Ti3+-mediated MIL-125(Ti) by metal substitution for boosting photocatalytic N2 fixation

Photocatalysis, which uses sunlight, N2 and H2O to produce NH3, is a more sustainable approach to N2 fixation than the Haber-Bosch process. However, its efficiency is severely limited by the difficulty of activating NN bonds. This work presents metal (M = Cu, Fe, V)-substituted MIL-125(Ti) (MIL-(MTi)) for photocatalytic N2 fixation without using any sacrificial agents. Structural characterizations reveal that the active sites including oxygen vacancies (OV) and Ti3+ species are formed by the resulting crystal distortion due to the partial substitution of Ti4+ by other metal ions (Cu+, Fe2+, V3+) in MIL-125(Ti). MIL-(CuTi) possesses a larger number of OV and Ti3+ compared to MIL-(FeTi) and MIL-(VTi) due to the larger valence difference between Cu+ and Ti4+. These active sites not only promote the adsorption and activation of N2 and H2O, but also facilitate the photogenerated charge mobility. Photogenerated holes oxidize H2O to produce O2 and H+. Photogenerated electrons reduce N2 activated on Ti3+ sites by combining with H+ to form NH4+. Therefore, MIL-(CuTi) shows the highest NH4+ production rate 46.5 µmol·h-1·g-1, which is much higher than that (1.2 µmol·h-1·g-1) of the pristine MIL-125(Ti). This work provides a new insight into rational design for artificial N2 fixation systems by the construction of the active site.

Ti-based MOFs with acetic acid pendings as an efficient catalyst in the preparation of new spiropyrans with biological moieties

The strategy of designing heterogeneous porous catalysts by a post-modification method is a smart strategy to increase the catalytic power of desired catalysts. Accordingly, in this report, metal-organic frameworks based on titanium with acetic acid pending were designed and synthesized via post-modification method. The structure of the target catalyst has been investigated using different techniques such as FT-IR, XRD, SEM, EDX, Mapping, and N2 adsorption/desorption (BET/the BJH) the correctness of its formation has been proven. The catalytic application of Ti-based MOFs functionalized with acetic acid was evaluated in the preparation of new spiropyrans, and the obtained results show that the catalytic performance is improved by this modification. The strategy of designing heterogeneous porous catalysts through post-modification methods presents a sophisticated approach to enhancing the catalytic efficacy of desired catalysts. In this context, our study focuses on the synthesis and characterization of metal-organic frameworks (MOFs) based on titanium, functionalized with acetic acid pendants, using a post-modification method. Various characterization techniques, including Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), mapping, and N2 adsorption/desorption (BET/BJH), were employed to investigate the structure and composition of the synthesized catalyst. These techniques collectively confirmed the successful formation and structural integrity of the target catalyst. The structure of the synthesized products was confirmed by melting point, 1H-NMR and 13C-NMR and FT-IR techniques. Examining the general process of catalyst synthesis and its catalytic application shows that the mentioned modification is very useful for catalytic purposes. The presented catalyst was used in synthesis of a wide range of biologically active spiropyrans with good yields. The simultaneous presence of several biologically active cores in the synthesized products will highlight the biological properties of these compounds. The present study offers a promising insight into the rational design, synthesis, and application of task-specific porous catalysts, particularly in the context of synthesizing biologically active candidate molecules.

Heterometallic MIL-125(Ti-Al) frameworks for electrochemical determination of ascorbic acid, dopamine and uric acid

The detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA) is not only of great significance in the areas of biomedicine and neurochemistry but also helpful in disease diagnosis and pathology research. Due to their diverse structures, designability, and large specific surface areas, metal-organic frameworks (MOFs) have recently caught considerable attention in the electrochemical field. Herein, a family of heterometallic MOFs with amino modification, MIL-125(Ti-Al)-xNH2 (x = 0%, 25%, 50%, 75%, and 100%), were synthesized and employed as electrochemical sensors for the detection of AA, DA, and UA. Among them, MIL-125(Ti-Al)-75%NH2 exhibited the most promising electrochemical behavior with 40% doping of carbon black in 0.1 M PBS (pH = 7.10), which displayed individual detection performance with wide linear detection ranges (1.0-6.5 mM for AA, 5-100 μM for DA and 5-120 μM for UA) and low limits of detection (0.215 mM for AA, 0.086 μM for DA, and 0.876 μM for UA, S/N = 3). Furthermore, the as-prepared MIL-125(Ti-Al)-75%NH2/GCE provided a promising platform for future application in real sample analysis, owing to its excellent anti-interference performance and good stability.

