Synthesis of Metal Oxide Nanoparticles by Rapid, High-Temperature 3D Microwave Heating

Microwave-assisted fabrication has propelled the recent synthesis and processing approaches of various nanomaterials. However, in most previous studies, the synthesis temperature is limited to below 1100 K, which restricts its application. Here, a rapid, in situ 3D heating method to manufacture well-dispersed metal oxide nanoparticles on a 3D carbonized wood (denoted as C-wood) host using microwaves as the driving power is reported. The moderate electronic conductivity of C-wood contributes to the local Joule heating and the good thermal conductivity guarantees the rapid 3D heating of the overall material. The temperature of the C-wood increases from room temperature to approximate to 2200 K in 4 s (approximate to 550 K s(-1)), stabilizing to 1400 K, and then cooling back down to room temperature within 2 s. The preloaded precursor salts rapidly decompose and form ultrafine (approximate to 11 nm) metal oxide nanoparticles on the surface of the C-wood during the rapid quenching. The process takes place in air, which helps prevent the metal oxides from being reduced by the carbon. The 3D heating method offers an effective route to the rapid and scalable synthesis of metal oxide nanoparticles.