Non-hyd oly ic sol-gel syn hesis o amine- unc ionalized silica: Templa e-
and ca alys - ee p epa a ion o mesopo ous ca alys s o CO
2
alo iza ion
Thai Q. Bui
a
, Tomas Poko ny
a
, Pe Machac
a
, Zdenek Mo a ec
a
, E a Dominco a Be ge o a
b
,
Ales S yskalik
a,*
a
Depa men o Chemis y, Facul y o Science, Masa yk Uni e si y, Ko la ska 2, CZ-61137 B no, Czech Republic
b
Cen e o Polyme Sys ems, Tomas Ba a Uni e si y in Zlin, . Tomase Ba i 5678, CZ-76001, Zlin, Czech Republic
ARTICLE INFO
Keywo ds:
Non-aqueous condensa ion
Silsesquioxane
Te ia y amine
He e ogeneous ca alysis
Ca bon dioxide
Epoxide
Cyclic ca bona e
ABSTRACT
Ca bon dioxide u iliza ion p esen s an impo an and opical esea ch opic. Howe e , he pe o mance o ca -
alys s needed o CO
2
ans o ma ions does no achie e he necessa y le els o hei widesp ead applica ion. To
his end, we decided o s udy non-aqueous condensa ions p o iding amine- unc ionalized silica ca alys s,
possibly ac i e in CO
2
-epoxide cycloaddi ion eac ion. While non-hyd oly ic sol-gel me hod is well-known o i s
e iciency in p o iding highly po ous Lewis and B øns ed acid me allosilica es, he e we show o he i s ime i s
applica ion o he p epa a ion o silica-based ca alys s con aining basic g oups. Fi s , he eac ion condi ions
we e sc eened o ep oducibly ob ain po ous ma e ials wi h p ese ed amine moie ies. These we e iden i ied as
ollows: silicon e aace a e and b idging e ia y amine silanes as p ecu so s, oluene as a sol en , and em-
pe a u e be ween 160 and 180 ◦C. In such a way, ma e ials wi h up o 776 m
2
g
−1
and 1.58 cm
3
g
−1
we e
ob ained in one-s ep p ocess, wi hou any empla e, a e con en ional d ying s ep. Nex , he amine-
unc ionalized ma e ials we e es ed in CO
2
-epoxide coupling p o iding cyclic o ganic ca bona es wi h high
selec i i y (>99 %) and mode a e ac i i y (up o 86 % epichlo ohyd in con e sion a e 1 h a 120 ◦C and 10 ba
CO
2
). The cha ac e iza ion o spen ca alys s e ealed a p esence o cyclic o ganic ca bona es a he ca alys
su ace as well as con e sion o e ia y amine g oups o qua e na y ammonium moie ies.
1. In oduc ion
O ganic-ino ganic hyb id ma e ials (OIHMs) ha e been s udied
ex ensi ely in bo h academia and indus y because hey can be ailo ed
o possess desi able p ope ies o sui a wide ange o applica ions
hanks o possibili y o combine he e sa ili y o o ganic species wi h
he ad an ages o ino ganic componen s such as excellen he mal s a-
bili y and obus s uc u e [1]. Gene ally, OIHMs can be classi ied in o
wo majo classes depending on he na u e o in e ac ions be ween
o ganic and ino ganic phases. Class I hyb ids con ain weak in e ac ions
( an de Waals,
π
–
π
, hyd ogen bonding, elec os a ic) while class II
hyb ids con ain s ong (co alen ) bonds be ween wo cons i uen s.
In he ield o he e ogeneous ca alysis, class II hyb ids a e p e e able
o class I ones because s ong bonds be ween o ganic and ino ganic
building blocks in he o me would a o p ese a ion o he hyb id
ca alys s du ing ca aly ic eac ion, minimizing leaching o he ac i e
o ganic moie y in o eac ion media [2]. Mesopo ous silica-based hyb ids
de i ed om he sol-gel syn hesis me hod a e pa icula ly a ac i e as
po en ial hyb id he e ogeneous ca alys s due o he wide a ailabili y o
o ganosilicon p ecu so s in he ma ke , he ease o p epa a ion and
uning as well as he high accessibili y o ac i e si es and he e icien
mass anspo [2]. So a , hese hyb ids ha e been syn hesized mainly
by using he adi ional sol-gel me hod, aka he hyd oly ic sol-gel (HSG),
whose mechanism is ela ed o hyd olysis and polycondensa ion e-
ac ions. Howe e , he e a e wo majo limi a ions in his me hod when
wa e is used as a sol en [3]. Fi s , di e en me al/silicon p ecu so s (e.
g., Si(OR)
4
s. Ti(OR)
4
o Si(OR)
4
s. R’
x
Si(OR)
4-x
) may ha e signi i-
can ly di e en hyd olysis as well as polycondensa ion a es unde
aqueous condi ions leading o phase sepa a ion o he e ogenei y. Sec-
ond, due o high su ace ension o wa e , he po e s uc u es o we gel
may collapse du ing he d ying p ocess esul ing in ma e ials wi h poo
ex u al p ope ies.
To o e come he limi a ions o he HSG men ioned abo e, he non-
hyd oly ic sol-gel (NHSG) can be seen as an al e na i e me hod whe e
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (A. S yskalik).
Con en s lis s a ailable a ScienceDi ec
Mic opo ous and Mesopo ous Ma e ials
jou nal homepage: www.else ie .com/loca e/mic omeso
h ps://doi.o g/10.1016/j.mic omeso.2024.113371
Recei ed 2 Augus 2024; Recei ed in e ised o m 9 Oc obe 2024; Accep ed 11 Oc obe 2024
Mic opo ous and Mesopo ous Ma e ials 381 (2025) 113371
A ailable online 12 Oc obe 2024
1387-1811/© 2024 The Au ho s. Published by Else ie Inc. This is an open access a icle unde he CC BY license (
h p://c ea i ecommons.o g/licenses/by/4.0/ ).
he sol-gel p ocesses ake place in wa e - ee en i onmen s. The NHSG
me hod elies on non-hyd oly ic polycondensa ion eac ions be ween
me al/silicon p ecu so s and oxygen dono s o he han wa e unde non-
aqueous condi ions and leads o he o ma ion o me al/silicon oxides
[3,4]. On one hand, such app oach b ings se e al di icul ies and en i-
onmen al conce ns including applica ion o o ganic sol en s, leng hy
p ocedu es, and wo k unde d y N
2
a mosphe e (ei he in he glo ebox
and/o applying he N
2
/ acuum mani old). Howe e , hese down alls
a e coun e balanced by decisi e ad an ages. Fi s , The condensa ion
eac ion a es a e usually lowe and le elled o compa ed o ones unde
aqueous en i onmen s, leading o he o ma ion o ma e ials wi h
well-con olled p ope ies such as homogenei y, composi ion,
mo phology, ex u e, and su ace chemis y. Second, a con en ional gel
d ying p o ides o en highly po ous ma e ials. O ganic sol en s exhibi
much lowe su ace ension in compa ison o wa e and he e o e he
applica ion o empla es o supe c i ical/ eeze d ying is no necessa y.
Thanks o hese ad an ages (bu no limi ed o), ma e ials p epa ed om
he NHSG me hod ha e ound many applica ions in indus y such as
he e ogeneous ca alys s, luminescen ma e ials, ca alys suppo s, and
Li-ion ba e y elec odes [3,5].
