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Since the original report in 2004 by Novoselov and Geim, Graphene gained incredible attention due to its fascinating properties. In the past 20 years, the synthesis and functionalization of graphene has evolved significantly[3]. Different synthesis techniques were developed which led to other graphenerelated materials such as graphene oxide (GO) or elemental-doped graphene. Further chemical functionalization can enhance but also alter or reduce specific properties of the graphene. To reveal the nature of these materials a proper physico‑chemical characterization with different analytical techniques is crucial.
Single-layer GO flakes kindly provided by Graphenea (Spain) were prepared for systematic image analysis. These flakes were disposed on an alignment-marked SiO2 substrate and correlatively imaged by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Raman spectroscopy. The high lateral resolution and/ or extreme surface sensitivity of the mentioned
techniques is necessary to explore monolayers. The ToF-SIMS images match well with the SEM and AFM images and provide information about the chemistry. With 2D Raman spectroscopy it is possible to differentiate between the number of stacked single-layer flakes. This is visualized in a 3D image (Figure b). Well-defined GO flakes could be used as a reference material for imaging of graphene-like structures but also of other types of 2D materials.
In addition to these monolayer GO flakes, commercial graphene-containing inks (Haydale) with a more complex morphology were also correlatively imaged. ToF-SIMS and SEM images were merged to identify the origin of different chemical fragments. The findings correlate closely with the expectation that the specific functionalizations (with fluorine and nitrogen as marker elements) are present only on the graphene flakes as presumed from the SEM images. Energy-dispersive X-ray spectroscopy (EDX) supports these results, yet with a much lower sensitivity compared to ToF-SIMS.
Since the original report in 2004 by Novoselov and Geim, Graphene gained incredible attention due to its fascinating properties. In the past 20 years, the synthesis and functionalization of graphene has evolved significantly[3]. Different synthesis techniques were developed which led to other graphenerelated materials such as graphene oxide (GO) or elemental-doped graphene. Further chemical functionalization can enhance but also alter or reduce specific properties of the graphene. To reveal the nature of these materials a proper physico‑chemical characterization with different analytical techniques is crucial.
Single-layer GO flakes kindly provided by Graphenea (Spain) were prepared for systematic image analysis. These flakes were disposed on an alignment-marked SiO2 substrate and correlatively imaged by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Raman spectroscopy. The high lateral resolution and/ or extreme surface sensitivity of the mentioned
techniques is necessary to explore monolayers. The ToF-SIMS images match well with the SEM and AFM images and provide information about the chemistry. With 2D Raman spectroscopy it is possible to differentiate between the number of stacked single-layer flakes. This is visualized in a 3D image (Figure b). Well-defined GO flakes could be used as a reference material for imaging of graphene-like structures but also of other types of 2D materials.
In addition to these monolayer GO flakes, commercial graphene-containing inks (Haydale) with a more complex morphology were also correlatively imaged. ToF-SIMS and SEM images were merged to identify the origin of different chemical fragments. The findings correlate closely with the expectation that the specific functionalizations (with fluorine and nitrogen as marker elements) are present only on the graphene flakes as presumed from the SEM images. Energy-dispersive X-ray spectroscopy (EDX) supports these results, yet with a much lower sensitivity compared to ToF-SIMS.
Luminescence lifetimes are an attractive analytical method for detection due to its high sensitivity and stability. Iridium probes exhibit luminescence with long excited-state lifetimes, which are sensitive to the local environment. Perfluorooctanoic acid (PFOA) is listed as a chemical of high concern regarding its toxicity and is classified as a “forever chemical”. In addition to strict limits on the presence of PFOA in drinking water, environmental contamination from industrial effluent or chemical spills requires rapid, simple, accurate, and cost-effective analysis in order to aid containment. Herein, we report the fabrication and function of a novel and facile luminescence sensor for PFOA based on iridium modified on gold surfaces. These surfaces were modified with lipophilic iridium complexes bearing alkyl chains, namely, IrC6 and IrC12, and Zonyl-FSA surfactant. Upon addition of PFOA, the modified surfaces IrC6-FSA@Au and IrC12-FSA @Au show the largest change in the red luminescence signal with changes in the luminescence lifetime that allow monitoring of PFOA concentrations in aqueous solutions. The platform was tested for the measurement of PFOA in aqueous samples spiked with known concentrations of PFOA and demonstrated the capacity to determine PFOA at concentrations >100 μg/L (240 nM).
