- Email: [email protected]
silica aerogel composite monoliths and microspheres
Accepted Manuscript Zeolite/silica aerogel composite monoliths and microspheres Kseniya A. Sashkina, Pavel A. Gurikov, Artem B. Ayupov, Irina Smirnova, Ekaterina V. Parkhomchuk PII:
S1387-1811(17)30791-6
DOI:
10.1016/j.micromeso.2017.12.010
Reference:
MICMAT 8699
To appear in:
Microporous and Mesoporous Materials
Received Date: 26 September 2017 Revised Date:
5 December 2017
Accepted Date: 10 December 2017
Please cite this article as: K.A. Sashkina, P.A. Gurikov, A.B. Ayupov, I. Smirnova, E.V. Parkhomchuk, Zeolite/silica aerogel composite monoliths and microspheres, Microporous and Mesoporous Materials (2018), doi: 10.1016/j.micromeso.2017.12.010. 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 Zeolite/silica aerogel composite monoliths and microspheres Kseniya
A.
Sashkinaa,b,*,
Pavel
A.
Gurikovc,
Artem B. Ayupova,
Irina
Smirnovac,
Ekaterina V. Parkhomchuka,b
Boreskov Institute of Catalysis SB RAS, 5 Lavrentieva St., Novosibirsk 630090, Russia.
b c
Novosibirsk State University, 2 Pirogova St., Novosibirsk 630090, Russia.
Institute of Thermal Separation Processes, Hamburg University of Technology, Eißendorfer
RI PT
a
Straße 38, Hamburg, Germany. * corresponding author
SC
Abstract
A series of silica aerogels and composite materials based on Fe-silicalite-1 nanocrystals
M AN U
embedded into silica aerogel matrix in the form of monoliths and microspheres have been synthesized by drying with supercritical CO2. Using equivolume water/ethanol mixture as a medium for the aging of monoliths enabled to produce monoliths of silica aerogel and composite without cracks. The synthesis of the composite and silica aerogel microspheres by the emulsion/gelation technique has been designed. The different effects of the stirring rate during the emulsification on the particle size and texture of composites and silica aerogels has been
TE D
observed. The synthesized samples were characterized by X-ray diffraction, scanning electron
Keywords
EP
microscopy and nitrogen adsorption measurements.
Silica aerogel, zeolite, Fe-silicalite-1, composite, monolith, emulsion/gelation, supercritical CO2
AC C
Introduction
Silica aerogels also referred to as “solid air” are mesoporous materials with extremely low density and an open pore structure. The bulk density of aerogels can be as low as 0.003 g/cm3, i.e. just three times larger than the density of air (0.001 g/cm3). Ultralight SiO2 aerogels are generally prepared by the supercritical extraction of self-standing gels by the sol–gel method [1]. This technique allows the liquid to be slowly removed without strongly altering the network structure or the volume of the gel body [2,3]. Owing to their special structure, silica aerogels possess unique physical properties such as ultralow density [4], low thermal conductivity [5], enormous surface area (> 800 m2/g) [6] and high transparency [7]. On account of the properties mentioned above, silica aerogels find a variety of applications in very different fields as 1
ACCEPTED MANUSCRIPT
adsorbents [8,9,10], catalysts [11,12,13,14,15,16], thermal [17] or acoustic insulators [18], sensors [19,20], carrier materials [21,22,23,24], storage media [25,26], Cherenkov counters in particle physics experiments [27,28,29] and cosmic dust capturing [30,31]. It should be noted, that silica aerogels can be obtained in various sizes and forms, ranging from microbeads [32,33,34] to large monoliths [35] and tiles [36]. Another large class of porous materials is zeolites. They are crystalline silicates and
RI PT
aluminosilicates with regular and uniform pores and channels of molecular dimensions, resulting in high surface area (350−450 m2/g) [37]. Zeolites and zeotypes consist of tetrahedral units of T (where T is typically Si and Al for zeolites, but can also be transition metals and other elements such as B, Ga, Fe, Ge, Ti, Cu etc. for zeotypes) bonded by oxygen atoms resulting in a
SC
framework containing cages and channels of distinct sizes and shapes [38]. The adjustable microporosity of zeolites makes them shape-selective molecular sieves [39]. Besides, catalytic
M AN U
sites [40,41,42] or gas sensing agents [43,44] can be arranged within well-defined micropores in a ship-in-a-bottle architecture preventing them from sintering and leaching. Zeolites and zeotypes find the wide use as adsorbents [45,46,47], catalysts [48,49] and ion-exchangers [50]. The emerging applications of zeolites include sensors for gases [51,52], photovoltaic solar cells [53], drug delivery [54,55] and gas storage [56]. The key problems of zeolites in the majority of applications are intracrystalline diffusion constraints resulting in low utilization of the zeolite
TE D
surface [57] and poor molding properties requiring the use of binders [58]. The diffusion constrains may be eliminated by decreasing the size of zeolite particles [59,60] or creating a hierarchical pore architecture combining micropores and transport meso/macropores [61,62]. The molding of zeolites using binders often cause the problem of hindering mass transport
EP
resulting from the obstruction of micropores [63]. Silica aerogel composites are generally prepared by dispersing the guest particles in the wet
AC C
silica sol before the gelation or by impregnating the dry silica aerogel with molecular precursors [64]. The literature data concerning silica aerogel composites cover a wide variety of different dispersed materials such TiO2 [64], Ag, Au [65], Pd [66], CuO [67], SnO2 [68] nanoparticles, wollastonite [69], sepiolite fibers [70], carbon [71] and MOFs [72]. However, reports on aerogel/zeolite composites are scarce [73,74]. It was shown that it is possible to design novel materials for a specific application by using the silica sol as a nanoglue and to combine the adjustable properties of the silica aerogels with the desirable properties of the guest materials. Here we present the synthesis of novel composite materials based on Fe-containing zeolite nanocrystals embedded into silica aerogel matrix. Possible catalytic applications of Fecontaining zeolite/silica aerogel composites are benzene hydroxylation to phenol by N2O [75] catalytic reduction of nitric oxide by ammonia [76], partial oxidation of organic compounds by 2
ACCEPTED MANUSCRIPT
hydrogen peroxide to produce valuable products [77], water purification by total oxidation of organic contaminators [78] and radionuclides removal from radioactive waste [79]. Monodispersed Fe-silicalite-1 nanocrystals are recently reported materials [80] that have been successfully tested for decontamination purposes [79]. However, the utilization of zeolite nanocrystals as such is difficult due to tedious separation required after the oxidation process. Dispersing zeolite nanocrystals in the continuous matrix of mesoporous silica aerogel bypasses
RI PT
the mass-transport barriers and the obstruction of micropores associated with the conventional molding. The zeolite/silica aerogel composites have been synthesized in the form of monoliths and microspheres. Composite monoliths were observed to be crack-free. Composite microspheres were prepared by the emulsion/gelation technique. The size and texture of
SC
zeolite/silica aerogel microspheres were adjusted by varying the stirring rate under the
M AN U
emulsification.
Experimental Materials
Tetrapropylammonium hydroxide (TPAOH, 25 wt. % solution in water, Acros), tetraethylorthosilicate (TEOS, ≥98%, Angara-reactive, silica (fumed, ≥99 %, Aldrich), ethanol (EtOH, 95%, Pharmaceya) and Fe(NO3)3·9H2O (≥99%, Merck) were used for producing
TE D
Fe-silicalite-1 nanocrystals. Tetraethylorthosilicate (TEOS, Merck), ethanol denatured (more than 99.5 %, 1% MEK, Roth), ammonia solution (28−30 wt. %, for analysis, Merck), HCl (30 wt. %, Merck) and dimethylcyclohexylamine (BASF) were employed for the synthesis of
EP
silica aerogel composite materials.
Synthesis of Fe-silicalite-1 nanocrystals
AC C
The typical synthesis of Fe-silicalite-1 nanocrystals was carried out as follows. 120 mL of TEOS diluted with 120 mL of ethanol was added at once to 240 mL of TPAOH (12.5 wt. %) under vigorous stirring for 20 min, then 2.6 g of Fe(NO3)3·9H2O dissolved in 5 mL of distilled water were added dropwise. After stirring for 20 min, the resultant clear light-yellow gel with 1.00 SiO2 : 0.28 TPAOH : 0.006 Fe2O3: 4.79 EtOH : 1.75 H2O molar composition was placed in Teflon-lined stainless steel autoclaves and subjected to hydrothermal treatment in an oven at 90 °C for 7 days. Milky Fe-silicalite-1 suspension produced was purified in a series of three steps consisting of centrifugation at a relative acceleration of 3000 g for 5 h, followed by removal of the mother liquor and redispersion in ethanol under ultrasonication. The final concentration of Fe-silicalite-1 in ethanol suspension was 35 wt. %. 3
ACCEPTED MANUSCRIPT
Synthesis of Fe-silicalite-1/silica alcogel monoliths
Silica/nanozeolite alcogels were synthesized by hydrolysis and subsequent condensation of tetraethylorthosilicate. In a typical synthesis, 4.0 g of TEOS were mixed with required quantity of ethanol (3.00, 2.89, 2.78 g) and Fe-silicalite-1 suspension (0, 0.20, 0.38 g, respectively) and stirred at ambient temperature for 10 min. For the hydrolysis, 1.4 mL of HCl (1 g/L) were added dropwise and mixture was stirred for 30 min. For the following condensation, 1.0 g of NH3
RI PT
solution in ethanol (3.60 g/L) was added drop by drop under vigorous stirring. Finally, the mixture was poured into molds, gelled and aged in an equivolume mixture of EtOH and H2O (thermostatic bath at 50 °C for 20 h). Before supercritical drying obtained monoliths were rinsed
SC
3 times with ethanol.
