Theoretical study of transition metal-doped ß12 borophene as a new single-atom catalyst for carbon dioxide electroreduction.

The electrocatalytic carbon dioxide reduction reaction (CO2RR) presents a viable and cost-effective approach for the elimination of CO2 by transforming it into valuable products. Nevertheless, this process is impeded by the absence of exceptionally active and stable catalysts. Herein, a new type of electrocatalyst of transition metal (TM)-doped ß12-borophene (TM@ß12-BM) is investigated via density functional theory (DFT) calculations. Through comprehensive screening, two promising single-atom catalysts (SACs), Sc@ß12-BM and Y@ß12-BM, are successfully identified, exhibiting high stability, catalytic activity and selectivity for the CO2RR. The C1 products methane (CH4) and methanol (CH3OH) are synthesized with limiting potentials (UL) of -0.78 V and -0.56 V on Sc@ß12-BM and Y@ß12-BM, respectively. Meanwhile, CO2 is more favourable for reduction into the C2 product ethanol (CH3CH2OH) compared to ethylene (C2H4) via C-C coupling on these two SACs. More importantly, the dynamic barriers of the key C-C coupling step are 0.53 eV and 0.73 eV for the "slow-growth" sampling approach in the explicit water molecule model. Furthermore, Sc@ß12-BM and Y@ß12-BM exhibit higher selectivity for producing C1 compounds (CH4 and CH3OH) than C2 (CH3CH2OH) in the CO2RR. Compared with Sc@ß12-BM, Y@ß12-BM demonstrates superior inhibition of the competitive hydrogen evolution reaction (HER) in the liquid phase. These results not only demonstrate the great potential of SACs for direct reduction of CO2 to C1 and C2, but also help in rationally designing high-performance SACs.

Screening of Transition Metal Supported on Black Phosphorus as Electrocatalysts for CO2 Reduction.

The electrocatalytic CO2 reduction (CO2RR) is an effective and economical strategy to eliminate CO2 through conversion into value-added chemicals and fuels. However, exploring and screening suitable 2D material-based single-atom catalysts (SACs) for CO2 reduction are still a great challenge. In this study, 27 (3d, 4d, and 5d, except Tc and Hg) transition metal (TM) atom-doped black phosphorus (TM@BP) electrocatalysts were systematically investigated for CO2RR by density functional theory calculations. According to the stability of SACs and their effectiveness in activating the CO2 molecule, three promising catalysts, Zr@BP, Nb@BP, and Ru@BP, were successfully screened out, exhibiting outstanding catalytic activity for the production of carbon monoxide (CO), methyl alcohol (CH3OH), and methane (CH4) with limiting potentials of -0.79, -0.49, and -0.60 V, respectively. A catalytic relationship between the d-band centers of SACs and the limiting potential of CO2RR was used to estimate the catalytic activity of catalysts. Furthermore, Nb@BP has high selectivity for CO2RR to CH3OH compared to H2 formation, while the hydrogen evolution reaction significantly impacts the synthesis of CO and CH4 on Zr@BP and Ru@BP. Nitrogen atom doping in BP is beneficial for enhancing the selectivity of CO2RR, but it is detrimental to the activity of CO2RR. This study offers theoretical guidance for synthesizing highly efficient CO2RR electrocatalysts and further enhances structural modulation methods for layered 2D materials.

Single and double transition metal atoms doped graphdiyne for highly efficient electrocatalytic reduction of nitric oxide to ammonia.

The electrocatalytic conversion of nitric oxide (NORR) to ammonia (NH3) represents a pivotal approach for sustainable energy transformation and efficient waste utilization. Designing highly effective catalysts to facilitate the conversion of NO into NH3 remains a formidable challenge. In this work, the density functional theory (DFT) is used to design NORR catalysts based on single and double transition metal (TM:Fe, Co, Ni and Cu) atoms supported by graphdiyne (TM@GDY). Among eight catalysts, the Cu2@GDY is selected as a the most stable NORR catalyst with high NH3 activity and selectivity. A pivotal discovery underscores that the NORR mechanism is thermodynamically constrained on single atom catalysts (SACs), while being governed by electrochemical processes on double atom catalysts (DACs), a distinction arising from the different d-band centers of these catalysts. Therefore, this work not only introduces an efficient NORR catalyst but also provides crucial insights into the fundamental parameters influencing NORR performance.

In situ rapid synthesis of ionic liquid/ionic covalent organic framework composites for CO2 fixation.

