CO2 Capture Ability Research Articles

Constructing CO2 capture nanotraps via tentacle-like covalent organic frameworks towards efficient CO2 separation in mixed matrix membrane

The structure and morphology of fillers are crucial factors in the process of CO2 separation within mixed matrix membranes (MMMs). In this study, the tentacle-like covalent organic framework (COF) as a filler was incorporated into the Pebax matrix for CO2/CH4 separation. The COF has abundant Lewis base sites (O atom and N atom) and porous pores, thereby constructing efficient CO2 capture nanotraps in the MMMs. The CO2 capture nanotraps facilitate the CO2 transport in the MMMs, and this can be verified by the Grand Canonical Monte Carlo (GCMC) simulation and density functional theory (DFT) calculation. Simultaneously, the CO2 capture nanotraps are distributed on the surface of tentacle-like COF, which is conducive to strengthening CO2 capture ability. Therefore, Pebax/COF MMMs exhibited superior CO2 gas separation performance compared to the pure Pebax membrane. Among them, the MMM with 3 wt% COF loading displayed the highest CO2 gas separation performance, exhibiting permeability and selectivity that were 73.4% and 32.9% higher than the pure Pebax membrane, respectively. Thus, CO2 capture nanotraps constructed in the MMMs via tentacle-like COF showed a promising potential for CO2 separation.

Modulation of p-Block Electron Orbits in Metal-Organic Frameworks for CO2 Capture and Electrochemical Reduction.

Developing catalysts with excellent CO2 capture capability and electrochemical CO2 reduction reaction (CO2RR) at a wide potential range simultaneously is significant but remains a formidable challenge. Here, two novel InMg defective trinuclear cluster-based MOFs (SNNU-41 and SNNU-42) with abundant p-block unsaturated coordinated sites were reported and exhibited good CO2 capture and CO2RR performance simultaneously. Due to the suitable micropores, SNNU-41 showed higher CO2 capture ability at different adsorption pressure conditions. On account of the rigid framework and the closer p band center to Fermi level, SNNU-42 accelerated the conversion of CO2 molecule to C1 efficiency. Notably, via adjusting the ratio of p-block metal (In) in the SNNU-42 framework, the performance of the CO2RR was promoted drastically. SNNU-42 with the InMg (1:1.8) mixed cluster delivered an excellent Faradaic efficiency of 91.3% for C1 products and high selectivity of 72.0% for HCOOH at -2.5 V (vs Ag/Ag+) with a total current density of 77.2 mA cm-2. This work provides a possibility for efficient CO2 capture and CO2RR electrocatalysts through the modulation of electronic structures and composition in MOFs.

Optimized Porous Carbon Particles from Sucrose and Their Polyethyleneimine Modifications for Enhanced CO2 Capture

Carbon dioxide (CO2), one of the primary greenhouse gases, plays a key role in global warming and is one of the culprits in the climate change crisis. Therefore, the use of appropriate CO2 capture and storage technologies is of significant importance for the future of planet Earth due to atmospheric, climate, and environmental concerns. A cleaner and more sustainable approach to CO2 capture and storage using porous materials, membranes, and amine-based sorbents could offer excellent possibilities. Here, sucrose-derived porous carbon particles (PCPs) were synthesized as adsorbents for CO2 capture. Next, these PCPs were modified with branched- and linear-polyethyleneimine (B-PEI and L-PEI) as B-PEI-PCP and L-PEI-PCP, respectively. These PCPs and their PEI-modified forms were then used to prepare metal nanoparticles such as Co, Cu, and Ni in situ as M@PCP and M@L/B-PEI-PCP (M: Ni, Co, and Cu). The presence of PEI on the PCP surface enables new amine functional groups, known for high CO2 capture ability. The presence of metal nanoparticles in the structure may be used as a catalyst to convert the captured CO2 into useful products, e.g., fuels or other chemical compounds, at high temperatures. It was found that B-PEI-PCP has a larger surface area and higher CO2 capture capacity with a surface area of 32.84 m2/g and a CO2 capture capacity of 1.05 mmol CO2/g adsorbent compared to L-PEI-PCP. Amongst metal-nanoparticle-embedded PEI-PCPs (M@PEI-PCPs, M: Ni, Co, Cu), Ni@L-PEI-PCP was found to have higher CO2 capture capacity, 0.81 mmol CO2/g adsorbent, and a surface area of 225 m2/g. These data are significant as they will steer future studies for the conversion of captured CO2 into useful fuels/chemicals.

