Fabrication of hollow SiO2 and Au (core)-SiO2 (shell) nanostructures of different shapes by CdS template dissolution

Core-shell silica (SiO2) coated CdS nanorods (NR) and nanospheres (NS) were prepared (SiO2@CdS) by deposition of a Si-O-Si amorphous layer over the CdS surface through the hydrolysis of 3-mercaptopropyltrimethoxysilane and tetraethylorthosilicate. Nanoporous SiO2 matrix (NPSM), hollow SiO2 nanotubes (HSNT) and nanospheres (HSNS) useful for efficient adsorption and catalytic processes were prepared by chemical dissolution of CdS-NS (size: 9-10 nm) and CdS-NR (length: 116-128 nm and width: 6-11 nm) template from SiO2@CdS with 2 M HNO3. These SiO2 nanostructures were characterized by optical absorption, TEM, EDX, SAED and BET surface area analysis. TEM images revealed the fabrication of slightly distorted HSNS (size: 9-12 nm) and closed HSNT (length: 30-45 nm and diameter: 9-14 nm) of shorter dimensions than the CdS-NR template used. The BET surface area (112-134 m(2) g(-1)) of NPSM and HSNS is found to be larger than the surface area (29-51 m(2) g(-1)) of SiO2@CdS composites indicating hollow SiO2 morphology. Silica coated Au (SiO2@Au) composites formed by CdS dissolution from Au (2 wt%) deposited CdS-NR core-encapsulated into SiO2 shell (SiO2@Au-CdS-NR) exhibited a surface plasmon band at 550 nm and displayed high catalytic activity for 4-nitrophenol reduction by Au nanoparticle.