Polyaromatic Hydrocarbon Inclusion Complexes with 2-Hydroxylpropyl-ß/γ-Cyclodextrin: Molecular Dynamic Simulation and Spectroscopic Studies.

In aqueous and solid media, 2-HP-ß/γ-CD inclusion complexes with poly aromatic hydrocarbon (PAH) Phenanthrene (PHN), Anthracene (ANT), Benz(a)pyrene (BaP), and Fluoranthene (FLT) were investigated for the first time. The inclusion complexes were characterized and investigated using fluorescence and 1HNMR spectroscopy. The most prevalent complexes consisting of both guests and hosts were those with a 1:1 guest-to-host ratio. The stability constants for the complexes of PHN with 2-HP-ß-CD and 2-HP-γ-CD were 85 ± 12 M-1 and 49 ± 29 M-1, respectively. Moreover, the stability constants were found to be 502 ± 46 M-1 and 289 ± 44 M-1 for the complexes of ANT with both hosts. The stability constants for the complexes of BaP with 2-HP-ß-CD and 2-HP-γ-CD were (1.5 ± 0.02) × 103 M-1 and (9.41 ± 0.03) × 103 M-1, respectively. The stability constant for the complexes of FLT with 2-HP-ß-CD was (1.06 ± 0.06) × 103 M-1. However, FLT was observed to form a weak complex with 2-HP-γ-CD. Molecular dynamic (MD) simulations were used to investigate the mechanism and mode of inclusion processes, and to monitor the atomic-level stability of these complexes. The analysis of MD trajectories demonstrated that all guests formed stable inclusion complexes with both hosts throughout the duration of the simulation time, confirming the experimental findings. However, the flexible Hydroxypropyl arms prevented the PAHs from being encapsulated within the cavity; however, a stable exclusion complex was observed. The main forces that influenced the complexation included van der Waals interactions, hydrophobic forces, and C-H⋯π interaction, which contribute to the stability of these complexes.

Metal-Organic Frameworks in Mixed-Matrix Membranes for High-Speed Visible-Light Communication.

Mixed-matrix membranes (MMMs) based on luminescent metal-organic frameworks (MOFs) and emissive polymers with the combination of their unique advantages have great potential in separation science, sensing, and light-harvesting applications. Here, we demonstrate MMMs for the field of high-speed visible-light communication (VLC) using a very efficient energy transfer strategy at the interface between a MOF and an emissive polymer. Our steady-state and ultrafast time-resolved experiments, supported by high-level density functional theory calculations, revealed that efficient and ultrafast energy transfer from the luminescent MOF to the luminescent polymer can be achieved. The resultant MMMs exhibited an excellent modulation bandwidth of around 80 MHz, which is higher than those of most well-established color-converting phosphors commonly used for optical wireless communication. Interestingly, we found that the efficient energy transfer further improved the light communication data rate from 132 Mb/s of the pure polymer to 215 Mb/s of MMMs. This finding not only showcases the promise of the MMMs for high-speed VLC but also highlights the importance of an efficient and ultrafast energy transfer strategy for the advancement of data rates of optical wireless communication.

Introducing a Cantellation Strategy for the Design of Mesoporous Zeolite-like Metal-Organic Frameworks: Zr-sod-ZMOFs as a Case Study.

Herein we report novel mesoporous zirconium-based metal-organic frameworks (MOFs) with zeolitic sodalite (sod) topology. Zr-sod-ZMOF-1 and -2 are constructed based on a novel cantellation design strategy. Distinctly, organic linkers are judiciously designed in order to promote the deployment of the 12-coordinated Zr hexanuclear molecular building block (MBB) as a tetrahedral secondary building unit, a prerequisite for zeolite-like nets. The resultant Zr-sod-ZMOFs exhibit mesopores with a diameter up to ≈43 Å, while the pore volume of 1.98 cm3·g-1 measured for Zr-sod-ZMOF-1 is the highest reported experimental value for zeolite-like MOFs based on MBBs as tetrahedral nodes.

Access to Highly Efficient Energy Transfer in Metal-Organic Frameworks via Mixed Linkers Approach.

Herein, we report a new light-harvesting mixed-ligand Zr(IV)-based metal-organic framework (MOF),with underlying fcu topology, encompassing the [Zr6(µ3-O)4(µ3-OH)4(O2C-)12] cluster and an equimolar mixture of thiadiazole- and benzimidazole-functionalized ligands. The successful integration of ligands with similar structural features but with notable chemical distinction afforded the attainment of a highly efficient energy transfer (ET). Notably, the very strong spectral overlap between the emission spectrum of benzimidazole (energy donor) and the absorption spectrum of thiadiazole (energy acceptor) provided an ideal platform to achieve very rapid (picosecond time scale) and highly efficient energy transfer (around 90% efficiency), as evidenced by time-resolved spectroscopy. Remarkably, the ultrafast time-resolved experiments quantified for the first time the anticipated close proximity of the two linkers with an average distance of 17 Å. This finding paves the way for the design and synthesis of periodic MOFs affording very efficient and fast ET to mimic natural photosynthetic systems.

Deployment of Superhydrophilic and Super-antifouling Cr-soc-MOF-1-Based Membrane for Ultrafast Separation of Stabilized Oil-in-Water Emulsions.

