Internal Surface Area Research Articles

Antiaromatic Covalent Organic Frameworks Based on Dibenzopentalenes

Despite their inherent instability, 4n π systems have recently received significant attention due to their unique optical and electronic properties. In dibenzopentalene (DBP), benzanellation stabilizes the highly antiaromatic pentalene core, without compromising its amphoteric redox behavior or small HOMO-LUMO energy gap. However, incorporating such molecules in organic devices as discrete small molecules or amorphous polymers can limit the performance (e.g., due to solubility in the battery electrolyte solution or low internal surface area). Covalent organic frameworks (COFs), on the contrary, are highly ordered, porous, and crystalline materials that can provide a platform to align molecules with specific properties in a well-defined, ordered environment. We synthesized the first antiaromatic framework materials and obtained a series of three highly crystalline and porous COFs based on DBP. Potential applications of such antiaromatic bulk materials were explored: COF films show a conductivity of 4 × 10-8 S cm-1 upon doping and exhibit photoconductivity upon irradiation with visible light. Application as positive electrode materials in Li-organic batteries demonstrates a significant enhancement of performance when the antiaromaticity of the DBP unit in the COF is exploited in its redox activity with a discharge capacity of 26 mA h g-1 at a potential of 3.9 V vs. Li/Li+. This work showcases antiaromaticity as a new design principle for functional framework materials.

Influence of internal and external surface area on impregnation and activity of 3D printed catalyst carriers

Direct ink writing as additive manufacturing technique was used to print two different boehmite based shapes, cylinders and monoliths, serving as catalyst carriers. These were wet impregnated targeting 0.3–0.9 wt% platinum loadings. ICP-OES, μCT and microscopy revealed dependencies from calcination temperature, geometry and platinum loading. Dehydrogenation reactions of perhydro dibenzyltoluene as liquid organic hydrogen carrier were performed examining the catalytic performance. Differences when executing full particle measurements led to the conclusion that direct ink writing as shaping technique for catalyst carriers and the respective impregnation is highly beneficial as more complex shapes can be obtained, resulting in higher activities.

Vinyl-functionalized covalent organic frameworks for effective radioactive iodine capture in aqueous solution

131I radioisotopes have been widely employed in diagnostic and therapeutic medicine processes, particularly for thyroid cancer. The radiation hazard of 131I offers a potential threat to environmental safety or human health, so the wastewater generated from the production of 131I drugs must be effluent disposed of on time. In this study, we developed novel vinyl-functionalized covalent organic frameworks (COFs) with large pore volume and internal surface area for highly effective radioactive iodine ions adsorption in water. The as-produced spherical COFs (COF-V) exhibited a rapid adsorption rate (0.318 g g−1 min−1) and exceptionally high adsorption capacity of up to 437.8 mg g−1 for iodine ions in water. Furthermore, it demonstrated more than 90% removal of Na131I in water with radiation doses ranging from 181.3 MBq (4.9 mCi) to 1017.5 MBq (27.5 mCi). Additional characterizations and density functional theory (DFT) calculations revealed that the vinyl groups were linked with a benzene ring and imine to form a large and complete π-π conjugate system with 1D open channels. These channels provided sufficient sites for the effective adsorption of I ions on vinyl groups and benzene rings through hydrogen bonding. The excellent adsorption performance and radiation stability make the developed spherical COF-V a promising candidate for efficient radioactive iodine removal in wastewater.

Degradable Biocompatible Porous Microtube Scaffold for Extended Donor Cell Survival and Activity.

Cell therapy has significant therapeutic potential but is often limited by poor donor cell retention and viability at the host implantation site. Biomaterials can improve cell retention by providing cells with increased cell-cell and cell-matrix contacts and materials that allow three-dimensional cell culture to better recapitulate native cell morphology and function. In this study, we engineered a scaffold that allows for cell encapsulation and sustained three-dimensional cell culture. Since cell therapy is largely driven by paracrine secretions, the material was fabricated by electrospinning to have a large internal surface area, micrometer-thin walls, and nanoscale surface pores to allow for nutrient exchange without early cell permeation. The material is degradable, which allows for less invasive removal of the implant. Here, a biodegradable poly(lactic-co-glycolic acid) (PLGA) microtube array membrane was fabricated. In vitro testing showed that the material supported the culture of human dermal fibroblasts for at least 21 days, with paracrine secretion of pro-angiogenic FGF2. In vivo xenotransplantation of human cells in an immunocompetent mouse showed that donor cells could be maintained for more than one month and the material showed no obvious toxicity. Analysis of gene expression and tissue histology surrounding the implant showed that the material produced muted inflammatory and immune responses compared to a permanent implant and increased markers of angiogenesis.

