Influence of gel composition and microwave-assisted hydrothermal time in MCM-41 synthesis

Accepted Manuscript Influence of gel composition and microwave-assisted hydrothermal time in MCM-41 synthesis Krittanun Deekamwong, Chokchai Kaiyasuan, Juthamas Jitcharoen, Jatuporn Wittayakun PII:

S0254-0584(17)30681-8

DOI:

10.1016/j.matchemphys.2017.08.058

Reference:

MAC 19956

To appear in:

Materials Chemistry and Physics

Received Date: 29 May 2017 Revised Date:

15 August 2017

Accepted Date: 21 August 2017

Please cite this article as: K. Deekamwong, C. Kaiyasuan, J. Jitcharoen, J. Wittayakun, Influence of gel composition and microwave-assisted hydrothermal time in MCM-41 synthesis, Materials Chemistry and Physics (2017), doi: 10.1016/j.matchemphys.2017.08.058. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

Influence of gel composition and microwave-assisted hydrothermal time

RI PT

in MCM-41 synthesis

Krittanun Deekamwonga, Chokchai Kaiyasuanb, Juthamas Jitcharoenb and Jatuporn

a

SC

Wittayakuna,*

School of Chemistry, Institute of Science, Suranaree University of Technology, Nakhon

b

M AN U

Ratchasima, 30000 Thailand

Department of Chemistry, Faculty of Science, Ubon Ratchathani University, Ubon

Ratchathani, 34190 Thailand

AC C

EP

TE D

*E-mail: [email protected]

1

ACCEPTED MANUSCRIPT

Abstract This work reports syntheses of siliceous mesoporous MCM-41 by microwave-

RI PT

assisted hydrothermal process with CTAB:SiO2 ratio from 0.025 to 0.400 and NaOH:SiO2 ratio of 1.0, 1.3 and 2.0. From XRD results, the MCM-41 phase increased with CTAB:SiO2 ratio until 0.300. Another amorphous phase was produced from the gel with CTAB:SiO2

SC

ratio of 0.400. MCM-41 from the optimal CTAB:SiO2 ratio (0.300) had surface area of 1138

M AN U

m2.g-1 and pore wall thickness of 12.70 Å. With CTAB:SiO2 ratio fixed at 0.300, the optimal NaOH:SiO2 ratio was 1.0. Then, an influence of microwave hydrothermal time was studied from 0 to 180 min on the gels with CTAB:SiO2 ratio of 0.300 and NaOH:SiO2 ratio of 1.0. All MCM-41 samples had essentially similar XRD pattern, surface area and pore-wall

TE D

thickness. However, their TEM images indicated that the longer hydrothermal time produced MCM-41 with the less defects.

AC C

EP

Keywords: MCM-41, CTAB, microwave, hydrothermal method, gel composition

2

ACCEPTED MANUSCRIPT

1. Introduction MCM-41 (Mobil Composition of Matter No. 41) is a mesoporous siliceous material

RI PT

which has been widely studied and employed in various applications including adsorption [1,2] and catalysis [3,4,5,6]. MCM-41 is normally synthesized by a conventional hydrothermal method using cetyltrimethylammonium bromide (CTAB) as a template.

For example, Cheng et al. reported a

M AN U

temperature and time have been explored.

SC

Various strategies have been employed and parameters such as gel composition, pH,

conventional hydrothermal synthesis of MCM-41 in an alkali-free media and influence of source and concentration of reactants, gel aging time, temperature and duration of the synthesis [7]. With the synthesis at 100 °C, hexagonal phase was the major product which An optimal

TE D

did not transform to other phases with the longer hydrothermal time.

CTAB:SiO2 ratio was 0.27. Park et al. illustrated a conventional hydrothermal method at 110 °C that NaOH:SiO2 ratio of 0.5, 1 and 2 gave a highly periodic hexagonal structure

EP

when the gel pH was adjusted to optimal values [8]. However, the conventional method

AC C

requires a long hydrothermal time of at least 24 h which is not efficient in term of energy consumption.

