Ionothermal carbonization in [Bmim][FeCl4]: An opportunity for the valorization of raw lignocellulosic agrowastes into advanced porous carbons for CO2capture

Article abstract of DOI:10.1039/d0gc01510e

In this study, we investigated the ionothermal carbonization (ITC) in 1-butyl-3-methylimidazolium tetrachloroferrate, [Bmim][FeCl4], of cocoa bean shells, a raw lignocellulosic agrowaste. The beneficial inputs of this ITC approach towards mass yield, carbon yield and specific surface area of the solid chars (namely, ionochars) were clearly evidenced. The coordination of [FeCl4]- anions to the oxygen atoms of lignocellulosic materials and ionochars seems to stabilize carbon oxygenated groups-accounting for enhanced mass and carbon yields-and to favor the generation of micropores. We showed that the use of wet starting agrowastes in the ITC process might be advantageous for the production of highly porous ionochars. Importantly, the contributions of lignin and cellulose were highlighted and the recyclability of [Bmim][FeCl4] was clearly evidenced, proving the sustainability of ITC and making this process easily applicable to other raw lignocellulosic agrowastes. The subsequent activation of the as-obtained ionochars under CO2-rich atmosphere allowed producing activated carbons with specific surface area superior to 2000 m2 g-1 and remarkable CO2 uptake as high as 4.4 mmol g-1 at 25 °C and 1 bar. This value is the highest post-combustion CO2 uptake reported to date in literature for CO2 activated biomass-derived carbons. This journal is

Full text of DOI:10.1039/d0gc01510e

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DOI: 10.1039/D0GC01510E
Ionothermal Carbonization in [Bmim][FeCl4]: an Opportunity for the Valorization of
Raw Lignocellulosic Agrowastes into Advanced Porous Carbons for CO2 Capture†
Laure Cibien,‡,1 Maxime Parot, ‡,1 Patrick Nkuigue Fotsing,2 Philippe Gaveau,1 Emmanuel
Djoufac Woumfo,2 Julien Vieillard,3 Alfredo Napoli,4 Nicolas Brun*,1
1ICGM, Univ Montpellier, CNRS, ENSCM, Montpellier (France)
2Laboratoire de Chimie Inorganique Appliquée, Département de Chimie Inorganique, Faculté
des Sciences, Université de Yaoundé I, Yaoundé (Cameroun)
3Normandie Univ., UNIROUEN, INSA Rouen, CNRS, COBRA (UMR 6014), Rouen
(France)
4CIRAD, UR BioWooeb, Montpellier (France)
*Email: nicolas.brun@enscm.fr
†Electronic Supplementary Information (ESI) available: [Additional analytical data]. See
DOI: 10.1039/x0xx00000x
‡These authors contributed equally to this work

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DOI: 10.1039/D0GC01510E
Abstract
In this study, we investigated the ionothermal carbonization (ITC) in 1-butyl-3-
methylimidazolium tetrachloroferrate, [Bmim][FeCl4], of cocoa bean shells, a raw
lignocellulosic agrowaste. The beneficial inputs of this ITC approach towards mass yield,
carbon yield and specific surface area of the solid chars (namely, ionochars) were clearly
evidenced. The coordination of [FeCl4]- anions to the oxygen atoms of lignocellulosic materials
and ionochars seems to stabilize carbon oxygenated groups – accounting for enhanced mass
and carbon yields – and to favor the generation of micropores. We showed that the use of wet
starting agrowastes in the ITC process might be advantageous for the production of highly
porous ionochars. Importantly, the contributions of lignin and cellulose were highlighted and
the recyclability of [Bmim][FeCl4] was clearly evidenced, proving the sustainability of ITC and
making this process easily applicable to other raw lignocellulosic agrowastes. The subsequent
activation of the as-obtained ionochars under CO2-rich atmosphere allowed producing activated
carbons with specific surface area superior to 2000 m2.g-1 and remarkable CO2 uptake as high
as 4.4 mmol.g-1 at 25°C and 1 bar. This value is the highest post-combustion CO2 uptake
reported to date in literature for CO2 activated biomass-derived carbons.

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DOI: 10.1039/D0GC01510E
1. Introduction
With the concept of biorefinery, the conversion of renewable feedstocks into energy and
marketable products, e.g. platform chemicals and advanced materials, has constituted a major
field of research.1, 2 This assessment is particularly true for the agro-industry sector, which
generates a large amount of organic residues, namely agrowastes. These agrowastes are cheap,
renewable and abundant, making them attractive raw materials for sustainable industrial
processes. Amongst biorefinery’s end products, porous carbonaceous materials3, 4, 5 and
particles6 have attracted much interest as they offer a wide range of potential applications in
energy storage and conversion,7-9 energy harvesting,10 biomedicine,11 catalysis12 and
environmental remediation13-15. Until relatively recently, the thermochemical conversion of
renewable feedstocks into porous carbons was limited to dry pyrolysis and/or activation
processes. In the past years, wet pyrolysis in water, also called hydrothermal carbonization
(HTC), has been seen as a promising alternative to design porous carbonaceous materials on
demand from renewable feedstocks.16-21 Those carbonaceous materials, also called hydrochars,
can be obtained from a large range of natural precursors, including untapped byproducts
generated during degradation of lignocellulose in paper mills22 and biorefineries8. The
hydrothermal approach is based on the degradation/dehydration of (poly)saccharides into furan-
based intermediates at relatively mild conditions; typically at a temperature between 130 and
250°C and at a pressure below 10 bars. HTC usually yields microscopic nonporous spheres
with limited control over morphology and texture. When applied to soluble carbohydrates, e.g.
monosacharides, HTC has been frequently combined with sacrificial templates23-28, catalysts
and/or structuring agents29-32 to yield porous hydrochars. Conversely, the hydrothermal
carbonization of insoluble feedstocks, e.g. cellulose and raw lignocellulosic materials, remains
limited in terms of textural and morphological control.18
Since 2002 and the first article demonstrating their ability to dissolve cellulose,33 ionic
liquids (ILs) have been widely employed in biorefinery, both as derivatizing34-36 and
nonderivatizing33, 37 solvents. Particularly, short-chain imidazolium-based room temperature
ILs with strong hydrogen bond acceptors as anions, such as 1-butyl-3-methylimidazolium
chloride (i.e. [Bmim]Cl), appeared to be very efficient in solubilizing cellulose. R.D. Rogers et
al. demonstrated that such solvation involves stoichiometric hydrogen-bonding between the
hydroxyl protons of the polysaccharide and the anions of the IL.33, 38 From that moment on, few
other hydrophilic ILs, with various anions (e.g. chloride, phosphate, phosphonate and acetate)
and cations (e.g. imidazolium, ammonium and phosphonium), demonstrated similar abilities.39

