Noble Metal-based Nanomaterials Research Articles

Lattice engineering of noble metal-based nanomaterials via metal-nonmetal interactions for catalytic applications.

Noble metal-based nanomaterials possess outstanding catalytic properties in various chemical reactions. However, the increasing cost of noble metals severely hinders their large-scale applications. A cost-effective strategy is incorporating noble metals with light nonmetal elements (e.g., H, B, C, N, P and S) to form noble metal-based nanocompounds, which can not only reduce the noble metal content, but also promote their catalytic performances by tuning their crystal lattices and introducing additional active sites. In this review, we present a concise overview of the recent advancements in the preparation and application of various kinds of noble metal-light nonmetal binary nanocompounds. Besides introducing synthetic strategies, we focus on the effects of introducing light nonmetal elements on the lattice structures of noble metals and highlight notable progress in the lattice strain engineering of representative core-shell nanostructures derived from these nanocompounds. In the meantime, the catalytic applications of the light element-incorporated noble metal-based nanomaterials are discussed. Finally, we discuss current challenges and future perspectives in the development of noble metal-nonmetal based nanomaterials.

Continuous Phase Regulation of a Pd-Te Hexagonal Nanoplate Library.

Phase regulation of noble metal-based nanomaterials provides a promising strategy for boosting the catalytic performance. However, realizing the continuous phase modulation in two-dimensional structures and unveiling the relevant structure-performance relationship remain significant challenges. In this work, we present the first example of continuous phase modulation in a library of Pd-Te hexagonal nanoplates (HNPs) from cubic-phase Pd4Te, rhombohedral-phase Pd20Te7, rhombohedral-phase Pd8Te3, and hexagonal-phase PdTe to hexagonal-phase PdTe2. Notably, the continuous phase regulation of the well-defined Pd-Te HNPs enables the successful modulation of the distance between adjacent Pd active sites, triggering an exciting way for tuning the relevant catalytic reactions intrinsically. The proof-of-concept oxygen reduction reaction (ORR) experiment shows a Pd-Pd distance-dependent ORR performance, where the hexagonal-phase PdTe HNPs present the best electrochemical performance in ORR (mass activity and specific activity of 1.02 A mg-1Pd and 1.83 mA cm-2Pd at 0.9 V vs RHE). Theoretical investigation reveals that the increased Pd-Pd distance relates to the weak *OH adsorption over Pd-Te HNPs, thus contributing to the remarkable ORR activity of PdTe HNPs. This work advances the phase-controlled synthesis of noble metal-based nanostructures, which gives huge impetus to the design of high-efficiency nanomaterials for diverse applications.

Rational construction of ultrafine noble metals onto carbon nanoribbons with efficient oxygen reduction in practical alkaline fuel cell

In pursuit of sustainable and eco-friendly energy output, fuel cells are well-recognized as the most promising candidates in clean energy conversion and storage technology. Noble metal-based nanomaterials have long been regarded as the most efficient electrocatalysts for the oxygen reduction reaction (ORR) in terms of activity, selectivity, and stability. Here, we propose a self-template strategy where a type of hexagonal tubular InOF-25 could be tuned by adding a different amount of surfactants. Owing to the suitable pore size, these fabricated X-CTAB@InOF-25 (X = 50–300) series are used as precursors to encapsulate a series of discrete metal complexes, including Ag(NH3)2+, AuCl4-, PdCl42-, and PtCl62-. Then, the as-prepared carbon nanoribbons doped with precious metals (M@CNR, M = Pd, Pt, Ag, Au) exhibit good performance in the electrocatalytic ORR as well as Zn-air battery due to their large surface area, rich active sites, and extremely active noble metal nanoparticles. Among them, the most optimal Pd@CNR shows an onset potential of 0.94 V vs. RHE, high diffusion-limited current density of 5.87 mA cm-2, small Tafel slope of 51.74 mV dec-1, and satisfying stability with current retention of 95.4% after 10 h. Meanwhile, these obtained M@CNR as cathode catalysts are modeled and proved by the theoretical calculation with strong oxygen adsorption for efficient ORR. In this context, the main issues, large overpotential required for ORR and fast degradation of the electrocatalysts, impair practical application, which could be relieved by the active noble metals well-protected by carbon nanomaterials from the rational design and preparation of precursors.

