Mesoporous magnesium oxide nanoparticles derived via complexation-combustion for enhanced performance in carbon dioxide capture

A sustainable and economical solution for CO2 capture with biobased carbon materials derived from palm kernel shells

This study investigates the synthesize of activated carbon for carbon dioxide adsorption using palm kernel shell (PKS), a by-product of oil palm industry. The adsorbent synthesis involved a simple two-step carbonization method. Firstly, PKS was activated with potassium oxide (KOH), followed by functionalization with magnesium oxide (MgO). Surface analysis revealed that KOH activated PKS has resulted in a high specific surface area of 1086 m2/g compared to untreated PKS (435 m2/g). However, impregnation of MgO resulted in the reduction of surface area due to blockage of pores by MgO. Thermogravimetric analysis (TGA) demonstrated that PKS-based adsorbents exhibited minimal weight loss of less than 30% up to 500 °C, indicating their suitability for high-temperature applications. CO2 adsorption experiments revealed that PKS-AC-MgO has achieved a higher adsorption capacity of 155.35 mg/g compared to PKS-AC (149.63 mg/g) at 25 °C and 5 bars. The adsorption behaviour of PKS-AC-MgO was well fitted by both the Sips and Langmuir isotherms, suggesting a combination of both heterogeneous and homogeneous adsorption and indicating a chemical reaction between MgO and CO2. Thermodynamic analysis indicated a spontaneous and thermodynamically favourable process for CO2 capture by PKS-AC-MgO, with negative change in enthalpy (- 0.21 kJ/mol), positive change in entropy (2.44 kJ/mol), and negative change in Gibbs free energy (- 729.61 J/mol, - 790.79 J/mol, and - 851.98 J/mol) across tested temperature. Economic assessment revealed that the cost of PKS-AC-MgO is 21% lower than the current market price of commercial activated carbon, indicating its potential for industrial application. Environmental assessment shows a significant reduction in greenhouse gas emissions (381.9 tCO2) through the utilization of PKS-AC-MgO, underscoring its environmental benefits. In summary, the use of activated carbon produced from PKS and functionalised with MgO shows great potential for absorbing CO2. This aligns with the ideas of a circular economy and sustainable development.

Magnesium Oxide/Poly(l-lactide-co-ε-caprolactone) Scaffolds Loaded with Neural Morphogens Promote Spinal Cord Repair through Targeting the Calcium Influx and Neuronal Differentiation of Neural Stem Cells

Because of the limited regenerative ability of the central nervous system (CNS), effective treatments for spinal cord injury (SCI) are still lacking. After SCI, neuron loss and axon regeneration failure often result in irreversible functional impairment. The calcium overload induced by the N-methyl-D-aspartate receptor (NMDAR) overactivation is critical for cell death in SCI. It has been reported that the magnesium ion (Mg2+ ) can competitively block the NMDAR and reduce the calcium influx, and that sonic hedgehog (Shh) and retinoic acid (RA) are the critical regulators of neuronal differentiation of endogenous neural stem cells (NSCs). Here, magnesium oxide (MgO)/poly (l-lactide-co-ε-caprolactone) (PLCL) scaffold loaded with purmorphamine (PUR, a Shh signaling agonist) and RA is developed and its feasibility in SCI repair is tested. The results showed that the Mg2+ released from MgO attenuated cell apoptosis by blocking the calcium influx, and the PUR/RA promoted the recruitment and neuronal differentiation of endogenous NSCs, thereby reducing the glial scar formation at the SCI lesion site. Furthermore, implantation of PUR/RA-loaded MgO/PLCL scaffold facilitates the partial recovery of a locomotor function of SCI mouse in vivo. Together, findings from this study imply that PUR/RA-loaded MgO/PLCL scaffold may be a promising biomaterial for the clinical treatment of SCI.

Assessing CO2 Adsorption on Amino-Functionalized Mesocellular Foams Synthesized at Different Aging Temperatures

A wide variety of solid sorbents has recently been synthesized for application in CO2 adsorption. Among them, mesoporous silicas deserve attention because of their ability to accommodate large concentrations of different chemicals as a consequence of their surface chemistry and tunable pore structure. Functionalized materials exhibit promising features for CO2 adsorption at high temperatures and low CO2 concentrations. This work aimed to assess the influence of the textural properties on the performance of CO2 adsorption on functionalized mesoporous silica. With this goal, several mesoporous silica foams were synthesized by varying the aging temperature, obtaining materials with larger pore diameter. Thus, the synthesized materials were functionalized by grafting or impregnation with 3-aminopropyltriethoxysilane, polyethylenimine, and tetraethylenepentamine as amine sources. Finally, the amino functionalized materials were assessed for CO2 capture by means of equilibrium adsorption isotherms at 25, 45, and 65°C. Among the most outstanding results, high aging temperatures favor the performance of impregnated materials by exposing greater pore diameters. Low or intermediate temperatures favor grafting by preserving an appropriate density of silanol groups.