The rise of metal-organic framework based micromotors.

Micromotors (MMs) are micro and nanoscale devices capable of converting energy into autonomous motion. Metal-organic frameworks (MOFs) are crystalline materials that display exceptional properties such as high porosity, internal surface areas, and high biocompatibility. As such, MOFs have been used as active materials or building blocks for MMs. In this highlight, we describe the evolution of MOF-based MMs, focusing on the last 3 years. First, we covered the main propulsion mechanisms and designs, from catalytic to fuel-free MOF-based MMs. Secondly, we discuss recent applications of new fuel-free MOFs MM to give a critical overview of the current challenges of this blooming research field. The advantages and challenges discussed provide a useful guide for the design of the next generation MOF MMs toward real-world applications.

Characterization of Agnihotra ash

Agnihotra is a traditional domestic solemnity, performed to maintain harmony between living beings and nature, without harming and by giving respect. Agnihotra, the simplest forms of Yajnya performed at sunset/ sunrise in which cow dung is burned in the copper pot by using cow ghee and brown rice as oblations along with chanting of mantras of sun and fire. The ash produced after performance of Agnihotra yajnya has various applications in the agricultural sector, environmental pollution control, medical sector, etc. In the present study we have characterized the Agnihotra ash. Elemental analysis of Agnihotra ash was done with the help of Atomic Absorption Spectroscopy. Characterization of Agnihotra ash was done by using X-Ray Diffraction analysis and Fourier Transform Infrared analysis. Analysis of ash compounds was done by X-Ray Diffraction – Theta-2-Theta spectrum and Energy Dispersive X-Ray spectrum. Agnihotra ash mainly consists of silicon dioxide (SiO2) as major compound. The Agnihotra ash was a highly porous material with a large internal specific surface area.

Effect of Horizontal Resolution of Printer on Trueness of 3D-Printed Provisional Crown: An In Vitro Study

Abstract Objectives Provisional crowns play an integral role in prosthodontic therapy and need to be fabricated with high accuracy to ensure good marginal fit and proper contour. The aim of this study is to evaluate the effect of 3D printer's horizontal pixel resolution on trueness of the intaglio surface, external surface, and marginal area and the actual marginal adaptation of the interim crowns. Materials and Methods A gypsum reference model of mandible with a prepared right first molar was scanned with a dental laboratory scanner (AutoScan-DS-MIX, Shining 3D) and a digital provisional crown was design using the computer-aided design (CAD) software (Exocad). The provisional crown was manufactured by two printers with different horizontal resolutions (Sonic Mini 4K Printer and Sonic Mini 8K Printer). The printed crowns were scanned using the aforementioned scanner. The trueness of the external surface, internal surface, and marginal area of the provisional crowns was evaluated by comparing the scanned data with the reference CAD design data using a 3D inspection software (Geomagic Control X, 3D systems). The trueness of the crown manufactured by two printers was compared by a two-sided test (α = 0.05). Finally, the marginal adaptation of the provisional crowns was evaluated on the printed removable dies and compared. Results The results revealed that there was a significant difference in the trueness of the marginal area and the marginal adaptation (p < 0.05). Conclusions It can be concluded that the trueness of provisional crown marginal area and the marginal adaptation was affected by the horizontal resolution of the 3D printer.

Heat transfer enhancement in inserted extruded aluminum finned tubes

Heat transfer enhancement in tubes is widely applied in various industrial processes. The traditional method of heat transfer enhancement is to insert radial fins to expand the internal surface area and destroy the flow. However, there is a flue gas corridor in the central area of the tube, and the cost of expanding the inner fin is high. A centrally symmetrical bent extruded aluminum fin was developed to enhance the heat transfer in the tube. An experimental platform was constructed to test the performance of inner finned tubes and explore the process of combining extruded aluminum inner fin with steel tube. The bent extruded aluminum fins with two side fins extending to the central axis possesses the best comprehensive heat transfer performance. The heat transfer correlation of the optimal fin structure is Nu = 0.864Re0.4275Pry0.3818(Pry/Prw)?0.1004. With low cost and strong heat transfer performance, the bent extruded aluminum inner fin tube will gain wide applications in the engineering field.

