Synthesis and Formation Mechanism of Colloidal Janus-Type Cu_2–xS/CuInS₂ Heteronanorods via Seeded Injection

Abstract

Colloidal heteronanocrystals allow for the synergistic combination of properties of different materials. For example, spatial separation of the photogenerated electron and hole can be achieved by coupling different semiconductors with suitable band offsets in one single nanocrystal, which is beneficial for improving the efficiency of photocatalysts and photovoltaic devices. From this perspective, axially segmented semiconductor heteronanorods with a type-II band alignment are particularly attractive since they ensure the accessibility of both photogenerated charge carriers. Here, a two-step synthesis route to Cu 2 –x S/CuInS 2 Janus-type heteronanorods is presented. The heteronanorods are formed by injection of a solution of preformed Cu 2 –x S seed nanocrystals in 1-dodecanethiol into a solution of indium oleate in oleic acid at 240 °C. By varying the reaction time, Janus-type heteronanocrystals with different sizes, shapes, and compositions are obtained. A mechanism for the formation of the heteronanocrystals is proposed. The first step of this mechanism consists of a thiolate-mediated topotactic, partial Cu + for In 3+ cation exchange that converts one of the facets of the seed nanocrystals into CuInS 2 . This is followed by homoepitaxial anisotropic growth of wurtzite CuInS 2 . The Cu 2 –x S seed nanocrystals also act as sacrificial Cu + sources, and therefore, single composition CuInS 2 nanorods are eventually obtained if the reaction is allowed to proceed to completion. The two-stage seeded growth method developed in this work contributes to the rational synthesis of Cu 2 –x S/CuInS 2 heteronanocrystals with targeted architectures by allowing one to exploit the size and faceting of premade Cu 2 –x S seed nanocrystals to direct the growth of the CuInS 2 segment.

Anion-Directed Synthesis of Core–Shell and Janus Hybrid Nanostructures

“…They promote a controlled reaction important for the nucleation control of CZTS onto the Ag core, ultimately leading to core–shell nanoparticles. The 1-DDT is used as a sole sulfur precursor for the formation of chalcogenide-based disk-shaped and bullet-like morphologies . It acts as both a sulfur source and a ligand, minimizing the surface area of the high-energy (112) plane and promoting the growth of (100) nanocrystal facet growth.…”

“…Consequently, they can greatly improve charge separation, prevent charge recombination, and lower the overpotential for electrochemical reactions resulting in improved photocatalytic activity. Janus nanoparticles are generally synthesized using cation exchange approaches. − The process includes the diffusion of reactant atoms and exchange of ions leading to their conversion into the corresponding material, for example, the exchange of Ag + ions in CdS, CdSe, and CdTe nanorods generating silver chalcogenides. , Similarly, CdS–Cu 2 S nanorods are formed by partial Cu + exchange . The partial or total conversion of the primary nanocrystals depends on the stoichiometry of the reactants and experimental parameters such as growth temperature or time …”

Semiconductor Nanocrystals Emitting in the Second Near‐Infrared Window: Optical Properties and Application in Biomedical Imaging

“…[52,81,141] Donega's group and Manna's group have made considerable efforts in this respect. [52,[142][143][144][145][146][147][148][149] There have been several successful examples of NIR-II emitting I-III-VI SNCs prepared by cation exchange method. For example, starting from a Cu 2-x S nanocrystal template, Donega and co-workers obtained wurtzite phase CuInS 2 SNCs by topotactic partial exchange of Cu + for In 3+ , which showed a PLQY of 25% at 1050 nm after ZnS shell coating.…”

Vacancy assisted growth of copper tantalum sulfide nanocrystals

“…46 Donega et al , have indeed reported the CuInS 2 NCs and Cu 2− x S-CuInS 2 heterostructured NCs by partial indium cation exchange into Cu 2− x S NCs. 47,48 Steimle et al , have demonstrated a multi-step sequential cation exchange of Cu 1.8 S nanorod to form multicomponent axially segmented heteronanorods having eight segments, six different elements, and 11 interfaces. 49…”

“…47,48 Steimle et al, have demonstrated a multi-step sequential cation exchange of Cu 1.8 S nanorod to form multicomponent axially segmented heteronanorods having eight segments, six different elements, and 11 interfaces.…”