Cation-Exchanged Zeolitic Chalcogenides for CO2 Adsorption

Synthesis of "Ice Cube" Shaped Zeolite A Type and Cu2+ Ion-Exchanged Zeolites and Study of Their CO2 Adsorption Performance

In this study, zeolite type A and four Cu2+ ion-exchanged zeolites were synthesized through cationic ion exchange process with Cu concentrations of 0.05, 0.1, 0.15, and 0.2 M respectively. The physicochemical properties of both the prepared and ion-exchanged zeolites were thoroughly analyzed. Field Emission Scanning Electron Microscopy (FESEM) micrographs revealed that the synthesized zeolites exhibited an "ice cube"-shaped morphology, and this morphology was maintained even after the ion exchange process. N2 adsorption/desorption studies indicated a typical type IV isotherm with an H3 hysteresis loop for both the prepared and Cu2+ ion-exchanged zeolites. CO2 adsorption data followed a type I isotherm, with the highest adsorption capacity of 4.02 mmol/g observed for the 0.1 M Cu2+ ion-exchanged zeolites. The adsorption behavior was modeled using a nonlinear isotherm, with good agreement between experimental and fitted data.

Equilibrium and Kinetic Insights into the Comprehensive Investigation of CO2, CH4, and N2 Adsorption on Cation-Exchanged X and Y Faujasite Zeolites

The adsorption equilibria and kinetic performance of CO2, CH4, and N2 on pelletized cation-exchanged faujasite zeolites (with alkali, alkaline earth, and transition metal ions) have been investigated by an innovative volumetric apparatus simultaneously. The standard instrumental analytical techniques, including X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy (EDX), and atomic absorption spectroscopy (AAS), were utilized to characterize binder-free modified zeolites. EDX and AAS analyses revealed that the ion exchange was successfully achieved. The results indicate that the type of cation present in the zeolite framework and the Si/Al ratio can have a significant impact on the adsorption capacity and kinetic performance. The obtained isotherms were determined by three isotherm models, and the Langmuir-Freundlich (Sips) model was found to show the best agreement with the experimental isotherm data for all gases. The CO2 uptakes of KX, MgX, and CaX reached 4.13, 4.79, and 5.48 mmol/g, respectively. The effective binary and kinetic selectivities of CO2/CH4 and CO2/N2 were also calculated. Among all samples, KX showed the highest CO2/CH4 and CO2/N2 selectivities of 54.46 and 91.62, respectively. Pseudo-first-, pseudo-second-order, and Avrami kinetic models were fitted to the experimental kinetic data to analyze the adsorption kinetics. Finally, the macropore diffusion coefficient (Dp) and microporous diffusional time constant (Dc/rc2) were estimated by correlating the micropore-macropore kinetic model with the experimental fractional uptake curves. Among the ion-exchanged zeolite samples, the K+ form exhibits a suitable performance in terms of kinetic behavior and adsorption capacity.

Synthesis of methanol over highly dispersed Cu-Fe based catalysts derived from layered double hydroxides

In this paper, catalysts with different aluminum contents were prepared by a co-precipitation method using LDHs (layered double hydroxides) as the precursors through the adjustment of Cu2+ : Fe2+, and the catalysts were named LDO catalysts. The effect of aluminum on CO2 hydrogenation to methanol was investigated by evaluating the characterization. With the addition of Al, Ar physisorption results showed an increase in BET-specific surface area, TEM demonstrated a decrease in catalyst particle diameter, XRD showed that Cu and Fe existed in the catalyst mainly in the form of CuFe2O4 and CuO, XPS demonstrated a decrease in electron cloud density and an increase in base sites and oxygen vacancies, and CO2-TPD and H2-TPD results indicated that Al promoted the dissociation and adsorption of CO2 and H2. When the reaction temperature was 230 °C, the pressure was 4 MPa, H2/CO2 = 2.5 and the space velocity was 2000 ml (h gcat)-1, the best conversion (14.87%) and the highest methanol selectivity (39.53%) of the catalyst were obtained at 30% aluminum content.

