Bimetallic Nanomaterials Research Articles

Synthesis of Composition-Tunable Ag-Cu Bimetallic Nanoparticles Through Plasma-Driven Solution Electrolysis.

Bimetallic nanomaterials have shown great potential across various fields of application. However, the synthesis of many bimetallic particles can be challenging due to the immiscibility of their constituent metals. In this study, we present a synthetic strategy to produce compositionally tunable silver-copper (Ag-Cu) bimetallic nanoparticles using plasma-driven liquid surface chemistry. By using a low-pressure nonthermal radiofrequency (RF) plasma that interacts with an Ag-Cu precursor solution at varying electrode distances, we identified that the reduction of Ag and Cu salts is governed by two "orthogonal" parameters. The reduction of Cu2+ is primarily influenced by plasma electrons, whereas UV photons play a key role in the reduction of Ag+. Consequently, by adjusting the electrode distance and the precursor ratios in the plasma-liquid system, we could control the composition of Ag-Cu bimetallic nanoparticles over a wide range.

Antimony removal using zero-valent iron-manganese bimetallic nanomaterial: Adsorption behavior and mechanism

Although the effectiveness of zero-valent iron (ZVI) and zero-valent manganese (ZVMn) in heavy metal removal is well-established, their combined synergistic potential for antimony (Sb) remediation from wastewater has remained largely unexplored. Addressing this gap, this study introduced a magnetic zero-valent iron-manganese bimetallic material (ZVIM), synthesized via the borohydride reduction method, to investigate its capabilities and underlying mechanisms for Sb reduction and adsorption. The ZVIM, characterized by a high specific surface area of 220 m²/g, exhibited a high adsorption capacity (614.6 mg/g for Sb(III) and 241.7 mg/g for Sb(V)), facilitating over 96.7 % removal for both Sb(III) and Sb(V). The adsorption conformed to the pseudo-second-order kinetic model, and the isotherm data aligned with the Freundlich model, indicative of a heterogeneous adsorption process. The removal of Sb(III) predominantly occurred via surface complexation and electrostatic adsorption to the positively charged ZVIM surface, accompanied by a partial oxidation of Sb(III) to Sb(V). In contrast, the elimination of Sb(V) was primarily facilitated through surface complexation mechanism, encompassing both reduction and electrostatic adsorption. The outcomes of this study shed light on the intricate interactions between Sb species and the ZVIM, revealing the material as a promising candidate for the efficacious removal of Sb from wastewater.

PdAg alloy nanowheats: Facile interfacial synthesis and highly selective catalysis in the hydrogenation of 4-nitrobenzaldehyde

Developing a simple and mild one-step method for the preparation of bimetallic nanomaterials with both free-standing features and excellent catalytic performance is highly desirable but remains technically difficult. Herein, a facile liquid-liquid interface route is exploited to grow the wheat-like PdAg nanostructures at the interface of chloroform and water under mild conditions without the use of any surfactants and supports. To implement this scheme, Na2PdCl4 and AgNO3 as precursors are dissolved in aqueous phase and α-naphthol as reducing agent in chloroform phase to build up the interfacial reaction system. At 40°C, the PdAg nanowheats are orderly grown, fused and assembled by many newly generated nanoparticles at the interface region, which have uniform shapes with the length of about 340 nm and the diameter of about 45 nm, abundant defects and strong electronic interaction between Au and Pd, as well as free-standing features. In the hydrogenation reaction of 4-nitrobenzaldehyde, PdAg-1 nanowheats exhibit excellent catalytic activity, selectivity and durability. Within 60.0 min of reaction at 35°C under atmospheric pressure, 99.8 % conversion of 4-nitrobenzaldehyde and 99.5 % selectivity toward 4-aminobenzaldehyde can be realized. After 5 cycles, 99.4 % conversion of 4-nitrobenzaldehyde and 98.0 % selectivity toward 4-aminobenzaldehyde can be maintained.