Freestanding molybdenum carbide nanowires electrode for high specific capacity and superior rate performance Li–CO2 batteries

Li–CO2 batteries have attracted wide attention owing to unique CO2 capture ability and potential power source for Mars exploration. However, the practical application of Li–CO2 batteries are severely restricted by the sluggish reaction kinetics of 4–electron Li2CO3 as discharged products. Herein, we design efficient freestanding Mo2C nanowires electrode following low electron Li2C2O4–product route to achieve high–performance Li–CO2 batteries. More importantly, we propose a regulation and evolution mechanism of discharge products Li2C2O4 and Li2CO3 on Mo2C cathode in Li–CO2 battery with different discharge depths. Based on reasonable regulation of discharge products, Li–CO2 batteries with the Mo2C nanowires exhibit excellent electrochemical performance with an ultra–low overpotential 0.35 V at 0.05 mA cm–2 and a cycle life of 165 cycles below charge potential of 3.8 V. The Mo2C nanowires electrode also delivers high discharge capacity of 8.47 mAh cm–2 and superior rate capability compared to a conventional Mo2C cathode reported. Moreover, the superior flexibility and stability of the binder–free Mo2C nanowires electrode under different deformations assists in the development of wearable Li–CO2 batteries with safety and sustainability.

Co-carbonation behaviors of blast furnace ferronickel slag-cement in aqueous conditions and the associated mechanisms

Blast furnace ferronickel slag (BFNS) has the potential to sequester CO2 for building materials. This study used cement to enhance reactivity of BFNS and found that cement can not only improve the CO2 capture ability of BFNS via stimulating the carbonation of Mg, but also stabilize the formed carbonation products. Co-carbonation of 70 % BFNS and 30 % cement (B70C30) shows higher CO2 uptake capacity (20.57 %) than the theoretical value (16.93 %). The main reason is the formation of the relatively more stable low-Mg calcite in the carbonated B70C30, compared to formed metastable monohydrocalcite in carbonated BFNS. Carbonation kinetics showed that pure BFNS and cement reached almost complete carbonation after 7 h, while B70C30 took 20 h to reach a stable state, resulting from the fact that Mg calcite forms in B70C30 at a low rate, due to incorporation of Mg and calcite crystal structure during growth. This study provides theoretical guidance for BFNS-cement CO2 capture to make building materials.

Highly efficient capture and conversion of CO2 into cyclic carbonates from actual flue gas under atmospheric pressure

Chemical conversion of CO2 to cyclic carbonates is one of the most attractive strategies for CO2 capture and storage utilization. Herein, a binary organocatalyst of 3-aminobenzylalcohol/n-Bu4NI was used to gently catalyze the insertion of CO2 into the terminal/internal epoxides to generate cyclic carbonates under metal-free and solvent-free conditions. Twelve representative terminal epoxides reacted with CO2 to achieve excellent cyclic carbonate yields of up to 98.3 % at 30 °C and 1 atm CO2 and six low activity internal di-substituted epoxides were converted to corresponding cyclic carbonates with yields of up to 96.2 %. Experiments on actual flue gas and water resistance revealed the potential industrial value of this binary organocatalyst. The yield of cyclic carbonate reached 99 % by using actual flue gas under very mild conditions of 60 °C and 1 atm. The results of 4-fold epoxide amplification experiment showed that the residual CO2 in the flue gas was only 793 ppm after reaction at 1 atm and 60 °C, indicating the good CO2 capture and conversion ability. Reaction kinetics and catalytic mechanism of the cycloaddition were investigated in detail. The synergistic effect among functional groups of catalysts on substrates is the essential factor for the high activity of the catalyst.