Effects of Hydrothermal Treatment on Mesopore Structure and Connectivity in Doped Ceria-Zirconia Mixed Oxides.

Pore size and pore connectivity control diffusion-based transport in mesopores, a crucial property governing the performance of heterogeneous catalysts. In many cases, transition-metal oxide catalyst materials are prepared from molecular precursors involving hydrothermal treatment followed by heat treatment. Here, we investigate the effects of such a hydrothermal aftertreatment step, using an aqueous ammonia solution, on the disordered mesopore network of CexZr1-x-y-zYyLazO2-δ mixed oxides. This procedure is a common synthesis step in the preparation of such ceria-based oxygen storage materials applied in three-way catalysis, employed to improve the materials' thermal stability. We perform state-of-the-art Ar-physisorption analysis, especially advanced hysteresis scanning, to paint a detailed picture of the alterations in mesopore space caused by the hydrothermal aftertreatment and subsequent aging at 1050 °C. Furthermore, we investigate the network characteristics by electron tomography in combination with suitable statistical analysis, enabling a consistent interpretation of the desorption scans (physisorption). The results indicate that the hydrothermal aftertreatment enhances the mesopore connectivity of the continuous 3D network by widening pores and especially necks, hence facilitating accessibility to the particles' internal surface area and the ability to better withstand high temperatures.

Diastereoselective Synthesis of Trans-1H-Chromeno[2,3-d]Pyrimidine-2,4,6(3H)-Trione Derivatives by KF/Stilbite Zeolite NPs as a Novel Heterogeneous Nanocatalyst and Evaluation of Their Antimicrobial and Antioxidant Activity

A green protocol for diastereoselective synthesis of trans-trans-1H-Chromeno[2,3-d]pyrimidine-2,4,6(3H)-trione was applied by tandem aldol-Michael reactions between 1,3-dimethylbarbituric acid, aldehydes, and dimedone at room temperature on the water as well as the present of KF/Stilbite nanoparticles. Also, the catalytic activity of the nanocatalyst (NC) was evaluated in the reduction of organic pollutants such as 4-nitrophenol (4-NP) in water at mild conditions. The results indicated that the NCs have very high and effective catalytic activity for organic pollutants within a few seconds. Antioxidant abilities of synthesized compounds were revealed using radical trapping of diphenyl-picrylhydrazine (DPPH) and ferric reduction power experiments. The compounds 4a–d had excellent DPPH• radical scavenging. Also, the antimicrobial activity of some synthesized compounds was proved by employing the disk diffusion test on Gram-positive and Gram-negative bacteria. HIGHLIGHTS Synthesis of diastereomer derivatives is important in medicinal chemistry. This research was designed for easy synthesis of diastereoisomer derivatives of 1H-chromeno[2,3-d]pyrimidine-2,4,6(3H)-triones. The heterocyclic compounds have a recognized subject due to having a wide range of medicinal properties. The synthesized compounds revealed biological activities. Zeolites have cation replacement. Stilbite (ST), a natural zeolite with a framework structure and high internal surface area, is more effective because of its exchange capability for cations particularly for Na+ and Ca2+. Therefore, stilbite was used as a catalyst.

Metal-organic Frameworks for Natural Gas Storage

Methane, as the transitional fuel, still emits CO2 during combustion but less than gasoline. Developing new adsorption materials can improve the efficiency of methane storage and then achieve the goal safely and economically. Metal-organic Frameworks (MOF) with the advantage of high porosity and adjustable pore surface area, are considered one of the promising materials for natural storage. Here, this article briefly introduces the preparation of MOF and mentions some details during this process such as the solvothermal technique, and electrochemical synthesis methods, covering some defects in the preparation process. Many kinds of materials have different volumetric adsorption rates and mass adsorption rates compared with DOE standards. In chronological order, this paper lists some typical materials and discusses specific structures inside MOFs corresponding to relative performance. Changing or adjusting organic ligands can improve capacities so that a series of MOFs are designed like MFM-132, MFM-112 and MFM-115. In addition, the factors influencing adsorption rate are also considered including internal factors, surface area, porosity, structure, adsorption isotherm and external factors, pressure, and temperature, respectively

Impact of Interfaces, and Nanostructure on the Performance of Conjugated Polymer Photocatalysts for Hydrogen Production from Water.

