Effect of Adsorption of ZrO2 in Catalysts on the Efficiency of Hydrolysisof Cellulose to Sugar in Aqueous System under Microwave Radiation

Article abstract of DOI:10.1002/cjoc.201900434

Five types of ZrO₂ are used to simply establish an effective aqueous catalytic system with sulfuric acid for the hydrolysis of cellulose to sugar, respectively. By adjusting surface roughness and particle size of ZrO₂, different adsorption is produced. Accordingly, following the thought to inhibit the self-aggregation nature of cellulose, after the introduction of ZrO₂ with adsorption in catalysts, the efficiency of the hydrolysis of cellulose to sugar is improved. The results show different ZrO₂ can produce different effects during the hydrolysis of the cellulose with relatively low crystallinity. Under the optimal conditions, the conversion of cellulose and TRS yield reaches 95.5% and 93.6%, respectively. Through this research, it reveals the critical point to organize a feasible and useful way for the hydrolysis of cellulose to sugar with high efficiency in an aqueous system. An important theoretical and technical support is also provided for the conversion and utilization of cellulose in the future.

Full text of DOI:10.1002/cjoc.201900434

Chinese Journal
of Chemistry
CJC 中 国 化 学 - An International Journal
Accepted Article
Title: Effect of Adsorption of ZrO2 in Catalysts on the Efficiency of Hydrolysis of
Cellulose to Sugar in Aqueous System under Microwave Radiation
*
*
Authors: Ying Qiao, Lixin Feng, Zhongqiu Li, Zhenyu Zhang, Jing Chen, Haining Na,
Jin Zhu, Lai Chen
This manuscript has been accepted and appears as an Accepted Article online.
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Effect of Adsorption of ZrO2 in Catalysts on the Efficiency of Hydrolysis
of Cellulose to Sugar in Aqueous System under Microwave Radiation
Ying Qiao,a,b Lixin Feng, Zhongqiu Li,c,d,* Zhenyu Zhang, Jing Chen, Haining Na, Jin Zhu, Lai Chena
c
b
b
b,*
b
a
Department of Polymer, College of Material Science and Engineering, Shanghai University, Shanghai 200444, China
b
Key Laboratory of Bio-based Polymeric Materials of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of
Sciences, Ningbo, Zhejiang 315201, China
c
Chemical College, Shijiazhuang University, Shijiazhuang, Hebei 050035, China
Hebei Building Ceramics Engineering Research Center, Shijiazhuang University, Shijiazhuang, Hebei 050035, China
d
Cite this paper: Qiao, Y.; Feng, L. X.; Li, Z. Q.; Zhang, Z. Y.; Chen, J.; Na, H. N.; Zhu, J.; Chen, L. Chin. J. Chem. 2019, 37, XXX—XXX. DOI:
1
0.1002/cjoc.201900XXX
Summary of main observation and conclusion Five types of ZrO
sulfuric acid for the hydrolysis of cellulose to sugar. By adjusting surface roughness and particle size of ZrO
Accordingly, following the thought to inhabit the self-aggregation nature of cellulose, after the introduction of ZrO
efficiency of the hydrolysis of cellulose to sugar is improved. Results show different ZrO can produce different effects during the hydrolysis of the
2
are respectively used to simply establish an effective aqueous catalytic system with
, different adsorption is produced.
with adsorption in catalysts, the
2
2
2
cellulose with relative low crystallinity. Under the optimal conditions, the conversion of cellulose and TRS yield respectively reaches 95.5% and 93.6%.
Through this research, it reveals the critical point to organize a feasible and useful way for the hydrolysis of cellulose to sugar with high efficiency in an
aqueous system. An important theoretical and technical support is also provided for the conversion and utilization of cellulose in the future.
acid catalyst and thus increases the difficulty of hydrolysis.[3,14] In
Background and Originality Content
order to reduce the crystallinity as much as possible, some
Cellulose is a kind of non-food renewable biomass resource
[14,15]
pretreatment including of dissolution-regeneration,
milling,
ball
[
1]
with an annual output of more than 100 billion tons and
[16-18]
[11]
and boiling with supercritical water are
[2]
accounts for 30%-50% of the biomass. If cellulose can be
converted into energy and material to supply and even replace
non-renewable fossil resources, it will produce an important
impact on maintaining the sustainable development of human
society in the future. The use of chemical methods to efficiently
hydrolyze cellulose into sugar is an important way to directly
disassemble the molecular structure and to obtain bio-based
emphasized to utilize. By obtaining the cellulose with relative low
crystallinity, a novel two-step methodology is formed to hydrolyze
cellulose effectively. This process extremely provides a great
contribution for green conversion during the hydrolysis of
cellulose to sugar with high efficiency particularly in aqueous
system.
