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Rationally Turning the Interface Activity of Mesoporous Silicas for Preparing Pickering Foam and ‘Dry Water’ Xia Rong, Hengquan Yang, and Ning Zhao Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b01702 • Publication Date (Web): 13 Aug 2017 Downloaded from http://pubs.acs.org on August 15, 2017
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Rationally Turning the Interface Activity of Mesoporous Silicas for Preparing Pickering Foam and ‘Dry Water’ Xia Rong,† Hengquan Yang*,† and Ning Zhao,*,‡ †
School of Chemistry and Chemical Engineering, Shanxi University, Wucheng Road 92, Taiyuan 030006, China State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taoyuan South Road 27, Taiyuan 030001, China
‡
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[email protected]; *
[email protected] ABSTRACT: We develop a novel protocol to prepare smart, gas/water interface-active, mesoporous silica particles. This protocol involves modification of highly mesoporous silicas with a mixture of hydrophobic octyl organosilane and hydrophilic triamine organosilane. Their structure and compositions are characterized by transmission electron microscopy (TEM), N2 sorption, solid state NMR, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FT−IR), Thermogravimetric analysis (TGA) and elemental analysis. It is demonstrated that our protocol enables the interface-activity of mesoporous silica particles to be facilely tuned, so that the stable gas-water interfaces ranging from air bubbles dispersed in water (Pickering foam) and water droplets dispersed in air (‘dry water’) can be achieved, depending on the molar ratio of these two organosilanes. The ‘dry water’ is not otherwise attainable for the analogous nonporous silica particles, indicting the uniqueness of the chosen mesoporous structures. Moreover, these particles-stabilized Pickering foams and ‘dry waters’ can be disassembled in response to pH. Interestingly, it was found that aqueous potassium carbonate droplets stabilized by these interface-active mesoporous silica particles (‘dry K2CO3-containing water’) could automatically capture CO2 from a simulated flue gas with enhanced adsorption rate and adsorption capacity when compared to the aqueous potassium carbonate bulk solution. This study not only supplies a novel type of efficient, smart, gas/water interface-active mesoporous silica particles but also demonstrate an innovative application of mesoporous materials in gas adsorption.
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interfacial silver mirror reactions.23 Tian et al. and Bormashenko et al. demonstrated that liquid marbles could be used as gas sensor.24 Also, Cooper and co-workers found that silica-stabilized ‘dry water’ dramatically enhanced methane uptake rates.16 Driven by so intriguing applications, diverse inorganic and organic micro/nanoparticles such as hydrophobic silica particles,16, 22, 25, 26 carbon black,27, 28 Janus microspheres,29 magnetic particles,30-32 surface-modified lycopodium powder,33-35 or polymer latexes36-38 have been successfully prepared for stabilizing gas-water interfaces. Despite progressive advances made so far, these materials are often amenable to preparing liquid marbles through rolling water droplets on a layer of the hydrophobic particle powders. However, liquid marbles still have limited gas-water interface areas and are less mechanically robust since their sizes are as large as several millimeters to centimeters, which impede their practical applications.39 These demerits can be overcome by ‘dry water’ because its size is as small as dozens of micrometers. However, preparation of ‘dry
INTRODUCTION
Recent years have witnessed an ever-growing interest in oil/water, gas/water, and solid/water interfaces stabilized by particles because they contribute to new concepts and materials such as Pickering emulsions,1-7 Pickering foams/bubbles,8-12 liquid marbles13-15 and ‘dry waters’.16 Compared to commonly used molecular surfactants, solid particles can be easily separated from the mixtures after accomplishing missions and render the interfaces more robust due to their high interfacial adsorption energy.17 Their benefits for applications have been demonstrated in multiphase catalysis,1, 2 miniature reactors,18, 19 sensors,20 and energy storage.16, 21 Amongst these interfaces, gas-water interfaces, namely Pickering foams and ‘dry waters’, are emerging as an updated platform for more innovative applications. For instance, very recently, we found that the particle-stabilized microbubble reaction systems significantly boosted catalysis efficiency in comparison to conventional multiphase systems.22 To Ngai et al. attested that liquid marbles could be used as microreactors to carry out
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water’ typically necessitates high-speed shear mixing because it requires particles to rapidly migrate from a bulk phase to a gas-water interface and immediately stabilize the interface before the naked droplets merge.40 As far as I know, only hydrophobic silica particles with an average diameter of 20 nm are reported to fabricate ‘dry water’. In this context, search for more efficient particles to stabilize ‘dry water’ are still highly desirable. Based on a thermodynamic consideration, the energy required to remove a particle from a gas-water interface given by41 ΔE aw 1 rcos
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can be disassembled in response to an external stimuli after accomplishing designated missions. Amongst the various available methods for inducing disassembly, including pH, temperature, magnetic, light, electric fields and ultrasonic,8, 55-57 pH may be a good option because it can be readily realized through simple addition of acid or base. For instance, Fujii and co-workers demonstrated that sterically-stabilized poly-styrene latexes synthesized using poly[2-(diethylamino)ethyl methacrylate] (PDEA) macromonomer could be used to prepare pH-responsive ‘liquid marbles’.36 Liu et al. also prepared fluorinated polymeric micelles based on the self-assembly of a fluoropolymer, poly(styrene-co-acrylic acid-co-2,2,3,4,4,4-hexafluorobutyl methacrylate), which could stabilize liquid marbles and disassemble in response to pH.57 To the best of our knowledge, the pH-responsive gas-water interface stabilized by particles, however, are limited to polymers. Their inorganic analogues are still desirable due to their high mechanical robustness and chemical stability. Herein, we prepared large-sized, gas/water interface-active, mesoporous silica particles through modification with a mixture of hydrophobic octyl organosilane and hydrophilic triamine organosilane. As illustrated in Scheme 1A, this modification protocol allows the interface-activity of mesoporous silica particles to be facilely tuned by changing the molar ratio of these two organosilanes, so that the stable gas-water interfaces ranging from air bubbles dispersed in water (Pickering foam) and water droplets dispersed in air (‘dry water’) can be achieved. Moreover, the particles-stabilized Pickering foam or ‘dry water’ can be disassembled by addition of acid due to the change of the surface activity of particles (Scheme 1B). Significantly, the mesoporous silica-stabilized ‘dry K2CO3-containing water’ could automatically capture CO2 from a simulated flue gas.
