Carboxymethyl cellulose/alginate/chitosan-based polyelectrolyte complex hydrogel with irregularly shaped multi-metallic nanowires for efficient continuous-flow Cr(VI) remediation

The efficient removal of hexavalent chromium (Cr(VI)) from industrial wastewater is a pressing environmental challenge. A natural polyelectrolyte complex (PEC) hydrogel composed of carboxymethyl cellulose, alginate and chitosan, was developed to support Pd/Au/Ag/Pt nanowires for the continuous-flow catalytic reduction of Cr(VI) to the less toxic Cr(III). PEC hydrogels are formed through the association of oppositely charged polyelectrolytes, a process that is primarily driven by entropy gain due to the release of counterions, resulting in highly porous networks with tunable physical and chemical properties. These characteristics make them ideal platforms for nanoparticle stabilization and catalytic applications. Crosslinking with glutaraldehyde, citric acid and calcium ions further improved the stability and porosity of the hydrogels. Pd/Au/Ag/Pt nanowires, synthesised through galvanic replacement and co-reduction of Pd/Au/Ag nanowires formed via an oriented attachment mechanism, exhibit a distinctive, irregular, undulating morphology that enhances their suitability for introduction into hydrogel matrices. These multi-metallic nanowires achieved complete Cr(VI) reduction within 15 min. When incorporated into a nanocomposite hydrogel, the Pd/Au/Ag/Pt nanowires significantly enhanced catalytic activity while maintaining structural integrity and high catalytic efficiency. Notably, the system achieved complete Cr(VI) reduction within 5 h of continuous-flow operation, highlighting its potential as a robust and scalable solution for industrial wastewater remediation.

γ-Al2O3 selectively adsorbs transition group metals from contaminated waters to produce bi-metallic catalysts for efficient nitrate reduction

Metals present in industrial or mining wastewater are hazardous to human health and the environment, and their remediation is costly. In this study, we used γ-Al2O3 to capture transition metals (e.g., Pd, Cu, Ni, and Co) from wastewater and used the spent adsorbent as catalysts for nitrate reduction. Based on a pH-dependent surface-mediated redox reaction mechanism, Pd and Cu ions are selectively adsorbed onto γ-Al2O3 at ambient temperature without involving the use of chemical reductants, thus transforming these pollutants into active catalytic sites. We particularly focused on Pd/Cu bimetallic catalysts, finding that the Pd and Cu ion concentrations in contaminated water impacted both nitrate reduction efficiency and nitrogen selectivity. The best nitrate reduction occurred with 0.74 wt% Pd and 0.66 wt% Cu on γ-Al2O3, achieving high nitrate reactivity and ∼81 % selectivity for N2 formation over 10 cycles. Ni and Co, which have smaller redox potential differences than Pd and Cu, showed limited interference with Pd and Cu adsorption, allowing γ-Al2O3 to form Pd-Cu bimetallic catalysts selectively in batch and column tests. Overall, metal-based catalysts can be fabricated under ambient conditions while remediating metal-contaminated wastewater, thereby producing functional products (e.g., hydrogenation catalysts), which is consistent with circular economy principles.

Au-Added CuS Hollow Spheres to Regulate the Strength and Active Area of N2 Adsorption Sites for Electrochemical NH3 Production

Ammonia is a chemical compound in considerable global demand and plays a crucial role as an environmentally friendly energy carrier for hydrogen energy storage. The electrochemical nitrogen reduction reaction (eNRR) using copper sulfide catalysts is being extensively studied as an environmentally sustainable approach to the energy-intensive Haber-Bosch process for ammonia production. In this study, we aimed to prepare CuS hollow spheres modified with Au nanoparticles using an antisolvent crystallization-based method to be used as the catalysts for eNRR. During the addition of Au to the CuS catalysts, the nitrogen adsorption strength and surface area of the CuS catalysts are significantly regulated and expanded, leading to a noticeable enhancement in electrocatalytic performance for eNRR. Specifically, the ammonia production rate of 2.4 μmol cm-2 h or jNH3 = 0.2 mA cm-2 is achieved at a selectivity of 52% in neutral aqueous electrolyte, which is more than a 2-fold increase compared to the unmodified CuS catalyst. The findings of this study can contribute to the development of sustainable and environmentally friendly ammonia production in the future.

Dynamically Reconstructed Fe-CoOOH Semi-Crystalline Electrocatalyst for Efficient Oxygen Evolution Reaction

The development of robust and efficient electrocatalysts for the oxygen evolution reaction (OER) has been the main focus of water electrolysis but remains a great challenge. Here, the synthesis of a highly active and ultra-stable Fe-CoOOH electrocatalyst is reported by steering raw cobalt foam via an in situ solution combustion method assisted by a galvanic replacement reaction and subsequent electrochemical reconstruction of the CoFeOx pre-catalyst. In/ex situ electrochemical analysis and physicochemical characterizations show that the CoFeOx undergoes quick chemical and slow morphological reconstruction to Fe-CoOOH nanosheets. The Fe-CoOOH possesses a semi-crystalline nature with distinct short-range ordering and outstanding OER activity with overpotentials as low as 271 and 291 mV at current densities of 500 and 1,000 mA cm-2, respectively. The remarkable stability under 1,000 mA cm-2 for at least 700 h is achieved. Theoretical calculations confirm the crucial role of Fe doping in facilitating surface reconstruction, enhancing OER activity, and improving the stability of the Fe-CoOOH. Comparative analysis with other transition metals doping reveals the unique ability of Fe to adsorb onto the CoOOH surface, thereby modulating the electronic density and facilitating faster adsorption of reaction intermediates. This work represents valuable insights into the surface reconstruction and doping processes.

A press-actuated slidable microfluidic colorimetric biosensor for Salmonella detection utilizing nickel mesh sheet and MIL-88@Pd/Pt nanoparticles

A press-actuated slidable microfluidic colorimetric biosensor was designed for rapid, sensitive and multi-channel detection of Salmonella. The nickel mesh sheet (NMS) modified with capture antibodies was employed for capturing target bacteria, and metal organic frameworks decorated with palladium (Pd) and platinum (Pt) nanoparticles (MIL-88@Pd/Pt NPs) modified with detection antibodies were used for amplifying colorimetric signals. The capture efficiency of the immune NMS reached 83 %, and the detection limit of this colorimetric biosensor was 35 CFU/mL in 20 min. The average recoveries for Salmonella in spiked chicken meats ranged from 92.2 % to 102.5 % with a variation from 3.7 % to 7.2 %. The press-actuated slidable microfluidic chip was elaboratively developed with multiple functions, including mixing, separation, washing, catalysis and detection.

