Preparation, Modification And Photocatalytic Decomposition Of Hydrogen From Hydrogen From Surface Plasmas - TiO 2 Nanoparticles

Titanium dioxide （TiO₂） is a widely used multifunctional ceramic material due to its excellent stability and physical-chemical properties as well as its unique orderly features. It is also a pioneering material to gas sensors, solar cells, and expecially as a photocatalyst for photocatalytic hydrogen production. In this paper, TiO₂ nanotube arrays （TiO₂ NTs） were successfully fabricated by electrochemical anodic oxidation. Then the Fe/TiO₂ NTs and Ce/TiO₂ NTs with different amounts of Fe ions and Ce ions were obtained by controlling the concentration of Fe（NO3）3 and Ce（NO3）3. Ag nanoparticles （Ag NPs） were deposited on Fe/TiO₂ NTs and Ce/TiO₂ NTs by microwave-assisted chemical reduction, Ag-Fe/TiO₂ NTs and Ag-Ce/TiO₂ NTs were obtained, respectively. The morphology features and some other properties of the samples were characterized by XRD, SEM, PL, UV-vis and Raman, respectively. Furthermore, the prepared Ag-Fe/TiO₂ NTs and Ag-Ce/TiO₂ NTs were applied in photocatalytic experiments to evaluate their photocatalytic activity. Finally, the mechanism of photocatalyst activity co-enhanced by SPR effect, transition metal and rare earth element was also proposed.The results showed that TiO₂ NTs were highly ordered and vertically aligned structure and the diameter the nanotube is around 150 nm, its thickness is around 25 μm. Ag NPs were uniformly attached on both the outside and inside of the TiO₂ NTs with metal state, and Ag NPs deposition process does not damage the ordered array structure of TiO₂ NTs. Compared with pure TiO₂ NTs, their light absorption spectrum of Fe/TiO₂ NTs, Ag/TiO₂ NTs, Ag-Fe/TiO₂ NTs and Ag-Ce/TiO₂ NTs move remardably with a red shift and Ag/TiO₂ NTs, Ag-Fe/TiO₂ NTs and Ag-Ce/TiO₂ NTs show a stronger photoabsorption in the visible region mainly due to the surface plasmonic resonance （SPR） effect of Ag NPs. The optimal value of Fe/Ti, Ce/Ti and Ag/Ti is 0.3 mM,0.3mM and 0.2mM, respectively. The depositing of Ag NPs could efficiently decrease the recombination rate of electron-hole pairs of TiO₂. The surface plasmon resonance effect of Ag NPs could strengthen the visible light response and enhance the absorption activity of TiO₂. Therefore, the sample 0.2mM Ag-0.3mM Fe/TiO₂ NTs and 0.2mM Ag-0.3mM Ce/TiO₂ NTs showed the best experimental results. The photocatalytic activity of TiO₂ NTs should be improved through loading with Ag NPs and doping with Fe ions and Ce ions, due to its higher visible absorption activity and lower electron-hole pair recombination rate. Moreover, the result of photocatalytic water splitting indicated that the highest hydrogen evolution rate and quantum efficiency of 0.2mM Ag-0.3mM Fe/TiO₂ NTs was 2.87 and 2.91 times bigger of the un-modified TiO₂ NTs, respectively, and the highest hydrogen evolution rate and quantum efficiency of 0.2mM Ag-0.3mM Ce/TiO₂ NTs was 3.12 and 3.21 times bigger of the un-modified TiO₂ NTs, respectively.The mechanism of SPR and transition metal, rare earth element co-enhanced TiO₂ photocatalysis was also preliminary elaborated. The results showed that co-modify TiO₂ can broaden the photoresponse to visible light, also facilitate these electrons transfer, then react with electron acceptors more easily, finally photocatalytic activity was enhanced effectively.