Versatile Pickering Emulsions Stabilized by Polyphenolic 2D Janus Nanosheets Enhance Foliar Deposition of Agrochemicals

Abstract

Pesticide emulsion, as an important agrochemical formulation, usually suffers from poor stability, weak foliar deposition, and pollution caused by too much dosage of conventional surfactants. Herein, we propose an effective strategy to solve these issues via designing a green and functional surfactant, 2D Janus nanosheets (JNSs), based on adhesive catecholamine compounds to stabilize a pesticide-loaded Pickering emulsion. First, amphipathic 2D octadecylamine–polypyrogallol JNSs (ODA–PPG JNSs) are prepared by a facile and one-step route and are applied to construct a versatile Pickering emulsion. The JNSs-stabilized Pickering emulsions present a remarkable tolerance stability toward ultra-pH (pH = 3, 11) and can achieve an unusual phase inversion accompanying the variation of emulsion viscoelasticity. Owing to the outstanding adhesivity and surfactivity endowed by ODA–PPG JNSs, the pesticide emulsion loaded with a model pesticide avermectin (Av-Emul) performs significantly enhanced foliar deposition than the commercial Av-Tech. Combined with the theoretical calculation, the adhesion mechanism involved in the synergistic action of π–π stacking and H-bonds is unraveled in a molecular scale. The “JNSs-stabilized pesticide emulsions” not only present excellent adhesion on both the hydrophilic and hydrophobic surfaces but also outperform the other conventional pesticide emulsions stabilized by small-molecule surfactants in wettability and spreadability to reduce droplets bouncing on the foliage. This work provides an insight into the structure–adhesivity relationship derived from the non-covalent interaction of polyphenolic JNSs. The proposed innovative strategy for facilitating pesticide utilization demonstrates great promise in formulating agrochemicals.