Well-defined Microporous Structure Research Articles

Encapsulated Pd clusters in S-1 promote the reactivity of chemical looping via synergistic effect of catalysis and oxygen storage

Chemical looping reforming of CH4 coupled with CO2 reduction technology offers a compelling way for effective CO2 emission with the production of syngas and CO. However, the reaction temperature in chemical looping is relatively higher (>800 °C). To solve this problem, it is critical to explore efficient oxygen carriers. In this work, 3DOM LF0.85N0.15/Pd@S-1 oxygen carrier with hierarchical pore structure obtained high reactivity. 3DOM LF0.85N0.15/Pd@S-1 contained three major components, playing different roles. The 3DOM LF0.85N0.15 with ordered macroporous structure possessed excellent oxygen storage capacity and diffusion property. Pd clusters as active sites promoted CH4 activation and strengthen Lewis acid sites. Silicalite-1 zeolite, with larger surface area and well-defined microporous structure, exhibited superior adsorption properties and used as an ideal support to encapsulate Pd clusters. The well-dispersed Pd clusters further strengthened the reducibility at low temperature. Among all samples, 3DOM LF0.85N0.15/Pd@S-1 exhibited highest reactivity and stability during the successive chemical looping.

Hybridizing zeolite MFI nanosheets with PTMSP membranes for enhanced butane isomer separations

Hybridizing zeolite nanosheets with a high aspect ratio has the potential to improve the gas separation performance of polymeric materials due to their good mechanical strength, thermal stability, and well-defined microporous structure. However, the use of zeolite-nanosheet-based mixed matrix membranes (MMMs) has been limited, and their effects on polymeric materials have not been studied thoroughly. In this study, zeolite MFI nanosheets were directly synthesized and introduced into PTMSP polymer using the shear-coating method. This resulted in a horizontally aligned structure with preferentially b-oriented zeolite MFI fillers. The straight b-channels of zeolite MFI facilitated fast gas permeation, while the high aspect ratio increased the tortuosity for non-permeable gases. The elastic modulus of the composite increased from 306 MPa to 2069 MPa as the zeolite MFI nanosheet content was increased to 50 wt%. The membrane was thermally stable up to 285 °C due to the protection provided by the zeolite MFI filler, which prevented thermal degradation by oxygen. The gas separation performance was improved, with a butane isomer selectivity of 7.3 and a permeability of 5400 barrer, a 20% increase from the neat PTMSP membrane. The selectivity was well preserved even in the binary mixture of butane isomers gas permeation test at 1 bar, while the neat PTMSP membrane showed a dramatic decrease in selectivity under this condition. The compatibility between the nanosheets and the polymer is expected to be important in achieving high separation performance of the composite membrane, as can be inferred from the large difference between the performance predicted by the modified Cussler model and the actual performance.

Electrospinning UiO-66-NH2/polyacrylonitrile fibers for filtration of VOCs

The use of high-performance and low-cost electrospinning fibers to manufacture filters to remove harmful pollutants from the air has a high value in terms of commercial applications. We report the first use of electrospinning UiO-66-NH2/PAN fibers filter with the well-defined microporous structure to filter volatile organic compounds (VOCs). Two different VOCs, methylbenzene (MB) and ethylbenzene (EB), have been used to measure the filtration capacity of the different filters. The filtration capacity of the filter is improved with the increase of the UiO-66-NH2 loading amount in the composites. The PAN fibers with 50 wt% UiO-66-NH2 (U50/P) showed the highest VOC filtration capacity, which was 80.6% greater than that of pristine PAN fibers. Furthermore, the VOCs separation capacity was almost unchanged within 8 h, indicating the long-time stable protection from VOCs. The suppleness, lightness, high air permeability, and ideal VOCs exclusion rate make the UiO-66-NH2/PAN fibers filter promising candidates as anti-VOCs filters in the masks.

