The effect of copper on the redox behaviour of iron oxide for chemical-looping hydrogen production probed by in situ X-ray absorption spectroscopy.

The production of high purity hydrogen with the simultaneous capture of CO2, can be achieved through a chemical looping (CL) cycle relying on an iron oxide-based oxygen carrier. Indeed, the availability of active and cyclically stable oxygen carriers is a key criterion for the practical implementation of this technology. In this regard, improving our understanding of the reduction pathway(s) of iron-based oxygen carriers and the development of concepts to increase the reduction kinetics are important aspects. The aim of this work is to evaluate the effect of the addition of copper on the redox behaviour of iron oxide based oxygen carriers stabilized on ZrO2. In situ pulsed-H2 XANES (Fe K-edge) experiments allowed for the determination of the reduction pathways in these materials, viz. the reduction of both Fe2O3 and CuFe2O4 proceeded via a Fe2+ intermediate: Fe2O3 (CuFe2O4) → Fe3O4 (Cu0) → FeO (Cu0) → Fe0 (Cu0). In the first step CuFe2O4 is reduced to Cu0 and Fe3O4, whereby Cu0 promotes the further reduction of iron oxide, increasing their rate of formation. In particular, the rate of reduction of FeO → Fe0 is accelerated most dramatically by Cu0. This is an encouraging result as the FeO → Fe0 transition is the slowest reduction reaction.

Cooperativity and Dynamics Increase the Performance of NiFe Dry Reforming Catalysts.

The dry reforming of methane (DRM), i.e., the reaction of methane and CO2 to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a MgxAlyOz matrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m2/gcat), pore volume (0.51-0.66 cm3/gcat), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, Ni4Fe1 with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.

CaO-Based CO2 Sorbents Effectively Stabilized by Metal Oxides.

Calcium looping (i.e., CO2 capture by CaO) is a promising second-generation CO2 capture technology. CaO, derived from naturally occurring limestone, offers an inexpensive solution, but due to the harsh operating conditions of the process, limestone-derived sorbents undergo a rapid capacity decay induced by the sintering of CaCO3 . Here, we report a Pechini method to synthesize cyclically stable, CaO-based CO2 sorbents with a high CO2 uptake capacity. The sorbents synthesized feature compositional homogeneity in combination with a nanostructured and highly porous morphology. The presence of a single (Al2 O3 or Y2 O3 ) or bimetal oxide (Al2 O3 -Y2 O3 ) provides cyclic stability, except for MgO which undergoes a significant increase in its particle size with the cycle number. We also demonstrate a direct relationship between the CO2 uptake and the morphology of the synthesized sorbents. After 30 cycles of calcination and carbonation, the best performing sorbent, containing an equimolar mixture of Al2 O3 and Y2 O3 , exhibits a CO2 uptake capacity of 8.7 mmol CO2 g-1 sorbent, which is approximately 360 % higher than that of the reference limestone.

The development of effective CaO-based CO2 sorbents via a sacrificial templating technique.

A carbon-based sacrificial templating approach was employed to realize single-pot synthesis of cyclically stable CaO-based CO2 sorbents. The sacrificial carbonaceous template was formed through resorcinol-formaldehyde polymerization reaction. The resultant sorbents following the thermal decomposition of the carbonaceous template featured an inverse opal-like macrostructure composed of a highly porous nanostructured backbone. In addition to pure CaO, sorbents supported with Al2O3, MgO, Y2O3, and ZrO2 were synthesized. SEM and XRD were utilized to characterize the morphology and the chemical composition of the synthetic CO2 sorbents, respectively. The cyclic CO2 uptake performance of the synthetic sorbents was assessed by TGA and compared to limestone. All of the synthetic sorbents exhibited an improved CO2 uptake performance when compared to limestone. The performance enhancement became more pronounced in the case of supported sorbents. The sorbent with the best CO2 uptake performance was supported by a mixture of Al2O3 and Y2O3, and exhibited a CO2 uptake of 0.61 g CO2/g CaO after 10 cycles of calcination and carbonation under practically relevant operating temperatures, which exceeded the CO2 uptake of limestone by more than 350%.