[3]
small molecular platform compounds. In the process of
obtaining bio-based renewable energy and material from
cellulose, the hydrolysis of cellulose to sugar can be recognized as
However, the highly efficient hydrolysis of cellulose to sugar in
aqueous system is also not easy to simply achieve. It was found
that cellulose can produce rapid recrystallization during hydrolysis
[
4-6]
[19-21]
the key control step.
and thus form the inhibition of hydrolysis again.
This
phenomenon in fact derived from the self-aggregation nature of
cellulose molecular chains. The particular nature of
During the past decades, many hydrolytic systems have been
[7-9]
tried by researchers. With the use of ionic liquid and some
self-aggregation of cellulose molecular chains can be understood
from the research of single-molecule force spectroscopy and
molecular dynamics simulation, which was operated by Cui and
[
10-13]
polar aprotic solvents,
it achieves rather high efficiency of
the hydrolysis of cellulose to sugar. Although these hydrolytic
systems are very effective, they exist huge difficulty in separating
and purify sugar products. In recent years, with the enhanced
requirement to achieve green conversion and to strengthen the
recovery of sugar products during the hydrolysis of cellulose, the
aqueous system with low acidity is recognized as very necessary
to use in hydrolysis. Under this situation, the hydrolysis of
cellulose to sugar is always taken place in a heterogeneous
environment. The inherent high crystallinity of cellulose can
significantly hinder the contact of the glycosidic bond with the
[22]
coworkers. Owing to the β-type bonding, it produces relative
hydrophobic and hard hydrolysis of the hydroxyl-rich single chain
of cellulose in comparison with starch and accordingly exhibits
strong self-aggregation nature, which leads to the insolubility of
[23,24]
cellulose in water. From the studies of Zhang and coworkers,
it further indicates that self-aggregation is a universal
phenomenon of the molecular chains of cellulose to induce its
parallel arrangement during the processing of nanofibers. In fact,
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the control of self-aggregation nature of cellulose chains is also
the basic principle and method to initiate high mechanical
properties of cellulose nanofibers. During the hydrolysis of
cellulose, partial dissociation of glycosidic bonds increases the
degree of freedom and the thermal motion ability of residual
cellulose molecular chains. As a result, the self-aggregation nature
of cellulose molecular chains will initiate the real rapid
respectively prepared in the experiment, which are marked with
ZrO
(Figure 1). From Figure 1, it can be seen that all the ZrO
granular structure. The surface of the amorphous ZrO particle is
rough, but the crystalline ZrO have relative smooth surface. The
microscopic scale of ZrO is summarized in Table 1. The particle
diameter of amorphous ZrO before and after ball milling (ZrO -1
and ZrO -2) is around 15-18nm. Relative larger particle diameter
at 43.4±13.7nm is shown by nano ZrO (ZrO -5). Ordinary ZrO
particles (ZrO -3) have the largest particle diameter of
144.6±27.6nm. After ball milling, the particle diameter of ordinary
ZrO particles (ZrO -4) also retains at 101.9±26.0nm. Not only the
microscopic scale, but the actual size of various ZrO is also
detected by DLS measurement. As shown in Table 1, the actual
size of ZrO -1 is 0.5-5mm. After ball milling, the actual size of
ZrO -2 decreases to 528nm. ZrO -3, ZrO -4 and ZrO -5
2
1-5. The morphologies of various ZrO
2
are observed by SEM
2
shows
2
2
2
2
2
aggregation of the molecular chains of cellulose. Accordingly,
rapid recrystallization of cellulose during the short period of
hydrolysis is produced, as elucidated in our previous research
2
2
2
2
2
[19-21,25,26]
works.
2
2
In order to achieve completely high efficiency in the hydrolysis
of cellulose to sugar in aqueous system, it is very necessary to
carry out the inhibition on the self-aggregation nature of cellulose
2
2
[21]
chains. In our previous work, synchronous cooling assisted
microwave driving is tried to change the interaction between the
hydroxyl groups and thus reduces the recrystallization of
cellulose. Experimental results showed the hydrolytic efficiency of
cellulose to sugar is enhanced to some extent. From this result, it
can be understood that the inhibition of the self-aggregation
nature of cellulose molecular chains could be achieved just
through the change of the interaction with hydroxyl groups on
the molecular chains of cellulose. On the basis of that, an
important thought is formed to pursue a high efficiency of
hydrolysis of cellulose to sugar. Following this thought, some
carbonaceous catalysts with the ability to adsorb hydroxyl
2
2
2
2
respectively show the actual size at 500nm, 280nm and 150nm.
