Self-assembled membrane manufactured by metal–organic framework (UiO-66) coated γ-Al2O3 for cleaning oily seawater

[Zirconium-based metal-organic framework composites for solid phase extraction of brevetoxin-A from seawater]

Red tides are a type of natural marine disaster caused by harmful algae characterized by a high toxicity, wide distribution, and long duration. Since the concentration of algal toxins in seawater increases with the occurrence of red tides, algal toxins detected in seawater could be used to predict the occurrence and evolution of red tides. Brevetoxin-A (BTX-A) is a secondary metabolite produced by the harmful algae Karenia brevis, whose detection in seawater could form the basis of an accurate warning system for incoming red tides. However, due to the inherent complexity of the seawater matrix and the extremely low levels of BTX-A in seawater, the use of instruments for its direct detection is difficult. Therefore, there is an urgent need to develop a sample pretreatment method for the efficient enrichment of BTX-A in seawater. In this study, a metal-organic backbone material (UiO-66) and its composite with silica microspheres (SiO2@UiO-66) were successfully synthesized using the solvothermal method. The prepared SiO2@UiO-66 exhibited good hydrophilicity, water stability, and large specific surface area. Furthermore, it also exhibited hydrogen bonding and electrostatic interactions with BTX-A, had a strong affinity for BTX-A, and was able to efficiently adsorb BTX-A in complex matrices. Therefore, SiO2@UiO-66 showed potential as a novel packing material for the extraction of BTX-A from solid phase extraction columns. Combined with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), a highly sensitive detection method for the determination of BTX-A in marine water was established. The established analytical method had a low detection limit (3.0 pg/mL), a wide linear range (10.0 -200.0 pg/mL), and a good linear relationship (R=0.9992). Combined with the Fujian Province Red Tide Monitoring and Early Warning Information 2021 issued by the Fujian Provincial Oceanic and Fisheries Bureau, the analytical method established herein was successfully applied to analyze and monitor the content of BTX-A in actual seawater samples. This highlights the proposed system's potential for use as an early warning factor in the monitoring of red tides, representing a simple and fast pretreatment methodology for the detection of BTX-A in seawater.

Solid-phase extraction and separation of indium with P2O4-UiO-66-MOFs (di-2-ethylhexyl phosphoric acid-UiO-66-metal-organic frameworks)

Compared with the traditional liquid-liquid extraction method, solid-phase extraction agents are of great significance for the recovery of indium metal due to their convenience, free of organic solvents, and fully exposed activity. In this study, P₂O₄ (di-2-ethylhexyl phosphoric acid) was chemically modified by using UiO-66 to form the solid-phase extraction agent P₂O₄-UiO-66-MOFs (di-2-ethylhexyl phosphoric acid-UiO-66-metal-organic frameworks) to adsorb In(III). The results show that the Zr of UiO-66 bonds with the P-OH of P₂O₄ to form a composite P₂O₄-UiO-66-MOF, which was confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The adsorption process of indium on P₂O₄-UiO-66-MOFs followed pseudo first-order kinetics, and the adsorption isotherms fit the Langmuir adsorption isotherm model. The adsorption capabilities can reach 192.8 mg/g. After five consecutive cycles of adsorption-desorption-regeneration, the indium adsorption capacity by P₂O₄-UiO-66-MOFs remained above 99%. The adsorption mechanism analysis showed that the P=O and P-OH of P₂O₄ molecules coated on the surface of P₂O₄-UiO-66-MOFs participated in the adsorption reaction of indium. In this paper, the extractant P₂O₄ was modified into solid P₂O₄-UiO-66-MOFs for the first time. This work provides a new idea for the development of solid-phase extractants for the recovery of indium.

A thin film nanocomposite membrane with pre-immobilized UiO-66-NH2 toward enhanced nanofiltration performance

A facile controlled interfacial polymerization strategy was proposed for the synthesis of novel thin film nanocomposite (TFN) membranes for enhanced nanofiltration performance. UiO-66 nanoparticles were aminated and pre-immobilized onto a polymer substrate via polydopamine (PDA) coating to achieve a continuous and defect-free polyamide dense layer. The mediation of the PDA coating could not only enhance the structural stability of TFN nanofiltration membranes, but also improve the dispersion and anchorage of UiO-66-NH2, thus closely fixing the position of UiO-66-NH2 nanoparticles on the polymer substrate. Moreover, since the amino group (-NH2) further reacted with PDA via Michael addition or Schiff base reaction, the in situ mutual reaction reduced the nanoparticle losses significantly during the draining off of the monomer solution in the fabrication process, which effectively cut down the actual dosage. The results showed that the PDA interlayer could induce the tight attachment of the PA layer to the support, enhancing the structural stability of TFN membranes. Furthermore, the dosage of UiO-66-NH2 in the as-prepared TFN membranes could also be decreased to as low as 0.01 w/v%, which was nearly a 10-20-fold reduction in the required amount of UiO-66-NH2 for the synthesis. The fabricated TFN/UiO-66-NH2 membranes exhibited very high water permeance and competitive salt rejections in cross-flow nanofiltration, which shows the huge potential for the application of novel TFN membranes with controlled nanoparticle incorporation in industrial separation.