Preparation, characterization and application of RHA/TiO2 nanocomposites in the acetylation of alcohols, phenols and amines

Article abstract of DOI:10.1016/j.crci.2016.03.004

In this work, anatase-phase nano-titania was prepared by embedding in rice husk ash, and identified using a variety of techniques. The obtained nanocomposite (RHA/TiO₂) was used as a green and inexpensive catalyst for the promotion of the acetylation of alcohols, phenols and amines with Ac₂O at room temperature under solvent free conditions. The procedure gave the products in excellent yields during all reaction times. Also this catalyst can be reused for several times without loss of its catalytic activity.

Full text of DOI:10.1016/j.crci.2016.03.004

C. R. Chimie xxx (2016) 1e8
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Full paper/Memoire
Preparation, characterization and application of RHA/TiO2
nanocomposites in the acetylation of alcohols, phenols and
amines
Mohadeseh Seddighi, Farhad Shirini*, Omid Goli-Jolodar
Department of Chemistry, College of Science, University of Guilan, Rasht, 41335, I.R. Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work, anatase-phase nano-titania was prepared by embedding in rice husk ash, and
identified using a variety of techniques. The obtained nanocomposite (RHA/TiO2) was used
as a green and inexpensive catalyst for the promotion of the acetylation of alcohols,
phenols and amines with Ac2O at room temperature under solvent free conditions. The
procedure gave the products in excellent yields during all reaction times. Also this catalyst
can be reused for several times without loss of its catalytic activity.
Received 25 January 2016
Accepted 7 March 2016
Available online xxxx
Keywords:
Rice husk ash
TiO2
ꢀ
© 2016 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
RHA/TiO2
Nanocomposite
Acetylation
Protection
1. Introduction
amounts of the acylating agents and harsh reaction con-
ditions. Therefore there is still a need to find an alternative
Protection of functional groups is often necessary dur-
ing a multistep organic synthesis, so the development of
economical and efficient methods for this purpose is very
important. Hydroxyl and amino groups in alcohols, phenols
and amines are often present in organic molecules, and
their protection is an important process during organic
reactions. Among various procedures for the protection of
hydroxyl and amino groups, acetylation with acetic anhy-
dride or acetyl chloride in the presence of an acidic or basic
catalyst is an efficient and common route due to the sta-
bility of the products in acidic media and easy introduction
and removal of the acetyl group. For this purpose many
method which might be mild and catalytically and
economically efficient.
In recent years, synthesis of nanocrystalline metal ox-
ides has attracted much attention due to their unusual
catalytic properties compared to bulk metals [7]. Among
various metal oxides, TiO2 nanoparticles is one of the most
utilized ones which have been widely investigated as the
catalyst, pigment, food coloring substance, etc [8e9].
Preparation of the non-agglomerated TiO2 nanoparticles,
with a narrow size distribution in anatase form, is very
important to achieve higher catalytic activity and more
readily handling than the commercial TiO2 [10e11]. On the
basis of this subject, the synthesis of TiO2 over a silica
support was explored as a useful way for preventing the
agglomeration and formation of dispersed TiO2 aggregates
[12]. Siliceous materials are desirable because they are
chemically inert and have a high specific surface area and
thermal stability.
€
Bronsted and Lewis acidic catalysts have been used [1e6].
Although these methods are improved, most of them suffer
from disadvantages such as long reaction times, use of
organic solvents, expensive catalysts, use of excess
Rice husk, the outer covering of rice grains, is one of the
main agricultural residues which is obtained during the
* Corresponding author.
E-mail address: shirini@guilan.ac.ir (F. Shirini).
http://dx.doi.org/10.1016/j.crci.2016.03.004
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1631-0748/© 2016 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: M. Seddighi, et al., Preparation, characterization and application of RHA/TiO2 nanocomposites
in the acetylation of alcohols, phenols and amines, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.03.004

2
M. Seddighi et al. / C. R. Chimie xxx (2016) 1e8
milling process. Application of rice husk as an energy
source for biomass power plants, rice mills and brick fac-
tories is increasing due to its high calorific power [13]. In
this combustion, rice husk ash (RHA) is produced. RHA
contains a considerable amount of amorphous silica up to
80% and small proportion of impurities such as K2O, Na2O
and Fe2O3 [14].