In spite of massive progress in oil-water separation, attributable to the use of advanced materials, the separation process faces challenges such as low permeance and fouling problems. Therefore, superwettable materials used in several fields are considered potential candidates for oily wastewater treatment. Metal-organic frameworks (MOFs) are receiving more and more interest in various separation applications due to their wide potential applications. Nevertheless, MOFs have been rarely explored for separating stabilized oil-in-water emulsions due to the difficulty in finding highly hydrolytic stable MOF candidates for this application. Furthermore, oil can clog water-stable materials owing to its high density, causing the degradation of MOF particles. As a result, there is a need to develop better MOF materials that can fulfill these requirements. Herein, we have explored Cr-soc-MOF-1 as a candidate for this application and deployed it as a membrane, which exhibited superhydrophilicity and underwater superoleophobicity for separating stabilized oil-in-water emulsions. The Cr-soc-MOF-1 membranes were synthesized by assembling the as-prepared MOF particles on a mixed cellulose ester substrate using a vacuum-assisted self-assembly technique. The Cr-soc-MOF-1 membrane exhibited ultrahigh water permeance (7465.9 L·m-2·h-1·bar-1), very high oil rejection (99.9%), and excellent anti-oil-fouling properties. The Cr-soc-MOF-1 membranes also exhibited excellent recyclability over 10 continuous separation cycles. Further, they exhibited an outstanding performance in separating various surfactant-stabilized oil-in-water emulsions. Thus, the Cr-soc-MOF-1 membranes exhibit a high potential in treating oily wastewater.

Institution of Metal-Organic Frameworks as a Highly Sensitive and Selective Layer In-Field Integrated Soil-Moisture Capacitive Sensor.

The ongoing global industrialization along with the notable world population growth is projected to challenge the global environment as well as pose greater pressure on water and food needs. Foreseeably, an improved irrigation management system is essential and the quest for refined chemical sensors for soil-moisture monitoring is of tremendous importance. Nevertheless, the persisting challenge is to design and construct stable materials with the requisite sensitivity, selectivity, and high performance. Here, we report the introduction of porous metal-organic frameworks (MOFs), as the receptor layer, in capacitive sensors to efficiently sense moisture in two types of soil. Namely, our study unveiled that Cr-soc-MOF-1 offers the best sensitivity (≈24,000 pF) among the other tested MOFs for any given range of soil-moisture content, outperforming several well-known oxide materials. The corresponding increase in the sensitivities for tested MOFs at 500 Hz are ≈450, ≈200, and ≈30% for Cr-soc-MOF-1, Al-ABTC-soc-MOF, and Zr-fum-fcu-MOF, respectively. Markedly, Cr-soc-MOF-1, with its well-known water capacity, manifests an excellent sensitivity of ≈450% in clayey soil, and the analogous response time was 500 s. The noted unique sensing properties of Cr-soc-MOF-1 unveils the great potential of MOFs for soil-moisture sensing application.

Mixed Matrix Membranes with Surface Functionalized Metal-Organic Framework Sieves for Efficient Propylene/Propane Separation.

Membrane technology, regarded as an environmentally friendly and sustainable approach, offers great potential to address the large energy penalty associated with the energy-intensive propylene/propane separation. Quest for molecular sieving membranes for this important separation is of tremendous interest. Here, a fluorinated metal-organic framework (MOF) material, known as KAUST-7 (KAUST: King Abdullah University of Science and Technology) with well-defined narrow 1D channels that can effectively discriminate propylene from propane based on a size-sieving mechanism, is successfully incorporated into a polyimide matrix to fabricate molecular sieving mixed matrix membranes (MMMs). Markedly, the surface functionalization of KAUST-7 nanoparticles with carbene moieties affords the requisite interfacial compatibility, with minimal nonselective defects at polymer-filler interfaces, for the fabrication of a molecular sieving MMM. The optimal membrane with a high MOF loading (up to 45 wt.%) displays a propylene permeability of ≈95 barrer and a mixed propylene/propane selectivity of ≈20, far exceeding the state-of-the-art upper bound limits. Moreover, the resultant membrane exhibits robust structural stability under practical conditions, including high pressures (up to 8 bar) and temperatures (up to 100 °C). The observed outstanding performance attests to the importance of surface engineering for the preparation and plausible deployment of high-performance MMMs for industrial applications.

Optimized Charge Storage in Aza-Based Covalent Organic Frameworks by Tuning Electrolyte Proton Activity.

Proton activity in electrolytes plays a crucial role in deciding the electrochemical performance of aqueous batteries. On the one hand, it can influence the capacity and rate performance of host materials because of the high redox activity of protons. On the other hand, it can also cause a severe hydrogen evolution reaction (HER) when the protons are aggregated near the electrode/electrolyte interface. The HER dramatically limits the potential window and the cycling stability of the electrodes. Therefore, it is critical to clarify the impact of electrolyte proton activity on the battery macro-electrochemical performance. In this work, using an aza-based covalent organic framework (COF) as a representative host material, we studied the effect of electrolyte proton activity on the potential window, storage capacity, rate performance, and cycle stability in various electrolytes. A tradeoff relationship between proton redox reactions and the HER in the COF host is revealed by utilizing various in situ and ex situ characterizations. Moreover, the origin of proton activity in near-neutral electrolytes is discussed in detail and is confirmed to be related to the hydrated water molecules in the first solvation shell. A detailed analysis of the charge storage process in the COFs is presented. These understandings can be of importance for utilizing the electrolyte proton activity to build high-energy aqueous batteries.