Design And Site-selective Doping Of Niobate And Tantalate Photocatalyst

At present,the energy shortage and environmental pollution are becoming increasingly serious and threat to the long-term development of human society.The government and scientists are trying to explore a sustainable way to solve these issues by using green technology.Among the potential solutions,semiconductor-based photocatalytic technology has incalculable advantages.It is an economical,clean,renewable,and safe technology.In the photocatalyst research at this stage,although there are many catalysts being used,there are still many inefficient photocatalysts and unknown regions need to be developed.The theoretical simulations based on the density functional have been developed at this stage.It is possible to use simulation technology to realize the interpretation of experimental phenomena,the experimental feasibility,and the prediction of experimental results.Therefore,based on the density functional theory,this thesis is focused on the niobate and lanthanide salts to investigate the effect of the site-selective doping on the modification of the surface performance.1.We synthesized the pure phase In NbO₄ under solid-state melting method at1050°C and its electronic properties were calculated based on the density functional theory.The three intrinsic defects in InNbO₄?two kinds of oxygen defects and one of the interstitial defects added to the In atoms?were considered during the calculation,of which the O₁ defect is the most stable structure.Due to the intrinsic defects,there are two cell types with different conductivity in this crystalline phase at the same time.After analyzing the surface energy,their stable order is{011}>{111}>{200},where the electrons on the{111}plane are easier to transfer.We constructed three surface models to simulate the formaldehyde molecules adsorbed on the surface of InNbO₄ by building the defects at the top of In,Nb,and O sites,respectively.After comparing the atomic adsorption energy,we found that all of them were physically adsorbed and the adsorption on the{011}surface was more strong than others.2.Based on the density functional theory,we calculated the influence of the energy,electronic structure and redox properties for the system of Fe and La site-selective doped into InNbO₄.The results show that the Fe-doped and La-doped systems are preferentially entering the In position due to the available larger space.When Fe and La atoms are co-doped into the crystalline of InNbO₄,the exchanged electrons between Fe atoms and La atoms are observed.This indicates that dopants.Under this synergistic action of Fe and La co-doping,we can achieve the adjustment of specific regulation for catalyst redox,so as to increase the light absorption range and enhance the photocatalytic activity.3.We performed a series of calculations on the systems of InTaO₄ doped with transition elements M?M=Sc,Ti,V,Cr,Mn,Fe,Co,Ni?.The results show that the volumes of M-doped systems are gradually reduced,and the volume of the Ni-doped model is minimized.For doping stability,the order from low to high is:Co<Ni<Sc<Fe<Mn<Ti<V<Cr.With the number of d electrons increases,their valence bands increase substantially,while the conduction band firstly decreases and subsequently increases with the doping of Mn,Fe and Ni.For light response,the light absorption of Fe or Mn doped model is better under UV light,and Ni-doped effect is best in the visible region.4.We simulated different models of Eu³⁺-doped NaTaO₃ by density functional theory.Through the selective doping of Eu³⁺ions at different sites,the redox reaction could be enhanced.We have constructed three different NaTaO₃ models with Na⁺-rich environment.The results show that the Eu³⁺-doped electron state moves to the lower energy when the non-stoichiometric molar ratio of Na/Ta is lower.With the increase of Na/Ta molar ratio,the density of electron states is increased significantly in the conduction band of NaTaO₃,leading to the increase of the carrier migration rate and the photocatalytic activity.