Preparation Of Highly Active ?-Fe₂O₃ Nanomaterials And Their Photocatalytic Properties

As an important n-type semiconductor material,hematite??-Fe₂O₃?has good superparamagnetic,chemical stability,acid and alkali corrosion resistance,low cost and environmental friendliness.Due to these advantages,it has been widely used in the fields of coatings,gas sensors,catalysts,lithium-ion batteries and biomedical applications.In particular,?-Fe₂O₃ has a narrow bandgap?1.9eV to 2.2 eV?and can absorb most of visible light?⁴5%?in the solar spectrum,which has great application values in the field of photocatalysis.Its photocatalytic activity is not only related to its crystal structure,but also closely related to its size,morphology,activity and dispersibility.Accurately controlling the crystal growth of?-Fe₂O₃ and achieving controlled adjustment of its particle size and morphology structure is of great significance for the study of its photoelectrocatalytic properties.In this paper,a variety of morphologies of?-Fe₂O₃ nanocrystals were successfully prepared by a hydrothermal method.The formation process and growth mechanism of?-Fe₂O₃ nanocrystals were investigated and a series of studies have been conducted on their photoelectrocatalytic properties.By regulating the morphological structure of?-Fe₂O₃,the mechanism of their visible light catalytic enhancement was studied to improve their visible light catalytic performance.?1?Using iron chloride as an iron source and 1,2-propanediamine as a structure-directing agent,single-crystalline?-Fe₂O₃ nanorods with a diameter of90±5 nm and a length of 600±30 nm were synthesized by a simple and direct hydrothermal method in large quantities.Selective adsorption of1,2-propanediamine to different crystal faces of iron oxide during the initial reaction is the main reason for the formation of?-Fe₂O₃ nanorods.By prolonging the reaction time,hydrogen ions produced by the hydrolysis of Fe³⁺can erode the surface of the?-Fe₂O₃ nanorods,resulting in the formation of?-Fe₂O₃ nanobars.Compared with the typical?-Fe₂O₃ nanorods,the etched?-Fe₂O₃ nanobars have a rough surface edge,the bandgap width is reduced by0.19 eV,and the photocurrent response is increased by 61.3%,resulting in a48.8%increase in visible light photocatalytic degradation rate.?2?Using iron chloride as the iron source,single-crystal?-Fe₂O₃icositetrahedra with a diameter of 146±8 nm and an axial length of 120±10nm was successfully synthesized with the aid of sulfate ion.Using a phosphate ion as an etching agent,single-crystalline?-Fe₂O₃ concave and hollow nanocrystals with uniform size can be synthesized by etching pristine icositetrahedra along their[006]direction in a top-down manner.Compared with the icositetrahedra,the?-Fe₂O₃ concave and hollow nanocrystals have more rough edge structures,and the specific surface area?SSA?increases from10.31 m²g^-1 to 12.71 m²g^-1.Therefore,the degradation rate of the cationic dye Rhodamine-B was increased by 30.4%and 15.9%,respectively.?3?The ultrafine?-Fe₂O₃ nanoparticles with an average particle size of 5.5nm and a hexagonal bipyramidal structure were successfully synthesized by a simple hydrothermal method.With the help of dihydrogen phosphate ions,they were assembled into new nanolayered saucer-like structure with a diameter of160±13 nm and a thickness of 60±8 nm.Based on the small size,rough surface and loose edge features of the three-dimensional assembly structure,the photocatalytic degradation rate on Rhodamine-B of?-Fe₂O₃ nanosaucers was increased by 123.1%and 75.1%,respectively,compared to ultrafine?-Fe₂O₃nanoparticles and icositetrahedra with similar size.Through ten recycling cycles,the prepared?-Fe₂O₃ exhibited good stability and recyclability.These characteristics make them promising candidates for catalysts and sensing materials.