Ligation of Titanium-oxide and {Mo2} Units for Solar CO2 Storage.

Two Mo-Ti-mixed oxide clusters, Ti6Mo4 and Ti4Mo4, which contain the {Mo2V} unit commonly observed in many polyoxomolybdates, were successfully synthesized. The introduction of a {Mo2V} dopant into a titanium-oxide cluster (TOC) results in a red shift of the absorption edge, hence leading to a substantial enhancement of visible-light absorption. The band gap electron transition mainly involves the ligand-to-metal charge transfer (LMCT, benzoate-to-Mo) and MoV d-d transition. Both clusters show favorable visible-light responsiveness and charge-separation efficiency. Both serve as heterogeneous photocatalysts and exhibit excellent catalytic activity in CO2/epoxide cycloadditions under very mild conditions. The mechanism study suggests that the catalytically active sites are mainly MoV, and the photogenerated electrons and holes are both involved. Ti6Mo4 exhibits better photocatalytic activity than Ti4Mo4, demonstrating the crucial role of the titanium-oxide core, which corresponds to improved light absorption and charge-separation efficiency. Our findings highlight the potential of the {Mo2V} unit in constructing Mo-Ti-mixed oxide clusters with interesting topologies and excellent solar-light-harvesting activity.

Divalent Heterometal Doped Titanium-Oxide Cluster Polymers: Structures, Photoresponse, and Photocatalysis.

Five cluster polymers based on heterometal-doped titanium-oxide cluster (TOC) monomers are reported. The monomers feature Ti10-oxide cluster cores and are connected to the divalent closed-shell heterometal anchors by salicylate ligands. The Sr2+, Ba2+, and Pb2+ dopants cause the monomers to bind head-to-head and generate linear chains, while the Ca2+ and Cd2+ lead to head-to-tail connections and zigzag chains. The cluster polymers are responsive to visible-light up to 565 nm and photo-catalytically active in both H2 evolution and CO2/epoxide cycloaddition reactions. The photo-absorption, photo-charge separation, and photocatalytic properties of the cluster polymers are dependent on the heterometal dopants in order Cd > Pb > Ba > Sr > Ca. Heterometals serve as the catalytic sites in the cluster polymers, which depending on the contribution of the pCB bottom, facilitate photo-charge separation and interfacial charge transfer, further enhancing catalytic activity. The tunable compositions and topologies of the cluster polymers shown herein may inspire the design and synthesis of more multidimensional functional metal-oxide cluster materials for a variety of applications in the future.

Lead-Decorated Titanium Oxide Compound with a High Performance in Catalytic CO2 Insertion to Epoxides.

The CO2 cycloaddition to epoxides is an efficient method for CO2 capture and storage, important not only for reducing greenhouse gas emission but also for producing cyclic carbonates, which are valuable industrial materials. In this study, we report a novel high-nuclearity titanium oxide cluster (TOC) inlayed with main-group element Pb2+, H2Ti16Pb9O24(SA)18(DMF)10(OH2)2 (denoted as 1; SA = salicylate; DMF = N,N-dimethylformamide), which has the property of visible-light absorption and has shown high catalytic activities for cycloadditions of CO2 under visible-light irradiation. The cluster was synthesized in a high yield in a facial solvothermal process. Its structure and electronic structure were characterized by single-crystal X-ray diffraction, density functional theory calculations, and complementary techniques. The cycloaddition reactions were performed under solvent-free conditions. While the catalytic activity due to the Lewis acidity was moderate, visible-light irradiation further folded the reaction rates. The turnover number reached 3400 with a turnover frequency of 120 h-1. Mechanism studies indicated a synergistic effect of the Lewis acidity and photogenerated charge carriers. The performance of 1 in reversible I2 uptake was also investigated. This study demonstrates the high potential of heterometal-decorated TOCs in the cost-effective and efficient CO2 cycloaddition reaction under mild conditions.

A Mesoporous Lead-Doped Titanium Oxide Compound with High Performance and Recyclability in I2 Uptake and Photocatalysis.

