Enhanced CO2 Adsorption Research Articles

S-scheme CuWO4@g-C3N4 core-shell microsphere for CO2 photoreduction

Utilizing solar energy to achieve artificial photosynthesis of chemical fuel is prevalent in tackling CO2 excessive emissions and energy deficiency. Engineering tailored morphology and constructing matched heterostructure are two significant schemes to elevate the CO2 photoconversion efficiency of g–C3N4–based composite. Herein, a novel S-scheme CuWO4@g-C3N4 core-shell microspheres were designed by a template-free hydrothermal and annealing approach. The CuWO4@g-C3N4 composite exhibits improved visible light harvesting, increased BET specific area, and enhanced CO2 adsorption ability. Further, S-scheme CuWO4@g-C3N4 heterojunction facilitates charge separation and realizes strong redox capability, contributing to elevated CO2 photoreduction performance. The CO yield rate for CuWO4@g-C3N4 composite reaches about 4.15 μmol g−1 h−1, which is 2.7 folds that of bare g-C3N4 (1.56 μmol g−1 h−1). Theoretical calculations unveil that the hydrogenation and reduction of *OCHO to *HCOOH are involved in a higher Eb of 0.39 eV than CO (0.24 eV), contributing to a high selectivity for CO yield. This work can be employed to fabricate more various g–C3N4–based composites for artificial photosynthesis.

Influence of mesoporous iron based nanoparticles on Chlorella sorokiniana metabolism during photosynthetic biogas upgrading

Three different mesoporous iron based nanoparticles (NPs) were added to Chlorella sorokiniana batch cultures devoted to photosynthetic biogas upgrading to enhance CO2 biofixation: Fe2O3, carbon coated zero valent iron NPs containing 7.26 % (wt%) of iron (CALPECH NPs) and carbon coated zero valent iron NPs containing 31.38 % (wt%) of iron (SMALLOPS NPS). The three types of NPs enhanced CO2 adsorption and therefore biogas upgrading in tests conducted in 1.2 L enclosed photobioreactors. However, the addition of 70 mg L−1 of CALPECH NPs resulted in a 2-fold enhancement in the microalgae productivity, and a carbohydrate and lipid content increase by 56 % and 25 %, respectively compared to the control assay. Under UV and visible light irradiation the addition of Fe2O3 NPs resulted in a 5.3-times fold enhancement in carbohydrate content when 70 mg L−1 was added. Similarly, the addition of 20 mg L−1 of SMALLOPS NPs increased the lipid content by 11 % under UV irradiation. Interestingly, CALPECH NPs did not significantly influence C. sorokiniana composition, suggesting that these particular NPs can act as UV scavengers. Therefore, the addition of mesoporous nanoparticles could improve CO2 fixation and microalgae productivity during photosynthetic biogas upgrading.

Conjugated Microporous Poly(aniline) Enabled Hierarchical Porous Carbons for Hg(II) Adsorption.

Hierarchical porous carbons equipped with heteroatoms and diffusion pores have a wide application prospect in adsorption. Herein, we report N-autodoped porous carbons (PTPACs), which were derived from rigid N-rich conjugated microporous poly(aniline)s (CMPAs) and show their all-around applicability in heavy metal adsorption. Their molecular structure could be delicately tuned from 3D organic networks to graphitic carbons through simply adjusting the pyrolysis temperature, affording unique hybrid features of hierarchical micro-meso-macroporosity and amount-tunable nitrogen defects, as validated by the enhanced CO2 adsorption capacities reaching 5.0 mmol g-1, a 230% increase compared to the precursor (2.15 mmol g-1). They therefore show promising a Langmuir adsorption capacity of 434.8 mg g-1 toward mercury ions, which could be rapidly achieved within a short 20 min. Based on the comprehensive experimental, characterization, and DFT calculation studies, we rationally reveal these impressive adsorptions arise from the hybrid function of chemisorption contributed by populated nitrogen defects and physical adsorption achieved by synergistic functions in the diffusion and storage pores. Outcomes mark the high merits of PTPACs in addressing recent global challenges in environmental engineering.