MCPath: Monte Carlo path generation approach to predict likely allosteric pathways and functional residues.

Allosteric mechanism of proteins is essential in biomolecular signaling. An important aspect underlying this mechanism is the communication pathways connecting functional residues. Here, a Monte Carlo (MC) path generation approach is proposed and implemented to define likely allosteric pathways through generating an ensemble of maximum probability paths. The protein structure is considered as a network of amino acid residues, and inter-residue interactions are described by an atomistic potential function. PDZ domain structures are presented as case studies. The analysis for bovine rhodopsin and three myosin structures are also provided as supplementary case studies. The suggested pathways and the residues constituting the pathways are maximally probable and mostly agree with the previous studies. Overall, it is demonstrated that the communication pathways could be multiple and intrinsically disposed, and the MC path generation approach provides an effective tool for the prediction of key residues that mediate the allosteric communication in an ensemble of pathways and functionally plausible residues. The MCPath server is available at http://safir.prc.boun.edu.tr/clbet_server.

Bio-Inspired Micro- and Nano-Scale Surface Features Produced by Femtosecond Laser-Texturing Enhance TiZr-Implant Osseointegration.

Surface design plays a critical role in determining the integration of dental implants with bone tissue. Femtosecond laser-texturing has emerged as a breakthrough technology offering excellent uniformity and reproducibility in implant surface features. However, when compared to state-of-the-art sandblasted and acid-etched surfaces, laser-textured surface designs typically underperform in terms of osseointegration. This study investigated the capacity of a bio-inspired femtosecond laser-textured surface design to enhance osseointegration compared to state-of-the-art sandblasted & acid-etched surfaces. Laser-texturing facilitates the production of an organized trabeculae-like microarchitecture with superimposed nano-scale laser-induced periodic surface structures on both 2D and 3D samples of titanium-zirconium-alloy. Following a boiling treatment to modify the surface chemistry, improving wettability to a contact angle of 10°, laser-textured surfaces enhance fibrin network formation when in contact with human whole blood, comparable to state-of-the-art surfaces. In vitro experiments demonstrate that laser-textured surfaces significantly outperform state-of-the-art surfaces with a 2.5-fold higher level of mineralization by bone progenitor cells after 28 days of culture. Furthermore, in vivo evaluations reveal superior biomechanical integration of laser-textured surfaces after 28 days of implantation. Notably, during abiological pull-out tests, laser-textured surfaces exhibit comparable performance, suggesting that the observed enhanced osseointegration is primarily driven by the biological response to the surface. This article is protected by copyright. All rights reserved.

Of Glasses and Crystals: Mitigating the Deactivation of CaO-Based CO2 Sorbents through Calcium Aluminosilicates.

CaO-based sorbents are cost-efficient materials for high-temperature CO2 capture, yet they rapidly deactivate over carbonation-regeneration cycles due to sintering, hindering their utilization at the industrial scale. Morphological stabilizers such as Al2O3 or SiO2 (e.g., introduced via impregnation) can improve sintering resistance, but the sorbents still deactivate through the formation of mixed oxide phases and phase segregation, rendering the stabilization inefficient. Here, we introduce a strategy to mitigate these deactivation mechanisms by applying (Al,Si)Ox overcoats via atomic layer deposition onto CaCO3 nanoparticles and benchmark the CO2 uptake of the resulting sorbent after 10 carbonation-regeneration cycles against sorbents with optimized overcoats of only alumina/silica (+25%) and unstabilized CaCO3 nanoparticles (+55%). 27Al and 29Si NMR studies reveal that the improved CO2 uptake and structural stability of sorbents with (Al,Si)Ox overcoats is linked to the formation of glassy calcium aluminosilicate phases (Ca,Al,Si)Ox that prevent sintering and phase segregation, probably due to a slower self-diffusion of cations in the glassy phases, reducing in turn the formation of CO2 capture-inactive Ca-containing mixed oxides. This strategy provides a roadmap for the design of more efficient CaO-based sorbents using glassy stabilizers.

CuO-based materials for thermochemical redox cycles: the influence of the formation of a CuO percolation network on oxygen release and oxidation kinetics.

