Pd Nanomaterials Research Articles

Surfactant-free synthesis of nanostructured palladium materials under mild conditions and their highly catalytic selective hydrogenation

Nanostructured palladium (Pd) materials are highly efficient noble metal catalysts in various fields, but developing a simple and mild strategy to prepare Pd nanomaterials with high activity and selectivity still remains a big challenge. In this study, uniform-sized Pd popcorn-like nanospheres (PNSs) were successfully synthesized by the slow reduction of Pd(OAc)2 in anhydrous methanol under ambient conditions in the dark without any surfactant, additional reductant and support. The obtained Pd PNSs have rough surface with the average diameter of approximately 140 nm, and are composed of many smaller PNSs with the average size of about 12 nm. Pd PNSs have excellent catalytic performance in the hydrogenation of 4-nitrobenzaldehyde to 4-aminobenzaldehyde under mild conditions. Specifically, using the as-prepared Pd PNSs as catalyst, the 98 % conversion of 4-nitrobenzaldehyde and 98 % selectivity to 4-aminobenzaldehyde can be achieved within 1.5 h at 35°C under atmospheric pressure. After three recycling, the Pd PNSs can still maintain highly catalytic activity and selectivity. The very simple strategy developed here will be a valuable supplement to the methodology for the surfactant-free fabrication of other surface-active metallic nanomaterials for advanced applications.

Non‐enzymatic hydrogen peroxide sensor based on palladium‐decorated poly(thionine) modified glassy carbon electrode

AbstractGlassy carbon electrode was modified with palladium‐decorated conducting poly(thionine) film to develop a simple, cost‐effective, and fast amperometric sensor for the detection of H2O2. Conducting PTH film served as a porous and stable support matrix for even distribution of the Pd nanomaterials. In order to get the maximum performance from the modified electrode system, experimental conditions were optimized using chronoamperometry. The Pd/PTH@GCE electrode showed maximum performance in buffer solution at pH = 7.5 meaning it is suitable for the detection of H2O2 at physiological pH (7.4). Scanning Electron Microscopy was performed for physical characterization of the modified electrodes using pencil graphite electrodes. The active surface area for Pd/PTH‐modified GCE was calculated as 1.103 cm2. The linear concentration range was determined as 0.2–7.0 mM and its sensitivity was determined as 40.0 μA mM−1. The detection limit (LOD) of the sensor was calculated as 12.3 μM with a signal/noise ratio of 3.

Hydrogen sensing towards palladium-based nanocomposites: A review

Hydrogen energy as the main path to accomplish the goal of carbon neutrality, sensors for hydrogen leak detection will become an essential component of the entire hydrogen industry chain. Among the various types of H2 sensors, palladium-based chemiresistive sensors are one of the most promising sensing systems due to their process simplicity and low cost. In this review, we first outline the latest technological advances made to improve hydrogen selectivity and response and identify Pd-based nanomaterials as the most promising candidates. The second part discusses the effects of different types of Pd nanomaterials and Pd alloy nanomaterials on hydrogen sensing. In addition, a comprehensive review of key advances and strategies for hydrogen sensors based on various Pd-based complexes, including metal oxides, carbon-based materials, Mxene, metal-organic framework, and others, is presented. The discussion of each material elucidates smethodologies in the pursuit of manufacturing high-quality hydrogen sensors. Finally, the outlook and future directions for the development of Pd-based hydrogen sensors is provided.

Nonclassical Nucleation and Growth of Pd Nanocrystals from Aqueous Solution Studied by In Situ Liquid Transmission Electron Microscopy

