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Human activities that involve diverse behaviors and feature a variety of participations and collaborations usually lead to varying and dynamic impacts on the ecological environment. Quantitative analysis of the dynamic changes and complex relationships between human activities and the ecological environment (eco-environment) can provide crucial insights for ecological protecting and balance maintaining. We proposed a two-dimensional four-quadrant assessment method based on the dynamic changes in Human Activity Index (HAI) - Environmental Ecological Condition Index (EECI) to analyze the dynamic trends and coupling coordination degree (CCD) between HAI and EECI. This approach was applied in an empirical study of Hainan Province. A comprehensive HAI at a resolution of 1 km × 1 km is established to measure human activities, while an EECI is developed to evaluate ecological environment quality. The eco-environment showed continuous improvement, with the HAI initially rising and then declining. Analysis of coupling coordination revealed a ratio of 6:1 between coordinated development regions and conflict regions, indicating a gradual improvement in overall coupling coordination. The interaction between the HAI and EECI is strengthening, though variations exist across different locations. Using the geodetector method, we identified Net Primary Productivity (NPP), Land use and land cover (LULC), and Particulate Matter (PM) as the primary factors influencing changes in coupling coordination between HAI and EECI. These factors indirectly affect the stability and carrying capacity of the ecological environment. This method facilitates a quantitative examination of the dynamic relationship between HAI and EECI in different regions, offering insights into ecosystem functionality, biodiversity maintenance, and the effect of HAI on the region.
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Iridium-catalyzed C-H borylation of aromatic and aliphatic hydrocarbons assisted by a directing group was theoretically investigated. Density functional theory (DFT) calculations revealed both Ir-catalyzed C(sp2)-H and C(sp3)-H borylations via an IrIII/IrV catalytic cycle, where the tetra-coordinated (C, N)IrIII(Bpin)2 complex with two vacant sites is an active species. Dramatically, the orientation of cyclometalation for C(sp2)-H bond activation assisted by a directing group is different from the C(sp3)-H one. The activation energy (ΔG° = 28.5 kcal mol-1) of the C(sp2)-H bond via trans-chelation to form cyclometalation is lower than that (41.4 kcal mol-1) via cis-chelation. In contrast, the ΔG° (26.6 kcal mol-1) of the C(sp3)-H bond via cis-chelation to form cyclometalation is lower than that (34.3 kcal mol-1) via trans-chelation. In addition, the rate-determining step of Ir-catalyzed C(sp2)-H borylation is oxidative addition of the C(sp2)-H bond, while that of C(sp3)-H analogues is hydride migration. Such differences arise from not only the differences in the steric hindrance of the C(sp2) and secondary C(sp3) atoms but also the differences in the trans effect and steric effect of the two vacant sites of active species. These findings were expected to facilitate further studies on the design and synthesis of innovative ligands for Ir-catalyzed C-H borylation.
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Pd-catalyzed borylation of fluorobenzene was theoretically studied. DFT calculations revealed that the reaction occurs through an unprecedented 3 + 6-membered ring transition state, in which one LiHMDS (HMDS = hexamethyldisilazane) acts as a ligand and another LiHMDS is essential to provide Li···N and Li···F interactions, overcoming the large destabilization of the strong phenyl-F bond distortion. The characteristic feature of LiHMDS was elucidated by comparing it with HMDS and NaHMDS analogues.
Assuntos
Fluorbenzenos , Paládio , Paládio/química , Modelos Moleculares , LigantesRESUMO
Developing advanced electrode materials with highly improved charge and mass transfer is critical to obtain high specific capacities and long-term cycle life for energy storage. Herein, three-dimensionally (3D) porous network electrodes with Cu(OH)2 nanosheets/Ni3S2 nanowire 2D/1D heterostructures are rationally fabricated. Different from traditional surface deposition, the 1D/2D heterostructure network is obtained by in situ hydrothermal chemical etching of the surface layer of nickel foam (NF) ligaments. The Cu(OH)2/Ni3S2@NF electrode delivers a high specific capacity (1855 F g-1 at 2 mA cm-2) together with a remarkable stability. The capacity retention of the electrode is over 110% after 35,000 charge/discharge cycles at 20 mA cm-2. The improved performance is attributed to the enhanced electron transfer between 1D Ni3S2 and 2D Cu(OH)2, highly accessible sites of 3D network for electrolyte ions, and strong mechanical bonding and good electrical connection between Cu(OH)2/Ni3S2 active materials and the conductive NF. Especially, the unique 1D/2D heterostructure alleviates structural pulverization during the ion insertion/desertion process. A symmetric device applying the Cu(OH)2/Ni3S2@NF electrode exhibits a remarkable cycling stability with the capacitance retention maintaining over 98% after 30,000 cycles at 50 mA cm-2. Therefore, the outstanding performance promises the architectural 1D/2D heterostructure to offer potential applications in future electrochemical energy storage.
