Unexpected Magnesium Oxide/Calcium Sulfide Barnacle-like Structures derived from Pyrolysed Carrageenans

The production of unexpected magnesium oxide/calcium sulfide barnacle-like structures from pyrolysed carrageenan is reported. The pyrolysis of the precursor aerogel, sans dopants, activating agents, or templates, afforded sulfur-rich (3.9-7.6%) mesoporous chars (BJH P.V. 0.15-0.18 cm3 g-1; 250-290 m2 g-1). Carbothermic reduction of inherent sulfate salts yielded unique magnesium oxide/calcium sulfide barnacle-like structures (0.94 ± 0.34 µm diameter) decorating the char surface. Eruption of CO2 in a volcano-like mechanism from MgO/CaS shells produced cavities affording barnacle-like structures. The chars at 800 °C (C800) were effective as copper(II) adsorbents (Qe, 120 mg g-1). Chemical precipitation of copper(II) hydroxy salts at barnacle sites exhibited pseudo-second order rate kinetics (k2, 8.4x10-5 g mg-1 min-1) and Freundlich adsorption characteristics (R2, 0.894). These unique seaweed-derived materials potentially offer a sustainable solution to critical metal recovery.