Study of high-pressure thermophysical properties of orthocarbonate Sr3CO5 using deep learning molecular dynamics simulations.

The exploration of the physical attributes of the recently discovered orthocarbonate Sr3CO5 is significant for comprehending the carbon cycle and storage mechanisms within the Earth's interior. In this study, first-principles calculations are initially used to examine the structural phase transitions of Sr3CO5 polymorphs within the range of lower mantle pressures. The results suggest that Sr3CO5 with the Cmcm phase exhibits a minimal enthalpy between 8.3 and 30.3 GPa. As the pressure exceeds 30.3 GPa, the Cmcm phase undergoes a transition to the I4/mcm phase, while the experimentally observed Pnma phase remains metastable under our studied pressure. Furthermore, the structural data of SrO, SrCO3, and Sr3CO5 polymorphs are utilized to develop a deep learning potential model suitable for the Sr-C-O system, and the pressure-volume relationship and elastic constants calculated using the potential model are in line with the available results. Subsequently, the elastic properties of Cmcm and I4/mcm phases in Sr3CO5 at high temperature and pressure are calculated using the molecular dynamics method. The results indicate that the I4/mcm phase exhibits higher temperature sensitivity in terms of elastic moduli and wave velocities compared to the Cmcm phase. Finally, the thermodynamic properties of the Cmcm and I4/mcm phases are predicted in the range of 0-2000 K and 10-120 GPa, revealing that the heat capacity and bulk thermal expansion coefficient of both phases increase with temperature, with the constant volume heat capacity gradually approaching the Dulong-Petit limit as the temperature rises.

[Contamination Levels and Exposure Risk via Drinking Water from Perfluoroalkyl Acids in Seven Major Drainage Basins of China].

To study the perfluoroalkyl acid (PFAAs) contamination in seven major drainage basins of China and the exposure risk to resident populations via drinking water sourced from these basins, a risk assessment model of the US EPA and a scenario-based risk assessment method were applied to analyze the PFAA pollution characteristics and to evaluate the average daily dose and health risk to adults, adolescents, and children. In the intermediate-exposure scenario, results showed that the ∑PFAAs median for the seven major drainage basins was 14 ng·L-1, with perfluorooctanoic acid (PFOA), perfluorobutanoic acid (PFBA), and perfluorooctane sulfonic acid (PFOS) the main contaminants, and that the contamination levels were the highest in the Songliao River and Taihu Lake basins. In the high-exposure scenario, the discharge proportion of perfluoroalkyl carboxylic acids with ≤ 6 carbon chains among the ∑PFAAs was higher than that in the intermediate-exposure scenario. In addition, certain sections tended to be more polluted than others in the Yellow River and Yangtze River basins. Risk assessment showed that PFOA and PFOS exposure via drinking water posed no health risk to Chinese residents, and that the average daily ingestion of drinking water of Chinese adolescents was below the suggested amount.

[Pollution Characteristics of Perfluorinated Compounds in Offshore Marine Area of Shenzhen].

In order to explore the pollution characteristics of perfluorinated compounds (PFCs), 10 surface seawaters and 7 surface sediments were collected in offshore marine area of Shenzhen (offshore distance >2 km) in September 2013. All the samples were prepared by solid-phase extraction and analyzed using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/ MS). The results showed that 10 PFCs, including C4, C6 and C8 perfluorinated sulfonates (PFSAs) and C5-C11, perfluorinated carboxylic acids (PFCAs) were detected in the surface waters. ∑ PFC concentrations ranged from 1.74 ng x L(-1) to 14.7 ng x L(-1) with PFBS, PFOS and PFOA being the dominant compounds. The spatial distribution of ∑ PFC concentrations displayed the characteristic of "the west being higher than the east", with ∑ PFC concentrations of Lingding Sea and Shenzhen Bay being higher than those of Daya Bay and Dapeng Bay (P < 0.05). The farther the sampling location was from the shore, the lower the ∑ PFC concentrations were. Direct sewage emissions and rivers emptying into the sea might be the primary sources of PFCs in the surface seawaters. 8 PFCs, including C6 and C8 PFSAs and C5, C6, and C8-C11 PFCAs were detected in the surface sediments. ∑ PFC concentrations ranged from 2.22 micorg x kg(-1) to 2.62 microg x kg(-1) with PFOS being the dominant compounds. There was a small change of ∑ PFC concentrations in surface sediments, which might be contributed by the adsorption from overlying water. The adsorption of PFCs on sediment significantly increased with the increasing length of carbon chain, and the adsorption of PFSA was higher than that of PFCA with the same length of carbon chain as PFSA. Additionally, the comparison with other seawater PFC measurements showed high PFBS pollution in this study, whereas the level of PFOS in sediment was close to those of other studies.

[Distribution of perfluorinated compounds in surface water of Shenzhen reservoir groups].

In order to study the concentrations of 14 perfluorinated compounds (PFCs) in 25 surface water samples collected from 12 Shenzhen reservoirs in November of 2012 and January of 2013, high performance liquid chromatography-tandem mass spectrometry was combined with solid phase extraction enrichment in this research. The results indicated that perfluorohexane sulfonate and long-chain (C > or = 11) PFCs were below the detection limit in all samples and perfluorooctane acid was the primary species. No significant difference in concentration was found between samples from the center of the reservoir and the outlet. Heavy precipitations diluted PFCs concentrations in surface water, but also led to PFOA input. PFCs concentrations in surface water of the reservoir were mainly affected by water inlet, source environment and geography. Although the water temperature had positive correlations with sigma PFCs concentration, the influence of heavy precipitations was stronger than that of water temperature.

[Influence of tap water treatment on perfluorinated compounds residue in the dissolved phase].

To study the perfluorinated compounds (PFCs) residues through water treatments including flocculation, sedimentation, sand filtration, ozonation with activated carbon and chlorination, as well as the seasonal variation of PFCs in the raw water of waterworks, 13 PFCs species in the dissolved phase of raw water, finished water, as well as the water samples after flocculation, sedimentation, sand filtration, and ozonation with activated carbon filtration were measured by the high performance liquid chromatography-tandem mass spectrometry combined with solid phase extraction. Results indicated that sigma PFCs residue in water was higher in spring and summer than that in fall and winter. The vast majority of PFCs in samples were of short and medium chains (C < or = 10), and perfluorooctane sulfonate was the most typical residue species. Among the five water treatment stages, sedimentation, sand filtration and ozonation with activated carbon filtration can remove PFCs, while flocculation and chlorination significantly raise the levels of short- (C < or = 6) and medium-chain (10 > or = C > or = 7) PFCs, respectively, causing sigma PFCs increase in finished water by 10%-44% compared to raw water. However, the PFCs residues in finished water are still far below their limit values, posing no threat against human health.