Efficient removal of 2,4,6-trinitrotoluene (TNT) from industrial/military wastewater using anodic oxidation on boron-doped diamond electrodes

With growing public concern about water quality particular focus should be placed on organic micropollutants, which are harmful to the environment and people. Hence, the objective of this research is to enhance the security and resilience of water resources by developing an efficient system for reclaiming industrial/military wastewater and protecting recipients from the toxic and cancerogenic explosive compound-2,4,6-trinitrotoluene (TNT), which has been widely distributed in the environment. This research used an anodic oxidation (AO) process on a boron-doped diamond (BDD) electrode for the TNT removal from artificial and real-life matrices: marine water and treated wastewater. During experiments, TNT concentrations were significantly decreased, reaching the anodic degradation efficiency of above 92% within two hours and > 99.9% after six hours of environmental sample treatment. The presented results show the great potential of AO performed on BDD anodes for full-scale application in the industry and military sectors for TNT removal.

Conductive printable electrodes tuned by boron-doped nanodiamond foil additives for nitroexplosive detection

An efficient additive manufacturing-based composite material fabrication for electrochemical applications is reported. The composite is composed of commercially available graphene-doped polylactide acid (G-PLA) 3D printouts and surface-functionalized with nanocrystalline boron-doped diamond foil (NDF) additives. The NDFs were synthesized on a tantalum substrate and transferred to the 3D-printout surface at 200 °C. No other electrode activation treatment was necessary. Different configurations of low- and heavy-boron doping NDFs were evaluated. The electrode kinetics was analyzed using electrochemical procedures: cyclic voltammetry and electrochemical impedance spectroscopy. The quasi-reversible electrochemical process was reported in each studied case. The studies allowed confirmation of the CV peak-to-peak separation of 63 mV and remarkably high heterogeneous electron transfer rate constant reaching 6.1 × 10⁻² cm s⁻¹ for 10 k ppm [B]/[C] thin NDF fitted topside at the G-PLA electrode. Differential pulse voltammetry was used for effective 2,4,6-trinitrotoluene (TNT) detection at the studied electrodes with a 87 ppb limit of detection, and wide linearity range between peak current density and the analyte concentration (0.064 to 64 ppm of TNT). The reported electrode kinetic differences originate primarily from the boron-dopant concentration in the diamond and the various contents of the non-diamond carbon phase.

Fluorophenol-Containing Hydrogen-Bond Acidic Polysiloxane for Gas Sensing-Synthesis and Characterization

In this work, the synthesis of a new polysiloxane, poly {dimethylsiloxane-co-[4-(2,3-difluoro-4-hydroxyphenoxy) butyl] methylsiloxane} (dubbed PMFOS), is presented. This polymer exhibits high hydrogen bond acidity and was designed to be used as a sensor layer in gas sensors. The description of the synthetic route of the PMFOS has been divided into two main stages: the synthesis of the functional substituent 4-(but-3-en-1-yloxy)-2,3-difluorophenol, and the post-polymerization functionalization of the polysiloxane chain (methylhydrosiloxane-dimethylsiloxane copolymer) via hydrosilylation. The synthesized material was subjected to instrumental analysis, which confirmed its structure. The performed thermal analysis made it possible to determine some properties important for the sensor application, such as glass transition temperature and decomposition temperature. The results showed that PMFOS meets the requirements for materials intended for use in gas sensors based on acoustoelectric transducers.

Properties of Polyethylene Terephthalate (PET) after Thermo-Oxidative Aging

The influence of the thermo-oxidative aging semi-crystalline polyethylene terephthalate process on the thermal and mechanical properties was analysed in the article. For this purpose, PET was aged at 140 °C for 21, 35 and 56 days. The research showed that as a result of aging, the amount of the crystalline phase increases by about 8%, which translates into the properties of the aged material. The glass transition and melt temperature of lamellar crystals formed during first and second crystallisation increase with aging. The mechanical properties of the material were analysed in the temperature range of 25 to 75 °C. The tests were showing an increase in Young’s modulus and a decrease in elongation at the break as a result of aging. This phenomenon was particularly visible during tests at 75 °C and during the morphological observation of the fracture surface, where the fracture character of the material changes from ductile to brittle. In the case of the material aged for the longest time, the temperature has a negligible influence on the elongation at break.

