Theoretical Studies of Adsorption Reactions of Aluminosilicate Aqueous Species on Graphene-Based Nanomaterials: Implications for Geopolymer Binders

Geopolymer nanocomposites incorporating carbon nanotube (CNT)/graphene-based nanomaterials have become an exciting area of research because of their exceptional interface compatibility, providing improved mechanical, electrical, and thermal properties for next-generation construction materials. Accordingly, geopolymers are superior candidates for the implementation of graphene-based nanocomposites. In this paper, a comprehensive examination through equilibrium density functional theory (DFT) with and without the contribution of van der Waals (vdW) dispersion interaction, along with ReaxFF molecular dynamics (ReaxFF-MD) computational modeling approaches, was carried out to comprehend the interaction mechanisms and adsorption energies between graphene-based nanosheets and primary aqueous species of geopolymer structure. Results showed that the interaction of Si(OH)(4 )aqueous species with the pristine graphene substrate has the weakest physical binding adsorption. The adsorption energy of silicate species on the pristine graphene substrate increased when involving interactions with sodium or potassium cations. Graphene-based nanomaterial surface functionalization with hydroxyl or carboxyl groups led to the higher adsorption energies of silicate and aluminate species due to the stronger electrostatic interaction. Computations also revealed that Na+, compared to K+, mostly increased the interfacial binding between the geopolymer and CNT/graphene-based nanomaterials. The computed MD results exhibited some qualitative agreement with ab initio calculations (at 0 K), with an overestimation tendency as expected due to the contribution of kinetic energy at 300 K. DFT results refute literature assumptions of a covalent oxo-bridging bond between silicon and carbon atoms, confirming electrostatic interactions (Coulomb interaction), with van der Waals (vdW) dispersion forces also playing a significant role in adsorption energy. Our study provides a systematic quantification of missing binding energy parameters and their implications for upscaling interface effects to the nanocomposite level.