Oriented Ultrathin π-complexation MOF Membrane for Ethylene/Ethane and Flue Gas Separations

Rational design and engineering of high-performance molecular sieve membranes towards C2 H4 /C2 H6 and flue gas separations remain a grand challenge to date. In this study, through combining pore micro-environment engineering with meso-structure manipulation, highly c-oriented sub-100 nm-thick Cu@NH2 -MIL-125 membrane was successfully prepared. Coordinatively unsaturated Cu ions immobilized in the NH2 -MIL-125 framework enabled high-affinity π-complexation interactions with C2 H4 , resulting in an C2 H4 /C2 H6 selectivity approaching 13.6, which was 9.4 times higher than that of pristine NH2 -MIL-125 membrane; moreover, benefiting from π-complexation interactions between CO2 and Cu(I) sites, our membrane displayed superior CO2 /N2 selectivity of 43.2 with CO2 permeance of 696 GPU, which far surpassed the benchmark of other pure MOF membranes. The above multi-scale structure optimization strategy is anticipated to present opportunities for significantly enhancing the separation performance of diverse molecular sieve membranes.

Electron-Donor Functional Groups, Band Gap Tailoring, and Efficient Charge Separation: Three Keys To Improve the Gaseous Iodine Uptake in MOF Materials

Metal-organic frameworks (MOFs) have been largely investigated worldwide for their use in the capture of radioactive iodine due to its potential release during nuclear accident events and reprocessing of nuclear fuel. The present work deals with the capture of gaseous I₂ under a continuous flow and its subsequent transformation into I₃^- within the porous structures of three distinct, yet structurally related, terephthalate-based MOFs: MIL-125(Ti), MIL-125(Ti)_NH₂, and CAU-1(Al)_NH₂. The synthesized materials exhibited specific surface areas (SSAs) with similar order of magnitude: 1207, 1099, and 1110 m² g^-1 for MIL-125(Ti), MIL-125(Ti)_NH₂, and CAU-1(Al)_NH₂, respectively. Because of that, it was possible to evaluate the influence of other variables over the iodine uptake capacity─such as band gap energies, functional groups, and charge transfer complexes (CTC). After 72 h of contact with the I₂ gas flow, MIL-125(Ti)_NH₂ was able to trap 11.0 mol mol^-1 of I₂, followed by MIL-125(Ti) (8.7 mol mol^-1), and by CAU-1(Al)_NH₂ (4.2 mol mol^-1). The enhanced ability to retain I₂ in the MIL-125(Ti)_NH₂ was associated with a combined effect between its amino group (which has a great affinity toward iodine), its smaller band gap (2.5 eV against 2.6 and 3.8 eV for CAU-1(Al)_NH₂ and MIL-125(Ti), respectively), and its efficient charge separation. In fact, the presence of a linker-to-metal charge transfer (LMCT) mechanism in MIL-125(Ti) compounds separates the photogenerated electrons and holes into the two distinct moieties of the MOF: the organic linker (which stabilizes the holes) and the oxy/hydroxy inorganic cluster (which stabilizes the electrons). This effect was observed using EPR spectroscopy, whereas the reduction of the Ti⁴⁺ cations into the paramagnetic Ti³⁺ species was evidenced after irradiation of the pristine Ti-based MOFs with UV light (<420 nm). In contrast, because CAU-1(Al)_NH₂ exhibits a purely linker-based transition (LBT)─with no EPR signals related to Al paramagnetic species─it tends to exhibit faster recombination of the photogenerated charge carriers as, in this case, both electrons and holes are located over the organic linker. Furthermore, the transformation of the gaseous I₂ into I_n^- [n = 5, 7, 9, ...] intermediates and then into I₃^- species was evaluated using Raman spectroscopy by following the evolution of their respective bands at about 198, 180, and 113 cm^-1. This conversion─which is favored by an effective charge separation and smaller band gaps─increases the I₂ uptake capacity of the compounds by creating specific adsorption sites for these anionic species. In fact, because the -NH₂ groups act as an antenna to stabilize the photogenerated holes, both I_n^- and I₃^- are adsorbed into the organic linker via an electrostatic interaction with these positively charged entities. Finally, changes regarding the EPR spectra before and after the iodine loading were considered to propose a mechanism for the electron transfer from the MOFs structure to the I₂ molecules considering their different characteristics.

