The present work reports a novel method of preparing elusive Co 3 O 4 /TiO 2 p-n heterojunction using Co-based metal organic frameworks (Co-MOFs) as TiO 2 -absorbent cum sacrificial template for nanocomposite formation. Four new Co-MOFs based on a bispyrazole ligand and different carboxylic acids, with wide variety of dimensionality, porosity and surface characteristics, were exploited for this purpose. We detail here, the synthesis of cobalt MOFs using hydro(solvo)thermal method and structural characterization by single crystal X-ray diffraction (XRD). We have also successfully demonstrated our strategy of using MOFs for fabricating superior p-n diode-type Co 3 O 4 /TiO 2 hetero-nanocomposites for photocatalytic hydrogen production. The characterization results suggested that the nanocomposites consisted of highly crystalline desired anatase TiO 2 nanoparticles and spinel Co 3 O 4 -like species. The nanocomposite with 2 wt% Co loading exhibited the maximum photoactivity with hydrogen evolution rate of ~7 mmol g −1 h −1 under UV-vis light irradiation. The above results indicate that the present preparative strategy is an amenable route for the synthesis of desirable synergistic photocatalysts joining a remarkable reactivity relevant to the solar energy conversion.
In
continuation of our research interest in pyrazole-based multifunctional
metal organic frameworks (MOFs), we report here three Cu(II) MOFs
using pyrazole and various aromatic carboxylic acid-based ligands.
The main theme of interest is to design functional MOFs by imparting
a multinuclear metal center as a secondary building unit (SBU). Accordingly,
three MOFs are synthesized based on a hexanuclear Cu-pyrazolate unit
as the SBU with some intriguing structural networks like (4,4) type
herringbone grid or an archetypal Kagomé topology. We have
successfully synthesized functional MOFs by incorporating hexanuclear
Cu-pyrazolate SBU-specific properties viz. magnetism and catalysis,
the central theme of this work. All the MOFs show some photocatalytic
degradation of toxic dye molecules. On the other hand, magnetic behaviors
of MOF-2 and MOF-3 associated with the Cu6 unit have also been investigated.
V-shaped ligands are commonly used for helical coordination polymer synthesis. However, employment of multiple V-shaped ligands does not always lead to a helical network. The mutual interplay of two V-shaped ligands, which is neither easily predictable nor well documented, plays a major role directing the self-assembly of the resultant network. We report here the construction of a series of novel{where H 2 OBA = 4,4′-oxybis(benzoic acid), H 2 FBA = 4,4′-(hexafluoroisopropylidene)bis(benzoic acid), H 2 IPA = isophthalic acid, H 2 ADA =1,3-adamantanediacetic acid, H 2 TNBA = 5,5′-dithiobis(2-nitrobenzoic acid), H 2 PPA 1,4-phenylenedipropionic acid, H 2 DPA = diphenic acid H 2 SBA= 4,4′-sulfonyldibenzoic acid} using a combination of mixed V-shaped ligands. The deployment of bent ligands yields a rich variety of network topologies with various helical motifs comprising both the linkers and the individual one. A detailed gas sorption study of porous networks, as evident from the presence of distinct nanoporous voids and channels inside the structures, is also investigated. Furthermore, chirality associated with helical networks and their role as potential functional materials are verified by solid state circular dichroism spectra.
Helical coordination polymers constructed from multiple ligand systems are not common despite the plethora of recent reports on helical networks. We report here the construction of a series of mixed ligand based helical coordination polymers showing metal dependent architecture. The strategy of using a combination of ligand molecules, each capable of forming helical networks, is novel and should enable us to design helical MOFs of interesting topology.
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