A Systemic Review on the Synthesis, Characterization, and Applications of Palladium Nanoparticles in Biomedicine

Palladium nanoparticles (Pd NPs) have been considered as a potential candidate in the field of biomedical applications due to its unique properties such as huge catalytic, hydrogen storage, and sensing behavior. Therefore, Pd NPs have shown to have a significant potential for the development of antimicrobials, wound healing, antioxidant, and anticancer property in recent days. There are plenty of reports that showed superior properties of noble metals. However, only very few studies have been undertaken to explore the advantage of Pd NPs in the field of biomedical applications. This review reports detailed and comprehensive studies comprising of the synthesis, characterization, and potential applications of Pd NPs in biomedicine. This report provides evidences in the literature documented by early researchers to understand the potential applications of Pd NPs to be explored in various fields.

Mace-Like Plasmonic Au-Pd Heterostructures Boost Near-Infrared Photoimmunotherapy

Photoimmunotherapy, with spatiotemporal precision and noninvasive property, has provided a novel targeted therapeutic strategy for highly malignant triple-negative breast cancer (TNBC). However, their therapeutic effect is severely restricted by the insufficient generation of tumor antigens and the weak activation of immune response, which is caused by the limited tissue penetration of light and complex immunosuppressive microenvironment. To improve the outcomes, herein, mace-like plasmonic AuPd heterostructures (Au Pd HSs) have been fabricated to boost near-infrared (NIR) photoimmunotherapy. The plasmonic Au Pd HSs exhibit strong photothermal and photodynamic effects under NIR light irradiation, effectively triggering immunogenic cell death (ICD) to activate the immune response. Meanwhile, the spiky surface of Au Pd HSs can also stimulate the maturation of DCs to present these antigens, amplifying the immune response. Ultimately, combining with anti-programmed death-ligand 1 (α-PD-L1) will further reverse the immunosuppressive microenvironment and enhance the infiltration of cytotoxic T lymphocytes (CTLs), not only eradicating primary TNBC but also completely inhibiting mimetic metastatic TNBC. Overall, the current study opens a new path for the treatment of TNBC through immunotherapy by integrating nanotopology and plasmonic performance.

Enhanced Catalytic Performance of N-Doped Carbon Sphere-Supported Pd Nanoparticles by Secondary Nitrogen Source Regulation for Formic Acid Dehydrogenation

The development of catalysts with high selectivity, good catalytic activity, and excellent cycle performance is of significance for the application of formic acid (HCOOH, FA) as a hydrogen support. Herein, Pd is deposited on a series of N-doped carbons, which are prepared by cocarbonization of N-containing zeolite imidazole frameworks (ZIF-8) and other N/C sources (melamine, xylitol, urea, and glucose), for hydrogen generation from FA. The results demonstrate that the introduction of a secondary N/C source further affects the catalytic performance of Pd by adjusting the morphology, specific surface area, N content, and type of carbon. The effects of N atoms and the favorable reaction pathways of FA dehydrogenation were revealed by theoretical calculation. This work will improve the understanding of N doping on the decomposition mechanism of FA and provide a new approach for the rational design of metal-N-C materials.

Porous PdAg alloy nanostructures with a concave surface for efficient electrocatalytic methanol oxidation

Tuning the composition and surface structure of the metal nanocrystals offered viable avenues for enhancing catalytic performances. Herein, we report a facile one-pot strategy for the formation of PdAg porous alloy nanostructures (PANs) with a concave surface. Due to their highly open nanostructures and tunable d-band center features, PdAg PANs exhibit superior electrocatalytic activity and long-term durability than Pd nanoparticles (NPs) and Pd/C for methanol oxidation reaction (MOR) in alkaline media. Our results provide a feasible and efficient approach for the controlled synthesis of high-performance Pd-based nanomaterials for alkaline MOR.

In Search of Excellence: Convex versus Concave Noble Metal Nanostructures for Electrocatalytic Applications

Controlling the shape of noble metal nanoparticles is a challenging but important task in electrocatalysis. Apart from hollow and nanocage structures, concave noble metal nanoparticles are considered a new class of unconventional electrocatalysts that exhibit superior electrocatalytic properties as compared with those of conventional nanoparticles (including convex and flat ones). Herein, several facile and highly reproducible routes for synthesizing nanostructured concave noble metal materials reported in the literature are discussed, together with their advantages over noble metal nanoparticles with convex shapes. In addition, possible ways of optimizing the synthesis procedure and enhancing the electrocatalytic characteristics of concave metal nanoparticles are suggested. Nanostructured noble metals with concave features are found to show better catalytic activity and stability hence improve their practical applicability in electrocatalysis.