Directed, Elliptic, and Higher Order Flow Harmonics of Protons, Deuterons, and Tritons in Au+Au Collisions at sqrt[s_{NN}]=2.4 GeV

Flow coefficients v_{n} of the orders n=1-6 are measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI for protons, deuterons, and tritons as a function of centrality, transverse momentum, and rapidity in Au+Au collisions at sqrt[s_{NN}]=2.4  GeV. Combining the information from the flow coefficients of all orders allows us to construct for the first time, at collision energies of a few GeV, a multidifferential picture of the angular emission pattern of these particles. It reflects the complicated interplay between the effect of the central fireball pressure on the emission of particles and their subsequent interaction with spectator matter. The high precision information on higher order flow coefficients is a major step forward in constraining the equation of state of dense baryonic matter.

Exploring time like tranistions in pp, πp and AA reactions with HADES

Radiative transition of an excited baryon to a nucleon with emission of a virtual massive photon converting to dielectron pair (Dalitz decays) provides important information about baryon-photon coupling at low q2 in timelike region. A prominent enhancement in the respective electromagnetic transition Form Factors (etFF) at q2 near vector mesons ρ/ω poles has been predicted by various calculations reflecting strong baryon-vector meson couplings. The understanding of these couplings is also of primary importance for the interpretation of the emissivity of QCD matter studied in heavy ion collisions via dilepton emission. Dedicated measurements of baryon Dalitz decays in proton-proton and pion-proton scattering with HADES detector at GSI/FAIR are presented and discussed. The relevance of these studies for the interpretation of results obtained from heavy ion reactions is elucidated on the example of the HADES results.

Interactions of Fe-N-S Co-Doped Porous Carbons with Bacteria: Sorption Effect and Enzyme-Like Properties

Carbon-based (nano)materials doped with transition metals, nitrogen and other heteroatoms are considered active heterogeneous catalysts in a wide range of chemical processes. Recently they have been scrutinized as artificial enzymes since they can catalyze proton-coupled electron transfer reactions vital for living organisms. Herein, interactions between Gram-positive and Gram-negative bacteria and either metal-free N and/or S doped or metal containing Fe-N-S co-doped porous carbons are studied. The Fe- and N-co-doped porous carbons (Fe-N-C) exhibit enhanced affinity toward bacteria as they show the highest adsorption capacity. Fe-N-C materials also show the strongest influence on the bacteria viability with visible toxic effect. Both types of bacteria studied reacted to the presence of Fe-doped carbons in a similar manner, showing a decrease in dehydrogenases activity in comparison to controls. The N-coordinated iron-doped carbons (Fe-N-C) may exhibit oxidase/peroxidase-like activity and activate O2 dissolved in the solution and/or oxygen-containing species released by the bacteria (e.g., H2O2) to yield highly bactericidal reactive oxygen species. As Fe/N/ and/or S-doped carbon materials efficiently adsorb bacteria exhibiting simultaneously antibacterial properties, they can be applied, inter alia, as microbiological filters with enhanced biofouling resistance.

