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Non-aqueous absorbents (NAAs) have attracted increasing attention for CO 2 capture because of their great energy-saving potential. Primary diamines which can provide high CO 2 absorption loading are promising candidates for formulating NAAs but suffer disadvantages in regenerability. In this study, a promising strategy that using tertiary amines (TAs) as proton-transfer mediators was proposed to enhance the regenerability of an aminoethylethanolamine (AEEA, diamine)/dimethyl sulfoxide (DMSO) (A/D) NAA. Surprisingly, some employed TAs such as N,N-diethylaminoethanol (DEEA), N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA), 3-dimethylamino-1-propanol (3DMA1P), and N,N-dimethylethanolamine (DMEA) enhanced not only the regenerability of the A/D NAA but also the CO 2 absorption performance. Specifically, the CO 2 absorption loading and cyclic loading were increased by about 12.7% and 15.5%-22.7%, respectively. The TA-enhanced CO 2 capture mechanism was comprehensively explored via nuclear magnetic resonance technique and quantum chemical calculations. During CO 2 absorption, the TA acted as an ultimate proton acceptor for AEEA-zwitterion and enabled more AEEA to form carbamate species (AEEACOO - ) to store CO 2 , thus enhancing CO 2 absorption. For CO 2 desorption, the TA first provided protons directly to AEEACOO - as a proton donor; moreover, it functioned as a proton carrier and facilitated the low-energy step-wise proton transfer from protonated AEEA to AEEACOO - . Consequently, the presence of TA made it easier for AEEACOO - to obtain protons to decompose, resulting in enhanced CO 2 desorption. In a word, introducing the TA as a proton-transfer mediator into the A/D NAA enhanced both the CO 2 absorption performance and the regenerability, which was an efficient way to "kill two birds with one stone"., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

High-temperature solid adsorbent Li 4 SiO 4 has received broad attention due to its high theoretical adsorption capacity, high regeneration capacity, and wide range of raw materials for preparation. In this paper, a Li 4 SiO 4 adsorbent was prepared by MCM-48 as the silica precursor and modified by doping with metal ions (Ca 2+ and Na + ) for high-temperature capture of low-concentration CO 2 . The results showed that the surface of the Ca-doped (or Na-doped) Li 4 SiO 4 adsorbent developed some particles that are primarily composed by Li 2 CaSiO 4 (or Li 3 NaSiO 4 ). Furthermore, the grains of the adsorbents became finer, effectively increasing the specific surface area and enhancing adsorption performance. Under 15 vol% CO 2 , the maximum CO 2 adsorption was 25.63 wt% and 32.86 wt% when the Ca 2+ doping amount was 0.06 and the Na + doping amount was 0.12, respectively. These values were both higher than the adsorption capacity before the metal ion doping. After 10 adsorption/desorption cycles, the adsorption capacity of Na-doped Li 4 SiO 4 increased by 9.68 wt%, while that of Ca-doped Li 4 SiO 4 decreased by 7.98 wt%. This difference could be attributed to the easy sintering of the Ca-containing adsorbent. Furthermore, a biexponential model was used to fit the CO 2 adsorption curve of the adsorbent in order to study the adsorption kinetics. Compared to the conventional Li 4 SiO 4 , the Ca/Na-doped adsorbent offers several advantages, such as a high CO 2 adsorption capacity and stable cycling ability., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

To address the problems of the relatively high energy penalty and corrosivity of aqueous biphasic solvents, a novel nonaqueous biphasic solvent composed of 2-((2-aminoethyl)amino)ethanol (AEEA), dimethyl sulfoxide (DMSO), and N , N , N' , N″ , N″ -pentamethyldiethylenetriamine (PMDETA) was proposed for CO 2 capture. With optimization, this novel AEEA-DMSO-PMDETA (A-D-P) biphasic solvent could achieve a high CO 2 loading of 1.75 mol·mol -1 , of which 96.8% of the absorbed CO 2 was enriched in the lower phase with only 49.6% of the total volume. 13 C NMR analysis and quantum calculations revealed that A-D-P could absorb CO 2 to form not only carbamate but also carbamic acid species, which were stabilized by DMSO via hydrogen-bonding interactions. Most products were highly polar and preferred to dissolve in polar DMSO rather than the less polar PMDETA, thus leading to the phase change. The thermodynamics results showed that the heat duty of A-D-P was only 1.66 GJ·ton -1 CO 2 (393.15 K), which was significantly lower than that of the benchmark MEA (3.59 GJ·ton -1 CO 2 ) and the reported aqueous biphasic solvents. Moreover, A-D-P presented a noncorrosive behavior to steel after CO 2 saturation, clearly showing its superiority over MEA and the aqueous biphasic solvents. Therefore, with superior properties of energy savings and noncorrosiveness, the A-D-P biphasic solvent could be a promising candidate for CO 2 capture.

