High CO2 Adsorption Capacity Research Articles

Valorization of Cyanophyta by hydrothermal carbonization: Co-production of CO2 adsorbents and fluorescent carbon dots

Cyanophyta blooms can lead to eutrophication and generate algal toxins. To reduce their environmental risks, hydrothermal carbonization was innovatively applied to simultaneously produce activated carbon (AC) and carbon dots (CDs). AC was further used for CO2 adsorption while CDs were for preparing fluorescent materials. Yields of AC and CDs were investigated under mild conditions of 160-240 °C and 15-240 min. Characterization results show that AC exhibited a large specific surface area of 990 m2·g-1 and pore volume of 1.14 cm3·g-1, contributing to high CO2 adsorption capacities of 3.26 mmol·g-1 (0 °C) and 2.06 mmol·g-1 (25 °C). Additionally, nitrogen and oxygen self-doping heteroatoms CDs, with a photoluminescence quantum yield of 2.58 %, emitted stable blue fluorescence under the ultraviolet light and were successfully applied to produce invisible ink. This work provides a paradigm for CO2 reduction and high-value material synthesis via the thermochemical conversion of hazardous biomass.

Chitosan-Based Porous Carbon Materials with Built-In Lewis Acid Boron Sites for Enhanced CO2 Capture and Conversion via an Electron-Inducing Effect.

Electron-induced effects, which are prevalent in adsorption and heterogeneous catalytic reactions, can significantly influence the state and uptake of adsorbates. Here, we demonstrate the in situ doping of electron-deficient boron into the backbone of chitosan-based porous carbon materials. Despite a reduction in specific surface area, the resulting boron-doped porous carbons (NBPCs) exhibit an enhanced CO2 adsorption performance, with sample NBPC-10 achieving CO2 adsorption capacities of 7.62 and 4.82 mmol·g-1 at 273 and 298 K, respectively. This improvement is attributed to the electron-induced effect of boron doping, which also enhances the separation selectivity of CO2 from N2. Additionally, the high CO2 adsorption capacity fosters synergism between NBPCs and the cocatalyst tetrabutylammonium bromide (TBAB), thereby augmenting the catalytic activity for the cycloaddition of CO2 and epoxide. Notably, cyclic carbonate yields exceeding 99% were attained even under 1 bar of CO2. Controlled experiments corroborated the pivotal role of boron-doping-induced modifications in the porous carbon structure in enhancing both CO2 selective adsorption and conversion performance. Furthermore, NBPCs demonstrated excellent recyclability as both adsorbents and catalysts, offering fresh perspectives for the design of functionalized porous carbon materials tailored for CO2 capture and conversion.

Hollow core-shell heterojunction TAPB-COF@ZnIn2S4 as highly efficient photocatalysts for carbon dioxide reduction.

The conversion of carbon dioxide (CO2) into carbon-neutral fuels using solar energy is crucial for achieving energy sustainability. However, the high carrier charge recombination and low CO2 adsorption capacity of the photocatalysts present significant challenges. In this paper, a TAPB-COF@ZnIn2S4-30 (TAPB-COFZ-30) heterojunction photocatalyst was constructed by in situ growth of ZnIn2S4 (ZIS) on a hollow covalent organic framework (HCOF) with a hollow core-shell structure for CO2 to CO conversion. Both experimental studies and theoretical calculations indicate that the construction of heterojunctions improves the efficiency of carrier separation and utilisation in photocatalysis. The yield of photoreduction of CO2 to CO by the TAPB-COFZ-30 heterojunction photocatalyst reached 2895.94 μmol g-1 with high selectivity (95.75%). This study provides a feasible strategy for constructing highly active core-shell composite photocatalysts to optimize CO2 reduction.

Building a Co-Salen-Immobilized Porous Organic Polymer Catalyst for CO2 Cycloaddition.

