Ordered Mesoporous Metal–Organic Frameworks Incorporated with Amorphous TiO₂ As Photocatalyst for Selective Aerobic Oxidation in Sunlight Irradiation

Among the very few efforts for preparation of stable mesoporous metal–organic frameworks (MOFs), there is no report of an additive-free example via a surfactant-assisted templating method. On the other hand, photocatalytic aerobic oxidation of alcohols mediated by crystalline TiO₂ has been known as a green route, which has the potential to replace current technology with transition-metal-containing heterogeneous systems. Here, a simple procedure for preparation of HKUST-1 containing ordered mesoporous domains has been developed using nonionic block copolymer in DMF as the solvent. All materials have been thoroughly characterized by FTIR, FESEM, HRTEM, XRPD, EDS, and TG analysis. Subsequently, it has been demonstrated that incorporation of amorphous TiO₂ within the prepared mesoporous MOF could successfully develope a new type of photocatalyst system for selective aerobic oxidation of benzylic alcohols with moderate to high yields in sunlight irradiation

Solid-State Structural Transformations of Two Ag^I Supramolecular Polymorphs to Another Polymer upon Absorption of HNO₃ Vapors

Solid-state structural transformation of two polymorphic forms of [Ag­(8-HqH)­(8-Hq)]_<i>n</i> (<b>1α</b> and <b>1β</b>, where 8-HqH = 8-hydroxyquinoline and 8-Hq^– = 8-hydroxyquinolate) to {[Ag­(8-HqH)₂]­NO₃}_<i>n</i> (<b>2</b>) has been observed upon solid–gas reaction of compounds <b>1α</b> and <b>1β</b> with HNO₃ vapors. Solid–gas reaction of compound <b>2</b> with hydrated vapors of NH₃ results in the formation of only the <b>1β</b> polymorph, while solid–solid reaction of compound <b>2</b> with KOH results in the formation of a <b>1α</b> and <b>1β</b> mixture with chiral and achiral space groups of <i>P</i>2₁2₁2₁ and <i>Pbcn</i>, respectively

High Capacity Arsenate Removal from Real Samples Using Dihydrotetrazine Decorated Zirconium-Based Metal–Organic Frameworks

Zirconium metal–organic frameworks (Zr-MOFs) are potential candidates for decontamination of water resources from harmful pollutants due to their modulable porosity and chemical stability in aqueous solutions. Linker functionalization is an approach for tuning the host–guest chemistry of Zr-MOFs and extends their applications in environmental monitoring. In this work, the structure of UiO-66(Zr) (formulated Zr6(OH)4O4(BDC)6, BDC2– = benzene-1,4-dicarboxylate) was functionalized with dihydrotetrazine group via postsynthesis linker exchange (PSLE) method. The functionalized framework, UiO-66(Zr)-DHTZ, was applied for the removal of arsenate ions from aqueous solutions. The results show that UiO-66(Zr)-DHTZ can adsorb 583 mg g–1 of As(V) at pH = 7 after 2 h, which is significantly higher than that of the UiO-66(Zr). According to X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR), the removal mechanism is based on possible hydrogen bindings between free −C–NH and −CN− sites of dihydrotetrazine function with −O– and −OH sites of As(V) species. Removal tests in real samples show that UiO-66(Zr)-DHTZ still has a high capacity (220 mg g–1) to As(V) ions in complex matrixes and also can decrease the concentration of As(V) below the detection limit (0.05 ppm) of the inductively coupled plasma optical emission spectroscopy (ICP-OES) method. Since the dihydrotetrazine-decorated UiO-66(Zr)-DHTZ reaches one the highest adsorption capacities to As(V) species, it can be considered a potential candidate for water treatment in real-life applications

Redox Metal–Organic Framework for Photocatalytic Organic Transformation: The Role of Tetrazine Function in Radical-Anion Pathway

Linker functionalization is a practical strategy to extend the applications of metal–organic frameworks (MOFs) in various fields. Here, this strategy is applied to synthesize a tetrazine-functionalized MOF [TMU-34­(-2H), formulated [Zn­(OBA) (DPT)0.5]·DMF; H2OBA and DPT are 4,4′-oxybis­(benzoic acid) and 3,6-di­(pyridin-4-yl)-1,2,4,5-tetrazine] for efficient photocatalytic synthesis of disulfides and benzimidazoles with maximum conversion after 90 and 120 min, respectively. The photocatalytic activity of TMU-34­(-2H) originates from the electronic properties of tetrazine function, including absorption in the visible region and photogenerated redox activity. In the proposed mechanism, neutral tetrazine sites are excited upon visible-light irradiation. Then, photoexcited tetrazine sites accept one electron from the reactants leading to generation of tetrazine radical anions as electron mediator sites. Finally, the electrons transfer from the tetrazine radical anion sites to other substrates in the reaction. The results show that organic chromophores, such as tetrazine, are good candidates for extension of application of MOFs in visible-light photocatalysis

Shape Control of Zn(II) Metal–Organic Frameworks by Modulation Synthesis and Their Morphology-Dependent Catalytic Performance

Micro- and nanorods and plates of three porous Zn­(II)-based metal–organic frameworks, [Zn₂(oba)₂(4-bpdb)]_<i>n</i>·2­(DMF) (TMU-4), [Zn­(oba)­(4-bpdh)_0.5]_<i>n</i>·1.5­(DMF) (TMU-5), and [Zn­(oba)­(4-bpmb)_0.5]_<i>n</i> 1.5­(DMF) (TMU-6) were synthesized by the coordination modulation method. The effects of concentration of modulator, temperature, and time of reaction on size and morphology have been investigated. Also, catalytic performance of TMU-5 nanosized metal–organic framework in Knoevenagel condensation reaction was evaluated

