A review of geopolymer and its adsorption capacity with molecular insights: A promising adsorbent of heavy metal ions

Due to severe consequences of the heavy metal ions (HMIs) accumulation in organisms throughout the aqueous phase, HMIs pollution treatment has received extensive attention. Geopolymer materials (GPMs) have been proposed as promising adsorbents for HMIs treatment due to its prominent production convenience, low cost, and environmental protection compared to traditional treatment methods. Various advanced experimental techniques have been adopted to observe the GPMs removal process and study their nanomechanical properties. However, some intricate material characteristics, including ion movement and the monitored reaction process of the targeted molecule, which are critical to the removal performance, still require fundamental investigation through molecular dynamics simulation. This paper summarizes the current research on GPMs for HMIs treatment, including how the GPMs adsorption capacity is influenced by solid raw materials, GPMs modalities, pH value, temperature, adsorbent dosage, ions concentration, and HMIs coexistence. The suitable production and application conditions of GPMs have been emphasized as: the 10 g/L porous geopolymer spheres with a Si/Al ratio below 2 are applied in the environment where pH value is about 7 under room temperature. The porous geopolymer spheres could be recycled as aggregates for lightweight building materials production that could also provide a second immobilization of adsorbed heavy metal ions. Compared with some nanomaterials with a surface area that could reach 2000 m²/g, although the surface area and adsorption capacity of GPMs is lower, the low cost with 0.0001$/g and convenient production method of GPMs attract wide attention from all over the world. Except of the suitable production and application conditions, the GPMs adsorption capacity could also be enhanced through molecular dynamics (MD) simulation method. MD simulation is used for modeling the removal behavior of HMIs by GPMs. With an emphasis on MD simulation studies associated with GPMs, the construction of an atomistic model, the selection of a forcefield, the dynamic simulation and analysis of HMIs removal are reviewed. The challenges and future perspectives of the application of molecular dynamics simulation when investigating the removal behavior of GP are thoroughly discussed, demonstrating the superior capability of the atomistic approach in optimizing the removal performance and guiding direction for the development of HMIs removal techniques.