Innovative chelation strategies for facile synthesis of bimetallic nanomaterials with remarkable photocatalytic and biochemical activities

Biological and chemical chelations of nanoparticles are becoming increasingly popular due to their low cost and absence of harsh chemicals. In this study, palladium-nickel nanoparticles (PdNi NPs) were synthesized using a semi-organic auto-chelation method with Glycyrrhiza glabra L. plant as a biological chelating agent and oxalic acid (OA) for chemical chelation. The aim was to compare biological chelation and chemical chelation. The synthesized NPs were then compared for their photocatalytic and antibacterial applications. The nanomaterials synthesized for each method were analyzed using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), and UV–VIS spectroscopy. The particle size of NPs synthesized with OA from the obtained structures was calculated as 22.48 nm. At the same time, the antibacterial activities of the acquired NPs against Escherichia coli and Staphylococcus aureus were evaluated. The results showed that NPs obtained by different synthesis methods provided 99.9 % inhibition against Escherichia coli (E. coli), and Staphylococcus aureus (S. aureus) within 24 h. Additionally, the photocatalytic effects of PdNi NPs on the removal of methylene blue (MB) dye were assessed. Furthermore, the photocatalytic activity towards MB was similar in the nanoarchitectures obtained with both chelation agents. When biological and chemical chelation were compared after 90 min under sunlight, photodegradation rates were found to be approximately 50 % the same. The obtained results demonstrated that PdNi NPs synthesized using biological agents yielded similar outcomes in photocatalytic and antibacterial applications when compared to PdNi NPs synthesized using chemical agents. The findings provide evidence that NP synthesis with favorable characteristics can be accomplished without the requirement of chemical agents, showcasing the feasibility of a cost-effective and eco-friendly synthesis.

Synthesis, Structural Analysis, and Peroxidase-Mimicking Activity of AuPt Branched Nanoparticles.

Bimetallic nanomaterials have generated significant interest across diverse scientific disciplines, due to their unique and tunable properties arising from the synergistic combination of two distinct metallic elements. This study presents a novel approach for synthesizing branched gold-platinum nanoparticles by utilizing poly(allylamine hydrochloride) (PAH)-stabilized branched gold nanoparticles, with a localized surface plasmon resonance (LSPR) response of around 1000 nm, as a template for platinum deposition. This approach allows precise control over nanoparticle size, the LSPR band, and the branching degree at an ambient temperature, without the need for high temperatures or organic solvents. The resulting AuPt branched nanoparticles not only demonstrate optical activity but also enhanced catalytic properties. To evaluate their catalytic potential, we compared the enzymatic capabilities of gold and gold-platinum nanoparticles by examining their peroxidase-like activity in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Our findings revealed that the incorporation of platinum onto the gold surface substantially enhanced the catalytic efficiency, highlighting the potential of these bimetallic nanoparticles in catalytic applications.

Redox transmetallation reaction mediated synthesis of Ni-Pd bimetallic nanocatalyst for pesticide degradation to value added product

In this work a wet-chemical recipe has been accounted for the synthesis of bimetallic Ni-Pd nanostructures at ambient condition involving pre-synthesized nickel nanoparticles and aqueous tetrachloropalladate, [PdCl4]2- solution. The Galvanic replacement reaction (GRR) starts instantaneously between less noble Ni0 nanoparticle i.e., zero valent nickel (ZVN) and more noble [PdCl4]2-. Thus ZVN is oxidatively etched out as soluble Ni2+ by more noble [PdCl4]2- depositing Pd0 onto the residual ZVN. Concurrently the Ni2+ ions move outwardly into the bulk solution and the Pd0enters into the inwardly fashion owing to their different diffusivities and results in the formation of hollow bimetallic nanostructures following diffusion limited nanoscale Kirkendall effect. Finally, the bimetallic nanomaterial was shown to be a competent heterogeneous catalyst for facile hydrolytic degradation of an organothiophosphate pesticide, methyl parathion (MP). After the completion of the degradation, the degraded product, 4-nitrophenolate (4-NP) was subsequently reduced to 4-aminophenolate (4-AP) in the same reaction pot in presence of the same catalyst using borohydride. 4-AP is the principal ingredient for the production of the medicine paracetamol. Hence the bimetallic Ni-Pd nanoparticles turn out to be a promising heterogeneous catalyst for water pollution abatement through pesticide degradation vis-à-vis generation of value added product out of the degraded product of the pesticide.