Direct Catalytic Conversion of Carbon Dioxide to Liquid Hydrocarbons over Cobalt Catalyst Supported on Lanthanum(III) Ion‐Doped Cerium(IV) Oxide

AbstractDirect CO2 conversion to liquid hydrocarbons (HCs) in a single process was achieved using cobalt (Co) catalysts supported on lanthanum ion (La3+)‐doped cerium oxide (CeO2) under a gas stream of H2/CO2/N2=3/1/1. The yield of liquid HCs was the highest for 30 mol% of La3+‐doped CeO2, which was because extrinsic oxygen vacancy formed by doping La3+ could act as an effective reaction site for reverse water gas shift reaction. However, the excess La3+ addition afforded surface covering lanthanum carbonates, resulting in depression of the catalytic performance. On the other hand, bare CeO2 lead to an increase in the selectivity of undesirable methane, which arose from reduction of CO2 to CO proceeding by intrinsic oxygen vacancy generated by only Ce3+, and weaker CO2 capture ability of intrinsic oxygen vacancy than extrinsic one, resulting in the proceeding of Sabatier reaction on Co catalyst. The rational design of reaction sites presented in this study will contribute to sustainability.

Versatile Activated Carbon Fibers Derived from the Cotton Fibers Used as CO2 Solid-State Adsorbents and Electrode Materials.

Activated carbon has an excellent porous structure and is considered a promising adsorbent and electrode material. In this study, activated carbon fibers (ACFs) with abundant microporous structures, derived from natural cotton fibers, were successfully synthesized at a certain temperature in an Ar atmosphere and then activated with KOH. The obtained ACFs were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), elemental analysis, nitrogen and carbon dioxide adsorption-desorption analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption measurement. The obtained ACFs showed high porous qualities and had a surface area from 673 to 1597 m2/g and a pore volume from 0.33 to 0.79 cm3/g. The CO2 capture capacities of prepared ACFs were measured and the maximum capture capacity for CO2 up to 6.9 mmol/g or 4.6 mmol/g could be achieved at 0 °C or 25 °C and 1 standard atmospheric pressure (1 atm). Furthermore, the electrochemical capacitive properties of as-prepared ACFs in KOH aqueous electrolyte were also studied. It is important to note that the pore volume of the pores below 0.90 nm plays key roles to determine both the CO2 capture ability and the electrochemical capacitance. This study provides guidance for designing porous carbon materials with high CO2 capture capacity or excellent capacitance performance.

Hierarchical Polyimide‐Covalent Organic Frameworks Carbon Fiber Structures Enhancing Physical and Electrochemical Properties

The multifunctionality of carbon fiber (CF) is being extensively explored. Herein, polyimide covalent organic frameworks (PI‐COFs) are grafted bound to CF to enhance their mechanical and electrochemical properties. Here, a range of COF scaffolds are grafted to the surface of CFs via a two‐step functionalization. First, melamine is tethered to the fiber surface to provide an anchoring point for the COFs followed by a “graft from” approach to grow three different sized PI‐COFs utilizing three differently sized dianhydride, PMDA to form MA‐PMDA, NTCDA to form MA‐NTCDA, and PTCDA to form MA‐PTCDA COFs. These COFs increase the capacitance of CF by a maximum of 2.9 F g−1 (480% increase) for the MA‐PTCDA, this coincides with an increase in interfacial shear strength by 67.5% and 52% for MA‐NTCDA and MA‐PTCDA, respectively. This data represents that the first‐time CF has been modified with PI‐COFs and allows access to COF properties including their porosity and CO2 capture ability while being attached to a substrate. This may lead to additional high‐value recyclability and second‐life applications for CFs.

Mechanistic insight into electrochemical CO2 reduction on Mo single-atom catalyst and its hydrate: A computational study

