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1. Nano-gate opening pressures for the adsorption of isobutane, n -butane, propane, and propylene gases on bimetallic Co–Zn based zeolitic imidazolate frameworks

   https://doi.org/10.1039/c9dt00222g  

   Awadallah-F, Ahmed; Hillman, Febrian; Al-Muhtaseb, Shaheen A.; Jeong, Hae-Kwon (April 2019, Dalton Transactions)

   null (Ed.)

   In this article, zeolitic-imidazolate framework-8 (ZIF-8) and its mixed metal CoZn-ZIF-8 were synthesized via a rapid microwave method. The products were characterized by Raman spectroscopy, XPS, XRD, EDX, TEM, NanoSEM, TGA, and DSC. The gas adsorption properties of samples were determined using C 3 and C 4 hydrocarbons, including propane, propylene, isobutane and n -butane at a temperature of 25 °C. The adsorption equilibrium and kinetics of these gases on various ZIFs were studied. It was noted that ZIF-8 and mixed metal CoZn-ZIF-8 samples start to adsorb these gases after certain pressures which are believed to result in the opening of their nano-gates ( i.e. , 6-membered rings) to allow the entry of gas molecules. The nanogate opening pressure value ( p 0 ) for each ZIF towards different gases was determined by fitting adsorption equilibrium data against a modified form of the Langmuir adsorption isotherm model. It was observed that the value of p 0 differs significantly for each gas and to various extents for various ZIFs. Therefore, it is possible that the distinct values of p 0 afford a unique technique to separate and purify these gases at the industrial scale. The overall mass transfer coefficient values of the adsorption process were also investigated. 

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2. Influence of doped metal center on morphology and pore structure of ZIF-8

   https://doi.org/10.1557/mrc.2018.221  

   Awadallah-F, Ahmed; Hillman, Febrian; Al-Muhtaseb, Shaheen A.; Jeong, Hae-Kwon (March 2019, MRS Communications)

   null (Ed.)

   Synthesis of ZIF with zinc, cobalt, or copper was carried out by microwaves. The effect of metal center on morphologies and pores of products was studied. Nitrogen adsorption/desorption onto ZIFs was examined by density functional theory. The micro, meso, and macropores of ZIF-8, Zn/Co-ZIF-8, and Cu/ZIF-8 ranged 99.814–99.969%, 0.055–0%, and 0.031–0.130%, respectively. Average pore sizes of ZIF-8, Zn/Co-ZIF-8, and Cu/ZIF-8 are 1.291, 1.194, and 1.164 nm, respectively. Monolayer saturation limits of nitrogen onto ZIF-8, Zn/Co-ZIF-8, and Cu/ZIF-8 were 21.152, 18.943, and 17.784 mmol/g, respectively. Further, the results included densities, total surface areas, total pore volumes, and average particle sizes of ZIF-8, Zn/Co-ZIF-8, and Cu/ZIF-8. 

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3. Unprecedented performance of N-doped activated hydrothermal carbon towards C ₂ H ₆ /CH ₄ , CO ₂ /CH ₄ , and CO ₂ /H ₂ separation

   https://doi.org/10.1039/C5TA08436A  

   Yuan, Bin; Wang, Jun; Chen, Yingxi; Wu, Xiaofei; Luo, Hongmei; Deng, Shuguang (January 2016, Journal of Materials Chemistry A)

   A series of N-doped porous carbons with different textural properties and N contents was prepared from a mixture of algae and glucose and their capability for the separation of CO 2 /CH 4 , C 2 H 6 /CH 4 , and CO 2 /H 2 binary mixtures under different conditions (bulk pressure, mixture composition, and temperature) were subsequently assessed in great detail. It was observed that the gas (C 2 H 6 , CO 2 , CH 4 , and H 2 ) adsorption capacity at different pressure regions was primarily governed by different adsorbent parameters (N level, narrow micropore volume, and BET specific surface area). More interestingly, it was found that N-doping can selectively enhance the heats of adsorption of C 2 H 6 and CO 2 , while it had a negligible effect on those of CH 4 and H 2 . The adsorption equilibrium selectivities for separating C 2 H 6 /CH 4 , CO 2 /CH 4 , and CO 2 /H 2 gas mixture pairs on the porous carbons were predicted using the ideal adsorbed solution theory (IAST) based on pure-component adsorption isotherms. In particular, sample NAHA-1 exhibited by far the best performance (in terms of gas adsorption capacity and selectivity) reported for porous carbons for the separation of these three binary mixtures. More significantly, NAHA-1 carbon outperforms many of its counterparts ( e.g. MOFs and zeolites), emphasizing the important role of carbonaceous adsorbents in gas purification and separation. 

