Preparation Of Upconversion Material/TiO₂ Photocatalyst And Its Application In Marine Aquaculture Wastewater

In recent decades,with the rapid development of the economy,the aquaculture industry has developed by leaps and bounds.At the same time,the discharge of a large amount of aquaculture wastewater has a huge impact on the surrounding water environment.Ammonia nitrogen is one of the main pollutants in aquaculture wastewater,and its continuous production will cause the accumulation of pollutants,which will cause biological toxicity.Among many ammonia nitrogen treatment methods,photocatalytic oxidation technology is favored by more researchers for its low cost,stability,high efficiency,low time consumption,no secondary pollution,and easy operation.The purpose of this paper is to use solar energy and high activity catalyst to degrade the ammonia nitrogen in marine aquaculture wastewater by catalytic oxidation,and the TiO₂ semiconductor photocatalyst is prepared by sol-gel method,and composite photocatalysts obtained by combining three rare earth up-conversion materials of CaF₂(Tm³⁺),Er₂O₃ and Pr₁₁O₆ with nano-TiO₂.The supported photocatalyst was prepared by the combination of polypropylene polysphere and photocatalyst.Using visible light as the light source and ammonia nitrogen as the target pollutant in marine aquaculture wastewater,the photocatalytic performance and photocatalytic kinetics of four TiO₂ composite photocatalysts were studied.The supported photocatalyst is used to treat ammonia nitrogen in seawater,which has achieved good results and laid a foundation for the treatment of ammonia nitrogen in marine aquaculture wastewater.The research conclusions are as follows:?1?Nano-TiO₂ was prepared by sol-gel method.The particle size,crystal form,morphology,composition and chemical properties of the self-made nano-TiO₂photocatalyst were characterized by XRD,SEM and UV-Vis.The removal of ammonia nitrogen in marine aquaculture wastewater by TiO₂ photocatalyst under visible/ultraviolet excitation was studied.The effects of various reaction conditions,including TiO₂ dosage,initial ammonia nitrogen concentration,H₂O₂ concentration,pH and illumination time on the degradation of ammonia nitrogen in marine aquaculture wastewater were studied.The conclusion is as follows:the TiO₂photocatalyst prepared by sol-gel method is stable,the activity is high,the crystal form is anatase,and the particle size is in the range of 15-25 nm.Under the same conditions,the removal rate of ammonia nitrogen under ultraviolet light is higher than that under visible light,the average removal rate is about 60-70%,and the ammonia nitrogen removal rate is low under visible light,about 30-40%.?2?CaF₂(Tm³⁺)/TiO₂ composite photocatalyst was prepared by sol-gel method.The composite photocatalysts of Er₂O₃/TiO₂ and Pr₆O₁₁/TiO₂ were prepared by coprecipitation method.The effects of doping ratio,catalyst dosage,initial concentration of ammonia nitrogen,H₂O₂ concentration,pH value and illumination time on theremoval of ammonia nitrogen in marine aquaculture wastewater were investigated,the photocatalytic conditions were optimized and the following conclusions were obtained:CaF₂(Tm³⁺)/TiO₂,Er₂O₃/TiO₂ and Pr₆O₁₁/TiO₂ composite photocatalysts have good dispersibility,and the average particle diameters are 20.67,44.95 and 19.96 nm,the optimum conditions for photocatalytic degradation of ammonia nitrogen in marine aquaculture wastewater are:when catalyst doping ratios were 15,40 and 40%,the dosage of catalyst were 0.2,0.4 and 0.8 g/L,the initial concentrations of ammonia nitrogen were 80,100 and 80 mg/L,the concentrations of H2O2 were all 0.3 g/L,the pH were 10,8 and 8,and the visible light duration were 2.5,3 and 4 h.Through the verification experiment,it can be concluded that the ammonia nitrogen removal rates were 63.26%,81.63%,75.78%,the order of influence factors of each factor on the removal of ammonia nitrogen is as follows:pH>dosage ofcatalyst>illumination time>initial concentration ofammonia nitrogen>CaF₂(Tm³⁺)upconversion material doping ratio>concentration of H2O2;dosage ofcatalyst>pH=catalyst doping Ratio>illumination time>initial concentration of NH₃-N>concentration of H₂O₂;pH=catalyst doping ratio>initial time>initial