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The reasonable design of the composition and hollow structure of electrode materials is beneficial for promoting the electrochemical properties and stability of electrode materials for high-performance supercapacitors, and it is of great significance to understand the inherent effect of these features on their performance. In this paper, the amorphous Ni-Co double hydroxide nanocages with hollow structures (Ni-Co ADHs) including quasi-sphere, cube and flower are delicately tailored via a Cu2O template-assisted approach. By combining experimental characterization and density functional theory (DFT) calculations, we systematically study the morphological growth of Cu2O templates under different conditions and the electrochemical performance of Ni-Co ADHs. Due to the coordination and synergistic effect between different components, the unique hollow structure and the nature of amorphous materials, Ni-Co ADHs deliver a high specific capacitance of 1707 F g-1 at 1 A g-1. The DFT calculations demonstrate that Ni-Co ADH nanocages exhibit an optimal redox reaction energy barrier and immensely promote the performance. In addition, a hybrid supercapacitor assembled with Ni-Co ADHs as a cathode and active carbon (AC) as an anode shows a high energy density of 33.8 W h kg-1 at a power density of 850 W kg-1 and exhibits an excellent cycling performance with a retention rate of 98% after 50 000 cycles. The successful synthesis of Ni-Co ADH nanocages, combined with rational computational simulations, indicates the excellent electrochemical performance and the potential utilization of amorphous hollow nanomaterials as electrodes for supercapacitors.
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Supercapacitors with high security, excellent energy and power densities, and superior long-term cycling performance are becoming increasingly essential for flexible devices. Herein, this study has reported a novel method to synthesize CoNi2S4, which delivered a high specific capacitance of 1836.6 F g-1 at 1 A g-1, with a slight fluctuation in the testing temperature rising up to 50 °C (1855.2 F g-1) or decreasing to 0 °C (1587.6 F g-1). In addition, the corresponding solid-state CoNi2S4//AC HSC could achieve a high energy density of 35.8 W h kg-1 at a power density of 800.0 W kg-1, with nearly no change when tested at 0 °C and 50 °C, and possessed excellent long-term electrochemical cycling stability of 132.3% after 50 000 cycles; the solid-state hybrid supercapacitor using biomass-derived carbon (BC) as the negative electrode (CoNi2S4//BC HSC) could also deliver a high energy density of 38.9 W h kg-1 at a power density of 850.0 W kg-1 and the specific capacitance retention was 101.2% after cycling for 50 000 times. This work has provided a promising method to prepare high-performance electrode materials for solid-state hybrid supercapacitors with superior cycling stability and energy density.
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The crystallization of magnesium ammonium phosphate (MAP) is one of the main processes for recovering P and N from wastewater. Chemically defined solution systems were designed; the saturation indices (SIs) of the solution systems with respect to MAP were derived by using a geochemical aqueous model Program, PHREEQC 2.11; the effects of the solution conditions were evaluated using thermodynamic theories. The concentrations of P and Mg in the tested solutions were 10-600 mg l(-1) and 24-720 mg l(-1), respectively, the molar ratios of N/P and pH values of the solutions varied in the ranges of 1-40 and 6.0-12.0, respectively. The temperature of all the tests was set at 25 degrees C. The test results show that the SI value of MAP is the logarithmic functions of the concentrations of P, ammonium-N and Mg, and increases with the increase of the concentration of each element. The SI value of MAP is a polynomial function of pH value of the solution, and the optimum pH value for the crystallization of MAP is 9.0 but increases slightly with the increase of the N/P. Moreover, the SI value of MAP is a power law function of the ionic strength of solutions but decreases with its increase. The adjustment of the Mg concentration and the control of solution pH are two effective methods for the control of the crystallization of MAP. The results obtained from the research can be used to guide the design and control of MAP crystallization process for the removal and recovery of P.