Abstract
Coatings offer a means to control nanoparticle (NP) size, regulate dissolution, and mitigate runoff when added to crops through soil. Simultaneously, coatings can enhance particle binding to plants and provide an additional source of nutrients, making them a valuable component to existing nanoparticle delivery systems. Here, the surface functionalization of metal and metal-oxide nanoparticles to inhibit aggregation and preserve smaller agglomerate sizes for enhanced transport to the rooting zone and improved uptake in plants is reviewed. Coatings are classified by type and by their efficacy to mitigate agglomeration in soils with variable pH, ionic concentration, and natural organic matter profiles. Varying degrees of success have been reported using a range of different polymers, biomolecules, and inorganic surface coatings. Advances in zwitterionic coatings show the best results for maintaining nanoparticle stability in solutions even under high salinity and temperature conditions, whereas coating by the soil component humic acid may show additional benefits such as promoting dissolution and enhancing bioavailability in soils. Pre-tuning of NP surface properties through exposure to select natural organic matter, microbial products, and other biopolymers may yield more cost-effective nonagglomerating metal/metal-oxide NPs for soil applications in agriculture.
Highlights
This review focuses on soil application of NPs and their resulting transformations including: (1) sorption
Soil pH influences the rate at which NPs dissolve into their constituent metals and dictates the Figure 2, the free Cu ion rapidly decreases as the pH becomes alkaline
Research by Zhang et al compared coatings made from sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfate (SDBS), Tween 80, and hexadecyltrimethyl ammonium bromide (HDTMA) on the efficacy of reducing not just inter-NP agglomeration and heterogenous adsorption to soil particulates [134]
Summary
Nanoparticles (NP)s are increasingly being investigated for agricultural applications to improve crop yield and performance while reducing waste and runoff. Due to unique soil transport properties and enhances their bioavailability in crops [10,11,12]. Due to their high surface area to volume ratio, and associated high surface energy, NPs often agglomerate under their high surface area to volume ratio, and associated high surface energy, NPs often agglomerate environmental conditions. Even if NP size throughout transport, factors in soils and soilin pore waters further after is preserved throughout transport, factors soils and may soil promote pore waters mayagglomeration promote further delivery This can result in phytotoxic effects in plants, loss of material from runoff, or reduced agglomeration after delivery.
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