Regulation of hierarchically porous structures based on multi-scale nanosheets derived from kaolinite for enhanced adsorption

Abstract Hierarchically porous structures were regulated based on the size and surface charge by adjusting the ratios of silica and γ-AlOOH nanosheets (SiNSs and AlNSs). Above multi-scale nanosheets were derived from layered kaolinite via a selective etching-assisted exfoliation and the subsequent hydrothermal approach, respectively. The diverse structures and surface properties of as-prepared hierarchically porous nanosheets (HPNSs) were studied. As a result, the broad-ranged surface areas (217–544 m2/g) and pore volumes (0.49–2.24 cm3/g) of HPNSs are significantly greater than that of as-received kaolinite (23 m2/g and 0.22 cm3/g). The composition, pore structure and Zeta potential analysis reveal the different contributions of SiNSs and AlNSs to the hierarchical micro/meso/macroporous structure based on the steric hindrance effects of multi-scale nanosheets with electrostatic repulsion (pH = 8.5), while the surface charges of as-prepared HPNSs under neutral conditions are originated from the competition between negatively charged Si−OH (SiNSs) and positively charged Al−OH (AlNSs). The adsorption tests toward Congo red anionic dye show larger sorption capacities of the kaolinite-based HPNSs (63–786 mg/g) than that of natural kaolinite, and fast kinetic (within 30 min), further indicating the favorable adsorption characteristics of HPNSs due to the surface Al−OH groups (electrostatic attraction) and the hierarchically porous structures (physisorption and transfer). It exhibits the great potential of diverse kaolinite-based HPNSs as advanced functional materials in the fields of adsorption, separation, catalysis, energy storage and conversion, and biomedicine.