Rational Design of Carbon-Based Porous Aerogels with Nitrogen Defects and Dedicated Interfacial Structures toward Highly Efficient CO2 Greenhouse Gas Capture and Separation

CO₂ capture from flowing flue gases through adsorption technology is essential to reduce the emission of CO₂ to the atmosphere. The rational design of highly efficient carbon-based absorbents with interfacial structures containing interconnected porous structures and abundant adsorption sites might be one of the promising strategies. Here, we report the synthesis of nitrogen-doped carbon aerogels (NCAs) via prepolymerized phenol-melamine-formaldehyde organic aerogels (PMF) by controlling the addition amount of ZnCl₂ and the precursor M/P ratio. It has been revealed that NCAs with a higher specific surface area and interconnected porous structures contain a large amount of pyridinic nitrogen and pyrrolic nitrogen. These would act as the intrinsic adsorption sites for highly effective CO₂ capture and further improve the CO₂/N₂ separation efficiencies. Among the prepared samples, NCA-1-2 with a high micropore surface area and high nitrogen content exhibits a high CO₂ adsorption capacity (4.30 mmol g^-1 at 0 °C and 1 bar) and CO₂/N₂ selectivity (36.5 at 25 °C, IAST). Under typical flue gas conditions (25 °C and 1.01 bar), equilibrium gas adsorption analysis and dynamic breakthrough measurement associated with a high adsorption capacity of 2.65 mmol g^-1 at 25 °C and 1.01 bar and 0.81 mmol g^-1 at 25 °C and 0.15 bar. This rationally designed N-doped carbon aerogel with specific interfacial structures and high CO₂ adsorption capacity, high selectivity, and adsorption performance remained pretty stable after multiple uses.

Two new metal-chalcogenide-cluster-based frameworks with single metal ions of Zn2+(/Sb3+) serving as inter-cluster linkers

Two new metal-chalcogenide-cluster-based frameworks, in which P1-ZnSnS clusters are linked to each other by both corner-shared S^2- ions and single metal ions of Zn²⁺ (or Sb³⁺) to form one new 3D (3,4)-connected network (MCCF-22) and one 2D-layered framework (MCCF-23), respectively, are reported. Notably, MCCF-22 exhibits good performance toward photodegradation of methylene blue compared with its analogue framework with only S^2- ions as the linker.

Atomically precise metal chalcogenide supertetrahedral clusters: frameworks to molecules, and structure to function

Metal chalcogenide supertetrahedral clusters (MCSCs) are of significance for developing crystalline porous framework materials and atomically precise cluster chemistry. Early research interest focused on the synthetic and structural chemistry of MCSC-based porous semiconductor materials with different cluster sizes/compositions and their applications in adsorption-based separation and optoelectronics. More recently, focus has shifted to the cluster chemistry of MCSCs to establish atomically precise structure-composition-property relationships, which are critical for regulating the properties and expanding the applications of MCSCs. Importantly, MCSCs are similar to II-VI or I-III-VI semiconductor nanocrystals (also called quantum dots, QDs) but avoid their inherent size polydispersity and structural ambiguity. Thus, discrete MCSCs, especially those that are solution-processable, could provide models for understanding various issues that cannot be easily clarified using QDs. This review covers three decades of efforts on MCSCs, including advancements in MCSC-based open frameworks (reticular chemistry), the precise structure-property relationships of MCSCs (cluster chemistry), and the functionalization and applications of MCSC-based microcrystals. An outlook on remaining problems to be solved and future trends is also presented.

