NiFe and CoFe nanocatalysts supported on highly dispersed alumina-silica: Structure, surface properties, and performance in CO2 methanation.

The hydrogenation of CO2 to CH4 has gained considerable interest in terms of sustainable energy and environmental mitigation. In this regard, the present work aims to investigate the adsorptive concentration and CO2 methanation performance over CoFe and NiFe bimetallic catalysts supported on fumed alumina-silica SA96 support at 170-450 °C and under atmospheric pressure. The catalysts were prepared by wet impregnation method, subjected to calcination and further reduced with hydrogen, and their performance in CO2 methanation was investigated in a hydrogen-rich 2%CO2-55%H2-43%He gas mixture. In this study, we describe the crystal and mesoporous structures of the prepared catalysts by in-situ XRD and ex-situ nitrogen adsorption, evaluate the NiFe and CoFe metal surface states before and after catalysis by XPS, visualize the surface morphology by SEM, estimate the catalytic activity by gas chromatography, and investigate the adsorbed surface species, showing the presence of *HCOO/*HCO and *CO intermediates, determine two possible pathways of CH4 formation on the studied catalysts by temperature-programmed desorption mass spectrometry, and correlate the structural and surface properties with high CO2 conversions up to 100% and methanation selectivities up to 72%. The latter is related to changes in the elemental chemical states and surface composition of CoFe and NiFe nanocatalysts induced by treatment under reaction conditions, and the surface reconstruction during catalysis transfers the part of active 3d transition metals into the pores of the SA96 support. Our thorough characterization study with complementary techniques allowed us to conclude that this high activity is related to the formation of catalytically active Ni/Ni3Fe and Co/CoFeOx nanoscale crystallites under H2 reduction and their maintenance under CO2 methanation conditions. The successfully applied combination of CO2 chemisorption and thermodesorption techniques demonstrates the ability to adsorb the CO2 molecules by supported NiFe and CoFe nanocatalysts and the pure alumina-silica SA96 support.

Ammonium nanochelators in conjunction with arginine-specific enzymes in amperometric biosensors for arginine assay.

Amino acid L-arginine (Arg), usually presented in food products and biological liquids, can serve both as a useful indicator of food quality and an important biomarker in medicine. The biosensors based on Arg-selective enzymes are the most promising devices for Arg assay. In this research, three types of amperometric biosensors have been fabricated. They exploit arginine oxidase (ArgO), recombinant arginase I (ARG)/urease, and arginine deiminase (ADI) coupled with the ammonium-chelating redox-active nanoparticles. Cadmium-copper nanoparticles (nCdCu) as the most effective nanochelators were used for the development of ammonium chemosensors and enzyme-coupled Arg biosensors. The fabricated enzyme/nCdCu-containing bioelectrodes show wide linear ranges (up to 200 µM), satisfactory storage stabilities (14 days), and high sensitivities (A⋅M-1⋅m-2) to Arg: 1650, 1700, and 4500 for ADI-, ArgO- and ARG/urease-based sensors, respectively. All biosensors have been exploited to estimate Arg content in commercial juices. The obtained data correlate well with the values obtained by the reference method. A hypothetic scheme for mechanism of action of ammonium nanochelators in electron transfer reaction on the arginine-sensing electrodes has been proposed.

Copper foam supported g-C3N4-metal-organic framework bacteria biohybrid cathode catalyst for CO2 reduction in microbial electrosynthesis.

Microbial electrosynthesis (MES) presents a versatile approach for efficiently converting carbon dioxide (CO2) into valuable products. However, poor electron uptake by the microorganisms from the cathode severely limits the performance of MES. In this study, a graphitic carbon nitride (g-C3N4)-metal-organic framework (MOF) i.e. HKUST-1 composite was newly designed and synthesized as the cathode catalyst for MES operations. The physiochemical analysis such as X-ray diffraction, scanning electron microscopy (SEM), and X-ray fluorescence spectroscopy showed the successful synthesis of g-C3N4-HKUST-1, whereas electrochemical assessments revealed its enhanced kinetics for redox reactions. The g-C3N4-HKUST-1 composite displayed excellent biocompatibility to develop electroactive biohybrid catalyst for CO2 reduction. The MES with g-C3N4-HKUST-1 biohybrid demonstrated an excellent current uptake of 1.7 mA/cm2, which was noted higher as compared to the MES using g-C3N4 biohybrid (1.1 mA/cm2). Both the MESs could convert CO2 into acetic and isobutyric acid with a significantly higher yield of 0.46 g/L.d and 0.14 g/L.d respectively in MES with g-C3N4-HKUST-1 biohybrid and 0.27 g/L.d and 0.06 g/L.d, respectively in MES with g-C3N4 biohybrid. The findings of this study suggest that g-C3N4-HKUST-1 is a highly efficient catalytic material for biocathodes in MESs to significantly enhance the CO2 conversion.