The CO2-epoxide addition to cyclic carbonate is of great significance but usually requires high temperatures and CO2 pressures. Herein, a spirobifluorene-based porous organic polymer catalyst is designed with a Co-salen complex immobilized on the backbone (ST-CoSalen-POP) to enable CO2 fixation under mild conditions. ST-CoSalen-POP possesses a high Co-loading content (9.35 wt%), a large pore volume, and high CO2 adsorption capacity. This catalyst achieves a 96% yield in the cycloaddition of CO2 with epoxides at 25°C and 0.1MPa CO2 pressures. Moreover, ST-CoSalen-POP also offers the advantages of wide adaptability over epoxide substrates and high structural stability for three consecutive cycles. This study presents a novel catalytic approach for promoting CO2 fixation, offering a significant advancement in the efficient synthesis of fine chemicals.

Functionalized Dual/Multiligand Metal-Organic Frameworks for Efficient CO2 Capture under Flue Gas Conditions.

Reducing carbon dioxide (CO2) emissions has become increasingly urgent for China, particularly in the industrial sector. Striking a balance between a high CO2 adsorption capacity and long-term stability under practical conditions is crucial for effectively capturing CO2 from flue gas. In this study, a series of functionalized MFM-136 adsorbents were synthesized in which -NO2 and -NH2 groups were grafted onto the kagome lattice of MFM-136. Modifications with -NH2 groups were found to be highly effective for CO2 adsorption, specifically, the CO2 adsorption capacity peaked at 4.35 mmol/g for NH2(0.6)-MFM-136, representing a 55% enhancement more than MFM-136. Concurrently, the CO2/N2 selectivity for NH2(0.6)-MFM-136 was increased 1.57 times. Verification of novel adsorption sites introduced by NH2-H2L4 was conducted by using in situ DRIFT analysis and DFT calculations. It turns out that NH2-H2L4 modification can effectively mitigate the chemical deposition from the impurity gases and significantly improve the adsorbent's hydrophobicity and its tolerance to impurity gases. Remarkably, the reduction in the CO2 absorption capacity for NH2(0.6)-MFM-136 was 34% less than that for MFM-136 after 24 h of exposure to simulated flue gas, making NH2(0.6)-MFM-136 a promising candidate for the potential application of stable and selective CO2 capture under industrial flue gas conditions.

Adsorption equilibria and kinetics of CO2 and N2 on silica-alumina gels for reducing gas production by CO2 removal from iron flue gases

In industrial fields, hydrogen-containing flue gases generally contain a certain amount of CO2 and N2. After removing CO2, the raffinate gases can be used in various applications to mitigate carbon emissions. Furthermore, the concentrated CO2-rich extract contributes to efficient CO2 capture. Silica-alumina gel can be a high potential adsorbent because of its high CO2 adsorption capacity and energy-saving desorption. Three different silica-alumina gels with different amounts of alumina (FJ, KD, and WS) were compared to study the impact of the alumina content on the adsorption characteristics. The adsorption behaviors of CO2 and N2 were measured at 293K, 308K, and 323K at pressures up to 1000 kPa. The isotherms correlated with the dual-site Langmuir model, showing that the adsorption capacity for CO2 was much higher than that for N2 across all the adsorbents. The surface areas and adsorption capacities followed the opposite order of alumina content: FJ > KD > WS. However, the difference intervals in the isotherms did not align consistently with the alumina content, but the micropore volume changed by alumina contributed highly to the adsorption capacity. In the adsorption kinetic analysis, the diffusional time constants and kinetic parameters in a non-isothermal adsorption kinetic model showed minor dependence on pressure and temperature. The adsorption rate was higher for N2 than for CO2. It increased with alumina content, following the order WS > KD >> FJ. The results contribute to the establishment of guidelines for the selection of silica-alumina gel and the design of the adsorption process.

Highly efficient CO2 capture on acid-treated sepiolite impregnated with mixed polyethyleneimine and diethanolamine