Cu doping and Ti3C2OH quantum dots co-modifications of Zn3In2S6 boosted photocatalytic reduction of CO2 to CO via accelerating carriers transfer and enhancing CO2 adsorption and activation

In this study, the Zn3In2S6 was modified by Cu doping and loading of Ti3C2OH quantum dots (QDs) by hydrothermal method for efficient and highly selective photoreduction of CO2. Various characterizations and tests demonstrated that the Cu0.05Zn2.95In2S6@Ti3C2OH QDs exhibited desired morphology, superior light utilization ability, and the most efficient carriers’ separation and transfer. This optimized material exhibited a CO yield of 51.848 μmol g-1 h-1, with selectivity up to 99%. This high CO yield was 22.3 and 3.48 times of those of the Zn3In2S6 and Cu0.05Zn2.95In2S6, respectively; demonstrating that synergistic effect of Cu-doping and Ti3C2OH QDs modification existed for enhancing CO2 reduction to CO. Results of CO2-TPD and in-situ FTIR showed that the Cu0.05Zn2.95In2S6@Ti3C2OH QDs possessed the greatest CO2 adsorption and activation ability. DFT (density functional theory) calculation revealed that greatest CO2 adsorption energy, CO desorption energy and charge density distribution were key factors for the Cu0.05Zn2.95In2S6@Ti3C2OH QDs to achieve efficient reduction of CO2. Possible CO2 reduction pathways and mechanism were proposed. This study could advance the development of photocatalysts for highly selective CO2 reduction to CO and enrich related mechanism insights.

Enhanced CO2 adsorption of activated carbon with simultaneous surface etching and functionalization by nitrogen plasma treatment

Enhanced CO2 adsorption of activated carbon with simultaneous surface etching and functionalization by nitrogen plasma treatment

Overturning photoreduction product of CO2 by defect- and COOH-functionalized multi-wall carbon nanotubes

We functionalize MWCNTs with defects and COOH groups to form MWCNTs30 through a novel discharge process. In the photoreduction of CO2 with pure H2O in the absence of sacrificial reagent, with CdS as light absorber, MWCNTs30 triggers a selective CH3OH production, with a CH3OH selectivity of 100% and an internal quantum efficiency of 3.9%, but CO is the only C-based product by using pristine MWCNTs without functionalization. The defects on MWCNTs30 are active sites for enhancing CO2 adsorption, H2O dissociation to produce H and H transfer to CO2, thus boosting CO2 hydrogenation to CH3OH. The COOH groups on MWCNTs30 provide H for promoting CO2 hydrogenation to CH3OH. The multiple roles of defects and COOH groups overturn the photoreduction product from CO to CH3OH. The results open a new way to achieve more efficient photoreduction of CO2 in the absence of noble metal and sacrificial reagent.

Surface and Defect Engineering Coupling of Halide Double Perovskite Cs2NaBiCl6 for Efficient CO2 Photoreduction

AbstractNon‐toxic halide double perovskite materials have many advantages of lead halide perovskite. Whereas, they usually exhibit poor stability and very low intrinsic photocatalytic CO2 reduction activity due to the insufficient separation of photogenerated charges and the lack of active sites. In this work, stable chlorine‐deficient 3D hierarchical Cs2NaBiCl6 porous microspheres assembled by highly crystalline nanoflakes were prepared by a simple grinding method. An unprecedented CO yield of 30.22 µmol g−1 h−1 was achieved in the gas‐solid photocatalytic reduction of CO2 without sacrificial agents, which is the highest value among lead‐free halide perovskite photocatalysts. Experimental results and density‐functional theory calculations show that the chlorine vacancy plays the triple role of suppressing photogenerated electron‐holes recombination, enhancing CO2 adsorption, and significantly reducing the free energy barrier for the key intermediate COOH* generation. In comparison with the pristine Cs2NaBiCl6, coupling of surface and defect engineering of the hierarchical sample brings 12.34 times enhancement of CO2 photoreduction activity. This work proposes a simple method to synthesize a chlorine‐vacancy rich 3D hierarchical lead‐free halide perovskite and offers a new design idea to substantially enhance the photocatalytic activity, opening a door for the prospective contribution of these materials to carbon neutralization.

