Diffusion-controlled Stage Research Articles

Nitrate-promoted gas–solid reactions of H2 and CaCO3 for mid-temperature integrated CO2 capture and methanation

Integrated CO2 capture and methanation (ICCM) technology has attracted increasing attention for Carbon Neutrality. However, in the mid-temperature ICCM studies dominated by MgO, which involves the gas–gas catalytic pathway, the problems of high CO2 escape and low CH4 yield are common. Replacing MgO with CaO reduced CO2 escape because the reaction proceeded via the gas–solid pathway. However, the lower CaCO3 conversion rate limits its further applications. Here, we present an ICCM process with efficient CaCO3 conversion using alkali metal nitrates (KNO3, LiNO3, and (Li-K)NO3) to promote Ru/CeO2-CaO. The results showed that the doping of nitrates led to a decrease in the specific surface area of CaO, thus losing part of the CO2 capture performance. On the other hand, forming the molten liquid layer facilitated the gas–solid reaction between CaCO3 and H2, which improved the CaCO3 conversion. Compared with the Ru/CeO2-Neat CaO without nitrate promotion, the CaCO3 conversion of Ru/CeO2-KNO3/CaO was increased by 42% and CH4 yield by 52% after five ICCM cycles. Furthermore, kinetic analysis and in situ DRIFTS experiments demonstrated that molten KNO3 facilitated mass transfer in the diffusion-controlled stage of direct CaCO3 hydrogenation.

Quantitative characterization of the contribution of electrogenerated active species for NH+ 4-N oxidation on Ti/RuO2-IrO2 anode

The contribution of active species for ammonia nitrogen (NH4+-N) oxidation has received much attention in recent decades through electrocatalytic oxidation (EO) technology. Here we describe the strong NH4+-N removal capacity (more than 98 %) with NaCl as electrolyte of Ti/RuO2-IrO2 anode. Electrochemical tests were used to characterize the excellent NH4+-N degradation performance of Ti/RuO2-IrO2 anode in presence of chlorides. The values of electron transfer number (n = 1.02) and transfer coefficient (α = 0.42) show that the reaction is in the diffusion control stage, which is more conducive to the degradation of NH4+-N. Additionally, three active species (•OH, Cl•, and ClO•) formation is related to the adsorption energy (obtained by density functional theory (DFT) calculation) during the electrolysis process. The difference charge density and density of state (DOS) calculation indicate that the O − in ClO• is more likely to break and react with pollutants in water, which is consistent with the results of active species detection experiments. The combination of kinetics (Tafel) and thermodynamics (adsorption energy) shows that the variation of Tafel slope is affected by the coverage of active species on the electrode surface.

Eco-friendly, sustainable and porous eggshell/tea waste-derived CaO nanoparticles as a high-temperature CO2 sorbent: Fabrication and textural/morphological evaluation

The CaO-based sorbents suffer from a high-intensity sintering rate and require costly promoters to improve their CO2 capture capacity through the Calcium Looping (CaL) technique. Herein, for the first time, the eco-friendly and efficient eggshell-derived CaO sorbents were promoted with tea waste for the CO2 capture process. 0, 2.5, and 5 wt.% of ball-milled tea waste nanoparticles (NPs) were merged with sieved eggshell-based NPs throughly. Their CO2 capture activity was evaluated under severe calcination conditions, including calcination under 100 vol.% CO2 for 5 min at 950 °C. According to the textural/morphological data, 92 % and 89.8 % enhancement were seen for the prepared sample's surface area and pore volume, including 5 wt.% tea waste NPs. Additionally, the average grain size of as-prepared specimens decreased from 39.3 nm to 25.2 nm. Furthermore, the sorbent having 5 wt.% tea waste presented the multicyclic durability of 48.1 % and the average CO2 uptake capacity of 0.133 g CO2/g sorbent during fifteen multiple carbonation/calcination cycles under severe calcination conditions. The incorporation of 5 wt.% tea waste as the structural promoter resulted in 100 % and 58 % improvements in the capture potential of CaO at kinetically- and diffusion-controlled carbonation stages of the 15th cycle.

