Preparation and Photocatalytic Performances of Bismuth Tantalum-based Nanoplates

Author:Hu Yi Dong

Supervisor:hao su e chen gang


Degree Year:2018





Photocatalysis is an environmentally friendly technology,because it directly converts solar energy into chemical energy for the photodegradation of target pollutants and photocatalytically splitting water into hydrogen.Semiconductor photocatalysis is a techenique widely used to remove high toxicity,low concentration and hardly self-degradable pollutants for environmental remediation.It has the advantage of complete degradation and without generating secondary pollutants.Therefore,the photocatalytic technique for treatment of water pollutants has become a hot research topic because of its green and renewable nature.This thesis mainly focus on the synthesis of various photocatalysts by employing the molten salt synthetic methods.We systematically studied many determing factors on the performance of several bismuth-tantalum-based photocatalysts such as morphology features,crystal structures,electronic structures,band gap regulation and photoelectric chemical properties,and so on.Using the simple molten salt synthetic methods,the {010} facet dominant Bi Ta O4 single-crystal nanoplates(BiTaO4SCNs)photocatalyst is prepared.BiTaO4SCNs show excellent photocatalytic activities in decomposing organic dyes and phenol into non-toxic small molecules and splitting water into H2.The band positions of BiTaO4SCNs are determined by UV-vis DRS,XPS valence band and Mott-Schottky measurements.The percentage of the exposed {010} facets on the surface of the BiTaO4SCNs was estimated to be ca.86%,and they are preferentially O-terminated on the basis of crystal structure analysis.DFT calculations demonstrated that the valence band of BiTaO4SCNs is mainly composed of O 2p orbitals and the conduction band is mainly composed of Ta 5d and O 2p orbitals.The exposure of many oxygen atoms lead to the up-shift of the VB maximum and the CB minimum.The up-shift of conduction band minimum of the BiTaO4SCNs results in their excellent photocatalytic activities not only for the reduction of Cr(Ⅵ)but also for the splitting of water into H2.Novel NBTO SCNs(Na0.5Bi2.5Ta2O9 single-crystal nanoplates)with exposed {001} facets are successfully developed as photocatalysts via a mixed molten-salt synthetic method.The obtained NBTO SCNs exhibit excellent photocatalytic activities for the degradation of both Rh B and tetracycline contaminants.Under visible light irradiation,the photodegradation of Rh B takes place via an indirect dye photosensitization process.In addition,it shows excellent photocatalytic activity and stability for the splitting of water into H2.DFT calculations demonstrated that the valence band of NBTO SCNs is mainly composed of O 2p orbitals and the conduction band is mainly composed of Ta 5d orbitals.NBTO SCNs with mixed A-site cations(Na+ and Bi3+)are typical layered perovskite compounds,the unbalanced local charge of NBTO SCNs leads to giant spontaneous polarization along the [001] directions.The photogenerated carriers can easily diffuse along the polarization direction to the surface of the catalyst,thus enhancing the photocatalytic activities.Na0.5Bi2.5Ta2O9/Bi4 Ta O8Cl-n(NBTO/BTOC-n)heterostructure photocatalysts is prepared via a simple one-pot mixed molten salt reaction.It is demonstrated that a controllable BTOC in-situ loading on the surface of NBTO has been realized.This heterostructure photocatalyst exhibits excellent activity for the decomposition of Rh B dyes under both visible and UV-vis light irradiation.Active species trapping experiments reveals that the photogenerated holes and ·O2-are the two main reactive species in the photocatalytic degradation process.The photosensitization degradation activities of NBTO/BTOC is ascribed to the presence of the NBTO,which is confirmed by monochromatic wavelength irradiation method.The photoelectrochemical EIS and PL analyses demonstrate that the NBTO/BTOC-n heterostructure is beneficial for the separation and transfer of photogenerated electron-hole pairs.NBTO(Na0.5Bi2.5Ta2O9 nanoplates)photocatalyst is prepared via a mixed molten-salt synthetic method.g-C3N4 nanoplates is successfully prepared by thermal polymerization followed by sonication of urea.The NBTO/g-C3N4-n heterostructure photocatalysts are then obtained by the ethanol dispersion method.The NBTO/g-C3N4-n heterostructure photocatalysts exhibit excellent photocatalytic activity and stability for Rh B degradation under visible light irradiation.UV-vis DRS results indicate that the absorption edge of NBTO/g-C3N4-n extends to the visible light region.SEM,TEM and FT-IR analyses demonstrate that NBTO and g-C3N4-n are combined face to face.Moreover,the photoelectrochemical EIS and PL analyses demonstrate that the NBTO/g-C3N4-n heterostructure can promote the migration of photogenerated carriers,which is beneficial for photocatalytic performance.Photocatalytic control experiments indicate that NBTO/g-C3N4-4 heterostructure show the highest photocatalytic activity than TiO2 based(P25,N-TiO2 and Zn,N-Ti O2-x),BiTaO4SCNs,NBTO SCNs and NBTO/BTOC-10 photocatalysts for the degradation Rh B.