Bi-amine functionalized mesostructured silica nanospheres for enhanced CO2 adsorption performance and fast desorption kinetics

A novel solid bi-amine adsorbent was synthesized by simultaneously impregnating pentaethylenehexamine (PEHA) and aminoethylethanolamine (AEEA) on the surfaces of mesoporous MCM–41 nanospheres. AEEA and PEHA had a synergistic effect during the CO2 adsorption of the bi-amine adsorbent and the highest CO2 adsorption capacity was 4.03 mmol·g−1. The bi-amine adsorbent exhibited the favorable recyclability because its saturated CO2 adsorption capacity decreased by 6.20 % after the initial eight adsorption/desorption cycles while by only 2.23 % in the following seven cycles. The adsorption activation energy and the desorption activation energy were determined to be 12.53 and 16.81 kJ·mol−1, respectively. The low value of the desorption activation energy suggested an inconsiderable energy requirement in the multicycles of the adsorbent. The characterization results indicated that hydrogen bonds were formed between the hydrogen atom in hydroxyl groups of AEEA and the oxygen atom in carbonyl groups of the carbamate. The synergistic effect between AEEA and PEHA was unveiled on the CO2 adsorption of the bi-amine adsorbent. The formed hydrogen bonds facilitated the release of protons from carbamic acids, enhanced the stability of the produced carbamate anions, and thus boosted the CO2 adsorption performance.

Microwave-assisted synthesis of bimetallic NiCo-MOF-74 with enhanced open metal site for efficient CO2 capture

Metal–organic frameworks (MOFs) containing two different inorganic metal nodes (known as bimetallic MOFs) could exhibit enhanced CO2 adsorption compared to their monometallic counterparts. Herein, a series of bimetallic NiCo-MOF-74 synthesized by microwave-assisted method were investigated for CO2 adsorption. It was revealed that narrow micropore channel with open metal site (OMS) of the bimetallic NiCo-MOF-74 influence CO2 binding affinity and CO2/N2 adsorption. The CO2 uptake of Ni1Co1-MOF-74 at 0 ​°C and 1 ​bar (100 ​kPa) was 8.30 ​mmol ​g−1 which is higher than those of Ni-MOF-74 (3.99 ​mmol ​g−1), Ni6Co1-MOF-74 (3.62 ​mmol ​g−1), Ni1Co6-MOF-74 (6.40 ​mmol ​g−1) and Co-MOF-74 (5.03 ​mmol ​g−1). While this could be related to the high specific surface area of Ni1Co1-MOF-74, Ni1CO2-MOF-74 with relatively low specific surface areas still shows good CO2 adsorption capacity up to 5.70 ​mmol/g, which is higher than those of adsorbents Ni-MOF-74, Ni6Co1-MOF-74 and Co-MOF-74, indicating that adsorption performance mainly relies on coordinated metals. Ni1Co1-MOF-74 showed remarkable recyclability performance, ranking selectivity of CO2/N2 reach up to 34, and suitable isosteric heat (31–23 ​kJ ​mol−1), manifesting a great probability for industrial CO2 capture. As revealed, incorporated Ni2+/Co2+ nodes within Ni1Co1-MOF-74, which are acting as active and open sites for CO2 capture, led to the synergetic effects comprising of micropores as well as dense dual-metal sites.

Advances in Biomimetic Photoelectrocatalytic Reduction of Carbon Dioxide.

Emerging photoelectrocatalysis (PEC) systems synergize the advantages of electrocatalysis (EC) and photocatalysis (PC) and are considered a green and efficient approach to CO2 conversion. However, improving the selectivity and conversion rate remains a major challenge. Strategies mimicking natural photosynthesis provide a prospective way to convert CO2 with high efficiency. Herein, several typical strategies are described for constructing biomimetic photoelectric functional interfaces; such interfaces include metal cocatalysts/semiconductors, small molecules/semiconductors, molecular catalysts/semiconductors, MOFs/semiconductors, and microorganisms/semiconductors. The biomimetic PEC interface must have enhanced CO2 adsorption capacity, preferentially activate CO2 , and have an efficient conversion ability; with these properties, it can activate CO bonds effectively and promote electron transfer and CC coupling to convert CO2 to single-carbon or multicarbon products. Interfacial electron transfer and proton coupling on the biomimetic PEC interface are also discussed to clarify the mechanism of CO2 reduction. Finally, the existing challenges and perspectives for biomimetic photoelectrocatalytic CO2 reduction are presented.

