Synthesis of Submicrometer Hollow Particles with a Nanoscale Double-Layer Shell Structure

Abstract

The morphology of hollow, double-shelled submicrometer particles is generated through a rapid aerosol-based process. The inner shell is an essentially hydrophobic carbon layer of nanoscale dimension (20 nm), and the outer shell is a hydrophilic silica layer of approximately 40 nm, with the shell thickness being a function of the particle size. The particles are synthesized by exploiting concepts of salt bridging to lock in a surfactant (CTAB) and carbon precursors together with iron species in the interior of a droplet. This deliberate negation of surfactant templating allows a silica shell to form extremely rapidly, sealing in the organic species in the particle interior. Subsequent pyrolysis results in a buildup of internal pressure, forcing carbonaceous species against the silica wall to form an inner shell of carbon. The incorporation of magnetic iron oxide into the shells opens up applications in external stimuli-responsive nanomaterials.

Preparation of Double-Shelled C/SiO2 Hollow Spheres with Enhanced Adsorption Capacity

“…Subsequent pyrolysis in N 2 led to a high internal pressure, forcing carbonaceous species against the silica wall to form an inner shell of carbon. 24 Ferric chloride has a crucial role in the formation of the hollow particles because of its salt bridging effect with CTAB. The combination led to a phase of segregation, and a rapidly forming shell of silica at the droplet interface simultaneously disrupted the formation of silica based porous particles.…”

“…The combination led to a phase of segregation, and a rapidly forming shell of silica at the droplet interface simultaneously disrupted the formation of silica based porous particles. 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 from the previously reported techniques where the transition of solid silica particle or shell to a porous silica shell was generally performed by surface-protected etching. In the previous dissolution-regrowth process, the cores were metal oxides or noble metal nanoparticles, and the products were limited to single-shelled hollow spheres or yolk-shell particles.…”

Hollow Silica Particles: Recent Progress and Future Perspectives

“…Figure 1 depicts the common approaches to HSP synthesis, while Figure 2 shows TEM images of HSPs synthesized using representative approaches. Not only have HSPs been created with a shell made of silica alone, but also hybrid HSPs with a shell made of two materials have been reported [56]. Wang et al used an aerosol-based method in which a solution of ferric chloride, CTAB, sucrose, and a TEOS solution in ethanol were used.…”

“…Additionally, HSPs filled with perfluoropentane gas were also employed as ultrasound contrast agents, whereby perfluorpentane generates the ultrasound signal and HSPs act as the gas carrier. Compared to the conventional liposomal or polymeric gas carriers, the HSPs showed longer in vivo stability and a better imaging lifetime [56,[97][98][99].…”

“…Not only have HSPs been created with a shell made of silica alone, but also hybrid HSPs with a shell made of two materials have been reported [ 56 ]. Wang et al used an aerosol-based method in which a solution of ferric chloride, CTAB, sucrose, and a TEOS solution in ethanol were used.…”