Novel kapok pods (Ceiba pentandra (l.) Gaerth) adsorbent and its reusability by transformation on hydrochar with an outstanding adsorptive capacity for Rhodamine B removal

Among the residual biomasses, it can be cited the kapok capsule from Ceiba pentandra (L.) Gaerth, which to this date does not have any application described in the literature. Hence, the present work aims to evaluate the kapok capsule as an adsorbent to remove Rhodamine B dye from aqueous solutions. The material was characterized by SEM, OM, FTIR, XRD, pHPZC and TGA/DTG. The adsorptive performance was evaluated by kinetics, adsorbent mass, adsorbate concentration, aqueous matrix, pH and fixed-bed column. Furthermore, a destination to the material as a hydrochar was proposed, which can also be employed as adsorbent or as part of a soil compost. The morphology of the kapok pod exhibits several pores and functional groups characteristics of lignocellulosic material. The adsorption assays showed strong interactions at natural pH, with a minimal of 71 % RhB removal in batch test, best fitted to a pseudo-second order kinetic model, and, even when using real water under the most severe conditions applied, RhB removal was superior to 59 %. In the fixed bed assays, the overall removal of the pollutant was higher than 54 %. The hydrochar prepared from the residual adsorbent - kapok pod used in the previous adsorption tests - remarkably presented an even higher adsorptive capacity, removing a minimum of 92 % of dye at natural pH. In addition to this exceptional adsorption result, the application of the product to soil did not show acute toxicity towards tomato seeds, which makes the production of hydrochar an excellent alternative to the destination of the kapok pod.