MOF-derived Fe/Ni@C marigold-like nanosheets as heterogeneous electro-Fenton cathode for efficient antibiotic oxytetracycline degradation.

The widespread occurrence of organic antibiotic pollution in the environment and the associated harmful effects necessitate effective treatment method. Heterogeneous electro-Fenton (hetero-EF) has been regarded as one of the most promising techniques towards organic pollutant removal. However, the preparation of efficient cathode still remains challenging. Herein, a novel metal-organic framework (MOF)-derived Fe/Ni@C marigold-like nanosheets were fabricated successfully for the degradation of oxytetracycline (OTC) by serving as the hetero-EF cathode. The FeNi3@C (Fe/Ni molar ratio of 1:3) based hetero-EF system exhibited 8.2 times faster OTC removal rate than that of anodic oxidation and possessed many advantages such as excellent OTC degradation efficiency (95.4% within 90 min), broad environmental adaptability (satisfactory treatment performance for multiple antibiotics under various actual water matrixes), good stability and reusability, and significant toxicity reduction. The superior hetero-EF catalytic performance was mainly attributed to: 1) porous carbon and Ni existence were both conducive to the in-situ generation of H2O2 from dissolved O2; 2) the synergistic effects of bimetals together with electron transfer from the cathode promoted the regeneration of ≡ FeII/NiII, thereby accelerating the production of reactive oxygen species; 3) the unique nanosheet structure derived from the precursor two-dimensional Fe-Ni MOFs enhanced the accessibility of active sites. This work presented a promising hetero-EF cathode for the electrocatalytic treatment of antibiotic-containing wastewaters.

Sources, Enrichment, and Geochemical Fractions of Soil Trace Metals in Ulaanbaatar, Mongolia.

Mongolia is a rapidly developing country that has experienced growing industrialization and urbanization in recent decades. This study was conducted to evaluate the enrichment and labile fractions of metals in urban soils of Mongolia and to identify major sources of soil metal pollution. The concentrations and geochemical fractions of Al, Fe, Mn, Cr, Cu, Cd, Co, Zn, V, Mo, As, Sb, and Pb in soils of the city Ulaanbaatar were investigated. The results demonstrate that only Fe, Mn, Co, Mo, and V occur at natural levels with enrichment factors close to unity. The majority of investigated toxic metals, including Cu, Zn, Cr, Sb, As, Cd, and Pb, are serious pollutants in urban soils, with enrichment factors of up to 2.8, 5.1, 2.1, 16, 13, 15, and 11, respectively. Studies of the chemical fractions of metals demonstrate that Zn is mainly found in its labile form and is considered a high risk to humans and biota. Industrial release, household ash, coal combustion, and tire abrasion were identified as key sources of toxic metals entering into the soil of Ulaanbaatar City, which should be controlled effectively to prevent the population as well as pollution distribution over a wider area by long-range atmospheric transport.

Improvement of the anthropogenic emission rate estimate in Ulaanbaatar, Mongolia, for 2020-21 winter.

Ulaanbaatar (UB), the fast-growing capital of Mongolia, is known for its world's worst level of particulate matter (PM) concentrations in winter. However, current anthropogenic emission inventories over the UB are based on data from more than fifteen years ago, and satellite observations are scarce because UB is in high latitudes. During the winter of 2020-21, the first period of the Fine Particle Research Initiative in East Asia considering the National Differences (FRIEND), several times higher concentrations of PM in UB compared to other urban sites in East Asia were observed but not reproduced with a chemical transport model mainly due to the underestimated anthropogenic emissions. Therefore, we devised a method for sequentially adjusting emissions based on the reactivity of PM precursors using ground observations. We scaled emission rates for the inert species (CO, elemental carbon (EC), and organic carbon (OC)) to reproduce their observed ambient concentrations, followed by SO2 to reproduce the concentration of SO42-, which was examined to have the least uncertainty based on the abundance of observed NH3, and finally NO and NH3 for NO3-, and NH4+. This improved estimation is compared to regional inventories for Asia and suggests more than an order of magnitude increase in anthropogenic emissions in UB. Using the improved emission inventory, we were able to successfully reproduce independent observation data on PM2.5 concentrations in UB in December 2021 from the U.S. Embassy. During the campaign period, we found more than 50% of the SO42-, NO3-, and NH4+ increased in UB due to the improvement could travel to Beijing, China (BJ), and about 20% of the SO42- could travel to Noto, Japan (NT), more than 3000 km away. Also, the anthropogenic emissions in UB can effectively increase OC, NO3-, and NH4+ concentrations in BJ when Gobi dust storms occur.