A three-dimensional (3D) mesoporous material with an atomically precise structure, Ti16Pb5O16(C6H5CO2)2(OCH3)40 (Ti16Pb5), comprised of a novel high-nuclearity Pb-doped titanium oxide cluster (TOC), was synthesized. Ti16Pb5 exhibited a surface area of 45 m2 g-1 and a pore diameter of 3.5 nm. It exhibited an uptake capacity of I2 of ≤2.2 g g-1 in vapor, and the performance was maintained after seven uptake-release cycles. Ti16Pb5 also showed a high adsorption ratio and capacity (93% and 3.1 g g-1) in hexane. The characterization data, including Fourier transform infrared, Raman, and powder X-ray diffraction, suggested the lattice structure of Ti16Pb5 was rigid and I2 was accommodated in the pores of Ti16Pb5. To the best of our knowledge, this is the first example of using a TOC in I2 adsorption. In addition, Ti16Pb5 showed excellent activity and recyclability in visible-light degradation of dye pollutants and photocurrent generation. Our structural analysis suggested the alkoxide ligands within the channels of Ti16Pb5 build up a confined polar environment and thereby facilitate I2 accommodation, and meanwhile, the improved performances and stabilities of Ti16Pb5 are correlated with its cluster-based, 3D hierarchical structure.

Cr-Ti Mixed Oxide Molecular Cages: Synthesis, Structure, Photoresponse, and Photocatalytic Properties.

The solvothermal reaction of titanium isopropoxide and chromate in the presence of benzoate produced two novel host-guest clusters encapsulating Cs+ or H3O+, (H3O)@Ti7Cr14 and Cs@Ti7Cr14. The most remarkable feature is that the Ti7O7 ring is concentrically embraced by a Cr14O14 ring to form a rigid Ti7Cr14 host. ESI-MS and 133Cs NMR revealed that the overall framework structures are preserved, whereas the benzoate ligands on the two clusters may be labile in solutions. Both (H3O)@Ti7Cr14 and Cs@Ti7Cr14 exhibit good UV-vis light-responsive properties and photocatalytic activities, with absorption edges extending up to 780 nm. Cs@Ti7Cr14 is an effective visible-light-responsive photocatalyst in both the heterogeneous methylene dye degradation and homogeneous CO2 cycloaddition reaction under mild conditions like room temperature and 1 bar of CO2. According to the mechanism studies, Cs+, as a rigid guest, can significantly improve the photogenerated charge separation efficiency of the Ti7Cr14 host, thereby improving its interface charge separation properties, photocurrent, and photocatalytic activities. Our findings not only provide new members of heterometallic titanium oxide clusters to enrich the metal oxide cluster family but also open up new possibilities for their photoresponses, which may play an important role in solar energy harvesting for sustainable chemistry.

A cryptand-like Ti-coordination compound with visible-light photocatalytic activity in CO2 storage.

A cryptand-like Ti-coordination compound, namely Ti12Cs, comprising two Ti6-salicylate cages and hosting two Cs+ ions, was synthesized by the solvothermal method. It exhibits strong visible-light absorption with an absorption band edge of 652 nm, attributed to the electron transition from salicylate ligands to Ti ions. Electrochemical impedance, visible-light transient photocurrent response, and photoluminescence spectra confirm that Ti12Cs has excellent visible-light response and charge-separation properties. Ti12Cs can be used as a heterogeneous and recyclable photocatalyst for CO2/epoxide cycloaddition, with high utilization efficiency of visible-light under mild conditions. The mechanism investigation points to a synergistic effect of photocatalysis and Lewis acid catalysis.

Enhancing the photocatalytic performance of a rutile unit featuring a titanium-oxide cluster by Pb2+ doping.