Synthesis of Fe-silicalite-1/silica alcogel microspheres by emulsion gelation method
M AN U
At the hydrolysis step 5 g of TEOS were mixed with required quantity of ethanol (3.75 and 3.05 g) and Fe-silicalite-1 suspension (0 and 1.07 g, respectively). Then, 1.9 mL of HCl (1 g/L) were added dropwise and mixture was stirred for 30 min. The mixture was then diluted with 1.25 g of ethanol to obtain the desired density of the aerogel. The sol with zeolite was emulsified as follows. Continuous phase was prepared by the saturation of 150 g of sunflower oil with 17 g of ethanol under vigorous stirring. A typical emulsion was generated by adding the precursor
TE D
suspension to 20 g of saturated oil followed by the agitation using a propeller stirrer at the required rotation rate (300, 500, 800 rpm) for 10 min. To induce gelation 1 g of dimethylcyclohexylamine solution (5 wt.%) in ethanol-saturated oil was added dropwise to the emulsion (oil was saturated by ethanol due to their partial miscibility; this addition eliminates
EP
any transfer of ethanol from the particles into continuous phase). After instant gelation alcogel
AC C
microspheres were separated from the oil by the filtration followed by the rinsing with ethanol.
Supercritical drying of Fe-silicalite-1/silica alcogel particles The apparatus for supercritical drying is described in detail elsewhere [81]. In a typical experiment, the nanozeolite/silica alcogel monoliths and microspheres packed into coffee filters were placed into preheated a 250 mL cylindrical high-pressure stainless steel autoclave. The gels were covered with an excess of ethanol to avoid untimely drying of the gels. Liquid CO2 was delivered using a high-pressure diaphragm pump, preheated and introduced into the autoclave. The temperature was controlled using an electrical heating jacket: initial temperature was set to 40 °C followed by linear heating up to 60 °C for 4 h and maintaining at 60 °C for 12 h to ensure complete extraction of ethanol. Pressure in autoclave was maintained constant at 120 bars. When 4
ACCEPTED MANUSCRIPT
the extraction was completed, the nanozeolite/silica aerogel monoliths and microspheres were removed from the autoclave and calcined at 500 °C for 5 h.
Characterization The densities of calcined monoliths were calculated as their volume divided by the mass. Powder X-ray diffraction (XRD) patterns were recorded from a Siemens D500 diffractometer
RI PT
equipped with a Cu Kα radiation (λ = 0.154 nm). The hydrodynamic diameters of zeolite particles dispersed in ethanol measured with a Malvern Zetasizer Nano. The chemical composition of the samples was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Nitrogen adsorption-desorption isotherms of Fe-silicalite-1/silica
SC
aerogel monoliths and microspheres were measured at 77 K with a Quadrasorb EVO and Quantachrome Nova 3000e surface area analyzers, respectively. Prior to the analysis, samples
M AN U
were outgassed at 573 K for 10 h. Specific surface areas were determined by BET equation [82] using direct method for evaluation of BET adsorbed monolayer capacity [83]. Pore size distributions were estimated by the BJH method [84]. Micropore volume and external surface area were also calculated by means of αs-method using the isotherm of adsorption of N2 on the reference LiChrospher Si-1000 silica gel, reported in the literature [85]. Scanning electron microscopy (SEM) images were taken with a JEOL JSM-6460LV and Leo (Zeiss) 1530
TE D
microscopes at an operating voltage of 15−20 kV after a sputtering with gold. The diameter of silica and composite aerogel microspheres was measured by another method with Retsch Camsizer XT. The measurement principle of the equipment is following: particles pass in front of two bright, pulsed light-emitting diode (LED) sources. The shadows of the particles are
EP
captured with two digital cameras. One camera is optimized to analyze the small particles with high resolution; the other camera detects the larger particles with good statistics, due to a large
AC C
field of view. Particle size and particle shape are analyzed with software which calculates the respective distribution curves in real time.
Results and discussion
Firstly, Fe-silicalite-1 suspension was prepared by the hydrothermal treatment of the mixture with 1.00 SiO2 : 0.28 TPAOH : 0.006 Fe2O3: 4.79 EtOH : 1.75 H2O molar composition at 90 °C for 7 days followed by the purification and redispersion of crystals in ethanol under ultrasonication. The final concentration of as-synthesized Fe-silicalite-1 in ethanol suspension was 35 wt. %. Fe-silicalite-1 crystals with aggregate-like morphology have a mean diameter of about 180 nm and narrow size distribution (Fig. 1). 5
ACCEPTED MANUSCRIPT
RI PT
Fig. 1. Dynamic light scattering data for Fe–silicalite-1 suspension (left) and TEM image of Fe-silicalite-1 nanocrystals (right).
The powder obtained by drying Fe-silicalite-1 suspension followed by calcination has XRD
SC
patterns typical for MFI structure [86] and high crystallinity (Fig. 2). The Fe content in calcined Fe-silicalite-1 powder is 1.35 wt. % according to ICP-OES. The iron species representing small
against sintering and leaching [87].
M AN U
clusters no more than 3 nm in size are located inside zeolite mesopores, making them stable
The XRD patterns of Fe-silicalite-1/silica aerogel composites in the form of monoliths and microspheres confirm that Fe-silicalite-1 nanocrystals have been embedded into the aerogel matrix and preserved their structure during the synthesis. We evaluated the relative crystallinity of composites by the peaks integration in the range from 22.5 to 25 degrees relative to calcined
TE D
Fe-silicalite-1 nanocrystals powder under identical measurement conditions (Table 1). Relative crystallinity of composite microspheres increases when the stirring rate in the water-oil emulsion
AC C
EP
becomes more vigorous, apparently resulting from the incomplete gelation.
Fig. 2. XRD patterns of calcined Fe-silicalite-1 nanocrystals and Fe-silicalite-1/silica aerogel composites. Green patterns refer to the reference silica aerogels. 6
ACCEPTED MANUSCRIPT
Concentrated Fe-silicalite-1 suspension as described above was used for preparing Fe-silicalite-1/silica aerogel composite in the form of monoliths and microspheres. Besides, the reference samples of silica aerogel were synthesized at identical conditions. For producing aerogel materials, the following steps were carried out: the preparation of alcogel, drying with supercritical CO2 and calcination. The silica alcogels including those with Fe-silicalite-1 crystals were synthesized by the hydrolysis and following condensation of TEOS. The hydrolysis was
RI PT
conducted by adding hydrochloric acid to TEOS mixed with water, ethanol and Fe-silicalite-1 suspension. To form monoliths, ammonia solution was added to the precursor suspension, inducing the condensation process. The mixture was quickly placed to the molds, whereupon the gelation immediately occurred. Fresh monoliths were placed to the equivolume water/ethanol
SC
mixture at 50 °C for aging for 20 h (Fig. 3, a). It should be emphasized that aging in the presence of water is the key stage of preparing strong silica aerogel monoliths. A number of the silica
M AN U
aerogel monolith syntheses without aging or with aging in pure ethanol were failed, because the cracks were formed under drying with supercritical CO2 (Fig. 3, b) followed by breaking the monolith into small pieces. In water/ethanol mixture besides the syneresis the Ostwald ripening giving a more rigid gel network takes place: the reprecipitation of silica dissolved from particle surface onto necks between particles and dissolution of smaller particles and precipitation onto larger ones. Aging of monoliths resulted in volume shrinkage of 30‒40 %. After aging in
TE D
water/ethanol mixture, the monoliths were rinsed 3 times with ethanol and subjected to drying with supercritical CO2 followed by calcination. The monoliths are pill-shaped and have no cracks, pure silica aerogel being transparent and opalescent, while Fe-silicalite-1/silica aerogel composites are white (Fig. 3, c). The densities of calcined aerogel materials depend on the
EP
amount of embedded Fe-silicalite-1: 0.17, 0.18 and 0.20 g/cm3 for monoliths containing 0, 5 and
AC C
10 wt. % of Fe-silicalite-1 crystals, respectively.
7
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig. 3. Photographs of Fe-silicalite-1/silica alcogel (a) and calcined aerogel monoliths prepared with aging in pure ethanol (b) and equivolume water/ethanol mixture (c). Percentage of Fesilicalite-1 from the left to the right: 0, ≈5 and ≈10 wt. % (a, c); ≈10 wt. % (b).
TE D
According to SEM images the Fe-silicalite-1 crystals have sufficiently uniform distribution
AC C
EP
inside aerogel composite materials (Fig. 4).
Fig. 4. SEM image of Fe-silicalite-1/silica alcogel monolith.
The scheme illustrating the formation of aerogel microspheres is represented in Fig. 5. The first step was adding precursor suspensions (disperse phase) to the sunflower oil (continuous phase). The second step was the emulsification using propeller stirrer with subsequent gelation induced by adding dimethylcyclohexylamine (condensation catalyst). 8
RI PT
ACCEPTED MANUSCRIPT
Fig. 5. The main steps for preparing aerogel microspheres by the emulsion method followed by
SC
drying with supercritical CO2.
The size of droplets was adjusted by varying the rate of stirring from 200 to 800 rpm, whereas
M AN U
the gelation rate to depend on the concentration of dimethylcyclohexylamine was precisely selected in the preliminary experiments so that to achieve the uniform gelation without aggregation of microparticles. The last step was the separation of alcogel microspheres from the oil phase by filtration followed by rinsing with ethanol, drying with supercritical CO2 and calcination.
The SEM images and particle size distributions of silica aerogel particles prepared at different
TE D
stirring rates are presented in Fig. 6. The average size of aerogel particles produced at stirring rate of 200, 500 and 800 rpm is 170, 125 and 290 µm, respectively. It is worth noting that the aerogel particles obtained at 500 rpm were partially aggregated, consisting of several
EP
microspheres with the size in the range of 10−70 µm (Fig. 6). The largest silica aerogel microspheres formed at the fastest rotation rate are remarkable for isolated macropores with the size of 5−50 µm. The occurrence of such macropores appeared to be resulted from the double
AC C
emulsion formation. Thus, increasing the rate of stirring resulted in decreasing the size of silica aerogel microspheres followed by its sharp growth.
9
SC
RI PT
ACCEPTED MANUSCRIPT
Fig. 6. SEM images and particle size distributions (insert pictures) of silica aerogel particles
M AN U
prepared at the different rotation rates.
