Holey graphene frameworks for highly selective post-combustion carbon capture

S-nitrosocysteamine-functionalised porous graphene oxide nanosheets as nitric oxide delivery vehicles for cardiovascular applications

Nitric oxide (NO) is a key signalling molecule released by vascular endothelial cells that is essential for vascular health. Low NO bioactivity is associated with cardiovascular diseases, such as hypertension, atherosclerosis, and heart failure and NO donors are a mainstay of drug treatment. However, many NO donors are associated with the development of tolerance and adverse effects, so new formulations for controlled and targeted release of NO would be advantageous. Herein, we describe the design and characterisation of a novel NO delivery system via the reaction of acidified sodium nitrite with thiol groups that had been introduced by cysteamine conjugation to porous graphene oxide nanosheets, thereby generating S-nitrosated nanosheets. An NO electrode, ozone-based chemiluminescence and electron paramagnetic resonance spectroscopy were used to measure NO released from various graphene formulations, which was sustained at >5 × 10-10 mol cm-2 min-1 for at least 3 h, compared with healthy endothelium (cf. 0.5-4 × 10-10 mol cm-2 min-1). Single cell Raman micro-spectroscopy showed that vascular endothelial and smooth muscle cells (SMCs) took up graphene nanostructures, with intracellular NO release detected via a fluorescent NO-specific probe. Functionalised graphene had a dose-dependent effect to promote proliferation in endothelial cells and to inhibit growth in SMCs, which was associated with cGMP release indicating intracellular activation of canonical NO signalling. Chemiluminescence detected negligible production of toxic N-nitrosamines. Our findings demonstrate the utility of porous graphene oxide as a NO delivery vehicle to release physiologically relevant amounts of NO in vitro, thereby highlighting the potential of these formulations as a strategy for the treatment of cardiovascular diseases.

Enhancing CO2 capture through innovating monolithic graphene oxide frameworks

The advancement and engineering of novel crystalline materials is facilitated through the utilization of innovative porous crystalline structures, established via KOH-treated monolithic graphene oxide frameworks. These materials exhibit remarkable and versatile characteristics for both functional exploration and applications within the realm of CO2 capture. In this comprehensive study, we have synthesized monolithic reduced graphene oxide-based adsorbents through a meticulous self-assembly process involving different mass ratios of GO/malic acid (MaA) (1:0.250, 1:0.500, and 1:1 by weight). Building upon this foundation, we further modified MGO 0.250 through KOH-treatment by chloroacetic acid method, leading to the creation of MGO 0.250_KOH, which was subjected to CO2 capture assessments. The comprehensive investigation encompassed an array of parameters including morphology, specific surface area, crystal defects, functional group identification, and CO2 capture efficiency. Employing a combination of FT-IR, XRD, Raman, BET, SEM, HR-TEM, and XPS techniques, the study revealed profound insights. Particularly notable was the observation that the MGO 0.250_KOH adsorbent exhibited an exceptional CO2 capture performance, leading to a significant enhancement of the CO2 capture capacity from 1.69 mmol g-1 to 2.35 mmol g-1 at standard conditions of 25 °C and 1 bar pressure. This performance enhancement was concomitant with an augmentation in surface area, elevating from 287.93 to 419.75 m2 g-1 (a nearly 1.5-fold increase compared to MGO 1.000 with a surface area of 287.93 m2 g-1). The monolithic adsorbent demonstrated a commendable production yield of 82.92%, along with an impressive regenerability of 98.80% at 100 °C. Additionally, adsorbent's proficiency in CO2 adsorption, rendering it a promising candidate for post-combustion CO2 capture applications. These findings collectively underscore the capacity adsorbents to significantly amplify CO2 capture capabilities. The viability of employing this strategy as an uncomplicated pre-treatment technique in various industrial sectors is a plausible prospect, given the study's outcomes.

Resembling Graphene/Polymer Aerogel Morphology for Advancing the CO2/N2 Selectivity of the Postcombustion CO2 Capture Process

