Exploring structures-properties and interactions of acrylic-hydrogel adsorbents with metal ions and organics using nuclear magnetic resonance and Fourier transform infrared spectroscopies

Abstract

Nowadays, multifunctional acrylic hydrogels are becoming extremely popular because of their prospective applications stemmed from improved durability, water retention capacity, recyclability, sustainability, and binding capacity through structural alterations at molecular/supramolecular level. Detailed spectrochemical investigations based on nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) analyses are mandatory for overall structural elucidation as well as the detection, quantification, and alteration of diverse functionalities influencing strength, population, and reversible/irreversible nature of inter-/intra-molecular covalent and non-covalent interactions inside the unloaded/loaded acrylic hydrogels, status of dispersion and aggregation, nature of water cluster, oxidation/reduction of adsorbed metal ions, and adsorption-desorption mechanism(s). Analyzing and comparing 1H/13C NMR spectra; spatial arrangement and involvement of various protons/carbons in covalent and non-covalent interactions; C–C, C–N, and C–O coupling; polymerization; incorporation of individual components; crosslinking; grafting; spacial arrangement of protons/carbons; and in situ comonomer formation can be understood from the alteration of signals through shielding and deshielding effects of electron clouds. Regarding this, FTIR spectra can indicate various key events including conventional/nonconventional hydrogen bonding interactions, protonation/deprotonation, mode of coordination, and reversible/irreversible nature of bonds. Accordingly, present review covers the principles of NMR and FTIR analyses followed by the collection, compilation, and discussion of major peaks, reason(s) for the variation in the peak shifting, and associated significances. Subsequently, factors responsible behind the alterations in spectrochemical data and key findings of these spectroscopic techniques are summarized and discussed in understanding the structures, properties, and interactions of acrylic hydrogels/similar polymeric materials with metal ions/organics.