Titanium-based Metal-organic Framework Research Articles

Synthesis and characterization of CdS/MIL-125 (Ti) as a photocatalyst for water splitting

Titanium based metal organic framework MIL-125 was incorporated with narrow band-gap semiconductor CdS through a solvothermal approach. Samples with different amounts of CdS loading were prepared and characterized using ICP, N2-physisorption, PXRD, DRS, SEM, TEM, HRTEM, STEM and EDS methods. The resulting composites were tested for photocatalytic hydrogen production through water splitting with platinum and lactic acid as co-catalyst and sacrificial agent, respectively. The optimized sample (with about 8 wt% CdS) showed 2.8 times higher activity compared to bulk CdS and retained its integrity through both long-term and recycling experiments. As an attempt to further elucidate the mechanism of photocatalytic activity enhancement, CdS/SBA-15 composite was investigated. Both CdS and MIL-125 proved to be active under irradiation but electron injection from CdS to MIL-125 is most likely to be the main mechanism for suppressing charge carrier re-combination and also prohibiting photo-corrosion.

An enhanced adsorption of organic dyes onto NH2 functionalization titanium-based metal-organic frameworks and the mechanism investigation

In this paper, the enhanced adsorption properties and mechanism of NH2 functionalization titanium-based metal-organic frameworks (NH2-MIL-125(Ti)) towards various organic dyes was investigated. First, MIL-125(Ti) and NH2-MIL-125(Ti) were successfully synthesized and characterized. The as-prepared Ti-MOFs can be facilely magnetized by adsorbing Fe3O4 nanoparticles on their surfaces via a Lewis acid-base interaction. Then, three types of dye (cationic dye, anionic dye and vat dye) adsorption measurements show that the electrostatic interaction, π-π stacking interaction and pore filling all play important roles in the adsorption process of both Ti-MOFs in aqueous solutions. Particularly, the amino group in NH2-MIL-125(Ti) can provide extra hydrogen bonding interaction towards target substances, which results in a stronger interaction force and a higher adsorption capacity than that of MIL-125(Ti). The adsorption kinetics and isotherm suggested the adsorption process of both Ti-MOFs towards methylene blue (MB) were better fitted to a pseudo-second-order kinetic and Freundlich isotherm model. The adsorption thermodynamic experiments demonstrated that adsorption of MB on both Ti-MOFs was spontaneous. However, their values of enthalpy and entropy were opposite, indicating that their adsorption processes were controlled by enthalpy and entropy effect, respectively.

Mesoporous TiO2 Embedded with a Uniform Distribution of CuO Exhibit Enhanced Charge Separation and Photocatalytic Efficiency.

Mixed metal oxide nanoparticles have interesting physical and chemical properties, but synthesizing them with colloidal methods is still challenging and often results in very heterogeneous structures. Here, we describe a simple method to synthesize mesoporous titania nanoparticles implanted with a uniform distribution of copper oxide nanocrystals (CuO@MTs). By calcining a titanium-based metal-organic framework (MIL-125) in the presence of Cu ions, we can trap the Cu in the TiO2 matrix. Removal of the organic ligand creates mesoporosity and limits phase separation so that tiny CuO nanocrystals form in the interstices of the TiO2. The CuO@MTs exhibits superior performance for photocatalytic hydrogen evolution (4760 μmol h-1) that is >90 times larger than pristine titania.

Porous NH2-MIL-125 as an efficient nano-platform for drug delivery, imaging, and ROS therapy utilized Low-Intensity Visible light exposure system

Metal-organic frameworks are a novel class of organic-inorganic hybrid polymer with potential applications in bioimaging, drug delivery, and ROS therapy. NH2-MIL-125, which is a titanium-based metal organic framework with a large surface area of 1540m2/g, was synthesized using a hydrothermal method. The material was characterized by powder X-ray diffreaction (PXRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM), and N2 isotherm analyses. The size of the polymer was reduced to the nanoscale using a high-frequency sonication process. PEGylation was carried out to improve the stability and bioavailability of the NMOF. The as-synthesized nano-NH2-MIL-125/PEG (NMOF/PEG) exhibited good biocompatibility over the (Cancer) MCF-7 and (Normal) COS-7 cell line. The interaction of NMOF/PEG with the breast cancer cell line (MCF-7) was examined by BIO-TEM analysis and laser confocal imaging. 2′,7′–dichlorofluorescin diacetate (DCFDA) analysis confirmed that NMOF/PEG produced free radicals inside the cancer cell line (MCF-7) upon visible light irradiation. NMOF/PEG absorbed a large amount of DOX (20wt.% of DOX) and showed pH, and photosensitive release. This controlled drug delivery was attributed to the presence of NH2, Ti group in MOF and a hydroxyl group in PEG. This combination of chemo- and ROS-therapy showed excellent efficiency in killing cancer MCF-7 cells.

