Valorization of Field-Spent Granular Activated Carbon as Heterogeneous Ozonation Catalyst for Water Treatment.

Developing sustainable cost-effective strategies for valorization of field-spent granular activated carbon (s-GAC) from industrial water treatment has gained much interest. Here, we report a cost-effective strategy for the regeneration of s-GAC as an adsorbent in a large-scale drinking water treatment plant and used as an efficient and durable ozonation catalyst in water. To achieve this, a series of samples is prepared by subjecting s-GAC to thermally controlled combustion treatments with and without pyrolysis. The catalytic performance of the optimized sample is evaluated for oxalic acid degradation as the model pollutant under batch (>15 h) and continuous flow operations (>200 h). The partially deactivated catalyst upon reuse is restored by thermal treatment. Electron paramagnetic resonance and selective quenching experiments show the formation of singlet oxygen (1O2) during catalytic ozonation. The GAC-ozonation catalyst is efficient to minimize the formation of chlorinated disinfection by-products like trihalomethanes and haloacetic acids in an urban wastewater effluent.

A Novel Porous Ti-Squarate as Efficient Photocatalyst in the Overall Water Splitting Reaction under Simulated Sunlight Irradiation.

A new porous titanium(IV) squarate metal-organic framework (MOF), denoted as IEF-11, having a never reported titanium secondary building unit, is successfully synthesized and fully characterized. IEF-11 not only exhibits a permanent porosity but also an outstanding chemical stability. Further, as a consequence of combining the photoactive Ti(IV) and the electroactive squarate, IEF-11 presents relevant optoelectronic properties, applied here to the photocatalytic overall water splitting reaction. Remarkably, IEF-11 as a photocatalyst is able to produce record H2 amounts for MOF-based materials under simulated sunlight (up to 672 µmol gcatalyst in 22 h) without any activity loss during at least 10 d.

Plasma-Induced Defects Enhance the Visible-Light Photocatalytic Activity of MIL-125(Ti)-NH2 for Overall Water Splitting.

Defect engineering in metal-organic frameworks is commonly performed by using thermal or chemical treatments. Herein we report that oxygen plasma treatment generates structural defects on MIL-125(Ti)-NH2 , leading to an increase in its photocatalytic activity. Characterization data indicate that plasma-treated materials retain most of their initial crystallinity, while exhibiting somewhat lower surface area and pore volume. XPS and FT-IR spectroscopy reveal that oxygen plasma induces MIL-125(Ti)-NH2 partial terephthalate decarboxylation and an increase in the Ti-OH population. Thermogravimetric analyses confirm the generation of structural defects by oxygen plasma and allowed an estimation of the resulting experimental formula of the treated MIL-125(Ti)-NH2 solids. SEM analyses show that oxygen plasma treatment of MIL-125(Ti)-NH2 gradually decreases its particle size. Importantly, diffuse reflectance UV/Vis spectroscopy and valence band measurements demonstrate that oxygen plasma treatment alters the MIL-125(Ti)-NH2 band gap and, more significantly, the alignment of highest occupied and lowest unoccupied crystal orbitals. An optimal oxygen plasma treatment to achieve the highest efficiency in water splitting with or without methanol as sacrificial electron donor under UV/Vis or simulated sunlight was determined. The optimized plasma-treated MIL-125(Ti)-NH2 photocatalyst acts as a truly heterogeneous photocatalyst and retains most of its initial photoactivity and crystallinity upon reuse.

A Semiconducting Bi2O2(C4O4) Coordination Polymer Showing a Photoelectric Response.

Inorganic semiconductors are extensively considered to be among the most promising materials to convert solar light into electricity or chemical energy owing to their efficiency in the separation of photoinduced electron/hole. Bismuth oxides, and, in particular, those built up of [Bi2O2]2+ layers, show an efficient charge separation and, thus, high photocatalytic activities. To explore a possible synergetic effect of bismuth metallic nodes combined with the electron-rich linker squarate, Bi2O2(C4O4) or IEF-3 (an IMDEA Energy framework) was hydrothermally prepared and adequately characterized. As determined from the X-ray structure, [Bi2O2]2+ layers are interconnected by squarate ligands, having a pronounced effect of the 6s2 lone pair on the bismuth local environment. IEF-3 shows high thermal and chemical robustness at industrially relevant model aggressive media. A large panel of physicochemical methods were applied to recognize IEF-3 as an UV-absorbing n-type semiconductor, showing a photocurrent response comparable to that of α-Bi2O3, offering further possibilities for tuning its electrochemical properties by modifying the ligand. In this way, the well-known compositional and structural versatility of coordination polymers may be applied in the future to fine-tune metal-organic semiconductor systems.