In recent years, investigation on the application of TiO2-
based reagents in organic reactions became an important
part of our ongoing research program [15e17]. In contin-
uation of these studies and because that RHA possesses
high silica content, we were interested to investigate the
possibility of the preparation of anatase-phase TiO2 over
this reagent.
mixture was stirred at room temperature. After completion
of the reaction (mentioned by TLC), dichloromethane
(20 mL) was added and the catalyst was separated by
filtration. The organic phase was washed with 10% aqueous
solution of sodium bicarbonate (2 ꢁ 20 mL) and dried over
Na2SO4. The solvent was removed under reduced pressure
to afford the desired product in good to high yields. The
spectral (IR, 1H and 13C NMR) data of new compounds are
presented below:
Benzene-1,2,3-triyl triacetate: White solid; IR (neat)
n
¼ 1765 cmꢂ1; 1H NMR (CDCl3, 400 MHz):
d
¼ 2.31 (s, 6H,
CH3), 2.32 (s, 3H, CH3),7.14 (d, J ¼ 8.2 Hz, 2H, ArH), 7.29 (dd,
J ¼ 8.3 and 0.8 Hz, 1H, ArH) ppm; 13C NMR (CDCl3,
100 MHz):
168.3 ppm.
d
¼ 20.6, 21.0, 121.1, 126.4, 135.1, 143.9, 167.4,
2. Experimental
N-(naphthalen-1-yl)acetamide: White solid; IR (neat)
3295, 1635 cmꢂ1 1H NMR (CDCl3, 400 MHz):
¼ 2.30 (s,
3H, CH3), 7.45e7.87 (m, 8H, ArH, NH) ppm; 13C NMR (CDCl3,
100 MHz):
n:
;
d
2.1. General
d
¼ 22.8, 118.5, 122.3, 122.8, 125.2, 126.1, 127.3,
Chemicals were purchased from Fluka, Merck, and
Aldrich chemical companies. All yields refer to the isolated
products. Products were characterized by comparison of
their physical constants, IR and NMR spectroscopy with
authentic samples and those reported in the literature. The
purity determination of the substrate and reaction moni-
toring were accompanied by TLC on silicagel polygram
SILG/UV 254 plates.
127.8, 128.4, 128.5, 133.1, 169.9 ppm.
2.5. Catalyst characterization
2.5.1. FT-IR analysis
Fig. 1 shows the FT-IR spectra of nano-TiO2 (anatase),
RHA and 20, 30 and 50 W% RHA/TiO2. In all cases, the peaks
at 3400 and 1630 cmꢂ1 are attributed to the stretching and
bending modes of the hydroxyl groups of SieOH or TieOH
and the adsorbed water [19]. The strong peak at 1100 cmꢂ1
and the peaks at 801 and 468 cmꢂ1 are assigned to the
asymmetric stretching, symmetric stretching and bending
modes of SieOeSi, respectively. Because the vibration
modes of TieOeTi lie in the range of 500e700 cmꢂ1 (Fig. 1,
spectrum of TiO2) [20], the peaks appearing at
500e700 cmꢂ1 in the prepared samples can be attributed
to TieOeTi (Fig. 1, spectra of RHA/TiO2 nanocomposites).
Increasing the intensity of these bands by increasing the
titanium content of the samples can be described on the
basis of this fact. Theoretically, the stretching vibration of
TieOeSi appeared as a weak peak at 960 cmꢂ1, whereas
such a peak was not observed in the prepared samples. So,
it could be resulted from the FT-IR spectra and there is no
binding between TiO2 and SiO2, and titania is only
embedded into the RHA matrix [10].
2.2. Instrumentation
The FT-IR spectra were run on a VERTEX 70 Brucker
company (Germany). Scanning election microphotographs
were obtained on a SEM-Philips XL30. X-ray diffraction
(XRD) measurements were performed at room tempera-
ture on a Siemens D-500 X-ray diffractometer (Germany),
using Ni-filtered Co K
a
radiation (
l
¼ 0.15418 nm).
