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The interaction of metallic nanoparticles with light excites a local surface plasmon resonance (LSPR). This phenomenon enables the transfer of hot electrons to substrates that release Reactive Oxygen Species (ROS). In this context, the present study was aimed at enhancing the antibacterial effect of citrate-covered silver nanoparticles (AgNPs), which already possess excellent antimicrobial properties, via LSPR excitation with visible LED against Pseudomonas aeruginosa, one of the most refractory organisms to antibiotic treatment. The Minimum Inhibitory Concentration (MIC) of AgNPs was 10 μg/ml under dark conditions and 5 μg/ml under light conditions. The combination of light and AgNPs led to 100% cell death after 60 minutes. Quantification of ROS via flow cytometry showed that LSPR stimulated AgNPs increased intracellular ROS concentration by 4.8-fold, suggesting that light-exposed AgNPs caused cell death via ROS production. Light exposition caused a small release of silver ions (0.4%) reaching a maximum after 6 hours. This indicates that silver ions play at most a secondary role in P. aeruginosa death. Overall, the results presented here show that LSPR generation from AgNPs by visible light enhances the antimicrobial activity of silver nanoparticles and can be an alternative for the treatment of topic infections caused by antibiotic-resistant bacteria such as P. aeruginosa.

Mechanochemistry is a promising alternative to solution-based protocols across the chemical sciences, enabling different types of chemistries in solvent-free and environmentally benign conditions. The use of mechanical energy to promote physical and chemical transformations has reached a high level of refinement, allowing for the design of sophisticated molecules and nanostructured materials. Among them, the synthesis of noble metal nanoparticles deserves special attention due to their catalytic applications. In this review, we discuss the recent progress on the development of mechanochemical strategies for the controlled synthesis of noble metal nanostructures. We start by covering the fundamentals of different preparation routes, namely top-down and bottom-up approaches. Next, we focus on the key examples of the mechanochemical synthesis of non-supported and supported metal nanoparticles as well as hybrid nanomaterials containing noble metals. In these examples, in addition to the principles and synthesis mechanisms, their performances in catalysis are discussed. Finally, a perspective of the field is given, where we discuss the opportunities for future work and the challenges of mechanochemical synthesis to produce well-defined noble metal nanoparticles.

Cited By :5 Export Date: 15 February 2021 CODEN: JSMME Correspondence Address: Liu, Y.; Department of Orthodontics, China; email: liuyuehua@fudan.edu.cn Although various efforts have been made to develop effective treatments for alveolar bone defect, alveolar regeneration has been emerging as the one with the most potential Herein, we investigated the potential of gelatin methacrylate (GelMA) hydrogels-encapsulated human periodontal ligament stem cells (hPDLSCs) to regenerate alveolar bone. The easy, rapid, and cost-effective nature of GelMA hydrogels makes them a promising mode of stem cell-delivery for clinically relevant alveolar bone regeneration. More importantly, GelMA hydrogels provide an optimal niche for hPDLSCs proliferation, migration and osteogenic differentiation, which are critical for alveolar bone regeneration. In this study, we examined the microstructure of GelMA hydrogels, and identified a highly porous and interconnected network. Compressive test of GelMA hydrogels showed that the stress reached a maximum value of 13.67 ± 0.03 kPa when the strain reached 55%. The maximum values of swelling ratio were 700 ± 47% at the fifth hour. The proliferation rate of hPDLSCs in the GelMA hydrogels resembled that in 2D culture and gradually increased. We established a critical-sized rat model of alveolar bone defects, and applied Micro-CT to assess new bone formation. Compared to the control group, there was substantial bone regeneration in the GelMA + hPDLSCs group at both 4 and 8 weeks after the operation. Histological analysis results were consistent with Micro-CT results. Our study demonstrates that the GelMA hydrogels-encapsulated hPDLSCs have a significant alveolar regenerative potential, and may represent a new strategy for the therapy of alveolar bone defects. [Figure not available: see fulltext.]. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

We develop herein plasmonic-catalytic Au-IrO2 nanostructures with a morphology optimized for efficient light harvesting and catalytic surface area; the nanoparticles have a nanoflower morphology, with closely spaced Au branches all partially covered by an ultrathin (1 nm) IrO2 shell. This nanoparticle architecture optimizes optical features due to the interactions of closely spaced plasmonic branches forming electromagnetic hot spots, and the ultra-thin IrO2 layer maximizes efficient use of this expensive catalyst. This concept was evaluated towards the enhancement of the electrocatalytic performances towards the oxygen evolution reaction (OER) as a model transformation. The OER can play a central role in meeting future energy demands but the performance of conventional electrocatalysts in this reaction is limited by the sluggish OER kinetics. We demonstrate an improvement of the OER performance for one of the most active OER catalysts, IrO2, by harvesting plasmonic effects from visible light illumination in multimetallic nanoparticles. We find that the OER activity for the Au-IrO2 nanoflowers can be improved under LSPR excitation, matching best properties reported in the literature. Our simulations and electrocatalytic data demonstrate that the enhancement in OER activities can be attributed to an electronic interaction between Au and IrO2 and to the activation of Ir-O bonds by LSPR excited hot holes, leading to a change in the reaction mechanism (rate-determinant step) under visible light illumination.

