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The crystal structures of lithium silicates. The largest balls (in pink) correspond to Li, the medium size balls (in yellow) stand for silicon while the smallest balls (in red) indicate O atoms. The c-axis is taken as the vertical axis for each structure.
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The lithium silicates have attracted scientific interest due to their potential use as high-temperature sorbents for CO2 capture. The electronic properties and thermodynamic stabilities of lithium silicates with different Li2O/SiO2 ratios (Li2O, Li8SiO6, Li4SiO4, Li6Si2O7, Li2SiO3, Li2Si2O5, Li2Si3O7, and α-SiO2) have been investigated by combining...
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... to the phase diagram of the ternary Li-Si-O system illustrated in Fig. 1 Fig. 2 and their corresponding experimental crystallographic structural data are summarized in Table 1. As shown in Fig. 2(a), Li 8 SiO 6 has a hexagonal structure with space group P6 3 cm (no. 185). 60 As discussed in our previous study, 23 lithium orthosilicate (Li 4 SiO 4 ) usually is found in a monoclinic structure with space group P2 1 ...
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... to the phase diagram of the ternary Li-Si-O system illustrated in Fig. 1 Fig. 2 and their corresponding experimental crystallographic structural data are summarized in Table 1. As shown in Fig. 2(a), Li 8 SiO 6 has a hexagonal structure with space group P6 3 cm (no. 185). 60 As discussed in our previous study, 23 lithium orthosilicate (Li 4 SiO 4 ) usually is found in a monoclinic structure with space group P2 1 /m (no. 11), but it also has another phase (g-Li 4 SiO 4 ) which is in triclinic structure with space group P% 1 (no. ...
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... 8 SiO 6 has a hexagonal structure with space group P6 3 cm (no. 185). 60 As discussed in our previous study, 23 lithium orthosilicate (Li 4 SiO 4 ) usually is found in a monoclinic structure with space group P2 1 /m (no. 11), but it also has another phase (g-Li 4 SiO 4 ) which is in triclinic structure with space group P% 1 (no. 2). As shown in Fig. 2(b Fig. 2(e) and (f): monoclinic with space group Ccc2 (no. 37) 64 and a meta-stable orthorhombic structure with space group Pbcn (no. 60). 65 Very recently, based on single crystal X-ray diffraction Kruger et al. 37 determined the structure of Li 2 Si 3 O 7 silicate sheets for which a space group Pmca (no. 57) was found as shown in Fig. ...
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... has a hexagonal structure with space group P6 3 cm (no. 185). 60 As discussed in our previous study, 23 lithium orthosilicate (Li 4 SiO 4 ) usually is found in a monoclinic structure with space group P2 1 /m (no. 11), but it also has another phase (g-Li 4 SiO 4 ) which is in triclinic structure with space group P% 1 (no. 2). As shown in Fig. 2(b Fig. 2(e) and (f): monoclinic with space group Ccc2 (no. 37) 64 and a meta-stable orthorhombic structure with space group Pbcn (no. 60). 65 Very recently, based on single crystal X-ray diffraction Kruger et al. 37 determined the structure of Li 2 Si 3 O 7 silicate sheets for which a space group Pmca (no. 57) was found as shown in Fig. 2(g). ...
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... in Fig. 2(b Fig. 2(e) and (f): monoclinic with space group Ccc2 (no. 37) 64 and a meta-stable orthorhombic structure with space group Pbcn (no. 60). 65 Very recently, based on single crystal X-ray diffraction Kruger et al. 37 determined the structure of Li 2 Si 3 O 7 silicate sheets for which a space group Pmca (no. 57) was found as shown in Fig. 2(g). Under ambient conditions, Li 2 O has an antifluorite structure with space group Fm3m, 66 and Li 2 CO 3 has a monoclinic structure with space group C2/c (no. 15). 67 According to the phase diagram from Fig. 1, the Li 6 SiO 5 phase may also exist, but no crystal structure is currently available for this phase. For this reason this phase ...
