Researches On The Photoluminesence And Photocatalytic Properties Of FTO Nanoparticels

Tin oxide?SnO₂?is an important n-type semiconductor metal oxide material,the band gap of which reaches up to 3.6 eV at room temperature and the exciton binding reaches 130 meV.F doped SnO₂?FTO?nanoparticles?NPs?are important inorganic materials with large number of defects,which have significant influences on the properties of FTO NPs.To the best of our knowledge,few systematical works have been conducted on the defect microstructures of FTO NPs,and significant differences of FTO NPs performances are still existed in the the recent literature reports.In this work,FTO NPs were prepared by hydrothermal method with subsequent annealing process.XRD,HRTEM,Raman and XPS are performed to analysis the microstructure and defect evolution of FTO NPs.The photoluminescence?PL?property and photocatalytic property were performed,and the influence of oxygen defects on PL property and photocatalytic mechanism were emphatically studied.The energy level structure model and photocatalytic model of FTO NPs are established.The main conclusions are as follows:1.All of the FTO NPs belong to tetragonal rutile structures,with obviously agglomerated features.The average grain sizes and band gaps vary from 3 nm to 25 nm and 3.64eV to 3.91 eV,respectively.When doping,O^2-in the lattice sites were replaced by F^-,thus inhibiting the growth of grains.When the doping concentration is low,oxygen defect concentration increases.When high,oxygen defect concentration decreases.Heat treatment provides energy for atomic migration,promotes grain growth and makes its dispersion better.therefore,oxygen defect concentration decreases.2.The room temperature PL researchs show that V_O⁰level and V_O⁺level are located at 0.40 eV and 0.87 eV below the bottom of conduction band.The V_O⁺⁺level is located at0.63 eV above the top of valence band.The strong near-band-edge?NBE?emission peaks at about 367 nm can be attributed to the electron transition on the V_O⁰level to the valence band.The emission peaks at 429 nm can be assigned to the electron transition from the donor level formed by V_O⁺to the valance band.The emission peaks at 392 nm are due to the electron transition from the conduction band to the acceptor level formed by V_O⁺⁺.Meanwhile,a series of small emission peaks around 462 nm are attributed to the electron transition from V_O⁰level to V_O⁺⁺level.3.When the F^-doping concentration increases from 0 at.%to 50 at.%,the specific surface area of FTO NPs increases from 46.94 m²/g to 89.21 m²/g.When the heat treatment temperature increases from room temperature to 800?,the specific surface area of FTO NPs from 145.55 m²/g 38.84 m²/g.Among all samples,The degradation of methyl orange solution?10 mg/L?of as-synthesized FTO NPs could reach up to 97%in 80min under UV light irradiation.Analysis shows that surface oxygen defects could improve the photocatalytic activity by capturing electrons or holes generated in the internal of grains to promote the effective separation efficiency of electron-hole pairs.