Mn-doped Ti-based MOFs for magnetic resonance imaging-guided synergistic microwave thermal and microwave dynamic therapy of liver cancer

Currently, precise ablation of tumors without damaging the surrounding normal tissue is still an urgent problem for clinical microwave therapy of liver cancer. Herein, we synthesized Mn-doped Ti MOFs (Mn–Ti MOFs) nanosheets by in-situ doping method and applied them for microwave therapy. Infrared thermal imaging results indicate Mn–Ti MOFs can rapidly increase the temperature of normal saline, attributing to the porous structure improving microwave-induced ion collision frequency. Moreover, Mn–Ti MOFs show higher ¹O₂ output than Ti MOFs under 2 W of low-power microwave irradiation due to the narrower band-gap after Mn doping. At the same time, Mn endows the MOFs with a desirable T₁ contrast of magnetic resonance imaging (r₂/r₁ = 2.315). Further, results on HepG2 tumor-bearing mice prove that microwave-triggered Mn–Ti MOFs nearly eradicate the tumors after 14 days of treatment. Our study offers a promising sensitizer for synergistic microwave thermal and microwave dynamic therapy of liver cancer.

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Mn-doped Ti-MOFs nanosheets (Mn–Ti MOFs) were synthesized as novel microwave sensitizers.

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Mn–Ti MOFs can significantly generate heat and produce ROS under low-power microwave irradiation.

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The combination of microwave thermal therapy and microwave dynamic therapy can effectively inhibit the growth of tumor cells in vitro and in vivo.

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The microwave sensitizers have potential application in MRI-guided microwave therapy for liver cancer.

Morphology control through the synthesis of metal-organic frameworks

Designable morphology and predictable properties are the most challenging goals in material engineering. Features such as shape, size, porosity, agglomeration ratio significantly affect the final properties of metal-organic frameworks (MOFs) and can be regulated throughout synthesis parameters but require a deep understanding of the mechanisms of MOFs formation. Herein, we systematically summarize the effects of the individual synthesis factors, such as pH of reaction mixture, including acidic or basic character of modulators, temperature, solvents types, surfactants type and content and ionic liquids on the morphology of growing MOFs. We identified main mechanisms of MOFs' growth leading to different morphology of final particles and next systematically discuss the effect of miscellaneous parameters on MOFs morphology based on the main mechanisms related to the nucleation, growth and formation of final MOFs structure, including coordination modulation, protonation/deprotonation acting and modulation by surfactants or capping agents. The effect of microwaves and ultrasound employment during synthesis is also considered due to their affecting especially nucleation and particles growing steps during MOFs formation.

Facet-Dependent Photocatalytic Behavior of Fe-soc-MOF for Carbon Dioxide Reduction

Exposing different facets on metal-organic frameworks (MOFs) is an efficient approach to regulate their photocatalytic performance for CO₂ reduction. Herein, Fe-soc-MOFs exposed with different facets were successfully synthesized, and the morphologies of Fe-soc-MOF exposed with eight {111} facets (Fe-soc-O) and that exposed with eight {111} and six {100} crystal facets (Fe-soc-M) are first reported. Fe-soc-MOFs have facet-dependent active sites on their surface and correspondingly different catalytic performance for photocatalytic CO₂ reduction. Fe-soc-O has the highest CO production of 1804 μmol g^-1 h^-1, while the Fe-soc-MOF exposed with six {100} facets (Fe-soc-C) has the best CO selectivity of 94.7%. Density functional theory (DFT) calculations demonstrate that the (111) facet has more favorable thermodynamic potential for CO₂ reduction and H₂ evolution compared with the (100) one, deriving from its facet-dependent active sites. This work shows that utilizing the facet-engineering strategy to regulate the active sites exposed on the surface of MOFs is feasible. The results display the relation between the facet of MOFs and the photocatalytic behavior for CO₂ reduction.