Electrocatalysis is and will continue to play a central role in the development of a new and modern sustainable economy, especially for chemicals and fuels. The storage of excess electrical energy into chemical energy by splitting water into hydrogen and oxygen is a feasible solution in this economic sector. A major drawback of electrical energy lies in the storage. Therefore, hydrogen is discussed as promising alternative. Fortunately, this issue can be effectively addressed through the implementation of chemical storage mechanisms. Due to their abundance on Earth and inherent stability in alkaline solutions, transition-metal oxides have become one of several viable alternatives to conventional noble-metal catalysts. Since FeNi oxide is one of the most active oxygen evolution reaction (OER) electrocatalysts for alkaline water electrolysis, it has been the subject of extensive research.
A series of different types of FeNi oxide nanoparticles (NPs) with atomic ratios covering a broad range, and various sizes with specific stoichiometric and non-stoichiometric iron and nickel ratios was synthesized and characterized by the combination of surface analysis techniques, such as time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The morphology was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed the coexistence of mixed and unmixed iron and nickel NPs with comparable sizes in the range of 30–40 nm across all ratios. The synthesis technique displayed control over the iron-nickel ratio, as evidenced by energy dispersive X-ray spectroscopy (EDS) data. The presence of magnetite (Fe3O4) was detected in all samples investigated by X-ray diffraction (XRD). Furthermore, the existence of nickel ferrite (NiFe2O4) was shown in the Fe2Ni by XRD analysis. For the cyclic voltammetry (CV) measurements, the NPs were deposited onto glassy carbon electrodes using Nafion® as an ionomer, and 1 M KOH was employed as the electrolyte. Subsequently, the NPs/Nafion® electrode was transferred into the ToF-SIMS chamber to allow surface analysis and depth profiling.
The ToF-SIMS analysis revealed distinct peaks corresponding to Fe, Ni, and other peaks associated with Nafion®, whereas a straightforward correlation between the Ni.Fe ratio and the SIMS peak pattern is not possible.
The catalytic activity towards OER was evaluated through CV measurements, where the Fe2Ni3 ratio exhibited the most favorable performance, displaying a lower overpotential.
Electrocatalysis is and will continue to play a central role in the development of a new and modern sustainable economy, especially for chemicals and fuels. The storage of excess electrical energy into chemical energy by splitting water into hydrogen and oxygen is a feasible solution in this economic sector. A major drawback of electrical energy lies in the storage. Therefore, hydrogen is discussed as promising alternative. Fortunately, this issue can be effectively addressed through the implementation of chemical storage mechanisms. Due to their abundance on Earth and inherent stability in alkaline solutions, transition-metal oxides have become one of several viable alternatives to conventional noble-metal catalysts. Since FeNi oxide is one of the most active oxygen evolution reaction (OER) electrocatalysts for alkaline water electrolysis, it has been the subject of extensive research.
A series of different types of FeNi oxide nanoparticles (NPs) with atomic ratios covering a broad range, and various sizes with specific stoichiometric and non-stoichiometric iron and nickel ratios was synthesized and characterized by the combination of surface analysis techniques, such as time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The morphology was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed the coexistence of mixed and unmixed iron and nickel NPs with comparable sizes in the range of 30–40 nm across all ratios. The synthesis technique displayed control over the iron-nickel ratio, as evidenced by energy dispersive X-ray spectroscopy (EDS) data. The presence of magnetite (Fe3O4) was detected in all samples investigated by X-ray diffraction (XRD). Furthermore, the existence of nickel ferrite (NiFe2O4) was shown in the Fe2Ni by XRD analysis. For the cyclic voltammetry (CV) measurements, the NPs were deposited onto glassy carbon electrodes using Nafion® as an ionomer, and 1 M KOH was employed as the electrolyte. Subsequently, the NPs/Nafion® electrode was transferred into the ToF-SIMS chamber to allow surface analysis and depth profiling.
The ToF-SIMS analysis revealed distinct peaks corresponding to Fe, Ni, and other peaks associated with Nafion®, whereas a straightforward correlation between the Ni.Fe ratio and the SIMS peak pattern is not possible.
The catalytic activity towards OER was evaluated through CV measurements, where the Fe2Ni3 ratio exhibited the most favorable performance, displaying a lower overpotential.
