Abstract
Hydrothermal synthesis autoclave reactor offers simple, safer and environmentally friendlier process for the preparation of valuable nanoparticles. In this study, cadmium selenide (CdSe) quantum dot (QD) were successfully synthesized via one-step hydrothermal synthetic route at 195 oC. The reactant mixtures used for the synthesis was added into Teflon and comprises 15 mg of selenium (Se) powder, 15 mg of cadmium oxide (CdO), 20 ml of octadecene (OTD), 10 ml of oleic acid (OA) and 1 ml of trioctylphosphine (TOP). The synthesis lasted for 3 hours 20 minutes. The synthesized CdSe QDs were characterized using optical absorption spectroscopy, fluorescence spectroscopy (PL), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDAX). The broad absorption peak of the sample depicted the suitability of the sample for photovoltaic application while the fluorescence peaks was assigned to band edge emission to shallow and deep trap states. AFM and SEM microstructure images revealed the surface morphology and the crystal orientation of CdSe QD while the QD size and particles distribution were obtained using TEM and FESEM. The EDX were used to obtain the compositional ratio of the materials in the synthesized CdSe QD sample. The formation mechanisms were discussed on the basis of the experimental results and the quantum dots were found to be stable for about three months.
Highlights
The size of the cadmium selenide (CdSe) nanoparticles was calculated from the bandgap values, using the Brus equation as simplified below; The hydrothermal synthesis of the CdSe quantum dot (QD) started by adding the reaction mixture which comprises 15 mg of selenium powder, 15 m g of cadmium oxide, 20 m l of octadecene, 10 ml of oleic acid and 1 ml of trioctylphosphine oxide into a Teflon housed with a stainless steel wall
The operation lasted for 3 h rs 20 min and the resulting sample were characterized using optical absorption spectroscopy, fluorescence spectroscopy (PL), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDAX)
Various controllable qualities of the CdSe QDs sample such as particle size were not directly controlled, the synthesis produced varied particle sizes of CdSe which implies that different solar spectrum can be absorbed by specific particle size
Summary
Hydrothermal synthesis entails synthesis by chemical reactions of substances in a sealed-heated solution above ambient temperature and pressure. Research on hydrothermal synthesis was initiated in the middle of the 19th century and focuses on laboratory simulations of natural hydrothermal phenomena. In the 20th century, hydrothermal synthesis was clearly identified as an important technology for materials synthesis predominantly for single crystal growth [1]. Understanding of the underlying processes occurring in aqueous solution could be useful during hydrothermal synthetic processes. Control of thermodynamic variables such as reaction time, temperature and concentrations of the reactants and non-thermodynamic variable such as stirring speed during hydrothermal synthesis processes could be useful in commercial manufacturing of chemicals and these variables can be varied to obtain customized resultant samples
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