We report the optimization of both the support and the active phase of PdPt NPs supported on TiO2 nanowires to obtain highly active electro/photocatalysts for the oxygen reduction and water splitting reactions. This system displayed strong metal-support interactions, high concentration of oxygen vacancies, and PdPt NP were similar to 2 nm in size. By optimizing the loading of PdPt, both the photo- and electrocatalytic activities were improved compared to commercial materials. Interestingly, a volcano plot was obtained from the activity and the PdPt composition, and the Pd0.22P0.78-TiO2/C sample afforded the optimal performance. For instance, the amount of hydrogen produced from water splitting was 11.6 mmol/g(catalyst). For the ORR, the activity was similar to a commercial Pt catalyst, but a lower E-onset (0.87 V-RHE vs w 0.95 V-RHE) was detected. The variations in the activities with the composition correlated well with the variations in the electronic effects and the concentration of oxygen vacancies.

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 polymer microbead-supported metal and metal oxide nanoparticles and their application as recoverable nanocatalysts for reactions under batch and flow conditions. Au, Ag and Fe3O4 nanoparticles were prepared directly at the surface of benzylamine-coated spherical polymer beads in water by using low energy microwave radiation. The morphology and size of the nanoparticles, and therefore their catalytic properties, were tuned by modifying the bead surface using betalamic acid, an antioxidant from plant origin. The catalytic performance and recovery of these environmentally friendly nanocatalysts was demonstrated towards model redox chemical transformations. We anticipate the results reported herein can provide important insights into the controlled and facile synthesis of microparticle supported nanocatalysts under mild conditions.

A mechano-colloidal approach was developed to produce Au nano-tadpoles. It comprises the generation of seeds by ball-milling from a solid mixture containing a precursor, reductant, and capping agent, followed by the dispersion of this mixture in water leading to seeded-growth to generate the target nanoparticle morphology.

Sodium (Na)- and potassium (K)-doped δ-MnO

Due to the complexity and heterogeneity of tumors, the therapeutic effectiveness of monomodal phototherapy is still limited. As aggressive tumors become more vulnerable to ferroptosis, synergistic ferroptosis/phototherapy has recently emerged as a promising noninvasive anti-cancer strategy. However, desirable phototherapeutic materials exhibiting altogether the required properties including excellent photothermal/photocatalytic performance, long-term biosafety and ferroptosis-inducing capability remains challenging. Herein, the present study proposed a novel strategy to construct a multifunctional nanoplatform based on band gap engineering of semiconductor nanomaterials for synergistic phototherapy. Specifically, a novel alkali-metal doped δ-MnO2 nanoflower with tunable band gap and controllable degradability was developed to realize a highly efficient and safe synergistic ferroptosis/photothermal/photocatalytic therapy. The desirable near-infrared light (NIR)-excited photothermal/photocatalytic properties of MnO2 nanoflowers were endowed and enhanced by narrowing band gap via increasing the doping alkali metal ionic radius (Mg2+

Metallic nanoparticles have been extensively studied towards applications in catalysis. Among the several methods for their controlled synthesis, galvanic replacement is particularly attractive as it enables the production of bimetallic and hollow nanomaterials displaying ultrathin walls in a single reaction step. This procedure is versatile, but final morphologies are often limited to shapes that represent the hollow analogues of the starting template nanocrystals. For catalytic applications, it is highly desirable to broaden the scope of physicochemical control that can be achieved by this method. This feature article discusses recent strategies developed in our group for the synthesis of hollow bimetallic nanomaterials by galvanic replacement that enable a further level of control over surface morphologies and composition. We begin by briefly explaining the fundamentals of the conventional galvanic replacement reaction between Ag and AuCl4-. This is one of the most characteristic galvanic replacement reactions, and it can be tuned to create a huge variety of nanoparticle morphologies. We will discuss how advanced electron microscopy characterization enables us to uncover surface-segregation behavior as a function of compositions, and relate this to the detected catalytic performance. We will also discuss how galvanic replacement can be extended to trimetallic compositions, leading to improvements in catalytic activities compared to mono or bimetallic counterparts. Furthermore, we will show how surface morphology, size, and anisotropic growth can be controlled by tuning the temperature during the synthesis and by combining galvanic replacement reaction with co-reduction. Finally, we will demonstrate how these approaches are promising for large-scale synthesis of controlled hollow nanostructures and their incorporation into supports to produce catalysts at the gram-scale. We believe the developments described herein shed important insights and may inspire the development of sophisticated and controlled nanomaterials at relatively larger scales for catalytic applications.

