Preparation Of Carbon-Hybrid/Doped Nb₃O₇F Nanomaterials And Their Photocatalytic Properties

Photocatalysis has been regarded as one of effective strategies to solve the environmental pollution and energy cleaning.Currently,developing novel photocatalysts with wide spectral response,high carrier separation efficiency and low carrier recombination is becoming a hot topic in photocatalytic field.In recent years,niobium oxyfluoride?Nb₃O₇F?has attracted wide attention due to its excellent UV photocatalytic activities,photocorrosion resistance,thermal stability and phase stability.However,the practical application still suffers from the low photocatalytic efficiency in sewage disposal because of its large band gap?about 3.12 eV?and relatively low quantum efficiency.Moreover,as a novel semiconductor,the chemical property of Nb₃O₇F still keeps unclear up to now.Therefore,it is meaningful to investigate the chemical properties of Nb₃O₇F and find an effective strategy to broaden spectral response and improve carrier separation efficiency.The objectives of this work include:probing the chemical property of Nb₃O₇F and optimizing its photocatalytic activities.Based on the viewpoint of acid resistance,alkali resistance,carrier transfer and optical absorption,the evolution of Nb₃O₇F in acid and alkali environment was investigated in detail.Meantime,hybridization with carbon materials and doping with rare metal element were also conducted in this work to improve its optical absorption,photogenerated carrier separation,and finally find the way to improve its photocatalytic activity.The main contents of the study are as follows:?1?Study on the acid and alkali resistance of Nb₃O₇F.The stability of Nb₃O₇F in acid and alkali solutions was investigated in the environment simulated by NaOH and H₂SO₄ solutions.Firstly,the changing trend of photocatalytic activity about Nb₃O₇F in the acid and alkali environment at room temperature was investigated;then the hydrothermal method was applied to magnify the influence of acid and alkali parameters,including concentration,hydrothermal temperature and time,on the microstructure and optoelectronic property.Finally,evolution rule of Nb₃O₇F in acid and alkali solution were summarized deeply.It was found that Nb₃O₇F is extremely unstable in NaOH solution,and it would transform from Nb₃O₇F nanosheet into NaNO₃ nanorod.The evolution rates could be controlled by the alkali concentration and hydrothermal parameters.Moreover,blue shift of absorption edge could be clearly observed after the reaction in NaOH solution.The band gap increased from3.12 eV to 3.38 eV due to the phase change and the photocatalytic activity got deterioration.Importantly,Nb₃O₇F could keep relatively stable in H₂SO₄ solution,and the structural evolution and photocatalytic activity changed slowly.?2?Preparation of carbon/Nb₃O₇F hybrids and their optoelectrical properties.Here,carbon nanotubes?CNTs?,Nb₃O₇F/hollow carbon spheres?HCSs?and graphene?G?with good conductivity were employed as second components,and carbon/Nb₃O₇F hybrids were synthesized through a hydrothermal method.The results showed that the dye absorption and optical absorption properties could be significantly enhanced by the introduction of CNTs and HCSs;the optimized CNTs/Nb₃O₇F photocatalysts with band gap?2.95 eV?exhibited improved photodegradation performance towards methylene blue within 90 min;the optimized HCSs/Nb₃O₇F photocatalyst with band gap?2.77 eV?only need half of the time during the process of degrading rhodamine B,compared to pure Nb₃O₇F.Besides,G/Nb₃O₇F heterostructures with enhanced the light-harvesting capacity have been constructed through chemical etching solvothermal method.The band gaps decreased from 3.0 eV to 2.88 eV.The absorption edge and band gap can be effectively tuned according to the degree of oxyfluorinated functionalization.?3?Preparation of rare-earth-ion doped Nb₃O₇F nanomaterials and their optoelectrical property.In order to further improve the carrier separation,Eu³⁺and Tb³⁺ions were applied to modify Nb₃O₇F.The influence of species and dosage of rare-earth ions on the structure,phase and photocatalytic activity were investigated in detail.It was found that the doping of Eu³⁺and Tb³⁺resulted in higher surface area and be served as capture centers of photo-generated electrons to accelerate the carrier separation significantly.The photocatalytic rate constants for Eu³⁺and Tb³⁺doped Nb₃O₇F were 3.45 and 4.09 times as that of pure Nb₃O₇F,respectively.