Exotic quantum phenomena have been demonstrated in recently discovered intrinsic magnetic topological insulator MnBi2Te4. At its two-dimensional limit, the quantum anomalous Hall effect and axion ...insulator state were observed in odd and even layers of MnBi2Te4, respectively. Here, we employ low-temperature scanning tunneling microscopy to study the electronic properties of MnBi2Te4. The quasiparticle interference patterns indicate that the electronic structures on the topmost layer of MnBi2Te4 are different from those of the expected out-of-plane A-type antiferromagnetic phase. The topological surface states may be embedded in deeper layers beneath the topmost surface. Such novel electronic structure is presumably related to the modification of crystalline structure during sample cleaving and reorientation of the magnetic moment of Mn atoms near the surface. Mn dopants substituted at the Bi site on the second atomic layer are observed. The electronic structures fluctuate at atomic scale on the surface, which can affect the magnetism of MnBi2Te4.
Cu/Ni-bearing wastewater contamination has recently been a challenge for the environmental protection worldwide. Herein, a novel poly(2-acrylamide-pentanedihydroxamic acid) (PAPDA) resin containing ...–CONHOH and –COOH groups was prepared and applied to effectively remove Cu2+ and Ni2+ from heavy metal wastewater. The batch adsorption experiments revealed that the maximum adsorption capacities of PAPDA resin for Cu2+ and Ni2+ were 436.08 and 195.05 mg·g−1, respectively, which were 10.20 and 9.45 times higher than that of polyacrylic resin. Specifically, the adsorption kinetics and thermodynamics of PAPDA were respectively consistent with the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating that the adsorption is a single-layer chemisorption process. Besides, the adsorption mechanism was investigated by SEM, XRD, FT-IR, XPS, DFT calculations, suggesting that the PAPDA resin possessing abundant active sites could effectively adsorb the heavy metal ions. Noticeably, the –CONHOH groups represented the strong affinity towards Cu2+ and Ni2+ by forming stable five-membered rings. In addition, column experiments were conducted to study the practical adsorption process of PAPDA resin to heavy metal ions. Overall, the results proved that the novel PAPDA resin as a green and highly efficient adsorbent has a promising potential for the treatment of heavy metals-containing wastewater.
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•Novel acylamino dihydroxamic acid chelating resin (PAPDA) is designed and prepared.•PAPDA resin possessed multiple active sites that can be bound with the metal ions.•PAPDA resin achieved an excellent adsorption capacity for Cu2+and Ni2+.•PAPDA resin exhibited the faster adsorption rate for Cu2+ than that of Ni2+.•PAPDA resin presented effective stability and good regeneration property.
Heteroatom-doped carbonaceous materials are the most promising substitutes of noble metals as green catalysts for electrochemical water splitting. In this study, nitrogen and sulfur co-doped graphene ...(N,S-G) is synthesized via a one-pot calcination method. Subsequently, N,S-G is activated by ZnCl2 to enlarge the specific surface areas to construct a porous structure (a-N,S-G) The chemical activation can simultaneously regulate the elemental composition and porous structure of SNG toward enhanced carbocatalysis. As a result, in the OER process, the overpotential of a-N,S-G is only 330 mV vs. RHE at 10 mA cm−2 in 1 M KOH, which surpasses the most reported carbon catalysts. In the HER process, −10 mA cm−2 can be achieved at an overpotential of 0.29 V vs. RHE in 1 M KOH and 0.31 V vs. RHE in 0.5 M H2SO4. By combination with commercial carbon black (CB), the Tafel slopes of a-N,S-G@CB is lower than the metal-based catalysts. A new turnover frequencies (TOF) calculation method is involved to analyze the reactivity of specific active sites of carbocatalyst including both heteroatoms and structural defects. Therefore, the study provides an effective strategy for simultaneous modifications of surface chemistry and porous structure of graphene as high-performance and robust carbocatalysts toward electrochemical water splitting.