Thermochemical redox cycles such as chemical looping combustion (CLC) are an economically promising CO2 capture technology that rely on the combustion of a hydrocarbon fuel with lattice oxygen that is derived from a solid oxygen carrier. The oxygen carrier is typically regenerated with air. To increase the agglomeration resistance and redox stability of the oxygen carriers, the active phase is often stabilized with high Tammann temperature ceramics, resulting in the formation of so-called cermet structures. It has been hypothesized that the redox performance of the cermets depends critically on the conduction pathways for solid-state ionic diffusion and the activation energy for charge transport. Here, we investigate the influence of the formation of a percolation network on the electrical conductivity and the rate of oxidation for CeO2-stabilized Cu. We found that for oxygen carriers that contained 60 wt. % CuO, the charge transport occurred predominately via Cu/CuO conduction pathways. Below the percolation threshold of CuO, the conduction of charge carriers took place via CeO2 grains, which formed a continuous network. The measurements of charge transport and redox characteristics confirmed that the activation energy for charge transport through the cermet increased with decreasing Cu content. This indicates that the solid-state diffusion of charge carriers plays an important role during re-oxidation. Supplementary Information: The online version contains supplementary material available at 10.1007/s43938-022-00013-2.

Na-ß-Al2O3 stabilized Fe2O3 oxygen carriers for chemical looping water splitting: correlating structure with redox stability.

Chemical looping is an emerging technology to produce high purity hydrogen from fossil fuels or biomass with the simultaneous capture of the CO2 produced at the distributed scale. This process requires the availability of stable Fe2O3-based oxygen carriers. Fe2O3-Al2O3 based oxygen carriers exhibit a decay in the H2 yield with cycle number, due to the formation of FeAl2O4 that possesses a very low capacity for water splitting at typical operating conditions of conventional chemical looping schemes (700-1000 °C). In this study, the addition of sodium (via a sodium salt) in the synthesis of Fe2O3-Al2O3 oxygen carriers was assessed as a means to counteract the cyclic deactivation of the oxygen carrier. Detailed insight into the oxygen carrier's structure was gained by combined X-ray powder diffraction (XRD), X-ray absorption spectroscopy (XAS) at the Al, Na and Fe K-edges and scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDX) analyses. The addition of sodium prevented the formation of FeAl2O4 and stabilized the oxygen carrier via the formation of a layered structure, Na-ß-Al2O3 phase. The material, i.e. Na-ß-Al2O3 stabilized Fe2O3, showed a stable H2 yield of ca. 13.3 mmol g-1 over 15 cycles.

Novel sodalite stabilized zero-valent iron for super stable and outstanding efficiency in activating persulfate for organic pollutants fast removal.

In this study, novel porous sodalite (SOD) was synthesized through Reactive Oxidation Species (ROS) route from industrial waste lithium silicon fume (LSF) to stabilize nZVI (SOD@nZVI), and used as an outstanding persulfate (PS) activator for efficient organic degradation. Characterization results revealed nZVI evenly distributed on SOD via ion-exchange, and the fabricated SOD@nZVI exhibited high stability and superior reactivity over a wide pH range of 2-12 during oxidation reaction. The mechanism responsible for fast organic degradation in the SOD@nZVI+PS system was carefully investigated, and weak magnetic field (WMF) and friction were found to contribute to improved SOD@nZVI performance. The fast redox cycle of Fe2+/Fe3+ on SOD@nZVI can be stimulated by changing the mixing condition and altering the friction layer to harvest mechanical energy during the reaction, which can maximum persulfate activation to generate more reactive radicals for organic fast degradation. This study is of great significance, as it offers a practical route turning waste into excellent PS activator for in-situ organic pollution remediation, as well as proposing a new idea to maximum PS activation performance by manipulating the inner lining of reactor.

Photoelectrochemical glycerol oxidation on Mo-BiVO4 photoanodes shows high photocharging current density and enhanced H2 evolution.

