Nonmetallic quantum dots are nontoxic alternative to metallic cousins

April 10, 2024
Nonmetallic quantum dots, synthesized from Earth-abundant carbon and sulfur sources, are cost-effective, versatile, biocompatible, and environmentally friendly.

By opting for carbon- and sulfur-based nanomaterials, researchers at Aligarh Muslim University in India are developing ecofriendly nonmetallic quantum dots (QDs) as a “greener” alternative to fluorescent toxic nanomaterials (see video).

QDs are synthetic nanometer-scale semiconductor crystals that emit light and can be used in applications ranging from electronics displays to solar cells. But QDs derived from heavy metals come with a huge downside: they’re toxic.

Tiny-but-mighty QDs are also governed by the rules of quantum mechanics—where the quantum magic happens. As you might guess, they don’t emit light as you’d expect. At this scale, for example, gold materials appear blue.

 “They’re a system akin to ‘excited electrons within a nanobox’ and emit different colors of light depending on size and shape,” says Md Palashuddin Sk, an assistant professor of chemistry, whose lab develops nanoscale nonmetallic QDs. “And we can use solvothermal and microwave methods to tailor their properties.”

Sk’s passion for nanochemistry ignited from a simple but profound desire to make alternatives to toxic fluorescent nanomaterials that have the opposite impact on the environment. “The inspiration behind our research comes from a commitment to finding ecofriendly solutions within the field of QDs,” he says. “By focusing on nonmetallic QDs like carbon or sulfur dots, we want to pave the way for safer and more sustainable technologies.”

Carbon and sulfur are both abundant, cost-effective materials that can be easily synthesized into QDs. And the beauty of using these materials for QDs is that “you can make carbon dots from waste materials, then use them for removing pollutants—they’re a way to make the process come full circle,” Sk says.

Sk’s lab setup uses solvothermal synthesis and microwave-assisted synthesis techniques to fabricate carbon and sulfur dots systematically. Solvothermal synthesis, conducted under elevated temperature and pressure, allows controlled nucleation and growth of QDs. And microwave-assisted synthesis accelerates reaction kinetics to yield rapid formation of QDs with enhanced reproducibility.

“The beauty of our work lies within its simplicity yet effectiveness,” says Sk. “Developing nonmetallic QDs with exciting new properties and subsequent applications in environmental remediation—sensing and removing contaminants within water samples—is always a ‘wow’ moment for us. It’s a reminder that sometimes the smallest solutions can have the biggest impact.”

Nonmetallic QD challenges

To fully harness their potential, nonmetallic QDs do face several challenges that must be addressed: achieving uniform size distribution during synthesis, developing a complete understanding of the structural characteristics that influence their properties to optimize functionalization for specific applications, and enhancing photoluminescence efficiency for improved performance in sensing, bioimaging, and light-emitting diode development. 

“Overcoming these obstacles requires innovative synthesis techniques, precise defect manipulation methods, and thorough characterization to unlock the diverse applications and benefits of nonmetallic QDs across various fields,” says Sk.

Wide range of applications for nonmetallic QDs

Nonmetallic QDs have a diverse array of applications—ranging from environmental sustainability to advancements in healthcare and technology—across multiple fields because they’re considered to be safe nanomaterials. 

“Conventionally, nonmetallic QDs are an alternative to heavy-metal-derived QDs and promising for biological applications where precise biomolecule detection and targeting capabilities are invaluable for medical diagnostics and research,” says Sk.

These versatile nanoparticles are instrumental in sensing and removing toxic contaminants from diverse environments, including heavy metals, surfactants, pesticides, antibiotics, and dyes—to aid environmental remediation efforts. They also show potential for absorbing automotive oil and aiding oil spill cleanup initiatives. 

Nonmetallic QDs also show potential for energy applications. And these nanoparticles hold promise for enhancing the performance of electronic devices. Overall, the applications of nonmetallic QDs span from.

“Next, we’re planning to apply laboratory findings for practical applications in daily life, focusing on water purification in the nearby region,” Sk says. “With our interest in addressing water contamination issues, the team aims to develop a low-cost nonmetallic QDs-based technology to identify and separate various contaminants to provide clean water and better healthcare. The goal is to functionalize the nonmetallic QDs to capture as many contaminants as possible on their surfaces for easy removal.” 

Beyond this, they’re exploring applications of light-emitting nonmetallic QDs for electronic devices like TV screens.

About the Author

Sally Cole Johnson | Senior Technical Editor

Sally Cole Johnson, Laser Focus World’s senior technical editor, is a science and technology journalist who specializes in physics and semiconductors. She wrote for the American Institute of Physics for more than 15 years, complexity for the Santa Fe Institute, and theoretical physics and neuroscience for the Kavli Foundation.

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