Observation of Surface Ligands-Controlled Etching of Palladium Nanocrystals

Regulating Plasmonic Properties through Asymmetric Oxidative Etching of Octahedral Au@Ag Core-Shell Nanocrystals with Iridium Chloride

We present the engineering of plasmonic nanostructures and their optical properties through the asymmetric oxidative etching of octahedral Au@Ag core-shell nanocrystals. This process utilizes iridium chloride to produce Au@Ag-AgCl-IrOx products under hydrothermal conditions. This method deviates from conventional techniques that involve the oxidative etching of Ag nanocubes with Au precursors, which typically results in an isotropic and gradual etching process. Our protocol uniquely initiates with the rounding of the octahedral nanocrystals' sharp corners, followed by the selective removal of roughly half of the Ag shell, thus exposing portions of the Au core. Continued etching leads to the creation of yolk-shell structures, where the Au core remains intact while most of the outer shell is converted into silver chloride (AgCl). Comprehensive structural analyses confirm the presence of IrOx in the final products, playing a crucial role in directing the observed anisotropic oxidative etching pattern. Additionally, we examined the practical applications of these synthesized materials in plasmonic catalysis, revealing a significant enhancement in the catalytic performance under UV-vis light irradiation. The FDTD simulation confirms the effect of different shell materials and structures on the plasmonic properties and temperature distribution. These findings highlight the potential utility of our approach in the rational design of plasmonic nanostructures.

Preparation of recyclable magnetic palladium nanocatalysts by dispersion strategy based on sodium alginate for reduction of p-nitrophenol and Suzuki-Miyaura coupling

Palladium (Pd) has excellent catalytic performance, its application is seriously limited by low atomic utilization and weak recovery capacity. To solve these problems, we report a universal palladium nanocatalysts preparation strategy by taking advantage of the rich chemistry of sodium alginate (SA). SA units not only self-assemble into a cross-linked porous carboxyl and hydroxyl framework but also can coat different substrates. Benefiting from the distinguished chelation of SA, metallic nanocatalysts can be achieved. As a proof-of-concept demonstration, Pd loading on nano-Fe3O4 modified with SA and investigated their catalytic capabilities. The catalyst was Fe3O4 nanoparticles encapsulated by SA film loaded with 0.4 wt% of Pd. It has a particle size around 100 nm and has good superparamagnetism with a saturation strength of 76.26 emu/g. It exhibited good catalytic activity at TOF = 660 h-1 and TOF = 4311 h-1 in typical Suzuki-Miyaura coupling reaction and the reduction of p-nitrophenol, respectively, and showed appreciable recyclability in the test of recyclability. Thus, our findings demonstrate that recyclable magnetic palladium nanocatalysts have several attractive features, such as easy preparation, outstanding catalytic activity and reusability. This work lays the foundation for the preparation of palladium nanocatalysts and the potential application of SA in the field of catalysts.

Bottom-Up Then Top-Down Synthesis of Gold Nanostructures Using Mesoporous Silica-Coated Gold Nanorods

Gold nanostructures were synthesized by etching away gold from heat-treated mesoporous silica-coated gold nanorods (AuNR@mSiO2), providing an example of top-down modification of nanostructures made using bottom-up methodology. Twelve different types of nanostructures were made using this bottom-up-then-top-down synthesis (BUTTONS), of which the etching of the same starting nanomaterial of AuNR@mSiO2 was found to be controlled by how AuNR@mSiO2 were heat treated, the etchant concentration, and etching time. When the heat treatment occurred in smooth moving solutions in round-bottomed flasks, red-shifted longitudinal surface plasmon resonance (LSPR) was observed, on the order of 10-30 min, indicating increased aspect ratios of the gold nanostructures inside the mesoporous silica shells. When the heat treatment occurred in turbulent solutions in scintillation vials, a blue shift of the LSPR was obtained within a few minutes or less, resulting from reduced aspect ratios of the rods in the shells. The influence of the shape of the glassware, which may impact the flow patterns of the solution, on the heat treatment was investigated. One possible explanation is that the flow patterns affect the location of opened pores in the mesoporous shells, with the smooth flow of solution mainly removing CTAB surfactants from the pores along the cylindrical body of mSiO2, therefore increasing the aspect ratios after etching, and the turbulent solutions removing more surfactants from the pores of the two ends or tips of the silica shells, hence decreasing the aspect ratios after etching. These new stable gold nanostructures in silica shells, bare and without surfactant protection, may possess unique chemical properties and capabilities. Catalysis using heat-treated nanomaterials was studied as an example of potential applications of these nanostructures.

Shape-Controlled Synthesis of Platinum-Based Nanocrystals and Their Electrocatalytic Applications in Fuel Cells

To achieve environmentally benign energy conversion with the carbon neutrality target via electrochemical reactions, the innovation of electrocatalysts plays a vital role in the enablement of renewable resources. Nowadays, Pt-based nanocrystals (NCs) have been identified as one class of the most promising candidates to efficiently catalyze both the half-reactions in hydrogen- and hydrocarbon-based fuel cells. Here, we thoroughly discuss the key achievement in developing shape-controlled Pt and Pt-based NCs, and their electrochemical applications in fuel cells. We begin with a mechanistic discussion on how the morphology can be precisely controlled in a colloidal system, followed by highlighting the advanced development of shape-controlled Pt, Pt-alloy, Pt-based core@shell NCs, Pt-based nanocages, and Pt-based intermetallic compounds. We then select some case studies on models of typical reactions (oxygen reduction reaction at the cathode and small molecular oxidation reaction at the anode) that are enhanced by the shape-controlled Pt-based nanocatalysts. Finally, we provide an outlook on the potential challenges of shape-controlled nanocatalysts and envision their perspective with suggestions.