Ordered mesoporous graphene for heterogeneous catalysis; Control oversize, shape and ordering

Abstract

Graphene derived materials are an interesting novel class of materials, due to their uniqueproperties which can be utilized in a variety of applications. Currently, these materialsare used in applications such as, displays, filters, electronics and catalysis. The synthesisof ordered mesoporous graphene has however shown to be challenging in the past, dueto the inherent amorphous nature of the porous structure of prior synthetic methods.Additionally, control over size, shape and consistency of the ordered mesopores in thesemethods was lacking.In this master thesis, a novel synthetic route for producing ordered mesoporous grapheneis presented. We show that by using monodisperse nanoparticles (NPs) coated with c-18alkyl chain ligands as building blocks for self-assembly (SA) template, an ordered meso-porous graphene structure can be produced. Additionally, we investigate the use of differentsizes, shapes, compositions and orderings of the template NP building blocks in this work.To investigate the possibilities in variation of size and shape of the porous structure,7-13 nm spherical FexOyNCs with a polydispersity of<7%, 22 nm rounded and sharpcubic FexOy/CoFe2O4NCs with a polydispersity of 9% were prepared using a thermaldecomposition method. These monodisperse NCs showed capable of self-assembling intosimple crystal structures such as face centered cubic and simple cubic. After two heat-treatment steps for carbonization and graphitization of the ligands and etching the NPs,the synthetic route showed the preservation of shape and size of the pores. Physisorptionresults of the OMG structure templated with 7 nm iron oxide NCs showed a monodispersepore structure of 4 nm with interconnecting pores of 2 nm.To explore the tunability of the ordering of pores, the SA process was sphericallyconfined using slowly drying emulsion droplets, giving rise to non-bulk crystalline structurescalled supraparticles (SPs). These SPs were confirmed to have icosahedron structure, whichhas a characteristic 5-fold symmetry and varies slightly depending on the amount of NPspresent during SA. After carbonization, etching and graphitization, it was clear that thisstructure could also be retained, opening up many pathways to prepare ordered structuringof pores different from bulk SA.In addition to the synthesis of ordered mesoporous graphene, several experiments fortheir application in heterogeneous catalysis were conducted. These experiments showedthat the NC template could be partially etched to have an active catalytic material, suchas Fe3O4or Fe, readily present in the ordered structure.Besides metal oxide template, also silica NP templates were attempted. These experi-ments showed the challenges of carbonization of ligands combined with monodisperse NPsynthesis, stable drying of self-assembled structures and the stability of the carbon walls.We found that iron content and the porous structure have a large positive influence onthe carbonization process of hydrocarbon ligands. Additionally, we found that for NPs of∼44 nm in diameter, the amount of carbon surrounding the NPs as ligands is not enough,resulting in a collapsed structure.