Another effect of the stirring rate on the size and texture of microspheres was observed under introducing Fe-silicalite-1 crystals into the precursor solution (Fig. 7). As expected the largest macroporous Fe-silicalite-1/silica aerogel microspheres were prepared at the lowest stirring rate of 200 rpm. The most part of 1−2 mm particles were damaged during gelation, filtration and drying, therefore the average size of Fe-silicalite-1/silica aerogel particles is quite small, 125 µm.
TE D
The growth of the stirring rate up to 500 rpm led to decreasing the microspheres size, Fe-silicalite-1/silica aerogel particles being also macroporous. This finding indicates that the energy input was sufficient for the formation of double emulsion. In our experiments this
EP
transition seems to occur between 200 and 500 rpm. Further increase in the stirring rate facilitated the generation of Fe-silicalite-1/silica aerogel microspheres with narrow size distribution and the average size of 80 µm. The changes of the size and texture of aerogel
AC C
microspheres prepared from emulsions containing Fe-silicalite-1 may be attributed to the stabilizing effect of solid Fe-silicalite-1 nanocrystals bound to the surface of the interface, i.e. the Pickering emulsion formation. Actually, SEM images show that Fe-silicalite-1 nanocrystals are located on the surface of silica aerogel microspheres and their macropores (Fig. 7). For macroporous Fe-silicalite-1/silica aerogel composites prepared at 200 and 500 rpm, nanocrystals are assembled in 5−10 µm brain-like islands on the surface of microspheres and their macropores, while for macroporous Fe-silicalite-1/silica aerogel microspheres produced at 800 rpm nanocrystals are uniformly distributed on the surface. The synthesis of composite materials might be optimized in the future to ensure a homogeneous distribution of the Fesilicalite-1 nanocrystals within all volume of the microspheres. 10
SC
RI PT
ACCEPTED MANUSCRIPT
Fig. 7. SEM images and particle size distributions (insert pictures) of Fe-silicalite-1/silica
M AN U
aerogel microspheres prepared at the different rotation rates.
Textural characteristics of Fe-silicalite-1/silica aerogel materials calculated from nitrogen adsorption-desorption data are represented in Table 1. All samples exhibit high BET surface areas, SBET, (780‒890 m2/g) and total pore volumes, Vtotal, (1.18‒5.37 cm2/g). Monoliths exhibited by a factor of three higher total pore volume and average pore diameter compared with
TE D
microspheres, most likely due to the different condensation conditions (ammonia versus organic amine). Composite and silica aerogel monoliths have narrow mesopore size distributions with a maximum at around 23 nm (Fig. 8). Embedding Fe-silicalite-1 nanocrystals during the synthesis of monoliths causes broadening the pore size distribution and increasing the percentage of
AC C
EP
pores < 10 nm.
Fig. 8. Pore size distributions for Fe-silicalite-1/silica aerogel monoliths estimated by the BJH method. 11
ACCEPTED MANUSCRIPT
SBET, m /g
Silica
0
Vtotal, cm /g
Average pore diameter, nm
Relative crystallinity, %
820
4.64
22.6
0
5
780
4.43
10
916
5.37
905
SC
Sample
Fe-silicalite-1, wt. %
1.54
6.8
0
900
1.55
6.9
0
850
1.25
5.9
0
2
3
Microspheres
Silica aerogels
200
500
TE D
22.7
12
23.4
18
200
835
1.74
8.3
36
500
890
1.54
6.9
51
815
1.18
5.8
64
EP
Composites
800
M AN U
Stirring, rpm
RI PT
Composites
Monoliths
Form
Table 1. Textural characteristics Fe-silicalite-1/silica aerogel materials.
AC C
800
Conclusions
We have synthesized a series of silica aerogels and composite materials with Fe-silicalite-1 nanocrystals embedded into silica aerogel matrix in the form of monoliths and microspheres. Using equivolume water/ethanol mixture as a medium for the aging enabled to produce crackfree monoliths of silica aerogel and the composites. Fe-silicalite-1 crystals are sufficiently uniformly distributed within the aerogel matrix. The composite and silica aerogel microspheres were prepared by the emulsion gelation technique with optimized gelation step preventing alcogel microparticles aggregation. The size of composite and silica aerogel microspheres was adjusted in the range of 80-1200 µm by varying the stirring rate from 200 to 800 rpm at the 12
ACCEPTED MANUSCRIPT
emulsification step. The effect of the stirring rate on the particle size and the texture of the composites differs from that on silica aerogels due to the stabilizing effect of solid Fe-silicalite-1 nanocrystals located at the interfacial surface. The composite and silica aerogel microspheres with isolated macropores of 5−50 µm in size were produced resulting from the double emulsion formation. Fe-silicalite-1 nanocrystals either form clusters on the surface of silica aerogel microspheres and their macropores or are uniformly distributed in the sample. All composite
RI PT
materials exhibit high BET surface areas (780‒890 m2/g) and total pore volumes (1.18-5.37 cm2/g). Zeolite/aerogel composite materials seem to be promising materials for adsorption, catalysis, sensors and as carriers.
SC
Acknowledgements
The catalysts syntheses were conducted within the framework of budget project No.
M AN U
0303−2016−0002 for Boreskov Institute of Catalysis. Textural studies by A.B. Ayupov were performed within the framework of budget project No. 0303-2016-0010 for Boreskov Institute of Catalysis.
References
1. A.S. Dorcheh, M.H. Abbasi, Journal of materials processing technology. 199 (2008) 10–26.
TE D
2. I. Smirnova, P. Gurikov, Annual Review of Chemical and Biomolecular Engineering. 8 (2017) 307–334.
3. N. Hüsing, U. Schubert, Angew. Chem. Int. Ed. 37 (1998) 22−45.
EP
4. L. Kocon, F. Despetis, J. Phalippou, Journal of Non-Crystalline Solids. 225 (1998) 96–100. 5. M. Reim, W. Körner, J. Manara, S. Korder, M. Arduini-Schuster, H.-P. Ebert, J. Fricke, Solar Energy. 79 (2005) 131-139.
AC C
6. H.D. Gesser, P.C. Goswami, Chem. Rev. 89 (1989) 765−788. 7. T.M. Tillotson, L.W. Hrubesh, Journal of Non-Crystalline Solids. 145 (1992) 44−50. 8. S. Štandeker, Z. Novak, Ž. Knez, Journal of Colloid and Interface Science 310 (2007) 362-368.
9. H. Ramadan, A. Ghanem, H. El-Rassy, Chemical Engineering Journal 159 (2010) 107–115. 10. S. Štandeker, Z. Novak, Ž. Knez, Journal of Hazardous Materials 165 (2009) 1114–1118. 11.
T.V. Konkova,
A.M. Katalevich,
P.A. Gurikov,
A.P. Rysev,
N.V. Menshutina,
Russ. J. Phys. Chem. B. 8 (2014) 999–1003. 12. S. Martínez, M. Meseguer, L. Casas, E. Rodríguez, E. Molins, M. Moreno-Manãs, A. Roig, R.M. Sebastián, A. Vallribera, Tetrahedron 59 (2003) 1553–1556. 13
ACCEPTED MANUSCRIPT 13. B. Heinrichs, F. Noville, J.-P. Pirard, Journal of catalysis. 170 (1997) 366–376. 14. P. Fabrizioli, T. Bürgi, A. Baiker, Journal of Catalysis 206 (2002) 143–154. 15. S. Martínez, A. Vallribera, C.L. Cotet, M. Popovici, L. Martín, A. Roig, M. Moreno-Manãs, E. Molins, New J. Chem. 29 (2005) 1342–1345. 16. B.C. Dunn, P. Cole, D. Covington, M.C. Webster, R.J. Pugmire, R.D. Ernst, E.M. Eyring,
RI PT
N. Shah, G.P. Huffman, Applied Catalysis A: General 278 (2005) 233–238. 17. R. Baetens, B.P. Jelle, A. Gustavsen, Energy and Buildings 43 (2011) 761–769.
18. Yu. K. Akimov, Instruments and Experimental Techniques. 46, 3 (2003) 287−299. 19. M.R. Ayers, A.J. Hunt, Solids. 225 (1998) 343–347.
SC
20. C.-T. Wang, C.-L. Wu, I-C. Chen, Y.-H. Huang, Sensors and Actuators B. 107 (2005) 402-410.
10.1016/j.supflu.2017.03.005.
M AN U
21. P. Gurikov, I. Smirnova, J. of Supercritical Fluids, in press. DOI:
22. I. Smirnova, J. Mamic, W. Arlt, Langmuir. 19 (2003) 8521−8525. 23. I. Smirnova, S. Suttiruengwong, M. Seiler, W. Arlt, Pharmaceutical Development and Technology. 9, 4 (2004) 443−452.
24. M. Alnaief, S. Antonyuk, C.M. Hentzschel, C.S. Leopold, S. Heinrich, I. Smirnova. Microporous and Mesoporous Materials. 160 (2012) 167–173.
TE D
25. B.S.K. Gorle, I. Smirnova, M.A. McHugh. J. of Supercritical Fluids. 48 (2009) 85–92. 26. J. Reynes, T. Woignier, J. Phalippou, Journal of Non-Crystalline Solids. 285, 1−3 (2001) 323−327.
EP
27. T. Sumiyoshi, I. Adachi, R. Enomoto, T. Iijima, R. Suda, M. Yokoyama, H. Yokogawa, Journal of Non-Crystalline Solids. 225 (1998) 369–374. 28. J.P. Randall, M.A.B. Meador, S.C. Jana, ACS Appl. Mater. Interfaces. 3 (2011) 613–626.
AC C
29. M.Yu. Barnyakov, V.S. Bobrovnikov, A.R. Buzykaev, A.F. Danilyuk, S.F. Ganzhur, I.I. Goldberg, G.M. Kolachev, S.A. Kononov, E.A. Kravchenko, G.D. Minakov, A.P. Onuchin, G.A. Savinov, V.A. Tayursky, Nuclear Instruments and Methods in Physics Research A. 453 (2000) 326−330.
