Lignin is the largest carrier of aromatics on earth, and its depolymerization can afford value-added aromatic products. Direct cleavage of the C–C bonds in lignin linkages is significant, but it is ...challenging to obtain low-molecular-weight aromatic monomers. Herein, using vanadium catalysts under visible light, we selectively cleave the C–C bonds in β-1 and β-O-4 interlinkages occluded in lignin models and extracts by an oxidative protocol. Visible light irradiation triggered single electron transfer between the substrate and the catalyst, which further induced the selective Cα–Cβ bond cleavage and generated the final aromatic products through radical intermediates. Using this photocatalytic chemistry, the reactivity of lignin models and the selectivity of Cα–Cβ bond cleavage were significantly improved. More importantly, this protocol affords aromatic monomers through the fragmentation of organosolv lignins even at room temperature, indicating the potential of photocatalytic C–C bond cleavage of lignin linkages under ambient conditions.
As the focus of the research field of curved beam dynamics, the simulation of curved beam dynamic system has become the focus of the research of curved beam dynamics. This paper creatively takes the ...unit value of curved beam in the dynamic system of curved beam as the perturbation value, and solves the problem of mode superposition in the perturbation system. In the experimental verification part, the perturbation simulation results of curved beam element are directly compared with that of straight beam element. The experimental results show that the curved beam element model proposed has good convergence and effectiveness.
Photocatalysis is one potential solution to the energy and environmental crisis and greatly relies on the development of the catalysts. Niobium pentoxide (Nb2O5), a typically nontoxic metal oxide, is ...eco‐friendly and exhibits strong oxidation ability, and has attracted considerable attention from researchers. Furthermore, unique Lewis acid sites (LASs) and Brønsted acid sites (BASs) are observed on Nb2O5 prepared by different methods. Herein, the recent advances in the synthesis and application of Nb2O5‐based photocatalysts, including the pure Nb2O5, doped Nb2O5, metal species supported on Nb2O5, and other composited Nb2O5 catalysts, are summarized. An overview is provided for the role of size and crystalline phase, unsaturated Nb sites and oxygen vacancies, LASs and BASs, dopants and surface metal species, and heterojunction structure on the Nb2O5‐based catalysts in photocatalysis. Finally, the challenges are also presented, which are possibly overcome by integrating the synthetic methodology, developing novel photoelectric characterization techniques, and a profound understanding of the local structure of Nb2O5.
Niobium pentoxide (Nb2O5), a typically nontoxic metal oxide, exhibits unique redox ability and acidity. Recently, the applications of Nb2O5‐based photocatalysts are reported in the photodegradation of plastics, reduction of CO2, photocatalytic hydrogen evolution, and organic synthesis. Herein, an overview is provided for the synthesis, application of Nb2O5‐based photocatalysts, and corresponding structure–activity relationship.
Combined chemo/chemodynamic therapy is a promising strategy to achieve an improved anticancer effect. However, the hypoxic microenvironment and limited amount of H2O2 in most solid tumors severely ...restrict the efficacy of this treatment. Herein, the construction of a nanocatalytic medicine, CaO2@DOX@ZIF‐67, via a bottom‐up approach is described. CaO2@DOX@ZIF‐67 simultaneously supplies O2 and H2O2 to achieve improved chemo/chemodynamic therapy. In the weakly acidic environment within tumors, CaO2@DOX@ZIF‐67 is broken down to rapidly release the Fenton‐like catalyst Co2+ and the chemotherapy drug doxorubicin (DOX). The unprotected CaO2 reacts with H2O to generate both O2 and H2O2. The generated O2 relieves the hypoxia in the tumor and further improve the efficacy of DOX. Meanwhile, the generated H2O2 reacts with Co2+ ions to produce highly toxic •OH through a Fenton‐like reaction, resulting in improved chemodynamic therapy.
