Synthesis And Visible-light Photocatalytic Properties Of TiO₂Nanotube Composites Loaded With Ag And Ag₃PO₄

With the increasingly serious energy depletion and environment pollution, it isurgent to develop a new way to utilize energy and improve environment.Photocatalysis process, as a prominent approach to exploit solar energy effectively,has received much attention recently, and showed huge potential in the field of energyutilization and environment improvement. Titanium dioxide (TiO2), as a photocatalystwith superior catalytic activity, non-toxity and high chemical stability, has been aresearch focus in the field of photocatalysis. However, TiO2is a wide band gap(anatase,3.2eV) semiconductor which can only absorb the UV light of λ＜387nm. Itseriously decreases the efficiency of solar energy utilization. In order to improve thevisible light photocatalytic activity of TiO2, in this dissertation, Ag/TNT andAg3PO4/TNT nanocomosites were synthesized by using TiO2nanotubes (TNT) as thesupport. The structure, morphology and chemical composition of thesenanocomposites were characterized by TEM, XRD, XPS, FT-IR and DRS. Moreover,their visible light photocatalytic property and corresponding mechanism inphotocatalytic process were studied in detail.Firstly, the3-(3,4-Dihydroxyphenyl) propionic acid (diHPP), which possesseshigh affinity for Ti4+and high reducing capacity for Ag+, was used to synthesizeAg/TNT nanocomposites. The characterization results show that Ag nanoparticlesabout3.77nm in diameter distribute over the TNT surface uniformly. Furhermore, itis concluded that the diHPP can serve not only as a reducing agent, but also a cappingagent to stabilize the Ag nanoparticle and hinder their agglomeration. By adjusting theconcentration of AgNO3solution, the loading amount of Ag on TNT can be controlled,and the visible light absorbtion ability of Ag/TNT enhances with the increasing Agloading amount. The visible light photocatalytic activity was evaluated by thedegradation capability of Rhodamine B (RhB). The result shows that the Ag/TNTnanocomposites possess high visible light photocatalytic activity, which canphotocatalytically degrade99.8%RhB in4hours. The results of mechanism studyindicate that the high visible light photocatalytic activity can be attributed to the LocalElectric Field caused by the Surface Plasmon Resonance (SPR) of Ag nanoparticles. Meanwhile, the high dye molecules adsorption of TNT caused by the large specificsurface area would further improve the photocatalytic activity.Secondly, the Ag3PO4/TNT nanocomposites were fabricated by an in situ growthmethod. The characterization results exhibit that Ag3PO4nanoparticles with uniformdiameter distribute over the TNT surface uniformly. Ag3PO4and TNT are combinedby the Ti-O-Ag bond, and the phenomenon of lattice integration between TNT andAg3PO4nanoparticles can be observed. By adjusting the concentration of AgNO3solution, the size of Ag3PO4can be controlled, and the higher concentration, thebigger size. The DRS result shows that the Ag3PO4/TNT nanocomposites have twokinds of band gap. The photocatalytic activity evaluation results indicate that theAg3PO4/TNT nanocomposites show a high visible light photocatalytic activity, whichcan be ascribed to the efficient separation of electron/hole pairs. The photocatalyticprocess study conclude that the hole (h+) and hydroxyl radical (OH) take animportant role in visible light photocatalytic process.