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Gold nanoparticles (Au NPs) have been extensively used as artificial enzymes, but their performance is still limited. We address this challenge by focusing on multimetallic nanorattles comprising an Au core inside a bimetallic AgAu shell, separated by a void (Au@AgAu NRs). They were prepared by a galvanic replacement approach and contained an ultrathin and porous shell comprising an AgAu alloy. By investigating the peroxide-like activity using TMB oxidation as a model transformation, we have found an increase of 152 fold in activities for the NRs relative to conventional Au NPs. Based on the kinetics results, the NRs also showed the lowest K-m, indicating better interaction with the substrate and faster product formation. We also observed a linear relationship between the concentration of the product and oxTMB as a function of H2O2 concentration, which could be further applied for H2O2 sensing applications (colorimetric detection). These data suggest that the NRs enable the combined effect of an increased surface area relative to solid counterparts, the possibility of exposing highly active surface sites, and the exploitation of nanoconfinement effects due to the void regions between the core and shell components. These results provide important insights into the optimization of peroxidase-like performances beyond what can be achieved in conventional NPs and may inspire the development of better-performing artificial enzymes.

Plasmonic catalysis enables the use of light to accelerate molecular transformations. Its application to the control reaction selectivity is highly attractive but remains challenging. Here, we have found that the plasmonic properties in AgPd nanoparticles allowed different reaction pathways for tunable product formation under visible light irradiation. By employing the hydrogenation of phenylacetylene as a model transformation, we demonstrate that visible light irradiation can be employed to steer the reaction pathway from hydrogenation to homocoupling. Our data showed that the decrease in the concentration of H species at the surface due to plasmon-enhanced H2 desorption led to the control in selectivity. These results provide important insights into the understanding of reaction selectivity with light, paving the way for the application of plasmonic catalysis to the synthesis of 1,3-diynes, and bringing the vision of light-driven transformations with target selectivity one step closer to reality.

Single-particle reconstruction can be used to perform three-dimensional (3D) imaging of homogeneous populations of nano-sized objects, in particular viruses and proteins. Here, it is demonstrated that it can also be used to obtain 3D reconstructions of heterogeneous populations of inorganic nanoparticles. An automated acquisition scheme in a scanning transmission electron microscope is used to collect images of thousands of nanoparticles. Particle images are subsequently semi-automatically clustered in terms of their properties and separate 3D reconstructions are performed from selected particle image clusters. The result is a 3D dataset that is representative of the full population. The study demonstrates a methodology that allows 3D imaging and analysis of inorganic nanoparticles in a fully automated manner that is truly representative of large particle populations.

Metal nanoparticles have been widely exploited in catalysis, but their full impact on the environment and human health is still under debate. Here we describe the one-step fabrication of recoverable and reusable polymer microbead-supported metal and metal oxide nanocatalysts for application in batch reactions and flow systems. Au, Ag, and Fe3O4 nanoparticles were prepared directly at the surface of commercial benzylamine-coated spherical polymer beads in water by using low-energy microwave radiation for 5 min. The functionalization of microbead surface with betalamic acid, an antioxidant from plant origin, before irradiation changes the morphology and catalytic properties of the grafted nanoparticles. No leaching of the active phase was observed during the application of these effective and ready-to-use nanocatalysts on the reduction of 4-nitrophenol and oxidation of dihydrorhodamine 123. The supported nanocatalysts were recovered by filtration and/or magnetic separation and reused up to three times without significant drop in catalytic performance. These results can stimulate the controlled and facile synthesis of recoverable microbead-supported magnetic and nonmagnetic nanocatalysts that can be applied under myriad reaction conditions and reused multiple times.

Herein, we describe the synthesis, characterization and electrochemical performance of four phosphonium-based ionic liquids (ILs) as electrolytes, Physicochemical properties such as viscosity, density, ionic conductivity, and thermal stability of ILs and conventional organic solvent ethylene carbonate (EC)/diethyl carbonate (DEC) were experimentally determined at different temperatures. All ILs showed thermal stability greater than 300 degrees C, surpassing the stability of the conventional organic solvent, whose flash points were 145 and 23 degrees C for EC and DEC, respectively. Nevertheless, at room temperature, all ILs are much more viscous than EC/DEC. The composite Si -[P-2224][FSI] (triethyl-n-butylphosphonium bis(fluoromethylsulfonyl)imide) and Si-EC/DEC anodes exhibit initial specific capacities at 0.15 A/g of 2409 and 2631 mAh/g, respectively. This demonstrates that despite the inferior transport properties of ILs, short alkyl-substituted phosphonium ILs like [P-2224][FSI] are potentially competitive for the new generation of electrolytes for LIBs. NMR, DSC, TGA, and galvanostatic discharged/charged were used as characterization techniques.

Localized surface plasmons generated on metallic nanostructures can be used to accelerate molecular transformations; however, the efficiency is limited by the challenge to control the energy/charge transfer at the interfaces. Here, we combine density functional theory (DFT) calculations and experiments to reveal the mechanism of nitrophenol reduction on Au nanoparticles under visible-light irradiation and propose a strategy to further enhance the reaction rates. DFT calculations show a reduced activation barrier under electronic excitation on Au(111), thus explaining the measured higher rates under visible-light irradiation. Furthermore, we propose a heterostructure with Au nanoparticles covered by a thin film of hexagonal boron nitride; the latter is used to decouple the molecular orbitals from the metal to enable charge localization in the molecule. DFT calculations show that by this electronic decoupling, the activation barrier can be lowered by a factor of five. This work thus provides a valuable strategy for optimizing catalytic efficiency in plasmonic photocatalysis.

