Carbon Dioxide Capture Adsorbents: Chemistry and Methods

Tannin-derived micro-mesoporous carbons prepared by one-step activation with potassium oxalate and CO2

Micro-mesoporous carbons (MMCs) were successfully prepared using natural polyphenolic compounds, condensed tannins, and glyoxal, a nontoxic aldehyde, in lieu of synthetic phenolic compounds like formaldehyde and resorcinol as carbon precursors. Such MMCs were fabricated by a soft-templating strategy under mild conditions. Porosity development was achieved by varying the amount of potassium oxalate as an in-situ activator coupled with one-step CO₂ activation at 700 °C. This strategy allowed for the enhancement of microporosity as well as retention of the uniform mesoporous structure of the carbons. The CO₂ uptakes of 5.2 mmol/g at 0 °C and 3.6 mmol/g at 25 °C were achieved at 1 bar pressure for the tannin-derived activated MMC sample with a surface area of 1192 m²/g, a volume of fine micropores (sizes below 1 nm) of 0.33 cm³/g, and a mesopore volume of 0.49 cm³/g. This study opens new opportunities for a facile and green synthesis of MMCs from less toxic precursors with tailored porosity by synergistic effects of chemical and physical activation. The resulting MMCs exhibit the potential applicability not only as CO₂ sorbents but also in other environmental applications such as adsorption of organic volatile compounds and dye molecules, which require slightly larger pores.

Feasibility of CO2 Capture from O2-Containing Flue Gas Using a Poly(ethylenimine)-Functionalized Sorbent: Oxidative Stability in Long-Term Operation

Amine-functionalized sorbents are investigated widely for CO₂ capture from flue gas, to mitigate the crisis of global CO₂ emission, with the advantages of excellent adsorption and regeneration performance. However, the presence of O₂ in flue gas (3-10%) would induce the degradation of the sorbents, and some previous works proposed the strategies at the sacrifice of partial CO₂ adsorption capacity. Herein, we focused on the oxidation behavior of PEI-functionalized silica in the long-term operation and analyzed the degradation mechanism by characterizing the oxidized sorbents. The sorbent proved to be oxidative stable under a lower temperature of air exposure, but the oxidative degradation would indeed occur at more harsh temperatures (above 90 °C). This study demonstrated that CO₂ capture from O₂-containing flue gas was feasible by controlling the operating temperature (below 75 °C), and the effective capacity of above 135 mg/g could be maintained in the cyclic CO₂ capture.

Carbon Dioxide Capture from Flue Gas Using Tri-Sodium Phosphate as an Effective Sorbent

Fossil fuels are dominant as an energy source, typically producing carbon dioxide (CO2) and enhancing global climate change. The present work reports the application of low-cost tri-sodium phosphate (TSP) to capture CO2 from model flue gas (CO2 + N2) mixture, in a batch mode and fixed-bed setup. It is observed that TSP has a high CO2 capture capacity as well as high CO2 selectivity. At ambient temperature, TSP shows a maximum CO2 capture capacity of 198 mg CO2/g of TSP. Furthermore, the CO2 capture efficiency of TSP over a flue gas mixture was found to be more than 90%. Fresh and spent materials were characterized using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and Fourier transformed infrared spectroscopy (FTIR). Preliminary experiments were also conducted to evaluate the performance of regenerated TSP. The spent TSP was regenerated using sodium hydroxide (NaOH) and its recyclability was tested for three consecutive cycles. A conceptual prototype for post-combustion CO2 capture based on TSP material has also been discussed.

Synthesis of Porous Organic Polymers with Tunable Amine Loadings for CO2 Capture: Balanced Physisorption and Chemisorption

The cross-coupling reaction of 1,3,5-triethynylbenzene with terephthaloyl chloride gives a novel ynone-linked porous organic polymer. Tethering alkyl amine species on the polymer induces chemisorption of CO₂ as revealed by the studies of ex situ infrared spectroscopy. By tuning the amine loading content on the polymer, relatively high CO₂ adsorption capacities, high CO₂-over-N₂ selectivity, and moderate isosteric heat (Q_st) of adsorption of CO₂ can be achieved. Such amine-modified polymers with balanced physisorption and chemisorption of CO₂ are ideal sorbents for post-combustion capture of CO₂ offering both high separation and high energy efficiencies.