[Display omitted] • Proposing an innovative strategy of using a regulator to trigger the phase transition of PCAs. • The AEEA/EAE/PMDETA/DMSO PCA exhibited tunable phase transition behavior. • The AEEA/EAE/PMDETA/DMSO PCA featured good CO 2 absorption and desorption performance. • The AEEA-regulated phase transition mechanism was elucidated from the molecular level. • The combined sensible heat and latent heat amounted to 0.32 GJ·ton−1 CO 2 , 84% less than 30 wt% MEA. Secondary amines are highly suitable candidates for constructing non-aqueous phase change absorbents (PCAs) that boast low viscosity and regeneration heat. However, the secondary amine-based PCAs often encounter the challenge of inadequate phase separation. This study proposed an innovative strategy of tailoring the polarity of absorption products to facilitate the controllable phase transition of the secondary amine-based PCA. Specifically, using aminoethylethanolamine (AEEA) as a regulator of product polarity to endow the 2-(ethylamino)ethanol (EAE)/pentamethyldiethylenetriamine (PMDETA)/dimethyl sulfoxide (DMSO) non-aqueous absorbent with tunable liquid–liquid phase transition behavior. The AEEA/EAE/PMDETA/DMSO (A/E/P/D) PCA realized a high CO 2 loading of 0.77 mol·mol−1, with over 92% of the absorbed CO 2 being enriched in the CO 2 -rich phase, which exhibited a low viscosity of 13.83 mPa·s. The A/E/P/D PCA also possessed good reusability, maintaining a cyclic loading of 0.65 mol·mol−1 even after five absorption–desorption cycles. Analysis of the phase change mechanism indicated that AEEA reacted with CO 2 to form highly polar AEEA-derived products, which played a pivotal role in driving the phase transition of the A/E/P/D system. In brief, the AEEA-derived product easily combined with polar DMSO, creating a "polar sink" that continually attracted the medium-polar EAE-derived products. Consequently, these products clustered together to form the CO 2 -rich phase with less polar PMDETA being isolated to form the CO 2 -lean phase. Moreover, estimation of the regeneration heat demonstrated that the combined sensible heat and latent heat of A/E/P/D amounted to 0.32 GJ·ton−1 CO 2 , representing a significant reduction of 84% compared to 30 wt% MEA. This study provided a novel idea to manipulate the phase behavior of PCAs and offered a promising A/E/P/D PCA for energy-efficient CO 2 capture. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel solid–liquid biphasic solvent with controllable phase transition behavior was proposed. • The AEEA/AMP/NMP biphasic solvent produced solid precipitates near CO 2 saturation. • AEEA/AMP/NMP realized 48.9% reduction in regeneration heat compared to 30 wt% MEA. • AEEA's regulatory effect on the phase transition was unraveled from a molecular level. Solid-liquid biphasic solvents (SLBSs) hold promise as energy-efficient candidates for CO 2 capture. Nevertheless, the premature phase transition of current SLBSs leads to inopportune solid precipitation, posing operational challenges for the CO 2 capture system. This study proposed a promising strategy that using aminoethylethanolamine (AEEA) as a regulator to fine-tune the phase transition time node of the 2-amino-2-methyl-1-propanol (AMP)/N-methylpyrrolidone (NMP) SLBS, enabling the phase transition to occur precisely as desired. Experimental results showed that the AEEA/AMP/NMP (A/A/N) SLBS exhibited tunable phase transition time nodes, modulated by the concentration of AEEA. Specifically, with the addition of 0.2 mol·L−1 AEEA, the CO 2 loading associated with the phase transition increased significantly, from 0.19 to 0.54 mol·mol−1, approaching the saturation loading of 0.57 mol·mol−1. The delayed phase transition would facilitate the CO 2 absorption operation. The regulatory mechanism of AEEA on the phase transition were thoroughly studied via 13C NMR and quantum calculations. AMP reacted with CO 2 to produce AMPCOO− and AMPH+, which had a significantly stronger affinity for each other than for the solvent NMP, mediated by strong hydrogen bond interactions. Consequently, the continuous and fast aggregation of AMPCOO− and AMPH+ caused their swift precipitation from NMP. With the introduction of AEEA, the derived product AEEAH+ (S) COO– (P) acted as a bridge-builder, connecting AMPCOO− or AMPH+ and NMP via hydrogen bonds, increasing the solubility of the AMP-derived products in NMP, thus effectively delaying the phase transition. Thermodynamic analysis revealed that the A/A/N SLBS exhibited a total regeneration energy consumption of 1.94 GJ·ton−1 CO 2 , representing a significant reduction of 48.9 % compared to that of 30 wt% MEA. This study provided a novel idea for designing SLBSs with controllable phase transition behavior, and offered a promising A/A/N SLBS for energy-efficient CO 2 capture. [ABSTRACT FROM AUTHOR]

