Multistage reclamation of Co2+-containing alginate hydrogels as excellent reduction catalyst and subsequent microwave absorber by facile transformation

Abstract The multistage reclamation of materials has made contributions to sustainable development, but further progress is still sought after. In this work, functionalized seaweed-based composites were successfully prepared and utilized in multiple stages. Specifically, Co2+-containing alginate hydrogels (CHB-Co2+) prepared by sol-gel self-assembly and adsorption method using interior/exterior co-functionalized calcium alginate as raw materials were utilized for efficient reduction of p-nitrophenol. After coupling with freeze-drying and carbonization procedures, a high-performance Co/N co-doped carbonaceous microwave absorber was obtained and investigated in detail. By virtue of unique 3D interconnected network, heterogeneous interfaces and doped heteroatom N species, by which endowing the absorber with optimal impedance matching and attenuation ability, as-fabricated NC-Co-700 exhibited prominent microwave absorption performance with −54.2 dB of RLmin at 6.4 GHz and 5.3 GHz of maximum absorption bandwidth (from 12.7 to 18.0 GHz). Additionally, in view of the dielectric loss and magnetic loss caused by the synergy effect among the functional components, the underlying absorption mechanism was proposed. This work provided a novel idea for designing biomass-based functional materials and simultaneously achieved economic benefits through the rational utilization of other products in the preparation process.