Synthesis of Negative-Charged Metal-Containing Cyclomatrix Polyphosphazene Microspheres Based on Polyoxometalates and Application in Charge-Selective Dye Adsorption.

A negative-charged, metal-containing cyclomatrix polyphosphazene microsphere (MCPM) is synthesized using the strategy of precipitation polymerization of di-functionalized polyoxometalates (POMs) and hexachlorocyclotriphosphazene. The chemical structure of these MCPMs is well characterized by 13 C MAS NMR and 31 P MAS NMR, as well as FT-IR, electron microscopy, and X-ray photoelectron spectroscopy. The covalent grafting of the rigid POMs clusters into the framework of these microspheres prevents the collapsing of the pores, making these MCPMs porous materials. Taking advantage of the porous structure and the negative charges in the frameworks, these materials show interesting charge-selective adsorption properties, as demonstrated by the selective adsorption of positive-charged dyes in comparison with negative-charged dyes.

Actinide-Based Porphyrinic MOF as a Dehydrogenation Catalyst.

Uranyl-organic frameworks (UOFs) have recently been the object of many research endeavors due to the unique coordination mode of uranyl ions and their attractive physicochemical properties. Here, a new (3,4)-connected UOF (U-IHEP-4) assembled from uranyl and porphyrin ligand tetrakis(4-carboxyphenyl)porphyrin (H4TCPP) is reported, which represents the first case of actinide porphyrinic MOFs. Adsorption experiments in DMF solution demonstrated that U-IHEP-4 selectively adsorbs positively charged dyes, which is in line with its negatively charged framework and large pore volume ratio (90 %). Remarkably, U-IHEP-4 exhibited high catalytic activity for the dehydrogenation of N-heterocycles to synthesize the corresponding aromatic heterocycles and it can be used as an efficient heterogeneous catalyst.

Solvent-Dependent Synthesis of Porous Anionic Uranyl-Organic Frameworks Featuring a Highly Symmetrical (3,4)-Connected ctn or bor Topology for Selective Dye Adsorption.

Two highly symmetrical (3,4)-connected uranyl-organic frameworks (UOFs) were synthesized by a judicious combination of D3h -symmetrical triangular [UO2 (COO)3 ]- and Td symmetrical tetrahedral tetrakis(4-carboxyphenyl)methane (H4 MTB). These two as-synthesized UOFs possess similar structural units and coordination modes but totally different topological structures, namely ctn net and bor net. Solvent-induced interpenetration and a morphology change are observed. The two compounds exhibit crystal transformation via a dissolution-crystallization process. Adsorption experiments in CH3 OH solution indicate that both of them can selectively remove positively charged dyes over negatively charged and neutral dyes. Moreover, the electronic structural and bonding properties of the two compounds were systematically explored by density functional theory (DFT) calculations.

Preparation of Functionalized Ethylene-Vinyl-Alcohol Nanofibrous Membrane Filter for Rapid and Cyclic Removing of Organic Dye from Aqueous Solution.

A functionalized ethylene-vinyl-alcohol (EVOH) nanofibrous membrane (NFM) was fabricated via co-electrospinning H4SiW12O40 (SiW12) and EVOH first, and then grafting citric acid (CCA) on the electrospun SiW12@EVOH NFM. Characterization with FT-IR, EDX, and XPS confirmed that CCA was introduced to the surface of SiW12@EVOH NFM and the Keggin structure of SiW12 was maintained well in the composite fibers. Due to a number of carboxyl groups introduced by CCA, the as-prepared SiW12@EVOH-CCA NFM can form a high number of hydrogen bonds with CR, and thus can be used to selectively absorb congo red (CR) in aqueous solutions. More importantly, the CR enriched in the NFM can be rapidly degraded via photocatalysis. SiW12 in the NFM acted as a photocatalyst, and the hydroxyl groups in the NFM acted as an electron donor to accelerate the photodegradation rate of CR. Meanwhile, the SiW12@EVOH-CCA NFM was regenerated and then exhibited a relatively stable adsorption capacity in five cycles of filtration-regeneration. The bifunctional nanofibrous membrane filter showed potential for use in the thorough purification of dye wastewater.

Charge-controllable mussel-inspired magnetic nanocomposites for selective dye adsorption and separation.

Magnetic polydopamine (PDA) nanocomposites were prepared with a facile and sustainable synthetic method. The as-synthesized polymer-based hybrid composites inherited the intrinsic adhesiveness contributed by catechol and amino moieties of PDA as well as the magnetic property of Fe3O4. With the unique properties of PDA, the surface charges of Fe3O4@PDA could be easily tuned by pH for smart adsorption-desorption behaviors. Four commercially available dyestuffs including crystal violet, rhodamine B, direct blue 71 and orange G with different structures and surface charges in solution were selected to investigate the adsorption ability and universality of Fe3O4@PDA in wastewater treatment. It was found that the nanocomposites could successfully adsorb these cationic and anionic dyes under suitable pH conditions. This confirmed the ability of the nanoadsorbents for the removal of common textile dyes. The dispersed magnetic nanoadsorbents also demonstrated the ease of collection from dye mixtures, and the possibility of reusing them for several cycles. Selective dye separation was found to be achievable via simple charge control without large consumption of organic solvent and energy. These bio-inspired nanocomposite adsorbents have shown high potential in wastewater treatment and selective recovery of dye waste, especially for wastewater containing ionic dyes.

Metal-Ion Metathesis and Properties of Triarylboron-Functionalized Metal-Organic Frameworks.

An anionic metal-organic framework, H3[(Mn4Cl)3L8]⋅30H2O⋅2.5 DMF⋅5 Diox (UPC-15), was successfully prepared by the reaction of MnCl2 with tris(p-carboxylic acid)tridurylborane (H3 L) under solvothermal conditions. UPC-15 with wide-open pores (∼18.8 Å) is constructed by packing of octahedral and cuboctahedral cages, and exhibits high gas-sorption capabilities. Notably, UPC-15 shows selective adsorption of cationic dyes due to the anion framework. Moreover, the catalytic and magnetic properties were investigated, and UPC-15 can highly catalyze the cyanosilylation of aromatic aldehydes. UPC-15 exhibits the exchange of metal ions from Mn to Cu in a single-crystal-to-single-crystal manner to generate UPC-16, which could not be obtained by the direct solvothermal reaction of CuCl2 and H3L. UPC-16 exhibits similar properties for gas sorption, dye separation, and catalytic activity. However, the magnetic behaviors for UPC-15 and UPC-16 are distinct due to the metal-specific properties. Below 47 K, UPC-15 exhibits a ferromagnetic coupling but UPC-16 shows a dominant antiferromagnetic behavior.