Sinteza, karakterizacija i primena hidrogelova na bazi N-izopropilakrilamida i anjonskih komonomera za uklanjanje hroma, mangana i olova iz vodenih rastvora

Abstract

In this doctoral dissertation, the hydrogels sensitive to temperature and pH changes based on N-isopropylacrylamide (NIPAM) and anionic comonomers (acrylic acid, AA, and methacrylic acid, MAA) were synthesized and investigated as adsorbent materials for removal of Cr(VI), Mn(II) and Pb(II) ions from aqueous solutions. The hydrogels were synthesized by radical polymerization process by varying the content of comonomer and crosslinker. The obtained poly(Nisopropylacrylamide- co-acrylic acid) (p(NIPAM/AA)) and poly(Nisopropylacrylamide- co-methacrylic acid) (p(NIPAM/MAA)) hydrogels were characterized using the following methods: Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), high pressure liquid chromatography (HPLC) and determining the swelling intensity in aqueous solutions of different temperatures and pH values. Kinetics of hydrogel swelling before and after the lyophilization process, as well as swelling reversibility through 3 alternate swell-shrink cycles under the influence of temperature were investigated. A full three-level experimental design was applied in order to describe the swelling of synthesized hydrogels as a function of temperature, pH value and crosslinker content by a mathematical model. Characterization of p(NIPAM/AA) and p(NIPAM/MAA) hydrogels with adsorbed metal ions was performed by FTIR and SEM method. Heavy metal ions in the structure of hydrogels were identified by energydispersive X-ray spectroscopy (EDX). The influence of pH, temperature, contact time and initial concentration of heavy metals on adsorption capacity of hydrogels was investigated. The kinetic and equilibrium data match best to the pseudo-second order model and Langmuir adsorption isotherm. Based on the thermodynamic results, it has been concluded that the adsorption of Cr(VI), Mn(II) and Pb(II) ions from aqueous solutions onto hydrogels was spontaneous and exothermic process. The adsorption capacity of p(NIPAM/AA) and p(NIPAM/MAA) hydrogels for investigated metal ions decreases in the following order: Pb(II)>Cr(VI)>Mn(II). Hydrogels based on NIPAM and AA or MAA are considered to be suitable adsorbents for removal of Cr(VI), Mn(II) and Pb(II) ions from aqueous solutions, due to high efficiency in the temperature range from 25 to 45 °C.