Polymer nanocomposites functionalised with nanocrystals of zeolitic imidazolate frameworks as ethylene control agents

Ethylene (C2H4) management involves the usage of materials such as KMnO4 or processes such as ozone oxidation or combined photocatalysis/photochemistry. The ubiquity of C2H4, especially in an industrial context, necessitates a simpler and much more effective approach, and herein we propose the usage of tuneable polymer nanocomposites for the adsorption of C2H4 through the modification of the polymer matrices via the incorporation of nanocrystals of zeolitic imidazolate frameworks (nano-ZIFs). We demonstrate that the inclusion of ZIF-8 and ZIF-7 nanocrystals into polymeric matrices (Matrimid and polyurethane [PU]) yields robust nanocomposites that preserve the C2H4 adsorption/desorption capacity of nanocrystals while shielding it from degrading factors. We report new insights into the adsorption/desorption kinetics of the polymer and its corresponding nanocomposites, which can be tailored by exploiting the underlying polymeric molecular interactions. Importantly, we also elucidated the retention of the intrinsic structural framework dynamics of the nano-ZIFs even when embedded within the polymeric matrix, as evidenced from the breathing and gate-opening phenomena. Our findings pave the way for bespoke designs of novel polymer nanocomposites, which will subsequently impact the deployment of tailored nanomaterials for effective industrial applications.E. M. Mahdi would like to thank Yayasan Khazanah (YK) for the DPhil scholarship that made this work possible. The research in the MMC Lab (J.C.T.) was supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 771575 - PROMOFS), and the EPSRC grant no. EP/N014960/1. The authors acknowledge the provision of the TGA and TEM by the Research Complex at Harwell (RCaH), in Rutherford Appleton Laboratory, Oxfordshire. J.S.A. acknowledges financial support by MINECO (Project MAT2016-80285-p), H2020 (MSCA-RISE-2016/NanoMed Project), and GV (PROMETEOII/2014/004)

Preparation of Porous Carbons from Petroleum Pitch and Polyaniline by Thermal Treatment for Methane Storage

The methane storage capacity of two series of activated carbons, obtained from a graphitizable (petroleum pitch) and a nongraphitizable precursor (polyaniline), has been evaluated after different thermal treatments. Both samples have been pyrolyzed and subsequently activated with KOH to obtain a highly developed microporous structure. After the synthesis, samples have been heat-treated at different temperatures, between 1000 and 1500 °C, to introduce structural changes that could have an effect on two parameters defining the methane adsorption capacity: the porosity and the density. The physicochemical characterization of the samples has shown that the activation process destroys the pregraphitic structure, with a development of microporosity. However, during the subsequent thermal treatment, the graphitic order can be partially recovered, especially with the graphitizable material, together with a decrease in the micropore volume and an enhancement of the density. The electrical conductivity of the activated carbon obtained from a graphitizable precursor improves much more with an increase in the temperature of the thermal treatment than that of the activated carbon obtained from a nongraphitizable precursor. It is worth highlighting that the high methane adsorption capacities achieved with some of these samples, reaching values as high as 180 V/V. These values are among the highest reported in the literature so far.The authors would like to acknowledge financial support from MINECO (MAT2016-80285-p)

Carbon-based monoliths with improved thermal and mechanical properties for methane storage

A series of activated carbon materials have been prepared from petroleum residue using KOH as activating agent. The gravimetric adsorption capacity for methane of the synthesized samples increases with the activation degree, albeit at a lower packing density of the carbon material. These results anticipate an optimum pitch/KOH ratio (1:3) to achieve an upper limit in the volumetric storage capacity. Activated carbon powders have been conformed into monoliths using a small amount of a binder (5 wt%), either carboxymethyl cellulose or polyvinyl alcohol, with proper mechanical properties. Incorporation of graphite or graphene in the initial formulation does not alter and/or modify significantly the textural properties of the original activated carbon. However, once conformed into monoliths, the presence of graphite or graphene allows to improve i) the packing density of the monoliths (up to 0.52 g/cm3), ii) their mechanical properties (compressive strength ≈ 12.3 MPa) and iii) their thermal conductivity (up to 0.49 W/mK) without compromising the methane storage capacity (ca. 100 V/V).Authors would like to acknowledge financial support from the Ministerio de Ciencia e Innovación (Project PID2019-108453GB-C21), MCIN/AEI/10.13039/501100011033 and EU “NextGeneration/PRTR (Project PCI2020-111968 /3D-Photocat) and NATO SPS program (Project G5683)

Activated carbon materials with a rich surface chemistry prepared from L-cysteine amino acid