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While the role of the anion seems to be clear (i.e. related to hydrogen bonding basicity), the
DOI: 10.1039/D0GC01510E
way cationic structure affects the dissolution of cellulose is still open to discussion.40 Besides,
functional ILs with acidic properties have been employed both as solvent and catalyst for the
hydrolysis and conversion of lignocellulosic biomass to platform chemicals.41-43
Beyond dissolution and selective deconstruction, ILs were also employed for the
thermochemical conversion of carbohydrates into porous carbonaceous materials. Usually,
ionic liquid is involved either as a soft-template in water44, 45 or as a functional solvent playing
the role of catalyst and/or porogenic agent 46-49. While the first approach falls in the category of
HTC, the second one can be regarded as ionothermal carbonization (ITC; by analogy with
hydrothermal carbonization) yielding ionochars (by analogy with hydrochars). While full of
promise, the ITC process is still a young topic with reaction mechanisms yet to elucidate and a
limitless variety of carbon precursor/IL systems to investigate. Thus far, such ionothermal
treatment has not been fully exploited and was mainly restricted to monosaccharides,47-49 except
for rare examples dealing with raw lignocellulosic agrowastes50, 51. Using Bmim-type ILs with
-
different anions (i.e. Cl-, BF4 and Tf2N-), Wang et al.50 applied the ITC process to cellulose
and sugar cane bagasse. The authors showed a correlation between the size of the anion and the
textural properties of the ionochar – i.e. larger anions yield higher pore volume – revealing a
bit more the versatility of the ITC process. More recently, Xie et al.51 applied the ITC approach
to Jujun grass. After treatment at 180°C in a Lewis acid ionic liquid (i.e. 1-butyl-3-
methylimidazolium tetrachloroferrate, [Bmim][FeCl4]) and subsequent chemical activation
with KOH, the authors obtained hierarchical porous carbons with high surface area and
significant mesoporous contribution. The beneficial input of the ITC pre-treatment in terms of
porosity and capacitive performance was clearly evidenced, making this two-step approach
really promising. However, in this last study, the authors considered ionochars as synthetic
intermediates and mainly focused on the final activated carbons and their electrochemical
properties. More recently, X. Li et al.52, 53 demonstrated synergistic effects that make
[Bmim][FeCl4] an efficient catalyst for the depolymerization of lignin through γ-O ester bond
cleavage. Even though the authors focused on the production of methyl p-hydroxycinnamate, a
platform molecule for a variety of fine chemicals, rather than on the production of ionochars,
this study further supported the relevance of using [Bmim][FeCl4] for the conversion of
lignocellulosic materials.
In this study, we propose to provide further insights into the ITC process applied to
lignocellulosic biomass via thorough textural and structural characterizations and comparison

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with hydrochars analogous. With this aim, we applied the ITC approach to a raw lignocellulosic
DOI: 10.1039/D0GC01510E
agrowaste model, i.e. cocoa bean shells (CS) from Cameroon. The cocoa industry is a pertinent
model as it generates a large amount of agrowastes. Through on-farm processing, ca. 80 wt.%
of the cocoa fruit is discarded as residues, including cocoa pod husk, cocoa pulp and CS.54
Herein, both [Bmim]Cl, a well-known commercial ionic liquid, and [Bmim][FeCl4], a Lewis
acid ionic liquid analogous, were employed as reaction media for the treatment of CS. The
beneficial inputs of the ITC approach towards mass yield, carbon yield and specific surface area
were clearly evidenced. Importantly, the contributions of lignin and cellulose were highlighted
and the recyclability of [Bmim][FeCl4] was clearly evidenced, proving the sustainability of the
ITC approach and making this process easily applicable to other raw agrowastes. The
subsequent activation of the as-obtained ionochars with carbon dioxide allowed producing
activated carbons with specific surface area superior to 2000 m2.g-1 and remarkable CO2 uptake
as high as 4.4 mmol.g-1 at 25°C and 1 bar. This value is amongst the highest values reported to
date in literature for nitrogen-free biomass-derived carbons. In this contribution, we wish to
provide useful insight and understanding of the transformation mechanism involved in the ITC
of lignocellulosic biomass in [Bmim][FeCl4]. Besides, we believe that this study further
contributes to demonstrate that ITC can be a promising approach into the circular economy for
the valorization of raw agrowastes into advanced carbonaceous materials.
2. Experimental section
2.1. Materials
Iron (III) chloride hexahydrate was purchased from Acros Organics. 1-Butyl-3-
methylimidazolium chloride (99 %) was purchased from Iolitec (Germany) and kept under
vacuum to avoid hydration. Sigmacell cellulose (type 50, 50 µm) and kraft lignin were
purchased from Sigma Aldrich. All reagents were used without further purification.
2.2. Preparation of the cocoa bean shells (CS)
The cocoa bean shells (CS) were collected from a local farm managed by the IRAD (Institute
of Agricultural Research for Development) at Yaoundé, Cameroon. The shells were cut, washed
with acidic water (1M HCl) to remove organic matter, sun-dried for 5 days, and heated at 70°C
overnight to remove moisture. Finally, CS were ground and sifted at 160 µm.
2.3. Extraction of lignin by the Klason method