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... deal with a-quartz, which is the common phase at room-temperature. This phase could exist either as amorphous (P3 2 21, no. 154) or low quartz (P3 1 21, no. 152). Above 573 1C, the a-quartz could transform into b-quartz (P6 2 22, no. 180). Since SiO 2 is involved in our capture reactions, here, we only consider the a-phase of SiO 2 as shown in Fig. 2(d) with the crystallographic parameters taken from ref. ...
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... of VB 1 is determined by interactions among Li, O and Si. Similar to VB 1 , the upper sub-band of VB 2 is also mainly determined by the interaction between the s and p orbitals of Li and the s orbital of O, while the lower two sub- bands contain the interactions among the p orbitals of Li, the s orbital of O and the s and p orbitals of Si. From Fig. 2(a), one can see that the Li atoms are just located around the [SiO 4 ] tetrahedra with various Li-O distances. The shortest Li-O bond is only 1.224 Å. Around each O, there are at most four Li atoms with bond lengths less than 4.0 Å. Since the location of Li atoms is not symmetric with [SiO 4 ] tetrahedra, the Si-O bond-lengths in the [SiO ...
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... larger contributions than its s orbital and all of them involved to form all VBs and CB. The p orbitals of O mainly contribute to VB 1 while its s orbital mainly contributes to VB 2 . Both s and p orbitals of Si contribute to the lower portion of VB 1 and VB 2 . The upper portion of VB 1 is mainly determined by interactions between Li and O. From Fig. 2(a) and (b) and ref. 23, one can see that in these Li 2 O-rich (Li 2 O/SiO 2 ratio >1) lithium silicates, Fig. 3(c), the calculated band gap is an indirect one between the high symmetry points Z and C of the Brillouin zone with a value of 5.16 eV, which is close to the value of 5.7 eV determined by Du and Corrales 44 using a similar ...
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... its DOS shown in Fig. 4 Fig. 2(e) and (f). The main difference between them is in the direction in which the silicon oxygen tetrahedra are pointing within the silicon oxygen layers. As shown in Fig. 3(d) and (e), although these two phases have similar band-structure and VB widths, the stable phase (no. 37) has a direct band-gap of 5.25 eV while its meta-stable phase ...
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... (in our case to react with CO 2 ), is mainly dominated by the interaction of the s and p orbitals of Li and the p orbitals of O. The lower portion of VB 1 is mainly formed by s and p orbitals of Si interacting with the p orbital of O and a small contribution from Li, while their VB 2 are from the interactions among orbitals of Li, O and Si. From Fig. 2(e) 4 ] tetrahedra of these two phases are not equal, they are very close to each other. For the stable phase the Si-O bond-lengths are 1.595, 1.628, 1.666, and 1.672 Å while for the meta-stable phase the Si-O bond-lengths are 1.598, 1.626, 1.664, and 1.671 Å respectively. Fig. 3(d) and (e)), its VB 1 has a wider band-width and is ...
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... 7 , the p orbitals of Si have a larger contribution to VB 1 while its s orbital mainly involves in VB 2 . As Li 2 Si 3 O 7 is the most SiO 2 -rich lithium silicate in this series, the orbitals of Si have a larger influence on VB 1 formation, and therefore, will be significantly involved in interaction with CO 2 during absorption-desorption. From Fig. 2(f), one can see that in Li 2 Si 3 O 7 , the [SiO 4 ] tetrahedra are connected by bridge oxygen and form [SiO 4 ] n chain. Li atom layers separate these [SiO 4 ] n chains. Again, the Si-O bond- lengths in [SiO 4 ] of Li 2 Si 3 O 7 are not equal but they have close values of 1.594 Å, 1.631 Å, 1.668 Å, and 1.673 Å ...
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... VBs are also separated into two sub-bands with a small gap. From its DOS as shown in Fig. 5(b), the upper portion of VB 1 is mainly the interaction of p orbitals of O and Si while its lower portion is given by contributions of p orbitals of O and s and p orbitals of Si. The VB 2 is mainly from s orbital of O and the s and p orbitals of Si. From Fig. 2(d ...