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This work aims to investigate the sulfate resistance of geopolymer composites prepared by alkali activation of metakaolin (MK) and reinforced with polypropylene fiber (PP), polyvinyl alcohol fiber ...(PVA) and wollastonite (WS). Compressive and flexural strength were measured to determine the optimum mix proportion of the composites. The sulfate resistance properties were evaluated by strength loss, mass loss, microstructure and pore structure changes after sulfate exposure. The experimental results show that the two groups containing 1% of PP + 1% of PVA and 2% of PVA +15% of WS, respectively, exhibit the highest compressive strength and flexural strength compared to non-reinforced mixtures. After sulfate exposure, the decreased compressive strength and mass loss are correlated to the concentration of sulfate and exposure period. In the simulated extreme marine environment, the deterioration of composites induced by high concentration of sulfate after 28 days of exposure reaches to the maximum level or a threshold. The average pore size and porosity increase after the sulfate exposure. The role of fibers in mechanical properties and microstructure after sulfate exposure were also investigated. The uses of hybrid organic fiber and inorganic mineral microfiber reinforcement are effective to enhance the resistance to sulfate attack.
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Nitrogen and sulfur co-doped graphene (N,S-G) is activated using ZnCl2, KOH, and CO2 to develop different defects and functionalities. The modified carbo-catalysts are used to activate ...peroxymonosulfate (PMS) for phenol degradation. Compared with nitrogen-doped graphene (N-G), N,S-G exhibits better catalytic activity, and KOH activation further enhances the oxidation efficiency. Radical quenching experiments, electrochemical characterization, and electron paramagnetic resonance characterization reveal that N-G activates PMS via a nonradical pathway. The involvement of a secondary sulfur dopant will transform the reaction pathway into radical-dominated oxidation (SO4 •–and •OH). KOH activation further promotes the generation of the two radical species and further involves superoxide ion radicals (O2 •–), thus achieving deeper mineralization of the organic pollutants. Different from the nonradical species confined on the catalyst surface, radical oxidation (including the singlet oxygen (1O2) transformed from O2 •–) occurs in bulk solution and protects the carbo-catalyst from corrosion, herein securing better structural integrity and stability of carbo-catalysts. Based on the structure–activity features, we designed a high-performance scalable carbo-catalyst of KOH-activated and N,S-codoped graphene (N,S-G-rGO-KOH) using a facile strategy, which is promising for practical applications.
•Riverine COD content showed high values in the cropland-dominated areas.•Three seasonal variation types were identified for station-based riverine COD.•Variations in riverine COD were co-determined ...by human and natural factors.
Rivers connect terrestrial and aquatic ecosystems and export approximately 55.47 % of the net terrestrial carbon fixation. However, due to unavailable high-frequency monitoring data, litter is known about diurnal variation in riverine carbon transport on a national scale. Based on daily measurements between March 2021 and February 2022 at 1491 stations across China, this study clarified the spatiotemporal variations in riverine organic matter indicated by chemical oxygen demand (COD). Spatially, COD content showed a spatial pattern with high values in the northwest (p < 0.05), and COD flux was determined by water discharge (84.01 %). Human activities explained 73.20 % of the spatial variations in riverine COD content; in particular, agricultural planting significantly elevated riverine COD (r = 0.73, p < 0.01). Seasonally, 95.53 % of stations showed significant seasonal variations in COD contents (p < 0.05); 69.72 % (25.81 %) were identified as Type II (III) typically had the maximum (minimum) COD in summer (autumn). Moreover, except for human activities (41.08 ± 22.94 %), natural factors also contributed 47.41 ± 24.04 % to the seasonal variations. In summer, high temperatures increased COD by promoting algal proliferation at Type II stations; however, heavy precipitation diluted COD contents at Type III stations. In these cases, seasonal measurements were essential for estimating riverine organic matter transport, especially the values measured in spring and winter. This study has significant implications for managing the aquatic environment, estimating riverine organic matter transport, and balancing the global carbon budget.
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The aromatization-driven redox-neutral cascade 1,5-hydride transfer/spirocyclization and cascade 1,5-hydride transfer/hydrolysis from para-quinone methide in HFIP were developed. These protocols ...enabled the synthesis of azaspirocyclohexadienones and ortho-benzylated anilines in good to high yields under mild conditions, featuring room temperature, additive-free, and good functional group tolerance.