Organophosphate (OP) detoxification is a worldwide problem due to the high stability of P–O bonds. Here, we designed several imidazole-coated nanocatalysts targeted towards the cleavage of OP and thus their detoxification. Specifically, Ag, Au and bimetallic AgAu nanoparticles (NPs) supported on SiO2 were functionalized with methimazole (MTZ), which comprises thiol and imidazole groups, foreseeing enabling freely available imidazole groups. Raman analyses indicate that MTZ interacts preferably via its sulfur atom over Au NPs and via the nitrogen of the imidazole ring over Ag NPs. The MTZ-derived nanocatalysts were effective towards OP cleavage. For instance, rate enhancements of 108 fold were obtained for the toxic pesticide Paraoxon, compared to the uncatalyzed reaction. Interestingly, Au-derived nanocatalysts were significantly more effective since the imidazole group is free to react with the OP, which is not possible when Ag–N interactions take place.

AgPd nanoshells (AgPd NSs) were used as dual catalysts for hydrogen production and reduction of organic compounds in a one-pot protocol. AgPd NSs were very efficient catalysts for the reduction of several functional groups, including alkenes, alkynes, imines, nitro compounds, and azides. Excellent chemoselectivities were observed for α,β-unsaturated ketones, esters, and cinnamonitrile. Also, deuterium-labeled compounds were prepared by using D2O instead of H2O. A packed-bed reactor containing the immobilized AgPd NSs in silica (AgPd/SiO2) was designed to be used in continuous-flow conditions. An optimized flow system with AgPd NSs was able to give the desired compounds in high conversions with 30–60 min residence time (tR).

Bimetallic and asymmetric heterostructures represent an emerging class of nanomaterials. They allow for the combination of distinct compositions, shapes, and physicochemical features within a single particle, thus leading to intriguing properties. We demonstrate herein the synthesis of asymmetric Au@Pd-Au tadpoles having a tail comprising a single Au nanorod and a spherical head composed of core@shell Au@Pd decorated with small Au NPs. This material was produced by a combination of Au deposition and Ostwald ripening at the surface of Au@Pd core-shell NPs. The overall morphology could be tailored both by controlling the amount of AuCl4− employed as precursor and by altering the reaction time, leading to shape-dependent optical and catalytic properties. We believe that these results may have important implications for the synthesis nanomaterials having novel morphologies and complex functionalities that can combine properties from their different components.

This paper describes a systematic investigation on the synthesis of CeO2 supported on SiO2 by two different methods: (i) the in situ incorporation of CeO2 onto MCM-41 and (ii) wet impregnation. We were interested in investigating how the CeO2 preparation could influence their physicochemical properties and catalytic performances towards the benzene, toluene, and o-xylene (BTX) oxidation reactions. Our results showed that the catalytic performances were strongly dependent on the synthetic approach, in which the CeO2–MCM-41 material prepared by the in situ incorporation showed better BTX oxidation activities than the CeO2-based catalysts prepared by conventional wet impregnation. This result could be assigned to the higher specific surface area, better interaction between CeO2 and the support, improved Ce4+/Ce3+ redox process, and higher concentration of oxygen vacancies as enabled by the in situ approach. The influence of CeO2 content in the ordering of the SiO2 mesoporous structure was also demonstrated.

Ternary nanocomposites have been widely studied as new design-controlled materials for the next generation of high-performance electrochemical electrodes. However, several drawbacks have hampered their widespread exploration, especially regarding the understanding of the influence in the synthesis methodology over the performances. We investigate herein the properties of a novel ternary nanocomposite GO/WO3NW/PAni, derived from two distinct synthesis methods: chemical and electrochemical. The obtained materials were fully characterized, and their electrochemical performance were compared according to the method employed for their synthesis. Our results demonstrated that the type of synthesis influences directly on the final structure of the ternary nanocomposite. The electrochemically synthesized nanocomposite (E-GO/WO3NW/PAni) presented a disorganized structure, which increases the doping level in the polymeric chain, the porosity, and also allows a superior synergistic effect between the GO, WO3NW and PAni when compared to the chemical synthesized nanocomposite (C-GO/WO3NW/PAni). As a result of these significant differences, E-GO/WO3NW/PAni presented higher specific capacitance, of 0.62 F cm−2, and higher cyclability when compared to the C-GO/WO3NW/PAni, that has achieved values up to 0.50 F cm−2. These remarkable results show directly the influence and importance of the optimization of synthetic methods over the performances, producing nanocomposites with different structures and good synergic effect that can be regarded as promising materials for energy storage field.

Selective hydrogenation of alkynes to alkenes and reductive amination are industrially important reactions to synthesize a variety of fine and bulk chemicals. We report herein on a green and convenient approach for Z-alkenes and secondary amines using gold catalyst and formic acid (FA) as a green reductant. Furthermore, we highlight that the key to successfully obtain high reaction rates is to use an appropriate amine, which acts cooperatively with the gold surface, to activate formic acid. Studies with deuterium-labeled hydrogen donors gave insights that the decomposition of Au-formate species is involved in the rate-determining step. Moreover, various valuable secondary amines could be synthetized from readily available nitro and carbonyl compounds. This new strategy provides a cleaner, safer, more efficient and selective way to catalyze the synthesis of Z-alkenes and valuable amines.