In this study, a novel N-doped carbon-coated dual Co and Co 3 S 4 nanoparticles composite (Co-Co 3 S 4 @NC) has been developed by pyrolysis of an ideal flower-like Co-ZIF precursor followed via subsequent hydrothermal sulfidation. Under visible-light irradiation, the Co-Co 3 S 4 @NC exhibits outstanding performances for CO 2 reduction with H 2 O vapor into CO (23.14 μmol g−1 h−1) and CH 4 (0.62 μmol g−1 h−1) in a continuous flow system, significantly outperforming the single Co@NC photocatalyst. The experimental results demonstrate that the energy band structure in Co-Co 3 S 4 @NC can provide a more favorable reduction potential for the effective reduction of CO 2. Moreover, the presence of Co 3 S 4 is beneficial for the rapid separation and transfer of charges, thereby enhancing the utilization of photogenerated charge carriers. Thanks to its unique composition, Co-Co 3 S 4 @NC possesses abundant active sites for chemisorption and activation of CO 2 , which facilitates CO 2 photoreduction. The reaction mechanism is revealed in detail by analyzing the key intermediate species obtained through in situ DRIFTS. The current work offers a facile route for the construction of MOF-derived composites for promising photocatalytic reactions. [Display omitted] • A novel flower-like Co-Co 3 S 4 @NC photocatalyst derived from Co-ZIF was designed. • The presence of dual Co and Co 3 S 4 nanoparticles in Co-Co 3 S 4 @NC enhanced the activation capacity of CO 2. • Co-Co 3 S 4 @NC exhibited excellent photocatalytic activity for CO 2 reduction. • The reaction mechanism was revealed in detail based on in-situ DRIFTS. [ABSTRACT FROM AUTHOR]

Highlights • A novel approach that introduces AMP to regulate the biphasic solvent was developed. • The viscosity of CO 2 -loaded solvent was significantly reduced upon introducing AMP. • The sensible heat of solvent regeneration was reduced by 42.6–58.9% upon introducing AMP. • The regulatory mechanism of AMP in biphasic system was comprehensively elucidated. Abstract Biphasic solvents have attracted increasing attention in recent years due to their great potential to reduce the energy consumption of carbon dioxide (CO 2) capture. In the present work, 2-amino-2-methyl-1-propanol (AMP) was used as a regulator to overcome the defects of a diethylenetriamine and pentamethyldiethylenetriamine (DETA-PMDETA) biphasic solvent—particularly, its high viscosity and inferior regenerability. The viscosity of the CO 2 -saturated biphasic solvent significantly decreased from 541.0 to 152.0 mPa·s and the CO 2 cyclic capacity increased from 1.85 to 4.28 mol·L−1 (M) when the formula of the biphasic solvent was changed from 2 M DETA + 3 M PMDETA (2D3P) to 0.5 M DETA + 1.5 M AMP + 3 M PMDETA (0.5D1.5A3P). The sensible heat requirement for the regeneration of the solvent 0.5D1.5A3P could be reduced by 58.9% compared with that of 2D3P. The results indicated the positive regulatory effects of AMP on the biphasic solvent. Based on the characterizations and quantum chemical calculation, the regulatory mechanism of AMP in the biphasic system was elucidated. In the DETA-PMDETA system, CO 2 was absorbed to mainly form DETA-carbamate. In the DETA-AMP-PMDETA system, CO 2 was first absorbed to form DETA-carbamate and AMP-carbamate, while AMP-carbamate was rapidly hydrolyzed to HCO 3 −/CO 3 2−, resulting in fewer carbamate products in the saturated solvent. Since HCO 3 −/CO 3 2− did not tend to form hydrogen bonds and decomposed more easily than DETA-carbamate, the DETA-AMP-PMDETA system presented a lower viscosity and better regeneration performance. Moreover, in the presence of AMP, free protons were easily generated by multiple pathways to facilitate the dissociation of DETA-carbamate, which resulted in a deep CO 2 stripping. Therefore, an AMP-regulated DETA-PMDETA biphasic solvent for low-viscosity and efficient regeneration of CO 2 capture would further reduce the associated energy consumption. [ABSTRACT FROM AUTHOR]

