Preparation Of Magnetical ZnFe₂O₄@SiO₂@TiO₂-F/N Composite Photocatalysts And Their Properties

In this paper,the F-N co-doped magnetic ZnFe₂O₄@SiO₂@TiO₂ composite photocatalysts were prepared to improve the recyclability and low visible light photocatalytic activity of nano-TiO₂ photocatalyst.Firstly,ZnFe₂O₄@SiO₂?ZS?binary composite nanoparticles were prepared by sol-gel method using ZnFe₂O₄ nanoparticles and TEOS as the precursor.Then ZnFe₂O₄@SiO₂@TiO₂-F/N?HZST-F/N and CZST-F/N?ternary composite photocatalysts were prepared via hydrothermal method and calcination method,meanwhile F and N elements were co-doped into TiO₂ using NH₄F as dopants.The photocatalytic activities of the hybrids were evaluated by the degradation rates of methyl orange?MO?,and the magnetic separation performance of the catalysts were also investigated.The results showed that the degradation rates of MO on HZST-F/N prepared by hydrothermal method reached 100%under UV light irradiation for 120min or visible light irradiation for 120min,and the degradation rates of MO on CZST-F/N prepared by calcination method were 100%and 95%,respectively.XRD confirmed that ZnFe₂O₄ was spinel structure,the inert layer SiO₂ was amorphous,and the outer layer TiO₂ was anatase.SEM and TEM showed that ZS had core-shell structure and its diameter was about 120nm,and HZST-F/N and CZST-F/N had a spherical morphology and their grain sizes were about 1.07 and 1.01?m in diameter,respectively.VSM displayed that HZST-F/N and CZST-F/N possessed superparamagnetism and their saturation magnetizations were 7.5 and 6.0emu/g.BET suggested that the specific surface areas of HZST-F/N and CZST-F/N were 272.3 and129.8m²/g.The photocurrent densities of HZST-F/N and CZST-F/N were 0.12 and0.08?A·cm^-2.Therefore,the catalyst prepared by hydrothermal method had better property.To explore the photocatalytic mechanism of ZST-F/N,the active group scavengers BQ,EDTA,TBA and AgNO₃ were added to the reaction system.The results found that all of them can inhibit the rates of photocatalytic degradation of MO compared to no scavenger,and the photodegradation of MO was remarkably inhibited in the presence of BQ and EDTA,which indicated that the active groups O₂?^-and h⁺played a major role in the photocatalytic reaction.UV-Vis DRS showed that the absorption edge of ZST-F/N had a red-shift compared to P25,the band gap energy was reduced,and visible light absorption was enhanced.XPS displayed that F and N were co-doped into the lattice of TiO₂ to form O-Ti-N and Ti-F,which can reduce the band gap of TiO₂ and promote visible light absorption.PL spectra and photocurrent density results suggested that the photogenerated electron-holes recombination was effectively suppressed after fluorine and nitrogen co-doping.It is due to the synergistic effects of the narrow bandgap energy semiconductor ZnFe₂O₄,the inert layer SiO₂ and F-N co-doped TiO₂ that the absorption of visible light and the separation of photogenerated electron-holes of the composite photocatalyst can be enhanced.Finally,ZST-F/N exhibited efficient and stable UV-Vis photocatalytic activity.