The Ga-promoted Ni/CeO2 catalysts for dry reforming of methane with high stability induced by the enhanced CO2 activation

Ni based catalyst performs high activity in methane dry reforming reaction but suffers from severe carbon deposition and deactivation. A series of CeO2 supported Ni catalysts promoted with various amounts of Ga were synthesized, and regulated the basic site of the catalysts. The Ni/CeO2 catalyst with 3 wt% Ga-doped shows the highest activity (XCH4 = 74% and XCO2 = 88%) and stability with the H2/CO ratio of 0.94 after a 35-h reaction without any carbon deposition. The CH4-CO2-CH4 pulse experiments indicate that the doping of Ga can produce enough oxygen species to eliminate the carbon deposition and maintain the catalytic activity. Superior activity with the better stability can be attributed to the enhanced CO2 adsorption and activation over the basic site of the catalyst, which is regulated by the introduction of Ga. These results provide a fundamental understanding of the relationship between the basic site regulated by Ga and the catalyst stability the Ni/CeO2 catalytic system.

Enhancing the CO2 adsorption kinetics on Na-RHO and Cs-MER zeolites by NH4F/H2O2 etching induced mesoporosity

The Na+-form (Na-RHO) of zeolite rho has emerged as a potential CO2 adsorbent with excellent selectivities toward CH4 and N2, but the very slow CO2 adsorption kinetics hinders its practical use. Here we report that mesoporous Na-RHO, prepared by NH4F/H2O2 etching, shows remarkably enhanced CO2 adsorption kinetics (ca. 7 min vs > 2 h) compared to the Na-RHO, which was also observed for the NH4F/H2O2-etched, Cs+-form (Cs-MER) of merlinoite. A combination of SEM, TEM, and N2 adsorption measurements demonstrates that such kinetics enhancement originated from the mesopore creation by fluoride medium etching, while minimizing the loss of zeolite crystallinity. The observed differences in the zeolite crystal morphology of Na-RHO and Cs-MER and in the characteristics of their intrinsic defect sites appear to be responsible for those in the shape and average size of the secondary mesopores created. The overall results of this study suggest that NH4F/H2O2 etching can be also applied to other small-pore zeolites to improve CO2 adsorption kinetics.

Sawdust wastes-derived porous carbons for CO2 adsorption. Part 2. Insight into the CO2 adsorption enhancement mechanism of low-doping of microalgae

Porous carbons produced using poplar sawdust are promising CO2 adsorbent applied under ambient conditions due to the low-cost preparation approach. CO2 uptake capability of the porous carbons produced from poplar sawdust can be effectively enhanced via doping an approximate amount of microalgae. The N-doped porous carbon produced from poplar sawdust using microalgae as N-doping source (microalgae/poplar sawdust=0.5:1) possesses an excellent capacity of 4.14 mmol·g−1 for CO2 uptake, nearly over 1.7 times that of the carbon without N-doping. The improved performance for CO2 uptake of porous carbons is mainly ascribed to the two-fold effect of microalgae doping: (i) generating extensive narrow pores and channels within the porous carbons owe to co-pyrolysis; (ii) introduction of N-containing moieties derived from the intrinsic N of microalgae increasing the surface polarity and alkalinity. The N-doped porous carbon granules derived from poplar sawdust are inferior to the powdered porous carbons for CO2 adsorption due to the destroyed structure. They still maintain the relatively desirable capability for CO2 adsorption (~3.0 mmol·g−1 during 5 cycles) and good mechanical property (10.96 ± 1.43 Mpa). Comprehensively considering the advantaged properties (low-pressure drop, high bulk density) required for practical application, the N-doped porous carbon granules derived from poplar sawdust with low-doping of renewable microalgae possess strong practicability.

