Fluorine Content Research Articles

Geopolymer-based radiative cooling coating: Tailoring surface hydrophobic properties while retaining optical characteristics

The longevity of geopolymer-based radiative cooling coatings is questionable due to their hydrophilic nature. This study used four hydrophobic agents - sodium methyl silicate (SMS), polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), and triethoxyoctylsilane (TEOS) - to modify the surface hydrophobicity of geopolymer while maintaining its optical properties. The optimal agent contents were determined by optical performance and water contact angle: 5 % for SMS, 10 % for 50 cP viscosity PDMS, and a single-layer thickness for PTFE and TEOS (60 °C). The agents' working mechanisms were analyzed using FTIR and XRD characterization: SMS forms a hydrophobic alkylsilanol layer by reacting with the geopolymer's silanol group; PDMS lowers the geopolymer's surface energy with its hydrophobic methyl groups; PTFE's low electric polarizability is due to its fluorine content; and TEOS replaces the geopolymer surface's hydroxyl groups with hydrophobic octyl groups. The long-term durability of these modified coatings was evaluated through outdoor exposure tests, resulting in total solar reflectance losses of 0.74 %, 1.9 %, 3.9 %, and 0.05 % respectively. A slight reduction in the water contact angle confirmed their enduring hydrophobic characteristics. These modification methods open up possibilities for the practical use of hydrophobic geopolymer radiative cooling coatings.

Simultaneous evolutions in composition, structure, morphology, and upconversion luminescence of BiOxFy:Yb/Er microcrystals and their application for ratiometric temperature sensing

Lanthanide upconversion luminescent materials featuring multi-peak and tunable emissions allow for ratiometric luminescence thermometry in a remote detection manner. However, wide explorations are still required to develop relevant materials for efficient thermometric performances. Herein, Yb3+/Er3+ co-doped non-stoichiometric analogues of bismuth oxyfluoride were obtained by simply tuning the F−/(Bi3+ + Ln3+) molar ratio of the reactants in a solid-state reaction method, for the first time. We achieved simultaneous regulations in composition, structure, morphology, and upconversion luminescence properties of BiOxFy:Yb/Er (2/1 mol%) microcrystals. Compositional analysis revealed not only the predictable increase of fluorine content, but also the constant O/(Bi + Ln) atomic ratios in all nominal BiOxFy:Yb/Er. Experimental results showed the structure and morphology evolutions from hexagonal-phase micro-flowers, to tetragonal-phase microplates, and further to orthorhombic-phase irregular microcrystals. Benefiting from adjustable composition, structure and morphology, up-conversion luminescence with adjustable intensity and color was obtained. Temperature dependent upconversion properties and ratiometric thermometric performances based on the thermally coupled levels, 2H11/2 and 4S3/2 of Er3+, were explored. BiOF:Yb/Er, BiO0.67F1.66:Yb/Er, and BiF3:Yb/Er microcrystals were found as suitable temperature sensing candidates with operating temperature range as wide as 298−673/723 K, high relative sensitivity up to 1.24% K-1, and minimum temperature uncertainty of 0.15 K. These results benefit not only further explorations for high-performance lanthanide-based luminescence thermometers, but also the chemistry of fluorides made from the solid-state reaction method.

Fluorine contamination, mobility, and risks in soils at a phosphate-gypsum waste landfill: a new analytical method and comparison with previous methods.