Sigma phase kinetics in DSS filler metals: A comparison of sigma phase formation in the as-welded microstructure of super duplex stainless steel and hyper duplex stainless steel

This study investigates and compares the kinetics of sigma phase formation in established Super Duplex Stainless Steel (SDSS) and recently developed Hyper Duplex Stainless Steel (HDSS) filler metal wires. Experimental sigma phase time-temperature-transformation (TTT) maps were developed, revealing nearly equivalent interface area/volume, resulting in similar sigma phase kinetics for 1% volume despite the higher Cr and Mo content in HDSS. However, the growth rate to 5% and 10% sigma phase volumes was slightly higher in HDSS. The sigma phase kinetics in both SDSS and HDSS were analyzed using the exponential Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach based on experimental TTT data. Linearized plots from the JMAK calculations showed a transition in kinetics mechanism from eutectoid decomposition and interface-controlled growth to a diffusion-controlled growth stage in both materials. The higher volumes and morphologies of the sigma phase were found to be diffusion-dependent, mainly occurring during the second kinetics stage. The influence of HDSS's higher Cr and Mo content on the growth rate was observed for these higher volumes. For applications within the 1% sigma phase limit, both wires exhibited equivalent susceptibility to sigma phase formation, regardless of the higher alloying in HDSS.

Multiple kinetic processes of lamellar growth in crystallization of stretched lightly crosslinked polyethylene

The growth of polymer crystals is accompanied by the change of interior conditions as time evolves. Therefore, its underlying mechanism should be time-dependent. Here, we investigate the process of lamellar growth by measuring stretched lightly crosslinked high-density polyethylene samples with in situ small-angle X-ray scattering and wide-angle X-ray diffraction. Two analysis methods are used to track the lamellar radius. It is found that the lamellar growth sequentially undergoes three stages, i.e., the interface-controlled stage, the diffusion-controlled stage, and the crystal perfection stage through Ostwald ripening mechanism. The transition between the first and the second stages is related to the competition between the diffusion of chains towards the growth surface and the consumption of chains at the surface in the ideal interfacial kinetics. This transition is significantly affected by the yielding of the sample. The second transition corresponds to the depletion of crystallizable chains, and is directly reflected by the decrease of the polydispersity of lamella radius. These results highlight the importance of the chain consumption in determining the mechanism of lamellar growth.

Effects of CaO, Al2O3 and MgO on Kinetics of Lead-Rich Slag Reduction

Lead-rich slag as a green feedstock can be used in a blast furnace or smelting reduction furnace to produce lead metal. It is desirable to understand the reduction mechanisms of lead-rich slag to optimize the reduction operations. The volume of CO/CO2 gases was continuously measured in the experiments to determine the reduction degree of lead-rich slag by carbon. The effects of CaO, Al2O3 and MgO on reaction kinetics of lead-rich slag with carbon were investigated in the temperature range 1073 to 1473 K. The activation energies of the reduction were determined experimentally in the chemically controlled and diffusion-controlled stages, and the reduction mechanism is analyzed using experimental results and thermodynamic calculations. It was found that the activation energies at the chemically controlled and diffusion-controlled stages decrease with increasing optical basicity. CaO and MgO have a similar behavior to accelerate the reduction of the lead-rich slag by carbon. In contrast, Al2O3 can increase the activation energies at both chemically controlled and diffusion-controlled stages resulting in a slow reaction.

Revisiting transient coarsening kinetics: a new framework in the Lifshitz-Slyozov-Wagner space

Phase coarsening in multiphase materials is a fundamental and crucial process in the study of microstructure evolution, for which a thorough understanding of kinetics can make a significant contribution to material processing and performance design. In this work, a new framework in the dimensionless Lifshitz-Slyozov-Wagner space is developed to study the kinetics of transient coarsening co-controlled by interface and matrix diffusion. The dynamic equations for individual particles are derived from the thermodynamic extremal principle, in consideration of energy dissipations by matrix diffusion, interface migration/reaction, and trans-interface diffusion. The effects of initial particle size distribution and finite volume fractions are clarified. Different from the conventional viewpoints, the time for transient coarsening is found to change non-monotonically with the width and tail length of the initial distribution. The ultralong transient coarsening with ‘quasi-steady’ distributions can occur for systems initiated from both the ‘wide & long tail’ and ‘narrow & short tail’ distributions. Furthermore, this work proves the existence of a unique attractor state for the steady stage and reveals the numerical origin of ‘quasi-steady’ distributions, which answers Brown's unsolved puzzle for years [LC Brown. Acta Metall 1989;37:71]. Finally, an increase in volume fraction is shown to directly shorten the transient stage dominated by single mechanism (matrix diffusion or interface), but indirectly delay the transition from the interface-dominated state to the diffusion-controlled stage. These findings not only offer new insights into the previous observations in microgravity experiments [VA Snyder, J Alkemper, PW Voorhees, Acta Mater 2001;23:699], but also theoretically describe the limiting coarsening behaviors at ultrahigh volume fractions [H Yan, KG Wang, ME Glicksman. Acta Mater 2022;117964].

