A simple route for making surfactant free lead sulfide (PbS) quantum dots

• Surfactant free PbS NCs were successfully synthesised using CoSP technique.
• The technique eliminates the requirements of washing to remove the ligands.
• Grinding using mortar and pestle creates well separated PbS QDs.
• Surfactant free PbS NCs are stable and do not show any degradation with time.

An efficient, cost effective and less time consuming method suitable for mass production of surfactant free quantum dots (QDs) of lead sulfide (PbS) is reported. PbS nanocrystals (NCs) are first synthesised by continuous spray pyrolysis (CoSP) technique and de-agglomeration into PbS quantum dots (QDs) is achieved by vigorous mechanical grinding using mortar and pestle. Lead acetate and thiourea were used as the precursor materials for preparation of surfactant free PbS NCs. The broadening in XRD peaks of ground NCs as compared to as synthesized PbS NCs clearly indicated the reduction in particle size to be QDs of PbS. The TEM images also showed that ground PbS NCs were nearly spherical in shape having an average diameter in the range of 4–6 nm. The shift in optical gap from 0.41 eV to 1.47 eV supported the QD formation.

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