The separation of CO2 from N2 remains a highly challenging task in postcombustion CO2 capture processes, primarily due to the relatively low CO2 content (3-15%) compared to that of N2 (70%). This challenge is particularly prominent for carbon-based adsorbents that exhibit relatively low selectivity. In this study, we present a successfully implemented strategy to enhance the selectivity of composite aerogels made of reduced graphene oxide (rGO) and functionalized polymer particles. Considering that the CO2/N2 selectivity of the aerogels is affected on the one hand by the surface chemistry (offering more sites for CO2 capture) and fine-tuned microporosity (offering molecular sieve effect), both of these parameters were affected in situ during the synthesis process. The resulting aerogels exhibit improved CO2 adsorption capacity and a significant reduction in N2 adsorption at a temperature of 25 °C and 1 atm, leading to a more than 10-fold increase in selectivity compared to the reference material. This achievement represents the highest selectivity reported thus far for carbon-based adsorbents. Detailed characterization of the aerogel surfaces has revealed an increase in the quantity of surface oxygen functional groups, as well as an augmentation in the fractions of micropores (<2 nm) and small mesopores (<5 nm) as a result of the modified synthesis methodology. Additionally, it was found that the surface morphology of the aerogels has undergone important changes. The reference materials feature a surface rich in curved wrinkles with an approximate diameter of 100 nm, resulting in a selectivity range of 50-100. In contrast, the novel aerogels exhibit a higher degree of oxidation, rendering them stiffer and less elastic, resembling crumpled paper morphology. This transformation, along with the improved functionalization and augmented microporosity in the altered aerogels, has rendered the aerogels almost completely N2-phobic, with selectivity values ranging from 470 to 621. This finding provides experimental evidence for the theoretically predicted relationship between the elasticity of graphene-based adsorbents and their CO2/N2 selectivity performance. It introduces a new perspective on the issue of N2-phobicity. The outstanding performance achieved, including a CO2 adsorption capacity of nearly 2 mmol/g and the highest selectivity of 620, positions these composites as highly promising materials in the field of carbon capture and sequestration (CCS) postcombustion technology.

Experimental kinetics and thermodynamics investigation: Chemically activated carbon-enriched monolithic reduced graphene oxide for efficient CO2 capture

In this research, we have developed solid MGOs by self-assembled reduction process of GO at 90 °C with different weight ratios of oxalic acid (1:1, 1:0.500, and 1:0.250). The as-synthesized monoliths were carbonized (at 600 °C) and chemically activated with varying proportions of NaOH (1:1, 1:2, and 1:3). This materials offer the CO2 adsorption effect under dynamic conditions, fast mass transfer, easy handling, and outstanding stability throughout the adsorption-desorption cycle. FE-SEM, and HR-TEM analyses confirmed the porous nature and shape of the adsorbents, while XPS examination revealed the presence of distinct functional groups on the surface of the monolith. By increasing the mass ratios (MGO:NaOH) from 1:1 to 1:2, the surface areas increased by approximately 2.6 times, ranging from 520.8 to 753.9 m2 g⁻1 (surface area of the untreated MGO was 289.2 m2 g⁻1). Consequently, this resulted in a notable enhancement of 2.10 mmol g⁻1 in dynamic CO2 capture capacity. The assessment encompassed the evaluation of production yield, selectivity, regenerability, kinetics, equilibrium isotherm, and isosteric temperatures of adsorption (Qst). The decrease in CO2 capture effectiveness with rising adsorption temperature indicated an exothermic and physisorption process. The regenerability of 99.1 % at 100 °C and excellent cyclic stability with efficient CO2 adsorption make this monolithic adsorbent appropriate for post-combustion CO2 capture. The significant Qst lend support to the heterogeneity of the adsorbent's surface, and the pseudo-second-order kinetic model along with the Freundlich isotherm model emerged as the most fitting. Therefore, the current investigation shows that the carbon-enriched adsorbents enhance the CO2 adsorption capacity. It may be used as a low-cost pretreatment method on an industrial scale before carbon capture.

Developments in mineral carbonation for Carbon sequestration

Mineral technology has attracted significant attention in recent decades. Mineral carbonation technology is being used for permanent sequestration of CO2 (greenhouse gas). Temperature programmed desorption studies showed interaction of CO2 with Mg indicating possibility of using natural feedstocks for mineral carbonation. Soaking is effective to increase yields of heat-activated materials. This review covers the latest developments in mineral carbonation technology. In this review, development in carbonation of natural minerals, effect of soaking on raw and heat-activated dunite, increasing reactivity of minerals, thermal activation, carbonations of waste materials, increasing efficiency of carbonation process and pilot plants on mineral carbonation are discussed. Developments in carbonation processes (single-stage carbonation, two-stage carbonation, acid dissolution, ph swing process) and pre-process and concurrent grinding are elaborated. This review also highlights future research required in mineral carbonation technology.

