PFAS in the water supply: source water contamination

Water contamination with per- and polyfluoroalkyl substances (PFAS) is a serious problem for water suppliers in many regions. Due to persistence of the substances and a complex distribution mechanism, PFAS can have an adverse impact on water quality. Reported toxicological and health effects, make it very important to minimise the of wildlife and human exposure to PFAS. The exposure path is, however, associated with the most vital resource as water.Mitigation of the PFAS contamination is an extensive challenge that requires a multidisciplinary investigation of the pollution nature and distribution mechanisms in the aquatic environment. Furthermore, since conventional drinking water treatment is insufficient in PFAS removal, development of the treatment alternative is necessary. Not least due to substantial number of contaminated water sources and an increasing worldwide demand on drinking water.Present thesis was built around investigation of the historical source water contamination and human exposure to PFAS at studied locations in Ronneby (primarily) and Luleå in Sweden. Several interconnected studies were conducted regarding present contamination levels, transport and distribution mechanism, contamination and emission history, as well as PFAS treatment alternatives for drinking water.PFAS analysis and assessment of the contamination levels in surface water, groundwater, and sediments were conducted. PFAS occurrence at studied locations was connected to historical use of PFAS containing aqueous film forming foam (PFAS-AFFF). By means of core analysis, accumulation period was studied for the exposed recipient (Lake). Furthermore, influence of the media characteristics (i.e., mineral composition, density, moisture, and organic matter content) on PFAS distribution in sediment was studied and corresponding distribution (partitioning) predictors were estimated. Regarding emission source, profiling of the possible PFAS-AFFF compositions was conducted (based on groundwater analysis), and possible application and emission scenarios were evaluated (based on available fire-training history and related protocols). Investigation of PFAS treatment methods for drinking water was conducted and implementation of ex-situ treatment technique, based on UVC/VUV induced removal, was suggested. The laboratory scale treatment unit was developed and tested in series of experimental trials with PFCAs, PFSAs, FTSAs, and FASAs

Thermally induced evolution of the structure and optical properties of silicon nanowires

In the present paper, we report on the investigation of thermal annealing (TA) effect on structural and optical properties of crystalline silicon nanowires produced by metal-assisted chemical etching approach. In particular, the impact of TA on nanowire length, relative volume and size distribution of voids is described in terms of Lifshitz-Slyozov-Wagner theory considering the TA induced Oswald ripening in the SiNW arrays. It was also found that TA leads to a decrease of the SiNWs total reflection in the wide UV–VIS-IR spectral range. The reported effects can be used for tuning of crystalline SiNWs arrays in view of their further applications in photonics related fields. © 2020 The Author

PFAS in the Drinking Water Source: Analysis of the Contamination Levels, Origin and Emission Rates

Groundwater contamination caused by the use of the aqueous film-forming foam (AFFF) containing per- and polyfluoroalkyl substances (PFAS) was investigated in southern Sweden. sigma PFAS concentrations in groundwater ranged between 20 and 20,000 ng L-1; PFAS composition was primarily represented by PFOS and PFHxS. The PFAS chain length was suggested to have an impact on the contaminant distribution and transport in the groundwater. PFAS profiling showed that the use of PFSAs- and PFCAs/FTSAs-based PFAS-AFFF can be a contributor to PFAS contamination of the drinking water source (groundwater). PFAS emission was connected to PFAS-AFFF use during the fire-training and fire-fighting equipment tests at the studied location. PFAS emission per individual fire training was (semi-quantitatively) estimated as [1.4 < 11.5 +/- 5.7 < 43.7 kg] (n = 20,000). The annual emission estimates varied as [11 < 401 +/- 233 < 1125 kg yr(-1)] (n = 1005) considering possible [2 < 35 +/- 20 < 96] individual fire-training sessions per year

Impact of the Sediment Organic vs. Mineral Content on Distribution of the Per- and Polyfluoroalkyl Substances (PFAS) in Lake Sediment

Contamination of the water and sediment with per- and polyfluoroalkyl substances (PFAS) was studied for the lake impacted by the release of PFAS-containing aqueous film forming foam (AFFF). PFAS concentrations were analyzed in lake water and sediment core samples. ΣPFAS concentrations were in the range of 95–100 ng L−1 in the lake water and 3.0–61 µg kg−1 dry weight (dw) in sediment core samples, both dominated by perfluorohexane sulfonate, perfluorooctane sulfonate; 6:2 fluortelomer sulfonate was inconsistently present in water and sediment core samples. The sediment–water partitioning coefficients (log Kd) were estimated and ranged 0.6–2.3 L kg−1 for individual perfluoroalkyl carboxylates (PFCAs) and 0.9–5.6 L kg−1 for individual perfluoroalkane sulfonates (PFSAs). The influence of the sediment inorganic content and organic matter on PFAS distribution was investigated. In studied sediments, the mineral content (corresponding to <5% of the bulk media mass) was mainly represented by sulfur, iron and calcium. The PFAS distribution was found strongly connected to the sediment mineral content (i.e., Fe, Pb, Rb and As), whereas the sediment organic carbon content did not to have a direct influence on the PFAS distribution. The aim of this study was to improve our understanding of the PFAS distribution in the natural heterogeneous media

PFAS in the Drinking Water Source: Analysis of the Contamination Levels, Origin and Emission Rates

