Novel sulfur-doped niobium pentoxide nanoparticles: fabrication, characterization, visible light sensitization and redox charge transfer study

Novel sulfur-modified niobium(V) oxide nanoparticles (SNON) that firstly exhibited good visible light sensitization were fabricated by a modified sol-gel technique using a very stable sol containing niobium(V) chloride, oxalic acid, isopropanol as chelating agent and thiourea as sulfur source. The resulting S-doped Nb2O5 nanomaterials were characterized by cyclic voltammetry (CV), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDAX), scanning electron microscope (SEM), ultra-violet diffuse reflectance (UV-DRS) and thermogravimetry thermal Analysis (TG-DTA). As against the response of unmodified niobium(V) oxide nanoparticles (UNON), the doped samples show different electrochemical response indicating an induced charge transfer across the niobium pentoxide/solution interface, thus forming two anodic peaks and a cathodic peak. This important observation was confirmed by UV-DRS in terms of band bending due to sulfur doping. Upon sulfur-modification, the absorption edge extends into the visible light region. The SEM observation shows that the SNPN existed in the mode of polycrystalline structure and the average grain size 63 nm. The EDAX analysis of undoped Nb2O5 and sulfur doped Nb2O5 shows the Nb2O5 (98%) and S (2%) content of nanopowder. These SNON nanoparticles are expected to be suitable candidates as visible light niobium(V) oxide nanoparticles sensitization.