Made available in DSpace on 2022-04-28T19:45:51Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-15 The development of negative electrode materials with better performance than those currently used in Li-ion technology has been a major focus of recent battery research. Here, we report the synthesis and electrochemical evaluation of in situ-formed nitrogen-doped carbon/SiOC. The materials were synthesized by a sol–gel process using 3-(aminopropyl)triethoxysilane (APTES), sodium citrate and glycerol. The electrochemical performance of pyrolyzed materials was studied using poly(acrylic acid) binder and commercial organic electrolyte. Our reported approach enables changes in both the amount of nitrogen and the morphology as a function of the molar ratio of APTES:citrate and reaction time. Spherical-shaped NC/SiOC composite electrodes deliver a delithiation capacity of 622 mAh/g at 0.1 A/g and an initial coulombic efficiency of ∼63%, while in the large bulk material, respective values of 367 mAh/g and ∼55% were obtained. After 1000 charge/discharge cycles at 1.6 A/g, the latter material exhibits 98% of the initial capacity once it returned to lower current cycling. Overall, our results indicate that NC/SiOC materials are quite promising for electrochemical applications since both their large capacity and stability demonstrate superior performance compared to traditional graphite. Moreover, our synthesis is simple and, more importantly, environmentally friendly chemicals, such as sodium citrate and glycerol, are used. Departamento de Química Fundamental Instituto de Química – Universidade de São Paulo, Av. Prof. Lineu Prestes 748 Departamento de ciencias Universidad de Ingenieria y Tecnologia – UTEC Instituto de Química. UNESP, Rue Francisco Degni, 55 Department of Chemistry University of Helsinki, A.I. Virtasen Aukio 1 NanoQAM and Département de Chimie Université du Québec à Montréal, Case Postale, 8888 Succursale Centre-Ville Instituto de Química. UNESP, Rue Francisco Degni, 55

Recently, the widespread use of antibiotics is becoming a serious worldwide public health challenge, which causes antimicrobial resistance and the occurrence of superbugs. In this context, MnO2 has been proposed as an alternative approach to achieve target antibacterial properties on Streptococcus mutans (S. mutans). This requires a further understanding on how to control and optimize antibacterial properties in these systems. We address this challenge by synthesizing δ-MnO2 nanoflowers doped by magnesium (Mg), sodium (Na), and potassium (K) ions, thus displaying different bandgaps, to evaluate the effect of doping on the bacterial viability of S. mutans. All these samples demonstrated antibacterial activity from the spontaneous generation of reactive oxygen species (ROS) without external illumination, where doped MnO2 can provide free electrons to induce the production of ROS, resulting in the antibacterial activity. Furthermore, it was observed that δ-MnO2 with narrower bandgap displayed a superior ability to inhibit bacteria. The enhancement is mainly attributed to the higher doping levels, which provided more free electrons to generate ROS for antibacterial effects. Moreover, we found that δ-MnO2 was attractive for in vivo applications, because it could nearly be degraded into Mn ions completely following the gradual addition of vitamin C. We believe that our results may provide meaningful insights for the design of inorganic antibacterial nanomaterials.

Treatments of simulated effluent solutions containing the Reactive Black 5 (RB5) were carried out by electrochemical, photoelectrochemical, electro-Fenton and photoelectro-Fenton methods using a one-compartment cell with a boron-doped diamond anode and a 3% of manganese dioxide nanoflowers supported on a carbon Vulcan XC72 gas diffusion electrode cathode. In the photo-assisted processes, the solution was irradiated using a 40-W UVC lamp immersed in the treated solution. For Fenton-based processes, only 5 min was required to attain 95% (photoelectro-Fenton) and 93% (electro-Fenton) RB5 dye degradation. When conversion to CO2 is taken into account after 6-h treatment, electrochemical method mineralized ~ 13% of the organic load whereas removals greater than 90% were attained using the Fenton-based processes. These completely different results can be explained by the distinct spatial availability of the generated hydroxyl radical: only near the anode surface as in electrochemical-based processes or added to those distributed across the solution bulk as in Fenton-based processes.

Control over the bottom up synthesis of metal nanoparticles (NP) depends on many experimental factors, including the choice of stabilising and reducing agents. By selectively manipulating these species, it is possible to control NP characteristics through solution-phase synthesis strategies. It is not known, however, whether NPs produced from mechanochemical syntheses are governed by the same rules. Using the Au NPs mechanosynthesis as a model system, we investigate how a series of common reducing agents affect both the reduction kinetics and size of Au NPs. It is shown that the relative effects of reducing agents on mechanochemical NP synthesis differ significantly from their role in analogous solution-phase reactions. Hence, strategies developed for control over NP growth in solution are not directly transferrable to environmentally benign mechanochemical approaches. This work demonstrates a clear need for dedicated, systematic studies on NP mechanosynthesis.

Gold nanoparticles (NPs) combined with Lewis bases, such as piperazine, were found to perform selective hydrogenation reactions via the heterolytic cleavage of H2. Since gold nanoparticles can be prepared by many different methodologies and using different capping ligands, in this study, we investigated the influence of capping ligands adsorbed on gold surfaces on the formation of the gold–ligand interface. Citrate (Citr), poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), and oleylamine (Oley)-stabilized Au NPs were not activated by piperazine for the hydrogenation of alkynes, but the catalytic activity was greatly enhanced after removing the capping ligands from the gold surface by calcination at 400 °C and the subsequent adsorption of piperazine. Therefore, the capping ligand can limit the catalytic activity if not carefully removed, demonstrating the need of a cleaner surface for a ligand–metal cooperative effect in the activation of H2 for selective semihydrogenation of various alkynes under mild reaction conditions.

