Preparation And Performance Of ZIF-8 Thiacloprid Based Nanocontrolled Release Formulation

Thiacloprid is a new type of chlorinated nicotine insecticide with strong systemic,tactile and gastric toxic effects.In this study,α-CD@T@ZIF-8 was prepared by processing the formulation of Thiacloprid with ZIF-8.Experiments were carried out on three aspects:release kinetics,bioactivity against pea aphids and safety,to investigate the selective release of Thiacloprid between pea aphids and earthworms,and to provide a new method for the safe application of Thiacloprid.The main studies and results of this paper are as follows:1.Preparation ofα-CD@T@ZIF-8Three room temperature"one pot"methods were chosen to prepare Thiacloprid-loaded T@ZIF-8 using ZIF-8 as the carrier material.The method was based on the addition of Thiacloprid methanol solution to 2-methylimidazole aqueous solution and the addition of zinc nitrate solution drop by drop to the 2-methylimidazole solution using a syringe with controlled drop acceleration.T@ZIF-8 was synthesized with a 12%drug loading and a uniform particle size distribution without agglomeration.Theα-CD@T@ZIF-8 nanoparticles were successfully prepared by coating the outer layer ofα-cyclodextrin by physical adsorption on the basis of the synthesis of T@ZIF-8.2.Characterization ofα-CD@T@ZIF-8The preparedα-CD@T@ZIF-8 was characterized and its properties were determined using scanning electron microscopy,transmission electron microscopy,infrared spectroscopy,X-ray diffraction,adsorption and desorption of nitrogen,thermogravimetric analysis,contact angle,etc.The results showed thatα-CD@T@ZIF-8 was Orth hexahedral with an average particle size of 125.96±0.43nm and good dispersion,and the prepared samples were in accordance with the experimental design.The Thiacloprid drug was piggybacked on the center of ZIF-8 andα-cyclodextrin was wrapped in the outer layer.The preparation process did not affect the crystal properties within ZIF-8,while ZIF-8 improved the thermal stability and adhesion ability of Thiacloprid on the leaves and had better stability in water.3.Study of the release behavior ofα-CD@T@ZIF-8The release profiles ofα-CD@T@ZIF-8 were measured in different environments and the results showed that the release of Thiacloprid fromα-CD@T@ZIF-8 was pH-dependent,with the release rate acidic>basic>neutral,and thatα-amylase was able to shorten the time to reach release equilibrium.The equations fitted to the different release profiles were more in line with the Higuchi release model,with the concentration of Thiacloprid determining the release rate,and the release of Thiacloprid fromα-CD@T@ZIF-8 following the Fick diffusion law regardless of the environment,indicating that the structural stability of ZIF-8 plays a role in determining release.4.Insecticidal activity ofα-CD@T@ZIF-8 against pea aphidThe insecticidal activity ofα-CD@T@ZIF-8 was higher than that of Thiacloprid OD,which prolonged the control of pea aphids by Thiacloprid.The LC₅₀ data showed thatα-CD@T@ZIF-8 was less active than Thiacloprid OD,indicating thatα-CD@T@ZIF-8 was more active than Thiacloprid OD at the same concentration of Thiacloprid.The sustained control of pea aphids byα-CD@T@ZIF-8 and Thiacloprid OD was then investigated by spraying on broad bean leaves.The results showed that Thiacloprid OD was more effective against pea aphids in the early stages,but thatα-CD@T@ZIF-8 had higher insecticidal activity against pea aphids in the later stages.5.Safety study ofα-CD@T@ZIF-8α-CD@T@ZIF-8 had no effect on pea seed germination and growth in the short term and was less toxic to earthworms than Thiacloprid and Thiacloprid OD.The effects of different concentrations ofα-CD@T@ZIF-8 on pea seed germination,root length,stem length and fresh weight were investigated using the flat dish method and the results showed thatα-CD@T@ZIF-8 did not affect pea growth even at high concentrations,but also had a slight promoting effect.The acute toxicity to earthworms was investigated using the filter paper contact method,and the enrichment of Thiacloprid in earthworms was measured on the basis of the filter paper method.The enrichment of Thiacloprid OD in earthworms was much greater than that ofα-CD@T@ZIF-8,indicating that the presence of the carrier reduced the exposure of Thiacloprid to earthworms and made it safer for earthworms.In this study,the formulation processing of Thiacloprid has enhanced the selectivity of Thiacloprid,facilitated the reduction of toxicity to non-target organisms and provided a new way of applying Thiacloprid in agriculture.