Adsorption of heavy metal ions on organosilica composites prepared using rice husks ash as a silica source

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University of Dar es Salaam
Triaminopropyl-silica hybrids were prepared via post synthetic technique using Rice Husks Ash (RHA) as silica source and (3-trimethoxysilylpropyl) diethylenetriamine. The prepared materials were characterized by acid titration, Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM), nitrogen adsorption-desorption analysis and thermogravimetric analysis. Results show that the amine group loading of the triaminopropyl-silica hybrid prepared using rice husks ash (TSH-R) was 2.15 mmol/g. The TSH-R was found to have characteristic functional groups, namely, O-Si-O (900-1150 cm-1), CH (2800-3000 cm-1), O-H (3000-3500 cm-1) and N-H (1530 cm-1) which were obtained by ATR-FTIR analysis. SEM and FE-SEM micrographs of the prepared materials showed rough surfaces with protuberances, cracks and holes. The RHA, rice husks silica (RHS) and TSH-R materials had average particle sizes of 336.8, 296.4 and 1054.1 nm, respectively. EDX gave the elemental composition whereby Si and O were present in high proportion in all samples. The BET surface areas of RHA, RHS and TSH-R were 17.8, 20.2 and 5.7 m2/g respectively. The total pore volumes were 0.43 cm3/g for RHA, 0.49 cm-3/g for RHS and 0.02 cm3/g for TSH-R. On the other hand, the average pore width of RHA, RHS and TSH-R were 95.9, 97.6 and 17.3 nm respectively. The materials had pores in the mesoporous range and exhibited very small change in weight beyond 500 ºC. Adsorption studies of Ni(II), Zn(II), Pb(II), Cu(II) and Co(II) ions showed that RHA and TSH-R were good adsorbents with the average maximum adsorption of 99 and 95% for RHA and TSH-R, respectively when 1.0 g of adsorbent and initial metal ions concentration of 21 - 27 mg/L at pH 4 were employed. Both Langmuir and Freundlich isotherms indicated that the adsorption was favorable. Thus RHA and TSH-R can be used to remove mixtures of toxic heavy metals from contaminated water. Based on the findings of this study RHA is the best adsorbent because, it has overall superior adsorptive properties and it is cost effective.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF TD427M44L53)
Heavy metals, Metal ions, Adsorption, Absorption and adsorption
Ligate, F. J (2014) Adsorption of heavy metal ions on organosilica composites prepared using rice husks ash as a silica source, Master dissertation, University of Dar es Salaam. Dar es Salaam.