This study used a new X-ray fluorescence (XRF)-based analytical method with better precision and sensitivity to evaluate the fluorine concentrations in soil. It was hypothesized that the XRF method with a pellet-synthesizing procedure may effectively analyze the fluorine concentrations in soil with ease and reliability. The total fluorine concentrations determined using XRF were compared with those determined using three different types of analytical protocols-incineration/distillation, alkaline fusion, and aqua regia extraction procedures. Among the three procedures, the incineration/distillation procedure did not show reliable precision and reproducibility. In contrast, the total fluorine concentrations determined using the XRF analysis were linearly correlated with those determined using the alkaline fusion and aqua regia extraction procedures. Based on the results of the Korean waste leaching procedure and toxicity characteristics leaching procedure, the leachability of fluorine from soil and waste was not directly related to total fluorine concentrations in soil. Risk assessment also revealed that the fluorine-rich soils did not show non-carcinogenic toxic effects, despite exceeding the regulation level (800mg/kg) in South Korea for total fluorine concentrations in soil. Our results suggest that XRF analysis in combination with the newly developed pretreatment method may be a promising alternative procedure for easily and rapidly determining the total fluorine concentration in soil. However, further efforts are needed to evaluate fluorine leachability and its associated risks in fluorine-contaminated soils.

Identifying PFAS hotspots in surface waters of South Carolina using a new optimized total organic fluorine method and target LC-MS/MS

Per- and polyfluoroalkyl substances (PFAS) are environmental contaminants of concern due to their long persistence in the environment, toxicity, and widespread presence in humans and wildlife. Knowledge regarding the extent of PFAS contamination in the environment is limited due to the need for analytical methods that can reliably quantify all PFAS, since traditional target methods using liquid chromatography (LC)-mass spectrometry (MS) fail to capture many. For a more comprehensive analysis, a total organic fluorine (TOF) method can be used as a screening tool. We combined TOF analysis with target LC-MS/MS analysis to create a statewide PFAS hotspot map for surface waters throughout South Carolina. Thirty-eight of 40 locations sampled contained detectable concentrations of organic fluorine (above 100 ng/L). Of the 33 target PFAS analyzed using LC-MS/MS, the most prevalent were perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluoroheptanoic acid (PFHpA), and perfluorohexanesulfonate (PFHxS). On average, LC-MS/MS only accounted for 2 % of the TOF measured. Locations with high TOF did not necessarily correlate to high total quantified PFAS concentrations and vice-versa, demonstrating the limitations of target PFAS analysis and indicating that LC-MS may miss highly contaminated sites. Results suggest that future surveys should utilize TOF to more comprehensively capture PFAS in water bodies.

Gamma-irradiated janus electrospun nanofiber membranes for desalination and nuclear wastewater treatment

This study presents the fabrication of double-layer electrospun nanofibrous membranes (DL-ENMs) using polyvinylidene fluoride (PVDF) and polyether sulfone (PES) based polymers with different degrees of hydrophilicity (PES, sulfonated PES, and PES with hydroxyl terminals). A comparative analysis was carried out with single-layer electrospun nanofiber membranes (SL-ENM) with a total thickness of about 375 μm. Using feed solutions, including sodium chloride, sodium nitrate, and simulated nuclear wastewater (SNWW), the performance of DL-ENMs was evaluated for desalination and radionuclide decontamination by direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) techniques. The results showed that DL-ENMs, especially those incorporating a sulfonated PES-based hydrophilic layer, exhibited superior permeate fluxes, reaching values of 72.72 kg/m2.h and 73.27 kg/m2.h in the DCMD using aqueous feed solutions of NaCl and NaNO3, respectively, and 70.80 kg/m2.h and 41.96 kg/m2.h using aqueous feed solutions of SNWW in DCMD and AGMD, respectively. Both SL-ENMs and DL-ENMs exhibited high rejection efficiencies and decontamination factors for the feed solutions (>99.9%). In addition, the prepared ENMs were exposed to gamma radiation to evaluate their applicability in real-life applications. The result of irradiation revealed the negative impact of gamma radiation on the fluorine content of PVDF which could be a critical point in using PVDF as a hydrophobic material for decontaminating nuclear wastewater by membrane distillation.

