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Quantum spin liquids (QSLs) are in a quantum disordered state that is highly entangled and has fractional excitations. As a highly sought-after state of matter, QSLs were predicted to host spinon excitations and to arise in frustrated spin systems with large quantum fluctuations. Here we report on the experimental observation and theoretical modeling of QSL signatures in monolayer 1T-NbSe2, which is a newly emerging two-dimensional material that exhibits both charge-density-wave (CDW) and correlated insulating behaviors. By using scanning tunneling microscopy and spectroscopy (STM/STS), we confirm the presence of spin fluctuations in monolayer 1T-NbSe2 by observing the Kondo resonance as monolayer 1T-NbSe2 interacts with metallic monolayer 1H-NbSe2. Subsequent STM/STS imaging of monolayer 1T-NbSe2 at the Hubbard band energy further reveals a long-wavelength charge modulation, in agreement with the spinon modulation expected for QSLs. By depositing manganese-phthalocyanine (MnPc) molecules with spin S = 3/2 onto monolayer 1T-NbSe2, new STS resonance peaks emerge at the Hubbard band edges of monolayer 1T-NbSe2. This observation is consistent with the spinon Kondo effect induced by a S = 3/2 magnetic impurity embedded in a QSL. Taken together, these experimental observations indicate that monolayer 1T-NbSe2 is a new promising QSL material.Recently, signatures of quantum spin liquid have been reported in monolayer transition metal dichalcogenides. Here the authors report evidence of such state in 1T-NbSe2 via the measurements of the Kondo effect in a 1T-1H heterostructure, further supported by measurements for magnetic molecules on 1T-NbSe2. [ABSTRACT FROM AUTHOR]

Background and aims: Nitrogen enrichment and biodiversity affects the stoichiometry of plants, soils, and soil microbes. However, combined effects of nitrogen addition and biodiversity on interactions among the stoichiometry of plants, soils, and soil microbes (stoichiometric networks, PSMNs) have largely been overlooked, even though PSMNs are likely critical predictors of ecosystem structure and functions. Methods: To quantify effects of nitrogen addition and plant species richness on stoichiometric relations among plants, soils, and soil microbes, a common garden experiment with two nitrogen addition levels (0 and 6 g N m− 2 year− 1) and four plant species richness levels (1, 2, 4, and 8 species) was conducted in which those driving factors were manipulated. Results: Nitrogen addition had minor effects on most stoichiometries of plant–soil–microbes, but plant species richness showed significant association with most stoichiometries. With nitrogen addition, increases in soil ammonium nitrogen led to a decrease in PSMNs connectivity but an increase in modularity. Plant species richness was negatively associated with network connectivity but positively correlated with modular complexity because of changes in soil nutrient availability and increased niche differentiation. Conclusions: The findings demonstrate mechanistic links of biodiversity with the stoichiometry of plant–soil–microbes and stoichiometric networks, suggesting that biodiversity loss and resources decrease under global changes may enable a looser complexity in whole ecosystem element structure as indicated by the stoichiometric network architecture. [ABSTRACT FROM AUTHOR]

Grain boundaries in two-dimensional (2D) semiconductors generally induce distorted band alignment and interfacial charge, which impair their electronic properties for device applications. Here, we report the improvement of band alignment at the grain boundaries of PtSe2, a 2D semiconductor, with selective adsorption of a presentative organic acceptor, tetracyanoquinodimethane (TCNQ). TCNQ molecules show selective adsorption at the PtSe2 grain boundary with strong interfacial charge. The adsorption of TCNQ distinctly improves the band alignment at the PtSe2 grain boundaries. With the charge transfer between the grain boundary and TCNQ, the local charge is inhibited, and the band bending at the grain boundary is suppressed, as revealed by the scanning tunneling microscopy and spectroscopy (STM/S) results. Our finding provides an effective method for the advancement of the band alignment at the grain boundary by functional molecules, improving the electronic properties of 2D semiconductors for their future applications. [ABSTRACT FROM AUTHOR]

Chirality is essential for various phenomena in life and matter. However, chirality and its switching in electronic superlattices, such as charge density wave (CDW) superlattices, remain elusive. In this study, we characterize the chirality switching with atom-resolution imaging in a single-layer NbSe2 CDW superlattice by the technique of scanning tunneling microscopy. The atomic arrangement of the CDW superlattice is found continuous and intact although its chirality is switched. Several intermediate states are tracked by time-resolved imaging, revealing the fast and dynamic chirality transition. Importantly, the switching is reversibly realized with an external electric field. Our findings unveil the delicate switching process of chiral CDW superlattice in a two-dimensional (2D) crystal down to the atomic scale. Single-layer NbSe2 has a charge density wave with two degenerate domains, related by mirror reflection. Here, using scanning tunneling microscopy, the authors observe the time-dependent movement of domain walls, and demonstrate reversible switching between the two domain types using a voltage pulse from the microscope tip. [ABSTRACT FROM AUTHOR]

