The performance of carbons produced from the cold-pressed cake of Raphanus sativus (L. var.), a residue from the biodiesel industry, was evaluated for the adsorption of methylene blue (MB) from synthetic aqueous solutions. The study has focused on the following three topics: (i) physical and textural characterization of the carbon, (ii) batch investigation of equilibrium and kinetics of MB adsorption at room temperature, and (iii) analysis of MB adsorption mechanism onto such carbonaceous structures. Regarding the fi rst topic, carbon was characterized using several methods such as Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), scanning electron microscopy (SEM), and Raman spectroscopy. A microporous carbon was found thus indicating that MB adsorption may occur predominantly at the surface of the carbon. Regarding the second topic, equilibrium tests revealed that Langmuir-based maximum MB uptake capacity was 19.8 mg g -1 and that MB kinetics onto carbon was best described by a pseudo second-order model. Data fi tting analysis confi rmed that MB adsorption onto such carbons was predominantly superfi cial. And fi nally, regarding the third topic, MB adsorption may probably occur by bonding of monomer MB through the central nitrogen atom of its molecule and through sulfur atom while MB bonding through amino nitrogen atom does not seem probable. The study reveals that carbons made of R. sativus are suitable materials for the removal of dyes from aqueous solutions, mainly if fi ner fraction of carbons is used, because MB adsorption was found to be predominantly superfi cial.

In this study, an adsorbent produced from Raphanus sativus (L. var.), a residue from the biodiesel industry, was investigated for the removal of methylene blue (MB) from textile effluents aiming to: (i) obtain physical and textural characteristics of the given carbon, and (ii) understand the MB adsorption mechanism onto such carbonaceous structures. The following methods were employed: SEM-EDS microscopy, gas adsorption and Raman spectroscopy. Physical and textural characteristics of the carbon obtained by classical methodologies such as BET, BJH and SEM analyses were corroborated by the Raman analysis. For the experimental conditions used on the preparation of the activated carbon of Raphanus sativus, the main physical parameters measured were specific surface area (236.3 m 2 .g -1 ), total pore volume (0.06 cm 3 .g -1 ) and average pore size (1.4 nm). SEM and Raman analysis revealed that a microporous structure of carbon was obtained as the ratio between the disorder band and the graphite band was higher than unity, thus indicating that MB adsorption may occur predominantly at the surface of the adsorbent, given that the diameter of MB molecule was estimated to be nearly 1.5 nm. Raman analysis of solid MB revealed that MB molecules are predominantly found as dimmers in the solid however they are adsorbed as monomer in the Raphanus sativus carbon. MB through the central nitrogen atom of its molecule; MB bonding through sulfur atom may also occur but at lesser intensity while MB bonding through amino nitrogen atom does not seem probable.