Bixin as a new class of biosorbent for Hg2+ removal from aqueous solutions

In this study, the apocarotenoid bixin was investigated as a potential biosorbent for Hg2+ in aqueous solutions. Bixin was used to form a thin film on an inert support using the drop-coating technique. This film was characterised using ATR-FTIR, SEM, and TGA-DTG techniques. Parameters that influence adsorption, such as pH, temperature, NaCl concentration, salt type, bixin mass, and supports for the bixin film, were evaluated. Using 0.112 mg of a bixin covering on a cellulose filter, the sorbent material was able to remove 75 % of Hg2+ from a 2.0 mL, 0.3 mg g−1, pH 6.00, 25 °C solution after 180 min of contact. Kinetics studies were carried out between 5 and 1440 min, and the pseudo-first-order adsorption model was applied. Equilibrium isotherm data were analysed, and the best fit was for the non-linear Freundlich model, with an R2 of 0.9868, RMSE of 0.37, and maximum sorption capacity of 85.38 mg g−1 obtained by the Langmuir model. The bixin film was applied in spiked environmental samples (lake and mining effluent), and it achieved 86 % Hg2+ removal. The results show that the bixin film is a suitable alternative for efficiently removing mercury from various aqueous systems. This introduces a new class of biosorbent based on apocarotenoids, which are sustainable, low cost, nontoxic, and easily obtainable.