Modelling Selective CO2 Absorption and Validation via Photosynthetic Bacteria and Chemical Adsorbents for Methane Purification in Anaerobic Fermentation Bioreactors.

This study delves into advanced methane purification techniques within anaerobic fermentation bioreactors, focusing on selective CO2 absorption and comparing photosynthetic bacteria (PNSB) with chemical adsorbents. Our investigation demonstrates that MgO-Mg(OH)2 composites exhibit remarkable CO2 selectivity over CH4, substantiated through rigorous bulk and surface modelling analyses. To address the challenges posed by MgCO3 shell formation on MgO particles, hindering CO2 transport, we advocate for the utilisation of MgO-Mg(OH)2 composites. In on-site experiments, these composites, particularly saturated MgO-Mg(OH)2 solutions (S2), achieved an astonishing 100% CO2 removal rate within a single day while preserving CH4 content. In contrast, solid MgO powder (S3) retained a mere 5% of CH4 over a 10 h period. Although PNSB (S1) exhibited slower CO2 removal, it excelled in nutrient recovery from anaerobic effluent. We introduce a groundbreaking hybrid strategy that leverages S2's swift CO2 removal and S1 PNSB's nutrient recovery capabilities, potentially resulting in a drastic reduction in bioreactor processing time, from 10 days when employing S1 to just 1 day with the use of S2. This represents a remarkable efficiency improvement of 1000%. This pioneering strategy has the potential to revolutionise methane purification, enhancing both efficiency and sustainability. Importantly, it can be seamlessly integrated into existing bioreactors through an additional CO2 capture step, offering a promising solution for advancing biogas production and promoting sustainable waste treatment practices.

Enhancing MgO efficiency in CO2 capture: engineered MgO/Mg(OH)2 composites with Cl-, SO42-, and PO43- additives.

The formation of a MgCO3 shell hampers CO2 capture efficiency in MgO. Our previous studies developed MgO/Mg(OH)2 composites to facilitate CO2 diffusion, improving capture efficiency. However, MgCO3 still formed along the interfaces. To tackle this issue, we engineered the MgO/Mg(OH)2 interfaces by incorporating Cl-, SO42-, and PO43- additives. Novel MgO-H2O-MgX (X = Cl-, SO42-, and PO43-) composites were synthesized to explore the role of additives in preventing MgCO3 formation. MgO-Mg(OH)2-MgCl2 nano-composites displayed enhanced CO2 adsorption and stability. This breakthrough paves the way for effective bio-inspired strategies in overcoming CO2 transport barriers in MgO-based adsorbents.

Bioinspired bi-phasic 3D nanoflowers of MgO/Mg(OH)2 coated melamine sponge as a novel bactericidal agent.

By roughly mimicking the surface architectural design of dragonfly wings, novel bi-phasic 3D nanoflowers of MgO/Mg(OH)2 were successfully synthesized via the electrospinning technique. The 3D nanoflowers were coated over a commercial melamine sponge and extensively characterized by SEM, XRD, FTIR, and EDS. The formation of distinct dense 3D nano petals was revealed by SEM images whereby the mean petal thickness and mean distance between the adjacent petals were found to be 36 nm and 121 nm, respectively. The bactericidal activities of synthesized 3D nano-flowers coated melamine sponges were assessed against five different bacteria (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa). This study demonstrated significant bactericidal activity of MgO/Mg(OH)2 3D nanoflowers coated MS against Gram-positive and Gram-negative bacteria. Plausible bactericidal mechanisms include envelope deformation, penetration, and induction of oxidative stress. This study introduces novel bioinspired biomaterial with the capacity to reduce the risk associated with pathogenic bacterial infections, especially in medical devices.

Counter-Intuitive Magneto-Water-Wetting Effect to CO2 Adsorption at Room Temperature Using MgO/Mg(OH)2 Nanocomposites.

MgO/Mg(OH)2-based materials have been intensively explored for CO2 adsorption due to their high theoretical but low practical CO2 capture efficiency. Our previous study on the effect of H2O wetting on CO2 adsorption in MgO/Mg(OH)2 nanostructures found that the presence of H2O molecules significantly increases (decreases) CO2 adsorption on the MgO (Mg(OH)2) surface. Furthermore, the magneto-water-wetting technique is used to improve the CO2 capture efficiency of various nanofluids by increasing the mass transfer efficiency of nanobeads. However, the influence of magneto-wetting to the CO2 adsorption at nanobead surfaces remains unknown. The effect of magneto-water-wetting on CO2 adsorption on MgO/Mg(OH)2 nanocomposites was investigated experimentally in this study. Contrary to popular belief, magneto-water-wetting does not always increase CO2 adsorption; in fact, if Mg(OH)2 dominates in the nanocomposite, it can actually decrease CO2 adsorption. As a result of our structural research, we hypothesized that the creation of a thin H2O layer between nanograins prevents CO2 from flowing through, hence slowing down CO2 adsorption during the carbon-hydration aging process. Finally, the magneto-water-wetting technique can be used to control the carbon-hydration process and uncover both novel insights and discoveries of CO2 capture from air at room temperature to guide the design and development of ferrofluid devices for biomedical and energy applications.