Exploring the capture and desorption of CO2 on graphene oxide foams supported by computational calculations

In the last decade, the highest levels of greenhouse gases (GHG) in the atmosphere have been recorded, with carbon dioxide (CO2) being one of the GHGs that most concerns mankind due to the rate at which it is generated on the planet. Given its long time of permanence in the atmosphere (between 100 to 150 years); this has deployed research in the scientific field focused on the absorption and desorption of CO2 in the atmosphere. This work presents the study of CO2 adsorption employing materials based on graphene oxide (GO), such as GO foams with different oxidation percentages (3.00%, 5.25%, and 9.00%) in their structure, obtained via an environmentally friendly method. The characterization of CO2 adsorption was carried out in a closed system, within which were placed the GO foams and other CO2 adsorbent materials (zeolite and silica gel). Through a controlled chemical reaction, production of CO2 was conducted to obtain CO2 concentration curves inside the system and calculate from these the efficiency, obtained between 86.28 and 92.20%, yield between 60.10 and 99.50%, and effectiveness of CO2 adsorption of the materials under study. The results obtained suggest that GO foams are a promising material for carbon capture and the future development of a new clean technology, given their highest CO2 adsorption efficiency and yield.

High performance CO2 capture at elevated temperatures by using cenospheres prepared from solid waste, fly ash

Cenospheres (CS) are spherical shaped inorganic frameworks present in with fly ash which is generated from coal-fired thermal power plants. These spherical structures were functionalized with imidazole and amine moieties to capture CO₂ selectively from flue gases at elevated temperature. The functionalized CS have shown a high selectivity for CO₂ adsorption (4.68 mmol g^-1) over N₂ (0.46 mmol g^-1) at 333 K/1 bar from a simulated flue gas (0.15 CO₂ and 0.85 N₂, v%) composition of thermal power plants. When the moisture content reached to 30 vol% the adsorption capacity of CS materials was reduced to 20 vol% as compared to dry flue gas. The functionalized CS can be used repeatedly for 50 cycles without losing its adsorption capacity. The cost estimate for CO₂ capture by using the proposed adsorption system would be $12.01/ton of CO₂ which is lower as compared to amine absorption system and zeolite-based adsorption system reported in the literature. The CS materials are prepared from solid wastes reduce the cost of production and their large scale manufacturing is technically feasible to capture CO₂ from industrial flue gases efficiently in near future.

Synthesis of holey graphene for advanced nanotechnological applications

Holey or porous graphene, a structural derivative of graphene, has attracted immense attention due to its unique properties and potential applications in different branches of science and technology. In this review, the synthesis methods of holey or porous graphene/graphene oxide are systematically summarized and their potential applications in different areas are discussed. The process-structure-applications are explained, which helps relate the synthesis approaches to their corresponding key applications. The review paper is anticipated to benefit the readers in understanding the different synthesis methods of holey graphene, their key parameters to control the pore size distribution, advantages and limitations, and their potential applications in various fields.

In situ casting of rice husk ash in metal organic frameworks induces enhanced CO2 capture performance

Incorporation of rice-husk-ash (RHA), an agricultural waste, in situ during the synthesis of MIL-101(Cr) resulted in a significant improvement in the CO2 adsorption properties over the synthesized RHA-MIL-101(Cr). The newly synthesized RHA-MIL-101(Cr) composite exhibited an enhancement of 14-27% in CO2 adsorption capacity as compared to MIL-101(Cr) at 25 °C and 1 bar. The content of RHA incorporated in RHA-MIL-101(Cr) fine tuned the CO2 capture performance to achieve high working capacity (0.54 mmol g-1), high purity (78%), superior CO2/N2 selectivity (18) and low isosteric heat of adsorption (20-30 kJ mol-1). The observed superior CO2 adsorption performance of RHA-MIL-101(Cr) is attributed to the fine tuning of textural characteristics-enhancement of 12-27% in BET surface area, 12-33% in total pore volume and 18-30% in micropore volume-upon incorporation of RHA in MIL-101(Cr).

Adsorption-induced clustering of CO2 on graphene

Utilization of graphene-based materials for selective carbon dioxide capture has been demonstrated recently as a promising technological approach. In this study we report results from density functional theory calculations and molecular dynamics simulations on the adsorption of CO2, N2, and CH4 gases on a graphene sheet. We calculate adsorption isotherms of ternary and binary mixtures of these gases and reproduce the larger selectivity of CO2 to graphene relative to the other two gases. Furthermore it is shown that the confinement to two-dimensions, associated with adsorbing the CO2 gas molecules on the plane of graphene, increases their propensity to form clusters on the surface. Above a critical surface coverage (or partial pressure) of the gas, these CO2-CO2 interactions augment the effective adsorption energy to graphene, and, in part, contribute to the high selectivity of carbon dioxide with respect to nitrogen and methane. The origin of the attractive interaction between the CO2 molecules adsorbed on the surface is of electric quadrupole-quadrupole nature, in which the positively-charged carbon of one molecule interacts with the negatively-charged oxygen of another molecule. The energy of attraction of forming a CO2 dimer is predicted to be around 5-6 kJ mol-1, much higher than the corresponding values calculated for N2 and CH4. We also evaluated the adsorption energies of these gases to a graphene sheet and found that the attractions obtained using the classical force-fields might be over-exaggerated. Nevertheless, even when the magnitudes of these (classical force-field) graphene-gas interactions are scaled-down sufficiently, the tendency of CO2 molecules to cluster on the surface is still observed.