Impact of hydrogen plasma treatment on fluorine-contained silicon nitride films

It has been suggested that the trap energy level in silicon nitride (SiN) films becomes shallow due to hydrogen and fluorine incorporation, which causes a charge migration in the MONOS memory cells and deteriorates the data retention characteristics. To solve these issues, we have proposed the hydrogen plasma treatment and demonstrated the reduction of the shallow trap density consequent to the removal of hydrogen from SiN films. In this study, the hydrogen plasma treatment is applied to the fluorine-contained SiN films. The results show that deepening of the trap energy level contributing to hole current, decreasing of the shallow trap density contributing to charging and the fluorine concentration near at the SiN surface. These results are regarded to be due to the removal of fluorine in the SiN film through the reaction with hydrogen radicals (H*) during the hydrogen plasma treatment.

Room-temperature synthesis of fluorinated covalent organic framework decorated superhydrophobic sponges for highly efficient crude oil spill cleanup

Frequent oil spills cause substantial economic losses and pose a significant threat to human life. Urgent measures must be taken to develop a highly effective approach to mitigating oil spills and minimizing their potential consequences. Herein, we synthesized MS@COFs-F, fluorinated covalent organic framework-decorated superhydrophobic sponges, to clean up crude oil spills efficiently. The synthesis method involved a simple and effective room-temperature approach, utilizing 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) as the amine monomer and binding it with three aldehyde monomers of varying fluoride content. The MS@COFs-F with the highest fluorine content, known as MS@COFs-F4, exhibited low surface energy, superhydrophobicity (water contact angle of 155.7°), a large specific surface area of 180 m2/g, and exceptional chemical, mechanical, and thermal stability. MS@COFs-F4 demonstrated remarkable effectiveness in adsorbing crude oils and organic solvents of diverse viscosities, exhibiting an adsorption capacity between 68.5 and 125.9 g/g, achieving an oil–water separation efficiency exceeding 97.0 %. Additionally, MS@COFs-F4 showcased self-cleaning and flame-retardant properties, further enhancing its suitability for real-world applications. MS@COFs-F4 holds the potential to offer a novel, safe, and effective approach in addressing oil spill incidents.

Analysis of per- and polyfluoroalkyl substances (PFAS) in raw materials intended for the production of paper-based food contact materials – evaluating LC-MS/MS versus total fluorine and extractable organic fluorine

Per- and polyfluoroalkyl substances (PFAS) analysis has become crucial due to their presence in the environment, their persistence and potential health risks. These compounds are commonly used in food contact materials (FCM) as a coating to provide water and grease-repellent properties. One of the pathways for PFAS to enter the human body is either through direct consumption of contaminated food or indirectly through migration from FCM into food. The purpose of this study was to investigate where the initial contamination of paper FCM occurs. We analysed paper material consisting of fresh fibre and secondary materials, intended to produce food packaging for the presence of PFAS. The samples were extracted and analysed for 23 different PFAS substances using the targeted approach with LC tandem mass spectrometry (LC-MS/MS). This analytical technique detects specific, easily ionisable PFAS with high sensitivity. However, one drawback of this approach is that it allows the identification of less than 1% of the PFAS known today. For this reason, we used combustion ion chromatography (CIC) to determine the content of extractable organic fluorine compounds (EOF) and compare it to the total fluorine content. The targeted analysis using LC-MS/MS measured an average sum concentration of PFAS of 0.17 ng g−1 sample. Our research shows that the primary PFAS contamination happens during the recycling process since all of the samples in which the targeted PFAS were measured belonged to the secondary material. The most frequently detected analytes were PFOA and PFOS, detected in 90% and 62% of the samples, respectively, followed by PFBS (in 29% of the samples). CIC showed that measured PFAS via LC-MS/MS amount to an average of 2.7 × 10−4% of total fluorine content, whereas the EOF was under the LOD in all of the measured samples. This result highlights the complexity of the accurate determination of PFAS compounds, displaying what kind of information the chosen methods provide.

