Relation between chemical reduction and crystalline growth in mixtures of low-dimensional NiO and reduced graphene oxide

[Display omitted] •Nano-level process differences between CTR and GTR are not understood.•Relationship between crystalline growth and chemical reduction is investigated.•Crystalline growth of RGO and NiO took precedence.•Above the threshold, drastic Ni formation (chemical reduction) was observed. The carbothermal and graphenothermal reduction of metal oxide and graphite or graphene systems are critical for obtaining pure metals and designing new energy materials. However, the nano-level differences between these processes have not been investigated in detail. Herein, we investigate the relationship between crystalline growth and chemical reduction during the heat-treatment of reduced graphene oxide (RGO) and NiO nanoparticles. The heat-treated RGO/NiO mixtures exhibit complex interactions. Below a critical NiO concentration, the crystalline growth of RGO and NiO take precedence. Above this threshold, drastic Ni formation occurs by the chemical reduction of NiO. This demonstrates a concentration-dependent competitive relationship between chemical reduction and crystalline growth. Two factors require further study, namely, the low-dimensional shape/contact-dependent chemical reactivity between RGO and NiO, and the thermodynamic size-dependent driving force for crystalline growth of individual RGO and NiO crystals.