Titanium-oxide clusters (TOCs) are well-defined molecular models for TiO2 materials and provide the opportunity to study the structure-activity relationships of TiO2. Here, we report a new Pb-doped TOC, Ti12Pb2, which resembles a two-layer decker of the {TiTi6} structural units of rutile TiO2 with two Ti4+ ions replaced by two Pb2+ ions. Its electronic structure, photoresponse, and photocatalytic performances were investigated and compared with those of the Ti14 cluster, which is isostructural to Ti12Pb2. Our results indicate that Pb2+ does not affect the electronic structure, but it greatly enhances the photocatalytic activity by improving the charge-separation and interfacial charge-transfer properties of the TOC. The successful synthesis of Ti12Pb2 highlights the roles of closed-shell heterometal ions in the construction of new TOCs. Our mechanism may be an inspiration for understanding the structure-activity relationships of closed-shell heterometal-doped TiO2.

Shrub encroachment alters plant trait response to nitrogen addition in a semi-arid grassland.

Encroachment of shrubs over large regions of arid and semi-arid grassland can affect grassland traits and growth under a background of increasing nitrogen (N) deposition. However, the effects of N input rates on species traits and the growth of shrubs on grasslands remain unclear. We examined the effects of six different N addition rates on the traits of Leymus chinensis in an Inner Mongolia grassland encroached by the leguminous shrub, Caragana microphylla. We randomly selected 20 healthy L. chinensis tillers within shrubs and 20 tillers between shrubs in each plot, measuring the plant height, number of leaves, leaf area, leaf N concentration per unit mass (LNCmass), and aboveground biomass. Our results showed that N addition significantly enhanced the LNCmass of L. chinensis. The aboveground biomass, heights, LNCmass, leaf area, and leaf number of plants within the shrubs were higher than those between shrubs. For L. chinensis growing between shrubs, the LNCmass and leaf area increased with N addition rates, leaf number and plant height had binomial linear relationships to N addition rates. However, the number of leaves, leaf areas and heights of plants within shrubs did not vary under various N addition rates. Structural Equation Modelling revealed N addition had an indirect effect on the leaf dry mass through the accumulation of LNCmass. These results indicate that the response of dominant species to N addition could be regulated by shrub encroachment and provide new insights into management of shrub encroached grassland in the context of N deposition.

A butterfly-like lead-doped titanium-oxide compound with high performance in photocatalytic cycloaddition of CO2 to epoxide.

The cycloaddition reaction of CO2 to epoxides is quite promising for CO2 capture and storage as well as the production of value-added fine chemicals. Herein, a novel atomically precise lead-doped titanium-oxide cluster with the formula Ti10Pb2O16(phen)4(Ac)12(DMF)2 (denoted as Ti10Pb2; phen = 1,10-phenanthroline; Ac = acetate; DMF = dimethylformamide) was synthesized through a facile solvothermal process, and is a molecular photocatalyst with surface-anchored main-group metal active sites. Its structure was characterized by single-crystal X-ray diffraction and other complementary techniques. Ti10Pb2 showed high photo-response and charge-separation efficiency under simulated sunlight irradiation. Ti10Pb2 was successfully used in the cycloaddition reaction of CO2 with epoxides under solvent-free conditions. While its catalytic activity due to the Lewis acidity was moderate, simulated solar light irradiation further enhanced the reaction rate, demonstrating the synergistic effect of photocatalysis and Lewis-acid thermocatalysis.

Tree characteristics and drought severity modulate the growth resilience of natural Mongolian pine to extreme drought episodes.

Global climate change and the increase in the frequency and intensity of drought have led to widespread forest decline and tree mortality. Studying the resilience components of tree growth to drought, including resistance (Rt), recovery (Rc), and resilience (Rs) and the influencing factors, helps assess forests' production and ecological stability under a changing climate. This study analyzed the responses of three resilience components of natural Mongolian pine (Pinus sylvestris var. mongolica) to drought events by examining individual-tree characteristics in two sites of Hulunbuir using the linear mixed effect model. The result showed that drought severity, diameter at breast height (dbh), pre-drought growth, and growth variability prior to drought had significant effects on the three resilience components of Mongolian pine growth. Specifically, as drought severity, dbh and growth variability increased, the Rt and Rs decreased, but Rc increased, showing a trade-off relationship with Rt. However, the Rt, Rc, and Rs decreased with pre-drought growth. Inter-tree competition and tree age also significantly impacted two resilience components. Besides, the interaction term between tree competition and tree age negatively affects Rt and Rs but positively affects Rc. Our findings highlight the influence of drought severity and individual-tree characteristics on drought resilience components, which can serve the adaptive management of natural Mongolian pine forests in the future.