For its high potential in reducing energy penalty of power plant, the biphasic solvent for CO 2 capture has recently attracted increasing attention. In this work, a novel blend of N,N,N ′ ,N ″, N ″-pentamethyldiethylenetriamine (PMDETA) and diethylenetriamine (DETA) was used to obtain a liquid-liquid phase separation solvent. The CO 2 absorption loading of the PMDETA-DETA solvent (5 M, 4:1) was 0.613 mol CO 2 /mol of total amine, in which 99.7% of the capacity was contributed by the lower phase with 57% of the total volume. In addition, the PMDETA-DETA solvent maintained a high CO 2 absorption capacity and good phase separation at 30–60 °C. Based on the absorption results and the 13 C NMR analysis, the reaction mechanism of CO 2 absorption into PMDETA-DETA solvent was clarified. In the blend system, DETA played as a reactant to attack CO 2 and PMDETA played as a proton acceptor to deprotonate the zwitterion. Therefore, the presence of PMDETA in the solution helped DETA to react with CO 2 rather than participate in the deprotonation process of zwitterion, which ensured a high CO 2 absorption capacity. The phase change mechanism indicated that, as more CO 2 was absorbed into the system, the more products of carbamate and HCO 3 − /CO 3 2− migrated to the lower phase while more PMDETA migrated to the upper phase, which led to the phase separation. [ABSTRACT FROM AUTHOR]

Biphasic solvents are regarded as promising candidates for CO 2 capture but still suffer from the deficiency of inferior regenerability, which negatively affects their energy-saving potential. 2-Amino-2-methyl-1-propanol (AMP)-based absorbents have superior regenerability but poor phase-change performance. In this study, an effective strategy that using tetraethylenepentamine (TEPA) to regulate the phase change behavior of an AMP-pentamethyldiethylenetriamine (PMDETA) aqueous solution was proposed, aiming to develop a novel AMP-PMDETA-TEPA (A-P-T) biphasic solvent with good regenerability and excellent phase separation performance. The A-P-T biphasic solvent could realize a high CO 2 loading of 0.73 mol mol−1 and a high desorption efficiency of 75.3%. Its sensible heat requirement significantly decreased to 0.14 GJ·ton−1 CO 2 , 78.1% less than the monoethanolamine solution. The 13C NMR characterization and quantum chemistry calculations indicated that with the introduction of TEPA, high polar TEPA-associated products were generated, which broke the original assimilation state of the A-P-T system and drove it to undergo phase change. Since the TEPA-associated products had a strong affinity to other CO 2 -captured products and H 2 O, they gathered together to form the CO 2 -rich phase. In contrast, less polar PMDETA showed a relatively weak affinity to the TEPA-associated products and was solely separated from the solution to form the CO 2 -lean phase. [Display omitted] • A novel TEPA-regulated AMP-PMDETA biphasic solvent was proposed for CO 2 capture. • TEPA could effectively trigger the phase separation of the biphasic solvent. • The biphasic solvent realized 78.1% reduction in sensible heat compared to 30 wt% MEA. • The regulatory mechanism of TEPA was verified by 13C NMR and quantum calculations. [ABSTRACT FROM AUTHOR]

Biphasic solvents have been widely studied for CO 2 capture due to their remarkable energy-saving potentiality. However, most existing biphasic solvents suffer from the high viscosity of their CO 2 -rich phase. This study proposed a novel low-viscous secondary amine-based nonaqueous biphasic solvent for CO 2 capture. With dimethyl sulfoxide (DMSO) as the organic diluent and pentamethyldiethylenetriamine (PMDETA) as the phase splitting agent, the secondary amine of 2-methyl-ethynolamine (MAE) was proved to be the optimal candidate for preparing the biphasic solvent. The MAE/DMSO/PMDETA (M/D/P) biphasic solvent could realize a high CO 2 loading of 0.84 mol mol−1 and the viscosity of its CO 2 -rich phase was only 8.87 mPa s, which was significantly lower than that of most reported biphasic solvents. The reaction mechanism analysis revealed that M/D/P absorbed CO 2 to form products of protonated amines, carbamate, and carbamic acid species. Since the products were polar and showed a stronger affinity to polar DMSO, while less polar PMDETA was isolated, thereby resulting in a phase change. Thermodynamics analysis showed that the