Activated biochar derived from cactus fibres – Preparation, characterization and application on Cu(II) removal from aqueous solutions

The adsorption efficiency of activated biochar prepared from cactus fibres regarding the removal of Cu(II) from aqueous solutions has been investigated as a function of various physicochemical parameters (e.g. pH, initial metal concentration, ionic strength, temperature and contact time). Activation of the biochar took place using nitric acid oxidation and characterisation was performed by SEM analysis, FTIR spectroscopy, N2 adsorption and acid–base titrations. The results show that laminar structures constitute the material and carboxylic moieties are the predominant binding sites. The experimental data were analyzed by the Langmuir, Freundlich and Dubinin–Radushkevich adsorption models and the monolayer adsorption capacity was found to be 3.5 mol kg−1. The effect of ionic strength and temperature on the adsorption efficiency indicates that at low pH outer-sphere and at near neutral pH inner-sphere complexes are the predominant surface species and the kinetic data obtained were fitted very well by the Lagergren rate expression.