Kinetics of carbon dioxide absorption from air in a flow reactor with a fixed bed of K<Subscript>2</Subscript>CO<Subscript>3</Subscript>-based sorbent

Sorption of carbon dioxide from air in a flow reactor with a bulky fixed bed of the K₂CO₃/Al₂O₃ composite sorbent was studied. The dynamic sorption capacity of the material was shown to depend on the relative humidity of the inlet air. A numerical model was constructed for evaluating the profile of СО₂ concentration in the layer and kinetic curves of CO₂ breakthrough at the outlet of the reactor. The results of simulation allowed us to adequately describe the experimental kinetic curves at 20–40% humidity.     

CO2 Capture from Ambient Air by Crystallization with a Guanidine Sorbent

Carbon capture and storage is an important strategy for stabilizing the increasing concentration of atmospheric CO₂ and the global temperature. A possible approach toward reversing this trend and decreasing the atmospheric CO₂ concentration is to remove the CO₂ directly from air (direct air capture). Herein we report a simple aqueous guanidine sorbent that captures CO₂ from ambient air and binds it as a crystalline carbonate salt by guanidinium hydrogen bonding. The resulting solid has very low aqueous solubility (K _sp=1.0(4)×10⁻⁸), which facilitates its separation from solution by filtration. The bound CO₂ can be released by relatively mild heating of the crystals at 80–120 °C, which regenerates the guanidine sorbent quantitatively. Thus, this crystallization‐based approach to CO₂ separation from air requires minimal energy and chemical input, and offers the prospect for low‐cost direct air capture technologies.     

An Interfacial Solar Heating Assisted Liquid Sorbent Atmospheric Water Generator

Harvesting water from air is a promising strategy for fresh‐water production, and it is particularly desirable for areas that lack direct access to clean water. While high‐concentration liquid sorbent is well‐known for high sorption, it has not been widely used for atmospheric water collection, being primarily limited by the difficulty in desorption. Interfacial solar heating based on a salt‐resistant GO‐based aerogel is now shown to enable a high‐concentration liquid sorbent (CaCl₂ 50 wt % solution) based atmospheric water generator. Fresh water (2.89 kg m^?2 day^?1) can be produced at about 70 % relative humidity, with only solar energy input and energy efficiency of desorption as high as 66.9 %. This low‐cost and effective approach provides an attractive pathway to extract water from air, to relieve the thirst of arid, land‐locked, and other areas where fresh water is scarce.     

Removal of Oil Products from Water Using a Combined Process of Sorption and Plasma Exposure to DBD

The paper presents the results of studies of a combined process involving the sorption of engine oil on a sorbent (diatomite) followed by regeneration of the sorbent by plasma-oxidative destruction of oil in DBD of atmospheric pressure in oxygen. The process parameters (gas flow rate, sorbent mass, power, treatment time), which provide the possibility of fivefold regeneration of the sorbent and 100% degree of oil decomposition, are revealed. It was found that the kinetics of oil degradation obeys the pseudo-first kinetic order equation with a rate constant of 0.017 s^?1. The energy efficiency of the decomposition was 0.169 molecules of oil per 100 eV of input energy. It is shown that treatment of the sorbent for 5 min leads to the complete decomposition of oil. The products of oil decomposition are carboxylic acids, aldehydes and CO₂. Complete removal of acids and aldehydes requires the time of about 40 min. The possible participation of ozone in the oxidative degradation of oil is discussed.     

Capture CO2 from Ambient Air Using Nanoconfined Ion Hydration

Water confined in nanoscopic pores is essential in determining the energetics of many physical and chemical systems. Herein, we report a recently discovered unconventional, reversible chemical reaction driven by water quantities in nanopores. The reduction of the number of water molecules present in the pore space promotes the hydrolysis of CO₃^2? to HCO₃^? and OH^?. This phenomenon led to a nano‐structured CO₂ sorbent that binds CO₂ spontaneously in ambient air when the surrounding is dry, while releasing it when exposed to moisture. The underlying mechanism is elucidated theoretically by computational modeling and verified by experiments. The free energy of CO₃^2? hydrolysis in nanopores reduces with a decrease of water availability. This promotes the formation of OH^?, which has a high affinity to CO₂. The effect is not limited to carbonate/bicarbonate, but is extendable to a series of ions. Humidity‐driven sorption opens a new approach to gas separation technology.     