Oxidation state regulation of iron-based bimetallic nanoparticles for efficient and simultaneous electrochemical detection of Pb2+ and Cu2+

In this work, bimetallic nanocomposites were synthesized by an emulsion hydrothermal method, and the electronic structure of the nanocomposite’s surface was adjusted to make it optimal by introducing different transition metal salts, providing more active adsorption sites for detecting heavy metal ions (HMIs). The results showed that different transition metal cations underwent redox reactions with Fe3+ at high temperature, resulting in generation of more Fe2+ as well as high valence transition metal ions. And this process formed more oxygen vacancies (OVs) on the material surface, enhancing the adsorption properties of HMIs. Among these nanocomposites, CoFe2O4 produced the most Fe2+ (Fe2+/Fe3+ = 1.29) and Co3+ (Co3+ = 44.0%) at a high temperature, suggesting the generation of the most active sites on the material surface. The corresponding modified electrode CoFe2O4 (CoFe2O4/GCE) also exhibited good electrochemical performance for simultaneously detecting Pb2+ and Cu2+, with the limit of detections of 3.94 and 8.27 nM, respectively. Compared with other nanocomposites, adsorption experiments showed that the CoFe2O4/GCE had the largest adsorption capacity of Pb2+ and Cu2+ (QPb2+=49.82 μC, QCu2+=48.88 μC). Therefore, this work showed that the interaction between metal ions in bimetallic nanomaterials can regulate the electronic structures of the material surface at high-temperature treatment, improve the adsorption capacity of nanomaterials, and lead to good electrochemical detection performance of HMIs.

Construction of Porphyrin-Based Bimetallic Nanomaterials with Photocatalytic Properties

The efficient synthesis of nanosheets containing two metal ions is currently a formidable challenge. Here, we attempted to dope lanthanide-based bimetals into porphyrin-based metal-organic skeleton materials (MOFs) by microwave-assisted heating. The results of the EDX, ICP, and XPS tests show that we have successfully synthesized porphyrin-based lanthanide bimetallic nanosheets (Tb-Eu-TCPP) using a household microwave oven. In addition, it is tested and experimentally evident that these nanosheets have a thinner thickness, a larger BET surface area, and higher photogenerated carrier separation efficiency than bulk porphyrin-based bimetallic materials, thus exhibiting enhanced photocatalytic activity and n-type semiconductor properties. Furthermore, the prepared Tb-Eu-TCPP nanomaterials are more efficient in generating single-linear state oxygen under visible light irradiation compared to pristine monometallic nanosheets due to the generation of bimetallic nodes. The significant increase in catalytic activity is attributed to the improved separation and transfer efficiency of photogenerated carriers. This study not only deepens our understanding of lanthanide bimetallic nanosheet materials but also introduces an innovative approach to improve the photocatalytic performance of MOFs.

Fabrication of core-shell-like bimetallic SERS substrates with inter-coordination effect for catalysis of p-mercaptoaniline.

The present study discusses the core-shell structures of Au@Ag prepared by a seed-growth method. The morphology and composition of Au@Ag nanoparticles were analyzed, indicating that they were successfully prepared. By studying the surface-enhanced Raman scattering spectra (SERS) of p-mercaptoaniline (PATP) molecules adsorbed on Au@Ag substrates, it was found that PATP molecules could be oxidized to form p-mercaptoazobenzene (DMAB) on Au@Ag substrates, indicating that the gold-silver bimetallic nanomaterials could catalyze the PATP molecules with excellent enhancement effect and stability. In order to further study the enhancement effect of the Au@Ag substrate, the electric field strength of Au nanoparticles and Au@Ag nanoparticles was simulated by using the finite difference time domain (FDTD) method, which showed that the SERS enhancement effect of Au@Ag nanoparticles was more significant as well as consistent with the experimental results. This work provides a reference for further preparation of efficient and stable bimetallic SERS substrates.

A label-free electrochemical biosensor based on a bimetallic organic framework for the detection of carbohydrate antigen 19-9.