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Lignin was extracted from CS and quantified using the Klason method as described in
DOI: 10.1039/D0GC01510E
literature.55 In brief, 3 g of CS were treated in 30 mL of concentrated sulfuric acid (72 wt.%
H2SO4) at 25 °C for 1 hour under vigorous stirring. The slurry was diluted with deionized water
to decrease the H2SO4 concentration to 4 wt.%, autoclaved at 121 °C for 60 min and filtrated
through a 0.22 µm PVDF membrane. The insoluble lignin fraction, namely Klason lignin (KL),
was dried at 100°C overnight in a vacuum oven and weighed. The ash content was determined
by thermogravimetric analysis under a dry air atmosphere. The soluble lignin fraction was
quantified by UV–vis spectroscopy.
2.4. Hydrothermal carbonization (HTC)
Typically, CS powder (1 g) was dispersed in deionized water (10 mL), sealed in a Teflon lined
autoclave (37 mL) and heated at 240 °C for 20 h. After cooling down to room temperature
(through quenching in cold water), samples were filtered, successively washed two times with
deionized water (50 mL) and two times with ethanol (50 mL), then dried at 80 °C overnight.
The as-obtained samples were named HC-240. Similar experiments were carried out in the
presence of FeCl3. FeCl3.6H2O (10.86 g, corresponding to 40.2 mmol of FeCl3) was mixed with
deionized water (c.a. 4 mL) until the gauge of a 10 mL volumetric flask was reached. The 10
mL solution was mixed with CS powder (1 g) and sealed in a Teflon lined autoclave (37 mL)
and heated at 240 °C for 20 h. After filtration, washing and drying, the as-obtained samples
were named HC-Fe-240.
2.5. Ionothermal carbonization (ITC)
2.5.1. ITC in [Bmim]Cl
Typically, CS powder (1 g) was mixed with [Bmim]Cl (10.8 g), sealed in a Teflon lined
autoclave (37 mL) and heated at 240 °C for 20 h. After cooling down to room temperature
(through quenching in cold water), samples were filtered, successively washed two times with
deionized water (50 mL) and two times with ethanol (50 mL), then dried at 80 °C overnight.
The as-obtained samples were named IC-240.
2.5.2. Preparation of [Bmim][FeCl4]
[Bmim][FeCl4] was prepared using the well-established procedure reported in literature.47, 56
Typically, equimolar amounts of FeCl3.6H2O (64.86 g, 0.24 mol) and [Bmim]Cl (41.92 g, 0.24
mol) were mixed in a round-bottom flask for 30 min at room temperature under vigorous
stirring. [Bmim][FeCl4] was then dried under vacuum at 100 °C overnight.

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DOI: 10.1039/D0GC01510E
2.5.3. ITC in [Bmim][FeCl4]
Typically, CS (1 g) was dispersed in [Bmim][FeCl4] (13.56 g, c.a. 10 mL and 40.2 mmol),
sealed in a Teflon lined autoclave (37 mL) and heated at 240 °C for 20 h. After cooling down
to room temperature (through quenching in cold water), samples were filtered, successively
washed two times with deionized water (50 mL) and two times with ethanol (50 mL), then dried
at 80 °C overnight. The as-obtained samples were named IC-Fe-240. Some experiments were
conducted in 10 mL of [Bmim][FeCl4]/water mixtures. The as-obtained samples were named
IC-Fe-240-yw, where y is the water content in wt.%.
All experiments were performed at least in triplicate. All the data reported in this study
correspond to average values. Standard deviation was used to measure the statistical dispersion
and error bars were included on all graphs accordingly.
2.6. High temperature post-treatment
2.6.1. Pyrolysis
Pyrolysis was carried out in a horizontal tube furnace at 900 °C for 2 h with a heating rate of
5 °C min-1 under argon flow (50 mL min-1). Samples were then allowed to cool down to room
temperature through a natural convection step. The as-obtained samples were named with the
suffix P9.
2.6.2. CO2 activation
CO2 activation was carried out in a vertical tube furnace following two different procedures.
In a first procedure, the samples were pretreated at 950 °C for 10 min under nitrogen flow
(100 mL min-1) with a heating rate of 10 °C min-1 and an intermediate drying plateau at 110°C
for 60 min, and subsequently treated at 950°C for 120 min under a CO2 enriched nitrogen flow
(10 mL min-1 CO2, 90 mL min-1 N2). The as-obtained samples were named with the suffix A1.
In a second procedure, the samples were treated at 950 °C for 130 min under a CO2 enriched
nitrogen flow (10 mL min-1 CO2, 90 mL min-1 N2) with a heating rate of 10 °C min-1 and an
intermediate drying plateau at 110°C for 60 min. The intermediate drying plateau was carried
out under nitrogen flow (100 mL min-1). The as-obtained samples were named with the suffix
A2.

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In all cases, samples were allowed to cool down to room temperature through a natural
DOI: 10.1039/D0GC01510E
convection step.
2.7. Mass and carbon yields
The mass yield and the corrected mass yield were calculated as follows:
푴풂풔풔 풐풇 풅풓풊풆풅 풄풉풂풓 (품)
푴풂풔풔 풚풊풆풍풅 (%) =
× ퟏퟎퟎ
푴풂풔풔 풐풇 풅풓풊풆풅 풊풏풊풕풊풂풍 풃풊풐풎풂풔풔 (품)
푴풂풔풔 풐풇 풅풓풊풆풅 풄풉풂풓 (품) ― 푴풂풔풔 풐풇 풓풆풔풊풅풖풂풍 풂풕풐풎풔 (품)
푴풂풔풔 풐풇 풅풓풊풆풅 풊풏풊풕풊풂풍 풃풊풐풎풂풔풔 (품)
푪풐풓풓풆풄풕풆풅 푴풂풔풔 풚풊풆풍풅 (%) =
× ퟏퟎퟎ
Residual atoms correspond to any atom present in the dried char and coming from the salt
(FeCl3) or the ionic liquid ([Bmim]Cl or [Bmim][FeCl4]), i.e., iron, chloride and nitrogen
excess. Iron and chloride contents were determined by SEM-EDX (section 2.7). Nitrogen
content was determined by elemental analysis. The nitrogen excess coming from the ionic liquid
was determined by subtracting the nitrogen coming form the initial biomass. HC-240 and HC-
180 were used as references.
The carbon yield was calculated as follows:
푪 풄풐풏풕풆풏풕 풊풏 풅풓풊풆풅 풄풉풂풓 (풘풕.%)
푪풂풓풃풐풏 풚풊풆풍풅 (%) = 푴풂풔풔 풚풊풆풍풅 (%) ×
× ퟏퟎퟎ
푪 풄풐풏풕풆풏풕 풊풏 풅풓풊풆풅 풊풏풊풕풊풂풍 풃풊풐풎풂풔풔 (풘풕.%)
2.8. Characterization
Scanning electron microscopy (SEM) analyses were performed on a Hitachi S-4800 electron
microscope. SEM-EDX (Energy Dispersive X-ray spectroscopy) analyses were performed on
a Zeiss EVO HD15 electron microscope. Transmission electron microscopy (TEM) analyses
were performed on a JEOL 1200 microscope. High resolution TEM analysis was performed on
a JEOL 2200FS microscope operated at 200 kV, from the MEA platform (Université de
Montpellier). This microscope is equipped with a field emission gun (FEG) and an in-column
Omega-type energy filter. STEM-EDX (Scanning Transmission Electron Microscopy) mapping
were performed using a probe size of 1.5 nm and X-rays measured with a silicon drift detector
(30 mm2, JEOL) with a collection solid angle of 0.13sr. N2 (at 77 K) and CO2 (at 273, 293 and
298 K) physisorption experiments were carried out on a Micromeritics 3Flex apparatus.
Ionochars and hydrochars were degassed at 150 °C and carbons (i.e., materials post-treated at
high temperature) were degassed at 250 °C for 6 h under high vacuum (ca. 0.1 Pa) before
physisorption measurements. 13C solid-state NMR was carried out on a VARIAN VNMRS 300

