Effect of water content on the characteristics of hydro-compacted nanosilica

Highlights: • Controlled hydro-compaction of nanosilica appropriately changes the textural characteristics of the material. • Primary nanoparticles remain practically the same after hydro-compaction of nanosilica. • Activity and mobility of nanoparticles in compacted nanosilica renew after additional wetting. The morphological and textural characteristics of hydro-compacted nanosilicas (wetted by various water amounts in the range of h_cp = 0.3–5.0 g per gram of dry silica, and then dried) were analyzed using low-temperature ¹H NMR spectroscopy, SAXS, SEM, TEM, IR spectroscopy, and nitrogen adsorption methods. The results of the hydro-compaction of nanosilica A-300 depend strongly on the h_cp value, which can be varied to control reorganization of secondary and ternary structures formed by nanoparticles. The compaction is accompanied by non-monotonic changes in the textural characteristics; however, the nanoparticles per se are practically not affected by the treatment. At h_cp ≤ 1 g/g, the reorganization of secondary/ternary structures does not lead to diminution of the specific surface area (S_BET); however, at h_cp ≥ 1.5 g/g, the S_BET value decreases, but the pore volume increases despite the empty volume of the powder decreases from 21.8 cm³/g for initial A-300 (bulk density ρ_b = 0.045 g/cm³) to 3.45 cm³/g on compaction at h_cp = 4.5 g/g (ρ_b = 0.256 g/cm³). The structural reorganization of hydro-compacted powders is possible after addition of new water amount. This suggests that the chemical bonds between neighboring nanoparticles do not practically form upon the hydro-compaction. Thus, hydro-compacted nanosilica can lose a dust-forming property but remains active with respect to nanoparticles mobility and possibility of reorganization of the secondary structures with nanoparticles.