2.3. Preparation of RHA/TiO2 nanocomposites
1.0 g of rice husk ash (used in our previous report [18])in
absolute ethanol (6 mL) was stirred for 30 min at room
temperature. Then the required amount of titanium tet-
raisopropoxide (TTIP) (volume ratio TTIP:EtOH of 1:6) was
added dropwise to the solution with stirring for 2 h. In
continue, deionized water was slowly added to the result-
ing mixture (TTIP:water with a ratio of 1:60) and the stir-
ring was maintained for 2 h to hydrolyze the remaining
TTIP completely. The prepared material was separated by
filtration, washed with water, and dried at 80 ꢀC in an oven.
Finally, the obtained solid was calcinated at 500 ꢀC for 3 h to
obtain RHA/TiO2 nonocomposites. [Caution: Throughout
the subsequent discussion, the samples will be named by
indicating the titania content and support, as RHA/
TiO2(20%), RHA/TiO2(30%) and RHA/TiO2(50%).]
2.5.2. Powder X-ray diffraction
Fig. 2 represents the X-ray diffraction (XRD) patterns of
the RHA and RHA/TiO2 nanocomposites. The broad peak
appeared around 2q equal to 22 in the RHA pattern clearly
indicating that the silica of rice husk ash is mainly in the
amorphous form [21]. The peaks appearing around
2
q
¼ 25.3, 37.8, 47.8, 54.1 and 62.3 in RHA/TiO2 nano-
composites are related to the (101), (004), (200), (105) and
(211) reflections which indicate that the anatase phase is
the only phase present in all the prepared materials
[22e23]. The intensity of anatase peaks increased by
increasing in the titania contents, however broadening of
these peaks show that the nanocomposite particles have
very small size. These observations strongly suggested that
not only the RHA inhibited the formation of the rutile
2.4. General procedure for acetylation with Ac2O catalyzed by
RHA/TiO2(30%)
1 mmol of the substrate (alcohol, phenol or amine) was
added to a mixture of RHA/TiO2(30%) (20 mg) and acetic
anhydride (1.5 mmol per OH/NH2 group) and the resulting
Please cite this article in press as: M. Seddighi, et al., Preparation, characterization and application of RHA/TiO2 nanocomposites
in the acetylation of alcohols, phenols and amines, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.03.004

M. Seddighi et al. / C. R. Chimie xxx (2016) 1e8
3
Fig. 1. FT-IR spectra of RHA, TiO2 and various RHA/TiO2 nanocomposites.
Please cite this article in press as: M. Seddighi, et al., Preparation, characterization and application of RHA/TiO2 nanocomposites
in the acetylation of alcohols, phenols and amines, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.03.004

4
M. Seddighi et al. / C. R. Chimie xxx (2016) 1e8
Fig. 2. XRD patterns of RHA and various samples of RHA/TiO2 nanocomposites.
phase, but also inhibited growth of crystal grain of titan
[24].
The average crystalline sizes of nanocomposites were
estimated by XRD using Scherrer’s equation by considering
the full width and half maximum (FWHM) value (Table 1).
As can be seen, all of the synthesized nanocomposites have
almost the same crystalline sizes.
Table 1
XRD data of RHA/TiO2 nanocomposites.
Entry
Nanocomposite
2
q
Peak width
[FWHM]
Size
[nm]
1
2
3
RHA/TiO2(20%)
RHA/TiO2(30%)
RHA/TiO2(50%)
25.35
22.38
25.36
0.40
0.38
0.36
20
21
22
2.5.3. SEM and TEM analysis
Scanning electron microscopy (SEM) and transmission
electron microscopy (TEM) were performed for the
Fig. 3. SEM images of RHA (a) and RHA/TiO2(30%) (b).
Please cite this article in press as: M. Seddighi, et al., Preparation, characterization and application of RHA/TiO2 nanocomposites
in the acetylation of alcohols, phenols and amines, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.03.004

M. Seddighi et al. / C. R. Chimie xxx (2016) 1e8
5
Scheme 1. Preparation of RHA/TiO2 nanocomposites.
Table 2
Optimization of the best ratio of RHA/TiO2 nanocomposites in the
acetylation of 4-chlorobenzyl alcohol.
