Development of calcium oxide sorbent from waste natural materials for CO2 capture

This study aims to develop calcium oxide (CaO) sorbents for carbon oxide (CO2) capture by using various waste natural materials: eggshells, crab shells, and green mussel shells. These natural materials were used as precursors for the synthesis of CaO sorbents using the citric acid-assisted sol-gel method. Various characterization techniques, including N2 physisorption, XRD, XRF, CO2-TPD, TG/DTG, and FE-SEM, were performed to assess the physicochemical and thermal properties of the synthesized sorbents. The sorbent is investigated for its CO2 adsorption and recycle ability, as it has been a major issue for large-scale deployment of cyclic CO2 capture technology. This study also examined the effect of carbonation temperature between 550 and 750 °C, total gas flow rates from 60 to 100 mL/min, and the stability of the developed CaO sorbent during cyclic CO2 capture. CaO derived from green mussel shells showed the most advantageous porous structure and textural properties for the diffusion of CO2 through the pores and surface layer to enhance the interaction of CO2 and interior CaO particles, promoting the highest CO2 capture capacity compared to that derived from eggshells, crab shells, and commercial CaO, with the maximum CO2 adsorption capacity of 0.69 g-CO2/g-sorbent (or 0.75 g-CO2/g-CaO) at 700 °C and exhibited robust cyclic performance in carbonation/calcination reactions, maintaining a CO2 adsorption capacity of approximately 0.65 g-CO2/g-sorbent (or 0.71 g-CO2/g-CaO) after 20 cycles. The results highlight the excellent resistance of the sorbent to crystallite sintering during the carbonation/calcination reaction sequence. This study also developed hydrogel beads from natural materials composed of bacterial cellulose-activated carbon /montmorillonite/alginate for liquid adsorption and applied for the removal of methylene blue from aqueous solution. The hydrogel beads are prepared by the ionotropic gelation method with calcium chloride used as a cross-linking agent. The developed sorbent showed a remarkable MB adsorption uptake of 678.2 mg/g at pH 7 and 30 °C. The adsorption isotherm showed the best fit for the nonlinear Redlich-Peterson isotherm model. The bead demonstrated easy regeneration with high reusability for around 75% of MB removal after being used for six cycles.