Surface treated Phoenix sylvestris for bioadsorption of oil from aqueous solution: Isotherms and kinetic studies

Biosorption is a versatile technique of removing the oil spill – one of the major toxicants that causes water pollution, which threatens the ecological balance of the aquatic ecosystem. The proposed research aims in developing a viable adsorbent from discarded agricultural waste, Phoenix sylvestris, which was surface altered, assessed and utilised as a biosorbent for the effective removal of diesel from aqueous solution in batch adsorption trials. Waste palm leaves, Phoenix sylvestris (RPS)was physically (PMPS) and chemically modified (CMPS) to adsorb diesel in the emulsion. The synthesised materials were characterised by FTIR, SEM, and EDS, confirming a well-defined microporous structure consisting of ionisable groups. The studies indicated optimised conditions of 10 g, 4.5 g and 2 g of RPS, PMPS and CMPS respectively at 303K for an optimised adsorption time of 60 min. Freundlich isotherm agreed well with experimental data, and the kinetic mechanism claimed better results with RPS, PMPS and CMPS for Pseudo first-order model. The adsorbents could be reused five times without much loss of efficiency. From the performed studies, it can be inferred that good adsorption capacities at optimised conditions followed the order of CMPS > PMPS > RPS. Thermodynamic analysis proved the feasibility of such biosorption with exothermic nature predicting spontaneous attraction of oil components to the surface of PMPS and CMPS. Moreover, the density of the CMPS layer rendered proven results for such biosorption displaying a hyperbolic dependency assuring its efficacy. Hence, it can be concluded that the prepared adsorbent from Phoenix sylvestris, an agricultural waste, possess good adsorptive properties.

Biomass-derived activated carbons for the removal of pharmaceutical mircopollutants from wastewater: A review

Biomass-derived activated carbons (biochars) have attracted great attention due to their excellent physicochemical properties such as high specific area, large pore volume, well-defined microporous structure and tunable surface chemistry. Although pharmaceuticals are an emerging class of micropollutants in wastewater through the sewerage disposal by pharmaceutical factories, hospitals and households, only a few recent studies have reviewed the adsorption and removal of pharmaceuticals from wastewater by biochars and they lack the systematic insights into total adsorption process from biochars preparation to adsorption mechanism. This paper aims to provide a comprehensive review on recent publications and to propose future research directions. The effects of lignocellulosic biomass as well as the pyrolysis, activation and modification conditions on the physicochemical properties of biochars and their adsorption capacities are discussed. The adsorption kinetics and isotherms of different pharmaceuticals onto various biochars are analyzed based on commonly used models. Finally, the potential adsorption mechanisms of pharmaceuticals by biochars are summarized.

Novel amino-functionalized hypercrosslinked polymer nanoparticles constructed from commercial macromolecule polystyrene via a two-step strategy for CO2 adsorption

Commercial polymers have large cost advantage to drive HCPs to industrialize. The AHCPNPs using commercial PS as main block prove that it still has well-defined microporous structure, high specific surface area and extremely CO2 capture capacity.

Cost-Efficient Strategy for Sustainable Cross-Linked Microporous Carbon Bead with Satisfactory CO2 Capture Capacity.

Cross-linked microporous carbon beads (MCBs) were successfully synthesized via a green, convenient, and cost-efficient strategy derived from a renewable sugar source. Such an approach avoids the time-consuming procedure and the use of corrosive chemical activating agents and toxic solvents and only involves a simple carbonization process, which makes it to be applicable for rapid and large-scale industrial production of MCB materials. The obtained MCBs possessed well-defined microporous structure, narrow pore size, and high surface area. Particularly, the microporosity of the resultant MCBs could be easily tailored to arise primary pores of size 0.5–0.9 nm by adjusting the carbonization temperature and reaction time, which remarkably favor the CO2 capture. The optimal sample of MCBs-9-5 carbonized at 900 °C for 5 h was characterized by high microporosity (80% of the surface area from micropores), especially ultrahigh narrow microporosity (53% of pore volume from micropores of size <1 nm), which endowed it a great satisfactory CO2 uptake of 4.25 mmol g–1 at 25 °C and 1 bar. Significantly, a prominent CO2/N2 selectivity and superior recyclability of MCBs-9-5 were also achieved. Combined with the simple fabrication, the satisfactory adsorption capacity, and high selectivity, MCBs-9-5 should be a promising adsorbent for CO2 capture and separation.

