Carbon sequestered in phytoliths, the silicified features of plants, may accumulate in soils and sediments for several hundreds to thousands of years depending mainly on the morphology and chemical ...composition of phytoliths and environmental conditions. Phytolith carbon sequestration is thought to be one of the key biogeochemical carbon sequestration mechanisms. This review summarizes the current state of understanding of occurrence, turnover and carbon sequestration potential of phytoliths in terrestrial ecosystems. The accumulation rate of phytoliths in soils is controlled not only by plant litter inputs but also by geochemical stability and turnover of phytoliths. Most of the organic carbon in phytoliths is from photosynthesis of atmospheric carbon dioxide (CO2) during formation of phytoliths. Phytolith carbon sequestration in terrestrial ecosystems is a promising biogeochemical carbon sequestration mechanism and may contribute to the mitigation of global climate warming. Further questions such as the turnover of phytoliths with different properties and under different environmental conditions, the relative contribution of different ecosystems to the global terrestrial phytolith carbon sequestration, and the cost and potential of each management measure to enhance phytolith carbon sequestration should be investigated.
Black carbon (BC) has emerged as an important short-lived climate forcer. Due to its light absorption properties, BC can darken the snow/ice surface, affect the energy balance, and further lead to ...acceleration of the melting of the cryosphere (e.g., glaciers, snow cover, and sea ice). By reviewing the recent published literatures, we present an overview of the historical changes, spatial distribution of BC in snow/ice, and how these changes are related to the cryospheric melting. Ice core records show a rapid increase of BC concentrations that began in the 1850s and continued throughout the 20th century, which is consistent with an increase of BC emissions owing to industrialization. A decrease of BC amount since 1970s in Arctic and European ice cores has been partially attributed to the Clean Air Act. However, in the Himalayas, BC records show a continuous increase during this period. Generally, BC concentrations in snow and ice in the mid-latitude regions are one to two orders of magnitude higher than those in the polar regions. In particular, BC concentrations in aged snow and granular ice in the ablation areas of mountain glaciers are one to three orders of magnitude higher than those in fresh snow or snowpits in the glacier accumulation areas due to BC accumulation during melting season. BC in the surface snow/ice is responsible for about 20% of the albedo reduction in the Tibetan Plateau during glacier melt season. Globally, observations and modeling results indicate that radiative forcing (RF) induced by BC in snow and ice is highest in the mid-latitudes, ranging from several W m−2 in fresh snow to hundreds of W m−2 in aged snow and granular ice in the glacier ablation areas. The large BC-in-snow RF and associated snow albedo feedback lead to an acceleration in the total glacier melt (approximately 20%) and/or a reduction in the duration of the snow cover by several days, resulting in an increase of glacier discharge. Given our limited understanding of quantifying the role of BC in cryospheric melting, it is important to synthesize the existing research on the multi-scale processes related to BC in snow and ice to identify the gaps in our understanding of these processes and to propose a path forward to improve the quality of our observations of the aforementioned phenomena to fill these gaps.
Hydrogen-bonded organic framework (HOF)-based catalysts still remain unreported thus far due to their relatively weak stability. In the present work, a robust porous HOF (HOF-19) with a ...Brunauer–Emmett–Teller surface area of 685 m2 g–1 was reticulated from a cagelike building block, amino-substituted bis(tetraoxacalix2arene2triazine), depending on the hydrogen bonding with the help of π–π interactions. The postsynthetic metalation of HOF-19 with palladium acetate afforded a palladium(II)-containing heterogeneous catalyst with porous hydrogen-bonded structure retained, which exhibits excellent catalytic performance for the Suzuki–Miyaura coupling reaction with the high isolation yields (96–98%), prominent stability, and good selectivity. More importantly, by simple recrystallization, the catalytic activity of deactivated species can be recovered from the isolation yield 46% to 92% for 4-bromobenzonitrile conversion at the same conditions, revealing the great application potentials of HOF-based catalysts.