XRD and FTIR are further used to characterize the microstructure
of ZrO (see Figure 2). ZrO -1 and ZrO -2 are both amorphous ZrO
2 2 2 2
and don’t show any crystal peaks on XRD curves (Figure 2(a)). Ball
milling doesn’t change its amorphous structure. As to the
crystalline ZrO
2
2
(ZrO
2
o
-3, ZrO
2
-4), obvious diffraction peaks at
8.4 , 31.7 and 34.2 are observed, which are related to
monoclinic crystal of ZrO . The ZrO -5 is composed of 96.6%
monoclinic phase and 3.4% tetragonal phase. The obvious
o
o
2
2
o
o
o
diffraction peaks at 28.4 , 31.7 and 34.2 refer to the monoclinic
o
ZrO
amorphous ZrO
crystalline structure of ZrO
and ZrO -5). From FTIR spectra, both amorphous and crystalline
ZrO don’t exhibit obvious absorption peaks at 700-3000 cm . It
2
and 30.4 is concerned with tetragonal ZrO
, ball milling doesn’t cause any change in the
2
as well (see the XRD curves of ZrO -4
2
. Similarly as the
[
27-30]
groups
are prepared to control the hydrolysis of cellulose to
2
sugar. As reported, the efficiency of hydrolysis is obviously
improved.
2
2
-
1
2
With the aim to explore the relatively simple but effective
catalytic system and to achieve the green conversion with high
efficiency during the hydrolysis of cellulose to sugar, we focus on
further reflects that no change in the crystalline structure of ZrO
is taken place during the ball milling.
2
the use of ZrO
2
with adsorption in catalysts as the particular
assistant to inhabit the self-aggregation nature of cellulose chains.
[31,32]
As narrated in literatures,
2
ZrO is to play the role of acid
-
mediate in pure water (mainly through the adsorption of OH ) and
+
accordingly improves the concentration of H . Accordingly, in acid
aqueous system, ZrO
adsorption with hydroxyl groups on the molecular chains of
cellulose. In fact, in our previous work, the use of ZrO in acid
2
is expected to produce adequate
2
[
26]
aqueous system was proved rather effective. Results show the
efficiency of the hydrolysis of cellulose to sugar even exceeds the
pure acid system with higher acidity. In this research, by
controlling the surface microstructure of ZrO
different adsorption of ZrO is expected to produce. And
furthermore, the relation between the adsorption of ZrO
2
particles, the
2
2
and the
efficiency of the hydrolysis of cellulose to sugar is investigated.
Accordingly, a green conversion with high efficiency in the
hydrolysis of cellulose to sugar is also expected to be established.
Figure 1 SEM images of (a) ZrO
amorphous ZrO after ball milling), (c) ZrO
ZrO -4 (ordinary ZrO particles after ball milling) and (e) ZrO
ZrO ).
2
-1 (amorphous ZrO
2
), (b) ZrO
particles), (d)
-5 (nano
2
-2
(
2
2
-3 (ordinary ZrO
2
Results and Discussion
Structure and adsorption of ZrO2
2
2
2
2
Five different kinds of ZrO
amorphous ZrO after ball milling, ordinary ZrO
ordinary ZrO particles after ball milling and nano ZrO
2
(namely amorphous ZrO
particles,
) are
2
,
Table 1 Size and adsorption of ZrO .
2
2
2
2
2
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Chin. J. Chem.
a
after microwave radiation at 160oC
Adsorption of ethylene glycol by ZrO
2
for 15min. The concentration of ethylene glycol solution was tested by
GC-MS.
b
Adsorption of cellobiose by ZrO after 1h and 24h. The concentration of
2
cellobiose in aqueous solution was measured by HPLC.
Figure 3 Adsorption of ethylene glycol (a), cellobiose for 1h (b) and
cellobiose for 24h (c) by ZrO .
2
c
The specific surface area of ZrO was measured with ASAP-2020M
2
adsorption analyzer and the value was calculated by using the BET
method.
As a model chemical of hydroxyl-rich carbohydrates, cellobiose
is also utilized to show the adsorption of ZrO . From Figure 3(b)
and 3(c), amorphous ZrO with rough surface shows relatively
higher adsorbance. At 1h and 24h, the adsorbance of ZrO -2
respectively reaches 46.6% (Figure 3(b)) and 63.4% (Figure 3(c)).
However, crystalline ZrO particles with relative smooth surface
exhibit lower adsorbance at 8.6-22.0%. Further as shown in Figure
(b) and 3(c), no matter amorphous or crystalline ZrO , ZrO
particles with larger diameter exhibit lower adsorbance. These
results clearly show that the absorption of ZrO with hydroxyl-rich
2
2
2
2
3
2
2
2
carbohydrates is similar to the results of ethylene glycol. That is
also impacted by the surface roughness and the particle size of
2
ZrO particles.
Figure 2 XRD patterns (a) and FTIR spectra (b) of ZrO
2
.