Tunable Periodically Ordered Mesoporosity in Palladium Membranes Enables Exceptional Enhancement of Intrinsic Electrocatalytic Activity for Formic Acid Oxidation

Developing superior electrocatalysts for formic acid oxidation (FAO) is the most crucial step in commercializing direct formic acid fuel cells. Herein, we electrodeposited palladium membranes with periodically ordered mesoporosity obtained by asymmetrically replicating the bicontinuous cubic phase structure of a lyotropic liquid-crystal template. The Pd membrane with the largest periodicity and highest degree of order delivered up to 90.5 m²  g^-1 of electrochemical active surface area and 3.34 A mg^-1 electrocatalysis capability towards FAO, 3.8 and 7.8 times the values of the commercial Pd/C catalyst, respectively. By controlling the temperature and potential of the electrodeposition procedure, the periodicity area and order degree of the mesoporosity are highly tunable. These Pd membranes gave prototype formic acid fueled cells with 4.3 and 2.4 times the maximum current and power density of the commercial Pd/C catalyst.

Pore structure dependent activity and durability of mesoporous rhodium nanoparticles towards the methanol oxidation reaction

A significant porous structure effect of mesoporous rhodium nanoparticles on the electrocatalytic methanol oxidation reaction was reported.

An Up-To-Date Review on Biomedical Applications of Palladium Nanoparticles

Palladium nanoparticles (PdNPs) have intrinsic features, such as brilliant catalytic, electronic, physical, mechanical, and optical properties, as well as diversity in shape and size. The initial researches proved that PdNPs have impressive potential for the development of novel photothermal agents, photoacoustic agents, antimicrobial/antitumor agents, gene/drug carriers, prodrug activators, and biosensors. However, very few studies have taken the benefit of the unique characteristics of PdNPs for applications in the biomedical field in comparison with other metals like gold, silver, or iron. Thus, this review aims to highlight the potential applications in the biomedical field of PdNPs. From that, the review provides the perceptual vision for the future development of PdNPs in this field.

Porosity controls the catalytic activity of platinum nanoparticles

Dendritic/mesoporous nanoparticle structures arise naturally and result from aggregation based growth mechanisms. The resulting porous particles exhibit high total surface areas (internal and external) but determining the magnitude of the interface remains challenging. Furthermore, assessing the chemical accessibility of the catalytic interface presents an additional difficulty. Taking three structurally related but different sized platinum nanoparticle samples (30-70 nm), we demonstrate how the catalytic rate of two archetypal surface limited reactions scale not with the square of the particle radius but with a power law of 2.6-2.9. This power law directly reflects the mesoporosity of the nanoparticles; the internal surface of the nanoparticles is both chemically accessible and contributes to the catalytic activity. For the 70 nm particles, up to 60% of the catalytic surface is contained in the internal structure of the particle.

Chemical Design of Palladium-Based Nanoarchitectures for Catalytic Applications

Palladium (Pd) plays an important role in numerous catalytic reactions, such as methanol and ethanol oxidation, oxygen reduction, hydrogenation, coupling reactions, and carbon monoxide oxidation. Creating Pd-based nanoarchitectures with increased active surface sites, higher density of low-coordinated atoms, and maximized surface coverage for the reactants is important. To address the limitations of pure Pd, various Pd-based nanoarchitectures, including alloys, intermetallics, and supported Pd nanomaterials, have been fabricated by combining Pd with other elements with similar or higher catalytic activity for many catalytic reactions. Herein, recent advances in the preparation of Pd-based nanoarchitectures through solution-phase chemical reduction and electrochemical deposition methods are summarized. Finally, the trend and future outlook in the development of Pd nanocatalysts toward practical catalytic applications are discussed.

