Lignocellulosic Interfacially Complexed Cryogels as Robust Electromagnetic Wave Dissipators

The poor structural integrity of the lignin-containing cellulosic cryogels and the requirement for delignification processes restricted their functionality. The development of lignocellulose nanofibrils (LCNFs) directly from lignocellulosic biomass has addressed these limitations. However, their application in electromagnetic (EM) shielding presents new challenges, including their inherently insulating nature and significant shrinkage during thermal annealing. This was addressed using the art of interfacial complexation. The employed approach leverages the jamming of synergized LCNFs with graphene oxide (GO) and/or metal-organic frameworks (MOFs) at the oil/water interface, driven by electrostatic interactions with amine-terminated ligands. This process forms a stable lignocellulosic jammed emulsion gel template, which can be converted into cryogels through freezing and lyophilization. The resulting ultralightweight GO-LCNF cryogels (density: 2.69 mg cm^-3) exhibited exceptional flexibility, with 80% compressibility and instant shape recovery after thermal annealing. This hybridization enables the minimization of volume shrinkage upon thermal treatment, achieving structural integrity comparable to that of cryogels derived from delignified cellulose nanofibrils (CNFs). The fabricated cryogels exhibited promising electromagnetic (EM) shielding performance, with a shielding effectiveness (SE) of 46.7 dB and specific shielding effectiveness over thickness (SSE/t) ranging from 19,184 to 24,327 dB cm² g^-1. Upon complexation with magnetic MOFs, the thermally annealed cryogels transform into potent absorption-dominant EM shielding systems with an absorbance of 0.62-0.67. These cryogels effectively mitigate induced surface reflections on metallic substrates, positioning them as powerful solutions to meet the growing technological demand for robust absorption-dominant EM shielding materials.