Molten salt assisted synthesis of microporous polyaniline nanosheets with superior gas sorption properties

Porous polyaniline (PANI) nanosheet has unique structure and properties that can be applied in gas separation, gas storage, and energy storage and conversion devices. To date, it is still a great challenge to construct microporous PANI nanosheet materials. Here, we present an inorganic salt template pyrolysis route for the direct synthesis of ultrathin PANI nanosheets with well-defined microporous structure from hexaaminobenzene monomer. The obtained PANI nanosheets give an ultrathin thickness of 1.6 nm, high surface area (∼395 m2 g−1), and well-defined microporous structure (centered at ∼0.54 nm). The PANI nanosheets with plenty of micropores exhibit superior gas sorption property for CO2 and CH4 at room temperature, which is also expected to improve the performances of PANI nanosheets in other application fields.

Electrochemical water splitting using nano-zeolite Y supported tungsten oxide electrocatalysts

Zeolites are often used as supports for metals and metal oxides because of their well-defined microporous structure and high surface area. In this study, nano-zeolite Y (50–150 nm range) and micro-zeolite Y (500–800 nm range) were loaded with WO3, by impregnating the zeolite support with ammonium metatungstate and thermally decomposing the salt thereafter. Two different loadings of WO3 were studied, 3 wt.% and 5 wt.% with respect to the overall catalyst. The prepared catalysts were characterized for their morphology, structure, and surface areas through scanning electron microscope (SEM), XRD, and BET. They were further compared for their electrocatalytic activity for hydrogen evolution reaction (HER) in 0.5 M H2SO4. On comparing the bare micro-zeolite particles with the nano-form, the nano-zeolite Y showed higher currents with comparable overpotentials and lower Tafel slope of 62.36 mV/dec. WO3 loading brought about a change in the electrocatalytic properties of the catalyst. The overpotentials and Tafel slopes were observed to decrease with zeolite-3 wt.% WO3. The smallest overpotential of 60 mV and Tafel slope of 31.9 mV/dec was registered for nano-zeolite with 3 wt.% WO3, while the micro-zeolite gave an overpotential of 370 mV and a Tafel slope of 98.1 mV/dec. It was concluded that even with the same metal oxide loading, nano-zeolite showed superior performance, which is attributed to its size and hence easier escape of hydrogen bubbles from the catalyst.

Hollow mesoporous silica sphere-embedded composite separator for high-performance lithium-ion battery

A high-performance composite separator based on hollow mesoporous silica spheres, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), and poly(ethylene terephthalate) nonwoven was explored as lithium-ion battery separator via a dip coating technique followed by a phase separation wet process. Systematical investigations including morphology characterization, porosity measurement, electrolyte wettability, thermal shrinkage testing, and cell performance examination are carried out. It is demonstrated that the unique mesoporous structures of silica spheres endow the composite separator with well-defined microporous structure. Owing to the preferable microstructure and relatively polar constituents, the composite separator exhibits higher porosity, superior electrolyte wettability, and outstanding thermal stability. Based on the above advantages, the composite separator shows better electrochemical performances, such as the discharge C-rate capability and cycling performance, as compared to the commercialized PE separator. This research presents a simple approach to prepare high-performance separator, which is demonstrated to be a good candidate for lithium-ion batteries.