Diffusion controlled electrochemical analysis of MoS2 and MOF derived metal oxide-carbon hybrids for high performance supercapacitors.

In the context of emerging electric devices, the demand for advanced energy storage materials has intensified. These materials must encompass both surface and diffusion-driven charge storage mechanisms. While diffusion-driven reactions offer high capacitance by utilizing the bulk of the material, their effectiveness diminishes at higher discharge rates. Conversely, surface-controlled reactions provide rapid charge/discharge rates and high power density. To strike a balance between these attributes, we devised a tri-composite material, TiO2/Carbon/MoS2 (T10/MoS2). This innovative design features a highly porous carbon core for efficient diffusion and redox-active MoS2 nanosheets on the surface. Leveraging these characteristics, the T10/MoS2 composite exhibited impressive specific capacitance (436 F/g at 5 mV/s), with a significant contribution from the diffusion-controlled process (82%). Furthermore, our symmetrical device achieved a notable energy density of ~ 50 Wh/kg at a power density of 1.3 kW/kg. This concept holds promise for extending the approach to other Metal-Organic Framework (MOF) structures, enabling enhanced diffusion-controlled processes in energy storage applications.

Tunable-wavelength nanosecond laser tailoring of plasmon resonance spectra of gold nanoparticle colloids.

Metal nanoparticles have applications across a range of fields of science and industry. While there are numerous existing methods to facilitate their large-scale production, most face limitations, particularly in achieving reproducible processes and minimizing undesirable impurities. Common issues are varying particle sizes and aggregates with unfavorable spectral properties. Researchers are currently developing methods to separate or modify nanoparticle sizes and shapes post-synthesis and to eliminate impurities. One promising approach involves laser light irradiation and enables the changing of nanoparticle sizes and shapes while controlling crucial spectral parameters. In this work, we present a novel extension of this method by irradiating nanoparticle colloids with variable-wavelength nanosecond laser pulses on both sides of the extinction band. Our results demonstrate the use of gradual laser wavelength tuning to optimize the photothermal reshaping of gold nanorods and achieve precise control over the plasmon resonance band. By irradiating both sides of the plasmon resonance band, we execute a multistep tuning process, controlling the band's width and spectral position. A statistical analysis of SEM images reveals differences in the nanorod morphology when irradiated on the long- or short-wavelength side of the plasmon resonance band. The fine-tuning of plasmonic spectral properties is desirable for various applications, including the development of sensors and filters and the exploitation of the photothermal effect. The findings of this study can be extended to other plasmonic nanostructures.

Evaluation of local oxygen flux produced by photoelectrochemical hydroxide oxidation by scanning electrochemical microscopy.

Several in-situ electrochemical approaches have been developed for performing a localized photoelectrochemical investigation of the photoanode. One of the techniques is scanning electrochemical microscopy (SECM), which probes local heterogeneous reaction kinetics and fluxes of generated species. In traditional SECM analysis of photocatalysts, evaluation of the influence of radiation on the rate of studied reaction requires an additional dark background experiment. Here, using SECM and an inverted optical microscope, we demonstrate the determination of O2 flux caused by light-driven photoelectrocatalytic water splitting. Photocatalytic signal and dark background are recorded in a single SECM image. We used an indium tin oxide electrode modified with hematite (α-Fe2O3) by electrodeposition as a model sample. The light-driven flux of oxygen is calculated by analysis of SECM image recorded in substrate generation/tip collection mode. In photoelectrochemistry, the qualitative and quantitative knowledge of oxygen evolution will open new doors for understanding the local effects of dopants and hole scavengers in a straightforward and conventional manner.

Nanofunctionalization of Additively Manufactured Titanium Substrates for Surface-Enhanced Raman Spectroscopy Measurements.

