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.
As a candidate material proposed for the geological disposal of the high level radioactive waste, bentonite has been studied extensively in terms of its engineering properties. One of the properties ...is the pressure generated during wetting compacted bentonite under rigorously confined condition. This pressure is designated apparent swelling pressure ( p s ) herein. On the other hand, due to the extremely low hydraulic conductivity (e.g. 10 -9 -10 -14 m/s) of compacted bentonite, it is often very time consuming to measure p s . For instance, test duration is typically 1-2 month for a specimen with thickness ( h sp ) of 20 mm, and 1-2 weeks for h sp = 10 mm. Though testing duration can be reduced by using thinner specimens, it becomes difficult to control measurement accuracy. Recently, the author reported a series of datasets obtained with newly developed testing method using h sp = 2 mm specimens to measure p s , by which testing duration was reduced to 1-2 days and data repeatability was also extraordinarily good. In this paper, the author made further developments on such testing techniques and introduced a device to measure p s for h sp = 0.4 mm specimen, by which testing duration can be reduced to 1-2 hours. The p s measured by this device on a bentonite was compared with previous database, which implies that data repeatability is very good in generally, though the data scattering is observed for h sp =0.4 mm specimens.
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.
Porous organic cages (POCs) represent an emerging class of organic materials with intrinsic porosity. They have found various applications in supramolecular chemistry, materials science, and many ...other related disciplines, which stem from their molecular host-guest interactions, intrinsic and inter-cage porosity in solid state as well as the diversity of functionalities. Post-synthetic modification (PSM) has emerged as a highly viable strategy for broadening the functions and applications of POCs. Intricate structures, enhanced stability, tunable porosity and guest binding selectivity and sensitivity have been realized through PSM of POCs, which cannot be directly achieved
via
the predesign and bottom-up assembly from small molecule building blocks. For example, an unstable imine-linked POC can be transformed into a more stable amine-linked cage, whose cavity size can be further tuned by selective binding of some amine groups, offering unusual gas adsorption selectivity for noble gases (
e.g.
, preferred uptake of Xe over Kr). Such improvement of the chemical stability and gas separation properties through the consolidation of linkage and adjustment of porosity is challenging to achieve otherwise. In this tutorial review, we highlight the importance and impact of PSM in engineering the properties of POC molecules, their frameworks, and composites going beyond the direct predesign synthetic strategy. The primary PSM strategies for exploring new compositions, functions and applications as well as their structure-property relationship have been summarized, including cage-to-cage transformation at the molecular level, covalent or noncovalent assembly of POCs into frameworks, and formation of composites with guest species or other additives encapsulated.
This tutorial review summarizes the recent progress in utilizing the post-synthetic modification to develop porous organic cage-based novel structures and materials that cannot be easily accessed
via
conventional predesign and synthesis.
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.
Hydrogen-bonded organic frameworks (HOFs) represent an interesting type of polymeric porous materials that can be self-assembled through H-bonding between organic linkers. To realize permanent ...porosity in HOFs, stable and robust open frameworks can be constructed by judicious selection of rigid molecular building blocks and hydrogen-bonded units with strong H-bonding interactions, in which the framework stability might be further enhanced through framework interpenetration and other types of weak intermolecular interactions such as π π interactions. Owing to the reversible and flexible nature of H-bonding connections, HOFs show high crystallinity, solution processability, easy healing and purification. These unique advantages enable HOFs to be used as a highly versatile platform for exploring multifunctional porous materials. Here, the bright potential of HOF materials as multifunctional materials is highlighted in some of the most important applications for gas storage and separation, molecular recognition, electric and optical materials, chemical sensing, catalysis, and biomedicine.
This review provides an overview of development in the design, synthesis, and application of multifunctional porous hydrogen-bonded organic framework (HOF) materials.
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.
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.
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.
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