New picolinate-functionalized titanium-oxide clusters: syntheses, structures and photocatalytic H2 evolution.

Two nanosized titanium-oxide clusters (TOCs), Ti12(µ2-O)14(µ3-O)4PA16 (1; PA = 2-picolinate) and Ti12(µ2-O)18PA18 (2) were synthesized by using 2-picolinic acid and Ti(OiPr)4 in one-pot reactions. Their structures were determined using single-crystal X-ray diffractometry. Although both have the same core composition of Ti12O18, 1 exhibited superior H2 evolution activity of up to 180 µmol h-1 g-1, which is nearly eight times faster than 2. Mechanism studies revealed that 1 could induce the assembly of 2.3 nm PtNPs into 10-30 nm supra-nanoparticle structures, which contributed to the increased H2 evolution rate.

Grazing Altered the Pattern of Woody Plants and Shrub Encroachment in a Temperate Savanna Ecosystem.

Ulmus pumila-dominated temperate savanna is an important tree-grass complex ecosystem in the Otindag sand land, northern China. To date, few investigations have been undertaken on the spatial patterns and structure of this ecosystem and its driving factors under different grazing pressures. The objective of our study therefore is to explore whether grazing has affected the population structure/pattern of woody plants and shrub encroachment in a temperate savanna ecosystem. Results indicate that species richness and seedlings decreased with increasing grazing pressure. An increase in grazing pressure did not significantly affect adult-tree density, but it hindered the normal regeneration of U. pumila seedlings, further inducing population decline. U. pumila seedlings had a more significant aggregated distribution than juvenile or adult trees. The adult and juvenile trees had an aggregated distribution at the small scale and a random distribution at the large scale. Shrubs also showed a significant aggregated distribution. No clear effect on the spatial patterns of adult trees was observed; however, there was a noticeable effect for juveniles and seedlings under different grazing pressures. U. pumila seedlings had a positive association with their juveniles and Spiraea aquilegifolia, but a negative association with Caragana microphylla. Shrub encroachment occurred with decreasing grazing pressures. In conclusion, overgrazing led to the decline of U. pumila population, but the decrease in grazing pressure increased shrub encroachment in the temperate savanna ecosystem. Moderate grazing management may be a better way to enhance the stability of U. pumila population and reduce shrub encroachment.

Heavy grazing reduces grassland soil greenhouse gas fluxes: A global meta-analysis.

Grazing degrades worldwide grasslands and possibly suppresses soil greenhouse gas (GHG: CO2, CH4 and N2O) fluxes. However, the global patterns of these three gas fluxes in response to grazing and the general mechanisms remain poorly understood. Here, we performed a meta-analysis of 63 independent grazing studies that measured soil GHG fluxes across global grasslands. Our results revealed that light and moderate grazing had no significant effect on soil CH4 uptake, N2O and CO2 emission, but heavy grazing consistently reduced them. The magnitudes of their responses to grazing were regulated by grazing duration and precipitation. In comparison with CO2 emission, soil CH4 uptake and N2O emission were reduced much more under heavier grazing, longer grazing duration or less precipitation. The decrease in soil CO2 emission was possibly caused by grazing-induced reduction in root biomass and soil moisture, while the decline in soil CH4 uptake and N2O emission was due to decreased soil moisture and substrate availability. Overall, this study provides the first large-scale evaluation on three main soil GHG fluxes in response to grazing, highlighting grazing inhibition of GHG emission but at the cost of plant productivity and soil fertility. We call for future efforts to identify an appropriate grazing intensity that is optimal to balance these complicated impacts.

