SYNTHESIS AND SORPTION PROPERTIES FOR Cu (II), Cd (II) AND Pb (II) IONS OF BENTONITE-­BASED HYBRID MATERIALS WITH IN SITU IMMOBILIZED POLY[5-(4 NITROPHENYLAZO)-­8-METHACRYLOXYQUINOLINE] AND ADSORBED COPOLYMER BASED ON IT

Abstract

Composite materials were synthesized based on bentonite from the Tulchyn district of the Vinnytsia region with in situ immobilized on the surface poly[5-(4-nitrophenylazo)-8-methacryloxyquinoline] (Bent]–AzoQN (in situ)) and adsorbed copolymer of 5-(4-nit­ro)phenylazo-8-methacryloxyquinoline and me­thyl methacrylate with an initial molar ratio of 1:3 (Bent]–AzoQN-MMA (adsorb)). Thermogravimetric analysis confirmed the mass fraction of modifiers to be 20–23 wt.%, with the in situ polymer proving to be more thermally stable. Thermogravimetric analysis was used to determine the patterns of thermal destruction of polymer modifiers of bento­nite surfaces and to record their mass fraction in the composition of synthesised materials. The morphological changes in the surface of the obtained composites were analysed using low-temperature adsorption desorption of nitrogen and scanning electron microscopy. It has been established that modification leads to a decrease in specific surface area, pore vo­lume and an increase in average pore diameter, which confirms the formation of polymer layers on the surface of the mineral.
The adsorption processes are effectively approximated by the Langmuir isotherm, which made it possible to determine the maximum sorption capacity of the composites. As a result of studying the sorption properties of synthesized composites with respect to Cu(II), Cd(II) and Pb(II) cations, it was found that modification of bentonite with these polymers increases the sorption capacity of the initial mineral only with respect to Cu(II) ions. The high selecti­vity to these ions is explained by the formation of stable chelate complexes between the nitrogen and oxygen atoms of the quinoline structure and copper cations. In contrast, for Cd(II) and Pb(II) cations, the sorption capacity either remains unchanged or even decreases (in the case of adsorbed copolymer), which is explained by the blocking of the mineral pores by a dense polymer layer.
The composite materials obtained demonstrate significant potential for use as selective sorbents for the purification of industrial wastewater from Cu(II) ions. The results indicate limited effectiveness of the synthesized composites for complex purification from Cd(II) and Pb(II).