Cellulose Nanofiber and Magnetic Nanoparticles as Building Blocks Constructing Biomass-Based Porous Structured Particles and Their Protein Adsorption Performance

Nanostructured fine particles have attracted attention as next generation materials because of their unique features and ease of handling compared with those of nanoparticles. However, most previously reported studies are limited to using nanoparticles or precursor solutions (e.g., atoms or molecules) as building blocks. In this study, we successfully developed a new type of porous structured fine particles via self-assembly of TEMPO-oxidized cellulose nanofibers (TOCNs) and magnetic nanoparticles (Fe3O4 NPs) as building blocks by spray-drying followed by template removal method. The resulting porous structured TOCN–Fe3O4 particles possessed unique macro–meso–microporous structures with a highly negative charge (ζ potential = −55 mV) and sufficient magnetization (Ms = 15 emu/g). The Fe3O4 NPs played an important role not only in enabling effective collection through magnetic separation but also in increasing the specific surface area by inhibiting aggregation of the TOCNs during the drying process while maintaining the intrinsic ζ potential value of the TOCNs. The porous structured TOCN–Fe3O4 particles allowed excellent mass transfer of lysozyme (a model protein adsorbate), which led to high adsorption capacities of >950 mg/g, rapid equilibrium (<10 min), magnetic separation capability, good reusability, and excellent selectivity in a binary solution of lysozyme and bovine serum albumin.