Controllable Preparation And Photocatalytic Application Of ?-Fe₂O₃-based“junction”catalysts

Iron oxides has excellently visible-light responsive performance due to its advantages of narrow band gap and often are used in the field of photocatalysis and exhibit excellent application prospect.The photocatalytic activity of iron oxides differs greatly from its theoretical value because of defects of iron oxides,such as low photogenerated electron-hole separation efficiency,short diffusion length and fast recombination.High efficient iron oxides photocatalyst are one of the challenges on how to effectively promote the separation and diffusion of photogenerated electrons and holes and restrain or reduce the recombination of electrons and holes.A strategy for the construction of"junctions"on the surface of photocatalysts can form built-in electric field and effectively promote the separation and diffusion of photogenerated electrons and holes.In this paper,based on?-Fe₂O₃?s?photocatalyst,there are three kinds of different"junction"photocatlysts constructed in?-Fe₂O₃?s?surface to form Fe₃O₄/?-Fe₂O₃?s?heterojunction,?-Fe₂O₃/?-Fe₂O₃?s?heterophase junction and?-Fe₂O₃/?-Fe₂O₃?s?homophase junction,Their photocatalytic machanism and photocatalytic degradation of organic pollutants properties were studied.XRD,UV-vis Raman spectrum,SEM were used to characterize the crystalline phase,chemical composition and morphology of Fe₃O₄/?-Fe₂O₃?s?,?-Fe₂O₃/?-Fe₂O₃?s?and?-Fe₂O₃/?-Fe₂O₃?s?.From the perspective of separation efficiency and transmission resistance of photogenerated electron and holes,the difference in photocatalytic performance of the there types of“junction”photocatalysts were investigated by means of SPV and EIS.The main content of this paper is as follows:First,the Fe₃O₄/?-Fe₂O₃?s?nanoparticles were fabricated by a facile and simple hydrothermal mathod and impregnation mothed.SEM images indicate Fe₃O₄ nanoparticles coated on the surface of shuttle-like?-Fe₂O₃?s?and form the heterojunction in Fe₃O₄/?-Fe₂O₃?s?nanoparticles.The photocatalytic activities of Fe₃O₄/?-Fe₂O₃?s?,Fe₃O₄ and?-Fe₂O₃?s?samples were evaluted for photodegradation of RhB which is one of the most harmful and toxic organic dye pollutants.11%Fe₃O₄/?-Fe₂O₃?s?nanoparticles are excellent photocatalyst for the photocatalytic degradation of RhB,the observed first-order kinetic constants of photodecomposition for 11%Fe₃O₄/?-Fe₂O₃?s?nanoparticles are 8.3times and 15.5 times as higher as that of?-Fe₂O₃?s?nanoparticles and that of Fe₃O₄ nanoparticles under visible light irradiation,respectively.SPV signal intensity and EIS Nyquist plots of prepared Fe₃O₄/?-Fe₂O₃?s?and?-Fe₂O₃?s?nanoparticles demonstrated the heterostructure of Fe₃O₄/?-Fe₂O₃?s?nanoparticles can effectively promote the separation efficiency and restrain the transmission resistance across interface of photogenerated electrons and holes.In addition,Fe₃O₄ has suerparamagnetism behavior,so Fe₃O₄/?-Fe₂O₃?s?photocatalyst with certain magnetism can be easy to separate from RhB aqueous solution at an external magnetic field when photocatalytic degradation reaction completed.Next,?-Fe₂O₃/?-Fe₂O₃?s?samples were obtained through calcining Fe₃O₄/?-Fe₂O₃?s?nanoparticles at 400?.SEM images show that the junction structure of?-Fe₂O₃/?-Fe₂O₃?s?photocatalyst nanoparticles are more densification,and there are either not altered significantly the morphology of?-Fe₂O₃?s?carriers.Besides,?-Fe₂O₃/?-Fe₂O₃?s?samples also have magnetism.The photocatalytic activities of?-Fe₂O₃/?-Fe₂O₃?s?nanoparticles were estimated for the same method evaluted of Fe₃O₄/?-Fe₂O₃?s?nanoparticles.The detailed first-order kinetic constants of obtained samples revealed that prepared?-Fe₂O₃/?-Fe₂O₃?s?with best loading nanoparticles exhibited approximately 10.4 times and 4.0 times better photocatalytic performance compared to synthesized?-Fe₂O₃nanoparticles and?-Fe₂O₃?s?nanoparticles,SPV signal intensity and EIS Nyquist plots of prepared Fe₃O₄/?-Fe₂O₃?s?nanoparticles and?-Fe₂O₃/?-Fe₂O₃?s?samples manifested that the interface separation efficiency sharply increases and resistance extremely decreases in presence of?-Fe₂O₃/?-Fe₂O₃?s?particles better than Fe₃O₄/?-Fe₂O₃?s?particles.Thus,the charges transfer across?-Fe₂O₃/?-Fe₂O₃?s?interface becomes easy,and photocatalytic activity of?-Fe₂O₃/?-Fe₂O₃?s?particles is better than that of Fe₃O₄/?-Fe₂O₃?s?particlesThird,based on the studies of phase transformation of Fe₃O₄particles at high temperature.synthetized Fe₃O₄/?-Fe₂O₃?s?samples were calcined to form through calcining?-Fe₂O₃/?-Fe₂O₃?s?homophase junction photocatalyst nanoparticles at 800?.Comparing the first-order reaction rates obtained for?-Fe₂O₃/?-Fe₂O₃?s?,?-Fe₂O₃ and?-Fe₂O₃?s?samples.The maximum reaction rate of photodegradating RhB aqueous solution was obtained for 11%?-Fe₂O₃/?-Fe₂O₃?s?which displays2.81-fold enhancement over?-Fe₂O₃ and 5.43-fold enhancement over?-Fe₂O₃?s?.and the maximum specific reaction rate from?-Fe₂O₃/?-Fe₂O₃?s?is between that of Fe₃O₄/?-Fe₂O₃?s?and that of?-Fe₂O₃/?-Fe₂O₃?s?,and exhibits 3.31 times highter than that of Fe₃O₄/?-Fe₂O₃?s?and 1.47 times lower than that of?-Fe₂O₃/?-Fe₂O₃?s?.SPV signal intensity and EIS Nyquist plots of obtained for different samples,the interface separation efficiency of?-Fe₂O₃/?-Fe₂O₃?s?is the hightest,?-Fe₂O₃/?-Fe₂O₃?s?is the second and the last is Fe₃O₄/?-Fe₂O₃?s?.the charges transfer across interface resistance of Fe₃O₄/?-Fe₂O₃?s?is the hightest,?-Fe₂O₃/?-Fe₂O₃?s?is the second and the last is?-Fe₂O₃/?-Fe₂O₃?s?sample.