Nano Fe ₂ O Modification And Graphene Composite Mechanism Of The Catalytic Material Visible 3

Semiconductor photocatalytic technology has the merits of high degree ofmineralization and no secondary pollution, so it has been widely used in environmentalmanagement. In the solar spectrum, the visible light is about44%, so that the key torealize the practical photocatalytic technology is to synthesize the photocatalysts withhigh visible-light activity. As a typical N-type semiconductor with narrow band gap,Fe2O3has become a promising photocatalyst. However, it usually exhibits low visibleactivity which is attributed to its high charge recombination rate. Hence, it is of greatsignificance to improve the photogenerated charge separation efficiency of Fe2O3for itspractical application. It is well known that the photogenerated electrons captured by O2is a very important step in the photocatalytic process, and increasing the amount of O2adsorption would be favorable for the separation of photogenerated charges. Accordingto the above investigation, we attempt to introduce graphene to improve thephotogenerated charges separation efficiency of Fe2O3. Then, the graphene wasmodified by phosphoric acid and doping N atom to increase the amount of O2adsorption of the nanocomposites, so as to promote the photogenerated chargesseparation of Fe2O3in this paper. In addition, the mechanism is also revealed in detail.We adopted the simple wet-chemical method to prepare graphene-Fe2O3andphosphate-functionalized graphene-Fe2O3nanocomposite photocatalysts. The resultsshow that the visible-light activity of α-Fe2O3is greatly enhanced by coupling with anappropriate amount of unfunctionalized and phosphate-functionalized graphene,especially the latter. The mechanism of the enhanced photocatalytic activity is based onthe measurements of surface photovoltaic spectroscopy, transient photovoltaicspectroscopy and O2temperature-programmed desorption. It is demonstrated that theintroduction of graphene and phosphate-functionalized graphene, especially the latter,could remarkably increase the amount of adsorbed O2of Fe2O3, so as to promote thephotoelectron captured by O2, and immensely improve the photogenerated chargesseparation efficiency of α-Fe2O3.The N-doped graphenes with diferent amounts of N are prepared through a one-pot hydrothermal process, and then successfully coupled them with nanocrystallineα-Fe2O3by a wet-chemical method. On the basis of the atmosphere-controlled surfacephotovoltage spectra and time-resolved surface photovoltage responses, it is confirmedthat the photogenerated charge separation of α-Fe2O3could be enhanced after couplingwith a certain ratio of graphene, and it is especially obvious with the graphene dopedwith a proper amount of nitrogen, leading to the obviously improved visible activities ofα-Fe2O3for photoelectrochemical water oxidation to produce O2and visiblephotocatalytic activity. It is suggested that the increased amount of dopedquaternary-type N would be quite favorable for photogenerated charge separation,mainly by means of XPS data, electrochemical impedance spectra and O2temperature-programmed desorption curves. It is because the quaternary-type N couldincrease the amount of O2adsorption, and promote the photoelectron captured by O2.Furthermore, the quaternary-type N could enhance the electrical conductivity of thematerial, so as to accelerate the transfer and transportation of the photoelectron.This work will provide a feasible reference to design carbon material-Fe2O3nanocomposite photocatalysts with high visible-light activity, and offer the foundationof research to realize practical application of Fe2O3as soon as possible.