|dc.description.abstract||Safe and abundant water is crucial for the good health of human beings and animals. Across Africa, a third of the population has no access to clean water and sanitation and this affects the continent’s economic productivity adversely due to water-related diseases.
The contamination of water by organic dyes such as malachite green has become a global challenge owing to their toxicity. Stringent discharge guidelines have been imposed on Kenyan industries releasing dye-loaded effluents to the environment and this has accelerated the search for efficient and economically viable low-cost sorbent materials.
Rice husks, chitosan- zinc oxide and poly (ε-caprolactone) – rice husks blend films were categorized as potential low-cost and highly effective sorbents for the uptake of malachite green from aqueous media.
Adsorbent characterization was achieved using selected analytical tools such as scanning electron microscope, thermogravimetric analyzer, Fourier transform infrared and powder X-ray diffractometer instruments. The equilibrium experiments were achieved through the application of batch experiments and the analysis of the solutions was done using a UV-Vis spectrophotometer. The equilibrium data was evaluated using three commonly utilized models namely Langmuir, Freundlich and Temkin models whereas the kinetic data was evaluated via first and second-order rate graphs. The intraparticle diffusion model was applied in testing the sorption mechanisms.
The sorbent materials were found to be mesoporous, thermally stable and contained carbonyl, hydroxyl, phenyl and amino groups on their surface.
The quantity of the colorant removed was impacted by the solution pH, colorant concentration, sorbent particle size, solution temperature, adsorbent quantity and contact time. The adsorbent
quantities utilized for the adsorption of MG onto RH, CS-ZnO and polycaprolactone – rice husks (PCL-RH) were 0.1, 0.6 and 0.3 g respectively with an optimal pH of 7 (RH & PCL-RH) and 8 for CS-ZnO. The percentage adsorption for the dye using the three adsorbents rose with increasing material dose, uptake time and reducing particle sizes. Conversely, the sorption efficacy reduced with increasing dye strength. The thermodynamic data signified an exothermic reaction process.
The sorption equilibrium data was perfectly depicted by the Langmuir uptake model in comparison with the other two isotherms with R2 values > 0.90. The maximum adsorption capacities of RH, PCL-RH and CS-ZnO were 6.5, 9.09 and 11 mg/g respectively.
The rate of MG removal onto the three adsorbents corresponded to the second-order chemical kinetics denoting that chemisorption depicted the rate-determining step and therefore intraparticle diffusion was not exclusively controlling the reaction.
These results demonstrate that unmodified RH, chitosan–ZnO composites and PCL- RH blend films could be utilized as complementary low-cost and eco-friendly materials for textile water purification.||en_US