Hierarchical Porous and Zinc-Ion-Crosslinked PIM-1 Nanocomposite as a CO2 Cycloaddition Catalyst with High Efficiency

CO₂ cycloaddition to epoxides is an effective and economical utilization method to alleviate the current excessive CO₂ emission situation. The development of catalysts with both high catalytic efficiency and high recyclability is necessary but challenging. In this context, a heterogeneous catalyst was synthesized based on a zinc-ion-crosslinked polymer with intrinsic microporosity (PIM-1). The high microporosity of PIM-1 promoted a high Zn²⁺ loading rate. Additionally, the relatively stable ionic bond formed between Zn²⁺ and the PIM-1 framework through electrostatic interaction ensured high loading stability. In the process of CO₂ cycloaddition with propylene epoxide, an optimized conversion of 90 % with a turnover frequency as high as 9533 h^-1 could be achieved within 0.5 h at 100 °C and 2 MPa. After 15 cycles, the catalytic efficiency did not demonstrate a significant decline, and the catalyst was able to recover most of its activity after Zn²⁺ reloading. This work thereby provides a strategically designed CO₂ conversion catalyst based on an ionic crosslinked polymer with intrinsic microporosity.

Effects of Alkali Metal (Li, Na, and K) Incorporation in NH₂⁻MIL125(Ti) on the Performance of CO₂ Adsorption

A series of titanium-based, metal–organic framework (MOF) materials, xM@NH₂-MIL125(Ti) (x is the alkali metal loading percentage during the synthesis; M = Li, Na, K), have been synthesized solvothermally. Alkali metal doping in the NH₂–MIL125(Ti) in situ solvothermal process demonstrated a vital modification of the material structure and surface morphology for the CO₂ adsorption capacity at ambient conditions. By changing the reactants’ precursor, including different kinds of alkali metal, the morphology of xM@NH₂–MIL125(Ti) can be adjusted from a tetragonal plate through a circular plate to a truncated octahedron. The variation of the alkali metal loading results in substantial differences in the CO₂ adsorption. The properties of xM@NH₂–MIL125(Ti) were evaluated via functional group coordination using FT-IR, phase identification based on X-ray diffraction (XRD), surface morphology through scanning electron microscopy (SEM), as well as N₂ and CO₂ adsorption by physical gas adsorption analysis. This work reveals a new pathway to the modification of MOF materials for high-efficiency CO₂ adsorption.

A new approach to enhancing the CO2 capture performance of defective UiO-66 via post-synthetic defect exchange

Zirconium-based metal-organic frameworks (Zr-MOFs) are a subclass of MOFs known for their remarkable stability, especially in the presence of water. This makes them extremely attractive for practical applications, including CO₂ capture from industrial emission sources; however, the CO₂ adsorption capacity of Zr-MOFs is moderate compared to that of the best performing MOFs reported to date. Functionalization of Zr-MOFs with amino groups has been demonstrated to increase their affinity for CO₂. In this work, we assessed the potential of post-synthetic defect exchange (PSDE) as an alternative approach to introduce amino functionalities at missing-cluster defective sites in formic acid modulated UiO-66. Both pyridine-containing (picolinic acid and nicotinic acid) and aniline-containing (3-aminobenzoic acid and anthranilic acid) monocarboxylates were integrated within defective UiO-66 with this method. Non-defective UiO-66 modified with linkers bearing the same amino groups (2,5-pyridinedicarboxylic acid and 2-aminoterephthalic acid) were prepared by classical post-synthetic ligand exchange (PSE), in order to compare the effect of introducing functionalities at defective sites versus installing them on the backbone. PSDE reduces the porosity of defective UiO-66, but improves both the CO₂ uptake and the CO₂/N₂ selectivity, whereas PSE has no effect on the porosity of non-defective UiO-66, improving the CO₂ uptake but leaving selectivity unchanged. Modification of defective UiO-66 with benzoic acid reveals that pore size reduction is the main factor responsible for the observed uptake improvement, whereas the presence of nitrogen atoms in the pores seems to be beneficial for increasing selectivity.

