Shumei Liu

Facile Synthesis of a Nanocrystalline Metal–Organic Framework Impregnated with a Phosphovanadomolybdate and Its Remarkable Catalytic Performance in Ultradeep Oxidative Desulfurization

Reducing the level of sulfur content in fuel oils has long been desired for environmental reasons. Polyoxometalates (POMs) can act as catalysts to remove sulfur‐containing heterocyclic compounds by the process of oxidative desulfurization under mild conditions. However, one key obstacle to the development of POM‐based catalysts is the poor solubility of POMs in the overall nonpolar environment. We report a novel strategy for the introduction of catalytically active POMs into nonpolar reaction systems by encapsulating the inorganic catalyst within the pores of a metal–organic framework structure in which the organic ligands act as hydrophobic groups. The nanocrystalline catalysts, obtained rapidly and conveniently by both solution and mechanochemical synthesis, showed remarkable activities in catalytic oxidative desulfurization reactions in both a model diesel environment and in real diesel wherein dibenzothiophene was converted rapidly and quantitatively into dibenzothiophene sulfone.

Aminated Graphene Oxide Impregnated with Photocatalytic Polyoxometalate for Efficient Adsorption of Dye Pollutants and Its Facile and Complete Photoregeneration

Contamination of industrial sewage by organic dye pollutants is one of the most common challenges to the daily life. De-contamination can be achieved by adsorption and photodegradation of the pollutants. However, the former technique is generally limited by the poor loading capacity of the adsorbent and/or the difficulty in its regeneration for reuse, while the latter often suffers from sluggish reaction kinetics and thus requires long reaction time and powerful light source to be successful. Herein, a solution to these challenges by creating nanocomposites featuring porous diamine-functionalized graphene oxide (FGO) impregnated with photocatalytically active polyoxometalates (POMs) is presented. Cross-linking of GO via diamination not only generates porous structures with positively charged interior that attracts and stabilizes the anionic POM guests, but also modulates the GO bandgap. The introduction of POMs improves loading capacity of FGO for cationic dyes and promotes effective separation of electron-hole pair by trapping and transferring photogenerated electron. Thus, the two components act in synergy to result in much improved adsorption of certain common organic dyes as well as enhanced oxidative degradation by both the GO host and the POMs that lead to complete regeneration of the adsorbents without compromising their performance in multiple rounds of reuse.

An arsenicniobate-based 3D framework with selective adsorption and anion-exchange properties

An arsenicniobate-based 3D porous framework, [Cu(dap)2]4[AsNb12O40(VO)4]·(OH)·7H2O (1) (dap = 1,2-diaminopropane), was hydrothermally prepared and characterized using the IR spectrum, elemental analysis, powder X-ray diffraction, thermogravimetric analysis and X-ray single-crystal diffraction. Structural analysis shows that the framework is constructed by tetra-vanadyl capped Keggin arsenicniobate [AsNb12O40(VO)4]7− and four [Cu(dap)2]2+ linkers. The framework contains the 1D quadrangular channels of 5.7 × 5.7 A along the crystallographic c axis. The overall framework is cationic and OH− anions reside in the channels of the framework for charge balance. Considering such a structural feature, we concentrated on the probability of the framework for selective adsorption and anion-exchange. The adsorption properties show that 1 can selectively adsorb water molecules over ethanol to make them separate. Besides, anion-exchange studies for 1 suggest that the OH− anions in the channels can be quantitatively exchanged by SCN− anions.

Controllable proton-conducting pathways via situating polyoxometalates in targeting pores of a metal–organic framework

Proton conductivity is traditionally affected by proton concentration, mobility, hopping sites, etc. in metal–organic frameworks (MOFs). The influence of the profile of proton-conducting pathway has not been demonstrated due to lack of a suitable model. MIL-101 contains two types of tunnels with zigzag and linear profiles constructed by cages with different sizes. However, it is hard to construct an exclusive proton-conducting pathway with only one profile in MIL-101 because the introduced carriers usually locate without targeting a specific location. Keggin-type H3PW12O40 (HPW) has a unique nano size, which is between the window sizes of the cages in MIL-101, strong acidity, good stability, and abundant proton-hopping sites. Herein, two types of hydrogen bond networks were constructed by situating HPWs in the targeting pores of MIL-101. Linear pathways provide about 2.1-fold faster proton diffusion rates compared to zigzag pathways. Further modification of an HPW-impregnated MIL-101 with flexible polyamine resulted in a conductivity of 1.52 × 10−2 S cm−1.

A gel-like/freeze-drying strategy to construct hierarchically porous polyoxometalate-based metal–organic framework catalysts

Hierarchically porous metal–organic frameworks combining the merits of micropores with high surface areas and mesopores/macropores with large diffusion channels are highly desired in catalysis, especially for reactions involving large substrates. In this work, a simple and common solvent templating strategy for the construction of hierarchically micro- and mesoporous polyoxometalate-based metal–organic frameworks by a gel-like/freeze-drying method was achieved. Fast nucleation and interconnection of nanoparticles with micropores were realized in the gel-like stage. Subsequently, the synthesized mesopores were strengthened by the squeezing by ice crystals due to volumetric swelling during the process of freezing water into ice. The hierarchically porous material showed improved catalytic activities for the oxidation of alcohols compared to the catalyst without hierarchical pores, due to it having more easily accessible catalytic sites and the acceleration of mass transfer.

Recognition of trace organic pollutant and toxic metal ions via a tailored fluorescent metal–organic coordination polymer in water environment

A novel fluorescence material H2Sr2(bqdc)3(phen)2 (1) for trace recognition of organic pollutant and toxic metal ions is designed and prepared by two weak fluorescent ligands and Sr2+. The latter was selected although it played no role in the modulation process of luminescence and despite low-cost, alkaline earth, metal–organic coordination polymers lacking competitive functionality. The strong fluorescence of the fluorescence material was based on the propeller configuration of the metal–organic coordination polymer, which was characterized by X-ray single crystal diffraction showing that the N active sites inside the crystal channels can interact with external guests. Convenient fluorescence detection of 3-AT can be realized using an ultraviolet lamp and test strip and the determination of Cd2+ showed good reusability with a detection limit of 1 × 10−9 mol L−1, which is lower than the standard stipulated by the Environmental Protection Agency. Detailed experiments results revealed that the material was a promising candidate for specifically recognizing amitrole and Cd2+ because of its selective fluorescence quenching and sensitive detection in water.

Lewis-Basic Lanthanide Metal-Organic Framework-Derived Versatile Multi-Active-Site Synergistic Catalysts for Oxygen Reduction Reaction

Oxygen reduction reaction underpins the development of the whole fuel-cell field, where there is a strong impetus to develop efficient and stable catalysts that can replace the precious metal Pt/C. Herein, a series of excellent catalysts for ORR derived from Ce/La dual lanthanide metal-organic framework with functional Lewis-basic sites were synthesized for the first time. The synergistic effect of high concentration of oxygen vacancies from La-embedded CeO2 and Fe-N x sites as well as porous structure endows the catalyst superior performance to Pt/C, with a half-wave potential ( E1/2) of 0.870 V and a current density ( j) of 5.43 mA/cm2. Furthermore, the catalysts are also effective for other nonelectrocatalytic reactions. It is expected that this research will contribute to synthesis of an excellent nonplatinum electrocatalyst for fuel-cell applications, and the oxygen vacancies stabilized in carbon matrix offer a method for versatile catalyst design for other reactions.