Interlayer engineering in 3D graphene skeleton realizing tunable electronic properties at a highly controllable level for piezoresistive sensors

Three-dimensional (3D) graphene is a promising active component for various engineering fields, but its performance is limited by the hidebound electrical conductivity levels and hindered electrical transport. Here we present a novel approach based on interlayer engineering, in which graphene oxide (GO) nanosheets are covalently functionalized with varied molecular lengths of diamine molecules. This has led to the creation of an unprecedented class of 3D graphene with highly adjustable electronic properties. Theoretical calculations and experimental results demonstrate that ethylenediamine, with its small diameter acting as a molecular bridge for facilitating electron transport, has the potential to significantly improve the electrical conductivity of 3D graphene. In contrast, butylene diamine, with its larger diameter, has a reverse effect due to the enlarged spacing of the graphene interlayers, resulting in conductive degradation. More importantly, the moderate conductive level of 3D graphene can be achieved by combining the interlayer spacing expansion effect and the π-electronic donor ability of aromatic amines. The resulting 3D graphene exhibits highly tunable electronic properties, which can be easily adjusted in a wide range of 2.56–6.61 S·cm⁻¹ compared to pristine GO foam (4.20 S·cm⁻¹). This opens up new possibilities for its use as an active material in a piezoresistive sensor, as it offers remarkable monitoring abilities.