Hydrolysis of cellulose to sugar
The cellulose hydrolysis only with 0.04mol/L H SO , the
2 4
The adsorption of various ZrO is carefully tested during
2
experimental research. Considering cellulose as a particular
polyhydroxy compound, ethylene glycol and cellobiose are
respectively chosen as the hydroxyl-rich model chemicals to show
conversation of cellulose and TRS yield is 62.9%, 56%,
respectively. Different kinds of ZrO were separately added into a
mixture of the cellulose and 0.04mol/L H SO for the following
hydrolysis under microwave radiation at 160°C for 15min. The
dosage of ZrO for each reaction is 0.0493g. Figure 4 shows the
conversion of cellulose and the TRS yield obtained from the
hydrolysis. By the use of ZrO -1, 75.5% conversion of cellulose and
2.3% TRS yield can be formed. This hydrolytic efficiency is
relatively low and equal to the effect produced by the use of
ZrO -3, which is lower than the effect induced by ZrO -5.
However, after ball milling, the catalytic capability of amorphous
ZrO is extremely enhanced. With the utilization of ZrO -2, the
2
the adsorption of ZrO
cellobiose by different kinds of ZrO
Table 1. As to ethylene glycol, amorphous ZrO
ZrO -2) exhibit relative high adsorbance. After ball milling, the
adsorbance of ZrO -2 reaches to 25.9% (Figure 3(a)). Low
adsorbance is found by using ZrO -3, ZrO -4 and ZrO -5. This
phenomenon is attributed to the specific surface area and pore
volume of different ZrO (Table 1). Increase of surface roughness
and decrease of the size of ZrO particles become the two
2
. The adsorbance of ethylene glycol and
is shown in Figure 3 and
(ZrO -1 and
2
4
2
2
2
2
2
2
2
6
2
2
2
2
2
2
2
important factors to improve the specific surface and thus
produce stronger adsorption.
2
2
conversion of cellulose and the TRS yield are respectively
increased to 95.5% and 93.6%. The hydrolytic efficiency is even
2
superior to that of ZrO -4.
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Figure 5 Conversion of cellulose (a) and yield of TRS (b) obtained by the
2 2
hydrolysis of cellulose by utilization of ZrO -2 and ZrO -5 with 0.04mol/L
H
2
SO under microwave radiation at different temperature, respectively.
4
Figure 4 Conversion of cellulose (a) and yield of TRS (b) obtained from the
ZrO
of hydrolytic conditions. As shown in Figure 5(a), with the use of
ZrO -2 and ZrO -5, the conversion of cellulose shows obvious
2 2
-2 and ZrO -5 are further selected to detect the impact
hydrolysis of cellulose by using different kinds of ZrO
2
with 0.04mol/L
o
H
2
SO
4
under microwave radiation at 160 C for 15min.
2
2
increases from 39.5% to 91.4% and from 44.4% to 95.5% at
140-160 C, respectively. And the conversion of cellulose
As narrated in the background and originality Content, from the
o
[22]
[23]
research work of Cui, Zhang and coworkers, we can clearly
understand the self-aggregation nature of cellulose molecular
chains in aqueous system. With the progress of hydrolysis, the
degree of freedom and the thermal motion ability of residual
cellulose molecular chains are increased. Under this situation,
rapid aggregation of the molecular chains of cellulose is
decreases slightly from 91.4% to 83.4% and from 95.5% to 89.8%
o
at 160-180 C. As to the yield of TRS (see Figure 5(b)), with the use
of ZrO
2
-2 and ZrO
2
-5, significant increases from 21.8% to 91.0%
o
and from 23.4% to 93.6% at 140-160 C is firstly obtained,
respectively. But, at 160-180 C, there shows a sharp decrease
o
from 91.0% to 33.0% and from 93.6% to 32.9%. That is to say, the
optimal hydrolytic efficiency can only be achieved at an
appropriate temperature. If the temperature is lower than 160 C,
produced. Accordingly, we can easily consider that an orderly
arrangement of the molecular chains of cellulose will be induced
to produce by the rapid aggregation. In fact, in our previous
o
19-21,25,26]
it is not enough to produce sufficient hydrolytic activation and
thus to form efficient hydrolysis. However, hydrolytic
works,[
rapid recrystallization of residual cellulose during
the short period of hydrolysis is clearly noticed. Consequently, the
hydrolytic reactivity and efficiency of cellulose are obviously
reduced. In order to effectively inhibit the self-aggregation nature
o
temperatures over 160 C may strengthen the ability of the rapid
self-aggregation. It is not good for the conversion of cellulose.
Furthermore, the high temperature is more likely to produce side
reaction. Unstable TRS will cause unnecessary losses. The above
in aqueous system, ZrO
hydrolysis. As proved above, all kinds of ZrO
2
is chosen as a catalytic assistant in
have adsorption
2
results show the optimal hydrolytic temperature is decided at
with hydroxyl-rich chemicals. Because cellulose is also a
polysaccharide with plenty of hydroxyl groups on its molecular
o
1
60 C with the presence of ZrO
2
.
