Organic Framework Nanosheets Research Articles

Liquid phase exfoliation of metal–organic frameworks in aqueous quaternary ammonium hydroxide solution enables highly efficient photocatalytic CO2 reduction

Metal−organic framework nanosheets (MONs) show promising applications in many fields, but the production of large amounts of high-quality MONs remains a challenge. Here, we report a general liquid-phase stripped approach to exfoliate a benzoic acid linked MOF (Al2(OH)2TCPP-Co) in water by using quaternary ammonium hydroxides as deprotonation reagent, intercalator and stabilizer simultaneously. It is shown that the stripped yield is high up to 27.5%, the thickness of MONs is mainly 1–3 nm, and the horizontalsize is less than one hundred nanometers. The molecular geometry and alkalinity of quaternary ammonium hydroxides play vital roles in the exfoliation of MONs. Moreover, the MONs have been applied as photocatalysts for the conversion of CO2 to CO in a gas–solid model under UV–visible light illumination without using anyphotosensitizer and sacrificialagents. The productivity rate of CO is 118.7 μmol g−1 h−1, which outperforms most of the photocatalysts reported previously. Thus, the liquid phase stripping method reported in this work has great potential in the large-scale production of MONs for efficient photocatalysis of CO2 reduction in the gaseous phase.

Fabrication of novel thin-film composite membrane based on ultrathin metal-organic framework interlayer for enhancing forward osmosis performance

To improve operation efficiency, an interlayered thin-film composite forward osmosis (iTFC-FO) membrane was designed by introducing an ultrathin and porous interlayer based on aluminum tetra-(4-carboxyphenyl)porphyrin (a stable metal−organic framework nanosheet, Al-MOF). Surface characterization results revealed that Al-MOF spread evenly in the macro-porous substrate, and provided a flat and smooth reaction interface with moderate hydrophilicity and uniform small aperture. The resultant polyamide (PA) layer had a thin base (without intrusion into substrate) and crumpled surface (with abundant leaves). The leaves size and cross-linking degree of PA layer firstly increased and then decreased with the Al-MOF loading. Compared to the original membrane, the iTFC-FO showed an enhanced water permeability and a reduced reverse sodium flux in both modes of active layer facing feed solution (AL-FS) and active layer facing draw solution (AL-DS). To be specific, the specific reverse sodium flux (reverse sodium flux/pure water flux) decreased from 0.27 g/L to 0.04 g/L in the AL-FS mode, while from 1.36 g/L to 0.23 g/L in the AL-DS mode with 2 mol/L NaCl as DS. Moreover, the iTFC-FO maintained high stability and high permeability under high-salinity and contaminated environment. This study offers a new possibility for the rational fabrication of high-performance TFC-FO membranes.

Symbiotically Reinforced Bimetallic Photocatalysis in Conjugated Metal−Organic Framework Nanosheets

AbstractCompared to monometallic counterparts, bimetallic two‐dimensional conjugated metal‐organic framework (2D c‐MOF) nanosheets possess preferable metal tunability and synergistic effect for performance optimization, yet rarely developed in photocatalytic hydrogen evolution to date. In this study, a feasible post‐synthetic strategy of second metal installation (SMI) is proposed and applied to construct a crystalline bimetallic 2D c‐MOF nanosheet, HTHATN‐Ni‐Pt‐NS. HTHATN‐Ni‐Pt‐NS exhibits high electrical conductivity and efficient hydrogen evolution with the rate of 47.2 mmol g−1 h−1, which is 13.5‐fold higher than that of pristine HTHATN‐Ni‐NS without PtII decoration under visible light irradiation. Experimental and theoretical analysis reveal that introduction of low amount of PtII provides catalytically active metal sites and optimizes the ΔGH* value of NiII centers, thus resulting in the enhanced performance of proton reduction. This study represents the first example of symbiotic bimetallic centers in MOF nanosheets highlighting SMI strategy as an efficient approach to construct photocatalysts.