Direct visualization and understanding of the atomic mechanisms governing the growth of nanomaterials are crucial for designing synthesis strategies of high specificity. Aside from playing a key role in numerous technological applications, palladium clusters and nanoparticles are particularly valuable due to their outstanding catalytic activity. Studies show that the properties of Pd nanomaterials depend on shape and size. Therefore, optimizing the synthesis to control the final size and shape of Pd nanoparticles is important for a large number of current and future applications. In this work, we exploit in situ liquid cell scanning transmission electron microscopy to track at the atomic scale the growth of Pd nanoparticles from the very early stage to mature, crystalline nanoparticles. We find that the formation of Pd nanoparticles consists of multiple steps. The first step in nanoparticle formation, representing a nonclassical nucleation step, can be described by the formation of agglomerates of Pd atoms. In the second step, these agglomerates grow via atomic addition to form primary nanoclusters, which coalesce to form amorphous clusters. In the third stage, these clusters continue to coalesce, leading to the formation of amorphous Pd NPs, while in parallel, growth by monomer attachment continues. Then, in the fourth step, the amorphous nanoparticles undergo a nanocrystallization process, where the continuous improvement of crystallinity and the establishment of a distinct morphology eventually give rise to the formation of facetted, crystalline nanoparticles. Similar to our earlier work with Au and Pt nanoparticles, these results confirm that even for simple systems, nonclassical nucleation and growth processes dominate and that these multi-step mechanisms are highly element-specific. Despite the fact that the synthesis conditions are identical, the element-specific interactions define the pathway of the formation of crystalline nanoparticles.

Morphological Evolution Trajectory of Multifaceted Palladium Nanoparticles.

Precise control over the morphology and facets of Pd nanomaterials has great importance in catalytic and sensing applications. In this study, we synthesized Pd nanoparticles with multiple types of low-Miller-index-faceted morphologies by systematically defining the synthesis conditions of the seed-mediated colloidal preparation method. We discovered the morphological evolution of Pd nanoparticles by following the trajectory of the surface Miller indices, which were determined by the cooperative effects of cetyltrimethylammonium bromide and ascorbic acid. By precise control of the morphological trajectory, Pd nanoparticles with a new cuborhombicube morphology, composed of 36 facets and concave edges, were discovered. This study provides important insight into the design of the surface Miller indices and morphologies of functional nanomaterials.

Facile Surfactant-Free synthesis of Pd-Sn1.1Nb2O5.5F0.9@SnO2 Core–Shell Nano-Octahedrons for efficient photocatalytic ethylene oxidation

A ternary core–shell structure composed of Sn1.1Nb2O5.5F0.9 (SNOF), Pd nanoparticles, and the SnO2 was fabricated by a facile one-step process at room temperature. In this structure, the SNOF nano-octahedrons were coated with thin layers of SnO2, and Pd nanoparticles were embedded in the SnO2 matrix. The formation of SnO2 and Pd nanomaterials was induced by the redox reaction between the reductive Sn2+ ions of the SNOF and the H2PdCl4 solution. During this process, there are no organic species or foreign reducing agents involved. The as-obtained Pd-Sn1.1Nb2O5.5F0.9@SnO2(Pd-SNOF@SnO2) nanocomposites showed efficient photoactivities for C2H4 oxidation under simulated sunlight irradiation, which was significantly higher than that of the blank SNOF. The mineral ratio was determined to be ∼ 100%, and the catalyst was stable after five cycles. This result was ascribed to the core–shell structure of SNOF and SnO2 as well as the embedded Pd nanoparticles functioning as an electron trapping site, which can effectively accept the photo-excited electrons.

Smart PdH@MnO2 Yolk-Shell Nanostructures for Spatiotemporally Synchronous Targeted Hydrogen Delivery and Oxygen-Elevated Phototherapy of Melanoma.

Hydrogen therapy, an emerging therapeutic strategy, has recently attracted much attention in anticancer medicine. Evidence suggests that hydrogen (H2) can selectively reduce intratumoral overexpressed hydroxyl radicals (•OH) to break the redox homeostasis and thereby lead to redox stress and cell damage. However, the inability to achieve stable hydrogen storage and efficient hydrogen delivery hinders the development of hydrogen therapy. Furthermore, oxygen (O2) deficiency in the tumor microenvironment (TME) and the electron-hole separation inefficiency in photosensitizers have severely limited the efficacy of photodynamic therapy (PDT). Herein, a smart PdH@MnO2/Ce6@HA (PHMCH) yolk-shell nanoplatform is designed to surmount these challenges. PdH tetrahedrons combine stable hydrogen storage and high photothermal conversion efficiency of palladium (Pd) nanomaterials with near-infrared-controlled hydrogen release. Subsequently, the narrow bandgap semiconductor manganese dioxide (MnO2) and the photosensitizer chlorin e6 (Ce6) are introduced into the PHMCH nanoplatform. Upon irradiation, the staggered energy band edges in heterogeneous materials composed of MnO2 and Ce6 can efficiently facilitate electron-hole separation for increasing singlet oxygen (1O2). Moreover, MnO2 nanoshells generate O2 in TME for ameliorating hypoxia and further improving O2-dependent PDT. Finally, the hyaluronic acid-modified PHMCH nanoplatform shows negligible cytotoxicity and selectively targets CD44-overexpressing melanoma cells. The synergistic antitumor performance of the H2-mediated gas therapy combined with photothermal and enhanced PDT can explore more possibilities for the design of gas-mediated cancer therapy.