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... Li 8 SiO 6 . As shown in Fig. 2(a) and Table 1, in the Li 8 SiO 6 unit cell there are two f.u. Its primitive cell is the same as its unit cell. Therefore, there are 90 phonon modes as shown in Fig. 6(a). Along the C-A wave-vector and around the high symmetry point A, there is a small negligible imaginary frequency mode (soft mode), indicating instability. Since the ...
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... Li 2 Si 2 O 5 . As shown in Fig. 2(e) and (f) and Table 1, Li 2 Si 2 O 5 has two phases. In its stable phase (no. 37) there are four f.u. in its unit cell, but only two f.u. in its primitive cell, while in its metastable phase (no. 60) there are four f.u. in its both unit cell and primitive cell. Therefore, the metastable phase has twice the number of phonon modes (108 ...
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... a-SiO 2 . As shown in Fig. 2(d) and Table 1, the a-SiO 2 unit cell coincides with its primitive cell and both contain three f.u. Therefore, there are 27 phonon modes in a-SiO 2 as shown in Fig. 8. Along the C-L wave-vector, there is a slow relaxation mode, indicating a slight instability. Since the space group of a-SiO 2 is P3 2 21 (no. 154), 72 its corresponding ...
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... these lithium silicates, we present experimental results on Li 8 SiO 6 , Li 4 SiO 4 and Li 2 SiO 3 as possible CO 2 captors. 16,32,85,86 Here, Fig. 12 shows our dynamic TGA data on the CO 2 capture of these lithium silicates, in addition to the Li 2 O. From these curves, it is clearly seen how the Li 2 O/SiO 2 ratio modified the amount of CO 2 captured and the temperature range in which the process is performed. We note that these experiments are not quantitative, thus the weight ...
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... 380 1C. The weight increase at this stage is associated with the CO 2 superficial reaction. Then, once the diffusion processes are activated, the second weight increment was produced between 580 and 710 1C. Here, the CO 2 capture is produced in the silicate bulk. A similar interpretation is possible for the other curves depicted as an inset in Fig. 12, although the reaction process and the external shell composition may differ in each lithium silicate whose reactions are proposed in Table ...
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Citations
... -Alkali-metal ceramics (Li 4 SiO 4 , Li 8 SiO 6 , Li 2 ZrO 3 , Li 6 Zr 2 O 7 , Li 5 AlO 4 , LiAlSiO 4 , LiFeO 2 , Li 5 FeO 4 , Li 4 TiO 4 , Li 2 TiO 3 , Li 4 GeO 4 , Li 8 PbO 6 , Na 2 ZrO 3 , Li 2 CuO 2 , etc.) (Dang et al. 2018;Duan et al. 2013;Durán-Muñoz et al. 2013;Lara-García et al. 2017;Pfeiffer and Bosch 2005;Wang et al. 2021;Yañez-Aulestia et al. 2018;Yang et al. 2016;Zhao et al. 2007), -Alkali-metal silicates (Pan et al. 2017), -Magnesium oxide (Hwang et al. 2018), -Calcium oxide (Sun et al. 2015), -Potassium-based sorbents (Cho et al. 2018;Wang et al. 2020), -Ionic liquid sorbents (Xu et al. 2017;Zhou et al. 2016), -Layered double hydroxides (LDHs) (Hanif et al. 2014). ...
The Li4SiO4 seems to be an excellent sorbent for CO2 capture at post-combustion. Our work contributes to understanding the effect of the natural Algerian diatomite as a source of SiO2 in the synthesis of Li4SiO4 for CO2 capture at high temperature. For this purpose, we use various molar % (stoichiometric and excess) of calcined natural diatomite and pure SiO2. To select the best composition, CO2 sorption isotherms at 500 °C on the prepared Li4SiO4 are obtained using TGA measurements under various flows of CO2 in N2. The sorbent having 10% molar SiO2 in diatomite (10%ND-LS) exhibits the best CO2 uptake, probably due to various factors such as the content of the different secondary phases. A comparative study was performed at 400 to 500 °C on this selected 10%ND-LS and those with stoichiometric composition obtained with diatomite and pure SiO2. The obtained isotherms show the endothermic character of CO2 sorption. In addition, the evolution of isosteric heat highlights the nature of the involved CO2/Li4SiO4 interactions, by considering the double-shell mechanism. Finally, the experimental sorption isotherms are confronted with some well-known adsorption models to explain the phenomenon occurring over our prepared sorbents. Freundlich and Jensen–Seaton models present a better correlation with the experimental results.