Replacing the Gallium Oxide Shell with Conductive Ag: Toward a Printable and Recyclable Composite for Highly Stretchable Electronics, Electromagnetic Shielding, and Thermal Interfaces

Liquid metal (LM)-based composites hold promise for soft electronics due to their high conductivity and fluidic nature. However, the presence of α-Ga2O3 and GaOOH layers around LM droplets impairs conductivity and performance. We tackle this issue by replacing the oxide layer with conductive silver (Ag) using an ultrasonic-assisted galvanic replacement reaction. The Ag-coated nanoparticles form aggregated, porous microparticles that are mixed with styrene-isoprene-styrene (SIS) polymers, resulting in a digitally printable composite with superior electrical conductivity and electromechanical properties compared to conventional fillers. Adding more LM enhances these properties further. The composite achieves EMI shielding effectiveness (SE) exceeding 75 dB in the X-band frequency range, even at 200% strain, meeting stringent military and medical standards. It is applicable in wireless communications and Bluetooth signal blocking and as a thermal interface material (TIM). Additionally, we highlight its recyclability using a biodegradable solvent, underscoring its eco-friendly potential. This composite represents a significant advancement in stretchable electronics and EMI shielding, with implications for wearable and bioelectronic applications.

Strain-Controlled Galvanic Synthesis of Platinum Icosahedral Nanoframes and Their Enhanced Catalytic Activity toward Oxygen Reduction

The unique strain distribution on the surface of a Pd icosahedral nanocrystal is leveraged to control the sites for oxidation and reduction involved in the galvanic replacement reaction. Specifically, Pd is oxidized and dissolved from the center of each {111} facet due to its tensile strain, while the Pt(II) precursor adsorbs onto the vertices and edges featuring a compressive strain, followed by surface reduction and conformal deposition of the Pt atoms. Once the galvanic reaction is initiated, the {111} facets become more vulnerable to oxidation and dissolution, as the vertices and edges are protected by the deposited Pt atoms. The site-selected galvanic reaction naturally results in the formation of Pt icosahedral nanoframes covered by compressively strained {111} facets, which show enhanced catalytic activity and durability toward oxygen reduction relative to commercial Pt/C.

Green stabilization of silver nanoparticles over the surface of biocompatible Fe3O4@CMC for bactericidal applications

The emergence of antimicrobial resistance in bacteria, especially in agents associated with urinary tract infections (UTIs), has initiated an exciting effort to develop biocompatible nanoparticles to confront their threat. Designing simple, cheap, biocompatible, and efficient nanomaterials as bactericidal agents seems to be a judicious response to this problem. Here, a solvothermal method was hired for the one-pot preparation of the cellulose gum (carboxymethyl cellulose, CMC) magnetic composite to prepare a cost-effective, efficient, and biocompatible support for the plant-based stabilization of the silver NPs. The green stabilization of the Ag NPs is performed using Euphorbia plant extract with high efficiency. Various characterization methods, including FT-IR, XRD, SEM, EDS, TEM, and VSM were used to study the composition and properties of Fe3O4@CMC/AgNPs. The composite shows well integrity and monodispersity with a mean diameter of <300 nm, indicating its potential for bio-related application. The CMC functionalities of the proposed material facilitated the stabilization of the Ag NPs, resulting in their monodispersity and enhanced performance. The manufactured composite was used as an antibacterial agent for the removal of UTIs agents, collected from 200 hospitalized patients with acute coronary syndrome, which showed promising results. This study showed that the concentration of the Ag NPs has a direct relationship with the antibacterial properties of the composite.

Synthesis of trimetallic iron-boron core and gold shell nanoparticles for experimental cancer radiotherapy

Cancer is a significant and constantly growing clinical problem all over the word. For many types of cancer there has been little change in mortality rate of CRC in the past decades and treatment options are limited. A striking example is malignant Glioblastoma (GBM) which exhibits a high degree of infiltration of surrounding healthy brain tissue, extremely high mortality rate, morbidity and most life-years lost of any cancer. Considerable research efforts in the last several decades have failed to improve these outcomes. Boron Capture Neutron Therapy (BNCT) is an experimental radiotherapy (RT) that shows the best hope for the patients for whom all current therapies fail. BNCT involves the intracellular release of alpha and Li-ion particles from boron in response to neutron beam and therefore its success is critically dependent on achieving high intracellular concentrations of boron atoms within the cancerous cells. Boron phenylalanine (BPA) is the most used compound to deliver boron atoms, but achieving high intracellular concentration of BPA is difficult with this small molecule compound and is an absolute limiting factor for the better outcome of BNCT. Our approach focused on a delivery of a high and stable concentration of boron atoms in a form of novel trimetallic core-shell nanoparticles, combining boron for BNCT and iron for magnetic targeting in the core, and a gold shell for stability and attachment of targeting therapeutic peptides. The research was targeted towards comparing different synthesis variables to form these core-shell particles and incorporate as much boron into the core as possible via redox-transmetalation. Partial gold shells were formed around the core via island growth with a molar ratio of Fe/B of 0.64 and high incorporation of boron.

Metal-Metal Redox Exchange to Produce Heterometallic Manganese-Cobalt Oxo Cubanes via a "Dangler" Intermediate

Pendent metals bound to heterocubanes are components of well-known active sites in enzymes that mediate difficult chemical transformations. Investigations into the specific role of these metal ions, sometimes referred to as "danglers", have been hindered by a paucity of rational synthetic routes to appropriate model structures. To generate pendent metal ions bonded to an oxo cubane through a carboxylate bridge, the cubane Co4(μ3-O)4(OAc)4(t-Bupy)4 (OAc = acetate, t-Bupy = 4-tert-butylpyridine) was exposed to various metal acetate complexes. Reaction with Cu(OAc)2 gave the structurally characterized (by X-ray diffraction) dicopper dangler Cu2Co4(μ4-O)2(μ3-O)2(OAc)6(Cl)2(t-Bupy)4. In contrast, the analogous reaction with Mn(OAc)2 produced the MnIV-containing cubane cation [MnCo3(μ3-O)4(OAc)4(t-Bupy)4]+ by way of a metal-metal exchange that gives Co(OAc)2 and [CoIII(μ-OH)(OAc)]n oligomers as byproducts. Additionally, reaction of the formally CoIV cubane complex [Co4(μ3-O)4(OAc)4(t-Bupy)4][PF6] with Mn(OAc)2 gave the corresponding Mn-containing cubane in 80% yield. A mechanistic examination of the related metal-metal exchange reaction between Co4(μ3-O)4(OBz)4(py)4 (OBz = benzoate) and [Mn(acac)2(py)2][PF6] by ultraviolet-visible (UV-vis) spectroscopy provided support for a process involving rate-determining association of the reactants and electron transfer through a μ-oxo bridge in the adduct intermediate. The rates of exchange correlate with the donor strength of the cubane pyridine and benzoate ligand substituents; more electron-donating pyridine ligands accelerate metal-metal exchange, while both electron-donating and -withdrawing benzoate ligands can accelerate exchange. These experiments suggest that the basicity of the cubane oxo ligands promotes metal-metal exchange reactivity. The redox potentials of the Mn and cubane starting materials and isotopic labeling studies suggest an inner-sphere electron-transfer mechanism in a dangler intermediate.

