Nanoscale insight into the reconstruction reaction mechanism of alkali-activated silicate materials

As a green alternative to cement-based materials, alkali-activated silicate materials (AASM) have garnered attention for their ability to reduce greenhouse gas emissions and efficiently utilize industrial waste. During AASM preparation, Si monomers such as [SiO2(OH)2]2-, [SiO(OH)3]-, Si(OH)4 play a crucial role in governing the formation rate and unique gel structure of AASM. Despite their widespread use in construction, the microscopic mechanism of Si monomer formation from reactive SiO2 groups via reconstruction reactions (RR) remains unclear. This study comprehensively explored the structural transformations, formation pathways, and electron transfer mechanisms of Si monomers in AASM gels during RR using molecular dynamics (MD) simulations and first-principles calculations. We identified six distinct formation pathways for three Si monomers, with SiO2 -> SiO2H2O -> SiO2(H2O)2 -> SiO(OH)2H2O exhibiting the highest energy barrier of 16.61kJ/mol. Further analysis revealed a correlation between energy barriers and orbital hybridization strength, providing new insights into Si monomer formation mechanisms in AASM. This lays a solid foundation for optimizing AASM's preparation and enhancing its performance, further promoting the environmental friendliness and efficient utilization of AASM.