Modified Polyacrylamide Hydrogel and its Characterization as a Model System Towards Applications in Agriculture and Environment

Abstract

The thesis focuses on the development of a Polyacrylamide (PAAm) hydrogel capable of forming a three-dimensional network that retains significant amounts of water. The key objective was to enhance the hydrogel's porosity to facilitate rapid nutrient diffusion for agricultural applications. A cost-effective, portable device was created to measure the diffusivity of nitrogen (N), phosphorus (P), and potassium (K) nutrients in a soil-less setup, relying on spectroscopic absorption principles for nutrient detection. This device can quantify nutrient concentrations ranging from 0.25 mM to 10 mM, using the Lambert-Beer law to derive measures based on optical absorption. Experimental findings indicate that nutrients diffuse across a ~ 4 mm diameter area within the hydrogel in about 20 minutes at ambient conditions. Among various samples tested, one with approximately 0.55 % cross-linker displayed optimal rigidity and water retention properties. Surface studies revealed that mili-patterns on the hydrogel improved water retention duration by nearly 60 %. Even after prolonged drying, a patterned hydrogel maintained a length ~ 35 % greater than a non-patterned counterpart, showcasing a retention efficiency (RE) of ~ 97 % versus ~ 70 % for flat hydrogels. Additionally, this study also discusses the antibacterial effectiveness of aged Silver nano prisms embedded in PAAm hydrogels. The [111] crystallographic facets of these prisms enhance silver dissolution and Ag+ ion release, significantly improving antibacterial activity due to sustained interaction with microbial cells. The synergy between the silver nanoparticles and the hydrophilic nature of the PAAm matrix enables extended antibacterial action through mechanisms like membrane disruption and oxidative stress induction. Moreover, the study focuses on the capacity of PAAm hydrogels embedded with silver Nano prisms to sequester Pb2+ ions from household water. The synthesized nano-composites exhibit effective Pb2+ removal at neutral pH, achieving high removal efficiencies while conforming to WHO standards. The adsorption is rapid, following a pseudo-second-order kinetics model, with maximum capacities varying according to initial Pb2+ concentrations. Moreover, the presence of silver conferred additional antibacterial properties, maintaining Ag+ ion levels conducive to microbial safety. The findings affirm the potential of PAAm–AgNP composite hydrogels for multi-functional applications in water purification, addressing both heavy metal and microbial contamination.