Adsorption of Congo red and malachite green using chitosan derived from blue crab shells

The aim of this work was to evaluate the adsorption capacities of the acidic dye Congo red (CR) and the basic dye malachite green (MG), which are hazardous to the environment and human health in aquatic environments, using chitosan derived from blue crab shells, which are considered waste materials. By first extracting chitin and then chitosan from blue crabs, the maximum adsorption capacities of these dyes in aquatic solutions were investigated. Parameters such as pH, contact time, initial concentration of MG/CR, and temperature were analyzed. Characterization of the adsorbent was performed using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy. The FTIR findings showed that hydrogen bonds and C=O and N-H bending contributed to the adsorption of MG/CR. The equilibrium data were analyzed with Langmuir and Freundlich isotherms, and kinetic models were applied. The highest maximum adsorption capacities were 68 mgg-1 for CR at 25 degrees C and 140 mgg-1 for MG at 45 degrees C. Thermodynamic analysis revealed that MG adsorption was spontaneous and endothermic, whereas CR adsorption was exothermic. These results show that MG dye has a higher adsorption capacity (140 mgg-1) compared to CR (68 mgg-1) using chitosan derived from blue crab shells.