Polyallylamine functionalized palladium icosahedra: one-pot water-based synthesis and their superior electrocatalytic activity and ethanol tolerant ability in alkaline media

Gold versus platinum for chemical modification of carbon quantum dots from carboxymethyl cellulose: Tunable biomedical performance

Urgent requirements for medication from chronic inflammation and cancer are considerably interested, while, the recent reports were considered with investigating simple methods for synthesis. Metal-modified carbon quantum dots ("M-CQDs") were successfully ingrained from carboxymethyl cellulose under the assistance of infra-red irradiation. The current approach demonstrates a study for the effect of structural tuning for biomedical performance of CQDs via modifying of CQDs with either gold (Au-CQDs) or platinum (Pt-CQDs). Successive nucleation of Au-CQDs and Pt-CQDs was confirmed via different instrumental analyses like, TEM micrographs, Zeta potential, XRD, FTIR, 1HNMR& 13CNMR spectra. The data reveal that, modification of CQDs (8.7 nm) with gold was reflected in insignificant effect on the mean size of CQDs (8.9 nm), whereas, doping of platinum resulted in slight enlargement of the size (12.4 nm). However, Pt-CQDs were exhibited with the highest anti-inflammatory (cell viability percent 78 %) and antimicrobial action. On the other hand, Au-CQDs were shown with the highest anticancer affinity (reduction of cell viability 83 %) compared to the others. The current study approved the superiority of CQDs modified with either gold or platinum to be successfully applicable as potential therapeutic reagents for the treatment of either cancer or inflammation diseases.

Palladium atomic layers coated on ultrafine gold nanowires boost oxygen reduction reaction

Palladium-based nanocatalysts play an important role in catalyzing the cathode oxygen reduction reaction (ORR) for fuel cells working under alkaline conditions, but the performance still needs to be improved to meet the requirements for large-scale applications. Herein, Au@Pd core-shell nanowires have been developed by coating Pd atomic layers on ultrafine gold nanowires and display outstanding electrocatalytic performance towards alkaline ORR. It is found that Pd overlayers with atomic thickness can be coated on 3 nm Au nanowires under CO atmosphere and completely cover the surfaces. The obtained ultrafine Au@Pd nanowires exhibit an electrochemical active area (ECSA) of 68.5 m2/g and a mass activity of 0.91 A/mg (at 0.9 V vs. RHE), which is around 3.1 and 15.2 times higher than that of commercial Pd/C. The activity loss of the ultrafine Au@Pd nanowire after 10,000 cycles of accelerated degradation tests is only ∼20 %, demonstrating its much better stability compared to commercial Pd/C. Further characterizations combined with density functional theory (DFT) calculations demonstrate that the electronic interactions between Pd atomic layers and underlying Au can increase the electronic density of Pd and promote the efficient activation of oxygen, thus leading to the improved ORR performance.

Nanostructure engineering of Pt/Pd-based oxygen reduction reaction electrocatalysts

Increasing the atomic utilization of Pt and Pd elements is the key to the advancement and broad dissemination of fuel cells. Central to this task is the design and fabrication of highly active and stable Pt- or Pd-based electrocatalysts for the oxygen reduction reaction (ORR), which requires a comprehensive understanding of the ORR pathways and mechanism. Past endeavors have accumulated a wealth of knowledge about the Pt/Pd-based ORR electrocatalysts based on structure engineering, while a systematic review of the nanostructure engineering of Pt/Pd-based ORR electrocatalysts has been rarely reported. In this review, we provide a systematic discussion about the current status of Pt/Pd-based ORR electrocatalysts from the perspective of nanostructure engineering, and we highlight the ORR pathways, mechanisms and theories in order to understand the ORR in a more complex nanocatalyst. Particularly, the underlying structure-function relationship of Pt/Pd-based ORR electrocatalysts is specifically highlighted, which will guide the future synthesis of more efficient ORR electrocatalysts.