Concurrent Sensing of CO2 and H2O from Air Using Ultramicroporous Fluorinated Metal-Organic Frameworks: Effect of Transduction Mechanism on the Sensing Performance

Conventional materials for gas/vapor sensing are limited to a single probe detection ability for specific analytes. However, materials capable of concurrent detection of two different probes in their respective harmful levels and using two types of sensing modes have yet to be explored. In particular, the concurrent detection of uncomfortable humidity levels and CO₂ concentration (400-5000 ppm) in confined spaces is of extreme importance in a great variety of fields, such as submarine technology, aerospace, mining, and rescue operations. Herein, we report the deliberate construction and performance assessment of extremely sensitive sensors using an interdigitated electrode (IDE)-based capacitor and a quartz crystal microbalance (QCM) as transducing substrates. The unveiled sensors are able to simultaneously detect CO₂ within the 400-5000 ppm range and relative humidity levels below 40 and above 60%, using two fluorinated metal-organic frameworks, namely, NbOFFIVE-1-Ni and AlFFIVE-1-Ni, fabricated as a thin film. Their subtle difference in a structure-adsorption relationship for H₂O and CO₂ was analyzed to unveil the corresponding structure-sensing property relationships using both QCM- and IDE-based sensing modes.

Enhancing CO2 Adsorption and Separation Properties of Aluminophosphate Zeolites by Isomorphous Heteroatom Substitutions

Mg, Co-substituted aluminophosphate zeolites with ERI framework topology (denoted as MgAPO-ERI and CoAPO-ERI) have been synthesized under hydrothermal conditions by using N, N, N', N'-tetramethyl-1,6-hexanediamine as organic template. Their CO₂ adsorption properties are investigated in comparison to those of the pure aluminophosphate counterpart AlPO-ERI. CoAPO-ERI shows the highest CO₂ uptake of 57.3 cm³ g^-1 (273 K and 1 bar) and the highest isosteric heat of 39.0 kJ mol^-1 among the three samples. Importantly, the incorporation of Mg²⁺ and Co²⁺ ions in the framework of AlPO-ERI can greatly improve the adsorption selectivities of CO₂ over CH₄ and N₂. Whereafter, transient breakthrough simulations were investigated and further proved the advantages of heteroatoms for separations. These results demonstrate that isomorphous heteroatom substitutions in aluminophosphate zeolites play a key role in enhancing CO₂ adsorption and separation abilities.

Unusual Moisture-Enhanced CO2 Capture within Microporous PCN-250 Frameworks

Developing metal-organic frameworks (MOFs) with moisture-resistant feature or moisture-enhanced adsorption is challenging for the practical CO₂ capture under humid conditions. In this work, under humid conditions, the CO₂ adsorption behaviors of two iron-based MOF materials, PCN-250(Fe₃) and PCN-250(Fe₂Co), were investigated. An interesting phenomenon is observed that the two materials demonstrate an unusual moisture-enhanced adsorption of CO₂. For PCN-250 frameworks, H₂O molecule induces a remarkable increase in the CO₂ uptake for the dynamic CO₂ capture from CO₂/N₂ (15:85) mixture. For PCN-250(Fe₃), its CO₂ adsorption capacity increases by 54.2% under the 50% RH humid condition, compared with that under dry conditions (from 1.18 to 1.82 mmol/g). Similarly, the CO₂ adsorption uptake of PCN-250(Fe₂Co) increases from 1.32 to 2.23 mmol/g, exhibiting a 68.9% increase. Even up to 90% RH, for PCN-250(Fe₃) and PCN-250(Fe₂Co), obvious increases of 43.7 and 70.2% in the CO₂ adsorption capacities are observed in comparison with those under dry conditions, respectively. Molecular simulations indicate that the hydroxo functional groups (μ₃-O) within the framework play a crucial role in improving CO₂ uptake in the presence of water vapor. Besides, partial substitution of Fe³⁺ by Co²⁺ ions in the PCN-250 framework gives rise to a great improvement in CO₂ adsorption capacity and selectivity. The excellent moisture stability (stable even after exposure to 90% RH humid air for 30 days), superior recyclability, as well as moisture-enhanced feature make PCN-250 as an excellent MOF adsorbent for CO₂ capture under humid conditions. This study provides a new paradigm that PCN-250 frameworks can not only be moisture resistant but can also subtly convert the common negative effect of moisture to a positive impact on improving CO₂ capture performance.

