Nanomaterials cooked up in microwave

US chemists have developed a method that uses a commercial microwave oven to control the dimensions and properties of nanoscale rods and wires during synthesis.



The researchers from Virginia Commonwealth University (VCU) used a method known as microwave irradiation (MWI). MWI is considered a fast and easy way to create highly versatile, tailored nanorods and nanowires because microwave heating can provide significant enhancement in reaction rates. The materials made can be used in medical applications, drug delivery, sensors, communications and optical devices



M. Samy El-Shall, professor of chemistry and affiliate professor of chemical engineering at VCU, said, “MWI is unique in providing scaled-up processes thus leading to a potentially important industrial advancement in the large-scale synthesis of nanomaterials.”



Most methods currently used to synthesise nanomaterials are complicated, require specific equipment and produce small amounts of nanomaterials. Although the MWI process involves the use of a conventional microwave, it requires a defined recipe of chemicals and solvents to create the nanomaterials in the laboratory setting.



The advantage of using a microwave is that the energy goes directly through molecules compared to thermal heat which applies heat to everything. In addition, El-Shall said that the nanorods and nanowires made by this method self-assemble into uniform aligned arrays of rods with well-controlled spacing between the rods. This is critical to be able to measure their individual conductivity and fluorescence.



“The key issue here is the control of the size, shape and lateral dimensions of nanostructures because these nanoparticles in the form of rods, wires, belts, cubes and so on are the building blocks used in devices and processes such as light-emitting diodes, solar cells, single electron transistors, lasers and biological labels,” he said.



El-Shall and his research team found that nanorods that are 1nm wide and 5-6nm long could be synthesised in just 30-60 seconds, while longer nanowires, 1.5nm wide and 350nm long, could be synthesised in two minutes. Traditional methods take many more hours to synthesise such materials.



El-Shall and his team are currently examining how to apply this basic principal to a broader scale to synthesise nanowires with multiple functions such as fluorescence, conductivity and magnetism.