M/D/P biphasic solvent could sharply cut down the sensible heat and latent heat during CO 2 desorption. Eventually, the total regeneration energy penalty of M/D/P was significantly reduced by 46.3% compared with the benchmark aqueous MEA solution. [Display omitted] • A novel secondary amine-based nonaqueous biphasic solvent was proposed. • The biphasic solvent could realize a high CO 2 loading of 0.84 mol mol−1. • The viscosity of the CO 2 -rich phase was significantly reduced to 8.87 mPa s. • The mechanism of CO 2 absorption was comprehensively elucidated. • 46.3% reduction in regeneration energy penalty was achieved compared to 30 wt% MEA. [ABSTRACT FROM AUTHOR]

[Display omitted] • A nonaqueous monoethanolamine-based biphasic solvent was proposed for CO 2 capture. • The rich phase stored 95.3% of the absorbed CO 2 with only 56.8% of the total volume. • The mechanism of CO 2 absorption into the solvent was comprehensively elucidated. • The biphasic solvent significantly reduced the sensible heat and vaporization heat. • The biphasic solvent was noncorrosive to carbon steel during CO 2 capture. To advance carbon dioxide (CO 2) capture technology by simultaneously reducing the energy penalty and mitigating equipment corrosion, a novel nonaqueous biphasic solvent comprising monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), dimethyl sulfoxide (DMSO), and N,N,N',N'',N''- pentamethyldiethylenetriamine (PMDETA) was proposed for CO 2 capture in this study. The performance testing results demonstrated that the MEA-AMP-DMSO-PMDETA (M-A-D-P) biphasic solvent with the optimal composition could realize a high CO 2 loading of 0.88 mol·mol−1 and that its rich phase stored 95.3% of the absorbed CO 2 but constituted only 56.8% of the total volume. 13C NMR analysis and quantum chemical calculations showed that both MEA and AMP could absorb CO 2 to form carbamate and carbamic acid species, with the latter being the dominant reaction product. Since the products were polar and could form hydrogen bonds with polar DMSO, the two had satisfactory mutual solubility, while less polar PMDETA was isolated, thereby leading to a phase change. After phase separation, only the CO 2 -rich phase required regeneration. Consequently, M-A-D-P significantly reduced the sensible heat and vaporization heat by 63.1% and 94.8%, respectively, compared to the benchmark MEA solution. Moreover, the results of the corrosion test demonstrated that M-A-D-P was virtually noncorrosive to carbon steel; thus, it clearly outperformed the MEA solution. Therefore, the novel M-A-D-P biphasic solvent may be a promising candidate for advancing energy-efficient and noncorrosive CO 2 capture. [ABSTRACT FROM AUTHOR]

[Display omitted] • A C-modified porous In 2 O 3 catalyst were successfully synthesized through a hydrothermal method. • C-In 2 O 3 catalyst exhibited a superior CO 2 conversion under simulated point-concentrated sunlight irradiation. • The incorporation of C into In 2 O 3 exhibited a significant impact on its basic sites and CO 2 adsorption capabilities. • The synergistic effect of photocatalysis and thermal catalysis promoted the photothermal RWGS reaction. The solar-driven photothermal CO 2 conversion serves as an effective approach for addressing the substantial challenges of energy crises and global environmental issues. In this work, various forms of In 2 O 3 catalysts, including In 2 O 3 -c, In 2 O 3 -r, In 2 O 3 -s, and porous spherical In 2 O 3 , along with a C-modified porous spherical In 2 O 3 catalyst (C-In 2 O 3), were successfully synthesized through a hydrothermal method. An in-depth analysis was conducted to evaluate the performance of these catalysts in the point-concentrated solar-driven photothermal CO 2 hydrogenation. As a result, the porous C-In 2 O 3 catalyst exhibited a superior CO 2 conversion rate of approximately 13.2 % under simulated sunlight irradiation, with a light intensity of 44.6 mW/cm2. Notably, all catalysts demonstrated nearly 100 % selectivity towards CO (CO production rate of around 8.51 mmol g cat −1h−1) during the photothermal catalytic reaction, without any formation of CH 4. The outstanding performance of the C-In 2 O 3 catalyst was attributed to the modification of In 2 O 3 band structure by the incorporation of C, which significantly enhanced the intensive solar light absorption of the catalyst. Furthermore, incorporating C