La(III)-based MOFs with 5-aminoisophthalic acid for optical detection and degradation of organic molecules in water

Synthesis of fenugreek gum-based metal-organic framework (FG/Zr-AIPA MOF) composite beads for sequestration of heavy metal ions from aqueous solution

Metal-organic frameworks (MOFs) are a prominent class of materials due to their large surface area and customized structures. This gives them specificity and high adsorption capacity while they lack mechanical strength and reusability. Integrating MOFs with polysaccharide matrix may retain MOF characteristics along with imparting structural integrity. In the present study, zirconium MOF-based fenugreek composite (FG/Zr-AIPA) beads were synthesised by a single droplet method and utilised for removal of Cr(VI), Pb(II) and Fe(III) from aqueous solution. The structure, morphology and composition of beads were evaluated by FTIR, XRD, TGA, BET, FESEM, EDX, XPS and zeta potential analysis. Adsorption isotherm, kinetics and thermodynamics were studied for Cr(VI), Pb(II) and Fe(III) adsorption. Adsorption kinetics and isotherm study revealed that all the metal ions were adsorbed through a monolayer chemisorption process. The maximum adsorption capacity was 344.43, 270.02 and 223.21 mg g-1 for Cr(VI), Pb(II) and Fe(III), respectively, based on the Langmuir isotherm study. The thermodynamics study revealed that the interaction between the metal ions and the composite beads was spontaneous and endothermic. The FG/Zr-AIPA composite beads exhibited good reusability for the removal of Cr(VI), Pb(II) and Fe(III). The results open new possibilities for the preparation of polysaccharide MOF-based composite beads which exhibit substantial potential for water treatment applications.

A fluorescent terbium-metal-organic framework material for high-sensitivity detection of vomitoxin and oxytetracycline hydrochloride in water

A unique luminescent lanthanide metal-organic framework (LnMOF)-based fluorescence detection platform was utilized to achieve sensitive detection of vomitoxin (VT) and oxytetracycline hydrochloride (OTC-HCL) without the use of antibodies or biomolecular modifications. The sensor had a fluorescence quenching constant of 9.74 × 106 M-1 and a low detection limit of 0.68 nM for vomitoxin. Notably, this is the first example of a Tb-MOF sensor for fluorescence detection of vomitoxin. We further investigated its response to two mycotoxins, aflatoxin B1 and ochratoxin A, and found that their Stern-Volmer fluorescence quenching constants were lower than those of VT. In addition, the fluorescence sensor realized sensitive detection of OTC-HCL with a detection limit of 0.039 μM. In conclusion, the method has great potential as a sensitive and simple technique to detect VT and OTC-HCL in water.

Removal of copper using chitosan beads embedded with amidoxime grafted graphene oxide nanohybids

This study explores a biopolymer-based composite system for metal decontamination of water using copper {Cu (II)} as a model pollutant. Novel composite beads of chitosan and amidoxime grafted graphene oxide (AOGO) were successfully prepared and used for the Cu (II) removal from aqueous solutions. For this purpose, acrylonitrile was first polymerized onto a gamma-irradiated and silanized graphene oxide substrate. The nitrile groups of polyacrylonitrile grafted graphene oxide (GO-g-PAN) were then chemically modified into amidoxime groups to form AOGO nanohybrids. These nanohybrids were mixed with a blend of chitosan (CS) and polyvinyl alcohol (PVA) and crosslinked using tetraethylorthosilicate (TEOS) to form composite CP/AOGO beads. Fourier transform infrared spectroscopy (FTIR) was used to study the structural changes at each step during the formation of composite beads. Scanning electron microscopic (SEM) analysis demonstrated that the beads had a well-developed spherical structure. The adsorption of Cu (II) onto CP/AOGO composite beads was studied under different conditions (initial concentration, pH, and contact time). The results revealed the potential of composite beads in copper removal from aqueous solutions.

Preparation and photocatalytic performance of UIO-66/La-MOF composite

To improve the photocatalytic degradation efficiency of photocatalytic materials UIO-66 and La-MOFs under visible-light irradiation, a series of photocatalytic materials with La and Zr as metal centers and terephthalic acid (H₂BDC) and 2-amino terephthalic acid (H₂ATA) as organic ligands were prepared by solvothermal method. The photocatalytic materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible (UV-vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and Mott-Schottky test. The photocatalytic degradation performance to Rhodamine B of the catalysts was fully investigated. Results show that the H₂ATA series had stronger visible-light absorption capacity and better photocatalytic performance. The 0.35 La/Zr-H₂ATA composite showed the best photocatalytic degradation. The quenching experiments confirmed that the active species in the photocatalytic degradation were the holes and superoxide radicals. The possible mechanisms of the carrier migration paths in the energy level matching for La/Zr-H₂BDC and La/Zr-H₂ATA were also discussed in detail.

