Natural green raw-based Biochar@Co/C composites: Simple water bath synthesis and excellent electromagnetic wave absorption properties

Over the last few years, wave absorbing materials synthesized based on green and eco-friendly natural materials were less studied. Carbon materials derived from natural materials, for example, have a limited absorption performance due to impedance mismatch in electromagnetic wave absorption applications. In this work, composites of MOF derivatives and biochar with strong wave absorbing capability were prepared by biochar and MOF. Biochar was green raw material originated from kapok trees in the school. Then it was compounded with MOF derivatives by pretreatment and water bath to form Biochar@Co/C composites. The effect of annealing temperature on the absorption properties was investigated by varying the annealing temperature. According to the results of the transmission line theory analysis, Biochar@Co/C-700 have RLmin value of −55.22 dB at 5.43 GHz and 3.69 mm. Also, the effective absorption bandwidth EAB can reach 6.37 GHz at 1.94 mm. And the above absorption properties were measured when the filling ratio was only 15 %. Electromagnetic parameter analyses showed that the combination between biochar and MOF derivatives greatly improves the impedance matching of the carbon-based materials, which is a vital factor that enables Biochar@Co/C-700 to have excellent wave-absorbing properties. In addition, the loss mechanism of the complexes to electromagnetic waves was also analyzed and summarized. These results provide a reference path for the preparation of high-performance electromagnetic wave absorption composites from green materials.