Indoleamine 2,3-dioxygenase (IDO), an immune checkpoint protein, can cause the depletion of tryptophan (Trp) and accumulation of its metabolite of kynurenine (Kyn) in cancer cells, and generates the immunosuppressive microenvironment that supports tumor cell growth. A novel immunoregulatory prodrug micelle based on polyethylene glycol-derivatized an IDO-selective inhibitor of 1-methyltryptophan (1-MT), PEG-Fmoc-1-MT, was developed for inhibiting the IDO activity of the conversion of Trp to Kyn in tumor microenvironments. To investigate the 1-MT distribution and Trp/Kyn ratios in mice tumors with PEG-Fmoc-1-MT prodrug micelles treatment, a HPLC–MS/MS method for simultaneous determination of 1-MT and IDO biomakers of Trp and Kyn in mouse tumors was developed and validated. Triple-quadrupole mass spectrometry with positive electrospray ionization as source ionization in multiple reaction monitoring at m/z 219.0 → 160.1, 205.0 → 118.2, 209.0 → 146.1 and 249.3 → 148.3 was used for determination of 1-MT, Trp, Kyn and matrine (internal standard). The method demonstrated good linearity at the concentrations ranging from 10 to 10,000 ng/mL and lower limits of quantitation of 1 ng/mL for 1-MT, Trp and Kyn, respectively. The validated method was successfully applied to 1-MT tumor biodistribution and Trp/Kyn ratio studies in 4T1 tumor bearing mice i.v. with PEG-Fmoc-1-MT prodrug micelles. The mice tumors with PEG-Fmoc-1-MT prodrug micelles treatment exhibited higher 1-MT accumulation and lower Trp/Kyn ratio, in comparison with those of mice with 1-MT solution treatment. The developed PEG-Fmoc-1-MT prodrug micelles could be a promising IDO immunoregulatory prodrug micelles for cancer immunotherapy. [ABSTRACT FROM AUTHOR]

Understanding Mott insulators and charge density waves (CDW) is critical for both fundamental physics and future device applications. However, the relationship between these two phenomena remains unclear, particularly in systems close to two-dimensional (2D) limit. In this study, we utilize scanning tunneling microscopy/spectroscopy to investigate monolayer 1T-NbSe2 to elucidate the energy of the Mott upper Hubbard band (UHB), and reveal that the spin-polarized UHB is spatially distributed away from the dz2 orbital at the center of the CDW unit. Moreover, the UHB shows a √3 × √3 R30° periodicity in addition to the typically observed CDW pattern. Furthermore, a pattern similar to the CDW order is visible deep in the Mott gap, exhibiting CDW without contribution of the Mott Hubbard band. Based on these findings in monolayer 1T-NbSe2, we provide novel insights into the relation between the correlated and collective electronic structures in monolayer 2D systems. The relationship between Mott state and charge density wave state in two dimensional materials remains unclear. Here, Liu et al. reveal spatial distribution of a Mott-Hubbard band in monolayer 1T-NbSe2 forming a new periodic pattern in addition to the well-known CDW pattern. [ABSTRACT FROM AUTHOR]

Background and aims: Microbial communities play an important regulatory role in soil carbon and nutrient cycling in terrestrial ecosystems. Most studies on microbial communities and biogeochemical cycling focus on surface soils (0–20 cm). However, relatively little is known about how structure and functioning of microbial communities shift with depth in a soil profile, which is crucial to understand biogeochemical cycling in deep soils. Methods: We combined a number of complementary techniques to investigate the microbial biomass, community composition and diversity, and potential functioning along soil profile (0–70 cm) in two alpine ecosystems (meadow and shrubland) on the Tibetan Plateau. Results: The microbial biomass and fungi:bacteria ratio declined significantly with depth, while the ratio of Gram-positive to Gram-negative bacteria increased with depth in both ecosystems. Microbial community composition showed significant differences among soil depths and between ecosystems. The relative abundance of some phylum of archaea, bacteria or fungi (e.g. Basidiomycota, Bacteroidetes) changed significantly with soil depth and ecosystem type. Bacteria diversity declined with depth, while archaea richness (OTU number) increased with depth and fungi diversity and richness did not show clear trend with depth. The co-occurrence network analysis further showed that surface soil microbes were more connected and interacted among each other compared to deep soil microbes. Moreover, total enzymatic activities and soil C mineralization rate declined with depth in both ecosystems. We also detected shifts with depth in some functional guilds of bacteria (based on faprotax database) in both ecosystems and fungi (based on FUNGuild database) only in shrubland. Conclusions: The biomass, community composition and diversity, and potential functioning of microbial communities all shifted significantly along soil profile in both ecosystems, and the vertical patterns of diversity varied among different microbial groups. This may have important implications for carbon and nutrient cycling along the soil profile in alpine ecosystems. [ABSTRACT FROM AUTHOR]