The direct conversion of sunlight into hydrogen through water splitting, and by converting carbon dioxide into useful chemical building blocks and fuels, has been an active area of research since early reports in the 1970s. Most of the semiconductors that drive these photocatalytic processes have been inorganic semiconductors, but since the first report of carbon nitride organic semiconductors have also been considered. Conjugated materials have been relatively extensively studied as photocatalysts for solar fuels generation over the last 5 years due to the synthetic control over composition and properties. The understanding of materials' properties, its impact on performance and underlying factors is still in its infancy. Here, we focus on the impact of interfaces, and nanostructure on fundamental processes which significantly contribute to performance in these organic photocatalysts. In particular, we focus on presenting explicit examples in understanding the interface of polymer photocatalysts with water and how it affects performance. Wetting has been shown to be a clear factor and we present strategies for increased wettability in conjugated polymer photocatalysts through modifications of the material. Furthermore, the limited exciton diffusion length in organic polymers has also been identified to affect the performance of these materials. Addressing this, we also discuss how increased internal and external surface areas increase the activity of organic polymer photocatalysts for hydrogen production from water.

Reduced graphene aerogels as energy efficient selective oil sorbents

Graphene aerogels are widely used in the oil–water system as they possess high internal surface area and super-oleophilic properties. However, they tend to absorb water along with oil, and to overcome this problem; surface coatings are generally employed using expensive fluoro-silane compounds. It leads to an increase in production costs and environmental concerns. Herein, we report super-hydrophobic 3D graphene aerogels as selective oil sorbent for oil–water​ separation. The reduction of oxygen-containing functional groups on the surface of graphene aerogels has been studied and characterized with FTIR. The thermal treatment of up to 700 °C was carried out using an in-house flow system. The gases used to reduce graphene oxide aerogel are H2 and N2 with an optimized ratio of 5:95. The presence of H2 significantly decreased the oxygen-containing functional groups in graphene aerogel. The increase in the C/O ratio results in higher uptake capacity due to higher surface area and pore volume. The thermal reduction yields a C/O ratio of 24:1, slightly higher than most reported values.

Rapid Removal of Cr(VI) from Aqueous Solution Using Polycationic/Di-Metallic Adsorbent Synthesized Using Fe3+/Al3+ Recovered from Real Acid Mine Drainage

The mining of valuable minerals from wastewater streams is attractive as it promotes a circular economy, wastewater beneficiation, and valorisation. To this end, the current study evaluated the rapid removal of aqueous Cr(VI) by polycationic/di-metallic Fe/Al (PDFe/Al) adsorbent recovered from real acid mine drainage (AMD). Optimal conditions for Cr(VI) removal were 50 mg/L initial Cr(VI), 3 g PDFe/Al, initial pH = 3, 180 min equilibration time and temperature = 45 °C. Optimal conditions resulted in ≥95% removal of Cr(VI), and a maximum adsorption capacity of Q = 6.90 mg/g. Adsorption kinetics followed a two-phase pseudo-first-order behaviour, i.e., a fast initial Cr(VI) removal (likely due to fast initial adsorption) followed by a slower secondary Cr(VI) removal (likely from Cr(VI) to Cr(III) reduction on the surface). More than 90% of adsorbed Cr(VI) could be recovered after five adsorption–desorption cycles. A reaction mechanism involving a rapid adsorption onto at least two distinct surfaces followed by slower in situ Cr(VI) reduction, as well as adsorption-induced internal surface strains and consequent internal surface area magnification, was proposed. This study demonstrated a rapid, effective, and economical application of PDFe/Al recovered from bona fide AMD to treat Cr(VI)-contaminated wastewater.

(PEFC&E 2022 Student Poster Award Winner - 1st Place) MEA Performance of Pd@Pt Core-Shell Catalysts Supported on Different Particle Sizes of Mesoporous Carbon