Silver nanoprism-mediated colourimetric sensing probe for efficient detection of Pd(II) and Pt(II) ions in water and reuse of formed bimetallic nanoprisms

Sensitive and selective methods for detecting Pd(II) and Pt(II) ions in water are crucial for environmental monitoring and remediation. Although traditional methods for detection of Pd(II) and Pt(II) ions are accurate and sensitive, they face substantial challenges due to high costs, reliance on specialised equipment and limited field applicability, thereby presenting notable limitations. In this study, we introduce a novel colourimetric sensing probe designed specifically to identify Pd(II) and Pt(II) ions in aqueous solutions. This probe utilises the enhanced chemical stability of Ag nanoprisms achieved through Pd or Pt deposition on their surfaces. Our approach features exceptionally low limits of detection of 2.6 nM for Pd(II) and 0.3 nM for Pt(II), indicating an impressive detection range. Furthermore, the probe's ease of use, cost-effectiveness and compatibility with both naked eye and UV-Vis spectrophotometric detection make it a selective, reliable and affordable option for point-of-care analysis. Beyond its impressive sensitivity for ion detection, this methodology offers the additional benefit of enabling the on-demand synthesis of customised bimetallic catalysts. The synthesised Ag/Pd and Ag/Pt bimetallic nanoprisms demonstrate promising catalytic potential for environmental remediation. This advancement paves the way for efficient recycling and reuse of valuable Pd(II) and Pt(II) ions in various catalytic applications.

A 66-Nuclear All-Alkynyl Protected Peanut-Shaped Silver(I)/Copper(I) Heterometallic Nanocluster: Intermediate in Copper-Catalyzed Alkyne-Azide Cycloaddition

Ligand-protected heterometallic nanoclusters in contrast to homo-metal counterparts show more broad applications due to the synergistic effect of hetero-metals but their controllable syntheses remain a challenge. Among heterometallic nanoclusters, monovalent Ag-Cu compounds are rarely explored due to much difference of Ag(I) and Cu(I) such as atom radius, coordination habits, and redox potential. Encouraged by copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction, comproportionation reaction of Cu(II)X2 and Cu(0) in the presence of (PhC≡CAg)n complex and molybdate generated a core-shell peanut-shaped 66-nuclear Ag(I)-Cu(I) heterometallic nanocluster, [(Mo4O16)2@Cu12Ag54(PhC≡C)50] (referred to as Ag54Cu12). The structure and composition of Ag-Cu heterometallic nanocluster are fully characterized. X-ray single crystal diffraction reveals that Ag54Cu12 has a peanut-shaped silver(I)/copper(I) heterometallic nanocage protected by fifty phenylacetylene ligands in µ3-modes and encapsulated two mutually twisted tetramolybdates. Heterometallic nanocage contains a 54-Ag-atom outer ellipsoid silver cage decorated by 12 copper inside wall. Nanosized Ag54Cu12 is a n-type narrow-band-gap semiconductor with a good photocurrent response. Preliminary experiments demonstrates that Ag54Cu12 itself and activated carbon supported Ag54Cu12/C are effective catalysts for 1,3-dipole cycloaddition between alkynes and azides at ambient conditions. The work provides not only a new synthetic route toward Ag(I)-Cu(I) nanoclusters but also an important heterometallic intermediate in CuAAC catalytic reaction.

Tuning the Selectivity of Nitrate Reduction via Fine Composition Control of RuPdNP Catalysts

Herein, aqueous nitrate (NO3 -) reduction is used to explore composition-selectivity relationships of randomly alloyed ruthenium-palladium nanoparticle catalysts to provide insights into the factors affecting selectivity during this and other industrially relevant catalytic reactions. NO3 - reduction proceeds through nitrite (NO2 -) and then nitric oxide (NO), before diverging to form either dinitrogen (N2) or ammonium (NH4 +) as final products, with N2 preferred in potable water treatment but NH4 + preferred for nitrogen recovery. It is shown that the NO3 - and NO starting feedstocks favor NH4 + formation using Ru-rich catalysts, while Pd-rich catalysts favor N2 formation. Conversely, a NO2 - starting feedstock favors NH4 + at ≈50 atomic-% Ru and selectivity decreases with higher Ru content. Mechanistic differences have been probed using density functional theory (DFT). Results show that, for NO3 - and NO feedstocks, the thermodynamics of the competing pathways for N-H and N-N formation lead to preferential NH4 + or N2 production, respectively, while Ru-rich surfaces are susceptible to poisoning by NO2 - feedstock, which displaces H atoms. This leads to a decrease in overall reduction activity and an increase in selectivity toward N2 production. Together, these results demonstrate the importance of tailoring both the reaction pathway thermodynamics and initial reactant binding energies to control overall reaction selectivity.

Mechanism of WS2 Nanotube Formation Revealed by in Situ/ex Situ Imaging

Multiwall WS2 nanotubes have been synthesized from W18O49 nanowhiskers in substantial amounts for more than a decade. The established growth model is based on the "surface-inward" mechanism, whereby the high-temperature reaction with H2S starts on the nanowhisker surface, and the oxide-to-sulfide conversion progresses inward until hollow-core multiwall WS2 nanotubes are obtained. In the present work, an upgraded in situ SEM μReactor with H2 and H2S sources has been conceived to study the growth mechanism in detail. A hitherto undescribed growth mechanism, named "receding oxide core", which complements the "surface-inward" model, is observed and kinetically evaluated. Initially, the nanowhisker is passivated by several WS2 layers via the surface-inward reaction. At this point, the diffusion of H2S through the already existing outer layers becomes exceedingly sluggish, and the surface-inward reaction is slowed down appreciably. Subsequently, the tungsten suboxide core is anisotropically volatilized within the core close to its tips. The oxide vapors within the core lead to its partial out-diffusion, partially forming a cavity that expands with reaction time. Additionally, the oxide vapors react with the internalized H2S gas, forming fresh WS2 layers in the cavity of the nascent nanotube. The rate of the receding oxide core mode increases with temperatures above 900 °C. The growth of nanotubes in the atmospheric pressure flow reactor is carried out as well, showing that the proposed growth model (receding oxide core) is also relevant under regular reaction parameters. The current study comprehensively explains the WS2 nanotube growth mechanism, combining the known model with contemporary insight.

Cellulose/GO monolith covered with Pd-Pt bimetallic nanocrystals for continuous-flow catalytic reduction of hexavalent chromium

Cellulose monolith materials have interconnected open porous structures with very high porosity, making them attractive structures for use as support materials in heterogeneous catalysis applications. In this study, we developed a highly efficient and reusable continuous-flow reactor for Cr(VI) remediation by combining the advantageous features of cellulose monoliths with suitable reinforcement techniques. We fabricated a porous monolithic cellulose/graphene oxide (GO) composite with a continuous three-dimensional skeletal framework using the thermally induced phase separation technique. Pd nanocrystals were synthesized in situ on the surface of the composite monolith, and then converted to porous Pd-Pt bimetallic nanocrystals through a galvanic replacement reaction. This approach eliminated the need for additional reductants and stabilizers, making the process simpler and more environmentally friendly. Under carefully optimized conditions, the cellulose/GO/Pd-Pt nanocomposite monolith exhibited outstanding performance in continuous-flow reactions for Cr(VI) reduction, achieving a maximum conversion rate of 98 %. Moreover, the nanocomposite monolith-based heterogeneous catalyst exhibited remarkable long-term stability, maintaining its catalytic activity even after extended periods of storage in the dried state. These findings highlight the potential of cellulose-based composite monoliths as versatile and robust support materials for heterogeneous catalysis.

