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

Hierarchically porous structures were regulated based on the size and surface charge by adjusting the ratios of silica and gamma-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 m(2)/g) and pore volumes (0.49-2.24 cm(3)/g) of HPNSs are significantly greater than that of as-received kaolinite (23 m(2)/g and 0.22 cm(3)/g). The composition, pore structure and Zeta potential analysis reveal the different contributions of SiNSs and A1NSs to the hierarchical micro/meso/macmporous 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.

Automated summary

Hierarchically porous structures were created by regulating the size and surface charge through adjusting the ratios of silica and gamma-AlOOH nanosheets. These hierarchically porous nanosheets showed significantly greater surface areas and pore volumes compared to natural kaolinite, leading to higher adsorption capacities for Congo red dye. This study highlights the potential of diverse kaolinite-based hierarchically porous nanosheets as advanced functional materials in various fields.