Synthesis of hollow PbS nanospheres in pluronic F127/cyclohexane/H 2O microemulsions

Abstract

A block copolymer microemulsion based approach is reported for the synthesis of hollow PbS nanospheres with a wall thickness of about 40 nm. The synthesis is achieved by the reaction of lead acetate (Pb(Ac) 2) with the S 2− ions released slowly from thioacetamide (TAA) in the amphiphilic triblock copolymer F127/cyclohexane/H 2O microemulsions at room temperature. It has been revealed that a F127 concentration range is required for the formation of hollow PbS nanospheres, and the diameter of the obtained hollow spheres increases with increasing F127 concentration from 1.32 × 10 −3 to 2.65 × 10 −3 mol/L. The addition of cyclohexane makes both the diameter of hollow spheres and the amount of PbS particles in the sphere cores decrease. Increasing the temperature of the microemulsions can significantly decrease the diameter of hollow spheres. The hollow PbS nanospheres can be produced only when the molar concentration ratio of Pb(Ac) 2 to TAA is equal to or larger than 1:1. When Pb(NO 3) 2 is used as the lead source instead of Pb(Ac) 2, no hollow PbS nanospheres can be obtained due to the dissolution of PbS by the byproduct HNO 3. A template mechanism is proposed for the formation of hollow PbS nanospheres. The complex microemulsion droplets formed by F127 microemulsion droplets and Pb 2+ act as soft templates for the precipitation of PbS particles around the surface of the spherical aggregates, which results in final hollow PbS nanospheres.