Carbohydrate antigen 19-9 (CA19-9) is an important marker for pancreatic cancer, ovarian cancer and other tumors, and its rapid and stable detection is the basis for early diagnosis and treatment. In this paper, a label-free electrochemical immunosensor for the sensitive detection of CA19-9 has been developed. First, the synthesis of two novel core-shell bimetallic nanomaterials, namely Ce-MOF-on-Fe-MOF and Fe-MOF-on-Ce-MOF, was accomplished using the MOF-on-MOF approach. The poor electrical conductivity of MOF materials was addressed by incorporating polyethylenimide (PEI) functionalized rGO with Ce-MOF-on-Fe-MOF and Fe-MOF-on-Ce-MOF nanomaterials. Simultaneously, toluidine blue (Tb) was employed as a redox probe and physically adsorbed onto the synthesized materials, resulting in the formation of two nanomaterials: rGO@Ce-MOF-on-Fe-MOF@Tb and rGO@Fe-MOF-on-Ce-MOF@Tb. The fundamental characterization reveals that the sensing performance of the rGO@Ce-MOF-on-Fe-MOF@TB-based immune sensor surpasses that of the rGO@Fe-MOF-on-Ce-MOF@TB-based immune sensor, which is attributed to the fact that, unlike the interlayer-constrained structure of Fe-MOF-on-Ce-MOF, in Ce-MOF-on-Fe-MOF, Ce-MOF penetrates into Fe-MOF to form a heterogeneous structure due to the relatively large pore size of Fe-MOF, which better combines the excellent biocompatibility and strong anchoring effect of Fe MOFs on antibodies, as well as the high electrochemical activity and conductivity of Ce-MOF, to enhance sensing performance. The proposed label-free immunosensor based on rGO@Ce-MOF-on-Fe-MOF@Tb has a wide linear range (1-100 000 mU mL-1), a low detection limit (0.34 mU mL-1), good stability, reproducibility, and repeatability, and satisfactory applicability, which provides a potential platform for clinical applications.

High-performance electrochemical immunosensor based on bimetallic gold/silver functionalized carbon spheres for CYFRA 21-1 detection and information protection.

Bimetallic nanomaterial-based systems have been widely utilized across various fields due to their remarkable expandability and flexibility, including nanomedicine, diagnostics, and molecular information technology. Here, we constructed an electrochemical immunosensor using bimetallic gold/silver functionalized carbon spheres (AuAg@CSs) and mesoporous silica nanoparticles (MSNs) for the sensitive determination of cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) and ensuring information protection for textual data. The AuAg@CSs demonstrated exceptional catalytic activity towards hydrogen peroxide, generating a significant current signal. The introduction of CYFRA 21-1 facilitated the binding of MSNs, thereby forming a sandwich-type electrochemical immunosensor that resulted in a notable decrease in current. Notably, the detection limit for CYFRA 21-1 was determined to be 31 fg mL-1, accompanied by high selectivity. Furthermore, extensive textual information can be encrypted and concealed within the current responses of the electrochemical nanosensing system. By establishing a threshold, these current signals can be represented as a series of binary strings, which can subsequently be segmented into shorter strings. Through information coding methods, these shorter binary strings can be assembled and decrypted, ultimately merging into meaningful textual content. This study promotes the synthesis and multifunctional application of bimetallic nanomaterials, providing innovative solutions to enhance the sensing sensitivity of electrochemical immunosensors and paving the way for advancements in molecular digitization.

Detection of Explosive Residues Using Nanomaterial-based Sensors: A Review

Abstract: Due to the recent rise in explosive-based terrorism and ecological issues, the invention of good capacity detectors for the identification of explosives has emerged as one of the major thirsts in the scientific community. Due to their unique optical and electrical properties, nanocomposites can meet all of the prerequisites for developing preferential, responsive, easy, and cost-effective sensor nodes for the sensing of various explosives. This study primarily throws light on current developments in explosives detection using nanomaterial-based sensors. In particular, it describes how quantum dots, carbon nanomaterials, monometallic nanomaterials, and bimetallic nanomaterials have been used to detect explosives optically and electrochemically. The accurate and consistent features of the nanomaterials, including their synthesis, the explosive detection technique, and the analytical facets, are all thoroughly examined.

