Facile synthesis of eco-friendly activated carbon from leaves of sugar beet waste as a superior nonconventional adsorbent for anionic and cationic dyes from aqueous solutions

Abstract

The current study presents a unique and innovative approach to sustainable activated carbon (AC) synthesis using non-conventional agricultural wastes, leaves of sugar beet (LSB), via a thermo-chemical activation process. This approach not only offers a sustainable solution for LSB elimination, but also provides an eco-friendly alternative to commercially available activated carbon. The thermo-chemical activation process was conducted at various ratios of H3PO4 / LSB (0.5:1, 1:1, 2:1, and 3:1 w/w ratios) at a fixed temperature (550 °C/2h). The unique amorphous nature, porous structure, BET surface area (SBET = 700.7 m2/g), and surface chemistry nominated the synthesized AC at 2:1 ratio as a superior adsorbent material for methyl orange, MO, and methylene blue, MB, from standard solutions in the batch system at different experimental conditions. Kinetic investigations revealed that the pseudo-second order equation explained the sorption data well. In contrast, intra-particle diffusion was not the only limiting stage in the adsorption of the addressed dyes. Similarly, the linear Langmuir equation described the adsorption data of the investigated dyes better than Freundlich one with maximum removal capacity (qmax) of 185.2 and 140.8 mg/g for MB and MO, orderly. This confirms the homogenous/monolayer nature of the adsorbed ions through isoenergetic active sites upon the AC(2:1) surface. Furthermore, the electrostatic attraction was not the only leading mechanism of adsorption of both dyes, but substantial participations by hydrophobic hydrogen-bonding forces may be considered.

Keywords

• Sugar beet leaves waste
• Thermo-chemical activation
• Active carbon
• Methylene blue
• Methyl orange