Au nanoparticle@hollow mesoporous carbon with FeCo/graphitic shell nanoparticls as a magnetically recyclable yolk\u2013shell nanocatalyst for catalytic reduction of nitroaromatics

Yonghoon Hong,In Ae Choi,Won Seok Seo

doi:10.1038/s41598-018-25795-w

Abstract

We have developed a highly stable and magnetically recyclable yolk–shell nanocatalyst for catalytic reduction of nitroaromatics. This nanocatalyst is composed of a ~13 nm Au nanoparticle encapsulated in a hollow mesoporous carbon (hmC) shell with a diameter of ~120 nm and a thickness of ~15 nm. The hmC shell contains ~6 nm FeCo/graphitic carbon shell (FeCo/GC) nanoparticles. We have synthesized the Au@hmC-FeCo/GC nanocatalyst by thermal decomposition of Fe and Co precursors in silica of a solid core/mesoporous shell structure containing a Au nanoparticle within the core, subsequent ethylene chemical vapor deposition (CVD), and then removal of the silica by treatment with aqueous HF. The Au@hmC-FeCo/GC has superparamagnetism and high saturation magnetization (29.2 emu g−1) at room temperature. It also shows a type IV sorption isotherm, typical for mesoporous carbon (pore diameter = 3.5 nm), thereby ensuring ready accessibility to the Au core by substrates. We have shown that the Au@hmC-FeCo/GC catalyses the reduction of 4-nitrophenol and 4-nitrotoluene more efficiently than Au nanoparticles do, can be separated very quickly from the reaction mixture using an magnet, and can be reused for the same reduction reaction at least five times without loss of the initial level of catalytic activity.

Highlights

Supported nanocatalysts, made by embedding metal nanoparticles (NPs) such as Au, Ag, Pd, and Pt on mesoporous supports, have attracted considerable attention for their high catalytic activities and efficiency toward various types of reactions, because they reduce aggregation between metal NPs and enable isolation and recovery of the very small metal NPs through filtration or centrifugation methods[4]
The common procedure used to synthesize hollow mesoporous carbon (hmC) is based on the growth of carbon inside the mesoporous silica shell and subsequent removal of the siliceous components by treatment with aqueous HF
We have found that the prepared carbon shells are thin and they include partially broken ones when the ethylene flow time is decreased to 15 min (Supplementary Fig. S2a)

Summary

Introduction

Made by embedding metal nanoparticles (NPs) such as Au, Ag, Pd, and Pt on mesoporous supports, have attracted considerable attention for their high catalytic activities and efficiency toward various types of reactions (e.g., hydrogenation, oxidation-reduction, reforming, and coupling1–3), because they reduce aggregation between metal NPs and enable isolation and recovery of the very small metal NPs through filtration or centrifugation methods[4]. Iron oxides are not desirable for certain applications because they are inherently unstable in acidic media[12,13], not inert in some catalytic processes[14,15,16], not very strong in magnetic properties (Ms of bulk magnetite ≤92 emu g−1)[17], and can provide an oxygen source in catalytic reactions, eventually giving unexpected product mixtures[18] To circumvent such problems, graphitic carbon-coated metal NPs with very strong magnetic properties have been used as magnetic materials for magnetically recoverable catalysis. Yao et al prepared yolk–shell composites with a movable iron oxide core and mesoporous silica shell, together with Pd NPs anchored on the inner silica surface[13], for the catalytic reduction of 4-nitrophenol These composites did not have a single catalytic NP inside the hollow mesoporous sphere, but instead, hosted some catalytic NPs in the void space of the yolk–shell structure.

Methods

Results

Conclusion