To reduce the energy consumption in the MCM-41 synthesis, microwave is applied

as an alternative heat source. Wu and Bein obtained aluminum containing MCM-41 with a high quality from a microwave-assisted hydrothermal method [9]. The samples synthesized at 150 °C for 1 h showed hexagonal mesoporous structure with surface areas in the range

3

ACCEPTED MANUSCRIPT

of 900 – 1000 m2.g-1. Park et al. synthesized siliceous MCM-41 at 100-120 °C within 1 h or less with ethylene glycol as a co-solvent. The obtained MCM-41 had a surface area about

RI PT

1000 m2.g-1 [10]. Song et al. synthesized MCM-41 from 1-3 h at 100 °C and a high quality MCM-41 was produced in 2 h [11]. However, most of the previous microwave-assisted

SC

syntheses were only conducted with a fixed gel ratio. Therefore, it is an aim of this work to understand an influence of CTAB:SiO2 and NaOH:SiO2 ratio in the synthesis of MCM-41

M AN U

by microwave-assisted method. The optimal gel ratio is then employed in a further investigation on the effect of hydrothermal time.

2. Experimental

TE D

2.1 Synthesis of MCM-41 by microwave-assisted hydrothermal method MCM-41 was synthesized by microwave-assisted hydrothermal method with a

EP

procedure modified from the literature [12,13]. All chemicals were used as received including SiO2 (silica gel 60, 0.015-0.040 mm, Merck), cetyltrimethylammonium bromide

AC C

(CTAB, >99 % ACROS), sodium hydroxide (NaOH, pellet, Carlo Erba) and sulfuric acid (96% H2SO4, Carlo Erba).

A gel was prepared at 25 °C by dissolving a desired amount of CTAB in 20 mL

deionized water. Then, SiO2 (3.55 g) was added to a 40-mL solution containing 2.22 g NaOH within 1 h under stirring. The mixture was further stirred for 18 h. Then, the gel pH was

4

ACCEPTED MANUSCRIPT

adjusted to 10 within 30 min by 3 M H2SO4 and the resulting mixture was stirred for 2 h. The obtained gel with a total volume of 60 mL was transferred into a 100-mL Teflon-lined

RI PT

microwave vessel, closed and heated to 100 °C in a Microwave MARs 6-One Touch with a heating rate 5 °C/min and held for 90 min. The temperature was monitored by an IR sensor

SC

with an adjustable power output (1200 W). After cooling to room temperature, the solid product was separated by centrifugation, washed with deionized water and oven-dried at 80

M AN U

°C. The obtained powder was called “as-synthesized sample”. A portion of the assynthesized sample was calcined 550 °C for 6 h with a heating rate 2 °C/min. The CTAB:SiO2 mole ratios were ranged from 0.025 to 0.400. Afterward, the gel producing MCM-41 with the best quality was further studied on the influence of NaOH:SiO2 at 1.0,

TE D

1.3 and 2.0. These ratios were limited due to the solubility of silica. Finally, effect of microwave hydrothermal time was studied from 0 min (heated to 100 °C and suddenly

EP

cooled down) to 180 min (heated to 100 °C, held for 180 min and cooled down) with the

AC C

synthesis gel with the optimal ratios of CTAB:SiO2 and NaOH:SiO2 from the above studies.

2.2 Characterization

Calcined samples were characterized by X-ray diffraction (XRD) on a Bruker D8

Advance using Cu Kα radiation (1.5418 Å) and Bragg-Brentano geometry. The (100) interplanar spacing (d100) was calculated by Bragg’s law. The lattice parameter (a0)

5

ACCEPTED MANUSCRIPT

representing the distance between centers of two adjacent pores was calculated from 2/√3 ⋅ d100 [14].

RI PT

The as-synthesized samples were analyzed by thermogravimetric method on a TA Instruments SDT 2960. Fifteen milligrams of each sample was loaded in an alumina pan

SC

and heated to 600 °C with a rate of 20 °C/min under a flow of air zero with a rate of 100 mL/min. The weight loss from each sample was from the template removal. The remaining

M AN U

weight of each sample was used to calculate the solid yield.

Nitrogen adsorption-desorption isotherm was obtained from a Micromeritics ASAP 2010. Two hundred and fifty milligrams of each sample was purged with He gas at room temperature and heated at 300 °C under vacuum for 12 h. Surface area (S) was calculated

TE D

from Brunauer-Emmett-Teller (BET) method between 0.05-0.15 of relative pressures. The pore size (DNL-DFT) was determined from the maximum peak of the pore size distribution

EP

(PSD) calculated in the Non-Local Density Functional Theory (NL-DFT) methods [15]. The pore wall thickness (t) was determined from the difference between a0 and pore size [16].