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MHz spectrometer at 75.44 MHz. A VARIAN T3 MAS probe was used with 3.D2OI:m10m.103Z9/rDO0G2C01510E
rotors. Experiments were performed using Cross Polarization Magic Angle Spinning (CP-
MAS) with a contact time of 1 ms and a recycle delay of 5 s. Rotors were spun at 15 kHz.
Plastic inserts were removed from the rotor and short caps were used to minimize the 13C
background signal. Spectra were normalized and the background signal was removed by
subtracting the spectrum obtained with the empty rotor. FTIR spectroscopy was performed in
attenuated total reflectance (ATR) mode on a PerkinElmer Spectrum Two spectrometer. XRD
patterns were recorded on a Bruker D8 Advance diffractometer with a Bragg-Brentano
geometry and equipped with a Bruker Lynx Eye detector, with the Kα radiation of Cu (λ =
1.5418 Å) and an angular step size of 0.02° into the 10°-80° interval. X-ray photoelectron
spectroscopy (XPS) analyses were performed on a ESCALAB 250 ThermoElectron
spectrometer using a monochromatized Al Kα source (h = 1486.6 eV) and a 500 µm spot size.
GC-MS was performed on a Shimadzu QP2010SE gas chromatograph-mass spectrometer with
a Phenomenex Zebron ZB-5ms column (30m x 0.18mm x 0.18µm). Injection: Split 1:30 @ 250
°C. Oven program: 50 °C (hold 2 min) 50-280 °C @ 22 °C/min (Hold 2 min).
Thermogravimetric analyses (TGA) were carried out using a Netzsch Simultaneous Thermal
Analyzer STA 409 PC Luxx, with a heating rate of 10 °C min-1 in the 20-1000 °C range, under
a dry air atmosphere (50 mL min-1).
3. Results and discussion
3.1. Ionothermal (ITC) versus hydrothermal (HTC) carbonization
In the manner of hydrothermal carbonization (HTC), ionothermal carbonization (ITC) is a
thermochemical process which allows carbonization of carbohydrates and raw lignocellulosic
materials under mild conditions (i.e. < 10 bars and < 240 °C).17, 18 ITC of carbohydrates in
[Bmim][FeCl4] (BFe) was previously described by Xie et al., and the multiple role played by
this iron-containing IL was clearly evidenced.47 FeCl3 acts as a Lewis acid catalyst involved in
the different stages of the carbonization process. Its combination with [Bmim]Cl yields a room-
temperature IL which acts as a porogen and as a solvent with good moisture-stability and
superior solvation properties compared to water. Thus, ITC of carbohydrates in BFe generated
porous ionochars with a higher carbonization yield compared with analogous hydrochars
obtained by the HTC process. These features were confirmed in our study with raw biomass,
i.e., cocoa bean shell (CS). CS is an abundant and often underexploited lignocellulosic
agrowaste from the cocoa industry that is mainly used as fuel for boilers or as fertilizer for

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cocoa trees.54 The valorization of CS into valuable and marketable products will help improving
DOI: 10.1039/D0GC01510E
waste disposal and developing local circular bioeconomy.54, 57, 58 The cocoa shells employed in
this study are constituted of ca. 25-30 wt.% lignin, ca. 55-60 wt.% holocellulose and ca. 6 wt.%
ash (Figure S1, Tables S1 and S2). Figure 1a represents the mass yield and the carbon yield
for CS treated at 240°C for 20 hours in water (HC-240), in water with FeCl3 (HC-Fe-240), in
[Bmim]Cl (IC-240) and in BFe (IC-Fe-240). Both mass yield (43.4 wt.%) and carbon yield (73
wt.%) were significantly improved for IC-Fe-240 as compared with its analogous obtained in
water or in [Bmim]Cl (Table S3). Similarly, the textural properties of IC-Fe-240 were
significantly improved. The nitrogen sorption isotherms obtained at 77 K are shown in Figure
2b. IC-Fe-240 displays a type I/II isotherm with a H3 hysteresis loop, related to micro-
macroporous materials. This ionochar is mainly microporous with a BET equivalent specific
surface area (SSABET) of 550 m2.g-1 (Figure 1c and Table S4). A similar shape was obtained
for HC-Fe-240. This hydrochar presents a high SSABET of 284 m2.g-1 with equal SSA
contributions from micropores and macropores (Figure 1c and Table S4). On the contrary,
HC-240 depicts a type II isotherm, typical of macroporous materials, with a low SSABET of 20
m2.g-1 while IC-240 is non-porous. These observations were confirmed by scanning (SEM,
,
Figure S2) and transmission electron microscopy (TEM, Figure 2). As shown by TEM (Figure
2a), HC-240 is made of aggregated nanoparticles with a diameter of ca. 50-100 nm. These
particles are mainly not dispersible and supported on the preserved natural macrostructure of
the native CS (Figure S2). As for IC-240, SEM observations confirm the absence of porosity
even at the macroscopic scale (Figure S2). As shown by SEM and TEM, the presence of iron
chloride either in water or in BFe, significantly affects the nanoparticle size. HC-Fe-240
(Figure 2b) and IC-Fe-240 (Figure 2c) are made of aggregated nanoparticles with smaller
diameters of ca. 10-40 nm, in good agreement with the higher external SSA obtained by
nitrogen sorption analyses (Figure 1). These results suggest that iron not only has a role of
Lewis acid catalyst in the carbonization process, it is also involved in the generation of porosity.
Importantly, a synergistic effect was clearly evidenced when processing ITC in BFe. IC-Fe-
240 shows improved mass yield, carbon yield and textural properties as compared with its two
analogous obtained in the sole presence of [Bmim]Cl or FeCl3 in water, i.e. IC-240 and HC-
Fe-240 respectively. As suggested by Xie et al. for the ITC of carbohydrates,47 BFe might
closely interact with the biopolymers and the carbonaceous particles through hydrogen bonds,
but also via the π-system of the imidazolium ring. As imidazolium is amphiphilic, complex
liquid structures might form59 and favor the nucleation of small particles and the generation of
meso- and macropores.