IL/ICOF composites were in situ synthesized via a one-pot route in half an hour under ambient conditions for catalytic cycloaddition of CO2 with epoxides into cyclic carbonates. The prepared composites feature a decent CO2 adsorption capacity of 1.63 mmol g-1 at 273 K and 1 bar and exhibit excellent catalytic performance in terms of yield and durability. This work may pave a new way to design and construct functionalized porous organic frameworks as heterogeneous catalysts for CO2 capture and conversion.

Construction adsorption and photocatalytic interfaces between C, O co-doped BN and Pd-Cu alloy nanocrystals for effective conversion of CO2 to CO.

Photocatalytic reduction of carbon dioxide (CO2) into fuels is an auspicious route to alleviate the energy and environmental crisis brought by the continuous depletion of fossil fuels. The CO2 adsorption state on the surface of photocatalytic materials plays a significant role in its efficient conversion. The limited CO2 adsorption capacity of conventional semiconductor materials inhibit their photocatalytic performances. In this work, a bifunctional material for CO2 capture and photocatalytic reduction was fabricated by introducing palladium (Pd)-copper (Cu) alloy nanocrystals onto the surface of carbon, oxygen co-doped boron nitride (BN). The elemental doped BN with abundant ultra-micropores had high CO2 capture ability, and CO2 was adsorbed in the form of bicarbonate on its surface with the presence of water vapor. The Pd/Cu molar ratio had great impact on the grain size of Pd-Cu alloy and their distribution on BN. The CO2 molecules tended to be converted to carbon monoxide (CO) at interfaces of BN and Pd-Cu alloys due to their bidirectional interactions to the adsorbed intermediate species while methane (CH4) evolution might occur on the surface of Pd-Cu alloys. Owing to the uniform distribution of smaller Pd-Cu nanocrystals on BN, more effective interfaces were created in the Pd5Cu1/BN sample and it gave a CO production rate of 7.74 µmolg-1h-1 under simulated solar light irradiation, higher than the other PdCu/BN composites. This work can pave a new way for constructing effective bifunctional photo-catalysts with high selectivity to convert CO2 to CO.

Covalent Organic Framework/g-C3N4 van der Waals Heterojunction toward H2 Production.

Photocatalytic water splitting into H2 is the most economic and environmentally friendly strategy for H2 production, and rationally constructing a heterojunction retains enormous influence on a photocatalytic system. Herein, 2D/2D covalent organic framework/graphitic carbon nitride (COF/CN) van der Waals heterojunctions were readily prepared via an ultrasonic method for high-efficiency visible-light photocatalytic H2 production. The photocatalytic H2 production performance of optimized COF/CN composites can reach up to 449.64 µmol·h-1, which is approximately 5 times that of pure CN (89.08 µmol·h-1). The characterization and experimental studies reveal that the synergistic effect between COF and CN contributes to promoting the interfacial migration and spatial separation of photoinduced e--h+ pairs, further boosting the photocatalytic hydrogen production activity. This work may open a new window to design and fabricate effective heterojunction photocatalysts for photocatalytic energy conversion.

Boosting CO2 methanation on ceria supported transition metal catalysts via chelation coupled wetness impregnation.

The incipient wetness impregnation (IWI) method is widely used in the preparation of supported transition metal catalysts for its high throughput and cost-effective synthesis, yet suffers from poor metal-support interaction, restricting its further application at an industrial scale. Herein, a universal strategy of chelation coupled impregnation (CCI) is presented. The as-prepared Ni/CeO2(CCI) showed superior catalytic performance for CO2 conversion (84.3%) and CH4 selectivity (100%) under the experimental conditions (WGHSV = 24,000 mL g-1 h-1 and H2/CO2 = 4:1) even at low temperatures (T = 275 °C). The surface characterization results confirmed that the agglomeration of metal active sites in Ni/CeO2(CCI) was restricted and more surface oxygen vacancies were generated on CeO2. Further, the in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) analysis suggested that the surface oxygen vacancies that served as active sites could facilitate the direct dissociation of CO2 more favorably than the associative route, thus significantly promoting CO2 methanation activity.

Constructing highly porous carbon materials from porous organic polymers for superior CO2 adsorption and separation.

The increase in atmospheric carbon dioxide (CO2) concentration has led to numerous problems related to our living environment, seeking an efficient carbon capture and storage (CCS) strategy associated with low energy consumption and expenditures is highly desirable. Here, we demonstrate a facile approach to synthesize a series of highly porous carbon materials derived from porous organic polymers synthesized from three low-cost isomers of triphenyl using chemical activation with KOH at different temperatures. Compared with the precursor porous organic polymers, the porosity of the prepared porous carbon materials is significantly enhanced with surface areas as high as 3367 m2 g-1 and pore volumes up to 1.224 cm3 g-1. Notably, such porous carbon materials deliver an exceptionally high CO2 adsorption capacity of 7.78 mmol g-1 at 273 K and 1 bar, a value that is superior to most of the previously reported adsorbents. In addition, these porous organic polymers and derived porous carbon materials exhibit high CO2/N2 selectivity at ambient conditions. Therefore, the facile construction of highly porous carbon materials from porous organic polymers may offer an efficient strategy for CO2 adsorption and separation and further mitigates greenhouse effect.

