Electro-Oxidation of Titanium Carbide Nanoparticles in Aqueous Acid Creates TiC@TiO2 Core-Shell Structures

Titanium carbide (TiC) is an attractive support material used in electro-catalysis and sensing. We report the electrochemistry of TiC nanoparticles (NPs, 35–50 nm in diameter) in different electrolytes in the pH range of 0 to 8. The TiC NPs undergo irreversible oxidation in acidic, basic, and neutral media, attributed to the partial conversion into titanium dioxide (TiO2) with the amount of oxidation highly dependent on the pH of the solution. In H2SO4 (pH 0), multiple voltammetric scans revealed the conversion to be partial but repeated scans allowed a conversion approaching 100% to be obtained with 20 scans generating a ca 60% level of oxidation. The process is inferred to lead to the formation of TiC@TiO2 core-shell nanoparticles (~12.5 nm core radius and ~5 nm shell width for a 60% conversion) and this value sharply decreases with an increase of pH. Independent measurements were conducted at a single NP level (via nano-impact experiments) to confirm the oxidation of the NPs, showing consistent agreement with the bulk measurements

Acoustic cavitation generates molecular mercury (II) hydroxide, Hg(OH)₂, from biphasic water/mercury mixtures

Emulsification of elemental mercury in aqueous solution in the form of grey particles occurs upon exposure to intense sound fields. We show the concomitant formation of molecular Hg(OH)2 in the solution phase reaching a saturation limit of 0.24 mM at 25°C. The formation of Hg(OH)2 is consistent with the ‘hot spot’ model which suggests the formation of OH. as a result of acoustic cavitation; such radicals are proposed to combine with Hg to form the Hg(OH)2 species here characterised using voltammetry

Quantifying the Polymeric Capping of Nanoparticles with X-Ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy was used to characterise silver nanoparticles capped with poly(ethylene) glycol (PEG) in a room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4 ]). The amounts of oxygen and silver present in nanoparticles capped with different molecular weight thiolated PEG chains were monitored, and the number of thiolated PEG chains per nanoparticle was calculated, an in situ characterisation not previously possible

Handheld electrochemical device for the determination of the strength of garlic

A handheld electrochemical sensor has been demonstrated for the quantification of the strength of garlic. The device is based on the enhanced voltammetric response in the presence of organosulfur compounds extracted from garlic. Convenient and disposable platinum screen-printed electrodes are employed. All measurements and data analyses are performed within the device. A linear response of the voltammetric peak current enhancement as a function of garlic concentration was observed, indicating the ability of the device to be applied to garlic samples of any strength. Importantly, this portable sensor can be used by non-scientifically skilled personnel and does not require expensive laboratory equipment. It is thus suitable for application in the food industry

Porosity control of the catalytic activity of platinum nanoparticles

Dendritic/mesoporous nanoparticle structures arise naturally and result from aggregation based growth mechanisms. These particles exhibit high surface areas but determining both the magnitude and chemical accessibility of the catalytic interface is not facile. Taking three structurally related but different sized platinum nanoparticle samples (30-70 nm), we demonstrate how the catalytic rate of two archetypal surface limited reactions scale not with the square of the particle radius but with a power law of 2.6-2.9. This power law directly reflects the mesoporosity of the nanoparticles; the internal surface of the nanoparticles is both chemically accessible and contributes to the catalytic activity. For 70 nm particles, up to 60% of the catalytic surface is contained in the internal structure of the particle

Singlet Oxygen and the Origin of Oxygen Functionalities on the Surface of Carbon Electrodes

The generation of oxygen-containing functionalities on pristine carbon surfaces is investigated and shown to be light sensitive, specifically to infra-red radiation. A mechanistic route involving singlet oxygen, 1 O2 , is proposed and evidenced

