Evaluation of Sapucaia (Lecythis pisonis Cambess) Shell as a Natural Biosorbent for Chloroquine Removal in Sustainable Water Treatment

Chloroquine (CQN) is a persistent emerging contaminant whose environmental footprint expanded significantly following its large-scale and off-label use during the SARS-CoV-2 pandemic. Conventional water treatment systems do not effectively remove CQN, and its accumulation in aquatic environments poses risks to ecological balance and public health. This study reports, for the first time, the use of Sapucaia (Lecythis pisonis Cambess) shell powder (SPC), an underexplored agro-industrial residue native to the Amazon region and Atlantic Forest, as a biosorbent for CQN removal from aqueous solutions. Physicochemical characterisation revealed a predominantly amorphous material with a strongly negative surface and abundant carboxylic, phenolic, and hydroxyl groups, providing favourable sites for interactions with CQN. Adsorption kinetics were best described by the pseudo-second-order model (R2 = 0.966), while the Weber–Morris model indicated a three-stage mass-transfer process. Isotherm analysis showed comparable fits for the Langmuir and Freundlich models, with a maximum experimental adsorption capacity of 97.26 mg g−1 and a Langmuir-fitted qmax of 293.69 mg g−1, both at 298 K. Post-adsorption zeta potential measurements showed a marked neutralisation of the surface charge, supporting the contribution of electrostatic attraction to CQN uptake. After four adsorption–desorption cycles at 26.05 mg L−1 using water as the sole desorbent, SPC retained approximately 65% of its initial adsorption capacity, although lower retention was observed at higher adsorbate loadings. Overall, these findings highlight SPC as a low-cost and environmentally friendly biosorbent with promising potential for sustainable water treatment.