Optimizing dispersion of graphene oxide/carbon nanotube hybrids for enhanced performance in nano-engineered cement composites

The graphene oxide/carbon nanotube (GO/CNT) hybrid offers unparalleled synergistic advantages over individual GO or CNT reinforcements for enhancing the mechanical properties of nano-engineered cement composites. However, the dispersion mechanisms of GO/CNT hybrids in aqueous and cementitious systems remain poorly understood, and the influence of dispersing agents on cement matrix properties has not been fully elucidated. This study addresses these gaps by systematically investigating the dispersion behavior of GO/CNT hybrids and optimizing the performance of nano-engineered cement pastes using four dispersants: melamine, naphthalene sulfonic acid derivative, lignosulfonate, and polycarboxylate. Results reveal that dispersants significantly enhance the dispersion of GO/CNT hybrids, with polycarboxylate emerging as the most effective due to its dual electrostatic repulsion and steric hindrance effects, as well as its ability to chelate Ca²⁺ ions, thereby mitigating their detrimental charge screening and complexation effects on carbon nanoparticles. The dispersion performance is pH-dependent, with an optimal pH of 11.5. Additionally, dispersants improve the fluidity of fresh mixtures and enhance the mechanical properties of nano-reinforced pastes. Polycarboxylate dispersants, in particular, increase the compressive and flexural strengths of the plain matrix by up to 43% and 35%, respectively. The synergistic combination of GO/CNT hybrids and polycarboxylate dispersants also promotes cement hydration and refines both micro- and macro-pore structures. This study provides critical insights into the dispersion mechanisms of GO/CNT hybrids and establishes a foundation for the development of high-strength, nano-engineered cement composites, paving the way for their broader application in sustainable construction materials.