Hydrophobicity-induced electrostatic interfacial self-assembly for porous silica nanospheres with tunable pore sizes and pore hierarchies

Porous materials have distinct advantages in catalysis, adsorption, and biomedicine due to their excellent loading spaces and high stability. However, the precise control on the sizes and hierarchies/distributions of pore channels in a nanoscale matrix is still challenging. Herein, a simple but efficient hydrophobicity-induced electrostatic interfacial self-assembly (HEISA) strategy is developed to synthesize porous silica nanospheres (PSNs) with large tunable pore sizes (10–30 nm) and pore hierarchies (dual-pores and tri-modal pores). In the synthesis processes, hydrophobic homopolymers polystyrene (PS) can not only act as pore-swelling agents for the enlargement of pore channels up to ∼30 nm, but also induce the evolution of pore hierarchies from dual-modal PSNs to tri-modal PSNs. By employing hydrophobic homopolymers as hydrophobicity-induced agents, a “homopolymer-mediated enlarging mesopore and creating macropore” mechanism is proposed. The degradation behaviors of PSNs in phosphate buffer saline (PBS) exhibited a pore size- and concentration-dependent manners. Furthermore, the maximum loading amount of PSNs reached 143 ± 46 mg/g of bovine serum albumin (BSA) and 258 ± 30 mg/g of catalase (CAT). More interestingly, a magnetic functionalized tri-modal PSNs with unique “vesicular” morphology was obtained by employing hydrophobic magnetite nanocrystals as hydrophobicity-induced agents via this HEISA approach, which showed an ultra-high transverse relaxivity up to 670.5 mMFe⁻¹·S⁻¹ in the T₂-weighted magnetic resonance imaging. We therefore conceive that this proposed HEISA methodology provides a general pathway for developing ultra-large-pore mesoporous silica nanoparticles and hierarchical pore structures with various compositions and functions, further allowing the improvement of properties in biomedicine, catalysis, energy conversion and storage and adsorption or separation.