[Synthesis of porous organic framework materials based on deep eutectic solvents and their application in solid-phase extraction].

This paper reviews the application of deep eutectic solvents (DESs) in the synthesis of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) as well as their prospects in the field of solid-phase extraction (SPE). Porous organic frameworks (POFs) have unique properties such as a large specific surface area, high porosity, and easy modification. Thus, these materials are widely applied in the fields of catalysis, adsorption, drug delivery, gas storage, and separation. POFs include MOFs, COFs, conjugated microporous polymers (CMPs), porous aromatic frameworks (PAFs), and covalent triazine frameworks (CTFs). MOFs are constructed from metal ions/clusters and organic ligands through coordination bonds and can be extended in two or three dimensions by repeated coordination with potential voids. COFs are formed from two monomers containing light elements (such as carbon, hydrogen, oxygen, nitrogen, boron, and other elements) via coordination bonds and have large two- or three-dimensional structures. However, conventional POF synthesis methods generally suffer from disadvantages such as long synthesis times, high temperature and pressure requirements, and the use of toxic and hazardous reaction solvents. DES consists of a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) bound by hydrogen-bonding interactions. It is a promising green solvent for material synthesis owing to its low vapor pressure, high stability, and ease of preparation. DES can be used to prepare MOFs and COFs and, in specific cases, acts as a structure-directing agent, which has an important impact on the structure and properties of the resulting frameworks. Using appropriate DES formulations, researchers can modulate the crystal structures, pore sizes, and surface properties of MOFs and COFs, resulting in materials with excellent characteristics. SPE is an analytical technique in which a sample solution is added to an SPE column; the sample solution is forced through the stationary phase, and the target compounds are collected for analysis by elution with an organic solvent. Therefore, suitable stationary-phase materials are critical for SPE. Owing to their large specific surface areas and abundant active sites, MOFs and COFs exhibit outstanding adsorption capacity and selectivity in SPE and can effectively enrich target analytes from complex samples. DES-based MOFs and COFs have shown potential use in a wide range of applications, such as in environmental analysis, food testing, and biological sample analysis. Although DES-based MOFs and COFs for SPE are still in the early stages of development, their properties such as efficient enrichment and high selectivity offer good prospects for practical applications. Future research should continue to explore DES-based synthesis methods in depth to prepare other MOFs and COFs with the desired properties and investigate their potential applications in various fields. These efforts are expected to apply these novel materials in commercialized solid-phase extraction methods, bringing new development opportunities in the field of analytical chemistry.

[N2O Emissions from a Tea Field with Deep Application of Nitrogen Fertilizer and Intercropping with White Clover].

In recent years, the area of tea fields in China has expanded. The application rate of nitrogen fertilizer is usually high in tea fields, which causes high N2O emissions. Tea fields are important sources of N2O emissions; thus, it is necessary to research N2O emission reduction in tea fields. A three-year field study was conducted to investigate soil N2O emissions and influencing factors under different fertilization measurements in a typical tea field in a subtropical hilly region of China. Three treatments-conventional fertilization, deep application of nitrogen fertilizer, and intercropping with clover-were studied to measure the soil N2O fluxes and the related soil and environmental properties. The results showed that the subtropical hilly tea field had high N2O emissions, and the cumulative annual emissions of N2O-N were as high as 5.1-10.1 kg·hm-2. The N2O emissions occurred mainly in spring and summer. When the soil temperature was lower than 15℃, the N2O flux shown mainly a positive correlation with the soil temperature. However, when the soil temperature was higher than 15℃, the positive correlation was mainly with the soil water, soil NH4+-N, and NO3--N contents. Compared with conventional fertilization, the intercropping of white clover did not significantly reduce N2O emissions, although deep application of fertilizer increased annual N2O emissions when the rainfall was high. Neither intercropping of white clover or deep application of fertilizer affected the tea yield or the yield-scaled N2O emissions compared with conventional fertilization. Our study indicates that both intercropping of white clover and deep application of fertilization without reducing the nitrogen application rate did not reduce the soil N2O emissions in subtropical tea fields. Further studies are needed to determine the effects of deep fertilization application combined with a reduction in the nitrogen application rate on N2O emissions from tea fields.