In this work we propose the use of statistical mixture design in the construction of a biosensor device based on graphite oxide, platinum nanoparticles and biomaterials obtained from Botryosphaeria rhodina MAMB-05. The biosensor was characterized by electrochemical impedance spectroscopy. Under optimized experimental parameters by factorial design, the biosensor was applied to the voltammetric determination of chlorogenic acid (CGA) measured as 5-O-caffeoylquinic acid (5-CQA). The biosensor response was linear (R2 = 0.998) for 5-CQA in the concentration range 0.56–7.3 µmol L−1, with limit of detection and quantification of 0.18 and 0.59 µmol L−1, respectively. The new biosensing device was applied to quality control analysis based upon the determination of CGA content in specialty and traditional coffee beverages. The results indicated that specialty coffee had a significantly higher content of CGA. Principal component analysis of the voltammetric fingerprint of brewed coffees revealed that the laccase-based biosensor can be used for their discrimination.

Noble-metal nanoparticles have been widely employed in catalysis. As catalytic properties are dependent on their physical/chemical parameters, strategies for their controlled synthesis and the understanding of performance relationships have gained attention. In this review, we discuss developments on well-defined noble-metal nanoparticles focusing on relationships between performance and physical/chemical features. We begin with the control over shape, composition, and size. Then, we focus on nanoparticles with hollow interiors, which provide further possibilities for performance optimization. We provide a case-by-case discussion to illustrate how, in addition to the hollow interiors, the control over their composition, size, and surface morphology relate to catalytic performance.

PtSnNi electrocatalysts (60: 40: 40 mass ratio) supported on Vulcan® XC-72 (Cabot) carbon and COOH-functionalized multiwalled carbon nanotubes (Cheaptubes®) with 15% of metal loading were prepared. The nanoparticles size of 2–3 nm for both supports was estimated by HRTEM. In the direct ethanol fuel cell experiments, PtSnNi/C presents 50 mA cm−2 reaching the maximum power density (MPD) of 12 mW cm−2 and decreasing at higher currents, while PtSnNi/MWCNT-COOH obtains similar values of MPD (60 mA cm−2), but keeping the best performance. By GC (gas chromatography) technique, it was possible to observe that the electrocatalyst supported on MWCNT-COOH favored the ethanol oxidation to acetaldehyde and acetic acid, although the material supported on Vulcan® XC-72 carbon presented almost 100% of selectivity for acetaldehyde. This behavior was maintained also when the current of 0.1 A was applied for 80 min. For the PtSnNi/C electrocatalyst, the selectivity to only acetaldehyde can be related to Sn and Ni dissolution process that can become the electrocatalytic activity similar to Pt/C, decreasing the power density as observed in our experiments. Established by EDS analysis, after 80 min of polarization, the Ni and Sn relative atomic ratio was lower on the catalytic anodic layer of PtSnNi/C than on PtSnNi/MWCNT-COOH.

Pt nanoparticles (Pt NPs) supported on carbon have been widely employed as electrocatalysts toward oxygen reduction reaction. The development of more efficient electrocatalysts that enable one to reduce or even not require the use of Pt is a central challenge. In addition to the control over the physical and chemical features of Pt NPs, metal support interactions can be employed to enhance activities via the generation and exposure of surface-active sites. In this context, we report herein the development of electrocatalysts composed of Pt NPs supported on TiO2 microspheres, that were subsequently impregnated onto carbon. We have found that, by optimizing the loading of Pt at the TiO2 surface, the electrocatalytic activity toward the ORR could be improved compared to that of the commercial Pt/C (E-TEK) material, even at lower Pt loadings. The enhancement in activities could be assigned to the balance between Pt loading and generation of reactive surface sites, such as adsorbed oxygenated species. Moreover, the utilization of TiO2 as support enabled improved stabilities relative to Pt/C (E-TEK). We believe that the results described herein may inspire the development of electrocatalysts for the ORR with improved activities and stabilities.

Tandem reactions consist of a sequence of two or more distinct transformations that can be achieved in a single synthetic step. A new article by Sun and colleagues demonstrates how the catalytic properties of bimetallic nanoparticles can be rationally optimized to enable the one-pot synthesis of polybenzoxazole (PBO).

Sodium (Na)- and potassium (K)-doped δ-MnO2, which presented different band gaps, were synthesized by a hydrothermal method. Then, uniform Au nanoparticles (NPs) were deposited on MnO2 to form metal-semiconductor nano-heterojunctions (MnO2-Au). By comparing their temperature-dependent thermal catalytic performances, p-aminothiophenol to p, p'-dimercaptoazobenzene conversion was used as proof-of-concept transformations. MnO2-Au hybrid materials demonstrated better thermal catalytic performances relative to individual Au NPs. Meanwhile, K-doped MnO2-Au, with a MnO2 support displaying a narrower bandgap, displayed superior catalytic activities relative to Na-doped MnO2-Au. To get the same catalytic performance by individual Au NPs, it can be ∼50 K less by Na-doped MnO2-Au and ∼100 K less by K-doped MnO2-Au. The enhancement is mainly attributed to the thermally excited electrons in MnO2, which were transferred to Au NPs. The additional electrons in Au NPs increase the electron density and thus contribute to the improvement of thermal catalysis. Our findings show that the establishment of a nano-heterojunction formed by metal NPs on a semiconductor support has a significant impact on thermal catalysis, where a narrower band gap can facilitate thermally excited carriers and thus bring about better catalytic performances. Thus, the results presented here shed light on the design of a nano-heterojunction catalyst to approach reactions with superior performance under moderate conditions.