Electrochemical determination of nitroaromatic explosives at boron-doped diamond/graphene nanowall electrodes: 2,4,6-trinitrotoluene and 2,4,6-trinitroanisole in liquid effluents

The study is devoted to the electrochemical detection of trace explosives on boron-doped diamond/graphene nanowall electrodes (B:DGNW). The electrodes were fabricated in a one-step growth process using chemical vapour deposition without any additional modifications. The electrochemical investigations were focused on the determination of the important nitroaromatic explosive compounds, 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitroanisole (TNA). The distinct reduction peaks of both studied compounds were observed regardless of the pH value of the solution. The reduction peak currents were linearly related to the concentration of TNT and TNA in the range from 0.05-15 ppm. Nevertheless, two various linear trends were observed, attributed respectively to the adsorption processes at low concentrations up to the diffusional character of detection for larger contamination levels. The limit of detection of TNT and TNA is equal to 73 ppb and 270 ppb, respectively. Moreover, the proposed detection strategy has been applied under real conditions with a significant concentration of interfering compounds - in landfill leachates. The proposed bare B:DGNW electrodes were revealed to have a high electroactive area towards the voltammetric determination of various nitroaromatic compounds with a high rate of repeatability, thus appearing to be an attractive nanocarbon surface for further applications.

Analysis of samples of explosives excavated from the Baltic Sea floor

After World War II, conventional and chemical ammunition containing mainly secondary and primary explosives was dumped in the sea. Explosives have medium toxicity to aquatic organisms, earthworms and indigenous soil microorganisms. Therefore, environmental monitoring is required, especially for dumped munitions. The main aspect of this work was to analyse the samples of lumps and sediments taken from the Baltic seabed. These samples were potentially explosives. The main goal of the study was to identify the type and composition of studied materials. In order to determine the chemical composition of samples of explosives, we used as follows: GC-MS/MS, LC-HRMS and NMR. Additionally, to determine the energetic properties we performed microcalorimetric-thermogravimetric analysis. Based on the obtained results, the composition of this explosive was TNT (41%), RDX (53%), aluminium powder (5%), and degradation products (below 1%). The resulting composition indicates that the analysed material can be classified in the "torpex" family, widely used during World War II. Regarding the results of the microcalorimetric analysis, we can conclude that excavated fragments of explosives are in very good condition and they still can detonate after being initiated. Therefore, there is a threat that they could be used for criminal or terrorist purposes.

Sea-dumped ammunition as a possible source of mercury to the Baltic Sea sediments

After World War II, as a move toward Germany demilitarization, up to 385,000 t of munitions were sunk in the Baltic Sea. Munition containing various harmful substances, including chemical warfare agents (CWA) and explosives, that can affect marine biota were dumped on the seafloor. Some of those objects contained mercury, either as elemental mercury or mercury compounds (e.g., mercury fulminate, a common explosive primer), and thus could act as a specific local source of mercury in the dumping areas. Unfortunately, there is a lack of information on how dumped munitions impact the mercury concentrations in the Baltic Sea sediments. This report aims to answer the question how much sedimentary mercury in the dumping areas originates from munitions and to determine to what extent the mercury present in those areas originates from mercury fulminate. Concentrations of total sedimentary mercury- Hg_TOT in samples collected from conventional (Kolberger Heide) and chemical (Bornholm Deep) munitions dumping sites are characterized by high variability. However, an increase in Hg_TOT concentrations was observed with a decreasing distance to particular munition objects at both study sites. Moreover, mercury speciation in sediments from Kolberger Heide proves that the mercury there can be traced back directly to mercury fulminate. Results of our study confirm that munitions dumpsites are a local point sources of mercury. Due to the ecosystem constrains, varying transport modes and pathways, and both unknown and varying decomposition rates, these sea-bed mercury concentrations are hard to evaluate quantitatively. Therefore we recommend that further detailed studies should be conducted to assess sedimentary mercury provenience in munitions dumpsites more accurately.