Proton Conduction in Tröger's Base-Linked Poly(crown ether)s

Exactly 50 years ago, the ground-breaking discovery of dibenzo[18]crown-6 (DB18C6) by Charles Pedersen led to the use of DB18C6 as a receptor in supramolecular chemistry and a host in host-guest chemistry. We have demonstrated proton conductivity in Tröger's base-linked polymers through hydrogen-bonded networks formed from adsorbed water molecules on the oxygen atoms of DB18C6 under humid conditions. Tröger's base-linked polymers-poly(TBL-DB18C6)- t and poly(TBL-DB18C6)- c-synthesized by the in situ alkylation and cyclization of either trans- or cis-di(aminobenzo) [18]crown-6 at room temperature have been isolated as high-molecular-weight polymers. The macromolecular structures of the isomeric poly(TBL-DB18C6)s have been established by spectroscopic techniques and size-exclusion chromatography. The excellent solubility of these polymers in chloroform allows the formation of freestanding membranes, which are thermally stable and also show stability under aqueous conditions. The hydrophilic nature of the DB18C6 building blocks in the polymer facilitates retention of water as confirmed by water vapor adsorption isotherms, which show a 23 wt % water uptake. The adsorbed water is retained even after reducing the relative humidity to 25%. The proton conductivity of poly(TBL-DB18C6)- t, which is found to be 1.4 × 10^-4 mS cm^-1 in a humid environment, arises from the hydrogen bonding and the associated proton-hopping mechanism, as supported by a modeling study. In addition to proton conductivity, the Tröger's base-linked polymers reported here promise a wide range of applications where the sub-nanometer-sized cavities of the crown ethers and the robust film-forming ability are the governing factors in dictating their properties.

Zeolite-templated carbons - three-dimensional microporous graphene frameworks

Zeolite-templated carbons (ZTCs) are ordered microporous carbons synthesized by using zeolite as a sacrificial template. Unlike well-known ordered mesoporous carbons obtained by using mesoporous silica templates, ZTCs consist of curved and single-layer graphene frameworks, thereby affording uniform micropore size (ca. 1.2 nm), developed microporosity (∼1.7 cm3 g-1), very high surface area (∼4000 m2 g-1), good compatibility with chemical modification, and remarkable softness/elasticity. Thus, ZTCs have been used in many applications such as hydrogen storage, methane storage, CO2 capture, liquid-phase adsorption, catalysts, electrochemical capacitors, batteries, and fuel cells. Herein, the relevant research studies are summarized, and the properties as well as the performances of ZTCs are compared with those of other materials including metal-organic frameworks, to elucidate the intrinsic advantages of ZTCs and their future development.

Hydrogen-motivated electrolysis of sodium carbonate with extremely low cell voltage

Hydrogen-motivated electrolysis of Na2CO3 for energy-saving production of NaOH and CO2/NaHCO3 is realized by the hydrogen oxidation reaction to insert proton into anolyte and the hydrogen evolution reaction to extract proton out of catholyte. Electrolytic voltage at 100 mA cm-2 is as low as 0.88 V; this voltage is only 35% of the voltage used in the traditional electrolysis.

Highly Efficient Catalytic Cyclic Carbonate Formation by Pyridyl Salicylimines

Cyclic carbonates as industrial commodities offer a viable nonredox carbon dioxide fixation, and suitable heterogeneous catalysts are vital for their widespread implementation. Here, we report a highly efficient heterogeneous catalyst for CO₂ addition to epoxides based on a newly identified active catalytic pocket consisting of pyridine, imine, and phenol moieties. The polymeric, metal-free catalyst derived from this active site converts less-reactive styrene oxide under atmospheric pressure in quantitative yield and selectivity to the corresponding carbonate. The catalyst does not need additives, solvents, metals, or co-catalysts, can be reused at least 10 cycles without the loss of activity, and scaled up easily to a kilogram scale. Density functional theory calculations reveal that the nucleophilicity of pyridine base gets stronger due to the conjugated imines and H-bonding from phenol accelerates the reaction forward by stabilizing the intermediate.

Cyclophosphazene-Based Hybrid Nanoporous Materials as Superior Metal-Free Adsorbents for Gas Sorption Applications

Cyclophosphazene-based inorganic-organic hybrid nanoporous materials (CHNMs) have been synthesized by a facile solvothermal method. The condensation of pyrrole with the reaction product of phosphonitrilic chloride trimer and 4-hydroxybenzaldehyde resulted in the formation of high-surface-area CHNMs. The maximum specific surface area (SA_BET) of 1328 m² g^-1 with hierarchical pore structures having micropores centered at 1.18 nm and mesopores in the range of 2.6-3.6 nm was estimated from the N₂ sorption analysis. Observation of high SA_BET could be attributed to the synergy effect exerted by the cyclophosphazene moiety owing to its three-dimensional paddle wheel structure. The metal-free adsorbent exhibited a high and reversible CO₂ uptake of 22.8 wt % at 273 K and 1 bar. The performance is on the higher side among the reported metal-free inorganic-organic hybrid nanoporous adsorbents. Moreover, the high H₂ uptake of 2.02 wt % at 77 K and 1 bar is an added advantage. The superior performance of the adsorbents for the gas sorption applications could be attributed to the combined effect of high SA_BET and hierarchical pore structure, which has made CHNMs good candidates for energy and environmental applications.