A series of activated carbon materials have been successfully prepared from a non-essential amino acid, such as L-cysteine. The synthesized carbons combine a widely developed porous structure (BET surface area up to 1000 m2/g) and a rich surface chemistry (mainly oxygen, nitrogen and sulphur functionalities). These surface functional groups are relatively stable even after a high temperature thermal treatment (O>N∼S). Experimental results show that these samples with a rich surface chemistry exhibit a significant improvement in their hydrophilic character. Although the role of the surface functional groups is less pronounced for the adsorption of non-polar molecules such as CO2, CH4 and C2H4, their adsorption at atmospheric pressure is to some extend conditioned by the characteristics of the adsorbent-adsorbate interactions. The synthesized carbons exhibit an excellent adsorption performance for CO2 (up to 3 mmol/g at 0°C). Furthermore, samples with a low activation degree exhibit molecular sieving properties with very promising CO2/CH4 (up to 4.5) and C2H4/CH4 (up to 6) selectivity ratios. These results anticipate that non-essential amino acids are a versatile platform to obtain carbon materials combining a tailored porous structure and rich multifunctional surface chemistry and with potential application for gas adsorption/separation processes.Authors would like to acknowledge financial support from the MINECO (Projects PID2019-108453GB-C21 and PCI2020-111968/ERANET-M/3D-Photocat) and NATO SPS program (Project G5683)

Freezing/melting of water in the confined nanospace of carbon materials: Effect of an external stimulus

Freezing/melting behavior of water confined in the nanopores of activated carbon materials has been evaluated using differential scanning calorimetry (DSC) at different water loadings, and after the application of an external stimulus. Under atmospheric pressure conditions, the DSC scans show a depression in the freezing/melting point of confined water compared to the bulk system. Interestingly, water confined in narrow micropores (pores below 0.7 nm) does not exhibit any phase transition, i.e. it is non-freezable water. Inelastic neutron scattering (INS) data confirm the presence of a distorted molecular assembly in narrow micropores, whereas synchrotron X-ray powder diffraction data (SXRPD) demonstrate the non-freezable nature of the water confined in these narrow-constrictions. Similar experiments under high-pressure CH4 give rise to a completely different scenario. Under high-pressure conditions methane hydrates are formed with a water-to-hydrate yield of 100% for the under-saturated and saturated samples, i.e. in the presence of an external stimulus even water in narrow micropores is prone to experience a liquid-to-solid phase transition. These results confirm the beneficial role of carbon as a host structure to promote nucleation and growth of methane hydrates with faster kinetics and a higher yield compared to the bulk system and to other porous materials.The authors would like to acknowledge financial support from the MINECO (MAT2016-80285-p), Generalitat Valenciana (PROMETEOII/2014/004), H2020 (MSCA-RISE-2016/NanoMed Project), Spanish ALBA synchrotron (Projects 2018022707 & 2019023322) and Oak Ridge beam time availability (Project IPTS-20843.1)

Structural Deterioration of Well‐Faceted MOFs upon H2S Exposure and Its Effect in the Adsorption Performance

The structural deterioration of archetypical, well‐faceted metal–organic frameworks (MOFs) has been evaluated upon exposure to an acidic environment (H2S). Experimental results show that the structural damage highly depends on the nature of the hybrid network (e.g., softness of the metal ions, hydrophilic properties, among others) and the crystallographic orientation of the exposed facets. Microscopy images show that HKUST‐1 with well‐defined octahedral (111) facets is completely deteriorated, ZIF‐8 with preferentially exposed (110) facets exhibits a large external deterioration with the development of holes or cavities in the mesoporous range, whereas UiO‐66‐NH2 with (111) exposed facets, and PCN‐250 with (100) facets does not reflect any sign of surface damage. Despite the selectivity in the external deterioration, X‐ray diffraction and gas adsorption measurements confirm that indeed all MOFs suffer an important internal deterioration, these effects being more severe for MOFs based on softer cations (e.g., Cu‐based HKUST‐1 and Fe‐based PCN‐250). These structural changes have inevitable important effects in the final adsorption performance for CO2 and CH4 at low and high pressures.JSA would like to acknowledge financial support from the MINECO (Project MAT2016-80285-p). I.I. and D.M. would like to acknowledge financial support from the Spanish MINECO (Project RTI2018-095622-B-100), and Catalan AGAUR (Project 2017 SGR 238), the ERC, under the EU-FP7 (ERC-Co 615954) and the CERCA Program/Generalitat de Catalunya. ICN2 is supported by the Severo Ochoa Program from the Spanish MINECO (Grant No. SEV-2017-0706)

Methane hydrate formation in the confined nanospace of activated carbons in seawater environment

