Preparation Of Fe₂O₃ Based Inverse Opal Photocatalysts And Their Performence For Degradation Of Organic Pollutants

In recent years,a large number of organic pollutants have been discharged into the water environment,which threatens the survival and development of human beings and the healthy balance of ecology.Photocatalytic technology can make use of solar energy t o remove organic pollutants from water without secondary pollution,which is a green,efficient and low-cost environmental remediation method.The key to the wide application of this technology lies in the development of photocatalytic materials.At presen t,many photocatalysts have been synthesized and applied,among which iron oxide（Fe ₂O₃）has been widely studied because of its narrow band gap,low cost and non-toxic to the environment.However,the shortcomings of faster photo-induced electron（e^-）and holes（h⁺）recombination rate,the lower utilization rate of sunlight and poorer quantum conversion efficiency also limit the practical application of Fe₂O₃ materials.Inverse opal（IO）is a special three-dimensional photonic crystal with a three-dimensional ordered macroporous structure and photonic crystal characteristics.inverse opal photocatalysts can not only make use of the three-dimensional ordered macroporous structure to improve the material transfer efficiency,to increase the reaction activity si tes,and to reduce the composite efficiency of photo-induced e^-and h⁺,but also make use of its slow photons effect and multiple scattering effects to improve the light capture ability and photo efficiency of photocatalyst and photosensitization effect of the dye.Therefore,In this study,by introducing inverse opal structure,carbon,Si O ₂and bismuth chloride oxide（BiOCl）to the base of Fe ₂O₃,we prepared a variety of Fe₂O₃-based inverse opal composite photocatalysts and used them to deg rade organic pollutants in water.The details are as follows:（1）In order to improve the photocatalytic performance of Fe ₂O₃,C/Fe₂O₃inverse opal（CF IO）composite photocatalysts were prepared by using PS photonic crystal as a template and ferric chlori de（Fe Cl₃）solution as precursor solution,and they were used to degrade rhodamine B（Rh B）.In comparison with Fe₂O₃,CF IO’s specific surface area,visible light absorption performance,light utilization ratio,material transfer efficiency and photocarrie r separation efficiency are significantly improved because of the synergistic effect of carbon,inverse opal structure and homogenous heterogeneous junction.A s a result,the photocatalytic activity of CF IO is significantly improved.After exposing to light for 30 minutes,the degradation efficiency of Rh B by CF IO reached98.2%,and the degradation rate was 0.1339 min^-1.However,Under the same conditions,the degradation efficiency of Rh B by Fe ₂O₃ was 13.7%,and the degradation rate was only 0.0041 min^-1.The capture experiment showed that·O₂^-,h⁺and·OH were the main active substances involved in photocatalytic degradation of Rh B.The experimental results show that the inverse opal structure and carbon can effectively improve the photocatalytic performance of photocatalysts,which also provides a way to improve the photocatalytic materials.（2）In order to improve the adsorption and stability of the composites,C/Si O₂/Fe₂O₃ inverse opal（CSF IO）composite photocatalysts were prepared,and they were used to degrade tetracycline（TC）.The results showed that the adsorption efficiency of CSF IO and CF IO for TC was 24.3%and 6.7%,respectively,after a dark adsorption reaction for 30 minutes.Under the catalysis of CSF IO,the degradation efficiency of TC could reach 90.0%when exposed to light for 30 minutes.After exposing to light for 90 minutes,TC was completely degraded,and the degradation rate was about 9 times that of CF IO.After four cycles of CSF IO degradation,the degradation efficiency of TC remained above 95.0%.Compared with CF IO,T he adsorption efficiency and degradation efficiency of TC and the cycling stability of CSF IO are improved.The main reason is that Si O ₂ with good thermal stability is introduced into the inverse opal skeleton,which increases the specific surface area of the composite material,and TC can better penetrate into the composite and enters the reactive site to participate in degradation.Meanwhile,the dispersion effect of Si O ₂ on Fe₂O₃ is also cond ucive to the light absorption of the composite and the separation of e^-and h⁺.The results show that the combination of the appropriate amount of Si O₂ and photocatalytic material can promote the photocatalytic degradation process,and the composite materi al is expected to be used in practical water samples.（3）In order to improve the separation efficiency of photo-induced carriers,The p-n heterojunction between BiOCl and Fe ₂O₃ was constructed in the inverse opal structure by the co-sol-gel method.The C/Si O₂/BiOCl/Bi/Fe₂O₃ inverse opal（CSBF IO）composite photocatalysts were prepared and they were used to degrade methylene blue（MB）.Since the Fermi energy level of Fe ₂O₃ is close to the conduction band and the Fermi energy level of BiOCl is close to the valence band,after Fe₂O₃ and BiOCl are coupled,e^-from Fe₂O₃ will flow to BiOCl until the Fermi energy level of the two is equal,which causes the band gap energy of BiOCl to rise while the band gap energy of Fe ₂O₃ decreases.P-n type heterojunction is formed.It was found that under the catalysis of CSBF IO-300,the degradation efficiency of MB could reach 93.5%when exposed to light for20 minutes.The degradation efficiency of MB could reach 98.5%after exposing to light for 40 minutes,and the degradation rate was about 5 times that of CSF IO-300.B ecause p-n heterojunction can effectively promote the transmission and separation of e^-and h⁺,the recombination efficiency of photogenerated carriers is reduced.Therefore,the photocatalytic degradation performance is improved.The results show an effective modifi cation method to construct heterojunction in reverse opal structure.