In he ield o he e ogeneous ca alysis, he NHSG me hod is pa ic-
ula ly bene icial o he p epa a ion o mesopo ous mixed oxide ca a-
lys s compa ed o he HSG me hod in e ms o simplici y, e sa ili y, and
p ope ies con ol [6,7]. In addi ion, his me hod could also be use ul o
he p epa a ion o o ganic-ino ganic hyb id ca alys s [8]. Howe e , o
he bes o ou knowledge, only mixed oxide ca alys s unc ionalized
wi h alkyl and/o a yl g oups ha e been so a epo ed as class II hyb id
ca alys s p epa ed by he NHSG me hod [8–16]. The e o e, i is s ill in i s
in ancy and, indeed, needs mo e e o s o exploi u he he po en ial o
he NHSG me hod in he p epa a ion o class II hyb id ma e ials,
pa icula ly in he ield o he e ogeneous ca alysis.
One way o b oadening hei spec a o class II hyb id ca alys s
de i ed om he NHSG me hod is h ough he in oduc ion o amine
g oups in o ino ganic ma e ials s uc u e. Amine is one o he mos
a ac i e o ganic unc ional g oups due o i s wide applica ions.
Pa icula ly, e ia y amines and he e ocyclic amines a e p omising
me al- and halogen- ee o ganoca alys s o he syn hesis o cyclic
o ganic ca bona es om CO
2
and epoxides [17–21]. This cycloaddi ion
eac ion is one o he mos p omising ou es o chemical ixa ion o CO
2
on indus ial scale due o 100 % a om economy and p oducing aluable
cyclic ca bona e p oduc s. While homogeneous ca alys s p o ide
excellen ca aly ic ac i i y, he e ogeneous ca alys s a e echnically
p e e able in indus y due o he ease o ca alys sepa a ion and ecy-
cling as well as he ease o applica ion in con inuous- low p ocesses.
Se e al ypes o he e ogeneous ca alys s con aining ni ogen-amine
ac i e si es o his eac ion ha e been success ully de eloped such as
N-doped ca bons [22], mesopo ous melamine- o maldehyde esins
[23], co alen o ganic amewo ks (COFs) [24], me al-o ganic ame-
wo ks (MOFs) [25], poly(ionic liquid)s (PILs) [26], and mesopo ous
amine-silica hyb ids [27–29]. Among hem, mesopo ous amine-silica
hyb ids a e pa icula ly a ac i e due o me al- and halogen- ee na-
u e, low-cos , simple p epa a ion, e icien mass anspo , and obus
s uc u e. So a , mesopo ous amine-silica ca alys s o he cycloaddi ion
eac ion ha e been p epa ed mainly by g a ing amine p ecu so s on
mesopo ous silica suppo s [27–29]. Al hough his pos -modi ica ion
me hod exhibi ed conside able success in he p epa a ion o meso-
po ous amine-silica ca alys s, an e ec i e and simple one-po syn hesis
(aka di ec syn hesis) is highly desi ed. In his ega d, he use o b idged
ialkoxysilyla ed amine p ecu so s o di ec sol-gel syn hesis o mes-
opo ous amine-silica hyb ids is highly p omising. Se e al mesopo ous
amine-silica hyb ids de i ed om b idged ialkoxysilyla ed amine
p ecu so s showed high po osi y, high he mos abili y, high con en o
su ace amine g oups [30–32], and we e applied in se e al applica ions
such as he e ogeneous o ganoca alys s [33,34], CO
2
adso ben s
[35–37], pe luo ina ed compounds adso ben s [38], Hg(II) adso ben s
[39], and dyes adso ben s [40]. Howe e , he e is li le in o ma ion
abou applying hese ma e ials o he cycloaddi ion eac ion be ween
epoxides and CO
2
. In addi ion, hese ma e ials ha e been p epa ed
mainly ia adi ional hyd oly ic sol-gel and using s uc u e-di ec ing
agen s o c ea e mesopo es (Table S1).
In his epo , we applied a empla e- ee and one-po NHSG me hod
o co-condense mono/bis/ is- ime hoxysilyla ed amine p ecu so s
bea ing alipha ic amine moie ies wi h silica p ecu so s (SiCl
4
and Si
(OAc)
4
). Ou aim was o p epa e mesopo ous amine-silica class II hy-
b ids as po en ial me al- and halogen- ee ca alys s o he CO
2
-epoxide
cycloaddi ion eac ion. Fi s , he ideal eac ion condi ions we e unam-
biguously iden i ied. Second, he s uc u e and he adso p ion p ope ies
o he esul ing ma e ials we e desc ibed in de ail. Finally, he com-
pa ison o ca aly ic pe o mance o amine-silica ma e ials wi h hei
homogeneous analogues as well as cha ac e iza ion o spen ca alys s
e ealed an in e es ing beha io o he e ogeneous ca alys s p epa ed by
NHSG polycondensa ion.
2. Expe imen al
Gene al in o ma ion is w i en in Suppo ing In o ma ion.
2.1. Syn hesis o hyb id amine-silica xe ogels
No el hyb id amine-silica ma e ials we e p epa ed in one po using
non-hyd oly ic sol-gel (NHSG) me hod, speci ically ia alkyl halide and
es e elimina ion ou es [3,5]. The s uc u es o amine and silica p e-
cu so s in his s udy a e p esen ed in Fig. 1. Anhyd ous dichlo ome hane
(DCM), e ahyd o u ane (THF), and oluene (TOL) we e used as
sol en s.
Typically, we mixed 3 g o a silica p ecu so SiX
4
(X =CH
3
COO o Cl)
wi h 10 mL o an ap o ic sol en (DCM/THF/TOL) in a Te lon-lined
s ainless-s eel au ocla e (100 mL) unde N
2
a mosphe e in a d y box.
Subsequen ly, we added o he mix u e a s oichiome ic amoun o an
amine p ecu so (Equa ions (1)─4, Fig. 1), which con ains ei he a e -
minal p ima y amine g oup (deno ed as N1) o a b idging seconda y/
e ia y amine g oup (deno ed as N2/N3-Me/N3). The esul ing mix u e
was magne ically s i ed un il we go a clea solu ion. Nex , he au o-
cla e was sealed and aged a a desi ed empe a u e (140─200 ◦C) in an
o en o 4 days unde au ogenous p essu e. A e his, he au ocla e was
cooled o oom empe a u e and hen opened inside a d y box. The
ob ained gel was c ushed, ans e ed o a Schlenk essel, and d ied
unde acuum a 120 ◦C o e nigh o emo e ola ile p oduc s (e.g.,
CH
3
X) and sol en . The ola ile p oduc s we e iden i ied by using GC-
MS.
3 SiX
4
+4 (CH
3
O)
3
Si(CH
2
)
3
NH
2
(N1) →12 CH
3
X+Si
7
O
12
(CH
2
)
12
(N-
H
2
)
4
(eq. 1)
3 SiX
4
+2 [(CH
3
O)
3
Si(CH
2
)
3
]
2
NH (N2) →12 CH
3
X+
Si
7
O
12
(CH
2
)
12
(NH)
2
(eq. 2)
3 SiX
4
+2 [(CH
3
O)
3
Si(CH
2
)
3
]
2
NCH
3
(N3-Me) →12 CH
3
X+
Si
7
O
12
(CH
2
)
12
(NCH
3
)
2
(eq. 3)
9 SiX
4
+4 [(CH
3
O)
3
Si(CH
2
)
3
]
3
N(N3) →36 CH
3
X+Si
21
O
36
(CH
2
)
36
-
N
4
(eq. 4)
3. Resul s and discussion
3.1. Es e elimina ion ou e: The NHSG condensa ion and po osi y o
hyb id ma e ials
In his ou e, Si(OAc)
4
was used as a silica p ecu so oge he wi h 4
amine p ecu so s (N1/N2/N3-Me/N3) con aining ime hoxysilyl
g oups o syn hesize hyb id amine-silica ma e ials (Equa ions (1)─4).
