Polymer-modified halloysite nanotubes with high adhesion and UV-shielding properties for chlopyrifos application on cotton leaves

Photodegradation and the low retention rate of pesticides on crop leaves seriously affect their utilization rate. Regarding this problem, we have developed an anti-ultraviolet and high-adhesion pesticide carrier based on halloysite nanotubes (Hal) and was loaded with chlorpyrifos (CPF). By grafting polyethylenimine (PEI) and protocatechuic acid (PCA) onto Hal, PEI-g-Hal (pH) and PCA-g-(PEI-g-Hal) (PPH) were obtained. Load CPF into the cavity of PPH by negative pressure to obtain PPH @ CPF. Its structure and morphology were confirmed by TEM, XPS, FT-IR, zeta potential, TG and XRD, etc. The results indicated that the retention rate of PPH@CPF on cotton leaves was 74.33%, estimated as 1.8 times more efficient than that of PH@CPF. The fluorescence intensity of PPH@FITC was better than that of PH@FITC after 5 times of simulated rain wash. With the decrease in pH, the amino group was protonated gradually, PPH@CPF hydrophilicity was enhanced, and the release rate of PPH@CPF increased gradually. At pH = 5-7 (roughly the same as the pH environment on the leaf surface), PPH@CPF has a faster initial rate and a longer sustained release period than in other pH environments. The photodegradation rate of PPH@CPF was 70% after 24 h, which was much lower than the original CPF. The high adhesion and UV-shielding properties of organic modified Hal played a positive role in reducing the photo-degradation and improved the retention rate of pesticides on the crop leaf surface, thus having an extensive significance in crop protection and environmental protection.