Silanized humic substances act as hydrophobic modifiers of soil separates inducing formation of water-stable aggregates in soils

- Mineral adhesive humic materials are obtained by modification with organosilanes.
- Silanized humics sorb onto clays and hydrophobic surfaces.
- Silanized humics induce formation of water-stable macroaggregates from separates.
- Application of silanized humics improved soil structure in the field experiment.
- Pickering emulsion concept is proposed for explanation of soil aggregate stability.

In this study we successfully enhanced surface activity of natural humic substances (HS) with respect to mineral surfaces by functionalization with organosilanes. Of particular importance was that modification was conducted in water. Humates from coal and peat and 3-aminopropyl-triethoxysilane (APTES) were used as starting materials. Atomic force microscopy showed silanized HS produced self-assembled adsorption monolayers at the water-solid interface. These adlayers caused an increase in the surface hydrophobicity with contact angles equaling 56°. Application of silanized HS for treatment of different soil compartments including mineral soil separates and soil aggregates revealed an efficacy with respect to both re-assembly of soil aggregates and restoration of their water stability. Furthermore, field trials on the treatments of native sod-podzolic soil with silanized HS indicated improvements in soil structure as compared to non-treated soil or treatment with the non-functionalized humate. Results demonstrating the use of silanized HS as ecologically-safe, nature-inspired soil conditioners were promising.