Reduced Graphene Oxide/Polymer Monolithic Materials for Selective CO2 Capture

Polymer composite materials with hierarchical porous structure have been advancing in many different application fields due to excellent physico-chemical properties. However, their synthesis continues to be a highly energy-demanding and environmentally unfriendly process. This work reports a unique water based synthesis of monolithic 3D reduced graphene oxide (rGO) composite structures reinforced with poly(methyl methacrylate) polymer nanoparticles functionalized with epoxy functional groups. The method is based on reduction-induced self-assembly process performed at mild conditions. The textural properties and the surface chemistry of the monoliths were varied by changing the reaction conditions and quantity of added polymer to the structure. Moreover, the incorporation of the polymer into the structures improves the solvent resistance of the composites due to the formation of crosslinks between the polymer and the rGO. The monolithic composites were evaluated for selective capture of CO₂. A balance between the specific surface area and the level of functionalization was found to be critical for obtaining high CO₂ capacity and CO₂/N₂ selectivity. The polymer quantity affects the textural properties, thus lowering its amount the specific surface area and the amount of functional groups are higher. This affects positively the capacity for CO₂ capture, thus, the maximum achieved was in the range 3.56–3.85 mmol/g at 1 atm and 25 °C.

Porous Silsesquioxane-Imine Frameworks as Highly Efficient Adsorbents for Cooperative Iodine Capture

The efficient capture and storage of radioactive iodine (¹²⁹I or ¹³¹I), which can be formed during nuclear energy generation or nuclear waste storage, is of paramount importance. Herein, we present highly efficient aerogels for reversible iodine capture, namely, porous silsesquioxane-imine frameworks (PSIFs), constructed by condensation of octa(3-aminopropyl)silsesquioxane cage compound and selected multitopic aldehydes. The resulting PSIFs are permanently porous (Brunauer-Emmet-Teller surface areas up to 574 m²/g), thermally stable, and present a combination of micro-, meso-, and macropores in their structures. The presence of a large number of imine functional groups in combination with silsesquioxane cores results in extremely high I₂ affinity with uptake capacities up to 485 wt %, which is the highest reported to date. Porous properties can be controlled by the strut length and rigidity of linkers. In addition, PSIF-1a could be recycled at least four times while maintaining 94% I₂ uptake capacity. Kinetic studies of I₂ desorption show two strong binding sites with apparent activation energies of 77.0 and 89.0 kJ/mol. These energies are considerably higher than the enthalpy of sublimation of bulk I₂.

Surface modification of co-doped reduced graphene oxide through alkanolamine functionalization for enhanced electrochemical performance

The synergistic effect of heteroatom co-doping and triethanolamine functionalization on reduced graphene oxide resulted in impressive electrochemical features.

Sulfonated Holey Graphene Oxide (SHGO) Filled Sulfonated Poly(ether ether ketone) Membrane: The Role of Holes in the SHGO in Improving Its Performance as Proton Exchange Membrane for Direct Methanol Fuel Cells

Sulfonated holey graphene oxides (SHGOs) have been synthesized by the etching of sulfonated graphene oxides with concentrated HNO₃ under the assistance of ultrasonication. These SHGOs could be used as fillers for the sulfonated aromatic poly(ether ether ketone) (SPEEK) membrane. The obtained SHGO-incorporated SPEEK membrane has a uniform and dense structure, exhibiting higher performance as proton exchange membranes (PEMs), for instance, higher proton conductivity, lower activation energy for proton conduction, and comparable methanol permeability, as compared to Nafion 112. The sulfonated graphitic structure of the SHGOs is believed to be one of the crucial factors resulting in the higher performance of the SPEEK/SHGO membrane, since it could increase the local density of the -SO₃H groups in the membrane and induce a strong interfacial interaction between SHGO and the SPEEK matrix, which improve the proton conductivity and lower the swelling ratio of the membrane, respectively. Additionally, the proton conductivity of the membrane could be further enhanced by the presence of the holes in the graphitic planes of the SHGOs, since it provides an additional channel for transport of the protons. When used, direct methanol fuel cell with the SPEEK/SHGO membrane is found to exhibit much higher performance than that with Nafion 112, suggesting potential use of the SPEEK/SHGO membrane as the PEMs.

Interaction between a water drop and holey graphene: retarded imbibition and generation of novel water–graphene wetting states

Water nanodrop imbibition in holey graphene is studied unraveling novel fiber-like wetting state that enhances water–accessible graphene surface area.