Involvement of silver and palladium with red peanuts skin extract for cotton functionalization

A systematic study is currently demonstrated approach for approving the superior role of silver and palladium metallic particles in acting the role of mordant with acquiring the dyed cotton fabrics excellence in color fastness with additional functions of antimicrobial potentiality and UV-protection action. Whereas, samples were dyed with extract of red peanuts skin as natural textile colorant (RPN dye). The represented data revealed that, in absence of mordant, the samples treated with metal precursors prior to dyeing were exhibited with the excellent color strength, color fastness, antimicrobial action and UV-protection action. Color fastness (washing, rubbing and light fastness) was estimated to be in the range of very good-excellent. Sample pretreated with silver salt and dyed in the absence of mordant was graded with excellent UV-protection action (UPF 31.5, UVB T% 2.6% and UVB blocking percent 97.4%). Antimicrobial potency against E. coli, S. aureus and Candida albicans through inhibition zone and the reduction percent was approved to be in the range of excellence (93.01-99.51%) for the samples dyed in absence of mordant and pretreated with either silver or palladium precursors.

Shape-Controlled Photochemical Synthesis of Noble Metal Nanocrystals Based on Reduced Graphene Oxide

The fabrication of supported noble metal nanocrystals (NCs) with well-controlled morphologies have been attracted considerable interests due to their merits in a wide variety of applications. Photodeposition is a facile and effective method to load metals over semiconductors in a simple slurry reactor under irradiation. By optimizing the photodeposition process, the size, chemical states, and the geometrical distribution of metal NCs have been successfully tuned. However, metal NCs with well-controlled shapes through the photodeposition process have not been reported until now. Here, we report our important advances in the controlled photodeposition process to load regular noble metal NCs. Reduced graphene oxide (rGO) is introduced as a reservoir for the fast transfer of photoelectrons to avoid the fast accumulation of photogenerated electrons on the noble metals which makes the growth process uncontrollable. Meanwhile, rGO also provides stable surface for the controlled nucleation and oriented growth. Noble metal NCs with regular morphologies are then evenly deposited on rGO. This strategy has been demonstrated feasible for different precious metals (Pd, Au, and Pt) and semiconductors (TiO₂, ZnO, ZrO₂, CeO₂, and g-C₃N₄). In the prototype application of electrochemical hydrogen evolution reaction, regular Pd NCs with enclosed {111} facets showed much better performance compared with that of irregular Pd NCs.

The use of amino-based functional molecules for the controllable synthesis of noble-metal nanocrystals: a minireview

Controlling the morphologies and structures of noble-metal nanocrystals has always been a frontier field in electrocatalysis. Functional molecules such as capping agents, surfactants and additives are indispensable in shape-control synthesis. Amino-based functional molecules have strong coordination abilities with metal ions, and they are widely used in the morphology control of nanocrystals. In this minireview, we pay close attention to recent advances in the use of amino-based functional molecules for the controllable synthesis of noble-metal nanocrystals. The effects of various amino-based molecules on differently shaped noble-metal nanocrystals, including zero-, one-, two-, and three-dimensional nanocrystals, are reviewed and summarized. The roles and mechanisms of amino-based small molecules and long-chain ammonium salts relating to the morphology-control synthesis of noble-metal nanocrystals are highlighted. Relationships between shape and electrocatalytic properties are also described. Finally, some key prospects and challenges relating to the controllable synthesis of noble-metal nanocrystals and their electrocatalytic applications are proposed.

Recent Advances in Amino-Based Molecules Assisted Control of Noble-Metal Electrocatalysts

Morphology-control synthesis is an effective means to tailor surface structure of noble-metal nanocrystals, which offers a sensitive knob for tuning their electrocatalytic properties. The functional molecules are often indispensable in the morphology-control synthesis through preferential adsorption on specific crystal facets, or controlling certain crystal growth directions. In this review, the recent progress in morphology-control synthesis of noble-metal nanocrystals assisted by amino-based functional molecules for electrocatalytic applications are focused on. Although a mass of noble-metal nanocrystals with different morphologies have been reported, few review studies have been published related to amino-based molecules assisted control strategy. A full understanding for the key roles of amino-based molecules in the morphology-control synthesis is still necessary. As a result, the explicit roles and mechanisms of various types of amino-based molecules, including amino-based small molecules and amino-based polymers, in morphology-control of noble-metal nanocrystals are summarized and discussed in detail. Also presented in this progress are unique electrocatalytic properties of various shaped noble-metal nanocrystals. Particularly, the optimization of electrocatalytic selectivity induced by specific amino-based functional molecules (e.g., polyallylamine and polyethyleneimine) is highlighted. At the end, some critical prospects, and challenges in terms of amino-based molecules-controlled synthesis and electrocatalytic applications are proposed.