Facile synthesis of anionic porous organic polymer for ethylene purification.

The removal of acetylene from ethylene is of vital significance in the petroleum and chemical industry, the presence of trace acetylene impurities in ethylene polymerization process could lead to the interruption of ethylene polymerization. Herein, we construct a new anionic porous organic polymer using potassium tetraphenylborate via Friedel-Crafts alkylation reaction under mild conditions. The resulting material, APOP, possesses good thermal stability and a decent BET surface area, as exemplified by thermogravimetric analysis measurement and nitrogen gas sorption experiment. Acetylene and ethylene adsorption isotherms reveal that APOP has a higher adsorption capacity of acetylene than that of ethylene under same conditions. Ideal adsorbed solution theory calculations and breakthrough experiments both demonstrate that APOP is capable of selective adsorption of acetylene over ethylene. To the best of our knowledge, APOP represents the first anionic porous organic polymer material capable of selective adsorption of acetylene over ethylene, and the exploration of APOP may provide a new way for these key gas separations using ionic porous organic polymer materials.

Enhanced flux and fouling resistance forward osmosis membrane based on a hydrogel/MOF hybrid selective layer.

Although forward osmosis (FO) technology has been widely adopted for water treatment, it still faces great challenges, including low permeability and fouling problem. Herein, a novel forward osmosis membrane was developed with a stable, uniform and defect-free polyvinyl alcohol/polydopamine coated zeolitic imidazolate framework (PVA/PDA@ZIF-8) hybrid selective layer to simultaneously enhance its transport property and fouling resistance. The prepared FO membrane exhibits improved water flux without losing the selectivity, since the PDA@ZIF-8 provide additional preferential passageway for water transporting while hinder the diffusion of salt. The optimized membrane shows a higher water flux than pristine PVA membrane (14.2 vs. 8.7 L m-2 h-1 in FO mode, 24.3 vs. 14.8 L m-2 h-1 in PRO mode) with a reasonable selectivity considering as Js/Jw value (0.44 vs. 0.4 g L-1 in FO mode, 0.38 vs. 0.33 g L-1). Moreover, the dynamic fouling experiments with organic foulants (protein and polysaccharide) indicate that the prepared membrane exhibits strong antifouling property and excellent permeation recovery ability (>95.0%) due to the optimized surface property. This study opens a new avenue for treatment wastewater by developing a forward osmosis membrane based on a hydrogel/MOF hybrid selective layer.

Dramatic enhancement of photocatalytic H2 evolution over hydrolyzed MOF-5 coupled Zn0.2Cd0.8S heterojunction.

MOF-5 has been criticized for its poor water stability, which results in complete damage of its traditional functionality. Therefore, there are very few researches about the further application of hydrolyzed MOF-5 (h-M). However, in this work, the h-M can function as both superior support and semiconductor for photocatalytic reaction after a water-based process. Herein, a rational design of Zn0.2Cd0.8S@h-MOF-5 (ZCS@h-M) heterojunction photocatalyst has been synthesized via a hydrothermal method with different mass ratio of ZCS. As demonstrated in the results of SEM and TEM, during the hydrothermal process, MOF-5 exfoliated into two-dimensional small sheets and ZCS nanoparticles embedded into h-M frameworks, which is in favor for the dispersion of ZCS and better interface connection, thus further boosts the migration of photogenerated charge carriers and protect the photocorrosion of ZCS, ultimately improves the photocatalytic hydrogen production. Optimal ZCS content of 10 wt% exhibited a significantly enhanced visible light photocatalytic hydrogen production efficiency of 15.08 mmol h-1 g-1, which far surpassed bare ZCS at 7.62 times. Furthermore, the ZCS@h-M showed outstanding stability during photocatalytic hydrogen production over a number of cycles.

Confining Polyoxometalate Clusters into Porous Aromatic Framework Materials for Catalytic Desulfurization of Dibenzothiophene.