Ti3C2Tx MXene@MOF decorated polyvinylidene fluoride membrane for the remediation of heavy metals ions and desalination

Nowadays, the evolution of two-dimensional materials like transition metal carbides (MXene) prepares a novel path to surpass the “trade-off” between the membrane permeation and rejection rates. Based on water swelling and oxidation vulnerability, MXene membranes showed vivid defects such as inadequate stability, detrimental adsorption, and haphazardly stacked nanosheets. Here, we prepared Ti3C2Tx MXene@metal–organic frameworks nanosheets from aminated metal-organic framework-101 (NH2-MIL-101(Al)) via the in-situ growth method and incorporated them into the thin-film polymer to acquire desirable MXene nanosheets with tailor-made structures. The earned modified thin-film nanocomposite membrane showed high salt rejection for Na2SO4 (98.6 ± 0.5%), MgSO4 (96.9 ± 0.7%), MgCl2 (84.5 ± 0.8%), and NaCl (82.5 ± 0.8%), and also showed an improved permeation rate by three times (17.1 ± 0.2 L m−2. h−1. bar−1). Concurrently, the rejection rate of five different types of heavy metal ions (Ni2+, Cd2+, Mn2+, Cu2+, and Zn2+) was tested and denoted more than a 95.2 ± 0.5% rejection rate for all of them, notably high for Mn2+ (97.6 ± 0.4%). After modification, the flux recovery rate was as high as 95.3 ± 0.4%, denoting more than 30% improvement; besides, anti-compactness features enhanced by nearly 34 ± 0.7%. The long-term water permeation kept 91.5 ± 0.9% of its initial rate indicating almost 40 ± 0.8% enhancement. In addition, the rejection performance of Na2SO4 for the optimized membrane was more than 97% even after two weeks.

Covalent‐Bonding Oxidation Group and Titanium Cluster to Synthesize a Porous Crystalline Catalyst for Selective Photo‐Oxidation Biomass Valorization

AbstractThe selective photo‐oxidation of biomass‐derived 5‐hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA) is important due to its substitute‐role in polyester‐fabrication. Here, a titanium‐cluster based metal‐covalent organic framework nanosheet has been synthesized through the covalent‐coupling between Ti6‐NH2 and benzotrithiophene tricarbaldehyde (BTT). The integration of them endows the nanosheet with a visible‐light‐adsorption region, effective electron‐hole separation‐efficiency and suitable photo‐oxidation ability. Specifically, its photo‐selectivity for HMF‐to‐FDCA can be >95 % with ≈100 % conversion, which is more than 2, 5, and 10 times higher than MOF‐901 (43 %), Ti6‐NH2 (19 %) and under‐darkness (9 %), respectively. Notably, an O2‐based mechanism is proposed and the vital roles of Ti6‐NH2 and BTT are verified by DFT calculations. This work might facilitate the exploration of porous‐crystalline‐catalysts for selective biomass‐valorization.

Synthesis of metal-2D metal-organic framework composite Nanosheets and Their Application in Cascade Catalytic Reactions

Cascade reactions have always had an irreplaceable position in biocatalysis. In this work, we are inspired by the cascade reactions catalyzed by natural enzymes and combining the peroxidase mimetic activity of metal organic frameworks (MOF) nanosheets and the glucose oxidation mimetic enzyme activity of gold nanoparticles (AuNPs) constitutes a dual nanozyme mimetic cascade reaction. AuNPs/Zn-TCPP nanosheets with dual mimetic enzyme activities were prepared by in situ reduction to generate AuNPs on the surface of 2D MOF. And used to further detect the content of hydrogen peroxide or glucose.

MOF-Derived Ultrathin Cobalt Phosphide Nanosheets as Efficient Bifunctional Hydrogen Evolution Reaction and Oxygen Evolution Reaction Electrocatalysts.

The development of a highly efficient and stable bifunctional electrocatalyst for water splitting is still a challenging issue in obtaining clean and sustainable chemical fuels. Herein, a novel bifunctional catalyst consisting of 2D transition-metal phosphide nanosheets with abundant reactive sites templated by Co-centered metal−organic framework nanosheets, denoted as CoP-NS/C, has been developed through a facile one-step low-temperature phosphidation process. The as-prepared CoP-NS/C has large specific surface area and ultrathin nanosheets morphology providing rich catalytic active sites. It shows excellent electrocatalytic performances for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic and alkaline media, with the Tafel slopes of 59 and 64 mV/dec and a current density of 10 mA/cm2 at the overpotentials of 140 and 292 mV, respectively, which are remarkably superior to those of CoP/C, CoP particles, and comparable to those of commercial noble-metal catalysts. In addition, the CoP-NS/C also shows good durability after a long-term test.