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The interaction of contaminants and nutrients with soil constituents is controlled by processes in intergranular and intragranular pore spaces of organic matter or/and common secondary minerals such as ferrihydrite, ∼Fe3+ 10O14(OH)2. This contribution shows that distribution and clustering of the contaminants As, P, Pb, Si, Sn, and Zn in a porous ferrihydrite grain is greatly affected by the heterogeneous size distribution and chemical composition of the pores as well as the ability of their polyhedra to polymerize with the same type of polyhedron. Transmission electron microscopy (TEM) and atom probe tomography (APT) studies are conducted on focused ion beam (FIB) sections extracted from a porous ferrihydrite grain from the smelter-impacted topsoil in Sudbury, Ontario, Canada. The ferrihydrite grain has pore spaces ranging in diameter from tens to hundreds of nanometers. TEM and scanning-TEM studies indicate that the surfaces of the pore walls are enriched in Si. APT data in conjunction with First Near Neighbor (1NN) analyses indicate different degrees of clustering of Pb, As, Sn, Zn, Si, and P within the sample and selected domains. Careful evaluations of 3D atomic plots and 1NN distances indicates the occurrence of polymerized arsenite-, silica-, Sn-, and Zn-polyhedra within pore spaces of the ferrihydrite. Deciphering adsorption, polymerization, and nucleation processes in porous Fe-(hydr)­oxides and other soil constituents requires multianalytical approaches and, in this regard, we discuss the advantages and disadvantages of the combination of TEM and APT for characterizing complex environmental samples at the atomic to nanometer scale.

Vitamin B6 was nano-encapsulated in between modified montmorillonite nanolayers. Results indicated that electrostatic interaction forces dominate the adsorption onto different sites of the nanolayers. The successful nano-encapsulation was achieved when the interlayers spaces of the nanolayer were saturated with cations of Na+ or Ca2+ resulted in adsorption of vitamin B6 in between nanosheets. At these conditions, controlled pH-responsive desorption properties were detected and vitamin B6 was released mostly from the interlayer spaces. The presented modified montmorillonite could be used for nanoencapsulation of drugs and biomolecules with high protection of carrying materials during storage and even through the digestion process.

This study investigates the sequestration of silver and arsenic ions in soil organic matter at the nanoscale using the combination of atom probe tomography, transmission electron microscopy, ion mill thinning and scanning electron microscopy.