Among the several classes of chemical reactions, the green oxidation of organic compounds has emerged as an important topic in nanocatalysis. Nonetheless, examples of truly green oxidations remain scarce due to the low activity and selectivity of reported catalysts. In this paper, we present an approach based on the optimization of both the support material and the active phase to achieve superior catalytic performances towards green oxidations. Specifically, our catalysts consisted of ultrasmall Au NPs deposited onto MnO2 nanoflowers. They displayed hierarchical morphology, large specific surface areas, ultrasmall and uniform Au NPs sizes, no agglomeration, strong metal-support interactions, oxygen vacancies, and Auδ+ species at their surface. These features led to improved performances towards the green oxidations of CO, benzene, toluene, o-xylene, glucose, and fructose relative to the pristine MnO2 nanoflowers, commercial MnO2 decorated with Au NPs, and other reported catalysts. We believe that the catalytic activities, stabilities, and mild/green reaction conditions described herein for both gas and liquid phase oxidations due to the optimization of both the support and active phase may inspire the development of novel catalytic systems for a wealth of sustainable transformations.

Further improvements and mechanistic understanding of the electrocatalytic enhancements towards the oxygen reduction reaction (ORR) are required to meet cost/energy demands and thus enable their practical applications in polymer electrolyte fuel cells. An investigation of the electrocatalytic enhancement mechanisms and stability of controlled electrocatalysts comprised Pt nanoparticles supported on TiO2/C materials was herein performed. The catalysts were prepared by depositing Pt, over the surface of TiO2 colloidal spheres. These materials were then supported onto Vulcan carbon to produce Pt/TiO2/C. The effect of Pt coverage at the TiO2 surface as well as the Pt/TiO2 loading on carbon over their ORR activity and stability were investigated. Results indicate that the control over Pt coverage at the surface played a pivotal role on activity optimization, in which an association between Pt content at the TiO2 surface and ORR activity was established. The ORR activity and stability were superior as compared to commercial Pt/C (E-TEK). Variations in catalytic activity could be correlated with the morphological features and with the concentration of surface reactive groups. Results described herein suggest that the understanding of the electrocatalytic enhancement mechanism together with the controlled synthesis of Pt-based nanomaterials may lead to tailored surface properties and thus ORR activities.

The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles has been used to accelerate several catalytic transformations under visible-light irradiation. In order to fully harness the potential of plasmonic catalysis, multimetallic nanoparticles containing a plasmonic and a catalytic component, where LSPR-excited energetic charge carriers and the intrinsic catalytic active sites work synergistically, have raised increased attention. Despite several exciting studies observing rate enhancements, controlling reaction selectivity remains very challenging. Here, by employing multimetallic nanoparticles combining Au, Ag, and Pt in an Au@Ag@Pt core–shell and an Au@AgPt nanorattle architectures, we demonstrate that reaction selectivity of a sequential reaction can be controlled under visible light illumination. The control of the reaction selectivity in plasmonic catalysis was demonstrated for the hydrogenation of phenylacetylene as a model transformation. We have found that the localized interaction between the triple bond in phenylacetylene and the Pt nanoparticle surface enables selective hydrogenation of the triple bond (relative to the double bond in styrene) under visible light illumination. Atomistic calculations show that the enhanced selectivity toward the partial hydrogenation product is driven by distinct adsorption configurations and charge delocalization of the reactant and the reaction intermediate at the catalyst surface. We believe these results will contribute to the use of plasmonic catalysis to drive and control a wealth of selective molecular transformations under ecofriendly conditions and visible light illumination.

There is a growing interest in controlling the synthesis of colloidal metal nanocrystals and thus tailoring their properties toward various applications. In this context, choosing an appropriate combination of reagents (e.g., salt precursor, reductant, capping agent, and stabilizer) plays a pivotal role in enabling the synthesis of metal nanocrystals with diversified sizes, shapes, and structures. Here we present a comprehensive review that highlights one of the key reagents for the synthesis of metal nanocrystals via chemical reduction: the reductants. We start with a brief introduction to the compounds commonly employed as reductants in the colloidal synthesis of metal nanocrystals by showing their oxidation half-reactions and the corresponding oxidation potentials. Then we offer specific examples pertaining to the controlled synthesis of metal nanocrystals, followed by some fundamental aspects covering the general mechanisms of metal ion reduction based on the Marcus Theory. Afterwards, we present a case-by-case discussion on a wide variety of reductants, including their major properties, reduction mechanisms, and additional effects on the final products. We illustrate these aspects by selecting key examples from the literature and paying close attention to the underlying mechanism in each case. At the end, we conclude by summarizing the highlights of the review and providing some perspectives on future directions.