Soft-Pillared@Magadiite: influence of the interlayer space and amine type on CO2 adsorption

Layered silicates are versatile materials that can be grafted with different organosilanes for several applications. Despite this, there are few studies on the use of layered silicate-based materials in CO₂ adsorption. In this regard, the present study describes the synthesis of organo-magadiite followed by simultaneous grafting with two organosilanes ((3-glycidyloxypropyl)trimethoxysilane (GPTS) and N¹-(3-trimethoxysilylpropyl)diethylenetriamine (TMSPETA)) to prepare an adsorbent labeled Soft-Pillared@Magadiite. The adsorbents were characterized through XRD, ¹³C- and ²⁹Si-NMR, TGA/DTG, and elemental analyses of carbon, hydrogen, and nitrogen (CHN). The results suggest that this adsorbent has an expanded interlayer space (3.05 nm) that is larger than the interlayer space when the layered material is grafted with the organosilanes separately, and it may display improved CO₂ adsorption. The CO₂ adsorption was evaluated by TGA, CO₂-TPD, and DSC. Moreover, the adsorption isotherms were fitted using a pseudo-second order, a fractional order, and Avrami models. The optimum adsorption temperature of Soft-Pillared@Magadiite was 25 °C, and the adsorption capacity and efficiency were 0.36 mmol g^-1 and 0.15, respectively, obtained using 5 vol% CO₂ in He for 3 h. The CO₂-TPD shows that the desorption of CO₂ occurs below 90 °C, and from DSC, it is found that thermodynamic parameters, specifically sensible heat and heat of regeneration, are low as compared to those of aqueous MEA solution; the current technology indicates that Soft-Pillared@Magadiite has a good potential for CO₂ adsorption.

Inedible saccharides: a platform for CO2 capturing

The economic viability of eco-friendly and renewable materials promotes the development of an alternative technology for climate change mitigation. Investigations reported over the past few years have allowed understanding the mechanism of action for a wide spectrum of saccharides toward carbon dioxide (CO2), in terms of reactivity, reversibility, stability and uptake. Exploiting bio-renewables, viz., inedible saccharides, to reduce the anthropogenic carbon footprint upon providing a sustainable and promising technology that is of interest to different groups of scientists, to overcome demerits associated with the current state-of-the-art aqueous amine scrubbing agents, following a "green chemistry guideline", by employing materials with properties relevant to the environment toward sustainable development. The interdisciplinary nature of research in this area provides a large body of literature that would meet the interest of the broad readership of different multidisciplinary fields. Although many reports emphasize the use of biomass in various industrial products ranging from pharmaceutics, medical preparations, soaps, textiles, cosmetics, household cleaners, and so on, to our knowledge there is no focused article that addresses the application of saccharides for CO2 sequestration. In this review, we highlight the recent advances on the use of oligo-, poly- and cyclic saccharides to achieve a reversible binding of CO2. The future research directions are discussed to provide insight toward achieving sustainable development through implementing bio-renewables.

Optimization of the Pore Structure of Biomass-Based Carbons in Relation to Their Use for CO2 Capture under Low- and High-Pressure Regimes

A versatile chemical activation approach for the fabrication of sustainable porous carbons with a pore network tunable from micro- to hierarchical micro-/mesoporous is hereby presented. It is based on the use of a less corrosive and less toxic chemical, i.e., potassium oxalate, rather than the widely used KOH. The fabrication procedure is exemplified for glucose as precursor, although it can be extended to other biomass derivatives (saccharides) with similar results. When potassium oxalate alone is used as activating agent, highly microporous carbons are obtained (S_BET ≈ 1300-1700 m² g^-1). When a melamine-mediated activation process is used, hierarchical micro-/mesoporous carbons with surface areas as large as 3500 m² g^-1 are obtained. The microporous carbons are excellent adsorbents for CO₂ capture at low pressure and room temperature, able to adsorb 4.2-4.5 mmol CO₂ g^-1 at 1 bar and 1.1-1.4 mmol CO₂ g^-1 at 0.15 bar. However, the micro-/mesoporous carbons provide record-high room temperature CO₂ uptakes at 30 bar of 32-33 mmol g^-1 CO₂ and 44-49 mmol g^-1 CO₂ at 50 bar. The findings demonstrate the key relevance of pore size in CO₂ capture, with narrow micropores having the leading role at pressures <1 bar and supermicropores/small mesopores at high pressures. In this regard, the fabrication strategy presented here allows fine-tuning of the pore network to maximize both the overall CO₂ uptake and the working capacity at any target pressure.