AC C

Morphology of each calcined sample was studied by transmission electron

microscopy (TEM) and scanning electron microscopy (SEM). TEM was performed on a FEI Tecnai G2 20 with an accelerating voltage of 200 kV. The sample was dispersed in ethanol, sonicated for 5 min and dropped on a 300-mesh Formvar/carbon copper grid. SEM was

6

ACCEPTED MANUSCRIPT

performed on a Carl Zeiss Auriga Field Emission Scanning Electron Microscope at 5.00

3. Results and discussion 3.1 Effect of CTAB:SiO2 ratio in the range of 0.025-0.400

RI PT

kV of working acceleration voltage and secondary electron (SE) detector.

SC

Fig. 1 displays XRD patterns of calcined samples with various CTAB:SiO2 ratio.

M AN U

Sample from the ratio of 0.400 shows only one broad peak at 2.58 degree suggesting that another amorphous phase was produced instead of MCM-41. Sample from the ratio of 0.300 displays the strongest characteristic peaks of MCM-41 at 2.25, 3.90 and 4.50 degree corresponding to the plane (100), (110) and (200), respectively [17]. The peaks at 6.00 and

TE D

6.80 degree corresponding to the plane (210) and (300), respectively can be seen with magnification (Fig S1 in the Supplementary Materials). Intensities of all peaks decrease

EP

with the CTAB:SiO2 ratio indicating the decrease of MCM-41 phase. Thus, the ratio 0.3 is considered the optimal ratio in this work for the microwave-assisted synthesis. These

AC C

phenomena are similar to the result from a conventional synthesis that the optimal CTAB:SiO2 ratio was 0.27 [18]. Moreover, a slight shift of the (100) plane to higher angle indicates a smaller a0 (Table 1). According to the MCM-41 formation mechanism [19], the higher amount of CTAB facilitates formation the structure of MCM-41. CTAB first interacts with silicate to produce rod-like structure and further condenses to hexagonal

7

ACCEPTED MANUSCRIPT

structure. The CTAB deficiency leads to the lower amount of rod-like structure and weak XRD intensities.

RI PT

Fig. 2 shows thermograms of as-synthesized samples from different CTAB:SiO2 ratios. Weight losses from all samples occur in the range of 140 – 450 °C corresponding to

SC

the CTA+ removal from mesopores [20]. The more loss is observed from the sample prepared from the gels with the higher CTAB:SiO2 ratio implying that the more

M AN U

mesoporous phase is produced with the higher concentration of CTAB. However, the loss from sample with the ratio 0.300 is only slightly higher than that from the ratio 0.200 indicating that they a similar amount of mesoporous phase. Note that the sample from the ratio 0.400 shows the highest and the most rapid weight loss. This result is consistent with

TE D

the XRD result that it is not MCM-41.

N2 adsorption-desorption isotherm of calcined samples from different CTAB:SiO2

EP

ratios are shown in Fig. 3. All samples displays type IV(b) isotherms corresponding to conical or cylindrical mesopores [21]. The adsorption at the P/P0 between 0.2 and 0.4

AC C

corresponds to capillary condensation in the mesopores. The sharpest rise is observed from the sample from the CTAB:SiO2 ratio of 0.300 indicating that it has the most uniform pores. Pore size distribution of all samples can be found in Fig. S2 (Supplementary Materials). The greater CTAB:SiO2 ratio provides the smaller full width at half maximum (FWHM) corresponding to the more uniform pore [22]. BET surface areas and pore volumes are

8

ACCEPTED MANUSCRIPT

summarized in Table 1. The sample with the higher CTAB:SiO2 ratios has the larger adsorbed volume (Va) and higher BET surface area. The sample from CTAB:SiO2 ratio of

RI PT

0.300 has a larger pore diameter (Table 1) and wall thickness than other MCM-41 samples. For a better understanding on the role of CTAB:SiO2 ratio in the synthesis of

SC

MCM-41, a relative intensity of the main XRD peak is plotted with BET surface area (Fig. 4). The graph is divided into 3 regions. In the first region with CTAB:SiO2 ratio 0.025 –

