Zeolitic imidazolate frameworks (ZIFs) represent a new and special class of metal organic frameworks comprised of imidazolate linkers and metal ions, with structures similar to conventional aluminosilicate zeolites Their intrinsic porous characteristics, abundant functionalities as well as exceptional thermal and chemical stabilities have led to a wide range of potential applications for various ZIF materials Explosive research activities ranging from synthesis approaches to attractive applications of ZIFs have emerged in this rapidly developing field in the past 5 years In this review, the development and recent progress towards different synthesis strategies to generate both powder and membrane/film-based ZIF materials are analysed and summarised Their attractive and potential applications in gas separation, catalysis, sensing and electronic devices, and drug delivery in the past years are discussed and reviewed In addition, the prospects and potential new development of ZIF materials are presented

Zeolitic imidazolate framework materials: recent progress in synthesis and applications

ZIF-8: A comparison of synthesis methods

Dialkyl carbonates are important organic compounds and chemical intermediates with the label of “green chemicals” due to their moderate toxicity, biodegradability for human health and environment. Indeed, owing to their unique physicochemical properties and versatility as reagents, a variety of phosgene-free processes derived from CO or CO2 have been explored for the synthesis of dialkyl carbonates. In this critical review, we highlight the recent achievements (since 1997) in the synthesis of dialkyl carbonates based on CO and CO2 utilization, particularly focusing on the catalyst design and fabrication, structure–function relationship, catalytic mechanisms and process intensification. We also provide an overview regarding the applications of dialkyl carbonates as fuel additives, solvents and reaction intermediates (i.e. alkylating and carbonylating agents). Additionally, this review puts forward the substantial challenges and opportunities for future research associated with dialkyl carbonates.

Recent advances in dialkyl carbonates synthesis and applications.

Herein we describe a novel, hollow-structured zeolitic imidazolate framework (ZIF-8-H) nanosphere as a highly efficient catalyst for [3+3] cycloaddition reactions. The programmed installation of acidic Zn2+ species and basic imidazolate moieties creates a synergistic catalytic system. Appropriate positioning of these functionalities in the catalytic system makes it possible to bring two substrates into close proximity and activate them cooperatively. Moreover, the flexible shell and the surface mesopores of ZIF-8-H provide the capacity for favorable binding of various sized substrates, stabilizing intermediates via their multiple force networks and the increased accessibility of the active sites. These features render ZIF-8-H a more highly active promoter than its homogeneous precursors, bulk ZIF-8 and ZIF-8-N nanoparticles. Finally, the robust catalyst can be easily recovered and reused 10 times without loss of catalytic activity.

Hollow zeolitic imidazolate framework nanospheres as highly efficient cooperative catalysts for [3+3] cycloaddition reactions.

The introduction of hierarchical porosity into metal-organic frameworks (MOFs) has been of considerable interest in gas separation and heterogeneous catalysis due to the efficient mass transfer kinetics through meso/macropores. Here, a facile, scalable approach is reported for the preparation of carbon nitride (CN) foams as structural templates with micrometer-sized pores and high nitrogen content of 25.6 wt% by the fast carbonization of low-cost melamine foam. The nitrogen functionalities of CN foam facilitate chemical anchoring and growth of ZIF-8 (zeolitic imidazolate frameworks) crystals, which leads to the development of hierarchical porosity. The growth of ZIF-8 crystals also renders CN foam, which is hydrophilic in nature, highly hydrophobic exhibiting 135° of water contact angle due to the enhanced surface roughness, thus creating a natural shield for the MOF crystals against water. The introduction of ZIF-8 crystals onto the CN foam enables selective absorption of oils up to 58 wt% from water/oil mixtures and also facilitates the highly efficient conversion of CO2 to chloropropene carbonate in a quantitative yield with excellent product selectivity. Importantly, this present approach could be extended to the vast number of MOF structures, including the ones suffering from water instability, for the preparation of highly functional materials for various applications.

Highly Hydrophobic ZIF-8/Carbon Nitride Foam with Hierarchical Porosity for Oil Capture and Chemical Fixation of CO2

A zeolitic imidazolate framework (ZIF-8) was developed as a novel efficient heterogeneous catalyst for the synthesis of ethyl methyl carbonate from dimethyl carbonate and diethyl carbonate. ZIF-8 was characterized by element analysis, X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), temperature programmed desorption (TPD), N2 adsorption–desorption and thermogravimetric analysis. The effects of catalyst amount, temperature and reaction time on the yield of ethyl methyl carbonate were also tested. The results showed that ZIF-8 performed excellent activity, selectivity and reusability under mild reaction conditions.

Shan Shan Zheng

Papers

Zeolitic imidazolate framework as efficient heterogeneous catalyst for the synthesis of ethyl methyl carbonate