By using density functional theory calculation, we investigated the CO2 reduction to CH4 on molybdenum-doped graphene (Mo@Gra) and identified two major paths from the HCOO* and COOH* intermediates with different onset potential. Both HCOO* and COOH* would continent hydrogenating to CH4 by an eight proton-electron coupling transfer process via HCOO path and COOH path. By the HCOO path, the formation of HCOO* is exergonic and the potential determining step (PDS) is OH* to H2O* by an endergonic process of 0.70 eV. On the other hand, the formation of COOH* from CO2* is endergonic with the same PDS and a limiting potential (UL) of –0.70 V. In addition, nitrogen coordinated Mo-graphene (Mo@3N-Gra) also illustrated for CO2 reduction and the corresponding UL is found to be –1.88 V. In addition, we also explore the mechanisms of CO2 reduction on the water pre-adsorption surface for realistic experiments. The UL required to overcome was reduced to –0.25 V for 3H2O*Mo@Gra with three H2O co-adsorption environment, suggesting the catalytic performance can be enhanced by water promotion effect. Two structures of hydrated structures, 2H2O*OH*Mo@3N-Gra and 3H2O*Mo@3N-Gra, were selected for stimulate realistic experiments. Compared to the Mo@3N-Gra catalyst, the UL reduces to –0.48 and –0.70 V for 2H2O*OH*Mo@3N-Gra and 3H2O*Mo@3N-Gra, respectively. Although, Mo-N doped graphene has better CO2 capture ability and selectivity, it needs more onset potential to produce CH4. Our calculations demonstrated that the electrocatalytic performance can be enhanced by the hydration effect.

Efficient Capture and Electroreduction of Dilute CO2 into Highly Pure and Concentrated Formic Acid Aqueous Solution.

High-purity CO2 rather than dilute CO2 (15 vol %, CO2/N2/O2 = 15:80:5, v/v/v) similar to the flue gas is currently used as the feedstock for the electroreduction of CO2, and the liquid products are usually mixed up with the cathode electrolyte, resulting in high product separation costs. In this work, we showed that a microporous conductive Bi-based metal-organic framework (Bi-HHTP, HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) can not only efficiently capture CO2 from the dilute CO2 under high humidity but also catalyze the electroreduction of the adsorbed CO2 into formic acid with a high current density of 80 mA cm-2 and a Faradaic efficiency of 90% at a very low cell voltage of 2.6 V. Importantly, the performance in a dilute CO2 atmosphere was close to that under a high-purity CO2 atmosphere. This is the first catalyst that can maintain exceptional eCO2RR performance in the presence of both O2 and N2. Moreover, by using dilute CO2 as the feedstock, a 1 cm-2 working electrode coating with Bi-HHTP can continuously produce a 200 mM formic acid aqueous solution with a relative purity of 100% for at least 30 h in a membrane electrode assembly (MEA) electrolyzer. The product does not contain electrolytes, and such a highly concentrated and pure formic acid aqueous solution can be directly used as an electrolyte for formic acid fuel cells. Comprehensive studies revealed that such a high performance might be ascribed to the CO2 capture ability of the micropores on Bi-HHTP and the lower Gibbs free energy of formation of the key intermediate *OCHO on the open Bi sites.

Low-crystallinity porous Ni2P2O7 nanowires with excellent CO2 capture ability for highly-efficient CO2 reduction

In this study, we prepared the porous Ni2P2O7 nanowires with low-crystallinity (LC-NPO) and high-crystallinity Ni2P2O7 nanosheets (HC-NPO), and employed them for the first time as catalyst in the CO2 photoreduction reaction. The photocatalytic performance of them was tested under the UV–Vis light irradiation and compared with the TiO2 commercial powder (P25). The CO2 photoreduction experiments shown that the LC-NPO had the highest ability than the HCNPO and the P25. Specifically, with triethanolamine (TEOA) as the sacrificial agent, LC-NPO achieved CO and CH4 yields of approximately 56.06 and 12.13 μmol·g−1 after 4 h UV–Vis light irradiation, which were 4.67 and 5.00 times of P25, respectively. The experimental results, and Density Functional Theory calculations proved that the unique porous nanowire structure enables LC-NPO to have a larger specific surface area, higher quantity of oxygen defects, and superior CO2 capture ability compared to HC-NPO. These features maybe the primary reasons for the excellent CO2 photoreduction ability. Besides, the photo-electrochemical characterizations revealed that the LC-NPO had the much superior photoelectrochemical properties than the HC-NPO, which was another reason for enhanced photocatalytic ability. In-situ FTIR and 13C isotope labeling experiments were used to monitor the CO2 reduction process, and finally a potential enhanced mechanism had been discussed.

