Development Of Visible Light Response Catalyst And Its Photocatalytic Degradation Of Organic Matter In Seawater System

In view of the characteristics of seawater system,in order to develop efficient and stable photocatalyst responsive to visible light,the mature commercialized Ti02 nano-photocatalyst?P25?was selected as the object of study and modified preparation.By the use of Solvent heat reduction,hydrothermal process and other methods,the heterojunction structure and Ti³⁺ were introduced into the P25 structure,which easily expanded the visible light response of the P25 nano-photocatalyst.Combined with the photodegradation of phenol in artificial seawater under visible light excitation,the relationship between heat treatment conditions,the microstructure of catalyst and the activity of visible light degradation was correlated and its mechanism was studied.It was also pointed out that the effects of different heat treatments on the formation of two key microstructures(heterojunction structure and Ti³⁺)in the catalyst were different.Finally,the effects on the visible light response and photodegradation activity of the modified P25 under visible light were also different.The main research of paper could be divided into several progressive contents:Based on the extended study on the visible light response of Ti³⁺auto-doping to TiO₂,this paper firstly designed the study on thermal reduction modification of P25 nanoparticles in the presence of a reducing agent.The ascorbic acid,glucose and ethanol were used as the three reducing agents,and the study on thermal reduction modification of P25 had been completed.The results showed that the disordered structure appeared on the surface of nanoparticles of all the samples after the three reducing agents were modified.Although the reducing performance of ascorbic acid and glucose was better than that of ethanol,the molecule was decomposed during the heat treatment due to the fact that the C element was pervasive and less stable in its molecular structure.Therefore,a large amount of carbon deposition was formed on the surface of P25 particles after the two reducing agent's heat treatment,and the modified P25 photocatalyst didn't show any visible light degradation activity.However,after thermal reduction of ethanol,not only did the disordered structure appear on the surface of P25 nanoparticles,but also the phenomenon of carbon deposition did not occur.Thus,this modified P25 developed an obvious visible-light response and a degradation activity under visible light excitation.In the second part,this paper had systematically studied the mechanism of effect of different thermal reduction times and temperatures on the microstructure and visible light activity of P25 nanoparticles in the process of ethanol thermal reduction.It was found that after being treated by ethanol thermal reduction,the crystal structure of Ti02 was firstly changed,and the obvious highly-exposed?001?crystal planes and A/R heterojunction structure were introduced into P25,which would lead to the formation of oxygen vacancy in the crystal lattice structure of TiO₂.Oxygen vacancy expanded the visible light response of TiO₂ by introducing impurity energy level between the conduction and valence band of TiO₂.In addition,after the ethanol reduction,the disordered structure TiO₂ would also be formed on the surface of the catalyst,which led to the formation of a small amount of Ti³⁺ structure.With a combined effect of the both,the ethanol-modified P25 was made to have a better visible-light response and catalytic activity.When the thermal reduction temperature increased from 150 °C to 180 °C or the thermal reduction time increased from 3 h to 24 h,the number of oxygen vacancies and Ti³⁺ structures in the catalyst would firstly increase and then decrease.This is because the high temperature and prolonged heat treatment process enabled the overall growth of Ti02 crystalline structure to be perfect,thus weakening the heterojunction structure in the Ti02 lattice and reducing its visible light activity.When the reaction temperature was 170 °C and the reaction time was 6 h,the catalyst prepared by ethanol thermal preparation showed the highest visible light activity and it degraded the phenol by 62.8%.The visible-light-responsive photocatalyst was obtained from the thermal reduction of ethanol,but it was also showed that the Ti³⁺structures introduced by the thermal reduction process were few.The oxygen vacancy structure produced by the highly exposed?001?crystal planes and the A/R heterojunction structure was the key factor affecting the visible light response and activity of modified P25.In the third part of this paper,P25 was directly processed by a hydrothermal process and compared with the P25 treated with high-temperature calcination.It was found that the hydroxyl effect during hydrothermal or ethanol heat treatment was key to the formation of highly-exposed?001?crystal planes and A/R heterojunction structure in the P25 lattice structure.There was no presence of reducing agent in the Hydrothermal process,so the surface of P25 did not generate a disordered Ti02 structure,nor did the Ti³⁺ doping phenomenon appear.However,a highly exposed?001?crystal plane and an A/R heterojunction structure were still formed in the P25 lattice structure,which in turn formed an oxygen vacancy structure to generate a visible light response.However,after being treated with calcination at high temperature,P25 tended to be perfectly crystallized due to the overall growth of the crystalline structure of Ti02,failing to develop a lattice distortion that was necessary for formation of the oxygen-vacancy structure.Visible light response and visible light degradation activity also failed to occur.Similarly,this was because the high temperature and prolonged heat treatment process made the overall growth of TiO₂ crystalline structure tend to perfect,thereby weakening the heterojunction structure in the TiO₂ lattice and reducing its visible light activity.After hydrothermal treatment at 170 °C for 6 h,the hydrothermally-prepared catalyst had the highest activity in visible light and its phenol degradation rate reached up to 53.7%.However,due to the lack of the synergistic effect of Ti³⁺,its catalytic activity under visible light was weaker than that of the P25 catalyst that had been thermally reduced with ethanol.The last part of this paper was intended for the application of photocatalytic degradation in the actual sea area,taking the ethanol-modified P25 photocatalyst with the highest visible light degradation activity in the study as an active component.Through the combination of surface treatment and silane coupling agent,it was loaded on the surface of a transparent hollow organic glass ball to prepare a floating type TiO₂/organic glass ball photocatalyst.Through preliminary experiments,it was found that the modified TiO₂/organic glassball composite photocatalytic material could be suspended in seawater and could effectively degrade trace phenol in seawater under the excitation of visible light.And it could maintain a good stability with the advantages of recyclability and high recycle rate.This provided a feasible method and a research idea for the advanced treatment of high-toxic organic pollutants in the sea area.