Application of Two Cobalt-Based Metal–Organic Frameworks as Oxidative Desulfurization Catalysts

Two new porous cobalt-based metal–organic frameworks, [Co₆(oba)₅(OH)₂(H₂O)₂(DMF)₄]_<i>n</i>·5DMF (<b>TMU-10</b>) and [Co₃(oba)₃(O) (Py)_0.5]_<i>n</i>·4DMF·Py (<b>TMU-12</b>) have been synthesized by solvothermal method using a nonlinear dicarboxylate ligand. Under mild reaction conditions, these compounds exhibited good catalytic activity and reusability in oxidative desulfurization (ODS) reaction of model oil which was prepared by dissolving dibenzothiophene (DBT) in <i>n</i>-hexane. FT-IR and Mass analysis showed that the main product of DBT oxidation is its corresponding sulfone, which was adsorbed on the surfaces of catalysts. The activation energy was obtained as 13.4 kJ/mol

A MoO₃–Metal–Organic Framework Composite as a Simultaneous Photocatalyst and Catalyst in the PODS Process of Light Oil

Photo-oxidative desulfurization (PODS) properties of MoO₃–metal–organic framework composite photocatalysts were investigated by introducing the proper weight percent of MoO₃ into a Zn­(II)-based MOF, [Zn­(oba)­(4-bpdh)_0.5]_<i>n</i>·1.5DMF (TMU-5), for the mineralization of dibenzothiophene from model oil. The addition of 3 wt % of MoO₃ into a TMU-5 host acting as a crystal growth inhibitor was confirmed by PXRD and BET results. For the first time, under mild and green reaction conditions, 5 wt % MoO₃–TMU-5 composite (MT-5) exhibited good photocatalytic activity in the model oil PODS reaction, which has no limitations in the current oxidative desulfurization catalytic systems. Only 3% of the total amount of MoO₃ content in the MT catalyst is leached during the reaction. In addition, the rate of PODS of MT-5 obeys a pseudo-first-order equation with an apparent rate constant of 0.0305 min^–1 and half-life <i>t</i>_1/2 of 22.7 min. Radical scavenger experiments and terephthalic acid fluorescence techniques confirmed that OH^<b>•</b> and O₂^{<b>•–</b>} are the main reactive species in the dibenzothiophene photocatalytic degradation. The synergic effects of the active surface of TMU-5 (organic linkers as antennas) together with the active sites of MoO₃ may lead to the further enhancement of the PODS activity of the MT-5 photocatalyst. Moreover, a possible photocatalytic desulfurization mechanism was proposed in the presence of MoO₃–TMU-5 composites

Effects of Orthohalogen Substituents on Nitrate Binding in Urea-Based Silver(I) Coordination Polymers

The urea group is a widely used functional group in anion recognition, owing to its ability to interact effectively with anions via formation of chelate hydrogen bonds. Previous solution state study shows that the presence of halogen substituents at <i>ortho</i>-positions to the urea moiety strongly enhances intermolecular hydrogen bonding interactions. In order to investigate the effect of the presence of <i>ortho</i>-halogen substituents on hydrogen bonding of aromatic ureas in the context of metallosupramolecular chemistry, three Ag­(I) coordination polymers were synthesized and characterized by different techniques. The nitrate binding and the supramolecular organization in these compounds were studied by different geometrical and theoretical calculations. Based on this study, we can conclude that, as expected, the N–H···O hydrogen bond plays a key role in nitrate binding for this type of ligands, while weak C–X···O halogen bonds assist the anion binding to the receptor

Metal–Organic Framework Based on Isonicotinate <i>N</i>‑Oxide for Fast and Highly Efficient Aqueous Phase Cr(VI) Adsorption

Synthesis of new porous materials has been developed for efficient capture of pollutants in environmental sciences. Here, the application of a new metal–organic framework (TMU-30) has been reported based on isonicotinate <i>N</i>-oxide as an adsorptive site for fast and highly efficient aqueous phase adsorption of Cr­(VI). The adsorption process showed no remarkable effect over a pH range of 2–9. The maximum capacity of the adsorption was reached in just less than 10 min and followed the pseudo-second-order kinetics. The maximum capacity of 2.86 mol mol^–1 (145 mg/g) was obtained according to Langmuir model at 298 K. The spontaneous adsorption and an endothermic process were controlled by positive entropy changes. XPS analysis revealed electrostatic interactions between <i>N</i>-oxide groups of TMU-30 and Cr­(VI) species, which were responsible for the adsorption process

Mechanistic, energetic and structural studies of carbon nanotubes functionalised with dihydroartemisinin drug in gas and solution phases

<p>In this work, using density functional theory, the molecular mechanism of noncovalent interactions of drug dihydroartemisinin (DHA) with (5, 5) pristine (NT) and COOH- functionalised carbon nanotube (NTCOOH) and two mechanisms of covalent functionalisation of this drug with NTCOOH and COCl- functionalised carbon nanotube (NTCOCl) have been studied. Quantum molecular descriptors for five (DHA/NT1-5) and three (DHA/NTCOOH1-3) configurations of noncovalent interaction were calculated. It was specified that binding of DHA with pristine and COOH functionalised CNT is thermodynamically favourable. Using NTCOOH is more desirable due to a stronger interaction between the DHA and carbon nanotube and higher solubility. DHA can bond to NTCOOH via hydroxyl group. The reaction of DHA with NTCOCl has activation energy lower than NTCOOH, being the reason for suitability of NTCOCl for covalent functionalisation of DHA onto carbon nanotubes. These results could be generalised to other similar drugs.</p