Fabrication of core–shell MIL-101(Cr)@UiO-66(Zr) nanocrystals for hydrogen storage

The fabrication of core–shell nanocrystals by incorporating microporous UiO-66 into mesoporous MIL-101 is reported. The growth of the core–shell MIL-101@UiO-66 nanocrystals was observed and supported by TEM and PXRD. The accessible pore volumes of the individual metal-organic framework (MOF) components and the core–shell hybrid crystals were also characterized. The hydrogen storage capacity exhibited by the resulting core–shell nanocrystals was 26% and 60% higher than those of pure phase MIL-101 and UiO-66, respectively. Finally, the fabricated core–shell MIL-101@UiO-66 structure exhibited a high degree of moisture tolerance.     

Asymmetric supercapacitor based on novel coal fly ash derived metal–organic frameworks as positive electrode and its derived carbon as negative electrode

Journal of Applied Electrochemistry - The paper presents a comparative study between aluminum fumarate metal–organic framework (Al-FumMOF) and a novel coal fly ash derived aluminum MOF...     

Synthesis of templated carbons starting from clay and clay‐derived zeolites for hydrogen storage applications

Clay and its recrystallized zeolitic derivatives were used in this study as templating agents for carbon nanostructured materials. The conventional nanocasting process that involves impregnation with furfural alcohol and subsequent chemical vapour deposition was followed. Several techniques such as X‐ray diffraction (XRD), scanning electron microscopy (SEM), thermo‐gravimetric analysis (TGA) and surface area analysis were used to characterize the parent templating materials including the resulting nanocasted carbons. The study demonstrated that there is greater potential for the use of value‐added clays rather than their pristine form and hence presents a cost‐effective alternative for producing carbonaceous materials with more attractive properties for hydrogen storage applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Structure and properties of urban household food demand in Nairobi,Kenya: implications for urban food security

Urban household food insecurity continues to be a major problem in many urban households of Sub-Saharan Africa. The ineffectiveness of policies addressing the problem has hinged in particular on the paucity of information about consumption patterns under changing economic conditions. Elasticities of food demand were estimated through the Linear Approximated Almost Ideal Demand System (LA/AIDS) and inferences about access to food were drawn. Shifts in consumption were evident when changes occurred in income, prices and household demography. As the urban poor are sensitive to variation in food prices and income, they should be cushioned against their negative effects in order for their access to food to be enhanced and hence their food security improved. Dairy and dairy products and wheat and wheat products were identified as subsidy carriers which would improve the nutrition of the urban poor. These results provide guidance for the design of food security and nutrition strategies and programs at the micro and macro-economic levels.     

Co-pelletization of a zirconium-based metal-organic framework (UiO-66) with polymer nanofibers for improved useable capacity in hydrogen storage

We report on a concept of co-pelletization using mechanically robust hydroxylated UiO-66 to develop a metal-organic framework (MOF) monolith that contains 5 wt% electrospun polymer nanofibers, and consists of an architecture with alternating layers of MOF and nanofiber mats. The polymers of choice were the microporous Polymer of Intrinsic Microporosity (PIM-1) and non-porous polyacrylonitrile (PAN). Co-pelletized UiO-66/PIM-1 and UiO-66/PAN monoliths retain no less than 85% of the porosity obtained in pristine powder and pelletized UiO-66. The composition of the pore size distribution in co-pelletized UiO-66/PIM-1 and UiO-66/PAN monoliths is significantly different to that of pristine UiO-66 forms, with pristine UiO-66 forms showing 90% of the pore apertures in the micropore region and both UiO-66/nanofiber monoliths showing a composite micro-mesoporous pore size distribution. The co-pelletized UiO-66/nanofiber monoliths obtained improved useable H₂ capacities in comparison to pristine UiO-66 forms, under isothermal pressure swing conditions. The UiO-66/PIM-1 monolith constitutes the highest gravimetric (and volumetric) useable capacities at 2.3 wt% (32 g L^?1) in comparison to 1.8 wt% (12 g L^?1) and 1.9 wt% (29 g L^?1) obtainable in pristine UiO-66 powder and UiO-66 pellet, respectively. The co-pelletized UiO-66/PAN monolith, however, shows a significantly reduced surface area by up to 50% less in comparison to pristine UiO-66, but its pore volume only 13% less in comparison to pristine UiO-66. As a result, total gravimetric H₂ capacity of the co-pelletized UiO-66/PAN monolith is 50% less in comparison to that of pristine UiO-66, but crucially the useable volumetric H₂ capacity is 50% higher for the UiO-66/PAN monolith in comparison to pristine UiO-66 powder. The co-pelletization strategy provides a simple method for generating hierarchical porosity into an initially highly microporous MOF without changing the structure of the MOF through complex chemical modifications. The UiO-66/nanofiber monoliths offer improvements to the typically low H₂ useable capacities in highly microporous MOFs, and open new opportunities towards achieving system-level H₂ storage targets.     

South African hydrogen infrastructure (HySA infrastructure) for fuel cells and energy storage: Overview of a projects portfolio

The paper provides brief introduction to the National South African Program, branded HySA (Hydrogen South Africa) as well as discusses potential business cases for deployment of hydrogen and fuel cell technology in South Africa. This paper also describes some key activities in the area of hydrogen production and storage within HySA Infrastructure Center of Competence in South Africa. The content of this paper is based on the presentation given during the recent WHEC 2016 Congress in Zaragoza, Spain. More specifically, the discussion of activities at HySA Infrastructure Center of Competence in the paper includes hydrogen production and storage.     

Modulated synthesis of chromium-based metal-organic framework (MIL-101) with enhanced hydrogen uptake

Modulated synthesis of MIL-101(Cr) in high yield and with good reproducibility using formic acid as a modulator is reported. Higher molar ratio of formic acid/CrCl₃ was found to form better shape-defined MIL-101(Cr) crystals with higher surface area, larger pore volume and better hydrogen uptake performance. The highly crystalline MIL-101(Cr), composed of crystals in the size range of 100–150 nm with multifaceted surface, could be obtained in an optimized molar regime of CrCl₃·6H₂O/H₂BDC/100HCOOH/550H₂O at 210 °C for 8 h. The MIL-101(Cr) obtained from the modulated synthesis also showed high thermal and moisture stabilities as well as enhanced hydrogen storage capacity, making this material particularly promising for practical hydrogen storage applications.     

Oxolane-2,5-dione modified electrospun cellulose nanofibers for heavy metals adsorption

Functionalized cellulose nanofibers have been obtained through electrospinning and modification with oxolane-2,5-dione. The application of the nanofibers for adsorption of cadmium and lead ions from model wastewater samples is presented for the first time. Physical and chemical properties of the nanofibers were characterized. Surface chemistry during preparation and functionalization was monitored using Fourier transform-infrared spectroscopy, scanning electron microscopy, carbon-13 solid state nuclear magnetic resonance spectroscopy and Brunauer Emmett and Teller. Enhanced surface area of 13.68 m² g⁻¹ was recorded for the nanofibers as compared to the cellulose fibers with a surface area of 3.22 m² g⁻¹. Freundlich isotherm was found to describe the interactions better than Langmuir: K_f = 1.0 and 2.91 mmol g⁻¹ (r² = 0.997 and 0.988) for lead and cadmium, respectively. Regenerability of the fiber mats was investigated and the results obtained indicate sustainability in adsorption efficacy of the material.