30. P. Tsou, Journal of Non-Crystalline Solids. 186 (1995) 415−427. 31. M.J. Burchell, G. Graham, A. Kearsley, Annu. Rev. Earth Planet. Sci. 34 (2006) 385–418. 32. M. Alnaief, I. Smirnova, J. of Supercritical Fluids. 55 (2011) 1118–1123. 33. S. Yun, H. Luo, Y. Gao, RSC Adv. 4 (2014) 4535–4542. 34. R. Sui, A.S. Rizkalla, P.A. Charpentier, J. Phys. Chem. B. 108 (2004) 11886−11892.
14
ACCEPTED MANUSCRIPT 35. C.A. García-González, M.C. Camino-Rey, M. Alnaief, C. Zetzl, I. Smirnova. J. of Supercritical Fluids. 66 (2012) 297–306. 36. A.Yu. Barnyakov, M.Yu. Barnyakov, K.I. Beloborodov, V.S. Bobrovnikov, A.R. Buzykaev, V.B. Golubev, B.V. Gulevich, A.F. Danilyuk, S.A. Kononov, E.A. Kravchenko, K.A. Martin, A.P. Onuchin, V.V. Porosev, S.I. Serednyakov. Nuclear Instruments and Methods in Physics
37. C.S. Cundy, P.A. Cox. Chem. Rev. 103 (2003) 663−701. 38. A. Corma. Journal of Catalysis. 216 (2003) 298–312. 39. S.M. Csicsery, Zeolites. 4, 3 (1984) 202–213.
RI PT
Research A. 639 (2011) 225–226.
SC
40. D.E. De Vos, M. Dams, B.F. Sels, P.A. Jacobs. Chem. Rev. 102 (2002) 3615−3640. 41. F. Bedioui. Coordination Chemistry Reviews. 144 (1995) 39−68.
42. J. de Graaf, A.J. van Dillen, K.P. de Jong, D.C. Koningsberger, Journal of Catalysis. 203,
M AN U
307–321 (2001).
43. D.J. Wales, J. Grand, V.P. Ting, R.D. Burke, K.J. Edler, C.R. Bowen, S. Mintova, A.D. Burrows, Chem. Soc. Rev. 44 (2015) 4290.
44. K. Sahner, G. Hagen, D. Schönauer, S. Reiß, R. Moos, Solid State Ionics. 179 (2008) 2416-2423.
45. J. Caro, M. Noack. Microporous and Mesoporous Materials. 115 (2008) 215–233.
TE D
46. S. Velu, X. Ma, C. Song. Ind. Eng. Chem. Res. 42 (2003) 5293−5304. 47. E. Erdem, N. Karapinar, R. Donat. Journal of Colloid and Interface Science. 280 (2004) 309-314.
EP
48. A. Corma. Chem. Rev. 97 (1997) 2373−2419. 49. M.E. Davis. Microporous and Mesoporous Materials. 21 (1998) 173−182. 50. V.J. Inglezakis. Journal of Colloid and Interface Science. 281 (2005) 68–79.
AC C
51. P. Payra, P.K. Dutta. Microporous and Mesoporous Materials. 64 (2003) 109–118. 52. M.A. Zanjanchi, Sh. Sohrabnezhad. Sensors and Actuators B. 105 (2005) 502–507. 53. H.S. Kima, K.B. Yoon. Coordination Chemistry Reviews. 263−264, 1 (2014) 239−256. 54. N. Vilaça, R. Amorim, A.F. Machado, P. Parpot, M.F.R. Pereira, M. Sardo, J. Rocha, A.M. Fonseca, I.C. Neves, F. Baltazar. Colloids and Surfaces B: Biointerfaces. 112 (2013) 237-244. 55. D.G. Fatouros, D. Douroumis, V. Nikolakis, S. Ntais, A.M. Moschovi, V. Trivedi, B. Khima, M. Roldo, H. Nazara, P.A. Cox. J. Mater. Chem. 21 (2011) 7789–7794. 56. R.E. Morris, P.S. Wheatley. Angew. Chem. Int. Ed. 47 (2008) 4966–4981.
15
ACCEPTED MANUSCRIPT 57. J. Perez-Ramírez, C.H. Christensen, K. Egeblad, C.H. Christensen, J.C. Groen, Chem. Soc. Rev. 37 (2008) 2530–2542. 58. S. Mitchell, N.-L. Michels, J. Pérez-Ramírez, Chem. Soc. Rev. 42 (2013) 6094−6112. 59. H. Konno, T. Okamura, T. Kawahara, Y. Nakasaka, T. Tago, T. Masuda, Chemical Engineering Journal. 207–208 (2012) 490–496.
RI PT
60. T. Tago, H. Konno, M. Sakamoto, Y. Nakasaka, T. Masuda, Applied Catalysis A: General. 403 (2011) 183–191.
61. M. Choi, K. Na, J. Kim, Y. Sakamoto, O. Terasaki, R. Ryoo, Nature. 461, 7261 (2009) 246-249.
SC
62. Y. Sun, R. Prins, Applied Catalysis A: General. 336 (2008) 11–16.
63. S. Schwarz, M. Kojima, C.T. O’Connor. Applied Catalysis, 68 (1991) 81−96. 64. J. Kuhn, T. Gleissner, M.C. Arduini-Schuster, S. Korder, J. Fricke, Journal of Non-
M AN U
Crystalline Solids. 186 (1995) 291−295.
65. J.F. Hund, M.F. Bertino, G. Zhang, C. Sotiriou-Leventis, N. Leventis, A.T. Tokuhiro, J. Farmer, J. Phys. Chem. B. 107 (2003) 465−469. 66.
K.S. Morley,
P. Licence,
P.C. Marr,
J.R. Hyde,
P.D. Brown,
R. Mokaya,
Y. Xia,
S.M. Howdle, J. Mater. Chem. 14 (2004) 1212–1217.
67. J.L. Mohanan, S.L. Brock, Chem. Mater. 15 (2003) 2567−2576.
TE D
68. T.-Y. Wei, C.-Y. Kuo, Y.-J. Hsu, S.-Y. Lu, Y.-C. Chang. Microporous and Mesoporous Materials. 112 (2008) 580–588.
69. A. Santos, J.A. Toledo-Fernández, R. Mendoza-Serna, L. Gago-Duport, N. de la Rosa-Fox,
EP
M. Piñero, L. Esquivias, Ind. Eng. Chem. Res. 46 (2007) 103−107. 70. X. Li, Q. Wang, H. Li, H. Ji, X. Sun, J. He, Journal of Sol-Gel Science and Technology. 67, 3 (2013) 646−653.
AC C
71. B. Dou, J. Li, Y. Wang, H. Wang, C. Ma, Z. Hao, Journal of Hazardous Materials. 196 (2011) 194–200.
72. Z. Ulker, I. Erucar, S. Keskin, C. Erkey, Microporous and Mesoporous Materials. 170 (2013) 352−358.
73. M.L. Anderson, R.M. Stroud, C.A. Morris, C.I. Merzbacher, D.R. Rolison, Advanced engineering materials. 2, 8 (2000) 481−488. 74. C.A. Morris, M.L. Anderson, R.M. Stroud, C.I. Merzbacher, D.R. Rolison, Science. 284 (1999) 622−624. 75. A. Ribera, I. W.C.E. Arends, S. de Vries, J. Pérez-Ramírez, R.A. Sheldon, Journal of Catalysis.195 (2000) 287–297. 16
ACCEPTED MANUSCRIPT 76. R.Q. Long, R.T. Yang. J. Am. Chem. Soc. 121(1999) 5595–5596. 77. M.M. Forde, R.D. Armstrong, C. Hammond, Q. He, R.L. Jenkins, S.A. Kondrat, N. Dimitratos, J.A. Lopez-Sanchez, S.H. Taylor, D. Willock, C.J. Kiely, G.J. Hutchings. J. Am. Chem. Soc. 135 (2013) 11087–11099. 78. S. Navalon, M. Alvaro, H. Garcia. Applied Catalysis B: Environmental. 99 (2010) 1–26.
RI PT
79. Sashkina Kseniya A., Polukhin Alexander V., Labko Vera S., Ayupov Artem B., Lysikov Anton I., Parkhomchuk Ekaterina V. Applied Catalysis B: Environmental. 185 (2016) 353–361. 80. K.A. Sashkina, E.V. Parkhomchuk, N.A. Rudina, V.N. Parmon. Microporous and Mesoporous Materials. 189 (2014) 181–188.
SC
81. I. Smirnova, W. Arlt, Journal of Sol-Gel Science and Technology. 28 (2003) 175–184. 82. M. Thommes, K. Kaneko, A.V. Neimark, J. P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing, Pure and Applied Chemistry. 87, 9–10 (2015) 1051–1069.
M AN U
83. Mel’gunov, A.B. Ayupov Microporous and Mesoporous Materials. 243 (2017) 147−153. 84. E.P. Barrett, L.G. Joyner, P.P. Halenda, J. Am. Chem. Soc. 73 (1951) 373. 85. M. Jaroniec, M. Kruk, J.P. Olivier, Langmuir 15 (1999) 5410. 86. M.M.J. Treacy, J.B. Higgins, R. Ballmoos, Collection of Simulated XRD Powder Patterns for Zeolites, published by, Third revised edition, The Commission of the International Zeolite Association, 1996. K.A. Sashkina,
E.V. Parkhomchuk,
TE D
87.
N.A. Rudina,
AC C
EP
Mesoporous Materials. 189 (2014) 181–188.
17
V.N. Parmon,
Microporous
and
ACCEPTED MANUSCRIPT
Highlights •
New composite materials based on zeolite/SiO2 aerogel in the form of monoliths
and microspheres have been designed. •
Crack-free silica aerogel and composite monoliths are formed after alcogel aging
in equivolume water/ethanol mixture. The size and texture of of silica aerogel and composite microspheres are tuned by
AC C
EP
TE D
M AN U
SC
the stirring rate during emulsion/gelation step.