Mo-doped BiVO4's lower efficiency can be attributed in part to exciton recombination losses. Recombination losses during photoelectrochemical water oxidation can be eliminated by using glycerol as a hole acceptor. This results in an enhanced photocurrent density. In this research, we present the synthesis of a Mo-doped BiVO4 photoelectrode with a greater photocurrent density than a traditional pristine photoanode system. Increased photon exposure duration in the presence of glycerol leads to 8 mA cm-2 increase in photocurrent density due to the creation of a capacitance layer and a decrease in charge transfer resistance on the photoelectrode in a neutral-phosphate buffer solution thus confirming the photo charging effect. Glycerol photooxidation improves the photoelectrode's rate of hydrogen evolution. Research into the effects of electrolyte and electrode potential on photoelectrodes has revealed that when the applied potential increases, the light absorbance behaviour changes following its absorption distribution over the applied potential. Under a transmission electron microscope (TEM), a unique dynamical crystal fringe pattern is found in the nanoparticles scratched from the photoelectrode.

One-step fabrication of oxygen vacancy-enriched Fe@Ti/C composite for highly efficient degradation of organic pollutants through persulfate activation.

In this work, cost-effective, magnetic carbon-supported Fe@Ti composite (Fe@Ti/Cs) with abundant active sites was synthesized by one-step carbothermal reduction of ilmenite with the assistance of microwave oven and utilized as a highly efficient persulfate (PS) activator for the wastewater purification. The coexistence of Fe0/2+/3+, Ti3+/4+ and oxygen vacancies on Fe@Ti/Cs was found to favor for the electron transfer to PS, which facilitate the generation of reactive oxygen species (ROS). Catalytic experiment results showed that the Fe@Ti/C-4 produced from ilmenite/carbon with a mass ratio of 4:1 exhibited the best catalytic activation performance towards PS for the degradation of Rhodamine B (RhB). Usage of merely 0.12 g/L Fe@Ti/C-4 enabled the removal of 94.01% RhB (200 mg/L) within 30 min in the PS containing system, significantly outperforming ilmenite + PS (29.29%) and carbon + PS (49.91%) systems tested under the same conditions. The physico-chemical properties of the produced Fe@Ti/Cs before and after the reaction were carefully characterized. Radical scavenging experiments and electron paramagnetic resonance (EPR) analysis were carried out to better understand the underlying mechanism. The results indicate that oxygen vacancies in Fe@Ti/C-4 promoted the electron transfer and participated in the transition metal redox cycle to generate ROS in the PS-containing system, which was highly efficient for degrading RhB into small molecules and finally enabling mineralization. This work offers a new perspective for designing highly efficient and stable PS activators with long life derived from natural ore for environmental remediation.

Structural insight into an atomic layer deposition (ALD) grown Al2O3 layer on Ni/SiO2: impact on catalytic activity and stability in dry reforming of methane.

The development of stable Ni-based dry reforming of methane (DRM) catalysts is a key challenge owing to the high operating temperatures of the process and the propensity of Ni for promoting carbon deposition. In this work, Al2O3-coated Ni/SiO2 catalysts have been developed by employing atomic layer deposition (ALD). The structure of the catalyst at each individual preparation step was characterized in detail through a combination of in situ XAS-XRD, ex situ 27Al NMR and Raman spectroscopy. Specifically, in the calcination step, the ALD-grown Al2O3 layer reacts with the SiO2 support and Ni, forming aluminosilicate and NiAl2O4. The Al2O3-coated Ni/SiO2 catalyst exhibits an improved stability for DRM when compared to the benchmark Ni/SiO2 and Ni/Al2O3 catalysts. In situ XAS-XRD during DRM together with ex situ Raman spectroscopy and TEM of the spent catalysts confirm that the ALD-grown Al2O3 layer suppresses the sintering of Ni, in turn reducing also coke formation significantly. In addition, the formation of an amorphous aluminosilicate phase by the reaction of the ALD-grown Al2O3 layer with the SiO2 support inhibited catalysts deactivation via NiAl2O4 formation, in contrast to the reference Ni/Al2O3 system. The in-depth structural characterization of the catalysts provided an insight into the structural dynamics of the ALD-grown Al2O3 layer, which reacts both with the support and the active metal, allowing to rationalize the high stability of the catalyst under the harsh DRM conditions.

Ultrafast removal of Cu(II) by a novel hierarchically structured faujasite-type zeolite fabricated from lithium silica fume.

