ZnO@ activated carbon derived from wood sawdust as adsorbent for removal of methyl red and methyl orange from aqueous solutions

Abstract

Activated carbon (AC) and ZnO@AC composite derived from wood sawdust were prepared to be utilized as adsorbents for methyl red (MR) and methyl orange (MO) anionic dyes from the aqueous solutions. The maximum adsorption capacity of the AC and ZnO@AC composite toward both dyes was achieved in the strong acidic medium (pH = 3), and under stirring for 60 min. The kinetic studies revealed that the adsorption of MR and MO dyes onto the AC and ZnO@AC composite fitted well with the pseudo-second-order model. Furthermore, the intraparticle diffusion and Elovich kinetic models confirmed the adsorption is controlled by external surfaces, and the adsorption is chemisorption process. The isotherm results indicated that the MR and MO dye adsorption occurred via monolayer adsorption, and the estimated maximum adsorption capacities of both dyes onto the ZnO@AC composite were higher than those achieved by AC. Thermodynamic analysis suggested that the adsorption is endothermic and spontaneous. The mechanism for MR, and MO dyes adsorption onto the AC and ZnO@AC composite is proposed to be controlled by electrostatic bonding, π–π interactions, and ion exchange, while H-bonding and n–π interactions were minor contributors. This study reveals the potential use of carbon-based adsorbents derived from wood sawdust for the removal of anionic dyes from wastewater.