Mg-Ion Inversion in MgO@MgO-Al2 O3 Oxides: The Origin of Basic Sites

Although MgO-Al₂ O₃ is well known as having a spinel structure, the inversion of which occurs by exchange of the trivalent (Al³⁺ ) and divalent (Mg²⁺ ) cations, little analytical study of the degree of inversion has been carried out. This study concerns a simple methodology to identify the inversion by solid-state NMR spectroscopy, whereby its correlation with the CO₂ capture capacity of MgO-rich MgO@MgO-Al₂ O₃ spinel structures is verified. Through ²⁷ Al and ²⁵ Mg NMR spectroscopy, temperature-programmed CO₂ desorption, and thermogravimetric analysis, higher inversion is found to occur at low Mg/Al ratios and the inversion is found to decrease as the Mg/Al ratio increases. Moreover, the degree of inversion correlates with CO₂ sorption, which is associated with the medium-strength basic sites induced by formation of the unsaturated O^2- species. These results will open new pathways to exploit defects in complex oxides beyond spinels and their derivatives for desired applications. This demonstration of MgO-Al₂ O₃ for CO₂ sorption can contribute to the design of future CO₂ sorbents.

Stabilization of NaNO3-Promoted Magnesium Oxide for High-Temperature CO2 Capture

NaNO₃-promoted MgO sorbents are known to achieve enhanced CO₂ sorption uptake but fail to maintain their capacity after multiple sorption-regeneration cycles. In this study, commercially available hydrotalcites (Pural Mg30, Pural Mg70, and synthetic hydrotalcite) were used as stabilizers for NaNO₃-impregnated MgO (MgONaNO₃) sorbents to improve their cyclic stability. Results show that the Mg30-stabilized MgONaNO₃ attained higher and stable overall CO₂ sorption performance as compared to bare MgONaNO₃ after multiple sorption cycles. XRD analyses reveal that the hydrotalcites act as templates for MgCO₃ by restricting the formation of large and nonuniform product crystallites. Furthermore, CO₂-TPD results show that the hydrotalcites cause a change in the basic sites of the sorbent, which may be attributed to its high interaction with both MgO and NaNO₃. This interaction becomes stronger as cycles proceed due to the structural rearrangements occurring, thus contributing to the stable behavior of the sorbents. However, these characteristics were not found on MgONaNO₃ and the α-Al₂O₃-stabilized samples, thus proving the unique ability of hydrotalcites. From these results, we then derived the formation scheme of MgCO₃ on the hydrotalcite-stabilized sorbents. This study presents a simple yet effective method of improving the stability of molten salt-promoted sorbents with promising potential for industrial use.

Enhanced CO₂ Adsorption by Nitrogen-Doped Graphene Oxide Sheets (N-GOs) Prepared by Employing Polymeric Precursors

Nitrogen-doped graphene oxide sheets (N-GOs) are prepared by employing N-containing polymers such as polypyrrole, polyaniline, and copolymer (polypyrrole-polyaniline) doped with acids such as HCl, H₂SO₄, and C₆H₅-SO₃-K, which are activated using different concentrations of KOH and carbonized at 650 °C; characterized using SEM, TEM, BET, TGA-DSC, XRD, and XPS; and employed for the removal of environmental pollutant CO₂. The porosity of the N-GOs obtained were found to be in the range 1-3.5 nm when the KOH employed was in the ratio of 1:4, and the XRD confirmed the formation of the layered like structure. However, when the KOH employed was in the ratio of 1:2, the pore diameter was found to be in the range of 50-200 nm. The SEM and TEM analysis reveal the porosity and sheet-like structure of the products obtained. The nitrogen-doped graphene oxide sheets (N-GOs) prepared by employing polypyrrole doped with C₆H₅-SO₃-K were found to possess a high surface area of 2870 m²/g. The N-GOs displayed excellent CO₂ capture property with the N-GOs; PPy/Ar-1 displayed ~1.36 mmol/g. The precursor employed, the dopant used, and the activation process were found to affect the adsorption property of the N-GOs obtained. The preparation procedure is simple and favourable for the synthesis of N-GOs for their application as adsorbents in greenhouse gas removal and capture.