Adsorption of an Organic Dye with Cellulose Nanocrystals
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In developing countries many industries use dyes to colour their products, such as textiles, rubber, paper, cosmetics, leather, plastics, and food industries. Such a wide range of using dyes in many industries increases the demand of dye, and currently 100,000 dyes are commercially available with a rough estimated production of 10⁶ tones/year. Without proper treatment, dye effluent can be mixed with surface and ground water system and it may finally enter the drinking water system. Therefore, the treatment of dye effluents before discharge to the environment has become an global challenge due to the stability and adverse effects of dyes. Among the present methods, adsorption has been preferred to other conventional techniques due to the simple design and operation, low initial investment, effectiveness and insensitivity to toxic substances. The high surface area and the presence of permanent negative charge on the surface makes cellulose nanocrystal (CNC) an excellent candidate for the adsorption of basic (cationic) dyes. The objective of this project is to evaluate the adsorption properties of CNC for the removal of methylene blue from aqueous solution by changing the parameters, such as adsorbent dosage, initial dye concentration, pH, temperature and salt concentration. It was found that the adsorption is independent of pH, however increase in temperature and ionic strength decreased the removal percentage slightly. The Langmuir and Freundlich isotherms were used to evaluate the feasibility of the adsorption process. The adsorption capacity of CNC was determined using the linearized form of Langmuir model. It possessed a value of 118 mg/g at pH 9 and 25 °C. To enhance the adsorption, CNC was oxidized with TEMPO reagent to convert primary hydroxyl groups to carboxyl groups that provides more negative charge. After the oxidation, the adsorption capacity increased from 118 to 769 mg/g.