The hypoxic microenvironment and limited amount of H2O2 in most solid tumors severely restrict the efficacy of chemotherapy and chemodynamic therapy, respectively. Herein, a nanocatalytic medicine, CaO2@DOX@ZIF‐67, is synthesized via a bottom‐up approach. By virtue of simultaneously producing O2 and H2O2 under acidic conditions, the fabricated nanocatalytic medicine can eliminate hypoxic tumors via enhanced chemo/chemodynamic therapy.
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•The aged hydrocarbon contaminated site investigation is done using geochemical and geophysical methods.•The low resistivity anomalies in ERT are related to by-products of hydrocarbon ...degradation.•The ERT and Waxman and Smits models are used to obtain the by-product plume distribution range.•Quantify the amount of hydrocarbon degradation corresponding to the by-product plume.
During the investigation of aged hydrocarbon contaminated sites using electrical resistivity tomography (ERT), the low-resistivity anomalies in the detection profile have been widely considered to be caused by the hydrocarbon degradation by-products. However, these low-resistivity anomalies are a comprehensive reflection of the formation’s electrical characteristics. In this study, we used ERT and geochemical methods to investigate a hydrocarbon-contaminated site that has been abandoned for more than 30 years. There are several obvious low resistivity anomalies in the site, which are related to hydrocarbon mineralization. Based on the law of Waxman and Smits, a petrophysical relationship formula suitable for this specific site was fitted, and the true resistivity after inversion was input into the formula to calculate the pore water resistivity. The electrolytic conduction contribution of the pore water was isolated, and the distribution of the by-product plume was determined based on the electrolytic conduction contribution of the pore water. Based on mineralogical identification and geochemical data analysis, the biogeochemical model of hydrocarbon mineralization was clarified. The degradation by-products (Fe2+ and H+) are the controlling factors that lead to changes in the groundwater resistivity. Based on electrochemical experiments and titration analysis experiments, the quantitative relationship between the low resistivity anomalies of the pore water and the degradation by-products (Fe2+ and H+) was established, and the biodegradation model was used to calculate the hydrocarbon degradation corresponding to the by-product plume. The results show that the hydrocarbon degradation corresponding to the by-product plume determined from the ERT detection results in the selected study area is approximately 2.8% of the total hydrocarbon content. Although this is a rough estimate based on a small amount of discrete geochemical data and ERT detection results, it improves our understanding of the natural attenuation state of hydrocarbon-contaminated sites and provides convincing data to support future estimations of the site's natural attenuation time.
Understanding Holocene paleoclimate in arid Central Asia (ACA) is helpful for predicting future climate. However, Holocene climate patterns and their forcing mechanisms across ACA are vigorously ...debated in the context of global climate change. Here, we present a Holocene loess profile (SGX) from the Ili Basin in the Westerlies-dominated Central Asia. Based on high-resolution, medium-grained (38–63 μm) quartz optically stimulated luminescence (OSL) dating, and grain size and color measurements, we reconstruct the Holocene paleoclimate. OSL geochronology indicate that this SGX loess profile covers the last 11.5 ka, and grain size analyses reveal that the sediments are sandy loess, and the environmentally sensitive fractions are <35.6 μm and 35.6–252 μm, which represent suspensions after dust storms and proximal deposit components transported mainly during dust storms, respectively. And the redness and yellowness in the loess profile are closely related to the concentrations of hematite (Hm) and goethite (Gt); the ratio Hm/Gt also can be used to reflect the evolution of dry/humid conditions in Central Asian loess. The Holocene Westerlies-dominated climate in ACA is characterized by a dry early Holocene, persistently wet conditions in the middle and late Holocene, and a climatic optimum in the late Holocene. The winter solar insolation at 60°N is considered the major forcing of Holocene climate evolution in ACA.
•The color index can reflect the evolution of humidity.•A persistent Holocene wetting trend in arid Central Asia•Winter solar insolation is the driving factor of Holocene climate evolution.
•The total economic value of grasslands in China was 10,876 yuan/ha/yr.•Grassland soil fertility and erosion control were the most valuable services.•The grassland value was affected by the valuation ...methods.•Our findings are helpful for better accounting for grassland ecosystem services.
