Colorimetric Determination Of CdS Nanocrystals Concentration

Quantum confinement of semiconductor nanocrystals plays a key role on determination of optical properties of the nanocrystals. For this reason, such semiconductor nanocrystals are known as quantum dots. The unique properties of quantum dots make them useful for fundamental research and technical applications, such as LEDs, biomedical labeling, laser, solar cell, etc. However, some aspects in nanocrystal research need to be clarified, such as purification, extinction coefficient, and concentration of the particles. In this thesis, we studied these problems for CdS nanocrystals.1. Purified using existing purification procedures, CdS nanocrystal were proven still containing unreacted cadmium carboxylate salts. In our research, butylamine was employed to obtain high extraction efficiency by formation of complex with cadmium carboxylate. Results illustrated that such complex can be dissolved in methanol and the nanocrystals remain in heaxnes phase. According to IR spectra, there is barely any cadmium carboxylate left after four methanol/hexane extraction with butylamine addition.2. The absorption peak of cadion with Triton X-100 is at 569nm and the absorption peak of complex that cadion and cadmium formed is at 478nm. The difference between the absorbance of 478nm and 569nm is linear with the concentration of the complex in the range of 0～8μg/mL. In this concentration range, we could calculate the concentration of cadmium ions in acid-digested nanocrystal solution. By considering geometry and crystal sturcture, one can further calcuate the extinction coefficient of the particles. The advantage of colorimetry is simple and readily acessible.3. The colorimetric method can further be used for determination of CdS unit yield without knowing its size and shape. This assisted the determination of critical temperature in CdS nanocrystals synthesis.