Selective Synthesis of α or β-HgS Nanocrystals via Core/Shell Formation Using Surface Modified CdS Quantum Dots

Chalogenides (CdS, CdSe, ZnSe etc.) are well known to undergo cation exchange reactions with other cations, including metals. The cation exchange methods are highly efficient in obtaining core/shell as well as alloy type of nanostructures. Such synthesis approach is particularly useful for producing CdHgX (X = S, Se) alloys, CdX/HgX core/shell and HgX nanostructures as organometallic mercury precursors are very inconvenient to handle. In this work, we have first synthesized hydrophilic CdS quantum dots using various capping agents and studied its cation exchange reaction with Hg2+ ions. The CdS QDs readily reacts with Hg2+ ions at ambient conditions and neutral pH to form either HgS or CdS/HgS core/shell nanostructures. Interestingly, we have observed that capping agent of CdS QDs plays an crucial role in formation of specific form of HgS (α and β). The growth of HgS shell on CdS core with systematic increase in Hg ion concentration is also explored.