Efficient photocatalytic degradation of petroleum oil spills in seawater using a metal-organic framework (MOF)

Photocatalysis is a green approach that has appeared to be a viable option for the degradation of a variety of organic contaminants. This work outlines the process of preparing the titanium-based metal-organic framework (MIL-125) photocatalysts using a simple solvothermal method. Structural, morphological, and optical analysis of samples (MT18 and MT48) was carried out by XRD, FT-IR, Raman, SEM, TGA, BET, and UV-Vis. Results indicated that the sample prepared at 150 °C and reaction time of 48 h (MT48) has a low crystal size of 7 nm with an optical band gap of 3.2 eV and a surface area of 301 m² g^-1. Under UV-visible light irradiation, the as-prepared MOFs proved to upgrade photocatalytic activity in degrading crude oil spills in saltwater. Effects of catalyst dosage and exposure time on the degradation of an oil spill in seawater were studied and analyzed using UV-Vis spectrophotometry and gas chromatography (GC-MS) which emphasized that the use of 250 ppm of MT48 photocatalyst under UV-Vis irradiation can degrade about 99% of oil spills in water after 2 h of exposure. The study's data revealed that MIL-125 could be used to photocatalyzed the cleanup of crude oil spills.

De novo synthesis of a MIL-125(Ti) carrier for thermal- and pH-responsive drug release

Microporous round cake-like (diameter: 900 ± 100 nm) MIL-125(Ti) carrier with a central metal (Ti) exhibiting bio-affinity and possessing a great potential to be used as drug release platform, has been synthesized in the present study. The thermal and pH responsiveness of drug delivery systems (DDS) are the most important parameters for drug release and can be provided through polymer coating techniques. The Pluronic F127 (F127) and chitosan (CH) monomers were inserted into the crystal lattice of MIL-125(Ti) carrier during the de novo synthesis process, which were subsequently loaded with doxorubicin (DOX). The results reveal particle size changes (ranged between 30 and 50 %) from the original size of the MIL-125(Ti) carrier in response to temperature and pH when the carrier reaches acid environment. The drug release profiles have been completed through self-design device, which provides for the real-time release in the DOX amounts via UV-Vis spectra. The kinetics analysis was used to evaluate the R² values of first order, Higuchi, Korsmeyer-peppas, and Weibull fitting equations, where the Weibull fitting indicated the best R². An increase by 59.3 % of DOX released under the acid status (pH = 5.4) was observed, indicating that the CH-MIL-125(Ti) carrier is temperature and pH responsive. Moreover, the lattice explosion resulting from the temperature increase in the range of 25-42 °C caused an increase in F127-MIL-125(Ti) by 30.8-38.3 %. The simulated SAXS/WAXS studies for the microstructures of MIL-125(Ti) based DDS at different temperatures after polymer coating (F127-MIL-125(Ti)) provide the possible mechanism of lattice explosion. As such, the responsive Ti-MOF has a highly potential for use in the applications of cancer treatment.

De novo synthesis of photocatalytic bifunctional MIL-125(Ti)/gC3N4/RGO through sequential self-assembly and solvothermal route

In this study we have synthesized a heterostructured metal organic framework (MOF) consisting of self-assembled porous carbon nitride (gC₃N₄) and, reduced graphene oxide (RGO) with MIL-125(Ti) (CN-GO-MIL) through a simple synthesis route. As-synthesized CN-GO-MIL was characterized to determine its morphological, surface, structural, and optical properties. The synthesis produced a porous nanomaterial with efficient visible light capture and electron transport. CN-GO-MIL proved 2.23 and 1.23 times as effective as bare MIL-125(Ti) for Rhodamine B (RhB) degradation and chromium (Cr) reduction, respectively. We propose a governing photocatalytic degradation and reduction mechanism in which superoxide plays a major role in the photocatalytic degradation, followed by O₂¹, OH·, and holes, and identify methanol as a suitable hole scavenger for reduction of Cr. Moreover, Cr reduction can be best achieved at pH 2 in the presence of methanol. Performance of material in terms of apparent quantum yield (AQY), figure of merit (FOM), and catalyst surface efficiency (S.E), suggests 5% CN-GO-MIL is an efficient photocatalyst for degradation of RhB. Comparison of the AQY with previously reported MOF-based composites shows that the as synthesized 5% CN-GO-MIL can be regarded as one of best performing photocatalyst under visible light irradiation for abatement of organic and inorganic pollution.

