Recently, the Quality and Safety Research Group of the Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences (CAAS) has made important progress in the structure-activity grey correlation analysis of defective ZIF nanoframeworks, quantum theoretical calculations and their application of the capture and removal of fruit and vegetable nanoplastics. The recognition and interaction mechanism between ZIF nanoframeworks and nanoplastics was analyzed by density functional theory calculations, and was successfully applied to the capture and removal of nanoplastics in fruit and vegetable juice. The relevant research results are entitled in Nano Today (IF=13.2, Q1).

With the continuous use of plastic products, microplastics (MPs) and nanoplastics (NPs) are widely detected in the atmosphere, water and soil. The micro-nano plastics produced by the degradation of plastic film will migrate and transport during the growth and development of fruits and vegetables, and gradually accumulate in different parts of the plant. Due to their small size, high stability, refractory degradation, and enrichment and transformation in ecosystems and food, micro-nano plastics pose a great threat to the ecological environment and the quality safety of agricultural products. The detection, prevention and control of micro-nano plastics have become a hot area of scientific and public concern.

Fig.1 Flow chart of the preparation of ZIF-derived nanoframeworks.

MOFs based porous materials have significant advantages in the adsorption and trapping of MPs, such as large specific surface area, high porosity, excellent chemical stability and significant functional group tunability. However, MOFs exist some problems such as deep burial of active sites, slow mass transfer, and low efficiency in the adsorption and removal of MPs. Through defect engineering, the microstructure, chemical composition, and unsaturated coordination of MOFs can be precisely controlled, to fully expose the active sites in the framework, reduce the diffusion resistance of pollutants, improve the selection and identification characteristics, thus increasing the adsorption capacity and mass transfer rate. It is of great theoretical and practical significance to analyze the structure-activity relationship between the structural evolution of defective MOFs and the change of recognition performance, reveal the basic reaction theory of defective MOFs to identify and control micro-nano plastic pollutants, construct a new micro-nano plastic control removal technology.

Fig.2 Schematic diagram of the modified pore size structure of Zn-Co-Ni-ZIF and Zn-Co-TA-ZIF nanoframeworks with different molecular sizes.

Based on the above design, a series of defective ZIF nanoframework materials with different morphologies and structural characteristics (Zn-Co-Ni-ZIF, Zn-Co-TA-ZIF and ZIF67-Ni-ZIF) were prepared by defect engineering (chemical etching after synthesis). The correlation between the structural characteristics of defective ZIF nanoframework and the adsorption performance of PS-NPs was studied by using nano-characterization techniques and grey prediction models. Combined with DFT quantum theory calculations, the recognition and interaction mechanism between ZIF nanoframeworks and nanoplastics was analyzed. The results showed that the correlation between the adsorption performance of PS-NPs and the structural parameters were Co2p intensity> M-N intensity> number of linker defects> number of crystal defects> zeta potential. The grey model (GM) (1,1) was used to construct a correlation model between the structure of the ZIF nanoframework and the recognition adsorption performance (C < 0.342; RSD < 18.108%). The selective adsorption capacity of defective ZIF for polystyrene nanoplastics (PS-NPs) could be greatly improved by introducing additional defects and enhancing adsorbent-adsorbate interactions, including electrostatic and coordination interactions. Under the optimal experimental conditions, the defective ZIF nanoframeworks were successfully applied to the efficient adsorption of PS-NPs in watermelon, strawberry and carrot, with a removal rate of 83.55%-87.80%. The metal ion migration residue test further demonstrated the environmental safety of the defective ZIF nanoframework in the nanoplastic capture process.

Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences (CAAS) is the first unit to complete the paper. Ph.D. students Zhihao Lin and Prof. Guangyang Liu are the co-first authors of the paper, and Prof. Guangyang Liu, Prof. Jing Wang (Institute of Agricultural Quality Standards and Testing Technology, Chinese Academy of Agricultural Sciences) and Prof. Donghui Xu are the co-corresponding authors. The research was carried out in the State Key Laboratory of Vegetable Biological Breeding and Key Laboratory of Vegetables Quality and Safety Control, supported by National Key Research and Development Program of China, the National Bulk Vegetable Industry Technology System, Beijing Natural Science Foundation, and Agricultural Science and Technology Innovation Project of the Chinese Academy of Agricultural Sciences.

Web site of the paper: https://www.sciencedirect.com/science/article/pii/S1748013224002743?dgcid=author

By Guangyang Liu (liuguangyang@caas.cn)