Halloysite nanotubes-based composite material with acid/alkali dual pH response and foliar adhesion for smart delivery of hydrophobic pesticide

Smart pesticide delivery systems with pH response are arousing huge interests recently, but single pH sensitivity may bring about constraint in different agricultural situations. We have developed 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 (EDTA2-) complex and base-sensitive calcium alginate. During the loading of chlorpyrifos, assembly occurs spontaneously by mixing Ca2+-modified acid-treated halloysite nanotubes (a-HNTs) with EDTA2-, followed by the functionalization of alginate gel to obtain the foliar-adhesive pesticide, namely HCECA (each letter representing halloysite, Ca2+, EDTA2-, chlorpyrifos and alginate, respectively). With loading capacity and loading efficiency of chlorpyrifos at 130 mg/g and 65 %, this engineered pesticide exhibits characteristic sustained release behavior of chlorpyrifos with dual pH response, displaying the release ratio of 58 % and 83 % in 24 h at pH = 4.0 and pH = 8.5, respectively, which is further demonstrated by prolonged control efficiency of corn borers. Owing to the strong interaction of alginate with plant leaves, the foliar adhesion property of HCECA against rain rinsing was strengthened by 86 % and 45 %, in comparison to pristine chlorpyrifos and HCEC (the control pesticide without alginate). The stability of HCECA was investigated, showing its resistance to high temperature (50 °C) and ultraviolet irradiation. 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.