Biotin molecules on nitrogen-doped carbon nanotubes enhance the uniform anchoring and formation of Ag nanoparticles

An efficient method for anchoring silver nanoparticles (Ag-NPs) on the surface of nitrogen-doped multi-walled carbon nanotubes (CNx-MWCNTs) is reported. The process involves the attachment of biotin molecules on the surface of CNx-MWCNTs (both, pristine and acid treated) that act as a reducing agent for AgNO3, thus generating an efficient and homogeneous coating of Ag-NPs (∼3 nm in diameter). The reduction of AgNO3 on either pristine CNx-MWCNTs or acid treated CNx-MWCNTs (without biotin) results in Ag-NPs of large diameters and size distribution, in addition to a low anchoring efficiency. We confirmed that the use of biotin substantially improves the Ag-NPs anchoring efficiency, especially on acid treated CNx-MWCNTs. In order to elucidate the mechanism whereby Ag-NPs strongly bind to the surface of CNx-MWCNTs, density functional theory (DFT) calculations were carried out. These revealed the existence of covalent bonds established between one side of the biotin molecule and the CNx-MWCNT surface through oxygen atoms, leaving accessible the exposed sulfur atoms at the other end, which further provided an excellent interaction with the Ag-NPs via S-Ag bonds. Finally, we demonstrate that these Ag-NPs coated CNx-MWCNTs could be used as efficient sensors of CS2.