Synthesis and characterization of Al2O3-methanol nanofluid and its usage in bubble column for an improved mass transfer rate

Methanol-based physical absorption, known for its effective CO2 capture ability, has been employed in acid gas removal (AGR) unit. However, the high energy consumption associated cooling methanol and acid gas hampers its widespread adoption. To address this challenge, numerous studies have explored the use of nanoparticles to enhance the CO2 absorption at room temperature, thereby reducing the energy requirements. In this study, the objective is to synthesize and characterize the Al2O3-methanol nanofluid and investigate its application in a bubble column for improved mass transfer rates during CO2 absorption. The methanol based Al2O3 nanofluid was prepared using the two-step method with ultrasonication technology and CO2 absorption in the resultant product was investigated. Initially, 0.001 vol%, 0.01 vol % and 0.1 vol% Al2O3 nanoparticles was added to methanol solution and to mixture them well via ultrasonication technology. The static settlement method and zeta potential analysis were utilized to characterize the stability of the as-prepared nanofluid. Both impact of sonication power and time on the stability of nanofluid were discussed as well. Then, numerical simulations was employed to investigate the mass transfer coefficient for CO2 absorption and the numerical uncertainty was carefully analyzed to verify the reliability of the numerical method. It revealed a 7.3%, 29.2% and 60.7% enhancement in mass transfer coefficient during CO2 absorption for 0.001 vol%, 0.01 vol% and 0.1 vol% nanoparticles under room temperature, respectively. The visualized reason for this improvement was related to the enhanced bubble breakup and coalescence after adding nanoparticles to methanol. The expanded interfacial area between gas and liquid plays a vital role in the mechanism of this improvement.

Engineering hydrophobicity and high-index planes of gold nanostructures for highly selective electrochemical CO2 reduction to CO and efficient CO2 capture

In current study, we demonstrate a strategy for improving the catalytic performance of gold (Au) for carbon dioxide reduction reaction (CO2RR), specifically enhancing selectivity for CO over hydrogen evolution reaction (HER) and increasing low-level CO2 capture efficiency. This involved controlling nanostructures without any further modification. Au nanostructures having four different morphologies (i.e., degree of roughness) were fabricated via electrodeposition at varied deposition potential, resulting in different intrinsic surface hydrophobicity and exposure of high-index planes depending on the actual morphology. The roughest Au, with its combination of the most hydrophobic feature and abundant high-index planes, generated greater partial current density (jCO) and faradaic efficiency for CO (FECO) than the other Au deposits within a tested potential region: The roughest Au showed 6-fold higher FECO (95.8 %) and 327-fold higher jCO (normalized to electrode geometric surface area) at −0.75 VRHE compared to the smoothest Au. Moreover, the roughest Au exhibited excellent CO2 capture ability even at low CO2 concentration, confirmed with scanning electrochemical microscopy. These improvement at hierarchical Au for CO2RR could be ascribed to two factors. Firstly, the morphology-driven hydrophobicity provides an optimal gas–liquid-solid triple-phase interfaces, increasing the local CO2 concentration near the Au catalyst surface due to its superb CO2 capture ability. Secondly, the abundant high-index planes serve as stable active sites for CO2RR, expediting the reaction rates. Remarkably, Au with the highest hydrophobicity and enriched high-index planes, even without any chemical modification, showed excellent CO2RR catalytic performance comparable to or even better than the other previously reported Au-based catalysts.

Prediction of M3 B4 -type MBenes as Promising Catalysts for CO2 Capture and Reduction.

The rational design of novel catalysts with high activity and selectivity for carbon dioxide reduction reaction (CO2 RR) is highly desired. In this work, we have extensive investigations on the properties of two-dimensional transition metal borides (MBenes) to achieve efficient CO2 capture and reduction through first-principles calculations. The results show that all the investigated M3 B4 -type MBene exhibit remarkable CO2 capture and activation abilities, which proved to be derived from the lone pair of electrons on the MBene surface. Then, we emphasize that the investigated MBenes can further selectively reduce activated CO2 to CH4 . Moreover, a new linear scaling relationship of the adsorption energies of potential-determining intermediates (*OCH2 O and *HOCH2 O) versus ΔG(*OCHO) has been established, where the CO2 RR limiting potentials on MBenes are determined by the different fitting slopes of ΔG(*OCH2 O) and ΔG(*HOCHO), allowing significantly lower limiting potentials to be achieved compared to transition metals. Especially, two promising CO2 RR catalysts (Mo3 B4 and Cr3 B4 MBene) exist quite low limiting potentials of -0.48 V and -0.66 V, as well as competitive selectivity concerning hydrogen evolution reactions have been identified. Our research results make future advances in CO2 capture by MBenes easier and exploit the applications of Mo3 B4 and Cr3 B4 MBenes as novel CO2 RR catalysts.