Dark-field microscopic real-time monitoring the growth of Au on Cu2O nanocubes for ultra-sensitive glucose detection

Nanoparticle plasmon scattering can provide real-time imaging information on the formation process of noble metal-based nanomaterials. Due to the synergistic effect of the interface between metal and oxide supporting pores, metal nanoparticles (NPs), especially Au NPs, generally exhibit higher catalytic activity on oxide carriers than single-component NPs. Here, we use the dark field scattering microscope to in situ monitor the growth of Au on Cu2O surface by oxidation-reduction reactions and the nanostructures could be precisely controlled via the scattering signal. The prepared Cu2O/Au nanocomposite has a higher electrocatalytic activity toward Glucose. When being used as a potential biosensor for nonenzyme glucose detection, excellent performance, such as high sensitivity with a detection limit of 4 μM, high selectivity and outstanding stability, was obtained. The scattering imaging strategy is a convenient and universal approach in controllable synthesis of plasmonic heterostructures, and leads to the improvement of electrocatalysts in biosensing.

General Synthesis of Amorphous PdM (M = Cu, Fe, Co, Ni) Alloy Nanowires for Boosting HCOOH Dehydrogenation.

Noble metal-based nanomaterials with amorphous structures are promising candidates for developing efficient electrocatalysts. However, their synthesis remains a significant challenge, especially under mild conditions. In this paper, we report a general strategy for preparing amorphous PdM nanowires (a-PdM NWs, M = Fe, Co, Ni, and Cu) at low temperatures by exploiting glassy non-noble metal (M) nuclei generated by special ligand adsorption as the amorphization dictator. When evaluated as electrocatalysts toward formic acid oxidation, a-PdCu NWs can deliver the mass and specific activities as high as 2.93 A/mgPd and 5.33 mA/cm2, respectively; these are the highest values for PdCu-based catalysts reported thus far, far surpassing the crystalline-dominant counterparts and commercial Pd/C. Theoretical calculations suggest that the outstanding catalytic performance of a-PdCu NWs arises from the amorphization-induced high surface reactivity, which can efficiently activate the chemically stable C-H bond and thereby significantly facilitate the dissociation of HCOOH.

Metal-support interactions in designing noble metal-based catalysts for electrochemical CO2 reduction: Recent advances and future perspectives

Electrochemical CO2 reduction reaction (CO2RR) offers a practical solution to current global greenhouse effect by converting excessive CO2 into value-added chemicals or fuels. Noble metal-based nanomaterials have been considered as efficient catalysts for the CO2RR owing to their high catalytic activity, long-term stability and superior selectivity to targeted products. On the other hand, they are usually loaded on different support materials in order to minimize their usage and maximize the utilization because of high price and limited reserve. The strong metal-support interaction (MSI) between the metal and substrate plays an important role in affecting the CO2RR performance. In this review, we mainly focus on different types of support materials (e.g., oxides, carbons, ligands, alloys and metal carbides) interacting with noble metal as electrocatalysts for CO2RR. Moreover, the positive effects about MSI for boosting the CO2RR performance via regulating the adsorption strength, electronic structure, coordination environment and binding energy are presented. Lastly, emerging challenges and future opportunities on noble metal electrocatalysts with strong MSI are discussed.

Universal strategies to multi-dimensional noble-metal-based catalysts for electrocatalysis