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4. Dynamically Unveiling Metal–Nitrogen Coordination during Thermal Activation to Design High‐Efficient Atomically Dispersed CoN ₄ Active Sites

   https://doi.org/10.1002/anie.202017288  

   He, Yanghua; Shi, Qiurong; Shan, Weitao; Li, Xing; Kropf, A. Jeremy; Wegener, Evan C.; Wright, Joshua; Karakalos, Stavros; Su, Dong; Cullen, David A.; et al (March 2021, Angewandte Chemie International Edition)

   Abstract We elucidate the structural evolution of CoN₄sites during thermal activation by developing a zeolitic imidazolate framework (ZIF)‐8‐derived carbon host as an ideal model for Co²⁺ion adsorption. Subsequent in situ X‐ray absorption spectroscopy analysis can dynamically track the conversion from inactive Co−OH and Co−O species into active CoN₄sites. The critical transition occurs at 700 °C and becomes optimal at 900 °C, generating the highest intrinsic activity and four‐electron selectivity for the oxygen reduction reaction (ORR). DFT calculations elucidate that the ORR is kinetically favored by the thermal‐induced compressive strain of Co−N bonds in CoN₄active sites formed at 900 °C. Further, we developed a two‐step (i.e., Co ion doping and adsorption) Co‐N‐C catalyst with increased CoN₄site density and optimized porosity for mass transport, and demonstrated its outstanding fuel cell performance and durability. 

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5. Interannual, summer, and diel variability of CH ₄ and CO ₂ effluxes from Toolik Lake, Alaska, during the ice-free periods 2010–2015

   https://doi.org/10.1039/D0EM00125B  

   Eugster, Werner; DelSontro, Tonya; Shaver, Gaius R.; Kling, George W. (January 2020, Environmental Science: Processes & Impacts)

   Accelerated warming in the Arctic has led to concern regarding the amount of carbon emission potential from Arctic water bodies. Yet, aquatic carbon dioxide (CO 2 ) and methane (CH 4 ) flux measurements remain scarce, particularly at high resolution and over long periods of time. Effluxes of methane (CH 4 ) and carbon dioxide (CO 2 ) from Toolik Lake, a deep glacial lake in northern Alaska, were measured for the first time with the direct eddy covariance (EC) flux technique during six ice-free lake periods (2010–2015). CO 2 flux estimates from the lake (daily average efflux of 16.7 ± 5.3 mmol m −2 d −1 ) were in good agreement with earlier estimates from 1975–1989 using different methods. CH 4 effluxes in 2010–2015 (averaging 0.13 ± 0.06 mmol m −2 d −1 ) showed an interannual variation that was 4.1 times greater than median diel variations, but mean fluxes were almost one order of magnitude lower than earlier estimates obtained from single water samples in 1990 and 2011–2012. The overall global warming potential (GWP) of Toolik Lake is thus governed mostly by CO 2 effluxes, contributing 86–93% of the ice-free period GWP of 26–90 g CO 2,eq m −2 . Diel variation in fluxes was also important, with up to a 2-fold (CH 4 ) to 4-fold (CO 2 ) difference between the highest nighttime and lowest daytime effluxes. Within the summer ice-free period, on average, CH 4 fluxes increased 2-fold during the first half of the summer, then remained almost constant, whereas CO 2 effluxes remained almost constant over the entire summer, ending with a linear increase during the last 1–2 weeks of measurements. Due to the cold bottom temperatures of this 26 m deep lake, and the absence of ebullition and episodic flux events, Toolik Lake and other deep glacial lakes are likely not hot spots for greenhouse gas emissions, but they still contribute to the overall GWP of the Arctic. 

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