NIR-Active Gold Dogbone Nanorattles Impregnated in Cationic Dextrin Nanoparticles for Cancer Nanotheranostics

Theranostic systems, which integrate therapy and diagnosis into a single platform, have gained significant attention as a promising approach for noninvasive cancer treatment. The field of image-guided therapy has revolutionized real-time tumor detection, and within this domain, plasmonic nanostructures have garnered significant attention. These structures possess unique localized surface plasmon resonance (LSPR), allowing for enhanced absorption in the near-infrared (NIR) range. By leveraging the heat generated from plasmonic nanoparticles upon NIR irradiation, target cancer cells can be effectively eradicated. This study introduces a plasmonic gold dogbone-nanorattle (AuDB NRT) structure that exhibits broad absorption in the NIR region and demonstrates a photothermal conversion efficiency of 35.29%. When exposed to an NIR laser, the AuDB NRTs generate heat, achieving a maximum temperature rise of 38 °C at a concentration of 200 μg/mL and a laser power density of 3 W/cm2. Additionally, the AuDB NRTs possess intrinsic electromagnetic hotspots that amplify the signal of a Raman reporter molecule, making them an excellent probe for surface-enhanced Raman scattering-based bioimaging of cancer cells. To improve the biocompatibility of the nanorattles, the AuDB NRTs were conjugated with mPEG-thiol and successfully encapsulated into cationic dextrin nanoparticles (CD NPs). Biocompatibility tests were performed on HEK 293 A and MCF-7 cell lines, revealing high cell viability when exposed to AuDB NRT-CD NPs. Remarkably, even at a low laser power density of 1 W/cm2, the application of the NIR laser resulted in a remarkable 80% cell death in cells treated with a nanocomposite concentration of 100 μg/mL. Further investigation elucidated that the cell death induced by photothermal heat followed an apoptotic mechanism. Overall, our findings highlight the significant potential of the prepared nanocomposite for cancer theranostics, combining effective photothermal therapy along with the ability to image cancer cells.

Development of surface-enhanced Raman scattering-sensing Method by combining novel Ag@Au core/shell nanoparticle-based SERS probe with hybridization chain reaction for high-sensitive detection of hepatitis C virus nucleic acid

The ultrasensitive detection of hepatitis C virus (HCV) nucleic acid is crucial for the early diagnosis of hepatitis C. In this study, by combining Ag@Au core/shell nanoparticle (Ag@AuNP)-based surface-enhanced Raman scattering (SERS) tag with hybridization chain reaction (HCR), a novel SERS-sensing method was developed for the ultrasensitive detection of HCV nucleic acid. This SERS-sensing system comprised two different SERS tags, which were constructed by modifying Ag@AuNP with a Raman reporter molecule of 4-ethynylbezaldehyde, two different hairpin-structured HCR sequences (H1 or H2), and a detection plate prepared by immobilizing a capture DNA sequence onto the Ag@AuNP layer surface of the detection wells. When the target nucleic acid was present, the two SERS tags were captured on the surface of the Ag@AuNP-coated detection well to generate many "hot spots" through HCR, forming a strong SERS signal and realizing the ultrasensitive detection of the target HCV nucleic acid. The limit of detection of the SERS-sensing method for HCV nucleic acid was 0.47 fM, and the linear range was from 1 to 105 fM.

Tungsten Oxide Coated Liquid Metal Electrodes via Galvanic Replacement as Heavy Metal Ion Sensors

Gallium liquid metals (LMs) like Galinstan and eutectic Gallium-Indium (EGaIn) have seen increasing applications in heavy metal ion (HMI) sensing, because of their ability to amalgamate with HMIs like lead, their high hydrogen potential, and their stable electrochemical window. Furthermore, coating LM droplets with nanopowders of tungsten oxide (WO) has shown enhancement in HMI sensing owing to intense electrical fields at the nanopowder-liquid-metal interface. However, most LM HMI sensors are droplet based, which show limitations in scalability and the homogeneity of the surface. A scalable approach that can be extended to LM electrodes is therefore highly desirable. In this work, we present, for the first time, WO-Galinstan HMI sensors fabricated via photolithography of a negative cavity, Galinstan brushing inside the cavity, lift-off, and galvanic replacement (GR) in a tungsten salt solution. Successful GR of Galinstan was verified using optical microscopy, SEM, EDX, XPS, and surface roughness measurements of the Galinstan electrodes. The fabricated WO-Galinstan electrodes demonstrated enhanced sensitivity in comparison with electrodes structured from pure Galinstan and detected lead at concentrations down to 0.1 mmol·L-1. This work paves the way for a new class of HMI sensors using GR of WO-Galinstan electrodes, with applications in microfluidics and MEMS for a toxic-free environment.

Plasmonic gold dogbone nanorattles sniff out trace molecules through surface enhanced Raman scattering

In this study, a highly sensitive and efficient surface-enhanced Raman spectroscopy (SERS) substrate was developed using Au dogbone nanorattles (Au-DBNRTs) deposited on a 3D wrinkled polymeric heat shrink film. The plasmonic structures of Au-DBNRTs, which possess a solid gold dogbone-shaped core and a thin, porous gold shell, and Au nanorod nanorattles (Au-NRNRTs), which have a rod-shaped core, were synthesized and their SERS performance was evaluated. Au-DBNRTs exhibited better Raman signal enhancement. The substrate was used to detect the pesticide thiabendazole with a limit of detection of up to 10-8 M. The unique optical properties and geometry of the Au-DBNRT nanoparticles, which have portruding corners in the vicinity of the metal shell, along with the shrinkage of the film after heat treatment, led to the creation of a 3D surface morphology, resulting in the generation of plasmonic electromagnetic hot spots. The fabricated substrate achieved an enhancement factor of 2.77 × 1010 for BDT, and the detection limit was 10-13 M. The current work offers a simple, cost-effective, and sensitive SERS substrate design that has great potential for sensing and detecting trace analytes.

Solvent-Free Aerobic Oxidative Cleavage of Methyl Oleate to Biobased Aldehydes over Mechanochemically Synthesized Supported AgAu Nanoparticles

The performance of mechanochemically synthesized supported bimetallic AgAu nanoalloy catalysts was evaluated in the oxidative cleavage of methyl oleate, a commonly available unsaturated bio-derived raw material. An extensive screening of supports (SiO2 , C, ZrO2 , Al2 O3 ), metallic ratios (Ag : Au), reaction times, temperatures, and use of solvents was carried out. The performance was optimized towards productivity and selectivity for the primary cleavage products (aldehydes and oxoesters). The optimal conditions were achieved in the absence of solvent, using Ag8 Au92 /SiO2 as catalyst, at 80 °C, reaction time of 1 h, substrate to catalyst=555 and 10 bar of molecular oxygen. A strong support effect was observed: the selectivity to aldehydes was best with silica as support, and to esters was best using zirconia. This shows not only that mechanochemical preparation of bimetallic catalysts is a powerful tool to generate useful catalyst compositions, but also that a safe, green, solventless synthesis of bio-derived products can be achieved by aerobic oxidative cleavage.