Surface Ligand Environment Boosts the Electrocatalytic Hydrodechlorination Reaction on Palladium Nanoparticles

We present an enhanced catalytic efficiency of palladium (Pd) nanoparticles (NPs) for the electrocatalytic hydrodechlorination (EHDC) reaction by incorporating the tetraethylammonium chloride (TEAC) ligand into the surface of NPs. Both experimental and theoretical analyses reveal that the surface-adsorbed TEAC is converted to molecular amine (primarily triethylamine) under reductive potentials, forming a strong ligand-Pd interaction that is beneficial to the EHDC kinetics. Using the EHDC of 2,4-dichlorophenol (2,4-DCP), a dominant persistent pollutant identified by the U.S. Environmental Protection Agency, as an example, the Pd/amine composite delivers a mass activity of 2.32 min^-1 g_Pd^-1 and a specific activity of 0.16 min^-1 cm^-2 at -0.75 V versus Ag/AgCl, outperforming Pd and most of the previously reported catalysts. The mechanistic study reveals that the amine ligand offers three functions: the H⁺-pumping effect, the electronic effect, and the steric effect, providing a favorable environment for the generation of reactive hydrogen radicals (H*) for hydrogenolysis of the C-Cl bond. It also weakens the adsorption strength of EHDC products, alleviating their poisoning on Pd. Investigation into the intermediate products of EHDC on Pd/amine and the biological safety of the 2,4-DCP-contaminated water after EHDC treatment demonstrates that EHDC on Pd/amine is environmentally benign for halogenated organic pollutant abatement. This work suggests that the tuning of NP catalysis using facile ligand post-treatment may lead to new strategies to improve EHDC for environmental remediation applications.

Synthesis of low- and high-index faceted metal (Pt, Pd, Ru, Ir, Rh) nanoparticles for improved activity and stability in electrocatalysis

Driven by the quest for future energy solution, faceted metal nanoparticles are being pursued as the next generation electrocatalysts for renewable energy applications. Thanks to recent advancement in solution phase synthesis, different low- and high-index facets on metal nanocrystals become accessible and are tested for specific electrocatalytic reactions. This minireview summarises the key approaches to prepare nanocrystals containing the most catalytically active platinum group metals (Pt, Pd, Ru, Ir and Rh) exposed with low- and high-index facets using solution phase synthesis. Electrocatalytic studies related to the different facets are highlighted to emphasise the importance of exposing facets for catalysing these reactions, namely oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), alcohol oxidation including methanol (MOR) and ethanol oxidation reactions (EOR), formic acid oxidation reaction (FAOR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The future outlook discusses the challenges and opportunities for making electrocatalysts that are even more active and stable.

Synthesis and facile structure-adjusting of Pd–Pt nanocrystal electrocatalysts with improved activity for ethanol oxidation reaction

Illustration of the synthesis of the nanospheroid-, nanoflower- and nanoworm-Pd–Pt NCs and their electrocatalytic activity for ethanol oxidation.

Surface-modulated palladium-nickel icosahedra as high-performance non-platinum oxygen reduction electrocatalysts

The search for high-performance non-platinum (Pt) electrocatalysts is the most challenging issue for fuel cell technology. Creating bimetallic non-Pt nanocrystals (NCs) with core/shell structures or alloy features has widely been explored as the most effective way for enhancing their electrochemical properties but still suffered from undesirable performance due to the limited interactions between the different components. By addressing the above issue, we report on a new class of active and stable bimetallic non-Pt electrocatalysts with palladium (Pd) icosahedra as the core and nickel (Ni) decorating the surface toward cathodic oxygen reduction reaction (ORR) under alkaline conditions. The optimized Pd₆Ni icosahedra with unique interaction between an icosahedral Pd core and surface Ni yield the highest ORR activity with a mass activity of 0.22 A mg_Pd^-1, which is better than those of the conventional Pd₆Ni icosahedra with alloy surfaces or Pd-rich surfaces, and even two times higher than that of the commercial Pt/C (0.11 A mg_Pt^-1), representing one of the best non-Pt electrocatalysts. Simulations reveal that the Pd icosahedra decorated with Ni atoms emerged in the subsurface can weaken the interaction between the adsorbed oxygen and Pd (111) facet and enhance the ORR activities due to an obvious shift of d-band center. More significantly, under electrochemical accelerated durability test, the Pd₆Ni icosahedra can endure at least 10,000 cycles with negligible activity decay and structural change. The present work demonstrates an important advance in surface tuning of bimetallic NCs as high-performance non-Pt catalysts for catalysis, energy conversion, and beyond.