Powder bed fusion using a laser beam (PBF-LB) is a commonly used additive manufacturing (3D printing) process for the fabrication of various parts from pure metals and their alloys. This work shows for the first time the possibility of using PBF-LB technology for the production of 3D titanium substrates (Ti 3D) for surface-enhanced Raman scattering (SERS) measurements. Thanks to the specific development of the 3D titanium surface and its nanoscale modification by the formation of TiO2 nanotubes with a diameter of ~80 nm by the anodic oxidation process, very efficient SERS substrates were obtained after deposition of silver nanoparticles (0.02 mg/cm2, magnetron sputtering). The average SERS enhancement factor equal to 1.26 × 106 was determined for pyridine (0.05 M + 0.1 M KCl), as a model adsorbate. The estimated enhancement factor is comparable with the data in the literature, and the substrate produced in this way is characterized by the high stability and repeatability of SERS measurements. The combination of the use of a printed metal substrate with nanofunctionalization opens a new path in the design of SERS substrates for applications in analytical chemistry. Methods such as SEM scanning microscopy, photoelectron spectroscopy (XPS) and X-ray diffraction analysis (XRD) were used to determine the morphology, structure and chemical composition of the fabricated materials.

Physicochemical changes of the chitosan/ß-1,3-glucan/hydroxyapatite biocomposite caused by mesenchymal stem cells cultured on its surface in vitro.

In the present study structural characteristics and physicochemical properties of tri-component biomaterial (consisting of chitosan, ß-1,3-glucan and hydroxyapatite) seeded with mesenchymal stem cells were investigated with the use of diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). In this study we use non-conventional approach of DRIFT spectroscopy for investigating biomaterial changes under simulated physiological conditions. Particular cell-induced changes were intended to be properly evaluated with analytical methods. Abovementioned techniques allowed to precisely assess the changes on the surface of the biomaterial caused by two kinds of stem cells (ADSCs - Adipose tissue-Derived Stem Cells and BMDSCs - Bone Marrow-Derived Stem Cells) cultured directly on the surface of bioceramic-based biomaterial. The bioactivity and biocompatibility of designed bone biomaterial were demonstrated and hence it seems to be a promising scaffold used in tissue engineering. Designed chitosan, ß-1,3-glucan, and hydroxyapatite biomaterial was proven to be non-toxic, surgically handy with cellular compatibility. The obtained results are interesting and promising in terms of spectroscopic methods suitability for qualitative assessment of material-cell interactions.

Materials characterization of TiO2 nanotubes decorated by Au nanoparticles for photoelectrochemical applications.

The structural and chemical modification of TiO2 nanotubes (NTs) by the deposition of a well-controlled Au deposit was investigated using a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), Raman measurements, UV-Vis spectroscopy and photoelectrochemical investigations. The fabrication of the materials focused on two important factors: the deposition of Au nanoparticles (NPs) in UHV (ultra high vacuum) conditions (1-2 × 10-8 mbar) on TiO2 nanotubes (NTs) having a diameter of ∼110 nm, and modifying the electronic interaction between the TiO2 NTs and Au nanoparticles (NPs) with an average diameter of about 5 nm through the synergistic effects of SMSI (Strong Metal Support Interaction) and LSPR (Local Surface Plasmon Resonance). Due to the formation of unique places in the form of "hot spots", the proposed nanostructures proved to be photoactive in the UV-Vis range, where a characteristic gold plasmonic peak was observed at a wavelength of 580 nm. The photocurrent density of Au deposited TiO2 NTs annealed at 650 °C was found to be much greater (14.7 µA cm-2) than the corresponding value (∼0.2 µA cm-2) for nanotubes in the as-received state. The IPCE (incident photon current efficiency) spectral evidence also indicates an enhancement of the photoconversion of TiO2 NTs due to Au NP deposition without any significant change in the band gap energy of the titanium dioxide (E g ∼3.0 eV). This suggests that a plasmon-induced resonant energy transfer (PRET) was the dominant effect responsible for the photoactivity of the obtained materials.

Noble Metal Nanoparticles in Pectin Matrix. Preparation, Film Formation, Property Analysis, and Application in Electrocatalysis.

Stable polymeric materials with embedded nano-objects, retaining their specific properties, are indispensable for the development of nanotechnology. Here, a method to obtain Pt, Pd, Au, and Ag nanoparticles (ca. 10 nm, independent of the metal) by the reduction of their ions in pectin, in the absence of additional reducing agents, is described. Specific interactions between the pectin functional groups and nanoparticles were detected, and they depend on the metal. Bundles and protruding nanoparticles are present on the surface of nanoparticles/pectin films. These films, deposited on the electrode surface, exhibit electrochemical response, characteristic for a given metal. Their electrocatalytic activity toward the oxidation of a few exemplary organic molecules was demonstrated. In particular, a synergetic effect of simultaneously prepared Au and Pt nanoparticles in pectin films on glucose electro-oxidation was found.