Amine-functionalized solid adsorbents exhibit broad prospects in CO2 capture from flue gases due to their high adsorption capacity and selectivity. However, reported adsorbents are still facing challenges, including high costs, the easy agglomeration of polyamines, and limited adsorption temperature ranges. In this study, sepiolite-based mixed amine adsorbents are prepared by synergistically impregnating acid-treated sepiolite with a mixture of polyethyleneimine (PEI) and diethanolamine (DEA). Results show that at a PEI/DEA loading ratio of 1:1 and a mixture loading of 60wt%, the CO2 adsorption capacity of the resulting adsorbent increases from 0.58mmol/g for acid-treated sepiolite to 2.89mmol/g at 60°C, and remains above 2.50mmol/g after 10 cycles. Meanwhile, the optimized adsorbent maintains a capacity of over 2.44mmol/g within the temperature range of 30–70°C. Additionally, the CO2 selectivity and maximum heat of adsorption for the optimized adsorbent are calculated to be 1184 and 60.08kJ/mol, respectively. An improved CO2 adsorption capacity is obtained, an increase from 0.052mmol/g for acid-treated sepiolite to 1.60mmol/g. Furthermore, an in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) analysis reveals that the introduction of DEA into PEI helps in polyamine dispersion, thereby enhancing CO2 adsorption capacity. The CO2 capture mechanism follows a zwitterionic reaction, where CO2 is ultimately converted into carbamate and carbamic acid. Overall, the as-prepared sepiolite-based mixed amine adsorbents, which are characterized by high CO2 adsorption capacity and selectivity, low cost, broad adsorption temperature range, moderate heat of adsorption, and good cycle stability, show promising potential for industrial applications.

Exploring enthalpies of CO2 and N2 adsorption on Zn- and Co-based zeolitic frameworks at varying temperatures and pressures

This study investigates the thermodynamics of CO2 and N2 adsorption on zeolitic imidazolate frameworks (ZIFs), focusing on the effects of metal ions under varying temperatures and pressures. Zn- and Co-based ZIFs were synthesized using 2-methylimidazole and characterized by XRD, FT-IR, Raman spectroscopy, and BET isotherms, confirming high microporosity. Gas adsorption experiments were performed at pressures up to 3000 kPa and temperatures between 268 and 323 K. The CO2 adsorption capacities vary from 274 to 157 cm³/g, while N2 ranged from 67 to 29 cm³/g as temperature increased. The synergistic dynamics of temperature and pressure enhanced CO2 diffusion and induced pore structure changes via a gate-opening mechanism. Isosteric enthalpy (ΔHads) values, determined using Freundlich-Langmuir/Clausius-Clapeyron and virial fits, were -22 ± 5 kJ/mol for CO2 and -15 ± 2 kJ/mol for N2, confirming that physisorption is the dominant mechanism. Gibbs free energy (ΔGads) for CO2 ranged from -12 to -18 kJ/mol, and entropy (ΔSads) from -0.01 to -0.03 kJ/mol/K, suggesting spontaneous and thermodynamically favorable CO2 adsorption, though spontaneity decreased with rising temperature. ZIFs containing Zn exhibited high CO2 adsorption capacity, while those with Co showed better CO2 selectivity over N2, highlighting their potential for efficient CO2 capture under various temperature and pressure conditions.

Enhancing water resistance of metal-organic frameworks

Developing metal-organic frameworks (MOFs) with high water resistance is of high significance because it can largely extend their applications, such as catalysis and adsorption in aqueous solutions. Herein, we present a typical MOF, i.e., CuBTC [Cu3(BTC)2(H2O)3]n (BTC = benzene-1,3,5-tricarboxylate) with high water resistance by post-modification reactions with six commercially available silanes at room temperature, resulting in CuBTC@SILANE. Various techniques demonstrated that the modification successfully incorporates organosilicon moieties on the surface of CuBTC without altering its original structure, significantly enhancing its water resistance. In contrast to pristine CuBTC, CuBTC@SILANE maintains its crystallinity, morphology, and pore structure even after prolonged exposure to water. The modified MOF also exhibits superior stability in various solvents and enhances CO2 adsorption efficiency, retaining high CO2 adsorption capacity even after exposure to water for 1 day. This simple silane modification approach not only addresses the water sensitivity of CuBTC but also holds promise for extending the aqueous applications of other similar MOFs, thereby broadening their potential uses in catalysis and adsorption.

Direct Conversion of CO2 to Olefins over a Cr2O3/ZSM-5@CaO Cooperative and Bifunctional Material Under Isothermal Conditions.

