Transformation Law Of Titanium-based Photocatalysts And Degradation Of Tetracycline Hydrochloride

Tetracycline hydrochloride（TCH）,as a broad-spectrum antibiotic,is often used to treat biological diseases.However,the naphthol ring structure in TCH is difficult to be completely metabolized by organisms,making most of TCH remain in the environment.Residues promote the production of various drug-resistant bacteria and pose a threat to human living environment.Photocatalytic technology has attracted much attention in environmental pollution control because of its advantages of green environmental protection,energy saving and high efficiency and low cost.Titanium based semiconductors such as titanium oxyfluoride hydrogen（HTiOF₃）,titanium oxyfluoride（TiOF₂）,titanium dioxide（TiO₂）and hydrogen titanate（H₂Ti₃O₇）have the application potential as environmental functional materials because of their convenient source,non-toxic and low price.However,the conversion law between HTiOF₃,TiOF₂,TiO₂ and H₂Ti₃O₇ is not clear,and its photocatalytic performance still needs to be improved.The research goal of this paper is to explore the transformation law between HTiOF₃,TiOF₂,TiO₂ and H₂Ti₃O₇ under specific conditions,and obtain photocatalysts for efficient degradation of TCH.The specific research contents and results of this paper are as follows:（1）HTiOF₃ can be transformed into TiOF₂,TiO₂ and H₂Ti₃O₇ respectively under specific conditions.Using butyl titanate as titanium source,hydrofluoric acid as fluorine source and glacial acetic acid as inhibitor,cylindrical granular HTiOF₃ with good crystal shape can be synthesized by solvothermal method at 180℃ for 1 h.When the reaction time is 3 h,cylindrical granular HTiOF₃ is transformed into TiOF₂ cube.Using HTiOF₃ as precursor and absolute ethanol as solvent,the cylindrical granular HTiOF₃ was transformed into TiOF₂ nanoclusters at 150℃ for 10 h.Using HTiOF₃ as precursor,sodium hydroxide as etchant and hydrochloric acid as ion exchanger,the cylindrical granular HTiOF₃ was transformed into H₂Ti₃O₇ wave edge nanoflowers at 150℃ for 10 h.（2）Study on the conversion of HTiOF₃ to TiOF₂ and its photocatalytic activity.Using butyl titanate as titanium source,hydrofluoric acid as fluorine source and glacial acetic acid as inhibitor,titanium based photocatalysts（T-X）with different reaction times（X=0.5,1,2,3）were synthesized by solvothermal method at 180℃ to explore the phase evolution and photocatalytic activity of HTiOF₃ to TiOF₂.The results showed that with the increase of solvothermal reaction time,the sample changed from spherical nano granular HTiOF₃ phase（T-0.5）to smooth cubic TiOF₂ phase（T-3）.The titanium based photocatalysts obtained at different reaction times have different photocatalytic degradation effects on TCH,and T-0.5 shows the best photocatalytic degradation effect.When the dosage of T-0.5 photocatalyst is 0.3 g/L and the simulated sunlight is irradiated for 1 h,the TCH removal rate of 20 mg/L is 51%,which needs to be further improved.（3）Study on the conversion of HTiOF₃ to TiO₂ and its photocatalytic activity.HTiOF₃（T1）with the best crystal form in（1）was used as the precursor,and then it was put into anhydrous ethanol solvent for ethanol thermal reaction.A series of titanium based photocatalysts（HT-X）were synthesized by adjusting the alcohol thermal reaction time（X=1,3,5,10）at 150℃ to explore the phase evolution and photocatalytic activity between HTiOF₃ and TiO₂.The results show that the prolongation of alcohol thermal reaction time can make the HTiOF₃ precursor（T1）of cylindrical nanoparticles transform into TiO₂ nanoclusters（HT-10）.Among them,the removal rate of TCH in the sample（HT-5）with an alcohol thermal reaction time of 5 h is twice as high as that of T-1.When HT-5 dosage was 0.3 g/L and simulated sunlight was irradiated for 1 h,the TCH removal rate of 20 mg/L was 90%.HT-5 has a large specific surface area（193 m²/g）and strong adsorption for TCH.In addition,the LMCT and sensitization synergy between HT-5 and TCH widened their absorption range under visible light and promoted carrier migration.Importantly,the surface heterojunction formed by the close contact between {001}and {101} crystal planes of TiO₂ inhibits the recombination of carriers and improves the utilization efficiency of carriers·O₂^-is the main active species degrading TCH.In addition,HT5 has stronger photochemical corrosion resistance.After five repeated tests,HT-5 still has good degradation performance（83%）for TCH.（4）Study on the conversion of HTiOF₃ to H₂Ti₃O₇ and its photocatalytic activity.A series of titanium based photocatalysts（HTO-X）were synthesized by adjusting the alkaline hydrothermal reaction time（X=1,3,5,10）at 150℃ with HTiOF₃（T-1）,the best crystal form in（2）,sodium hydroxide as the etchant and hydrochloric acid as the ion exchanger.The results showed that the HTO-X catalysts prepared under different alkaline hydrothermal reaction time showed H₂Ti₃O₇ phase.With the increase of reaction time,the crystalline form of H₂Ti₃O₇ becomes better and better.Among them,the sample（HTO-5）with alkaline hydrothermal reaction time of 5 h showed filamentous nanoflower morphology,ordered mesoporous structure,high specific surface area of 200 m²/g and pore volume of 0.26 cm³/g.The LMCT effect and sensitization synergy between TCH and HTO-5 not only expand the visible light absorption region of HTO-5,but also improve the carrier separation ability.When the dosage of HTO-5 was 0.3 g/L and the simulated sunlight was irradiated for 1 h,the TCH removal rate of 20 mg/L was 94%.In addition,HTO-5 has stronger photochemical corrosion resistance.After five repeated tests,it still has excellent degradation performance（88%）for TCH.