Where is the radius of the particle, aw is the interface tension between air and water, and r is the surface roughness factor. According to this equation, the desorption energy of particles from an interface, ΔE, scales with the square of the particle radius, meaning that larger particles make ‘dry water’ more stable. However, it is more difficult for larger particles to rapidly migrate from a bulk phase to an interface due to its larger mass. Such a trade-off urges us to conceive of mesoporous materials in that they are relatively light in mass due to their high porosity.42-48 Meanwhile, the flexible synthesis protocol of mesoporous materials and ease of functionalization enable their architecture and surface chemistry properties to be facilely tailored.49-53 Moreover, mesoporous materials sitting at the gas-water interface may construct more sophisticated colloidosomes since their inherent nanopores can provide permeability-controllable passageways for molecule transports between the interior and exterior of the colloidsomes.54 Furthermore, in practical applications, it is expected that particle-stabilized bubbles or marbles, ‘dry waters’
2. RESULTS AND DISCUSSION 2.1. Preparation and characterization. As aforementioned, one possible way to obtain the ‘dry water’ and Pickering foam stabilized by large particles is to search for highly porous particles. Amongst various mesoporous materials, the mesoporous silica synthesized using nonpolar alkane as a swelling agent, may be a good candidate because it possesses very large pores,58 certainly leading to an extremely low density. By improving the synthesis temperature reported previously,59 we successfully prepared mesoporous silica particles (MSP) with larger pore sizes. Scanning electron microscopy (SEM) was used to characterize the morphology (Figure 1a and 1b). The irregular rod-like particles with size from hundreds of nanometres to microns are observed. Pore sizes as large as 19 nm could clearly be discerned from the TEM image (Figure 1c),
Scheme 1. (A) Schematic illustration of the phase transition from Pickering foam (air-in-water) to ‘dry water’ (water-in-air), and (B) structural description of the modified mesoporous silica particles in response to pH. Notes: The organosilanes also existed in the pores, and for better illustration, the size of organosilanes was enlarged.
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observed with TEM. Such a large pore originates from the swelling effect of the nonpolar alkene used. The textural parameters determined by N2 sorption are summarized in Table 1. Its specific surface area and pore volume are 597 m2/g and 2.2 cm3/g, respectively. Its bulk density is as low as 0.1 g/cm3, which is consistent with it large pore size and pore volume. It is well documented that the key for achieving responsive, interface-active particles is to tune the surface chemistry of the particles.26, 60 To this end, we used a mixture of hydrophobic (MeO)3Si(CH2)7CH3 and hydrophilic, pH sensitive (MeO)3SiCH2CH2CH2(NHCH2CH2)2NH2 to modify MSP, leading to triamine-octyl- bifunctionalized mesoporous silica particles MSP-NO(x), where O refers to octyl organosilane, N refers to triamine organosilane, and x refers to the molar fraction of octyl organosilane in the total organosilanes (x=40, 50, 60, 70, 80, 85, 90 respectively). For comparison, we also synthesized octyl-monofunctionalized and triamine-monofunctionalized MSP, which are denoted as MSP-O and MSP-N, respectively. N2 adsorption/desorption isotherms of the monofunctionalized MSP-N, MSP-O, and a typical bifunctionalized sample MSP-NO(85) are shown in Figure 2a and their physical parameters determined by N2 sorption are summarized in Table 1. After introduction of octyl or/and triamine groups, the isotherms of the synthesized samples are still similar to
Figure 1. Structural characterization of synthesized pristine MSP. (a) and (b) SEM images, (c) TEM image, (d) N2 adsorption/desorption isotherm.