T.Q. Bui e al. Mic opo ous and Mesopo ous Ma e ials 381 (2025) 113371
2
The silica and amine p ecu so s we e mixed wi h an equal numbe o
ace oxy and me hoxy unc ional g oups in an ap o ic sol en . The
p esence o me hyl ace a e as a ola ile p oduc in all syn hesis expe i-
men s was con i med by GC-MS analysis o esidue sol en s a e he
non-hyd oly ic sol-gel (NHSG) syn hesis. The so-called es e elimina ion
has been epo ed o p o ide a b oad a ie y o ma e ials including
silicophospha es [41], hei hyb id de i a i es [42], me allosilica es
[43,44], and me al ime hylsiloxides [45]. While Lewis acidi y o he
me al cen e s has usually been epo ed o d i e he NHSG condensa ion
[45], such si es a e lacking in ou case. Based on he ac ha he e was
no gela ion be ween Si(OAc)
4
and ime hoxyme hylsilane CH
3
Si
(OCH
3
)
3
unde simila syn hesis condi ions (10 mL o DCM, 180 ◦C, 4
days), we belie e ha N-si es om amine p ecu so s could play a ole as
a ca alys o he NHSG syn hesis o amine- unc ionalized silicas.
I should be no ed ha ca boxylic acid es e s (i.e., me hyl ace a e,
silicon e aace a e) can eac wi h p ima y and seconda y amines
o ming seconda y and e ia y amides, espec i ely [27,46]. This e-
ac ion should be accompanied by me hanol o ma ion. GC-MS analysis
con i med MeOH p esence in esidue ola iles a e NHSG syn heses
when applying N1 and N2 p ecu so s. The e o e, he possible amide
o ma ion was ca e ully checked (see sec ion 3.2 Es e elimina ion ou e:
The s uc u e o hyb id ma e ials).
The N
2
adso p ion–deso p ion iso he ms and co esponding NLDFT
po e size dis ibu ions o some selec ed hyb id xe ogels ob ained om
he es e elimina ion ou e unde di e en condi ions (amine p ecu so ,
ap o ic sol en , empe a u e) a e gi en in Fig. S1. The iso he ms adop
ype IV ypical o mesopo ous ma e ials (excep o sample N1 which
was non-po ous, see discussion below). The hys e esis loops a e mos ly
H2- ype indica ing he p esence o i egula mesopo es wi h complex
po e s uc u es [47]. Some samples exhibi s eep N
2
adso p ion a p/p
0
>0.9 indica ing he p esence o in e pa icle oids [47]. Indeed, he
NLDFT models (Fig. S1, igh ) show po e sizes anging in he mesopo e
egion (and o some ex en in he mac opo e egion) o e ens o
nanome e s as can be expec ed o he NHSG syn hesis applying no
empla ing agen s. The quali a i e N
2
adso p ion-deso p ion iso he ms
e alua ion ag ees well wi h he mo phology o he ma e ials obse ed by
SEM and TEM (Figs. S2 and S3). The mic og aphs show i egula
sponge-like pa icles wi h sizes in he mic on ange ha appea o
con ain bo h meso- and mac opo es.
Table 1 summa izes he quan i a i e ex u al p ope ies o hyb id
amine-silica ma e ials syn hesized om he es e elimina ion ou e
unde di e en syn he ic condi ions (amine p ecu so , ap o ic sol en ,
Fig. 1. Chemical s uc u es o silica and amine p ecu so s in his s udy.
Table 1
Tex u al p ope ies o hyb id amine-silica xe ogels ob ained om he es e elimina ion ou e (Si(OAc)
4
as a silica p ecu so ) unde di e en condi ions.
Gel Amine p ecu so Ap o ic sol en Temp. (◦C) S
BET
(m
2
g
−1
)
a
V
o al
(cm
3
g
−1
)
b
V
mic o
/V
o .
(%)
c
PS
DFT
(nm)
d
PS
a e .
(nm)
1 N1 TOL 180 <10 n.d.
e
n.d. n.d. n.d.
2 N2 DCM 180 664 0.43 12.6 2.6 2.6
3THF 180 708 1.18 4.2 10.5 6.7
4TOL 180 624 1.32 3.1 7.0 8.5
5TOL 160 426 0.53 3.6 6.6 5.0
6 N3-Me DCM 180 604 0.58 2.9 2.6 3.8
7THF 180 700 0.63 9.0 2.6 3.6
8TOL 200 303 0.92 1.0 29.4 12.2
9TOL 180 776 1.58 0.7 13.9 8.1
10 TOL 160 666 0.93 1.9 3.2 5.6
11 TOL 140 141 0.47 0.0 7.0 13.2
12 N3 TOL 180 761 1.26 2.7 6.8 6.6
13 TOL 140 396 0.61 0.5 6.8 6.1
a
Es ima ed a p/p
o
=0.97.
b
Based on -plo analyses (Fig. S4).
c
The maximum alue o he po e size dis ibu ion cu e (NLDFT, ads, cyl. po e model).
d
4V
o al
/S
BET
.
e
No de e mined.
T.Q. Bui e al. Mic opo ous and Mesopo ous Ma e ials 381 (2025) 113371
3
empe a u e). I is clea ly seen om Table 1 ha ma e ials de i ed om
b idging amine p ecu so s (N2/N3-Me/N3) o en exhibi ed high speci ic
su ace a eas (S
BET
; 141─776 m
2
g
−1
), high o al po e olumes (V
o al
;
0.43─1.58 cm
3
g
−1
), and la ge mesopo es. All h ee b idging amine
p ecu so s (N2/N3-Me/N3) eac ed wi h Si(OAc)
4
a di e en empe -
a u es and in a ious sol en s. The compa ison o bo h S
BET
and V
o al
clea ly highligh s 180 ◦C as he ideal syn he ic empe a u e; speci ic
su ace a eas and o al po e olumes a e lowe a bo h highe (200 ◦C)
and lowe (140 ◦C, 160 ◦C) empe a u es (Table 1). This obse a ion is
p obably connec ed wi h he condensa ion deg ee: he ma e ials syn-
hesized a 180 ◦C exhibi only low signals o un eac ed o ganic g oups
and, a he same ime, no signs o decomposi ion (see sec ion 3.2 Es e
elimina ion ou e: S uc u e o hyb id ma e ials). Rega ding he e ec o
sol en s on po osi y, ma e ials syn hesized in dichlo ome hane (DCM),
e ahyd o u an (THF), and oluene exhibi ed simila S
BET
anging om
604 o 776 m
2
g
−1
. Howe e , he V
o al
was always signi ican ly highe in
nonpola oluene han in pola DCM o THF (Table 1).
In con a y o samples p epa ed wi h b idging amine p ecu so s (N2/
N3-Me/N3), he ma e ial de i ed om he e minal amine p ecu so
(N1) was non-po ous (S
BET
<10 m
2
g
−1
) unde empla e/addi i e/
ca alys - ee and NHSG syn hesis condi ions. This obse a ion ag ees
wi h epo ed esul s om NHSG syn hesis o hyb id silicophospha e
xe ogels [42]. Speci ically, he co-condensa ion eac ions be ween Si
(OAc)
4
and e minal p ecu so s R─P(O)(OSiMe
3
)
2
(R =alkyl o a yl
g oup) p oduced non-po ous ma e ials while he co-condensa ion e-
ac ions be ween Si(OAc)
4
and b idged ones (Me
3
SiO)
2
(O)P─R─P(O)
(OSiMe
3
)
2
p oduced highly po ous ma e ials (553─617 m
2
g
−1
). Simila
esul s we e also obse ed om he use o e minal and b idged silane
p ecu so s (MeSi(OAc)
3
s. (AcO)
3
Si─R─Si(OAc)
3
, espec i ely) wi h
is( ime hylsilyl)phospha e P(O)(OSiMe
3
)
3
[42]. The imp o ed
po osi y when applying b idging p ecu so s comes om he addi ional
c oss-linking in oduced by he o ganic b idge, while he o ganosilane
p ecu so s wi h e minal o ganic g oups p o ide, in ac , a lowe con-
nec i i y in compa ison o bo h b idged and con enien (i.e.,
ou -connec ed) silica p ecu so s [42].