1. Introduction Very high performance, especially on output power density (6 kW/L), for PEFCs in FCVs is targeted for 2030 in Japan [1]. Therefore, we need to improve not only ORR activity, but also oxygen diffusivity of Pt-based cathode catalysts for PEFCs. In this study, highly interconnected mesoporous carbon (MPC) [2] was selected as a support of Pd@Pt core-shell catalyst. The Pd@Pt core-shell catalyst NPs were supported on different particle size of the MPC and cell performance was investigated. 2. Experimental We selected CNovel®MH-18 (central mesopore diameter: 4 nm, SBET: 1,334 m2/g, TOYO TANSO) as a MPC support. As-received MPC with an average size of ca. 2 μm was pulverized to ca. 800, 450, and 250 nm by a wet bead-milling process. The Pd core NPs were loaded on MPCs by an impregnation-thermal reduction method and the Pt shell was formed on the Pd core NPs by a direct displacement reaction method [3]. Characterizations of the MPC, the Pd/MPC cores and the Pt/Pd/MPC catalysts were conducted by N2 gas adsorption, TG-DTA, XRD, XRF, TEM, SEM, CV and the ORR activity of the catalysts was evaluated by the RDE method. MEAs with 1×1 cm2 were fabricated by a decal method using a reinforced membrane (12 µm in thickness, Gore) and a GDL (TORAY). The Pt metal loading at the cathode was 0.1 mg-Pt/cm2. Nafion® DE2020 was used as an ionomer for the catalyst ink preparation (I/C was set to 0.83). I-V performance was evaluated at 80oC, 35-95% RH. H2 gas (418 mL/min.) and air (998 mL/min.) were supplied to the anode and the cathode, respectively, and H2 gas was pressurized to 150 kPa (ambient + 50 kPa) at gas-outlet. 3. Results and Discussion N2 gas adsorption data were analyzed by the t-plot method and the changes in the total, external and internal surface area of the MPCs pulverized for different times are shown in Figure 1. It was shown that the total and the external surface area increased, while the internal surface area decreased with pulverization time. These results suggest that fresh surface was newly formed by the pulverization, and the fraction of the internal surface was decreased. Figure 2 shows cross-sectional TEM images of the Pt/Pd/MPC catalysts using different sizes of MPC supports (ca. 2,000, 800, 450 and 250 nm), which indicates that the catalyst NPs were uniformly supported throughout the interior of MPC regardless of the particle size of MPC. The ECSA of the Pt/Pd/MPC catalysts changed little with the particle size of MPC (ca. 120 m2/g-Pt), while the ORR mass activity at 0.9 V was the highest (1,533 A/g-Pt) when the catalyst NPs were supported on relatively large MPC (800 nm).I-V curves at 80oC, 35% RH of the MEAs using the Pt/Pd/MPC cathode catalysts using different sizes of MPC supports are demonstrated in Figure 3. Interestingly, the cell voltage was higher over the entire current density range for Pd@Pt catalysts using MPCs with larger particle sizes (2000 and 800 nm). This tendency was also observed at a high relative humidity of 95% RH. These results suggest that the Pd@Pt catalyst NPs supported on larger MPC (2,000 and 800 nm) contributed to ORR in the high current density range even when the relative humidity was low. Figure 4 compares the connectivity of mesopores in Ketjen Black EC-600JD (KB-600JD, LION) and CNovel® MH-18 visualized from 3D-TEM observation results. It is clear that the MPC has a higher mesopore’s connectivity than KB-600JD. Figure 5 shows cross-sectional SEM images of the Pt/Pd/MPC. Larger pores were observed inside of the MPC support. Therefore, it is considered that the high connectivity of the mesopores and the presence of larger pores inside of the MPC support contributed to the superior I-V performance observed in MEAs using the catalysts supported on MPCs with particle size of ca. 2,000 and 800 nm. At present, it is not clear why the catalysts supported on smaller MPCs (450 and 250 nm) exhibited inferior I-V performance, though the oxygen diffusion inside MPCs should be easier than that for larger ones.This study was partly supported by NEDO, Japan. The CNovel®MH-18 supports with different size were supplied by Dr. Shodai of TOYO TANSO.

Modeling Electrochemical Direct Air Capture of CO2 using Redox-Functionalized Electrodes