2
chains, the adsorption of ZrO is no doubt helpful to slow down
The concentration of sulfuric acid is the other important
parameter to investigate in hydrolysis. As shown in the Figure
(a), with the use of ZrO -2 and ZrO -5, the conversion of
cellulose increases remarkably from 22.7% to 91.4% and 30.6% to
5.5% with the concentration of sulfuric acid (0-0.04mol/L) in the
catalyst system, respectively. As to the TRS yield (see Figure 6(b)),
with the use of ZrO -2 and ZrO -5, significant increases from 7.1%
and weaken the self-aggregation of the molecular chains of
cellulose. As a result, the hydrolysis reactivity and efficiency of
cellulose would be improved. And the stronger adsorption should
induce higher hydrolytic efficiency. As exhibited in Figure 4, with
6
2
2
9
the use of ZrO
conversion of cellulose and the high TRS yield. By utilization of the
ZrO with the strongest adsorption (namely ZrO -2), the hydrolytic
efficiency reaches the highest. The only exception is linked with
ZrO -1. The relative strong adsorption of ZrO -1 doesn’t induce a
relative high hydrolytic efficiency. This phenomenon is attributed
to the excessive large actual size of ZrO -1. As calculated, the
average particle diameter of cellulose is 254.1μm, and this size is
equal to even less than the actual size of ZrO -1. The excessive
large size of ZrO -1 is difficult to form good adsorption with
cellulose. With the use of ZrO -1, the hydrolytic efficiency of
2
, all the hydrolytic systems show the high
2
2
2
2
to 91.0% and from 8.0% to 93.6% with the concentration of
sulfuric acid (0-0.04mol/L) in the catalyst system is firstly
2
2
obtained, respectively. These results show that too low acidity
could not initiate adequately efficient hydrolysis of cellulose. It
can only exhibit low conversion of cellulose and TRS yield. After
increasing the concentration of sulfuric acid to 0.06-0.08mol/L,
the conversion of cellulose remains above 90.0% (see Figure 6(a)).
And 0.06-0.08mol/L sulfuric acid leads to sharp decreases of the
TRS yield from 91.0% to 55.1% and from 93.6% to 55.9% with the
2
2
2
2
cellulose to sugar is a little low.
2 2
use of ZrO -2 and ZrO -5, respectively. That is to say, the high
concentration sulfuric acid is also not fit for the highly efficient
hydrolysis. High acidity is not helpful to improve the conversion of
cellulose, but also causes the loss of unstable TRS.
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Chin. J. Chem.
Figure 6 Conversion of cellulose (a) and yield of TRS (b) obtained from the
hydrolysis of cellulose by using ZrO
2
-2 and ZrO
2
-5 with different
o
concentrations H
2
SO
4
under microwave radiation 160 C for 15min,
respectively.
By analyzing the impact of temperature and sulfuric acid
concentration on the hydrolytic efficiency to sugar in detail, the
optimal hydrolytic condition is clearly understood. ZrO
2
-2 with
o
0.04mol/L sulfuric acid at 160 C for 15min is the most suitable
Figure 8 XRD patterns and FTIR spectra of ZrO
before and after microwave radiation in 0.04mol/L H
5min.
2
-2 (a)(c) and ZrO
SO
2
-5 (b)(d)
at 160 C for
condition to induce the highest efficiency of the hydrolysis of
cellulose to sugar driven by microwave radiation in aqueous
system.
o
2
4
1
Impact of ZrO
After hydrolysis, the microstructure of ZrO
detected. From Figure 7, it can be seen that ZrO
still exhibited as a granular structure. There is almost no
difference from the structure before hydrolysis (see Figure 1).
Further detecting the microstructure of ZrO -2 and ZrO -5, no
obvious change can be observed on XRD patterns and FTIR
spectra (Figure 8) of the ZrO before and after hydrolysis. The
ZrO -5 before and after microwave radiation are composed of
6.6% monoclinic phase and 3.4% tetragonal phase as shown in
2
on hydrolysis of cellulose
Residual cellulose obtained from the hydrolysis with and
o
without ZrO
2
in 0.04mol/L H
2
SO
4
at 160 C for 5min under
2
-2 and ZrO
2
-5 are
-5 are
microwave radiation was characterized by XRD. In Figure 9,
cellulose shows a relatively low crystallinity. After hydrolysis only
by sulfuric acid, the XRD diffraction peaks of residual cellulose
become strong and thus present the increase of crystallinity.
2
-2 and ZrO
2
2
2
2
However, after hydrolysis by ZrO with sulfuric acid, relatively
weak diffraction peaks of residual cellulose are obtained in the
XRD pattern. Although specific crystallinity has some fluctuation
along with the change of the degree of hydrolysis, all the values
decrease. Figure 10 gives the FTIR spectra of the residual
cellulose. From the figure, it can be seen that all the residual
celluloses mainly exhibit a similar type II crystalline structure as
original cellulose.