Methane hydrate formation studies in saline environment show that activated carbons are excellent host structures able to promote the water-to-hydrate conversion. Under confinement conditions, methane hydrate formation takes place at mild temperatures (−10 °C), low pressures (<6 MPa), with extremely fast kinetics (within minutes) and with a large adsorption capacity (up to 66 wt% CH4 for seawater, i.e. a 128% improvement compared to the dry carbon). Similar studies using ultrapure water give rise to a total methane adsorption capacity of 93 wt%, i.e. entropic effects exerted by salt play a crucial role in the methane hydrate nucleation and growth. Synthesized methane hydrates exhibit a sI crystal structure and a stoichiometry that mimics natural hydrates. These findings open the gate towards the application of activated carbons with a highly developed nanoporous network as host structure for offshore methane storage in marine reservoirs.Authors acknowledge financial support from MINECO: Projects MAT2016-80285-P and CONCERT Project-NASEMS (PCIN-2013-057), and Generalitat Valenciana (PROMETEOII/2014/004). J.S.A. also acknowledge the Spanish synchrotron ALBA for beam time availability (Project 2016021724)

Influence of the oxygen-containing surface functional groups in the methane hydrate nucleation and growth in nanoporous carbon

Petroleum pitch-derived activated carbon (PP-AC) has proved to be an excellent platform to promote the methane hydrate formation in milder condition than nature, even though the water-to-hydrate yield at the threshold formation pressure of 3.3 MPa is rather low (ca. 13%). Herein, we report that the presence of oxygen-containing surface functional groups in the oxidized carbon analogue (PP-AC_Ox) plays a significant role in the nucleation and growth in the low-pressure region. High-pressure methane adsorption/desorption isotherms revealed an enhancement in the water-to-hydrate yield up to ca. 51% around 3.3 MPa and 2 °C, in an extremely narrow working pressure window, with no hysteresis associated.Authors acknowledge financial support from MINECO Projects: MAT2016-80285-P and CONCERT Project-NASEMS (PCIN-2013-057), and Generalitat Valenciana (PROMETEOII/2014/004). MEC thanks Alexander von Humboldt foundation for financial support

Reverse Hierarchy of Alkane Adsorption in Metal–Organic Frameworks (MOFs) Revealed by Immersion Calorimetry

Immersion calorimetry into liquids of different dimensions is a powerful tool to learn about the pore size and shape in nanoporous solids. In general, in the absence of specific interactions with the solid surface, the accessibility of the liquid probe molecule to the inner porosity and the associated enthalpy value decreases with an increase in its kinetic diameter (bulkier molecules have lower accessibility and packing density). Although this is true for the majority of solids (e.g., activated carbons and zeolites), this study anticipates that this is not straightforward in the specific case of metal–organic frameworks (MOFs). The evaluation of different hydrocarbons and their derivatives reveals the presence of reverse selectivity for C6 isomers (2,2-dimethylbutane > 2-methylpentane > n-hexane) in UiO-66 and HKUST-1, whereas size exclusion effects take place in ZIF-8. The immersion calorimetric findings have been compared with vapor adsorption isotherms and computational studies. Monte Carlo simulations suggest that the reverse selectivity in UiO-66 is attributed to the strong confinement of the dibranched hydrocarbons in the small tetragonal cages, whereas the presence of strong interactions with the open metal sites accounts for the preferential adsorption in HKUST-1. These results open the gate toward the application of immersion calorimetry for the prescreening of MOFs to identify in an easy, fast and reliable way interesting characteristics and/or properties such as separation ability, reversed hierarchy, pore-window size, presence of unsaturated metal sites, molecular accessibility, and so on.Authors would like to acknowledge financial support from MINECO (MAT2016-80285-p), Generalitat Valenciana (PROMETEOII/2014/004) and H2020 (MSCA-RISE-2016/NanoMed Project). P.Z.M. is grateful for start-up funds from the University of Sheffield

Rapid and efficient hydrogen clathrate hydrate formation in confined nanospace

Clathrate hydrates are crystalline solids characterized by their ability to accommodate large quantities of guest molecules. Although CH4 and CO2 are the traditional guests found in natural systems, incorporating smaller molecules (e.g., H2) is challenging due to the need to apply higher pressures to stabilize the hydrogen-bonded network. Another critical limitation of hydrates is the slow nucleation and growth kinetics. Here, we show that specially designed activated carbon materials can surpass these obstacles by acting as nanoreactors promoting the nucleation and growth of H2 hydrates. The confinement effects in the inner cavities promote the massive growth of hydrogen hydrates at moderate temperatures, using pure water, with extremely fast kinetics and much lower pressures than the bulk system.We would like to acknowledge financial support from Ministerio de Ciencia e Innovación (Project PID2019-108453GB-C21), MCIN/AEI/10.13039/501100011033 and EU “NextGeneration/PRTR” (Project PCI2020-111968 /3D-Photocat) – JSA. Neutron scattering experiments were performed at ORNL’s Spallation Neutron Source, IPTS-27062, supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC0500OR22725 with UT Battelle, LLC—J.S.A., Y.Q.C., L.D., A.J.R.C.. We gratefully acknowledge research support from the Hydrogen Materials—Advanced Research Consortium (HyMARC), established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technology Office, under Contract Number DE-AC05-00OR22725—R.B.-X. This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The publisher acknowledges the US government license to provide public access under the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan)