Photocatalytic Degradation Of Naproxen By Titanium Dioxide Nanotubes Loaded Carbon Quantum Dots And Effect Of Photocatalyst On Aquatic Organism

Titanium dioxide（TiO₂）has high photocatalytic activity,low toxicity and stability,and is widely used in photocatalysis.Titanium dioxide nanotubes（TNTs）have a larger specific surface area,stronger adsorption capacity and higher photocatalytic activity than TiO₂,and have become one of the research hotspots in the field of nanomaterial synthesis and catalytic applications in recent years.In this paper,the TiO₂ nanotubes were modified by carbon quantum dots to prepare a composite photocatalytic material that can respond to visible light,and it was applied to the photocatalytic degradation of typical PPCPs.At the same time,considering its biological toxicity after entering the water environment..The research results provide a theoretical basis for the popularization and application of titanium dioxide nanotube-loaded carbon quantum dots（TNTs/CDs）.The research results are as follows:（1）TiO₂ nanotubes（TNTs）with large specific surface area were prepared by hydrothermal method.The CDs prepared by solvent method were loaded onto TNTs by co-thermal polymerization to obtain TNTs/CDs composites.Characterized by high transmission electron microscopy（HRTEM）,TNTs/CDs have a diameter of about 9.5 nm,a tube wall of about 3.5 nm,a tube length of about 150 nm,and a uniform loading of CDs on the surface of TNTs.The specific surface area of TNTs/CDs was found to be 174.108 m²/g by N₂ static adsorption method.X-ray diffraction showed that the crystal structure did not change significantly.UV-vis/DRS showed the introduction of CDs to absorb wavelengths of TNTs.From 385 nm to 431 nm,the recombination rate of electron-holes was confirmed by a fluorescence spectrophotometer（PL）.The photocatalytic degradation of Rhodamine B by TNTs/CDs was used to characterize the activity of TNTs/CDs.It was found that the degradation ratio of Rhodamine B was the best when the mass ratio of CDs to TNTs was 5%.Rhodamine B degradation accords with quasi-first-order kinetics,and its degradation rate is0.0479 min^-1,which is 14 times that of TNTs.（2）The photocatalytic degradation of naproxen（NPX）was carried out by using the prepared composite TNTs/CDs and its mechanism was studied.The results showed that NPX accorded with quasi-first-order kinetics under photocatalytic degradation of TNTs/CDs;the rate of NPX degradation by TNTs/CDs was 0.0198 min^-1,which was 33 times that of NPX alone;NPX degraded at pH=4.The fastest rate;O₂.^-and ¹O₂ are the main active substances in the photocatalytic process by electron spin resonance（ESR）and quenching experiments;the NPX degradation pathway is presumed based on the degradation products.The degradation of NPX mainly includes the decarboxylation reaction and the hydroxylation pathway.（3）Three strains of S.obliquus,Daphnia magna and Zebrafish aquatic ecosystems were selected for acute toxicity testing of composite TNTs/CDs.The results showed that it had certain effects on the growth of Scenedesmus obliquus.The EC50 at 48h,72h and 96h were96.37mg/L,65.91mg/L and 64.55mg/L,respectively.After 24 hours of exposure,the inhibition rate of the low concentration group was higher than that of the high concentration group.After 72 hours of exposure,the inhibition rate of the high concentration group was higher than that of the low concentration group.TNTs/CDs had no significant effect on the growth of zebrafish.There was a certain oxidative stress on zebrafish within 96 hours of exposure.