Solvothermal Preparation Of Nonstoichiometric LaFeO_3-δ/TiO₂ And Their Photocatalytic Activity

In recent years, the advanced multifunctional semiconductor materials have widely applied in the field of photocatalysis. Titanium dioxide(TiO2) is an n-type semiconductor with the advantages of safe, low costs, stable chemical property. But TiO2 has a wide band gap(Eg =3.2 eV), so it has weak responsiveness to visible light, greatly hinders the application in the visible region. Therefore, it is one of hot spots that improving the responsiveness to visible light by modifying. LaFeO3 is a p-type semiconductor, has a narrow band gap(2.07~3.87eV), can respond to visible light better. But the generated electron-hole pairs will reorganize after light excitation, affecting photocatalytic activity. Thus, the modification of LaFeO3 by doping can inhibit electron-hole recombination, improve the photocatalytic activity. A-site non-stoichiometric can promote the lattice distortions, and facilitate the disorder of oxygen vacancies in some degree, which improve the performance of materials. So, this paper report the preparation of non-stoichiometric LaFeO3/TiO2 nano-materials by simple solvothermal, study the structure, morphology, photocatalytic activity of the sample by a series of structural characterization, analysis and discussion on the mechanism of the photocatalyst. The details and results of the studying as following:(1)LaFeO3, La0.8Sr0.2FeO3-δ and non-stoichiometric(La0.8Sr0.2)xFeO3-δ(x = 0.97, 1.03) nanoparticles were fabricated via a simple solvothermal method. The structures and morphologies of the samples were characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM), ultraviolet-visible(UV-Vis) diffuse reflectance spectra and X-ray photoelectron spectroscopy(XPS). Malachite Green(MG) photodegradation was used as a model reaction to investigate the photocatalytic activity of these samples under the maximum absorption wavelength(616.9 nm). The results indicate that the doping of Sr2+ reduce the grain size and cause lattice defects and oxygen vacancies to be formed, which are in favor of hindering the recombination of electrons and holes, increasing the quantum efficiency. Doping Sr2+ and changing nonstoichiometric make the catalysts have strong absorption in visible region. The specific surface area are also different,(La0.8Sr0.2)1.03FeO3-δ is the largest(20.1644 m2/g),and the visible degradation efficiency is the highest(83.8%). The photocatalytic activity of doped Sr2+ and nonstoichiometric are higher than that of pure LaFeO3 under the visible light.(2)Different ratio composites LaFeO3/TiO2 micro/nano materials prepared by solvothermal. The samples were characterized, and test the visible light degradation of these catalysts. The coupling of semiconductor LaFeO3 and TiO2 can inhibit electron-hole recombination and increase quantum efficiency, n(LaFeO3): n(TiO2) from 1:0.25 to 1:0.75, the photocatalytic efficiency increases, continues to increase the molar ratio to 1:1, 1:1.25, the band gaps composite catalysts grow wider, the property in response to visible light are weaken and photocatalytic efficiency decreases. So, the best ratio of LaFeO3/TiO2 composite be optimized based on the tests of photocatalytic activity.(3)According to the optimum ratio of composite, non-stoichiometric(La0.8Sr0.2)xFeO3-δ/TiO2 micro/nano materials were fabricated via a solvothermal method. The samples were characterized, and simulated photocatalysis test, SEM showed that the agglomeration between crystal grains of(La0.8Sr0.2)xFeO3-δ/TiO2 composite materials, and form larger particles, the diameter are about 1μm. Compared to the stoichiometric LaFeO3/TiO2, the band gaps of non-stoichiometric composite samples are broader, resulting in lower photocatalytic activity under visible light.