Unexpected magnesium oxide/calcium sulfide barnacle-like structures derived from pyrolysed carrageenans

Abstract

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 (Q_e, 120 mg g⁻¹). Chemical precipitation of copper(II) hydroxy salts at barnacle sites exhibited pseudo-second order rate kinetics (k₂, 8.4 × 10–5 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.