Study On Construction And Performance Of Three-dimensional Tantalum-based Ordered Macroporous Photocatalytic Materials

Constructing photocatalytic materials into a three-dimensional ordered macroporous（3DOM）structure can improve the mass transfer efficiency,shorten the carrier migration distance,and increase the reaction sites,thereby increasing the photocatalytic hydrogen production rate.Tantalum semiconductor photocatalytic materials,mainly composed of tantalum oxides,nitrogen（oxide）compounds and tantalate materials,have been widely studied as an important member of solar water splitting hydrogen production materials.However,the hydrogen production efficiency of tantalum-based photocatalytic materials cannot be further improved due to low surface area,high carrier recombination rate and so on.Based on the three-dimensional ordered macroporous structure,this thesis will explore new breakthroughs in the structure and application of tantalum-based photocatalytic materials to improve the efficiency of photocatalytic hydrogen production.Firstly,a three-dimensional ordered single-crystal macroporous Ta₂O₅（SCOM-Ta₂O₅）photocatalytic material was designed and constructed.While constructing three-dimensional ordered macroporous structures is an effective strategy to improve mass transport and shorten electron migration paths,long-range carrier transport and structural continuity are also required to realize the maximum potential for target applications.Three-dimensional single-crystal ordered macroporous structures are well suited to meet the above requirements.Constructing a continuous single crystal structure is challenging due to the rapid formation of grain boundaries.In this study,highly ordered poly（methyl methacrylate）（PMMA）spheres were chosen to construct a nanoreactor to create a suitable growth environment for SCOM-Ta₂O₅.SCOM-Ta₂O₅with different pore sizes and structural units was constructed by manipulating the nanoreactor space to systematically study the effects of mass transfer channels and carrier migration distance on the photocatalytic performance of SCOM-Ta₂O₅.The construction of SCOM-Ta₂O₅ achieves a substantial improvement in the photocatalytic hydrogen production performance.This design strategy aims to overcome the negative effects of particle stacking macroporous grain boundaries to improve the long-range carrier transport efficiency,thereby effectively enhancing the photocatalytic performance.In order to further study the three-dimensional ordered macroporous tantalum-based materials,the application potential of three-dimensional ordered macropores in ternary tantalum-based materials was further explored based on the three-dimensional ordered macroporous Ta₂O₅.Since the synthesis of three-dimensional ordered macroporous ternary materials ternary materials involve homogeneous mixing and mutual solid solution of two cationsand and the crystal size is difficult to control,the construction of ternary materials with three-dimensional ordered macroporous structure is more complicated.Ternary materials need to face the structural instability brought by the macroporous morphology,which limits the application of 3D ordered macroporous structures.In this work,we design a novel and general two-step crystal nucleation strategy for the construction of stable three-dimensional ordered macroporous Na Ta O₃（3DOM Na Ta O₃）.Compared with non-porous Na Ta O₃,which has no catalytic activity in pure water,3DOM Na Ta O₃ achieves efficient photocatalytic H₂ and H₂O₂ production with excellent structural and performance stability.The two-step crystal nucleation method enables the structural advantages of three-dimensional ordered macropores to be continuously and stably exerted in the photocatalytic reaction of ternary materials,thereby promoting the application of three-dimensional ordered macroporous structures in ternary photocatalytic materials.Finally,in order to expand the photoresponse band of the three-dimensional ordered macroporous tantalum-based materials and obtain widen light absorption band for catalytic activity,we adopted a nitrogen doping strategy,constructing the doping level on Ta₂O₅,to expand the light absorption band.Using melamine as the nitrogen source,nitrogen-doped 3DOM Ta₂O₅（3DOM N-Ta₂O₅）was successfully constructed using a microreactor in air,and the light absorption band was successfully extended to600 nm.Compared with 3DOM Ta₂O₅,which only exhibits catalytic activity in the strong ultraviolet band of less than 320 nm,3DOM N-Ta₂O₅ exhibits excellent photocatalytic H₂ production activity under single-wavelength light sources of 365 nm and 380 nm,which are attributed to the successful construction of nitrogen-doped energy band and the structural advantages of three-dimensional ordered macropores.