Direct conversion of point-source CO2 into fine chemicals over cooperative and bifunctional materials (BFMs) - composed of adsorbents and catalysts - has emerged as a promising approach to improve the energy efficiency of the carbon capture and conversion processes. In this study, a bifunctional material consisting of Cr2O3/ZSM-5 catalyst and CaO adsorbent was developed and tested in the CO2-oxidative dehydrogenation of propane (CO2-ODHP) for reactive capture of CO2 in a fixed bed reactor. First, CaO was prepared using two distinct methods: solid-state and citrate sol-gel. The citrate sol-gel method resulted in small and finely-distributed CaO particles, allowing more accessible sites for CO2 adsorption. Consequently, a high CO2 adsorption capacity of ∼14 mmol/g was achieved with fast adsorption kinetics compared to CaO prepared by the solid-state method. The CaO adsorbent was then combined with the Cr2O3/ZSM-5 catalyst for BFM synthesis and tested in the CO2-ODHP process, targeting propylene production. The BFM was extensively characterized to provide insights into the BFM's surface chemistry, morphology, and reaction mechanism in the reactive capture process of CO2-ODHP. The results revealed that under isothermal adsorption-reaction conditions at 600 °C, a propane conversion of 22.5%, a propylene selectivity of 55.3%, and an olefin selectivity of 67.3% were achieved. The excellent propylene selectivity was attributed to the catalyst acidity and redox property of the Cr2O3/ZSM-5 catalyst, which facilitated the reaction pathway of propane dehydrogenation in the process of CO2-ODHP. Overall, this study renders Cr2O3/ZSM-5@CaO as promising BFMs with high CO2 capture capacity and catalytic activity for integrated CO2 capture and conversion in the ODHP reaction.

Potassium-Based Solid Sorbents for CO2 Adsorption: Key Role of Interconnected Pores.

Industrial CO2 emissions contribute to pollution and greenhouse effects, highlighting the importance of carbon capture. Potassium carbonate (K2CO3) is an effective CO2 absorbent, yet its liquid-phase absorption faces issues like diffusion resistance and corrosion risks. In this work, the solid adsorbents were developed with K2CO3 immobilized on the selected porous supports. Al2O3 had an optimum CO2 adsorption capacity of 0.82 mmol g-1. After further optimization of its pore structure, the self-prepared support Al2O3-2, which has an average pore diameter of 11.89 nm and a pore volume of 0.59 cm3 g-1, achieved a maximum CO2 adsorption capacity of 1.12 mmol g-1 following K2CO3 impregnation. Additionally, the relationship between support structure and CO2 adsorption efficiency was also analyzed. The connectivity of the pores and the large pore diameter of the support may play a key role in enhancing CO2 adsorption performance. During 10 cycles of testing, the K2CO3-based adsorbents demonstrated consistent high CO2 adsorption capacity with negligible degradation.

N-doped Porous Carbon Derived from the Pyrolysis of a Polydopamine-coated Hypercross-linked Polymer for Enhanced CO2 Adsorption.

Porous carbon materials can simultaneously capture and convert carbon dioxide, helping to reduce greenhouse gas emissions and using carbon dioxide as a feedstock for the production of valuable chemicals or fuel. In this work, a series of N-doped porous carbons (PDA@HCP(x:y)-T) was prepared; the CO2 adsorption capacity of the prepared PDA@HCP(x:y)-T was enhanced by coating polydopamine (PDA) on a hypercross-linked polymer (HCP) and then adjusting the mass ratio of PDA to HCP and the carbonization temperature. The results showed that the prepared PDA@HCP(1 : 1)-850 exhibited a high CO2 adsorption capacity due to abundant micropores (0.6762 cm3/g), a high specific surface area (1220.8 m2/g), and moderate surface nitrogen content (2.75 %). Notably, PDA@HCP(1 : 1)-850 exhibited the highest CO2 uptake of 6.46 mmol/g at 0 °C and 101 kPa. Critically, these N-doped porous carbons can also be used as catalysts for the reaction of CO2 with epichlorohydrin to form chloropropylene carbonate, with chloropropylene carbonate yielding up to 64 % and selectivity of the reaction reaching 94 %. As a result, these N-doped porous carbons could serve as potential candidates for CO2 capture and conversion due to their high reactivity, excellent CO2 uptake, and good catalytic performance.