A flexible nanofiber membrane containing dendritic oxygen probe for visual monitoring pressure distribution

Pressure-sensitive paints (PSP) enable non-intrusive visualization of surface pressure distribution on model surface which is important for aerodynamic studies. However, conventional PSP materials suffer from photobleaching and inadequate sensitivity. In this work, we rationally designed and synthesized novel dendritic oxygen probes (PT1 and PT2) by covalently grafting fluorinated dendrons onto platinum tetrakis(pentafluorophenyl)porphyrin (PT0) (a common oxygen probe). Subsequently, PT2 loaded nanofibers membranes from polycaprolactone (PCL) were fabricated by electrospinning. Fabricated membranes showed high oxygen sensitivity (I0/I100 = 35.3) with excellent flexibility, good reversibility, and outstanding photostability (merely 2.0% intensity loss after prolonged irradiation). The pressure sensitivity was found around 0.73 % per kilopascal. Furthermore, significant variation in emission intensity with respect to the variation in air pressure (1.3–101.32 kPa), facilitates the naked eye visualization of the pressure distribution on the membrane surface. Such excellent oxygen and pressure sensitivity and photostability might be due to high fluorine contents of complex dendritic structure of PT2. This flexible fluorine-functionalized dendritic oxygen probe puts forward a facile and effective strategy to develop advanced PSP materials enabling accurate pressure mapping for aerodynamic studies.

Effect of fluorine on terrace-ledge-kink morphology and valence state of copper and titanium ions in CaCu3Ti4O12

Ceramic CaCu3Ti4O12 (ССТО), Ca0.98Cu3Ti4O11.96F0.04 (CΔCTOF), and CaCu3Ti4O11.92F0.08 (CCTOF) were synthesized by the solid-state reaction technique. Fluorine stimulates the formation of Cu-depleted grains, Cu3+ ions, and Cu-rich composites CuO-xCCTO-yTiO2-zSiO2-wСaF2 (w < z < y < x < 1), which include parts of grinding bodies. The observed structures are distinct from simple grain boundaries of the perovskite phase. They exhibit a terrace-ledge-kink (TLK) morphology and, in some cases, the presence of twinning planes, both independent of fluorine content. They are responsible for the nanoscale barrier layer capacitance (NBLC) component of the dielectric response of both CCTO and CuO ceramics. Changes in the unit cell parameter a, and titanium and copper valences indicate that Ca2+ ions occupy part of Cu vacancies in the grains of CCTO and CCTOF. In CΔCTOF, Ti3+ ions in the copper sublattice were found for the first time using NMR. The maximum ε′1kHz = 6.9 × 104 demonstrates CΔCTOF and the minimum tan δ = 0.045 is characteristic of CCTOF.

Enabling the use of lithium bis(trifluoromethanesulfonyl)imide as electrolyte salt for Li‐ion batteries based on silicon anodes and Li(Ni0.4Co0.4Mn0.2)O2 cathodes by salt additives

AbstractLithium bis(trifluoromethanesulfonyl)imide (LiFSI) is a promising alternative salt for Li‐ion batteries. Unlike the conventional LiPF6, it is not prone to HF formation, and thus resistant to moisture. However, for cell voltages relevant for high energy cathodes (&gt;4.2 V), the aluminium current collector will corrode in electrolytes based on this salt, and mitigation strategies are needed. Here, the use of Lithium tetrafluoroborate (LiBF4) and Lithium difluoro(oxalato)borate (LiDFOB) salts as additives is investigated, in order to enable the use of LiFSI‐based electrolytes. The performance of the electrolytes is evaluated separately for high content silicon anodes, (NMC442) cathodes and the aluminium current collector by electrochemical methods and post mortem analysis by SEM imaging and X‐ray photoelectron spectroscopy (XPS). Electrolytes with LiDFOB as additive showed the best performance for all components, and were therefore selected for cycling in full cells, composed of silicon anodes and NMC442. Results show that LiFSI‐based electrolytes with LiDFOB additive has an electrochemical performance similar to conventional electrolytes, and is thus a competitive, alternative electrolyte with a low fluorine content. Furthermore, it is verified that the good SEI forming properties of LiFSI based electrolytes known from cycling in half cells, is also preserved during cycling in full cells