Removal of notorious sulfur compounds to produce low-sulfur-content (≤10 ppm) diesel is necessary and vital for modern industry and environmental protection. A new type of inorganic-organic hybrid material has been designed and synthesized via confining molybdenum-containing polyoxometalate (POM) clusters within porous aromatic framework-1 (PAF-1) cavities named POM-PAF-1. Deep oxidative desulfurization experiments reveal that POM-PAF-1 possesses excellent reactivity under mild conditions, exemplified by a sulfur removal degree of 98.5% dibenzothiophene within 30 min at 30 °C. The improvement in oxidative desulfurization reactivity from traditional porous POM-based catalysts is owing to uniform POMs and lipophilic and porous PAF-1. The high performance of POM-PAF-1 in terms of excellent reactivity and good stability means it has potential in new heterogeneous catalysis.

Light Hydrocarbon Separations Using Porous Organic Framework Materials.

Light hydrocarbons (C1 -C3 ) are used as basic energy feedstocks and as commodity organic compounds for the production of many industrially necessary chemicals. Due to the nature of the raw materials and production processes, light hydrocarbons are generated as mixtures, but the high-purity single-component products are of vital importance to the petrochemical industry. Consequently, the separation of these C1 -C3 products is a crucial industrial procedure that comprises a significant share of the total global energy consumption per year. As a complement to traditional separation methods (distillation, partial hydrogenation, etc.), adsorptive separations using porous solids have received widespread attention due to their lower energy costs and higher efficiency. Extensive research has been devoted to the use of porous materials such as zeolites and metal-organic frameworks (MOFs) as solid adsorbents for these key separations, owing to the high porosity, tunable pore structures, and unsaturated metal sites present in these materials. Recently, porous organic framework (POF) materials composed of organic building blocks linked by covalent bonds have also shown excellent properties in light hydrocarbon adsorption and separation, sparking interest in the use of these materials as adsorbents in separation processes. This Minireview summarizes the recent advances in the use of POFs for light hydrocarbon separations, including the separation of mixtures of methane/ethane, methane/propane, ethylene/ethane, acetylene/ethylene, and propylene/propane, while highlighting the relationships between the structural features of these materials and their separation performances. Finally, the difficulties, challenges, and opportunities associated with leveraging POFs for light hydrocarbon separations are discussed to conclude the review.

Construction of a Stable Crystalline Polyimide Porous Organic Framework for C2 H2 /C2 H4 and CO2 /N2 Separation.

Utilization of porous materials for gas capture and separation is a hot research topic. Removal of acetylene (C2 H2 ) from ethylene (C2 H4 ) is important in the oil refining and petrochemical industries, since C2 H2 impurities deactivate the catalysts and terminate the polymerization of C2 H4 . Carbon dioxide (CO2 ) emission from power plants contributes to global climate change and threatens the survival of life on this planet. Herein, 2D crystalline polyimide porous organic framework PAF-120, which was constructed by imidization of linear naphthalene-1,4,5,8-tetracarboxylic dianhydride and triangular 1,3,5-tris(4-aminophenyl)benzene, showed significant thermal and chemical stability. Low-pressure gas adsorption isotherms revealed that PAF-120 exhibits good selective adsorption of C2 H2 over C2 H4 and CO2 over N2 . At 298 K and 1 bar, its C2 H2 and CO2 selectivities were predicted to be 4.1 and 68.7, respectively. More importantly, PAF-120 exhibits the highest selectivity for C2 H2 /C2 H4 separation among porous organic frameworks. Thus PAF-120 could be a suitable candidate for selective separation of C2 H2 over C2 H4 and CO2 over N2 .

A Crystalline Polyimide Porous Organic Framework for Selective Adsorption of Acetylene over Ethylene.

The separation of acetylene from ethylene is a crucial process in the petrochemical industry, as even small acetylene impurities can lead to premature termination of ethylene polymerization. Herein, we present the synthesis of a robust, crystalline naphthalene diimide porous aromatic framework via imidization of linear naphthalene-1,4,5,8-tetracarboxylic dianhydride and triangular tris(4-aminophenyl)amine. The resulting material, PAF-110, exhibits impressive thermal and long-term structural stability, as indicated by thermogravimetric analysis and powder X-ray diffraction characterization. Gas adsorption characterization reveals that PAF-110 has a capacity for acetylene that is more than twice its ethylene capacity at 273 K and 1 bar, and it exhibits a moderate acetylene selectivity of 3.9 at 298 K and 1 bar. Complementary computational investigation of each guest binding in PAF-110 suggests that this affinity and selectivity for acetylene arises from its stronger electrostatic interaction with the carbonyl oxygen atoms of the framework. To the best of our knowledge, PAF-110 is the first crystalline porous organic material to exhibit selective adsorption of acetylene over ethylene, and its properties may provide insight into the further optimized design of porous organic materials for this key gas separation.