Strong Absorption of Hadrons with Hidden and Open Strangeness in Nuclear Matter

We present the first observation of K^{-} and ϕ absorption within nuclear matter by means of π^{-}-induced reactions on C and W targets at an incident beam momentum of 1.7  GeV/c studied with HADES at SIS18/GSI. The double ratio (K^{-}/K^{+})_{W}/(K^{-}/K^{+})_{C} is found to be 0.319±0.009(stat)_{-0.012}^{+0.014}(syst) indicating a larger absorption of K^{-} in heavier targets as compared to lighter ones. The measured ϕ/K^{-} ratios in π^{-}+C and π^{-}+W reactions within the HADES acceptance are found to be equal to 0.55±0.04(stat)_{-0.07}^{+0.06}(syst) and to 0.63±0.06(stat)_{-0.11}^{+0.11}(syst), respectively. The similar ratios measured in the two different reactions demonstrate for the first time experimentally that the dynamics of the ϕ meson in nuclear medium is strongly coupled to the K^{-} dynamics. The large difference in the ϕ production off C and W nuclei is discussed in terms of a strong ϕN in-medium coupling. These results are relevant for the description of heavy-ion collisions and the structure of neutron stars.

Time-Like Baryon Transitions studies with HADES

The HADES collaboration uses the e+e− production as a probe of the resonance matter produced in collisions at incident energies of 1-3.5 GeV/nucleon at GSI. Elementary reactions provide useful references for these studies and give information on resonance Dalitz decays (R→Ne+e−). Such processes are sensitive to the structure of time-like electromagnetic baryon transitions in a kinematic range where (off-shell) vector mesons play a crucial role. Results obtained in proton-proton reactions and in a commissioning pion-beam experiment are reported and prospects for future pion beam experiments and for first hyperon Dalitz decay measurements are described. The connection with the investigations of medium effects to be continued with HADES in the next years at SIS18 and SIS100 is also discussed.

Development of analytical methods used for the study of 2,4,6-trinitrotoluene degradation kinetics in simulated sediment samples from the Baltic Sea

Large amounts of ammunition containing 2,4,6-trinitrotoluene (TNT) and other substances were dumped in the Baltic Sea after WWII. Considering progressive corrosion processes, studying the transformation of TNT occurring in the environment constitutes an important aspect of a possible associated risk. This study focused on the transformations of TNT in simulated conditions of the Baltic Sea bottom sediment. Methods of analysis of TNT and selected products of its transformations were developed for that purpose. The developed methods allowed for the determination of selected compounds below 1 ng/g. Systematic monitoring of TNT transformations in the environment of the bottom sediment was performed. This allowed for the determination of the kinetics of TNT degradation and identification of degradation reaction products. Based on the obtained results, the TNT decay half-time in conditions present in the Baltic Sea was estimated to be 16.7 years for the abiotic environment and 5.6 for the biotic environment.

5,5',6,6'-Tetranitro-2,2'-bibenzimidazole: A Thermally Stable and Insensitive Energetic Compound

A new energetic compound, namely a secondary explosive (5,5',6,6'-tetranitro-2,2'-bibenzimidazole, TNBBI) with high thermal stability is described. TNBBI is synthesized through direct nitration of 2,2'-bibenzimidazole with nitric acid. TNBBI decomposes exothermically at 394 °C without visible melting. The heat of combustion and the standard enthalpy of formation are determined experimentally. The detonation parameters calculated for the new compound are slightly lower than those for TNT. However, the combination of TNBBI's high decomposition temperature and low sensitivity make it a promising thermally stable energetic compound. The structure of the new compound is confirmed by NMR and IR spectroscopy.

Characterization of prospective explosive materials using terahertz time-domain spectroscopy

We investigated six prospective explosive materials in the terahertz range using time-domain spectroscopy. A family of energetic azotetrazolate salts and two caged nitramines were studied. A number of distinct spectral features were observed in the 0.8-3.2 THz frequency range. In transmission configuration in ambient temperature, we determined the absorption coefficient and the refractive index of the materials, which were compressed as pellets. Because the visibility of some absorption peaks was not clear, additionally we performed characterization of these materials in a temperature range from -175°C to 0°C, which resulted in highlighting peaks with low amplitude. Because the considered explosives are insensitive to compression, we also measured them using an attenuated total reflection (ATR) technique, in which sample preparation is easier than with pressed pellets. The absorption peaks measured by ATR agree well with those determined in transmission. This suggests that ATR also can be used for identification of these classes of materials.