Current time-resolvedin situapproaches limit the scope of mechanochemical investigations possible. Here we develop a new, general approach to simultaneously follow the evolution of bulk atomic and electronic structure during a mechanochemical synthesis. This is achieved by coupling two complementary synchrotron-based X-ray methods: X-ray absorption spectroscopy (XAS) and X-ray diffraction. We apply this method to investigate the bottom-up mechanosynthesis of technologically important Au micro and nanoparticles in the presence of three different reducing agents, hydroquinone, sodium citrate, and NaBH4. Moreover, we show how XAS offers new insight into the early stage generation of growth species (e.g.monomers and clusters), which lead to the subsequent formation of nanoparticles. These processes are beyond the detection capabilities of diffraction methods. This combined X-ray approach paves the way to new directions in mechanochemical research of advanced electronic materials.

Colloidal particles with a spherical shape and diameters in the range of 0.01−1 μm have been a subject of extensive research, with applications in areas such as photonics, electronics, catalysis, drug delivery, and medicine. For most of these applications, it is of critical importance to achieve monodispersity for the size while expanding the diversity in terms of structure and composition. The uniformity in size allows one to establish rigorous correlations between this parameter and the physicochemical properties of the colloidal particles while ensuring experimental repeatability and measurement accuracy. On the other hand, the diversity in structure and composition offers additional handles for tailoring the properties. By switching from the conventional plain, solid structure to a core-shell, hollow, porous, or Janus structure, it offers immediate advantages and creates new opportunities, especially in the context of self-assembly, encapsulation, and controlled release. As for composition, monodispersed colloidal spheres were traditionally limited to amorphous materials such as polystyrene and silica. For metals and semiconducting materials, which are more valuable to applications in photonics, electronics, and catalysis, they tend to crystallize and thus grow anisotropically into non-spherical shapes, especially when their sizes pass 0.1 μm. Taken together, it is no wonder why chemical synthesis of monodispersed colloidal spheres has been a constant theme of research in areas such as colloidal science, materials chemistry, materials science, and soft matter. In this account, we summarize our efforts over the past two decades in developing solution-phase methods for the facile synthesis of colloidal spheres that are uniform in size, together with a broad range of compositions (including metals and semiconductors) and structures (e.g., solid, core-shell, hollow, porous, and Janus, among others). We start with the synthesis of monodispersed colloidal spheres made of semiconductors, metals with low melting points, and precious metals. Through chemical reactions, these colloidal spheres can be transformed into core-shell or hollow structures with new compositions and properties. Next, we discuss the synthesis of colloidal spheres with a Janus structure while taking a pseudo-spherical shape. Specifically, metal-polymer hybrid particles comprised of one metal nanoparticle partially embedded in the surface of a polymer sphere can be produced through precipitation polymerization in the presence of metal seed. With these Janus particles serving as templates, other types of Janus structures such as hollow spheres with a single hole in the surface can be obtained via site-selected deposition. Alternatively, such hollow spheres can be fabricated through a physical transformation process that involves swelling of polymer spheres, followed by freeze-drying. All these synthesis and transformation processes are solution-based, offering flexibility and potential for large-scale production. At the end, we highlight some of the applications enabled by these colloidal spheres, including fabrication of photonic devices, encapsulation, and controlled release for nanomedicine.

We focus herein on understanding how the oxidation mechanism of glucose may be affected by the nature of the surface facets of Cu2O-based electrocatalytic sensors. To this end, we performed a series of in situ FTIR spectroelectrochemical experiments and DFT simulations by employing Cu2O cubes and octahedra as electrocatalytic sensors for glucose and other interferents. Interestingly, our in situ results demonstrated that the glucose oxidation mechanism displayed shape-dependent behavior, indicating that the glucose molecule can selectively adsorb on the Cu2O {1 0 0} facets relative to ascorbate and urate interferents in a process that probably occurs without the need for an external potential. However, when the same reaction was performed in the presence of Cu2O octahedra ({1 1 1} facets), the reaction was not selective, and the final product remained on the surface, blocking the sites for further glucose oxidation and leading to significantly lower electrocatalytic activities. Surprisingly, no bands related to the formation of Cu3+ species were detected, indicating that Cu3+ species do not participate in the reaction mechanism. This is very important because these species have been assumed to be the catalytically active sites for glucose oxidation. We believe that the results presented herein provide new insights into different aspects of the oxidation of carbohydrates and may inspire a deeper mechanistic investigation of other semiconductor materials and the development of optimized electrocatalysts.

We reported herein a systematic investigation on how the nature of the support affected the catalytic performances of Rh nanoparticles. The prepared catalysts were denoted as Rh/MxOy, where M corresponded to Ce, Ti, Si, Zn, and Al, and Rh was Rh3+ reduction to Rh nanoparticles on the surface of oxides. This strategy was performed in a single step using urea as a mediator and in the absence of any other stabilizer or capping agent. The Rh nanoparticles displayed relatively similar sizes, shapes, and uniform distribution over the supports, differing only in terms of the nature of the support. This strongly affected the metal–support interaction between Rh nanoparticles and the respective oxides, leading to significant differences in their catalytic performances toward the ethanol steam reforming. Here, not only the catalytic activity (in terms of ethanol conversion) was affected, but both the selectivity and stability were also influenced by the nature of the oxide support. Interestingly, the reaction paths as well as the deactivation profile were completely changed as function of the employed support. Such differences were associated with differences in the oxygen storage, oxygen mobility, and acidity/basicity of the supports. We believe that our results can contribute to the development and understanding of Rh-supported catalysts for the applications toward gas-phase transformations such as the ethanol steam reforming reaction.

