Preparation And Photocatalytic Water Splitting Properties Of The Thin Film Photocatalysts Of NaTaO₃

Nowadays, due to the consumption of huge amount of fossil fuel, environment pollution and the energy crisis have become crucial issues. A great number of laboratories have been devoted themselves to search for clean and renewable energy source for sustainable development. One of the most interesting routes to produce renewable H2 with high purity and without CO2 emissions is the photocatalytic water splitting using solar light as energy source.Among these photocatalysts, Na Ta O3 has relatively high photocatalytic activity. It has been observed that the perovskite phase of Na Ta O3 exhibits high efficiency in water splitting. When under the UV irradiation, the electrons and holes will be separated of Na Ta O3, then reduction and oxidation with water to liberate hydrogen and oxygen. However, the traditional powdered photocatalysts have some disadvantages: First, in the process of water splitting, the powdered photocatalysts must be dispersed into the water. So those photocatalysts on the top must be block the lights illuminate to the underlying photocatalysts. So it may be decrease the gas production. The water will be polluted and the powdered photocatalysts are not easy to recycle use again; Furthermore, those powdered photocatalysts can’t be liberating H2 and O2 separately from H2O; Finally, the producing hydrogen site and oxygen site are all on the surface of the powdered photocatalysts. That may be lead to the secondary compound of hydrogen and oxygen atoms.Based on the above shortcomings of the traditional powdered photocatalysts, we made the modification of Na Ta O3. Firstly, we choose Ti foil as substrate to prepare Ti/Na Ta O3(Ni O) thin film photocatalysts, so that we can get the photocatalysts can easy recycling and pollution-free. Secondly, the thin film photocatalysts of Ti/Na Ta O3(Ni O) is improved. The p-i-n junction and Na Ta O3(Ni O) are combined with each other first time. That can form a novel thin film photocatalysts of Ti/TNTs/N-I-P/Na Ta O3(Ni O), which can separate the evolution gas of H2 and O2 into the different sides of the Ti substrate. So that it can inhibit the recombination of the generating oxygen and hydrogen atoms, when compared with the traditional powdered photocatalysts. The main work of this paper is as follows:(1) We take the Ta2O5 and Na2CO3 as reaction materials. The Na Ta O3 powders prepared by high temperature solid phase method, and then loaded Ni O on it by photo-deposition method. We choose Ti foil as the substrate to prepare Ti/Na Ta O3(Ni O) thin film photocatalysts by silk-screen process. We found that we can get the highest water splitting activity when the reaction precursor’s concentration of Ni(NO3)2 is 0.5 M. The photocatalytic activities of the Ti/Na Ta O3(Ni O) thin film photocatalysts is improved to 1.50 μmol/h·cm2 in Na OH solution(PH=13).(2) We chose Ti foil as the substrate to prepare of Ti O2 nanotubes as electrical conduction layer(defined as TNTs). Then the Ti O2 nanoparticles layer(defined as N) is sensitized by Pb S quantum dots(defined as I), and the Ni O film(defined as P) is coated on the top of N-I layers, this sample order can form p-i-n junction structure. That p-i-n junction is growed on the top of the TNTs layer. This nanostructure is defined as Ti/TNTs/N-I-P. Then covered Na Ta O3(Ni O) on the top of the p-i-n junction structure. This thin film photocatalysts nanostructure is defined as Ti/TNTs/N-I-P/Na Ta O3(Ni O). The electronic conduction layer of Ti O2 nanotubes and p type semiconductor layer Ni O are investigated to find out the best preparation conditions. We found that we can get the best crystallinity Ti O2 nanotubes when the anodic oxidation time is 1 h and the length is about 1.5 μm. For the Ni O p-type semiconductor layer, we found the best heat treatment temperature is 400 ℃. Finally, the photocatalytic activities for water splitting are carried by the different thin film photocatalysts. We found that the Ti/TNTs/N-I-P/Na Ta O3(Ni O) thin film photocatalysts has the highest activity is 9.13 μmol/h·cm2, which is 7 times higher than that of Ti/Na Ta O3(Ni O) film photocatalysts.