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

The performances of catalysts are highly dependent on their crystallinities. It is a significant challenge to successively manipulate the crystallinities of noble metal nanocatalysts due to the strong metallic bonds, especially under ambient conditions. Herein, a post-crystallization approach is developed for successive control of the crystallinity of Pd nanosheets via selective oxidation etching of the amorphous domains. This strategy can be extended to crystallize other Pd and Ru nanomaterials. By carefully modulating the crystallinity of Pd nanosheets, the time for the complete conversion of 4-nitrostyrene via hydrogenation is reduced by 20 times. Also, crystallization can turn the selectivity of the products and improve the stability of Pd nanosheets. These findings may advance the crystal engineering of metal nanomaterials for wide applications.

Toward Overcoming the Challenges in the Comparison of Different Pd Nanocatalysts: Case Study of the Ethanol Oxidation Reaction

Precious metal nanoparticles, in particular palladium nanomaterials, show excellent catalytic properties and are key in the development of energy systems. For instance, ethanol fuel cells are promising devices for sustainable energy conversion, where Pd-based catalysts are key catalysts for the related ethanol oxidation reaction (EOR). Pd is a limited resource; thus, a remaining challenge is the development of efficient and stable Pd-based catalysts. This calls for a deeper understanding of the Pd properties at the nanoscale. This knowledge can be gained in comparative studies of different Pd nanomaterials. However, such studies remain challenging to perform and interpret due to the lack of cross-studies using the same Pd nanomaterials as a reference. Here, as-prepared sub 3 nm diameter surfactant-free Pd nanoparticles supported on carbon are obtained by a simple approach. The as-prepared catalysts with Pd loading 10 and 30 wt % show higher activity and stability compared to commercially available counterparts for the EOR. Upon electrochemical testing, a significant size increase and loss of electrochemical active surface are observed for the as-prepared catalysts, whereas the commercial samples show an increase in the electrochemically active surface area and moderate size increase. This study shines light on the challenging comparison of different catalysts across the literature. Further advancement in Pd (electro)catalyst design will gain from including self-prepared catalysts. The simple synthesis detailed easily leads to suitable nanoparticles to be used as a reference for more systematic comparative studies of Pd catalysts across the literature.

Palladium nanoplates scotch breast cancer lung metastasis by constraining epithelial-mesenchymal transition

Abstract Metastasis accounts for the majority of cancer deaths in many tumor types including breast cancer. Epithelial-mesenchymal transition (EMT) is the driving force for the occurrence and progression of metastasis, however, no targeted strategies to block the EMT program are currently available to combat metastasis. Diverse engineered nanomaterials (ENMs) have been reported to exert promising anti-cancer effects, however, no ENMs have been designed to target EMT. Palladium (Pd) nanomaterials, a type of ENM, have received substantial attention in nanomedicine due to their favorable photothermal performance for cancer therapeutics. Herein, Pd nanoplates (PdPL) were found to be preferentially biodistributed to both primary tumors and metastatic tumors. Importantly, PdPL showed a significant inhibition of lung metastasis with and without near-infrared (NIR) irradiation. Mechanistic investigations revealed that EMT was significantly compromised in breast cancer cells upon the PdPL treatment, which was partially due to the inhibition of the transforming growth factor-beta (TGF-β) signaling. Strikingly, the PdPL was found to directly interact with TGF-β proteins to diminish TGF-β functions in activating its downstream signaling, as evidenced by the reduced phosphorylation of Smad2. Notably, TGF-β-independent pathways were also involved in undermining EMT and other important biological processes that are necessary for metastasis. Additionally, NIR irradiation elicited synergistic effects on PdPL-induced inhibition of primary tumors and metastasis. In summary, these results revealed that the PdPL remarkably curbed metastasis by inhibiting EMT signaling, thereby indicating the promising potential of PdPL as a therapeutic agent for treating breast cancer metastasis.

