Abstract
The discharge of untreated wastewater, often contaminated by harmful substances, such as industrially used dyes, can provoke environmental and health risks. Among various techniques, the adsorption of dyes, using three-dimensional (3D) networks consisting of hydrophilic polymers (hydrogels), represents a low-cost, clean, and efficient remediation method. Three industrially used dyes, Methylene Blue, Eosin, and Rose Bengal, were selected as models of pollutants. Poly(acrylamide) (poly(AM)) and poly(acrylamide-co-acrylic acid) (poly(AM-co-AA)) networks were chosen as adsorbent materials (hydrogels). These polymers were synthesized by crosslinking the photopolymerization of their respective monomer(s) in an aqueous medium under exposure to UV light. Experimental adsorption measurements revealed substantially higher dye uptakes for poly(AM-co-AA) compared to poly(AM) hydrogels. In this report, a theoretical model based on docking simulations was applied to analyze the conformation of polymers and pollutants in order to investigate some aspects of the adsorption process. In particular, hydrogen and halogen interactions were studied. The presence of strong hydrogen bonding plays a crucial role in the retention of dyes, whereas halogen bonding has a small or negligible effect on adsorption. An evaluation of binding energies allowed us to obtain information about the degree of affinity between polymers and dyes. The number of rotatable bonds in the copolymer exceeds those of poly(AM),meaning that poly(AM-co-AA) is revealed to be more suitable for obtaining a high retention rate for pollutants.
Highlights
Water is an important liquid for human beings, the universe, and all life existing on earth [1,2]. This liquid can be polluted by different dyes [3,4]. Both water and dyes are still largely used in the textile industry, meaning that the wastewater after production is a mixture of dyes and water
Adsorption processes have been studied intensively because of their low cost, easy access, and effective dye removal, in which the dissolved dye compounds adsorb on the surface of suitable adsorbents [21]
In the case of crosslinked poly(AM) hydrogel, the distances between chlorine and oxygen atoms are greater than 3.55 Å, which shows that the interactions are weak
Summary
Water is an important liquid for human beings, the universe, and all life existing on earth [1,2]. The docking method was applied to analyze different interactions, with the receptor and ligand representing the polymer matrix and dye, respectively. This simulation method has the advantage of enabling us to predict the preferred orientation of one molecule to a second one when bound to each other to form a stable complex [38–40]. In the case of crosslinked poly(AM) hydrogel, the distances between chlorine and oxygen atoms are greater than 3.55 Å, which shows that the interactions are weak. In the case of crosslinked poly(AM) hydrogel, the distances between chlorine and oxygePnolayt(AomMs-cao-rAeAg)r/eRaBter than 3.55 Å, whIi.c..hO shows that the interaction3.s82a3re weak. The hydrogen bond with 2.24 Å represents a strong interaction, because the copolymer is charged in the aqueous
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