Oxidative Etching of Hexagonal Boron Nitride Toward Nanosheets with Defined Edges and Holes

Lateral surface etching of two-dimensional (2D) nanosheets results in holey 2D nanosheets that have abundant edge atoms. Recent reports on holey graphene showed that holey 2D nanosheets can outperform their intact counterparts in many potential applications such as energy storage, catalysis, sensing, transistors, and molecular transport/separation. From both fundamental and application perspectives, it is desirable to obtain holey 2D nanosheets with defined hole morphology and hole edge structures. This remains a great challenge for graphene and is little explored for other 2D nanomaterials. Here, a facile, controllable, and scalable method is reported to carve geometrically defined pit/hole shapes and edges on hexagonal boron nitride (h-BN) basal plane surfaces via oxidative etching in air using silver nanoparticles as catalysts. The etched h-BN was further purified and exfoliated into nanosheets that inherited the hole/edge structural motifs and, under certain conditions, possess altered optical bandgap properties likely induced by the enriched zigzag edge atoms. This method opens up an exciting approach to further explore the physical and chemical properties of hole-and edge-enriched boron nitride and other 2D nanosheets, paving the way toward applications that can take advantage of their unique structures and performance characteristics

Soil functions and ecosystem services research in the Chinese karst Critical Zone

Covering extensive parts of China, karst is a critically important landscape that has experienced rapid and intensive land use change and associated ecosystem degradation within only the last 50 years. In the natural state, key ecosystem services delivered by these landscapes include regulation of the hydrological cycle, nutrient cycling and supply, carbon storage in soils and biomass, biodiversity and food production. Intensification of agriculture since the late-20th century has led to a rapid deterioration in Critical Zone (CZ) state, evidenced by reduced crop production and rapid loss of soil. In many areas, an ecological ‘tipping point’ appears to have been passed as basement rock is exposed and ‘rocky desertification’ dominates. This paper reviews contemporary research of soil processes and ecosystems service delivery in Chinese karst ecosystems, with an emphasis on soil degradation and the potential for ecosystem recovery through sustainable management. It is clear that currently there is limited understanding of the geological, hydrological and ecological processes that control soil functions in these landscapes, which is critical for developing management strategies to optimise ecosystem service delivery. This knowledge gap presents a classic CZ scientific challenge because an integrated multi-disciplinary approach is essential to quantify the responses of soils in the Chinese karst CZ to extreme anthropogenic perturbation, to develop a mechanistic understanding of their resilience to environmental stressors, and thereby to inform strategies to recover and maintain sustainable soil function. © 2019 Elsevier B.V

CuB monolayer: a novel 2D anti-van’t Hoff/Le Bel nanostructure with planar hyper-coordinate boron/copper and superconductivity

To achieve specific applications, it is always desirable to design new materials with peculiar topological properties. Herein, based on a D2h B2Cu6H6 molecule with the unique chemical bonding of planar pentacoordinate boron (ppB) as a building block, we constructed an infinite CuB monolayer by linking B2Cu6 subunits in an orthorhombic lattice. The planarity of the CuB sheet is attributed to the multicenter bonds and electron donation-back donation, as revealed by chemical bonding analysis. As a global minimum confirmed by the particle swarm optimization method, the CuB monolayer is expected to be highly stable, as indicated by its rather high cohesive energy, absence of soft phonon modes, and good resistance to high temperature, and thus is highly feasible for experimental realization. Remarkably, this CuB monolayer is metallic and predicted to be superconducting with an estimated critical temperature (Tc) of 4.6 K, and the critical temperature could be further enhanced by tensile strains (to 21 K at atmospheric pressure)

Effects of Land Cover Change on Vegetation Carbon Source/Sink in Arid Terrestrial Ecosystems of Northwest China, 2001–2018