Oxygen Plasma Induced Nanochannels for Creating Bimetallic Hollow Nanocrystals

Platinum-based metal catalysts are considered excellent converters in various catalytic reactions, particularly in fuel cell applications. The atomic structure at the nanocrystal surface and the metal interface both influence the catalytic performance, controlling the efficiency of the electrochemical reactions. Here we report the synthesis of Ag/Pt and Ag/Pd core/shell nanocrystals and insight into the formation mechanism of these bimetallic core/shell nanocrystals when undergoing oxygen plasma treatment. We carefully designed the oxidation treatment that determines the structural and compositional evolution. The accelerated oxidation-triggered diffusion of Ag toward the outer metal shell leads to the Kirkendall effect. After prolonged oxygen plasma treatment, most core/shell nanocrystals evolve into hollow spheres. At the same time, a minor fraction of the metal remains unchanged with a well-protected Ag core and a monocrystalline Pt or Pd shell. We hypothesize that the O2 plasma disturbs the Pt or Pd shell surface and introduces active O species that react with the diffused Ag from the inside out. Based on EDX elemental mapping, combined with several electron microscopic techniques, we deduced the formation mechanism of the hollow structures to be as follows: (I) the oxidation of Ag within the Pt or Pd lattice causes a disrupted crystal lattice of Pt or Pd; (II) nanochannels arise at the defect locations on the Pt or Pd shell; (III) the remaining Ag atoms pass through these nanochannels and leave a hollow crystal behind. Our findings deepen the understanding of interface dynamics of bimetallic nanostructured catalysts under an oxidative environment and unveil an alternative approach for catalyst pretreatment.

Galvanic Replacement Reaction: Enabling the Creation of Active Catalytic Structures

The galvanic replacement reaction (GRR) is recognized as a redox process where one metal undergoes oxidation by the ions of another metal possessing a higher reduction potential. This reaction takes place at the interface between a substrate and a solution containing metal ions. Utilizing metal or metal oxide as sacrificial templates enables the synthesis of metallic nanoparticles, oxide-metal composites, and mixed oxides through GRR. Growing evidence showed that GRR has a direct impact on surface structures and properties. This has generated significant interest in catalysis and opened up new horizons for the application of GRR in energy and chemical transformations. This review provides a comprehensive overview of the synthetic strategies utilizing GRR for the creation of catalytically active structures. It discusses the formation of alloys, intermetallic compounds, single atom alloys, metal-oxide composites, and mixed metal oxides with diverse nanostructures. Additionally, GRR serves as a postsynthesis method to modulate metal-oxide interfaces through the replacement of oxide domains. The review also outlines potential future directions in this field.

Recent developments in the investigation of driving forces for transforming coinage metal nanoclusters

Metal nanoclusters serve as an emerging class of modular nanomaterials. The transformation of metal nanoclusters has been fully reflected in their studies from every aspect, including the structural evolution analysis, physicochemical property regulation, and practical application promotion. In this review, we highlight the driving forces for transforming atomically precise metal nanoclusters and summarize the related transforming principles and fundamentals. Several driving forces for transforming nanoclusters are meticulously reviewed herein: ligand-exchange-induced transformations, metal-exchange-induced transformations, intercluster reactions, photochemical transformations, oxidation/reduction-induced transformations, and other factors (intrinsic instability, pH, temperature, and metal salts) triggering transformations. The exploitation of transforming principles to customize the preparations, structures, physicochemical properties, and practical applications of metal nanoclusters is also disclosed. At the end of this review, we provide our perspectives and highlight the challenges remaining for future research on the transformation of metal nanoclusters. Our intended audience is the broader scientific community interested in metal nanoclusters, and we believe that this review will provide researchers with a comprehensive synthetic toolbox and insights on the research fundamentals needed to realize more cluster-based nanomaterials with customized compositions, structures, and properties.

Glutathione-Mediated Synthesis of Yolk-Shell AuAg Nanostructures Containing a Spherical Core and Cuboctahedral Skeletons and Their Applications in Plasmonic Catalysis

Frame/skeleton-like nanostructures are of great value in plasmonic catalysis as a result of the synergetic structural advantages arising from both maximized surface atomic exposure and efficient incident light absorptions. Herein, we report the size-tunable fabrication of yolk-shell AuAg nanoparticles containing a spherical core and cuboctahedral skeletons (AuAg YSCNSs), together with the exploration of their applications for assisting the reduction of 4-nitrophenol (4-NP) under ultraviolet-visible (UV-vis) light irradiation. The use of glutathione (GSH) at an appropriate amount to mediate the galvanic replacement reaction between Au@Ag core-shell nanocubes and HAuCl4 is found to be crucial in regulating the shape evolution. Their sizes could be readily tuned by altering the edge lengths of Au@Ag core-shell nanocubes. When working as the photocatalyst assisting the reduction of 4-NP, the AuAg YSCNSs exhibit a higher apparent rate constant under UV-vis light irradiation. The current work demonstrates the feasibility to create skeleton-like noble metal nanocrystals with the shape largely deviated from that of the original template via the "top-down" carving strategy by introducing non-metallic surface doping, which could be potentially extended to other noble metals or alloys.

Peroxidase-Mimicking Ir-Te Nanorods for Photoconversion-Combined Multimodal Cancer Therapy

Owing to multiple physicochemical properties, the combination of hybrid elemental compositions of nanoparticles can be widely utilized for a variety of applications. To combine pristine tellurium nanorods, which act as a sacrificing template, with another element, iridium-tellurium nanorods (IrTeNRs) were synthesized via the galvanic replacement technique. Owing to the coexistence of iridium and tellurium, IrTeNRs exhibited unique properties, such as peroxidase-like activity and photoconversion. Additionally, the IrTeNRs demonstrated exceptional colloidal stability in complete media. Based on these properties, the IrTeNRs were applied to in vitro and in vivo cancer therapy, allowing for the possibility of multiple therapeutic methodologies. The enzymatic therapy was enabled by the peroxidase-like activity that generated reactive oxygen species, and the photoconversion under 473, 660 and 808 nm laser irradiation induced cancer cell apoptosis via photothermal and photodynamic therapy.

Cutting-Edge Electrocatalysts for CO2RR

A world-wide growing concern relates to the rising levels of CO₂ in the atmosphere that leads to devastating consequences for our environment. In addition to reducing emissions, one alternative strategy is the conversion of CO₂ (via the CO₂ Reduction Reaction, or CO₂RR) into added-value chemicals, such as CO, HCOOH, C₂H₅OH, CH₄, and more. Although this strategy is currently not economically feasible due to the high stability of the CO₂ molecule, significant progress has been made to optimize this electrochemical conversion, especially in terms of finding a performing catalyst. In fact, many noble and non-noble metal-based systems have been investigated but achieving CO₂ conversion with high faradaic efficiency (FE), high selectivity towards specific products (e.g., hydrocarbons), and maintaining long-term stability is still challenging. The situation is also aggravated by a concomitant hydrogen production reaction (HER), together with the cost and/or scarcity of some catalysts. This review aims to present, among the most recent studies, some of the best-performing catalysts for CO₂RR. By discussing the reasons behind their performances, and relating them to their composition and structural features, some key qualities for an "optimal catalyst" can be defined, which, in turn, will help render the conversion of CO₂ a practical, as well as economically feasible process.