Photoluminescence of LaI3 switched on and off by association and dissociation of non-luminescent tetrahydrofuran

Although luminescent lanthanide-containing molecular complexes are well-known, it is not the case for La³⁺ with no 4f or 5d electrons, and the few luminescent complexes of La³⁺ contain luminescent ligands. Herein, we report an unexpected photoluminescence phenomenon of the LaI₃(THF)₄ complex that was easily prepared by immersing commercial anhydrous LaI₃ in THF. Strong blue emission was observed when LaI₃(THF)₄ was subjected to UV irradiation at 254 nm, which contrasts the non-luminescence character of either LaI₃ or THF. The absolute emission quantum yield was determined to be 50.5%. The observed luminescence of LaI₃(THF)₄ results from metal-to-ligand charge transition (MLCT) which differs from the known charge transition types for lanthanum complexes according to DFT/TDDFT calculations. The photoluminescence of LaI₃ can be switched on and off by reversible THF association and dissociation. THF concentrations as low as 0.1 vol% in n-hexane and 0.5 vol% in the gas phase can be detected, indicating the capability of anhydrous LaI₃ as a sensor for convenient and rapid THF detection.

Interpenetration Control in Thorium Metal-Organic Frameworks: Structural Complexity toward Iodine Adsorption

The rational design and synthesis of metal-organic frameworks with well-controlled interpenetration have been active research areas of inquiry, particularly for porosity-related applications. Herein, we extend the use of the ligand steric modulation strategy to initiate the first study of the interpenetration control of thorium-based MOFs. The approximate "hardness" of the Th⁴⁺ cation, which was conjugated with aromatic substitutions and delicately modified synthetic conditions, allows for the crystallization of single crystals of seven new Th-MOFs with five distinct topologies. Solvothermal reactions of Th(NO₃)₄ with the triphenyl H₂TPDC ligand under variable conditions exclusively gave rise to an interpenetrated Th-MOF with a hex topology, namely Th-SINAP-16. Modifications of the ligand sterics with two pendant methyl groups to 2',5'-Me₂TPDC^2- and 2,2″-Me₂TPDC^2- afforded two noninterpenetrated UiO-68-type Th-MOFs (Th-SINAP-17 and Th-SINAP-20, respectively) with record-high pore volumes (74.8% and 75.3%, respectively) among all the thorium MOFs. Moreover, another four Th-MOFs Th-SINAP-n (n = 18, 19, 21, and 22) with three different topologies were obtained by a simple synthetic modulation. Notably, Th-SINAP-16 and Th-SINAP-21 represent the second rare examples of interpenetrated Th-MOFs reported to date. These findings revealed the unprecedented structural complexity and synthetic accessibility of Th-MOFs among all tetravalent metal containing MOFs. Such features make Th-MOFs as an ideal platform to elucidate the structure-property relationship for various applications, e.g. iodine adsorption.

Syntheses, design strategies, and photocatalytic charge dynamics of metal–organic frameworks (MOFs): a catalyzed photo-degradation approach towards organic dyes

The presented review focuses on design strategies to develop tailor-made MOFs/CPs of main group, transition and inner-transition elements and their photocatalytic properties to decompose dyes in wastewater discharge and their photocatalytic mechanism.

Syntheses of a series of lanthanide metal–organic frameworks for efficient UV-light-driven dye degradation: experiment and simulation

Three Ln-MOFs show unique 3,8-connected 3D networks and have been used as photocatalysts for the degradation of organic dye methyl violet under UV light.

From Discrete Complexes to Metal-Organic Layered Materials: Remarkable Hydrogen Bonding Frameworks

A series of metal-organic coordination complexes based on alkaline-earth metal centers [Mg(II), Ca(II), and Ba(II)] and the ligand 5-aminoisophthalate (aip2-) revealed notable structural diversity, both in the materials' dimensionality and in their hydrogen bonding networks: [Mg(H2O)6]∙[Mg2(Haip)(H2O)10]∙(Haip)∙3(aip)∙10(H2O) (1) and [Mg(aip)(phen)(H2O)2]∙(H2O) (2) were isolated as discrete complexes (0D); [Ca(aip)(H2O)2]∙(H2O) (3), [Ca(aip)(phen)(H2O)2]∙(phen)∙(H2O) (4), and [Ba2(aip)2(phen)2(H2O)7]∙2(phen)∙2(H2O) (5) revealed metal-organic chain (1D) structures, while the [Ba(aip)(H2O)] (6) showed a metal-organic layered (2D) arrangement. Furthermore, most of these metal-organic coordination materials revealed interesting thermal stability properties, being stable at temperatures up to 450 °C.

Two Ln-based metal–organic frameworks based on the 5-(1H-1,2,4-triazol-1-yl)-1,3-benzenedicarboxylic acid ligand: syntheses, structures, and photocatalytic properties

Two new 3D Ln-based complexes showing (6,8)-connected topology were synthesized and the photocatalytic activity of the Sm(iii)-based MOF towards the degradation of methyl violet (MV) in water explored.