Preparation Of Fe₂O₃/g-C₃N₄ And Aupd/meso-Fe₂O₃ Catalysts And Their Photocatalytic Performance Forthe Degradation Of Organic Compounds

Industrial wastewater contains a variety of organic pollutants,which is harmful to water environment and human health.Therefore,it is of great theoretical and practical significance to eliminate organic compounds in wastewater.Photocatalytic oxidation is considered as an effective pathway that is clean,nontoxic,high efficiency,mild reaction conditions,and no secondary pollution,in which the key issue is the development of high-efficiency photocatalytic materials.Among various semiconductors investigated,graphitic carbon nitride（g-C₃N₄）and Fe₂O₃ attract great public concerns due to their low cost,high photocatalytic performance,and environmentally benign property.g-C₃N₄ with a two-dimensional layered structure and a bandgap energy of 2.7 e V is a promising visible-light-driven photocatalyst in the remediation of environmental pollutants.Iron oxides with a narrow bandgap energy of 2.0–2.2 e V and high visible-light absorption capacities have been reported to be effective photocatalysts.Up to now,no reports on the preparation and photocatalytic applications of Fe₂O₃/g-C₃N₄ hybrid photocatalysts for the degradation of 4-nitrophenol（4-NP）under visible-light illumination have been seen in the literature.Also,there have been no reports on the applications of Au–Pd alloy nanoparticles（NPs）supported on mesoporous（meso-Fe₂O₃）for the photocatalytic oxidation of acetone.The main contents of this thesis include the following two parts:（i）The g-C₃N₄ and x wt% Fe₂O₃/g-C₃N₄（x = 0.1-0.8）catalysts were prepared using the thermal polymerization and incipient wetness impregnation methods,respectively.The Fe₂O₃/g-C₃N₄ heterojunction structure and narrow bandgap could increase the ability to capture and convert light energy;and（ii）the three-dimensionally mesoporous silica（KIT-6）was used as hard template to generate meso-Fe₂O₃,and the polyvinyl alcohol（PVA）-protected reduction strategy was adopted to prepare the meso-Fe₂O₃-supported Au-Pd alloy NPs(x Au Pdy/meso-Fe₂O₃（x = 0.08-0.72 wt%;Pd/Au molar ratio（y）= 1.48-1.85）.Construction of Schottky junction between noble metal and semiconductor could lead to efficient charge separation for photocatalytic reactions.Physicochemical properties of the catalysts were characterized by means of numerous analytical techniques,and their photocatalytic activities were evaluated for the photodegration of 4-NP and acetone.The relationship between physicochemical properties and photocatalytic performance of the materials has been established.The main results obtained in the thesis are as follows:1.Graphitic carbon nitride and its supported iron oxide（x wt% Fe₂O₃/g-C₃N₄,x = 0.1-0.8）photocatalysts were fabricated using the guanidine hydrochloride calcination and incipient wetness impregnation methods,respectively.The x wt% Fe₂O₃/g-C₃N₄ photocatalysts contained a two-dimensional nanosheet structure with high dispersion of Fe₂O₃ NPs（2-3 nm in size）,a surface area of 27-29 m²/g,and a bandgap energy of 1.92-2.68 e V.The 0.5 wt% Fe₂O₃/g-C₃N₄ catalyst showed the highest photocatalytic activity（90 % of 4-NP conversion was achieved within 40 min of visible-light illumination）.Effects of p H value,H₂O₂ amount,and initial 4-NP concentration on photocatalytic activity of the typical catalyst were also examined.It is concluded that the enhanced photocatalytic activity of 0.5 wt% Fe₂O₃/g-C₃N₄ was associated with its unique two-dimensional layered structure,Fe₂O₃/g-C₃N₄ heterojunction,high surface oxygen adsorbed species concentration,and easy transfer and separation of photogenerated charge carriers.2.The meso-Fe₂O₃ and its supported Au,Pd,and Au-Pd alloy（x Au Pdy/meso-Fe₂O₃;x = 0.08-0.72 wt%;Au/Pd molar ratio（y）=1.48-1.85）nanocatalysts were prepared using the KIT-6-templating and polyvinyl alcohol（PVA）-protected reduction methods,respectively.It is found that the meso-Fe₂O₃ with a high surface area of 133.5 m²/g was rhombohedral in crystal structure,a bandgap energy of 1.98-2.12 e V,and the noble metal NPs with a partical size of 3-4 nm were uniformly dispersed on the surface of meso-Fe₂O₃.The 0.72 Au Pd1.48/meso-Fe₂O₃ catalyst showed the highest photocatalytic activity（100 % acetone was degraded within 4 h of visible-light illumination）.It is concluded that the porous structure,high surface oxygen adsorbed species concentration,and plasmonic resonance effect between Au-Pd NPs and meso-Fe₂O₃ were responsible for the enhanced photocatalytic activity of 0.72 Au Pd1.48/meso-Fe₂O₃.