M AN U

0.100, both XRD intensity and BET surface area increase with the CTAB content due to the presence of more mesoporous phase. The more amount of CTAB leads to the more rodlike structures which further condense to hexagonal arrays [19]. In the second region from the ratio 0.100 – 0.300, the highest XRD intensity is from the sample with the ratio of 0.300

TE D

but the surface area is similar to that from the ratio 0.200. The results indicate that the most uniform hexagonal structure is from the ratio 0.300. In the last region, the XRD peak

EP

decreases significantly implying the loss of 2D-hexaganol ordering whereas the surface area increases. The highest surface area from the ratio of 0.400 could be from a non-

AC C

ordering mesoporous structure or interpenetration channel of 3D mesostructure such as KIT-1 and MCM-48 [23]. The high concentration of CTAB could lead to aggregation of the template to form cubic and lamellar phase rather than hexagonal phase [24]. According to the results, the gel with CTAB:SiO2 ratio of 0.300 give the optimal MCM-41 quality and is used in the further investigation.

9

ACCEPTED MANUSCRIPT

3.2 Effect of NaOH:SiO2 ratio of 1.0, 1.3 and 2.0

RI PT

Fig 5a shows XRD patterns of MCM-41 synthesized with NaOH:SiO2 mole ratio of 1.0, 1.3 and 2.0 when the CTAB:SiO2 mole ratio is fixed at 0.3. Only the samples from the NaOH:SiO2 ratio of 1.0 and 1.3 displays characteristic of MCM-41. Intensity of the (100)

SC

peak from the ratio 1.0 is higher than that from the ratio 1.3. Moreover, a slightly lower

M AN U

diffraction angle indicates a slightly larger lattice parameter. Their nitrogen adsorptiondesorption isotherms (Fig. 5b) and pore size distribution (Fig. S3) are similar, exhibiting the characteristic of MCM-41. Regarding to the lattice parameter and pore size, the sample from the ratio 1.0 has a thicker mesopore wall than that from the ratio 1.3. The relationship

TE D

between the NaOH:SiO2 ratio and wall thickness is shown in Scheme 1 and Table 1. Na+ can affect to charge density of interface between surfactant and silicate ions and disturb the

EP

formation of mesostructure [8,24]. Thus, the gel with NaOH:SiO2 ratio of 1.0 further investigates on the effect of hydrothermal time. The sample from the ratio 2.0 only displays

AC C

a broad peak around 2.8 degree which is not the characteristic of MCM-41. Consequently, the nitrogen sorption is no longer of interest.

3.3 Effect of microwave-assisted hydrothermal time

10

ACCEPTED MANUSCRIPT

The XRD patterns of MCM-41 with different hydrothermal times are shown in Fig. 6a and 6c. The main diffraction peaks of MCM-41 are observed from all samples. The

RI PT

relationship between hydrothermal time from 0 – 60 min and XRD peak intensity is not clear. Kamarudin et al. [25] studied the synthesis of mesoporous silica by using microwave-

SC

assisted method with different heating power and time. They suggested that the formation of “hot spot” at a short irradiation time did not provide the homogeneous heating leading to

M AN U

an irregular structure. From the hydrothermal time between 60 and 180 min, the intensity increases with the hydrothermal period indicating the more uniform MCM-41. This behavior is common for the conventional hydrothermal method. The longer hydrothermal time facilitates the rate of condensation to produce the more ordered hexagonal structure

TE D

[26,27,28].

N2 adsorption-desorption isotherms of MCM-41 from different hydrothermal times

EP

are shown in Fig. 6b. The sample from hydrothermal time of 0 min demonstrates type II isotherm corresponding to a macroporous material. This sample has the lowest BET

AC C

surface. The other samples exhibit the isotherm type IV(b) with surface area higher than 1000 m2/g (Table 1).

TEM images of MCM-41 samples from various hydrothermal times are shown in

Fig. 7 and 8. Additional images are included in the Supplementary Materials. TEM Images in Fig. 7 show a variety of morphology. For examples, regions A and B are obtained when

11

ACCEPTED MANUSCRIPT

the electron beam is perpendicular and parallel to the pores, respectively. Region C shows morphology of the less uniform pores. In Fig. 8, all samples display the hexagonal structure

RI PT

of MCM-41. However, non-uniform phases such as defects and amorphous particles are observed. The samples from the longer hydrothermal time are more uniform. The sample from 90 min has TEM images essentially similar to the sample from conventional

SC

hydrothermal method [29]. SEM images of the sample with the hydrothermal time of 90 min

M AN U

or longer (Fig. S10 in the Supplementary Materials) reveal similar morphology of fibre-like particles [30]. Thus, the longer hydrothermal time does not have a significant impact to the morphology.

