Preparation And Properties Of Nitrogen-Doped TiO₂ By Hydrothermal Method

Titanium dioxide has high photocatalytic activity,but does not have visible light photocatalytic activity.It can be made to have visible light photocatalytic activity by doping,which broadens its application field.In this thesis,hydrothermal method,titanium tetrachloride is used as titanium source,water is used as oxygen source,hydrochloric acid as an inhibitor,TiO₂ nanorods are prepared on ITO glass,and various experimental conditions are studied for nanorod crystal form.Morphology,photocatalytic properties and hydrophilic properties.Nitrogen doping experiments were carried out on the prepared TiO₂ nanorods with ammonia as nitrogen source.The effects of ammonia addition and reaction temperature on the content of nitrogen doping were also investigated.And the differences in photocatalytic and hydrophilic properties of the samples before and after doping were compared.The prepared samples were characterized and tested by XRD,SEM,TEM,UV-VIS and XPS.The results of this research show that:High-density single crystal rutile phase TiO₂ nanorods were successfully prepared by one-step hydrothermal method on ITO glass substrates.The nanorods have a diameter of 90 nm and a length of 2?m.The nanorods grow along the?101?crystal plane.As the amount of TiCl₄ added increases,the amount of reactant raw materials increases,prompting the reaction to proceed,and more and more titanium dioxide crystals are formed.When the amount of TiCl₄ added is 0.2ml,the length and diameter of the nanorods are 90nm and 2?m.When the amount of TiCl₄ added exceeds 0.2ml,the increase of hydrogen ions generated by hydrolysis of TiCl₄ inhibits the progress of the reaction of TiOH³⁺?TiO₂+H⁺and TiO₂+H₂O?TiO₂+2H⁺.As the reaction time increases,the nanorods have sufficient time for nucleation and growth.However,when the reaction time exceeds 7h,the concentrated hydrochloric acid is corrosive to the sample,so that the nanorods are corroded while growing,and thus the length of the nanorods is gradually increased first and then decreased.Therefore the optimal reaction time is 7h.With the increase of hydrochloric acid concentration,the inhibitory effect of hydrochloric acid on TiCl₄ increased gradually.It was beneficial to the growth of nanorods in the early stage.When the concentration of hydrochloric acid was 6mol/L,the nanorods were basically developed.However,as the concentration of hydrochloric acid exceeds 6 mol/L,the hydrogen ions generated by the electrolysis of hydrochloric acid inhibit the latter two steps of hydrolysis of TiCl₄,and the nucleus of TiO₂ which can be deposited and form nanorods is also reduced.As the reaction temperature increases,the amount of heat supplied increases,and the atomic activity increases,which is more conducive to the growth and crystallization of TiO₂ nanorods.However,too much energy will make the diameter of the nanorods too large and will cover the original nanorod morphology.Therefore,too high a temperature is not conducive to the formation of nanorods,and the optimum reaction temperature is 160°C.As the annealing temperature increases,the nanorods have higher crystallinity and larger crystal grains,so the average diameter of the nanorods increases as the annealing temperature increases.When the annealing temperature continues to increase,the diameter of the nanorods continues to increase,and the nanorods are squeezed each other.Numerous nanorods are connected to each other to form a disordered block structure,and the morphology of the nanorods is completely affected damage.Therefore the optimum annealing temperature is 450°C.The prepared samples were tested for photocatalytic performance and hydrophilicity.The photocatalytic experiments were based on the simulated degradation of acid red and the absorbance of high pressure mercury lamps.The highest degradation rate of acid red is 72.1%.The detection of hydrophilicity is based on the optical contact angle when the water droplets are tiling.The optical contact angle of the water droplets to the sample after irradiation with the ultraviolet lamp is at least9.8°.Nitrogen doping experiments were carried out on the preparation of nanorods under the optimal reaction conditions.The effects of ammonia content and reaction temperature on nitrogen doping content and properties after doping were investigated.When the amount of ammonia added is relatively small,the ammonia produced by the ammonia cannot be lining the entire PTFE lining,and the doped nitrogen element will increase as the ammonia content increases.When the ammonia content exceeds 15ml,the ammonia in the entire reaction space has reached saturation.On the surface of the sample,the N element replacing a part of the O element together with the Ti element forms an O-Ti-N bond,and the internal O atom cannot be in contact with the ammonia gas,so the growth of the nitrogen content tends to be gentle.As the reaction temperature increases,the same system provides more and more heat to the reaction,so the nitrogen retention will be higher and higher.The electrolysis reaction of ammonia water NH₃·H₂O?NH₄+OH^-is an endothermic reaction.Excessive temperature will cause the reaction to proceed to the right,so that the ammonia content in the space is reduced,so the nitrogen content of the sample will be reduced.The photocatalytic performance test and the hydrophilicity test were carried out on the sample after nitrogen doping.The photocatalytic experiment was based on the simulated degradation of acid red,and the absorbance of the high pressure mercury lamp was used as the standard.The highest degradation rate of acid red is 95%.The detection of hydrophilicity is based on the optical contact angle when the water droplets are tiling.The optical contact angle of the water droplets to the sample after irradiation with the ultraviolet lamp is at least 6.4°.