Selective ligand removal to improve accessibility of active sites in hierarchical MOFs for heterogeneous photocatalysis

Metal-organic frameworks (MOFs) are commended as photocatalysts for H2 evolution and CO2 reduction as they combine light-harvesting and catalytic functions with excellent reactant adsorption capabilities. For dynamic processes in liquid phase, the accessibility of active sites becomes a critical parameter as reactant diffusion is limited by the inherently small micropores. Our strategy is to introduce additional mesopores by selectively removing one ligand in mixed-ligand MOFs via thermolysis. Here we report photoactive MOFs of the MIL-125-Ti family with two distinct mesopore architectures resembling either large cavities or branching fractures. The ligand removal is highly selective and follows a 2-step process tunable by temperature and time. The introduction of mesopores and the associated formation of new active sites have improved the HER rates of the MOFs by up to 500%. We envision that this strategy will allow the purposeful engineering of hierarchical MOFs and advance their applicability in environmental and energy technologies.

Low temperature curable titanium-based sols for visible light photocatalytic coatings for glass and polymeric substrates

Titanium oxide (TiO2) is a widely used material in photocatalytic coatings in which efficiency generally lies in the ultraviolet (UV) spectrum of light. Sol-gel method provides a simple and versatile...

A super-hydrophilic NH2-MIL-125 composite film with dopamine-modified graphene oxide is used for water treatment

It is always concerning about how to remove oil–water emulsions and dyes simultaneously and how to find a suitable separation film.

Zwitterion-functionalized MIL-125-NH2-based thin-film nanocomposite forward osmosis membranes: towards improved performance for salt rejection and heavy metal removal

Incorporating zwitterion-functionalized MIL-125-NH2 nanoparticles in the rejection layer of TFN FO membranes improves their water/ion separation performance and antifouling ability.

Enhanced Degradation of Rhodamine B by Metallic Organic Frameworks Based on NH2-MIL-125(Ti) under Visible Light

Samples of the bimetallic-based NH2-MIL-125(Ti) at a ratio of Mn+/Ti4+ is 0.15 (Mn+: Ni2+, Co2+ and Fe3+) were first synthesized using the solvothermal method. Their fundamental properties were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectra, scanning electron microscopy (SEM), N2 adsorption-desorption measurements, and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The as-acquired materials were used as high-efficiency heterogeneous photocatalysts to remove Rhodamine B (RhB) dye under visible light. The results verified that 82.4% of the RhB (3 × 10-5 M) was degraded within 120 min by 15% Fe/Ti-MOFs. Furthermore, in the purpose of degrading Rhodamine B (RhB), the rate constant for the 15% Fe/Ti-MOFs was found to be 2.6 times as fast as that of NH2-MIL-125(Ti). Moreover, the 15% Fe/Ti-MOFs photocatalysts remained stable after three consecutive cycles. The trapping test demonstrated that the major active species in the degradation of the RhB process were hydroxyl radicals (HO∙) and holes (h+).

Unlocking active metal site of Ti-MOF for boosted heterogeneous catalysis via a facile coordinative reconstruction

Constructing sophisticated hollow structure and exposing more metal sites in metal-organic frameworks (MOFs) can not only enhance their catalytic performance but also endow them with new functions. Herein, we present a facile coordinative reconstruction strategy to transform Ti-MOF polyhedron into nanosheet-assembled hollow structure with a large amount of exposed metal sites. Importantly, the reconstruction process relies on the esterification reaction between the organic solvent, i.e. ethanol and the carboxylic acid ligand, allowing the conversion of MOF without the addition of any other modulators and/or surfactants. Moreover, the surface and internal structure of the reconstructed MOF can be well tuned via altering the conversion time. Impressively, the reconstructed MOF exhibits ∼5.1-fold rate constant compared to the pristine one in an important desulfurization reaction for clean fuels production, i.e. the oxidation of dibenzothiophene.

Surfactant-assisted synthesis of titanium nanoMOFs for thin film fabrication

We use dodecanoic acid as a modulator to yield titanium MOF nanoparticles with good control of size and colloid stability and minimum impact to the properties of the framework to enable direct fabrication of crystalline, porous thin films.