Rebirth of Coffee-Wiped Wastepaper: Flavor Activation of Cellulose for Eco-Friendly/Cost-Competitive Carbon Electrode Materials

Forthcoming smart energy era, which will find widespread use of flexible/wearable electronics, electric vehicles, and stationary electricity storage systems, is in incessant pursuit of advanced rechargeable power sources with reliable/sustainable electrochemical performance. Among a wide variety of functional materials for use in energy storage systems, cellulose can be suggested as a promising candidate due to its natural abundance, recyclability, and low cost. Among numerous application fields of cellulose, cellulose-mediated activated carbons have been extensively investigated as an alternative electrode active material for energy storage systems including electric double-layer capacitors (EDLCs), A primary requirement of the activated carbons is the acquisition of well-defined microporous structure (pore size < 2 nm) with high specific surface area. To achieve this goal, chemical activation agents based on potassium ion (K+)-containing salts (e.g., potassium hydroxide (KOH)) are combined with cellulose. The salts play a viable role in catalyzing dehydration and decomposition reaction in initial pyrolysis stage, eventually facilitating pyrolysis kinetics. However, the chemical hazards and environmental pollution of the chemical activation agents remain formidable obstacles for their widespread use in the carbonization process. In our daily lives, when we spill coffee on table, clothes or any substances, a paper towel is often used to wipe the spilled one. Here, inspired by such daily happenings, we demonstrate a new class of coffee-mediated flavor activation as a new eco-friendly strategy to address the aforementioned longstanding issue of chemical activation in the cellulose carbonization. Simply describing, wiping coffee with a paper towel is anticipated to open a new route for synthesis of cellulose-mediated activated carbon materials. Coffee, one of the most popular drinks in the world, is known to contain potassium ion (K+) as a core element. Espresso, which is known to have the highest content of K+ in a variety of coffee commercially available, is selected as an eco-friendly alternative chemical activation agent for cellulose carbonization. Kimwipes®, one of the most popular paper towels, is chosen as a model material of cellulose. A piece of Kimwipes was soaked into the espresso solution and then subjected to heat treatment at 600 oC for 2 h, leading to the preparation of (espresso-assisted) carbonized Kimwipes (referred to as “c-EK”). As a control sample, simply carbonized Kimwipes without the aid of espresso (denoted as “c-K”) was synthesized. Structural uniqueness of the c-EK was investigated, with a particular focus on K+-induced micropore formation. The introduction of espresso led to the significant increase in the specific surface area of c-EK (= 255.78 m2 g-1) over the control sample (=198.89 m2 g-1). Moreover, the well-developed peaks (assigned to micropores) in the N2 adsorption-desorption isotherms were clearly observed at the c-EK. In addition to the progress in the microporous structure, the c-EK exhibited the process advancement in pyrolysis kinetics than the c-K, including the lower decomposition temperature and also higher yields of activated carbon. The aforementioned results demonstrate the advantageous effects of espresso as a new environmentally-benign chemical activation agent. Subsequently, the potential applicability of the c-EK as an alternative electrode active material for supercapacitors (SCs) was explored. The SC cell assembled with the c-EK showed the significant improvement in capacity (= 131 F g-1 at a scan rate of 1 mV s-1) and cycling performance (over 10,000 cycles) far beyond those achievable with a control cell containing the c-K. Spurred by the structural/performance superiority of the c-EK as an exceptional activated carbon material, we developed all-paper flexible SCs that were composed of c-EK/CNT electrodes, Kimwipes separator, and PVA/KOH gel electrolyte. The physical compliance of Kimwipes, in combination with the highly-reticulated CNT networks in the electrodes, enabled the resultant paper SCs to maintain good electrochemical performance upon being subjected to mechanical deformation such as bending and folding. Notably, no appreciable loss in the capacity and cell resistance was observed even after repeated bending over 10,000 cycles. We envision that the “wiping coffee with Kimwipes” strategy proposed herein, specifically, espresso-assisted flavor activation of cellulose for activated carbons and also all-paper flexible SCs, is highly facile and also effective, thus opening up a new opportunity for eco-friendly/cost-competitive materials/systems in urgent need for next-generation power sources.

