Activated Carbons Derived from Brewing Cereal Residues and Pineapple Peelings for Removal of Acid Orange 7 (AO7) Dye.

Abstract

The tremendous increase in agro-industrial waste poses major environmental problems and highlights the need for innovative, sustainable solutions. One promising solution would be converting these organic wastes, such as unvalued pineapple peels (ANA) and brewer's grains (ECB), into activated carbons to meet the impending challenge of wastewater treatment. In particular, Acid Orange 7 (AO7) is one of the most widely used synthetic dyes, a significant portion of which ends up in water, posing environmental and health problems with limiting decentralized and cost-effective solutions. To address these two challenges, we investigated the best conditions for converting these organic wastes into alternative activated carbons (named CA-ANA and CA-ECB) for AO7 dye removal under representative adsorption conditions. Extensive characterization (SEM, EDX, XRD, BET) revealed an amorphous, mesoporous structure with specific surface areas of 1150-1630 m² g^-1, outperforming the majority of other biomass-derived activated carbons reported for AO7 removal. Adsorption followed pseudo-second-order kinetics and the Langmuir isotherm, with record AO7 removal efficiencies of 90-99% for AO7 concentrations of 25-35 mg L^-1 in a batch reactor, the driving forces being electrostatic attraction, π-π interactions, and hydrogen bonding. These results undoubtedly highlight the potential of current waste-derived activated carbons as sustainable solutions for efficient wastewater treatment.