Stable 3D neutral gallium thioantimonate frameworks decorated with transition metal complexes for a tunable photocatalytic hydrogen evolution

Incorporating transition metal (TM) complexes into cluster-based chalcogenide frameworks is an effective synthetic strategy to induce structural diversity and control the optoelectronic properties, which may further improve their photocatalytic performance. However, limited studies have been conducted on frameworks constructed by TM complexes covalently bonded with supertetrahedral Tn clusters, let alone on their properties, especially photocatalytic H₂ activity. Herein, three new isostructural three-dimensional (3D) neutral inorganic-organic open frameworks of gallium thioantimonate comprised of thiogallate-based supertetrahedral T3 clusters that are covalently bonded with TM complexes ([TM(TEPA)]²⁺, TM = Mn/Ni/Fe, TEPA = tetraethylenepentamine) at the edges and are linked by single Sb³⁺ ions at the corner, namely, NCF-3-Mn/Ni/Fe have been solvothermally synthesized and structurally characterized, and display good thermal and chemical stability. Benefiting from an adjustable TM centre, the title compounds possess tunable photocatalytic H₂ evolution activity, among which NCF-3-Mn exhibits the highest photocatalytic activity probably due to its favourable band structure and enhanced carrier separation efficiency.

A pillar-layered chalcogenide framework assembled by [Mn5S12N12]n layers and [Sb2S5] inorganic pillars

Reported here is an attractive pillar-layered metal chalcogenide open framework, in which [Sb₂S₅] building units act as pillars between [Mn₅S₁₂(N₂H₄)₆]_n layers. The obtained compound exhibits high stability in both acid and base media and good performance in the electrocatalytic oxygen reduction reaction (ORR).

A novel copper-rich open-framework chalcogenide with chiral topology constructed from distinctive bimetallic [Cu5SnSe10] clusters

Reported here is the first chiral copper-rich open-framework chalcogenide with a quartz (qtz) topology built on distinctive [Cu₅SnSe₁₀] clusters connected by [SnSe₄] bridging units. Through in situ sulfur doping, sulfurized compounds could be obtained that exhibit improved photocatalytic performance. This work expands the family of COCs with new building blocks and topologies and demonstrates the significance of chalcogen doping in COCs.

Metal Chalcogenide Supertetrahedral Clusters: Synthetic Control over Assembly, Dispersibility, and Their Functional Applications

ConspectusMetal chalcogenide supertetrahedral clusters (MCSCs) bear the closest structural resemblance to II-VI or I-III-VI semiconductor nanocrystals and can be considered as well-defined ultrasmall "quantum dots" (QDs). Compared to traditional colloidal QDs that are typically associated with size dispersity, irregular surface atomic structures, poorly defined core-ligand interfaces, and random defect/dopant sites, the nano- or subnano-sized MCSCs feature precise structural properties such as atomically uniform size, precise structure, and ordered dopant distribution, all of which offer ample opportunities for a broad and in-depth understanding of the correlation between the precise local structure and site- or size-dependent properties, which are critical to the exploitation of their functional applications. Our previous Account in 2005 provided a narrative on the efforts to expand the structural diversity of open-framework materials using different-sized and compositionally tunable clusters as building blocks with a primary objective of integrating the semiconducting properties with porosity in zeolite-type solids. Over the past 15 years, significant progress has been made, particularly in the synthetic control of discrete clusters, allowing the establishment of the composition-structure-property correlation of the MCSCs to guide the optimization of their properties for various applications. In the present Account, the recent progress in MCSC-based chemistry is reviewed from three aspects: (1) controllable synthesis of new members and types of MCSC models and the development of organic-ligand-directed hybrid assembly modes for MCSC-based open frameworks; (2) new synthetic strategies for the discretization of MCSCs in crystal lattice and their dispersibility in solvents, affording practical applications of pure inorganic MCSCs as nanomaterials; and (3) functionality of MCSC-based materials including photochemical and electrochemical properties triggered by precise dopant/defect sites, open-framework-related functional expansion via host-guest chemistry, and dispersed cluster-based composite materials with synergy from functional multimetallic components. All these advances show that MCSCs with well-defined structures and atomically precise dopant/defect sites are powerful model systems for establishing the precise structure-composition-property correlation and understanding the photophysical dynamic behaviors, both of which are difficult or impossible to achieve in the traditional QD system. Perspectives on their potential applications are presented in terms of the amorphous assemblies of monodispersed MCSCs, MCSC-based two-dimensional layered materials, and optical/electronic devices.

