Belowground Phytolith-Occluded Carbon of Monopodial Bamboo in China: An Overlooked Carbon Stock

Phytolith-occluded carbon (PhytOC), a highly stable carbon (C) fraction resistant to decomposition, plays an important role in long-term global C sequestration. Previous studies have demonstrated that bamboo plants contribute greatly to PhytOC sink in forests based on their aboveground biomass. However, little is known about the contribution of belowground parts of bamboo to the PhytOC stock. Here, we reported the phytolith and PhytOC accumulation in belowground trunk and rhizome of eight monopodial bamboo species that widely distributed across China. The results showed that the belowground parts made up an average of 39.41% of the total plant biomass of the eight bamboo species. There were significant (p < 0.05) variations in the phytolith and PhytOC concentrations in the belowground trunk and rhizome between the bamboo species. The mean concentrations of PhytOC in dry biomass ranged from 0.34 to 0.83 g kg-1 in the belowground rhizome and from 0.10 to 0.94 g kg-1 in the belowground trunk across the eight bamboo species, respectively. The mean PhytOC stocks in belowground biomass ranged from 2.57 to 23.71 kg ha-1, occupying an average of 23.36% of the total plant PhytOC stocks. This implies that 1.01 × 105 t PhytOC was overlooked based on the distribution of monopodial bamboos across China. Therefore, our results suggest that the belowground biomass of bamboo represents an important PhytOC stock, and should be taken into account in future studies in order to better quantifying PhytOC sequestration capacity

Isolating hydrogen in hexagonal boron nitride bubbles by a plasma treatment

Atomically thin hexagonal boron nitride (h-BN) is often regarded as an elastic film that is impermeable to gases. The high stabilities in thermal and chemical properties allow h-BN to serve as a gas barrier under extreme conditions.In this work, we demonstrate the isolation of hydrogen in bubbles of h-BN via plasma treatment.Detailed characterizations reveal that the substrates do not show chemical change after treatment. The bubbles are found to withstand thermal treatment in air,even at 800 degree celsius. Scanning transmission electron microscopy investigation shows that the h-BN multilayer has a unique aligned porous stacking nature, which is essential for the character of being transparent to atomic hydrogen but impermeable to hydrogen molecules. We successfully demonstrated the extraction of hydrogen gases from gaseous compounds or mixtures containing hydrogen element. The successful production of hydrogen bubbles on h-BN flakes has potential for further application in nano/micro-electromechanical systems and hydrogen storage.Comment: 55 pages, 33figure

Strong optical response and light emission from a monolayer molecular crystal

Excitons in two-dimensional (2D) materials are tightly bound and exhibit rich physics. So far, the optical excitations in 2D semiconductors are dominated by Wannier-Mott excitons, but molecular systems can host Frenkel excitons (FE) with unique properties. Here, we report a strong optical response in a class of monolayer molecular J-aggregates. The exciton exhibits giant oscillator strength and absorption (over 30% for monolayer) at resonance, as well as photoluminescence quantum yield in the range of 60-100%. We observe evidence of superradiance (including increased oscillator strength, bathochromic shift, reduced linewidth and lifetime) at room-temperature and more progressively towards low temperature. These unique properties only exist in monolayer owing to the large unscreened dipole interactions and suppression of charge-transfer processes. Finally, we demonstrate light-emitting devices with the monolayer J-aggregate. The intrinsic device speed could be beyond 30 GHz, which is promising for next-generation ultrafast on-chip optical communications

Spectroscopic investigation of defects in two-dimensional materials

Two-dimensional (2D) materials have been extensively studied in recent years due to their unique properties and great potential for applications. Different types of structural defects could present in 2D materials and have strong influence on their properties. Optical spectroscopic techniques, e.g. Raman and photoluminescence (PL) spectroscopy, have been widely used for defect characterization in 2D materials. In this review, we briefly introduce different types of defects and discuss their effects on the mechanical, electrical, optical, thermal, and magnetic properties of 2D materials. Then, we review the recent progress on Raman and PL spectroscopic investigation of defects in 2D materials, i.e. identifying of the nature of defects and also quantifying the numbers of defects. Finally, we highlight perspectives on defect characterization and engineering in 2D materials