Seed-Mediated Growth of Colloidal Metal Nanocrystals

Seed-mediated growth is a powerful and versatile approach for the synthesis of colloidal metal nanocrystals. The vast allure of this approach mainly stems from the staggering degree of control one can achieve over the size, shape, composition, and structure of nanocrystals. These parameters not only control the properties of nanocrystals but also determine their relevance to, and performance in, various applications. The ingenuity and artistry inherent to seed-mediated growth offer extensive promise, enhancing a number of existing applications and opening the door to new developments. This Review demonstrates how the diversity of metal nanocrystals can be expanded with endless opportunities by using seeds with well-defined and controllable internal structures in conjunction with a proper combination of capping agent and reduction kinetics. New capabilities and future directions are also highlighted.

Polyhedral Palladium-Silver Alloy Nanocrystals as Highly Active and Stable Electrocatalysts for the Formic Acid Oxidation Reaction

Polyhedral noble–metal nanocrystals have received much attention and wide applications as electrical and optical devices as well as catalysts. In this work, a straightforward and effective hydrothermal route for the controllable synthesis of the high-quality Pd–Ag alloy polyhedrons with uniform size is presented. The morphology, composition and structure of the Pd–Ag alloy polyhedrons are fully characterized by the various physical techniques, demonstrating the Pd–Ag alloy polyhedrons are highly alloying. The formation/growth mechanisms of the Pd–Ag alloy polyhedrons are explored and discussed based on the experimental observations and discussions. As a preliminary electrochemical application, the Pd–Ag alloy polyhedrons are applied in the formic acid oxidation reaction, which shows higher electrocatalytic activity and stability than commercially available Pd black due to the “synergistic effects” between Pd and Ag atoms.

Arginine-assisted synthesis and catalytic properties of single-crystalline palladium tetrapods

Noble metallic nanocrystals (NMNCs) with highly branched morphologies are an exciting new class of nanomaterials because of their great potential application in catalysis, sensing, optics, and electronics originating from their unique structures. Herein, we report a facile water-based method to synthesize high-quality palladium (Pd) tetrapods with the assistance of arginine molecule, which is more economical and environmentally friendly than the previous reported carbon monoxide (CO)-assisted synthesis in the organic system. During the synthesis, arginine molecule plays an essential role in controlling the tetrapod-like morphology. The as-synthesized Pd tetrapods have a potential application in the formic acid (HCOOH)-induced reduction of highly toxic hexavalent chromium (Cr(VI)) owing to their improved catalytic performance for the HCOOH decomposition.

Polyol syntheses of palladium decahedra and icosahedra as pure samples by maneuvering the reaction kinetics with additives

This article reports a robust method based upon polyol reduction for the deterministic synthesis of Pd decahedra or icosahedra with tunable sizes and a purity approaching 100%. The success of such a selective synthesis relies on an ability to fine-tune the reaction kinetics through the addition of Na2SO4 and HCl for decahedra and icosahedra, respectively. In the absence of any additive, the product of a similar synthesis in diethylene glycol contained 10% decahedra and 90% icosahedra. By optimizing the amount of Na2SO4 (or HCl) added into the reaction solution, the percent of decahedra (or icosahedra) in the product could be increased up to 100%. The roles of Na2SO4 and HCl were also investigated in great detail, and two plausible mechanisms were proposed and validated through a set of experiments. In general, a faster reduction rate is needed for the synthesis of Pd decahedra when compared with what is needed for Pd icosahedra. This work not only offers a simple approach to the deterministic syntheses of Pd decahedra and icosahedra but also provides an in-depth understanding of the mechanisms involved in shape-controlled syntheses of noble-metal nanocrystals from the perspective of reaction kinetics. On the basis of the mechanistic understanding, we have also achieved successful synthesis of Pd decahedra as pure samples by adding a proper amount of NaOH into the system to speed up the reduction kinetics.

