Quaternary Phosphonium Modified Hierarchically Macro/Mesoporous Silica for Fast Removal of Perrhenate

A new quaternary phosphonium modified hierarchically macro/mesoporous silica (named HPS-P) was prepared by a sol–gel method accompanied by phase separation by using PEG-10000 as surfactant and tetramethoxysilane as silicon source, followed by reacting with quaternary phosphonium. The resultant HPS-P containing large macroporous skeleton with an average diameter of 0.67 μm and mesopores with an average diameter of 10.3 nm has a specific area of ca. 254.7 m2 g–1. The adsorption of HPS-P for ReO4 – was investigated, and the adsorption equilibrium could be achieved within 1 min; the adsorption isotherm data for ReO4 – could be well fitted with a modified Langmuir model. Moreover, HPS-P has excellent adsorption selectivities toward ReO4 – with competing anions, including NO3 –, SO4 2–, and Cl–. The ΔH Θ and ΔS Θ of the Cl–/ReO4 – ion-exchange reaction of HPS-P were calculated to be −4.5 kJ mol–1 and 12.6 J mol–1 K–1, respectively, indicating that the adsorption of ReO4 – onto HPS-P is a spontaneous physical adsorption process. In dynamic column experiment, HPS-P could be recycled by 2.2 mol L–1 HNO3 with a good performance within 3 min. IR and XPS analysis confirmed that the adsorption mechanism is ion-exchange.