研究兴趣1：金属纳米团簇的精准合成和可控自组装
研究兴趣2：金属纳米团簇的催化应用
研究兴趣3：金属纳米团簇的光电应用
Representative Research Work
1. Supercrystal Engineering of Atomically Precise Gold Nanoparticles Promoted by Surface Dynamics
(Nature Chemistry , 2023, 15, 230-239.）
Controllable packing of functional nanoparticles (NPs) into supercrystals is of core interest in the development of NP-based metamaterials. Compared with the conventional crystallization method that treats NPs as hard spheres, in this work, we demonstrate at the molecular level that the size, morphology, and symmetry of unary supercrystals can be tailored by using the surface dynamics of NPs (Figure 1). In the presence of excess tetraethylammonium cations, atomically precise [Au25(SR)18]- NPs (SR = thiolate) can be crystallized into micro-meter-sized hexagonal rod-like supercrystals. Experimental characterization and theoretical modeling reveal a R-3m space group, in which NPs are aligned into polymeric chains through a unique SR-[Au(I)-SR]4 inter-particle linker. This linker is established by the asymmetric conjugation of the dynamically detached SR-[Au(I)-SR]2 protecting motifs between neighbored NPs, which is made possible by intensive CH∙∙∙π enhanced ion-pairing interactions between tetraethylammonium cations and SR ligands. By changing the dosage and type of tetraalkylammonium cations, the symmetry, morphology, and size of supercrystals can be systematically tuned. This work not only provides a convenient method for supercrystal engineering, but also highlights the importance of surface dynamics in dictating the assembly behavior of NPs.
Figure 1. Schematic illustration of surface dynamics promoted size, morphology, and packing symmetry engineering of [Au25(SR)18]- nanoparticles.
2. Understanding Seed-Mediated Growth of Gold Nanoclusters at Molecular Level
(Nature Communications 2017, 8, 927.)
Figure 2. Schematic illustration of seeded growth (a) and its detailed size evolution pathways (b) from [Au25(SR)18]- to [Au44(SR)26]2-, where [Aun(SR)m]q denote nanoclusters with n Au atoms, m thiolate (SR) ligands and q intrinsic charge.
The continuous development of total synthesis chemistry has allowed many organic and biomolecules to be produced with known synthetic history -- that is, a complete set of step reactions in their synthetic routes. In this work, we extend such molecular-level precise reaction routes to nanochemistry, particularly to a seed-mediated synthesis of inorganic nanoparticles. By systematically investigating the time-dependent abundance of 35 intermediate species in total, we map out step-by-step reactions at unprecedented molecular level in a model size growth reaction from molecularly pure Au25 to Au44 nanoclusters (NCs, Figure 2a). In particular, the size growth of Au NCs involves two different size-evolution processes, i.e., monotonic LaMer growth (top pathway of Figure 2b) and volcano-shaped aggregative growth (bottom pathway of Figure 1b), which are driven by a sequential 2-electron boosting of the valence electron count of Au NCs. Such fundamental findings not only provide guiding principles to produce other sizes of Au NCs (e.g., Au38), but also represent molecular-level insights on long-standing puzzles in nanochemistry, including LaMer growth, aggregative growth, and digestive ripening.
3. Revealing Isoelectronic Size Conversion Dynamics of Metal Nanoclusters at Atomic Level
(Nature Communications 2018, 9, 1979)
Atom-by-atom engineering of nanomaterials requires atomic-level knowledge of size evolution mechanism of nanoparticles, which remains as one of the greatest mysteries in nanochemistry. In this contribution, we reveal atomic-level dynamics of size evolution reaction of molecular-like nanoparticles, i.e., nanoclusters by delicate mass spectrometry (MS) analyses. The model size conversion reaction is [Au23(SR)16]- à [Au25(SR)18]- (SR = thiolate ligand). We demonstrate that such isoelectronic (valence electron count is 8 in both clusters) size conversion occurs by a surface motif exchange (SME) induced symmetry-breaking core structure transformation mechanism (Figure 3), surfacing as a definitive reaction of [Au23(SR)16]- + 2 [Au2(SR)3]- à [Au25(SR)18]- + 2 [Au(SR)2]-. The detailed tandem MS analyses further suggest the bond susceptibility hierarchies in feed and final Au NCs, shedding mechanistic light on cluster reaction dynamics at atomic level. The MS-based mechanistic approach developed in this study also opens a complementary avenue to X-ray crystallography to reveal size evolution kinetics and dynamics.