Recent Advances in Metal-Organic Frameworks Derived Nanocomposites for Photocatalytic Applications in Energy and Environment

Solar energy is a key sustainable energy resource, and materials with optimal properties are essential for efficient solar energy-driven applications in photocatalysis. Metal-organic frameworks (MOFs) are excellent platforms to generate different nanocomposites comprising metals, oxides, chalcogenides, phosphides, or carbides embedded in porous carbon matrix. These MOF derived nanocomposites offer symbiosis of properties like high crystallinities, inherited morphologies, controllable dimensions, and tunable textural properties. Particularly, adjustable energy band positions achieved by in situ tailored self/external doping and controllable surface functionalities make these nanocomposites promising photocatalysts. Despite some progress in this field, fundamental questions remain to be addressed to further understand the relationship between the structures, properties, and photocatalytic performance of nanocomposites. In this review, different synthesis approaches including self-template and external-template methods to produce MOF derived nanocomposites with various dimensions (0D, 1D, 2D, or 3D), morphologies, chemical compositions, energy bandgaps, and surface functionalities are comprehensively summarized and analyzed. The state-of-the-art progress in the applications of MOF derived nanocomposites in photocatalytic water splitting for H2 generation, photodegradation of organic pollutants, and photocatalytic CO2 reduction are systemically reviewed. The relationships between the nanocomposite properties and their photocatalytic performance are highlighted, and the perspectives of MOF derived nanocomposites for photocatalytic applications are also discussed.

Efficient removal of heavy metals from polluted water with high selectivity for Hg(ii) and Pb(ii) by a 2-imino-4-thiobiuret chemically modified MIL-125 metal-organic framework

A highly porous adsorbent based on a metal-organic framework was successfully designed and applied as an innovative adsorbent in the solid phase for the heavy metal removal. MIL-125 was densely decorated by 2-imino-4-thiobiuret functional groups, which generated a green, rapid, and efficacious adsorbent for the uptake of Hg(ii) and Pb(ii) from aqueous solutions. ITB-MIL-125 showed a high adsorption affinity toward mercury(ii) ions of 946.0 mg g-1 due to covalent bond formation with accessible sulfur-based functionality. Different factors were studied, such as the initial concentration, pH, contact time, and competitive ions, under same circumstances at the room temperature. Moreover, the experimental adsorption data were in excellent agreement with the Langmuir adsorption isotherm and pseudo-second order kinetics. At a high concentration of 100 ppm mixture of six metals, ITB-MIL-125 exhibited a high adsorption capacity, reaching more than 82% of Hg(ii) compared to 62%, 30%, 2%, 1.9%, and 1.6% for Pb(ii), Cu(ii), Cd(ii), Ni(ii), and Zn(ii), respectively.

Construction of NH2-MIL-125(Ti)/CdS Z-scheme heterojunction for efficient photocatalytic H2 evolution

Designing efficient semiconductor-based photocatalysts for hydrogen production is a challenging but promising prospect in energy conversion. Herein, a novel Z-scheme CdS/NH₂-MIL-125(Ti) heterojunction is successfully fabricated through a facile solvethermal method. The detailed characterizations reveal that CdS nanoparticles are in-suit archored on NH₂-MIL-125(Ti) nanoplates. Benefited from the intrinsic band alignment and intimate contact of two species, this established structure gives a positive effect regarding charge separation. In consequence, the optimal CdS/NH₂-MIL-125(Ti) nanocomposites exhibit excellent photocatalytic performance with hydrogen evolution rate of 6.62 mmol·h^-1·g^-1 under visible light illumination, which was 3.5 times higher than that of the pristine CdS. We believe that this work will provide a new avenue to develop high-efficiency heterojunction catalyst for solar-driven energy conversions and other application.