Mineralization characteristics of coal fly ash in the transition from non-supercritical CO2 to supercritical CO2

The accelerated mineralization of fly ash is a potential way to achieve CO2 emissions reduction. However, the slow reaction at the diffusion control stage is the bottleneck. Due to the strong diffusion of supercritical CO2, it has been to strengthen mineralization, but the degree of improvement in mineralization efficiency and the changes that take place in the transition from non-supercritical to supercritical CO2 are not clear. In the mineralization process, CaO in the ash reacts with CO2 to form CaCO3. In order to exclude the influence of other alkaline oxides, powdered and block CaO were used to research the mechanism, and experiments were then carried out on samples of fly ash with different CaO content. Firstly, powdered CaO was used to conduct dry and wet mineralization experiments. In dry mineralization, the mineralization efficiency of the process changes in two stages as the pressure increases, first undergoing a gentle-increase and then a rapid one. Diffusion depth experiments on block CaO show that the supercritical diffusion depth is higher than the non-supercritical diffusion depth by a factor of 1.22, indicating that supercritical CO2 can improve the degree of mineralization in diffusion stage. The presence of water could promote mineralization. In wet mineralization, the efficiency of the process changes in three stages as the pressure increases, with first a gentle increase then a more rapid one and finally an attenuated rate of increase. The supercritical mineralization efficiency at 8 MPa was 55.27%, a factor of 2.09 larger than for non-supercritical mineralization at 3 MPa (26.39%). This is because that supercritical CO2 has increased the diffusion and greatly improved solubility in water. The results of DFT calculations show that H2O can promote the adsorption of CO2 by CaO, which is one of the reasons why water promotes mineralization. Finally, wet mineralization experiments on fly ash show that at 8 MPa, the mineralization efficiencies of HB, SD, SX and YN fly ashes are 1.94, 1.30, 2.03 and 1.62 times their values at 3 MPa. Although the difference in efficiency is affected by the CaO content, supercritical CO2 can effectively improve the mineralization efficiency.

Supercritical CO2 coupled with mechanical force to enhance carbonation of fly ash and heavy metal solidification

Accelerated carbonation of fly ash is a potential way to achieve CO2 emission reduction and heavy metal solidification. Slow conversion in the diffusion control stage is the bottleneck of the carbonation technical route. Based on the strong diffusion and permeability of supercritical CO2, and the modification of mechanical force to produce more fresh surfaces and pores, a method consisting of supercritical CO2 coupled with mechanical force was carried out to strengthen the carbonation of fly ash. Research results show that the carbonation efficiency of fly ash under supercritical CO2 is generally higher than under low-pressure conditions, and carbonation under supercritical CO2 can effectively stabilize heavy metals in fly ash. In this work, the optimal amount of carbon sequestration under low-pressure was found to be 42.3 g-CO2/kg-fly ash (g/kg), with a carbonation efficiency of 18.65%. Under the supercritical condition of 8 MPa, the maximum carbon sequestration by fly ash is 54.9 g/kg, and the carbonation efficiency is 24.20%. In experiments with mechanical ball milling modification, the order of carbonation efficiency is: wet milling modified ashes > dry milling modified ashes > raw ashes. Additionally, carbonation has an obvious inhibitory effect on the leaching of Pb, Cr and Cd from fly ash.

Effect of Extended Carbonation Curing on the Properties of γ-C2S Compacts and Its Implications on the Multi-Step Reaction Mechanism

Accelerated carbonation of the cement-based materials has attracted worldwide attention due to the advantages of rapid strength gain and CO₂ sequestration. This work was designed to investigate the mechanism of γ-C₂S compacts under extended carbonation curing to further develop the accelerated carbonation technology. Based on the variation of the mechanical properties, microstructure, and the phase assemblages through the extended carbonation, a multi-step reaction mechanism is proposed in this work. The process can be divided into three stages: phase-boundary-controlled stage; product layer CO₂ diffusion-controlled stage; and CO₂ diffusion and calcium ion dissolution-controlled stage. Correlation between the calcium carbonate polymorph and the controlling factors is also investigated, in which the high calcium ion concentration is beneficial to the formation of calcite. Meanwhile, the stepwise pressurization curing regime based on the multi-steps is proposed to increase the strength obviously, which further verifies the mechanism of multi-step reactions.

