Water Bridges Substitute for Defects in Amine-Functionalized UiO-66, Boosting CO2 Adsorption

The Open DAC 2023 Dataset and Challenges for Sorbent Discovery in Direct Air Capture

Direct air capture (DAC) of CO2 with porous adsorbents such as metal-organic frameworks (MOFs) has the potential to aid large-scale decarbonization. Previous screening of MOFs for DAC relied on empirical force fields and ignored adsorbed H2O and MOF deformation. We performed quantum chemistry calculations overcoming these restrictions for thousands of MOFs. The resulting data enable efficient descriptions using machine learning.

A Zero-Gap Gas Phase Photoelectrolyzer for CO2 Reduction with Porous Carbon Supported Photocathodes

A modified Metal-Organic Framework UiO-66-NH2-based photocathode in a zero-gap gas phase photoelectrolyzer was applied for CO2 reduction. Four types of porous carbon fiber layers with different wettability were employed to tailor the local environment of the cathodic surface reactions, optimizing activity and selectivity towards formate, methanol, and ethanol. Results are explained by mass transport through the different type and arrangement of carbon fiber support layers in the photocathodes and the resulting local environment at the UiO-66-NH2 catalyst. The highest energy-to-fuel conversion efficiency of 1.06 % towards hydrocarbons was achieved with the most hydrophobic carbon fiber (H23C2). The results are a step further in understanding how the design and composition of the photoelectrodes in photoelectrochemical electrolyzers can impact the CO2 reduction efficiency and selectivity.

Defective copper-based metal-organic frameworks for the efficient extraction of organosulfur compounds from garlic-processing wastewater

Organosulfur compounds (OSCs) in garlic-processing wastewater are decomposed and generated to toxic and harmful substances with unpleasant odors under anaerobic conditions. Herein, were report the successful development of novel copper-based metal organic framework (Cu-MOF) adsorbents with high adsorption capacities for OSCs in aqueous media. Defect-rich Cu-MOF-X samples, with particle sizes between 360 and 750 nm, synthesized hydrothermal in the presence of acetic acid (where X denotes the molar ratio of acetic acid relative to the pentadentate MOF linker H4PPYD). OSC adsorption experiments using allicin, ajoene and 2-ethenyl-4H-1,3-dithiine (2-VDT) showed that Cu-MOF-200 delivered fast adsorption kinetics and high OSC adsorption capacities (149.02-171.33 mg g-1) owing to the pore accessibility and range of adsorption sites in the MOF. FT-IR, Raman, and XPS analyses, together with density functional theory (DFT) calculations, verified the strong yet reversible adsorption of OSCs in Cu-MOF-200. Results guide the development of improved adsorbents for OSC capture from garlic-processing wastewater.

Modeling and spectroscopic investigation of U(VI) removal on porous amidoxime-functionalized metal organic framework derived from macromolecular carbohydrate

The investigation of interaction mechanism of U(VI) selective removal on amidoxime-functionalized metal organic framework (i.e., UiO-66(Zr)-AO) derived from macromolecular carbohydrate is conducive to apply metal organic frameworks in actual environmental remediation. The batch experiments showed that UiO-66(Zr)-AO displayed the fast removal rate (equilibrium time of 0.5 h), high adsorption capacity (384.6 mg/g), excellent regeneration performance (<10 % decrease after three cycles) towards U(VI) removal due to the unprecedented chemical stability, large surface area and simple fabrication. U(VI) removal at different pH can be satisfactorily fitted by diffuse layer modeling with cation exchange at low pH and an inner-sphere surface complexation at high pH. The inner-sphere surface complexation was further demonstrated by X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis. These findings revealed that UiO-66(Zr)-AO can be an effective adsorbent to remove the radionuclides from aqueous solution, which is crucial for recycling of uranium resource and decreasing the uranium harm to the environment.

Accessibility control of Cu sites to enhance adsorption capacity of ultra-low-concentration methyl mercaptan

Methyl mercaptan (MM) is a typical malodorous gas and low-concentration MM makes human uncomfortable. Adsorption is applied in industry to remove MM. However, adsorptive-site agglomeration results in that adsorbent is not fully utilized. In this work, pore size and unsaturated-site amount of Cu-based metal-organic frameworks (MOFs) were regulated by using different ligands to increase adsorptive-site accessibility for MM. As a result, when Cu²⁺ sites were imbedded in MOFs network, these sites were inaccessible for MM; when Cu²⁺ sites were occupied by none-network organics, these sites were accessible for MM after simple activation; when Cu²⁺ sites were occupied by water, these sites were the most effective for MM removal among above site species. Furthermore, with the increase of bonding sites in ligands, channel pore size of MOFs was increased. Both pore size and unsaturated-site amount were important to MM removal. When above MOFs were used in purification of ultra-low-concentration MM, the regulated MOFs with a big pore size (11 and 5 Å) and water-occupied sites showed a best removal capacity of 160.3 mg g^-1. The main result of this work is in favor of understanding structure-efficiency relationship in MOFs. This work also helps to develop effective adsorbents for ultra-low-concentration pollutants.

