Molten Salt Preparation Of Iron Oxide And Its Composite With Titanium Oxide Arrays And Their Photoelectrochemical Performance

Nano-iron and titanium oxide owning special physical and chemical properties are important inorganic functional materials and have received widespread attention from material science and technology researchers.They have wide application prospect and development potential in high-tech fields such as magnetic materials,electronics,ceramics,catalysis,aerospace,military and bioengineering.As a branch of inorganic synthetic chemistry,molten salt synthesis?MSS?is an important method for the preparation of multi-component oxide and ceramic materials.The synthesis of nano-oxides by MSS has advantages of low synthesis temperature,simple operation,uniform chemical composition,not easy to reunite and so on.This paper focuses on study of morphology control and preparation of nano-iron oxide by MSS.The nano-iron oxides and S/Fe₂O₃ complex with different morphologies were prepared by controlling the various kinds of parameters such as molten salt species,calcination temperature and calcination time during the growth process of iron oxide nanocrystals.Their photocatalytic and photoelectrochemical properties were studied.TiO₂nano-film prepared by anodic oxidation method on both titanium sheet and mesh is the matrix for molten salt heat treatment,respectively.Their photoelectrochemical properties after modification were studied systematically in the three-electrode system.The structure and properties of the sample were characterized by XRD,TEM,SEM,XPS,PL and TG-DTG.The specific researches are as follows:?1?Based on the near-spherical?-Fe₂O₃ prepared by precipitation method,prismatic Fe₂O₃ and flaky Fe₃O₄ nanocrystals were prepared by using different types of molten salts,calcination temperature and time to control the preferential growth of nanocrystalline grains.The photocatalytic degradation of the methyl orange solution was studied by using methyl orange solution as a simulated contaminant.The results showed that the prismatic Fe₂O₃nanocrystals prepared at temperature of 680?for 6 h in the NaCl+KCl molten salt system and the flaky Fe₃O₄ nanocrystals prepared at calcination temperature of 735?for 6 h in the MgCl₂ molten salt system were better than the near-spherical?-Fe₂O₃ in photocatalytic degradation of methyl orange solution.It is proved that the different morphological structure is the main factor that leads to the difference in the catalytic performance of nanometer iron oxide.?2?The?-Fe₂O₃ nanocrystals were prepared by using ferric nitrate as iron source in the sulfate and nitrate molten salt systems,respectively.The KNO₃+LiNO₃+Fe?NO₃?₃ molten salt system was systematically studied including photocatalysis,fenton,photoelectronchem-ical properties and its formation mechanism.The results showed that the photocatalytic degradation of rhodamine B solution was significantly improved by the S/Fe₂O₃ compound resulting from sulfur doping.Under simulated solar light irradiation,the rhodamine B solution was almost complete degraded by sulfured at 165?and 205?for 1h,lighted for10 min.The decomposition rate was about 2 times of undoped nano-iron oxide.The results of XPS test of the samples showed that a large number of negatively charged radical ions such as OH^-,SO₄^2-and Sn^2-were present on the surface of S/Fe₂O₃ compounds,which acted as the bridge of H₂O₂ and iron ion and formed peroxides on the surface of the compounds.It was easy to capture the electrons of intermolecular iron ions and decompose,so it would produce more reactive hydroxyl radicals,which can promote the absorption of positive charged RhB⁺molecules in the water.The photoelectrochemical performance of S/Fe₂O₃compound generated by Sulfur doping has improved,but S not into the?-Fe₂O₃ lattice internal,the morphology and crystal structure of iron oxide nanoparticles has not changed.With the sulfur doping temperature increasing,carrier concentration of S/Fe₂O₃ compounds increased,which was more conducive to promote the transmission of photogenerated electrons and holes.?3?Nanocrystalline TiO₂ films were prepared by anodic oxidation method on titanium sheets,then modified by different molten salt heat treatment processes.The molten salt treatment?only salting?at 400?for 1h contributed to the growth of TiO₂ nanotube arrays,but the molten salt treatment partly promoted the dissolution of the surface of the TiO₂nanotube arrays.After heating at 450?for 2h,then molten salt annealing at 200?for 1h,photocatalytic performance was obviously different.Heating at low temperature of 200?for 1h with molten salt after dipping in ferric nitrate solution,the special surface structures of Fe₂O₃/TiO₂ composites were formed on the surface of TiO₂ nanotube arrays.They were favorable for generation of photogenerated electrons and holes,and also beneficial for the light absorption.?4?The TiO₂ or Fe₂O₃/TiO₂ composites were prepared by modification with different molten salt heat treatment processes on titanium meshes.Different molten salt treatment processes have different effects on the charge transfer resistance of the samples.The charge transfer resistance showed an increasing trend with molten salt treatments at 400?for 1h and 450?for 2h.But in the low temperature of molten salt treatment at 200?for 1h,the charge transfer resistance of the samples were greatly reduced,and the value was basically1/600 of previous samples.The results showed that the special structures of Fe₂O₃/TiO₂nanotube arrays were more favorable to generate,which increased the carrier concentration and migration rate,promoted the separation of photogenerated electrons and holes,and significantly improved photoelectrochemical properties.The molten salt heat treatment is more likely to produce the Fe₂O₃/TiO₂ composite nanoarray structure in the titanium meshes compared with the titanium foil.