Preparation Of Cabon-based Quantum Dots And Their Mechanisms For Detection And Removal Of Environmental Pollutants

Carbon-based nanomaterials have widely applied to various fileds in recent years due to their desirable physical and chemical properties.The present dissertation has focused on the design and preparation of carbon-based-low-dimensional composites and their applications in environmental science.We have prepared a series of high-quality and high-performance low-dimensional carbon-based composite materials such as carbon quantum dots?CDs?and Graphene-TiO₂ composite,and then explored their properties for metal ion detection,pollutant adsorption and photocatalysis.The results demonstrated the promising applications of low-dimensional carbon-based composites in the field of environment.The research contents in this dissertation can be summarized in the following four sections:The first section focused on the rapid synthesis of CDs by microwave-assisted method,and the resulting CDs were characterized by TEM,FT-IR,XRD,and XPS.The effects of synthetic conditions such as reaction temperature and time on the quantum yields?QYs?were also investigated.The highest QYs up to 90%were achieved at temperature 180?.The QY did not change significantly between 5 and 60minutes of microwave heating,and nearly remained at about 80%.Moreover,the fluorescence intensity of CDs and their fluorescence response to ward different metal ions were studied.All results have demonstrated that the CDs derived-from citric acid and ethylenediamine are more suitable for sensitive detection of metal ions.?chapter2?.The second section developed a rapid and sensitive high-throughput assay for irons in aqueous solution and gasoline with highly fluorescent CDs.Combined with a microplate fluorescence reader,the whole process from the CD synthesis to the detection output is required only within 15 min.The limits of detection for Fe³⁺in aqueous solution and ferrocene in gasoline are determined down to 0.05 mmol/L.Furthermore,this method has been successfully used to determine the level of irons in real gasoline for quality evaluation.The results have an excellent agreement with atomic absorption spectrophotometric measurements.This facile assay with lower cost,use of less sample,and higher-throughput holds great promise as a screening inspection technique for irons in aqueous environments and fuel products.?chapter 3?.In the third section,we have used CDs as adsorbents for removing metal ions from aqueous solution,and conducted Cr???single factor adsorption studies.The effects of operating conditions such as pH,Cr???concentration and time on the Cr???adsorption were investigated.The results showed that the VC-Lys CDs had very good adsorption performance on Cr???ions in aqueous solution.The optimal Cr???removal efficiency of 100%was achieved at pH 2,and the adsorption process can be finished in a very short time.Also,the high adsorption uptake up to 79.09mg/g toward high concentration Cr????40mg/L?was demonstrated.The CD-based adsorption system thus exhibits great promising applications in the adsorption and removal of Cr???in aqueous environment.?chapter 4?.In the fourth section,the highly porous grapheme/TiO₂ nanofibers were directly prepared by electrospinning for the first time.The photocatalytic properties of the composites were studied by using Rhodamine B?RhB?as the degradation agent.The results show that the composites displayed excellent photocatalytic performance for degradation of Rhodamine B?RhB?.Within 30 minutes,the highly porous grapheme/TiO₂ nanofibers's absorption of RhB reached 70%.After 120 min irradiation,almost 100%of RhB molecules were decomposed by the grapheme composite highly porous TiO₂ nanofibers.Moreover,the grapheme/TiO₂ composite nanofibers exhibit very stable photocatalytic activity.There is no obvious decrease on the removal rate of RhB even after ten cycles.Such grapheme composite highly porous TiO₂ nanofibers may bring new insights into the design of highly efficient photocatalysts for organic compounds and may have potential technological applications?chapter 5?.