Heating aluminum dross: Harmless process and utilization as cement admixture

Phosphogypsum (PG) and aluminum dross (AD) with harmful impurities seriously hinder its large-scale engineering utilization. In this paper, the properties of AD and PG as cement admixture were investigated with the aim of reducing the environmental pollution and landfill stockpiling pressure. The migration and transformation rules under crucial factors were analyzed by different characterization methods while AD was heated at different temperature. Then, the compressive strength, soluble phosphorus and fluorine concentration, hydration heat and expansion rate of specimens prepared with AD, PG, and Portland cement (PC) were evaluated to illustrate the hydration mechanism. Compared to the other experiment sets, the results indicated that AD treated at 900°C not only had a higher nitrogen removal rate, but also maintained hydration activity at a relatively high level. Moreover, Heating AD at 900℃ effectively accelerated the dissolution of gypsum and calcium silicate, resulting in increased formation of ettringite (AFt), calcium silicate hydrates (C-S-H) and calcium aluminium hydrates (C-A-H). When the binder consisted of 14% heated aluminium dross (HAD), 6% PG, and 80% PC, the specimen reached the highest compressive strength value at 25.87 MPa. This work provided a new strategy for synergistic utilization of PG and AD, promoting the development of environment-friendly industrial wastes-based cementitious materials effectively.

Enhanced high-temperature tribological performance of fluorinated tetrahedral amorphous carbon (ta-C:F) coatings in sliding applications

This study investigated the dry sliding behaviour of fluorinated tetrahedral amorphous carbon (ta-C:F) coatings against uncoated 52100 steel at temperatures ranging from 25 °C to 300 °C. The ta-C:F coatings demonstrated significant reductions in both the coefficient of friction(COF) during the running-in stage and at steady state, particularly within the temperature range of 25 °C to 200 °C, surpassing the performance of well-established a-C:H coatings. SEM analyses revealed the formation of transfer layers on the contact surface of 52100 steel when tested against ta-C:F coatings at temperatures up to 200 °C, while none were detected at temperatures ≥250 °C. Raman spectroscopy indicated a transition from sp3 to sp2 carbon structures in the carbonaceous transfer layers with increasing temperature, and XPS scans confirmed an increase in fluorine (F) concentration within these layers, correlating with reduced COF. The comparative analysis at 120 °C emphasized the intrinsic advantages of ta-C:F coatings in high-temperature applications, demonstrating a nearly 50% lower COF (0.08) when compared to traditional boundary-lubricated steel-to-steel sliding contacts. These findings have significant implications for enhancing the efficiency and durability of various mechanical systems, particularly in industries like automotive and manufacturing.

Technological Methods for Increasing the Fluorine Content in SrO–Al2O3–P2O3–SiO2–F Glass for Glass-Ionomer Cement

Technological Methods for Increasing the Fluorine Content in SrO–Al2O3–P2O3–SiO2–F Glass for Glass-Ionomer Cement

PRESENT-DAY FLUORINE CONCENTRATION IN THE OB RIVER WATER

Based on the potentiometric measurements average fluorine concentrations for different phases of the hydrological regime were determined in water samples taken in 2018-2020 in the outlet of the Ob River: 0,103 mg/L in the winter low-water period, 0,079 mg/L in the spring - summer flood, and 0,095 mg/L in the summer - autumn low-water period. The present-day weighted average concentration of fluorine in the Ob River water (0,086 mg/L) closely corresponds to the values measured in 1954-1956 and 1976-1980 (0,090 and 0,084 mg/L, respectively), therefore the fluorine content of 0,08-0,09 mg/L could be taken as a natural background.