Acid-Base-Resistant Metal-Organic Framework for Size-Selective Carbon Dioxide Capture

The development of practical porous materials for the selective capture of CO₂ from flue gas and crude biogas is highly critical for both environment protection and energy safety. Here, a novel metal-organic framework (FJI-H29) has been prepared, which not only has excellent acid-base resistance but also possesses polar micropores (3.4-4.3 Å) that can match CO₂ molecules well. FJI-H29 can selectively capture CO₂ from N₂ and CH₄ with excellent separation efficiency and suitable adsorption enthalpy under ambient conditions. Breakthrough experiments further confirm its practicability for both CO₂/N₂ and CO₂/CH₄ separation. All of these confirm FJI-H29 is a practical CO₂ adsorbent. Modeling calculations reveal that the confinement effect of micropores and the polar environment synergistically promotes the selective adsorption of CO₂, which will provide a potential strategy for the synthesis of a practical metal-organic framework for CO₂ capture.

Theoretical studies on carbon dioxide adsorption in cation-exchanged molecular sieves

The capture and storage of the greenhouse gas, CO₂, has attracted much interest from scientists in recent years. In this work, density functional theory (DFT) was used to study the adsorption of CO₂ in different cation-exchanged molecular sieves. The results show that for the monovalent metal (Li, Na, K, Cu) ion-exchanged molecular sieves (zeolite Y, ZSM-5, CHA and A), the adsorption capacities for CO₂ decrease in the order of Li⁺ > Na⁺ > K⁺ > Cu⁺. Cu⁺-exchanged zeolites are not suitable as adsorbents for CO₂. For the CO₂ adsorption capacities in different zeolites with the same exchanged cation, the adsorption energy decreases in the order of Y > A > ZSM-5 ≈ CHA for Li-exchanged zeolites, and ZSM-5 still has the lowest CO₂ adsorption energy for both Na- and K-exchanged zeolites. In the cation-exchanged Y zeolites with divalent metals (Be, Mg, Ca and Zn), the CO₂ adsorption performance increases in the order of Zn²⁺ < Be²⁺ < Ca²⁺ < Mg²⁺. Thus, Zn²⁺-exchanged zeolites are not suitable as adsorbents for CO₂.

Density functional theory was used to study the adsorption of CO₂ in cation-exchanged zeolite Y, ZSM-5, CHA and A. The adsorption energies and the interactions of cations on various zeolitic topologies towards CO₂ molecule was discussed.

A Water-Stable Terbium(III)-Organic Framework as a Chemosensor for Inorganic Ions, Nitro-Containing Compounds and Antibiotics in Aqueous Solutions

Effective detection of organic/inorganic pollutants, such as antibiotics, nitro-compounds, excessive Fe³⁺ and MnO₄ ^- , is crucial for human health and environmental protection. Here, a new terbium(III)-organic framework, namely [Tb(TATAB)(H₂ O)]⋅2H₂ O (Tb-MOF, H₃ TATAB=4,4',4''-s-triazine-1,3,5-triyltri-m-aminobenzoic acid), was assembled and characterized. The Tb-MOF exhibits a water-stable 3D bnn framework. Due to the existence of competitive absorption, Tb-MOF has a high selectivity for detecting Fe³⁺ , MnO₄ ^- , 4-nirophenol and nitroimidazole (ronidazole, metronidazole, dimetridazole, ornidazole) in aqueous through luminescent quenching. The results suggest that Tb-MOF is a simple and reliable reagent with multiple sensor responses in practical applications. To the best of our knowledge, this work represents the first Tb^III -based MOF as an efficient fluorescent sensor for detecting metal ions, inorganic anions, nitro-compounds, and antibiotics simultaneously.

A new cluster-based chalcogenide zeolite analogue with a large inter-cluster bridging angle

A new cluster-based chalcogenide zeolite analogue with a large inter-cluster bridging angle.

Highly open chalcogenide frameworks built from unusual defective supertetrahedral clusters

Two highly open chalcogenide frameworks built from unusual supertetrahedral SBUs.