Research On Preparation Of Doped TiO₂ Nanomaterials And Their Photocatalytic Activities

S-Fe,B-S,N-S-codoped TiO₂ nanoparticle and Fe doped microspheres had been prepared by hydrothermal method.Their characteristics were investigated by XRD,UV-vis,XPS,FTIR and photocatalytic degradation for methyl orange(MO).Fe doped titania microspheres with a diameter of about 5-7μm have been synthesized using TiCl₄ and FeCl₃ as the precursor in the presence of Span-80 at 180℃for 48h.XRD indicated that the microspheres were a mixture of rutile,brookite and anatase.XPS showed that the oxidation state of iron in the lattices was probably Fe₂O₃.The UV-Vis DRS revealed that the absorption edge of microspheres had a remarkable shift to the visible light region,its absorption in the visible region was increased.The photocatalytic experiments revealed that the microspheres exhibited high photocatalytic activities under UV-light and solar irradiation.The degradation rate of MO were 100%under UV light irradiation for 3h and 91%under solar irradiation for 6h.In particular, the microspheres could be readily separated by sedimentation after the photocatalytic reaction.It is expected that the TiO₂ microspheres could be one of the ideal photocatalysts for the water purification.S and Fe co-doped TiO₂ nanoparticles(TiO₂-S-Fe) were prepared by in situ hydrothermal method using TiCl₄,FeCl₃ and thiurea as the precursor.The results of photocatalytic degradation MO demonstrated that the TiO₂-S-Fe catalyst obtained at 160℃for 2 h exhibited the highest photocatalytic activity,the degradation ratio of MO were 99%and 97%under sunlight irradiation for 50 min and UV light irradiation for 60 min,respectively.XRD indicated that the TiO₂-S-Fe is in conformity with anatase and rutile mixed phase TiO₂ form.UV-vis DRS showed that its absorption in the visible light district was strengthened and the band edge moved to longer wave obviously.XPS indicated that the partial S atoms occupied O-atom sites in the TiO₂ to form Ti-S bond,lowered the band gap and caused the absorption edge of TiO₂ to be shifted into the lower-energy region.The partial sulfur atoms existed in a six-oxidation state(S⁶⁺) and then enhanced the surface acidity that favored to the adsorption of both oxygen and organic molecules. Doping of Fe³⁺ reduced the recombination of electrons and holes.Both of the above doped effects are beneficial for improving the photocatalysis of TiO₂-S-Fe under UV-light and sun-light irradiation.B-S-codoped anatase TiO₂ nanoparticles(TiO₂-B-S) was prepared using Ti(SO₄)₂,H₂SO₄ and H₃BO₃ as starting materials.UV-vis DRS showed that its absorption in the visible light district was strengthened and the band edge moved to longer wave obviously.XPS showed that the content of hydroxyl group on its surface increased,compared with that of B or S-doped TiO₂, which favored its photocatalysis.The photocatalytic experimental results indicated that TiO₂-B-S prepared at 240℃for 12 hours exhibited the highest photocatalytic activity,the degradation ratio prepared at 240℃for 12 hours exhibited the highest photocatalytic activity,the degradation ratio of methyl orange were 99.8%and 92.0%under UV light irradiation for 50 min and sunlight irradiation for 230 min,respectively.The higher visible light photocatalytic activity of B-S co-doped TiO₂ was attributed to the doped boron that lowered the band gap,resulted in the localized crystal deformation and the doped sulfur which enhanced the surface acidity of TiO₂. Doping of B and S possessed the synergistic effects on enhancement of TiO₂ photocatalytic activity.N-S-codoped anatase TiO₂ nanoparticles(TiO₂-N-S) was prepared using Ti(SO₄)₂ with thiourea as N,S sources.A red shift of the absorption edge was brought out owing to N and S codoping, and the extension for photoabsorption range of it occurred.XPS and EA studies showed that N concentration decreased from the surface to the center.Especially,the photocatalytic tests indicated that it demonstrated a high photocatalytic activity for decomposition of methyl orange, comparing to S doped TiO₂ and undoped TiO₂.The degradation ratio of methyl orange were 88.2 %and 41.4%under UV light irradiation 90 min and sunlight irradiation for 120 min,respectively. The high activity of it can be related to the results of the synergetic effects of strong absorption in the UV-vis light region,red shift in adsorption edge,oxygen vacancies and the enhancement of surface acidity induced by N and S codoping.