Photocatalytic Degradation Of Pesticides By TiO₂-graphene And Optical Behaviors Of Amine-functional Graphene In Solvents

There has been a long lasting and recently increasing scientific interest onphotocatalysis. Although TiO2has been broadly used as a standard photocatalyst,there is a limited photoactivity in the visible range of Earth’s solar spectrum. So TiO2has been modified in order to enhance its solar photocatalytic activity. Graphene hasemerged as one of the most promising materials in the next generation ofphotocatalysts, due to its excellent mobility of charge carriers, large specific surfacearea, flexible structure, high transparency, and good electrical and thermalconduction.TiO2-graphene composites have been prepared by two different paths. The firstly,TiO2-graphene composite was synthesized by two steps, and was characterized byXRD, XPS and FTIR. The photocatalytic activity for degrading alachlor, cyprazineand diuron has been studied under the simulated sunlight irradiation. The secondly,TiO2-graphene composite was synthesized by a hydrothermal process through onestep. The photocatalytic activity of this composite has been analyzed using five amideherbicides and seven organophosphorus insecticides as well. In addition, threeamine-functionalized graphene composites have been synthesized by hydrothermalprocess. UV-Vis absorption wavelength and fluorescence emission wavelength of thethree amine-functionalized graphene composites were investigated in11differentsolvents.Experiment results showed that:1. The degradations of the composites synthesized by the first method were99.4%,100%and78.3%for alachlor, cyprazine and diuron after exposed under thesimulated sunlight irradiation for5h, respectively. In the case of degrading of diuron,the degradation ability was3.7times better than pure TiO2, and2.3times better thanDegussa P25, respectively; and TiO2-2wt%RGO composite shows the bestphotocatalytic performance.2. Under optimized options， The TiO2-graphene (3mg/mL) compositesynthesized by one-step can degrade the amide herbicides and organophosphate pesticides. But the degradation efficiency of graphene-TiO2composite synthesized bytwo steps was4.86times better (alachlor) and2.5times better (ethoprophos) thancomposite synthesized by one-step process through studying comparatively,respectively.3. Different UV-Vis absorption wavelength and fluorescence emissionwavelength were investigated in11different solvents. The amino chain length had anobvious influence on fluorescence emission wavelength in toluene，ethyl acetate，chloroform，dioxane，and DMF. However，the influence of amino chain length onUV-Vis absorption wavelength of the three nanomaterials was insignificant.