Ultrathin PtCu alloy nanosheets are synthesized by a facile, one-pot, templateless hydrothermal method with the use of carbon monoxide (CO) as the capping agent. Due to their unique structure and possible synergetic effect, the ultrathin nanosheets show higher catalytic activity in hydrogen evolution and hydrogenation reactions. The developed method is also expected to generate exciting opportunities in creating ultrathin nanostructures with a wide range of alloy compositions for various catalytic applications.

Two-dimensional ultrathin PdAg bimetallic nanosheets are fabricated and used as model catalysts for understanding the synergetic effects in bimetallic nanocatalysts. The ultrathin nature of the nanosheets allows us to probe the electronic and geometric structures using XPS and X-ray absorption spectroscopy. The as-prepared bimetallic nanosheets show high catalytic activity for selective dehydrogenation of formic acid, especially when the Ag/Pd ratio reaches 1. The superior activity is attributed to the electronic and geometric effect generated from the Pd–Ag interfaces in the catalysts. Our studies reveal increased bond distances of Pd–Pd and decreased Ag–Ag bond lengths in the PdAg bimetallic nanosheets. Pd is electronically promoted by Ag to give enhanced catalysis. Moreover, the geometric effect generated from the PdAg alloyed surface enhances the catalysis by suppressing CO poisoning on the catalysts, which is confirmed by electrochemical FTIR measurements.

The shape control of noble metal nanocrystals is crucial to their optical properties and catalysis applications. In this Progress Report, the recent progress of shape-controlled synthesis of Pd and Pt nanostructures assisted by small adsorbates is summarized. The use of small strong adsorbates (e.g., I⁻, CO, amines) makes it possible to fabricate Pd and Pt nanostructures with not only well-defined surface structure but also morphologies that have not been achieved by other synthetic strategies. The roles of small adsorbates in shape control of Pd and Pt nanocrystals are discussed in the Report. Also presented in the Report are unique optical and catalytic properties of several Pd and Pt nanostructures (e.g., ultrathin Pd nanosheets, concave Pt octapod, concave Pd tetrahedra), as well as their bioapplications, to demonstrate the power of using small strong adsorbates in the shape control of Pt and Pd nanostructures.

A smart drug delivery system integrating both photothermal therapy and chemotherapy for killing cancer cells is reported. The delivery system is based on a mesoporous silica-coated Pd@Ag nanoplates composite. The Pd@Ag nanoplate core can effectively absorb and convert near infrared (NIR) light into heat. The mesoporous silica shell is provided as the host for loading anticancer drug, doxorubicin (DOX). The mesoporous shell consists of large pores, ∼10 nm in diameter, and allows the DOX loading as high as 49% in weight. DOX loaded core–shell nanoparticles exhibit a higher efficiency in killing cancer cells than free DOX. More importantly, DOX molecules are loaded in the mesopores shell through coordination bonds that are responsive to pH and heat. The release of DOX from the core-shell delivery vehicles into cancer cells can be therefore triggered by the pH drop caused by endocytosis and also NIR irradiation. A synergistic effect of combining chemotherapy and photothermal therapy is observed in our core-shell drug delivery system. The cell-killing efficacy by DOX-loaded core–shell particles under NIR irradiation is higher than the sum of chemotherapy by DOX-loaded particles and photothermal therapy by core–shell particles without DOX.

Developing low-cost non-precious metal catalysts for high-performance oxygen reduction reaction (ORR) is highly desirable. Here a facile, in situ template synthesis of a MnO-containing mesoporous nitrogen-doped carbon (m-N-C) nanocomposite and its high electrocatalytic activity for a four-electron ORR in alkaline solution are reported. The synthesis of the MnO-m-N-C nanocomposite involves one-pot hydrothermal synthesis of Mn₃O₄@polyaniline core/shell nanoparticles from a mixture containing aniline, Mn(NO₃)₂, and KMnO₄, followed by heat treatment to produce N-doped ultrathin graphitic carbon coated MnO hybrids and partial acid leaching of MnO. The as-prepared MnO-m-N-C composite catalyst exhibits high electrocatalytic activity and dominant four-electron oxygen reduction pathway in 0.1 M KOH aqueous solution due to the synergetic effect between MnO and m-N-C. The pristine MnO shows little electrocatalytic activity and m-N-C alone exhibits a dominant two-electron process for ORR. The MnO-m-N-C composite catalyst also exhibits superior stability and methanol tolerance to a commercial Pt/C catalyst, making the composite a promising cathode catalyst for alkaline methanol fuel cell applications. The synergetic effect between MnO and N-doped carbon described provides a new route to design advanced catalysts for energy conversion.