Molecular‐Level Insights into the Oxidative Degradation of Grafted Amines

The oxidative degradation of CO₂ adsorbents consisting of amine‐grafted pore‐expanded mesoporous MCM‐41 silica was investigated. The adsorbents were treated under flowing air at various temperatures, and the degree of deactivation was evaluated through the measurement of their CO₂ adsorption capacity prior and subsequent to exposure to air. To decipher the chemical structure of surface species upon air‐deactivation of grafted amines, a solvent extraction procedure was developed using a deuterated basic solution. The obtained solutions were analyzed by a variety of 1D and 2D NMR spectroscopy techniques, such as ²⁹Si, ¹³C, ¹H, [¹H,¹⁵N] HMBC, [¹H,¹³C] HMQC, COSY and DOSY. The surface species generated by oxidative degradation of amine‐grafted silica were found to contain functional groups such as imine, amide and carboxylic groups. Several structural units were conclusively demonstrated.     

Lithium silicate nanosheets with excellent capture capacity and kinetics with unprecedented stability for high-temperature CO2 capture

An excessive amount of CO₂ is the leading cause of climate change, and hence, its reduction in the Earth''s atmosphere is critical to stop further degradation of the environment. Although a large body of work has been carried out for post-combustion low-temperature CO₂ capture, there are very few high temperature pre-combustion CO₂ capture processes. Lithium silicate (Li₄SiO₄), one of the best known high-temperature CO₂ capture sorbents, has two main challenges, moderate capture kinetics and poor sorbent stability. In this work, we have designed and synthesized lithium silicate nanosheets (LSNs), which showed high CO₂ capture capacity (35.3 wt% CO₂ capture using 60% CO₂ feed gas, close to the theoretical value) with ultra-fast kinetics and enhanced stability at 650 °C. Due to the nanosheet morphology of the LSNs, they provided a good external surface for CO₂ adsorption at every Li-site, yielding excellent CO₂ capture capacity. The nanosheet morphology of the LSNs allowed efficient CO₂ diffusion to ensure reaction with the entire sheet as well as providing extremely fast CO₂ capture kinetics (0.22 g g⁻¹ min⁻¹). Conventional lithium silicates are known to rapidly lose their capture capacity and kinetics within the first few cycles due to thick carbonate shell formation and also due to the sintering of sorbent particles; however, the LSNs were stable for at least 200 cycles without any loss in their capture capacity or kinetics. The LSNs neither formed a carbonate shell nor underwent sintering, allowing efficient adsorption–desorption cycling. We also proposed a new mechanism, a mixed-phase model, to explain the unique CO₂ capture behavior of the LSNs, using detailed (i) kinetics experiments for both adsorption and desorption steps, (ii) in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy measurements, (iii) depth-profiling X-ray photoelectron spectroscopy (XPS) of the sorbent after CO₂ capture and (iv) theoretical investigation through systematic electronic structure calculations within the framework of density functional theory (DFT) formalism.

Capturing CO₂ before its release. Lithium silicate nanosheets showed high CO₂ capture capacity (35.3 wt%) with ultra-fast kinetics (0.22 g g⁻¹ min⁻¹) and enhanced stability at 650 °C for at least 200 cycles, due to mixed-phase-model of CO₂ capture.     

Methane Carboxylation Using Electrochemically Activated Carbon Dioxide

Direct synthesis of CH₃COOH from CH₄ and CO₂ is an appealing approach for the utilization of two potent greenhouse gases that are notoriously difficult to activate. In this Communication, we report an integrated route to enable this reaction. Recognizing the thermodynamic stability of CO₂, our strategy sought to first activate CO₂ to produce CO (through electrochemical CO₂ reduction) and O₂ (through water oxidation), followed by oxidative CH₄ carbonylation catalyzed by Rh single atom catalysts supported on zeolite. The net result was CH₄ carboxylation with 100 % atom economy. CH₃COOH was obtained at a high selectivity (>80 %) and good yield (ca. 3.2 mmol g⁻¹_cat in 3 h). Isotope labelling experiments confirmed that CH₃COOH is produced through the coupling of CH₄ and CO₂. This work represents the first successful integration of CO/O₂ production with oxidative carbonylation reaction. The result is expected to inspire more carboxylation reactions utilizing preactivated CO₂ that take advantage of both products from the reduction and oxidation processes, thus achieving high atom efficiency in the synthesis.     

