Ultralight monolithic magnetite aerogel

We report the successful synthesis of magnetite aerogel, which has been a long-standing un-resolved challenge in magnetic materials and in aerogel materials. It is the first purely magnetic oxide-ceramic aerogel. So far, a leading approach in inducing magnetic properties in aerogels has been the dispersion of magnetic particles in various aerogel supports. This new aerogel has an ultralow density of 55 mg/mL, containing up to 98.7% air. The synthetic challenge required careful tailoring of the various steps, from the magnetite sol, through the gel, and up to the final aerogel. The rationale behind the various synthetic modifications is described in detail. We find that the ability to form monoliths is associated with dual porosity of the aerogel - interstitial microporosity of small magnetite aggregates that build the walls of the material, along with the wide macropores, typical of aerogels. Detailed mechanistic description is provided, along with intensive characterization of the material properties, the superparamagnetic properties, and more. Modifications of the magnetite are described, such as control of its density, mechanical reinforcement with glass fibers and inducing anisotropy by gelation under an external magnetic field. Magnetite aerogel was found to be very dark with extremely low reflectance in the IR range. Various applications of this ultra-light magnetic material are proposed, including lightweight magnetic actuator, support for separable catalysts and more. (C) 2021 The Authors. Published by Elsevier Ltd.