RI PT
•
S1387-1811(17)30791-6
DOI:
10.1016/j.micromeso.2017.12.010
Reference:
MICMAT 8699
To appear in:
Microporous and Mesoporous Materials
Received Date: 26 September 2017 Revised Date:
5 December 2017
Accepted Date: 10 December 2017
Please cite this article as: K.A. Sashkina, P.A. Gurikov, A.B. Ayupov, I. Smirnova, E.V. Parkhomchuk, Zeolite/silica aerogel composite monoliths and microspheres, Microporous and Mesoporous Materials (2018), doi: 10.1016/j.micromeso.2017.12.010. 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 Zeolite/silica aerogel composite monoliths and microspheres Kseniya
A.
Sashkinaa,b,*,
Pavel
A.
Gurikovc,
Artem B. Ayupova,
Irina
Smirnovac,
Ekaterina V. Parkhomchuka,b
Boreskov Institute of Catalysis SB RAS, 5 Lavrentieva St., Novosibirsk 630090, Russia.
b c
Novosibirsk State University, 2 Pirogova St., Novosibirsk 630090, Russia.
Institute of Thermal Separation Processes, Hamburg University of Technology, Eißendorfer
RI PT
a
Straße 38, Hamburg, Germany. * corresponding author
SC
Abstract
A series of silica aerogels and composite materials based on Fe-silicalite-1 nanocrystals
M AN U
embedded into silica aerogel matrix in the form of monoliths and microspheres have been synthesized by drying with supercritical CO2. Using equivolume water/ethanol mixture as a medium for the aging of monoliths enabled to produce monoliths of silica aerogel and composite without cracks. The synthesis of the composite and silica aerogel microspheres by the emulsion/gelation technique has been designed. The different effects of the stirring rate during the emulsification on the particle size and texture of composites and silica aerogels has been
TE D
observed. The synthesized samples were characterized by X-ray diffraction, scanning electron
Keywords
EP
microscopy and nitrogen adsorption measurements.
Silica aerogel, zeolite, Fe-silicalite-1, composite, monolith, emulsion/gelation, supercritical CO2
AC C
Introduction
Silica aerogels also referred to as “solid air” are mesoporous materials with extremely low density and an open pore structure. The bulk density of aerogels can be as low as 0.003 g/cm3, i.e. just three times larger than the density of air (0.001 g/cm3). Ultralight SiO2 aerogels are generally prepared by the supercritical extraction of self-standing gels by the sol–gel method [1]. This technique allows the liquid to be slowly removed without strongly altering the network structure or the volume of the gel body [2,3]. Owing to their special structure, silica aerogels possess unique physical properties such as ultralow density [4], low thermal conductivity [5], enormous surface area (> 800 m2/g) [6] and high transparency [7]. On account of the properties mentioned above, silica aerogels find a variety of applications in very different fields as 1
ACCEPTED MANUSCRIPT
adsorbents [8,9,10], catalysts [11,12,13,14,15,16], thermal [17] or acoustic insulators [18], sensors [19,20], carrier materials [21,22,23,24], storage media [25,26], Cherenkov counters in particle physics experiments [27,28,29] and cosmic dust capturing [30,31]. It should be noted, that silica aerogels can be obtained in various sizes and forms, ranging from microbeads [32,33,34] to large monoliths [35] and tiles [36]. Another large class of porous materials is zeolites. They are crystalline silicates and
RI PT
aluminosilicates with regular and uniform pores and channels of molecular dimensions, resulting in high surface area (350−450 m2/g) [37]. Zeolites and zeotypes consist of tetrahedral units of T (where T is typically Si and Al for zeolites, but can also be transition metals and other elements such as B, Ga, Fe, Ge, Ti, Cu etc. for zeotypes) bonded by oxygen atoms resulting in a
SC
framework containing cages and channels of distinct sizes and shapes [38]. The adjustable microporosity of zeolites makes them shape-selective molecular sieves [39]. Besides, catalytic
M AN U
sites [40,41,42] or gas sensing agents [43,44] can be arranged within well-defined micropores in a ship-in-a-bottle architecture preventing them from sintering and leaching. Zeolites and zeotypes find the wide use as adsorbents [45,46,47], catalysts [48,49] and ion-exchangers [50]. The emerging applications of zeolites include sensors for gases [51,52], photovoltaic solar cells [53], drug delivery [54,55] and gas storage [56]. The key problems of zeolites in the majority of applications are intracrystalline diffusion constraints resulting in low utilization of the zeolite
TE D
surface [57] and poor molding properties requiring the use of binders [58]. The diffusion constrains may be eliminated by decreasing the size of zeolite particles [59,60] or creating a hierarchical pore architecture combining micropores and transport meso/macropores [61,62]. The molding of zeolites using binders often cause the problem of hindering mass transport
EP
resulting from the obstruction of micropores [63]. Silica aerogel composites are generally prepared by dispersing the guest particles in the wet
AC C
silica sol before the gelation or by impregnating the dry silica aerogel with molecular precursors [64]. The literature data concerning silica aerogel composites cover a wide variety of different dispersed materials such TiO2 [64], Ag, Au [65], Pd [66], CuO [67], SnO2 [68] nanoparticles, wollastonite [69], sepiolite fibers [70], carbon [71] and MOFs [72]. However, reports on aerogel/zeolite composites are scarce [73,74]. It was shown that it is possible to design novel materials for a specific application by using the silica sol as a nanoglue and to combine the adjustable properties of the silica aerogels with the desirable properties of the guest materials. Here we present the synthesis of novel composite materials based on Fe-containing zeolite nanocrystals embedded into silica aerogel matrix. Possible catalytic applications of Fecontaining zeolite/silica aerogel composites are benzene hydroxylation to phenol by N2O [75] catalytic reduction of nitric oxide by ammonia [76], partial oxidation of organic compounds by 2
ACCEPTED MANUSCRIPT
hydrogen peroxide to produce valuable products [77], water purification by total oxidation of organic contaminators [78] and radionuclides removal from radioactive waste [79]. Monodispersed Fe-silicalite-1 nanocrystals are recently reported materials [80] that have been successfully tested for decontamination purposes [79]. However, the utilization of zeolite nanocrystals as such is difficult due to tedious separation required after the oxidation process. Dispersing zeolite nanocrystals in the continuous matrix of mesoporous silica aerogel bypasses
RI PT
the mass-transport barriers and the obstruction of micropores associated with the conventional molding. The zeolite/silica aerogel composites have been synthesized in the form of monoliths and microspheres. Composite monoliths were observed to be crack-free. Composite microspheres were prepared by the emulsion/gelation technique. The size and texture of
SC
zeolite/silica aerogel microspheres were adjusted by varying the stirring rate under the
M AN U
emulsification.
Experimental Materials
Tetrapropylammonium hydroxide (TPAOH, 25 wt. % solution in water, Acros), tetraethylorthosilicate (TEOS, ≥98%, Angara-reactive, silica (fumed, ≥99 %, Aldrich), ethanol (EtOH, 95%, Pharmaceya) and Fe(NO3)3·9H2O (≥99%, Merck) were used for producing
TE D
Fe-silicalite-1 nanocrystals. Tetraethylorthosilicate (TEOS, Merck), ethanol denatured (more than 99.5 %, 1% MEK, Roth), ammonia solution (28−30 wt. %, for analysis, Merck), HCl (30 wt. %, Merck) and dimethylcyclohexylamine (BASF) were employed for the synthesis of
EP
silica aerogel composite materials.
Synthesis of Fe-silicalite-1 nanocrystals
AC C
The typical synthesis of Fe-silicalite-1 nanocrystals was carried out as follows. 120 mL of TEOS diluted with 120 mL of ethanol was added at once to 240 mL of TPAOH (12.5 wt. %) under vigorous stirring for 20 min, then 2.6 g of Fe(NO3)3·9H2O dissolved in 5 mL of distilled water were added dropwise. After stirring for 20 min, the resultant clear light-yellow gel with 1.00 SiO2 : 0.28 TPAOH : 0.006 Fe2O3: 4.79 EtOH : 1.75 H2O molar composition was placed in Teflon-lined stainless steel autoclaves and subjected to hydrothermal treatment in an oven at 90 °C for 7 days. Milky Fe-silicalite-1 suspension produced was purified in a series of three steps consisting of centrifugation at a relative acceleration of 3000 g for 5 h, followed by removal of the mother liquor and redispersion in ethanol under ultrasonication. The final concentration of Fe-silicalite-1 in ethanol suspension was 35 wt. %. 3
ACCEPTED MANUSCRIPT
Synthesis of Fe-silicalite-1/silica alcogel monoliths
Silica/nanozeolite alcogels were synthesized by hydrolysis and subsequent condensation of tetraethylorthosilicate. In a typical synthesis, 4.0 g of TEOS were mixed with required quantity of ethanol (3.00, 2.89, 2.78 g) and Fe-silicalite-1 suspension (0, 0.20, 0.38 g, respectively) and stirred at ambient temperature for 10 min. For the hydrolysis, 1.4 mL of HCl (1 g/L) were added dropwise and mixture was stirred for 30 min. For the following condensation, 1.0 g of NH3
RI PT
solution in ethanol (3.60 g/L) was added drop by drop under vigorous stirring. Finally, the mixture was poured into molds, gelled and aged in an equivolume mixture of EtOH and H2O (thermostatic bath at 50 °C for 20 h). Before supercritical drying obtained monoliths were rinsed
SC
3 times with ethanol.