Selective Electrooxidation of Glycerol to Formic Acid over Carbon Supported Ni1–xMx(M = Bi, Pd, and Au) Nanocatalysts and Coelectrolysis of CO2

The composition effect of carbon supported NixM1–x (M = Bi, Pd, and Au) nanomaterials toward glycerol electrooxidation (GEOR) was evaluated in alkaline media. Ni-rich catalysts with different atomi...

Ligand-Exchange-Induced Amorphization of Pd Nanomaterials for Highly Efficient Electrocatalytic Hydrogen Evolution Reaction.

Various kinds of amorphous materials, such as transition metal dichalcogenides, metal oxides, and metal phosphates, have demonstrated superior electrocatalytic performance compared with their crystalline counterparts. Compared to other materials for electrocatalysis, noble metals exhibit intrinsically high activity and excellent durability. However, it is still very challenging to prepare amorphous noble-metal nanomaterials due to the strong interatomic metallic bonding. Herein, the discovery of a unique thiol molecule is reported, namely bismuthiol I, which can induce the transformation of Pd nanomaterials from face-centered-cubic (fcc) phase into amorphous phase without destroying their integrity. This ligand-induced amorphization is realized by post-synthetic ligand exchange under ambient conditions, and is applicable to fcc Pd nanomaterials with different capping ligands. Importantly, the obtained amorphous Pd nanoparticles exhibit remarkably enhanced activity and excellent stability toward electrocatalytic hydrogen evolution in acidic solution. This work provides a facile and effective method for preparing amorphous Pd nanomaterials, and demonstrates their promising electrocatalytic application.

Engineering the morphology of palladium nanostructures to tune their electrocatalytic activity in formic acid oxidation reactions.

Pd nanomaterials can be cheaper alternative catalysts for the electrocatalytic formic acid oxidation reaction (FAOR) in fuel cells. The size and shape of the nanoparticles and crystal engineering can play a crucial role in enhancing the catalytic activities of Pd nanostructures. A systematic study on the effect of varying the morphology of Pd nanostructures on their catalytic activities for FAOR is reported here. Palladium nanoparticles (Pd0D), nanowires (Pd1D) and nanosheets (Pd2D) could be synthesized by using swollen liquid crystals as ‘soft’ templates. Swollen liquid crystals are lyotropic liquid crystals that are formed from a quaternary mixture of a surfactant, cosurfactant, brine and Pd salt dissolved in oil. Pd1D nanostructures exhibited 2.7 and 19 fold higher current density than Pd0D and Pd2D nanostructures in the FAOR. The Pd1D nanostructure possess higher electrochemically active surface area (ECSA), better catalytic activity, stability, and lower impedance to charge transfer when compared to the Pd0D and Pd2D nanostructures. The presence of relatively higher amounts of crystal defects and enriched (100) crystal facets in the Pd1D nanostructure were found to be the reasons for their enhanced catalytic activities.

Improving the Performance of Hydrogen Sensors with Novel TiO2 Nanotube Arrays Hybrid Structure

In this paper, a kind of novel TiO2 nanotube arrays (TNTs) hybrid structure was presented to improve the performance of hydrogen sensors. In this novel structure, palladium functionalized TNTs hybrid nanostructure supported on titanium wire. TNTs arrays was prepared by anodizing Ti wire using a standard electrochemical procedure. Pd nanomaterials were deposited on TNTs. Optimized experiments showed the hydrogen sensor supported on titanium wire showed a good response time of 8 s and high sensitivity of 94.8% at 1.9 vol% H2 at room temperature (25 °C). The research work revealed potential good hydrogen sensitivity of this kind of hybrid nanostructure.

Anodic Oxidation of Butan-1-ol on Reduced Graphene Oxide-Supported Pd-Ag Nanoalloy for Fuel Cell Application.

