Synthesis of polymer networks for removal of azo dyes from aqueous solutions / Heather Lambi Apong

Rapid industrialization growth has led to the high volume of effluent discharges containing undesirable pollutants, such as dyes and heavy metal ions, into the environment, leading to environmental pollutions and raising health concerns. A variety of adsorbents have been reported recently for elimination of harmful dyes in wastewater without causing secondary contamination with different high capacities. Hydrogels are three-dimensional crosslinked polymer networks, which are soft and contain a huge amount of water. The presence of functional groups, such as hydroxyl, carboxylate and amine moieties, in the polymer-based adsorbents play a significant role in facilitating the removal of target dyes and other pollutants in aqueous solutions. In this work, polymer network consisting of sodium humate grafted poly(acrylic acid) (PAA-HA), poly(acrylamide-co-1-vinylimidazole) (P(AAm-co -VIm)) and commercial poly(vinyl alcohol) (PVA) were prepared via free radical polymerization, followed by cyclic freeze-thaw, where the polymers were first dissolved in aqueous solutions. The functional polymers and polymer networks were characterized using ATR-FTIR, NMR and SEM. Swelling behaviour of the polymer networks in deionized (DI) water and phosphate buffer saline (PBS) media at neutral pH was also investigated. The swelling ratio of the three-component polymer network (PVA/PAA-HA/P(AAm-co-VIm) was 3490% in DI water after 24 h of swelling, which was much higher compared to 492% in PBS media. Effects of polymer-based adsorbent dosage ranging from 1 to 2 g/L on the adsorption of selected azo dyes were investigated. Methylene blue (MB) and methyl orange (MO), which are azo dyes, were the model cationic and anionic dyes used to investigate the adsorption capacity of the polymer network in aqueous solutions. Removal efficiencies (>90%) were observed for MB for all adsorbent dosage using two-component, PVA/PAA-HA and three-component, PVA/PAA-HA/P(AAm-co-VIm) polymer networks compared to removal efficiencies for MO(<5%) for all polymer network systems. Therefore, the adsorbent dosage of 1 g/L was selected as the most suitable dosage for the adsorbent considering its high removal efficiency and amount of adsorbent materials, thus their cost-effectiveness for real-time applications in adsorbing pollutants from the wastewaters.