Interaction of Gram-Positive and Gram-Negative Bacteria with Ceramic Nanomaterials Obtained by Combustion Synthesis - Adsorption and Cytotoxicity Studies

This paper presents the interactions of Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas putida) bacteria with ceramic materials obtained by combustion synthesis. These studies were conducted based on an analysis of the adsorption of bacteria onto aggregates of ceramic materials in an aqueous suspension. The materials used in the studies were of a nanostructured nature and consisted mainly of carbides: silicon carbide (SiC) in the form of nanofibers (NFs) and nanorods (NRs), titanium carbide, and graphite, which can also be formed by combustion synthesis. Micrometric SiC was used as a reference material. Gram-positive bacteria adsorbed more strongly to these materials. It seems that both the point of zero charge value and the texture of the ceramic material affected the bacterial adsorption process. Additionally, the viability of bacteria adsorbed onto aggregates of the materials decreased. Generally, P. putida cells were more sensitive to the nanomaterials than S. aureus cells. The maximum loss of viability was noted in the case of bacteria adsorbed onto NRSiC and NFSiC aggregates.

Interaction of Gram-Positive and Gram-Negative Bacteria with Ceramic Nanomaterials Obtained by Combustion Synthesis – Adsorption and Cytotoxicity Studies

This paper presents the interactions of Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas putida) bacteria with ceramic materials obtained by combustion synthesis. These studies were conducted based on an analysis of the adsorption of bacteria onto aggregates of ceramic materials in an aqueous suspension. The materials used in the studies were of a nanostructured nature and consisted mainly of carbides: silicon carbide (SiC) in the form of nanofibers (NFs) and nanorods (NRs), titanium carbide, and graphite, which can also be formed by combustion synthesis. Micrometric SiC was used as a reference material. Gram-positive bacteria adsorbed more strongly to these materials. It seems that both the point of zero charge value and the texture of the ceramic material affected the bacterial adsorption process. Additionally, the viability of bacteria adsorbed onto aggregates of the materials decreased. Generally, P. putida cells were more sensitive to the nanomaterials than S. aureus cells. The maximum loss of viability was noted in the case of bacteria adsorbed onto NRSiC and NFSiC aggregates.

Oxidative stress in bacteria (Pseudomonas putida) exposed to nanostructures of silicon carbide

Silicon carbide (SiC) nanostructures produced by combustion synthesis can cause oxidative stress in the bacterium Pseudomonas putida. The results of this study showed that SiC nanostructures damaged the cell membrane, which can lead to oxidative stress in living cells and to the loss of cell viability. As a reference, micrometric SiC was also used, which did not exhibit toxicity toward cells. Oxidative stress was studied by analyzing the activity of peroxidases, and the expression of the glucose-6-phosphate dehydrogenase gene (zwf1) using real-time PCR and northern blot techniques. Damage to nucleic acid was studied by isolating and hydrolyzing plasmids with the formamidopyrimidine [fapy]-DNA glycosylase (also known as 8-oxoguanine DNA glycosylase) (Fpg), which is able to detect damaged DNA. The level of viable microbial cells was investigated by propidium iodide and acridine orange staining.