Reduced graphene oxide (RGO)-supported bimetallic PdxAgy alloy nanoparticles of various compositions were synthesized by one-pot coreduction of respective precursors with hydrazine for use in the anode catalysis of oxidation of butan-1-ol in alkali. The as-synthesized catalyst materials were characterized by microscopic, spectroscopic, and diffraction techniques. Cyclic voltammetry (CV), chronoamperometry, and polarization studies infer that a few PdxAgy materials exhibit an enhanced and synergistic catalytic activity in reference to Pd and Ag nanomaterials. Among the various RGO composites of PdxAgy alloy on graphite support, the one containing the Pd70Ag30@RGO composite is the best in catalytic activity. The cycle life of the catalyst is found to be very high, and PdO and Ag2O are found to be generated in the catalyst material with little change in the catalytic capability during the 100th cycle of CV operation. The addition of Ag upto 30 atom % in the PdxAgy alloy causes greater formation of butyraldehyde and butyl butanoate among the various products. Larger atom % of Pd helps to form sodium butyrate and sodium carbonate, as evident from the ex situ Fourier transform infrared and high-performance liquid chromatography study of the product mixtures and the separate CV studies of the intermediate products. A suitable mechanism is also proposed to fit the findings.

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.

Deposition and morphological evolution of nanostructured palladium during potential cycling: a liquid-cell TEM study.

In order to gain better control over the functionality of Pd nanostructures used in several CO2-mitigating electrochemical energy conversion systems, it is imperative to underpin different nanoscale phenomena influencing their structural durability. Hitherto, such analyses have been carried out before/after an electrochemical treatment, but not during the entire process. Here, we demonstrate monitoring of morphological evolution in Pd nanostructures over the entire course of electrochemical treatment using a liquid-cell transmission electron microscope (TEM) set-up. Our findings reveal new insights into nanoparticle growth, dissolution, detachment, and aggregation that are relevant for the development of functional Pd nanomaterials.

Distinct Differences in Peptide Adsorption on Palladium and Gold: Introducing a Polarizable Model for Pd(111)

Materials-binding peptides offer promising routes to the production of tailored Pd nanomaterials in aqueous media, enabling the optimization of catalytic properties. However, the atomic-scale detai...

Revisiting of Pd Nanoparticles in Cancer Treatment: All-Round Excellence of Porous Pd Nanoplates in Gene-Thermo Combinational Therapy.

Gold nanomaterials are commonly used in biomedical applications owing to their excellent biocompatibility and unique physicochemical and optical properties, whereas Pd nanomaterials are mainly used as catalysts. Here, we re-examined the possible applications of Pd nanomaterials. Reducing agent-assisted excessive galvanic replacement-mediated porous Au nanoplates, porous Pt nanoplates, and porous Pd nanoplate synthesis enabled us to compare the properties and efficiency of nanoplates composed of three metal elements (Au, Pt, and Pd). According to our analytical results, porous Pd nanoplates exhibited exceptional all-round excellence in photothermal conversion, therapeutic gene loading/releasing, cytotoxicity, and in vitro combination cancer treatment. We believe that this discovery broadens the potential applications of metal nanomaterials, with an emphasis on more efficient biomedical applications in limited conventional fields.

Tailoring the Selectivity of Bimetallic Copper–Palladium Nanoalloys for Electrocatalytic Reduction of CO2 to CO

Controlling the morphology and composition of bimetallic nanoalloys is an effective way to tailor their catalytic activity/selectivity for a given chemical reaction. Herein, we demonstrate the tailoring of bimetallic copper–palladium (Cu–Pd) nanoalloys with different morphologies and compositions for obtaining highly efficient electrocatalysts for the reduction of CO2 to CO. We further evaluate the catalytic performance of these Cu–Pd nanomaterials for the electrochemical conversion of CO2 to CO. In particular, the spherical Cu–Pd nanoalloys with Cu/Pd molar ratio of 1/0.3 have the highest Faradaic efficiency for CO conversion (93%), while the dendritic Cu–Pd nanoalloys have the highest Faradaic efficiency for H2 production (65.2%) via hydrogen evolution reaction at a polarized potential of −0.87 V. The balancing of the rate-determining steps during CO2 conversion is a key factor for the observed activity/selectivity of Cu–Pd nanoalloys with different morphologies/compositions. The findings revealed in th...