Grasslands provide a variety of ecosystem services (ESs) that contribute to human beings. However, most grassland ESs are public goods with no market value and consequently ignored in private land use decisions. Thus, it is important for grassland conservation to consider the potential economic value of grassland ESs in policymaking. We tried to provide a comprehensive evaluation of the economic value of grassland ESs and the influential factors via a meta-regression analysis with 745 observations from 69 studies. The results showed that the total economic value of grasslands in China was 10,876 yuan/ha in constant year 2015, and also revealed large variations in the reported economic values of grassland ESs. Soil fertility (1,899 yuan/ha/yr) and erosion control (1,492 yuan/ha/yr) were the two most valuable services. Further, factors such as valuation methods, research characteristics and study site characteristics all affected the estimates of grassland values. The market price method was most likely to provide higher grassland ES values among all the methods. Lastly, the economic value of grassland ESs showed geographical differences, with eastern China higher than western China. These findings contributed to the literature evaluating the economic value of grassland ESs regarding discrepancies in economic values, thus helping to inform grassland management. Further, these findings are helpful for better accounting for the services provided by grassland ecosystems, which can significantly facilitate land use decision making for sustainable ecosystem management.
Soil provides various indispensable ecosystem services for human society. Soil's complex structure and property makes the soil ecological processes complicated and brings about tough challenges for ...soil ecosystem services study. Most of the current frameworks on soil services focus exclusively on services per se, neglecting the links and underlying ecological mechanisms. This article put forward a framework on soil services by stressing the underlying soil mechanisms and processes, which includes: 1) analyzing soil natural capital stock based on soil structure and property, 2) disentangling the underlying complex links and soil processes, 3) soil services valuation based on field investigation and spatial explicit models, and 4) enacting soil management strategy based on soil services and their driving factors. By application of this framework, we assessed the soil services of sediment retention, water yield, and grain production in the Upper-reach Fenhe Watershed. Based on the ecosystem services and human driving factors, the whole watershed was clustered into five groups: 1) municipal area, 2) typical coal mining area, 3) traditional farming area, 4) unsustainable urbanizing area, and 5) ecological conservation area. Management strategies on soils were made according to the clustering based soil services and human activities.
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•Soil provides multiple ecosystem services supporting human subsistence.•A process based framework for soil services was established with due attention to soil structure and property.•The framework is conducive to soil services mechanisms exploration and prudent soil management.
Depolymerization of lignin meets the difficulty in cleaving the robust aryl ether bond. Herein, through installing an internal nucleophile in the β-O-4′ linkage, the selective cleavage of aryl ether ...was realized by the intramolecular substitution on aryl rings affording non-phenolic arylamine products. In particular, nitrogen-modified lignin models and lignin samples were employed to generate the iminyl radical under photocatalytic reduction, which acted as the internal nucleophile inducing aryl migration from O to the N atom. The following hydrolysis released primary arylamines and α-hydroxy ketones. Mechanism studies including electron spin resonance (ESR), fluorescence quenching experiments, and density functional theory (DFT) calculations proved the aryl migration pathway. This method enables access to non-phenolic arylamine products from lignin conversion.
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•Cu(NO3)2 could catalyze the oxidative CC cleavage of ketones to acids.•A wide range of ketones have good to excellent yields.•In situ NMR and EPR gave possible intermediates and ...mechanism.•Electrochemical study of copper salts in various solvents has been conducted.
Catalytic oxidation of CC bond is a key technology to transform petroleum-based as well as sustainable biomass feedstock into more valuable oxygenates. We herein describe a convenient and useful oxidation strategy of converting ketones into carboxylic acids using homogeneous copper catalyst without additives and with O2 as the terminal oxidant. A wide range of aryl and aliphatic ketones as well as β–O–4 lignin models were selectively oxidized to acids via CC bond cleavage. Mechanism studies by EPR and in situ NMR elucidate the principles of Cu/O2 reactivity that involves CH bond and O2 activation via a peroxide species. This provides an important foundation for expanding the scope of useful aerobic oxidation reactions using copper catalysts.
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