Polyoxometalate-based materials in extraction, and electrochemical and optical detection methods: A review

Polyoxometalates (POMs) as metal-oxide anions have exceptional properties like high negative charges, remarkable redox abilities, unique ligand properties and availability of organic grafting. Moreover, the amenability of POMs to modification with different materials makes them suitable as precursors to further obtain new composites. Due to their unique attributes, POMs and their composites have been utilized as adsorbents, electrodes and catalysts in extraction, and electrochemical and optical detection methods, respectively. A survey of the recent progress and developments of POM-based materials in these methods is therefore desirable, and should be of great interest. In this review article, POM-based materials, their properties as well as their identification methods, and analytical applications as adsorbents, electrodes and catalysts, and corresponding mechanisms of action, where relevant, are reviewed. Some current issues of the utilization of these materials and their future prospects in analytical chemistry are discussed.

Preparation and catalytic property of composite ionic liquid immobilized on SBA-15

In this work, we report a more simple and efficient way to synthesize a composite ionic liquid (IL) ([BMIM][Zn2Br5]) by directly coupling the IL with molecular sieves. Two kinds of immobilized catalysts were successfully synthesized: SBA-15-[BMIM][Zn2Br5] and SBA-15-CPTES-[BMIM][Zn2Br5]. The catalysts were used to catalyze the cycloaddition reaction of continuous transformation of CO2 and propylene oxide, and the catalytic performance of catalysts was further studied. Compared with the traditional IL catalysts, the catalysts not only have excellent catalytic performance, but also have a significantly longer service life. This is because the catalysts are formed by a high energy chemical bond of silane between IL catalysts and molecular sieves, which can effectively solve the problem of the loss of IL active components in the catalytic process.

Synergistic Catalysis of Ionic Liquid-Decorated Covalent Organic Frameworks with Polyoxometalates for CO2 Cycloaddition Reaction under Mild Conditions

The cycloaddition of carbon dioxide (CO₂) with epoxides to yield highly value-added cyclic carbonates is an effective way to chemically utilize and convert CO₂. Here, a heterogeneous catalyst of imidazole ionic liquid-decorated covalent organic framework with polyoxometalates (POM@ImTD-COF) was constructed by the covalent modification of ionic liquids to COFs and the electrostatic interaction between POMs and ionic liquids. The obtained POM@ImTD-COF shows high catalytic activity for CO₂ cycloaddition reaction under mild conditions (1 atm and 80 °C) in the presence of a co-catalyst, and the catalytic activity of POM@ImTD-COF has no obvious decrease during reusing five times. The excellent catalytic performance is mainly attributed to the synergistic effect of ionic liquids, POMs, and COFs. In the cycloaddition process, ionic liquids and the co-catalyst weaken the C-O bond of epoxides and promote the ring opening of epoxides. POMs as the Lewis acids facilitate the insertion of CO₂ to form reaction intermediates. The multiple activation effect of ionic liquids and POMs together with the CO₂ adsorption effect and well-dispersed active sites in COFs contribute to the remarkable catalytic performance.

Immobilizing Polyether Imidazole Ionic Liquids on ZSM-5 Zeolite for the Catalytic Synthesis of Propylene Carbonate from Carbon Dioxide

Traditional ionic liquids (ILs) catalysts suffer from the difficulty of product purification and can only be used in homogeneous catalytic systems. In this work, by reacting ILs with co-catalyst (ZnBr₂), we successfully converted three polyether imidazole ionic liquids (PIILs), i.e., HO-[Poly-epichlorohydrin-methimidazole]Cl (HO-[PECH-MIM]Cl), HOOC-[Poly-epichlorohydrin-methimidazole]Cl (HOOC-[PECH-MIM]Cl), and H₂N-[Poly-epichlorohydrin-methimidazole]Cl (H₂N-[PECH-MIM]Cl), to three composite PIIL materials, which were further immobilized on ZSM-5 zeolite by chemical bonding to result in three immobilized catalysts, namely ZSM-5-HO-[PECH-MIM]Cl/[ZnBr₂], ZSM-5-HOOC-[PECH-MIM]Cl/[ZnBr₂], and ZSM-5-H₂N-[PECH-MIM]Cl/[ZnBr₂]. Their structures, thermal stabilities, and morphologies were fully characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The amount of composite PIIL immobilized on ZSM-5 was determined by elemental analysis. Catalytic performance of the immobilized catalysts was evaluated through the catalytic synthesis of propylene carbonate (PC) from CO₂ and propylene oxide (PO). Influences of reaction temperature, time, and pressure on catalytic performance were investigated through the orthogonal test, and the effect of catalyst circulation was also studied. Under an optimal reaction condition (130 °C, 2.5 MPa, 0.75 h), the composite catalyst, ZSM-5-HOOC- [PECH-MIM]Cl/[ZnBr₂], exhibited the best catalytic activity with a conversion rate of 98.3% and selectivity of 97.4%. Significantly, the immobilized catalyst could still maintain high heterogeneous catalytic activity even after being reused for eight cycles.

A helical chain-like organic–inorganic hybrid arsenotungstate with color-tunable photoluminescence

A 1-D helical chain-like organic–inorganic hybrid arsenotungstate Na₄H₈[{Pr(H₂O)₂}₂{As₂W₁₉O₆₈}{WO₂(mal)}₂]·24H₂O (1) exhibits excitation-wavelength-dependent emission behaviors with a reversible green–orange-yellow luminescence.

CO2 fixation at atmospheric pressure: porous ZnSnO3 nanocrystals as a highly efficient catalyst for the synthesis of cyclic carbonates

Self-assembled, ultra small, porous zinc stannate nanocrystals have been synthesized, which catalyzes the formation of cyclic carbonates from various epoxide and CO₂ under very mild reaction conditions.

Hollow-structured Si/SiC@C nanospheres as highly active catalysts for cycloaddition of epoxides with CO2 under mild conditions

Hollow-structured Si/SiC@C nanospheres, prepared through magnesiothermic reduction, exhibit excellent catalytic activities for chemical fixation of CO₂ under mild, solvent-free conditions.