Anion Exchange in Semiconductor Magic-Size Clusters

Photocatalytic Hydrogen Production Using Semiconductor (CdSe)13 Clusters

Atomically precise (CdSe)13 clusters, the smallest CdSe semiconductors, represent a unique class of materials at the boundary between nanocrystals and molecules. Despite their promising potential, low structural stability limits their applications as photocatalysts. Herein, we report photocatalytic hydrogen production using atomically precise (CdSe)13 clusters. To improve stability in aqueous environments, we induce self-assembly into suprastructures, making them suitable for water splitting. Our findings demonstrate that Co2+ doping enhances the electrical properties of these clusters, while bipyridine serves as cocatalyst by interacting with Co2+ dopants and providing catalytic active sites. Through the synergistic effects of Co2+ doping and bipyridine, Co2+-doped (CdSe)13 suprastructures achieve promising hydrogen evolution activity, surpassing those of undoped suprastructures or nanoclusters. Theoretical calculations confirm that Co2+ doping and bipyridine incorporation lower the hydrogen adsorption energy, consistent with the experimental results. These results highlight the potential of semiconductor (CdSe)13 clusters as photocatalysts for sustainable hydrogen production.

Semiconductor Quantum Dots in the Cluster Regime

The exciton Bohr radius is a defining feature in conventional quantum dot physics. Three distinct confinement regimes are usually recognized: the weak, intermediate, and strong confinement regimes. Which of these is relevant depends on the relative size of the quantum dot in terms of the exciton Bohr radius. However, this classification is primarily based on the linear optical properties of the nanocrystal. During the transition from the molecule to the bulk crystal, structural, mechanical, thermal, and chemical properties change as well. In this review, we discuss the cluster regime, where the exciton experiences extreme confinement. In the cluster regime, not only do linear optical properties deviate significantly from the effective mass approximation, but other material properties also begin to deviate from their bulk values. These deviations are only observable in the size regime, where the intrinsic length scales are much smaller than the exciton Bohr radius. Crucially, computational methods allow chemists to explore this region far more quantitatively than in the past.

Nucleation and Growth of Monodisperse CdTe and CdTe/ZnSe Core/shell Nanocrystals: Roles of Cationic Precursors, Ligands, and Solvents

With CdTe nanocrystals as a model system, we discover a new synthetic strategy for control of size and size distribution of colloidal semiconductor nanocrystals in both nucleation and growth stages. Especially in the nucleation stage, an in situ-formed cadmium complex with approximately one alkanoate and one alkylphosphonate ligand enables both high-yield nucleation by reacting the reactive cadmium-carboxylate bond with Te precursors and efficient size control by immediate passivation with the close-proximity alkylphosphonate ligand from the same complex. Conversely, control on size distribution during either homoepitaxial or heteroepitaxial growth requires reactive cadmium (or zinc) alkanoates as the cationic precursors with a minimum concentration of alkylphosphonate ligands in the novel synergistic solvents. This new strategy not only yields monodisperse CdTe and CdTe/ZnSe core/shell nanocrystals with unprecedented optical quality but also provides a much-needed alternative route for synthesizing monodisperse semiconductor nanocrystals, which is commonly hindered by the growth barrier of the dense ligand monolayer.

Photo-crosslinking of doped magic-sized nanoclusters for the construction of enhanced electrochemiluminescence biosensors

Semiconductor magic-sized nanoclusters (MSCs) possess atomic-level compositional precision and ultrasmall dimensions, allowing accurate modulation of electrochemiluminescence (ECL) properties, essential for advanced bioanalytical applications. However, low intrinsic ECL intensity and poor stability in bipolar electrode (BPE)-ECL systems hinder their broader use. In this work, we addressed these limitations through doping and direct optical crosslinking strategies, achieving a 24-fold boost in the ECL signal and a fivefold stability increase for doped (CdS)34:Ag MSCs compared with original (CdS)34 MSCs. The resulting BPE-ECL biosensing platform was used for the sensitive detection of glucose with a linear detection range of 10 μM to 1 mM and a detection limit of 3.64 μM. This approach provides a robust strategy to enhance MSC-based ECL biosensing, paving the way for ultrasensitive, stable biosensors for clinical diagnostics and bioanalysis.