Synthesis of Fe-silicalite-1/silica alcogel microspheres by emulsion gelation method
M AN U
At the hydrolysis step 5 g of TEOS were mixed with required quantity of ethanol (3.75 and 3.05 g) and Fe-silicalite-1 suspension (0 and 1.07 g, respectively). Then, 1.9 mL of HCl (1 g/L) were added dropwise and mixture was stirred for 30 min. The mixture was then diluted with 1.25 g of ethanol to obtain the desired density of the aerogel. The sol with zeolite was emulsified as follows. Continuous phase was prepared by the saturation of 150 g of sunflower oil with 17 g of ethanol under vigorous stirring. A typical emulsion was generated by adding the precursor
TE D
suspension to 20 g of saturated oil followed by the agitation using a propeller stirrer at the required rotation rate (300, 500, 800 rpm) for 10 min. To induce gelation 1 g of dimethylcyclohexylamine solution (5 wt.%) in ethanol-saturated oil was added dropwise to the emulsion (oil was saturated by ethanol due to their partial miscibility; this addition eliminates
EP
any transfer of ethanol from the particles into continuous phase). After instant gelation alcogel
AC C
microspheres were separated from the oil by the filtration followed by the rinsing with ethanol.
Supercritical drying of Fe-silicalite-1/silica alcogel particles The apparatus for supercritical drying is described in detail elsewhere [81]. In a typical experiment, the nanozeolite/silica alcogel monoliths and microspheres packed into coffee filters were placed into preheated a 250 mL cylindrical high-pressure stainless steel autoclave. The gels were covered with an excess of ethanol to avoid untimely drying of the gels. Liquid CO2 was delivered using a high-pressure diaphragm pump, preheated and introduced into the autoclave. The temperature was controlled using an electrical heating jacket: initial temperature was set to 40 °C followed by linear heating up to 60 °C for 4 h and maintaining at 60 °C for 12 h to ensure complete extraction of ethanol. Pressure in autoclave was maintained constant at 120 bars. When 4
ACCEPTED MANUSCRIPT
the extraction was completed, the nanozeolite/silica aerogel monoliths and microspheres were removed from the autoclave and calcined at 500 °C for 5 h.
Characterization The densities of calcined monoliths were calculated as their volume divided by the mass. Powder X-ray diffraction (XRD) patterns were recorded from a Siemens D500 diffractometer
RI PT
equipped with a Cu Kα radiation (λ = 0.154 nm). The hydrodynamic diameters of zeolite particles dispersed in ethanol measured with a Malvern Zetasizer Nano. The chemical composition of the samples was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Nitrogen adsorption-desorption isotherms of Fe-silicalite-1/silica
SC
aerogel monoliths and microspheres were measured at 77 K with a Quadrasorb EVO and Quantachrome Nova 3000e surface area analyzers, respectively. Prior to the analysis, samples
M AN U
were outgassed at 573 K for 10 h. Specific surface areas were determined by BET equation [82] using direct method for evaluation of BET adsorbed monolayer capacity [83]. Pore size distributions were estimated by the BJH method [84]. Micropore volume and external surface area were also calculated by means of αs-method using the isotherm of adsorption of N2 on the reference LiChrospher Si-1000 silica gel, reported in the literature [85]. Scanning electron microscopy (SEM) images were taken with a JEOL JSM-6460LV and Leo (Zeiss) 1530
TE D
microscopes at an operating voltage of 15−20 kV after a sputtering with gold. The diameter of silica and composite aerogel microspheres was measured by another method with Retsch Camsizer XT. The measurement principle of the equipment is following: particles pass in front of two bright, pulsed light-emitting diode (LED) sources. The shadows of the particles are
EP
captured with two digital cameras. One camera is optimized to analyze the small particles with high resolution; the other camera detects the larger particles with good statistics, due to a large
AC C
field of view. Particle size and particle shape are analyzed with software which calculates the respective distribution curves in real time.
Results and discussion
Firstly, Fe-silicalite-1 suspension was prepared by the hydrothermal treatment of the mixture with 1.00 SiO2 : 0.28 TPAOH : 0.006 Fe2O3: 4.79 EtOH : 1.75 H2O molar composition at 90 °C for 7 days followed by the purification and redispersion of crystals in ethanol under ultrasonication. The final concentration of as-synthesized Fe-silicalite-1 in ethanol suspension was 35 wt. %. Fe-silicalite-1 crystals with aggregate-like morphology have a mean diameter of about 180 nm and narrow size distribution (Fig. 1). 5
ACCEPTED MANUSCRIPT
RI PT
Fig. 1. Dynamic light scattering data for Fe–silicalite-1 suspension (left) and TEM image of Fe-silicalite-1 nanocrystals (right).
The powder obtained by drying Fe-silicalite-1 suspension followed by calcination has XRD
SC
patterns typical for MFI structure [86] and high crystallinity (Fig. 2). The Fe content in calcined Fe-silicalite-1 powder is 1.35 wt. % according to ICP-OES. The iron species representing small
against sintering and leaching [87].
M AN U
clusters no more than 3 nm in size are located inside zeolite mesopores, making them stable
The XRD patterns of Fe-silicalite-1/silica aerogel composites in the form of monoliths and microspheres confirm that Fe-silicalite-1 nanocrystals have been embedded into the aerogel matrix and preserved their structure during the synthesis. We evaluated the relative crystallinity of composites by the peaks integration in the range from 22.5 to 25 degrees relative to calcined
TE D
Fe-silicalite-1 nanocrystals powder under identical measurement conditions (Table 1). Relative crystallinity of composite microspheres increases when the stirring rate in the water-oil emulsion
AC C
EP
becomes more vigorous, apparently resulting from the incomplete gelation.
Fig. 2. XRD patterns of calcined Fe-silicalite-1 nanocrystals and Fe-silicalite-1/silica aerogel composites. Green patterns refer to the reference silica aerogels. 6
ACCEPTED MANUSCRIPT
Concentrated Fe-silicalite-1 suspension as described above was used for preparing Fe-silicalite-1/silica aerogel composite in the form of monoliths and microspheres. Besides, the reference samples of silica aerogel were synthesized at identical conditions. For producing aerogel materials, the following steps were carried out: the preparation of alcogel, drying with supercritical CO2 and calcination. The silica alcogels including those with Fe-silicalite-1 crystals were synthesized by the hydrolysis and following condensation of TEOS. The hydrolysis was
RI PT
conducted by adding hydrochloric acid to TEOS mixed with water, ethanol and Fe-silicalite-1 suspension. To form monoliths, ammonia solution was added to the precursor suspension, inducing the condensation process. The mixture was quickly placed to the molds, whereupon the gelation immediately occurred. Fresh monoliths were placed to the equivolume water/ethanol
SC
mixture at 50 °C for aging for 20 h (Fig. 3, a). It should be emphasized that aging in the presence of water is the key stage of preparing strong silica aerogel monoliths. A number of the silica
M AN U
aerogel monolith syntheses without aging or with aging in pure ethanol were failed, because the cracks were formed under drying with supercritical CO2 (Fig. 3, b) followed by breaking the monolith into small pieces. In water/ethanol mixture besides the syneresis the Ostwald ripening giving a more rigid gel network takes place: the reprecipitation of silica dissolved from particle surface onto necks between particles and dissolution of smaller particles and precipitation onto larger ones. Aging of monoliths resulted in volume shrinkage of 30‒40 %. After aging in
TE D
water/ethanol mixture, the monoliths were rinsed 3 times with ethanol and subjected to drying with supercritical CO2 followed by calcination. The monoliths are pill-shaped and have no cracks, pure silica aerogel being transparent and opalescent, while Fe-silicalite-1/silica aerogel composites are white (Fig. 3, c). The densities of calcined aerogel materials depend on the
EP
amount of embedded Fe-silicalite-1: 0.17, 0.18 and 0.20 g/cm3 for monoliths containing 0, 5 and
AC C
10 wt. % of Fe-silicalite-1 crystals, respectively.
7
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig. 3. Photographs of Fe-silicalite-1/silica alcogel (a) and calcined aerogel monoliths prepared with aging in pure ethanol (b) and equivolume water/ethanol mixture (c). Percentage of Fesilicalite-1 from the left to the right: 0, ≈5 and ≈10 wt. % (a, c); ≈10 wt. % (b).
TE D
According to SEM images the Fe-silicalite-1 crystals have sufficiently uniform distribution
AC C
EP
inside aerogel composite materials (Fig. 4).
Fig. 4. SEM image of Fe-silicalite-1/silica alcogel monolith.
The scheme illustrating the formation of aerogel microspheres is represented in Fig. 5. The first step was adding precursor suspensions (disperse phase) to the sunflower oil (continuous phase). The second step was the emulsification using propeller stirrer with subsequent gelation induced by adding dimethylcyclohexylamine (condensation catalyst). 8
RI PT
ACCEPTED MANUSCRIPT
Fig. 5. The main steps for preparing aerogel microspheres by the emulsion method followed by
SC
drying with supercritical CO2.
The size of droplets was adjusted by varying the rate of stirring from 200 to 800 rpm, whereas
M AN U
the gelation rate to depend on the concentration of dimethylcyclohexylamine was precisely selected in the preliminary experiments so that to achieve the uniform gelation without aggregation of microparticles. The last step was the separation of alcogel microspheres from the oil phase by filtration followed by rinsing with ethanol, drying with supercritical CO2 and calcination.
The SEM images and particle size distributions of silica aerogel particles prepared at different
TE D
stirring rates are presented in Fig. 6. The average size of aerogel particles produced at stirring rate of 200, 500 and 800 rpm is 170, 125 and 290 µm, respectively. It is worth noting that the aerogel particles obtained at 500 rpm were partially aggregated, consisting of several
EP
microspheres with the size in the range of 10−70 µm (Fig. 6). The largest silica aerogel microspheres formed at the fastest rotation rate are remarkable for isolated macropores with the size of 5−50 µm. The occurrence of such macropores appeared to be resulted from the double
AC C
emulsion formation. Thus, increasing the rate of stirring resulted in decreasing the size of silica aerogel microspheres followed by its sharp growth.
9
SC
RI PT
ACCEPTED MANUSCRIPT
Fig. 6. SEM images and particle size distributions (insert pictures) of silica aerogel particles
M AN U
prepared at the different rotation rates.