Autocatalysis and selective oxidative etching induced synthesis of platinum-copper bimetallic alloy nanodendrites electrocatalysts

The controllable synthesis of noble metal alloy nanostructures with highly branched morphology has attracted much attention because of their specific physical and chemical properties. This article reports the synthesis of platinum-copper bimetallic alloy nanodendrites (Pt-Cu BANDs) by a facile, one-pot, templateless, and seedless hydrothermal method in the presence of poly(allylamine hydrochloride) (PAH) and formaldehyde (HCHO). The morphology, composition, and structure of Pt-Cu BANDs are fully characterized by various physical techniques, demonstrating Pt-Cu BANDs are highly alloying, porous, and self-supported nanostructures. The formation/growth mechanism of Pt-Cu BANDs is explored and discussed based on the experimental observations. The autocatalytic growth and interdiffusion are responsible for the formation of Pt-Cu alloy whereas selective oxidative etching results in dendritic morphology of Pt-Cu alloy nanostructures. In addition, the electrocatalytic activity and stability of Pt-Cu BANDs for the methanol oxidation reaction (MOR) are investigated by various electrochemical techniques. The synthesized Pt-Cu BANDs show higher electrocatalytic activity and stability than commercially available Pt black.

Polyamine-assisted hydrothermal synthesis of bimetallic Pd1Cu3 multipods and their high catalytic ability in 4-nitrophenol reduction

Bimetallic Pd₁Cu₃ nanomultipods exhibited excellent catalytic activity for the 4-nitrophenol reduction.

A facile, one-pot synthesis of highly branched Au nanocorals and their enhanced electrocatalytic activity for ethanol oxidation

Dendritic Au nanocorals were prepared using a facile one-pot strategy, and exhibit excellent catalytic activity and stability for the ethanol oxidation reaction.

Controlled synthesis of nanosized palladium icosahedra and their catalytic activity towards formic-acid oxidation

Pd icosahedra with sizes controlled in the range of 5-35 nm were synthesized in high purity through a combination of polyol reduction and seed-mediated growth. The Pd icosahedra were obtained with purity >94 % and uniform sizes controlled in the range of 5-17 nm by using ethylene glycol as both the reductant and solvent. The studies indicate that the formation of Pd nanocrystals with an icosahedral shape was very sensitive to the reaction kinetics. The success of this synthesis relies on the use of HCl to manipulate the reaction kinetics and thus control the twin structure and shape of the resultant nanocrystals. The size of the Pd icosahedra could be further increased up to 35 nm by seed-mediated growth, with 17 nm Pd icosahedra serving as seeds. The multiply twinned Pd icosahedra could grow into larger sizes, and their shape and multiply twinned structure were preserved. Thanks to the presence of twin defects, the Pd icosahedra showed a catalytic current density towards formic-acid oxidation that was 1.9 and 11.6 times higher than that of single-crystal Pd octahedra, which were also fully covered by {111} facets, and commercial Pd/C, respectively.

Au@Pd core-shell nanobricks with concave structures and their catalysis of ethanol oxidation

Au@Pd core-shell nanobricks (CNBs) with concave surfaces and Pd shells with a thickness of approximately 5 nm were synthesized by co-reduction of HAuCl4 and H2 PdCl4 in the presence of Au seeds and Ag ions. These as-synthesized concave CNBs exhibit significantly enhanced catalytic activity for the electrooxidation of ethanol in alkaline media compared to the commercially-used Pd black. The improved performance of the Au@Pd CNBs can be attributed to the exposed stepped surfaces, high-index facets, and the synergistic effects of the core and shell metals.

One-pot, water-based and high-yield synthesis of tetrahedral palladium nanocrystal decorated graphene

This paper reports a facile, water-based and one-pot synthesis of tetrahedral Pd nanocrystals (Pd-TNPs) with high yield and good size monodispersity supported on reduced graphene oxide (RGO) nanosheets via a co-chemical reduction method. The key synthetic strategy employed a positively charged polyallylamine-Pd(II) complex (PAH-Pd(II)) with un-coordinated amine groups as a linker molecule to immobilize Pd(II) species on the negatively charged graphene oxide (GO) surface through electrostatic interaction. As characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) techniques, well-defined Pd-TNPs with an average size of 9 nm were uniformly distributed on the RGO surface. The as-prepared Pd-TNPs/RGO nanohybrid with excellent colloidal stability in aqueous solution exhibits superior catalytic activity towards the degradation of methylene blue (MB) compared to both unsupported Pd-TNPs and Pd black. Thus, the resultant Pd-TNPs/RGO nanohybrid, as a promising heterogeneous catalyst, might have wide potential applications in water-based catalysis systems for the future.