Removal of Cationic Neutral Red Dye from Aqueous Solutions using Natural and Modified Rice Straw

Modified colloidal carbons were prepared by reacting colloidal carbon obtained from rice straw with thermal oxidation, nitric acid and urea treatment. The textural and chemistry characteristics of the surface of non-modified and modified carbons were obtained from nitrogen adsorption at -196oC, elemental analysis and fourier transform infrared (FTIR) techniques. The uptake of cationic neutral red (NR) dye from aqueous solutions by these carbons was determined by kinetic and equilibrium experiments. The surface area and the total pore volume decreased, whereas the pore radius increased after the treatment with nitric acid.The surface pH of un–modified carbon was basic while those of modified carbons were acidic. Urea treated carbons with the lowest acidic character and high nitrogen content presented the lowest NR dye uptake capacity. The maximum removal of NR dye was obtained at a pH of 4. The amount of adsorption by the investigated carbons was found to depend on the amount of surface acidity. The adsorption results were analyzed considering Langmuir, Freundlich and Dubinin-Radushkevich(D-R) models. The adsorption of NR dye onto the assessed adsorbents is of the physical sorption type following pseudo – first – order kinetic.Nitric acid modification brought about a significant rise in NR dye adsorption which was ascribed to the formation of oxygen containing acidic groups on the surface of adsorbent.The equilibrium adsorption data of NR dye were well fitted with Langmuir and D-R models.