A large number of pharmaceutical drugs have been found in effluents because conventional treatments are not efficient in their removal. Among these drugs, paracetamol is a cause of concern due to its great use worldwide. In this context, electrochemical advanced oxidation processes (EAOPs) based on the Fenton process have been studied because they are able to remove these persistent organic pollutants. This work aims to use an electrocatalyst based on Vulcan XC-72 carbon black modified with 1% ceria high aspect ratio nanostructures (1% CeO2 HARN/Vulcan XC-72) as a gas diffusion electrode (GDE) for both hydrogen peroxide electrogeneration and paracetamol degradation using Fenton-like processes. These studies were evaluated using two different anodes, Pt and boron-doped diamond (BDD). The results obtained in the H2O2 electrogeneration indicated a large increase in the efficiency of the modified gas diffusion electrode (MGDE) with the 1% CeO2 HARN/Vulcan XC-72 electrocatalyst compared to the Vulcan XC-72 GDE without modification. Approximately 1463 mg L−1 of H2O2 with an energy consumption of 11.5 kWh kg−1 and a current efficiency of 44.9% was obtained. The tested EAOPs showed paracetamol mineralization rates of up to 98.4% after 6 h of electrolysis in 350 mL of acidic medium. The MGDE also showed a high stability without loss of H2O2 electrogeneration capacity after 130 h of use, making it promising in applications for EAOPs aiming at organic pollutant mineralization.

We reported herein the synthesis in high yields (>97%) of Ce0.9Sm0.1O2-δ nanowires displaying well-defined shape, size, and composition by a simple, fast, and low-cost two-step hydrothermal method. The Ce0.9Sm0.1O2-δ nanowires synthesis was followed by the wet impregnation of Ni without the utilization of any stabilizing agent. The Ni/Ce0.9Sm0.1O2-δ nanowires showed higher surface area, high concentration of oxygen vacancies at surface, and finely dispersed Ni particles with significantly higher metallic surface area as compared with catalysts prepared from commercial materials with similar compositions. Such unique and improved properties are reflected on the catalytic performance of the Ni/Ce0.9Sm0.1O2-δ nanowires towards ethanol steam reforming. The nanowires exhibited high yields for hydrogen production (∼60% of selectivity) and an exceptional stability with no loss of activity after 192 h of reaction at 550 °C. The reported results provide insights and can inspire high-yield production of nanostructured catalysts displaying controlled and superior properties that enable practical applications in heterogeneous catalysis.

Traditionally, bandgap materials are a prerequisite to photocatalysis since they can harness a reasonable range of the solar spectrum. However, the high impedance across the bandgap and the low concentration of intrinsic charge carriers have limited their energy conversion. By contrast, metallic nanoparticles possess a sea of free electrons that can effectively promote the transition to the excited state for reactions. Here, an atomic layer of a bimetallic concoction of silver–gold shells is precisely fabricated onto an Au core via a sonochemical dispersion approach to form a core–shell of Au–Ag that exploits the wide availability of excited states of Ag while maintaining an efficient localized surface plasmon resonance (LSPR) of Au. Catalytic results demonstrate that this mix of Ag and Au can convert solar energy to hydrogen at high efficiency with an increase of 112.5% at an optimized potential of −0.5 V when compared to light-off conditions under the electrochemical LSPR. This outperforms the commercial Pt catalysts by 62.1% with a hydrogen production rate of 1870 µmol g−1 h−1 at room temperature. This study opens a new route for tuning the range of light capture of hydrogen evolution reaction catalysts using fabricated core–shell material through the combination of LSPR with electrochemical means.

Active Pt-based catalysts at low temperature towards the preferential oxidation of carbon monoxide in hydrogen-rich stream reaction (CO-PROX) are of great importance for H-2-fueled fuel cells, but still remain a challenge. Herein, we propose a simple approach to synthesize a highly active Pt20Fe/CeO2 catalyst employing the borohydride reduction process. Transmission electronic microscopy revealed monodispersed 2.8 nm-Pt nanoparticles on CeO2, and the role of Fe species on the activity is discussed. The excellent CO conversion of 99.6% and CO2 selectivity of 92.3% carried out at ambient temperature meet the CO-PROX requirements for an adequate supply of hydrogen in fuel cell device. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Designing efficient anode CO-tolerant electrocatalysts is critical in low-temperature fuel cell catalysts fueled either by H-2/CO or alcohol. We demonstrate that the incorporation of TiO2 nanocubes (TiO2NCs) on Carbon Vulcan supports, followed by the synthesis of Pt NPs at their surface (Pt/TiO2NCs-C material), led to improvements in performance towards the electrooxidation of carbon monoxide, ethanol, methanol, ethylene glycol, and glycerol in acidic media relative to the commercial Pt/C and Pt/TiO2-C counterparts employing commercial TiO2. The nanocubes enabled changes in the electronic properties of Pt NPs while contributing to the bifunctional mechanism as compared to Pt/C and Pt/TiO2-C with commercial TiO2. Fuel cell experiments fed with H-2/CO steam showed that Pt/TiO2NCs-C employing nanocubes was resistant to CO-poisoning, yielding superior performance in operational conditions. The results reported herein have important implications for developing electrocatalysts with superior performances in PEMFCs.

The use of light as an external stimulus to control the enzyme activity is an emerging strategy that enables accurate, remote, and noninvasive biotransformations. In this context, immobilization of enzymes on plasmonic nanoparticles offers an opportunity to create light-responsive biocatalytic materials. Nevertheless, a fundamental and mechanistic understanding of the effects of localized surface plasmon resonance (LSPR) excitation on enzyme regulation remains elusive. We herein investigate the plasmonic effects on biocatalysis using Au nanospheres (AuNSp) and nanostars (AuNSt) as model plasmonic nanoparticles, lipase from Candida antarctica fraction B (CALB) as a proof-of-concept enzyme, and 808 nm as near-infrared light excitation. Our data show that LSPR excitation enables an enhancement of 58% in the enzyme activity for CALB adsorbed on AuNSt, compared with the dark conditions. This work shows how photothermal heating over the LSPR excitation enhances the CALB activity through favoring product release in the last step of the enzyme mechanism. We propose that the results reported herein shed important mechanistic and kinetic insights into the field of plasmonic biocatalysis and may inspire the rational development of plasmonic nanomaterial-enzyme hybrids with tailored activities under external light irradiation.