In summary, microwave-assisted hydrothermal time of at least 90 min could

TE D

produce MCM-41 with a good quality. The MCM-41 samples synthesized with the optimal CTAB:SiO2 and NaOH:SiO2 ratios from this work have surface areas above 1000 m2/g,

AC C

4. Conclusions

EP

comparable to those reported in the literature[7,8,9,11].

MCM-41 samples are synthesized by microwave-assisted hydrothermal method

with various CTAB:SiO2 and NaOH:SiO2 ratio and hydrothermal time. With the NaOH:SiO2 ratio fixed at 1.0, the more MCM-41 phase is obtained from the synthesis gel with the higher CTAB:SiO2 ratio. The optimal CTAB:SiO2 ratio from this work is 0.300

12

ACCEPTED MANUSCRIPT

whereas the higher ratio produces amorphous phase. With the CTAB:SiO2 fixed at 0.300, the influence of NaOH:SiO2 is investigated and the ratio 1.0 is the optimal one. Finally, an

RI PT

influence of hydrothermal time is investigate on gels with CTAB:SiO2 of 0.300 and NaOH:SiO2 of 1.0. MCM-41 is produced after microwave-assisted hydrothermal at 100 °C

SC

for 5 min. MCM-41 samples from various hydrothermal times have similar surface areas. However, the longer hydrothermal time produces MCM-41 with the less defects. The most

M AN U

suitable hydrothermal time from this work is 90 min. The MCM-41 samples from microwave-assisted hydrothermal method have properties similar to those from a conventional method and thus, could be employed in similar applications. The main benefit

Acknowledgement

TE D

from microwave-assisted method is the reduction of energy consumption in the synthesis.

A scholarship for K. Deekamwong was from Thai government under the

AC C

EP

Development and Promotion of Science and Technology Talents (DPST) Project.

References

[1] A. M. Showkat, Y.-P. Zhang, M. S. Kim, A. I. Gopalan, K. R. Reddy, K.-P. Lee, Analysis of Heavy Metal Toxic Ions by Adsorption onto Amino-functionalized Ordered Mesoporous Silica, Bulletin of the Korean Chemical Society, 28 (2007) 1985 - 1992.

13

ACCEPTED MANUSCRIPT

[2] W. Rongchapo, O. Sophiphun, K. Rintramee, S. Prayoonpokararach, J. Wittayakun, Paraquat adsorption on porous materials synthesized from rice husk silica, Water

RI PT

Science and Technology, 68 (2013) 863 - 869. [3] X. Ning, Y. Lu, H. Fu, H. Wan, Z. Xu, S. Zheng, Template-Mediated Ni(II) Dispersion in Mesoporous SiO2 for Preparation of Highly Dispersed Ni Catalysts: Influence of

SC

Template Type, ACS Applied Materials and Interfaces, 9 (2017) 19335 - 19344.

M AN U

[4] M. M. Ambursa, P. Sudarsanam, L. H. Voo, S. B. A. Hamid, S. K. Bhargava, Bimetallic CuNi catalysts supported on MCM-41 and Ti-MCM-41 porous materials for hydrodeoxygenation of lignin model compound into transportation fuels, Fuel Processing Technology, 162 (2017) 87 - 97.

TE D

[5] D. K. Ratnasari, M. A. Nahil, P. T. Williams, Catalytic pyrolysis of waste plastics using staged catalysis for production of gasoline range hydrocarbon oils, Journal of Analytical and Applied Pyrolysis, 124 (2017) 631 - 637.

EP

[6] Q. Huang, C. Liu, R. Wei, J. Wang, Experimental study of polyethylene pyrolysis and

AC C

combustion over HZSM-5, HUSY, and MCM-41, Journal of Hazardous Materials, 333 (2017) 10 - 22.

[7] C.-F. Cheng, D.H. Park, J. Klinowski, Optimal parameters for the synthesis of the mesoporous molecular sieve [Si]-MCM-41, Journal of the Chemical Society, Faraday Transactions. 93 (1997) 193 – 197.