A catalytic role of surface silanol groups in CO2 capture on the amine-anchored silica support

A new mechanism of CO₂ capture on the amine-functionalized silica support is demonstrated using density functional theory calculations, in which the silica surface not only acts as a support to anchor amines, but also can actively participate in the CO₂ capture process through a facile proton transfer reaction with the amine groups.

Enhanced carbon dioxide capture in an indole-based microporous organic polymer via synergistic effects of indoles and their adjacent carbonyl groups

A carbonyl-functionalized indole-based microporous organic polymer (PKIN) was designed and synthesized in the presence of the FeCl₃ catalyst by a facile direct oxidative coupling reaction.

Enhanced Trace Carbon Dioxide Capture on Heteroatom-Substituted RHO Zeolites under Humid Conditions

Boron and copper heteroatoms were successfully incorporated into the frameworks of high-silica RHO zeolite by adopting a bulky alkali-metal-crown ether (AMCE) complex as the template. These heteroatom-doped zeolites show both larger micropore surface areas and volumes than those of their aluminosilicate analogue. Proton-type RHO zeolites were then applied for the separation of CO₂ /CH₄ /N₂ mixtures, as these zeolites have weaker electric fields and, thus, lower heats of adsorption. The adsorption results showed that a balance between working capacity and adsorption heat could be achieved for these heteroatom-doped zeolites. Ideal adsorbed solution theory predictions indicate that these zeolites should have high selectivities even for remarkably dilute sources of CO₂ . Finally, the heteroatom-substituted zeolites, especially the boron-substituted one, could be thermally regenerated rapidly at 150 °C after full hydration and maintained high regenerability for up to 30 cycles; therefore, they are potential candidates for trace CO₂ removal under humid conditions.

Production and covalent immobilisation of the recombinant bacterial carbonic anhydrase (SspCA) onto magnetic nanoparticles

Carbonic anhydrases (CAs; EC 4.2.1.1) are metalloenzymes with a pivotal potential role in the biomimetic CO₂ capture process (CCP) because these biocatalysts catalyse the simple but physiologically crucial reaction of carbon dioxide hydration to bicarbonate and protons in all life kingdoms. The CAs are among the fastest known enzymes, with k_cat values of up to 10⁶ s^-1 for some members of the superfamily, providing thus advantages when compared with other CCP methods, as they are specific for CO₂. Thermostable CAs might be used in CCP technology because of their ability to perform catalysis in operatively hard conditions, typical of the industrial processes. Moreover, the improvement of the enzyme stability and its reuse are important for lowering the costs. These aspects can be overcome by immobilising the enzyme on a specific support. We report in this article that the recombinant thermostable SspCA (α-CA) from the thermophilic bacterium Sulfurihydrogenibium yellowstonense can been heterologously produced by a high-density fermentation of Escherichia coli cultures, and covalently immobilised onto the surface of magnetic Fe₃O₄ nanoparticles (MNP) via carbodiimide activation reactions. Our results demonstrate that using a benchtop bioprocess station and strategies for optimising the bacterial growth, it is possible to produce at low cost a large amount SspCA. Furthermore, the enzyme stability and storage greatly increased through the immobilisation, as SspCA bound to MNP could be recovered from the reaction mixture by simply using a magnet or an electromagnetic field, due to the strong ferromagnetic properties of Fe₃O₄.

Direct Access to Primary Amines and Particle Morphology Control in Nanoporous CO2 Sorbents

Chemical tuning of nanoporous, solid sorbents for ideal CO₂ binding requires unhindered amine functional groups on the pore walls. Although common for soluble organics, post-synthetic reduction of nitriles in porous networks often fails due to insufficient and irreversible metal hydride penetration. In this study, a nanoporous network with pendant nitrile groups, microsphere morphology was synthesized in large scale. The hollow microspheres were easily decorated with primary amines through in situ reduction by widely available boranes. The CO₂ capture capacity of the modified sorbent was increased to up to four times that of the starting nanoporous network with a high heat of adsorption (98 kJ mol^-1 ). The surface area can be easily tuned between 1 and 354 m²  g^-1 . The average particle size (ca. 50 μm) is also quite suitable for CO₂ capture applications, such as those with fluidized beds requiring spheres of micron sizes.