... Additional phases corresponding to nonporous minerals (e.g., lithium aluminum hydroxide, lithium silicate, and b-lithium aluminate) are present and become more prevalent at lower synthesis temperatures (Table S5 †). 38 This is counter to trends observed in organic-free zeolite synthesis where denser phases form at higher temperatures, which is in qualitative agreement with the Ostwald rule of stages where the metastability of a zeolite generally decreases with increasing density. 9 A similar line of reasoning for zeolites and nonporous minerals is difficult to make without knowledge of their relative solubility and crystallization kinetics. ...
... Based on the ndings in this study and those of other research groups, two mechanisms for the effects of hydration shells on zeolite crystallization are proposed: (1) electrostatic interactions between cations and aluminosilicate oligomers are weaker for ions with a larger hydration shell, which can affect local pH 56 and the distribution of (alumino)silicate species; 50,57 and (2) super-ions 58 (e.g., cations linked by water and/or hydroxide ligands) and/or hydrated cations 59 can function as structure-directing agents that facilitate the formation of certain cages or building units. It has been demonstrated that certain cations are preferentially sited at particular locations within the CHA framework, 38,49 thus suggesting that hydrated cations may promote or stabilize the formation of specic structural units. ...
Chabazite (CHA type) zeolite is notoriously difficult to synthesize in the absence of organic structure-directing agents owing to long synthesis times and/or impurity formation. The ability to tailor organic-free syntheses of zeolites is additionally challenging due to the lack of molecular level understanding of zeolite nucleation and growth pathways, particularly the role of inorganic cations. In this study, we reveal that zeolite CHA can be synthesized using six different combinations of inorganic cations, including the first reported seed- and organic-free synthesis without the presence of potassium. We show that lithium, when present in small quantities, is an effective accelerant of CHA crystallization; and that ion pairings can markedly reduce synthesis times and temperatures, while expanding the design space of zeolite CHA formation in comparison to conventional methods utilizing potassium as the sole structure-directing agent. Herein, we posit the effects of cation pairings on zeolite CHA crystallization are related to their hydrated ionic radii. We also emphasize the broader implications for considering the solvated structure and cooperative role of inorganic cations in zeolite synthesis within the context of the reported findings for chabazite.
... technologies [33][34][35]. Our results showed that by increasing the ratio of Li 2 O and SiO 2 , a series of lithium silicates can be formed and their corresponding turn-over temperatures are increased [34]. ...
... technologies [33][34][35]. Our results showed that by increasing the ratio of Li 2 O and SiO 2 , a series of lithium silicates can be formed and their corresponding turn-over temperatures are increased [34]. Additionally, by doping Li or K into NaZrO 3 the turn-over temperature can be increased or decreased depending on the doping levels and doped element [33]. ...
... The Vienna ab-initio simulation package(VASP) [43][44][45] was employed to calculate the electronic structures of these alkali aluminate and carbonate materials. Based on our previous tests on properly choosing the pseudo-potential and exchange-correlation functions for tin oxides [46], we employed the projector augmented wave (PAW) pseudo-potential and PW91 exchange-correlation functions in all the calculations, which are in accordance with our previous studies on other CO 2 sorbent materials [13,18,33,34]. As tested in our previous study on γ-LiAlO 2 and α-Li 5 AlO 4 systems [41,42], the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functions resulted in slightly better predictions for total energy but didn't change any conclusions. ...