A glassy carbon electrode was modified with a TiO2-gold nanoparticle hybrid integrated with multi-walled carbon nanotubes in a dihexadecylphosphate film (TiO2-Au NP-MWCNT-DHP/GCE) and applied to amperometric determination of ascorbic acid (AA). The modified sensor displays fast charge transfer and shows an irreversible anodic behavior for AA by cyclic voltammetry. Under optimal experimental conditions and using amperometry at 0.4 V, the analytical curve presented a statistical linear concentration range for AA from 5.0 to 51 μmol L-1, with a limit of detection of 1.2 μmol L-1. The electrode was successfully applied to the determination of AA in pharmaceutical and fruit juice without the need for major pretreatment of samples. Graphical abstract Schematic of a new sensing platform for ascorbic acid (AA). It is based on a glassy carbon electrode (GCE) modified with TiO2-Au nanoparticles integrated into carbon nanotubes in a dihexadecylphosphate film. The sensor was applied to amperometric determination of AA in juice and pharmaceutical samples.

This work describes the electrochemical degradation of Reactive Black 5 (RB5) by two methods: electrochemical and photo-assisted electrochemical degradation with and without a Fenton reagent. Two anodes were used, Pt and boron-doped diamond (BDD, 2500 ppm), and the cathode was 3% MnO2 nanoflowers (NFMnO2) on a carbon gas diffusion electrode (GDE). An electrochemical cell without a divider with a GDE with 3% w/w NFMnO2/C supported on carbon Vulcan XC72 was used. The decolorization efficiency was monitored by UV–vis spectroscopy, and the degradation was monitored by Total Organic Carbon (TOC) analysis. For dissolution monitoring, aliquots (1 mL) were collected during the degradation. After 6 h of H2O2 electrogeneration, the manganese concentration in the RB5 solution was only 23.1 ± 1.2 μg L−1. It was estimated that approximately 60 μg L−1 (

Among the several classes of chemical reactions, the green oxidation of organic compounds has emerged as an important topic in nanocatalysis. Nonetheless, examples of truly green oxidations remain scarce due to the low activity and selectivity of reported catalysts. In this paper, we present an approach based on the optimization of both the support material and the active phase to achieve superior catalytic performances towards green oxidations. Specifically, our catalysts consisted of ultrasmall Au NPs deposited onto MnO

By a combination of theoretical and experimental design, we probed the effect of a quasi-single electron on the surface plasmon resonance (SPR)-mediated catalytic activities of Ag nanoparticles. Specifically, we started by theoretically investigating how the E-field distribution around the surface of a Ag nanosphere was influenced by static electric field induced by one, two, or three extra fixed electrons embedded in graphene oxide (GO) next to the Ag nanosphere. We found that the presence of the extra electron(s) changed the E-field distributions and led to higher electric field intensities. Then, we experimentally observed that a quasi-single electron trapped at the interface between GO and Ag NPs in Ag NPs supported on graphene oxide (GO-Ag NPs) led to higher catalytic activities as compared to Ag and GO-Ag NPs without electrons trapped at the interface, representing the first observation of catalytic enhancement promoted by a quasi-single electron.

We describe herein the synthesis of solid Au@Pd and hollow AgPd nanoflowers displaying controlled sizes and compositions in order to investigate how their size, composition, and the presence of Au in the core of the nanoparticles influence their catalytic performance toward both liquid and gas-phase transformations. While the size and composition of Au@Pd and AgPd the nanoflowers could be controlled as function of growth time, their structure (solid or hollow) was dependent on the nature of the seeds employed for the synthesis, i.e., Au or Ag nanoparticles. Moreover, Au@Pd and AgPd nanoflowers were successfully supported onto commercial silica displaying truly uniform dispersion. The catalytic activities of Au@Pd and AgPd nanoflowers were investigated toward the 4-nitrophenol reduction and the benzene, toluene, and o-xylene (BTX) oxidation. The catalytic activities for the reduction of 4-nitrophenol decreased as follows: Au58@Pd42 > Au27@Pd73 > Ag20Pd80 and Ag8Pd92 > Au12@Pd88 > Ag38Pd62, suggesting that the Au core enhanced the catalytic activity relative to the hollow material when for Pd at.% was up to 80. Regarding the BTX oxidation, supported Au@Pd displayed higher catalytic activities than AgPd nanoflowers, also illustrating the role of the Au cores in the nanoflowers for improving catalytic performance. We believe these results may serve as a platform for the synthesis of Pd-based bimetallic nanomaterials that enable the correlation between these physical/chemical parameters and properties and thus optimized catalytic activities.

