Two Polyoxometalate-Encapsulated Two-Fold Interpenetrating Metal-Organic Frameworks for the Detection, Discrimination, and Degradation of Phenolic Pollutants

Assembly of Functional Co(II) Metal-Organic Frameworks through a Mixed Ligand Strategy: Structure and Photocatalytic Degradation Properties

Four Co(II)-based metal-organic frameworks (MOFs) were constructed by a mixed ligand strategy under solvothermal conditions. The controllable modification of the bridging groups in the secondary building units was realized by changing the anions in MOFs 1-3. The MOF 4 with 3D framework structure was obtained by regulating the solvent ratio following the synthesis process of MOF 3. Furthermore, the MOFs 1-4 exhibited efficient photocatalytic activity for the degradation of malachite green (MG) dye without any photosensitizer or cocatalyst under a low-energy light source, the decolorization ratio of MG all reached more than 96.0% within 60 min, and maximal degradation was obtained to be 99.4% (MOF 4). The recycling experiments showed that the degradation rate of MG was still higher than 91% after 10 cycles. In the MOF 4 as representation, the photocatalytic process was explored systematically. The possible mechanism of catalytic degradation was discussed, which proved the existence of efficient oxidation active factors (•O2-, •OH, and h+). The possible intermediates and degradation pathways were investigated based on high-performance liquid chromatography tandem mass spectrometry. Additionally, MOFs 1-4 also exhibited excellent photocatalytic activity for the degradation of methylene blue, methyl violet, rhodamine B, and basic red 9.

One-Step Synthesis of Hollow CoS2 Spheres Derived from Polyoxometalate-Based Metal-Organic Frameworks with Peroxidase-like Activity

In this work, hollow CoS2 particles were prepared by a one-step sulfurization strategy using polyoxometalate-based metal-organic frameworks as the precursor. The morphology and structure of CoS2 have been monitored by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray powder diffraction. The mechanism for the formation of CoS2 is discussed. The reaction time and sulfur content are found to be important factors that affect the morphology and pure phase formation of CoS2, and a hollow semioctahedral morphology of CoS2 with open voids was obtained when the sulfur source was twice as large as the precursor and the reaction time was 24 h. The CoS2 (24 h) particles show an excellent peroxidase-like activity for the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized (oxTMB) by hydrogen peroxide. The polyoxometalate used as a precursor helps to stabilize oxTMB during catalytic oxidation, forming a stable curve platform for at least 8 min. Additionally, the colorimetric detection of hydroquinone is developed with a low detection limit of 0.42 μM. This research provides a new strategy to design hollow materials with high peroxidase-mimicking activity.

Two 3D Two-Fold Interpenetrated Dia-Like Polyoxometalate-Based Metal-Organic Frameworks: Synthesis and Sulfide Selective Oxidation Activity

Two new three-dimensional (3D) polyoxometalate-based metal-organic frameworks (POMOFs), [M2(btap)4(H2O)4(HPMo10VI Mo2VO40)] (M = Co (1) and Cd (2); btap = 3, 5-bis(1', 2', 4'-triazol-1'-yl)pyridine), have been synthesized under mild hydrothermal conditions and characterized in detail. Single-crystal X-ray diffraction (SXRD) analysis indicates that 1 and 2 are isostructural. In complexes 1 and 2, the metal ion is coordinated with the ligand to form two different left and right helical one-dimensional chains, which are alternately connected in a twisted form to build a two-fold interpenetrated three-dimensional structure, and the polyoxometalate is encapsulated into in the pores generated by the interpenetrating structure. It is noteworthy that 1 and 2, as recyclable catalysts, possess favorable heterogeneous catalytic activity and excellent sulfoxide selectivity in sulfide oxidation reactions, with H2O2 as an oxidant. By reason of the high dispersion of polyoxometalate with good intrinsic activity in the skeleton structure, the title complex has high activity. In addition, no obvious decrease of sulfoxide yield is observed after at least five cycles. These results indicate the excellent catalytic activity and sustainability of 1 and 2.