Three-dimensional reduced graphene oxide support from spheric CaCO3 as sacrificial template applied to in-situ growth of HKUST-1 metal-organic framework

Three-dimensional (3D) composite materials have been recently investigated due to their excellent intrinsic properties and characteristics such as a self-sustained structure, porosity, and high specific surface area. 3D reduced graphene oxide (rGO) materials can be used to improve some properties of the other materials or compounds. An attractive approach is to use rGO aerogels as support of metal-organic frameworks (MOFs), leading to improvement in electrical, mechanical, adsorptive, and thermal properties. This paper presents a 3D structure made of a composite of rGO and HKUST-1 MOF where the pore morphology of the support was controlled by using spherical calcium carbonate as a sacrificial template covered with GO through a layer-by-layer method. After a thermal treatment and removal of the sacrificial template, a rGO porous monolith was obtained. This rGO monolith was used as a support in a solvothermal process to grow the HKUST-1 framework in situ within its pores and on its surface. The same procedure was repeated at three different synthesis times. The obtained materials were characterized by several techniques: infrared and Raman spectroscopies, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and physisorption analysis using N₂. The results confirmed the presence of HKUST-1 within the 3D rGO support. The HKUST-1 crystals in these supports maintained the characteristic octahedral shape of the MOF on the monolith's surface. However, it is important to note that the growth of the HKUST-1 was affected inside the three-dimensional porous structure.