Noticeable size dispersity and optical stability of sodium dodecyl sulphate (SDS)-coated MnSe quantum dots in extreme natural environment
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The pH of the dispersing media has an influential role on the optical and radiative features of quantum particles/dots (QDs). Herein, we report size dispersity and luminescence response of sodium dodecyl sulphate (SDS)-coated MnSe QDs dispersed in extreme natural extracts. The hydrothermally processed QDs exhibited wutzite phase and numerous Raman active modes as revealed through the X-ray diffraction and Raman spectroscopy studies; respectively. Of varied pH (typically, from 2.5 to 9), distinctly different extracts were derived from starfruit, sugarcane, chilli, and neem leaves available locally. The hydrodynamic size of the QDs experiences a declining trend with increasing pH, with dispersing media being a buffer solution or a natural extract. Zeta potential makes a clear transition from the positive to the negative values, as one moves from a low (acidic) to high (basic) pH of the natural extracts, and subsequently, the isoelectric point (IEP) of the QDs in a medium has been predicted at pH 6.3. Whereas a more acidic medium offered a relatively lowered luminescence profile, the extracts of high pH ensured an intense blue–violet emission of the QDs located at ~ 428 nm along with defect-mediated peaks, expected at relatively higher wavelengths. Furthermore, the acidic environment tends to suppress both near band edge and defect-mediated emissions substantially. The optical stability of surfactant-coated QDs would find immense value in the areas of nano-bio interface applications, such as nano-bioconjugation, bio-imaging, and drug formulation in nano-medicine.
The authors thank Prof. S. K. Dolui, Mr. K. Mohan, and Ms. A. Bora of the Department of Chemical Sciences, TU for extending DLS measurements along with their suggestive measures and assistance. One of the authors (AD) acknowledges Ms. S. Baidya of the Department of Environmental Science, TU for providing conductivity data in regular intervals.
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