State of the art electrocatalysts for the hydrogen evolution reaction (HER) are based on metal nanoparticles (NPs). It has been shown that the localized surface plasmon resonance (LSPR) excitation in plasmonic NPs can be harvested to accelerate a variety of molecular transformations. This enables the utilization of visible light as an energy input to enhance HER performances. However, most metals that are active toward the HER do not support LSPR excitation in the visible or near-IR ranges. We describe herein the synthesis of gold-rhodium core-shell nanoflowers (Au@Rh NFs) that are composed of a core made up of spherical Au NPs and shells containing Rh branches. The Au@Rh NFs were employed as a model system to probe how the LSPR excitation from Au NPs can lead to an enhancement in the HER performance for Rh. Our data demonstrate that the LSPR excitation at 533 nm (and 405 nm) leads to an improvement in the HER performance of Rh, which depends on the morphological features of the Au Rh NFs, offering opportunities for optimization of the catalytic performance. Control experiments indicate that this improvement originates from the stronger interaction of Au@Rh NFs with H2O molecules at the surface, leading to an icelike configuration, which facilitated the HER under LSPR excitation.

A photoelectrochemical biosensing strategy for the highly sensitive detection of the flavonoid rutin was developed by synergizing the photoelectrocatalytic properties of hematite (α-Fe2O3) decorated with palladium nanoparticles (PdNPs) and the biocatalysis towards laccase-based reactions. The integration of α-Fe2O3.PdNPs with a polyphenol oxidase as a biorecognition element yields a novel biosensing platform. Under visible light irradiation, the photoactive biocomposite can generate a stable photocurrent, which was found to be directly dependent upon the concentration of rutin. Under the optimal experimental conditions, the cathodic photocurrent, measured at 0.33 V vs. Ag/AgCl, from the square-wave voltammograms presented a linear dependence on the rutin concentration within the range of 0.008–30.0 × 10−8 mol L−1 (sensitivity: 1.7 μA·(× 10−8 M−1)·cm−2), with an experimental detection limit (S/N = 3) of 8.4 × 10−11 mol L−1. The proposed biosensor device presented good selectivity towards rutin in the presence of various organic compounds and inorganic ions, demonstrating the potential application of this biosensing platform in complex matrices. This bioanalytical device also exhibited excellent operational and analytical properties, such as intra-day (standard deviation, SD = 0.21%) and inter-day (SD = 1.30%) repeatability, and long storage stability (SD = 2.80% over 30 days). Graphical abstract

The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles (NPs) in the visible and near-infrared ranges is currently at the forefront of improving photocatalytic performances via plasmonic photocatalysis. One bottleneck of this field is that the NPs that often display the best optical properties in the visible and near-infrared ranges are based on expensive noble metals such as silver (Ag) and gold (Au). While earth-abundant plasmonic materials have been proposed together with catalytic metals in antenna-reactor systems, their performances remain limited by their optical properties. Importantly, the synthesis of plasmonic photocatalysts remains challenging in terms of scalability while often requiring several steps, high temperatures, and special conditions. Herein, we address these challenges by developing a one-pot, gram-scale, room-temperature synthesis of earth-abundant plasmonic photocatalysts while improving their activities beyond what has been dictated by the LSPR excitation of the plasmonic component. We describe the mechanochemical synthesis of earth-abundant plasmonic photocatalysts by using MoO3 (antenna) and Au (reactor) NPs as a proof-of-concept example and demonstrate that the dual plasmonic excitation of antenna and reactor sites enables the tuning of plasmonic photocatalytic performances toward the reductive coupling of nitrobenzene to azobenzene as a model reaction. In addition to providing a pathway to the facile and gramscale synthesis of plasmonic photocatalysts, the results reported herein may open pathways to improved activities in plasmonic catalysis.

In this work, the effect of interfacial sites between Pd particles and Nb2O5 species is investigated by testing a series of Pd-Nb2O5/SiO2 catalysts with different niobium loadings for the HDO reaction of phenol in the gas phase. Important differences in the selectivity to deoxygenated product were observed depending on the presence of niobium oxide close to Pd particles, which reveals the key role of the type of active phase in the control of reaction steps. It was found that Pd/SiO2 catalyst promotes hydrogenation pathways, producing cyclohex-anone as the major product. For Pd-Nb2O5/SiO2 catalyst containing a Nb/Pd molar ratio of 0.5, a sharp increase in the selectivity to benzene is observed (7.5-fold). Increasing the Nb/Pd molar ratio, the formation of benzene is enhanced. The results showed that the Pd-Nb2O5 interface, composed by an oxophilic oxide in the perimeter of the metal particle, is responsible for the activation of the C-O bond, promoting the deoxygenation reaction.