14

ACCEPTED MANUSCRIPT

[8] J. Park, Y. Han, H. Kim, Formation of mesoporous materials from silica dissolved in various NaOH concentrations: effect of pH and ionic strength, Journal of Nanomaterials.

RI PT

2012 (2012) 1 – 10.

[9] C.-G. Wu, T. Bein, Microwave synthesis of molecular sieve MCM-41, Chemical

SC

Communications. 8 (1996) 925 – 926.

[10] S.-E. Park, D.S. Kim, J.-S. Chang, W.Y. Kim, Synthesis of MCM-41 using microwave

M AN U

heating with ethylene glycol, Catalysis Today. 44 (1998) 301 – 308.

[11] M.-G. Song, J.-Y. Kim, S.-H Cho, J.-D. Kim, Rapid Synthesis of Mesoporous Silica by an Accelerated Microwave Radiation Method, The Korean Journal of Chemical Engineering. 21 (2004) 1224 – 1230.

TE D

[12] T. Jiang, Y. Tang, Q. Zhao, H. Yin, Effect of Ni-doping on the pore structure of pure silica MCM-41 mesoporous molecular sieve under microwave irradiation, Colloids and

EP

Surfaces A: Physicochemical and Engineering Aspects. 315 (2008) 299 – 303. [13] C.-F. Cheng, H.-H. Cheng, L.-L. Wu, B.-W. Cheng, Synthesis and characterization of

AC C

nanoscale aluminosilicate mesoporous materials by microwave irradiation, Studies in Surface Science and Catalysis. 156 (2005) 113 – 118. [14] P.M. Carraro, A.A. García Blanco, F.A. Soria, G. Lener, K. Sapag, G.A. Eimer, M.I. Oliva, Understanding the role of nickel on the hydrogen storage capacity of Ni/MCM-41 materials, Microporous Mesoporous Materials. 231 (2016) 31 – 39.

15

ACCEPTED MANUSCRIPT

[15] M. Beller, A. Renken, R.A. van Santen (Eds.), Catalysis: From Principles to Applications, Wiley-VCH: Weinheim, Germany, 2012.

RI PT

[16] Y. Wang, D. Cui, Q. Li, Synthesis, characterization and influence parameters on the overgrowth of micro/mesoporous Y-zeolite-MCM-41 composite material under acidic

SC

conditions, Microporous Mesoporous Materials. 142 (2011) 503 – 510.

[17] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, C.T.-W.

M AN U

Chu, D.H. Olson, E.W. Shepparol, S.B. Mc-Cullen, J.B. Higgins, J.L. Schlenker, A new family of mesoporous molecular sieves prepared with liquid crystal templates, Journal of the American Chemical Society. 114 (1992) 10834 – 10843.

[18] C.-F. Cheng, D.H. Park, J. Klinowski, Optimal parameters for the synthesis of the

TE D

mesoporous molecular sieve [Si]-MCM-41, Journal of the Chemical Society, Faraday Transactions. 93 (1997) 193 – 197.

EP

[19] S. Ahmed, A. Ramli, Effect of Surfactant Concentration on the Physico-chemical Characteristics of Mesoporous Molecular Sieve, Journal of Applied Sciences, 11 (2011)

AC C

1178 - 1184.

[20] J. Ryczkowski, J. Goworek, W. Gac, S. Pasieczna, T. Borowiecki, Temperature removal of templating agent from MCM-41 silica materials, Thermochimica Acta. 434 (2005) 2 – 8.

16

ACCEPTED MANUSCRIPT

[21] M. Thommes, K. Katsumi, A.V. Neimark, J.P. Olivier, F. Rodriquez-Reinoso, J. Rouquerol, K.S.W. Sing. Pure Appl. Chem. 87(2015) 1051 – 1069.

RI PT

[22] G. Du, S. Lim, Y. Yang, C. Wang, L. Pfefferle, G.L. Haller, Catalytic performance of vanadium incorporated MCM-41 catalysts for the partial oxidation of methane to

SC

formaldehyde, Applied Catalysis A: Geneal. 302 (2006) 48 – 61.

[23] F. Rouquerol, J. Rouquerol, P. Llewellyn, K.S.W. Sing, G. Maurin, Adsorption by

United States of America, 2013.

