The determination of catalytically active sites is crucial for the design of efficient and stable catalysts toward desired reactions. However, the complexity of supported noble metal catalysts has led to controversy over the locations of catalytically active sites (e.g., metal, support, and metal/support interface). Here we develop a structurally controllable catalyst system (Pd/SBA-15) to reveal the catalytic active sites for the selective hydrogenation of ketones to alcohol using acetophenone hydrogenation as model reaction. Systematic investigations demonstrated that unsupported Pd nanocrystals have no catalytic activity for acetophenone hydrogenation. However, oxidized Pd species were catalytically highly active for acetophenone hydrogenation. The catalytic activity decreased with the decreased oxidation state of Pd. This work provides insights into the hydrogenation mechanism of ketones but also other unsaturated compounds containing polar bonds, e.g., nitrobenzene, N-benzylidene-benzylamine, and carbon dioxide.

Copper-hydrides have been intensively studied for a long time due to their utilization in a variety of technologically important chemical transformations. Nevertheless, poor stability of the species severely hinders its isolation, storage and operation, which is worse for nano-sized ones. We report here an unprecedented strategy to access to ultrastable copper-hydride nanoclusters (NCs), namely, using bidentate N-heterocyclic carbenes as stabilizing ligands in addition to thiolates. In this work, a simple synthetic protocol was developed to synthesize the first large copper-hydride nanoclusters (NCs) stabilized by N-heterocyclic carbenes (NHCs). The NC, with the formula of Cu₃₁(RS)₂₅(NHC)₃H₆ (NHC = 1,4-bis(1-benzyl-1H-benzimidazol-1-ium-3-yl) butane, RS = 4-fluorothiophenol), was fully characterized by high resolution Fourier transform ion cyclotron resonance mass spectrum, nuclear magnetic resonance, ultra-violet visible spectroscopy, density functional theory (DFT) calculations and single-crystal X-ray crystallography. Structurally, the title cluster exhibits unprecedented Cu₄ tetrahedron-based vertex-sharing (TBVS) superstructure (fusion of six Cu₄ tetrahedra). Moreover, the ultrahigh thermal stability renders the cluster a model system to highlight the power of NHCs (even other carbenes) in controlling geometrical, electronic and surface structure of polyhydrido copper clusters.

We report herein a class of superatomic Au₁₃ clusters stabilized by different N-heterocyclic carbenes (NHCs). The clusters show diverse metal surface structures, properties and functions as exemplified by: (1) the first anionic Au₁₃ cluster [Au₁₃(NHC-1)₆Br₆]^-, which has bulky NHC-1 ligands that lead to a rather open metal surface contributing to its high catalytic activity; (2) the tricationic cluster [Au₁₃(NHC-2)₅Br₂]³⁺ which has bidentate, benzyl-rich NHC-2 ligands that make it ultra-stable and highly-luminescent, suitable for bio-imaging; and (3) by bearing two pyridyl groups on NHC-3, the dicationic cluster [Au₁₃(NHC-3)₉Cl₃]²⁺ exhibits reversible and stable visible absorption and solubility responses to protonation/deprotonation cycles, making it a potential pH sensor (NHC-1 = 1,3-diisopropylbenzimidazolin-2-ylidene; NHC-2 = 1,3-bis(1-benzyl-1H-benzimidazol-1-ium-3-yl)propane; NHC-3 = 1,3-bis(picolyl)benzimidazolin-2-ylidene). The study nicely demonstrates the importance of ligands in designing metal nanoclusters with desired functionalities.

Vulnerable atherosclerotic plaques are responsible for most cardiovascular diseases (CVDs). Folate receptor (FR) positive activated macrophages were thought to be a prominent component in the development of vulnerable plaque. The objective of this study is to develop folate conjugated two-dimensional (2D) Pd@Au nanomaterials (Pd@Au-PEG-FA) for targeted multimodal imaging of the FRs in advanced atherosclerotic plaques. Pharmacokinetic and imaging studies (single photon emission computed tomography (SPECT), computed tomography (CT) and photoacoustic (PA) imaging) were performed to confirm the prolonged blood half-life and enrichment of radioactivity in atherosclerotic plaques. Strong signals were detected in vivo with SPECT, CT and PA imaging in heavy atherosclerotic plaques, which were significantly higher than those of the normal aortas after injection of Pd@Au-PEG-FA. Blocking studies with preinjection of excess folic acid (FA) could effectively reduce the targeting ability of Pd@Au-PEG-FA in atherosclerotic plaques, further demonstrating the specific binding of Pd@Au-PEG-FA for plaque lesions. Histopathological characterization revealed that the signal of probe was in accordance with the high-risk plaques. In summary, the Pd@Au-PEG-FA has favorable pharmacokinetic properties and provides a valuable approach for detecting high-risk plaques in the presence of FRs in atherosclerotic plaques.