The arid terrestrial ecosystem carbon cycle is one of the most important parts of the global carbon cycle, but it is vulnerable to external disturbances. As the most direct factor affecting the carbon cycle, how land cover change affects vegetation carbon sources/sinks in arid terrestrial ecosystems remains unclear. In this study, we chose the arid region of northwest China (ARNWC) as the study area and used net ecosystem productivity (NEP) as an indicator of vegetation carbon source/sink. Subsequently, we described the spatial distribution and temporal dynamics of vegetation carbon sources/sinks in the ARNWC from 2001–2018 by combining the Carnegie-Ames-Stanford Approach (CASA) and a soil microbial heterotrophic respiration (RH) model and assessed the effects of land cover change on them through modeling scenario design. We found that land cover change had an obvious positive impact on vegetation carbon sinks. Among them, the effect of land cover type conversion contributed to an increase in total NEP of approximately 1.77 Tg C (reaching 15.55% of the original value), and after simultaneously considering the effect of vegetation growth enhancement, it contributed to an increase in total NEP of approximately 14.75 Tg C (reaching 129.61% of the original value). For different land cover types, cropland consistently contributed the most to the increment of NEP, and the regeneration of young and middle-aged forests also led to a significant increase in forest carbon sinks. Thus, our findings provide a reference for assessing the effects of land cover change on vegetation carbon sinks, and they indicated that cropland expansion and anthropogenic management dominated the growth of vegetation carbon sequestration in the ARNWC, that afforestation also benefits the carbon sink capacity of terrestrial ecosystems, and that attention should be paid to restoring and protecting native vegetation in forestland and grassland regions in the future

FeB₆ Monolayers: The Graphene-like Material with Hypercoordinate Transition Metal

By means of density functional theory (DFT) computations and global minimum search using particle-swarm optimization (PSO) method, we predicted three FeB₆ monolayers, namely α-FeB₆, β-FeB₆ and γ-FeB₆, which consist of the Fe©B_<i>x</i> (<i>x</i> = 6, 8) wheels with planar hypercoordinate Fe atoms locating at the center of six- or eight-membered boron rings. In particular, the α-FeB₆ sheet constructed by Fe©B₈ motifs is the global minimum due to completely shared and well delocalized electrons. The two-dimensional (2D) boron networks are dramatically stabilized by the electron transfer from Fe atoms, and the FeB₆ monolayers have pronounced stabilities. The α-FeB₆ monolayer is metallic, while the β-FeB₆ and γ-FeB₆ sheets are semiconductors with indirect band gaps and significant visible-light absorptions. Besides the novel chemical bonding, the high feasibility for experimental realization, and unique electronic and optical properties, render them very welcome new members to the graphene-like materials family

T₁- and T₂‑weighted Magnetic Resonance Dual Contrast by Single Core Truncated Cubic Iron Oxide Nanoparticles with Abrupt Cellular Internalization and Immune Evasion

Conventional T₁- or T₂-weighted single mode contrast-enhanced magnetic resonance imaging (MRI) may produce false results. Thereby, there is a need to develop dual contrast agents, T₁- and T₂-weighted, for more accurate MRI imaging. The dual contrast agents should possess high magnetic resonance (MR) relaxivities, targeted tumor linking, and minimum recognition by the immune system. We have developed nitrodopamine-PEG grafted single core truncated cubic iron oxide nanoparticles (ND-PEG-tNCIOs) capable of producing marked dual contrasts in MRI with enhanced longitudinal and transverse relaxivities of 32 ± 1.29 and 791 ± 38.39 mM^–1 s^–1, respectively. Furthermore, the ND-PEG-tNCIOs show excellent colloidal stability in physiological buffers and higher cellular internalization in cancerous cells than in phagocytic cells, indicating the immune evasive capability of the nanoparticles. These findings indicate that tNCIOs are strong candidates for dual contrast MRI imaging, which is vital for noninvasive real-time detection of nascent cancer cells in vivo and for monitoring stem cells transplants

Soil functions and ecosystem services research in the Chinese karst Critical Zone

Covering extensive parts of China, karst is a critically important landscape that has experienced rapid and intensive land use change and associated ecosystem degradation within only the last 50 years. In the natural state, key ecosystem services delivered by these landscapes include regulation of the hydrological cycle, nutrient cycling and supply, carbon storage in soils and biomass, biodiversity and food production. Intensification of agriculture since the late-20th century has led to a rapid deterioration in Critical Zone (CZ) state, evidenced by reduced crop production and rapid loss of soil. In many areas, an ecological \u27tipping point\u27 appears to have been passed as basement rock is exposed and \u27rocky desertification\u27 dominates. This paper reviews contemporary research of soil processes and ecosystems service delivery in Chinese karst ecosystems, with an emphasis on soil degradation and the potential for ecosystem recovery through sustainable management. It is clear that currently there is limited understanding of the geological, hydrological and ecological processes that control soil functions in these landscapes, which is critical for developing management strategies to optimise ecosystem service delivery. This knowledge gap presents a classic CZ scientific challenge because an integrated multi-disciplinary approach is essential to quantify the responses of soils in the Chinese karst CZ to extreme anthropogenic perturbation, to develop a mechanistic understanding of their resilience to environmental stressors, and thereby to inform strategies to recover and maintain sustainable soil function