TiO2–Au hybrid materials are promising as electrocatalysts for the in situ production of H2O2 via the oxygen reduction reaction (ORR). However, the synthesis of uniform and well-controlled TiO2–Au materials, which is crucial to establish morphology–performance relationships, remains challenging. We describe herein the synthesis of hybrid materials composed of TiO2 colloidal spheres and wires decorated with Au nanoparticles. We employed TiO2 colloidal spheres and wires as physical templates for Au deposition, which enabled the uniform deposition of Au NPs with monodisperse sizes over the TiO2 surface. Then, the electrocatalytic activities toward the electrogeneration of H2O2 by the ORR were investigated as a function of the TiO2 shape and TiO2–Au loading on Vulcan XC-72R carbon. We found that the electrocatalytic activities were strongly dependent on the TiO2 shape and TiO2–Au loading in the catalysts. The utilization of TiO2 colloidal spheres led to higher activities relative to pure carbon and commercial Pt/C, and the optimal TiO2–Au loading corresponded to 3%. Conversely, the TiO2 wires led to detrimental effects over the catalytic performances for all hybrid materials. These results could be explained based on the morphological and conductivity differences among TiO2–Au/C electrode materials. We believe the results described herein can have important implication for the design of TiO2-based hybrid nanostructures for the electrogeneration of H2O2 by the ORR.

The synthesis of trimetallic nanoparticles represents an emerging strategy to maximize catalytic performances in noble metal-based catalysts. However, the controllable synthesis of trimetallic nanomaterials as well as the exact role played by the addition of a third metal in their composition over catalytic performances remains unclear. In this paper, we describe the synthesis of trimetallic nanoshells having AgAuPd, AgAuPt, and AgPdPt compositions by a sequential galvanic replacement reaction approach between Ag nanospheres as sacrificial templates and the corresponding metal precursors, i.e., AuCl4 − (aq), PdCl4 2− (aq), and/or PtCl6 2− (aq). In each of these systems, the composition could be systematically tuned by varying the molar ratios between Ag and each metal precursor. Nanoshells having Ag56Au28Pd16, Ag78Au9Pt13, and Ag71Pd16Pt13 compositions were employed as model systems to investigate the effect of the addition of the third metal in their composition over the catalytic activities toward the 4-nitrophenol reduction. Our data demonstrate a significant enhancement in conversion percentages and thus the catalytic activities relative to the sum of their bimetallic counterparts, and this increase was dependent on the nature of the metals, corresponding to 826, 135, and 56 % for Ag56Au28Pd16, Ag78Au9Pt13, and Ag71Pd16Pt13 nanoshells relative to their bimetallic analogs. The results presented herein demonstrate the strong correlation between catalytic activity and composition in multimetallic nanoshells, and that the incorporation of a third metal may represent a promising approach to boost catalytic activities for a variety of transformations.

Although catalytic processes mediated by surface plasmon resonance (SPR) excitation have emerged as a new frontier in catalysis, the selectivity of these processes remains poorly understood. Here, the selectivity of the SPR-mediated oxidation of p-aminothiophenol (PATP) employing Au NPs as catalysts was controlled by the choice of catalysts (Au or TiO2-Au NPs) and by the modulation of the charge transfer from UV-excited TiO2 to Au. When Au NPs were employed as catalyst, the SPR-mediated oxidation of PATP yielded p,p-dimercaptobenzene (DMAB). When TiO2-Au NPs were employed as catalysts under both UV illumination and SPR excitation, p-nitrophenol (PNTP) was formed from PATP in a single step. Interestingly, PNTP molecules were further reduced to DMAB after the UV illumination was removed. Our data show that control over charge-transfer processes may play an important role to tune activity, product formation, and selectivity in SPR-mediated catalytic processes.

Electrochemical advanced oxidative processes (EAOPs) have been shown to be very efficient for the removal of organic pollutants that are not mineralized by conventional effluent treatments. These processes are based on the use of an electrocatalyst and/or photocatalyst for the in situ generation of hydrogen peroxide (H2O2) and hydroxyl radicals ( OH), and these species are capable of mineralizing organic pollutants. This work aims evaluate electrocatalysts produced from ceria high aspect ratio nanostructures (CeO2 HARN) supported on black carbon (Vulcan XC-72) in different mass proportions of CeO2 HARN (1%, 2.5%, 4%, 5.5% and 10%) by examining the oxygen reduction reaction (ORR) in alkaline medium (1 mol L−1 NaOH) for the electrogeneration of H2O2. Vulcan XC-72 was used as a support because it has a high surface area, high catalytic activity and low cost. The CeO2 HARN were prepared via a hydrothermal method and were supported on Vulcan XC-72 via an impregnation method. The CeO2 HARN/C-based electrocatalysts were characterized physically by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and contact angle measurements and electrochemically by the rotating ring-disc electrode (RRDE) technique. The results of the electrochemical characterization of the materials indicated a considerable improvement in H2O2 electrogeneration over that of pure Vulcan XC-72, and the electrocatalyst containing 1% CeO2 HARN showed a lower starting potential and transferred 2.1 electrons in the ORR, therefore favoring the 2-electron mechanism and consequently providing a higher rate for H2O2 electrogeneration, which was 95% compared with only 54% for pure Vulcan XC-72. These results show that the CeO2 HARN/C-based electrocatalysts evaluated in this work are promising for in situ H2O2 electrogeneration via EAOPs; in particular, the catalyst containing 1% CeO2 HARN shows more promising results and contains a low metallic oxide load supported on the carbon, increasing its cost-benefit.