Background and aims: Changes of soil organic matter (SOM) stability in alpine ecosystems can alter carbon release from the soil and consequently feed back to climate change. We sought to explore the altitudinal patterns of SOM stability and their relationships with climatic, vegetational and edaphic factors. Methods: We combined a number of biological, thermal, chemical, molecular and isotopic indices to characterize SOM stability in two soil layers (0–10 and 10–30 cm) of alpine grassland along two altitudinal gradients of 3200–4200 m (Haibei) and 4400–5200 m (Damxung) on the Tibetan Plateau, respectively. Results: There were significant altitudinal variations in SOM stability between the two transects. Greater biological, chemical and isotopic indices of SOM stability were observed in the middle altitude in Haibei, while opposite results were observed in Damxung. Except for a decreasing trend of SOM stability along altitudinal gradient in subsurface soils (10–30 cm) in Damxung, there was no significant altitudinal trend of thermal and molecular indices of SOM stability. The multiple indices of SOM stability were mutually associated and all showed greater SOM stability in subsurface soils than in surface soils across regions and altitudes. Conclusions: Along the altitudinal gradient, SOM stability showed opposite unimodal patterns in Haibei and Damxung, and had higher values in subsurface soils than in surface soils of the alpine grassland. Climatic, vegetational and edaphic factors collectively control SOM stability rather than just temperature or precipitation. [ABSTRACT FROM AUTHOR]

Background and aims: Long-term nitrogen (N) addition can affect soil organic carbon (SOC) pool within different soil fractions with different turnover rates. However, the mechanisms of these effects, particularly in alpine grassland ecosystems, are not clear. Methods: We studied the responses of SOC content in different soil fractions to N addition based on a six-year N addition field experiment in an alpine meadow ecosystem on the Tibetan Plateau. We measured soil chemical and microbial properties, and SOC content in bulk soil, particular organic matter (POM) and mineral-associated organic matter (MAOM) fractions in response to N addition. Results: N addition increased soil N availability, decreased soil pH and microbial biomass, but had minimal effect on plant biomass, soil enzyme activity, and SOC content in bulk soil. With increasing levels of N addition, SOC in the POM fraction (POC) showed a significant negative trend, while SOC in the MAOM fraction (MAOC) did not change significantly. Conclusions: As plant biomass input and soil enzyme activity were not significantly altered with N addition, the decline in POC was likely caused by changes in microbial physiology (carbon use efficiency), while the insignificant change in MAOC may be determined by the balance between input (from microbial necromass) and output (from microbial decomposition). Taken together, our study showed that the less-protected POC fraction is more vulnerable to N addition than the more-protected MAOC fraction in the alpine grassland. This finding may improve the prediction of soil C dynamics in response to N deposition in alpine grassland ecosystems on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

BiVO samples doped with different amounts of La or Zn ions have been synthesized successfully by a hydrothermal method, and their composition, microstructure and photocatalytic activity were characterized by means of modern analytical techniques. The results illustrated that these doped BiVO samples presented a better photocatalytic performance than the undoped BiVO sample, among which BiLaVO and BiZnVO exhibited the highest degradation efficiency. Under visible light illumination, their photocatalytic degradation on RhB was up to 95.4 and 98.56% in 60 min, respectively. In particular, the BiLaVO and BiZnVO had a good stability and still retained the photocatalytic activity of 93.7 and 94% after five cycling test. These results confirmed that the La/Zn -doped BiVO samples were a kind of efficient and stable visible-light-driven photocatalysts and had a promising application for the degradation of organic contaminant. [ABSTRACT FROM AUTHOR]

Uniform core-shell SiO@FeO@C microspheres were prepared by a one-step hydrothermal method with SiO microspheres as the template, and the hollow FeO@C (HFC) microspheres were achieved via etching SiO template. By changing the sizes of SiO microspheres, a series of HFC microspheres with variable cavity sizes were obtained to study the relationship between cavity size and microwave absorbing (MA) performance for the first time. The morphology and structure of samples were characterized in detail. The results showed that the MA performance of HFC sample depended on its cavity size. In particular, the hollow structure was good for improving MA performance and could make MA move to the high-frequency region. More importantly, as the cavity size increases, the resonance frequency of HFC- i ( i=1, 2, 3, 4) samples moved to a low frequency, and the optimal matching thickness of HFC- i samples was increasing. Among all HFC- i samples, HFC-3 showed the most excellent MA performance, which could be mainly explained by the quarter-wavelength matching model, intrinsical magnetic and dielectric loss. Furthermore, the MA performance of HFC mixture blended by the equal mass fraction of HFC-2, HFC-3 and HFC-4 was the comprehensive results of three HFC- i samples. All the above suggested that the cavity size in HFC sample had a great influence on the MA performance. [ABSTRACT FROM AUTHOR]

