Nanocomposites and nanomaterials

The regularities of sorption of substances of different nature by pH-sensitive acrylic hydrogels for plant nanofertilizer formation
Kalinichenko K.V.1, Nikovskaya G.N.1, Samchenko Yu.M.2
1 Colloidal Technologies of the Natural Systems Department, F.D. Ovcharenko Institute of Biocolloidal Chemistry, Natl. Acad. of Sci. of Ukraine. Vernadsky Blvd, 42, Kiev-03680, Ukraine.
E-mail: KirKa_@bigmir.net
2 Department of Functional Hydrogel, F.D. Ovcharenko Institute of Biocolloidal Chemistry, Natl. Acad. of Sci. of Ukraine. Vernadsky Blvd, 42, Kiev-03680, Ukraine.

At present, a great attention focuses on the learning of interaction of acrylic hydrogels with external medium and their influence on its properties. The special interest has pH-sensitive acrylic hydrogels with slightly acidic and slightly alkaline groups which capable to ionization at change of external solution pH values. The ionisation causes their swelling through electrostatic repulsion of the same charged parts of the polymeric chain and osmotic pressure of the counterions.
The synthetic polymeric hydrogels – acrylamide and acrylic acid copolymer (AA-AA), acrylamide and acrylonitrile copolymer (AA-AN), polyacrylamide hydrogel (PAAG) – were used in our study.
The acrylic hydrogels are able to sorb substances of different nature – heavy metal compounds as cations, anions or organic complexes, and organic molecules. The substances as to their affinity to the polymeric gels have the next sequence: organic stain (positively and negatively charged) > Fe3+ > Cu2+ > Mn2+ > MnO4- > (Cu-Humate)- > (Fe-Humate)- > H2PO4- ≥ (Fe-Citrate) ≥ (Cu-Citrate). The degree of their desorption has an opposite order. It points out that compounds of different nature are quite firmly held in the hydrogel matrix and only partially desorbed into the environment. Stains molecules, when concentrating inside gel matrix, interact with each other and form nanoparticles with the size ~ 10 nm. Similarly, at joint presence of metal salts and complexes in gel matrix they associate in nanoparticles which are able to gradual desorption in surrounded medium. The swelling of the pH-sensitive gels is observed simultaneously with sorbate sorption at alkaline pH values. Collapse of the hydrogels and desorption of the sorbed substances takes place in acidic medium.
The results obtained may be considered as an experimental base for a formation of plant nanofertilizer of prolonged action.