Mn–Fe-rich genthelvite from pegmatites associated with the Madeira Sn–Nb–Ta deposit, Pitinga, Brazil: new constraints on the magmatic-hydrothermal transition in the albite-enriched granite system

AbstractGenthelvite from pegmatite veins hosted by the albite-enriched granite (ca.1.8 Ga) corresponding to the Sn–Nb–Ta (F, REE, Li, Zr, U, Th) Madeira deposit, Amazonas, Brazil was studied. Genthelvite, the exclusive Be-bearing mineral within the deposit, occurs as massive crystals of up to 4.7 cm in size. Compositions are homogeneous within individual crystals, although there is moderate variation in the overall composition reflecting relatively limited substitutions within the helvine–genthelvite–danalite solid-solution series, with relatively high Zn contents (36.96 to 49.45 wt.% ZnO), lower Mn contents (0.61 to 3.03 wt.% MnO), and variable Fe contents (2.10 to 10.94 wt.% FeO), completing an existing compositional gap in this system. Genthelvite formed in an alkaline and subaluminous environment, under stable conditions within the late-evolved fluids, at relatively high temperature (&gt;400°C), in a reducing environment. The extremely high concentration of fluorine in the magma and the crystallisation of magmatic galena resulted in an effective reduction of H2S fugacity. This resulted in the stabilisation of genthelvite during the transition from the late magmatic to early hydrothermal stages of the albite-enriched granite evolution. The variability in Fe content within genthelvite is associated primarily with localised variations in the mineral assemblage (e.g. the presence of riebeckite and polylithionite). Genthelvite was altered by low-temperature aqueous fluids rich in F which resulted in the incorporation of Fe, Mn, Mg, Pb, Ba, Na, K, U and REE into the Zn2+ structural site and the allocation of excess Si, Al, Ti and P in the IVSi and IVBe structural sites. The substantial content of U and REE substituting for Zn, together with Si substituting for Be, is charge balanced by the presence of vacancies at the A site.

Calculations of solubility polytherms of phosphate salts in their mixtures with ammonium chloride and optimization of conditions for selective crystallization of ammonium orthophosphates

The purpose of the work was to determine the optimal conditions for preparation of chemically pure salts of ammonium orthophosphates based on solutions formed after purification of extractable orthophosphoric acid from toxic impurities of d-metals, lead, arsenic and fluorine by their coprecipitation with calcium hydrogen phosphate. Based on the Sechenov's modified formula, a method for calculating the solubility polytherms of orthophosphate salts in their mixtures with ammonium chloride was proposed. For its experimental confirmation, studies were conducted to determine the concentrations of saturated solutions of a number of orthophosphate salts in their mixtures with ammonium chloride at temperatures of 14, 40 and 800C. The results of the calculations were well confirmed by experiments on selective crystallization. It was shown that the following chemically pure products can be obtained from solutions of mixtures of (NH4)2HPO4 and NH4Cl by the methods of isothermal-isohydric crystallization: (NH4)2HPO4 (with a yield of up to 79.5%) and NH4H2PO4 (with a yield of up to 52.4%). Measurements of the concentrations of Cd(II), As(III), Cu(II), Pb(II) and fluorine in the synthesized salts showed that they were at levels lower than the current requirements for maximum permissible concentrations. Therefore, these salts can be recommended for use as food additives.

Fractional solubility of iron in mineral dust aerosols over coastal Namibia: a link to marine biogenic emissions?

Abstract. This paper presents the first investigation of the solubility of iron in mineral dust aerosols collected at the Henties Bay Aerosol Observatory (HBAO), in Namibia, from April to December 2017. During the study period, 10 intense dust events occurred. Elemental iron reached peak concentrations as high as 1.5 µg m−3, significantly higher than background levels. These events are attributed to wind erosion of natural soils from the surrounding gravel plains of the Namib desert. The composition of the sampled dust is found to be overall similar to that of aerosols from northern Africa but is characterized by persistent and high concentrations of fluorine which are attributed to local fugitive dust. The fractional solubility of Fe (%SFe) for both the identified dust episodes and background conditions ranged between 1.3 % and 20 % and averaged at 7.9 % (±4.1 %) and 6.8 (±3.3 %), respectively. Even under background conditions, the %SFe was correlated with that of Al and Si. The solubility was lower between June and August and increased from September onwards during the austral spring. The relation to measured concentrations of particulate MSA (methane sulfonic acid), solar irradiance, and wind speed suggests a possible two-way interaction whereby marine biogenic emissions from the coastal Benguela upwelling to the atmosphere would increase the solubility of iron-bearing dust according to the photo-reduction processes. This first investigation points to the western coast of southern Africa as a complex environment with multiple processes and active exchanges between the atmosphere and the Atlantic Ocean, requiring further research.

