Author(s): A.A. Bamigbade*, K.D. Oduntan and J.T. Bamgbose
Abstract
Malachite green dye adsorption from aqueous solution using silver nanoparticle (AgNP) stabilized with sodium tripolyphosphate cross-linked chitosan is reported in this study. Silver nanoparticle prepared was characterized by Fourier Transform Infra-Red Spectroscopy (FTIR), X-ray diffractometry (XRD), UV-visible spectrophotometer and Scanning Electron Microscopy (SEM). The crystalline nature of the AgNP was revealed with XRD. The cubic face-centered structure of the synthesized silver nanoparticle was confirmed. This was supported by the observed sharp four diffraction peaks with peaks intense appeared at 2θ=38.09°, 44.15°, 64.67°, and 77.54°. However, the SEM micrograph of the synthesized AgNP revealed the spherical shape of AgNP with a non-uniform granular shape attributed to bio-mediated ionic gelation process. The surface of the synthesized AgNP has a spherical shape and slightly elongated with a big tendency to aggregate and form larger particle clusters. Whereas, FTIR spectra of AgNP gave peaks at 1054 – 1645 cm-1 suggesting the presence of phosphonate linkages between ammonium, -NH3+ of chitosan and –PO32- moieties of NaTPP during cross linking process. The adsorption study was carried out under different conditions such as, pH, adsorbent dosage, contact time, temperature and initial concentration of dye to determine the best conditions and the maximum adsorption capacities. The results indicated that increase in temperature had very minimal effect on the adsorption process. The silver nanoparticle was effective in the removal of malachite green in acidic medium. This observation may be due to strong adsorption of the dye on the acidic surface of silver nanoparticle adsorbent by an acid-base interaction mechanism between the adsorbents and the adsorbates. Thus, the adsorption mechanism can be best described by electrostatic interaction. Langmuir, Freundlich and Tempkin model gave a better fit to adsorption isotherms while Dubinin Radushkevich model is not appropriate for the adsorption process. The results obtained from this study indicate that silver nanoparticle could be utilized as effective adsorbents for the removal of dyes from aqueous solution.