Morphology Design and Fabrication of Bio-Inspired Nano-MgO-Mg(OH)2 via Vapor Steaming to Enable Bulk CO2 Diffusion and Capture.

The absorption of CO2 on MgO is being studied in depth in order to enhance carbon engineering. Production of carbonate on MgO surfaces, such as MgCO3, for example, has been shown to hinder further carbon lattice transit and lower CO2 collecting efficiency. To avoid the carbonate blocking effect, we mimic the water harvesting nano-surface systems of desert beetles, which use alternate hydrophobic and hydrophilic surface domains to collect liquid water and convey condensed droplets down to their mouths, respectively. We made CO2-philic MgO and CO2-phobic Mg(OH)2 nanocomposites from electrospun nano-MgO by vapor steaming for 2-20 min at 100 °C. The crystal structure, morphology, and surface properties of the produced samples were instrumentally characterized using XRD, SEM, XPS, BET, and TGA. We observed that (1) fiber morphology shifted from hierarchical particle and sheet-like structures to flower-like structures, and (2) CO2 capture capacity shifted by around 25%. As a result, the carbonate production and breakdown processes may be managed and improved using vapor steaming technology. These findings point to a new CO2 absorption technique and technology that might pave the way for more CO2 capture, mineralization, and fuel synthesis options.

Engineering Electronic Structure and Band Alignment of 2D Mg(OH)2 via Anion Doping for Photocatalytic Applications.

The wide bandgap of 2D Mg(OH)2 inhibits its applications in visible-light photocatalytic applications. Besides, its mismatched band alignment to the redox potential of O2/H2O, brings about low efficacy of water-splitting performance. Therefore, to release the powder of 2D Mg(OH)2 in photocatalytic research, we explore anion doping strategies to engineer its electronic structure. Here, anion doping effects on electronic properties of 2D Mg(OH)2 are investigated by using DFT calculations for seven dopants (F, Cl, S, N, P, SO4, and PO4). We found (1) S, N and P doping remarkably reduces its band gap from 4.82 eV to 3.86 eV, 3.79 eV and 2.69 eV, respectively; (2) the band gap reduction is induced by the electron transfer to the dopant atoms; (3) F, Cl, SO4, and PO4 doping shifts its valence band to be lower than the oxidation potential of O2/H2O to render its band structure appropriate for photocatalytic water splitting. These results suggest that not only electrical conductivity of 2D Mg(OH)2 can be increased but also their band structure be aligned by using the proposed anion doping strategy. These results enable a new photocatalytic materials design approach while offering exciting possibilities in applications of high-current electrolysis, chemical gas sensing, and photocatalysis.

Synthesis, characterization, CO2 mineralization in air, and thermal decomposition of nano- C8H10MgO10·4H2O powder.

Effective solutions for efficient carbon dioxide (CO2) capture in air at room temperature are in high demand due to the major impacts CO2 has on global climatic changes. Solid adsorbents materials for CO2 capture received great attention over the past years, among them, magnesium-based sorbents have been identified as a promising solution for CO2 capture at intermediate temperatures. This study reports for the first time (1) the synthesis of monoclinic magnesium malate tetrahydrate by combining electrospinning and aging processes, and (2) its room temperature CO2 adsorption and mineralization in air. Commercial magnesium hydroxide (Mg(OH)2) powder was used as raw material in the synthesis of magnesium carbonate hydrates (MCH), by three processes; (1) direct calcination, (2) electrospinning and calcination, and (3) electrospinning, calcination, and aging (at room temperature and in air to incubate CO2 mineralization). The synthesized powder samples were characterized thoroughly using XRD, SEM, EDS, and TGA analyses. Effects of calcination temperature/aging time on CO2 adsorption (at room temperature), crystallization, and mineralization of MCH were studied. Interestingly, the results showed that the 6-month aged samples (via the third synthesis process above), recorded a CO2 adsorption capacity of 15.5 wt% within 90 min at 30 °C. Subsequently, three novel mechanisms of thermal decomposition CO2 adsorption/mineralization were proposed, and a theoretical upper limit of carbon saving potentials was estimated, i.e., 8 mol CO2 per 1 mol MgO. This work provides a novel CO2 mineralization approach that results in (1) effective and practical solutions of carbon dioxide (CO2) emission management and which holds (2) great potential for novel carbon-based fuels development.