2
2
9
o
o
o
Figure 8b. The obvious diffraction peaks at 28.4 , 31.7 and 34.2
o
refer to the monoclinic ZrO
tetragonal ZrO
2
and 30.4 is concerned with the
2
2
.Therefore, we can deduce that ZrO is in fact
chemical inertia during the hydrolysis. These results further prove
that the promotion on the efficiency of the hydrolysis of cellulose
2
by ZrO is only through physical adsorption.
2 2
Figure 7 SEM and TEM images of (a)(c) ZrO -2 and (b)(d) ZrO -5 obtained
Figure 9 XRD patterns of cellulose after hydrolysis with and without ZrO .
2
after hydrolysis of cellulose in 0.04mol/L H
2
SO
4
under microwave
o
radiation at 160 C for 15min.
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possible during hydrolysis will improve high efficiency in aqueous
system. The related method with the utilization of ZrO with
2
physical adsorption is helpful to avoid high acidity and organic
solvent and thus create a feasible condition for the green
conversion of cellulose.
Figure 10 FTIR spectra of cellulose after hydrolysis with and without ZrO .
2
It is well known that the hydrolysis of cellulose in aqueous
system is a solid-liquid heterogeneous reaction. And the sugar
product obtained in hydrolysis is unstable and it is easy to
produce side reaction. So that, in this process, whether the
catalyst (particular acid) can quickly enter into the inner of
cellulose particles and then interact with glycoside bond becomes
the key to achieve highly efficient hydrolysis. Because of the
particular β-bonding structure of molecular chains, original
Figure 11 The conversion of cellulose (a) and yield of TRS (b) obtained
[22,23]
cellulose owns a self-aggregation nature.
During the slow
from the use of ZrO
2
-2(a)(b) and ZrO
cellulose to sugar.
2
-5(c)(d) in multiple hydrolysis of
growth of plants, original cellulose forms a rather high
crystallinity. This crystalline structure hinders the rapid entry of
water and acid into the inner of cellulose particles and thus
reduces the speed of hydrolysis. Accordingly, a lot of researches
began to focus on the preparation of cellulose with the aim of
The conversion of cellulose and yield of TRS in multiple
hydrolysis of cellulose to sugar are summarized in Figure 11. From
Figure 11, it can be seen that both the conversion in multiple
hydrolysis of cellulose to sugar and yield of TRS are all above 90%
during the 3-time hydrolysis. Only a slight gradual decrease can
[16-18]
weakening the structural inhibition to hydrolyze.
However,
the removal of crystalline structure cannot fundamentally change
the self-aggregation nature of cellulose molecular chains. With
the progress of hydrolysis, the self-aggregation may be enhanced
with the increase of the degree of freedom of the residual
2
be found. The results reflect a good reusability of ZrO .
[19-21,25,26]
molecular chains. Our previous works
prove that the
Conclusions
With the aim to establish a highly effective and green method
to hydrolyze cellulose to sugar in aqueous system, following the
thought to inhabit the self-aggregation nature during the
hydrolysis, five kinds of ZrO as particular catalytic assistants are
2
selected to introduce into the catalytic system. By choosing
different surface roughness and particle size, the adsorption of
speed of the aggregation of the residual cellulose molecular
chains is very fast, and together with the formation of hydrogen
bonds and recrystallization. Usually, the crystallinity of the
residual cellulose produced by recrystallization is much higher
than the crystallinity of cellulose before hydrolysis. As a result,
the inhibition of hydrolysis has been formed again.
2
ZrO is controlled and thus improves the efficiency of the
hydrolysis of cellulose to sugar. On the basis of that, the optimal
condition to achieve highly efficient hydrolysis is obtained. By the
use of amorphous ZrO after ball milling (namely ZrO -2) with
2 2
0.04mol/L sulfuric acid as the catalysts, the conversion of
2
With the use of ZrO , the crystallinity of residual celluloses all
appears obvious decrease (see Figure 9). This result is in fact very
different from the enhanced crystallinity formed in rapid
recrystallization of cellulose, which is found in our previous
[
19-21,25,26]
works.
function of ZrO
Combination of the analysis on the structure and
, it can be inferred that the positive effect of
cellulose and TRS yield respectively reaches 95.5% and 93.6% with
2
15min microwave radiation in aqueous system.
physical adsorption on inhibition of the self-aggregation nature of
cellulose is further clarified and confirmed. On basis of the related
theoretical understanding of recrystallization, inhibition of the
self-aggregation nature of cellulose molecular chains as much as
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Running title
Chin. J. Chem.
Experimental
Materials
measured by Photoshop CS 6 (64Bit). The average value and
standard deviation of the size of ZrO were obtained by taking
00 points and calculated by Microsoft Office Excel 2016.