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular transformations. This opens possibilities for the use of visible or near-IR light as a sustainable input to drive and control reactions when plasmonic nanoparticles supporting LSPR excitation in these ranges are employed as catalysts. Unfortunately, this is not the case for several catalytic metals such as palladium (Pd). One strategy to overcome this limitation is to employ bimetallic NPs containing plasmonic and catalytic metals. In this case, the LSPR excitation in the plasmonic metal can contribute to accelerate and control transformations driven by the catalytic component. The method reported herein focuses on the synthesis of bimetallic silver-palladium (Ag-Pd) NPs supported on ZrO2 (Ag-Pd/ZrO2) that acts as a plasmonic-catalytic system. The NPs were prepared by co-impregnation of corresponding metal precursors on the ZrO2 support followed by simultaneous reduction leading to the formation of bimetallic NPs directly on the ZrO2 support. The Ag-Pd/ZrO2 NPs were then used as plasmonic catalysts for the reduction of nitrobenzene under 425 nm illumination by LED lamps. Using gas chromatography (GC), the conversion and selectivity of the reduction reaction under the dark and light irradiation conditions can be monitored, demonstrating the enhanced catalytic performance and control over selectivity under LSPR excitation after alloying non-plasmonic Pd with plasmonic metal Ag. This technique can be adapted to a wide range of molecular transformations and NPs compositions, making it useful for the characterization of the plasmonic catalytic activity of different types of catalysis in terms of conversion and selectivity.

The understanding of relaxation dynamics of metallic nanoshells is important for a range of nanotechnological applications. In this work, we present a combined experimental-theoretical study of the relaxation dynamics of AgAu nanoshells. This was investigated using ultrafast pump-probe experiments resonant with the surface plasmon of the nanoshells, as well as via atomistic molecular dynamics simulations of relaxation and temperature-jump (DT-jump) processes. Both techniques were then discussed and complemented using a non-equilibrium statistical mechanical model. Data collected at low energies were consistent with our previously reported work and allowed the characterization of intrinsic electron-phonon coupling times (EPCT) and of the overall relaxation dynamics in terms of a two-temperature model. Data at intermediate and higher energies, in turn, showed a nonlinear dependence of EPCT as a function of the pump power, faster relaxation being observed at higher pump energies. In the limit of small DT-jumps, relaxation based on a two-temperature model is recovered, whereas in the limit of large DT-jumps, the relaxation becomes faster with increasing temperature change. The results reported here give insight on the ultrafast dynamics of AgAu nanoshells and might also be applied to other metallic systems, paving the way to the better understanding of relaxation dynamics of nanoparticles in general.

A photoelectrochemical biosensing strategy for the highly sensitive detection of the flavonoid rutin was developed by synergizing the photoelectrocatalytic properties of hematite (α-Fe

The development of time-resolved in situ approaches for monitoring mechanochemicaltransformations has revolutionized the field of mechanochemistry. Currently, the established insitu approaches greatly limit the scope of investigations that are possible. Here we develop a newapproach to simultaneously follow the evolution of bulk atomic and electronic structure during amechanochemical synthesis. This is achieved by coupling two complementary synchrotron-basedX-ray methods: X-ray absorption spectroscopy and X-ray diffraction. We apply this method toinvestigate the bottom-up mechanosynthesis of technologically important Au nanoparticles in thepresence of three different reducing agents. Moreover, we demonstrate how X-ray absorptionspectroscopy offers unprecedented insight into the early stage generation of growth species (e.g.monomers and clusters), which lead to the subsequent formation of nanoparticles. Theseprocesses are beyond the detection capabilities of diffraction methods. The approach is general,and not limited to monitoring NP mechanosynthesis. This combined X-ray approach paves theway to new directions in mechanochemical research of advanced electronic materials.

In this paper, K-doped δ-MnO2 nanoflowers decorated with Au nanoparticles (MnO2–Au) were synthesized by a hydrothermal method. To probe the effect of the band gaps in the MnO2 support over the surface plasmon resonance (SPR)-mediated catalytic conversions on Au nanoparticles (NPs), the oxidation of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) was used as a model reaction. We found that the PATP conversion was significantly higher for the MnO2–Au hybrid compared with its individual Au NPs under excitation at 633 nm. Furthermore, the activities of the MnO2–Au materials increased as the MnO2 support displayed higher K-doped levels, which led to narrower band gaps. These results could be explained based on the transfer of photogenerated electrons from MnO2 to Au, increasing the electron density in Au NPs and thus contributing to improved SPR-mediated activity. In this case, our observations show that tuning the band gaps can have a significant impact on SPR-mediated conversions, in which narrower band gaps should facilitate the charge transfer of SPR-excited charge carriers and thus lead to better performances. Our findings presented may provide important insights into the role of the support materials in plasmonic catalysis, indicating that, in addition to the control over several physical and chemical parameters (such as shape, surface area, defects, among others), the proper tuning of the band gap can serve as an effective strategy for the optimization of activities.

Gold nanoparticles (Au NPs) have been widely employed in catalysis. Here, we report on the synthesis and catalytic evaluation of a hybrid material composed of Au NPs deposited at the surface of magnetic cobalt ferrite (CoFe2O4). Our reported approach enabled the synthesis of well-defined Au/CoFe2O4 NPs. The Au NPs were uniformly deposited at the surface of the support, displayed spherical shape, and were monodisperse in size. Their catalytic performance was investigated towards the reduction of 4-nitrophenol and the selective oxidation of dimethylphenylsilane to dimethylphenylsilanol. The material was active towards both transformations. In addition, the LSPR excitation in Au NPs could be employed to enhance the catalytic performance, which was demonstrated in the 4-nitrophenol reduction. Finally, the magnetic support allowed for the easy recovery and reuse of the Au/CoFe2O4 NPs. In this case, our data showed that no significant loss of performance took place even after 10 reaction cycles in the oxidation of dimethylphenylsilane to dimethylphenylsilanol. Overall, our results indicate that Au/CoFe2O4 are interesting systems for catalytic applications merging high performances, recovery and re-use, and enhancement of activities under solar light illumination. © 2019 The Royal Society of Chemistry.

