α-calcium sulfate hemihydrate with a 3D hierarchical straw-sheaf morphology for use as a remove Pb²⁺ adsorbent

Novel three-dimensional hierarchical α-calcium sulfate hemihydrate with a straw-sheaf morphology (3D α-HH straw-sheaves) are synthesized successfully in glycerin aqueous solution by a simple one-pot method, using as an efficient adsorbent for Pb²⁺ removal from water. The 3D straw-sheaf morphology, that closely depends on the glycerin/water volume ratio (V_Gly/V_H2O), can be accurately fabricated only when V_Gly/V_H2O is not lower than 3/1. 3D α-HH straw-sheaves are generated via multistep-splitting growth coupled with self-assembly. The obtained 3D α-HH straw-sheaves are further used as an adsorbent to remove Pb²⁺ from water, exhibiting excellent Pb²⁺ removal performance with an equilibrium adsorption capacity of 79.19 mg_Pbg_α-HH^-1 and removal efficiency of 98.98%, that both higher than those of plate- and columnar-like α-HH. Moreover, the experimental adsorption data for the 3D α-HH straw-sheaves is well fitted with pseudo-second-order kinetic model, and the adsorption isotherm is in good agreement with Langmuir model. The Pb²⁺ adsorption mechanism is thought to be a chemical adsorption process enforced by chemical bonding and ion exchange. This work demonstrates that 3D α-HH straw-sheaves are highly promising in removing Pb²⁺ from wastewater, thereby broadening the research field for the practical application of gypsum-based materials.