2
1
Cellulose (DP of 40, average particle diameter 254.1μm, and
crystallinity at 28.7%) was obtained by the pretreatment of
microcrystalline cellulose (Detailed process please see our
Dynamic light scattering (DLS) measurement was also utilized to
o
test the actual size of ZrO
2
. This test was operated at 25 C on
Malvern Zetasizer Nano-ZS Instrument with a detection range
[14]
o
previous work). Ordinary ZrO
ethylene glycol (AR grade, 99%) were purchased from Sinopharm
Chemical Reagent Co., Ltd. Nano-ZrO , D-(+)-glucose (GR grade,
99.5%) and cellobiose (AR grade, 98%) were obtained from
2
particles (AR grade, 99%) and
from 3 to 3000nm. The scattering angle was 90 C, and the
intensity autocorrelation functions were analyzed by the CONTIN
method. The specific surface area of different kinds of ZrO was
2
measured by the use of an ASAP-2020M adsorption analyzer. The
value of the specific surface area was calculated by using the
Brunauer-Emmett-Teller (BET) method.
2
>
Aladdin Co., Ltd. All the celluloses and sugar were dried under
vacuum at 100 C for 6h before using.
o
Amorphous ZrO
ZrOCl ·8H O was firstly dissolved in alcohol-aqueous solution (the
ratio between absolute ethyl alcohol and deionized water is
2
was prepared in our own laboratory.
2
The adsorption capacity of ZrO to the small molecular
hydroxyl-rich compound was tested by gas chromatography-mass
spectrometer (GC-MS). Ethylene glycol was selected to use as the
2
2
5
:1(mol/mol)) to form 0.01mol/L uniform solution. The obtained
model compound. During the experiment, different kinds of ZrO
were firstly mixed with 50mmol/L ethylene glycol aqueous
solution, respectively. Then, the mixture was put under
2
o
solution was heated at 75 C for 4h to form gelatinous precipitate.
After that, 3mol/L ammonia water was dropped into the
o
gelatinous precipitate with continuous stirring until the pH value
was adjusted to 11. The mixture was aged at room temperature
for 24h to form the precursor of amorphous zirconium hydroxide.
microwave radiation at 160 C for 15min. After that, the
concentrations of ethylene glycol solution were respectively
tested by GC-MS to show the amount of adsorption. The whole
-
After filtration, the precursor was washed with water until no Cl
test was recorded by an Agilent 7890B GC instrument fitted with
a DB-WAX capillary column (30m × 0.25mm × 0.25μm, Agilent),
tandem 5977A MS system. The temperature of the oven started
can be detected with 0.1mol/L AgNO
3
, and then dried in a
o
vacuum oven at 80 C. Finally, the dried precursor was placed in a
o
o
o
o
muffle furnace at 300 C for 5h to prepare amorphous ZrO
2
. The
at 50 C, ramped to 250 C at 15 C/min, and then held for 4min. A
constant pressure of 12.97 psi was used.
obtained amorphous ZrO
2
was also milled in a ball mill (XQM-0.2,
Tencan power, China) at 520r/min for 3h.
ꢀ
1−ꢀ2
Adsorbance percent (%) =
× 100%
(1)
ꢀ
1
Hydrolysis of cellulose
The hydrolysis of cellulose was operated in the autoclave vessel
35mL, 300Psi) of a high energy density microwave reactor (CEM
Where C
1
and C
2
are the concentration of initial ethylene glycol
, respectively.
(
and ethylene glycol after adsorbing with ZrO
2
Discover SP Microwave) with a frequency of 2.450±0.050GHz
[
21]
Adsorption capacity of ZrO on hydroxyl-rich carbohydrates was
recorded by the high performance liquid chromatography (HPLC).
In the experiment, cellobiose is used as the model. Different kinds
2
(
Output power 0-300W). Cellulose and ZrO
2
were mixed with
+
0
.04mol/L sulfuric acid (nZrO :nH =2:1) and then put into the
2
autoclave vessel. Continuous magnetic stirring was used during
the experiment to ensure uniform hydrolysis. The process was run
in dynamic mode with synchronous cooling provided by a
functional component named PowerMAX (from CEM Company).