The electronic properties and thermal stabilities of MAlO2 and M5AlO4 (M = Li, Na, K) are investigated by density functional theory and lattice phonon dynamics. Based on the calculated electronic and lattice thermodynamic properties, their abilities to capture CO2 as solid sorbents are analyzed. The calculated electronic structural properties of MAlO2 and M5AlO4 indicate that all these alkali aluminates are semiconductors with a bandgap range of 2.4 ~ 6.4 eV. The 1st valence bands of these alkali aluminates are located 0 ~ − 6 eV under Fermi levels and are mainly contributed by p orbitals of O, s and p orbitals of Al and M. The phonon vibrational frequencies of M5AlO4 spread at a lower frequency range compared to their MAlO2 phases. With increasing temperature, the calculated phonon free energies of M5AlO4 decrease faster than their corresponding MAlO2 while their entropies have opposite trends. The reaction 2MAlO2 + CO2 = M2CO3 + Al2O3 has higher reaction heat and Gibbs free energy change than those of corresponding reaction ²/5M5AlO4 + CO2 = M2CO3 + ¹/5Al2O3, which shows the former reaction possesses lower turnover temperature. Among the alkali aluminates studied, the β-NaAlO2, lt-KAlO2, and γ-LiAlO2 are better candidates that could be applied for CO2 capture technologies.
Graphical Abstract
... For this phase, only one crystal structure has been proposed [14]. Theoretical and experimental results have demonstrated that the formation of Li 8 SiO 6 is highly sensitive to small deviations from stoichiometry, which may generate impurities [15,16]. Therefore, very fine-tuning of the synthesis conditions seems to be critical to obtaining the lithium oxosilicate phase. ...
Lithium oxosilicate has the highest proportion of lithium among lithium silicates, which is desirable for applications. Although Li8SiO6 is a stable phase, its obtention as a polycrystalline pure phase is not reported yet, probably because of the high sensitivity of the system Li2O–SiO2 to the synthesis conditions. In this work, we adapted a citrate-based route used for the synthesis of Li4SiO4 as a novel approach to the obtention of Li8SiO6. We found that the lowest amount of impurities is achieved by using a Li:C6H8O7 molar ratio of 2.8:1, a pH value of 8.5, and a lithium excess of 20%. In a complementary way, we used the solid-state reaction method as a function of the excess of lithium and optimized the conditions that lead to a minimum amount of impurities. We found that the purest Li8SiO6 phase is obtained with low or no lithium excess. Samples obtained by both methods exhibited a higher purity compared to the reports available in literature. The crystal structure for this phase is confirmed by selected area electron diffraction.
... CO 2 capture application by various types of solid adsorbents (Reproduced from51,57,73,157,244,[287][288][289][291][292][293]. ...
The utilization of various conventional and emerging solid adsorbents is an attractive carbon capture method for post‐combustion and direct air capture (DAC). This review aims to identify adsorbents with the highest CO2 adsorption performance at various CO2 capture conditions inclusive of pre‐combustion, post‐combustion, and DAC to aid the selection of adsorbents. It presents the various adsorbents’ physical and chemical properties, their synthesis methods, CO2 adsorption performance, and their advantages as CO2 adsorbents. Findings of the review show that NaX@NaA core‐shell microspheres possess the highest CO2 adsorption capacity at 5.60 mmol g⁻¹ for adsorption at DAC conditions. MOF‐177‐TEPA exhibited the highest post‐combustion condition CO2 adsorption capacity at 4.60 mmol g⁻¹ given tetraethylenepentamine properties leading to low diffusion resistance for CO2 and easy access to active sites. Approximation of these adsorbents’ adsorption capacity within pre‐combustion capture temperature at 1 bar for oxy‐combustion process was 0.0000026–48.71 mmol g⁻¹. It is crucial to understand and evaluate these adsorbents’ characteristics for application in the appropriate adsorption conditions. This considers their usage limitations on pilot‐scale CO2 capture because of low productivity, poor durability, and stability for prolonged cyclic adsorption–desorption, expensive adsorption system, high gas flow rate, high adsorbate accommodation requirement, longer flow switching time, and low tolerance towards water and impurities present in flue gas. This paper hence presents future enhancements in overcoming their limitations to accommodate pilot scale carbon capture. These are beneficial in providing insights for capturing CO2 from flue gases emitted in industries. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.