We develop herein plasmonic-catalytic Au-IrO

We reported the organic template-free synthesis of gold (Au) nanoparticles (NPs) supported on TiO2, SiO2, and Al2O3 displaying uniform Au sizes and high dispersions over the supports. The Au-based catalysts were prepared by a deposition–precipitation method using urea as the precipitating agent. In the next step, the solvent-free oxidation of benzyl alcohol was investigated as model reaction using only 0.08–0.05 mol% of Au loadings and oxygen (O2) as the oxidant. Very high catalytic performances (TOF up to 443,624 h−1) could be achieved. Specifically, we investigated their catalytic activities, selectivity, and stabilities as well as the role of metal–support interactions over the performances. The conversion of the substrate was found to be associated with the nature of the employed support as the Au NPs presented similar sizes in all materials. A sub-stoichiometric amount of base was sufficient for the catalyst activation and the observation of the catalysts profile over the time enable insights on their recyclability performances. We believe this reported method represents a facile approach for the synthesis of uniform Au-supported catalysts displaying high performances.

By a combination of theoretical and experimental design, we unraveled the effect of {111} and {100} surface facets on the electrocatalytic sensing activities and stabilities of metal oxides by employing Cu2O crystals as a model substrate and glucose as the analyte. We started by theoretically investigating the potential energy curves for the glucose interaction with the Cu2O {111} and {100} surface facets. We found that the glucose interaction energy was significantly higher for the {100} facets than for the {111} facets. Then, we experimentally observed that their electrocatalytic sensing performance displayed shape-dependent behavior. While the catalytic activities followed the order cubes > cuboctahedrons > octahedrons, their stabilities showed the opposite trend. The higher catalytic activity enabled by the {100} facets is explained by their stronger interaction with glucose. On the other hand, the higher stability allowed by the {111} facets is justified by their lower concentration of oxygen vacanci...

Manganese oxide (MnO2) nanomaterials represent a promising low-cost electrocatalyst material for hydrogen peroxide (H2O2) production by the oxygen reduction reaction (ORR). In this material, the introduction of oxygen vacancies is an effective strategy for boosting their electrocatalytic activities. Although the importance of oxygen defects in MnO2-based catalysts has been shown in some electrochemical systems, a facile strategy for controlling the number oxygen vacancies in MnO2-based catalysts and the systematic investigation of the effect of the vacancies on their electrocatalytic activities towards the ORR and H2O2 electrogeneration remains limited. Here, we describe the synthesis of hybrid materials composed of MnO2 nanoflowers supported on Vulcan XC-72 carbon in which the concentration of the surface oxygen vacancy sites was increased. Surprisingly, we found a volcano-type relationship between the activity and the MnO2 loading. RRDE experiments showed the greatest formation of hydroperoxide ion in alkaline media for MnO2/C 3% on carbon, displaying the highest electrocatalytic activity. This result was maintained for hydrogen peroxide during the electrolytic process using gas diffusion electrodes in acidic media. We suggest that the optimized catalytic activities observed for the MnO2/C 3% catalyst are a result of (i) the high concentrations of oxygen vacancies at the catalyst surface, which promote the generation of highly catalytically active sites towards the ORR; (ii) their strong metal oxide-carbon interactions with modification of the carbon surface; (iii) the high surface area observed for the MnO2 nanoflowers supported on Vulcan XC-72; and (iv) the use of a MnO2 nanostructure displaying well-defined shapes and uniform sizes (with petals measuring 10 ± 5 nm in width) displaying a uniform dispersion over the carbon support. We believe the results described herein shed new light on the understanding of the role of the oxygen vacancies in the electrogeneration of H2O2, which has important implications for the design of MnO2-based electrocatalysts.

We described herein the facile synthesis of sub-15 nm CeO2 nanowires based on a hydrothermal method without the use of any capping/stabilizing agent, in which an oriented attachment mechanism took place during the CeO2 nanowire formation. The synthesis of sub-15 nm CeO2 nanowires could be achieved on relatively large scales (∼2.6 grams of nanowires per batch), in high yields (>94%), and at low cost. To date, there are only a limited number of successful attempts towards the synthesis of CeO2 nanowires with such small diameters, and the reported protocols are typically limited to low amounts. The nanowires displayed uniform shapes and sizes, high surface areas, an increased number of oxygen defects sites, and a high proportion of Ce3+/Ce4+ surface species. These features make them promising candidates for oxidation reactions. To this end, we employed the selective oxidation of aniline as a model transformation. The sub-15 nm CeO2 nanowires catalyzed the selective synthesis of nitrosobenzene (up to 98% selectivity) from aniline at room temperature using H2O2 as the oxidant. The effect of solvent and temperature during the catalytic reaction was investigated. We found that such parameters played an important role in the control of the selectivity. The improved catalytic activities observed for the sub-15 nm nanowires could be explained by: i) the uniform morphology with a typical dimension of 11 ± 2 nm in width, which provides higher specific surface areas relative to those of conventional catalysts; ii) the significant concentration of oxygen vacancies and high proportion of Ce3+/Ce4+ species at the surface that represent highly active sites towards oxidation reactions; iii) the crystal growth along the (110) highly catalytically active crystallographic directions, and iv) the mesoporous surface which is easily accessible by liquid substrates. The results reported herein demonstrated high activities under ambient conditions, provided novel insights into selectivities, and may inspire novel metal oxide-based catalysts with desired performances.

