A bimetallic (Ni/Co) metal-organic framework with excellent oxidase-like activity for colorimetric sensing of ascorbic acid.

A novel nanozyme of bimetallic (Ni/Co) metal-organic framework (Ni/Co-MOF) was synthesized using a simultaneous precipitation and acid etching method with a zeolitic imidazolate framework ZIF-67 as the template. The as-synthesized Ni/Co-MOF catalyst presented a three-dimensional hollow nanocage structure and exhibited excellent intrinsic oxidase-like activity. It was demonstrated that Ni/Co-MOF could directly catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue product (oxidized TMB, oxTMB) in the absence of H2O2. The mechanisms and kinetics of this nanozyme activity were investigated, and it was determined that the catalytic activity of Ni/Co-MOF was closely related to temperature and solution pH. Owing to its strong reducibility, ascorbic acid (AA) could reduce oxTMB, and the blue color of the reaction mixture faded over time. Therefore, a novel colorimetric platform was constructed to detect AA based on the oxidase-like activity of Ni/Co-MOF. Under optimal conditions, the absorbance of ox-TMB at 652 nm decreased linearly over the 0.015-50 µM AA range with a detection limit of 0.004 µM.

[Organic carbon and carbon mineralization characteristics in nature forestry soil].

Through field investigation and indoor analysis, the organic carbon content and organic carbon mineralization characteristics of six kinds of natural forest soil were studied, including the pine forests, evergreen broad-leaved forest, deciduous broad-leaved forest, mixed needle leaf and Korean pine and Chinese pine forest. The results showed that the organic carbon content in the forest soil showed trends of gradual decrease with the increase of soil depth; Double exponential equation fitted well with the organic carbon mineralization process in natural forest soil, accurately reflecting the mineralization reaction characteristics of the natural forest soil. Natural forest soil in each layer had the same mineralization reaction trend, but different intensity. Among them, the reaction intensity in the 0-10 cm soil of the Korean pine forest was the highest, and the intensities of mineralization reaction in its lower layers were also significantly higher than those in the same layers of other natural forest soil; comparison of soil mineralization characteristics of the deciduous broad-leaved forest and coniferous and broad-leaved mixed forest found that the differences of litter species had a relatively strong impact on the active organic carbon content in soil, leading to different characteristics of mineralization reaction.