Sea Urchin-like NiCo2O4 Catalyst Activated Peroxymonosulfate for Degradation of Phenol: Performance and Mechanism.

How to efficiently activate peroxymonosulfate (PMS) in a complex water matrix to degrade organic pollutants still needs greater efforts, and cobalt-based bimetallic nanomaterials are desirable catalysts. In this paper, sea urchin-like NiCo2O4 nanomaterials were successfully prepared and comprehensively characterized for their structural, morphological and chemical properties via techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), among others. The sea urchin-like NiCo2O4 nanomaterials exhibited remarkable catalytic performance in activating PMS to degrade phenol. Within the NiCo2O4/PMS system, the removal rate of phenol (50 mg L-1, 250 mL) reached 100% after 45 min, with a reaction rate constant k of 0.091 min-1, which was 1.4-times higher than that of the monometallic compound Co3O4/PMS system. The outstanding catalytic activity of sea urchin-like NiCo2O4 primarily arises from the synergistic effect between Ni and Co ions. Additionally, a comprehensive analysis of key parameters influencing the catalytic activity of the sea urchin-like NiCo2O4/PMS system, including reaction temperature, initial pH of solution, initial concentration, catalyst and PMS dosages and coexisting anions (HCO3-, Cl-, NO3- and humic acid), was conducted. Cycling experiments show that the material has good chemical stability. Electron paramagnetic resonance (EPR) and quenching experiments verified that both radical activation (SO4•-, •OH, O2•-) and nonradical activation (1O2) are present in the NiCo2O4/PMS system. Finally, the possible degradation pathways in the NiCo2O4/PMS system were proposed based on gas chromatography-mass spectrometry (GC-MS). Favorably, sea urchin-like NiCo2O4-activated PMS is a promising technology for environmental treatment and the remediation of phenol-induced water pollution problems.

Synthesis of ultra-thin Cu/Ag bimetallic nanosheets assisted by polyvinylpyrrolidone as template

Bimetallic nanomaterials have rich electronic structures due to unique interfacial effects and synergistic effects. In this study, the polyhedron Cu nanoparticles were synthesized by the solvothermal method using polyvinylpyrrolidone (PVP) as a template. Then Ag precursor was added to obtain ultra-thin Cu/Ag bimetallic nanosheets at room temperature. SEM and TEM results showed that the as-prepared Cu/Ag samples changed from polyhedron to nanosheet structure with increased Ag content. When Cu: Ag = 1:1, the specific surface area of the sample reached 17.318 m 2/ g. 8.76 times the specific surface area of pure Cu. At the same time, electrochemical testing showed that the prepared bimetallic nanosheets had high onset voltage and half-peak voltage in alkaline media. Therefore, this work provides a new method for preparing ultra-thin bimetallic nanosheets, expanding their applications in fields such as electrocatalysis, sensors, optical detection, biomedicine, and fuel cells.

Palladium Zinc Nanocrystals: Nanoscale Amalgamation Enables Multifunctional Intermetallic Colloids

AbstractIntermetallic nanocrystals are emerging materials for energy, catalysis, and biomedical applications, but combining two or more metals at the nanoscale remains challenging. The amalgamation reaction represents a convenient method for hundreds of intermetallic compositions, as it relies on fast and efficient alloying of liquid metals into presynthesized metallic seeds. Here, Pd–Zn nanocrystals, prepared via Zn amide thermolysis on the surface of Pd nanocrystals and subsequent amalgamation alloying, are investigated. Size‐uniform nanocrystals and control over a wide range of Pd–Zn compositions are achieved. This allows deriving a phase diagram at the nanoscale, in which miscibility gaps and three phases with broad solid solutions are detected. Furthermore, the formation of homogeneous ZnO shells for Pd–Zn compositions extending beyond phase solubility limits is observed. Full chemistry control for Pd–Zn nanocrystals enables a rational choice of materials for selected energy applications, achieveing an extended lifetime of Zn‐ion batteries for Zn‐rich PdZn2 stoichiometry, superior electrocatalytic properties for nearly stoichiometric PdZn halite phase, and the stability and efficiency of high‐voltage cathodes benefiting from ZnO shell protection around Pd3Zn10 nanocrystals are reported. This paper exemplifies the multifunctionality of intermetallics Pd–Zn nanocrystals, while this methodology can be extended to many other bimetallic nanomaterials.