Synthesis and evaluation in the CO2 capture process of potassium-modified lithium silicates produced from steel metallurgical slags

Lithium silicate-based CO2 sorbents were successfully synthesized using steel metallurgical slags as silica sources, with and without K2CO3 addition (10−30 wt%). The CO2 capture efficiency improved with K2CO3 addition because of the formation of a eutectic phase between K2CO3 and Li2CO3, which facilitated CO2 diffusion into the material bulk. The best capture capacity value (104 mgCO2/gmaterial) was obtained using the material produced from steel metallurgical slag with 20 wt% K2CO3 (SK0.2) at 600 °C and with either 5 or 20 vol% CO2. In addition, the CO2 capture rate increased up to four orders of magnitude in the diffusion-controlled stage compared to material prepared with fumed silica or F (K2 = 2.89 E-3 s−1 for SK0.2 and K2 = 4.21 E-8 s−1 for F). After 20 adsorption-desorption cycles using 20 vol% CO2, the CO2 capture capacity of SK0.2 was reduced by only 10 %, indicating excellent thermal stability.

Characterization based analysis on TiAl3 intermetallic phase layer growth phenomenon and kinetics in diffusion bonded Ti/TiAl3/Al laminates

In this article, new insights towards the layer growth phenomenon of TiAl3 phase in alternative Ti/Al based multilayer metal intermetallic laminate is discussed. Ti/Al multilayered metal intermetallic laminates were prepared at two different temperatures of 550 and 575 °C using solid-state diffusion bonding technique. TiAl3 was the only intermetallic layer formed along the Ti/Al metallic layer interfaces at the processed temperatures. The TiAl3 intermetallic layer grows (thickens) in two stages with respect to diffusion duration with each stage controlled by different growth phenomena viz. chemical reaction-controlled and diffusion-controlled growth respectively. The initial nucleation of TiAl3 grains takes place by chemical reaction between Ti and Al atoms without any specific nucleation sites in the intermix zone. Whereas, the triple junctions of the initially nucleated TiAl3 grains acts as a preferred TiAl3 nucleation site for further layer growth during reaction-controlled growth stage. During diffusion-controlled growth, the preferred nucleation site shifts to Ti/TiAl3 and Al/TiAl3 interfaces which makes the TiAl3 layer growth to be predominantly controlled by the diffusivities of Ti and Al atoms. The growth kinetics study exhibits higher layer growth rate during diffusion-controlled growth stage which is mainly due to faster Al diffusion and higher TiAl3 nucleation rate at Ti/TiAl3 interface.

Preferential interdendritic oxidation of laser additively manufactured Inconel 718

Preferential interdendritic oxidation of as-built additively manufactured Inconel 718 is observed. Interdendritic depletion of Cr and enrichment of Ti are responsible for a slow formation of fine-grain Cr2O3 external scale that aids the establishment of a high-level oxygen partial pressure along the interdendrtic region. Incomplete oxidation of carbides results in a large volume expansion. Oxidation of Laves phases leads to a discontinuous NbO interlayer that facilitates countercurrent diffusion channels. Preferential interdendritic oxidation dramatically promotes oxidation kinetics of both transient- and diffusion-controlled stages. Measures to homogenize the composition and to control the primary precipitates are desired to improve the oxidation performance.

Modelling of a fluidized bed carbonator reactor for post-combustion CO2 capture considering bed hydrodynamics and sorbent characteristics

This manuscript presents a general model for the fluidized bed carbonator reactor of the Calcium Looping (CaL) process based on bed hydrodynamics, kinetics and sorbent properties. The model proposed relies on the Kunii–Levenspiel theory for circulating fluidized beds in the fast fluidization regime and considers recent findings on the CO2 capture properties of CaO, including the effects of the diffusion-controlled carbonation stage and CaO modification by means of additives. By performing a sensitivity analysis, it is found that the solids inventory in the carbonator and superficial gas velocity are the main operational and hydrodynamic factors affecting the CO2 capture efficiency. Decay constant of the fraction of solids in the lean region and fraction of solids in the dense region are also identified as two important model parameters. Model predictions are shown to agree with experimental results retrieved from pilot-scale tests. The main novelty of the model is the consideration of a CaO/Al2O3 composite either as main CO2 sorbent used in the carbonator or as a make-up flow fed into the calciner. Using CaO/Al2O3 as the main CO2 sorbent leads to a 14.17% loss of capture efficiency after 100 cycles compared to 72.81% when using limestone derived CaO. It is demonstrated that feeding a very low ratio (~0.1) of the CaO/Al2O3 composite or a rather high ratio (~5) of limestone as makeup flow, leads to a significant improvement of the capture efficiency. The results obtained may be relevant for optimizing CaL operation conditions to be used in power plants.