Single copper sites dispersed on defective TiO2-x as a synergistic oxygen reduction reaction catalyst

Catalysts containing isolated single atoms have attracted much interest due to their good catalytic behavior, bridging the gap between homogeneous and heterogeneous catalysts. Here, we report an efficient oxygen reduction reaction (ORR) catalyst that consists of atomically dispersed single copper sites confined by defective mixed-phased TiO_2-x. This synergistic catalyst was produced by introducing Cu²⁺ to a metal organic framework (MOF) using the Mannich reaction, occurring between the carbonyl group in Cu(acac)₂ and the amino group on the skeleton of the MOF. The embedding of single copper atoms was confirmed by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy and x-ray absorption fine structure spectroscopy. Electronic structure modulation of the single copper sites coupling with oxygen vacancies was further established by electron paramagnetic resonance spectroscopy and first-principles calculations. Significantly enhanced ORR activity and stability were achieved on this special Cu single site. The promising application of this novel electrocatalyst was demonstrated in a prototype Zn-air battery. This strategy of the stabilization of single-atom active sites by optimization of the atomic and electronic structure on a mixed matrix support sheds light on the development of highly efficient electrocatalysts.

Early instability of MIL-125-NH2 in aqueous solution and mediation of the visible photogeneration of an NADH cofactor

MIL-125-NH₂ hydrolysis can be minimized by regulating the pH of the medium, thus defining a stability window where it is possible to use it as a photocatalyst for visible light-driven production of NADH.

Study on the influence of the introduction of the thiophene group on the photocatalytic performance of polymer

Two novel conjugated organic polymers BTTh-1 and BTTh-2 were designed and synthesized. They were prepared by the reaction of two aldehyde units with melamine. Both aldehyde units were based on benzothiadiazole. The difference between the final aldehyde units was the introduction of thiophene groups in the BTTh-2 aldehyde monomer units. The difference between the two materials in the photocatalytic degradation of tetracycline was discussed in the context of the thiophene unit. The degradation efficiency of tetracycline by BTTh-2 (90.9%) was much higher than that of BTTh-1 (40.7%). The characterization results showed that BTTh-2 has a strong charge separation ability and fast transmission rate. After light excitation, the recombination ability of photogenerated holes and electrons becomes weak, and it has better utilization ability for visible light; the bandgap width is narrower.

Selective separation of hibiscus acid from Roselle extracts by an amino-functionalized Metal Organic Framework

The separation and purification of biologically-active compounds from natural sources is of interest because such molecules find wide application in the pharmaceutical sector and in other industrial areas. Roselle (Hibiscus sabdariffa) plants are a good source of anthocyanins, flavonoids, hydroxycitric acid, tartaric acid, ascorbic acid and hibiscus acid. The separation of hibiscus acid from the Roselle extract is very challenging, requiring the use of selective methods. It is accomplished here by means of the indium-bearing Metal Organic Framework MIL-68-NH₂. Before and after exposure to MIL-68-NH₂, the Roselle extract is analyzed by thin-layer chromatography, ultraviolet-visible spectrophotometry, gas chromatography-mass spectrometry, and high-performance liquid chromatography. The structural integrity of MIL-68-NH₂ after the separations is investigated by powder X-ray diffraction, nuclear magnetic resonance and infrared spectroscopy, confirming the adsorption selectivity of MIL-68-NH₂ towards hibiscus acid.

Heterostructured g-CN/TiO2 Photocatalysts Prepared by Thermolysis of g-CN/MIL-125(Ti) Composites for Efficient Pollutant Degradation and Hydrogen Production

Photocatalysts composed of graphitic carbon nitride (g-CN) and TiO₂ were efficiently prepared by thermolysis of the MIL-125(Ti) metal organic framework deposited on g-CN. The heterojunction between the 12 nm-sized TiO₂ nanoparticles and g-CN was well established and the highest photocatalytic activity was observed for the g-CN/TiO₂ (3:1) material. The g-CN/TiO₂ (3:1) composite exhibits high visible light performances both for the degradation of pollutants like the Orange II dye or tetracycline but also for the production of hydrogen (hydrogen evolution rate (HER) up to 1330 μmolh⁻¹g⁻¹ and apparent quantum yield of 0.22% using NiS as a cocatalyst). The improved visible light performances originate from the high specific surface area of the photocatalyst (86 m²g⁻¹) and from the efficient charge carriers separation as demonstrated by photoluminescence, photocurrent measurements, and electrochemical impedance spectroscopy. The synthetic process developed in this work is based on the thermal decomposition of metal organic framework deposited on a graphitic material and holds huge promise for the preparation of porous heterostructured photocatalysts.