To he bes o ou knowledge, he e is no epo ela ed o using N1/
N2/N3-Me/N3 amine p ecu so s in he empla e/addi i e/ca alys - ee
and NHSG syn hesis o hyb id amine-silica ma e ials. Mos impo -
an ly, e en wi hou using any empla e/addi i e/ca alys , he meso-
po ous ma e ials (wi h a clea hys e esis loop) de i ed om b idging
amine p ecu so s (N2/N3-Me/N3) using NHSG exhibi ed compa able o
e en be e ex u al p ope ies compa ed o he ones using hyd oly ic
sol-gel (HSG) app oach (Table S1).
3.2. Es e elimina ion ou e: The s uc u e o hyb id ma e ials
In o de o con i m he s uc u al in eg i y o o ganic moie ies be o e
and a e NHSG syn hesis unde di e en condi ions, we pe o med
solid-s a e
13
C CP MAS NMR measu emen s o he hyb id amine-silica
xe ogels and compa ed he esul s wi h liquid-s a e
13
C NMR (in
CDCl
3
) spec a o hei co esponding amine p ecu so s. The esul s
show ha he syn hesis pe o med in oluene a 180 ◦C was he op imum
condi ion in ou s udy o p ese e he o ganic s uc u e o he amine
p ecu so s in hei co esponding hyb id xe ogels (Fig. 2,S5, S6) [30].
The addi ional signal a ~170 ppm ep esen s ca bonyl g oups in e-
sidual ace oxy o ace amide g oups (see explana ion below) [41]. The
signal o co esponding me hyl g oups (22.6 ppm in silicon e aace a e
[41]) is o e lapping wi h signals coming om me hylene moie ies in
amine p ecu so s. F om Fig. S5 we can clea ly see “unusual”peaks in
13
C
CP MAS NMR spec a o ma e ials syn hesized in DCM, especially in he
case o N3-Me p ecu so , compa ed o ones syn hesized in TOL o THF.
The possible easons o his obse a ion could be due o side eac ions
be ween amine si es and DCM unde syn he ic condi ions [48]. Simila
pa e ns we e obse ed in alkyl halide elimina ion (CH
3
Cl p oduced as
ola ile p oduc ) and in spen ca alys s ( eac ion wi h epichlo ohyd in
and/o [4-(chlo ome hyl)-1,3-dioxolan-2-one]) and we e explained by
occu ence o side eac ions on amine si es, i.e., qua e niza ion, e e se
Menschu kin, and Ho mann eac ions (see sec ion 3.6 Recyclabili y
s udies and spen ca alys s cha ac e iza ion) [48–51].
Rega ding he e ec o empe a u e, i can be seen om Fig. S6 ha
in ensi ies o me hoxy and ace oxy g oups dec ease when he syn he ic
empe a u e inc eases om 140 o 180 ◦C, indica ing a highe deg ee o
co-condensa ion. Howe e , he appea ance o unwan ed peaks a 65
ppm and 26 ppm oge he wi h he signi ican educing o in ensi ies o
signals a 63 ppm and 45 ppm indica e decomposi ion o o ganic moi-
e ies in oluene a 200 ◦C (Fig. S6). This obse a ion also ag ees wi h he
N
2
physiso p ion esul s in which he hyb id xe ogels syn hesized in
oluene a 180 ◦C showed he op imum ex u al p ope ies (Table 1).
Impo an ly, he quan i a i e
29
Si MAS NMR spec a (Fig. 3) o 4
hyb id ma e ials syn hesized unde op imum condi ions show ha he e
was a g ea ag eemen be ween he expe imen al s. heo e ical a io T-
ype silicon a oms o e Q- ype silicon a oms ( heo e ical a io T/Q =4/
3 o 1.33), indica ing he alidi y o p oposed co-condensa ion eac ions
(Equa ions (1)─4).
Resul s om he he mog a ime ic analysis (TGA) show ha hese
hyb id amine-silica ma e ials s a ed o decompose a a ound
200─225 ◦C unde ai low (Fig. S7a) while hey we e s able up o
a ound 350 ◦C unde N
2
low (Fig. S7b). These obse a ions indica e he
Fig. 2. Solid-s a e
13
C CP MAS NMR spec a o 4 ep esen a i e hyb id ma e ials syn hesized unde op imum condi ions ( oluene, 180 ◦C) om he es e elimina ion
ou e and liquid-s a e
13
C NMR (in CDCl
3
) spec a o hei co esponding amine p ecu so s. As e isk ma k deno es o a ional sidebands.
T.Q. Bui e al. Mic opo ous and Mesopo ous Ma e ials 381 (2025) 113371
4
p esence o o ganic unc ional g oups in he xe ogel s uc u e. We
assumed ha , i s , esidue solids a he end o TGA expe imen s ( ill
1000 ◦C) unde ai low we e composed o SiO
2
only (Fig. S7a) and,
second, all Si and N a oms om silica and amine p ecu so s we e
ans e ed comple ely o inal hyb id xe ogels (Equa ions (1)─4). I
should be no ed ha Equa ions (1)–(4) a e ideal equa ions whe e he
deg ees o condensa ion (DC) a e 100 %. In ou second assump ion, he
eal DC (<100 %) does no a ec he Si/N mola a io in he inal gel
because wi h di e en alues o DC, he inal gel will only ha e di e en
amoun o un eac ed me hoxy and ace oxy g oups (es e elimina ion
ou e). Based on ou 2 assump ions, we calcula ed N con en s o ep e-
sen a i e hyb id xe ogels based on TGA esul s pe o med in ai and
p esen ed hem in Table 2. An example o ou calcula ions o N con en
o SiOAc-N3 is p o ided in he Suppo ing In o ma ion. In e es ingly,
hese calcula ed alues o N con en ag eed e y well wi h expe imen al
alues ob ained om o ganic elemen al analysis (Table 2), indica ing
he alidi y o ou assump ions as well as ag eemen wi h he s uc u al
in eg i y o o ganic moie ies om solid-s a e NMR esul s men ioned
abo e (Figs. 2 and 3). Calcula ed Si con en s o hyb id xe ogels and mass
loss alues ob ained om TGA-Ai a e p esen ed in Table S2.
XPS and FT-IR measu emen s we e u he conduc ed o de e mine
he su ace elemen al composi ions and s uc u al uni s o he hyb id
amine-silica ma e ials. The su ey scan XPS spec a (no shown)
e ealed he appea ance o 4 elemen s (Si, N, C, and O) on he su ace o
hese ma e ials, indica ing he p esence o hyb id o ganic-ino ganic
s uc u e. The high- esolu ion XPS p o iles o hei Si2p, N1s, C1s, and
O1s b anches a e shown in Fig. 4. The Si2p spec a (Fig. 4a) show 2
majo peaks a binding ene gies (BE) ~102.7 and ~103.6 eV co e-
sponding o Q- ype silicon (SiO
4
) and T- ype silicon (SiO
3
C) con igu a-
ions, espec i ely [52,53]. I should be no ed ha he T/Q a io in Si2p
spec a was se o 1.33 o be consis en wi h he heo e ical T/Q a io in
bulk ma e ials when pe o ming he cu e- i ing by using CasaXPS
so wa e. The N1s spec a (Fig. 4b) show ha he main N-species in 2
ma e ials SiOAc-N3 and SiOAc-N3-Me was amine-N (BE 399.2 eV) as
expec ed while, in con as , he main N-species in he o he 2 ma e ials
SiOAc-N2 and SiOAc-N1 was amide-N (BE 399.9─400.0 eV) [54]. This
obse a ion was also consis en wi h he appea ances o amide-C
(O=C─N) a 287.8─288.2 eV in he C1s spec a (Fig. 4c) and amide-O
(O=C─N) a 531.0─531.4 eV in he O1s spec a (Fig. 4d) [54].