Galvanic Replacement Synthesis of Metal Nanostructures: Bridging the Gap between Chemical and Electrochemical Approaches

ConspectusGalvanic replacement synthesis involves oxidation and dissolution of atoms from a substrate while the salt precursor to another material with a higher reduction potential is reduced and deposited on the substrate. The driving force or spontaneity of such a synthesis comes from the difference in reduction potential between the redox pairs involved. Both bulk and micro/nanostructured materials have been explored as substrates for galvanic replacement synthesis. The use of micro/nanostructured materials can significantly increase the surface area, offering immediate advantages over the conventional electrosynthesis. The micro/nanostructured materials can also be intimately mixed with the salt precursor in a solution phase, resembling the setting of a typical chemical synthesis. The reduced material tends to be directly deposited on the surface of the substrate, just like the situation in an electrosynthesis. Different from an electrosynthesis where the two electrodes are spatially separated by an electrolyte solution, the cathodes and anodes are situated on the same surface, albeit at different sites, even for a micro/nanostructured substrate. Since the oxidation and dissolution reactions occur at sites different from those for reduction and deposition reactions, one can control the growth pattern of the newly deposited atoms on the same surface of a substrate to access nanostructured materials with diverse and controllable compositions, shapes, and morphologies in a single step. Galvanic replacement synthesis has been successfully applied to different types of substrates, including those made of crystalline and amorphous materials, as well as metallic and nonmetallic materials. Depending on the substrate involved, the deposited material can take different nucleation and growth patterns, resulting in diverse but well-controlled nanomaterials sought for a variety of studies and applications.In this Account, we recapitulate our efforts over the past two decades in fabricating metal nanostructures for a broad range of applications by leveraging the unique capability of galvanic replacement synthesis. We begin with a brief introduction to the fundamentals of galvanic replacement between metal nanocrystals and salt precursors, followed by a discussion of the roles played by surface capping agents in achieving site-selected carving and deposition for the fabrication of various bimetallic nanostructures. Two examples based on the Ag-Au and Pd-Pt systems are selected to illustrate the concept and mechanism. We then highlight our recent work on the galvanic replacement synthesis involving nonmetallic substrates, with a focus on the protocol, mechanistic understanding, and experimental control for the fabrication of Au- and Pt-based nanostructures with tunable morphologies. Finally, we showcase the unique properties and applications of nanostructured materials derived from galvanic replacement reactions for biomedicine and catalysis. We also offer some perspectives on the challenges and opportunities in this emerging field of research.

Plate-Like Colloidal Metal Nanoparticles

The pseudo-two-dimensional (2D) morphology of plate-like metal nanoparticles makes them one of the most anisotropic, mechanistically understood, and tunable structures available. Although well-known for their superior plasmonic properties, recent progress in the 2D growth of various other materials has led to an increasingly diverse family of plate-like metal nanoparticles, giving rise to numerous appealing properties and applications. In this review, we summarize recent progress on the solution-phase growth of colloidal plate-like metal nanoparticles, including plasmonic and other metals, with an emphasis on mechanistic insights for different synthetic strategies, the crystallographic habits of different metals, and the use of nanoplates as scaffolds for the synthesis of other derivative structures. We additionally highlight representative self-assembly techniques and provide a brief overview on the attractive properties and unique versatility benefiting from the 2D morphology. Finally, we share our opinions on the existing challenges and future perspectives for plate-like metal nanomaterials.

Modulating Dominant Facets of Pt through Multistep Selective Anchored on WC for Enhanced Hydrogen Evolution Catalysis

Facilitating the exposure of the active crystal facets on the surfaces of composite catalysts is a representative route to promote catalytic activity. Based on a tailored galvanic replacement reaction, herein, a self-assembly route is reported to prepare Pt-WC/CNT with Pt (200) preferential orientation and well-dispersed structure, which are capable of substantially boosting electrocatalysis in hydrogen evolution reaction (HER). Formation mechanism reveals that the (200)-dominated Pt-based catalysts form in galvanic replacement reaction through selective anchored on WC, and the multistep galvanic replacement process plays a critical role to realize the Pt (200)-dominated growth in higher Pt loading catalyst. These unique structural features endow the Pt-WC/CNT with a high turnover frequency of 94.18 H2·s-1 at 100 mV overpotential, 7-fold higher than that of commercial Pt/C (13.55 H2·s-1), ranking it among the most active catalysts. In addition, this method, which combines with gas-solid reaction and galvanic replacement reaction, paves the way to scalable synthesis as Pt facets-controllable composite catalysts to challenge commercial Pt/C.

Bio-Fabrication of Trimetallic Nanoparticles and Their Applications

Nanoparticles are materials whose size is less than 100 nm. Because of their distinctive physical and chemical characteristics, nanoparticles have drawn considerable interest in a variety of fields. Biosynthesis of nanoparticles is a green and environmentally friendly technology, which requires fewer chemical reagents, precursors, and catalysts. There are various types of nanomaterials, out of which trimetallic nanoparticles are receiving considerable interest in recent years. Trimetallic nanoparticles possess unique catalytic, biomedical, antimicrobial, active food packaging, and sensing applications as compared to monometallic or bimetallic nanoparticles. Trimetallic nanoparticles are currently synthesized by various methods such as chemical reduction, microwave-assisted, thermal, precipitation, and so on. However, most of these chemical and physical methods are expensive and toxic to the environment. Biological synthesis is one of the promising methods, which includes the use of bacteria, plants, fungi, algae, waste biomass, etc., as reducing agents. Secondary metabolites present in the biological agents act as capping and reducing agents. Green trimetallic nanoparticles can be used for different applications such as anticancer, antibacterial, antifungal, catalytic activity, etc. This review provides an overview of the synthesis of trimetallic nanoparticles using biological agents, and their applications in different areas such as anticancer, antimicrobial activity, drug delivery, catalytic activity, etc. Finally, current challenges, future prospects, and conclusions are highlighted.

Nano-Engineered Surface Comprising Metallic Dendrites for Biomolecular Analysis in Clinical Perspective

Metallic dendrites, a class of three-dimensional nanostructured materials, have drawn a lot of interests in the recent years because of their interesting hierarchical structures and distinctive features. They are a hierarchical self-assembled array of primary, secondary, and terminal branches with a plethora of pointed ends, ridges, and edges. These features provide them with larger active surface areas. Due to their enormous active areas, the catalytic activity and conductivity of these nanostructures are higher as compared to other nanomaterials; therefore, they are increasingly used in the fabrication of sensors. This review begins with the properties and various synthetic approaches of nanodendrites. The primary goal of this review is to summarize various nanodendrites-engineered biosensors for monitoring of small molecules, macromolecules, metal ions, and cells in a wide variety of real matrices. Finally, to enlighten future research, the limitations and future potential of these newly discovered materials are discussed.

Facile Synthesis of Highly Dispersed and Well-Alloyed Bimetallic Nanoparticles on Oxide Support

Supported alloy catalysts play a pivotal role in many heterogeneous catalytic processes of socioeconomic and environmental importance. But the controlled synthesis of supported alloy nanoparticles with consistent composition and tight size distribution remains a challenging issue. Herein, a simple yet effective method for preparation of highly dispersed, homogeneously alloyed bimetallic nanoparticles on oxide supports is reported. This method is based on solid solution of metal cations in parent oxide and strong electrostatic adsorption of a secondary metal species onto the oxide surface. In the reductive annealing process, hydrogen spillover occurs from the surface metal with a higher reduction potential to the solute metal in solid solution, leading to metal exsolution and homogenous alloying of the metals on the oxide surface. The ceria-supported Ni-Pt alloy is chosen as a model catalyst and hydrazine monohydrate decomposition is chosen as a probe reaction to demonstrate this method, and particularly its advantages over the conventional impregnation and galvanic replacement methods. A systematic application of this method using different oxides and base-noble metal pairs further elucidates its applicability and generality.