Dissolved organic matter (DOM) plays an essential role in the global lake carbon cycle. Understanding DOM composition and monitoring its spatiotemporal dynamics are of great significance for ...understanding the lake carbon cycle, controlling water pollution, and protecting water resources. However, previous studies have focused mainly on eutrophic freshwater lakes, with limited attention given to saline lakes. Based on in situ data collected in ten lakes in northwestern China, this study reported the changes in DOM components in different lake types. Parallel factor analysis (PARAFAC) was used to analyze the three-dimensional excitation emission matrix (EEMs) to obtain the DOM fluorescence components. The contributions of different environmental factors to the changes in DOM components were quantified by the generalized linear model (GLM). The results showed that the eutrophication index was significantly positively related to dissolved organic carbon (DOC) (R2 = 0.95, p < 0.01) and colored DOM (CDOM) (R2 = 0.96, p < 0.01) concentrations. Terrestrial humic-like and tryptophan-like components, which are highly correlated with human activities, explained 62% and 64% of the variations in DOC and CDOM, respectively. In sum, the contributions of human activities to the DOC and CDOM variations were 61% and 57%, respectively. Salinity also showed significant positive correlations with both DOC (R2 = 0.88, p < 0.01) and CDOM (R2 = 0.87, p < 0.01). Lake salinization led to increases in DOM concentration, and salinity contributed 20% and 16% to the DOC and CDOM variations, respectively. Therefore, human activities and salinity codetermined the DOM concentration and its composition in the western arid lakes.
Based on these findings, this study proposed a feasible flowchart for remotely estimating DOM in saline lakes using satellite data. This study is significant for the long-term monitoring of the carbon cycle and the effective protection of lake water resources in saline lakes.
•Human activities and salinization co-determined the DOM composition in the arid lakes.•Human activities explained 61% and 57% of the changes in DOC and CDOM, respectively.•Trophic state index can be used as a bridge to remotely observe lake DOM from space.
The synergistic effects of boron (B) and rare earth (RE) elements on the microstructure and stress rupture properties were investigated in a Ni-based superalloy. The stress rupture lifetime at 650 ...°C/873 MPa significantly increased with the addition of B as a single element. Furthermore, the stress rupture lifetime reached its peak (303 h), with a certain amount of B and RE added together in test alloys. Although the grain size and morphology of the γ' phase varied a little with the change in B and RE addition, they were not considered to be the main reasons for stress rupture performance. The enhancement in stress rupture lifetime was mostly attributed to the segregation of the B and RE elements, which increased the binding force of the grain boundary and improved its strength and plasticity. In addition, the enrichment of B and RE inhabited the precipitation of carbides along grain boundaries. Furthermore, nano-scale RE precipitates containing sulfur (S) and phosphorus (P) were observed to be distributed along the grain boundaries. The purification of grain boundaries by B and RE elements was favorable to further improve the stress rupture properties.
This work systematically investigated the influence of microstructure evolution and element segregation on tensile properties and fracture behaviors of GH4706 superalloy under different temperatures ...(25 °C, 400 °C, 500 °C, 600 °C and 650 °C). The advanced methods of TEM, AES and SIMS were conducted to characterize the variation of microstructure and element distribution. Experimental results showed that the yield and tensile strength of the test alloy decreased while the corresponding elongation increased as the increment of test temperature. The dominated fracture mode was intergranular brittle fracture at the temperature of 25 °C, gradually transforming to ductile dimple fracture as the temperature increased. This phenomenon was determined to be closely related to the increment of average grain size and size of γ'/γ″ coprecipitates as temperature rose. It was worth noticing that the elongation performed abnormally low (16.3%) at the temperature of 500 °C, exhibiting intermediate temperature brittleness (ITB) phenomenon. The SIMS analysis showed that the segregation of S towards grain boundary was the most obvious at the temperature of 500 °C, which was considered as the main factor leading to ITB. In addition, the coarsening of carbides at grain boundaries and local strain non-uniformity caused by dislocations could also resulted in ITB. The main reason for maintaining good strength and plasticity at the temperature of 650 °C was contributed to the softening of γ' phases by repeated cutting of dislocations and deformation twins, reducing the hindrance to the movement of dislocations. Moreover, composite strengthening effect of P and B could improve bonding strength, stabilize grain boundaries, and effectively suppress the initiation of intergranular cracks.
•High temperature tensile properties of GH4706 alloy were investigated.•Microstructure evolution with temperature in GH4706 alloy was explored.•Element segregation under different temperatures were characterized by SIMS and AES.•Reasons for intermediate temperature brittleness (ITB) at the temperature of 500 °C were revealed.
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