concentration of NH₃-N>dosage>concentration of H₂O₂.?3?The nitrite and nitrate in the solution were determined by naphthylethylenediamine spectrophotometry and ultraviolet spectrophotometry.Under the optimal conditions for removing ammonia nitrogen from each composite photocatalyst,the other major pollutants in marine aquaculture wastewater,including nitrite,nitrate and phosphate,were removed and the following conclusions were drawn:under laboratory conditions,the final experimental product of photocatalytic degradation of ammonia nitrogen by TiO₂ is N₂.The three composite photocatalysts have good removal rates for nitrite,nitrate and phosphate,the nitrite removal rate is about 60-70%;the nitrate removal rate is about 50-70%;phosphate The removal rate is low,about 40-60%.The removal efficiency of the three pollutants by Pr₁₁O₆/TiO₂composite photocatalyst was higher than that of the other two composite photocatalysts,which indicated that the photocatalytic activity of the by Pr₁₁O₆/TiO₂composite photocatalyst was higher than the other two.?4?The effects of photocatalyst doping ratio,dosing amount,initial concentration of ammonia nitrogen and H2O2 concentration on the reaction kinetics were investigated.The experimental data were subjected to the first-order reaction rate equation,the The results show that the correlation coefficient R2 of the first-order reaction rate equation for the removal of ammonia nitrogen from marine aquaculture wastewater by Er₂O₃/TiO₂ composite photocatalyst is greater than 0.94,and the fitting effect is better,which accords with the first-order reaction kinetics.Based on the L-H model,the total photocatalytic oxidation kinetic equation was calculated,and It is concluded that under certain conditions,the initial concentration of NH₃-N has a greater influence on the photocatalytic reaction rate.The factors affecting the removal of ammonia nitrogen in marine aquaculture wastewater by Er₂O₃/TiO₂ photocatalyst were as follows:initial concentration of ammonia nitrogen>hydrogen peroxide concentration?catalyst doping ratio>dosage of catalyst.The dosage of catalyst has a positive correlation,and the catalyst doping ratio,the initial concentration of ammonia nitrogen and the concentration of hydrogen peroxide have a negative correlation,that is to say,within a certain range,the dosage of Er₂O₃/TiO₂ composite photocatalyst is beneficial to the photocatalytic oxidation reaction,and the latter three factors inhibit the progress of photocatalytic oxidation..?5?A supported photocatalyst supported on polypropylene polyhedral spheres was prepared by a titanate coupling agent method.The effects of three kinds of rare earth doped photocatalysts on the removal of ammonia nitrogen from marine aquaculture wastewater were investigated.The photocatalytic performance and various reaction conditions of the three supported photocatalysts,including the catalyst loading,the initial concentration of ammonia nitrogen,the illumination time and the number of catalyst recovery times,were investigated for the removal of ammonia nitrogen in marine aquaculture wastewater.The following conclusions were drawn:the supported photocatalyst prepared by the titanate coupling agent method has good coverage,and the particles are evenly distributed on the surface of the polypropylene multi-faceted ball,and the film will not fall off in seawater.Moreover,the supported photocatalyst has better photocatalytic activity.Compared with pure TiO₂,the composite photocatalysis with three kinds of rare earth ions has strong photocatalytic activity,the photocatalytic activity of the three composite photocatalysts is ranked as:Pr₆O₁₁/TiO₂>Er₂O₃/TiO₂>CaF₂(Tm³⁺)/TiO₂.The supported photocatalyst has a short time,high speed and high removal rate of ammonia nitrogen in marine aquaculture wastewater.When the catalyst loading is0.3g,the ammonia nitrogen concentration in seawater is 100mg/L,the seawater pH is8,and 1mL 0.3g/L hydrogen peroxide is added,after 6h reaction under visible light,the ammonia nitrogen removal rate can reach 73.59%.The supported photocatalyst can be recycled at least three times,and the recovered supported photocatalyst has less loss and can maintain good photocatalytic activity and adsorption performance.