Heterogeneous Fenton Degradation of Organic Pollutants in Water Enhanced by Combining Iron-type Layered Double Hydroxide and Sulfate

Water pollution derived from organic pollutants is one of the global environmental problems. The Fenton reaction using Fe²⁺ as a homogeneous catalyst has been known as one of clean methods for oxidative degradation of organic pollutants. Here, a layered double hydroxide (Fe²⁺Al³⁺-LDH) containing Fe²⁺ and Al³⁺ in the structure was used to develop a “heterogeneous” Fenton catalyst capable of mineralizing organic pollutants. We found that sulfate ion (SO₄²⁻) immobilized on the Fe²⁺Al³⁺-LDH significantly facilitated oxidative degradation (mineralization) of phenol as a model compound of water pollutants to carbon dioxide (CO₂) in a heterogeneous Fenton process. The phenol conversion and mineralization efficiency to CO₂ reached >99% and ca. 50%, respectively, even with a reaction time of only 60 min.     

Characterization of SAPO-34 membranes by water adsorption

The effects of humidity on gas permeation were studied for five SAPO-34 membranes with different fractions of permeation through non-SAPO pores. Membranes with high CO₂/CH₄ separation selectivities (>20) were stable in humidified gases, but degradation was seen for some membranes after months of exposure to the laboratory atmosphere. Once the membranes started to degrade, the rate of degradation appeared to accelerate. The degradation created non-SAPO pores that were larger than the SAPO-34 pores, as indicated by i-C₄H₁₀ permeance, CO₂/CH₄ selectivity, and CO₂ flux dependence on pressure. The effect of humidity on gas permeance correlated with these indicators of non-SAPO pores. Adsorbed water appeared to completely block the SAPO pores, but permeation through non-SAPO pores increased with humidity. Therefore, water adsorption can be used to determine membrane quality and the fraction of transport through non-SAPO pores.     

Isotopic analysis for degradation diagnosis of calcite matrix in mortar

Mortar that was used in building as well as in conservation and restoration works of wall paintings have been analysed isotopically (δ¹³C and δ¹⁸O) in order to evaluate the setting environments and secondary processes, to distinguish the structural components used and to determine the exact causes that incurred the degradation phenomena. The material undergoes weathering and decay on a large proportion of its surface and in depth, due to the infiltration of water through the structural blocks. Mineralogical analysis indicated signs of sulphation and dissolution/recrystallisation processes taking place on the material, whereas stable isotopes provided information relative to the origin of the CO₂ and water during calcite formation and degradation processes. Isotopic change of the initial δ¹³C and δ¹⁸O in carbonate matrix was caused by alteration of the primary source of CO₂ and H₂O in mortar over time, particularly by recrystallisation of calcite with porewater, evaporated or re-condensed water, and CO₂ from various sources of atmospheric and biogenic origin. Human influence (surface treatment) and biological growth (e.g. fungus) are major exogenic processes which may alter δ¹⁸O and δ¹³C in lime mortar.     

Regulating Extra-Framework Cations in Faujasite Zeolites for Capture of Trace Carbon Dioxide

The development of cost-effective sorbents for direct capture of trace CO₂ (<1 %) from the atmosphere is an important and challenging task. Natural or commercial zeolites are promising sorbents, but their performance in adsorption of trace CO₂ has been poorly explored to date. A systematic study on capture of trace CO₂ by commercial faujasite zeolites reveals that the extra-framework cations play a key role on their performance. Under dry conditions, Ba−X displays high dynamic uptake of 1.79 and 0.69 mmol g⁻¹ at CO₂ concentrations of 10000 and 1000 ppm, respectively, and shows excellent recyclability in the temperature-swing adsorption processes. K−X exhibits perfect moisture resistance, and >95 % dry CO₂ uptake can be preserved under relative humidity of 74 %. In situ solid-state NMR spectroscopy, synchrotron X-ray diffraction and neutron diffraction reveal two binding sites for CO₂ in these zeolites, namely the basic framework oxygen atoms and the divalent alkaline earth metal ions. This study unlocks the potential of low-cost natural zeolites for applications in direct air capture.     

