Controlled Synthesis of Semiconductor PbS Nanocrystals and Nanowires Inside Mesoporous Silica SBA-15 Phase

Abstract

A new flexible approach is developed to fabricate uniform nanocrystals and nanowires of binary compound semiconductor PbS inside the channels of mesoporous silica SBA-15. The approach combines functionalization of the channel surface with thiol groups, absorption of Pb2+, and heating in N2 atmosphere at high temperature. The separate introduction of thiol groups and Pb2+ makes the loading of a binary compound efficient and as easy as the loading of a single element. The nanocrystals are uniform and their sizes (5 nm) are consistent with the diameter of mesoporous SBA-15. The diameter of the PbS nanowires is about 6 nm and the length is several hundred nanometers. TEM images first intuitively confirm the formation of binary sulfide nanocrystals and nanowires dispersing uniformly inside the channels of mesoporous SBA-15. The key for transition from nanocrystals to nanowires is to increase the amount of the Si−OH group on the channel surface of SBA-15, and ethanol extraction proves to be effective to keep large amount of Si−OH groups during removing of the block copolymer. A massive blue shift is observed in photoluminescence spectra, and this clearly shows the quantum size effects of the PbS nanocrystals and nanowires.