Groundwater contamination caused by the use of the aqueous film-forming foam (AFFF) containing per- and polyfluoroalkyl substances (PFAS) was investigated in southern Sweden. SPFAS concentrations in groundwater ranged between 20 and 20,000 ng L????1; PFAS composition was primarily represented by PFOS and PFHxS. The PFAS chain length was suggested to have an impact on the contaminant distribution and transport in the groundwater. PFAS profiling showed that the use of PFSAs- and PFCAs/FTSAs-based PFAS-AFFF can be a contributor to PFAS contamination of the drinking water source (groundwater). PFAS emission was connected to PFAS-AFFF use during the fire-training and fire-fighting equipment tests at the studied location. PFAS emission per individual fire training was (semi-quantitatively) estimated as [1.4 < 11.5 5.7 < 43.7 kg] (n = 20,000). The annual emission estimates varied as [11 < 401 233 < 1125 kg yr????1] (n = 1005) considering possible [2 < 35 20 < 96] individual fire-training sessions per year

Quantitative analysis of morphology of porous silicon nanostructures formed by metal-assisted chemical etching

Morphology features of porous layers consisting of silicon nanowire arrays, which were grown by metal-assisted chemical etching, have been analyzed by means of digital processing of their scanning electron microscopy (SEM) images. Informational-entropic and Fourier analysis have been applied to quantitatively describe the degree of order and chaos in nanostructure distribution in the layers. Self-similarity of the layer morphology has been quantitatively described via its fractal dimensions. The applied approach allows us to distinguish morphological features of as-called "black" (more ordered) and "white" (less ordered) silicon layers characterized by minimal and maximal optical reflection, respectively.This work was partially supported by the Committee of Science of the Ministry of Education and Science of the Republic of Kazakhstan (Grant AP05132854, Grant AP05132738). G.K.M. and V.Yu.T. acknowledge the support of the Comprehensive Program of NRNU “MEPhI”

Palladium catalysts supported on carbonized porous silicon for H2/O2 recombination

The article presents new research on the use of catalysts for H2/O2 recombination. The study emphasizes the importance of ensuring safe production, storage, and utilization of green hydrogen by recombining gas leaks. We suggest the utilization of innovative palladium catalysts for low-temperature hydrogen oxidation. These catalysts leverage molecular oxygen from the air to efficiently recombine small amounts of leaked hydrogen, resulting in the production of water. Recombination catalysts with a small amount of dispersed palladium metal on an inert support are the most efficient for production to prevent the risks of hydrogen explosion and fire. This study is focused on the development of laboratory prototypes for the H2/O2 recombination catalysts. We identified a potential catalytic system through monitoring of current literature to propose efficient hydrogen recombination catalysts. We present an optimized method for coating the surface of porous silicon nanoparticles with carbon layers, and introduce a technique for the production of supported palladium recombination catalysts. The proposed catalysts efficiently facilitate the recombination of hydrogen in lean air-hydrogen gas mixtures, offering a cost-effective alternative to more expensive commercial catalysts. Furthermore, they exhibit remarkable efficiency at both room and elevated temperatures. The final remarks underscore the necessity of creating new Pd catalysts to guarantee the secure storage and usage of hydrogen

SIZE-DEPENDENT PHONON-ASSISTED ANTI-STOKES PHOTOLUMINESCENCE IN NANOCRYSTALS OF ORGANOMETAL PEROVSKITES

Anti-Stokes photoluminescence (ASPL), which is an up-conversion phonon-assisted process of the radiative recombination of photoexcited charge carriers, was investigated in methylammonium lead bromide (MALB) perovskite nanocrystals (NCs) with mean sizes that varied from about 6 to 120 nm. The structure properties of the MALB NCs were investigated by means of the scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. ASPL spectra of MALB NCs were measured under near-resonant laser excitation with a photon energy of 2.33 eV and they were compared with the results of the photoluminescence (PL) measurements under nonresonant excitation at 3.06 eV to reveal a contribution of phonon-assisted processes in ASPL. MALB NCs with a mean size of about 6 nm were found to demonstrate the most efficient ASPL, which is explained by an enhanced contribution of the phonon absorption process during the photoexcitation of small NCs. The obtained results can be useful for the application of nanocrystalline organometal perovskites in optoelectronic and all-optical solid-state cooling devices

Efficient visible luminescence of nanocrystalline silicon prepared from amorphous silicon films by thermal annealing and stain etching

Films of nanocrystalline silicon (nc-Si) were prepared from hydrogenated amorphous silicon (a-Si:H) by using rapid thermal annealing. The formed nc-Si films were subjected to stain etching in hydrofluoric acid solutions in order to passivate surfaces of nc-Si. The optical reflectance spectroscopy revealed the nc-Si formation as well as the high optical quality of the formed films. The Raman scattering spectroscopy was used to estimate the mean size and volume fraction of nc-Si in the annealed films, which were about 4 to 8 nm and 44 to 90%, respectively, depending on the annealing regime. In contrast to as-deposited a-Si:H films, the nc-Si films after stain etching exhibited efficient photoluminescence in the spectral range of 600 to 950 nm at room temperature. The photoluminescence intensity and lifetimes of the stain etched nc-Si films were similar to those for conventional porous Si formed by electrochemical etching. The obtained results indicate new possibilities to prepare luminescent thin films for Si-based optoelectronics

Dedicated to the memory of scientist and developer of photovoltaics in Kazakhstan, obituary

Al-Farabi Kazakh National University, Faculty of Physics and Technology Institute of Experimental and Theoretical Physics National Nanotechnological Laboratory of Open Typ