Spreading kinetics of fluorocarbon surfactants on several liquid fuels surfaces

A facile sunflower pectin gel foam for liquid fuel fire suppression with ReaxFF characterisation on its char-enhancing ability

A biomass fire suppression gel foam (FSGF) with outstanding thermal stability and fire resistance performance was synthesised to improve the flame retardancy of foam agents on liquid fuel fires. The foam comprehensive index, microstructure, thermal stability, fire resistance and extinguishing properties of the FSGF were benchmarked against aqueous film-forming foam (AFFF). Subsequently, reactive forcefield (ReaxFF) molecular dynamics (MD) simulations were performed on the FSGF to study the thermokinetic properties. Based on the experimental results, a porosity layer was found on the external film of FSGF, which enhanced the thermal stability of the foam. The gelling mechanism of the foam is the formation of an O-Ca-O bond. Through MD simulations it was discovered that the remained calcium oxide/hydroxide species when deposited on fuel surfaces would promote char formation as they capture H/O atoms via dehydration. Alternatively, the foam showed better thermal stability than that of AFFF due to a lower weight loss rate and longer collapse time. The extinguishing performance tests demonstrated that the fire extinguishing time and resistance time of FSGF respectively are 72 s and 801 s, showing a significant potential to suppress the re-ignition of tank fires.

Physicochemical Properties of Aqueous Film-Forming Foams Based on Short Fluorocarbon Surfactant-Graft Hydrophilic Functional Groups

The key components of aqueous film foaming foam extinguishing agents are fluorocarbon surfactants. Due to their toxicity and bioaccumulation, long-chain fluorocarbon surfactants have limited application prospects. Therefore, it is of great significance to study short-chain fluorocarbon surfactants as substitutes. In this work, three short-chain fluorocarbon surfactants with various hydrophilic groups and corresponding fire extinguishing agents were prepared. The physical and chemical properties of a single system and mixed system of fluorocarbon surfactants, including surface activity, spreading property, foaming property, 25% drainage time, and AFFF fire extinguishing property, were studied. For the results of the mixed systems, it was found that the critical micelle concentrations did not exceed 3.97 mmol/L and the minimum surface tension did not exceed 17.21 mN/m. Fluorocarbon surfactant solutions spread effectively on the surface of all fuels. The foam expansion is greater than 7.2, and the shortest of all 25% drainage times is 3.31 min. The extinguishing time of AFFFs on several fuel fires does not exceed 55 s, and the shortest burn-back time is 15.08 min. Anyways, these results indicate that the grafted hydrophilic short-chain fluorocarbon surfactants have significant application prospects in AFFFs.

Molecular insight into optimizing the N- and P-doped fullerenes for urea removal in wearable artificial kidneys

Urea is the result of the breakdown of proteins in the liver, the excess of which circulates in the blood and is adsorbed by the kidneys. However, in the case of kidney diseases, some products, specifically urea, cannot be removed from the blood by the kidneys and causes serious health problems. The end-stage renal disease (ESRD) patients are not able to purify their blood, which endangers their life. ESRD patients require dialysis, a costly and difficult method of urea removal from the blood. Wearable artificial kidneys (WAKs) are consequently designed to remove the waste from blood. Regarding the great amount of daily urea production in the body, WAKs should contain strong and selective urea adsorbents. Fullerenes-which possess fascinating chemical properties-have been considered herein to develop novel urea removal adsorbents. Molecular dynamics (MD) has enabled researchers to study the interaction of different materials and can pave the way toward facilitating the development of wearable devices. In this study, urea adsorption by N-doped fullerenes and P-doped fullerenes were assessed through MD simulations. The urea adsorption was simulated by five samples of fullerenes, with phosphorous and different nitrogen dopant contents. For comparing the urea adsorption capacity in the performed simulations, detailed characteristics-including the energy analysis, radius of gyration, radial distribution function (RDF), root-mean-square fluctuation (RMSD), and H-bond analyses were investigated. It had been determined that the fullerene containing 8% nitrogen-with the highest reduction in the radius of gyration, the maximum RDF, a high adsorption energy, and a high number of hydrogen bonds-adsorbs urea more efficiently.

Two-dimensional spreading properties and sealing characteristics of fluorocarbon surfactants on several typical hydrocarbon fuels

A new method for studying the two-dimensional spreading properties and sealing characteristics of surfactant solution on oil surface was provided. The actual spreading situation of the C4-Br/oil systems in axisymmetric geometry was observed directly using HD camera for the first time and the results showed that the aqueous film expanded outwards in a circle with the guiding device as the center. Meanwhile, the relation between spreading radius and time was investigated and evaluated using the model for surface-tension-viscous regime. The root-mean-square deviation (RMSD) values obtained from the correlation for all of the systems we studied below 1.64, indicating a good agreement between the experimental and theoretical values. The results of sealing experiments showed that the aqueous film could absolutely seal the oil surface for 27–65 s and the sealing effect would be lost after 216–742 s for different systems. The stronger the volatility was, the shorter the sealing time was. Additionally, the volume percentage of oil vapor with film was always lower than that without film even when the evaporation was saturated. These findings were of great significance to guide the preparation of efficient AFFF.

Reductive Defluorination and Mechanochemical Decomposition of Per- and Polyfluoroalkyl Substances (PFASs): From Present Knowledge to Future Remediation Concepts

Over the past two decades, per- and polyfluoroalkyl substances (PFASs) have emerged as worldwide environmental contaminants, calling out for sophisticated treatment, decomposition and remediation strategies. In order to mineralize PFAS pollutants, the incineration of contaminated material is a state-of-the-art process, but more cost-effective and sustainable technologies are inevitable for the future. Within this review, various methods for the reductive defluorination of PFASs were inspected. In addition to this, the role of mechanochemistry is highlighted with regard to its major potential in reductive defluorination reactions and degradation of pollutants. In order to get a comprehensive understanding of the involved reactions, their mechanistic pathways are pointed out. Comparisons between existing PFAS decomposition reactions and reductive approaches are discussed in detail, regarding their applicability in possible remediation processes. This article provides a solid overview of the most recent research methods and offers guidelines for future research directions.