Plasmonic catalysis takes advantage of the surface plasmon resonance (SPR) excitation to drive or accelerate chemical transformations. In addition to the plasmonic component, the control over metal-support interactions in these catalysts is expected to strongly influence the performances. For example, CeO2 has been widely employed towards oxidation reactions due to its oxygen mobility and storage properties, which allow for the formation of Ce3+ sites and adsorbed oxygen species from metal-support interactions. It is anticipated that these species may be activated by the SPR excitation and contribute to the catalytic activity of the material. Thus, a clear understanding of the role played by the SPR-mediated activation of surface oxide species at the metal-support interface is needed in order to take advantage of this phenomenon. Herein, we describe and quantify the contribution from active surface oxide species at the metal-support interface (relative to O2 from air) to the activities in green SPR-mediated oxidation reactions. We employed CeO2 decorated with Au NPs (Au/CeO2) as a model plasmonic catalyst and the oxidation of p-aminothiophenol (PATP) and aniline as proof-of-concept transformations. We compared the results with SiO2 decorated with Au NPs (Au/SiO2), in which the formation of surface oxide species at the metal-support interface is not expected. We found that the SPR-mediated activation of surface oxide species at the metal-support interface in Au/CeO2 played a pivotal role in the detected activities, being even higher than the contribution coming from the activation of O2 from air.

Plasmonic photocatalysis has emerged as a prominent and growing field. It enables the efficient use of sunlight as an abundant and renewable energy source to drive a myriad of chemical reactions. For instance, plasmonic photocatalysis in materials comprising TiO2 and plasmonic nanoparticles (NPs) enables effective charge carrier separation and the tuning of optical response to longer wavelength regions (visible and near infrared). In fact, TiO2 -based materials and plasmonic effects are at the forefront of heterogeneous photocatalysis, having applications in energy conversion, production of liquid fuels, wastewater treatment, nitrogen fixation, and organic synthesis. This review aims to comprehensively summarize the fundamentals and to provide the guidelines for future work in the field of TiO2 -based plasmonic photocatalysis comprising the above-mentioned applications. The concepts and state-of-the-art description of important parameters including the formation of Schottky junctions, hot electron generation and transfer, near field electromagnetic enhancement, plasmon resonance energy transfer, scattering, and photothermal heating effects have been covered in this review. Synthetic approaches and the effect of various physicochemical parameters in plasmon-mediated TiO2 -based materials on performances are discussed. It is envisioned that this review may inspire and provide insights into the rational development of the next generation of TiO2 -based plasmonic photocatalysts with target performances and enhanced selectivities.

CoFe2O4 and NiFe2O4 nanoparticles (NPs) represent promising candidates for biomedical applications. However, in these systems, the knowledge over how various physical and chemical parameters influence their cytotoxicity remains limited. In this article, we investigated the effect of different calcination temperatures over cytotoxicity of CoFe2O4 and NiFe2O4 NPs, which were synthesized by a sol–gel proteic approach, toward L929 mouse fibroblastic cells. More specifically, we evaluated and compared CoFe2O4 and NiFe2O4 NPs presenting low crystallinity (that were calcined at 400 and 250 °C, respectively) with their highly crystalline counterparts (that were calcined at 800 °C). We found that the increase in the calcination temperature led to the reduction in the concentration of surface defect sites and/or more Co or Ni atoms located at preferential crystalline sites in both cases. A reduction in the cytotoxicity toward mouse fibroblast L929 cells was observed after calcination at 800 °C. Combining with induc...

Here, we have systematically investigated how the nature of the support influenced the oxygen mobility and activities in catalysts comprised of AgPt nanoshells deposited over inorganic oxides. We first synthesized AgPt nanoshells by galvanic replacement reaction between Ag nanospheres and PtCl6 2− (aq) combined with Pt reduction using hydroquinone as an auxiliary reducing agent. The nanoshells were then supported over TiO2, Al2O3 and CeO2. Through this methodology, we prepared materials with similar metallic nanoparticle AgPt compositions (~0.99 wt% Pt), sizes (43 ± 2 nm diameter), spherical shapes, surface morphologies, number of active sites $$ (\sim4.5\;\upmu{\text{mol}}\;{\text{g}}_{{{\text{cat}} .}}^{ - 1} ) $$ and uniform distribution over the supports, differing only in terms of the nature of the support. The oxide reduction temperature, its capability of re-oxidation and the presence of oxygen mobility were strongly dependent on the metal–support interaction between AgPt nanoshells and oxide supports. These properties have significantly influenced their catalytic performances toward the CO oxidation. At 230 °C, the CO oxidation TOF was 40.4 ± 0.4, 6.9 ± 1, 1.4 ± 0.8 min−1 for AgPt/CeO2, AgPt/TiO2, AgPt/Al2O3, respectively. These differences were attributed to the concentration of oxygen vacancies in each catalyst, which presented exactly the same trend as that of the catalytic activities. Our results may have important contributions to the design of highly active metal oxide-based catalysts toward gas-phase oxidation transformations.

Undergraduate-level laboratory experiments that involve the synthesis of nanomaterials with well-defined/controlled shapes are very attractive under the umbrella of nanotechnology education. Herein we describe a low-cost and facile experiment for the synthesis of Cu(OH)2 and CuO nanowires comprising three main parts: (i) synthesis of Cu(OH)2 nanowires by a precipitation approach followed by a calcination step that converts Cu(OH)2 to CuO; (ii) use of Cu(OH)2 and CuO nanowires as model systems to explore a variety of characterization techniques relevant in the context of solid-state chemistry, materials chemistry, and nanoscience; and (iii) presentation/discussion of the data. Other learning objectives include probing of chemical transformations at the nanoscale and the use of concepts borrowed from coordination chemistry to understand the formation mechanism of Cu(OH)2 and CuO nanowires from a Cu2+(aq) precursor. This experiment can be performed with a relatively simple laboratory infrastructure and with ...