A Long‐Life Lithium–Air Battery in Ambient Air with a Polymer Electrolyte Containing a Redox Mediator

Lithium–air batteries when operated in ambient air generally exhibit poor reversibility and cyclability, because of the Li passivation and Li₂O₂/LiOH/Li₂CO₃ accumulation in the air electrode. Herein, we present a Li–air battery supported by a polymer electrolyte containing 0.05 m LiI, in which the polymer electrolyte efficiently alleviates the Li passivation induced by attacking air. Furthermore, it is demonstrated that I⁻/I₂ conversion in polymer electrolyte acts as a redox mediator that facilitates electrochemical decomposition of the discharge products during recharge process. As a result, the Li–air battery can be stably cycled 400 times in ambient air (relative humidity of 15 %), which is much better than previous reports. The achievement offers a hope to develop the Li–air battery that can be operated in ambient air.     

A Long-Life Lithium–Air Battery in Ambient Air with a Polymer Electrolyte Containing a Redox Mediator

Lithium–air batteries when operated in ambient air generally exhibit poor reversibility and cyclability, because of the Li passivation and Li₂O₂/LiOH/Li₂CO₃ accumulation in the air electrode. Herein, we present a Li–air battery supported by a polymer electrolyte containing 0.05 m LiI, in which the polymer electrolyte efficiently alleviates the Li passivation induced by attacking air. Furthermore, it is demonstrated that I⁻/I₂ conversion in polymer electrolyte acts as a redox mediator that facilitates electrochemical decomposition of the discharge products during recharge process. As a result, the Li–air battery can be stably cycled 400 times in ambient air (relative humidity of 15 %), which is much better than previous reports. The achievement offers a hope to develop the Li–air battery that can be operated in ambient air.     

Selective extraction of CO2 from simulated flue gas using polymeric ionic liquid sorbent coatings in solid-phase microextraction gas chromatography

The CO₂ selectivity of two polymeric task-specific ionic liquid sorbent coatings, poly(1-vinyl-3-hexylimidazolium) bis[(trifluoromethyl)sulfonyl]imide [poly(VHIM-NTf₂)] and poly(1-vinyl-3-hexylimidazolium) taurate [poly(VHIM-taurate)], was examined using solid-phase microextraction (SPME) for the determination of CO₂ in simulated flue gas. For comparison purposes, a commercial SPME fiber, Carboxen™-PDMS, was also studied. A study into the effect of humidity revealed that the poly(VHIM-taurate) fiber exhibited enhanced resistance to water, presumably due to the unique mechanism of CO₂ capture. The effect of temperature on the performance of the PIL-based and Carboxen fibers was examined by generating calibration curves under various temperatures. The sensitivity, linearity, and linear range of the three fibers were evaluated. The extraction of CH₄ and N₂ was performed and the selectivities of the PIL-based and Carboxen fibers were compared. The poly(VHIM-NTf₂) fiber was found to possess superior CO₂/CH₄ and CO₂/N₂ selectivities compared to the Carboxen fiber, despite the smaller film thicknesses of the PIL-based fibers. A scanning electron microscopy study suggests that the amine group of the poly(VHIM-taurate) is capable of selectively reacting with CO₂ but not CH₄ or N₂, resulting in a significant surface morphology change of the sorbent coating.     

Efficient Solar-Driven Water Harvesting from Arid Air with Metal–Organic Frameworks Modified by Hygroscopic Salt

Freshwater scarcity is a global challenge threatening human survival, especially for people living in arid regions. Sorption-based atmospheric water harvesting (AWH) is an appealing way to solve this problem. However, the state-of-the-art AWH technologies have poor water harvesting performance in arid climates owing to the low water sorption capacity of common sorbents under low humidity conditions. We report a high-performance composite sorbent for efficient water harvesting from arid air by confining hygroscopic salt in a metal–organic framework matrix (LiCl@MIL-101(Cr)). The composite sorbent shows 0.77 g g⁻¹ water sorption capacity at 1.2 kPa vapor pressure (30 % relative humidity at 30 °C) by integrating the multi-step sorption processes of salt chemisorption, deliquescence, and solution absorption. A highly efficient AWH prototype is demonstrated with LiCl@MIL-101(Cr) that can enable the harvesting of 0.45–0.7 kg water per kilogram of material under laboratory and outdoor ambient conditions powered by natural sunlight without optical concentration and additional energy input.     