Advances in plasmonic-based MOF composites, their bio-applications and perspectives in this field

INTRODUCTION

Nanomaterials have been used for bio-applications since the late 20st century. In an attempt to tailor and optimize their properties, and by extension their efficiency, composites have attracted considerable attention. In this regard, recent studies on plasmonic nanoparticles and metal-organic framework (NP@MOF) composites suggested these materials show great promise in this field.

AREAS COVERED

This review focused on the more recent scientific advances in the synthetic strategies to optimize plasmonic MOF nanocomposites currently available, as well as their bio-application, particularly as biosensors and therapy.

EXPERT OPINION

Plasmonic MOF nanocomposites have shown great potential as they combine the properties of both materials with proven efficiency in bio-application. On the one hand, nanoMOFs have proven their potential particularly as drug nanocarriers, owing to their exceptional porosity and tunability. On the other hand, plasmonic nanoparticles have been an asset for imaging and phototherapy. Different strategies have been reported to develop these nanocomposites, mainly including core-shell, encapsulation, and in situ reduction. In addition, advanced composite structures should be considered, such as mixed metal nanoparticles, hollow structures or the combination of several approaches. Specifically, plasmonic MOF nanocomposites prove to be attractive stimuli responsive drug delivery systems, phototherapeutic agents as well as highly sensitive biosensors.

Tailoring Morphology and Elemental Distribution of Cu-In Nanocrystals via Galvanic Replacement

The compositional and structural diversity of bimetallic nanocrystals (NCs) provides a superior tunability of their physico-chemical properties, making them attractive for a variety of applications, including sensing and catalysis. Nevertheless, the manipulation of the properties-determining features of bimetallic NCs still remains a challenge, especially when moving away from noble metals. In this work, we explore the galvanic replacement reaction (GRR) of In NCs and a copper molecular precursor to obtain Cu-In bimetallic NCs with an unprecedented variety of morphologies and distribution of the two metals. We obtain spherical Cu₁₁In₉ intermetallic and patchy phase-segregated Cu-In NCs, as well as dimer-like Cu-Cu₁₁In₉ and Cu-In NCs. In particular, we find that segregation of the two metals occurs as the GRR progresses with time or with a higher copper precursor concentration. We discover size-dependent reaction kinetics, with the smaller In NCs undergoing a slower transition across the different Cu-In configurations. We compare the obtained results with the bulk Cu-In phase diagram and, interestingly, find that the bigger In NCs stabilize the bulk-like Cu-Cu₁₁In₉ configuration before their complete segregation into Cu-In NCs. Finally, we also prove the utility of the new family of Cu-In NCs as model catalysts to elucidate the impact of the metal elemental distribution on the selectivity of these bimetallics toward the electrochemical CO₂ reduction reaction. Generally, we demonstrate that the GRR is a powerful synthetic approach beyond noble metal-containing bimetallic structures, yet that the current knowledge on this reaction is challenged when oxophilic and poorly miscible metal pairs are used.

Hierarchical Design in Nanoporous Metals

Hierarchically porous metals possess intriguing high accessibility of matter molecules and unique continuous metallic frameworks, as well as a high level of exposed active atoms. High rates of diffusion and fast energy transfer have been important and challenging goals of hierarchical design and porosity control with nanostructured metals. This review aims to summarize recent important progress toward the development of hierarchically porous metals, with special emphasis on synthetic strategies, hierarchical design in structure-function and corresponding applications. The current challenges and future prospects in this field are also discussed.

Multimode Electron Tomography Sheds Light on Synthesis, Structure, and Properties of Complex Metal-Based Nanoparticles

Electron tomography has become a cornerstone technique for the visualization of nanoparticle morphology in three dimensions. However, to obtain in-depth information about a nanoparticle beyond surface faceting and morphology, different electron microscopy signals must be combined. The most notable examples of these combined signals include annular dark-field scanning transmission electron microscopy (ADF-STEM) with different collection angles and the combination of ADF-STEM with energy-dispersive X-ray or electron energy loss spectroscopies. Here, the experimental and computational development of various multimode tomography techniques in connection to the fundamental materials science challenges that multimode tomography has been instrumental to overcoming are summarized. Although the techniques can be applied to a wide variety of compositions, the study is restricted to metal and metal oxide nanoparticles for the sake of simplicity. Current challenges and future directions of multimode tomography are additionally discussed.

Noble-Metal-Based Hollow Mesoporous Nanoparticles: Synthesis Strategies and Applications

As second-generation mesoporous materials, mesoporous noble metals (NMs) are of significant interest for their wide applications in catalysis, sensing, bioimaging, and biotherapy owing to their structural and metallic features. The introduction of interior hollow cavity into NM-based mesoporous nanoparticles (MNs), which subtly integrate hierarchical hollow and mesoporous structure into one nanoparticle, produces a new type of hollow MNs (HMNs). Benefiting from their higher active surface, better electron/mass transfer, optimum electronic structure, and nanoconfinement space, NM-based HMNs exhibit their high efficiency in enhancing catalytic activity and stability and tuning catalytic selectivity. In this review, recent progress in the design, synthesis, and catalytic applications of NM-based HMNs is summarized, including the findings of the groups. Five main strategies for synthesizing NM-based HMNs, namely silica-assisted surfactant-templated nucleation, surfactant-templated sequential nucleation, soft "dual"-template, Kirkendall effect in synergistic template, and galvanic-replacement-assisted surfactant template, are described in detail. In addition, the applications in ethanol oxidation electrocatalysis and hydrogenation reactions are discussed to highlight the high activity, enhanced stability, and optimal selectivity of NM-based HMNs in (electro)catalysis. Finally, the further outlook that may lead the directions of synthesis and applications of NM-based HMNs is prospected.

Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion

There is a growing need to control and tune nanoparticles (NPs) to increase their stability and effectiveness, especially for photo- and electrochemical energy conversion applications. Exsolved particles are well anchored and can be re-shaped without changing their initial location and structural arrangement. However, this usually involves lengthy treatments and use of toxic gases. Here, the galvanic replacement/deposition method is used, which is simpler, safer, and leads to a wealth of new hybrid nanostructures with a higher degree of tailorability. The produced NiAu bimetallic nanostructures supported on SrTiO₃ display exceptional activity in plasmon-assisted photoelectrochemical (PEC) water oxidation reactions. In situ scanning transmission electron microscopy is used to visualize the structural evolution of the plasmonic bimetallic structures, while theoretical simulations provide mechanistic insight and correlate the surface plasmon resonance effects with structural features and enhanced PEC performance. The versatility of this concept in shifting catalytic modes to the hydrogen evolution reaction is demonstrated by preparing hybrid NiPt bimetallic NPs of low Pt loadings on highly reduced SrTiO₃ supports. This powerful methodology enables the design of supported bimetallic nanomaterials with tunable morphology and catalytic functionalities through minimal engineering.

