Metal-free hybrids possess many advantages when compared with metal-based materials, such as lightweight, low cost, and high stability, which offer great potential for them to be used in wide applications, such as microwave absorption. Bare carbon materials, especially for those derived from wasted biomass, normally cannot simultaneously exhibit strong and broadband absorption performance, due to their specific structures and high electronic conductivity, leading to more incident microwave reflected on surface. Herein, based on wasted grapefruit peels, 2D metal-free hybrids are designed and prepared with pre-exfoliated boron nanoflakes as the modulation. Noncovalent interaction is formed at their heterojunction, which endows them with properties that cannot be supplied by their individual components. As a result, interfacial polarizations and dipole polarizations are generated between the layers, benefiting the dielectric loss and impedance matching behaviors. Microwave absorption measurements demonstrate that the minimum reflection loss can reach - 47.9 dB and the effective absorption frequency band is 4.32 GHz, at 1.5 mm thickness. We hope these represent an addition to the family of sustainable biomass-derived microwave absorbents. [GRAPHICS] .