General Synthetic Approach to Heterostructured Nanocrystals Based on Noble Metals and I–VI, II–VI, and I–III–VI Metal Chalcogenides

Abstract

Solid metal precursors (alloys or monometals) can serve both as a starting template and as a source material for chemical transformation to metal chalcogenides. Herein, we develop a simple solution-based strategy to obtain highly monodisperse noble-metal-based heterostructured nanocrystals from such precursor seeds. By utilizing chemical and structural inhomogeneity of these metal seeds, in this work, we have synthesized a total of five I–VI (Ag₂S, Ag₂Se, Ag₃AuS₂, Ag₃AuSe₂, and Cu₉S₅), three II–VI (CdS, CdSe, and CuSe), and four I–III–VI (AgInS₂, AgInSe₂, CuInS₂, and CuInSe₂) chalcogenides, together with their fifteen associated heterodimers (Au–Ag₂S, Au–Ag₂Se, Au–Ag₃AuS₂, Au–Ag₃AuSe₂, Au–AgInS₂, Au–AgInSe₂, Au–CdS, Au–CdSe, Ag–Ag₂S, Ag–AgInS₂, Au–Cu₉S₅, Au–CuInS₂, Au–CuSe, Au–CuInSe₂, and Pt–AgInS₂) to affirm the process generality. Briefly, by adding elemental sulfur or selenium to AuAg alloy seeds and tuning the reaction conditions, we can readily obtain phase-pure Au–Ag₂S, Au–Ag₂Se, Au–Ag₃AuS₂, and Au–Ag₃AuSe₂ heterostructures. Similarly, we can also fabricate Au–AgInS₂ and Au–AgInSe₂ heterostructures from the AuAg seeds by adding sulfur/selenium and indium precursors. Furthermore, by partial or full conversion of Ag seeds, we can prepare both single-phase Ag chalcogenide nanocrystals and Ag-based heterostructures. To demonstrate wide applicability of this strategy, we have also synthesized Au-based binary and ternary Cu chalcogenide (Au–Cu₉S₅, Au–CuSe, Au–CuInS₂, and Au–CuInSe₂) heterostructures from alloy seeds of AuCu and Pt chalcogenides (e.g., Pt–AgInS₂) from alloy seeds of PtAg. The structure and composition of the above products have been confirmed with X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy methods. A kinetic investigation of the formation mechanism of these heterostructures is brought forward using Au–AgInS₂ and Ag–CuInS₂ as model examples