The Preparation Of Composite Materials Based On Quantum Dots And The Study On The Removal Of Cd²⁺ And The Degradation Of Rhodamine

With the development of nanomaterials, new preparation methods of nanomaterialsemerge in large numbers, and the performance of nanomaterials improve continually.Nowdays， composite nanomaterials exhibit a strong potential in wide range ofapplications due to its excellent combination property, especially, the designability of itsperformance. Quantum dots, magnetic materials and Graphene are top priorities in thedevelopment of nanomaterials in recent years. As an emerging fluorescentnanomaterials, Quantum dots shows many outstanding advantages such as highquantum yield, resistance to photobleaching, broad absorption spectra, narrow emissionspectra and optical quantum size effect, making it plays an important role in the field ofoptical detection, tracking and analytical science. Magnetic nanomaterials exhibitssuperparamagnetism, easy to separate and surface modification, so that it is widely usedin the construction of composite nanomaterials. Graphene is a one atom thick andclosely packed two-dimensional honeycomb-like lattiee, because its specialnano-structure and excellent performance, composite materials based on grapheneshows great application potential in many fields. In this paper, the quantum dots is themajoy research object, combine the characteristics of these three nanomaterials, weprepared magnetic fluorescent nanocomposites and graphene–nanocrystalline metalsulfide composites, and studied the building mechanism, optical properties, andapplication ability of each composite, The main tasks are as follows:（1） Synthesis and performance of water-soluble CdTe. In an aqueous solution, usingone-pot method when using MPA as modification stabilizer, Na₂TeO₃as stable Tesource and NaBH₄as reducing agent in the heating under reflux to synthetize theMPA-CdTe. The samples were characterized by scanning electron microscopy （SEM）,X-ray diffraction （XRD）, Fourier transform infrared （FTIR） spectroscopy, UV-visiblespectroscopy and fluorescence emission spectroscopy. By changing Cd/Te mole ratioto abtain CdTe with strongest fluorescence properties and controlling the reaction timecan get varisized CdTe with color from light yellow to dark red （fluorescence emissionpeak of CdTe from484nm to615nm）. Due to the complexation oF ethylene diaminetetraacetic acid （EDTA） and Cd²⁺, we take EDTA as the chemical etching reagent toerode CdTe, discuss the changes in the struture and fluorescence properties of CdTeduring the etching process. The results shows that after eching, we generate cavities ofCd²⁺on the surface of CdTe, the surface defects cause fluorescence quenching, continue to add Cd²⁺, the adding Cd²⁺can quickly fill the cavities so that the fluorescencerecovery.（2） A silica shell was coated onto the magnetic particles to form the Fe₃O₄/SiO₂structure by a sol-gel process, and under the silylating agent, Fe₃O₄/SiO₂was directlycoated with amorphous silica viathe hydrolysis of a sol-gel precursor to formFe₃O₄/SiO₂-SH, the thiol coordination was used to bind the CdTe QDs to the surface ofthe magnetic nanomaterial to form the magnetic fluorescent nanomaterial. The preparedsamples were characterized by SEM, UV-Vis, and fluorescence emission spectroscopy,the obtained composites with fluorescence had an average size of about200nm. Due tothe etching effect of EDTA for the CdTe mentioned above, the magnetic fluorescencenanomaterial was also processed by the EDTA, we can see from SEM that the surface ofthe composites became rough, the reason was the cavities of Cd²⁺formed on the surfaceof the composite material, after etching, the composites were used in the adsorption ofCd²⁺in water samples. The results show that the adsorption capacity ofuneched-composite and eched-composite reached8.03mg/g and17.57mg/g respectively.The kinetics studies show that the eched-composite have good adsorption rate, andadsorption process fit well with pseudo-second-order model.（3） The graphite oxide was prepared using the classic Hummers method, and peeledby ultrasound to obtain the graphene oxide. We used N-N Dimethyl Formamide （DMF）as solvent, the graphene oxide as a support material, zinc acetate as precursor, withdifferent sulfur source （Na₂S and thiourea） as reducing agent in the reaction process toreduce the graphene oxide to graphene, and the S2-combined with Zn²⁺to form ZnSquantum dot and loaded on the the graphene to obtain the graphene/ZnS composites.The structural and optical properties of the composites were characterized by scanningelectron microscopy （SEM）, X-ray diffraction （XRD）, Fourier transform infrared （FTIR）spectroscopy, UV-visible spectroscopy and fluorescence emission spectroscopy. Finally,under the conditions of simulated ultraviolet, we took the composite material as aphotocatalyst to investigate the degradation efficiency to Rhodamine B，the resultsshows that, relative to pure ZnS, the degradation efficiency to Rhodamine B of G-ZnSincreased obviously，the date of the products under optimal experimental condition canreached46.83%...