Single and binary sorption of reactive dyes onto red seaweed-derived biochar: multi-component isotherm and modelling

The ability of Kappaphycus alvarezii-derived biochar (KAB) to adsorb Reactive blue 4 (RB4) and Reactive orange 16 (RO16) in mono-and binary contaminated waters have been investigated. KAB, produced at 350 degrees C and 2 h through pyrolysis, exhibited dye sorption capacities 3.1 times higher than raw K. alverzii. The surface of biochar was analysed through FT-IR and SEM results. The pH edge experimental trails indicated that electrostatic attraction between biochar surface and reactive dye anions was favoured under acidic conditions. Biosorption isotherm experiments revealed that in mono-dye solutions, KAB excelled in RB4 sorption with highest experimental uptake of 0.324 mmol/g, compared to RO16 uptake of 0.140 mmol/g. In binary solutions, RO16 sorption capacity of KAB was inhibited by 68.5% in the presence of RB4; whereas RB4sorption capacity was slightly better. This inhibition effect is due to combination of several factors, and the crucial factor being the reactivity of the two dyes. Mono and binary Freundlich and Langmuir equations successfully described the single and binary RB4-RO16 sorption isotherms with high accuracy.