Entry
Catalyst
Time (min)
Conversion (%)
1
2
3
RHA/TiO2(20%)
RHA/TiO2(30%)
RHA/TiO2(50%)
15
8
8
85
100
100
2.5.4. N2 adsorptionedesorption measurements
N2 adsorptionedesorption measurements based on BET
and BJH methods, which have been a powerful tool for
nano- or meso-porous material characterization, were
performed to obtain more information about the catalyst.
The adsorptionedesorption isotherm of RHA and RHA/
TiO2(30%) nanocomposites is shown in Fig. 5a. Both sam-
ples exhibited a type IV isotherm with H3 hysteresis loop
categories according to the literature, which indicates that
Fig. 4. TEM images of RHA/TiO2 (30%).
determination of the size distribution, particle shape and
surface morphology, as shown in Fig. 3 and Fig. 4. It should
be noted that these analysis were carried out on RHA/
TiO2(30%) (the best ratio of RHA/TiO2 with the highest
catalytic activity was determined in the acetylation of 4-
chlorobenzyl alcohol). The SEM pictures show that RHA
has a porous and irregular shape [25], and the porosity was
substantially maintained over dispersion of TiO2 in RHA/
TiO2(30%). It is clear from the TEM images that TiO2
nanoparticles, which can be seen as dark particles, are
spherical with average size less than 10 nm in diameter,
which have been dispersed in the matrix of RHA, as shown
in Fig. 4.
Scheme 2. Acetylation of alcohols, phenols and amines catalyzed by RHA/
TiO2(30%).
Fig. 5. The N2 adsorptionedesorption isotherm (a), and pore size distribution (b) of RHA and RHA/TiO2(30%).
Please cite this article in press as: M. Seddighi, et al., Preparation, characterization and application of RHA/TiO2 nanocomposites
in the acetylation of alcohols, phenols and amines, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.03.004

6
M. Seddighi et al. / C. R. Chimie xxx (2016) 1e8
Table 3
Acetylation of alcohols, phenols and amines in the presence of RHA/TiO2(30%) under solvent-free conditions.
Entry
1
Aldehyde
Product
Time (min)
Yield (%)a
96
7
2
8 (8,9,10,10)b
97 (95,96,97,94)
3
10
10
10
20
10
15
12
14
0.5
0.5
12
15
91
93
94
94
95
90
88
93
96
96
94
90
4
5
6
7
8
9
10
11
12
13
14
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M. Seddighi et al. / C. R. Chimie xxx (2016) 1e8
7
Table 3 (continued)
Entry
Aldehyde
Product
Time (min)
20
Yield (%)a
91
15
16c
25
90
17
18
19
20
7
93
93
92
94
7
10
7
a
Isolated yields.
Results obtained using the recovered catalyst.
40 mg of the catalyst was used.
b
c
the samples are mesoporous materials with slit-like pores
[26]. These results also prove that the textural properties of
RHA were substantially maintained over the preparation of
the nanocomposite. The specific BET surface areas of RHA
and RHA/TiO2(30%) are 57 and 50 m2/g, respectively.
Furthermore, the curves of pore size distribution evaluated
from desorption data by utilizing the BJH model are also
shown in Fig. 5b. These curves show that there are some
particles with average size less than 10 nm in diameter in
RHA/(30%) which do not exist in RHA. These particles can
be attributed to the TiO2 nanoparticles.
acetic anhydride: i) the amounts of the catalyst; ii) solvent
or solvent-less media and iii) temperature. The obtained
results clarified that the best conditions are the ones which
are shown in Scheme 2.
After optimization of the reaction conditions, different
types of alcohols were subjected to the acetylation using
this method (Table 3). Acetylation of various benzylic al-
cohols containing electron-withdrawing and electron-
donating substituents proceeded efficiently with high iso-
lated yields (Table 3, Entries 1e7). Primary, secondary and
3. Results and discussion
On the basis of the information obtained from the
studies on RHA/TiO2 nanocomposites, it is expected that
this reagent can be used as a catalyst for the promotion of
the organic reactions. So this reagent was used in the
promotion of the conversion of alcohols, phenols and
amines to their corresponding acetates and/or amides with
acetic anhydride (Scheme 1).