Table S3 summa izes ou assignmen s o high- esolu ion XPS p o iles o
4 ep esen a i e hyb id ma e ials.
The FT-IR spec a ag eed well wi h he conclusions based on XPS
spec oscopy. The FT-IR spec um o SiOAc-N1 (Fig. 5, black) clea ly
con i med he p esence o seconda y amide g oup wi h 4 ypical bands:
N-H s e ch (3273 cm
−1
), o e one o N-H bend (3085 cm
−1
), C=O
s e ch (1633 cm
−1
), and N-H bend (1551 cm
−1
) [55] while he one o
SiOAc-N2 (Fig. 5, ed) con i med he p esence o e ia y amide g oup
ia he only C=O s e ch band a 1625 cm
−1
. The p esence o e ia y
amine g oups in SiOAc-N3 and SiOAc-N3-Me was also con i med by
hei FT-IR spec a (Fig. 5, blue and g een, espec i ely) ia he ypical
band a 2790─2802 cm
−1
ep esen ing o C-H s e ch o me hyl/-
me hylene g oups nex o N in e ia y amine [30,31,56]. Wi h esul s
ob ained om XPS and FT-IR, we conclude ha only e ia y amine
p ecu so s (N3 o N3-Me) could co-polyme ize wi h Si(OAc)
4
o o m
hyb id amine-silica ma e ials unde ou non-hyd oly ic sol-gel condi-
ions while p ima y (N1) and seconda y (N2) amine p ecu so s o med
hyb id seconda y and e ia y amide-silica ma e ials, espec i ely due o
in-si u eac ions be ween p ima y/seconda y amine si es and co-p oduc
me hyl ace a e and/o Si(OAc)
4
p ecu so [27,46].
In ag eemen wi h XPS esul s, he STEM-EDS analysis o a selec ed
hyb id ma e ial (SiOAc-N3-Me) showed he appea ance o 4 elemen s
(Si, N, C, and O) in i s elemen al composi ion. Mos impo an ly, he
STEM-EDS elemen al mapping (scale ba 50 nm) also e ealed a uni o m
dis ibu ion o hese 4 elemen s wi h no single clus e s (Fig. S8).
The FT-IR spec a (Fig. 5) also e eal ha SiOAc-N3 and SiOAc-N3-
Me con ained un eac ed ace oxy g oups in hei s uc u e (C=O
s e ch a 1740─1742 cm
−1
) while he o he 2 ma e ials SiOAc-N2 and
SiOAc-N1 did no con ain hem. This obse a ion also ag eed wi h he
weak signal o es e -C (O=C─O) a 288.7─289.1 eV in he high-
esolu ion C1s spec a (Fig. 4c), he weak signal o es e -O (O=C─O)
a 533.8─533.9 eV in he high- esolu ion O1s spec a (Fig. 4d), and he
p esence o un eac ed me hoxy and ace oxy g oups in he solid-s a e
13
C
CP MAS NMR spec a (Fig. 2) o SiOAc-N3 and SiOAc-N3-Me [54]. Since
he silica and amine p ecu so s we e mixed wi h an equal numbe o
ace oxy and me hoxy unc ional g oups a he beginning and he
non-hyd oly ic sol-gel eac ions ollowed he es e elimina ion ou e o
o m me hyl ace a e as a ola ile co-p oduc oge he wi h hyb id gels,
we assume ha he mo e un eac ed me hoxy g oups appea ed in hyb id
ma e ials, he mo e un eac ed ace oxy g oups emained as well. Based
on esul s om XPS and FT-IR as well as he absence o un eac ed
me hoxy g oups in he
13
C CP MAS NMR spec a (Fig. 2) o SiOAc-N1
and SiOAc-N2 ma e ials, we could also conclude ha he peaks a
174.0 &171.5 ppm we e no assigned o es e -C (O=C─O) bu amide-C
(O=C─N) ins ead in he
13
C CP MAS NMR spec a (Fig. 2) o SiOAc-N1
and SiOAc-N2 ma e ials, espec i ely. The absence o un eac ed
me hoxy and ace oxy g oups o SiOAc-N1 and SiOAc-N2 ma e ials could
be due o highe deg ees o co-polyme iza ion compa ed o SiOAc-N3
and SiOAc-N3-Me ma e ials and/o he in-si u o ma ion o amide
si es (con i med by IR and XPS spec oscopy) leading o MeOH
(obse ed by GC-MS) and/o ≡SiOH o ma ion unde syn he ic condi-
ions. Howe e , i should be no ed ha he FT-IR spec a (Fig. 5) showed
no signi ican bands in he ange 950─850 cm
−1
(i.e., abso p ion band
cha ac e is ic o Si−OH s e ching ib a ion [57]), indica ing insigni -
ican appea ance o silanol g oups (Si─OH) in ou hyb id ma e ials
compa ed o ones p epa ed ia hyd oly ic sol-gel me hod [30,31,56].
Fig. 3. Solid-s a e
29
Si MAS NMR (one pulse) spec a o 4 ep esen a i e hyb id
ma e ials syn hesized unde op imum condi ions ( oluene, 180 ◦C) om he
es e elimina ion ou e.
Table 2
Ni ogen con en s o 4 ep esen a i e hyb id ma e ials syn hesized unde op i-
mum condi ions ( oluene, 180 ◦C) om he es e elimina ion ou e.
Ma e ial SiOAc-N1 SiOAc-N2 SiOAc-N3-Me SiOAc-N3
a
Calc. N (w .%) 7.21 4.09 4.37 2.86
b
Exp. N (w .%) 6.99 4.00 4.34 2.80
a
Calcula ed om calc. Si con en s (Table S2) and heo e ical a ios Si/N o
ep esen a i e hyb id xe ogels (Equa ions (1)─4).
b
Ob ained om O ganic Elemen al Analysis (CHNS).
T.Q. Bui e al. Mic opo ous and Mesopo ous Ma e ials 381 (2025) 113371
5

3.3. Es e elimina ion ou e: CO
2
adso p ion on hyb id ma e ials
Fig. S9─12 illus a e CO
2
adso p ion iso he ms o 4 ep esen a i e
hyb id xe ogels and hei co esponding F eundlich–Langmui (aka
Sips) model i ings (R
2
=0.99996–1.00000) a 3 di e en empe a u es
(0, 15, and 25 ◦C) [58,59]. Fig. S13 illus a es changes o he isos e ic
en halpy o CO
2
adso p ion (ΔH
CO2_ads
) du ing he adso p ion p ocess
ob ained by Clausius–Clapey on app oach ia Sips i (i.e.,
F eundlich-Langmui model) o CO
2
adso p ion iso he ms [58,59].