Fluoride and acid enrichment in coal fire sponges in the Wuda coalfield, Inner Mongolia, Northern China

Coal fire sponges (CFSs) are a type of sponge-like contaminated soil bulge common in coal fire areas. However, the impacts of CFSs on the local environment are not yet understood. Thus, this study investigated soil samples from CFSs in the Wuda coalfield, Inner Mongolia, China, focusing on the acidity, sulfate, and fluorine content. The results showed that the CFSs were highly acidic, with an average pH of 0.76, and contained high levels of SO42− (257.29 × 103 μg/g), total fluorine (TF, 2011.6 μg/g), and water-soluble fluorine (WF, 118.94 μg/g), significantly exceeding those in the regional background soil and indicating that CFSs are a point source of heavy pollution. Soils in the 8000 m2 reclamation zone showed elevated acidity and high SO42− (129.6 × 103 μg/g), TF (1237.8 μg/g), and WF (43.05 μg/g) levels, which was likely the result of the weathering and dissemination of CFS. The CFS samples were rich in hydrogen fluoride, releasing 202.05 ppb of it when heated to 40 °C. Correlation analysis indicated that the acid sulfate soils in CFSs are likely caused by HSO4−/SO42−. Time-of-flight secondary ion mass spectrometry detected four characteristic ions (F−, H3O+, H2SO4+, and HSO4−) in all micro-domains of each sample, indicating that ionic fluorine compounds and sulfuric acid hydrate were found in the CFS samples. Sulfate minerals detected in CFSs included CaSO4, Fe2(SO4)3, CdSO4, NH4HSO4, and Na2SO4. Thus, the results identified CFSs as a transmission channel for contamination, with erosional surface soils as the carrier, for the first time. CFSs pose a serious threat of contamination, albeit over limited areas.

Multivalent Fluorinated Nanorings for On-Cell 19F NMR.

The design of imaging agents with a high fluorine content is necessary for overcoming the challenges of low sensitivity in 19F magnetic resonance imaging (MRI)-based molecular imaging. Chemically self-assembled nanorings (CSANs) provide a strategy to increase the fluorine content through multivalent display. We previously reported an 19F NMR-based imaging tracer, in which case a CSAN-compatible epidermal growth factor receptor (EGFR)-targeting protein E1-dimeric dihydrofolate (E1-DD) was bioconjugated to a highly fluorinated peptide. Despite good 19F NMR performance in aqueous solutions, a limited signal was observed in cell-based 19F NMR using this monomeric construct, motivating further design. Here, we design several new E1-DD proteins bioconjugated to peptides of different fluorine contents. Flow cytometry analysis was used to assess the effect of variable fluorinated peptide sequences on the cellular binding characteristics. Structure-optimized protein, RTC-3, displayed an optimal spectral performance with high affinity and specificity for EGFR-overexpressing cells. To further improve the fluorine content, we next engineered monomeric RTC-3 into CSAN, η-RTC-3. With an approximate eightfold increase in the fluorine content, multivalent η-RTC-3 maintained high cellular specificity and optimal 19F NMR spectral behavior. Importantly, the first cell-based 19F NMR spectra of η-RTC-3 were obtained bound to EGFR-expressing A431 cells, showing a significant amplification in the signal. This new design illustrated the potential of multivalent fluorinated CSANs for future 19F MRI molecular imaging applications.