Study On The Preparation Of Modified TiO₂nanotubes And The Degradation Of Organic Pollutants In Environment

With the large-scale development of printing and dyeing industry,how to deal with printing and dyeing wastewater has become an urgent problem.Photocatalytic technology can completely degrade the pollutants without causing secondary pollution,which is expected to become a new method of environmental governance.Among the photocatalytic materials,one-dimensional tubular nano-TiO₂ has a large specific surface area and more reactive sites;however,due to the wide band gap of the catalyst and the high probability of photocarrier recombination,its large-scale application is restricted.Modification is an effective way to improve the photocatalytic performance of TiO₂.In this paper,on the basis of one-dimensional nanotubes prepared by anodizing method,firstly,graphite phase carbon nitride（g-C3N4）was loaded onto TiO₂ nanotubes by chemical vapor deposition（CVD）.Then Er/g-C3N4/TiO₂ was prepared by hydrothermal method,and the azo dye Methyl Orange（MO）was used as the simulated dyeing wastewater to evaluate the visible light activity of the samples.The main contents of this paper are as follows.In order to broaden the absorption band of TiO₂ to visible light region,g-C3N4/TiO₂nanotubes were prepared by chemical vapor deposition using urea as precursor.Field emission scanning electron microscopy（FESEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,transmission electron microscopy（TEM）were used to characterize the phase structure,micro morphology,element composition and other properties of the samples.The results show that most of the modified TiO₂ is anatase and a few is rutile.The element analysis of EDS and XPS confirmed that g-C3N4 and TiO₂ were successfully compounded and the two semiconductors were connected by heterojunction.It was observed by SEM and TEM that g-C3N4 was loaded on the surface of nanotubes.In the photocatalytic performance test,the heterojunction nanotubes with 3 g precursor had the strongest activity,and the degradation rate constant was 5.28 times higher than that of unmodified TiO₂ nanotubes.In order to further improve the performance of the modified TiO₂ photocatalyst.Er,a lanthanide element with unique electronic structure,was introduced into the heterojunction catalyst to prepare the ternary photocatalyst:Er/g-C3N4/TiO₂ nanotubes.The composite was characterized by FESEM,XRD,TEM and XPS.It was found by FESEM that the catalyst prepared at 160℃had a good morphology,and the surface of the nanotubes was not smooth and flocculent with the increase of rare earth concentration.In the XRD diffraction pattern,the diffraction peak of the modified sample corresponding to the anatase（101）crystal plane shifted to the small angle,indicating that Er³⁺existed in the lattice gap at this time,which caused the lattice distortion.XPS and EDS analysis showed that there were five elements in the nanotubes,and Er2O3 was formed.The increase of lattice spacing of TiO₂ by TEM characterization confirmed the conclusion of XRD.Taking MO as the target pollutant,the influencing factors of degradation reaction of ternary composite were studied.The influence of different preparation conditions on the photocatalytic performance was discussed:the activity of the ternary modified catalyst prepared at the hydrothermal temperature of 160℃was the strongest;the maximum catalytic efficiency was obtained when the concentration of rare earth was 3 m M,and 88%of MO solution was degraded within 300 minutes.the photocatalysis rate constant was twice that of the binary catalyst.The effect of the change of the solution properties on the degradation reaction was discussed:the degradation rate of the solution decreased with the increase of the initial concentration of the solute,and it had the maximum degradation rate when the initial concentration of MO was 5 mg/L;the degradation rate of MO was affected by the initial p H value,and the active free radicals which played the main role in the degradation reaction were different in different acid-base systems.In the test of catalyst cycle life,it was found that the degradation rate decreased from 88%to 80%after five reactions,and the ternary catalyst still maintained good stability.Combined with the above analysis,in the process of photocatalytic reaction of Er/g-C3N4/TiO₂ nanotubes,three active substances,namely,·OH,·O2^-,and h⁺,act on the MO molecule and mineralize it into CO2,H2O and other small molecules.