Constructing of Core-Satellite Structure Bimetallic MOFs for Synergistic Enhanced Adsorption-Photocatalytic Degradation

Various industries generate a large amount of wastewater, which contains soluble organic compounds that can seriously jeopardize the environment and human health. Therefore, new photocatalytic materials with the function of efficiently degrading pollutants have become a research hotspot. In this research, bimetallic metal-organic frameworks (MOFs) with a core-satellite structure were prepared through a simple one-pot method in the presence of a polyvinylpyrrolidone structure-directing agent and crystal size. Also, the synergy of the adsorption-catalytic properties of the core-satellite structure bimetallic MOFs was achieved via the interaction of aluminum and iron groups. Meanwhile, the type I heterojunction structure based on MIL-53(Al@Fe)-OH realized the effective separation of the photogenerated carriers. Under the synergistic adsorption-catalytic degradation, the degradation efficiency of methylene blue (MB) was nearly 100% after adsorption (of 2 h) and photocatalysis (of 2 h), and the removal rate of MB still reached 90.43% after five cycles. This study provides a new strategy for the construction of bimetallic MOF structures for efficient adsorption-catalyzed degradation of environmental pollutants.

Advances in metal-organic frameworks for water remediation applications

Rapid industrialization and agricultural development have resulted in the accumulation of a variety of harmful contaminants in water resources. Thus, various approaches such as adsorption, photocatalytic degradation and methods for sensing water contaminants have been developed to solve the problem of water pollution. Metal-organic frameworks (MOFs) are a class of coordination networks comprising organic-inorganic hybrid porous materials having organic ligands attached to inorganic metal ions/clusters via coordination bonds. MOFs represent an emerging class of materials for application in water remediation owing to their versatile structural and chemical characteristics, such as well-ordered porous structures, large specific surface area, structural diversity, and tunable sites. The present review is focused on recent advances in various MOFs for application in water remediation via the adsorption and photocatalytic degradation of water contaminants. The sensing of water pollutants using MOFs via different approaches, such as luminescence, electrochemical, colorimetric, and surface-enhanced Raman spectroscopic techniques, is also discussed. The high porosity and chemical tunability of MOFs are the main driving forces for their widespread applications, which have huge potential for their commercial use.

Coordination-Driven Heterochiral Self-Assembly: Construction of Cd(II) Coordination Polymers with Sorption Behaviors for Iodine and Dyes

A racemic bispyridyl ligand (L) was synthesized via a Schiff base condensation reaction. Four Cd(II) complexes, {[CdL2Cl2]·2DMF}n (1), [CdLI2]n (2), {[CdL2Br2]·4H2O}n (3), and {[CdL2(H2O)2](NO3)2·2CH3OH·8H2O}n (4), were synthesized and further characterized based on this ligand. Single-crystal structures show that the coordination-driven assembly of the bispyridyl ligand with Cd(II) salts bearing different counteranions can lead to multidimensional coordination polymers via a heterochiral self-discrimination process. Complex 1 exists as a one-dimensional (1D) looped chain polymer, and complex 2 exists as a 1D zigzag chain polymer. Complex 3 is a 2D grid coordination polymer, and complex 4 exists as a 3D framework polymer. Furthermore, the iodine sorption capacities of the four complexes were investigated in the solution of n-hexane and water as well as in the iodine steam. The dye sorption behaviors were investigated in water, which showed that complex 2 exhibited good adsorption for crystal violet (CV), while complex 4 had good adsorption capability toward direct yellow 4 (DY).