Figure 3. Schematic illustration of isoelectronic size conversion mechanism from [Au23(SR)16]- to [Au25(SR)18]- NCs.
4. Precise Control of Alloying Sites of Bimetallic Nanoclusters via Surface Motif Exchange Reaction
(Nature Communications 2017, 8, 1555.)
Precise control of alloying sites has long been a challenging pursuit, yet little has been achieved at the atomic-level manipulation in metallic nanomaterials. In this work, we describe utilization of surface motif exchange (SME) reaction to selectively replace the surface motifs of parent [Ag44(SR)30]4- (SR = thiolate) NCs, leading to bimetallic NCs with well-defined molecular formula and atomically-controlled alloying sites in protecting shell. A systematic mass (and tandem mass) spectrometry analysis suggests that the SME reaction follows an association-dissociation mechanism (Figure 4), surfacing as a balanced equation of [Ag44(SR)30]4- + [Au2(SR')2Cl]- à [Ag43Au(SR)28(SR')2]4- + [Au(SR)2]- + AgCl. With sufficiently supplied Au(I)-SR complexes, such association-dissociation mechanism could then give rise to a core-shell [Ag32@Au12(SR)30]4- NC by atomically precise displacement of monomeric SR-Ag(I)-SR protecting modules of Ag NCs. Theoretical calculation suggests that the thermodynamically less favorable core-shell Ag@Au nanostructure is kinetically stabilized by the intermediate Ag20 shell, preventing inward diffusion of the surface Au atoms. The delicate SME reaction opens a door to precisely control the alloying sites in the protecting shell of bimetallic NCs with broad utility.
Figure 4. Schematic illustration of association-dissociation assisted surface motif exchange (SME) reaction on [Ag44(SR)30]4- NCs.
5. Introducing Amphiphilicity to Noble Metal Nanoclusters via Phase-Transfer Driven Ion-Pairing Reaction
(Journal of the American Chemical Society 2015, 137, 2128.)
Amphiphilicity is a surface property that has yet to be explored for the metal NCs. This work shows how amphiphilicity may be added to sub-2-nm metal NCs by patching hydrophilic NCs (e.g., Au25(MHA)18 where MHA is 6-mercaptohexanoic acid) with hydrophobic cations (e.g., cetyltrimethylammonium ion, CTA+) to about half of a monolayer coverage (Figure 5a and 5b). Specifically we demonstrate the preparation of amphiphilic Au25(MHA)18@xCTA NCs (x = 6−9 where x is the number of CTA+ per cluster) by the phase-transfer (PT) driven ion-paring reaction between CTA+ and −COO− (derived from the deprotonation of the terminal carboxyl group of MHA). Due to the coexistence of flexible hydrophilic MHA and hydrophobic MHA···CTA ligands in comparable amounts on the cluster surface, the Au25(MHA)18@xCTA (x = 6−9) NCs exhibit good amphiphilicity, which enable them to dissolve in solvents with distinctly different polarities and to self-assemble like a molecular amphiphile by a medium induced polarity modulation mechanism (Figure 5b and 5c). Consequently, the amphiphilic Au25(MHA)18@xCTA (x = 6−9) could self-organize into stacked bilayers at the air−liquid interface (Figure 5d), similar to the formation of lyotropic liquid crystalline phases by common surfactants. The good solubility and molecular-amphiphile-like self-assembly properties can significantly increase the utility of noble metal NCs in basic and applied research.
Figure 5. Schematic illustration of formation and self-assembly of amphiphilic Au25(MHA)18@xCTA NCs.