Fabrication Of Platinum Modified TiO₂Nanotube Array Films And Their Photocatalytic Activity

Rencently, pollution has been increasingly serious due to masses of home scrap and industrial waste.Among numbers of pollutant-degrading semiconductors, TiO₂array nanostructures, particularly TiO₂nanotube arrays fabricated by anode oxidation, have draw much attention owing to their strong oxidbillity,excellent mechanical and chemical stability, environmental innocuity and low cost. At the same time, as alarge-band-gap semiconductor, TiO₂can only be excited by UV irradiation wavelength under400nm, andthe recombination rate of photogenerated electron–hole pairs is high, which limit their further applicationto a great extent.For the aim of extending the photoresponse and reducing the recombination rate of TiO₂, many effortshave been put on modification. Nobel metal deposition is one of the most widespreaded method. In thiswork, we deposit nobel metal onto the catalysis, and the photocatalytic activities as well as photoelectricresponsibility were tested.Firstly, Pt-TiO₂were prepared respectively by hydrothermal method and photoassisted method. Theresult showed that Pt modification by photoassisted can largely enhance photodegradation rate andphotoresponsibility of semiconductor; comparing to that, modification by sol-gel distribute Ptnanoparticles less evenly than former method. So the activities of photoassisted is better than that ofsol-gel method. According to this, we take photoassisted as the deposition method in the follow-up tests.Secondly, series parameters such as photoassisted time, amount of deposition, heattreat temperature,and calcination atmosphere were generally investigated.Nevertheless, after annealed under different atmospheres at different temperatures, Pt nanoparticlesdeposited on TiO₂exhibited distinct form of existences which played an important role of catalyticactivities of TiO₂. Viewed from SEM, FE-SEM and HR-TEM, TiO₂still maintained tube-structure after Ptdeposition; on the HR-TEM and the sideview of FE-SEM it can be seen that Pt nanoparticles graduallygrowed along with calcination temperature arises; and XRD tests displayed that crystal form also tend tobecome more regular. XPS confirmed that Pt was indeed deposited onto TiO₂and existed in variousvalence states after annealed under hydrogen at different temperatures, yet the existence form of Pt varies with different treatments. Experiments of photocatalytic methyl orange （MO） degradation andphotoelectric responsibility further improved XPS analysis and indicated that sample with nulvalent anddivalent Pt formed by hydrogen heattreat under200oC presented the best catalytic activities. After heatedat500oC under hydrogen Pt nanoparticles existed by nulvalent and aggregated together, resulting specificsurface decreased and so did the active spot; thereby, photocatalytic activities lowered down significantly.