The enhanced local CO concentration for efficient CO2 electrolysis towards C2 products on tandem active sites

Electrochemical reduction of CO2 to C2 products on Cu-based catalysts provides a promising approach for controlling the global carbon balance and restoring renewable surplus electricity. The enhanced CO2 adsorption and CO local concentration are beneficial for CO2 conversion and C2 intermediates formation, promoting the progress of CO2 utilization. Here, we report a bimetallic MOF-derived Co3O4-CuOx/C (M-CuCo/C) catalyst constructed with Co3O4 and CuOx sites wrapped in the carbon skeleton, achieving efficient CO2 activation and C2 generation under low overpotential. The optimized M-CuCo/C catalyst (Cu/Co ratio of 1:2) exhibits a total current density of 19.28 mA/cm2 at −1.05 (V vs. RHE), which is 8.60 times than that on MOF-derived CuOx/C (M-Cu/C). The highest C2 faradic efficiency (FE) reaches 79.2% (-0.75 V vs. RHE), accompany with a C2 production rate of 275.6 μmol/(g·h). The special nanorods-like morphology assembled by dual sites significantly increases electrochemical surface area and electron transmission rate during eCO2RR. The local CO intermediates under real-time electrochemical environment are monitored via rotation ring disk electrode (RRDE) techniques. Combined with in situ infrared measurements and DFT studies, it’s demonstrated that CO2 could be efficiently converted to CO under low overpotential on Co3O4 sites, forming local CO-enriched environment around neighboring CuOx sites and further accelerating the process of C2 formation.

Synergetic enhancement of activity and selectivity for reverse water gas shift reaction on Pt-Re/SiO2 catalysts

Catalytic reduction of CO2 with renewable H2 to CO via the reverse water gas shift (RWGS) reaction is an attractive approach to recycle CO2 and control net emission of CO2 to atmosphere. However, low activity and high CH4 selectivity at low temperatures limited the practical implementation of the reaction. Herein, Pt-Re/SiO2 catalysts with varying amount of Re were prepared with co-impregnation and tested for the RWGS reaction. Characterization results indicated that the oxophilic ReOx (0 ≤ x ≤ 3.5) located in close proximity to Pt particle, modified the surface of Pt by both partial coverage and electronic interaction, resulting in the reduced number of sites for and weakened strength of CO adsorption. At 400 °C, the turnover frequency (2.30 s−1) on the optimal Pt-Re/SiO2 catalyst (Pt/Re = 1.91) is 3.9 times higher than that on Pt/SiO2 under differential conditions, and the apparent activation energy is lowered. In contrast to Re/SiO2 which produces significant amount of CH4, the CO selectivity on Pt-Re/SiO2 maintained > 96.2 % under integral conditions. Reaction order analysis revealed that Pt facilitates H2 activation whereas the oxophilic ReOx enhances CO2 adsorption and activation. The perimeter sites at the Pt/ReOx interface with a balanced hydrogenation and C-O cleavage properties synergistically improve the RWGS activity while inhibiting CH4 production.

Controlling the Reconstruction of Ni/CeO2 Catalyst during Reduction for Enhanced CO Methanation

Reductive pretreatment is an important step for activating supported metal catalysts but has received little attention. In this study, reconstruction of the supported nickel catalyst was found to be sensitive to pretreatment conditions. In contrast to the traditional activation procedure in hydrogen, activating the catalyst in syngas created supported Ni nanoparticles with a polycrystalline structure containing an abundance of grain boundaries. The unique post-activation catalyst structure offered enhanced CO adsorption and an improved CO methanation rate. The current strategy to tune the catalyst structure via manipulating the activation conditions can potentially guide the rational design of other supported metal catalysts.

Fabrication of long-life quasi-solid-state Na-CO2 battery by formation of Na2C2O4 discharge product

Rechargeable Na-CO2 batteries are promising energy-storage devices due to their high energy density, environmental friendliness, and cost effectiveness. However, the insulating nature and irreversibility of the Na2CO3 discharge product cause large polarization and poor cyclicity. Here, we report a reversible quasi-solid-state Na-CO2 battery that is constructed by the synergistic action of a Co-encapsulated N-doped carbon framework catalyst and gel electrolyte to ensure the formation of a highly reversible Na2C2O4 discharge product. Experiments and density functional theory calculations indicate that the electron-agglomeration effect of Co nanoparticles enhances CO2 adsorption and lowers energy barrier, as well as promotes Na2C2O4 generation. A gel electrolyte containing an imidazole organic cation is used to inhibit the decomposition of the thermodynamically unstable Na2C2O4. The fabricated Na-CO2 battery exhibits a high discharge capacity of 3,094 mAh g−1, a high-rate performance of 1,777 mAh g−1 at a current density of 0.5 mA cm−2, and excellent cycling performance of 366 cycles (2,200 h).