Table 3 summa izes main esul s ob ained om hese iso he ms
including he CO
2
up ake a 1 ba o CO
2
and he isos e ic hea o CO
2
adso p ion (Q
s
= − ΔH
CO2_ads
) a nea -ze o co e age. As expec ed, wi h
N si es in he o m o amide o e ia y amine and lack o o he si es o
CO
2
chemiso p ion, he Q
s
alues o hyb id ma e ials we e ound in he
ange o 15–33 kJ mol
−1
, ep esen ing mainly CO
2
physiso p ion (Q
s
<
50 kJ mol
−1
) [60]. The compa able Q
s
alues (~25–27 kJ mol
−1
) o
SiOAc-N3 and SiOAc-N3-Me ma e ials could be due o he simila i ies in
speci ic su ace a ea (761–776 m
2
g
−1
) and su ace unc ional g oups (e.
g., e ia y amine, ace oxy, me hoxy). Meanwhile, wi h sligh ly lowe
speci ic su ace a ea (624 m
2
g
−1
), he highes Q
s
alue (33.23 kJ
mol
−1
) o SiOAc-N2 could be due o he p esence o su ace unc ional
g oups wi h highe pola i ies (e.g., e ia y amide, silanol). In con as ,
he lowes Q
s
alue (14.54 kJ mol
−1
) o SiOAc-N1 could be due o i s
non-po osi y (<10 m
2
g
−1
) and he dissolu ion o CO
2
in o he ma e ial
ma ix a he han only in e ac ions on he ma e ial su ace [61]. Basi-
cally, he hea o CO
2
abso p ion in o dense ubbe y ma ices (Q =–ΔH)
includes 2 con ibu ions: he hea o binding ene gy o CO
2
in ma ix
(Q
1
>0) and he hea o eo ganiza ion (Q
2
<0) [62]. Speci ically, he
Q
s
alue o SiOAc-N1 is qui e compa able o he hea o CO
2
dissolu ion
in o he polyme ic ma ix o poly(me hyl p opyl siloxane) wi h Q =
14.69 kJ mol
−1
[63].
O e all, he CO
2
up ake o hyb id ma e ials dec eased when
inc easing so p ion empe a u e om 0 o 25 ◦C and did no each a
pla eau a 1 ba o CO
2
(Fig. S9─12), indica ing ha he CO
2
up ake
could be imp o ed u he a highe CO
2
p essu e. The CO
2
up ake
(mmol/g) a same condi ions is in he o de o SiOAc-N2 >SiOAc-N3 ~
SiOAc-N3-Me >SiOAc-N1 (Table 3). This o de also ag ees wi h he
di e ences in po osi y and su ace unc ional g oups o ma e ials
al eady men ioned abo e when compa ing Q
s
alues. I should be no ed
ha in ca bon dioxide physiso p ion, CO
2
molecules a e a ac ed by
solid adso ben mainly ia an-de -Waals o ces as well as elec os a ic
in e ac ions be ween CO
2
molecules and pola si es on adso ben su ace
hanks o ha ing CO
2
quad upole momen [64]. Al hough he simila -
i ies in speci ic su ace a ea (761–776 m
2
g
−1
) and su ace unc ional
g oups (e.g., e ia y amine, ace oxy, me hoxy) o 2 ma e ials SiOAc-N3
and SiOAc-N3-Me, he CO
2
up ake pe ni ogen si e (mmol CO
2
/mmol
N) in SiOAc-N3 is highe han SiOAc-N3-Me (e.g., 0.200 s 0.125 mmol
CO
2
/mmol N a 25 ◦C, espec i ely, Table 3), indica ing mino con i-
bu ion o e ia y amine o CO
2
up ake a 1 ba o CO
2
. Speci ically,
compa ing o SiOAc-N3 (simila speci ic su ace a ea), highe con en o
e ia y amine (highe N con en ) in SiOAc-N3-Me (4.34 s 2.80 w % N,
espec i ely, Table 4) did no lead o highe CO
2
up ake (mmol/g) a 1
ba o CO
2
bu lowe CO
2
up ake pe ni ogen si e (mmol CO
2
/mmol N).
The hyb id ma e ial SiOAc-N2 de i ed om NHSG also showed a
Fig. 4. High- esolu ion (a) Si2p, (b) N1s, (c) C1s, and (d) O1s XPS spec a o 4 ep esen a i e hyb id ma e ials syn hesized unde op imum condi ions ( oluene,
180
◦C) om he es e elimina ion ou e. A mino componen a 105.0 eV in Fig. 4a co esponds o SiO
4
and CSiO
3
moie ies in hyd ogen bonding (Table S3) [52].
T.Q. Bui e al. Mic opo ous and Mesopo ous Ma e ials 381 (2025) 113371
6
compa able o e en be e CO
2
so p ion capaci y compa ed o simila
hyb id ma e ials de i ed om HSG using he same amine p ecu so (N2)
p obably hanks o a highe speci ic su ace a ea o SiOAc-N2 [35,65].
3.4. Alkyl halide elimina ion ou e
In his ou e, SiCl
4
was used as a silica p ecu so oge he wi h 4
amine p ecu so s (N1/N2/N3-Me/N3) con aining ime hoxysilyl
g oups o syn hesis o hyb id ma e ials (Equa ion (1)─4). The silica and
amine p ecu so s we e mixed wi h an equal numbe o chlo ide and
me hoxy unc ional g oups in an ap o ic sol en . The p esence o me hyl
chlo ide as a ola ile p oduc in all syn hesis expe imen s was con i med
by GC-MS analysis o esidue sol en s a e he non-hyd oly ic sol-gel
(NHSG) syn hesis.
Table 4 summa izes he ex u al p ope ies o hyb id ma e ials syn-
hesized om he alkyl halide elimina ion ou e unde di e en syn-
he ic condi ions (amine p ecu so , ap o ic sol en ). Like he es e
elimina ion ou e, ma e ials de i ed om he e minal amine p ecu so
(N1) we e also low/non-po ous (2─14 m
2
g
−1
) in he alkyl halide
elimina ion ou e. In con as , e en hough oluene (TOL) was he
op imal sol en o p epa e highly po ous ma e ials wi h p ese ed
o ganic moie ies coming om b idging amine p ecu so s in he es e
elimina ion ou e (Table 1,Fig. 2 and S5), he ma e ial syn hesized om
SiCl
4
and N2 p ecu so in TOL was non-po ous (<10 m
2
g
−1
). The
Fig. 5. FT-IR spec a o 4 ep esen a i e hyb id ma e ials syn hesized unde op imum condi ions ( oluene, 180
◦C) om he es e elimina ion ou e.
Table 3
CO
2
up akes and isos e ic hea alues o CO
2
adso p ion o 4 ep esen a i e
hyb id xe ogels syn hesized unde op imum condi ions ( oluene, 180 ◦C) om
he es e elimina ion ou e.
Ma e ial CO
2
up ake a 1 ba o CO
2a
(mmol/g) Q
s
a nea -ze o
co e age (kJ mol
−1
)
0◦C 15 ◦C 25 ◦C
SiOAc-N1 0.174
(0.035)
0.136
(0.027)
0.092
(0.018)
14.54 ±5.41
SiOAc-N2 1.014
(0.355)
0.742
(0.260)
0.584
(0.204)
33.23 ±0.05
SiOAc-N3-
Me
0.674
(0.218)
0.482
(0.156)
0.386
(0.125)
24.67 ±1.62
SiOAc-N3 0.731
(0.366)
0.543
(0.272)
0.399
(0.200)
26.59 ±3.15
a
Numbe s in pa en hesis a e p esen ed in mmol CO
2
/mmol N. The N con en s
a e ob ained om O ganic Elemen al Analysis (CHNS).
Table 4
Tex u al p ope ies o hyb id amine-silica xe ogels ob ained om he alkyl halide elimina ion ou e (SiCl
4
as a silica p ecu so ) unde di e en condi ions.
Gel Amine p ecu so Ap o ic sol en Temp. (◦C) S
BET
(m
2
g
−1
)
a
V
o al
(cm
3
g
−1
)
b
V
mic o
/V
o .
(%)
c
PS
DFT
(nm)
d
PS
a e .
