Amorphous cellulose from dinoflagellates: A new microalgal platform for the removal of heavy metals (Cd, Ni, and Pb) from aqueous solution.

The removal of heavy metals (HMs) from water is one of the primary challenges of the world. Environmentally friendly and efficient natural adsorbents are needed as an alternative to conventional products. This work explores the biosorbent potential of hierarchically structured cellulose thecal plates (CTPs) from dinoflagellates. In a proof-of-principle study, dinoflagellate - Peridinium sp. and Prorocentrum micans-derived CTPs was utilised for the removal of Cd2+, Ni2+, and Pb2+ from aqueous solutions. The effect of several parameters, such as pH, temperature, adsorbent, and sorbate dosage was analysed. Adsorption efficiency and capacity were determined using ICP-OES. The sorbate distribution was analysed using SEM-EDX. In addition, the biosorption thermodynamics (Langmuir vs. Freundlich) and kinetics (pseudo-1st, pseudo-2nd, and intraparticle diffusion) and reusability was analysed. The results show that dinoflagellate-derived CTP is an effective adsorbent for HMs, exhibiting an outstanding adsorption efficiency (~100% at RT, 60 min) without the need for additional surface modification. After biosorption, CTPs can be easily separated from the solution via sedimentation or sieving. At sorbate concentration ≥100 mg/L, nucleation of crystalline CdCO3 was observed due to supersaturation. XPS and FTIR data indicate that the adsorption of HMs occurs primarily via the surface -OH groups of the CTPs. HMs adsorption on CTPs follows the Freundlich isotherm and pseudo-2nd-order kinetics. After only 3 regeneration cycles, ~85% desorption efficiency was achieved. The use of dinoflagellate CTPs for biosorption offers a number of advantages, such as rapid adsorption and lower desorption cycles, which makes it an energy-efficient and sustainable alternative to other adsorbents.