Activated Sawdust-Based Adsorbent for the Removal of Basic Blue 3 and Methylene Green from Aqueous Media

Abstract

Dye pollution is a serious threat to aquatic environment and human health. Although activated carbon is an efficient adsorbent for dye reclamation from effluents, its expressive nature renders its use on large commercial scales. On the other hand, waste biomasses are not effectively used for any beneficial purposes. Sawdust is a waste biomass of wood mills, and due to its small particle sizes, it has the potential to be used as adsorbent. In spite of its uses for cooking purposes, it is sometimes used as adsorbent as such or converted into activated carbon. In raw form, it is not a good adsorbent; however, its adsorption capacity can be increased by applying chemical modifications. In the present study, sawdust of paper mulberry (Broussonetia papyrifera) was used as adsorbent for the removal of basic blue 3 and methylene green from water after chemical modification with NaOH and HCl in 1 : 1. The prepared adsorbent was characterized by SEM and FTIR, whereas the surface area was estimated through an already reported method in literature. Batch experiments were performed to determine the isothermal and kinetic parameters of the selected dyes adsorption on activated sawdust. The effect of adsorbent dosage and temperature on adsorption were also evaluated. The best fit of the kinetic data was achieved with pseudosecond-order model for which $R^2$ values were approximately equal to 1 whereas Langmuir model was most suitable model to explain the isothermal data. The optimum adsorbent dosage was 0.05 g for both of the selected dyes. Different thermodynamic parameters, such as enthalpy ( $∆H=18.5$ and 8.334 kJ/mol respectively for basic blue 3 and methylene green), entropy ( $∆S^{°}=62.41$ and 29.22 kJ/molK respectively for basic blue 3 and methylene green), and Gibbs free energy ( $∆G^{°}=-83.6$ , -410, and -1658 kJ/mol (basic blue)/-65, -519, and -1139 kJ/mol (methylene green), were estimated, and the process was found to be endothermic, spontaneous, and feasible. The increase in $\Delta G^{°}$ with increase in temperature indicates that the adsorption process is favorable at high temperature. The prepared adsorbent could be effectively used in the reclamation of water loaded with other contaminants; however, further experiments are needed to increase the adsorption capacity of the adsorbent.