Damming rivers to generate hydropower can help mitigate the world's energy crisis and reduce the risk of global climate change; however, damming can also produce enormous negative effects on the ...environment and ecosystems. The mainstream Lancang-Mekong River within China has been planned as one of the thirteen state hydropower bases. To date, there have been six operational dams along the mainstream Lancang River, and the 15 remaining dams of the proposed Lancang cascade will be completed in the next decades. In this paper, we examined several crucial environmental changes and ecological responses that have resulted from the construction and operation of the existing dams of the Lancang cascade. The current literature and observational data suggest that the commissioned dams have led to a decline in the flood season water discharge and annual sediment flux within China's borders, reservoir aggradations, and water quality degradation in the reservoirs, which has negatively affected riverine aquatic biological communities and fish assemblages. In contrast, the dams have only had small unfavorable effects on downstream environments and ecosystems outside of China. Because of the potential environmental and geopolitical risks of the Lancang cascade dams, a long-term basin-wide terrestrial and aquatic monitoring program is urgently required to ensure that regional sustainable development occurs in the Lancang-Mekong River Basin.
The generation of green hydrogen (H2) energy using sunlight is of great significance to solve the worldwide energy and environmental issues. Particularly, photocatalytic H2 production is a highly ...promising strategy for solar‐to‐H2 conversion. Recently, various heterostructured photocatalysts with high efficiency and good stability have been fabricated. Among them, 2D/2D van der Waals (VDW) heterojunctions have received tremendous attention, since this architecture can promote the interfacial charge separation and transfer and provide massive reactive centers. On the other hand, currently, most photocatalysts are composed of metal elements with high cost, limited reserves, and hazardous environmental impact. Hence, the development of metal‐free photocatalysts is desirable. Here, a novel 2D/2D VDW heterostructure of metal‐free phosphorene/graphitic carbon nitride (g‐C3N4) is fabricated. The phosphorene/g‐C3N4 nanocomposite shows an enhanced visible‐light photocatalytic H2 production activity of 571 µmol h−1 g−1 in 18 v% lactic acid aqueous solution. This improved performance arises from the intimate electronic coupling at the 2D/2D interface, corroborated by the advanced characterizations techniques, e.g., synchrotron‐based X‐ray absorption near‐edge structure, and theoretical calculations. This work not only reports a new metal‐free phosphorene/g‐C3N4 photocatalyst but also sheds lights on the design and fabrication of 2D/2D VDW heterojunction for applications in catalysis, electronics, and optoelectronics.
A novel 2D/2D van der Waals heterostructure of a metal‐free phosphorene/graphitic carbon nitride (g‐C3N4) photocatalyst is prepared for the first time. The phosphorene/g‐C3N4 composite shows a highly enhanced visible‐light photocatalytic H2‐production activity of 571 µmol h−1 g−1. The improved performance arises from the strong electronic coupling at the 2D/2D interface, confirmed by both advanced characterization techniques and theoretical calculations.
An overview is presented with regard to applications of visible and near infrared (Vis/NIR) spectroscopy, multispectral imaging and hyperspectral imaging techniques for quality attributes measurement ...and variety discrimination of various fruit species, i.e., apple, orange, kiwifruit, peach, grape, strawberry, grape, jujube, banana, mango and others. Some commonly utilized chemometrics including pretreatment methods, variable selection methods, discriminant methods and calibration methods are briefly introduced. The comprehensive review of applications, which concentrates primarily on Vis/NIR spectroscopy, are arranged according to fruit species. Most of the applications are focused on variety discrimination or the measurement of soluble solids content (SSC), acidity and firmness, but also some measurements involving dry matter, vitamin C, polyphenols and pigments have been reported. The feasibility of different spectral modes, i.e., reflectance, interactance and transmittance, are discussed. Optimal variable selection methods and calibration methods for measuring different attributes of different fruit species are addressed. Special attention is paid to sample preparation and the influence of the environment. Areas where further investigation is needed and problems concerning model robustness and model transfer are identified.
