Fabrication, Properties And Applications Of The Transition Metal Doped Zn-based Nanocomposites

With the rapid development of nanotechnology, new type functional nanomaterials are continuous emerging. Among them, the doping and composite materials which can integrate several different functions into one show promising applications in the manufacturing, information technology, energy, environment, biomedical and many other fields. In this paper, the controlled growth, optical and magnetic properties of the transition metals(Cu²⁺, Mn²⁺, Cd²⁺) doped ZnS nanomaterials have been systematically studied. And then, ZnS:Mn²⁺ nanowires（NWs）, Fe₃O₄ quantum dots（QDs）, SiO₂ and PNIPAAm were used to synthesize the multifunctional nanocomposites and explore its applications in the biomedical field. The innovative research results were listed as follows:1. ZnS:Mn²⁺ QDs, ZnS:Mn²⁺, ZnS:Cu²⁺ and ZnS:Cu²⁺Mn²⁺ NWs with different doping concentrations were synthesized by a simple solvothermal or hydrothermal method. The results showed that the optimal doping concentration of Mn²⁺ ions in ZnS QDs、ZnS NWs、ZnS: Cu²⁺ NWs were 3%, 1%, 1% respectively; The optimal doping concentration of Mn²⁺ ions and Cu²⁺ ions in ZnS:Mn²⁺Cu²⁺ NWs were both 1%, and the room-temperature ferromagnetism of ZnS:Cu²⁺Mn²⁺ NWs could be attributed to the super exchange interaction between the Mn²⁺/Cu²⁺ ion’s d shell and the near neighbor S2- ion’s p shell, so the optical and magnetic properties of the ZnS:Cu²⁺Mn²⁺ NWs could be adjusted by adjusting the doping concentration of Mn²⁺ ions and Cu²⁺ ions.2. To further broaden the luminescence spectral range of the ZnS-based nanomaterials, we synthesized Zn_0.99-xCd_xMn_0.01 S QDs and Zn1-xCdxS, Zn0.99-xCdxCu0.01 S, Zn_0.99-xCd_xMn_0.01 S nanorods（NRs） by solvothermal method, and systematically investigated their structure, morphology and luminescence properties. For Zn_0.99-xCd_xMn_0.01 S QDs and Zn1-xCdxS NRs, the intensity of the defect state emission decreased, and the near band edge emission of CdS increased as the increase of Cd/Zn molar ratio. So the optical properties of the Zn_0.99-xCd_xMn_0.01 S QDs and Zn1-xCdxS NRs could be continuously adjusted by adjusting Cd/Zn molar ratio. The structure of Zn0.99-xCdxCu0.01 S and Zn_0.99-xCd_xMn_0.01 S NRs were transformed from the wurtzite-type ZnS to the wurtzite-type CdS as the increase of Cd/Zn molar ratio. After doping Mn²⁺（1%） ions into the Zn1-xCdxS NRs, the samples exhibited a better crystal quality and showed a strong yellow-orange emission peak centered at 583 nm. After doping Cu²⁺（1%） ions into the Zn0.1Cd0.9S NRs, the samples exhibited a highly crystalline coaxial Zn0.09Cd0.9Cu0.01S/ZnS core-shell NRs and showed a strong green emission peak centered at 509.6 nm, which was very favorable for preparing of the next generation electronic display and solid-state lighting.3. We synthesized the water-soluble, fluorescent, superparamagnetic ZnS:Mn²⁺ NWs/Fe₃O₄ QDs/SiO₂ nanocomposites by the st?ber method for their application in the field of biology. The diameter of the nanocomposites was between 10 and 18 nm. The ZnS:Mn²⁺ NWs and Fe₃O₄ QDs were modified by thioglycolic acid and citric acid. It was found that the QDs were covalently linked to the NWs and the covalent bonds between the NWs and QDs could effectively suppress the energy transfer from the ZnS:Mn²⁺ NWs to the Fe₃O₄ QDs, and further greatly improved the PL intensity. As the SiO₂ shell thickness increased, the fluorescence intensity reached the highest value when the hydrolysis time of tetraethyl orthosilicate was 5 hour. The superparamagnetic property of the heterostructures was observed at room temperature, which was decreased as the SiO₂ thickness increased. Therefore, the nanocomposites with the orange light emission, water-soluble and magnetic targeting properties could be used as fluorescent markers and drug targets materials.4. We successfully synthesized the ZnS:Mn²⁺（3%） QDs/SiO₂ and ZnS:Mn²⁺ QDs Fe₃O₄ QDs/SiO₂/PNIPAAm nanocomposites by reverse microemulsion and free radical polymerization method respectively, and systematically investigated their structure, morphology and luminescence properties. For ZnS:Mn²⁺（3%） QDs/SiO₂ nanocomposites, the results showed that the monodispersed core/shell nanocomposites were uniform in size, with the majority of the SiO₂ nanoparticles containing one QD in the center of the sphere. The quantum yield of the yellow-orange emission(coming from the Mn²⁺ ions 4T1-6A1 transition) for the ZnS:Mn²⁺（3%） QDs and ZnS:Mn²⁺（3%） QDs@SiO₂（when t=40 h） nanocomposites were measured to be 34.5% and 22.4%, respectively. All samples showed no significant cytotoxicity against the HeLa cells even at a high concentration of 500 μg/ml after incubation for 24 h, which further proving its potential application as the biolabeling agents. The water-soluble ZnS:Mn²⁺ QDs Fe₃O₄ QDs/SiO₂/PNIPAAm nanocomposites with the average diameter of 200 nm have possessed excellent magnetic, luminescent and thermosensitive properties, which could be used as drug carrier in the field of early diagnosis and treatment of cancer.