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DOI: 10.1039/D0GC01510E
Figure 1. (a) Mass and carbon yields, (b) Nitrogen sorption isotherms at 77 K and (c) specific surface
areas of HC-240, HC-Fe-240, IC-240 and IC-Fe-240.

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DOI: 10.1039/D0GC01510E
Figure 2. TEM micrographs of (a) HC-240, (b) HC-Fe-240 and (c) IC-Fe-240.
The chemical structure of the four samples was investigated by FTIR (Figure 3a) and
solid-state 13C CP NMR spectroscopy (Figure 3b). HC-Fe-240 and IC-Fe-240 present similar
FTIR spectra (Figure 3a) with two intense broad bands centered at 1600 (aromatic υC=C

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stretching vibrations) and 1220-1280 cm-1 (υC-O stretching vibrations in aromatiDcOeI:t1h0e.10rs39/aDn0dGC01510E
esters) and four shoulders centered at 1700 (υC=O stretching vibrations of aromatic carbonyl
groups), 1440 (aromatic υC=C stretching vibrations), 1374 (δCH3 bending vibrations of aromatic
methyl groups) and 1074 cm-1. These bands are mainly related to vibration modes in aromatic
networks except for the one at 1074 cm-1, which might correspond to alkoxy stretching
vibrations (υC-O) of residual ester linkages between lignin and carbohydrates. HC-240 and IC-
240 present similar FTIR spectra with three extra shoulders centered at 1040 (aromatic δCH in
plane deformations), 1270 (υC-O stretching vibrations in lignin) and 1504 cm-1 (aromatic υC=C
stretching vibrations in lignin). Moreover, the band centered at 1445 cm-1 is more intense. These
bands can be attributed to the native ligneous components of CS. The band centered at 1040
cm-1 can be also attributed to υC-O stretching vibrations in holocellulose. These features suggest
that lignin, and to a lesser extent holocellulose, are less affected in the absence of iron. The
chemical structure of these four samples was also investigated by 13C solid-state NMR
spectroscopy (Figure 3b). Two major domains can be clearly identified: the aliphatic region
between 0 and 50 ppm and the aromatic region centered at 120-125 ppm. At first glance, the
two samples treated in the absence of iron, i.e. HC-240 and IC-240, present more aliphatic
carbons than HC-Fe-240 and IC-Fe-240. This observation is particularly pronounced for IC-
240 with two narrow and intense peaks at 13 and 30 ppm and a shoulder at 19 ppm. This feature
can be attributed to the partial degradation of [Bmim]Cl during the thermochemical treatment,
as confirmed by GC-MS (Figure S3) and FTIR (Figure S4) of the recycled IL and by the
presence of 6.7 wt.% of nitrogen in IC-240 (Table S3). This will be further discussed in section
3.4. In the aromatic region, while IC-240 displays a relatively narrow and intense peak centered
at 122 ppm, HC-240 and, to a lesser extent, IC-Fe-240 and HC-Fe-240, present a shoulder
centered at 145-150 ppm. This peak can be attributed to aromatic carbons bounded to lignin
methoxy groups and suggests that lignin was mildly affected in these conditions. As for HC-
240, this observation is in good agreement with FTIR spectroscopy. As for HC-Fe-240 and IC-
Fe-240, however, this feature is contradictory with the conclusions drawn from FTIR. As
reported by Baccile et al.17, the peak at 145-150 ppm can be also attributed to a nonsubstituted,
protonated, α-carbon of the furan ring of furanic resins. At that stage, it is important to get back
to basics of the HTC process applied to carbohydrates and lignocellulosic materials. The
conversion of carbohydrates into hydrochars is assumed to proceed in three main steps: (i)
hydrolysis into monosaccharide units if starting from oligo- or polysaccharides, (ii) dehydration
of monosaccharides into furan derivatives, and (iii) polycondensation of furan derivatives into
polyfuranic species.3, 17, 18, 20 At high temperature, typically at 240 °C, the carbonization process

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continues via intramolecular reactions (i.e., condensation, dehydration and decarbonylation
DOI: 10.1039/D0GC01510E
reactions) which lead to the production of condensed polyaromatic domains. As for insoluble
feedstocks, e.g. cellulose and raw lignocellulosic materials, fundamental differences in the HTC
mechanism were observed. As reported by Baccile et al.,17, 18 the polyfuranic structures usually
reported from simple carbohydrates cannot be observed in cellulose and lignocellulosic-derived
hydrochars, which yield higher amounts of arene groups coming either from condensed furanic
units or from polyaromatic hydrocarbon clusters. In this article, the authors concluded that the
hydrolysis of cellulose to glucose and subsequent dehydration and polycondensation into
polyfuranic species is limited to the cellulose-water interface and accounts for a minor part of
cellulose conversion. Meanwhile, the HTC of bulky cellulose follows chemical reaction
pathways comparable to the classical dry pyrolysis process. The results obtained herein with
HC-240 are in good agreement with the mechanism proposed by Baccile et al. based on
hydrochars derived from cellulose and rye straw.
Besides residual lignin, the presence of a shoulder at 145-150 ppm for IC-Fe-240 can
suggest a higher furan-to-arene ratio in the carbonaceous structure. This feature could be
explained by a better solubility of the cellulosic component in IL that would increase the
cellulose-solvent interface. One may expect a similar behavior in [Bmim]Cl. However, no clear
shoulder was observed at 145-150 ppm for IC-240. Even though the presence of this peak is
still a matter of discussion, the presence of oxygenated functional groups in the carbonaceous
framework of IC-Fe-240 was confirmed by elemental analyses (Table S3) and X-ray
photoelectron spectroscopy (XPS, Figures 3c-f and S5, Tables S5 and S6). According to the
simulated C1s XPS spectra, IC-Fe-240 depicts less sp2 carbons and more oxygenated functional
groups than HC-Fe-240 and HC-240 (Figure 3c, Table S5). This behavior might be explained
by the coordination of [FeCl4]- to the oxygen atoms of carbohydrates and lignin which may
stabilize carbon oxygenated groups and generate micropores. This assumption was further
supported experimentally. Firstly, according to SEM-EDX analyses (Table S3), IC-Fe-240 has
more residual iron and chlorine than HC-Fe-240. Secondly, the simulated O1s XPS spectrum
of IC-Fe-240 (Figure 3f, Table S6) suggests the presence of Fe-O species (contribution at 531
eV),60 together with oxygen atoms in a strongly electronegative environment (contribution at
534.5 eV). The latter might refer to oxygen atoms in the second coordination sphere of [FeCl4]-
anions. These contributions are less pronounced for HC-Fe-240 and HC-240 (Figure 3d-e,
Table S6). Additionally, the O/C mass ratio of IC-Fe-240 extracted from XPS is significantly
lower than the one obtained from elemental analysis (0.27 vs. 0.40 wt.% respectively, Table
S6). This difference is less pronounced for HC-Fe-240 and HC-240. This feature suggests that

