Liquid metal-assisted rapid Joule heating for preparation of Janus metal oxides in one second

Abstract

Janus structure nanomaterials have demonstrated increasingly broad applications in catalysis, sensing, and air purification. However, the synthesis of Janus materials involves complex procedures and high costs. It often requires the use of toxic chemicals, posing risks to both the environment and human health. Therefore, developing a simple, cost-effective, stable and environmentally benign synthesis strategy is essential. Herein, based on the room-temperature fluidity, high thermal conductivity and internal reaction environment of liquid metals, we propose a rapid Joule heating process that constructs Janus structures in metal oxides within one second. Experimental and theoretical analyses indicate that Joule heating generates a temperature gradient in liquid metal gallium, which drives a Marangoni flow. This process has an extremely short duration, leading to significantly reduced energy consumption. Furthermore, it does not require any toxic reagents and generates no environmentally harmful byproducts. The Janus structure, due to its distinct dual properties, can facilitate the separation of charges during the catalytic process and also enhance the absorption performance of electromagnetic waves. Therefore, the Janus structure of cobalt oxide achieves a minimum reflection loss of −38 dB and an experimentally measured effective absorption bandwidth of 4.2 GHz at 2 mm. The oxygen evolution reaction exhibits an initial overpotential of 340 mV. This method provides a streamlined process with tunable structures and high universality. This method provides a greener, faster, and more efficient approach for synthesizing Janus-structured materials. It avoids the use of hazardous substances, such as organic solvents common in traditional methods. The process is simplified and significantly reduces the need for high-risk reagents.