Another effect of the stirring rate on the size and texture of microspheres was observed under introducing Fe-silicalite-1 crystals into the precursor solution (Fig. 7). As expected the largest macroporous Fe-silicalite-1/silica aerogel microspheres were prepared at the lowest stirring rate of 200 rpm. The most part of 1−2 mm particles were damaged during gelation, filtration and drying, therefore the average size of Fe-silicalite-1/silica aerogel particles is quite small, 125 µm.
TE D
The growth of the stirring rate up to 500 rpm led to decreasing the microspheres size, Fe-silicalite-1/silica aerogel particles being also macroporous. This finding indicates that the energy input was sufficient for the formation of double emulsion. In our experiments this
EP
transition seems to occur between 200 and 500 rpm. Further increase in the stirring rate facilitated the generation of Fe-silicalite-1/silica aerogel microspheres with narrow size distribution and the average size of 80 µm. The changes of the size and texture of aerogel
AC C
microspheres prepared from emulsions containing Fe-silicalite-1 may be attributed to the stabilizing effect of solid Fe-silicalite-1 nanocrystals bound to the surface of the interface, i.e. the Pickering emulsion formation. Actually, SEM images show that Fe-silicalite-1 nanocrystals are located on the surface of silica aerogel microspheres and their macropores (Fig. 7). For macroporous Fe-silicalite-1/silica aerogel composites prepared at 200 and 500 rpm, nanocrystals are assembled in 5−10 µm brain-like islands on the surface of microspheres and their macropores, while for macroporous Fe-silicalite-1/silica aerogel microspheres produced at 800 rpm nanocrystals are uniformly distributed on the surface. The synthesis of composite materials might be optimized in the future to ensure a homogeneous distribution of the Fesilicalite-1 nanocrystals within all volume of the microspheres. 10
SC
RI PT
ACCEPTED MANUSCRIPT
Fig. 7. SEM images and particle size distributions (insert pictures) of Fe-silicalite-1/silica
M AN U
aerogel microspheres prepared at the different rotation rates.
Textural characteristics of Fe-silicalite-1/silica aerogel materials calculated from nitrogen adsorption-desorption data are represented in Table 1. All samples exhibit high BET surface areas, SBET, (780‒890 m2/g) and total pore volumes, Vtotal, (1.18‒5.37 cm2/g). Monoliths exhibited by a factor of three higher total pore volume and average pore diameter compared with
TE D
microspheres, most likely due to the different condensation conditions (ammonia versus organic amine). Composite and silica aerogel monoliths have narrow mesopore size distributions with a maximum at around 23 nm (Fig. 8). Embedding Fe-silicalite-1 nanocrystals during the synthesis of monoliths causes broadening the pore size distribution and increasing the percentage of
AC C
EP
pores < 10 nm.
Fig. 8. Pore size distributions for Fe-silicalite-1/silica aerogel monoliths estimated by the BJH method. 11
ACCEPTED MANUSCRIPT
SBET, m /g
Silica
0
Vtotal, cm /g
Average pore diameter, nm
Relative crystallinity, %
820
4.64
22.6
0
5
780
4.43
10
916
5.37
905
SC
Sample
Fe-silicalite-1, wt. %
1.54
6.8
0
900
1.55
6.9
0
850
1.25
5.9
0
2
3
Microspheres
Silica aerogels
200
500
TE D
22.7
12
23.4
18
200
835
1.74
8.3
36
500
890
1.54
6.9
51
815
1.18
5.8
64
EP
Composites
800
M AN U
Stirring, rpm
RI PT
Composites
Monoliths
Form
Table 1. Textural characteristics Fe-silicalite-1/silica aerogel materials.
AC C
800
Conclusions
We have synthesized a series of silica aerogels and composite materials with Fe-silicalite-1 nanocrystals embedded into silica aerogel matrix in the form of monoliths and microspheres. Using equivolume water/ethanol mixture as a medium for the aging enabled to produce crackfree monoliths of silica aerogel and the composites. Fe-silicalite-1 crystals are sufficiently uniformly distributed within the aerogel matrix. The composite and silica aerogel microspheres were prepared by the emulsion gelation technique with optimized gelation step preventing alcogel microparticles aggregation. The size of composite and silica aerogel microspheres was adjusted in the range of 80-1200 µm by varying the stirring rate from 200 to 800 rpm at the 12
ACCEPTED MANUSCRIPT
emulsification step. The effect of the stirring rate on the particle size and the texture of the composites differs from that on silica aerogels due to the stabilizing effect of solid Fe-silicalite-1 nanocrystals located at the interfacial surface. The composite and silica aerogel microspheres with isolated macropores of 5−50 µm in size were produced resulting from the double emulsion formation. Fe-silicalite-1 nanocrystals either form clusters on the surface of silica aerogel microspheres and their macropores or are uniformly distributed in the sample. All composite
RI PT
materials exhibit high BET surface areas (780‒890 m2/g) and total pore volumes (1.18-5.37 cm2/g). Zeolite/aerogel composite materials seem to be promising materials for adsorption, catalysis, sensors and as carriers.
SC
Acknowledgements
The catalysts syntheses were conducted within the framework of budget project No.
M AN U
0303−2016−0002 for Boreskov Institute of Catalysis. Textural studies by A.B. Ayupov were performed within the framework of budget project No. 0303-2016-0010 for Boreskov Institute of Catalysis.
References
1. A.S. Dorcheh, M.H. Abbasi, Journal of materials processing technology. 199 (2008) 10–26.
TE D
2. I. Smirnova, P. Gurikov, Annual Review of Chemical and Biomolecular Engineering. 8 (2017) 307–334.
3. N. Hüsing, U. Schubert, Angew. Chem. Int. Ed. 37 (1998) 22−45.
EP
4. L. Kocon, F. Despetis, J. Phalippou, Journal of Non-Crystalline Solids. 225 (1998) 96–100. 5. M. Reim, W. Körner, J. Manara, S. Korder, M. Arduini-Schuster, H.-P. Ebert, J. Fricke, Solar Energy. 79 (2005) 131-139.
AC C
6. H.D. Gesser, P.C. Goswami, Chem. Rev. 89 (1989) 765−788. 7. T.M. Tillotson, L.W. Hrubesh, Journal of Non-Crystalline Solids. 145 (1992) 44−50. 8. S. Štandeker, Z. Novak, Ž. Knez, Journal of Colloid and Interface Science 310 (2007) 362-368.
9. H. Ramadan, A. Ghanem, H. El-Rassy, Chemical Engineering Journal 159 (2010) 107–115. 10. S. Štandeker, Z. Novak, Ž. Knez, Journal of Hazardous Materials 165 (2009) 1114–1118. 11.
T.V. Konkova,
A.M. Katalevich,
P.A. Gurikov,
A.P. Rysev,
N.V. Menshutina,
Russ. J. Phys. Chem. B. 8 (2014) 999–1003. 12. S. Martínez, M. Meseguer, L. Casas, E. Rodríguez, E. Molins, M. Moreno-Manãs, A. Roig, R.M. Sebastián, A. Vallribera, Tetrahedron 59 (2003) 1553–1556. 13
ACCEPTED MANUSCRIPT 13. B. Heinrichs, F. Noville, J.-P. Pirard, Journal of catalysis. 170 (1997) 366–376. 14. P. Fabrizioli, T. Bürgi, A. Baiker, Journal of Catalysis 206 (2002) 143–154. 15. S. Martínez, A. Vallribera, C.L. Cotet, M. Popovici, L. Martín, A. Roig, M. Moreno-Manãs, E. Molins, New J. Chem. 29 (2005) 1342–1345. 16. B.C. Dunn, P. Cole, D. Covington, M.C. Webster, R.J. Pugmire, R.D. Ernst, E.M. Eyring,
RI PT
N. Shah, G.P. Huffman, Applied Catalysis A: General 278 (2005) 233–238. 17. R. Baetens, B.P. Jelle, A. Gustavsen, Energy and Buildings 43 (2011) 761–769.
18. Yu. K. Akimov, Instruments and Experimental Techniques. 46, 3 (2003) 287−299. 19. M.R. Ayers, A.J. Hunt, Solids. 225 (1998) 343–347.
SC
20. C.-T. Wang, C.-L. Wu, I-C. Chen, Y.-H. Huang, Sensors and Actuators B. 107 (2005) 402-410.
10.1016/j.supflu.2017.03.005.
M AN U
21. P. Gurikov, I. Smirnova, J. of Supercritical Fluids, in press. DOI:
22. I. Smirnova, J. Mamic, W. Arlt, Langmuir. 19 (2003) 8521−8525. 23. I. Smirnova, S. Suttiruengwong, M. Seiler, W. Arlt, Pharmaceutical Development and Technology. 9, 4 (2004) 443−452.
24. M. Alnaief, S. Antonyuk, C.M. Hentzschel, C.S. Leopold, S. Heinrich, I. Smirnova. Microporous and Mesoporous Materials. 160 (2012) 167–173.
TE D
25. B.S.K. Gorle, I. Smirnova, M.A. McHugh. J. of Supercritical Fluids. 48 (2009) 85–92. 26. J. Reynes, T. Woignier, J. Phalippou, Journal of Non-Crystalline Solids. 285, 1−3 (2001) 323−327.
EP
27. T. Sumiyoshi, I. Adachi, R. Enomoto, T. Iijima, R. Suda, M. Yokoyama, H. Yokogawa, Journal of Non-Crystalline Solids. 225 (1998) 369–374. 28. J.P. Randall, M.A.B. Meador, S.C. Jana, ACS Appl. Mater. Interfaces. 3 (2011) 613–626.
AC C
29. M.Yu. Barnyakov, V.S. Bobrovnikov, A.R. Buzykaev, A.F. Danilyuk, S.F. Ganzhur, I.I. Goldberg, G.M. Kolachev, S.A. Kononov, E.A. Kravchenko, G.D. Minakov, A.P. Onuchin, G.A. Savinov, V.A. Tayursky, Nuclear Instruments and Methods in Physics Research A. 453 (2000) 326−330.