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the carbonization at the biomass-solvent interface is more advanced than the carbonization in
DOI: 10.1039/D0GC01510E
the bulk, especially for the ITC process in BFe. It also confirms the presence of oxygenated
functional groups in the aromatic carbonaceous framework of IC-Fe-240, mainly due to the
recalcitrant ligneous fractions.

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DOI: 10.1039/D0GC01510E
(a)
(b)
IC-Fe-240
IC-240
IC-Fe-240
IC-240
HC-Fe-240
HC-Fe-240
HC-240
HC-240
2200 2000 1800 1600 1400 1200 1000 800
Wavenumber, cm-1
250 200 150 100 50
0
-50
ppm
80
(c)
Csp2
Csp3
(d)
70
60
50
40
30
20
10
0
C-O
HC-240
C=O
COOR
536
534
532
530
528
HC-240 HC-Fe-240 IC-Fe-240
Binding energy (eV)
(e)
(f)
IC-Fe-240
HC-Fe-240
536
534
532
530
528
536
534
532
530
528
Binding energy (eV)
Binding energy (eV)
Figure 3. (a) FTIR and (b) 13C CP-MAS NMR spectra of HC-240, HC-Fe-240, IC-240 and IC-Fe-240.
(c) XPS data obtained from the deconvoluted C1s spectra of HC-240, HC-Fe-240 and IC-Fe-240. O1s

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XPS band-like spectra (black solid lines) and deconvoluted curves (colored filled curves) of (d) HC-
DOI: 10.1039/D0GC01510E
240, (e) HC-Fe-240 and (f) IC-Fe-240.
3.2. On the influence of hydration
At that stage, it is important to notice that ITC occurs under autogenous pressure induced
by water produced during dehydration/condensation reactions and by low-boiling point organic
by-products. The residual water present in IL and biomass might be also considered. In our
case, BFe was thoroughly dried prior to ITC (water content c.a. 0 wt.% according to TGA,
Figure S6) and the water content in CS was systematically controlled prior to thermochemical
treatment (c.a. 7.5 wt.% according to TGA). As both IL and lignocellulosic biomass are usually
hard to keep dry, we proposed to study the influence of water over the carbonization process
and to explore the possibility to extend ITC to wet starting products and agrowastes. In our
study, the bound water in CS represented an amount of c.a. 0.6 wt.% in relation to BFe. To
study the influence of hydration, we conducted three experiments at 240°C for 20 hours at
increasing water content in relation to BFe (2, 10 and 25 wt.%, corresponding to the ionochars
named IC-Fe-240-2w, IC-Fe-240-10w and IC-Fe-240-25w respectively) and we compared
with ITC (0 wt.%, IC-Fe-240) and HTC (100 wt.%, HC-240). The as-prepared ionochars were
thoroughly characterized by elemental analyses (Table S7) and nitrogen sorption at 77 K
(Table S8). The results are compiled in Figure 4. As shown in Figure 4a, IC-Fe-240 and IC-
Fe-240-2w depict similar mass and carbon yields of c.a. 43 and 73-75 wt.% respectively. While
increasing the water content from 2 to 25 wt.%, mass and carbon yields significantly decreased
to reach 38 and 62 wt.% respectively for IC-Fe-240-25w. This feature can be attributed to the
decrease in iron-based Lewis catalysts while diluting BFe. Meanwhile, the textural properties
of the ionochars were significantly affected by the water content. As shown in Figure 4b, all
the samples, except for the one treated in 100 wt.% water (i.e., HC-240), display a type I/II
isotherm with a H3 hysteresis loop, related to micro-macroporous materials. Interestingly, both
SSABET (Table S8) and pore volume (Figure 4c) reached a maximum for IC-Fe-240-10w of
c.a. 616 m2.g-1 and 0.57 cm3.g-1 respectively. Particularly, a significant difference was observed
for the contribution due to external pores (Figure 4c), i.e., meso- and macropores in which the
nitrogen adsorption occurs in multimolecular layers. While the micropore volume kept stable
from IC-Fe-240 to IC-Fe-240-10w with a value of c.a. 0.2 cm3.g-1, the external pore volume
increased from 0.26 to 0.36 cm3.g-1 while increasing the water content from 0 to 10 wt.%.
Reversely, while increasing the water content from 10 to 25 wt.%, the external pore volume

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drastically decreased to 0.2 cm3.g-1. As mentioned in section 3.1, BFe is amphiphilDicOIa: 1n0d.10m39i/gD0hGtC01510E
form complex liquid structures governed by the assembly of hydrophobic and hydrophilic
domains. The addition of water may cause a change in the hydration state of BFe and modify
the hydrophilic/hydrophobic balance that might affect these complex liquid structures. In our
case, a small amount of water seems to be beneficial for the formation of ionic liquid
nanodomains and, in fine, the generation of meso- and macropores in the ionochars. This result
suggests that the use of wet starting products and agrowastes in the ITC process might be
advantageous for the production of highly porous chars.

