Department of Physical Sciences
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Browsing Department of Physical Sciences by Subject "adsorption"
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Item Adsorption of selected heavy metals on modified nano cellulose(2016) Madivoli, Edwin S.; Kareru, Patrick G.; Gachanja, Anthony N.; Mugo, Samuel; Murigi, Martin K.; Kairigo, P. K.; Kipyegon, Cheruiyot; Mutembei, Jackson K.; Njonge, Francis K.Cellulose is an inexpensive, renewable, bio-based and an abundant raw material suitable for the development of filter membranes for water purification. This is because it has numerous functional groups that afford ease of modification to create active surfaces upon chemical modification. In this study, cellulose was isolated from two abundant biomasses, namely, Eichhornia crassipes and Cyperus papyrus using the soda process followed by bleaching with peracetic acid. The percent yield of cellulose nanofibrils (CNF) obtained from E. crassipes and C. papyrus was found to be 31.64 ± 1.46% and 29.55 ± 0.64% respectively. The degree of crystallinity and crystal sizes were calculated to be 71.42% and 0.059 nm for E. crassipes and 46.15% and 0.068 nm for C. papyrus respectively. The FT-IR absorption of the carbonyl functional group of an ester indicated that effective esterification of cellulose using citric acid was obtained when cellulose nanofibrils to citric acid ratio was 1:1. From batch adsorption studies, the capacity for citric acid modified cellulose to remove heavy metals was determined to be 8.36 mg/g Zn2+, 18.06 mg/g Cu2+, 42.69 mg/g Cd2+ and 21.64 mg/g Pb2+. In comparison to the % adsorption using unmodified cellulose of less than 5%, the heavy metals adsorption using modified nanocellulose materials were 86.47% Pb2+, 85.20% Cd2+, 77.40% Cu2+, and 70.04% Zn2+. From these results, it was concluded that modified cellulose could be used as a low cost adsorbent for removal of heavy metals and that development of household water filtration units using modified cellulose could be exploited.Item Improved accuracy in multicomponent surface complexation models using surface-sensitive analytical techniques: Adsorption of arsenic onto a TiO2/Fe2O3 multifunctional sorbent(2020) Bullen, Jay C.; Kenney, Janice; Fearn, Sarah; Kafizas, Andreas; Skinner, Stephen; Weiss, Dominik J.Novel composite materials are increasingly developed for water treatment applications with the aim of achieving multifunctional behaviour, e.g. combining adsorption with light-driven remediation. The application of surface complexation models (SCM) is important to understand how adsorption changes as a function of pH, ionic strength and the presence of competitor ions. Component additive (CA) models describe composite sorbents using a combination of single-phase reference materials. However, predictive adsorption modelling using the CA-SCM approach remains unreliable, due to challenges in the quantitative determination of surface composition. In this study, we test the hypothesis that characterisation of the outermost surface using low energy ion scattering (LEIS) improves CA-SCM accuracy. We consider the TiO2/Fe2O3 photocatalyst-sorbents that are increasingly investigated for arsenic remediation. Due to an iron oxide surface coating that was not captured by bulk analysis, LEIS significantly improves the accuracy of our component additive predictions for monolayer surface processes: adsorption of arsenic(V) and surface acidity. We also demonstrate non-component additivity in multilayer arsenic(III) adsorption, due to changes in surface morphology/porosity. Our results demonstrate how surface-sensitive analytical techniques will improve adsorption models for the next generation of composite sorbents.Item Uranium surface processes with sandstone and volcanic rocks in acidic and alkaline solutions(2023) Kenney, Janice; Lezama-Pacheco, Juan; Fendorf, Scott; Alessi, Daniel S.; Weiss, Dominik J.Understanding the behaviour of uranium waste, for disposal purposes, is crucial due to the correlation between pH values and the disposal of distinct types of waste, with low level waste typically associated with acidic pH values, and higher and intermediate level waste commonly related to alkaline pH values. We studied the adsorption of U(VI) on sandstone and volcanic rock surfaces at pH 5.5 and 11.5 in aqueous solutions with and without bicarbonate (2 mM HCO3–) using XAS and FTIR. In the sandstone system, U(VI) adsorbs as a bidentate complex to Si at pH 5.5 without bicarbonate and as uranyl carbonate species with bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbs as monodentate complexes to Si and precipitates as uranophane. With bicarbonate at pH 11.5, U(VI) precipitated as a Na-clarkeite mineral or remained as a uranyl carbonate surface species. In the volcanic rock system, U(VI) adsorbed to Si as an outer sphere complex at pH 5.5, regardless of the presence of bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbed as a monodentate complex to one Si atom and precipitated as a Na-clarkeite mineral. With bicarbonate at pH 11.5, U(VI) sorbed as a bidentate carbonate complex to one Si atom. These results provide insight into the behaviour of U(VI) in heterogeneous, real-world systems related to the disposal of radioactive waste.