into In 2 O 3 substantially augments its basic strength and significantly elevates the quantity of basic sites, thereby endowing it with outstanding CO 2 adsorption and conversion capabilities. This work provides a C-modified engineering strategy to design efficient photothermal catalysts for boosting point-concentrated photothermal CO 2 hydrogenation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Water impacts CO 2 capture and phase changes in non-aqueous absorbents. • Water catalyzes and enhances CO 2 absorption efficiency in reactions. • Water-induced H-bond competition significantly weakens species interactions. • Enhanced solvation limits key product aggregation, reducing phase changes. • Controlling the water content in flue gas is essential for efficient CO 2 capture. Non-aqueous liquid–solid biphasic absorbents show significant potential for reducing energy consumption in CO 2 capture. However, the high hygroscopic nature of amine compounds and the approximately 10 % to 20 % water vapor in natural gas plants' flue gases challenge their efficiency and stability. This study investigated water's effects on the CO 2 absorption/desorption performance, phase-change behavior, and products of the non-aqueous absorbent 1,4-Butanediamine (BDA)/ethylene glycol (EG). Experimental results show that water significantly impacts absorption/desorption performance. The maximum CO 2 loading and regeneration efficiency were 1.4199 mol·mol−1 and 89.85 %, respectively. Water leads to the gradual disappearance of phase changes, with solid-phase CO 2 loading decreasing from 0.008 to 0.004 mol·g−1. Quantitative NMR demonstrates that carbamates and CO 3 2- / HCO 3 - are the main CO 2 -related products in aqueous systems, with their relative proportions affected by water content. Quantum chemical calculations and molecular dynamics simulations reveal that water enhances absorption efficiency by participating in the catalytic environment and reaction process. Water-induced hydrogen bonding competition is the leading cause of weakened interactions between species. Specifically, H-bonds between carbamate/protonated amines were decreased by 23.94 %. The enhanced solvation effect reduces aggregation of the key products, contributing to the gradual disappearance of phase changes. This study provides insights into water's effect on non-aqueous biphasic absorbents at the molecular level, offering a theoretical foundation for the development and optimization of absorbents suitable for use with steam-containing flue gases. [ABSTRACT FROM AUTHOR]

Herein, a core-shell structured Co 3 S 4 /NC@ZnS/NC heterojunction has been constructed via elaborately synthesizing metal-organic framework (MOF)-on-MOF precursors (ZIF-67@ZIF-8) and following controlled carbonization-sulfidation processes. The developed Co 3 S 4 /NC@ZnS/NC achieves higher performances for CO 2 photoreduction with water vapor towards CO (28.44 μmol g−1 h−1), CH 4 (1.93 μmol g−1 h−1) and C 2 H 4 (12.23 μmol g−1 h−1) in a continuous-flow condition under visible-light irradiation, which are significantly superior than those of Co 3 S 4 /NC and ZnS/NC. 13CO 2 isotope tracer analysis verifies that CO, CH 4 and C 2 H 4 originate from the carbon source of CO 2. Experiments and DFT calculations confirm that constructing an electron transport layer (ZnS/NC) in Co 3 S 4 /NC@ZnS/NC can contribute to a feasible channel for the enhanced separation and transfer of charge carriers. In heterojunction, non-bonding Co and Zn atomic pairs as adsorption sites synergistically participate in the CO 2 activation through the unique electron transport channel and acquire the lower energy barriers of COOH* formation. Moreover, in situ DRIFTS reveals the key intermediates and possible conversion pathways to main products. This work presents an attractive strategy to construct dual MOFs-derived metal sulfide heterojunctions for high-performance CO 2 conversion. [Display omitted] • A MOF-on-MOF strategy was proposed to prepare core-shell Co 3 S 4 /NC@ZnS/NC catalyst. • ZnS/NC as an electron transport layer greatly accelerated interfacial charge separation and transfer. • Co and Zn atomic pairs synergistically participated in the CO 2 activation through a unique electron transport channel. • Co 3 S 4 /NC@ZnS/NC achieved efficient photocatalytic CO 2 conversion onto C 2 production under visible–light