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DOI: 10.1039/D0GC01510E

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Figure 4. (a) Mass and carbon yields, (b) Nitrogen sorption isotherms at 77 K and (c) pore volumes of
DOI: 10.1039/D0GC01510E
IC-Fe-240, IC-Fe-240-2w, IC-Fe-240-10w, IC-Fe-240-25w and HC-240.
3.3. On the contribution of cellulosic and ligneous components
As mentioned in section 3.1, the ligneous fractions of CS seem to be mildly affected as
compared to the cellulosic fractions. To get a better insight into the role of each component of
the lignocellulosic material, commercial cellulose and kraft lignin were treated in BFe at 240°C
for 20 hours, yielding IC-Fe-240-C and IC-Fe-240-L respectively. Those ionochars were
compared with the ones obtained from raw CS (IC-Fe-240) and Klason lignin extracted from
raw CS (IC-Fe-240-KL). The as-prepared ionochars were thoroughly characterized by
elemental analyses (Table S9) and nitrogen sorption at 77 K (Table S10). The results are
compiled in Figure 5. As shown in Figure 5a, the mass and carbon yields are significantly
higher for ligneous materials than for cellulosic ones. This behavior can be explained by the
fact that lignin contains more aromatic carbon and is more stable than hemicellulose and
cellulose in these conditions. Regarding mass and carbon yields, CS and cellulose behaved
similarly. This trend was confirmed by nitrogen sorption data. As shown in Figure 5b, IC-Fe-
240-C and IC-Fe-240 display similar type I/II isotherms with H3 hysteresis loops. IC-Fe-240-
C shows, however, a larger SSABET of c.a. 736 m2.g-1 (550 m2.g-1 for IC-Fe-240) mainly due
to micropores’ contribution (Table S10 and Figure 5c). Reversely, IC-Fe-240-L depicts a type
II isotherm and is mainly macroporous with a low SSABET of c.a. 40 m2.g-1. Evidently, cellulose
and hemicellulose, which undergo more severe structural rearrangement than lignin during the
ITC process, contribute more quantitatively to the generation of micropores in the final
ionochars. IC-Fe-240-KL depicts intermediate textural properties with a SSABET of c.a. 250
m2.g-1. The presence of residual carbohydrates or a higher H unit content in the Klason lignin
extracted from CS as compared with the commercial Kraft lignin (Figure S7) might explain
such difference. To elucidate this behavior, the ionothermal carbonization of different types of
lignin and raw agrowastes is currently under investigation.
Another significant difference lies in the fact that IC-Fe-240-L contains twice more
residual iron than the three other ionochars (i.e., 6 wt.% versus c.a. 3 wt.% for the others, Table
S9). As mentioned in section 3.1, [FeCl4]- moieties are willing to coordinate to the oxygen
atoms of carbohydrates and lignin. As reported by Li et al.,53 the low absolute binding energy
between the cation and the anion in BFe improves the efficient dissociation of [Bmim]+ and
[FeCl4]- and favors the coordination interactions between Fe atom of [FeCl4]- and O atom of

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ester and phenol groups from lignin. One may assume that the recalcitrant G and S units in
DOI: 10.1039/D0GC01510E
lignin53 are willing to form stable coordination complexes with [FeCl4]- and to trap more iron
atoms in the final carbonaceous framework.

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Figure 5. (a) Mass and carbon yields, (b) Nitrogen sorption isotherms at 77 K and (c) pore volumes of
DOI: 10.1039/D0GC01510E
IC-Fe-240, IC-Fe-240-C, IC-Fe-240-L and IC-Fe-240-KL.
3.4. Recyclability and reusability of [Bmim][FeCl4]
To support the sustainability of the ITC process, the recyclability of BFe was investigated.
The iron-containing ionic liquid was thoroughlty characterized by FTIR spectroscopy and ICP
atomic emission spectrometry (ICP-AES) before (BFe) and after ITC of raw CS at 180 and
240°C for 20 hours (BFe-r180 and BFe-r240 respectively, Figure 6a). While the chemical
signature of [Bmim][FeCl4] was preserved, the amount of iron decreased from 16.6 wt.% in
fresh BFe to 16.3 wt.% in BFe-r180 and 16.0 wt.% in BFe-r240. This result confirms the loss
of iron during ITC, partly due to the presence of remaining [FeCl4]- complexes in ionochars.
One may also consider the fact that both BFe-r180 and BFe-r240 were collected only after the
first filtration step, which allowed recovering c.a. 95 wt.% of the IL. [FeCl4]- moieties and
imidazolium cations were also present in the subsequent filtrates, making the recycling largely
improvable. BFe-r240 was also characterized by GC-MS and no degradation products were
detected, while imidazole by-products (e.g., imidazole, methylimidazole, 1-butylimidazole and
N-Propionylimidazole) were identified for [Bmim]Cl recovered after ITC of CS at 240°C
(Figure S3). These by-products were probably generated by the cleavage of the butyl and
methyl side chains by hydroxyl radicals.61 BFe-r240 was reused for the ITC of CS at 240°C for
20 hours, yielding IC-Fe-240-r1. This ionochar was compared with IC-Fe-240 (Tables S11
and S12). As shown in Figure 6b, IC-Fe-240 and IC-Fe-240-r1 display similar type I/II
isotherms with H3 hysteresis loops. Meanwhile, the mass and carbon yields were not affected
(Figure 6c). However, the SSABET slightly decreased from 550 m2.g-1 for IC-Fe-240 to 455
m2.g-1 for IC-Fe-240-r1 (Table S12). This difference results from a reduction in the micropore
contribution (Figure 6d), which is mainly related to the amount of [FeCl4]- moieties in the
reaction medium as mentioned above.

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Figure 6. (a) FTIR spectra of BFe, BFe-r180 and BFe-r240. (b) Nitrogen sorption isotherms at 77 K of
DOI: 10.1039/D0GC01510E
IC-Fe-240 and IC-Fe-240-r1. (c) Yields and (d) specific surface areas of IC-Fe-240 and IC-Fe-240-
r1.
3.5. Pyrolysis and CO2 activation: from ionochars to activated carbons
High temperature post-treatments (i.e., pyrolysis and CO2 activation) were carried out on
ionochars to further investigate their potential and extend their applicability. After pyrolysis at
900°C under argon (P9 series), porous carbon materials with increased carbon content (c.a. 90
wt.%) can be obtained (Tables S13 and S14). Interestingly, the remnant of iron in ionochars
was converted to iron-carbon core-shell nanoparticles as shown by high-resolution TEM
imaging (Figure 7a) and elemental EDX mapping (Figure 7b and Figure S8). According to
X-ray diffraction performed on IC-Fe-240-P9 (Figure S9a), the core of these core-shell
nanoparticles is composed of iron (α-Fe), iron carbide (Fe3C), and maghemite (γ-Fe2O3). TEM
imaging also revealed that highly ordered graphitic layers surround the iron-based core (Figure
S9b-c). The carbothermal reduction of iron salts to α-Fe and Fe3C at high temperature and the
formation of similar core-shell structures were already described for biomass derived
hydrochars62 and ionochars47. As a direct consequence, these ionochar-derived carbons are
strongly attracted to magnets (insert in Figure 7a) and might be easily separable from solution
by external magnetic fields. Besides, the textural properties of the ionochars were mainly
preserved after pyrolysis, with type I/II isotherms with H3 hysteresis loops and a slight increase
in micropore contributions (Table S13 and Figure 7c). Based on these advantageous properties,
we are currently investigating their use in magnetic separation for wastewater treatment and
depollution.

