Nanocrystal Growth on Graphene with Various Degrees of Oxidation

TL;DR

This study presents a versatile two-step method for growing nanocrystals of iron group elements on graphene with different oxidation levels, demonstrating how surface chemistry influences nanocrystal morphology and growth behavior.

Contribution

The paper introduces a novel approach to control nanocrystal growth on graphene by tuning its surface oxidation state and reaction temperature, enabling tailored nanomaterial morphologies.

Findings

Nanocrystals grow differently on low-oxidation and highly oxidized graphene.

Adjusting temperature influences nanocrystal size and shape.

Surface chemistry of graphene controls nanocrystal nucleation and growth.

Abstract

We show a general two-step method to grow hydroxide and oxide nanocrystals of the iron family elements (Ni, Co, Fe) on graphene with two degrees of oxidation. Drastically different nanocrystal growth behaviors were observed on low-oxidation graphene sheets (GS) and highly oxidized graphite oxide (GO) in hydrothermal reactions. Small particles pre-coated on GS with few oxygen-containing surface groups diffused and recrystallized into single-crystalline nickel hydroxide Ni(OH)2 hexagonal nanoplates or iron oxide Fe2O3 nanorods with well defined morphologies. In contrast, particles pre-coated on GO were pinned by the high-concentration oxygen groups and defects on GO without recrystallization into well-defined shapes. Adjusting reaction temperature can be combined to further control materials grown on graphene. For materials with weak interactions with graphene, increasing the reaction temperature can lead to diffusion and recrystallization of surface species into larger crystals even on highly oxidized and defective GO. Our results suggest an interesting new approach to controlling the morphology of nanomaterials grown on graphene by tuning the surface chemistry of graphene as substrates for crystal nucleation and growth.