Preparation And Application Of Carbon Nanotubes/Carbon Nitride Composite Photocatalyst

In this paper,the melamine and urea are used as precursors,adopts high-temperature polycondensation method,under the protection of nitrogen at a heating rate of 5^oC/min to 550 ^oC in a tube furnace and at the conditions for 4 hours,finally dried,grinded and then screened;The surface-modified carbon nanotubes were used as cocatalysts,and g-C₃N₄/CNTs composite photocatalysts with different reaction time and different content of carbon nanotubes were prepared by hydrothermal method through stirring,aging and drying.Finally,Rhodamine B,Methyl orange and methylene blue as simulated pollutants,and the photocatalytic activities of the composite photocatalysts were evaluated respectively.The effects of the amount of CNTs on the photocatalytic degradation efficiency of the photocatalysts were also investigated to determine the optimum technological parameters.The main research contents and main achievements of the dissertation are as follows:?1?Preparation of functionalized carbon nanotubes by surface modification of multi-walled carbon nanotubes using concentrated nitric acid,hydrochloric acid,and concentrated sulfuric acid;then using the surfactant,polyvinylpyrrolidone?K30?,to re-modify the different acids treated carbon nanotubes.XRD results showed that the diffraction angle of carbon nanotubes after acid treatment was 2?=26.00^o?d=0.343nm?and 2?=43,65^o?d=0.206nm?.Compared with the pure carbon nanotubes,the peak value did not change much,but the peak shape at 2?=26.00°was narrow.This indicates that the acidification caused the crystal structure of the multi-cerium carbon nanotubes to be damaged to some extent,but it did not affect the structure of graphite.Amphiphilic polymer polyvinylpyrrolidone?PVP?was modified by acid-treated multi-walled carbon nanotubes,the results showed that the amphiphilic polymer PVP was introduced into the surface of MWNTs,and the modified MWNTs were dissolved in ethanol,water and other solvents.Showed a good dispersion,which was conducive to the formation of carbon nanotube/carbon nitride nanocomposites.?2?The g-C₃N₄/CNTs nanocomposites prepared by hydrothermal method have obvious catalytic degradation effect on organic contaminants such as rhodamine B,under visible light irradiation,especially the catalytic effect of g-C₃N₄/CNTs-0.03 after120 min,it was almost 98.6%,much higher than that of the single g-C₃N₄ and other samples.In addition,the recycling experiment of the catalyst was conducted 5 times.It can be seen that the catalytic activity of the g-C₃N₄/CNTs-0.03 composite material changes little and is relatively stable.The catalytic rates of five cycles of rhodamine B were 98.6%,97.6%,96.2%,93.4%and 90.2%,respectively.Therefore,this stable performance makes it practical in the photocatalytic degradation of dye wastewater in the application has become very important.?3?Photocatalytic degradation of RhB by g-C₃N₄/CNTs nanocomposites shows that the photocatalytic properties gradually decreased with increasing concentration.When the amount of catalyst was increased from 0.1g to 0.3g,the photocatalytic activity of the catalyst increased first and then decreased,which was mainly due to the excessive release of the catalyst to make it react with Rhodamine B solution,so absorption-desorption phenomenon occurred;and another reason is that too much catalyst particles block the light irradiation,reducing the utilization of photons.The photocatalytic activity of the catalyst was different with the initial concentration of rhodamine B solution,and with the initial concentration of rhodamine B solution gradually increased,its photocatalytic properties gradually weakened.The results of this study show that the use of polyvinylpyrrolidone?PVP?to re-modify functionalized carbon nanotubes greatly enhanced its dispersion in solution,and has a good absorbance.The g-C₃N₄ nanocomposite was prepared by hydrothermal method using urea as precursor and at the condition of nitrogen.It has good photocatalytic performance for rhodamine B,methyl orange and other organic dyes,and no secondary pollution.Compared with other semiconductor photocatalytic technologies,it has some advantages,such as:low cost,stable catalytic performance and convenient operation,and has a large development potential.