Photocatalytic properties of V2O5/TiO2 Nanoheterostructure films prepared by sparking method

Abstract

Photocatalysis is widely studied to solve water scarcity in some countries which an increasingly serious problem. This process is clean and provides great products for environment. The designs of porous morphologies and composite with metal oxide into titanium dioxide (TiO2) films have been an effective way to improve photocatalytic efficiency. Therefore, in this research we studied the photocatalytic performance of porous vanadium pentoxide/titanium dioxide (V2O2/TiO2) nanoheterostructure films prepared by the one-step sparking method. The first part focuses on the concentration of vanadium in films, which annealed at 400 °C, to improve the uniformity of films prepared by the sparking method at room temperature and atmospheric pressure. The atomic ratios of titanium/vanadium (TiV) on films were observed at 4:1, 2:1, 1:1, and 1:2 for TiV-1, TiV-2, TiV-3, and TiV-4 samples, respectively. The as-deposited films had the porosity morphology of small particles for all prepared films, which the average secondary particle sizes increase with enhancing the proportion of vanadium. The existence of V4+ in V2O5/TiO2 nanoheterostructure films had an importance effect on photocatalytic efficiency. The energy band gap of all prepared films was reduced by increasing of vanadium portion and obtained at 3.28. 3.12. 2.84, 2.63. 2.56, and 2.32 eV for TiO2, TiV-1, TiV-2, TiV-3, TiV-4, and V2O5 films, respectively. Furthermore, TiV-3 sample, which Ti/V atomic ratio approximately 1:1, presents the highest degradation rate of methylene blue solution (MB) and large interface heterojunctions. The degradation rate of MB increased by 24% and 30% when compared with pure TiO2 and V2O5 films, respectively. Thus, this work provides the method, which can produce V2O5/TiO2 nanoheterostructure films in one step and can potentially apply to photocatalytic applications. In the second part, the V2O5 TiO2 nanoheterostructure films were fabricated on quartz substrates by a sparking method using a strong external magnetic field (0.5 T) with a different arrangement of magnetic flux. The effect of magnetic flux direction on V2O5/TiO2 films was investigated by placing the substrates on south, north, parallel, and 45 degrees of the magnetic poles, which were labeled as TVS, TVN, TVP, and TVH respectively. The samples, which pre- and post-annealed at 400 *C for one hour at atmospheric pressure without applying magnetic field during sparking were labeled as TV and TVA, respectively. The SEM images display that placing the substrates in different directions of the magnetic field clearly affects the morphology of composite films. TVP and TVH samples, which are positioned more strongly influenced by the magnetic force, show arrangement of particles along magnetic field lines, while TVN and TVS are evenly distributed. The TiO2 (anatase/ rutile) phase and V2O5-VO2 modification phase were fabricated that confirmed by Raman spectroscopy, and XPS results without the annealing process. we assumed that the phase transformation from amorphous to crystalline film is the result of the applied magnetic field during the parking process. The energy band gap (Eg) of TV, TVH, TVP, TVN, TVS, and TVA were obtained to 2.90, 2.45, 2.68, 2.70, 2.78, and 2.60 eV, respectively, which was modified by the strong magnetics field. The TVH sample show the highest photocatalytic performance up to 41%, which was a 30 % and 270% compared to the without magnetic fields TVA and TV samples, respectively after 1- hour visible light irradiation. This works offers an interesting approach to developing film synthesis without annealing process.