In the first step we focused our attention toward the
optimization of the ratio of RHA to TiO2 for obtaining the
highest catalytic activity. For this purpose, acetylation of 4-
chlorobenzyl alcohol was studied and the best results were
obtained using RHA/TiO2(30%) (Table 2). Further increase in
this ratio did not improve the activity of the prepared
nanocomposite. Then for obtaining the optimum reaction
conditions, we studied the influence of the following fac-
tors on the acetylation of 4-chlorobenzyl alcohol with
Scheme 3. Proposed mechanism of the reaction.
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8
M. Seddighi et al. / C. R. Chimie xxx (2016) 1e8
Table 4
4. Conclusions
Comparison of the results of the acetylation of benzyl alcohol catalyzed by
RHA/TiO2(30%) with those obtained by using some of the reported
catalysts.
In conclusion, rice husk ash was used as a silica support
for the synthesis of anatase-phase titania nanoparticles and
a RHA/TiO2 nanocomposite was obtained. Then, a simple
and efficient protocol for the acetylation of alcohols, phe-
nols and amines was developed using this nanocomposite.
The methodology has several advantages such as: (i) high
reaction rates and excellent yields, (ii) no side reactions,
(iii) ease of preparation and handling of the catalyst, (iv)
cost efficiency and effective reusability of the catalyst, (v)
use of an inexpensive catalyst with lower loading and (vi) a
simple experimental procedure and solvent free condi-
tions. Further work to explore this catalyst in other organic
transformations is in progress.
Entry Catalyst (loading)
Reaction
conditions
Time
(min)
Yield [Ref.]
(%)
1
Zeolite HSZ-360
(20 mg)
60 ꢀC/Neat
60
84
[1]
2
3
4
Cu(OTf)2 (2.5 mol%)
RuCl3 (5 mol%)
Saccharinsulfonic acid Reflux/CH2Cl2 120
r.t./CH2Cl2
r.t./CH3CN
30
10
97
98
85
[2]
[3]
[4]
(5 mol%)
5
6
7
RiH (300 mg)
RHA (50 mg)
TiO2 (30 mg)
80 ꢀC/Neat
80 ꢀC/Neat
100 ꢀC/Neat
60
15
15
94
93
95
[5]
[6]
This
work
This
work
8
RHA/TiO2(30%)
(20 mg)
r.t./Neat
0.5
95
Acknowledgments
We are thankful to the University of Guilan Research
Council for partial support of this work.
tertiary aliphatic alcohols were also efficiently converted to
their corresponding acetates in almost quantitative yields
at room temperature (Table 3, Entries 8e12). No elimina-
tion and rearrangement by-products were observed at all.
Phenol and its derivatives also undergo acetylation easily
using this method and their corresponding acetates can be
isolated in excellent yields (Table 3, Entries 13e16). In the
case of pyrogallol, higher amounts of the catalyst are
needed due to high steric hindrance (Table 3, Entry 16). This
method is also very useful for the acetylation of amines
with acetic anhydride. All reactions are performed under
mild reaction conditions in very short reaction times with
high yields (Table 3, Entries 17e20).
References
[1] R. Ballini, G. Bosica, S. Carloni, L. Ciaralli, R. Maggi, G. Sartori, Tet-
rahedron Lett. 39 (1998) 6049e6052.
[2] P. Saravanan, V.K. Singh, Tetrahedron Lett. 40 (1999) 2611e2614.
[3] S.K. De, Tetrahedron Lett. 45 (2004) 2919e2922.
[4] F. Shirini, M.A. Zolfigol, M. Abedini, Monatsh. Chem. 140 (2009)
1495e1498.
[5] F. Shirini, S. Akbari-Dadamahaleh, A. Mohammad-Khah, A. Aliakbar,
C. R. Chim. 17 (2014) 164e170.
[6] F. Shirini, S. Akbari-Dadamahaleh, A. Mohammad-Khah, Phos-
phorus, Sulfur Silicon Relat. Elem. 189 (2014) 577e586.
[7] Z. Zhang, C.C. Wang, R. Zakaria, J.Y. Ying, J. Phys. Chem. B 102 (1998)
10871e10878.