... In fact, most other alkali and alkaline earth metal-containing oxides (Li, Na, Ba, etc.) are capable of some level of CO 2 absorption as shown above and represent an underexplored parameter space compared to the more heavily investigated CaO and MgO systems. Thus, a different strategy for materials optimization is to widen the pool of explorable sorbent materials, both for improving the fundamental understanding of how CO 2 absorption and desorption proceeds and to find suitable materials for practical use. ) (see section 4.1.2). 489,490 One approach to overcome this limitation is to synthesize materials with a higher fraction of alkali metals, such as Li 6 ZnO 4 , 4 9 1 Li 6 CoO 4 , 4 9 2 Li 5 SbO 5 , 4 9 3 Li 4 WO 5 , 4 9 3 Li 6 WO 6 , 493,494 LiYO 2 , 495 Li 6 Si 2 O 7 , 496 503,504 Thermogravimetric studies have shown that these materials generally have relatively high gravimetric CO 2 uptake capacities and in many cases also a high cyclic stability, at least for the small number of cycles tested. An overview of these materials is shown in Table 7. ...
... The band gap of Na 2 SiO 3 has been theoretically estimated with values ranging from 4 to 6.46 eV [38][39][40]. In the case of Li 2 SiO 3 , the band gap has been predicted with values between 4.58 and 7.26 eV [41][42][43][44][45]. It is known that the band gaps calculated with DFT are underestimated; however, the values herein evaluated are within the range of experimental and calculated ones. ...
Surfaces of sodium and lithium silicates are theoretically investigated to account for the role of dissimilar atoms, towards the methanol adsorption/dissociation within the transesterification reaction producing biodiesel in heterogeneous processes. The definition of active site is elucidated on these materials on the basis of the following calculations: electronic density, electrostatic potential, charges, geometrical parameters and density of states (total and projected) computed with periodic Density Functional Theory (DFT). The structural requirements of a catalytic surface for biodiesel production are analyzed relying on different atomic configurations of the highest intensity peaks, according to experimental X-ray analysis. This information reveals that the alkaline metals (Na, Li) on the surface participate in the methanol adsorption, subsequently; Si acts as Lewis acid site to stabilize the methoxide anion, while the oxygen atoms perform as Brönsted basic sites to abstract the proton from methanol. This constitutes the early stages of the transesterification mechanism, and possibly the rate-controlling step (RCS) of the biodiesel generation. In the sodium silicate, the alkaline metal possesses the ability to stabilize the methoxide anion through electrostatic interactions unlike the lithium silicate. This behavior could establish the difference in catalytic activity on these silicate surfaces, presumably defining the best performance for Na2SiO3, as experimentally observed
... One approach to overcome this problem is to synthesize materials with a higher fraction of alkali metals. A number of such materials have been synthesized and subjected to thermogravimetric studies, including Li6WO6 [464], Li6Si2O7 [465], Li8SiO6 [465], [466], Li6Zr2O7 [455], [467], Li8ZrO6 ...
... One approach to overcome this problem is to synthesize materials with a higher fraction of alkali metals. A number of such materials have been synthesized and subjected to thermogravimetric studies, including Li6WO6 [464], Li6Si2O7 [465], Li8SiO6 [465], [466], Li6Zr2O7 [455], [467], Li8ZrO6 ...
Carbon dioxide capture and mitigation forms a key part of the technological response to combat climate change and reduce CO2 emissions. Solid materials capable of reversibly absorbing CO2 have been the focus of intense research for the past two decades, promising stability and low energy costs to implement and operate compared to the more widely used liquid amines. In this Review, we explore the fundamental aspects underpinning solid CO2 sorbents based on alkali and alkaline earth metal oxides operating at mid- to high temperature: how their structure, chemical composition and morphology impact their performance and long-term use. Various optimization strategies are outlined to improve upon the most promising materials, and we combine recent advances across disparate scientific disciplines including materials discovery, synthesis, and in situ characterization to present a coherent understanding of the mechanisms of CO2 absorption both at surfaces and within solid materials.