Nitro functionalized chromium terephthalate metal-organic framework as multifunctional solid acid for the synthesis of benzimidazoles.

In the present work, nitro functionalized chromium terephthalate [MIL-101(Cr)-NO2] metal- organic framework is prepared and characterized by powder X-ray diffraction (XRD), elemental analysis, infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area. The inherent Lewis acidity of MIL-101(Cr)-NO2 is confirmed by FT-IR spectroscopy using CD3CN as a probe molecule. The performance of MIL-101(Cr)-NO2 as bifunctional catalyst (acid and redox) promoting the synthesis of wide range of benzimidazoles has been examined by catalyzed condensation on acid sites and subsequent oxidative dehydrogenation. The catalytic activity of MIL-101(Cr)-NO2 is found to be superior than analogues catalysts like MIL-101(Cr)-SO3H, MIL-101(Cr)-NH2, UiO-66(Zr), UiO-66(Zr)-NO2, MIL-100(Fe) and Cu3(BTC)2 (BTC: 1,3,5-benzenetricarboxylate) under identical reaction conditions. The structural stability of MIL-101(Cr)-NO2 is supported by leaching analysis and reusability tests. MIL-101(Cr)-NO2 solid is used five times without decay in its activity. Comparison of the fresh and five times used MIL-101(Cr)-NO2 solids by powder XRD, SEM and elemental analysis indicate identical crystallinity, morphology and the absence of chromium leaching, respectively.

Design of cost-efficient and photocatalytically active Zn-based MOFs decorated with Cu2O nanoparticles for CO2 methanation.

Here we show for the first time a MOF that is photocatalytically active for light-assisted CO2 methanation under mild conditions (215 °C) without the inclusion of metallic nanoparticles or any sacrificial agent. The presence of Cu2O nanoparticles causes a 50% increase in the photocatalytic activity. This result paves the way for developing efficient and cost-effective materials for CO2 elimination.

Tuning the Microenvironment of Gold Nanoparticles Encapsulated within MIL-101(Cr) for the Selective Oxidation of Alcohols with O2 : Influence of the Amino Terephthalate Linker.

This manuscript reports a comparative study of the catalytic performance of gold nanoparticles (NPs) encapsulated within MIL-101(Cr) with or without amino groups in the terephthalate linker. The purpose is to show how the amino groups can influence the microenvironment and catalytic stability of incorporated gold nanoparticles. The first influence of the presence of this substituent is the smaller particle size of Au NPs hosted in MIL-101(Cr)-NH2 (2.45±0.19 nm) compared with the parent MIL-101(Cr)-H (3.02±0.39 nm). Both materials are highly active to promote the aerobic alcohol oxidation and exhibit a wide substrate scope. Although both catalysts can achieve turnover numbers as high as 106 for the solvent-free aerobic oxidation of benzyl alcohol, Au@MIL-101(Cr)-NH2 exhibits higher turnover frequency values (12 000 h-1 ) than Au@MIL-101(Cr)-H (6800 h-1 ). Au@MIL-101(Cr)-NH2 also exhibits higher catalytic stability, being recyclable for 20 times with coincident temporal conversion profiles, in comparison with some decay observed in the parent Au@MIL-101(Cr)-H. Characterization by transmission electron microscopy of the 20-times used samples shows a very minor particle size increase in the case of Au@MIL-101(Cr)-NH2 (2.97±0.27 nm) in comparison with the Au@MIL-101(Cr)-H analog (5.32±0.72 nm). The data presented show the potential of better control of the microenvironment to improve the performance of encapsulated Au nanoparticles.

Base-Controlled Heck, Suzuki, and Sonogashira Reactions Catalyzed by Ligand-Free Platinum or Palladium Single Atom and Sub-Nanometer Clusters.

The assumption that oxidative addition is the key step during the cross-coupling reaction of aryl halides has led to the development of a plethora of increasingly complex metal catalysts, thereby obviating in many cases the exact influence of the base, which is a simple, inexpensive, and necessary reagent for this paramount transformation. Here, a combined experimental and computational study shows that the oxidative addition is not the single kinetically relevant step in different cross-coupling reactions catalyzed by sub-nanometer Pt or Pd species, since the reactivity control is shifted toward subtle changes in the base. The exposed metal atoms in the cluster cooperate to enable an extremely easy oxidative addition of the aryl halide, even chlorides, and allow the base to bifurcate the coupling. With sub-nanometer Pd species, amines drive to the Heck reaction, carbonate drives to the Sonogahira reaction, and phosphate drives to the Suzuki reaction, while for Pt clusters and single atoms, good conversion is only achieved using acetate as a base. This base-controlled orthogonal reactivity with ligand-free catalysts opens new avenues in the design of cross-coupling reactions in organic synthesis.