The use of sunlight to drive chemical reactions via photocatalysis is of paramount importance towards a sustainable future. Among several photocatalysts, earth-abundant polymeric carbon nitride (PCN, often wrongly named g-C3N4) has emerged as an attractive candidate due to its ability to absorb light efficiently in the visible and near-infrared ranges, chemical stability, non-toxicity, straightforward synthesis, and versatility as a platform for constructing hybrid materials. Especially, hybrids with metal nanoparticles offer the unique possibility of combining the catalytic, electronic, and optical properties of metal nanoparticles with PCN. Here, we provide a comprehensive overview of PCN materials and their hybrids, emphasizing heterostructures with metal nanoparticles. We focus on recent advances encompassing synthetic strategies, design principles, photocatalytic applications, and charge-transfer mechanisms. We also discuss how the localized surface plasmon resonance (LSPR) effect of some noble metals NPs (e.g. Au, Ag, and Cu), bimetallic compositions, and even non-noble metals NPs (e.g., Bi) synergistically contribute with PCN in light-driven transformations. Finally, we provide a perspective on the field, in which the understanding of the enhancement mechanisms combined with truly controlled synthesis can act as a powerful tool to the establishment of the design principles needed to take the field of photocatalysis with PCN to a new level, where the desired properties and performances can be planned in advance, and the target material synthesized accordingly.

The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles can enhance or mediate chemical transformations. Increased reaction rates for several reactions have been reported due to this phenomenon; however, the fundamental understanding of mechanisms and factors that affect activities remains limited. Here, by investigating hydrogenation reactions as a model transformation and employing different reducing agents, H2 and NaBH4 , which led to different hydrogenation reaction pathways, we observed that plasmonic excitation of Au nanoparticle catalysts can lead to negative effects over the activities. The underlying physical reason was explored using density functional theory calculations. We observed that positive versus negative effects on the plasmonic catalytic activity is reaction-pathway dependent. These results shed important insights on our current understanding of plasmonic catalysis, demonstrating reaction pathways must be taken into account for the design of plasmonic nanocatalysts.

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This review describes some principles of the controlled synthesis of metal nanoparticles, focusing on how the fundamental understanding of their synthesis in the solution-phase can be put to tailor size, shape, composition, and architecture. The maneuvering over these parameters not only enable the tuning of properties, but also the maximization and optimization of performances for various applications. Herein, we start with a brief description of metallic nanoparticles, highlighting the motivation for achieving physicochemical control in their synthesis. After that, we turn our attention to some important definitions and classifications as well as their unique properties such as surface and quantum effects. Moreover, we discuss the strategies for the controlled synthesis of metal nanomaterials based on the top-down and bottom-up approaches, focusing our discussion on their formation mechanisms in liquid-phase in terms of both thermodynamic and kinetic control. Finally, we point out the promising applications of controlled nanomaterials in the field of nanocatalysis and plasmon-enhanced catalysis, describing some of the current challenges in these fields.

In hybrid materials containing plasmonic nanoparticles such as Au and Ag, charge-transfer processes from and to Au or Ag can affect both activities and selectivity in plasmonic catalysis. Inspired by the widespread utilization of commercial Si wafers in surface-enhanced Raman spectroscopy (SERS) studies, we investigated herein the effect of the native SiO

The surface plasmon resonance (SPR) excitation by visible light in plasmonic nanostructures can be put to work to mediate catalytic processes. However, the role of composition in bimetallic nanoparticles over the SPR-mediated catalytic activity remains unclear. We investigated herein the SPR-mediated catalytic activity of AgAu nanoparticles as a function of composition toward the oxidation of p-aminothiophenol to p,p′-dimercaptoazobenzene. Our results showed that a “volcano-type” relationship between composition and product conversion was observed, with a maximum activity observed for Ag0.19Au0.81 nanoparticles. The variations in catalytic activity could be explained by the balance between the matching of the excitation wavelength with SPR position and the plasmonic damping due to interband transitions above 500 nm. These data suggest that the precise control over composition allows the fine-tuning of catalytic activity in SPR-mediated catalytic processes.

International audience; Mono and bimetallic catalysts based on Pt and Pd were prepared by a co-precipitation method. They were tested in liquid phase hydrogenation reactions of glucose and furfural at low temperature and pressure. The bimetallic PtPd/TiO2 catalyst proved to be an efficient material in selectively hydrogenating glucose to sorbitol. Moreover, high furfural conversion was attained under relatively soft conditions, and the furfuryl alcohol selectivity was strongly affected by the chemical composition of the catalysts. Furfuryl alcohol (FA) was the major product in most cases, along with side products such as methylfuran (MF), furan, and traces of tetrahydrofuran (THF). These results showed that the PtPd bimetallic sample was more active relative to the monometallic counterparts. A correlation between the catalytic results and the physicochemical properties of the supported nanoparticles identified key factors responsible for the synergetic behavior of the PtPd system. The high activity and selectivity were due to the formation of ultra-small particles, alloy formation, and the Pt-rich surface composition of the bimetallic particles supported on the TiO2 nanowires.

Associating polyaniline and metallic nanoparticles may result in the combination/synergism of properties, which have been attracting great attention. This paper describes an investigation that veri...