Synthesis and sulfation of titanium based metal organic framework; MIL-125 and usage as catalyst in esterification reactions

In this study, titanium based metal organic framework, MIL-125, was synthesized and sulfated to gain the acidic property. The samples were characterized by XRD, TGA, N2 sorption–desorption measurements, SEM and FT-IR analysis. The catalytic activity of raw and sulfated MIL-125 was tested in esterification of acetic acid. The experiments were conducted by raw and sulfated MIL-125 to understand the positive effect of sulfation on the catalytic activity of MIL-125. Also, reusability of sulfated MIL-125 was investigated. By using sulfated MIL-125 as catalyst, high conversions were obtained in the production of esters which are among the most important chemical products.

Effect of Amino Functionality on the Uptake of Cationic Dye by Titanium-Based Metal Organic Frameworks

Titanium-based metal–organic frameworks (MOFs), named MIL-125 and NH2-MIL-125, have been successfully synthesized by the hydrothermal method. They were specially designed for the application of methylene blue (MB) removal from aqueous solution. The maximum adsorption capacity of MB was found to be 321.39 mg/g and 405.61 mg/g. The amount of dye that has been adsorbed 99.9% was 300 ppm within 20 and 120 intervals of time. The results show that NH2-MIL-125 is more effective in terms of both selectivity and capacity for the adsorption of MB cationic dye compared with MIL-125. The high adsorption selectivity was due to the unique electrostatic interaction between the amino groups of the dye molecules and NH2-MIL-125 but, on the other hand, owing to the more negative zeta potential (−32.4 mV), resulted from the charge balance for the protonation of −NH2. Moreover, reaction parameters including exposure time, adsorbent dose (0.02–0.05 mg), initial dye concentration (100–500 mg/L), and temperature were studied in...

A titanium-based metal-organic framework as an ultralong cycle-life anode for PIBs.

We achieved excellent anode performance for PIBs based on a metal-organic framework MIL-125(Ti) for the first time. It can deliver a capacity of 208 mA h g-1 at a rate of 10 mA g-1 and a high capacity retention of 90.2% after 2000 cycles at a high rate of 200 mA g-1 with a high coulombic efficiency. The K+ storage mechanism is investigated by the ex situ XRD and IR techniques and confirms that potassium ions are reversibly inserted into the organic moiety without direct engagement of Ti ions.

Harvesting the photoexcited holes on a photocatalytic proton reduction metal–organic framework

The highly porous titanium based metal-organic framework NH2-MIL-125(Ti) has recently attracted significant attention in the field of photocatalysis as a promising material for H+ reduction. This work reveals charge transfer upon visible light illumination from this MOF to two different charge acceptors, as an alternative to sacrificial electron donors. Charge transfer is demonstrated through a combined spectroscopic study between this MOF and: (1) 2-(1H-pyrazol-3-yl)phenol, a molecule that functionally mimics the tyrosine-histidine pair, responsible for shuttling the holes to the oxygen evolving centre in natural photosynthesis, and (2) TEMPO, a well known and stable radical. Charge transfer of the holes from the MOF to these occluded molecules takes place on the picosecond time scale. This work suggests that, by coupling a stable and recyclable charge acceptor to the photogenerated holes, the charges can be utilised for oxidation reactions and, thus, link the reduction to the oxidation reactions in water splitting.

The chemistry of titanium-based metal–organic frameworks

The chemistry of Ti-based MOFs, including their synthetic methods, crystal structures, topological evaluation, and promising applications, is precisely summarized and discussed.

Rapid synthesis of Titanium based Metal Organic framework (MIL-125) via microwave route and its performance evaluation in photocatalysis

In this work, we report rapid synthesis procedure of MIL-125 (or, Ti-BDC) Metal Organic Framework (MOF) via microwave route. The synthesized product was characterized using SEM, powder XRD, FT-IR analysis, TGA and UV–Vis diffused reflectance spectroscopy. The aim of this work was to establish a faster synthesis methodology for bulk synthesis of a potential MOF. The optimum synthesis temperature and time were found to be 120°C and 40min respectively. The variation of both microwave power and development of pressure during the synthesis conditions were closely monitored and it was observed that at optimum synthesis conditions, during the initial heating rate period, the pressure was linearly developed and reached a maximum value of ca. 14bar, however, during the holding time both the pressure and power remained fairly constant at around 6bar and 10 W respectively. The product was found photocatalytically active with a band gap energy of 3.14eV and successfully degraded methylene blue dye to ca. 96.77% in 360min.