Fmoc-diphenylalanine-based hydrogels as a potential carrier for drug delivery

Abstract Self-assembled hydrogels from 9-fluorenylmethoxycarbonyl-modified diphenylalanine (Fmoc-FF) peptides were evaluated as potential vehicles for drug delivery. During self-assembly of Fmoc-FF, high concentrations of indomethacin (IDM) drugs were shown to be incorporated into the hydrogels. The β-sheet arrangement of peptides was found to be predominant in Fmoc-FF–IDM hydrogels regardless of the IDM content. The release mechanism for IDM displayed a biphasic profile comprising an initial hydrogel erosion-dominated stage followed by the diffusion-controlled stage. Small amounts of polyamidoamine dendrimer (PAMAM) added to the hydrogel (Fmoc-FF 0.5%–IDM 0.5%–PAMAM 0.03%) resulted in a more prolonged IDM release compared with Fmoc-FF 0.5%–IDM 0.5% hydrogel. Furthermore, these IDM-loaded hydrogels demonstrated excellent thixotropic response and injectability, which make them suitable candidates for use as injectable self-healing matrices for drug delivery.

General rate equation theory for gas–solid reaction kinetics and its application to CaO carbonation

The kinetics of reactions between gases and solids are typically modeled using shrinking-core or shrinking-pore theoretical frameworks, in which the formation of a uniform solid product layer covering the entire solid surface with a sharp interface between the solid reactant and the product is assumed. However, theories involving a uniform solid product layer cannot predict the kinetic transition behavior that occurs in some gas–solid reactions. This work proposes that the growth of solid product islands occurs instead of the progressive formation of a uniform solid product layer in traditional shrinking-core and shrinking-pore models and establishes a general rate equation theory to model the kinetics of gas–solid reactions for solid reactants of various shapes. The growth of the product islands is calculated using the rate equation theory and is integrated into the shrinking-core model and shrinking-pore model, in which the microstructure of the solid reactant is also considered. Elemental steps of chemical reaction, surface diffusion and product layer diffusion are included in the general rate equation theory. The kinetic parameters included in the model are chemical reaction rate constant ks, surface diffusion coefficient Ds, and product layer diffusion coefficient Dp. The resulting model is analyzed at the limits where either the chemical reaction or product layer diffusion is the rate-controlling step. At very small or very high Ds values, the rate equation theory is equal to the kinetics-controlled regime or diffusion-controlled regime in traditional models; therefore, the traditional models represent special cases of this theoretical rate equation model. At intermediate Ds values, the so-called two-stage kinetic behavior occurs. The transition from the fast initial stage to the diffusion-controlled stage depends on the value of Ds, with the conversion at the transition point increasing with increasing Ds. The rate equation theory is demonstrated to successfully predict the CaO carbonation kinetics under a wide range of experimental conditions including temperature, CO2 concentration, sorbent type, and amount of added inert supports as well as for systems that exhibit a temperature rise during the carbonation reaction The rate equation theory is integrated into a particle model to account for the external diffusion of gas around the particle and intraparticle diffusion as well as the effect of particle structural changes on intraparticle diffusion, such as the pore plugging phenomenon. The developed rate equation theory is an analytical model that can be easily used in reactor-scale modeling or computational fluid dynamics simulations.

Unconditionally blue: Curing epoxy with polyethylene glycol (PEG) surface-functionalized ZnxFe3-xO4 magnetic nanoparticles

Nanoparticles govern early (chemical-controlled) and late (diffusion-controlled) stages of epoxy crosslinking, respectively. Surface functionalization of nanoparticles with macromolecules was recognized as an effective route to compensate for inadequate diffusion-controlled crosslinking. However, the effect of bulk composition amended with cations having catalytic effect towards epoxy ring opening has remained hitherto undescribed. In this work, cathodic electrochemical method was applied to obtain naked iron oxide nanoparticles (IONPs), polyethylene glycol (PEG) capped IONPs (PEG-IONPs) and zinc-doped IONPs (Zn-doped PEG-IONPs) for evaluation of the effects of surface (alone) and surface-bulk (concurrent) modification of IONPs. Various techniques including FTIR, XRD, VSM, and FE-SEM were employed to probe into changes in the surface and bulk of nanoparticles. Cure Index calculated based on nonisothermal differential scanning calorimetry (DSC) allowed for labeling epoxy nanocomposites as Poor (Red) or Good (Blue) cured networks. Partial substitution of Fe2+ cations by Zn2+ in the bulk of Zn-doped PEG-IONPs with respect to PEG-IONPs labeled their corresponding epoxy nanocomposites in Blue and Red. Although at low and high heating rates epoxy/PEG-IONPs was labeled Red, epoxy/Zn-doped PEG-IONPs nanocomposites was unconditionally labeled Blue thanks to a more significant catalytic effect springing from Zn2+ cations in Zn-doped IONPs compared to hydroxyl groups alone in PEG-IONPs.