(nm)
1 N1 TOL 180 <10 n.d. n.d. n.d. n.d.
2DCM 180 14 0.05 0 16.1 13.4
3 N2 TOL 180 <10 n.d. n.d. n.d. n.d.
4DCM 180 351 0.65 5.2 2.6 7.4
5 N3-Me DCM 180 300 0.50 12.0 2.6 6.7
6 N3 DCM 180 575 1.31 4.2 2.6 9.1
n.d. =no de e mined.
a
Es ima ed a p/p
o
=0.97.
b
Based on -plo analysis (Fig. S16).
c
The maximum alue o he po e size dis ibu ion cu e (NLDFT, ads, cyl. po e model).
d
4V
o al
/S
BET
.
T.Q. Bui e al. Mic opo ous and Mesopo ous Ma e ials 381 (2025) 113371
7
sample de i ed om b idging amine p ecu so N2 and SiCl
4
in
dichlo ome hane (DCM) showed high speci ic su ace a ea (351 m
2
g
−1
)
and high o al po e olume (0.65 cm
3
g
−1
). Acco dingly, eac ions be-
ween SiCl
4
and N3 and N3-Me we e pe o med in DCM and exhibi ed
high S
BET
(300─575 m
2
g
−1
), high V
o al
(0.50─1.31 cm
3
g
−1
), and po e
size dis ibu ion in mesopo e ange (Table 4).
The solid-s a e
13
C CP TOSS MAS NMR spec a e ealed he
complica ed o ganic s uc u es o he hyb id ma e ials ob ained om
he alkyl halide elimina ion ou e ei he in TOL o DCM (Fig. S14),
indica ing a nega i e e ec o using SiCl
4
as a silica p ecu so on he
s uc u al in eg i y o o ganic moie ies a e NHSG syn hesis. This
obse a ion could be mainly due o in-si u eac ions be ween amine si es
and co-p oduc CH
3
Cl unde syn he ic condi ions o o m a complica ed
mix u e including qua e na y ammonium chlo ide sal s as well as hei
co esponding he mal decomposi ion p oduc s ia he e e se Men-
schu kin and/o Ho mann eac ions (desc ibed in de ail in sec ion 3.6
Recyclabili y s udies and spen ca alys s cha ac e iza ion wi h [4-
(chlo ome hyl)-1,3-dioxolan-2-one] as he model qua e niza ion agen )
[49–51]. No ewo hy, he qua e na y (alkyl)ammonium halides a e
o en used as co-ca alys s o CO
2
cycloaddi ion eac ions wi h iodides
and b omides being highly p e e ed [66,67]. The e o e, applica ion o
SiB
4
o SiI
4
in alkyl halide elimina ion migh lead o ca aly ically
in e es ing ma e ials.
The su ey scan XPS spec a (no shown) e ealed he appea ance o
5 elemen s (Si, N, C, O, and Cl) on he su aces o ep esen a i e hyb id
ma e ials p epa ed in DCM o TOL by he alkyl halide elimina ion ou e.
The high- esolu ion N1s XPS spec a (Fig. 6a) showed 2 majo peaks a
binding ene gies (BE) ~399.5 and ~401.9 eV co esponding o amine-N
(N
A
) and qua e na y ammonium N (N
QA
), espec i ely [54]. The
N
QA
/N
A
a io dec eased om 8.3 o 1.8 when he s e ic hind ance on N
si e inc eased (i.e., om N1 o N3 p ecu so ), indica ing he dec ease in
deg ee o qua e niza ion o amine si es (Fig. 6a). Meanwhile, he
high- esolu ion Cl2p XPS spec a (Fig. 6b) e ealed he p esence o Cl
−
anions om qua e na y ammonium sal s a BE~197.7 eV as well as
C─Cl a BE~200.6 eV in he Cl2p3/2 spec a [54]. The appea ance o
C─Cl in he s uc u e could be due o side eac ions be ween amine si es
and DCM unde syn he ic condi ions as al eady obse ed in he es e
elimina ion ou e (Fig. S15) and/o he mal decomposi ion p oduc s o
qua e na y ammonium chlo ide sal s (see discussion in sec ion 3.6
Recyclabili y s udies and spen ca alys s cha ac e iza ion) [48,49].
3.5. In es iga ion o syn hesized hyb id ma e ials as he e ogeneous
ca alys s o he CO
2
cycloaddi ion o epoxides
In o de o in es iga e he ca aly ic po en ial o syn hesized hyb id
amine-silica ma e ials as al e na i e me al- and halogen- ee he e oge-
neous ca alys s o di ec con e sion o CO
2
o cyclic ca bona es unde
sol en - ee and co-ca alys - ee condi ions, sc eening ca aly ic es s
we e pe o med in a cus om-made high-p essu e ba ch eac o (Fig. S17)
using nea -s oichiome ic amoun o CO
2
(~14 mmol o 10 ba o ini ial
CO
2
p essu e) and epichlo ohyd in (10 mmol) a 120 ◦C o 1 h. Table 5
summa izes he main ca aly ic esul s om selec ed ca alys s syn he-
sized using non-hyd oly ic sol-gel (NHSG) me hod ia he es e elimi-
na ion ou e in TOL a 180 ◦C o 4 days (SiOAc). Inc easing he ini ial
CO
2
p essu e om 10 o 15 ba (en ies 9 and 10) jus imp o ed sligh ly
he epoxide con e sion, indica ing ha 10 ba o ini ial CO
2
p essu e is
he op imal p essu e o ou eac ion condi ions.
Fo he sake o compa ison o ca aly ic ac i i y, selec ed ca alys s
syn hesized using non-hyd oly ic sol-gel (NHSG) me hod ia he alkyl
halide elimina ion in DCM a 180 ◦C o 4 days (SiCl) we e also es ed a
simila ca aly ic eac ion condi ions (50 mg o ca alys , 10 ba o CO
2
,
10 mmol o epichlo ohyd in, 120 ◦C, 1 h). Resul s a e summa ized in
Table S4 e en hough he chemical s uc u e o hese ma e ials (SiCl)
was no well-de ined due o hei complica ed o ganic s uc u es
(Fig. S14). O e all, all syn hesized hyb id ma e ials we e ac i e wi h
high selec i i y o cyclic ca bona e (>99 %) and low- o-high con e sion
o epichlo ohyd in (11─86 %) unde in es iga ed condi ions. Com-
me cial po ous silica showed no ac i i y (en y 1), indica ing he ca a-
ly ic ole o N si es in hyb id ma e ials o he CO
2
cycloaddi ion o
epichlo ohyd in. The ma e ials p epa ed by alkyl halide elimina ion
exhibi highe epichlo ohyd in con e sions han co esponding samples
p epa ed by es e elimina ion excep o amine- unc ionalized silica
p epa ed om N3-Me (Table 5 and Table S4). On one hand, he ma e-
ials p epa ed om SiCl
4
con ain qua e na y alkylammonium chlo ide
si es ha migh be bene icial o CO
2
cycloaddi ion. On he o he hand,
poo ly de ined moie ies coming om he decomposi ion o qua e na y
ammonium si es migh be inco po a ed in SiCl ma e ials as well.
The e o e, i is no possible o explain unambiguously he di e ences
be ween SiCl and SiOAc samples.
Among hyb id ma e ials p epa ed by es e elimina ion, SiOAc-N3-
Me showed he highes ca aly ic ac i i y (TOF =358 h
−1
). Mos
impo an ly, he o de o ca aly ic ac i i y in dec easing o de o u n-
o e equency (TOF) was SiOAc-N3-Me >SiOAc-N3 ≫SiOAc-N2 >
SiOAc-N1 (en ies 2–4, 8), indica ing ha e ia y amine-N si es (SiOAc-
N3-Me and SiOAc-N3) we e much mo e ac i e o he eac ion han
Fig. 6. High- esolu ion (a) N1s and (b) Cl2p XPS spec a o 4 ep esen a i e hyb id ma e ials syn hesized in DCM om he alkyl halide elimina ion ou e.
