IRSPAS 2018
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Item Defluoridation of drinking water using physically and chemically modified chitosan(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Pathirannehe, P. N. S.; Fernando, T. D.; Rajapakse, C. S. K.Depending on the total intake, fluoride (F-) is known to have both beneficial and adverse effects on humans. As the occurrence of the Chronic Kidney Disease of unknown etiology (CKDu) is thought to be linked with excess levels of F- in drinking water, the search for efficient, readily available, more affordable and eco-friendly adsorbents that have defluoridation potential has intensified in recent years. Therefore, the current study focuses on use of chitosan-derived adsorbents, physically and chemically modified chitosan for the removal of F- from drinking water. Physically modified chitosan; chitosan beads (CB), and chemically modified chitosan; protonated glutaraldehyde cross-linked chitosan beads (GCLCB/H+) and protonated glycerol diglycidyl ether cross-linked chitosan beads (GDCLCB/H+) were prepared, and characterized by Fourier Transform Infrared Spectroscopy and Scanning Electron Microscope. Batch experiments were conducted to determine the effect of adsorbent dosage, initial F- concentration, pH and contact time on defluoridation capacity of GCLCB/H+ at 30 ± 20C and the defluoridation capacities of different chitosan derivatives were determined under the optimized conditions (adsorbent dosage = 0.6 g, initial F- content =15 mg/L, contact time = 30 min, pH = 7). Further, the adsorption isotherm studies were conducted to understand the F- sorption process. The results revealed that the defluoridation capacities of CB, GCLCB/H+ and GDCLCB/H+ under optimized conditions at 30 ± 20C were 76.04 mg/kg, 576.98 mg/kg and 655.37 mg/kg, respectively and these values were significantly greater than that of unmodified chitosan flakes (44.20 mg/kg). The results indicate that physical and chemical modification of chitosan have enhanced the F- adsorption capacity of chitosan-derived adsorbents. Further, the results of the isotherm experiments indicated that the adsorption process is well fitted to Langmuir and Freundlich isotherm models. Six water samples among the drinking water samples collected around Kirigollewa Grama Niladhari Division in Medawachchiya, have exceeded the permissible level of F- in drinking water as defined by WHO (1.5 mg/L), but were able to successfully reduce to the permissible range by treatment with GDCLCB/H+. The findings of this study demonstrate that chitosan derived adsorbents are efficient and cost-effective candidates to use in removing F- ions from drinking water.Item Simultaneous detection of Pb(II) and Cd(II) in aqueous solutions by UV-visible spectrophotometry(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Dikella, D. G. T. N.; Rajapakse, C. S. K.The pollution of water resources due to disposal of metals, especially heavy metals is one of the most concerned environmental issues in the current world. Therefore, detection of these heavy metal ions with rapid, sensitive and accurate analytical tools is important. In recent years, water soluble porphyrins, macrocyclic compounds have gained growing interest as colorimetric agents for heavy metal detection by UV-VIS spectrophotometry. Porphyrins are highly sensitive to metal ions and display new Soret band (~ 400 nm) as well as minor Q bands (500–700 nm) upon metal ion chelation. This property has been widely used for detecting heavy metal ions in aqueous solutions. In this work, the influence of pH, water hardness (Ca(II)) and presence of other foreign ions (Mg(II), Co(II), Al(III), Cr(III), Fe(III), Ba(II), K(I), Mn(II), Sn(II), Ni(II), Zn(II), Bi(III)) for simultaneous detection of Pb(II) and Cd(II) by a porpyrin; 5, 10, 15, 20-tetrakis (1-methyl-4-pyridinio) porphyrin tetra (p-toluenesulfonate); (TMPyP) under the selected experimental conditions were investigated. TMPyP displayed a characteristic Soret band in the UV-Vis spectrum at 422 nm. Upon addition of Pb(II) and Cd(II) into TMPyP, the band at 422 nm was disappeared and new Soret bands were appeared at 474 nm and 444 nm, respectively indicating that these characteristic absorption bands, attributed to corresponding Metal(II)-TMPyP complexes. The lower detection limit (LOD) for Pb(II) and Cd(II) with TMPyP was found to be 0.02 mg/L and 0.01 mg/L, respectively which are considerably below the maximum permissible levels for wastewater discharge according to WHO guidelines. The best pH range for simultaneous detection of Pb(II) and Cd(II) was found to be pH 7 to 9. The water hardness (Ca(II)) and the presence of other foreign ions also had no significant effect on the simultaneous detection of Pb(II) and Cd(II) ions in aqueous solutions. It was possible to remove TMPyP complexes as well as unbound TMPyP successfully using chitosan before discharging the analyzed solutions. The results revealed that the TMPyP can function as a single optical sensor capable of detecting Pb(II) and Cd(II) simultaneously in aqueous solutions in the pH range 7-9.