The fabrication of catalytically stable nanocatalysts containing fine noble metal nanoparticles is an important research theme. We report a method for the synthesis of a hierarchically structured Pd@hm-CeO₂ multi-yolk–shell nanocatalyst (h=hollow; m=mesoporous) containing sub-10 nm Pd nanoparticles from pre-made hydrophobic Pd nanoparticles. In the developed method, monodisperse hydrophobic Pd nanoparticles are first reacted with an iron oxide precursor iron(III) acetylacetonate to allow the deposition of iron oxide on their surface. In a Brij 56–water–cyclohexane reverse micelle system, the surface growth of iron oxide is found to mediate and, thus, facilitate the encapsulation of hydrophobic Pd nanoparticles in SiO₂ to yield Pd-Fe₂O₃@SiO₂ nanoparticles in a high concentration. After removal of Fe₂O₃ by acid, the obtained Pd@SiO₂ core–shell particles are reacted solvothermally with Ce(NO₃)₃ in an ethylene glycol–water–acetic acid mixture to produce multi-core–shell Pd@SiO₂@m-CeO₂ nanospheres. In each multi-core–shell Pd@SiO₂@m-CeO₂ nanosphere, several Pd@SiO₂ particles are separately embedded in mesoporous CeO₂. After selective removal of silica by NaOH, Pd@SiO₂@m-CeO₂ nanospheres are transformed into the multi-yolk–shell Pd@hm-CeO₂ nanocatalyst. Even with a low Pd loading at 0.4 wt %, the as-prepared multi-yolk–shell Pd@hm-CeO₂ nanocatalyst displays high catalytic activity in CO oxidation with 100 % CO conversion at 110 °C. In comparison, under the same catalytic conditions, the same amount of the same-sized Pd nanoparticles supported on SiO₂ achieves 100 % CO conversion at 180 °C. More importantly, the multi-yolk–shell structure of the Pd@hm-CeO₂ nanocatalyst significantly enhances the stability of the catalyst. No loss in catalytic activity was observed on the Pd@hm-CeO₂ nanocatalyst treated at 550 °C for six hours. The Pd@hm-CeO₂ nanocatalyst also exhibited excellent catalytic performance and stability in the aerobic selective oxidation of cinnamyl alcohol to cinnamaldehyde.

Hollow mesoporous zirconia nanocapsules (hm-ZrO₂) with a hollow core/porous shell structure are demonstrated as effective vehicles for anti-cancer drug delivery. While the highly porous feature of the shell allows the drug, doxorubicin(DOX), to easily pass through between the inner void space and surrounding environment of the particles, the void space in the core endows the nanocapsules with high drug loading capacity. The larger the inner hollow diameter, the higher their DOX loading capacity. A loading of 102% related to the weight of hm-ZrO₂ is achieved by the nanocapsules with an inner diameter of 385 nm. Due to their pH-dependent charge nature, hm-ZrO₂ loaded DOX exhibit pH-dependent drug releasing kinetics. A lower pH offers a faster DOX release rate from hm-ZrO₂. Such a property makes the loaded DOX easily release from the nanocapsules when up-taken by living cells. Although the flow cytometry reveals more uptake of hm-ZrO₂ particles by normal cells, hm-ZrO₂ loaded DOX release more drugs in cancer cells than in normal cells, leading to more cytotoxicity toward tumor cells and less cytotoxicity to healthy cells than free DOX.

Owing to its good affinity with Ag⁺, Br^– is able to truncate a silver thiolate polymer and induce the formation of a high-nuclearity silver thiolate nanocluster, [Br@Ag₃₆(SC₆H₄tBu-4)₃₆]^–. The nanocluster has a disc-like structure with one Br^– anion trapped at the center of the cluster in an octahedral coordination.