The adsorption property of in-situ synthesis of MOF in alginate gel for ofloxacin in the wastewater

Although metal-organic frameworks (MOFs) are advantageous to the removal of organic pollutants, the general MOFs in powder form is disadvantageous to their practical applications. In-situ MOF synthesis in alginate gel is a good way to fabricate an MOF composite for many applications, which is different from blending MOF particles with polymers. In-situ synthesis of Zeolitic Imidazolate Framework-8 (ZIF-8) in alginate gel is in the form of beads with rough wrinkles and has many pores inside. When used as an absorbent, in-situ synthesis of ZIF-8 in alginate gel could remove 97.7 ± 0.9% of ofloxacin from ofloxacin solution and the equilibrium adsorption capacity is up to 160.6 ± 1.3 mg/g. During the adsorption, ofloxacin is first brought into the gel by the solvent exchange and gel microchannel adsorption, and it can then be absorbed by in-situ ZIF-8. Moreover, the adsorption efficiency can reach 85.5% even after four cycles of adsorption. We believe that in-situ synthesis of ZIF-8 in alginate gel will be an appropriate material for the removal of ofloxacin in the wastewater.

A new two-dimensional cadmium(II) coordination polymer based on the asymmetric dicarboxylic acid homophthalic acid: synthesis, structure and properties

A new coordination polymer poly[[μ2-4,4′-bis(2-methylimidazol-1-yl)biphenyl-κ2 N 3:N 3′]bis[μ3-2-(2-carboxylatophenyl)acetato-κ5 O,O′:O′,O′′:O′′]dicadmium(II)], [Cd(C9H6O4)(C20H18N4)0.5] n or [Cd(HMPH)(4,4′-BMIBP)0.5] n [H2HMPH is homophthalic acid and 4,4′-BMIBP is 4,4′-bis(2-methylimidazol-1-yl)biphenyl], (I), was synthesized by the solvothermal method and was structurally characterized by means of single-crystal X-ray diffraction, IR spectroscopy and elemental analysis. Coordination polymer (I) exhibits a two-dimensional layer based on one-dimensional [Cd(HMPH)] n chains. Remarkably, photocatalytic degradation experiments on methylene blue (MB) indicated that (I) exhibits an obvious degradation effect. Moreover, an investigation of the luminescence properties of (I) revealed that it could be considered as a potential highly selective luminescence sensor for nitrofurantoin (NFT).

A cadmium(II) coordination polymer with a fivefold interpenetrating diamondoid three-dimensional framework: synthesis, crystal structure, luminescence and photocatalytic properties

A novel three-dimensional (3D) Cd^II coordination polymer, namely, poly[[μ₂-4,4'-bis(2-methylimidazol-1-yl)-[1,1'-biphenyl]](μ₂-5-methylisophthalato)cadmium(II)], [Cd(C₉H₆O₄)(C₂₀H₁₈N₄)]_n or [Cd(MIP)(4,4'-BMIBP)]_n, (I), was synthesized by the hydrothermal method using 5-methylisophthalic acid (H₂MIP), 4,4'-bis(2-methylimidazol-1-yl)-[1,1'-biphenyl] (4,4'-BMIBP) and Cd(NO₃)₂·6H₂O, and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy and thermogravimetric analysis. Compound (I) exhibits a novel fivefold interpenetrating 3D diamondoid framework. Additionally, it shows fluorescence emission in the solid state and promising photocatalytic activities for the degradation of methylene blue (MB) in water at room temperature.

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.

Construction of hollow ZnO/Mn-ZIF-67 heterojunction photocatalysts: enhanced photocatalytic performance and mechanistic insight

Thanks to the unique structure and properties of MOFs, a well-designed novel hollow ZnO/Mn-ZIF-67 composite photocatalyst was synthesized by a facile sonocrystallization approach successfully.

Six CoII coordination polymers exhibiting UV-light-driven photocatalysis for the degradation of organic dyes

Six different Co^II coordination polymers based on a new bis-pyridyl-bis-amide and polycarboxylates were obtained, showing photocatalytic activity for organic dyes.

Microwave Hydrothermally Synthesized Metal-Organic Framework-5 Derived C-doped ZnO with Enhanced Photocatalytic Degradation of Rhodamine B

C-doped ZnO particles have been successfully prepared by the calcination using microwave hydrothermally prepared metal-organic framework-5 (MOF-5) as the precursor. MOF-5 was turned into C-doped ZnO through calcination at 500 °C, and its cubic shape was well-maintained. X-ray photoelectron spectroscopic studies confirmed the C-doping in the ZnO. The as-prepared C-doped ZnO demonstrated a Rhodamine B (RhB) degradation efficiency of 98% in 2 h under an solar-simulated light irradiation, much higher than that of C-doped ZnO derived from MOF-5 synthesized by the ordinary hydrothermal method. The trapping experiment revealed that the crucial factors in the RhB removal were photogenerated h⁺ and •O₂^-.