... The inversion temperature was identified at 515 °C, which is in agreement to the thermodynamic calculations reported by Chowdhury et al. (Chowdhury et al. 2013) for the same condition (500 °C and a CO 2 partial pressure of 0.05). Duan et al. (Duan et al. 2013;Duan et al. 2012) also reported the turnover temperature for pure Li 4 SiO 4 in pre-and post-combustion conditions, as the temperature above at which lithium silicate cannot adsorb CO 2 and starts to release it according to the CO 2 partial pressure. ...
The use of solid wastes and industrial by-products to prepare CO2 adsorbents is an alternative to conventional reagent grade raw materials that has recently gained interest. Among waste materials, slag has a high content of silica and calcium and is the largest solid by-product from iron and steel industry, thus its use can reduce the production costs of CO2 adsorbent materials, such as lithium silicates, which are applied in capture processes at high temperatures. Li4SiO4 has potential applications in post-combustion CO2 capture as well as in H2 production by sorption enhanced steam reforming process. In this study, Li4SiO4 was prepared using solid-state reaction and two iron and steel slags as SiO2 sources to evaluate their characteristics and CO2 capture capacities. The slag-derived lithium silicates (S1-Li4SiO4 and S2-Li4SiO4) were characterized by XRD, adsorption-desorption N2 and SEM. Different capture tests at CO2 partial pressures (\(P_{{{\text{CO}}_{2} }}\)) of 0.05, 0.10, 0.15 and 0.20 were performed using thermogravimetric (TG) and temperature programmed (TPC-TPDC) techniques. The kinetic parameters of the CO2 capture process were obtained by fitting the experimental results to the Avrami–Erofeev model. Finally, the cyclic behavior of S1-Li4SiO4 and S2-Li4SiO4 was analyzed in \(P_{{{\text{CO}}_{2} }}\) of 0.2 and 0.05. XRD patterns showed that Li4SiO4 was the main crystal phase (60 wt%) present in S1-Li4SiO4 and S2-Li4SiO4 in addition to calcium phases such as Li2CaSiO4, Ca3SiO5 and CaO. According to the TG and TPC-TPDC tests, the derived lithium silicates showed CO2 uptake three times greater than the values recorded for Li4SiO4 (134 mgCO2/g sorbent for S1-Li4SiO4) produced from pure reagents, at \(P_{{{\text{CO}}_{2} }}\) between 0.2 and 0.05 and 650 °C. Furthermore, these materials had kinetic constants at least one order of magnitude higher than those reported for Li4SiO4, at the aforementioned operating conditions. Both materials exhibited an excellent stability during 20 cycles of CO2 adsorption/desorption. These results showed that slags can be used as silica source to produced adsorbents with better performance and stability in the CO2 capture process at high temperature than the one of Li4SiO4 produced from pure reagents, at \(P_{{{\text{CO}}_{2} }}\) of 0.2–0.05.
... 5 These glass values coincide with the calculations of Du and Corrales. 19 Several research groups have determined LS2 crystal bandgap indirectly through calculations to be 4.9 eV (theoretical ab-initio molecular dynamics [AIMD] approach), 20 5.1 eV (density functional theory [DFT] within generalized gradient approximation [GGA]), 21 5.25 eV (DFT with plane-wave basis sets and pseudopotential approximation; direct gap), 22 5.5 eV (DFT within GGA), 23 25 Furthermore, OLCAO is a semi-empirical method in which the calculation results change according to the exchange parameters. Overall, bandgap values depend on the parameters when obtaining the bandgaps of alkaline silicate crystals. ...
Lithium disilicate (LS2) has been a crucial parent composition for glass‐ceramics since the 1950s because of its excellent chemical and physical durability. In addition, a wide range of electrical properties can be obtained by changing the composition and crystallinity. Bandgap energy is one of the critical electrical properties for designing new lithium silicate‐based materials. In this study, the bandgap energy of a synthesized LS2 crystal is evaluated using electron energy‐loss spectroscopy and X‐ray photoelectron spectroscopy. These two techniques unambiguously establish that the bandgap energy of LS2 is 7.7‐7.8 eV, which is in the vacuum ultraviolet region. This confirms the insulating nature of the LS2 crystal.
