Preparation, Characterization And Phtocatalytic Hydrogen Evolution Of NaNbO₃under Different Atmospheres

Since the21st century, environment and energy issues are the main problems for human being. Hydrogen, which is known as "future oil", has been identified as a green energy because of its prominent properties, such as abundant raw materials, high fuel value and no secondary pollution. Hydrogen have widely attracted interest and investigation for addressing energy crisis due to its high energy capacity and environmental friendliness.The technology of semiconductor-based photocatalytic water splitting to produce hydrogen using solar energy has been considered as one of the most important approaches to achieving sustainable development. NaNbO3is a well-known perovskite oxide with unique physical and chemical properties, such as ferroelectricity, piezoelectricity, photorefractive properties and photocatalysis, As a photocatalyst for the reaction of photocatalytic hydrogen evolution, it can protect environment and alleviate the energy crisis.In this paper, NaNbO3photocatalysts were prepared under Air, H2/Ar and O2atmospheres by solid state reaction. These samples were characterized by X-ray diffraction, UV-vis spectroscopy, Raman spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of NaNbO3samples were evaluated from the hydrogen evolution from an aqueous methanol solution and investigated the effect of different methods of co-catalyst loading on the activity. We also investigated the relationship between photocatalytic performance and their preparation conditions, such as the ratio of Na to Nb, reaction temperature and reaction time. The main achievements in the paper are as follows:1. Starting materials Na2CO3and Nb2O5were mixed in a ratio of Na/Nb=1.05. Then the mixture was preheated under air at800℃for4h, and crystallized at900℃under air, H2/Ar, O2for4h. The obtained samples were investigated for the photocatalytic hydrogen evolution. The method of loading co-catalyst Pt impacted the performance significantly. Photodeposition method is superior to the impregnation method because it can quickly reduce Pt4+to metal Pt completely. The hydrogen evolution rate of NaNbO3under Air, H2/Ar and O2atmosphere showed the increasing trend in turn. Moreover, the hydrogen evolution rate exhibits a liner increase with the surface oxygen defects.2. The NaNbO3sample prepared according to the Na/Nb=1introduced impurities NaiMnO11with monoclinic system because of the volatilization of Na source at high temperatures. When samples were prepared at850℃,900℃,950℃and1000℃, the sample prepared at900℃exhibited the optimum photocatalytic activity for hydrogen evolution. Among NaNbO3prepared for2h,4h,6h and8h, the sample prepared for4h exhibited the best photocatalytic activity. The effect of reaction surroundings on the activity was investigaged by adding the Na2SO4and NaOH. Tha basic surroundings are negative to the hydrogen evolution. The more ion concentration is better to the hydrogen evolution.The NaNbO3sample prepared according to the Na/Nb=1introduced impurities Na2MnO11with monoclinic system because of the volatilization of Na source at high temperatures. When samples wereprepared at850℃,900℃,950℃and1000℃, the sample prepared at900℃exhibited the optimum photocatalytic activity for hydrogen evolution. Among NaNbO3prepared for2h,4h,6h and8h, the sample prepared for4h exhibited the best photocatalytic activity. The effect of reaction surroundings on the activity was investigaged by adding the Na2SO4and NaOH. Tha basic surroundings are negative to the hydrogen evolution. The more ion concentration is better to the hydrogen evolution.