The configuration entropy was manipulated by introducing atoms with unique properties using the high throughput calculations, and five new disilicates with ideal properties which have lower thermal ...conductivity and controllable thermal expansion coefficient were obtained through composition design. From a microstructural perspective, the inclusion of atoms with larger ionic radius differences (reaching a 4.11 % contrast with Yb2Si2O7) can cause sever lattice shrinkage (9.49 % compared to single-component disilicates), which leads to lower thermal conductivity and a change in the thermal expansion coefficient. At 1200 °C, the thermal expansion coefficient of the five high-entropy disilicates ranged from 4.57 × 10-6 K−1 to 4.84 × 10-6 K−1, and the minimum thermal conductivity was only 1.14 W/m·K. Additionally, the local charge disorder facilitates the transfer of electrons around Si-O to Sc, which reduces the covalent bond strength of Si-O and regulates the thermal expansion coefficient. This phenomenon has been proved in the five non-equimolar high-entropy disilicates with different contents of Sc, effectively regulating the thermal expansion coefficient in 4.08 × 10-6 K−1 to 5.04 × 10-6 K−1. This study presents a novel method for controlling the thermal properties of disilicates and expands the possibilities for selecting thermal protective coating materials for ultra-high temperature SiC-based ceramic composites.
DNA double-strand breaks (DSBs) are the most deleterious type of DNA damage in cells arising from endogenous and exogenous attacks on the genomic DNA. Timely and properly repair of DSBs is important ...for genomic integrity and survival. MMEJ is an error-prone repair mechanism for DSBs, which relies on exposed microhomologous sequence flanking broken junction to fix DSBs in a Ku- and ligase IV-independent manner. Recently, significant progress has been made in MMEJ mechanism study. In this review, we will summarize its biochemical activities of several newly identified MMEJ factors and their biological significance.
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•P-rich biochar was more effective in immobilizing Pb than raw and Fe-rich biochars.•Raw and Fe-rich green waste biochars were more feasible for Cd fixation than Pb.•Fe modification ...decreased the efficacy of green waste biochar for Pb stabilization.•Green waste biochars could immobilize Cd under both anoxic and oxic conditions.•Raw and Fe-rich green waste biochars immobilized Pb under Eh ≤ -300 mV.
Functionalized biochar has gained extensive interests as a sustainable amendment for an effective remediation of paddy soils contaminated with heavy metals (HMs). We examined the efficiency of pig carcass-derived biochar (P-rich biochar, total P = 8.3%) and pristine (raw biochar, total Fe = 0.76%) and Fe-modified (Fe-rich biochar, total Fe = 5.5%) green waste-derived biochars for the immobilization of cadmium (Cd) and lead (Pb) in a paddy soil under pre-defined redox conditions (Eh, from -400 to +300 mV). Average concentrations (μg L-1) of dissolved Cd increased under reducing conditions up to 10.9 in the control soil, and decreased under oxidizing conditions to below the detection limit (LDL = 2.7) in the raw and Fe-rich biochar treated soils. Application of the raw biochar decreased the concentrations of dissolved Cd by 43–59% under Eh ≤ -100 mV, compared to the non-treated control, which was more effective than the Fe-rich biochar (31–59%) and the P-rich biochar (8–19%). The immobilization of Cd under low Eh might be due to its precipitation with sulfide (S2-), whereas its immobilization under high Eh might be due to the associated increase of pH. Concentrations (μg L-1) of Pb ranged from 29.4 to 198.2 under reducing conditions, and decreased to LDL (12.5) under oxidizing conditions. The P-rich biochar was more effective in immobilizing Pb than the raw and Fe-rich biochars, particularly under Eh ≤ 0 mV (55–82%), which might be due to the retention of Pb by phosphates. The raw and Fe-rich biochars immobilized Pb under low Eh (≤ -300 mV), but both biochars, particularly the Fe-rich biochar mobilized Pb under Eh higher than -200 mV, especially at +100 mV, due to the decrease of pH at this point (pH = 6.0 to 6.5). These results improved our understanding of using P-rich and Fe-rich functionalized biochars for the immobilization of Cd and Pb in a paddy soil under stepwise redox changes. The amendment of P-rich pig carcass-derived biochar to paddy soils could be a promising approach for mitigating the risk of Pb for human health and the environment. The raw and Fe-rich green waste-derived biochars can be used for immobilizing Cd and mitigating its risk in paddy soils under both reducing and oxidizing conditions.
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