Synergistic effect of carbon molecular sieve and alkali metal nitrate on promoting intermediate-temperature adsorption of CO2 over MgAl-layered double hydroxide

The development of intermediate-temperature adsorbents with high CO2 adsorption capacity is crucial for the tandem integration with CO2 hydrogenation catalyst, aimed at enhancing economy viability and minimizing energy consumption in Carbon capture, utilization and storage (CCUS). Although certain porous carbon materials (PCM) have been employed to enhance CO2 adsorption capability of layered double hydroxide (LDH), there remains an urgent necessity to identify more cost-effective and efficient PCM alternatives. Herein, alkali metal nitrates ((Li0.3Na0.18K0.52)NO3, hereafter referred to as LiNaK) modified layered double hydroxide (LDH)/carbon molecular sieve (CMS) composite (LiNaK-LDH/CMS) as promising adsorbents for CO2 capture was reported. The effects of CMS addition and nitrate loading, the calcination and adsorption temperature, as well as the cycling stability were investigated systematically. The results revealed that the CO2 capture capacity of the LiNaK-modified layered double oxide (LDO)/CMS composite (30 mol%LiNaK-LDO/CMS15%)-incorporating with 15 wt% CMS addition and 30 mol% nitrate loading-achieved a remarkable CO2 adsorption capacity of 1.32 mmol/g at 300 °C due to the synergetic interactions between CMS and nitrate; this represents nearly a sevenfold enhancement compared to initial LDO performance. Moreover, the 30 mol%LiNaK-LDO/CMS15% adsorbent also demonstrated commendable cyclic stability after ten adsorption/desorption cycles, retaining over 85 % of its initial adsorption capacity within half of adsorption time. Based on both obtained adsorption performance and characterization data from the adsorbents, a pre-adsorption enhancing CO2 intermediate-temperature adsorption mechanism over LiNaK-LDH/CMS composite through air calcination processes is proposed. This study significantly advances LDH-based adsorbent for future research into CO2 intermediate-temperature adsorption.

Molecule‐level Design to Form Pocket Structures for Improving Amine Efficiency in CO2 Capture

AbstractSolid amine adsorbents represent a promising class of CO2 sorbents, but their amine efficiency is limited by the inaccessibility of peripheral amines. The surface of mesocellular silica foam (MCF) is functionalized with the mixture of short‐chain 3‐Glycidyloxypropyl) triethoxysilane (GPTES) and long‐chain Octadecyltrimethoxysilane (OTMS), forming pocket structures on the support surface, thereby exposing more amine sites and enhancing the amine efficiency of polyethylenimine (PEI). The resulting adsorbent demonstrates a high CO2 adsorption capacity (5.02 mmol g−1 at 50 °C, 10 vol.% CO2, and 50%RH), high amine efficiency (0.43 at the dry condition), outstanding cyclic stability (0.5% performance decline per cycle under the conditions of dry CO2 regeneration), and fast adsorption kinetics (15 min for adsorption saturation at 50 °C). First‐principles calculations and CO2 temperature‐programmed desorption (TPD) experiments demonstrate that the introduction of GPTES and OTMS is beneficial to decreasing adsorption energy and forming paired carbamic acid states and ammonium carbamate states.

Modeling of adsorption-controlled binary gas transport in ultratight porous media

Organic-rich ultratight porous media such as shales have complicated pore types and sizes, dictating their unique fluid transport and storage mechanisms. This paper introduces a diffusion-based binary gas (CH4 and CO2) transport model in such porous media, incorporating key transport and storage mechanisms. Binary gas mixture within the pore volume is divided into two domains: the free-phase and the sorbed-phase, both of which contribute to gas mass transport. Thermodynamic properties of the free phase are determined using the Peng-Robinson equation of state, while a modified extended Langmuir isotherm describes the sorbed phase. The bulk diffusion, Knudsen diffusion, and viscous diffusion are reconciled to describe binary gas transport in the free phase, while the surface diffusion is considered in the sorbed phase. The mass flux is finally related to the effective diffusion coefficient and the free-phase concentration gradient through coupling all transport mechanisms via the equivalent resister network model. The governing equations are solved numerically using a finite difference approach to simulate co-diffusion and counter-diffusion of a binary gas mixture in two nanoporous media, shale and coal.The results reveal that surface diffusion is more pronounced in coal than in shale due to coal's higher adsorption capacity. In co-diffusion cases, both free-phase and sorbed-phase concentrations decrease over time. However, the decline of sorbed-phase concentrations is slower than that of the free-phase. Moreover, CO2 tends to remain adsorbed within the coal matrix due to its stronger adsorption affinity, unlike CH4, which is more likely to flow out. In counter-diffusion cases, injected CO2 first accumulates near the fracture region and then diffuses further into the matrix. Despite shale's pore volume being twice that of coal, similar amounts of CO2 are injected, which can be attributed to coal's higher CO2 adsorption capacity.

