Harun M MbuviFrancis M MaingiKasimu, Titus Munyao2023-02-212023-02-212022http://ir-library.ku.ac.ke/handle/123456789/24814Thesis Submitted in Fulfillment of the Requirements for Award of the Degree of Doctor of Philosophy (Chemistry) in the School of Pure and Applied Sciences of Kenyatta University, 2022Superabsorbent hydrogels represent a set of polymeric materials with three-dimensional structure. They are capable of holding huge amounts of water and due to the hydrophilic nature in the structure. Their applications in industries and environment are of prime importance. Currently application of polyacrylic and polyacrylamide super absorbers hydrogel in irrigation farming has been reported in western countries making farming economically viable. However, these hydrogels are non-biodegradable, toxic and expensive. Therefore, the pursuit of cheap and biodegradable hydrogels is desirable. Hence this study reports the synthesis and characterization of super absorbent hydrogels derived from activated charcoal (AC) and citric acid from lemon juice (LJ) which are locally available. This involved crosslinking activated charcoal (AC) and lemon juice (LJ) with ethylenediamine (EDA) or glycerol (G) in the absence and presence of maleic acid as a cross linker. Effects of hydrogels dosage on growth and yield parameters were investigated on DH 02 maize crop grown in semi- arid region of Mwala Machakos County during the April - July 2020 rains. Characterization of the hydrogels was done using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), and X-ray diffraction (XRD). The synthesis conditions that produced optimal swelling conditions were determined by varying contact time and dosage of activated carbon, lemon juice and maleic acid respectively. The FT-IR results showed absorption peaks at 1591.34, 1079.83, 1590.99, 1639.48 cm-1 for crosslinked superabsorbent hydrogel of Citric acid Glycerol (HLG-2), Citric acid Ethylenediamine (HLE-2), Activated carbon Ethylenediamine (HCE-2) and Activated carbon Glycerol (HCG-2). The peaks were associated with –COO- stretching vibration, -COO- strong symmetric stretching, C-N- stretching vibration, and -COO- bending in non-conjugated ester respectively which were a proof of successful ester crosslink upon addition of maleic acid during the synthesis process. XRD analysis showed that upon crosslinking the phase polymer network changed from amorphous to crystalline form. SEM analysis showed clear pores with large surface area in cross linked hydrogels compared with rigid and constricted surface of uncross linked hydrogels. Superabsorbent hydrogels for maximum swelling capacity were prepared using the following ratios. Swelling capacity of hydrogels prepared at optimum conditions of volume ratio CA: G: MA (5.4: 3.75: 3.75) HLG-2, CA: EDA: MA (144: 90: 75) HLE-2 while a mass ratio of AC: G: MA (6: 5:1) HCG-2 and AC: EA: MA (6:5:2) HCE-2 show that activated carbon functionalized with glycerol and cross linked with maleic acid has higher swelling percentage of 1255.80±0.70 % when subjected to a contact time of 12 hours. The application of 60 kg/ha of Activated carbon Glycerol showed highest mean growth and yield parameters compared to other superabsorbent hydrogels. This indicates that the prepared hydrogels have potential of reducing moisture stress in maize crops grown in semi-arid region. Super absorbent hydrogels synthesized from Activated charcoal and citric acid have potential application in agriculture owing to their high swelling capacities.enSynthesis of Super Absorbent HydrogelsCross-Linking Activated CharcoalCitric AcidSustainable AgricultureSemi-Arid RegionsThesis