30. P. Tsou, Journal of Non-Crystalline Solids. 186 (1995) 415−427. 31. M.J. Burchell, G. Graham, A. Kearsley, Annu. Rev. Earth Planet. Sci. 34 (2006) 385–418. 32. M. Alnaief, I. Smirnova, J. of Supercritical Fluids. 55 (2011) 1118–1123. 33. S. Yun, H. Luo, Y. Gao, RSC Adv. 4 (2014) 4535–4542. 34. R. Sui, A.S. Rizkalla, P.A. Charpentier, J. Phys. Chem. B. 108 (2004) 11886−11892.
14
ACCEPTED MANUSCRIPT 35. C.A. García-González, M.C. Camino-Rey, M. Alnaief, C. Zetzl, I. Smirnova. J. of Supercritical Fluids. 66 (2012) 297–306. 36. A.Yu. Barnyakov, M.Yu. Barnyakov, K.I. Beloborodov, V.S. Bobrovnikov, A.R. Buzykaev, V.B. Golubev, B.V. Gulevich, A.F. Danilyuk, S.A. Kononov, E.A. Kravchenko, K.A. Martin, A.P. Onuchin, V.V. Porosev, S.I. Serednyakov. Nuclear Instruments and Methods in Physics
37. C.S. Cundy, P.A. Cox. Chem. Rev. 103 (2003) 663−701. 38. A. Corma. Journal of Catalysis. 216 (2003) 298–312. 39. S.M. Csicsery, Zeolites. 4, 3 (1984) 202–213.
RI PT
Research A. 639 (2011) 225–226.
SC
40. D.E. De Vos, M. Dams, B.F. Sels, P.A. Jacobs. Chem. Rev. 102 (2002) 3615−3640. 41. F. Bedioui. Coordination Chemistry Reviews. 144 (1995) 39−68.
42. J. de Graaf, A.J. van Dillen, K.P. de Jong, D.C. Koningsberger, Journal of Catalysis. 203,
M AN U
307–321 (2001).
43. D.J. Wales, J. Grand, V.P. Ting, R.D. Burke, K.J. Edler, C.R. Bowen, S. Mintova, A.D. Burrows, Chem. Soc. Rev. 44 (2015) 4290.
44. K. Sahner, G. Hagen, D. Schönauer, S. Reiß, R. Moos, Solid State Ionics. 179 (2008) 2416-2423.
45. J. Caro, M. Noack. Microporous and Mesoporous Materials. 115 (2008) 215–233.
TE D
46. S. Velu, X. Ma, C. Song. Ind. Eng. Chem. Res. 42 (2003) 5293−5304. 47. E. Erdem, N. Karapinar, R. Donat. Journal of Colloid and Interface Science. 280 (2004) 309-314.
EP
48. A. Corma. Chem. Rev. 97 (1997) 2373−2419. 49. M.E. Davis. Microporous and Mesoporous Materials. 21 (1998) 173−182. 50. V.J. Inglezakis. Journal of Colloid and Interface Science. 281 (2005) 68–79.
AC C
51. P. Payra, P.K. Dutta. Microporous and Mesoporous Materials. 64 (2003) 109–118. 52. M.A. Zanjanchi, Sh. Sohrabnezhad. Sensors and Actuators B. 105 (2005) 502–507. 53. H.S. Kima, K.B. Yoon. Coordination Chemistry Reviews. 263−264, 1 (2014) 239−256. 54. N. Vilaça, R. Amorim, A.F. Machado, P. Parpot, M.F.R. Pereira, M. Sardo, J. Rocha, A.M. Fonseca, I.C. Neves, F. Baltazar. Colloids and Surfaces B: Biointerfaces. 112 (2013) 237-244. 55. D.G. Fatouros, D. Douroumis, V. Nikolakis, S. Ntais, A.M. Moschovi, V. Trivedi, B. Khima, M. Roldo, H. Nazara, P.A. Cox. J. Mater. Chem. 21 (2011) 7789–7794. 56. R.E. Morris, P.S. Wheatley. Angew. Chem. Int. Ed. 47 (2008) 4966–4981.
15
ACCEPTED MANUSCRIPT 57. J. Perez-Ramírez, C.H. Christensen, K. Egeblad, C.H. Christensen, J.C. Groen, Chem. Soc. Rev. 37 (2008) 2530–2542. 58. S. Mitchell, N.-L. Michels, J. Pérez-Ramírez, Chem. Soc. Rev. 42 (2013) 6094−6112. 59. H. Konno, T. Okamura, T. Kawahara, Y. Nakasaka, T. Tago, T. Masuda, Chemical Engineering Journal. 207–208 (2012) 490–496.
RI PT
60. T. Tago, H. Konno, M. Sakamoto, Y. Nakasaka, T. Masuda, Applied Catalysis A: General. 403 (2011) 183–191.
61. M. Choi, K. Na, J. Kim, Y. Sakamoto, O. Terasaki, R. Ryoo, Nature. 461, 7261 (2009) 246-249.
SC
62. Y. Sun, R. Prins, Applied Catalysis A: General. 336 (2008) 11–16.
63. S. Schwarz, M. Kojima, C.T. O’Connor. Applied Catalysis, 68 (1991) 81−96. 64. J. Kuhn, T. Gleissner, M.C. Arduini-Schuster, S. Korder, J. Fricke, Journal of Non-
M AN U
Crystalline Solids. 186 (1995) 291−295.
65. J.F. Hund, M.F. Bertino, G. Zhang, C. Sotiriou-Leventis, N. Leventis, A.T. Tokuhiro, J. Farmer, J. Phys. Chem. B. 107 (2003) 465−469. 66.
K.S. Morley,
P. Licence,
P.C. Marr,
J.R. Hyde,
P.D. Brown,
R. Mokaya,
Y. Xia,
S.M. Howdle, J. Mater. Chem. 14 (2004) 1212–1217.
67. J.L. Mohanan, S.L. Brock, Chem. Mater. 15 (2003) 2567−2576.
TE D
68. T.-Y. Wei, C.-Y. Kuo, Y.-J. Hsu, S.-Y. Lu, Y.-C. Chang. Microporous and Mesoporous Materials. 112 (2008) 580–588.
69. A. Santos, J.A. Toledo-Fernández, R. Mendoza-Serna, L. Gago-Duport, N. de la Rosa-Fox,
EP
M. Piñero, L. Esquivias, Ind. Eng. Chem. Res. 46 (2007) 103−107. 70. X. Li, Q. Wang, H. Li, H. Ji, X. Sun, J. He, Journal of Sol-Gel Science and Technology. 67, 3 (2013) 646−653.
AC C
71. B. Dou, J. Li, Y. Wang, H. Wang, C. Ma, Z. Hao, Journal of Hazardous Materials. 196 (2011) 194–200.
72. Z. Ulker, I. Erucar, S. Keskin, C. Erkey, Microporous and Mesoporous Materials. 170 (2013) 352−358.
73. M.L. Anderson, R.M. Stroud, C.A. Morris, C.I. Merzbacher, D.R. Rolison, Advanced engineering materials. 2, 8 (2000) 481−488. 74. C.A. Morris, M.L. Anderson, R.M. Stroud, C.I. Merzbacher, D.R. Rolison, Science. 284 (1999) 622−624. 75. A. Ribera, I. W.C.E. Arends, S. de Vries, J. Pérez-Ramírez, R.A. Sheldon, Journal of Catalysis.195 (2000) 287–297. 16
ACCEPTED MANUSCRIPT 76. R.Q. Long, R.T. Yang. J. Am. Chem. Soc. 121(1999) 5595–5596. 77. M.M. Forde, R.D. Armstrong, C. Hammond, Q. He, R.L. Jenkins, S.A. Kondrat, N. Dimitratos, J.A. Lopez-Sanchez, S.H. Taylor, D. Willock, C.J. Kiely, G.J. Hutchings. J. Am. Chem. Soc. 135 (2013) 11087–11099. 78. S. Navalon, M. Alvaro, H. Garcia. Applied Catalysis B: Environmental. 99 (2010) 1–26.
RI PT
79. Sashkina Kseniya A., Polukhin Alexander V., Labko Vera S., Ayupov Artem B., Lysikov Anton I., Parkhomchuk Ekaterina V. Applied Catalysis B: Environmental. 185 (2016) 353–361. 80. K.A. Sashkina, E.V. Parkhomchuk, N.A. Rudina, V.N. Parmon. Microporous and Mesoporous Materials. 189 (2014) 181–188.
SC
81. I. Smirnova, W. Arlt, Journal of Sol-Gel Science and Technology. 28 (2003) 175–184. 82. M. Thommes, K. Kaneko, A.V. Neimark, J. P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing, Pure and Applied Chemistry. 87, 9–10 (2015) 1051–1069.
M AN U
83. Mel’gunov, A.B. Ayupov Microporous and Mesoporous Materials. 243 (2017) 147−153. 84. E.P. Barrett, L.G. Joyner, P.P. Halenda, J. Am. Chem. Soc. 73 (1951) 373. 85. M. Jaroniec, M. Kruk, J.P. Olivier, Langmuir 15 (1999) 5410. 86. M.M.J. Treacy, J.B. Higgins, R. Ballmoos, Collection of Simulated XRD Powder Patterns for Zeolites, published by, Third revised edition, The Commission of the International Zeolite Association, 1996. K.A. Sashkina,
E.V. Parkhomchuk,
TE D
87.
N.A. Rudina,
AC C
EP
Mesoporous Materials. 189 (2014) 181–188.
17
V.N. Parmon,
Microporous
and
ACCEPTED MANUSCRIPT
Highlights •
New composite materials based on zeolite/SiO2 aerogel in the form of monoliths
and microspheres have been designed. •
Crack-free silica aerogel and composite monoliths are formed after alcogel aging
in equivolume water/ethanol mixture. The size and texture of of silica aerogel and composite microspheres are tuned by
AC C
EP
TE D
M AN U
SC
the stirring rate during emulsion/gelation step.
RI PT
•