Hierarchical structured ZnFeO@reduced graphite oxide@TiO (ZnFeO@RGO@TiO) nanocomposite was prepared by an electrostatic layer-by-layer route, which played a synthetic effect of Fenton oxidation of ZnFeO and photocatalytic oxidation of TiO to degrade fulvic acid (FA) solution under visible-light irradiation. In this method, RGO, as the middle layer, can effectively promote the photo-induced electron flow between the ZnFeO and TiO and further improve the efficiency of the photo-Fenton oxidation. The influencing factors on photo-Fenton oxidation, including solution pH, catalyst, and HO dosage, have also been investigated. The results illustrated that the ternary composite presented the enhanced catalytic performance. Under visible light irradiation, the degradation efficiency of the sample on the FA solution can reach 95.4% within 3 h. In addition, the catalyst exhibited superior stability and reusability, and its degradation efficiency was still up to 90% after 5 cycles. Therefore, the composite will be a kind of efficient photocatalyst and had a promising application for visible-light driven destruction of organic pollutants. [ABSTRACT FROM AUTHOR]

ZnTiFeO and ZnTiFeO/Carbon nanotubes (ZTF/CNTs) composites were prepared by chemical co-precipitation method. The composition, microstructure, magnetic property, adsorption and photocatalytic activity of the prepared samples were characterized by means of modern analytical techniques. The results indicated that ZTF/CNTs composites not only held the original special structure and excellent adsorption properties of CNTs, but also had suitable magnetic property and excellent photocatalytic activity. The removal rate of the samples on Rhodamine B (RhB) depended on the adsorption of CNTs and the photocatalytic degradation of ZTF in the composites. The maximum adsorption amount ( q ) of ZTF/CNTs with the mass ratios of ZTF to CNTs ( m )=1 was up to 17.153 mg g for RhB, its adsorption behavior was in accord with Langmuir model, and its photocatalytic degradation activity on RhB had a positive correlation with the content of ZTF in the sample. The experimental results indicate that the total removal rate of composite with m =1 on RhB was more than 95% and the composite had good decontamination capability on industrial dye wastewater. In addition, the samples can be recovered conveniently, activated easily and had good performance for recycling. [ABSTRACT FROM AUTHOR]

AgZnO and AgZO/polyaniline (AZO/PANI) nanocomposites were prepared by citrate sol-gel method and in situ inverse microemulsion method, respectively. The composition, structure and morphology of the samples were characterized by means of modern testing techniques. The antibacterial activities of the as-prepared samples against Staphylococcus aureus, Escherichia coli and Candida albicans were carried out using inhibition zone, minimum inhibitory concentration and minimal bactericidal concentrations methods under the irradiation of sunlight. Results showed that the antibacterial activity of AgZnO was better than that of ZnO, and it was optimum when the mole ratio of Ag was 0.02. The AZO/PANI composites had preferable antibacterial effect than AZO, and shown the strongest antibacterial activity when the mass fraction of AZO was up to 60 %. [ABSTRACT FROM AUTHOR]

Alcohol dehydrogenase (ADH) catalyzes the final step in the biosynthesis of methanol from CO. Here, we report the steady-state kinetics for ADH, using a homogeneous enzyme preparation with formaldehyde as the substrate and nicotinamide adenine dinucleotide (NADH) as the cofactor. When changing NADH concentrations with the fixed concentrations of HCHO (more or less than NADH), kinetic studies revealed a particular zigzag phenomenon for the first time. Increasing formaldehyde concentration can weaken substrate inhibition and improve catalytic efficiency. The kinetic mechanism of ADH was analyzed using the secondary fitting method. The double reciprocal plots (1/ v∼1/[HCHO] and 1/[NADH]) strongly demonstrated that the substrate inhibition by NADH was uncompetitive versus formaldehyde and partial. In the direction of formaldehyde reduction, ADH has an ordered kinetic mechanism with formaldehyde adding to enzyme first and product methanol released last. The second reactant NADH can combine with the enzyme-methanol complex and then methanol dissociates from it at a slower rate than from enzyme-methanol. The reaction velocity depends on the relative rates of the alternative pathways. The addition of NADH also accelerates the releasing of methanol. As a result, substrate inhibition and activation occurred intermittently, and the zigzag double reciprocal plot (1/ v∼1/[NADH]) was obtained. [ABSTRACT FROM AUTHOR]

A Correction to this paper has been published: https://doi.org/10.1038/s41467-021-23418-z [ABSTRACT FROM AUTHOR]