Preparation Of Graphene-like Materials And The Study Of Their Photoelectric Properties

With the continuous development of the economy,energy problem is becoming more and more serious.At present,the development of new catalysts to promote the generation of clean energy hydrogen is one of the important means to sort out the energy crisis.Therefore it would be quite a lot of sense designing green and environment-protecting catalysts with high efficiency,high selectivity and low price.The graphene-like materials not only have excellent optical and electrical properties,but also are easily to synthesis and have a very low price.They have been widely used in photo-and electro-catalytic fields,such as catalytic oxidation of cyclohexane,recognition of small molecules and decomposition of water to produce hydrogen.In this work,several kinds of graphene-like materials were prepared by pyrolysis,such as polytriazine imide,chiral carbon quantum dots and molybdenum disulfide/carbon dots composites.And their chemical structures were characterized and optical or electrical properties were investigated and discussed.Specific work includes the following parts:(1)Polytriazine imide(PTI)was prepared through melamine pyrolysis at high temperature with the aid of lithium chloride and potassium chloride.And their morphology and structure were characterized by transmission electron microscopy(TEM),scanning electron microscope(SEM),fourier transform infrared(FT-IR),X-ray photoelectron spectroscopy(XPS),solid NMR and X-ray powder diffraction(XRD)separately.Then PTI served as a catalyst for the selective catalytic oxidation of cyclohexane to test its catalytic activity.After a reaction for 48 h,the conversion rate of cyclohexane oxidation was 5.81%and the selectivity to cyclohexanone was high to 99.9%.From the results,we found that within light illumination PTI could produce quite a lot of cavities and electrons which could be used to induce H2O and O2 to generate hydroxyl radicals and superoxicde radicals to catalyze the oxidation reaction of cyclohexane.This reaction was a green reaction without any oxidants,initiators or solvents.(2)Chiral carbon quantum dots(L-carbon quantum dots,L-CQDs;and D-carbon quantum dots,D-CQDs)were synthesized through the facile hydrothermal treatment with citric acid and L-cysteine(or D-cysteine)as raw materials.First,the chirality in L-CQDs and D-CQDs was demonstrated by circular dichroism.Then atomic force microscopy(AFM),TEM,XRD,XPS and other instruments were utilized to analysis the morphology and chemical structUres of chiral carbon quantum dots.Furthermore,electrochemical experiments were carried out to demonstrate that both L-carbon quantum dots and D-carbon quantum dots possess good enantioselective recognition ability.(3)Molybdenum disulfide/carbon dots composites(MoS2/CDs)with different carbon content were prepared by hydrothermal method with thiourea and sodium molybdate dihydrate as raw materials with adding different amounts of carbon dots at 180 ?,200 ? and 220 ?,respectively.Then SEM,TEM,XRD and XPS and Raman instruments were applied to analyze the morphologies and chemical structures of these samples.Finally,we utilized MoS2/CDs composites as the electrocatalysts to test their ability of hydrogen evolution(HER)with the electrochemical workstation.From the results,we could conclude that with the increase of reaction temperature,the amount of the exposed edge active sites of MoSZ/CDs composites decreased and their electrochemical activity also declined gradually;the addition of carbon dots made the molybdenum disulfide more easily form uniform balls through the accumulation of nanosheets,and it could improve the current intensity and onset potential of composites to some extent.This may be attributed to the addition of carbon dots resultilg in a decrease of S4+,While an increase of O2-and S22-.