Plasma Nitriding of TiO2 Nanotubes: N-Doping in Situ Investigations Using XPS.

The nitrogen doping of titanium dioxide nanotubes (TiO2 NTs) was investigated as a result of well-controlled plasma nitriding of TiO2 NTs at a low temperature. This way of nitrogen doping is proposed as an alternative to chemical/electrochemical methods. The plasma nitriding process was performed in a preparation chamber connected to an X-ray photoelectron spectroscopy (XPS) spectrometer, and the nitrogen-doped TiO2 NTs were next investigated in situ by XPS in the same ultrahigh vacuum (UHV) system. The collected high-resolution (HR) XPS spectra of N 1s, Ti 2p, O 1s, C 1s, and valence band (VB) revealed the formation of chemical bonds between titanium, nitrogen, and oxygen atoms as substitutional or interstitial species. Moreover, the results provided a characterization of the electronic states of N-TiO2 NTs generated by various plasma nitriding and annealing treatments. The VB XPS spectrum showed a reduction in the TiO2 band gap of about 0.6 eV for optimal nitriding and heat-treated conditions. The TiO2 NTs annealed at 450 or 650 °C in air (ex situ) and nitrided under UHV conditions were used as reference materials to check the formation of Ti-N bonds in the TiO2 lattice with a well-defined structure (anatase or a mixture of anatase and rutile). Scanning electron microscopy microscopic observations of the received materials were used to evaluate the morphology of the TiO2 NTs after each step of the nitriding and annealing treatments.

TiO2 Nanotubes with Pt and Pd Nanoparticles as Catalysts for Electro-Oxidation of Formic Acid.

In the present work, the magnetron sputtering technique was used to prepare new catalysts of formic acid electrooxidation based on TiO2 nanotubes decorated with Pt (platinum), Pd (palladium) or Pd + Pt nanoparticles. TiO2 nanotubes (TiO2 NTs) with strictly defined geometry were produced by anodization of Ti foil and Ti mesh in a mixture of glycerol and water with ammonium fluoride electrolyte. The above mentioned catalytically active metal nanoparticles (NPs) were located mainly on the top of the TiO2 NTs, forming 'rings' and agglomerates. A part of metal nanoparticles decorated also TiO2 NTs walls, thus providing sufficient electronic conductivity for electron transportation between the metal nanoparticle rings and Ti current collector. The electrocatalytic activity of the TiO2 NTs/Ti foil, decorated by Pt, Pd and/or Pd + Pt NPs was investigated by cyclic voltammetry (CV) and new Pd/TiO2 NTs/Ti mesh catalyst was additionally tested in a direct formic acid fuel cell (DFAFC). The results so obtained were compared with commercial catalyst-Pd/Vulcan. CV tests have shown for carbon supported catalysts, that the activity of TiO2 NTs decorated with Pd was considerably higher than that one decorated with Pt. Moreover, for TiO2 NTs supported Pd catalyst specific activity (per mg of metal) was higher than that for well dispersed carbon supported commercial catalyst. The tests at DFAFC have revealed also that the maximum of specific power for 0.2 Pd/TiO2 catalyst was 70% higher than that of the commercial one, Pd/Vulcan. Morphological features, and/or peculiarities, as well as surface composition of the resulting catalysts have been studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and chemical surface analytical methods (X-ray photoelectron spectroscopy-XPS; Auger electron spectroscopy-AES).

Cubic Silver Nanoparticles Fixed on TiO2 Nanotubes as Simple and Efficient Substrates for Surface Enhanced Raman Scattering.