Synthesis, structure and photocatalytic properties of coordination polymers based on pyrazole carboxylic acid ligands

The photocatalytic activities of two novel different 2-D coordination polymers constructed from 5-hydroxy-1H-pyrazole-3-carboxylic acid ligand have been explored.

Iron and chromium MOFs as sustainable catalysts for transfer hydrogenation of carbonyl compounds and biomass conversions

Fe and Cr based MOFs (MIL-88B) act as efficient and reusable catalysts for transfer hydrogenation of carbonyl compounds including bio-derived substrates.

Hourglass-type polyoxometalate-based crystalline materials as efficient cooperating photocatalysts for the reduction of Cr(vi) and oxidation of dyes

Hourglass-type polyoxometalate-based crystalline materials exhibit efficient photocatalytic activities towards simultaneous photocatalytic Cr(vi) reduction and organic MB oxidation.

Synthesis of alumina-based cross-linked chitosan–HPMC biocomposite film: an efficient and user-friendly adsorbent for multipurpose water purification

Novel alumina-based cross-linked chitosan–HPMC biocomposite is synthesized and its detailed characteristics with potential applications in water purification from both organic and inorganic contaminants elucidated.

Photocatalytic and Ferric Ion Sensing Properties of a New Three-Dimensional Metal-Organic Framework Based on Cuboctahedral Secondary Building Units

A new three-dimensional microporous metal-organic framework based on Zn(II) clusters with the formula {[Zn₇(NDC)_5.5(μ₄-OH)₃]·7DMF} _n (1) (H₂NDC = 1,4-naphthalenedicarboxylic acid) had been synthesized and characterized. The MOF 1 displays an uncommon bsn topology, which is based on a unique heptanuclear Zn₇(OH)₃(CO₂)₁₁ cluster as a secondary building unit. The MOF had been employed as a photocatalyst for the photodegradation of model organic dyes rhodamine B and methyl violet in light. The results of photocatalytic experiments showed that 1 can successfully be employed as the photocatalyst for the benign decomposition of these dyes. A mechanism for the photcatalysis exhibited by 1 had been proposed using the results of density of states (DOS) and partial DOS calculations. The fluorescence properties of the MOF have been investigated, which revealed that 1 could be exploited as the luminescent sensor to recognize Fe³⁺ ions with perceptible quenching (K _sv = 6.55 × 10⁴ M-¹) and a limit of detection of 1.16 ppm.

Polyoxometalate@MIL-101/MoS2: a composite material based on the MIL-101 platform with enhanced performances

MIL-101 was used as a platform to integrate two functional materials for achieving enhanced dye adsorption and separation performances.

Trifunctional metal–organic platform for environmental remediation: structural features with peripheral hydroxyl groups facilitate adsorption, degradation and reduction processes

A Cd(ii)-based metal–organic framework (MOF) has been demonstrated to have trifunctional properties, namely as an efficient and selective adsorbent for dyes, a visible-light-active photocatalyst for the degradation of dyes and a photocatalyst for Cr(vi) reduction.

Enhanced glucose sensing based on a novel composite CoII-MOF/Acb modified electrode

A novel electrochemical sensor composed of a composite of Co^II-MOF/acetylene black exhibits enhanced sensing behavior for glucose detection.

A new series of Cd(ii) metal–organic architectures driven by soft ether-bridged tricarboxylate spacers: synthesis, structural and topological versatility, and photocatalytic properties

Two multifunctional, ether-bridged tricarboxylic acids were used as unexplored and highly versatile building blocks for the hydrothermal generation of eight new cadmium(ii) metal–organic architectures.