Tuning interlayer coupling by laser irradiation and broadband photodetection in vertical MoTe2/WS2 vdW heterostructure

van der Waals (vdW) heterostructures constructed by stacking different two dimensional layered materials are extensively utilized in designing novel optoelectronic devices, such as photodetectors and light-emitting diodes. However, the performance of vertical heterostructures is impeded by challenges in effectively achieving interlayer coupling. Here, the systematic demonstration of vertical MoTe2/WS2 vdW heterostructures assembled by a mechanical transfer technique is reported, whereas the interlayer interaction is tuned from weak coupling to strong coupling by laser irradiation. Thereafter, the improved interlayer interaction of heterostructures is characterized by photoluminescence spectroscopy and further confirmed by electrical transport. Moreover, visible-infrared broadband photoresponse is achieved in the vertical stacking with the built-in field generated between MoTe2 and WS2. Thus, the outstanding findings of our experimental approach can facilitate novel two-dimensional devices for the optoelectronics industry

Intensive Management Increases Phytolith-Occluded Carbon Sequestration in Moso Bamboo Plantations in Subtropical China

Plantation management practices could markedly change the sequestration of phytolith-occluded carbon (PhytOC) in plants and soils. However, for Moso bamboo (Phyllostachys pubescens) plantations, the effect of intensive plantation management (including fertilization, tillage, and removal of understory vegetation) on the accretion rate of PhytOC in the soil-plant system is much less understood than extensive management (without fertilization, tillage, and removal of understory vegetation). The objectives of this study were to investigate the effect of intensive and extensive management practices on the production, accumulation, and runoff of PhytOC and their distribution in physical fractions in Moso bamboo plantations. Our results showed that intensive management (1) increased PhytOC production mainly due to increased forest productivity; (2) increased PhytOC storage in the heavy fraction but decreased its storage in the light fraction of organic matter, resulting in the lack of effect on soil PhytOC storage; (3) increased the rate of dissolution of phytolith and the loss of PhytOC in runoff; and (4) promoted PhytOC sequestration in the soil-plant system, mostly in the plants, due to the greater rate of PhytOC production than the rate of loss. We conclude that intensive bamboo plantation management practices are beneficial to increasing long-term PhytOC sequestration in the soil-plant system

Adsorption characteristics and mechanism of ammonia nitrogen and phosphate from biogas slurry by Ca2+-modified soybean straw biochar.

The utilization of biogas slurry is critical for the sustainable development of animal husbandry. Biomass carbon adsorption is a feasible method for the recycling of nutrients from biogas slurry. However, research on the co-adsorption of ammonia nitrogen and phosphate is scarce. Herein, soybean straw was utilized as the raw material to prepare Ca2+-modified biochar (CaSSB), which was investigated for its ammonia nitrogen and phosphate adsorption mechanisms. Compared with natural biochar (SSB), CaSSB possesses a high H/C ratio, larger surface area, high porosity and various functional groups. Ca2+-modified soybean straw biochar exhibited excellent adsorption performance for NH4+-N (103.18 mg/g) and PO43--P (9.75 mg/g) at pH = 6, using an adsorbent dosage of 2 g/L. The experimental adsorption data of ammonia nitrogen by CaSSB corresponded to pseudo-second-order kinetics and the Langmuir isotherm model, suggesting that the adsorption process was homogeneous and that electrostatic attraction might be the primary adsorption mechanism. Meanwhile, the adsorption of phosphate conformed to pseudo-second-order kinetics and the Langmuir-Freundlich model, whose mechanism might be attributed to ligand exchange and chemical precipitation. These results reveal the potential of CaSSBs as a cost-effective, efficient adsorbent for the recovery of ammonium and phosphate from biogas slurry