irradiation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel 3DOM Ag 2 S-CoO x /NC had been developed by integrating ultrafine Ag 2 S QDs on the surface of 3DOM CoO x /NC. • The 3DOM Ag 2 S-CoO x /NC composite exhibited remarkable performances for the photocatalytic conversion of CO 2 and H 2 O vapor to fuels. • There were dual Z-scheme charge transfer pathways in the 3DOM Ag 2 S-CoO x /NC. • The key role of Ag 2 S QDs was served as an auxiliary to improve the electronic structure and facilitate adsorption/activation capacity of CO 2 and H 2 O. • The multiple photocatalytic mechanisms of CO 2 reduction were further identified by in situ DRIFTS. Rational design of advanced architectural photocatalysts with efficient separation and transfer of photoinduced charge carriers, and well solar light absorption ability is of critical significance for solar energy utilization and CO 2 -to-fuel conversion. Herein, a novel three-dimensional (3D) ordered hollow-wall hybrid composite (3DOM Ag 2 S-CoO x /NC) has been developed by integrating ultrafine Ag 2 S quantum dots (QDs) on the surface of metal–organic frameworks (MOFs)-derived hierarchically ordered macroporous nitrogen-doped carbon skeletons with implanted CoO x nanoclusters (3DOM CoO x /NC). Compared with pristine 3DOM CoO x /NC and traditional ZIF-67-derived CoO x /NC, the constructed 3DOM Ag 2 S-CoO x /NC composite exhibits remarkable performances toward the photocatalytic conversion of CO 2 and H 2 O vapor without any sacrifice reagents to fuels (CO-66.00 μmol g−1h−1, CH 4 -1.21 μmol g−1h−1 and C 2 H 4 -2.33 μmol g−1h−1) and a higher C 2 H 4 selectivity (16.47%) in the gas–solid system under light irradiation (λ > 420 nm). Impressively, dual Z-scheme charge transfer pathways in the 3DOM Ag 2 S-CoO x /NC can provide good channels for boosting electron transfer and charge separation. Experimental characterizations combined with density functional theory (DFT) calculations further elucidate that the key role of Ag 2 S QDs is served as an auxiliary in the 3DOM Ag 2 S-CoO x /NC catalyst to improve the electronic structure and further facilitate adsorption/activation capacity of CO 2 and H 2 O. Moreover, the multiple photocatalytic mechanisms including related key intermediates and conversion process of CO 2 molecules are further identified by in-situ diffuse reflectance infrared fourier transform spectra (DRIFTS). This innovation provides a novel strategy to design well-designed hierarchically porous hybrid structures for photocatalytic CO 2 reduction to high-value fuels. [ABSTRACT FROM AUTHOR]

[Display omitted] • A strategy that using AMP as a gelatinous product inhibitor in NNAs was proposed. • AMP-regulated NAAs did not yield insoluble gelatinous products during CO 2 absorption. • AMP-regulated NAAs featured good CO 2 capture performance. • CO 2 absorption mechanism was studied based on 13C NMR and theoretical calculations. • The inhibitory mechanism of AMP on the formation of gelatinous products was clarified. Diamines or polyamines with two or more amino groups are suitable for formulating non-aqueous absorbents (NAAs) with high CO 2 loading capacity and low regeneration energy consumption. However, these two types of amines in NAAs are prone to produce insoluble gelatinous products after absorbing CO 2 , resulting in difficult operation of the CO 2 capture system. In this study, by using 2-amino-2-methyl-1-propanol (AMP) as an inhibitor, the insoluble gelatinous products of the aminoethylethanolamine (AEEA)-N-methyl-2-pyrrolidone (NMP) (A-A-N) and 3-(methylamino)propylamine (MAPA)-NMP (M-A-N) NAAs were successfully eliminated. The experimental results showed that the AMP-regulated NAAs possessed a high absorption rate, high CO 2 loading capacity, excellent desorption efficiency, and stable recyclability. The reaction mechanism of CO 2 absorption and the inhibitory mechanism of AMP on the formation of gelatinous products were comprehensively elucidated. Taking the A-A-N system as a representative, AEEA reacted with CO 2 to form zwitterionic protonated carbamate species (AEEACO 2 − (P) H+ (S)), which tended to self-aggregate via hydrogen-bond interaction, resulting in the formation of insoluble gelatinous products. With the introduction of AMP, the AMP-derived products could combine easily with AEEACO 2 − (P) H+ (S) via strong electrostatic attraction to form ion pairs, preventing the AEEACO 2 − (P) H+ (S) molecules from self-aggregating to form insoluble gelatinous products. The regeneration heat duty of the A-A-N system was 1.89 GJ∙ton−1 CO 2 , which was 49.9 % lower than that of the benchmark 30 wt% MEA. Overall, introducing AMP as a gelatinous product inhibitor was beneficial for the development of NNAs with high CO 2 absorption capacity and low-energy consumption. [ABSTRACT FROM AUTHOR]

