Low-cost microwave reactor for green synthesis of nanomaterials

Introduction: This contribution is about a low-cost microwave reactor for green synthesis of nanomaterials. The paper reflects research results achieved at the NanoFab group of the Universidad Militar Nueva Granada, within the line of nanophotonics, sensors and nanotechnology. Investigations and analyses were carried out during 2019. Problem: Conventional synthesis processes usually affect the environment and human health, due to contaminant reagents and generation of by-products. Objective: The aim of this research is the modification of a microwave oven that assists in the green synthesis of nanomaterials with potential applications in homeland security. Methodology: In this investigation, the modification of a domestic microwave was carried out. The implemented reactor features a heat exchange unit to reduce volatile elements, and a digital magnetic stirrer for local homogenization. Synthesis begins with a trisodium-citrate solution, continuously stirred at 37 °C. Next, the precursor is mixed with silver-nitrate for 2 minutes. Then, the mixture was treated for 20 minutes in the microwave reactor. Finally, the nanoparticles are recovered. Results: The homemade microwave reactor is suitable for producing nanoparticles. Particularly, the 20-minute microwave exposure time for the reactants results in a nanoparticle size between 80-90 nm. To probe reaction parameters, impedance spectroscopy analysis is performed. Results revealed that the resistance of the medium of silver nanoparticles is 2.5 ohms, while for sodium citrate and nitrate it is 8.8 and 11.8 ohms, respectively. Conclusion: It is demonstrated that the modified microwave reactor is suitable for nanomaterial production. Lower amounts of solvent are required during nanoparticle synthesis. Microwave synthesis allows for green nanomaterials production with a minor impact on the environment. Limitation: Homogeneous heating of reactants in a stationary microwave cavity is limited to waveguide design; in this case, to a multimodal-microwave waveguide. Originality: Low-cost reactor for nanomaterial production and greener synthesis.