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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

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.

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.

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.

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.

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).

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.

Sub-nanosecond charge dynamics in monodisperse Au nanoparticles (NPs) supported on TiO2 colloidal spheres are studied as a function of NP diameter using ultrafast transient absorption spectroscopy. The decay of the transmittance changes observed in the region of the plasmon resonance of the Au NPs following photoexcitation of the TiO2 spheres are well-described by a bi-exponential function consisting of a fast component of 2 ps duration associated with electron-phonon scattering, followed by a slow and relatively weak component associated with phonon-phonon scattering. The decay constant characterising the latter component was found to be dependent on the size of the Au NPs, rising from 49 ± 3 to 128 ± 6 ps as the diameter of the Au NPs increased from 12.2 ± 2.2 nm to 24.5 ± 2.8 nm, respectively. This journal is © the Partner Organisations 2014.

This perspective article highlights recent developments in a class of surface-enhanced Raman scattering (SERS) experiments that aim to correlate SERS enhancement factors with the physical parameters of metal nanostructures. In a typical study, the SERS substrate is fabricated by depositing colloidal nanoparticles on a silicon wafer to obtain individual particles isolated from each other, or small aggregates such as dimeric units. With the help of registration marks, the same nanoparticle, or dimer of nanoparticles, can be quickly located under a Raman microscope (for SERS spectra) and a scanning electron microscope (for structural characterization). The nanoscale characterization achieved by these studies has resulted in unparalleled investigations into the nature of polarization dependency for SERS, the hot spot nature of single nanoparticles and dimers, and the manipulation of hot spots through shape-controlled synthesis and self-assembly. We discuss the new insights these studies have offered, and the future progress they can deliver to the advancement of SERS.

We describe a systematic investigation on the SERS enhancement factors of individual dimers (EF dimer ) constructed from two Ag nanocubes that display a face-to-face, edge-to-face, or edge-to-edge structure. The highest field-enhancements were obtained for the dimers displaying a face-to-face and edge-to-face configuration. In these two systems, EF dimer was insensitive the dimer geometry and corresponded to 2.0 × 10 7 and 1.5 × 10 7 , respectively. However, EF dimer was decreased to 5.6 × 10 6 for the edge-to-edge structure. These variations in the detected field-enhancements could be explained based on the relative orientation of the nanocubes and the number of probe molecules enclosed in the hot-spot region for each dimer configuration.

This paper describes a simple approach to the synthesis of asymmetric, hybrid colloidal particles by precipitation polymerization. The key is to introduce Au or Ag colloids 2 min after (rather than before) starting the polymerization. The hybrid particles were uniform in size, and each one of them only contained one Au (or Ag) nanoparticle in its surface. Due to the simplicity of this procedure, it should be possible to use it for large-scale production. This method can be extended to metal nanoparticles other than Au and Ag and with a range of sizes, as long as they have appropriate stabilizers on the surface.

In a seed-mediated synthesis, nanocrystal growth is often described by assuming the absence of homogeneous nucleation in the solution. Here we provide new insights into the nucleation and growth mechanisms underlying the formation of bimetallic nanodendrites that are characterized by a dense array of Pt branches anchored to a Pd nanocrystal core. These nanostructures can be easily prepared by a one-step, seeded growth method that involves the reduction of K2PtCl4 by L-ascorbic acid in the presence of 9-nm truncated octahedral Pd seeds in an aqueous solution. Transmission electron microscopy (TEM) and high-resolution TEM analyses revealed that both homogeneous and heterogeneous nucleation of Pt occurred at the very early stages of the synthesis and the Pt branches grew through oriented attachment of small Pt particles that had been formed via homogeneous nucleation. These new findings contradict the generally accepted mechanism for seeded growth that only involves heterogeneous nucleation and simple growth via atomic addition. We have also investigated the electrocatalytic properties of the Pd-Pt nanodendrites for the oxygen reduction and formic acid oxidation reactions by conducting a comparative study with foam-like Pt nanostructures prepared in the absence of Pd seeds under otherwise identical conditions.