Upgrading recovered carbon black (rCB) from industrial-scale end-of-life tires (ELTs) pyrolysis to activated carbons: Material characterization and CO2 capture abilities

The current study presents for the first time how recovered carbon black (rCB) obtained directly from the industrial-scale end-of-life tires (ELTs) pyrolysis sector is applied as a precursor for activated carbons (ACs) with application in CO2 capture. The rCB shows better physical characteristics, including density and carbon structure, as well as chemical properties, such as a consistent composition and low impurity concentration, in comparison to the pyrolytic char. Potassium hydroxide and air in combination with heat treatment (500–900 °C) were applied as agents for the conventional chemical and physical activation of the material. The ACs were tested for their potential to capture CO2. Ultimate and proximate analysis, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), Raman spectroscopy, thermogravimetric analysis (TGA), and N2/CO2 gas adsorption/desorption isotherms were used as material characterization methods. Analysis revealed that KOH-activated carbon at 900 °C (AC-900K) exhibited the highest surface area and a pore volume that increased 6 and 3 times compared to pristine rCB. Moreover, the AC-900K possessed a well-developed dual porosity, corresponding to the 22% and 78% of micropore and mesopore volume, respectively. At 0 °C and 25 °C, AC-900K also showed a CO2 adsorption capacity equal to 30.90 cm3/g and 20.53 cm3/g at 1 bar, along with stable cyclic regeneration after 10 cycles. The high dependence of CO2 uptake on the micropore volume at width below 0.7–0.8 nm was identified. The selectivity towards CO2 in relation to N2 reached high values of 350.91 (CO2/N2 binary mixture) and 59.70 (15% CO2/85% N2).

A novel binder-free cathode catalyst Cu@NCNF/CP with three-dimensional self-supporting structure for Li-CO2 battery

The Li-CO2 battery is an emerging energy storage device that has garnered significant attention due to its high theoretical energy density and remarkable CO2 capture ability. However, the low reaction activity of Li2CO3 formation and decomposition may result in large overpotentials and poor cycling performance. In this work, a novel three-dimensional self-supporting high-performance cathode catalyst (Cu@NCNF/CP) was prepared. The Cu@NCNF/CP cathode catalyst is composed of Cu nanoparticles loaded on nitrogen-doped carbon nanotube fibers (NCNF) deposited on carbon paper (CP). The three-dimensional interconnected self-supporting structure of Cu@NCNF/CP eliminates the need for binders and can facilitate efficient electrolyte diffusion and electron transfer. Moreover, the nitrogen doping introduces enrichment active sites, and boosts the CO2 reduction reaction (CO2RR) activity, while the uniformly loaded Cu nanoparticles facilitate the adsorption and precipitation of CO2 molecules, thereby playing a crucial role in enhancing the electrocatalytic activity of the CO2 evolution reaction (CO2ER). Importantly, the Li-CO2 battery utilizing Cu@NCNF/CP as a cathode catalyst exhibits a large discharge capacity of 10.59 mAh cm−2 at a current density of 0.05 mA cm−2. When the cutoff capacity is limited to 0.15 mAh cm−2, the first-cycle overpotential is merely 1.28 V, and the cycle life can reach 1140 h due to the high reversibility of the Li2CO3 formation and decomposition. The successful application of a three-dimensional self-supporting Cu@NCNF/CP cathode catalyst in Li-CO2 battery systems introduces a novel concept for developing high-performance transition metal-based catalysts.