Synthesis of Two-dimensional Microporous Carbonaceous Polymer Nanosheets and Their Application as High-performance CO2 Capture Sorbent.

The synthesis of two-dimensional (2D) polymer nanosheets with a well-defined microporous structure remains challenging in materials science. Here, a new kind of 2D microporous carbonaceous polymer nanosheets was synthesized through polymerization of a very low concentration of 1,4-dicyanobenzene in molten zinc chloride at 400-500 °C. This type of nanosheets has a thickness in the range of 3-20 nm, well-defined microporosity, a high surface area (∼537 m(2) g(-1) ), and a large micropore volume (∼0.45 cm(3) g(-1) ). The microporous carbonaceous polymer nanosheets exhibit superior CO2 sorption capability (8.14 wt % at 298 K and 1 bar) and a relatively high CO2 selectivity toward N2 (25.6). Starting from different aromatic nitrile monomers, a variety of 2D carbonaceous polymer nanosheets can be obtained showing a certain universality of the ionothermal method reported herein.

Controlled incorporation of nanoparticles in metal–organic framework hybrid thin films

A facile encapsulation strategy was reported for preparing nanoparticles/metal-organic framework hybrid thin films which exhibit both the active (catalytic, magnetic, and optical) properties derived from the NPs and the size-selectivity originating from the well-defined microporous structure of the MOF thin films.

Direct NO decomposition over conventional and mesoporous Cu-ZSM-5 and Cu-ZSM-11 catalysts: Improved performance with hierarchical zeolites

Conventional Cu-ZSM-5 has for many years been recognized as a unique catalyst for direct NO decomposition. Zeolite-based catalysts have a crystallographically well-defined microporous structure. In such microporous catalysts, the creation and accessibility of the active sites is often influenced by the geometry of the pore system. To improve these catalysts, secondary mesoporous systems can benefitially be introduced into the structure of conventional zeolites. Here, this approach was used with Cu-containing ZSM-5 and ZSM-11 type mesoporous zeolite catalysts, which were used as catalysts for direct NO decomposition. It was discovered that introducing mesoporosity into the conventional materials leads to a significant improvement of the catalytic activity. Additionally, mesoporous Cu-ZSM-11 catalyst was found to be about twice as active as mesoporous Cu-ZSM-5. This difference is attributed to the fact that ZSM-11 has only straight microporous channels, while ZSM-5 has both straight and sinusoidal channels. Apparently, there is a preferential formation of active sites and/or improved accessibility in the straight channels compared to the sinusoidal channels, which make the ZSM-11 material a better catalysts than ZSM-5. All samples were characterized by XRPD, SEM, TPD-NH3, in situ EPR and N2 physisorption measurements. Thus, this confirms our previous observation that the special pore structure of Cu-ZSM-5 is not a decisive factor for the catalytic activity in NO decomposition.

Oxidation of SO2 catalysed by Mn-zeolites in aqueous phase

Mn2+ was heterogenised over six different zeolites by ion exchange and their activity for SO2 oxidation was studied by conductimetry. The activity of the heterogenised Mn2+ was compared with both, Mn2+ as a homogeneous catalyst and with a more conventional carbon based catalyst. Mn2+ was shown to be the only active phase, consequently the catalysts containing the higher content of ion exchanged Mn2+, were the most active ones. Additionally, the influence of the hydrophilia and the structure of the different zeolites used on the activity of the heterogenised Mn2+ were also analysed. Both the hydrophilia and the structure of the zeolites, which favour the interaction of the reaction intermediates and the Mn2+, were found to be the key parameters for the SO2 oxidation activity of the catalysts. The combination of hydrophilia, a high Mn2+ ion exchange capacity, and a well-defined microporous structure, allows that almost all the zeolites studied present higher activity for aqueous phase SO2 oxidation, than the homogeneous catalyst and significantly higher than the conventional carbon based catalyst for this reaction.