Regulation of Coordinating Anions around Single Co(II) Sites in a Covalent Organic Framework for Boosting CO2 Photoreduction.

While photocatalytic CO2 reduction has been intensively investigated, reports on the influence of anions coordinated to catalytic metal sites on CO2 photoreduction remain limited. Herein, different coordinated anions (F-, Cl-, OAc-, and NO3 -) around single Co sites installed on bipyridine-based three-component covalent organic frameworks (COFs) were synthesized, affording TBD-COF-Co-X (X = F, Cl, OAc, and NO3), for photocatalytic CO2 reduction. Notably, the presence of these coordinated anions on the Co sites significantly influences the photocatalytic performance, where TBD-COF-Co-F exhibits superior activity to its counterparts. Combined experimental and theoretical results indicate that the enhanced activity in TBD-COF-Co-F is attributed to its efficient charge transfer, high CO2 adsorption capacity, and low energy barrier for CO2 activation. This study provides a new strategy for boosting COF photocatalysis through coordinated anion regulation around catalytic metal sites.

Triptycene based microporous hypercrosslinked polymer with amino functionality for selective CO2 capture

AbstractThe increasing CO2 concentration in the atmosphere contributes significantly to global warming, necessitating effective capture techniques. Though amine‐based solvents are commonly used, they have drawbacks like high energy consumption and corrosion. Physical adsorption using microporous sorbents with polar groups emerges as a promising alternative, offering high efficiency and selectivity for CO2 capture. This work presents the design of a new microporous hypercrosslinked polymer with amino groups derived from the 3D molecular building block triptycene (TBMP‐NH2), for CO2 capture applications. The triptycene unit in the polymer backbone provides high surface area, thermal stability, and microporosity. TBMP‐NH2 demonstrates excellent thermal stability (Td > 350°C), considerable microporosity, and a high BET‐specific surface area of 866 m2/g, making it a promising microporous adsorbent. It exhibits a high CO2 adsorption capacity of 1.86 mmol/g at 273 K and 1.23 mmol/g at 298 K, with a Qst value of 33.95 kJ/mol, indicating a physisorption mechanism where the micropore volume (Vmic = 0.359 cm3/g) plays a crucial role. TBMP‐NH2 displays good CO2/N2 and CO2/CH4 selectivity, outperforming several reported porous polymers. Owing to its high physiochemical and thermal properties, and efficient and selective CO2 capture ability, TBMP‐NH2 can be considered a promising material for CO2 capture and environmental remediation application.

Novel synthesis and application of zeolite-Y from waste clay for efficient CO2 capture and water purification

In the present study, the microwave-assisted hydrothermal method using sodium hydroxide (NaOH) has been used to synthesise zeolite-Y from three different waste clays (WC) from Teesside, Northeast of England, UK. The effects of microwave time intervals and WC type were investigated to produce crystalline zeolite-Y. All WCs and synthesised zeolites were characterised by scanning electron microscopy (SEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller surface area measurement (BET). The characterisation results showed that the zeolite-Y samples synthesised at 6 min intervals exhibited larger total pore volumes, higher surface areas, and higher crystallinity compared to the samples synthesised at 4 min intervals. Especially, the synthesised zeolite-Y from Clay 1 displayed high CO2 adsorption capacity, achieving 5.23 mmol/g at 298 K and 1 bar, with a maximum methylene blue removal of 94.3 %. This sample showed a surface area of 485 m²/g and a pore volume of 0.24 cm³/g, alongside an Si/Al ratio of 3.7, highlighting its excellent thermal stability at elevated temperatures. The high CO2 adsorption capacity combined with the high methylene blue removal efficacy makes the synthesised zeolite-Y from WC an excellent candidate for efficient CO2 capture and removal of methylene blue from contaminated water. Additionally, this study illustrates the potential for waste valorisation through the conversion of low-value WC into high-performance, value-added materials. This transformation not only mitigates waste disposal issues but also contributes to sustainable resource management and environmental protection by offering a practical solution for treating industrial effluents and gas emissions.