Electrochemical Deposition: An Advanced Approach for Templated Synthesis of Nanoporous Metal Architectures

Well-constructed porous materials take an essential role in a wide range of applications, including energy conversion and storage systems, electrocatalysis, photocatalysis, and sensing. Although the tailored design of various nanoarchitectures has made substantial progress, simpler preparation methods are compelled to meet large-scale production requirements. Recently, advanced electrochemical deposition techniques have had a significant impact in terms of precise control upon the nanoporous architecture (i.e., pore size, surface area, pore structure, etc.), enabling access to a wide range of compositions. In this Account, we showcase the uniqueness of electrochemical deposition techniques, detail their implementation toward the synthesis of novel nanoporous metals, and finally outline the future research directions. Nanoporous metallic structures are attractive in that they can provide high surface area and large pore volume, easing mass transport of reactants and providing high accessibility to catalytically active metal surface. The great merit of the electrochemical deposition approach does not only lie in its versatility, being applicable to a wide range of compositions, but also in the nanoscale precision it affords when it comes to crystal growth control, which cannot be easily achieved by other bottom-up or top-down approaches. In this Account, we describe the significant progress made in the field of nanoporous metal designed through electrochemical deposition approaches using hard templates (i.e., porous silica, 3D templates of polymer and silica colloids) and soft templates (i.e., lyotropic liquid crystals, polymeric micelles). In addition, we will point out how it accounts for precise control over the crystal growth and describe the unique physical and chemical properties emerging from these novel materials. Up to date, our group has reported the synthesis of several nanoporous metals and alloys (e.g., Cu, Ru, Rh, Pd, Pt, Au, and their corresponding alloys) under various conditions through electrochemical deposition, while investigating their various potential applications. The orientation of the channel structure, the composition, and the nanoporosity can be easily controlled by selecting the appropriate surfactants or block copolymers. The inherent properties of the final product, such as framework crystallinity, catalytic activity, and resistance to oxidation, are depending on both the composition and pore structure, which in turn require suitable electrochemical conditions. This Account is divided into three main sections: (i) a history of electrochemical deposition using hard and soft templates, (ii) a description of the important mechanisms involved in the preparation of nanoporous materials, and (iii) a conclusion and future perspectives. We believe that this Account will promote a deeper understanding of the synthesis of nanoporous metals using electrochemical deposition methods, thus enabling new pathways to control nanoporous architectures and optimize their performance toward promising applications such as catalysis, energy storage, sensors, and so forth.

Pt supraparticles with controllable DNA valences for programmed nanoassembly

Supraparticles are self-limiting nanoparticle ensembles with attractive properties from their unique hierarchical (primary and secondary) structures. Aiming at relieving the bottleneck of the very limited material building blocks in DNA nanotechnology, we herein demonstrate Pt-based supraparticles as catalytic materials for valence-controllable and high density DNA functionalizations toward DNA-programmed nanoassembly.

Boosting Hot Electrons in Hetero-superstructures for Plasmon-Enhanced Catalysis

Hetero-nanostructures featured with both strong plasmon absorption and high catalytic activity are believed to be ideal platforms to realize efficient light-driven catalysis. However, in reality, it remains a great challenge to acquire high-performance catalysis in such hetero-nanostructures due to poor generation and transfer of plamson-induced hot electrons. In this report, we demonstrate that Au nanorod@Pd superstructures (Au@Pd SSs), where the ordered Pd nanoarrays are precisely grown on Au nanorod surfaces via solution-based seed-mediated approach, would be an excellent solution for this challenge. Both experiment and theory disclose that the ordered arrangement of Pd on Au nanorod surfaces largely promotes hot electron generation and transfer via amplified local electromagnetic field and decreased electron-phonon coupling, respectively. Each effect is separately highlighted in experiments by the significant plasmon-enhanced catalytic activity of Au@Pd SSs in two types of important reactions with a distinct time scale of bond-dissociation event: molecular oxygen activation and carbon-carbon coupling reaction. This work opens the door to design and application of new generation photocatalysts.