[Display omitted] • A ternary MOF-on-MOF strategy was introduced to synthesize the core double-shell FeS x @ZnS@CoS x catalyst. • FeS x @ZnS@CoS x exhibited the excellent catalytic activity for the CO 2 photoreduction. • FeS x @ZnS@CoS x structure with dual type II heterojunctions improved the separation of electron-hole pairs. • The superstructure of CoS x species provided abundant active sites and broadened light absorption capacity. The construction of core–shell structures derived from metal-organic framework (MOF) precursors is considered as a promising strategy for promoting photocatalytic CO 2 reduction. Herein, a core double-shell structure catalyst (FeS x @ZnS@CoS x) has been rationally fabricated by ternary MOF-on-MOF synthetic strategies combined with subsequent sulfidation treatments. The obtained FeS x @ZnS@CoS x exhibited appealing activity for photocatalytic CO 2 conversion with H 2 O vapor, affording a high CO generation rate of 69.90 μmol g−1 h−1 and CH 4 generation rate of 2.01 μmol g−1 h−1. The outstanding performances could benefit from the distinctive core double-shell structure, which effectively formed dual type II charge transfer channels to improve the separation and migration of photogenerated carriers. Besides, the superstructure of CoS x species can provide abundant active sites to increase CO 2 adsorption and meanwhile enhance the absorption spectrum in the visible light region, facilitating the CO 2 conversion. The possible reduction pathways and key reaction intermediates were revealed by in situ DRIFTS results. This work offers a feasible ternary MOFs strategy to develop multi core–shell structures for high photocatalytic performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • AMP as a regulator was used to tune the viscosity of the solid products of SLPCAs. • The AMP-regulated SLPCAs successfully yielded easily separated crystalline powders. • The TETA/AMP/NMP SLPCA was found to exhibit the best CO 2 capture performance. • The phase-change mechanism of CO 2 absorption into TETA/AMP/NMP was elucidated. • The regulatory effect of AMP on the physical form of the solid products was studied. Solid-liquid phase-change absorbents (SLPCAs) have a great potential to reduce the energy consumption of CO 2 capture. The main issue in the practical application of SLPCAs is the difficulty in the phase separation of gelatinous solid products. In this study, 2-amino-2-methyl-1-propanol (AMP) was used as a regulator to tune the physical form of the solid products of triethylenetetramine (TETA)-based SLPCAs. Experimental results showed that the AMP-regulated TETA-based SLPCAs successfully avoided the formation of gelatinous products (viscosity up to more than 1000 mPa·s) and yielded easily separated crystalline powders. Among the investigated SLPCAs, TETA/AMP/ N -methyl-2-pyrrolidone (NMP) (TETA:AMP = 2:8, 1 M) exhibited the best CO 2 capture performance with a high CO 2 loading of 0.94 mol·mol−1 and a high regeneration efficiency of 84.14 %. XRD, FT-IR and 13C NMR analyses indicated that TETA/AMP/NMP absorbed CO 2 to form highly polar carbamate species and protonated amines, which could break the original assimilation state of the SLPCA system; thus, the polar products precipitated out from less polar NMP, leading to a phase change. The theoretical calculations revealed that in the absence of AMP, the TETA-derived products had a tendency to form gelatinous aggregation with large amounts of hydrogen bonds; with the introduction of AMP, the AMP-derived products tended to combine with the TETA-derived products via strong electrostatic attraction and Van der Waals force and effectively inhibited the aggregation formation. Since there was only one hydrogen bond forming between the AMP- and TETA-derived product molecules, the amount of hydrogen bonds was significantly reduced. Eventually, the TETA/AMP/NMP SLPCA avoided the formation of gelatinous products and yielded crystalline powder products. [ABSTRACT FROM AUTHOR]