tons of rice husk waste globally each year.

“Since typical QDs often involve toxic material, such as cadmium, lead or other heavy metals, environmental concerns have been frequently deliberated when using nanomaterials. Our proposed process and fabrication method for QDs minimises these concerns,” said Ken-ichi Saitow, lead study author and a professor of chemistry at Hiroshima University.

The technology makes use of porous silicon (Si), a material that is non-toxic and found abundantly in nature with photoluminescence properties, stemming from its microscopic (quantum-sized) dot structures that serve as semiconductors. Waste rice husks have been found to an excellent source of high-purity silica (SiO2) and value-added Si powder.

The team used a combination of milling, heat treatments and chemical etching to process the rice husk silica. They milled rice husks and extracted silica (SiO2) powders by burning off organic compounds of milled rice husks before heating the resulting silica powder in an electric furnace to obtain Si powders via a reduction reaction. They then reduced the purified Si powder to 3 nanometres in size through a chemical etching process.

“This is the first research to develop an LED from waste rice husks,” said Saitow, adding that the non-toxic quality of silicon makes them an attractive alternative to current semiconducting quantum dots available today.

“The present method becomes a noble method for developing environmentally friendly quantum dot LEDs from natural products. It is possible that one day these processes could be implemented on a large scale, like other high-yield chemical processes.”

The team’s next steps include developing higher efficiency luminescence and exploring the possibility of producing LEDs other than the orange-red colour they have created so far.

The researchers also suggest that the method they have developed could be applied to other plants, such as sugar cane bamboo, wheat, barley or grasses that contain SiO2. These natural products and their wastes might hold the potential for being transformed into non-toxic optoelectronic devices.