Novel hierarchically structured Faujasite Type (FAU) zeolite was fabricated from industrial waste lithium silica fume (LSF) via hydrothermal method without the addition of templates. The FAU zeolites exhibited spherical filler morphology with maximum surface area of 372.8 m2/g, enriched microporosity (0.164 cm3/g), and abundant mesoporosity. Owing to its unique structure, the FAU zeolite allowed ultrafast diffusion and rapid trap of copper ion inside the cages of zeolite crystals, and achieved maximum removal (78.76%) of Cu(II) within the very first 2 min, with adsorption rate constant 5.46-6.27 times greater than that of mesoporous commercial zeolite (CZ) between 15 and 45 °C. The physico-chemical structures of the FAU zeolites were carefully studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier Transform Infrared Spectrometry (FT-IR), surface area analyzer (BET) and X-ray photoelectron spectroscopy (XPS). The maximum qe toward Cu(II) achieved by FAU zeolite (i.e., Z9, S/A of 9) featuring a qe of 94.46 mg/g at 25 °C as per calculated from Langmuir model, which is more than twice amount achieved by CZ (39.15 mg/g). Z9 also showed outstanding selectivity for Cu(II) over various coexisting ions. The saturated Z9 can be regenerated with a mild washing procedure, and the spent zeolite can be reused as effective antibacterial agent. This work proposes a cost-effective and green synthesis route for the hierarchically structured zeolite with high copper selective removal capacity from industrial waste.

Effect of molten sodium nitrate on the decomposition pathways of hydrated magnesium hydroxycarbonate to magnesium oxide probed by in situ total scattering.

The effect of NaNO3 and its physical state on the thermal decomposition pathways of hydrated magnesium hydroxycarbonate (hydromagnesite, HM) towards MgO was examined by in situ total scattering. Pair distribution function (PDF) analysis of these data allowed us to probe the structural evolution of pristine and NaNO3-promoted HM. A multivariate curve resolution alternating least squares (MCR-ALS) analysis identified the intermediate phases and their evolution upon the decomposition of both precursors to MgO. The total scattering results are discussed in relation with thermogravimetric measurements coupled with off-gas analysis. MgO is obtained from pristine HM (N2, 10 °C min-1) through an amorphous magnesium carbonate intermediate (AMC), formed after the partial removal of water of crystallization from HM. The decomposition continues via a gradual release of water (due to dehydration and dehydroxylation) and, in the last step, via decarbonation, leading to crystalline MgO. The presence of molten NaNO3 alters the decomposition pathways of HM, proceeding now through AMC and crystalline MgCO3. These results demonstrate that molten NaNO3 facilitates the release of water (from both water of crystallization and through dehydroxylation) and decarbonation, and promotes the crystallization of MgCO3 and MgO in comparison to pristine HM. MgO formed from the pristine HM precursor shows a smaller average crystallite size than NaNO3-promoted HM and preserves the initial nano-plate-like morphology of HM. NaNO3-promoted HM was decomposed to MgO that is characterized by a larger average crystallite size and irregular morphology. Additionally, in situ SEM allowed visualization of the morphological evolution of HM promoted with NaNO3 at a micrometre scale.

Facile synthesis of novel 3D flower-like magnetic La@Fe/C composites from ilmenite for efficient phosphate removal from aqueous solution.

In this study, a novel 3D flower-like La@Fe/C magnetic composite was successfully synthesized by carbothermal reduction of ilmenite via microwave radiation. The physico-chemical properties of the composite were investigated. The results showed that La@Fe/C features a 3D flower-like morphology with an S BET and V mic of 114 m2 g-1 and 0.017 cm3 g-1, respectively. Zerovalent iron and metal oxides were detected by XRD and XPS on the surface of the adsorbent, which formed as a result of carbothermal reduction of ilmenite using coconut shell-based carbon followed by the introduction of lanthanum. This resultant magnetic La@Fe/C exhibited remarkable phosphate selectivity performance even in the presence of a 50-fold excess of competing ions, which is superior to the pristine ilmenite and coconut activated carbon. Adsorption isotherms and adsorption kinetics fitted well with the Langmuir model and pseudo-second-order model, respectively. A thermodynamic study indicated that the adsorption of phosphate was spontaneous and endothermic. The adsorption-regeneration cyclic experiments of the La@Fe/C composite demonstrated a good level of recyclability. These results indicated that carbothermal reduction of ilmenite followed by the introduction of lanthanum could result in highly efficient and recoverable magnetic particles for the removal of phosphate from wastewater.