Biochar as an electron shuttle loaded with Fe/Ni bimetallic nanoparticles for efficient removal of 2,4-dichlorophenols: Performance, degradation pathway and mechanism

Biochar can be served as a substrate for immobilizing bimetallic particles and applied in the pollutant removal, however, its specific role and mediated electron shuttle mechanism against 2,4-dichlorophenol (2,4-DCP) have not been elucidated. In this study, biochar loaded with Fe/Ni bimetallic nanoparticles (BC@Fe/Ni) was optimally synthesized, and its dechlorination performance, pathway and mechanism towards 2,4-DCP were investigated. The results showed that BC@Fe/Ni was more effective compared to Fe/Ni nanoparticles in the 2,4-DCP removal due to its well-dispersed Fe/Ni nanoparticles and increased electron-shuttling capability. The optimal parameters for 2,4-DCP removal by BC@Fe/Ni were assessed, the highest removal efficiency equivalent to 50 mg L−1 of 2,4-DCP was achieved at pH 4.0 with a dosage of 2 g L−1. The 2,4-DCP removal was an adsorption-dechlorination-adsorption pathway, primarily through para-Cl elimination, ortho-Cl elimination and finally phenol adsorption. The removal mechanism of 2,4-DCP by BC@Fe/Ni may involve the 2,4-DCP reductive dechlorination by nZVI, atomic hydrogen and biochar-mediated electron transfer, and final adsorption by biochar. In summary, this study demonstrates that biochar is a promising electron shuttle for immobilizing bimetallic particles and serves as a reference for the dechlorination mechanism of chlorinated organic pollutants by biochar-based bimetallic nanomaterials.

Photothermally Enhanced Dual Enzyme‐mimic Activity of Gold‐Palladium Hybrid Nanozyme for Cancer Therapy

Comprehensive SummaryBased on characteristics of the tumor microenvironment (TME), including acidity, hypoxia, inflammation and hydrogen peroxide overload, combined with emerging nanotechnologies, designing nanoplatforms with TME specificity/responsiveness for tumor treatment is a promising nanotherapeutic strategy. In this work, a multifunctional gold‐palladium bimetallic cascade nanozyme was constructed for effective photothermal‐enhanced cascade catalyzed synergistic therapy of tumors. The dumbbell‐like Au‐Pd bimetallic nanomaterial (Au NRs‐Pd@HA) was obtained by reducing palladium on gold nanorods with ascorbic acid (AA) and further modified with hyaluronic acid (HA). The introduction of HA brings biocompatibility and targeting properties. The zebrafish embryos model showed that Au NRs‐Pd@HA had good biocompatibility and low biotoxicity. Au NRs‐Pd@HA can induce catalytic conversion of glucose to generate H2O2 efficiently, and subsequently undergo cascade reaction to produce abundant ·OH radicals, exhibiting peroxidase‐like (POD‐like) and glucose oxidase‐like (GOD‐like) capabilities. The generated ·OH was a key factor for tumor ablation. Meanwhile, Au NRs‐Pd@HA exhibits good photothermal performance under 808 nm irradiation, in favor of photothermal therapy (PTT). Especially, the POD‐like and GOD‐like activities were significantly enhanced due to the photothermal effect. The synergistic PTT and photothermal‐enhanced nanozymes with cascade catalytic effect enabled efficient and safe cancer therapy.

