Facile synthesis of flower-cluster ZIF nanocarriers: Performance in controlled release of thiamethoxam and insecticidal activity.

At present, it is highly important to develop nanopesticide, which can improve the effect of pesticides and reduce the risks of environmental. Zeolitic imidazolate framework (ZIF) is usually used as a nanocarrier of nanopesticide, which has a porous structure and stimuli-responsive properties. However, the drug loading performance and stability of ZIF are poor. To solve these disadvantages, we successfully prepared bimetallic ZIF nanocarriers by hybridizing and structurally regulating ZIF-L with Co. Here, we propose that Zn and Co bimetallic ZIF (ZnCo-ZIF) was used for efficient loading and controlled release of thiamethoxam (THX). Notably, the specific surface area of ZnCo-ZIF with flower-cluster structure was 8.7338 m/g, which could provide a large number of active sites for THX loading. Besides, it was found that the maximum THX loading rate of ZnCo-ZIF was 12.7% by optimizing the load experimental conditions, which was 1.4 times higher than that initial. After that, ZnCo-ZIF@THX was modified by the metal-phenol network (MPN), which formed through the chelation of tannic acid (TA) and iron ions. In the PBS release medium, the cumulative release rate of the ZnCo-ZIF@THX@MPN reaches 100% for 24h. In addition, the photostability of ZnCo-ZIF@THX@MPN had been greatly improved, which the photodegradation half-life of it was 4.17 times that of THX technical drug. After MPN encapsulation, the maximum retention and rainwater resistance of the nanopesticide on vegetable leaves were also improved. The bemisia tabaci was used as the model insect, and the mortality of ZnCo-ZIF@THX@MPN against was increased to 88.15%. Finally, the safety experiment shows ZnCo-ZIF@THX@MPN had no inhibitory effect on pakchoi seed germination and had good biosafety. This work provides a new idea for the development that the facile synthesis of bimetallic flower-cluster nanocarriers and load of thiamethoxam.