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Boron (B) is an essential micronutrient for plant growth. Lack of valid methods for pretreatment and measurement of δ11B in plant restrict applications of it in the biosphere. Dry ashing, one step cation exchange and micro-sublimation were combined to separate and purify boron (B) in plant tissues. The low procedure blank, high B recovery and the accurate δ11B values of the plant reference materials demonstrate that this method is suitable and valid for B pretreatment and δ11B measurement in plant samples by MC-ICP-MS. Based on this method, the δ11B in different plants (Brassica napus, Chenopodium album L, moss, lichen, and Nostoc commune) was analyzed. For Brassica napus, δ11B increased gradually from root to leaf, and then decreased to rapeseed. For the same parts, the δ11B increased from the lower parts to the higher parts. This variation may be due to the B(OH)3 transporter of NIP6;1 and the incorporation of B into the cell. The reason for lower δ11B values in shell and rapeseed compared to those in leaves presumably is to the preferred Transport of borate in the phloem. The largest δ11B fractionation between leaf and root in Brassica napus and Chenopodium album L was +24.2‰ and +26.6‰, respectively. The large variation and fractionation of δ11B within plants indicates that δ11B is a good tracer to study the B translocation mechanisms and metabolism within plants. The δ11B in Nostoc commune, lichen, and moss showed variations of -4.1‰ to +21.5‰, −9.4‰ to +7.3‰, and −18.3‰ to +11. 9‰, respectively. In the same site, δ11B in different plants ranked Nostoc commune>moss>lichen and δ11B in mosses growing in different environment ranked soil>tree>rock. Rain and soil available B are the main B sources for these plants. The δ11B in Nostoc commune, lichen, and moss may be a useful tracer to study the atmospheric B input. In the future, plants culture experiments under certain environments and studies from molecular level are necessary to decipher the variation of δ11B and fractionation mechanisms within plants.
Carbon dots have attracted much attention due to their unique optical, chemical and electronic properties enabling a wide range of applications. The properties of carbon dots can be effectively adjusted through modifying their chemical composition. However, a major challenge remains in understanding the core and surface contributions to optical and electronic transitions. Here, three blue luminescent carbon dots with carboxyl, amino and hydroxyl groups were comprehensively characterized by UV-vis absorption and emission spectroscopy, synchrotron-based X-ray spectroscopy, and infrared spectroscopy. The influence of the surface functionality on their fluorescence was probed by pH-dependent photoluminescence measurements. Moreover, the hydrogen bonding interactions between water and the surface groups of carbon dots were characterized by infrared spectroscopy. Our results show that both core and surface electronic states of blue luminescent carbon dots contribute to electronic acceptor levels while the chemical nature of the surface groups determines the hydrogen bonding behavior of the carbon dots. This comprehensive spectroscopic study demonstrates that the surface chemistry has a profound influence on the electronic configuration and surface–water interaction of carbon dots, thus affecting their photoluminescence properties.
The development of earth-abundant catalysts for selective electrochemical CO2 conversion is a central challenge. Cu-Sn bimetallic catalysts can yield selective CO2 reduction toward either CO or formate. This study presents oxide-derived Cu-Sn catalysts tunable for either product and seeks to understand the synergetic effects between Cu and Sn causing these selectivity trends. The materials undergo significant transformations under CO2 reduction conditions, and their dynamic bulk and surface structures are revealed by correlating observations from multiple methods—X-ray absorption spectroscopy for in situ study, and quasi in situ X-ray photoelectron spectroscopy for surface sensitivity. For both types of catalysts, Cu transforms to metallic Cu0 under reaction conditions. However, the Sn speciation and content differ significantly between the catalyst types: the CO-selective catalysts exhibit a surface Sn content of 13 at. % predominantly present as oxidized Sn, while the formate-selective catalysts display an Sn content of ≈70 at. % consisting of both metallic Sn0 and Sn oxide species. Density functional theory simulations suggest that Snδ+ sites weaken CO adsorption, thereby enhancing CO selectivity, while Sn0 sites hinder H adsorption and promote formate production. This study reveals the complex dependence of catalyst structure, composition, and speciation with electrochemical bias in bimetallic Cu catalysts.
Boron isotope fractionation in soil-plant systems and its influence on biogeochemical cycling
(2022)
Boron (B) is an essential mineral nutrient for higher plants. Although B plant nutrition is well studied, the B isotope fractionation at the soil-plant interface, within plant metabolism, and its influence on biogeochemical cycling is not fully understood. Boron concentrations and isotope variations (δ11B) of the dicotyledonous plants of Chenopodium album and Brassica napus and their growing soils along a climatic gradient were analyzed to decipher these unresolved issues of the B behavior. The boron concentrations and δ11B values show an increasing trend from roots to leaves for both plants, while a decreasing trend from flower to shell and to seed for Brassica napus. A large boron isotope fractionation occurs within the plants with median Δ11Bleaf-root ≈ +20‰, which is related to different boron transporters and transportation ways. Formation of borate dimerized rhamnogalacturonan II in cell and B(OH)3 transportation in xylem lead to heavier δ11B values from root to stem and leaf while B(OH)4 transportation in phloem lead to lighter δ11B values from flower to shell and seed. Although samples cover a distinct transect with systematically different climatic conditions, Δδ11B within the individual plant compartments and between the bulk plants and the soil available B do not show any systematic variation.
This suggests that B uptake from the soil into Chenopodium album and Brassica napus occurs without a distinct isotope fractionation at the soil-plant interface (median Δ11Bbulkplant-soil = 0.2‰) and plants are able to regulate boron uptake. Both the observed large B fractionation within plant and low or absent B isotope fractionation at the soil-plant interface may have profound implications for the biological and geological B cycle. If this observed boron behavior also exists in other plants, their litters would be an important source for exporting 11B-rich biological material from continental ecosystems via rivers to the global oceans. This may be helpful for the explanation of ocean B cycle and the increasing δ11B values over the Cenozoic.