Evidence of global-scale As, Mo, Sb, and Tl atmospheric pollution in the antarctic snow.

We report the first comprehensive and reliable time series for As, Mo, Sb, and Tl in the snowpack from Dome Fuji in the central East Antarctic Plateau. Our results show significant enrichment of these elements due to either anthropogenic activities or large volcanic eruptions during the past 50 years. With respect to the values reported from 1960 to 1964, we observed the maximum increases in crustal enrichment factors (EFs) for As (a factor of ~15), Mo (~4), Sb (~4), and Tl (~2) during the period between the 1970s and 1990s, reflecting the global dispersion of anthropogenic pollutants of these elements, even to the most remote areas on Earth. Such enrichments are likely related to emissions of trace elements from nonferrous metal smelting and fossil fuel combustion processes in South America, especially in Chile. A drastic decrease in the As concentration and its EF values was observed after the year 2000 in response to the introduction of environmental regulations in the 1990s to reduce As emissions from the copper industry, primarily in Chile. The observed decrease suggests that governmental regulations for pollution control are effective in reducing air pollution at both the regional and global level.

A 50-year record of platinum, iridium, and rhodium in Antarctic snow: volcanic and anthropogenic sources.

Antarctic snow preserves an atmospheric archive that enables the study of global atmospheric changes and anthropogenic disturbances from the past. We report atmospheric deposition rates of platinum group elements (PGEs) in Antarctica during the last ∼ 50 years based on determinations of Pt, Ir, and Rh in snow samples collected from Queen Maud Land, East Antarctica to evaluate changes in the global atmospheric budget of these noble metals. The 50-year average PGE concentrations in Antarctic snow were 17 fg g(-1) (4.7-76 fg g(-1)) for Pt, 0.12 fg g(-1) (<0.05-0.34 fg g(-1)) for Ir, and 0.71 fg g(-1) (0.12-8.8 fg g(-1)) for Rh. The concentration peaks for Pt, Ir, and Rh were observed at depths corresponding to volcanic eruption periods, indicating that PGEs can be used as a good tracer of volcanic activity in the past. A significant increase in concentrations and crustal enrichment factors for Pt and a slight enhancement in enrichment factors for Rh were observed after the 1980s. This suggests that there has been large-scale atmospheric pollution for Pt and probably for Rh since the 1980s, which may be attributed to the increasing emissions of these metals from anthropogenic sources such as automobile catalysts and metal production processes.

Spatial and temporal variations of sediment metals in the Tuul River, Mongolia.

Mongolia has been a pristine environment without much pollution. Our objective is to study a section of the Tuul River to evaluate the present condition of this pristine environment. Sediment metal (Al, Fe, Mn, Cu, Zn, Pb, Ni, Cd, Hg, and Cr) concentrations and Pb-210 were sampled and analyzed. Results showed that metal concentrations are much higher at areas near the capital city and municipal sewage outlet, with enrichment factor values up to 18 for Cu, and 26 for Cr. Higher copper concentrations were found at sites about ~ 50 km downstream from the source, an indication that pollutions are spreading further down the river. Vertical metal concentration profiles indicated that pollutions could be traced back to the 1960s. Inefficient sewage treatment plants and poorly managed power plant ash ponds were major sources of metals leaking into the Tuul River. Sewage wastewater is carrying metals through Tuul River to the lower river basin. Dusts from ash ponds are airborne and transport to greater area. These findings indicate that new and alternative measures have to be enforced to prevent further pollution entering the Tuul River drainage basin and airborne dust to other broader regions of the Asia and ocean.