Using recycled gangue to capture CO2 and prepare alkali-activated backfill paste: Adsorption and microevolution mechanisms

Gangue is a type of coal-based solid waste that can be used to prepare mine backfill and CO2 capture materials. However, the CO2 capture ability and activity of gangue are limited by its natural unreactive minerals and dense micro-structure. This study developed a novel chemical modification approach to modify recycled gangue and enhance its CO2 capture and hydration properties. Moreover, a new type of recycled gangue-based backfill paste was prepared to capture CO2. Multiple experiments were conducted to characterize the CO2 capture ability, mineral composition, and specific surface area of the modified gangue, as well as the hydration and microstructure of the alkali-activated modified gangue-based paste (ACM). The results reveal that the CO2 adsorbed ability and compressive strength of ACM can be significantly improved via acetic acid (AA) modification, and the optimum dosage of AA is 2 wt% of the gangue. At this dosage, the CO2 capture ability of gangue reaches 0.30 mmol/g, and the 3 d compressive strength of the ACM is doubled. This is because of the following reasons: 1) AA reacts with kaolinite and muscovite to generate acetate, which increases gangue activity; 2) the modification reduces the particle size and increases the specific surface area of the gangue, both of which are crucial for improving the CO2 capture capacity of the gangue. 3) More gels are generated in ACM, and the dense microstructure contributes to an increase in the compressive strength. This study develops an effective approach to improve the activity and CO2 capture ability of recycled gangue and thus provides guidance for backfill mining, recycled gangue utilization, and CO2 capture.

Construction of three-dimensional porous organic polymers with enhanced CO2 uptake performance via solid-state thermal conversion from tetrahedral benzoxazine-linked precursor

Porous organic polymers (POPs) with three-dimensional (3D) linkages have drawn great interest due to their potential applications in separation, adsorption, and sensing fields. Herein, a new 3D benzoxazine (BZ)-linked porous organic polymer (TPM-BZ-Py POP) was synthesized by linking a tetrahedral benzoxazine (TPM-BZ-Br4) with tetraethynylpyrene (Py-T) via Sonogashira coupling. Specifically, the synthesis of the tetrahedral benzoxazines with four oxazine rings in a single monomer involved the utilization of Schiff base formation, NaBH4 reduction as well as Mannich condensation reactions. To confirm the chemical structure of the benzoxazine monomers and their corresponding polybenzoxazines, Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), and carbon nuclear magnetic resonance (13C NMR) spectroscopy techniques were employed. The pore volume and specific surface area of the 3D TPM-BZ-Py POP were determined through N2 adsorption/desorption isotherms, and they were found to be 0.52 cm3/g and 185 m2/g, respectively. In addition, the solid-state chemical transformation occurred during thermal ring-opening polymerization (ROP), and the resulting 3D poly(TPM-BZ-Py) POP displayed higher CO2 capture ability (1.81 mmol/g) compared with TPM-BZ-Py POP (0.60 mmol/g) at room temperature. Such enhancement observed in poly(TPM-BZ-Py) POP was proposed to be caused by the formation of phenolic units and Mannich bridges within the polymer network by taking into consideration the structural transformation during the ring-opening polymerization (ROP). The functionalities in poly(TPM-BZ-Py) have great potential to interact with CO2 molecules through strong intermolecular hydrogen bonding or acid/base interactions, which further supports the benefit of incorporating oxazine rings into POP frameworks.

A dual-enzyme microreactor based on encapsulation and covalent bond for enzymatic electrocatalytic CO2 reduction

Enzymatic reduction of CO2 into high-value chemicals has become an emerging technology attributed to its high selectivity and catalytic efficiency under mild conditions. While, the low solubility of CO2 at room temperature, the expensive cofactors and the poor stability of free enzyme limit the application potential. To solve these problems, we used organic microcapsules together with MOF to protect formate dehydrogenase (FDH) by encapsulation and carbonic anhydrase (CA) by covalent bond with high CO2 capture ability to construct a dual-enzyme microreactor. Besides, the additional mesopores of the microreactor can ensure the efficient internal diffusion of the substrate and product. Electron mediator was used to enhance electrocatalytic NADH regeneration to efficiently reduce CO2 to formate in the enzyme electrocatalysis system. After optimization, the highest yield of formate in the electrocatalytic CO2 reduction system by the dual enzyme microreactor was 2.917 mM with a generation rate of 1.296 × 104 μmol gcat-1h−1, which was 8.9 times higher than free enzyme.