• Classifications of universal synthetic methods of MNMCs are summarized. • The surface, facet, electronic structure, and phase engineering of MNMCs are reviewed. • The electrocatalytic applications of MNMCs are concluded. • Opportunities and challenges of MNMCs are outlined for further development. Multi-dimensional noble metal-based catalysts (including zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) catalysts, MNMCs), have received great attention due to their unique physicochemical properties and enhanced catalytic properties. Recently, developing precise and universal strategies to synthesize MNMCs have achieved remarkable progress in electrocatalysis, yet lacking a comprehensive study on universal synthetic strategies to noble metal-based nanomaterials in different dimensions. In this review, we systematically summarized the latest research advances on universal strategies to MNMCs for electrocatalysis applications by structure optimizations. Generally, we concluded the classifications of various universal strategies on preparing MNMCs, involving universal hydro/solvothermal strategy, ligand-mediated method, template-assisted route, epitaxial growth, and CO-confinement strategy. Then we analyzed the structure optimizations on MNMCs for enhanced properties benefited from the use of universal strategies, including the increasement of active sites, construction of high-index facets, optimization of electronic interaction, and regulation of phase structure. The electrocatalysis application in direct alcohol fuel cells (anodic alcohol oxidation (AOR) and cathodic oxygen reduction reaction (ORR)), water electrolysis (hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)) have also been explored by illustrating specific examples. We finally outlined the opportunities and challenges for the further developments of universal strategies to MNMCs.

A platinum nanoparticle doped self-assembled peptide bolaamphiphile hydrogel as an efficient electrocatalyst for the hydrogen evolution reaction.

Noble metal-based nanomaterials have shown great potential for catalytic application with higher selectivity and activity. Owing to their self-assembly properties with various molecular interactions, peptides play an essential role in the controlled synthesis of noble metal-based catalysts with high surface area. In this work, a phenylalanine (F) and tyrosine (Y) based peptide bolaamphiphile is prepared by solution-phase peptide synthesis. The peptide bolaamphiphile readily self-assembles into a hydrogel with a cross-linked nanofibrillar network. The platinum nanoparticles (Pt NPs) are in situ generated within the cross-linked nanofibrillar network of the hydrogel matrix of the peptide bolaamphiphile. Benefiting from the synergistic properties of the Pt nanoparticles doped on three-dimensional fibrous networks, Pt6@hydrogel shows efficient catalytic activity for the electrochemical hydrogen evolution reaction (HER) in 0.5 M H2SO4 solution. The Pt6@hydrogel requires an overpotential of 45 mV at −10 mA cm−2 with a Tafel slope of 52 mV dec−1. The Pt6@hydrogel also shows electrocatalytic activity in basic and neutral pH solutions. The excellent activity and stability of Pt6@hydrogel for the HER shows great potential for energy conversion applications.

Through quorum sensing, Pseudomonas aeruginosa resists noble metal-based nanomaterials toxicity.

Noble metal-based nanomaterials (NMNs), such as platinum nanoparticles (Pt@NPs) and palladium nanoparticles (Pd@NPs), are increasingly being used as antibacterial agents. However, little information is available on bacterial resistance to NMNs. In this study, owing to their oxidase-like and peroxidase-like properties, both Pt@NPs and Pd@NPs induce reactive oxygen species (ROS) and manifest antibacterial activities: 6.25μg/mL of either Pt@NPs or Pd@NPs killed >50% of Staphylococcus aureus strain ATCC29213. However, Pseudomonas aeruginosa strain PAO1 completely resisted 12.5μg/mL of Pt@NPs and 6.25μg/mL of Pd@NPs. Compared to the non-NMN groups, these NMNs promoted 2-3-fold upregulation of the quorum sensing (QS) gene lasR in strain PAO1. In fact, the lasR gene upregulation induced a 1.5-fold reduction in ROS production and increased biofilm formation by 11% (Pt@NPs) and 27% (Pd@NPs) in strain PAO1. The ΔlasR mutants (lasR gene knock out in strain PAO1), became sensitive to NMNs. The survival rates of ΔlasR mutants at 12.5μg/mL Pt@NPs and Pd@NPs treatments were only 77% and 58%, respectively. This is the first report indicating that bacteria can resist NMNs through QS. Based on these results, evaluation of the ecological risks of using NMNs as antibacterial agents is necessary.

Synthesis and Crystal-Phase Engineering of Mesoporous Palladium-Boron Alloy Nanoparticles.