Amino Acid-Mediated Synthesis of the ZIF-8 Nanozyme That Reproduces Both the Zinc-Coordinated Active Center and Hydrophobic Pocket of Natural Carbonic Anhydrase

The zeolitic imidazolate framework-8 (ZIF-8) nanozyme has been synthesized using hydrophobic amino acid (AA) to regulate crystal growth. The as-synthesized ZIF-8 reproduces both the structural and functional properties of natural carbonic anhydrase (CA). Structurally, Zn²⁺/2-methylimidazole coordinated units mimic very well the active center of CA while the hydrophobic microdomains of the adsorbed AA simulate the CA hydrophobic pocket. Functionally, the nanozymes show excellent CA-like esterase activity by giving specific enzyme activity of 0.22 U mg^-1 at 25 °C in the case of Val-ZIF-8. More strikingly, such nanozymes are superior to natural CA by having excellent hydrothermal stability, which can give highly enhanced esterase activity with increasing temperature. The specific enzyme activity of Val-ZIF-8 at 80 °C is about 25 times higher than that at 25 °C. In addition, AA-ZIF-8 also shows an excellent catalytic efficiency toward carbon dioxide (CO₂) hydration. This study puts forward the important role of hydrophobic microdomains in biomimetic nanozymes for the first time and develops a facile and mild method for the synthesis of nanozymes with controlled morphology and size to achieve excellent catalytic efficiency.

Fabrication of Stable MIL-53(Al) for Excellent Removal of Rhodamine B

Adsorptive purification of organic dyes in wastewater is significant to protect the water environment. Herein, MIL-53(Al) was successfully fabricated through a facile and versatile solvothermal strategy. The stability of MIL-53(Al) under high temperature, acid, base, and peroxide conditions was investigated. The porous MIL-53(Al) had high chemical stability, and the thermal stability reached up to 500 °C, which provided a good foundation for dye removal. MIL-53(Al) showed excellent adsorption performance. The maximum adsorption capacity of MIL-53(Al) for rhodamine B (RhB) can reach 1547 mg g^-1 under 303 K, and the corresponding removal efficiency exceeded 90% at the equilibrium time (120 min). The Langmuir model and pseudo-second-order model can well fit RhB adsorption on MIL-53(Al). Thermodynamic study and activation energy values over the range of 298-323 K revealed that the adsorption of RhB was a spontaneous and endothermic physical process in nature. The batch experimental results, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared (FTIR) spectroscopy analyses suggested that the hydrogen bonding and electrostatic interactions between the hydroxyl/carboxyl groups of MIL-53(Al) and RhB were the primary adsorption mechanisms. Besides, MIL-53(Al) had a higher selectivity to RhB than the coexisting ions in aqueous solution and a superior adsorption performance after five cycles.

Strategies for induced defects in metal-organic frameworks for enhancing adsorption and catalytic performance

Metal-organic frameworks (MOFs) have emerged among porous materials. The designable structure and specific functionality make them stand out for diverse applications. In conceptual MOF, the metal ions/clusters and organic ligands...

Tailoring Defect Density in UiO-66 Frameworks for Enhanced Pb(II) Adsorption

Defect engineering of metal organic frameworks offers potential prospects for tuning their features toward particular applications. Herein, two series of defective UiO-66 frameworks were synthesized via changing the concentration of the linker and synthetic temperature of the reaction. These defective materials showed a significant improvement in the capability of Pb(II) removal from wastewater. This strategy for defect engineering not only created additional active sites, more open framework, and enhanced porosity but also exposed more oxygen groups, which served as the adsorption sites to improve Pb(II) adsorption. A relationship among degree of defects, texture features, and performances for Pb(II) removal was successfully developed as a proof-of-concept, highlighting the importance of defect engineering in heavy metal remediation. To investigate the kinetic and adsorption isotherms, we performed adsorption experiments influenced by the time and concentration of the adsorbate, respectively. For the practicality of the materials, the most significant parameters such as pH, temperature, adsorbent concentration, selectivity, and recyclability as well as simulated natural surface water were also examined. This study provides a clue for the researchers to design other advanced defective materials for the enhancement of adsorption performance by tuning the defect engineering.