In this work we show that ordered freestanding titanium oxide nanotubes (TiO2 NT) may be used as substrates for the simple and efficient immobilization of anisotropic plasmonic nanoparticles. This is important because anisotropic plasmonic nanostructures usually give greater spectral enhancement than spherical nanoparticles. The size of the pores in a layer of titanium oxide nanotubes can be easily fitted to the size of many silver plasmonic nanoparticles highly active in SERS (surface-enhanced Raman scattering) spectroscopy (for example, silver nanocubes with an edge length of ca. 45 nm), and hence, the plasmonic nanoparticles deposited can be strongly anchored in such a titanium oxide substrate. The tubular morphology of the TiO2 substrate used allows a specific arrangement of the silver plasmonic nanoparticles that may create many so-called SERS hot spots. The SERS activity of a layer of cubic Ag nanoparticles (AgCNPs) deposited on a tubular TiO2 substrate (AgCNPs@TiO2 NT) is about eight times higher than that of the standard electrochemically nanostructured surface of a silver electrode (produced by oxidation reduction cycling). Furthermore, a super hydrophilic character of the TiO2 nanotubes surface allows for a uniform distribution of AgCNPs, which are deposited from an aqueous suspension. The new AgCNPs@TiO2 NT hybrid layer ensures a good reproducibility of SERS measurements and exhibits a higher temporal stability of the achievable total SERS enhancement factor-one that is far better than standard SERS silver substrates. To characterize the morphology and chemical composition of such evidently improved SERS platforms thus received, we applied microscopic techniques (SEM, and scanning transmission electron microscopy (STEM)) and surface analytical techniques (Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS)).

Metal TiO2 Nanotube Layers for the Treatment of Dental Implant Infections.

Titanium oxide nanotube layers with silver and zinc nanoparticles are attracting increasing attention in the design of bone and dental implants due to their antimicrobial potential and their ability to control host cell adhesion, growth, and differentiation. However, recent reports indicate that the etiology of dental infections is more complex than has been previously considered. Therefore, the antimicrobial potential of dental implants should be evaluated against at least several different microorganisms cooperating in human mouth colonization. In this study, Ag and Zn nanoparticles incorporated into titanium oxide nanotubular layers were studied with regard to how they affect Candida albicans, Candida parapsilosis, and Streptococcus mutans. Layers of titanium oxide nanotubes with an average diameter of 110 nm were fabricated by electrochemical anodization, annealed at 650 °C, and modified with approx. 5 wt % Ag or Zn nanoparticles. The surfaces were examined with the scanning electron microscopy-energy dispersive X-ray analysis, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy techniques and subjected to evaluation of microbial-killing and microbial adhesion-inhibiting potency. In a 1.5 h long adhesion test, the samples were found more effective toward yeast strains than toward S. mutans. In a release-killing test, the microorganisms were almost completely eliminated by the samples, either within 3 h of contact (for S. mutans) or 24 h of contact (for both yeast strains). Although further improvement is advisable, it seems that Ag and Zn nanoparticles incorporated into TiO2 nanotubular surfaces provide a powerful tool for reducing the incidence of bone implant infections. Their high bidirectional activity (against both Candida species and S. mutans) makes the layers tested particularly promising for the design of dental implants.

Influence of the silver deposition method on the activity of platforms for chemometric surface-enhanced Raman scattering measurements: Silver films on ZrO2 nanopore arrays.

Deposition of plazmonic metal nanoparticles on nanostructured oxide templates is an important part in preparation and design of suitable substrates for surface-enhanced Raman scattering (SERS) measurements. In this contribution we analyze the influence of the Ag deposition methods (magnetron sputtering and evaporation in vacuum, which are often used interchangeably) on SERS activity of the resultant Ag-n/ZrO2/Zr composite samples fabricated. We found that deposition of the same amount of Ag (0.020mg/cm2) on the ZrO2 nanoporous layers using magnetron sputtering and evaporation in vacuum leads to formation of two different surface morphologies, which can be distinguished on the basis of high-resolution scanning electron microscopy (HR-SEM) measurements. Those differences distinctly affect SERS intensity measured for probe molecules: pyridine and sodium 2-mercaptoethanesulfonate. SERS substrates obtained using evaporation technique are ca. 1.5 times more efficient than substrates prepared using magnetron sputtering.

Graphene oxide vs. reduced graphene oxide as saturable absorbers for Er-doped passively mode-locked fiber laser.

In this work we demonstrate comprehensive studies on graphene oxide (GO) and reduced graphene oxide (rGO) based saturable absorbers (SA) for mode-locking of Er-doped fiber lasers. The paper describes the fabrication process of both saturable absorbers and detailed comparison of their parameters. Our results show, that there is no significant difference in the laser performance between the investigated SA. Both provided stable, mode-locked operation with sub-400 fs soliton pulses and more than 9 nm optical bandwidth at 1560 nm center wavelength. It has been shown that GO might be successfully used as an efficient SA without the need of its reduction to rGO. Taking into account simpler manufacturing technology and the possibility of mass production, GO seems to be a good candidate as a cost-effective material for saturable absorbers for Er-doped fiber lasers.