Study on super-long deep-hole drilling of titanium alloy.

INTRODUCTION: In this study, the super-long deep-hole drilling of a titanium alloy was investigated. METHODS: According to material properties of the titanium alloy, an experimental approach was designed to study three issues discovered during the drilling process: the hole-axis deflection, chip morphology, and tool wear. RESULTS: Based on the results of drilling experiments, crucial parameters for the super-long deep-hole drilling of titanium alloys were obtained, and the influences of these parameters on quality of the alloy's machining were also evaluated. CONCLUSIONS: Our results suggest that the developed drilling process is an effective method to overcome the challenge of super-long deep-hole drilling on difficult-to-cut materials.

Resource Reallocation of Two Grass Species During Regrowth After Defoliation.

Defoliation is widely used for grassland management. Our understanding of how grass species adjust their regrowth and regain balance after defoliation remains limited. In the present study, we examined the regrowth processes of two dominant species after defoliation in grasslands in Inner Mongolia. Our results showed that the aboveground biomass and total biomass of both species significantly decreased and did not completely recover to the control level after 30 days of regrowth. The leaf mass ratio of Leymus chinensis reached the control level at 15 days, but that of Stipa grandis did not recover to the control level. The root mass ratio of these species reached the same levels as that of the control plants within 10 days after defoliation. As indicated by the dynamics of water-soluble carbohydrates (WSCs), protein, and biomass-based shoot: root ratios, both species regained balances of WSCs and protein between above- and below-ground organs at day 10 after defoliation; however, the biomass regained balance 15 days after defoliation. We deduced that the biomass-based shoot:root ratio was regulated by the WSCs and protein concentrations. In conclusion, following defoliation, both grass species first restore their nutrient-based balance between above- and below-ground parts and then regain biomass balance.

Coronavirus phylogeny based on triplets of nucleic acids bases.

We considered the fully overlapping triplets of nucleotide bases and proposed a 2D graphical representation of protein sequences consisting of 20 amino acids and a stop code. Based on this 2D graphical representation, we outlined a new approach to analyze the phylogenetic relationships of coronaviruses by constructing a covariance matrix. The evolutionary distances are obtained through measuring the differences among the two-dimensional curves.

Prognostic value of CA4/DG volumetry with 3T magnetic resonance imaging on postoperative outcome of epilepsy patients with dentate gyrus pathology.

PURPOSE: Hippocampal sclerosis (HS), the most common feature of mesial temporal lobe epilepsy (MTLE), is widely accepted as surgical indication for refractory epilepsy. Pathological hallmarks in hippocampal dentate gyrus (DG), including granule cell loss (GCL) and granule cell dispersion (GCD), are known to be closely related to the status epilepticus and spontaneous seizure. Our aim was to assess the association between volumetric changes in the hippocampal CA4/DG determined with 3-Tesla (3T) magnetic resonance imaging (MRI) and the postoperative seizure outcomes in MTLE patients with or without dentate gyrus pathology (DGP). METHODS: High-resolution T2- and T1-weighted three-dimensional (3D) MRI scans were performed on 39 MTLE patients before surgery with a 3T Philips scanner. ITK-SNAP software was used for segmentation and volumetry of the CA4/DG segment, and NASP software was used for 3D reconstructions of the CA4/DG region. Immunostaining for Neuronal Nuclei (NeuN) was performed on resected hippocampal specimens after surgery to verify the accuracy of CA4/DG segmentation and histopathological changes in DG. RESULTS: The CA4/DG subfield could be precisely segmented with high-resolution 3T MRI and confirmed by comparison of NeuN-immunoreactive slices with MRI results. MTLE patients with DGP showed smaller CA4/DG volume and favorable postoperative seizure outcomes. CONCLUSION: The volumetry of CA4/DG was associated with the pathological changes in DG in MTLE patients. The volumetry of CA4/DG with preoperative 3T MRI could predict the postoperative seizure outcomes in those patients.