Adsorption studies of the gram-negative bacteria onto nanostructured silicon carbide

In this study, we demonstrated a significant adsorption of Pseudomonas putida bacteria onto aggregates of nanofibers (NFSiC) and nanorods (NRSiC) of silicon carbide (SiC) in aqueous suspensions. Langmuir and Freundlich isotherms were used to quantify adsorption affinities. It was found that adsorption of the bacteria strongly depended on the structure of the silicon carbide and the pH of the aqueous solution, which affected the isoelectric point of both the silicon carbide and the bacterial cells. The strongest affinity of bacteria was noted in the case of NRSiC aggregates. Affinity was inversely proportional to pH. Similarly, the adsorption of bacteria to the surface of the aggregates increased with decreasing pH. For NFSiC, the affinity of the bacteria for the surface of the aggregates was also inversely proportional to pH. However, adsorption increased at higher pH values. This discrepancy was explained by microscopic analysis, which showed that the bacterial cells were both adsorbed onto and trapped by NFSiC. The adsorption of bacteria onto a micrometric silicon carbide reference material was significantly smaller than adsorption onto nanostructured SiC.

Toxicity assessment of SiC nanofibers and nanorods against bacteria

In the present study, evidence of the antibacterial effects of silicon carbide (SiC) nanofibers (NFSiC) and nanorods (NRSiC) obtained by combustion synthesis has been presented. It has been shown that the examined bacteria, Pseudomonas putida, could bind to the surface of the investigated SiC nanostructures. The results of respiration measurements, dehydrogenase activity measurements, and evaluation of viable bacteria after incubation with NFSiC and NRSiC demonstrated that the nanostructures of SiC affect the growth and activity of the bacteria examined. The direct count of bacteria stained with propidium iodide after incubation with SiC nanostructures revealed that the loss of cell membrane integrity could be one of the main effects leading to the death of the bacteria.

Adsorption studies of azotetrazolate and 3,6-dihydrazinotetrazine on peat

The objective of our studies was the evaluation of the adsorption process of two high-nitrogen compounds-dihydrazinotetrazine (DHTz) and azotetrazolate ion (AZ)-on a chosen peat. The experiments were performed using a static method at three different temperatures (283, 298, and 333 K). The adsorption process of DHTz and AZ on peat was characterized by isotherms according to the Freundlich and Langmuir models. The obtained correlations between adsorption and equilibrium concentration were in good accordance with the Freundlich and Langmuir models, as confirmed by high values of the correlation coefficients (0.97-0.99). Adsorption of AZ on peat was less efficient than that of DHTz, and this inference was experimentally proven. The maximum surface coverages of peat particles with adsorbate according to the Langmuir model were calculated as 0.02 and 0.17 mol kg(-1) (at 298 K) for AZ and DHTz, respectively. The determined adsorption equilibrium constants confirmed greater adsorption of DHTz on the investigated peat. It can be concluded that adsorption of AZ occurred to a much lesser extent compared to that of DHTz, pointing to a potentially greater threat of migration of soluble azotetrazolates in soil. Standard enthalpies of adsorption estimated for AZ and DHTz were -11.1 and -23.7 kJ mol(-1), respectively. Based on these adsorption enthalpy values, it can be stated that both investigated compounds are adsorbed on peat by a physisorption process.

Combustion Synthesis as a Novel Method for Production of 1-D SiC Nanostructures

1-D nanostructures of cubic phase silicon carbide (beta-SiC) were efficiently produced by combustion synthesis of mixtures containing Si-containing compounds and halocarbons in a calorimetric bomb. The influence of the operating parameters on 1-D SiC formation yield was studied. The heat release, the heating rate, and the chamber pressure increase were monitored during the process. The composition and structural features of the products were characterized by elemental analysis, X-ray diffraction, differential thermal analysis/ thermogravimetric technique, Raman spectroscopy, scanning and transmission electron microscopy, and energy-dispersive X-ray spectrometry. This self-induced growth process can produce SiC nanofibers and nanotubes ca. 20-100 nm in diameter with the aspect ratio higher than 1000. Bulk scale Raman studies showed the product to be comprised of mostly cubic polytype of SiC and that finite size effects are present. We believe that the nucleation mechanism involving radical gaseous species is responsible for 1-D nanostructures growth. The present study has enlarged the family of nanofibers and nanotubes available and offers a possible, new general route to 1-D crystalline materials.