SORPTION OF IONIC FORMS OF ZINC (II) FROM AQUEOUS SOLUTIONS BY SURFACES OF MAGNETO-SENSITIVE NANOCOMPOSITES MODIFIED WITH HYDROXYAPATITE

Abstract

The problem of the quality of drinking water has been quite acute in recent decades. The mass release of harmful substances into the environment, especially heavy metal ions, which may enter during hostilities on the territory of Ukraine, pose a serious threat to living organisms and may negatively affect the stability of the ecosystem. Thus, the purification of polluted water to drinking quality remains a very urgent problem. One of the effective technologies for purifying natural waters from heavy metal ions is sorption purification, which involves the use of highly effective sorbents with the required set of physicochemical properties. Such materials include magnetite-based magnetite-sensitive nanomaterials, in particular, magnetite, the surface of which is modified with hydroxyapatite (Fe3O4/HA). In the work, the synthesis of nanosized magnetite was carried out, using electron microscopy methods it was established that spherical magnetite particles are prone to the formation of aggregates characterized by the size of 3–23 nm. The concentration of active –OH groups on the surface is 2,2 mmol/g for the specific surface area S = 90 m2/g. Modification of magnetite with hydroxyapatite by the sol-gel method was carried out, and it was determined that the nanocomposite contains active – OH surface groups, the concentration of which is 2,2 mmol/g for the specific surface area S = 110 m2/g. It was determined that the shape of the particles of the nanocomposite does not differ from the original magnetite, and the average size of the particles is 25–30 nm. Calculation of the average crystallite sizes of both the original magnetite and Fe3O4/HA using Scherrer’s method showed that the calculated data are in good agreement with microscopic studies. The sorption activity of zinc (II) ionic forms by the surfaces of magnetically sensitive nanosized magnetite (Fe3O4) and the magnetite/hydroxyapatite (Fe3O4/HA) nanocomposite created on its basis was investigated. It was established that under the conditions of static sorption of ionic forms of Zn2+ at 293 K and pH = 8,5, the maximum degree of extraction is 65,2% for the Fe3O4 surface and 98,5% for Fe3O4/HA, and the capacity of the sorbent under the specified sorption conditions is 21,7 mg/g for Fe3O4 and 32,8 mg/g for Fe3O4/HA, respectively. It was determined that the sorption process is described by a pseudo-second-order model, and the value of the distribution coefficient at the “sorbate – sorbent” interface indicates that the modification of the magnetite surface improves the sorption capacity of the nanocomposite. It was determined that the sorption process occurs on potentially heterogeneous surfaces, and the value of the sorption energy indicates the physical sorption of Zinc (II) ionic forms by both surfaces. The perspective of using the magnetically sensitive Fe3O4/HA nanocomposite as a sorbent of ionic forms of Zinc (II) from aqueous solutions is shown.