Atomic Layer Deposition of a Film of Al2O3 on Electrodeposited Copper Foams To Yield Highly Effective Oxygen Carriers for Chemical Looping Combustion-Based CO2 Capture.

A rapid electrochemical deposition protocol is reported to synthesize highly porous Cu foams serving as model oxygen carriers for chemical looping, a promising technology to reduce anthropogenic CO2 emission. To overcome the sintering-induced decay in the oxygen carrying capacity of unsupported Cu foams, Al2O3 films of different thicknesses (0.1-25 nm) are deposited onto the Cu foams via atomic layer deposition (ALD). An ALD-grown Al2O3 overcoat of 20 nm thickness (∼4 wt % Al2O3) is shown to be sufficient to ensure excellent redox cyclic stability. Al2O3-coated Cu foams exhibit a capacity retention of 96% over 10 redox cycles, outperforming their coprecipitated counterpart (equal Al2O3 content). The structural evolution of the stabilized foams is probed in detail and compared to benchmark materials to elucidate the stabilizing role of the Al2O3 overcoat. Upon heat treatment, the initially conformal Al2O3 overcoat induces a fragmentation of large Cu(O) branches into small particles. After multiple redox cycles, the Al2O3 overcoat transforms into sub-micrometer-sized grains of aluminum-containing phases (δ-Al2O3, CuAl2O4, and CuAlO2) that are dispersed homogeneously within the CuO matrix. Finally, the diffusion of Cu through an Al2O3 layer upon heat treatment in an oxidizing atmosphere is probed in model thin films.

Optimization of the structural characteristics of CaO and its effective stabilization yield high-capacity CO2 sorbents.

Calcium looping, a CO2 capture technique, may offer a mid-term if not near-term solution to mitigate climate change, triggered by the yet increasing anthropogenic CO2 emissions. A key requirement for the economic operation of calcium looping is the availability of highly effective CaO-based CO2 sorbents. Here we report a facile synthesis route that yields hollow, MgO-stabilized, CaO microspheres featuring highly porous multishelled morphologies. As a thermal stabilizer, MgO minimized the sintering-induced decay of the sorbents' CO2 capacity and ensured a stable CO2 uptake over multiple operation cycles. Detailed electron microscopy-based analyses confirm a compositional homogeneity which is identified, together with the characteristics of its porous structure, as an essential feature to yield a high-performance sorbent. After 30 cycles of repeated CO2 capture and sorbent regeneration, the best performing material requires as little as 11 wt.% MgO for structural stabilization and exceeds the CO2 uptake of the limestone-derived reference material by ~500%.

Multishelled CaO Microspheres Stabilized by Atomic Layer Deposition of Al2 O3 for Enhanced CO2 Capture Performance.

CO2 capture and storage is a promising concept to reduce anthropogenic CO2 emissions. The most established technology for capturing CO2 relies on amine scrubbing that is, however, associated with high costs. Technoeconomic studies show that using CaO as a high-temperature CO2 sorbent can significantly reduce the costs of CO2 capture. A serious disadvantage of CaO derived from earth-abundant precursors, e.g., limestone, is the rapid, sintering-induced decay of its cyclic CO2 uptake. Here, a template-assisted hydrothermal approach to develop CaO-based sorbents exhibiting a very high and cyclically stable CO2 uptake is exploited. The morphological characteristics of these sorbents, i.e., a porous shell comprised of CaO nanoparticles coated by a thin layer of Al2 O3 (<3 nm) containing a central void, ensure (i) minimal diffusion limitations, (ii) space to accompany the substantial volumetric changes during CO2 capture and release, and (iii) a minimal quantity of Al2 O3 for structural stabilization, thus maximizing the fraction of CO2 -capture-active CaO.