Microstructural Modulation And Photocatalytic Degradation Of Ammonia Nitrogen In Titanium Dioxide Nanomaterials

Ammonia nitrogen wastewater is the most abundant and widely distributed wastewater.Due to the existential threat to the environment,ammonia nitrogen pollution control is of increasing concern.Ammonia nitrogen(ammonia or ammonium)is widely present in natural water bodies and can significantly affect aquatic flora and fauna.It plays an extremely important role in human production and health as well as the stability of ecosystems.Reasonably effective control of the concentration of nitrogenous compounds in water bodies requires an urgent need for efficient,secondary pollution-free catalysts to match the nitrogen removal requirements.There are various ways to treat ammonia nitrogen wastewater,such as traditional biological denitrification,physical and chemical methods and electrochemical oxidation,but all these methods have certain limitations,such as not suitable for high concentration of ammonia nitrogen wastewater,high energy consumption and causing secondary pollution.The application of advanced oxidation technology(AOT)is gradually becoming a research hotspot.Advanced oxidation technology refers to the use of chemical-physical processes such as light,electricity,magnetism and sound to generate a large number of free radicals which are strongly oxidizing and can oxidatively degrade ammonia nitrogen in water.Among them,photocatalytic degradation of ammonia nitrogen has the advantages of low energy consumption,green environment and strong oxidation.TiO2 is a naturally occurring transition metal oxide of titanium and is the most common and efficient semiconductor material used as a photocatalyst.Of these,anatase exhibits the best photocatalytic activity in most cases,but it has also been shown that rutile and mixed phase TiO2 perform better in certain specific photocatalytic reactions.On the other hand,the application of TiO2 photocatalysts for ammonia nitrogen degradation has not been sufficiently studied compared to the application areas such as photocatalytic degradation of combustion and dyestuffs,therefore,an in-depth study on the performance and mechanism of photocatalytic ammonia nitrogen degradation by TiO2 nanomaterials is of great theoretical significance and application value.In this thesis,the performance differences of different microstructures of TiO2 photocatalytic degradation of ammonia nitrogen and their microscopic mechanisms were explored,taking ammonia nitrogen in water as the treatment object.The main contents are as follows:(1)TiO2 nanofibres were successfully prepared by electrostatic spinning method with simple component precursor solutions such as tetrabutyl titanate and polyvinylpyrrolidone.TiO2 nanofibres with different crystalline phases were designed for photocatalytic ammonia nitrogen degradation by varying the annealing temperature.The results showed that the rutile phase nanofibres exhibited excellent catalytic activity under alkaline environment and had excellent performance in photocatalytic degradation of ammonia nitrogen.The degradation efficiency reached 97.34%within a fixed degradation time of 8 h,which was higher than that of anatase nanofibres by about 30%,and the degradation rate was increased by 50%compared with that of mass-produced commercial TiO2 nanofibres,highlighting their advantages in the application of ammonia nitrogen degradation.(2)To address the problem of low catalytic efficiency of anatase phase TiO2 in the degradation of ammonia nitrogen,we achieved a breakthrough in the performance of anatase phase TiO2 in the degradation of ammonia nitrogen by using 2D anatase phase TiO2 as a model catalyst and by the strategy of anchoring single atom Pt on 2D TiO2 nanosheets.Specifically,when the Pt loading was 1.5 wt%,its photocatalytic degradation rate of ammonia nitrogen in water was 97.24%,which was 70%higher than the degradation efficiency of the unloaded nanosheets.Further studies showed that the loading of single atoms of Pt on the surface facilitated rapid carrier transfer and the two-dimensional layered morphology also provided favourable factors for the reaction to proceed,providing a high specific surface area to increase the active sites,and the loading of Pt could promote photogenerated electron transfer and transmigration.