Rational design and synthesis of noble metal nanomaterials with desired crystal phases (atomic level) and controllable structures/morphologies (mesoscopic level) are paramount for modulating their physiochemical properties. However, it is challenging to simultaneously explore atomic crystal-phase structures and ordered mesoscopic morphologies. Here, we report a simple synergistic templating strategy for the preparation of palladium–boron (Pd–B) nanoparticles with precisely controllable crystal-phases and highly ordered mesostructures. The engineering of crystal-phase structures at atomic levels is achieved by interstitially inserting metallic B atoms into face-centered cubic mesoporous Pd (fcc-mesoPd) confined in a mesoporous silica template. With the gradual insertion of B atoms, fcc-mesoPd is transformed into fcc-mesoPd5B, hcp-mesoPd2B with randomly distributed B atoms (hcp-mesoPd2B-r), and hcp-mesoPd2B with an atomically ordered B sequence (hcp-mesoPd2B-o) while preserving well-defined mesostructures. This synergistic templating strategy can be extended to engineer crystal-phase structures with various mesostructures/morphologies, including nanoparticles, nanobundles, and nanorods. Moreover, we investigate the crystal-phase-dependent catalytic performance toward the reduction reaction of p-nitrophenol and find that hcp-mesoPd2B-o displays much better catalytic activity. This work thus paves a new way for the synthesis of hcp-Pd2B nanomaterials with mesoscopically ordered structure/morphology and offers new insights of fcc-to-hcp evolution mechanisms which could be applied on other noble metal-based nanomaterials for various targeted applications.

Noble Metal Aerogels.

Noble metal-based nanomaterials have been a hot research topic during the past few decades. Particularly, self-assembled porous architectures have triggered tremendous interest. At the forefront of porous nanostructures, there exists a research endeavor of noble metal aerogels (NMAs), which are unique in terms of macroscopic assembly systems and three-dimensional (3D) porous network nanostructures. Combining excellent features of noble metals and the unique structural traits of porous nanostructures, NMAs are of high interest in diverse fields, such as catalysis, sensors, and self-propulsion devices. Regardless of these achievements, it is still challenging to rationally design well-tailored NMAs in terms of ligament sizes, morphologies, and compositions and profoundly investigate the underlying gelation mechanisms. Herein, an elaborate overview of the recent progress on NMAs is given. First, a simple description of typical synthetic methods and some advanced design engineering are provided, and then, the gelation mechanism models of NMAs are discussed in detail. Furthermore, promising applications particularly focusing on electrocatalysis and biosensors are highlighted. In the final section, brief conclusions and an outlook on the existing challenges and future chances of NMAs are also proposed.

Robust non-Pt noble metal-based nanomaterials for electrocatalytic hydrogen generation

Currently, the electrocatalytic hydrogen evolution reaction (HER) has been a key point of focus for developing sustainable hydrogen economy, but it is hampered by sluggish reaction kinetics. Despite the fact that various non-noble metal-based materials as electrocatalysts toward the HER are gaining considerable attention, noble metal-based nanomaterials (NMNs) for catalyzing the HER still have advantageous features, i.e., wide pH applicability, high intrinsic activity, and good stability. Considering a high chemical similarity to HER-benchmark Pt metals, various non-Pt NMNs with high atom utilization, super efficiency, and durability for HER catalysis are engineered through various structural/electronic tailoring strategies, which has become a significant trend in this research field. Herein, a panoramic review about recent representative efforts and progress in the design of non-Pt NMNs is presented. It first introduces the HER fundamentals and then generally describes the structural and electronic characteristics of non-Pt noble metals matching the HER. Followed on, different tuning strategies for fabricating effective non-Pt NMN catalysts, including composition optimizing by constructing alloys or novel compounds, morphological tuning via decreasing the particle size or designing unique nanostructures, and hybrid engineering as well as crystalline structure/facet controlling, are systemically summarized, with a special focus on the underlying structure–activity relationship for different catalysts. The features of pH universality and bifunctionality for these non-Pt NMN catalysts are also highlighted. At the end, existing challenges and future perspectives awaiting this emerging research field are discussed.

Eyeball-Like Yolk-Shell Bimetallic Nanoparticles for Synergistic Photodynamic-Photothermal Therapy.

