Microwave Synthesis of Super-Absorbent Hydrogels from Rice Husks Cellulose for Sustainable Agriculture
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Date
2021
Authors
Abdulhameed, Adamu
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
The phenomenon of climate change coupled with increased demand for water all over the world calls for innovations in water conservation and use. Moreover, rainfall variability and the corresponding implications are expected to continue worsening owing to the anticipated effect of global warming. Currently, inadequate water is considered as the key factor affecting crop growth and productivity in arid and semi-arid regions of Africa. Hence, there is need to explore and develop innovative ways to reserve and conserve water and nutrients and reduce moisture stress in food crops during mid-season drought. The use of superabsorbent hydrogels in crop growing as a means of ensuring sustained water supply to growing of plants has shown promising results. The superabsorbent hydrogels are capable of absorbing and retaining high amounts of water and releasing it under appropriate conditions. However, majority of the superabsorbent hydrogels are known to be expensive, non-degradable and environmentally unfriendly and are therefore unsuitable for use in agriculture. Hence, there is need for the development and optimization of non-toxic and environmentally friendly alternatives for use in agriculture. The objective of this study was to synthesize and characterize cellulose-based superabsorbent hydrogels from rice husks (Oryza sativa) cellulose under microwave heating and to evaluate their efficacy in the growing of maize in a green house. The cellulose used in this study was extracted from rice husks using acetic acid-nitric acid mixture. Some of the extracted cellulose was modified to carboxymethylcellulose by alkalization followed by reaction with monochloroacetic acid (MCA) under microwave heating. One half of the carboxymethylcellulose obtained was cross-linked using ethane-1,2-diol and the other with ethane-1,2-diamine, under microwave heating to form two different hydrogels. The unmodified cellulose was converted to hydrogels by crosslinking with phosphoric and boric acid, respectively. Separately, optimum synthesis conditions, that is, microwave power out-put, time (minutes), and amount of cross-linkers required were determined by measuring the percentage swelling of the hydrogels produced under different synthesis conditions in water. All hydrogels produced were characterized by Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The ethane-1,2-diamine superabsorbent hydrogel from carboxymethylcellulose showed the highest percentage swelling of 1175 %. The efficacy of the hydrogels in maize growing was determined by planting maize in pots in a greenhouse under different hydrogels and varied hydrogel dose treatments and measuring growth parameters over a period of twelve weeks. Yield parameters were determined at harvesting after 12 weeks allowing for complete drying. The values of plant growth and yield parameters were found to increase with hydrogel dose with the best results being observed among maize plants grown under the hydrogel dose of 5 g per pot for all the superabsorbent hydrogels. It was observed that the maize plants in pots without any hydrogel dried off without any yield as expected when rains fail. These results are significant in that they demonstrate that rice husks cellulose-based hydrogels are efficacious in maize growing in a greenhouse. Furthermore, the use of the agricultural waste, rice husks as a source of the cellulose means the rice husks now becomes a resource rather than an agricultural waste.
Description
A Thesis Submitted in Fulfillment of the Requirements for the Award of the Degree of Doctor of Philosophy (Chemistry) in the School of Pure and Applied Sciences of Kenyatta University, October, 2021
Keywords
Microwave Synthesis, Super-Absorbent, Hydrogels, Rice Husks, Cellulose, Sustainable, Agriculture