Yi Zuo

Solvothermal synthesis of NH2-MIL-125(Ti) from circular plate to octahedron

The MOF material NH2-MIL-125(Ti) was synthesized through the solvothermal method, and the morphology can be controlled by simply modulating the concentration of the reactants during crystallization, which ranges from circular plate through tetragon to octahedron. All samples were characterized by SEM, XRD, FT-IR, UV Raman spectra, TGA, Ar adsorption/desorption and UV-vis spectra. In situ XRD results show that this Ti-incorporated MOF is highly thermostable until 290 °C. It is interesting to find that the light response of NH2-MIL-125(Ti) crystals is closely related to their morphology, and the absorption edges of different morphologies range from 480 nm to 533 nm with band gaps of 2.6 to 2.3 eV, making them potential candidates for photocatalytic applications.

Facile synthesis of morphology and size-controlled zirconium metal-organic framework UiO-66: the role of hydrofluoric acid in crystallization

UiO-66 with crystal size ranging from hundreds of nanometers to a few micrometers and with cubic and cuboctahedral morphologies were synthesized. Crystal size and morphology varied with the additive amount of hydrofluoric acid and the concentration of reactants (ZrCl4 and H2BDC) during solvothermal synthesis. According to energy dispersive spectrometry (EDS) and 19F MAS NMR measurements, the fluorine ions directly bonded to Zr in the SBUs (secondary building units) in the MOF framework due to their strongest electronegativity. The bonding of the fluorine ions and Zr not only compensated for the charge imbalance of the framework caused by missing linkers but also competed with the linkers to coordinate with the Zr metal centers, thereby controlling the processes of nucleation and growth of the UiO-66 crystals. The samples were further characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and Ar sorption isotherms, showing that the introduction of fluorine enhanced the thermostability and porosity of UiO-66.

Role of Pentahedrally Coordinated Titanium in Titanium Silicalite-1 in Propene Epoxidation

Two titanium silicalite-1 samples with different crystal sizes were synthesized in the tetrapropylammonium bromide (TPABr) and tetrapropylammonium hydroxide (TPAOH) hydrothermal systems. The small-crystal TS-1 with a size of 600 nm was then treated with different organic bases. These TS-1 samples were evaluated in the epoxidation of propene, and characterized by ultraviolet-visible diffuse reflectance (UV-vis), X-ray absorption near edge structure (XANES) and Raman spectroscopies. The Ti L-edge absorption spectra show that a new Ti species, pentahedrally coordinated Ti, appears in some of the samples. This pentahedrally coordinated Ti species is correlated with the catalytic oxidation activity of TS-1, closely. Tetrahedrally coordinated Ti in TS-1 is the primary active center for selective oxidation reactions, but the existence of a small amount of pentahedrally coordinated Ti can further improve the catalytic activity. A high molar ratio of Si/Ti (n(Si/Ti)) in the synthesis process (n(Si/Ti) = 92.78) was beneficial for the generation of pentahedrally coordinated Ti. The improved catalytic activity of the TPAOH treated TS-1 is mainly due to the increasing amount of pentahedrally coordinated Ti, besides the elimination of diffusion limitation. Slowing down the crystallization rate can also increase the content of pentahedrally coordinated Ti.

Enhanced Catalytic Performance of Titanium Silicalite‐1 in Tuning the Crystal Size in the Range 1200–200 nm in a Tetrapropylammonium Bromide System

A facile method for the size‐controllable synthesis of titanium silicalite‐1 (TS‐1) is presented. A tetrapropylammonium bromide hydrothermal system was used, and the amount of seeds (silicalite‐1 suspension) and crystallization time were tuned to control the crystal size. The crystal size could be adjusted from 200 to 1200 nm by varying the seed amount from 12 to 0.05 wt %. Crystallization time plays a less important role than the seed amount on the crystal size. TS‐1 samples with different crystal sizes were characterized and evaluated in propene epoxidation. The catalytic activity and selectivity of propene oxide are enhanced by decreasing the crystal size from 1200 to 200 nm because the diffusion limitation is eliminated gradually. The seed is significant for this system, as a lack of seeds leads to poor crystallization and low catalytic activity. The mechanism of the seed function was studied by simulating the transformation process of the seed in the TS‐1 synthesis system.

Facile synthesis of Fe-containing metal–organic frameworks as highly efficient catalysts for degradation of phenol at neutral pH and ambient temperature

In this work, MIL-53(Fe) was synthesized using a solvothermal method under static conditions. However, it was interesting to find that another MIL-53 type material, Fe(BDC)(DMF,F), was obtained when stirring conditions were used while keeping the other conditions fixed. The Fe-containing metal–organic frameworks (MOFs) were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), 57Fe Mossbauer spectrometry and thermogravimetric analysis (TGA). By simply increasing the crystallization time under agitation, the morphology of the Fe(BDC)(DMF,F) crystals went through a striking transition from a bulky irregular shape to a rod-like morphology. The catalytic performance of the Fe-MOFs was evaluated in the degradation of phenol solution at near neutral pH at 35 °C. A significantly better catalytic activity was achieved for Fe(BDC)(DMF,F) than for MIL-53(Fe) and NH2-MIL-53(Fe) due to the existence of Fe(II) in its framework. Phenol was almost completely decomposed in 3 hours, and the conversions of hydrogen peroxide and chemical oxygen demand (COD) were 74.1% and 78.7%, respectively.

Synthesis of Fe/M (M = Mn, Co, Ni) bimetallic metal organic frameworks and their catalytic activity for phenol degradation under mild conditions

Partial isomorphic substitution of iron in an Fe(BDC)(DMF,F) metal organic framework by manganese, cobalt, and nickel has been described for the first time. Specifically, different amounts of Mn, Co and Ni have been incorporated into the Fe-based framework during a solvothermal crystallization procedure. Several characterization techniques, including XRD, FT-IR, SEM, EDS, TG, XPS and ICP-AES, strongly support the effective incorporation of Mn, Ni and Co into material frameworks. The catalytic performance of these materials was examined in liquid-phase degradation of phenol at 35 °C and near neutral pH of 6.2. The results show that the degradation efficiency can be evidently improved by the incorporation of Mn, while it can be inhibited by the incorporation of Ni. The incorporation of Co shows no remarkable influence on the degradation process. Moreover, the ratios of n(Fe)/n(Mn) in the bimetallic MOFs have a strong impact on the degradation process. The stability and reusability of these catalysts under mild conditions were also demonstrated in this study. This work illustrates the potential of bimetallic MOF structures in developing active heterogeneous catalysts for the degradation process of toxic compounds.

Synthesis of Titanium Silicalite-1 with High Catalytic Performance for 1-Butene Epoxidation by Eliminating the Extraframework Ti

Titanium silicalite-1 (TS-1) with little extraframework Ti was hydrothermally synthesized in a tetrapropylammonium hydroxide system using starch as the additive. The influences of the amount of starch added on the coordination states of titanium ions and the functional mechanism of starch were studied by various characterization means. The addition of starch slowed the crystallization rate of TS-1 so that the insertion rate of titanium to the framework matched well with that of silicon. Therefore, the generation of extraframework Ti, including the anatase TiO2 and octahedrally coordinated titanium, was eliminated. The catalytic performances of the TS-1 samples were evaluated in the epoxidation of 1-butene to produce butene oxide. The catalytic activity of TS-1 was improved significantly due to the increasing amount of framework Ti.