To check the reusability of the catalyst, the reaction of 4-
chlorobenzyl alcohol and acetic anhydride under the opti-
mized reaction conditions was studied. When the reaction
was completed, dichloromethane was added and the
catalyst was separated by filtration. The recovered catalyst
was washed with dichloromethane, dried and reused for
the same reaction. This process was carried out over five
runs and all reactions led to the desired products with high
efficiency (Table 3, Entry 2).
The possible mechanism for the acetylation of alcohols,
phenols and amines in the presence of RHA/TiO2(30%) as a
promoter is shown in Scheme 3. On the basis of this
mechanism, RHA/TiO2(30%) catalyzes the reaction by the
electrophilic activation of Ac2O to form a zwitterionic
species, making the carbonyl group susceptible to nucleo-
philic attack by the substrate. Successive elimination of
CH3CO2H results in the formation of the requested product
and regenerates RHA-SO3H in the reaction mixture.
To illustrate the efficiency of the proposed method,
Table 4 compares our results in the acetylation of 4-chlor-
obenzyl alcohol with those reported by using the relevant
reagents in the literature. It is clear that the present method
is superior in terms of the reaction time and catalyst
amount, especially compared with rice husk (RiH), rice
husk ash (RHA) and TiO2 (Table 4, Entries 5e7).
[8] S.M. Gupta, M. Triptha, Chin. Sci. Bull. 56 (2011) 1639e1657.
[9] X. Chen, S.S. Mao, Chem. Rev. 107 (2007) 2891e2959.
[10] K.Y. Jung, S.B. Park, J. Photochem. Photobiol., A 127 (1999) 117e122.
[11] J. Aguado, R. Van-Grieken, M. Lopez-Munoz, J. Marugan, Appl. Catal.
A: Gen. 312 (2006) 202e212.
[12] R. van Grieken, J. Aguado, M.J. Lopez-Munoz, J. Marugan, J. Photo-
chem. Photobiol., A 148 (2002) 315e322.
ꢀ
[13] C. Real, M.D. Alcala, J.M. Criado, J. Am. Ceram. Soc. 79 (1996)
2012e2016.
[14] Q. Feng, H. Yamamichi, M. Shoya, S. Sugita, Cem. Concr. Res. 34
(2004) 521e526.
[15] F. Shirini, M.A. Khoshdel, M. Abedini, S.V. Atghia, Chin. Chem. Lett.
22 (2011) 1211e1214.
[16] F. Shirini, S.V. Atghia, M.G. Jirdehi, Catal. Commun. 18 (2012) 5e10.
[17] F. Shirini, M. Abedini, S.A. Kiaroudi, Phosphorus Sulfur 189 (2014)
1279e1288.
[18] F. Shirini, M. Mamaghani, M. Seddighi, Catal. Commun. 36 (2013)
31e37.
[19] N.P. Hung, N.T.V. Hoan, N.V. Nghia, Nanosci. Nanotechnol. 3 (2013)
19e25.
[20] D.A. Kumar, J.M. Shyla, F.P. Xavier, Appl. Nanosci. 2 (2012) 429e436.
[21] H.T. Jang, Y. Park, Y.S. Ko, J.Y. Lee, B. Margandan, Int. J. Greenh. Gas
Control 3 (2009) 545e549.
[22] S. Wang, K. Wang, J. Jehng, L. Liu, Front. Environ. Sci. Eng. 6 (2012)
304e312.
[23] I. Pavlovska, K. Malnieks, G. Mezinskis, L. Bidermanis, M. Karpe, Surf.
Coat. Technol. 258 (2014) 206e210.
[24] J. Yang, J. Zhang, L. Zhu, S. Chen, Y. Zhang, Y. Tang, Y. Zhu, Y. Li, J.
Hazard. Mater. B 137 (2006) 952e958.
[25] G.A. Habeeb, H.B. Mahmud, Mater. Res. 13 (2010) 185e190.
[26] J.B. Condon, Surface Area and Porosity Determinations by
Physisorption, Elsevier, 2006. Chapter 1, pp. 1e27.
Please cite this article in press as: M. Seddighi, et al., Preparation, characterization and application of RHA/TiO2 nanocomposites
in the acetylation of alcohols, phenols and amines, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.03.004