Metal Bromide Controlled Interfacial Aromatization Reaction for Shape-Selective Synthesis of Palladium Nanostructures with Efficient Catalytic Performances

Herein, the effect of diverse metal bromides for the shape evolution of palladium nanostructures (Pd NS) has been demonstrated. Aromaticity-driven reduction of bromopalladate(II) is optimized to reproducibly obtain different Pd NS at the water/organic layer interface. In this soft interfacial strategy, a redox potential driven reaction has been performed, forming the thermodynamically more stable (>10(4) -fold) PdBr4 (2-) precursor from PdCl4 (2-) by adding extra metal bromides. In the process, the reductant, Hantzsch dihydropyridine ester (DHPE), is aromatized. Interestingly, alkali metal bromides devoid of coordination propensity exclusively evolve Pd nanowires (Pd NWs), whereas in the case of transition metal bromides the metal ions engage the 'N' donor of DHPE at the interface, making the redox reaction sluggish. Hence, controlled Pd nanoparticles growth is observed, which evolves Pd broccolis (Pd NBRs) and Pd nanorods (Pd NRs) at the interface in the presence of NiBr2 and CuBr2 , respectively, in the aqueous solution. Thus, the effect of diverse metal bromides in the reaction mixture for tailor-made growth of the various Pd NS is reported. Among the as-synthesized materials, the Pd NWs stand to be superior catalysts and their efficiency is almost 6 and 2.5 times higher than commercial 20 % Pd/C in the electrooxidation of ethanol and Cr(VI) reduction reaction by formic acid, respectively.

Towards rational design of core–shell catalytic nanoreactor with high performance catalytic hydrogenation of levulinic acid

Core–shell catalytic nanoreactor was designed, exhibiting high catalytic activity for levulinic acid hydrogenation.

A highly active Pd–P nanoparticle electrocatalyst for enhanced formic acid oxidation synthesized via stepwise electroless deposition

A highly active Pd–P nanoparticle electrocatalyst for formic acid oxidation was synthesized using NaH₂PO₂ as the reducing agent.

Palladium-Based Nanomaterials: A Platform to Produce Reactive Oxygen Species for Catalyzing Oxidation Reactions

Oxidation reactions by molecular oxygen (O2 ) over palladium (Pd)-based nanomaterials are a series of processes crucial to the synthesis of fine chemicals. In the past decades, investigations of related catalytic materials have mainly been focused on the synthesis of Pd-based nanomaterials from the angle of tailoring their surface structures, compositions and supporting materials, in efforts to improve their activities in organic reactions. From the perspective of rational materials design, it is imperative to address the fundamental issues associated with catalyst performance, one of which should be oxygen activation by Pd-based nanomaterials. Here, the fundamentals that account for the transformation from O2 to reactive oxygen species over Pd, with a focus on singlet O2 and its analogue, are introduced. Methods for detecting and differentiating species are also presented to facilitate future fundamental research. Key factors for tuning the oxygen activation efficiencies of catalytic materials are then outlined, and recent developments in Pd-catalyzed oxygen-related organic reactions are summarized in alignment with each key factor. To close, we discuss the challenges and opportunities for photocatalysis research at this unique intersection as well as the potential impact on other research fields.

Ru-assisted synthesis of Pd/Ru nanodendrites with high activity for ethanol electrooxidation

Due to the specific physical and chemical properties of a highly branched noble metal, the controllable synthesis has attracted much attention. This article reports the synthesis of Pd/Ru nanodendrites by a facile method using an oil bath in the presence of polyvinyl pyrrolidone, potassium bromide and ascorbic acid. The morphology, structure, and composition of the as-prepared catalysts were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. In the electrochemical measurement, the as-prepared Pd7/Ru1 bimetallic nanodendrites provide a large electrochemically active surface area and exhibit high peak current density in the forward scan toward ethanol electrooxidation, which is nearly four times higher than those of a pure Pd catalyst. The as-prepared Pd7/Ru1 catalysts also exhibit significantly enhanced cycling stability toward ethanol oxidation in alkaline medium, which are mainly ascribed to the synergetic effect between Pd and Ru. This indicates that the Pd7/Ru1 catalysts should have great potential applications in direct ethanol fuel cells.

Multimetallic Mesoporous Spheres Through Surfactant-Directed Synthesis

Multimetallic mesoporous spheres are successfully synthesized with ultra-large mesopores with the assistance of nonionic triblock copolymer (F127) as a structural directing agent. The kinetically controlled reduction rate of metal species and the concentration of F127 are critical to the formation of the large mesopores.