Two-dimensional (2D) nanosheets have emerged as an important class of nanomaterial with great potential in the field of biomedicines, particularly in cancer theranostics. However, owing to the lack of effective methods that synthesize uniform 2D nanomaterials with controlled size, systematic evaluation of size-dependent bio-behaviors of 2D nanomaterials is rarely reported. To the best of our knowledge, we are the first to report a systematic evaluation of the influence of size of 2D nanomaterials on their bio-behaviors. 2D Pd nanosheets with diameters ranging from 5 to 80 nm were synthesized and tested in cell and animal models to assess their size-dependent bioapplication, biodistribution, elimination, toxicity, and genomic gene expression profiles. Our results showed size significantly influences the biological behaviors of Pd nanosheets, including their photothermal and photoacoustic effects, pharmacokinetics, and toxicity. Compared to larger-sized Pd nanosheets, smaller-sized Pd nanosheets exhibited more advanced photoacoustic imaging and photothermal effects upon ultralow laser irradiation. Moreover, in vivo results indicated that 5-nm Pd nanosheets escape from the reticuloendothelial system with a longer blood half-life and can be cleared by renal excretion, while Pd nanosheets with larger sizes mainly accumulate in the liver and spleen. The 30-nm Pd nanosheets exhibited the highest tumor accumulation. Although Pd nanosheets did not cause any appreciable toxicity at the cellular level, we observed slight lipid accumulation in the liver and inflammation in the spleen. Genomic gene expression analysis showed that 80-nm Pd nanosheets interacted with more cellular components and affected more biological processes in the liver, as compared to 5-nm Pd nanosheets. We believe this work will provide valuable information and insights into the clinical application of 2D Pd nanosheets as nanomedicines.

Lithium-sulfur batteries have attracted increasing attention because of their high theoretical capacity. Using sulfur/carbon composites as the cathode materials has been demonstrated as an effective strategy to optimize sulfur utilization and enhance cycle stability as well. In this work, hollow-in-hollow carbon spheres with hollow foam-like cores (HCSF@C) are prepared to improve both capability and cycling stability of lithium–sulfur batteries. With high surface area and large pore volumes, the loading of sulfur in HCSF@C reaches up to 70 wt.%. In the resulting S/HCSF@C composites, the outer carbon shell serves as an effective protection layer to trap the soluble polysulfide intermediates derived from the inner component. Consequently, the S/HCSF@C cathode retains a high capacity of 780 mAh/g after 300 cycles at a high charge/discharge rate of 1 A/g.

Near-infrared (NIR) photothermal therapy has developed very quickly in recent years. However, its clinical applications are hindered by many practical problems, such as low accumulation in tumors, high laser power density and high biotoxicity in vivo. Herein, a versatile system combining chemotherapy with photothermal therapy for cancer therapy using ultrasmall Pd nanosheets (SPNS) has been developed. The SPNS can serve as pH-responsive drug carriers to efficiently deliver DOX into cancer cells and tumors. On the other hand, the coordinative loading of DOX on SPNS enhances its accumulation in tumor tissue. So we can efficiently ablate tumor using low-intensity laser radiation. Importantly, with ultrasmall size (~4.4 nm), SPNS surface-functionalized with reduced glutathione (GSH) can be cleared from the body through the renal system into the urine. This cancer therapeutic nanosystem, which exhibits a significant synergistic effect and low systemic toxicity, has great potential for clinical applications.

Au nanoparticles epitaxially grown on Fe₃O₄ in Au (6.7 nm)-Fe₃O₄ dumbbell nanoparticles exhibit excellent stability against sintering, but display negligible catalytic activity in CO oxidation. Starting from various supported Au (6.7 nm)-Fe₃O₄ catalysts prepared by the colloidal deposition method, we have unambiguously identified the significance of the Au-TiO₂ interface in CO oxidation, without any possible size effect of Au. In situ thermal decomposition of TiO₂ precursors on Au-Fe₃O₄ was found to be an effective way to increase the Au-TiO₂ interface and thereby optimize the catalytic performance of TiO₂-supported Au-Fe₃O₄ dumbbell nanoparticles. By reducing the size of Fe₃O₄ from 15.2 to 4.9 nm, the Au-TiO₂ contact was further increased so that the resulting TiO₂-supported Au (6.7 nm)-Fe₃O₄ (4.9 nm) dumbbell particles become highly efficient catalysts for CO oxidation at room temperature.