Magnetically Recyclable Fe3O4@TMU-32 Metal-Organic Framework Photocatalyst for Tetracycline Degradation Under Visible Light.

Metal-organic frameworks (MOFs) are a new class of porous crystalline materials being used as photocatalysts for efficient pollutant removal and environmental remediation. In this study, the TMU-32 MOF was synthesized as an effective photocatalyst for the photodegradation of tetracycline (TC) with 96% efficiency in 60 min under visible light. The high photocatalytic activity of the TMU-32 MOF is mainly due to its large specific surface area, which is beneficial for promoting both the adsorption of TC and the separation of the photoinduced charges. Moreover, its desired crystallinity makes it a semiconductor with an appropriate band gap energy. Next, a composite of the TMU-32 MOF with Fe3O4 nanoparticles (as Fe3O4@TMU-32) was prepared as a magnetically recyclable photocatalyst. The results showed that the photocatalytic activity of the Fe3O4@TMU-32 nanocomposite is slightly lower (68% degradation of TC within 60 min) than that of TMU-32 toward TC degradation since Fe3O4 nanoparticles are not acting as a photocatalyst and are used only to make the host photocatalyst (here, TMU-32) magnetically separable. The effects of the photocatalyst concentration and recyclability on the photodegradation of TC were studied under similar conditions. We found that the Fe3O4@TMU-32 composite is easily recycled without a significant loss of photocatalytic activity after being used several times, indicating the stability of the photocatalyst. Finally, a density functional theory study was also conducted to investigate the structural and electronic properties such as the band gap energy and density of states of the TMU-32 MOF and the Fe3O4@TMU-32 composite. Our computational results are in good agreement with the experimental ones. A photocatalytic degradation mechanism was finally proposed under visible-light photoirradiation.

High capacity Hg(II) and Pb(II) removal using MOF-based nanocomposite: Cooperative effects of pore functionalization and surface-charge modulation.

Water pollution by heavy metal ions especially Hg(II) and Pb(II) is one of the most important concerns because of their harmful effects on human health and environment sustainability. Here, we developed Fe3O4@TMU-32 metal-organic framework (MOF)-based nanocomposite by applying pore functionalization and surface-charge modulation strategies. Based on synergic effects of these strategies, Fe3O4@TMU-32 nanocomposite shows very high capacity toward Hg(II) and Pb(II) metal ions. TMU-32 (with formula [Zn(OBA)(DPU)]·2DMF·H2O where H2OBA and DPU are (4,4'-oxybis(benzoic acid)) and 1,3-di(pyridin-4-yl)urea)) is decorated with urea functional groups containing carbonyl and amine groups that can interact with metal ions. As results, TMU-32 show very high capacity toward Hg(II) and Pb(II) ions. To improve the TMU-32 capacity toward Hg(II) and Pb(II) cations, we tried to modulate the surface-charge of TMU-32 as a host-framework. Surface-charge modulation strategy had been conducted through encapsulation of Fe3O4 nanoparticles by TMU-32 in an in-situ synthesis procedure and synthesis of Fe3O4@TMU-32 nanocomposite. Fe3O4@TMU-32 nanocomposite shows improved removal capacity (45 % and 54 % toward Pb(II) and Hg(II)) rather pristine TMU-32 framework because of urea decorated framework and charge modulated surface. Fe3O4@TMU-32 nanocomposite adsorb 1600 mg.g-1 of Pb(II) and 905 mg.g-1 of Hg(II) which extremely rare in the literature. Such improvement can be related to the electrostatic interaction between cationic nature of Pb(II) and Hg(II) and negative charge of the Fe3O4@TMU-32 adsorbent.

Highly sensitive fluorescent metal-organic framework as a selective sensor of MnVII and CrVI anions (MnO4-/Cr2O72-/CrO42-) in aqueous solutions.

A luminescent ZnII-MOF named TMU-41, [Zn2(BDC)1.5(L)(DMF)]·1.5DMF, (L = pyridine 4-carboxylic acid and BDC = benzene-1,4-dicarboxylate), has been successfully assembled and well characterized by single-crystal X-ray crystallography, thermogravimetric analysis (TGA), X-ray diffraction (XRD) and N2 adsorption-desorption isotherms, which shows good stability especially in aqueous solutions. To fabricate open metal sites (OMS) of TMU-41(OMS), the coordinated DMF molecules were exchanged and removed by using acetonitrile as exchanging solvent and drying at 250 °C. The values of obtained surface areas after removing the coordinated DMF molecules are in the range of 740 m2/g. This MOF indicates high potential ability in detection of anions due to its strong luminescence effect and stability in water. All these results suggest TMU-41(OMS) to be a highly selective and recyclable luminescent sensing material for the quantitative detection of CrVI and MnVII anions in aqueous solutions. TMU-41(OMS) has the highest sensing ability in comparison to the reported MOFs-based fluorescent and the detection limits towards MnO4-, Cr2O72- and CrO42- ions are about 5 ppb which is among the lowest reported detection limits for the LMOFs.

Sonochemical synthesis and structural characterization of a new Zn(II) nanoplate metal-organic framework with removal efficiency of Sudan red and Congo red.

A 3-D Zn(II) based metal-organic framework (MOF) of [Zn4(oba)3(DMF)2] was synthesized using the nonlinear dicarboxylate ligand, 4,4'-oxybis(benzoic acid) (H2oba) via sonochemical and solvothermal routes. IR spectroscopy, single-crystal X-ray crystallography, scanning electron microscopy, and X-ray powder diffraction were used to characterize these MOF samples. The effect of different times of irradiation and various concentrations of primary reagents were experimented for obtaining monotonous morphology. The results show that uniform nanoplates can be achieved by increasing the time of irradiation and decreasing the concentration. N2 adsorption was applied to examine the effect of synthesis method on porosity of the framework. Also Congo red and Sudan red dyes were employed to explore the efficiency of this MOF in removal of the dye pollutants.