A Carbide Slag-Based, Ca12Al14O33-Stabilized Sorbent Prepared by the Hydrothermal Template Method Enabling Efficient CO2 Capture

Calcium looping is a promising technology to capture CO2 from the process of coal-fired power generation and gasification of coal/biomass for hydrogen production. The decay of CO2 capture activities of calcium-based sorbents is one of the main problems holding back the development of the technology. Taking carbide slag as a main raw material and Ca12Al14O33 as a support, highly active CO2 sorbents were prepared using the hydrothermal template method in this work. The effects of support ratio, cycle number, and reaction conditions were evaluated. The results show that Ca12Al14O33 generated effectively improves the cyclic stability of CO2 capture by synthetic sorbents. When the Al2O3 addition is 5%, or the Ca12Al14O33 content is 10%, the synthetic sorbent possesses the highest cyclic CO2 capture performance. Under harsh calcination conditions, the CO2 capture capacity of the synthetic sorbent after 30 cycles is 0.29 g/g, which is 80% higher than that of carbide slag. The superiority of the synthetic sorbent on the CO2 capture kinetics mainly reflects at the diffusion-controlled stage. The cumulative pore volume of the synthetic sorbent within the range of 10–100 nm is 2.4 times as high as that of calcined carbide slag. The structure of the synthetic sorbent reduces the CO2 diffusion resistance, and thus leads to better CO2 capture performance and reaction rate.

Comparison of diffusion kinetics during isothermal solidification and homogenisation stages of transient liquid phase bonding

ABSTRACTA numerical model that incorporates variable diffusion coefficient is used to study and compare the kinetics of solute penetration during diffusion-controlled isothermal solidification and homogenisation stages of transient liquid phase (TLP) bonding in planar and non-planar (cylindrical and spherical) systems. The study reveals new information regarding key differences between the two stages, depending on whether the diffusion coefficient is constant or varies with composition. Notwithstanding the fact that non-planar solid–liquid interfaces cause the solute penetration to depart from a linear relationship with , known as parabolic-law behaviour, during isothermal solidification, the penetration kinetics in all the systems follow the parabolic-law during the homogenisation stage, when the diffusivity is constant. Moreover, in the planar system, while a variation of diffusivity with concentration does not alter the solute penetration kinetics through deviation from the parabolic-law behaviour during the isothermal solidification, it causes a deviation during the homogenisation stage.

Accurate Control of Cage-Like CaO Hollow Microspheres for Enhanced CO2 Capture in Calcium Looping via a Template-Assisted Synthesis Approach.

Herein we report the development of synthetic CaO-based sorbents for enhanced CO2 capture in calcium looping via a template-assisted synthesis approach, where carbonaceous spheres (CSs) derived from hydrothermal reaction of starch are used as the templates. Cage-like CaO hollow microspheres are successfully synthesized only using urea as the precipitant, and the formation mechanism of this unique hollow microsphere structure is discussed deeply. Moreover, cage-like CaO hollow microspheres possess an initial carbonation conversion of 98.2% and 82.5% under a mild and harsh conditions, respectively. After the 15 cycles, cage-like CaO hollow microspheres still possess a carbonation value of 49.2% and 39.7% under the corresponding conditions, exceeding the reference limestone by 85.7% and 148.1%, respectively. Two kinetic models are used to explore the mechanism of carbonation reaction for cage-like CaO hollow microspheres, which are subsequently proved to be feasible for analysis of chemical-controlled stage and diffusion-controlled stage in the carbonation process. It is found the unique hollow microsphere structure can significantly reduce the activation energy of carbonation reaction according to the kinetic calculation. Furthermore, the energy and raw material consumptions related to the synthesis of cage-like CaO hollow microspheres are analyzed by the life cycle assessment (LCA) method.