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DOI: 10.1039/D0GC01510E
Figure 7. (a) HR-TEM micrograph and (b) STEM-EDX mapping of a core-shell structure observed in
IC-Fe-240-P9. The upper right insert is a picture of IC-Fe-240-P9 attracted to a magnet. Nitrogen
sorption isotherms at 77 K of some ionochars after (c) pyrolysis at 900°C under argon and (d) CO2
activation at 950°C.
To evaluate the potential of ITC as a pretreatment for the preparation of highly porous
carbons (i.e., activated carbons), we also studied the physical activation of a few samples under
a CO2-rich atmosphere at 950°C. HTC has been established as an efficient pretreatment in the
transformation of carbohydrates and raw lignocellulosic biomass to activated carbons.14, 15
Recently, Xie et al.51 also proposed to use ITC as an intermediate step prior to activation of raw
biomass. All these studies used KOH activation at high temperature (between 600 and 900°C).
The latter is a chemical activation commonly employed to prepare activated carbons with high
SSA and narrow micropores.63 In this study, we proposed to investigate another approach, i.e.
the physical activation in a CO2-rich atmosphere. CO2 activation has been less employed than
KOH activation as it usually yields activated carbons with lower SSA. Nonetheless, CO2

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activation usually offers higher yields and carbon content compared to chemical DaOcIt:i1v0.a10ti3o9/nD.0GC01510E
Moreover, CO2 activation is more advantageous in terms of time, cost and simplicity.63
Two samples were submitted to CO2 activation at 950°C: HC-240, the hydrochar serving as a
reference; and IC-Fe-240-10w, the ionochar with the highest SSABET. Two different procedures
were employed: A1, when the samples were submitted to CO2 activation for 2 hours at the
plateau only; and A2, when the sample was submitted to CO2 activation from the beginning of
the heating ramp, starting from 110°C. As shown in Figure 7d, the activated carbons still display
type I/II isotherms. Both pore volumes and SSABET were significantly increased as compared
with the carbons obtained by pyrolysis (P9 series, Table S15). Considering textural properties,
ITC seems to be favorable compared to HTC. After a similar activation procedure (A1), IC-
Fe-240-10w-A1 presents a SSABET of c.a. 1440 m2.g-1, mainly due to micropores’ contribution
(SSAmicropore of c.a. 1200 m2.g-1), while HC-240-A1 presents a SSABET of c.a. 800 m2.g-1 (Table
S15). Meanwhile, the activation procedure A2 allows reaching higher SSA. Thus, IC-Fe-240-
10w-A2 presents a SSABET of c.a. 2060 m2.g-1, with a micropores’ contribution of c.a. 1800
m2.g-1. Interestingly, mass yields of 35-44 wt.% were obtained (Table S16).
3.6. Preliminary results for post combustion CO2 capture
The hydrochars, ionochars and carbons prepared in this study were tested for post
combustion CO2 capture. The most representative isotherms recorded at 273 K are shown in
Figure 8a. For a purpose of comparison, the CO2 uptakes of each sample are represented in
Figure 8b as a function of their corrected mass yield. We believe that these two parameters,
i.e., mass yield and CO2 uptake, are crucial to evaluate both the efficiency and the sustainability
of the different materials prepared in this study. Interestingly, two regions can be clearly
identified. The ionochars and ionochar-derived carbons gather in the upper right region, which
corresponds to higher mass yields and/or higher CO2 uptakes. Reversely, all the other materials
gather in the bottom left region, which corresponds to lower mass yields and/or lower CO2
uptakes. In another representation, we proposed to express the CO2 uptakes of each sample per
gram of CS treated, i.e. the CO2 uptakes were weighted as a function of the total mass yields of
each activation procedure. The same trend was observed (Figure S10). The ionochars and
ionochar-derived carbons display weighted CO2 uptakes superior to 0.8 mmol of CO2 adsorbed
per gram of CS treated, while the other materials were below 0.6 mmol.g-1. These results further
demonstrate that ITC in [Bmim][FeCl4] is an advantageous pretreatment for the transformation
of raw lignocellulosic agrowastes into advanced activated carbons for CO2 capture.

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The CO2 uptake of the most efficient material, i.e., IC-Fe-240-10w-A2, was also tested at 293
DOI: 10.1039/D0GC01510E
and 298 K (Figure 8c). At 298 K and 1 bar, IC-Fe-240-10w-A2 was able to adsorb 4.4 mmol
of CO2 per gram. This value is amongst the highest values reported to date in literature for
nitrogen-free biomass-derived carbons (Table 1).13-15, 63 To the best of our knowledge, it’s also
the highest CO2 uptake reported to date for CO2 activated biomass-derived carbons.63, 64 Even
though this value is still far from the highest CO2 uptakes reported in literature for metal-organic
frameworks (MOFs)65 (e.g., a capacity of 8 mmol of CO2 per gram was reported for Mg-MOF-
74 at 296 K and 1 bar66), the activated carbons reported herein are very competitive with other
porous solid adsorbents, such as covalent organic frameworks67 or zeolites68. Moreover,
activated carbons are usually less moisture-sensitive than zeolites68 and MOFs69, which is
advantageous when considering the considerable amount of water in flue gas streams.70 Last
but not least, the valorization of cheap, renewable and abundant agrowastes falls into the
circular economy scheme. Thus, our approach represents a competitive and sustainable
alternative to more expensive crystalline microporous materials for post combustion CO2
capture. These results are highly promising and might encourage further studies in the field of
ionochars-derived activated carbons. With this aim, we are currently investigating different
chemical activation procedures (KOH and ZnCl2) to produce ionochars-derived carbons with
enhanced micropores’ contribution. Thorough characterizations of the CO2 adsorbents reported
here are also under investigation such as cyclic stability, adsorption kinetics, and CO2/N2
selectivity. Considering the advantageous textural properties of these materials, precombustion
CO2 capture at higher pressure should be also considered.

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DOI: 10.1039/D0GC01510E