Enhancing photocatalytic performance of rose-shaped Co/Ni bimetallic organic framework for reducing CO2 to CO under visible light

Co-MOF-74, composed of Co salt as the metal source and 2,5-dihydroxyterephthalic acid as the organic ligand, is widely used as a catalyst for the photocatalytic reduction of CO2 due to its open metal sites, high porosity, large specific surface area, and high CO2 adsorption capacity. However, its effectiveness in CO2 conversion is limited by weak electron transfer capabilities and a high rate of electron/hole pair recombination. To address these limitations, a bimetallic strategy was employed to significantly improve the catalytic performance of Co-MOF-74 for photocatalytic CO2 reduction. Stable bimetallic Co/Ni-MOF-74-x (x = 1, 2, 3) with controllable morphology and metal ratios were synthesized by adjusting the molar ratios of Co2+ and Ni2+ and combining them with 2,5-dihydroxyterephthalic acid. The introduction of Ni2+ led to a significant increase in the specific surface area, from 204.999 m2/g (Co/Ni-MOF-74) to 790.873 m2/g (Co/Ni-MOF-74-1). In addition, the band gap of bimetallic Co/Ni-MOF-74-1 was narrowed to 1.4 eV, which enhanced charge transfer. As a result, photocatalytic experiments demonstrated that the CO2 conversion efficiency of bimetallic Co/Ni-MOF-74-1 was significantly improved, reaching 4.539 mmol/g/h, compared to that of the monometallic Co-MOF-74. Finally, a synergistic photocatalytic mechanism involving ligand activation was proposed to explain the reaction process of the bimetallic Co/Ni-MOF-74 catalyst. Meanwhile, this study highlights that the bimetallic strategy is an effective approach to optimizing the performance of MOF catalysts for the photocatalytic reduction of CO2.

Continuous flow synthesis of MOF UTSA-16(Zn), mixed-metal and magnetic composites for CO2 capture – toward scalable manufacture

UTSA-16(Zn) is a zinc and citrate-based metal-organic framework (MOF) which has shown highly promising performance for CO2 capture. However, the transition of this MOF to industrial application has been hindered as a scalable synthesis method has not yet been reported. Herein we report the first scalable continuous flow synthesis of UTSA-16(Zn), demonstrating a production rate of 173 g/h, which is a 77-fold increase compared to previously reported batch methods. Sustainability of the synthesis was maximised using low-cost non-toxic reagents and a low-energy flow reactor operating at atmospheric pressure. Chemical (reactant ratios, Zn/Mg mixed-metal) and process parameters (solvent ratio, flow rate, temperature) were optimised to continuously produce UTSA-16(Zn) which also demonstrated a high CO2 adsorption capacity up to 3.8 mmol/g and conversion yield of up to 66 %. Pristine MOFs are typically thermally insulating, thus thermal regeneration is challenging. To overcome this limitation, magnetic nanoparticles can be embedded within the MOF. This enables fast and energy efficient regeneration through magnetic induction heating. Here, citrate-coated Fe3O4 magnetic nanoparticles (MNP-CA) were successfully incorporated into the flow synthesis process of UTSA-16(Zn) to form UTSA-16(Zn)@MNP-CA magnetic framework composites (MFCs), representing the highest production rate reported of any MFC to date (152 g/h c.f. 13 g/h for MgFe2O4@UiO-66-NH2). UTSA-16(Zn)@MNP-CA MFCs demonstrate rapid heating under a magnetic field (26–150 °C in 60 s). The flow method developed herein is also widely applicable for scalable manufacture of other MOFs and MFCs, enabling their broader transition towards industrial applications.