Increasing research attention is being devoted to designing electrochemical systems that can capture CO2 from air and thus mitigate climate change, as decarbonization of the energy sector is occurring very slowly. The low concentration of CO2 in air however makes large scale, energy-efficient and rapid CO2 capture challenging. Understanding how the energetic cost of CO2 capture depends on operational and material parameters that describe electrochemical systems is important for designing practical and cost-effective devices.We have previously shown that electrochemical CO2 capture is possible using a pH swing cycle that is driven by proton-coupled electron transfer (PCET) involving organic molecules [1]. More recently, we have begun to consider a new design for electrochemical CO2 capture in which PCET-active species are conformally attached to the internal surface area of a highly porous electrode, and effect a reversible pH swing in an adjacent layer of aqueous electrolyte upon redox cycling. We develop a continuum reaction-transport model that simulates reactive CO2 capture into and release from the electrolyte layer, as well as transport of (bi)carbonate species, and protons, in response to an applied current or voltage. The model permits an assessment of the energetic cost of CO2 separation under various current densities and concentration gradients, and decomposition of that cost into thermodynamic, kinetic, mass transport-related and Ohmic contributions. We then highlight potential pathways to achieving an energetic cost of CO2 capture from air of 100 kJ/molCO2, and discuss preliminary results from an experimental prototype.[1] Jin. S, Wu M., Gordon R., Aziz M., Kwabi D., pH Swing Cycle for CO2 Capture Electrochemically Driven through Proton-Coupled Electron Transfer

Internal Mass Transport Induced Voltage Losses during Water Electrolysis on Interconnected Nickel Nanowire Mesh Electrodes

Nickel nanowire mesh electrodes offer great potential for water electrolysis in alkaline environment, given their high internal surface area, mechanical strength, and alkaline resistance. Here we use a nickel nanowire mesh with a specific area of 26 m2/cm3, resulting in ~100-fold area enhancement for a 4µm thick nanowire mesh, compared to planar nickel. This highly benefits geometric current density, potentially into a regime where mass transport is the main limiting factor. Therefore, we performed a systematic study of electrode behaviour under various mass transport conditions to decouple kinetic and mass transfer related contributions to electrode voltage losses.An electrochemical flow cell was designed to measure the nanowire mesh electrode performance under optimal mass transport conditions. The cell provided electrolyte flow through the nanomesh, enabling convective supply of reagent into the nanopores as well as convective removal of reaction products. Facilitated by the inherent strength of the nanowire mesh, superficial flow velocities up to 1 cm/s could be obtained, with which geometric current densities as high as 320 mA/cm2 could be measured in the kinetically limited (flowrate independent) regime.Internal mass transport limitations were isolated by use of an inverted rotating disk electrode (iRDE). Koutecky-Levich analysis was performed to compensate for external mass transfer contributions on both nanowire mesh electrodes and planar electrodes. The nanowire mesh as iRDE resembles operating conditions in an electrolyzer, whereas the planar electrode provides a well-defined benchmark area for the electrode surface activity.For both the oxygen evolution reaction as the hydrogen evolution reaction, mass transport limitations were studies as function of current density and electrolyte (NaOH) concentration. Nanowire mesh electrode operation in the presence of internal mass transport limitations was compared to the non-limited condition and planar benchmark, from which the electrode effectiveness factor could be calculated. A 1-d simplified model of the electrode was used to explain the observed phenomena and to provide guidance for design optimization.

Modeling and Experimental Analysis of pH Swing-Based Approaches to Electrochemical CO2 Capture

The use of renewable electricity to drive large-scale electrochemical CO2 removal and concentration from point sources, air, and seawater is receiving considerable interest as one strategy for mitigating climate change.1 The low concentration of CO2 in air however makes rapid and energy-efficient CO2 capture challenging. Understanding and optimizing the energetic cost of CO2 separation at practically reasonable throughputs is a prerequisite for engineering devices that can be widely deployed.I will review our past and current efforts at developing electrochemical pH-swing-based CO2 separation (EPCS) using a combination of modeling and experiments. In EPCS, CO2 is captured from a mixture of gases into an aqueous electrolyte in the form of (bi)carbonate ions when its pH is increased from acidic to strongly alkaline conditions, and then released as a pure gas when the pH is reversed. We have shown that CO2 separation is experimentally possible for less than 100 kJ/molCO2 using such a pH swing cycle that is driven by proton-coupled electron transfer (PCET).2 Thermodynamic modeling shows that the minimum work input for electrochemical CO2 separation is the sum of exergy losses incurred from differences in CO2 partial pressure between the CO2 source/exit streams and the electrolyte. This framework rationalizes minimum work inputs for pH-swing and redox-mediator-based CO2 separation cycles, and motivates the measurement or estimation of the aforementioned CO2 partial pressures in future experimental studies.More recently, we have begun to consider a new design for EPCS in which PCET-active species are conformally attached to the internal surface area of a highly porous electrode, and effect a reversible pH swing in an adjacent layer of aqueous electrolyte upon redox cycling. We have formulated a continuum reaction-transport model that simulates reactive CO2 capture into and release from the electrolyte layer, as well as transport of (bi)carbonate species, and protons, in response to an applied current or voltage. Possible pathways toward achieving an energetic cost of direct air capture of CO2 less than 100 kJ/molCO2 will be discussed, as well as our efforts toward experimental demonstration of this concept. References Renfrew, S. E.; Starr, D. E.; Strasser, P., Electrochemical Approaches toward CO2 Capture and Concentration. ACS Catalysis 2020, 10 (21), 13058-13074.Jin, S.; Wu, M.; Gordon, R. G.; Aziz, M. J.; Kwabi, D. G., pH swing cycle for CO2 capture electrochemically driven through proton-coupled electron transfer. Energy & Environmental Science 2020.

