Effect of Polymer Removal on the Morphology and Phase of the Nanoparticles in All-Inorganic Heterostructures Synthesized via Two-Step Polymer Infiltration.

Diana Berman,Yuchen Sha,Elena V Shevchenko

doi:10.3390/molecules26030679

Abstract

Polymer templates play an essential role in the robust infiltration-based synthesis of functional multicomponent heterostructures with controlled structure, porosity, and composition. Such heterostructures are be used as hybrid organic–inorganic composites or as all-inorganic systems once the polymer templates are removed. Using iron oxide/alumina heterostructures formed by two-step infiltration of polystyrene-block-polyvinyl pyridine block copolymer with iron and aluminum precursors from the solution and vapor-phases, respectively, we show that the phase and morphology of iron oxide nanoparticles dramatically depend on the approach used to remove the polymer. We demonstrate that thermal and plasma oxidative treatments result in iron oxide nanoparticles with either solid or hollow morphologies, respectively, that lead to different magnetic properties of the resulting materials. Our study extends the boundaries of structure manipulations in multicomponent heterostructures synthesized using polymer infiltration synthesis, and hence their properties.

Highlights

Polymer templates have been widely used for the design of a broad range of functional composite materials and all-inorganic structures [1,2,3,4]
We aim to explore to what extent the polymer removal step affects the structure, size, and morphology of NPs in all-inorganic heterostructures synthesized via a two-step infiltration approach
Our study provides insights into the effect of polymer removal on the hybrid structures obtained via a two-step infiltration process by combining swelling-based infiltration (SBI) of iron oxide and sequential infiltration synthesis (SIS) of aluminum oxide

Summary

Introduction

Polymer templates have been widely used for the design of a broad range of functional composite materials and all-inorganic structures [1,2,3,4]. Thermal annealing and ultraviolet ozone treatment are the most common techniques used for polymer removal in structures synthesized by sequential infiltration synthesis (SIS). The selection of the polymer removal technique is usually made considering mainly acceptability of the residual carbon and stability of the substrate that was used for the growth of conformal coating or structure by SIS [21]. Previous studies on alumina synthesized by SIS and based on the infiltration of polymer block copolymers (BCPs) with trimethylaluminum (TMA) did not reveal a difference in alumina structures obtained by UV ozone treatment and thermal annealing polymer removal [26]. Our recent study on the synthesis of porous all-inorganic PdOx/alumina nanoheterostructures indicated that the technique used for polymer template removal drastically affects the size of the PdOx nanoparticles (NPs) uniformly distributed in the alumina matrix [16]

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