FT-IR study on CO<Subscript>2</Subscript> adsorbed species of CO<Subscript>2</Subscript> sorbents

The stability of amine-functionalized silica sorbents prepared through the incipient wetness technique with primary, secondary, and tertiary amino organosilanes was investigated. The prepared sorbents were exposed to different gaseous streams including CO₂/N₂, dry CO₂/air with varying concentration, and humid CO₂/air mixtures to demonstrate the effect of the gas conditions on the CO₂ adsorption capacity and the stability of the different amine structures. The primary and secondary amine-functionalized adsorbents exhibited CO₂ sorption capacity, while tertiary amine adsorbent hardly adsorbed any CO₂. The secondary amine adsorbent showed better stability than the primary amine sorbent in all the gas conditions, especially dry conditions. Deactivation species were evaluated using FT-IR spectra, and the presence of urea was confirmed to be the main deactivation product of the primary amine adsorbent under dry condition. Furthermore, it was found that the CO₂ concentration can affect the CO₂ sorption capacity as well as the extent of degradation of sorbents.     

Efficient Degradation of Iopromide by Using Sulfite Activated with Mackinawite

Iopromide (IOP), an iodinated X-ray contrast medium (ICM), is identified as a precursor to iodide disinfection byproducts that have high genotoxicity and cytotoxicity to mammals. ICM remains persistent through typical wastewater treatment processes and even through some hydroxyl radical-based advanced oxidation processes. The development of new technologies to remove ICMs is needed. In this work, mackinawite (FeS)-activated sulfite autoxidation was employed for the degradation of IOP-containing water. The experiment was performed in a 500 mL self-made temperature-controlled reactor with online monitoring pH and dissolved oxygen in the laboratory. The effects of various parameters, such as initial pH values, sulfite dosages, FeS dosages, dissolved oxygen, and inorganic anions on the performance of the treatment process have been investigated. Eighty percent of IOP could be degraded in 15 min with 1 g L⁻¹ FeS, 400 μmol L⁻¹ sulfite at pH 8, and high efficiency on the removal of total organic carbon (TOC) was achieved, which is 71.8% via a reaction for 1 h. The generated hydroxyl and oxysulfur radicals, which contributed to the oxidation process, were identified through radical quenching experiments. The dissolved oxygen was essential for the degradation of IOP. The presence of Cl⁻ could facilitate IOP degradation, while NO₃⁻ and CO₃²⁻ could inhibit the degradation process. The reaction pathway involving H-abstraction and oxidative decarboxylation was proposed, based on product identification. The current system shows good applicability for the degradation of IOP and may help in developing a new approach for the treatment of ICM-containing water.     

Characteristics of a simultaneous sampling system for the speciation of atmospheric T and 14C, and its application to surface and soil air

A simultaneous sampling system for the speciation of atmospheric T and ¹⁴C has been developed. Firstly tritiated moisture together with all water vapor in air is adsorbed on Drierite after coagulation using an electric cooler. Then ¹⁴CO₂ plus stable CO₂ in the dried air is adsorbed on molecular sieve 4A. Elemental tritium gas (HT) plus hydrogen gas (H₂) in the atmosphere along with H₂ gas generated from electrolysis of groundwater which does not contain any T, are oxidized on Pd catalyst to water and adsorbed on molecular sieve 3A. Tritiated methane (CH₃T) and ¹⁴CH₄ plus stable methane in the atmosphere are oxidized on Pt catalyst to water and CO₂ under 400 °C. Then, Drierite and molecular sieve 4A adsorb the oxidized T (HTO) and C-14 (¹⁴CO₂), respectively. Tritium and C-14 in surface and soil air have been measured using this system     

Selective Photoelectrochemical Reduction of Aqueous CO2 to CO by Solvated Electrons

Reduction of CO₂ by direct one‐electron activation is extraordinarily difficult because of the ?1.9 V reduction potential of CO₂. Demonstrated herein is reduction of aqueous CO₂ to CO with greater than 90 % product selectivity by direct one‐electron reduction to CO₂^.? by solvated electrons. Illumination of inexpensive diamond substrates with UV light leads to the emission of electrons directly into water, where they form solvated electrons and induce reduction of CO₂ to CO₂^.?. Studies using diamond were supported by studies using aqueous iodide ion (I^?), a chemical source of solvated electrons. Both sources produced CO with high selectivity and minimal formation of H₂. The ability to initiate reduction reactions by emitting electrons directly into solution without surface adsorption enables new pathways which are not accessible using conventional electrochemical or photochemical processes.