T.Q. Bui e al. Mic opo ous and Mesopo ous Ma e ials 381 (2025) 113371
8
amide-N si es (SiOAc-N2 and SiOAc-N1). This obse a ion also ag ees
wi h he use o e ia y amines as highly e icien o ganoca alys s o
CO
2
ixa ions [17]. While ca aly ic ac i i y appea o s ongly depend on
he ac i e si es ( e ia y amine-N s. amide N), he po osi y does no
seem o play a decisi e ole: Non-po ous SiOAc-N1 exhibi ed a simila
epichlo ohyd in con e sion as highly po ous SiOAc-N2.
The ca alys SiOAc-N3-Me was also ac i e o he CO
2
cycloaddi ion
o di e en epoxides o he han epichlo ohyd in such as s y ene oxide
and 1,2-bu ylene oxide (en ies 13–15). Among he 3 epoxides,
epichlo ohyd in is he mos eac i e one hanks o he p esence o an
elec on-wi hd awing chlo ome hyl g oup (─CH
2
Cl) ha ac i a ed he
epoxide ing, ende ing i mo e suscep ible o nucleophilic a ack by
e ia y amine-N si es and/o ac i a ed CO
2
[17]. The lowes eac i i y
o s y ene oxide could be due o he s e ic e ec o he phenyl g oup nex
o he epoxide ing. This obse ed end o epoxide eac i i y o mes-
opo ous e ia y amine-silica hyb id SiOAc-N3-Me ca alys is also in
ag eemen wi h mesopo ous melamine- o maldehyde esin MMFR
ca alys , whe e epoxide eac i i y dec eased in he same o de (i.e.,
epichlo ohyd in ≫1,2-bu ylene oxide >s y ene oxide) [23].
Repo ed mesopo ous amine-silica hyb id ca alys s in he li e a u e
o he syn hesis o cyclic ca bona es om CO
2
in ba ch eac o unde
sol en - ee condi ion a e also summa ized and compa ed wi h his
wo k in Table S5. Mo e speci ically, al hough he N con en s o ou
ca alys s a e lowe han he N con en s o Si-Imid and SiO
2
-His ma e-
ials, he ca aly ic pe o mances o ou ca alys s a e s ill compa able o
e en highe [27,28], indica ing ha alipha ic e ia y amine si es a e
mo e e icien han imidazole o his idine in his case. Signi ican ly
highe ca aly ic ac i i ies ha e been epo ed only o ca alys s
con aining me als and in he p esence o co-ca alys s: 16 w %
APTES@Z O
2
-MCM-41 and SBA-15/N-Au showed mo e han 90 % o
cyclic ca bona e yield a 80 ◦C [66,67]. Finally, wi h epichlo ohyd in as
an epoxide subs a e, ou ca alys s showed highe ca aly ic pe o mance
han mos o he epo ed mesopo ous amine-silica (wi h/wi hou
me al) ca alys s excep o PT@SBA-16, while i is no he case wi h
s y ene oxide o 1,2-bu ylene oxide as an epoxide subs a e [27–29,68].
This obse a ion is also ue when compa ing ou ca alys s wi h he
epo ed ca alys B-SBA-15-NH
2
in he p esence o co-ca alys KI [69].
The obse a ion could be explained by in-si u eac ions o ou ca alys s
wi h epichlo ohyd in and/o [4-(chlo ome hyl)-1,3-dioxolan-2-one] o
c ea e qua e na y ammonium chlo ide as ano he ac i e o m o he
syn hesis o cyclic ca bona e (see mechanism below in sec ion 3.6
Recyclabili y s udies and spen ca alys s cha ac e iza ion) [48–51].
In o de o unde s and be e he ca aly ic ac i i y o e ia y amine-
N si es in mesopo ous e ia y amine-silica hyb ids (SiOAc-N3-Me and
SiOAc-N3), he o ganic s uc u e analogues (me hyldip opylamine
(MDPA) and ip opylamine (TPA)) we e also es ed as homogeneous
ca alys s a simila ca aly ic eac ion condi ions (en ies 16–21) and
compa ed in e ms o u no e equency (TOF), appa en ac i a ion
ene gy (E
a
) and p e-exponen ial ac o (A) (Table 5,Fig. 7). The mass o
homogeneous ca alys s MDPA and TPA was aken o ha e a compa able
N con en in 50 mg o he e ogeneous ca alys s SiOAc-N3-Me (0.155
mmol o N) and SiOAc-N3 (0.100 mmol o N), espec i ely, based on
o ganic elemen al analysis. The empe a u e ange o compa ison was
chosen om 80 o 100 ◦C o a oid e y slow o as ini ial a e o
epichlo ohyd in con e sion unde ou eac ion condi ions. The ca aly ic
eac ion was assumed o ollow pseudo- i s -o de kine ics based on
Table 5
Summa y o ba ch ca aly ic expe imen s conduc ed on he cycloaddi ion eac ion o epoxides and CO
2
.
en y ca alys epoxide emp. (
◦C) ime (h) con .
a
(%) sel.
a
(%) k
ini.b
(h
−1
) TOF
c
(h
−1
)
1 Comme cial SiO
2
(Ae osil 300) epichlo ohyd in 120 1 0 – – –
2 SiOAc-N1 epichlo ohyd in 120 1 11 >99 0.12 4.7
3 SiOAc-N2 epichlo ohyd in 120 1 14 >99 0.15 10.5
4 SiOAc-N3 epichlo ohyd in 120 1 56 >99 1.81 181
5  100 1 34 >99 0.42 41.6
6  90 1 20 >99 0.22 22.3
7  80 1 10 >99 0.11 10.5
8 SiOAc-N3-Me epichlo ohyd in 120 1 86 >99 5.54 358
9  100 1 52 >99 0.89 57.6
10
d
  100 1 55 >99 n.d. n.d.
11   90 1 38 >99 0.51 33.0
12   80 1 25 >99 0.29 18.6
13 s y ene oxide 120 14 51 >99 n.d. n.d.
14   140 14 97 >99 n.d. n.d.
15 1,2-bu ylene oxide 120 14 55 >99 n.d. n.d.
16 T ip opylamine (14 mg, 0.098 mmol)
e
epichlo ohyd in 100 1 42 >99
g
0.42 43.0
17   90 1 16 >99
g
0.17 17.8
18   80 1 7 >99
g
0.07 7.4
19 Me hyldip opylamine (17 mg, 0.148 mmol)
epichlo ohyd in 100 1 80 >99
g
1.95 132
20   90 1 62 >99
g
0.65 43.9
21   80 1 32 >99
g
0.39 26.1
n.d. =no de e mined.
a
Based on
1
H NMR and GC-MS analysis.
b
Calcula ed based on he ini ial a e o epichlo ohyd in con e sion.
c
TOF =kini.*nepoxide
nN si es wi h n
N-si es
based on O ganic Elemen al Analysis.
d
Ini ial p essu e o CO
2
=15 ba .
e
O ganic s uc u e analog o SiOAc-N3, compa able N con en based on O ganic Elemen al Analysis.
O ganic s uc u e analog o SiOAc-N3-Me, compa able N con en based on O ganic Elemen al Analysis.
g
Excluding by-p oduc s de i ed om eac ions be ween amines and epichlo ohyd in/cyclic ca bona e due o di icul y in dis inguishing by NMR.
T.Q. Bui e al. Mic opo ous and Mesopo ous Ma e ials 381 (2025) 113371
9