Excellent adsorptive performance of a new nanocomposite for removal of toxic Pb(II) from aqueous environment: Adsorption mechanism and modeling analysis

Herein, a novel nanocomposite (Fe₃O₄@TATS@ATA) was prepared and used for adsorptive removal of Pb(II) ions from aqueous environment. The magnetic nanocomposite (Fe₃O₄@TATS@ATA) was characterized using FTIR, TEM, SEM, EDX, element mapping analysis (EMA), TGA analysis, XRD patterns, VSM, BET analysis, XPS spectrum, and zeta potential. The FTIR study confirmed the modification of Fe₃O₄ nanoparticles with triaminetriethoxysilane and 2-aminoterephthalic acid while XPS analysis (with peaks at 283.6, 285.1, 286.3, 284.5.0, 288.4 eV) displayed the presence of CSi, CN, OCNH, CC/CC and OCO functional groups, respectively on Fe₃O₄@TATS@ATA. The BET surface area, average pore size, pore volume and magnetization saturation for Fe₃O₄@TATS@ATA were found to be 114 m²/g, 6.4 nm, 0.054 cm^-3/g, and 22 emu/g, respectively. The adsorption isotherm data showed that Pb(II) adsorption onto Fe₃O₄@TATS@ATA fitted to Langmuir and Dubinin-Raduskevich isotherm model due to better R² value which was greater than 0.9 and q_m of Pb(II) was 205.2 mg/g at pH 5.7 in 150 min. Adsorption kinetics data displayed that Pb(II) adsorption onto Fe₃O₄@TATS@ATA was fitted to the pseudo-second-order and Elovich kinetic models. Thermodynamic outcomes exhibited the exothermic and spontaneous nature of adsorption. Results showed that Fe₃O₄@TATS@ATA nanocomposite was promising material for efficient removal of toxic Pb(II) from aqueous environment.

Synthesis of Nitrogen-Doped Mesoporous Structures from Metal-Organic Frameworks and Their Utilization Enabling High Performances in Hybrid Sodium-Ion Energy Storages

Sodium-ion energy storage is of the most attractive candidate for commercialization adoption due to the safety and cost demands of large-scale energy storage systems, but its low energy density, slow charging capability, and poor cycle stability are yet to be overcome. Here, a strategy is reported to realize high-performance sodium-ion energy storage using battery-type anode and capacitor-type cathode materials. First, nitrogen-doped mesoporous titanium dioxide (NMTiO2) structures are synthesized via the controlled pyrolysis of metal-organic frameworks. They exhibit interconnected open mesopores allowing fast ion transport and robust cycle stability with nearly 100% coulombic efficiency, along with rich redox-reactive sites allowing high capacity even at a high rate of ≈90 C. Moreover, assembling the NMTiO2 anode with the nitrogen-doped graphene (NG) cathode in an asymmetric full cell shows a high energy density exceeding its counterpart symmetric cell by more than threefold as well as robust cycle stability over 10 000 cycles. Additionally, it gives a high-power density close to 26 000 W kg-1 outperforming that of a conventional sodium-ion battery by several hundred fold, so that full cells can be charged within a few tens of seconds by the flexible photovoltaic charging and universal serial bus charging modules.

Development of a needle trap device packed with titanium-based metal-organic framework sorbent for extraction of phenolic derivatives in air

We developed a novel method of needle trap device packed with titanium-based metal-organic framework for the extraction of phenolic derivatives in air followed by gas chromatography-flame ionization detector analysis. The synthetized adsorbent was packed inside a 22-gauge spinal needle. This method was first tested at laboratory scale, and then was used for field sampling of phenolic derivatives in air. A glass chamber placed on a heater at 60°C was used to provide different concentrations of phenolic derivatives. The desorption conditions and breakthrough volume were optimized using response surface methodology. The limit of detection and limit of quantitation of the proposed method were estimated to be in the range of 0.001-0.12 and 0.003-0.62 ng/mL, respectively, indicating a high sensitivity for the suggested sampler. Storing the packed needle trap device in a refrigerator at 4˚C for 60 days did not dramatically affect the storage stability. Our findings indicated that there was a high correlation coefficient (R²  = 0.99) between the measurement results of this method and the NIOSH recommended method (XAD-7 sorbent tube). Therefore, it can be concluded that the needle trap device packed with titanium-based metal-organic framework can be used as a efficient method for extraction of phenolic derivatives in air.