Preparation Of Modified Titanium Dioxide And Its Photocatalytic Degradation Of Ammonia Nitrogen

With the rapid development of society,environmental problems are becoming more and more prominent.Among them,the pollution problem of ammonia nitrogen is more serious.The large amount of ammonia nitrogen in water leads to water eutrophication,destroys the ecosystem,causes the death of animals and plants,and seriously endangers the safety of water environment and human health.Therefore,the standard discharge of ammonia nitrogen in sewage has become an urgent problem to be solved.Compared with other water treatment technologies,photocatalytic oxidation technology has the advantages of high efficiency,strong oxidation and complete degradation.The removal of ammonia nitrogen in water by photocatalytic oxidation technology is expected to achieve good results.Therefore,the preparation of photocatalyst and the influencing factors in the photocatalytic process are worthy of in-depth exploration.The main research results of this paper are as follows:（1）Hydrothermally treated TiO₂ and Ag₂O-loaded TiO₂ were prepared by hydrothermal treatment and semiconductor compounding,and the catalysts were characterized and analyzed by XRD,XPS,FTIR,TEM,UV-vis DRS,BET,PL etc.;The performance study was carried out,and the effect of different influencing factors on the removal rate of ammonia nitrogen in simulated ammonia nitrogen wastewater was explored by combining reaction kinetics and orthogonal method,including initial p H value,light duration,hydrothermal treatment time,doping ratio,catalyst dosage,initial ammonia nitrogen concentration,coexisting ions,etc.;to explore the stability of the catalyst and its performance when the actual ammonia nitrogen wastewater is used as the wastewater to be treated.（2）Through characterization analysis,it is found that hydrothermal treatment will destroy the crystallinity of TiO₂,resulting in a decrease in its specific surface area.The hydroxyl functional groups on the surface of TiO₂,the photo response range,the average pore size and the total pore volume were all increased,and the photon absorption capacity of the catalyst and the catalyst activity were improved.Ag⁺in Ag₂O-loaded TiO₂ exists in the form of Ag₂O and is uniformly attached to the surface of TiO₂.The loading modification makes the catalyst have strong light absorption ability in the ultraviolet region and visible light region,and the formed heterojunction can enhance the electron-hole separation ability of the catalyst.（3）The optimal hydrothermal time of hydrothermal treatment of TiO₂ is 6 h,and the removal rate of ammonia nitrogen after 5 h of reaction is 43.32%.The primary and secondary relationship of each single factor in the orthogonal test is:initial p H>catalyst dosage>Initial concentration>hydrothermal time>light duration,the optimal combination is:light duration 6h,p H=10,hydrothermal time 12 h,initial concentration 100 mg/L,catalyst dosage 1.0 g/L,ammonia nitrogen removal rate 44.86%.Combined with the reaction kinetics,the k value of the reaction rate constant at p H=10 is 1.439×10^-3·min^-1,which is nearly 36 times that of the reaction rate constant at p H=6.67.Cl^-in the coexisting ions has no effect on the removal of ammonia nitrogen in the experimental concentration range,SO₄^2-,CO₃^2-,HCO₃^-have inhibitory effects on the removal of ammonia nitrogen,and the inhibition phenomenon of HCO₃^-is the most obvious.down 52%.In the process of removing ammonia nitrogen by photocatalytic reaction,h⁺,·O₂^-and·OH play the role of degradation in turn,among which h⁺plays the main role,with a contribution ratio of 58%.（4）It is found through experiments that the catalytic effect is the best when the doping ratio of semiconductor composite TiO₂ is 5%,and the removal rate reaches 78.76%;the influence of each single factor in the orthogonal test is:initial p H value>doping ratio>catalyst dosage Addition>reaction time>initial concentration,in which the initial p H value is the single most influential factor.Combined with kinetic analysis,it can be seen that when p H=12,the reaction rate constant is 4.951×10^-3·min^-1,which is when the p H value is not adjusted about 62times.Through single factor experiment and orthogonal experiment,the optimal experimental conditions were determined as follows:illumination time 5 h,p H=12,doping ratio 5%,initial ammonia nitrogen concentration 75 mg/L,catalyst dosage 0.75 g/L,and the removal rate reached 81.33%,the reaction rate constant k is 5.112×10^-3·min^-1.When the concentration ranged from 0 mmol/L to 5.0 mmol/L,Cl^-had no effect on the removal of ammonia nitrogen;SO₄^2-and CO₃^2-both had inhibitory effects on the removal of ammonia nitrogen,and CO₃^2-had a stronger inhibitory effect.When the concentration of CO₃^2-was 5.0 mmol/L,the removal rate decreased by 38%compared with that without adding CO₃^2-.The free radicals that play a role in degradation in the system are mainly·OH,h⁺and·O₂^-,of which the contribution ratio of·OH is 58%.The ammonia nitrogen removal rate decreased from 78.76%to 70.95%after the composite catalyst was cycled for four times.When the ammonia nitrogen in the actual water was taken as the target to be removed,the removal rate of ammonia nitrogen after 5 h of reaction was 66.56%,which was 12.20%lower than that of the simulated water sample.