A novel Zn-based-MOF for efficient CO2 adsorption and conversion under mild conditions

Amphiphilic Zeolitic Imidazolate Framework for Improved CO2 Separation in PIM-1 Mixed Matrix Membranes

This study aims to enhance the compatibility between filler and polymer in mixed matrix membranes (MMMs), addressing an important challenge in membrane development. ZIF-94, known for its affinity to CO2, was partially modified with 2-undecylimidazolate (umIm) through the solvent-assisted ligand exchange (SALE) method to improve its compatibility with the prototypical polymer of intrinsic microporosity PIM-1. The modified ZIF-94 (ZIF-94-umIm) can be considered as an amphiphilic MOF with both hydrophilic and hydrophobic moieties, while maintaining a considerably high CO2 adsorption capacity (2.34 mmol g-1 at 90 kPa and 0 °C). Gas separation experiments were performed using mixed gas compositions of 15/85 CO2/N2 at 3 bar and 35 °C. The resulting MMM with a 5 wt.% loading exhibited an enhanced CO2 separation performance, with ca. 70% and 10% increases in CO2 permeability (8900 Barrer) and CO2/N2 selectivity (20.2), respectively, compared to pristine PIM-1 membranes. In addition, thin film nanocomposite membranes were prepared showing a 23.5 CO2/N2 selectivity at 2350 GPU of CO2. This modification strategy shows a great potential for improving the CO2 capture technologies, highlighting the potential of tailoring MOF fillers for advanced membrane materials in gas separation applications.

Chemical CO2 fixation by a heterogenised Zn(ii)-hydrazone complex

A new Zn(ii) coordination compound, [Zn(HL)(OAc)2] (1), with ONN-donor hydrazone ligand (HL = (E)-4-amino-N'-(1-(pyridin-2-yl)ethylidene)benzohydrazide) was synthesized and structurally characterized by using spectroscopic techniques and X-ray analysis. These analyses indicated that the Zn(ii) ion in the resulting coordination compound is five coordinated and the compound has a free amine functionality on the phenyl ring. Thus, [Zn(HL)(OAc)2] (1) was immobilized on the surface of propionylchloride functionalized silica gel through an amidification process via the reaction of the aniline part of compound 1 and the acyl chloride group of the support. The synthesized heterogeneous catalyst, Si-[Zn(HL)(OAc)2], was characterized by several analytical methods and the results confirmed the successful support of 1 on the surface of the support. Si-[Zn(HL)(OAc)2] was used in a chemical CO2 fixation reaction and styrene epoxide was used as a model substrate to investigate the catalytic performance of the supported Zn(ii) catalyst. Si-[Zn(HL)(OAc)2] can efficiently catalyze the formation of cyclic carbonate from the reaction of epoxide and CO2 in the presence of TBAB as a co-catalyst.

The Impact of Metal Centers in the M-MOF-74 Series on Formic Acid Production

The confinement effect of porous materials on the thermodynamical equilibrium of the CO2 hydrogenation reaction presents a cost-effective alternative to transition metal catalysts. In metal-organic frameworks, the type of metal center has a greater impact on the enhancement of formic acid production than the scale of confinement resulting from the pore size. The M-MOF-74 series enables a comprehensive study of how different metal centers affect HCOOH production, minimizing the effect of pore size. In this work, molecular simulations were used to analyze the adsorption of HCOOH and the CO2 hydrogenation reaction in M-MOF-74, where M = Ni, Cu, Co, Fe, Mn, Zn. We combine classical simulations and density functional theory calculations to gain insights into the mechanisms that govern the low coverage adsorption of HCOOH in the surrounding of the metal centers of M-MOF-74. The impact of metal centers on the HCOOH yield was assessed by Monte Carlo simulations in the grand-canonical ensemble, using gas-phase compositions of CO2, H2, and HCOOH at chemical equilibrium at 298.15-800 K, 1-60 bar. The performance of M-MOF-74 in HCOOH production follows the same order as the uptake and the heat of HCOOH adsorption: Ni > Co > Fe > Mn > Zn > Cu. Ni-MOF-74 increases the mole fraction of HCOOH by ca. 105 times compared to the gas phase at 298.15 K, 60 bar. Ni-MOF-74 has the potential to be more economically attractive for CO2 conversion than transition metal catalysts, achieving HCOOH production at concentrations comparable to the highest formate levels reported for transition metal catalysts and offering a more valuable molecular form of the product.