Versatile electrochemical sensing platform for bacteria

Bacterial infections present one of the leading causes for mortality worldwide, resulting in an urgent need for sensitive, selective, cost efficient and easy to handle technologies to rapidly detect contamination and infections with pathogens. The presented research reports a fully functional chemical detection principle, addressing all of the above mentioned requirements for a successful biosensing device. At the examples of Escherichia coli and Neisseria gonorrhoeae, we present an electrochemical biosensor, based on the bacterial expression of cytochrome c oxidase, for the selective detection of clinically relevant concentrations within seconds after pathogen immobilization. The generality of the biochemical re-action, as well as the easy substitution of target specific antibodies make this concept applicable to a large number of different pathogenic bacteria. The successful transfer of this semi-direct detection principle onto inexpensive screen printed electrodes for portable devices represents a potential major advance in the field of biosensor development

Denitrification and nitrous oxide emissions from riparian forests soils exposed to prolonged nitrogen runoff

Compared to upland forests, riparian forest soils have greater potential to remove nitrate (NO3) from agricultural run-off through denitrification. It is unclear, however, whether prolonged exposure of riparian soils to nitrogen (N) loading will affect the rate of denitrification and its end products. This research assesses the rate of denitrification and nitrous oxide (N2O) emissions from riparian forest soils exposed to prolonged nutrient run-off from plant nurseries and compares these to similar forest soils not exposed to nutrient run-off. Nursery run-off also contains high levels of phosphate (PO4). Since there are conflicting reports on the impact of PO4 on the activity of denitrifying microbes, the impact of PO4 on such activity was also investigated. Bulk and intact soil cores were collected from N-exposed and non-exposed forests to determine denitrification and N2O emission rates, whereas denitrification potential was determined using soil slurries. Compared to the non-amended treatment, denitrification rate increased 2.7- and 3.4-fold when soil cores collected from both N-exposed and non-exposed sites were amended with 30 and 60 μg NO3-N g-1 soil, respectively. Net N2O emissions were 1.5 and 1.7 times higher from the N-exposed sites compared to the non-exposed sites at 30 and 60 μg NO3-N g-1 soil amendment rates, respectively. Similarly, denitrification potential increased 17 times in response to addition of 15 μg NO3-N g-1 in soil slurries. The addition of PO4 (5 μg PO4–P g-1) to soil slurries and intact cores did not affect denitrification rates. These observations suggest that prolonged N loading did not affect the denitrification potential of the riparian forest soils; however, it did result in higher N2O emissions compared to emission rates from non-exposed forests

Understanding nanoparticle porosity via nanoimpacts and XPS: electro-oxidation of platinum nanoparticle aggregates

The porosity of platinum nanoparticle aggregates (PtNPs) is investigated electrochemically via particle-electrode impacts and by XPS. The mean charge per oxidative transient is measured from nanoimpacts; XPS shows the formation of PtO and PtO2 in relative amounts defined by the electrode potential and an average oxidation state is deduced as a function of potential. The number of platinum atoms oxidised per PtNP is calculated and compared with two models: solid and porous spheres, within which there are two cases: full and surface oxidation. This allows insight into extent to which the internal surface of the aggregate is ‘seen’ by the solution and is electrochemically active

Fluoro-Electrochemistry Based Phytoplankton Bloom Detection and Enumeration; Field Validation of a New Sensor for Ocean Monitoring

Phytoplankton are essential for the health of our oceans, yet existing in situ methods for monitoring phytoplankton abundance and community structure are limited, with relatively poor spatiotemporal coverage and taxonomic resolution, particularly among the nanoplankton size range. Here, we build on previous work and present field testing of a novel reagent-free fluoro-electrochemical technique for monitoring changes in nanoplankton abundance and community structure in natural seawater samples. This was achieved through the construction of a prototype sensor, which was then tested over a 3-month Spring−Summer period in 2023 with samples collected from the L4 station (Western English Channel). The measurements made by our sensor were successfully validated alongside microscope-based taxonomic enumerations and analytical flow cytometry. Of the phytoplankton functional groups of interest, our results demonstrate particularly strong correlations between the sensor and both microscope-based taxonomy and flow cytometry for enumerating small coccolithophorids (i.e., calcifying Isochrysidales, of the Gephyrocapsa genus) and between the prototype and microscope-based taxonomy for enumerating diatoms. We demonstrate that the inclusion of traditionally hard to identify nanoflagellates in our classifications has minimal effect on our ability to monitor overall shifts in community structure and bloom detection. Taking things forward, the potential for in situ deployment is discussed