How the surface Cu layer affected the activity of Ni foil for alkaline hydrogen evolution

Synthesizing bimetallic nanomaterials, with noble metals as the surface layers and inert metals as the substrates, has been proven to be an effective way to reduce the use of noble metals with maintained catalytic activity. However, an atomic diffusion from the inert substrate to the surface during the long-term operation has been reported to significantly decrease the activity. In this work, a series of catalysis-inert Cu-coated Ni foil were fabricated through electrodeposition and their activities for alkaline hydrogen evolution were investigated. Notably, the Ni/Cu-60 sample showed a similar catalytic property with pure Ni foil and only a slight decrease in HER activity was observed. The X-ray photoelectron spectroscopy (XPS) results indicated a decreased electron concentration of Cu in Ni/Cu-60, and theoretical calculations further demonstrated the electron transfer between the Ni substrate and Cu layer. Our results reveal that a specific composition or structure of an inert metal layer might not significantly decrease the electrocatalytic activity of active metals. Moreover, there are more possibilities for the rational design of metal-based catalysts for electrocatalysis.

Electrochemical NO3- Reduction Catalyzed by Atomically Precise Ag30Pd4 Bimetallic Nanocluster: Synergistic Catalysis or Tandem Catalysis?

Electrochemically converting NO3- compounds into ammonia represents a sustainable route to remove industrial pollutants in wastewater and produce valuable chemicals. Bimetallic nanomaterials usually exhibit better catalytic performance than the monometallic counterparts, yet unveiling the reaction mechanism is extremely challenging. Herein, we report an atomically precise [Ag30Pd4 (C6H9)26](BPh4)2 (Ag30Pd4) nanocluster as a model catalyst toward the electrochemical NO3- reduction reaction (eNO3-RR) to elucidate the different role of the Ag and Pd site and unveil the comprehensive catalytic mechanism. Ag30Pd4 is the homoleptic alkynyl-protected superatom with 2 free electrons, and it has a Ag30Pd4 metal core where 4 Pd atoms are located at the subcenter of the metal core. Furthermore, Ag30Pd4 exhibits excellent performance toward eNO3-RR and robust stability for prolonged operation, and it can achieve the highest Faradaic efficiency of NH3 over 90%. In situ Fourier-transform infrared study revealed that a Ag site plays a more critical role in converting NO3- into NO2-, while the Pd site makes a major contribution to catalyze NO2- into NH3. The bimetallic nanocluster adopts a tandem catalytic mechanism rather than a synergistic catalytic effect in eNO3-RR. Such finding was further confirmed by density functional theory calculations, as they disclosed that Ag is the most preferable binding site for NO3-, which then binds a water molecule to release NO2-. Subsequently, NO2- can transfer to the vicinal exposed Pd site to promote NH3 formation.

Defect engineering on metal oxides (Zn, Mo and Fe) and their impact on the crude glycerol biofuel oxidation

Defect engineering is an interesting area to improve the activity for alcohols oxidation because it promotes electronic changes through induced defects like oxygen vacancies (Ov) or doping with heteroatoms. Herein, Pd/Ov‒induced metal oxides bimetallic nanomaterials (Pd/Ov‒Fe2O3, Pd/Ov‒ZnO and Pd/Ov‒MoO3) were successfully synthesized and defect‒engineered boosting oxygen vacancies in the order ∼9–15%. The resulting materials had similar crystallite sizes (∼7.1 nm), metal‒support compositions (∼20 wt %), and bimetallic compositions (metal oxide ∼20 wt %). Electrochemical tests demonstrated that despite ZnO presented improved Ov, the electronic interaction between Pd and Ov‒Fe2O3 allowed to obtain higher current density (jmax). Pd/Ov‒Fe2O3 presented a jmax of 197.66 mA mg−1, being up to 2.2 times higher to that of Pd/C, while Pd/Ov‒MoO3 presented the most negative onset potential (−0.30 V). Electrochemical impedance spectroscopy, apparent activation energy tests and cyclic voltammetry tests involving synthetic solutions of glycerol, methanol and glyceraldehyde confirmed that the decrease of the onset potential is related to an enhanced electron transfer by Pd/Ov‒MoO3 resulting also in a decrease of the apparent activation energy (11.22 kJ mol−1). While the improved jmax of Pd/Ov‒Fe2O3 was related to its capability to oxidize crude glycerol and the mixtures because the efficient interaction between the defected metal oxide and palladium.