The modern economy is dependent on catalysis, which is main efforts to create environmentally and energy-friendly technologies. The storage of excess electrical energy into chemical energy by splitting water into hydrogen and oxygen is a feasible solution to this energy demand. Due to their abundance on Earth and inherent stability in alkaline solution, transition-metal oxides have become one of several viable alternatives to noble-metal catalysts. Since NiFe oxide is one of the most active oxygen evolution reaction (OER) electrocatalysts for alkaline water electrolysis, it has been the subject of extensive research.
In this work, NiFe2O4 nanoparticles (NPs) of various sizes, specific stoichiometric and non-stoichiometric Fe:Ni surface ratios are synthesized. we will use a combination of ultra-high vacuum surface analysis techniques, such as time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS), to obtain the detailed characterization of the OER electrocatalysts top-surface layer, which is required to identify the rate-limiting step intermediates, and surface morphological changes at the electrolyte/catalyst.
Due to its large strength-to-weight ratio and excellent biocompatibility, titanium materials are of paramount importance for medical applications, e.g. as implant material for protheses. In this work, the evolution of various types of laser-induced micro- and nanostructures emerging on titanium or titanium alloys upon irradiation by near-infrared ultrashort laser pulses (925 fs, 1030 nm) in air environment is studied for various laser fluence levels, effective number of pulses and at different pulse repetition rates (1 – 400 kHz). The morphologies of the processed surfaces were systematically characterized by optical and scanning electron microscopy (OM, SEM). Complementary white-light interference microscopy (WLIM) revealed the corresponding surface topographies. Chemical and structural changes were analysed through depth-profiling time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray diffraction (XRD) analyses. The results point towards a remarkable influence of the laser processing parameters on the surface topography, while simultaneously altering the near-surface chemistry via laser-induced oxidation effects. Consequences for medical applications are outlined.
Corrosion is a very expensive and serious problem in the different industry sectors, eg. Petroleum-, On- and off-shore, infrastructure. It is estimated that 20% of all corrosion damage is caused by microorganisms or microbiologically influenced corrosion (MIC). Several microorganisms are known to cause corrosion, including sulfate-reducing bacteria, nitrate-reducing bacteria, methanogens etc. For several years, methanogens were regarded as a mild corroder (~0.065 mm/yr), largely due to a lack of detailed investigation on the corrosion mechanism under real-environment simulated conditions. Resulting in the common belief that siderite, a non-conductive compound, is the sole corrosion product (CP) of methanogen-induced MIC (Mi-MIC).
To simulate natural environmental conditions, we developed and introduced the multiport flow column system (MFC), a multi-sectional corrosion flow-cell. Using the MFC, we obtained ten times higher corrosion rates than previously reported. With a combination of several analytical techniques, such as ToF-SIMS, SEM-EDS and FIB-SEM, we found strong indication that siderite is not the sole corrosion product of Mi-MIC. The corrosion layers contained phosphorus, oxygen, magnesium, calcium and iron. The differences in the CP between static and dynamic environments demonstrated the impact of testing procedures on the corrosive potential of methanogens. To further verify and deepen our understanding of Mi-MIC, we are currently studying the influence of additional environmental parameters (e.g. pH, salinity, flow rate) on Mi-MIC.
Overall, results of this study will expand the current understanding of MIC from both analytical and mechanistic points of view, thus aiding the development of different mitigation strategies for various industry sectors.
Low-cost, high-efficient catalysts for water splitting can be potentially fulfilled by developing earthabundant metal oxides. In this work, surface galvanic formation of Co-OH on K0.45MnO2 (KMO) was achieved via the redox reaction of hydrated Co2+ with crystalline Mn4+. The synthesis method takes place at ambient temperature without using any surfactant agent or organic solvent, providing a clean, green route for the design of highly efficient catalysts. The redox reaction resulted in the formation of ultrathin Co-OH nanoflakes with high electrochemical surface area. X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the changes in the oxidation state of the bulk and
surface species on the Co-OH nanoflakes supported on the KMO. The effect of the anions, such as chloride, nitrate and sulfate, on the preparation of the catalyst was evaluated by electrochemical and spectrochemical means. XPS and Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis demonstrated that the layer of CoOxHy deposited on the KMO and its electronic structure strongly depend on the anion of the precursor used during the synthesis of the catalyst. In particular, it was found that Cl- favors the formation of Co-OH, changing the rate-determining step of the reaction, which enhances the catalytic activity towards the OER, producing the most active OER catalyst in alkaline media.