Noble metal-based nanomaterials offer great potential as cargoes for multifunctional cancer treatment. In this research, Au eyeball-like nanoparticles (NPs) with open-mouthed Pd shells were synthesized and their surface was functionalized with cell-targeting ligand folic acid (FA) and photodynamic agent Chlorin e6 (Ce6). Due to the broad near-infrared (NIR) absorption band of eyeball-like bimetallic Au and Pd, the photothermal therapy effects of this nanomaterial were studied in MCF-7 cancer cells. The anchored Ce6 not only addressed the hypoxia issue of tumor cells but also exhibited remarkable photodynamic efficacy upon irradiation. Results showed that the obtained Au@Pd-PEG-FA-Ce6 (APPFC) NPs were selectively accumulated at the tumor site and induced cell apoptosis effectively due to the target specificity and synergistic phototherapy effect. The high specificity, desirable biosafety, fast delivery, and drug functionalization demonstrated eyeball-like Au@Pd NPs are promising candidate for multifunctional therapy of breast cancer.

Structure regulation of noble-metal-based nanomaterials at an atomic level

Abstract Controlling the structure of noble-metal-based nanomaterials (NMNs) with precision at an atomic level has received considerable attention in recent years. However, the complexity of synthetic process poses great challenges in the delicate design and fine control of NMNs. In this review, we focus on recent progress made in the chemical synthesis of NMNs at an atomic level, which include surface engineering of NMNs, atomic layer coating of NMNs, metal doping or substitution, and intermetallic compounds. The catalytic properties of well-controlled NMNs are discussed. Finally, the major challenges and opportunities pertaining to the controllable synthesis of NMNs are presented. We believe this brief review provides up-to-date information on the fine tuning of NMNs structures, and offers some new perspectives of this rapidly developing field.

Differential Pd-nanocrystal facets demonstrate distinct antibacterial activity against Gram-positive and Gram-negative bacteria

Noble metal-based nanomaterials have shown promise as potential enzyme mimetics, but the facet effect and underlying molecular mechanisms are largely unknown. Herein, with a combined experimental and theoretical approach, we unveil that palladium (Pd) nanocrystals exhibit facet-dependent oxidase and peroxidase-like activities that endow them with excellent antibacterial properties via generation of reactive oxygen species. The antibacterial efficiency of Pd nanocrystals against Gram-positive bacteria is consistent with the extent of their enzyme-like activity, that is {100}-faceted Pd cubes with higher activities kill bacteria more effectively than {111}-faceted Pd octahedrons. Surprisingly, a reverse trend of antibacterial activity is observed against Gram-negative bacteria, with Pd octahedrons displaying stronger penetration into bacterial membranes than Pd nanocubes, thereby exerting higher antibacterial activity than the latter. Our findings provide a deeper understanding of facet-dependent enzyme-like activities and might advance the development of noble metal-based nanomaterials with both enhanced and targeted antibacterial activities.

PEGylated Copper Nanowires as a Novel Photothermal Therapy Agent.

Metal nanowires are promising for their applications including electrical connectors, transparent conductive electrodes and conductive additives, but the use of metal nanowires as photothermal agents to convert light to heat has yet to be reported. Here we synthesized dispersible polyethylene glycol-coated (PEGylated) copper nanowires (CuNWs) and showed for the first time that PEGylated CuNWs were able to convert near-infrared (NIR, 808 nm) light into heat at a photothermal efficiency of 12.5%. The PEGylated CuNWs exhibited good reusability and enabled rapid temperature rise to >50 °C in 6 min by NIR irradiation. The PEGylated CuNWs were flexible and intertwined around the cancer cells, which, upon NIR irradiation, allowed for direct heat transmission to cells and effectively triggered cancer cell ablation in vitro. Intratumoral injection of PEGylated CuNWs into colon tumor-bearing mice and ensuing NIR irradiation for 6 min significantly raised the local temperature to >50 °C, induced necrosis, and suppressed tumor growth. Compared with other NIR light absorbing noble metal-based nanomaterials, PEGylated CuNWs are relatively easy to synthesize in both laboratory and large scales using the low cost copper. This study demonstrated the potential of PEGylated CuNWs as a new cost-effective photothermal agent, and paved a new avenue to using CuNWs for cancer therapy.