Oxidation Etching-Induced Post-Crystallization of Palladium Nanosheets for Efficient Catalytic Hydrogenation

2D petal-like PdAg nanosheets promote efficient electrocatalytic oxidation of ethanol and methanol

The development of efficient alcohol electrooxidation catalysts is of vital importance for the commercialization of direct liquid fuel cells. As emerging advanced catalysts, two-dimensional (2D) noble metal nanomaterials have attracted much research attention due to their intrinsic structural advantages. Herein, we report the synthesis of petal-like PdAg nanosheets (NSs) with an ultrathin 2D structure and jagged edges via a facile wet-chemical approach, combining doping engineering and morphology tuning. Notably, the highly active sites and Pd-Ag composition endowed PdAg NSs with improved toxicity tolerance and substantially improved the durability toward the ethanol/methanol oxidation reaction (EOR/MOR). Moreover, the electronic effect and synergistic effect significantly enhanced the EOR and MOR activities in comparison with Pd NSs and commercial Pd/C. This work provides efficient catalysts for fuel electrooxidations and deep insight into the rational design and fabrication of novel 2D nanoarchitecture.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Etching suppression as a means to Pt dendritic ultrathin nanosheets by seeded growth

2D ultrathin metal nanostructures are emerging materials displaying distinct physical and chemical properties compared to their analogues of different dimensionalities. Nanosheets of fcc metals are intriguing, as their crystal structure does not favour a 2D configuration. Thanks to their increased surface-to-volume ratios and the optimal exposure of low-coordinated sites, 2D metal nanostructures can be advantageously exploited in catalysis. Synthesis approaches to ultrathin nanosheets of pure platinum are scarce compared to other noble metals and to Pt-based alloys. Here, we present the selective synthesis of Pt ultrathin nansosheets by a simple seeded-growth method. The most crucial point in our approach is the selective synthesis of Pt seeds comprising planar defects, a main driving force for the 2D growth of metals with fcc structure. Defect engineering is employed here, not in order to disintegrate, but for conserving the defect comprising seeds. This is achieved by in situ elimination of the principal etching agent, chloride, which is present in the PtCl₂ precursor. As a result of etching suppression, twinned nuclei, that are selectively formed during the early stage of nucleation, survive and grow to multipods comprising planar defects. Using the twinned multipods as seeds for the subsequent 2D overgrowth of Pt from Pt(acac)₂ yields ultrathin dendritic nanosheets, in which the planar defects are conserved. Using phenylacetylene hydrogenation as a model reaction of selective hydrogenation, we compared the performance of Pt nanosheets to that of a commercial Pt/C catalyst. The Pt nanosheets show better stability and much higher selectivity to styrene than the commercial Pt/C catalyst for comparable activity.

Tensile-Strained Palladium Nanosheets for Synthetic Catalytic Therapy and Phototherapy

Palladium nanosheets (Pd NSs) are well-investigated photothermal therapy agents, but their catalytic potential for tumor therapy has been underexplored owing to the inactive dominant (111) facets. Herein, lattice tensile strain is introduced by surface reconstruction to activate the inert surface, endowing the strained Pd NSs (SPd NSs) with photodynamic, catalase-like, and peroxidase-like properties. Tensile strain promoting the photodynamic and enzyme-like activities is revealed by density functional theory calculations. Compared with Pd NSs, SPd NSs exhibit lower photothermal effect, but approximately five times higher tumor inhibition rate. This work calls for further study to activate nanomaterials by strain engineering and surface reconstruction for catalytic therapy of tumors.

Photothermal-Driven High-Performance Selective Hydrogenation System Enabled by Delicately Designed IrCo Nanocages

The incorporation of a transition metal into a noble metal for the formation of nanoalloys paves a potential way to modulate the electronic structures and spatial arrangement modes, thereby manipulating the target catalysis under the desired reaction pathways. Herein, a top-down synthetic route to fabricate IrCo nanoalloys with delicately designed compositions and morphologies at an extremely low calcination temperature of 200 °C is reported, which efficiently breaks through the thermodynamic limitations caused by the large atomic radii and electronegativity discrepancies between Co and Ir. A high-performance selective hydrogenation system enabled by the synthesized IrCo nanoalloys and the light irradiation is further established. Significantly, the unique properties of IrCo alloy, involving the special capability of generating local heating rather than hot electrons under light irradiation (the hot-electron effect was considered detrimental to hydrogenation reactions), as well as the highly polarized surface which aids in the hydrogen transfer from borane-ammonia complex (AB) to 4-nitrostyrene (4-NS) are discovered.

Facile Synthesis of Urchin-like Hollow Au Crystals for In Situ SERS Monitoring of Photocatalytic Reaction

Hollow urchin-like Au nanocrystals have been widely studied due to their excellent surface plasmon resonance properties and large specific surface area, but the controllable preparation of hollow urchin-like Au nanocrystals is still a challenge. In this article, we successfully prepared hollow urchin-like Au nanocrystals using HAuCl4·3H2O and AgNO3 as precursors and ascorbic acid as the reducing agent. No surface ligands or polymer stabilizers are required in the preparation process. HAuCl4·3H2O and AgNO3 will first form AgCl cubes, then the reducing agent, ascorbic acid, will reduce the Au3+ in the solution to Au0, and Au0 will be deposited on the pre-formed AgCl cubes to form AgCl@Au nanocrystals. We characterized the morphology of the prepared Au nanocrystals by scanning electron microscopy and found that by increasing the amount of HAuCl4·3H2O in the reaction, the surface morphology of the Au nanocrystals would change from a rough spherical shape to an urchin-like shape. By further increasing the amount of the precursor HAuCl4·3H2O, urchin-like Au will convert into flake-like morphology. The AgCl in the interior was removed with ammonia water, and finally, hollow urchin-like Au crystals were formed. In addition, we used R6G molecule to explore the surface-enhanced Raman spectroscopy (SERS) enhancement effect of prepared Au crystals. The results show that the minimum detectable concentration of R6G reaches 10−8 M. Moreover, we applied hollow urchin-like Au nanocrystals as catalysts and SERS enhancing materials to detect the photocatalytic reaction of 4-NTP. We used a 785 nm laser as both the SERS light source and the catalytic light source to monitor the photocatalytic effect of the laser on 4-NTP in situ by adjusting the laser power.

Nanozyme with Robust Catalase Activity by Multiple Mechanisms and Its Application for Hypoxic Tumor Treatment

Utilizing catalase-mimicking nanozymes to produce O₂ is an effective method to overcome tumor hypoxia. However, it is challenging to fabricate nanozymes with ultrahigh catalytic activity. Palladium nanosheet (Pd NS), a photothermal agent for photothermal therapy (PTT), has superior catalase-mimicking activity. Here, titanium dioxide (TiO₂ ) is used to modify Pd NS (denoted Pd@TiO₂ ) by a simple one-step method to improve its catalytic activity about 8 times. The enhancement mechanism's fundamental insights are discussed through experiments and density functional theory calculations. Next, zinc phthalocyanine is loaded on Pd@TiO₂ to form a nanomotor (denoted PTZCs) with the synergistic activities of photodynamic therapy and PTT. PTZCs inherit the catalase activity of Pd@TiO₂ to facilitate the decomposition of endogenous H₂ O₂ to O₂ , which can relieve tumor hypoxia and propel PTZC migration to expand the reach of PTZCs, further enhancing its synergistic treatment outcome both in vitro and in vivo. It is proposed that this work can provide a simple and effective strategy for catalytic activity enhancement and bring a critical new perspective to studying and guiding the nanozyme design.