Therefore, cooling gas can be quantitatively injected into the
system to maintain the same temperature under different
microwave power. The whole system was equipped with an
infrared (IR) temperature sensor placed at the bottom of the
vessel and a fiber optic probe was used to measure the
2
of ZrO were added into a concentration of 6mmol/L cellobiose
aqueous solution, respectively. Then, the mixture was put at
room temperature for 1h and 24h, respectively. After that, the
concentration of cellobiose in solution was measured by HPLC to
calculate the amount of adsorption by using a column BIO-RAD
Aminex HPX-87H at 30 C. A differential detector (Agilent
2 4
Technologies) was used. The mobile phase was 5mM H SO with a
flow rate of 0.4mL/min. Each volume injection of the cellobiose
solution was 10μL. Standard samples and undetermined
cellobiose solutions were filtrated and analyzed.
o
temperature. The hydrolysis was operated in two steps. In the
first step, the vessel was heated with 300W microwave power
o
until the temperature reached to 140-180 C. In the second step,
ꢁ
1−ꢁ2
Adsorbance percent (%) =
× 100%
(2)
the temperature of the vessel was kept constant under 150W
together with synchronous cooling for the desired time. After the
ꢁ
1
o
reaction, the vessel was cooled rapidly to 50 C by compressed air.
Where D
cellobiose after adsorbing with ZrO
1
and D
2
are the concentration of initial cellobiose and
, respectively.
2
Characterization
Scanning electron microscope (SEM, Verios G4 UC, Thermo
scientific) was used to observe the morphologies of ZrO before
2
and after hydrolysis. All the samples were sputter-coated with
platinum by using an anion sputter coater (E-1045, Hitachi) before
The yield of the reducing sugar (TRS) was measured by the
,5-dinitrosalicylic acid (DNS) method. Glucose was considered as
3
the standard for the measurement of reducing sugar. Calculate
the conversion of cellulose and yield of TRS according to Equation
(
3), (4), respectively,
2
the test. The microscopic scale of ZrO in images of SEM was
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Report
Qiao et al.
m1−ꢂ2
ꢂ1
-1
Conversion of cellulose (%) =
× 100%
(3)
(4)
spectrometer. The spectra (4000−400cm ) were recorded with a
−
1
resolution of 0.9cm and 32 scans per sample.
ꢂꢃꢄꢅ
TRS yield (%) =
Where m
× 0.9 × 100%
ꢂ1
Acknowledgement
1
2
is the mass of initial cellulose, m is the mass of
We are grateful for the financial support by the National
Natural Science Foundation of China (51773217 & 21978310), the
Key Research and Development Program of Shandong Province
2019JZZY020217), Ningbo Natural Science Foundation
2019A610026), Youth Innovation Promotion Association CAS
2017339), and the National Key Research and Development
Program of China (2017YFE0102300). We are also grateful for the
help to use HPLC equipment provided by Dr. Yajie Zhang and his
research group in Ningbo Institute of Materials Technology and
Engineering, Chinese Academy of Sciences.
residual cellulose, and mTRS is the mass of TRS. Three parallel
experiments were taken at the same reaction condition to get an
average value. The yield of TRS was calculated on the basis of the
tests.
(
(
(
Crystal structure and crystallinity (Cr) of ZrO
respectively recorded with a Siemens D5000 X-ray Diffractometer
XRD). The diffracted intensity was tested with Cu Kα radiation at
2
and cellulose were
(
4
o
o
0kV and 40mA in a 2θ range between 5 and 45 . FTIR test was
and cellulose. FTIR
also used to show the crystal structure of ZrO
2
spectrum was implemented using a Cary660+660 infrared
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a
c
Department of Polymer, College of Material Science and Engineering,
Chemical College, Shijiazhuang University, Shijiazhuang, Hebei 050035,
Shanghai University, Shanghai 200444, China
China
b
d
Key Laboratory of Bio-based Polymeric Materials of Zhejiang Province,
Hebei Building Ceramics Engineering Research Center, Shijiazhuang
Ningbo Institute of Materials Technology and Engineering, Chinese
Academy of Sciences, Ningbo, Zhejiang 315201, China
University, Shijiazhuang, Hebei 050035, China
Chin. J. Chem. 2018, template
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Entry for the Table of Contents
Page No.
Effect of Adsorption of ZrO2 in Catalysts on the
Efficiency of Hydrolysis of Cellulose to Sugar in
Aqueous System under Microwave Radiation
Adjusting the adsorption of ZrO2 in catalysts effectively achieves the improvement of the
hydrolytic efficiency of cellulose to sugar.
Ying Qiao, Lixin Feng, Zhongqiu Li,* Zhenyu
Zhang, Jing Chen, Haining Na,* Jin Zhu, Lai Chen
a
c
Department of Polymer, College of Material Science and Engineering,
Shanghai University, Shanghai 200444, China
Chemical College, Shijiazhuang University, Shijiazhuang, Hebei 050035,
China
b
d
Key Laboratory of Bio-based Polymeric Materials of Zhejiang Province,
Hebei Building Ceramics Engineering Research Center, Shijiazhuang
University, Shijiazhuang, Hebei 050035, China
Ningbo Institute of Materials Technology and Engineering, Chinese
Academy of Sciences, Ningbo, Zhejiang 315201, China
Chin. J. Chem. 2018, template
© 2018 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
This article is protected by copyright. All rights reserved.