Covalent triazine-based frameworks confining cobalt single atoms for photocatalytic CO2 reduction and hydrogen production

• Covalent triazine framework confining single Co atoms catalysts were fabricated. • Co-SA/CTF exhibited superior activity for solar-to-chemical energy conversion. • The superiority was due to enhanced CO2 adsorption and accelerated separation/transfer of charge carriers. Single-atom catalysts (SACs) have emerged as an advanced frontier in heterogeneous catalysis due to their potential to maximize the atomic efficiency. Herein, covalent triazine-based frameworks (CTFs) confining cobalt single atoms (Co-SA/CTF) photocatalysts have been synthesized and used for efficient CO 2 reduction and hydrogen production under visible light irradiation. The resulted Co-SA/CTF demonstrate excellent photocatalytic activity, with the CO and H 2 evolution rates reaching 1665.74 µmol g − 1 h − 1 and 1293.18 µmol g − 1 h − 1 , respectively, far surpassing those of Co nanoparticles anchored CTF and pure CTF. A variety of instrumental analyses collectively indicated that Co single atoms sites served as the reaction center for activating the adsorbed CO 2 molecules, which significantly improved the CO 2 reduction performance. Additionally, the introduction of Co single atoms could accelerate the separation/transfer of photogenerated charge carriers, thus boosting the photocatalytic performance. This study envisions a novel strategy for designing efficient photocatalysts for energy conversion and showcases the application of CTFs as attractive support for confining metal single atoms. Graphical abstract

Confined Jet Impingement Continuous Microchannel Reactor Synthesis of Ultrahigh-Quality Mesoporous Silica Nanospheres for CO2 Capture

Li4SiO4 has been evaluated as one of the most promising CO2 absorbers to mitigate climate changes caused by excessive CO2 emissions. Li4SiO4 absorbents with a high specific surface area would hold higher CO2 capture capacity. However, with the lack of suitable SiO2 precursors, the synthesis of Li4SiO4 absorbents with a high specific surface area and a well-defined hollow sphere structure was still challenging. Here, a two-stream confined jet impingement continuous microchannel reactor was proposed to produce ultrahigh-quality mesoporous silica nanospheres (UHMSNs) with an ultrahigh specific surface area and a small particle size. The obtained UHMSNs possessed excellent water dispersibility, a uniform diameter (142–207 nm), tunable perpendicular mesopores (2.6–3.3 nm), a high surface area (1347∼1854 m2/g), and a large pore volume 0.86∼1.23 cm3/g). Moreover, MesoDyn simulation provided valuable information to optimize the nucleation stage and the crystallization stage of UHMSNs. Additionally, UHMSNs were used as the silicon source to synthesize the petal-like hollow structure of Li4SiO4 microspheres, which enhanced CO2 adsorption.

Perovskite Oxyfluoride Ceramic with In Situ Exsolved Ni-Fe Nanoparticles for Direct CO2 Electrolysis in Solid Oxide Electrolysis Cells.

Solid oxide electrolysis cell (SOEC) is a potential technique to efficiently convert CO2 greenhouse gas into valuable fuels. Thus, there is significant interest in developing highly active and stable electrocatalysts for the CO2 reduction reaction (CO2RR). Herein, a Ni and F co-doping strategy is proposed to facilitate the exsolution reaction and form a new cathode, Ni-Fe alloy nanoparticles embedded in ceramic Sr2Fe1.5Mo0.5O6-δ (SFM) doped with fluorine. F-doping and Ni-Fe exsolution enhance CO2 adsorption by a factor of 2.4 and increase the surface reaction rate constant (kchem) for CO2RR from 6.79 × 10-5 to 18.1 × 10-5 cm s-1, as well as the oxygen chemical bulk diffusion coefficient (Dchem) from 9.42 × 10-6 to 19.1 × 10-6 cm2 s-1 at 800 °C. Meanwhile, the interfacial polarization resistance (Rp) decreases by 52%, from 0.64 to 0.31 Ω cm2. At 800 °C and 1.5 V, an extremely high current density of 2.66 A cm-2 and a stability test over 140 h are achieved for direct CO2 electrolysis in the SOEC.