Revealing Anion Exchange in Two-Dimensional Nanocrystals

Ion exchange is a powerful postsynthesis tool for the design of functional nanomaterials. However, achieving anion exchange while maintaining the original morphology and crystal structure, as well as elucidating the mechanism, remains challenging. Here, we developed an anion-exchange strategy under mild conditions and revealed an unusual ion-exchange mechanism in the semiconductor nanoplatelets. Kinetic studies have demonstrated that the transformation follows first-order kinetics, with the ligand restricting the guest anion from diffusing only in one-dimensional directions. By monitoring the reaction process, we demonstrated that the anion exchange reaction occurs selectively on the polar surface of the NPLs and exhibits asymmetry at the two polar end faces. Theoretical simulations further confirmed that anion exchange began from the chalcogenide-dominated facet. The thermodynamic data suggest that guest ions diffuse into the crystal interior via a direct exchange mechanism. This study provides a pathway for anion exchange and the construction of functional nanocrystals and a platform for studying the optoelectronic behavior of single-sheet heterojunctions.

Ion exchange in semiconductor magic-size clusters

As a crucial post-synthesis method, ion exchange allows for precise control over the composition, interface, and morphology of nanocrystals at the atomic scale, achieving material properties that are difficult to obtain with traditional synthesis techniques. In nanomaterial science, semiconductor magic-size clusters (MSCs), with their atomic-level precision and unique quantum confinement effects, serve as a bridge between molecules and nanocrystals. Despite this, research on ion exchange in MSCs is still in its infancy. This review introduces the principles of ion exchange and reactions in colloidal nanocrystals and MSCs, analyzing the importance and challenges of ion exchange in studying MSCs. This paper begins with a focus on the current research progress of cation and anion exchange in II-VI and III-V semiconductor MSCs. Then, the common methods for characterizing MSCs during the ion exchange process are discussed. Finally, the article envisions future research directions based on MSCs' ion exchange. Research on MSCs' ion exchange not only aids in designing MSCs with complex functionalities, but also plays an essential role in elucidating the ion exchange mechanisms in nanocrystals, providing new insights for the innovative design and synthesis of nanomaterials.

Alloyed Zinc Chalcogenide Magic-Sized Nanoclusters and Their Transformation to Alloyed Quantum Dots

Alloying provides the opportunity to widen the physical and chemical properties of quantum dots (QDs); however, the precise controlled composition of alloyed QDs is still a challenge. In this work, a few quaternary alloyed zinc chalcogenide magic-sized nanoclusters (MSCs) were synthesized using the active chalcogen precursors of tri(dimethylamine)phosphine chalcogen, such as Zn21S4Se3Te4 (MSCs-348), Zn14S4Se4Te7 (MSCs-350), Zn15S1Se4Te6 (MSCs-349), and Zn17S2Se2Te7 (MSCs-355) MSCs. The composition of alloyed zinc chalcogenide MSCs was tuned with the different amounts of added chalcogen precursors. Finally, the produced alloyed zinc chalcogenide MSCs can be used as precursors to synthesize alloyed zinc chalcogenide QDs, and the composition of zinc chalcogenide QDs can be adjusted with different alloyed MSCs. This work provides methods to alloy MSCs with controlled composition, providing efficient precursors for alloyed QDs.

Anisotropic Growth of Covalent Inorganic Complexes to Nanoplatelets

Colloidal II-VI semiconductor nanoplatelets (NPLs) provide a new platform in material science due to their unique growth mode and advanced optical properties. However, in contrast to the rapid development of zinc blend structured NPLs, studies on the formation of wurtzite (WZ) NPLs have been limited to the lamellar assembly of specific magic-sized nanoclusters (MSCs). Therefore, the study of new precursors is important for enriching the synthesis strategy, improving the study of two-dimensional (2D) nanocrystal growth mechanisms, and constructing complex nanostructures. Here, we demonstrated that covalent inorganic complexes (CICs), as novel functional intermediates, can be directly used to form NPLs without involving MSCs. Using in situ absorption spectra, we demonstrated that the evolution followed a pseudo-first-order kinetics (kobs = 0.02 min-1 (t1/2 = 34.7 min)). Several types of binary WZ NPLs, including CdSe, CdS, CdTe, and ZnS, have been directly prepared based on this mechanism through the anisotropic growth of CICs. In addition, CICs can also be used to prepare Mn-doped CdSe NPLs. The present study not only affords new precursors for the synthesis of WZ NPLs but also advances our understanding of the synthesis mechanism of nanocrystals.