Light, electric field, alternating magnetic field, and pH have been used as triggers to boost the release of pesticides, among which the pH-responsive type attracts broad interest due to simple operation and low cost. Albeit this, most pH-controlled pesticides exhibit monotonic response to acid or alkali, and thus the large-scale application is limited, since pH of water for agricultural spraying may vary between weakly acidic and weakly alkaline among places. To meet this challenge, it is strategic to design acid/alkali dual pH-responsive controlled-release pesticides that are flexible in multiple application situations.

According to a paper published in Chemical Engineering Journal, a team led by Prof. WU Zhengyan from the Hefei institutes of physical science of the Chinese Academy of Sciences managed to develop a novel type of responsive material with acid/alkali dual pH sensitivity to deliver hydrophobic pesticide by the combination of acid-sensitive calcium ion (Ca²⁺)-ethylenediamine tetraacetate (EDTA^2-) complex and base-sensitive calcium alginate.

During the loading of chlorpyrifos, assembly occurred spontaneously by mixing Ca²⁺-modified acid-treated halloysite nanotubes (a-HNTs) with EDTA^2-, followed by the functionalization of alginate gel to obtain the smart pesticide delivery system (HCECA).

The loading capacity and loading efficiency of the system for chlorpyrifos were 130 mg/g and 65%, respectively, showing a dual pH-responsive controlled release behavior.

At the same time, the system displays excellent foliar adhesion performance, high temperature resistance and ultraviolet resistance, which can significantly reduce the loss, prolong the duration of pesticides, and improve the utilization rate.

Notably, the carrier material shows excellent biocompatibility by testing toxicity on zebrafish. Featured by green preparation, acid/alkali dual pH response and multifaceted stability, the halloysite nanotubes-based gel material serves as a promising carrier for hydrophobic pesticide to be applied in controlled management of agricultural hazards.

This research was supported by the University Synergy Innovation Program of Anhui Province, and the Science and Technology Major Project of Anhui Province.

Schematic illustration of fabrication and mechanism of HCECA. (Image by TENG Guopeng)