Current Status and Challenges for Metal-Organic-Framework-Assisted Conversion of Biomass into Value-Added Chemicals

Owing to the abundance of availability, low cost, and environmental-friendliness, biomass waste could serve as a prospective renewable source for value-added chemicals. Nevertheless, biomass conversion into chemicals is quite challenging due to the heterogeneous nature of biomass waste. Biomass-derived chemicals are appealing sustainable solutions that can reduce the dependency on existing petroleum-based production. Metal-organic frameworks (MOFs)-based catalysts and their composite materials have attracted considerable amounts of interest in biomass conversion applications recently because of their interesting physical and chemical characteristics. Due to their tunability, the catalytic activity and selectivity of MOF-based catalyst/composite materials can be tailored by functionalizing them with a variety of functional groups to enhance biomass conversion efficiency. This review focuses on the catalytic transformation of lignocellulosic biomass into value-added chemicals by employing MOF-based catalyst/composite materials. The main focus is given to the production of the platform chemicals HMF and Furfural from the corresponding (hemi)cellulosic biomass, due to their versatility as intermediates for the production of various biobased chemicals and fuels. The effects of different experimental parameters on the conversion of biomass by MOF-based catalysts are also included. Finally, current challenges and perspectives of biomass conversion into chemicals by MOF-based catalysts are highlighted.

CO2 Adsorption on N-Doped Porous Biocarbon Synthesized from Biomass Corncobs in Simulated Flue Gas

This study was to develop a low-cost N-doped porous biocarbon adsorbent that can directly adsorb CO₂ in high-temperature flue gas from fossil fuel combustion. The porous biocarbon was prepared by nitrogen doping and nitrogen-oxygen codoping through K₂CO₃ activation. Results showed that these samples exhibited a high specific surface area of 1209-2307 m²/g with a pore volume of 0.492-0.868 cm³/g and a nitrogen content of 0.41-3.3 wt %. The optimized sample CNNK-1 exhibited a high adsorption capacity of 1.30 and 0.27 mmol/g in the simulated flue gas (14.4 vol % CO₂ + 85.6 vol % N₂) and a high CO₂/N₂ selectivity of 80 and 20 at 25 and 100 °C and 1 bar, respectively. Studies revealed that too many microporous pores could hinder CO₂ diffusion and adsorption due to the decrease of CO₂ partial pressure and thermodynamic driving force in the simulated flue gas. The CO₂ adsorption of the samples was mainly chemical adsorption at 100 °C, which depended on the surface nitrogen functional groups. Nitrogen functional groups (pyridinic-N and primary and secondary amines) reacted chemically with CO₂ to produce graphitic-N, pyrrolic-like structures, and carboxyl functional groups (-N-COOH). Nitrogen and oxygen codoping increased the amount of nitrogen doping content in the sample, but acidic oxygen functional groups (carboxyl groups, lactones, and phenols) were introduced, which weakened the acid-base interactions between the sample and CO₂ molecules. It was demonstrated that SO₂ and water vapor had inhibition effects on CO₂ adsorption, while NO nearly has no effect on the complex flue gas. Cyclic regenerative adsorption showed that CNNK-1 possessed excellent regeneration and stabilization ability in complex flue gases, indicating that corncob-derived biocarbon had excellent CO₂ adsorption in high-temperature flue gas.

De novo synthesis of a MIL-125(Ti) carrier for thermal- and pH-responsive drug release

Microporous round cake-like (diameter: 900 ± 100 nm) MIL-125(Ti) carrier with a central metal (Ti) exhibiting bio-affinity and possessing a great potential to be used as drug release platform, has been synthesized in the present study. The thermal and pH responsiveness of drug delivery systems (DDS) are the most important parameters for drug release and can be provided through polymer coating techniques. The Pluronic F127 (F127) and chitosan (CH) monomers were inserted into the crystal lattice of MIL-125(Ti) carrier during the de novo synthesis process, which were subsequently loaded with doxorubicin (DOX). The results reveal particle size changes (ranged between 30 and 50 %) from the original size of the MIL-125(Ti) carrier in response to temperature and pH when the carrier reaches acid environment. The drug release profiles have been completed through self-design device, which provides for the real-time release in the DOX amounts via UV-Vis spectra. The kinetics analysis was used to evaluate the R² values of first order, Higuchi, Korsmeyer-peppas, and Weibull fitting equations, where the Weibull fitting indicated the best R². An increase by 59.3 % of DOX released under the acid status (pH = 5.4) was observed, indicating that the CH-MIL-125(Ti) carrier is temperature and pH responsive. Moreover, the lattice explosion resulting from the temperature increase in the range of 25-42 °C caused an increase in F127-MIL-125(Ti) by 30.8-38.3 %. The simulated SAXS/WAXS studies for the microstructures of MIL-125(Ti) based DDS at different temperatures after polymer coating (F127-MIL-125(Ti)) provide the possible mechanism of lattice explosion. As such, the responsive Ti-MOF has a highly potential for use in the applications of cancer treatment.