Green Chemical Synthesis of II-VI Semiconductor Quantum Dots

Nanotechnology is the science and technology of manipulating materials at atomic and molecular scale with properties different from bulk. Semiconductor QDs are important class of nanomaterials with unique physical and chemical properties owing to the quantum confinement effect. Size dependent optical properties make research on semiconductor QDs more attractive in the field of nanotechnology. Semiconductor QDs are usually composed of combination of elements from groups II–VI, III–V, or IV–VI of the periodic table. Group II-VI semiconductor QDs (ZnS, ZnSe, ZnO, CdSe, CdS) are most extensively studied systems, having bandgap which can be engineered through the variation of the material composition and size. Most common QDs are made of CdE (E=S, Se, Te) which are toxic. Recent environmental regulations restrict the use of toxic metals and therefore QDs containing nontoxic metals such as Zn are of great importance. The chemical synthesis of QDs involves different methods. Usually high temperature thermal decomposition of organometallic compounds in high boiling point organic solvents is used which needs long reaction time and involves complex synthesis procedures. New simpler and efficient synthetic routes with alternative solvents are required. Recently the synthesis of non-toxic QDs using green chemical routes is a promising approach receiving increasing attention. The aim of this Thesis is to develop novel routes for synthesis of semiconductor QDs employing green nanomaterial synthesis techniques. Therefore, in this work, we developed different green chemical routes mainly for the synthesis Zn-based QDs. Low temperature synthesis routes were developed for the synthesis of ZnS and ZnO QDs. Microwave irradiation was also used as efficient heating source which creates numerous nucleation sites in the solution, leading to the formation of homogeneous nanoparticles with small size and narrow size distribution. Different polar solvents with high MW absorption were used for synthesis of ZnS QDs. We also introduced ionic liquids as solvents in the synthesis of ZnS QDs using microwave heating. ILs are excellent reaction media for absorbing microwaves and are recognized as ‘green’ alternative to volatile and toxic organic solvents. For ZnS systems, the QDs produced by different methods were less than 5 nm in size as characterized by high-resolution transmission electron microscopy (HR-TEM). Selected area electron diffraction (SAED) patterns revealed that ZnS QDs synt