Many types of porous particles containing inorganic and organic substances, such as carbon, metals, metal oxides, inorganic−organic hybrids, and polymers, have been developed. However, natural polymer-derived particles are relatively rare. To our knowledge, this report describes the first synthetic method for obtaining meso-/macroporous particles made from pectin, which is a natural polymer with a wide range of biological activities suitable for active substance support applications. These porous particles were prepared using a template-assisted spray-drying method, followed by a chemical etching process. An organic template [i.e., poly(methyl methacrylate) (PMMA)] or an inorganic template [i.e., calcium carbonate (CaCO 3 )] was used to evaluate the resulting formation of macroporous structures in the pectin particles. Furthermore, the concentration of the templates in the precursor solution was varied to better understand the mechanism of porous pectin particle formation. The results showed that the final porous particles maintained the characteristic properties of pectin. The differences between the two templates resulted in two distinct types of porous particles that differed in their particle morphologies (i.e., spherical or wrinkled), particle sizes (ranging from 3 to 8 μm), pore sizes (ranging from 80 to 350 nm), and pore volume (ranging from 0.024 to 1.40 cm 3 g −1 ). Especially, the porous pectin particles using the CaCO 3 template have a significantly high specific surface area of 171.2 m 2 g −1 , which is 114 times higher than that of nonporous pectin particles. These data demonstrated the potential for using PMMA and CaCO 3 templates to control and design desired porous materials.

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.

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There has been much interest in developing protein adsorbents using nanostructured particles, which can be engineered porous materials with fine control of the surface and pore structures. A significant challenge in designing porous adsorbents is the high percentage of available binding sites in the pores owing to their large surface areas and interconnected pore networks. In this study, continuing the idea of using porous materials derived from natural polymers toward the goal of sustainable development, porous pectin particles are reported. The template-assisted spray drying method using calcium carbonate (CaCO 3 ) as a template for pore formation was applied to prepare porous pectin particles. The specific surface area was controlled from 177.0 to 222.3 m 2 g −1 by adjusting the CaCO 3 concentration. In addition, the effects of a macroporous structure, the specific surface area, and an interconnected pore network on the protein (lysozyme) adsorption capacity and adsorption mechanism were investigated. All porous pectin particles performed rapid adsorption (∼65% total capacity within 5 min) and high adsorption capacity, increasing from 1543 to the highest value of 2621 mg g −1 . The results are attributed to the high percentage of available binding sites located in the macropores owing to their large surface areas and interconnected pore networks. The macroporous particles obtained in this study showed a higher adsorption capacity (2621 mg g −1 ) for lysozyme than other adsorbents. Moreover, the rapid uptake and high performance of this material show its potential as an advanced adsorbent for various macromolecules in the food and pharmaceutical fields.

One of the main challenges in practical applications of nanocellulose-based particles is the maintenance of their high surface area and chemical properties during particle formation in the drying process. In this study, we report the preparation of nanostructured 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-oxidized cellulose nanofiber (TOCN) particles via a spray-drying process without changing their chemical functionalization. The physicochemical properties of TOCN particles prepared by various types and concentrations of organic solvents were investigated. The resulting particles possessed a high ζ-potential value (−51 to −63 mV). We found that the formation of the porous structure could be realized by controlling the solvent polarity, which effectively increased the surface area to 222 m2/g and led to a good adsorption capacity for macromolecules such as lysozyme protein (>3200 mg/g). These results show that this method has a wide range of potential applications, e.g., drug delivery agents, adsorbents, encapsulation, and composite technologies.