Ultralight Ti3C2Tx MXene foam with superior microwave absorption performance

Light weight is one significant pursuit for microwave absorption (MA) materials. Generally, constructing foams with porous structure and low density as the absorber is one efficient way to reduce the absorber content and the quality of MA materials since the porous structure can effectively cause multiple reflections of electromagnetic waves and enhance the MA performance. Herein, we report a new and simple method for fabricating ultralight Ti3C2Tx foams by hydrochloric acid induced self-assembly and freeze-drying, for which the pore structure and MA performance can be effectively regulated by pre-freezing temperature. The decrease of pre-freezing temperature from −20 °C to −196 °C results in a reduced pore size, more homogenous pore structure, a decreased electrical conductivity, a decreased dielectric constant and a significantly enhanced MA performance. 3.3 wt% Ti3C2Tx foams was immersed into molten paraffin to prepare composites for the MA performance tests. Due to the synergy of multiple reflection, conductive loss and polarization relaxation, the Ti3C2Tx foams pre-frozen at −196 °C shows the most superb and impressive MA performance, a minimum reflection loss (RL) of −50.6 dB at the thickness of 1.8 mm and an effective absorption bandwidth (EAB) of 4.2 GHz (13.8–17.6 GHz) at the thickness of 1.4 mm, and the EAB could be adjusted in a range of 11.9 GHz (6.1–18 GHz) by increasing the thickness from 1 mm to 3 mm. This is one of the most lightweight materials with excellent MA performance to our knowledge, which perfectly meet the combined pursuit of light weight, thin thickness, broad bandwidth and strong absorption. This work offers a simple strategy for constructing 3D porous Ti3C2Tx-based foams facing the application such as MA, electromagnetic shielding, environmental governance, energy storage and sensors.