M AN U

Powders and Porous Solids: Principles, MAthodology and applications, Academic Press,

[24] H.-P. Lin, C.-Y. Mou, Structural and Morphological Control of Cationic Surfactant-

AC C

EP

TE D

Templated Mesoporous Silica, Accounts of Chemical Research, 35 (2002) 927 - 935.

17

ACCEPTED MANUSCRIPT

Caption of figures

Fig. 1. XRD patterns of MCM-41 synthesized with various CTAB:SiO2 mole ratios with a fixed NaOH:SiO2 mole

RI PT

ratios at 1.0. The patterns of all samples are from the same scale and stacked with Y offset. Fig. 2. TGA thermograms of as-synthesized MCM-41 from different CTAB:SiO2 ratios. Solid lines are from the weight changes and the dash lines are derivative of weight change.

SC

Fig. 3. N2 adsorption-desorption isotherms of MCM-41 from different CTAB:SiO2 ratios; (filled) adsorption and (empty).

different CTAB:SiO2 ratios.

M AN U

Fig. 4. The Plot between relative XRD peak intensity of (100) plane versus BET surface areas of MCM-41 from

Fig. 5. (a) XRD patterns of MCM-41 synthesized with various NaOH:SiO2 mole ratios and fixed CTAB:SiO2 mole ratios at 0.3. The patterns of all samples are from the same scale and stacked with Y offset and (b) N2 adsorption-desorption isotherms of MCM-41 from NaOH:SiO2 ratios of 1.0 and 1.3.

TE D

Scheme 1. An effect of NaOH:SiO2 ratio on wall thickness. Fig. 6. A stack plot of XRD patterns (a, c) by Y offsets and N2 adsorption-desorption isotherms (b, d) from different

EP

hydrothermal times.

Fig. 7. Three representative regions of example TEM image of 15 min sample for phase identification.

AC C

Fig. 8. TEM images of MCM-41 from hydrothermal times of 0 min (a, b), 5 min (c, d), 15 min (e, f), 30 min (g, h), 60 min (i, j) and 90 min (k, l).

ACCEPTED MANUSCRIPT Table 1 The product yields, d100, a0, BET surface area (S), pore diameter (DNL-DFT), pore volume (Vtotal) and wall thickness (t) of all MCM-41 samples CTAB:

NaOH:S

Hydrothermal

d100

a0

S

DNL-DFT -1

Vtotal

t

3

-1

(Å)

(Å)

(m².g )

(Å)

(cm .g )

(Å)

0.400

53.8

-

-

1385

29.50

0.6990

-

0.300

85.3

39.06

45.10

1047

32.50

84.0

38.21

44.12

1065

32.00

0.100

75.1

38.21

44.12

914

32.00

0.050

72.8

38.21

44.12

575

30.00

0.025

76.1

38.05

43.93

372

82.7

39.06

45.10

1047

80.1

37.97

43.84

76.0

-

0

81.1

5

0.5292

12.60

0.5583

12.12

0.4805

12.12

0.3170

14.12

29.50

0.1951

14.43

32.50

0.5292

12.60

1147

31.30

0.5742

12.54

-

-

-

-

-

40.04

46.24

594

25.83

0.4655

-

83.7

41.19

47.56

1030

36.56

0.5059

11.00

15

81.1

38.78

44.78

1100

32.20

0.5551

12.58

30

84.0

38.78

44.78

1094

32.36

0.5515

12.42

60

83.2

38.91

44.93

1053

32.66

0.5298

12.27

90

85.7

38.78

44.78

32.08

0.5711

12.70

120

87.7

38.80

EP

1138

44.80

1046

32.32

0.5364

12.48

150

88.6

38.97

45.00

1067

32.01

0.5377

12.99

180

89.6

38.97

45.00

1093

33.32

0.5516

11.68

0.200

0.300

1.3

90

2.0

0.300

1.0

M AN U

1.0

SC

90

TE D

1.0

AC C

iO2

RI PT

yields (%)

SiO2

time (min)

Product

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Highlights A fast synthesis of MCM-41 is conducted by microwave-assisted hydrothermal method.

•

Influences of CTAB:SiO2, NaOH:SiO2 ratio and hydrothermal time are studied.

•

The optimum CTAB:SiO2 and NaOH:SiO2 are 0.300 and 1.0, respectively.

•

Hydrothermal time of 90 min is sufficient to produce high quality MCM-41.

AC C

EP

TE D

M AN U

SC

RI PT

•