Targeted micronutrient nanofertilizers of injectable actions based on Cu/B/I halloysite nanotube composites

The development of modern fertilizers includes the creation of various eco-friendly composites made from mineral or organic substance carrier combined with nutrient fillers. This study aims to design targeted micronutrient nanofertilizers with injectable properties by chemically activating halloysite nanotubes as carrier. The goal is to analyze the sorption of copper (Cu), boron (B), and iodine (I) on the meso- and micropores of halloysite to enhance their performance. Halloysite nanotubes were modified via intercalation and adsorption of aqueous solutions containing chelated copper, boric acid , or iodine solutions. As a result, nanotube composites with different concentrations were produced. The encapsulation of Cu/B/I in halloysite, as well as the modification of the nanotubes , was investigated using various techniques, including SEM with EDS , BET surface area analysis, TEM with SAED , TG-DSC with MS , and ICP-MS. Laboratory plant growth tests were conducted, along with detailed observations of how the composites affected the leaf surface, to analyze the effectiveness of the designed fertilizers. Copper, boron, and iodine were intercalated in the micropore space of the halloysite. As the concentration of the reacted solution increased, the average outer diameter of the nanotubes increased up to 300 nm, indicating that the macropore space, also known as the “site,” was filled. The results of the plant growth tests revealed a strong adhesion of activated halloysite nanotubes to arugula microgreens and a stimulating effect of the created composites on height and yield, which increased by up to 34 %. This phenomenon guarantees that the fertilizer remains on the plant's surface for an extended period and is less likely to wash away due to irrigation or rain. Surface spraying of halloysite nanotubes allows for the accurate delivery of micronutrients to plants while preventing soil and groundwater contamination , making this fertilizer ecologically sound. The proposed method of activating halloysite with Cu, B, and I solutions is promising and could lead to the development of fertilizers in the near future. • Halloysite nanotubes modified with Cu, B, and I enable controlled nutrient release. • Micronutrients are sorbed in meso- and micropores of halloysite nanotubes. • Structural modifications improve nutrient retention and slow-release properties. • The nanotubes penetrate plant leaves effectively, ensuring efficient nutrient uptake. • Cu/B/I-halloysite nanocomposites significantly promote plant growth and biomass accumulation.