Abstract:
Nymphaea lotus (water lily) leaves available in large quantities in water logged areas, was used as a low-cost adsorbent (treated and untreated) for removing cibacron blue (CB) and congo red (CR) dyes from their aqueous solution while comparing the results obtained with that of activated carbon (control). The adsorbents were characterized using Scanning Electron Microscopy (SEM) and Fourier Transform Infra Red (FTIR) techniques. The SEM micrograph for treated Nymphaea lotus revealed a lump material with distribution of large inter-agglomerate pores composite, the surface morphology of untreated N. lotus has a rough surface and small pores which might be as a result of impurities and the control activated carbon morphology has a rough texture revealing the high porosity of the adsorbent. FTIR analysis of the treated and untreated adsorbents shows a better peak resolution, shift in band and changes in wavelength numbers after carbonization and activation which indicate the possible functional groups present on these adsorbents that may likely be used for the removal of the dye ions from aqueous solution. The effect of varying parameters; pH, contact time, concentration, temperature and adsorbent dosage on CB and CR were evaluated. For untreated adsorbent, pH 7 was found to be favourable while a pH 3 was favourable for treated adsorbent for the adsorption of CB dye which were all obtained at a contact time of 90 min. It was observed that maximum adsorption was achieved for CR dye at pH 6 and a contact time of 60 min for all the adsorbents. Experimental data were analyzed by four different models: Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms and it was found to fit Freundlich equation most. Adsorption rate constants were determined using pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion model. The results clearly showed that the adsorption of both CB and CR dyes followed pseudo-second-order kinetic model. Intraparticle diffusion was also involved in the adsorption process. Thermodynamic parameters were obtained and it was found that the adsorption of CB revealed an exothermic, non-spontaneous process while for CR, the process is exothermic and spontaneous in nature.