Heterogeneous Trimetallic Nanoparticles as Catalysts

The development and application of trimetallic nanoparticles continues to accelerate rapidly as a result of advances in materials design, synthetic control, and reaction characterization. Following the technological successes of multicomponent materials in automotive exhausts and photovoltaics, synergistic effects are now accessible through the careful preparation of multielement particles, presenting exciting opportunities in the field of catalysis. In this review, we explore the methods currently used in the design, synthesis, analysis, and application of trimetallic nanoparticles across both the experimental and computational realms and provide a critical perspective on the emergent field of trimetallic nanocatalysts. Trimetallic nanoparticles are typically supported on high-surface-area metal oxides for catalytic applications, synthesized via preparative conditions that are comparable to those applied for mono- and bimetallic nanoparticles. However, controlled elemental segregation and subsequent characterization remain challenging because of the heterogeneous nature of the systems. The multielement composition exhibits beneficial synergy for important oxidation, dehydrogenation, and hydrogenation reactions; in some cases, this is realized through higher selectivity, while activity improvements are also observed. However, challenges related to identifying and harnessing influential characteristics for maximum productivity remain. Computation provides support for the experimental endeavors, for example in electrocatalysis, and a clear need is identified for the marriage of simulation, with respect to both combinatorial element screening and optimal reaction design, to experiment in order to maximize productivity from this nascent field. Clear challenges remain with respect to identifying, making, and applying trimetallic catalysts efficiently, but the foundations are now visible, and the outlook is strong for this exciting chemical field.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Synthesis of silver nanoparticles by sonogalvanic replacement on aluminium powder in sodium polyacrylate solutions

The process of the formation of silver nanoparticles (AgNPs) via the method of galvanic replacement (GR) of Ag+ with aluminum powder in sodium polyacrylate (NaPA) solutions in the ultrasonic (US) field has been studied. It was observed, that the yellow colloidal solutions of stabilized AgNPs with the absorption maximum at ∼ 410 nm were obtained under the application of US power by 20 W and frequency by 20 kHz in the wide range of AgNO3 and NaPA concentrations (0.1 - 0.5 mM and 0.5 - 5.0 g/L respectively) at 25 0C. It was shown, that the GR process under US field occurs without of the significant induction period. Using the UV-vis spectroscopy the kinetics of AgNPs formation has been studied and it was observed the first order kinetics with respect to Ag+ ions both for the nucleation and growth processes. It was found that observable rate constants of nucleation are close for the all experimental conditions but the observable rate constants of growth decreased with increasing of initial concentration of AgNO3. Based on the obtained kinetic data it was proposed a mechanism of the formation of AgNPs consisted of the following two main stages: 1) the nucleation with the formation of primary nanoclusters (AgNCs) on aluminum surface followed by their ablation from the surface of the sacrificial metal by ultrasound into bulk of solution; 2) the transformation of AgNCs in AgNPs via growth from the Al surface and / or agglomeration of AgNCs. Using TEM it was found that the size of obtained AgNPs does not exceed of 25 nm and slightly depends on the initial concentrations of precursors. High antimicrobial activity of obtained colloidal solutions against gram-negative and gram-positive bacteria as well as against fungi was observed.

Plasmonic catalysis with designer nanoparticles

Catalysis is central to a more sustainable future and a circular economy. If the energy required to drive catalytic processes could be harvested directly from sunlight, the possibility of replacing contemporary processes based on terrestrial fuels by the conversion of light into chemical energy could become a step closer to reality. Plasmonic catalysis is currently at the forefront of photocatalysis, enabling one to overcome the limitations of "classical" wide bandgap semiconductors for solar-driven chemistry. Plasmonic catalysis enables the acceleration and control of a variety of molecular transformations due to the localized surface plasmon resonance (LSPR) excitation. Studies in this area have often focused on the fundamental understanding of plasmonic catalysis and the demonstration of plasmonic catalytic activities towards different reactions. In this feature article, we discuss recent contributions from our group in this field by employing plasmonic nanoparticles (NPs) with controllable features as model systems to gain insights into structure-performance relationships in plasmonic catalysis. We start by discussing the effect of size, shape, and composition in plasmonic NPs over their activities towards LSPR-mediated molecular transformations. Then, we focus on the effect of metal support interactions over activities, reaction selectivity, and reaction pathways. Next, we shift to the control over the structure in hollow NPs and nanorattles. Inspired by the findings from these model systems, we demonstrate a design-driven strategy for the development of plasmonic catalysts based on plasmonic-catalytic multicomponent NPs for two types of molecular transformations: the selective hydrogenation of phenylacetylene and the oxygen evolution reaction. Finally, future directions, challenges, and perspectives in the field of plasmonic catalysis with designer NPs are discussed. We believe that the examples and concepts presented herein may inspire work and progress in plasmonic catalysis encompassing the design of plasmonic multicomponent materials, new strategies to control reaction selectivity, and the unraveling of stability and reaction mechanisms.

Mechanochemical Strategies for the Preparation of SiO2-Supported AgAu Nanoalloy Catalysts

Silver-gold nanoalloys were prepared from their metal salts precursors through bottom-up mechanochemical synthesis, using one-pot or galvanic replacement reaction strategies. The nanostructures were prepared over amorphous SiO2 as an inert supporting material, facilitating their stabilization without the use of any stabilizing agent. The nanomaterials were extensively characterized, confirming the formation of the bimetallic nanostructures. The nanoalloys were tested as catalysts in the hydrogenation of 2-nitroaniline and exhibited up to 4-fold the rate constant and up to 37% increased conversion compared to the respective single metal nanoparticles. Our approach is advantageous to produce nanoparticles with clean surfaces with available catalytic sites, directly in the solid-state and in an environmentally friendly manner.

Synthesis of gold nano-mushrooms via solvent-controlled galvanic replacement to enhance phototherapeutic efficiency

In advanced galvanic replacement, variable factors such as the combination of two elements where actual redox reaction and post-synthetic structural transformation take place. Research on manufacturing distinctive nanostructures has mainly focused on the shape of the sacrificial nanotemplate, the presence or absence of additives, and the reaction temperature. Here, we have attempted to confirm the dependency on the solvent, which was considered to simply serve as a medium for a homogeneous chemical reaction to proceed by aiding the dispersion of the nanotemplate and reactants. Thus, we obtained mushroom-like Au nanoplates (mAuNPs) by comprehensive galvanic replacement reaction between solvents, additives, and adsorbents. The mAuNPs with a porous Au nanoplate head and a hollow nanotube tail structure were formed via an optimization process in a 50 v/v% solvent comprising water and ethylene glycol. As a result of confirming the galvanic replacement in co-solvent conditions, in which various types of water miscible solvents were introduced, it was revealed that the most critical factors for regulating the surface polymeric environment of the nanoplate were the relative polarity index of the co-solvent and the hydrogen bonding type. These depend on the molecular structure of the solvent. The manufactured mAuNPs exhibited excellent absorbance in the near-infrared region, and efficient photothermal (PT) conversion-mediated heat dissipation under local laser irradiation. These results confirm the viability of the gene-thermo dual-modal combinatorial cancer therapy based on the surface loading of oligonucleotides and peptides, and the PT therapeutic approach in vitro and in vivo.