Internal bonding microstructures characterisation between plant nanocellulose and concrete mortar mixtures for indoor Radon-222 gas emanation reduction

• CNF crystallinity index fosters by high frequency ultrasonication. • Great CNF dissemination enhances mechanical strength of the composite brick. • CNF significantly impact internal porosity nanonization of the composite brick. • Tiniest internal porosity observed on 40 mL kenaf CNF composite brick. • Lowest 222 Rn concentration emanated from 40 mL oil palm CNF composite brick. Radon-222 ( 222 Rn) is a natural radioactive gas produced by the radium-226 ( 226 Ra) decay process, which is part of the uranium-238 ( 238 U) decay series. 222 Rn gas can penetrate into the respiratory system during the inhalation process and have an indirect effect on lung tissues due to energetic alpha particles. Brick is a common building material that consists of rock, water, and sand. It is the most prevalent source of 222 Rn gas emanation to humans in an indoor building environment. To reduce indoor 222 Rn gas emanation, kenaf and oil palm cellulose nanofibrils (CNF) were mixed into bricks in certain ratios and acted as liquid fillers. CNFs were produced by using chemical pulping, bleaching, and ultrasonic techniques. Ten composite bricks with different ratios of CNF and one control brick were fabricated by following Malaysia Standard (MS 7.6:1972). The characterization of CNF was done using Fourier Transformed Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). The Brunauer-Emmett-Teller (BET) was used to analyse the internal porosity and surface area of the fabricated bricks. 222 Rn concentrations in the bricks and humidity inside the prototype Perspex box were recorded using the Radon Sentinel Monitor Model 1030. The surface areas for control brick, 40 mL kenaf, and oil palm CNF composite bricks are 3.4473 m 2 /g, 4.449 m 2 /g, and 4.9025 m 2 /g, respectively. Meanwhile, pore sizes for control brick, 40 mL kenaf and oil palm CNF composite bricks are 2.92 nm, 0.347 nm and 2.27 nm, respectively. The highest 222 Rn concentration was measured in control brick, which is 3.77 pCi/L, followed by 40 mL kenaf CNF brick and 40 mL oil palm CNF brick, with readings of 1.4 pCi/L and 0.93 pCi/L. The incorporation of CNFs has the ability to reduce 222 Rn emissions while increasing the physical strength of the bricks.

Stress and permeability modelling in depleted coal seams during CO2 storage

Depleted coal seam gas reservoirs are considered as one of the best sites for underground CO2 sequestration which can contribute to climate change mitigation. Due to coal's high internal surface area, a large amount of CO2 can be stored in the coal matrix. Despite the high CO2 storage capacity, the swelling of coal near the injection wells remains a major challenge. Most field trials have shown a significant decline in injection rate and permeability in the vicinity of vertical injection wells, while horizontal wells showed no such decline. It is not well studied how matrix swelling and well trajectory affect permeability in horizontal carbon dioxide injection wells. In this study, a mathematical model is developed to determine stress distribution and permeability around vertical and horizontal CO2 injection wells in depleted coal seams. The model incorporates injection pressure, matrix swelling effect, in situ stresses, and wellbore trajectory. The results indicate that during CO2 injection, matrix swelling significantly impacts the stress path and increases both horizontal stresses. Stress distribution and permeability around the well are affected significantly by wellbore trajectory and swelling. As CO2 injection continues in vertical wells, radial, tangential, and mean effective stresses increase near the well and within the reservoir. As a result, permeability declines during injection in a vertical well. In horizontal wells, however, tangential and mean horizontal stress near the wellbore decrease with injection. Hence, the model confirms no decline in permeability near a horizontal injection well which is in good agreement with the field trial observations.