Carbon-coated rutile titanium dioxide derived from titanium-metal organic framework with enhanced sodium storage behavior

Abstract Carbon-coated rutile titanium dioxide (CRT) was fabricated through an in-situ pyrolysis of titanium-based metal organic framework (Ti8O8(OH)4[O2CC6H4CO2]6) crystals. Benefiting from the Ti O C skeleton structure of titanium-based metal organic framework, the CRT possesses abundant channels and micro/mesopores with the diameters ranging from 1.06 to 4.14 nm, shows larger specific surface area (245 m2 g−1) and better electronic conductivity compared with pure titanium dioxide (12.8 m2 g−1). When applied as anode material for sodium-ion batteries, the CRT electrode exhibits a high cycling performance with a reversible capacity of ∼175 mAh g−1 at 0.5 C-rate after 200 cycles, and obtains an excellent rate capability of ∼70 mAh g−1 after 2000 cycles even at a specific current of 3360 mA g−1(20 C-rate). The outstanding rate capability can be attributed to the carbon-coated structure, which may effectively prevent aggregation of the titanium dioxide nanoparticles, accelerate the mass transfer of Na+ and speed up the charge transfer rate. Considering these advantages of this particular framework structure, the CRT can serve as an alternative anode material for the industrial application of SIBs.

Organic Linker Defines the Excited-State Decay of Photocatalytic MIL-125(Ti)-Type Materials.

Recently, MIL-125(Ti) and NH2 -MIL-125(Ti), two titanium-based metal-organic frameworks, have attracted significant research attention in the field of photocatalysis for solar fuel generation. This work reveals that the differences between these structures are not only based on their light absorption range but also on the decay profile and topography of their excited states. In contrast to MIL-125(Ti), NH2 -MIL-125(Ti) shows markedly longer lifetimes of the charge-separated state, which improves photoconversion by the suppression of competing decay mechanisms. We used spectroelectrochemistry and ultrafast spectroscopy to demonstrate that upon photoexcitation in NH2 -MIL-125(Ti) the electron is located in the Ti-oxo clusters and the hole resides on the aminoterephthalate unit, specifically on the amino group. The results highlight the role of the amino group in NH2 -MIL-125(Ti), the electron donation of which extends the lifetime of the photoexcited state substantially.

Syngas Purification by Porous Amino-Functionalized Titanium Terephthalate MIL-125

The adsorption equilibrium of carbon dioxide (CO2), carbon monoxide (CO), nitrogen (N2), methane (CH4), and hydrogen (H2) was studied at 303, 323, and 343 K and pressures up to 7 bar in titanium-based metal–organic framework (MOF) granulates, amino-functionalized titanium terephthalate MIL-125(Ti)_NH2. The affinity of the different adsorbates toward the adsorbent presented the following order: CO2 > CH4 > CO > N2 > H2, from the most adsorbed to the least adsorbed component. Subsequently, adsorption kinetics and multicomponent adsorption equilibrium were studied by means of single, binary, and ternary breakthrough curves at 323 K and 4.5 bar with different feed mixtures. Both studies are complementary and aim the syngas purification for two different applications, hydrogen production and H2/CO composition adjustment, to be used as feed in the Fischer–Tropsch processes. The isosteric heats were calculated from the adsorption equilibrium isotherms and are 21.9 kJ mol–1 for CO2, 14.6 kJ mol–1 for CH4, 13.4 kJ...

Mixed matrix membranes incorporated with amine-functionalized titanium-based metal-organic framework for CO2/CH4 separation

High performance mixed matrix membranes arise from a targeted selection of constituent materials, especially the choice of fillers. An amine-functionalized metal-organic framework (MOF), NH2-MIL-125(Ti), was used in this work to prepare polysulfone-based mixed matrix membranes (MMMs). Permeation measurements on CO2/CH4 gas mixture demonstrate that the incorporation of NH2-MIL-125(Ti) particles can significantly improve the CO2 permeability compared to the pure polymer membrane, along with slightly enhanced CO2/CH4 separation factor. This work also shows that the separation factor at high pressures can remain almost unchanged for the prepared MMMs with the MOF loadings up to 20wt%. The obtained results may provide useful information in facilitating the applications of promising MOF-containing MMMs for the practical membrane-based natural gas purification.