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which is larger than the pore size reported previously.58 The mesoporous structure is further confirmed by N2 sorption measurement. As shown in Figure 1d, a rapid N2 adsorption occurred at a higher relative pressure (more than 0.9). This is attributed to the N2 capillary condensation in the large pores of the MSP. Based on such a result, the pore size are calculated to be 19.2 nm (inset in Figure 1d), which agrees well with the value
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Figure 2. Characterization of the synthesized interface-active MSP. (a) N2 adsorption/desorption isotherms of the samples MSP-O, MSP-N, and MSP-NO(85), MSP-NO(85) and MSP-O, offset vertically the prior one by 400, 700 respectively, (b) solid state 13C CP-MAS NMR spectrum of MSP-NO(85), (c) solid state 29Si CP-MAS NMR spectrum of MSP-NO(85), (d) X-ray photoelectron spectroscopy (XPS) spectrum of MSP-NO(85), (e) FT-IR spectra of MSP-N, MSP-O, MSP-NO(85), and MSP-NO(70), and (f) TGA curve of MSP-NO(85).
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Table 1. Textural parameters and elemental analysis results of the interface-active mesoporous silica particles. Sa Vb Pore size c Triamine Octyl Octyl/ 2 3 (m /g) (cm /g) (nm) (mmol/g) (mmol/g) Triamine d Pristine MSP 597 2.2 19.2 MSP-N 298 1.5 15.0 1.21 0 MSP-NO(40) 226 1.2 14.5 1.04 0.22 0.21 MSP-NO(50) 276 1.2 14.9 0.81 0.30 0.37 MSP-NO(60) 286 1.2 14.6 0.68 0.44 0.65 MSP-NO(70) 293 1.4 14.1 0.65 0.58 0.92 MSP-NO(80) 320 1.5 14.3 0.38 0.74 1.96 MSP-NO(85) 333 1.5 14.0 0.33 0.70 2.13 MSP-NO(90) 340 1.6 14.1 0.28 0.89 3.13 MSP-O 342 1.6 14.2 0.80 ∞ a BET surface area. b Single point pore volume calculated at relative pressure of P/P0 = 0.99. c Pore size, BJH method from the adsorption branch. d Octyl/triamine is the molar ratio according to the results of elemental analysis. Sample
the pristine MSP, indicating that the mesoporous structure was maintained. However, the specific surface area, pore size and pore volume decrease dramatically in comparison to the pristine mesoporous silica. For example, the specific surface area of MSP-N, MSP-O and MSP-NO(85) decreases down to 298, 342 and 333 m2 respectively. Such decreases are a result of the introduction of functionalities into the mesopor0us channels. The specific surface area of MSP-N is smaller than that of MSP-O because the triamine molecules are larger in size than octyl molecules. Furthermore, to know the impact of the introduced functionalities on the textual parameters, we determined the textual parameters of the set of bifunctionalized MSP-NO(x) samples with N2 sorption (Table 1 and Figure S2). As seen in Table 1, the textual parameters are significantly affected by the molar fraction of two organosilanes. For example, both the BET surface area and pore volume decreases with increasing triamine groups. Even though the specific surface area, pore volume and pore size decreases more or less after introducing organic functionalities into the mesopor0us channels, the mesoporous structure of large pores is essentially maintained (Figure S2). The compositions of bifunctionalized MSP-NO(x) were characterized with solid state NMR, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and elemental analysis. For a representative sample MSP-NO(85), the 13C CP-MAS NMR spectrum exhibits peaks assigned to the C atoms of these two organic functionalities. The peaks at 50 and 61 ppm are assigned to C atoms of the residual CH3O group of organosilanes and the N-neighboring C atoms of triamine organosilane, respectively (Figure 2b). The signals of other C atoms of octyl and triamine groups are also found between 12 and 42 ppm. These results indicate that both octyl and triamine groups are
successfully introduced on the silica surface. Figure 2c shows the 29Si CP-MAS NMR spectrum of MSP-NO(85). The signal at −110 ppm is attributed to the Q4 [Si(OSi)4] silicon. The signals at −58 and −66 ppm are attributed to the T2 [SiC(OH)(OSi)2] and T3 [SiC(OSi)3] silicon sites, respectively. The strong signal for Q bands confirms that the solid material is subjected to a high degree of condensation. The presence of the T peak further indicates that organic groups are covalently linked with MSP through covalent linkage. The survey XPS spectrum of the modified MSN-NO(85) is shown in Figure 2d. C, N, Si and O elements are all found, further indicating that octyl and triamine groups are both introduced on the silica surface. Figure 2e shows FT-IR spectra of MSP-N, MSP-O, and MSP-NO(85). The bands at 1563 cm−1 and 2931 cm−1 are respectively related to the N-H stretching vibrations of triamine groups and the C-H stretching vibrations of octyl groups, pointing to a successful introduction of these two functionalities onto MSP. Thermogravimetric analysis (TGA) is performed to estimate the functionality loading and to assess thermal stability of MSP-NO(85). As shown in Figure 2f, the first step of the weight loss in the range of 50−100 °C is due to the loss of the physically adsorbed water. In the temperature between 100 and 220 °C, the weight loss is negligible, indicating that the bifunctionalized mesoporous silica particles have a good thermal stability below 220 °C. The second step of apparent weight loss is observed from 220 to 700 °C, which is related to the decomposition of octyl and triamine groups. Based on the second step of weight loss, it can be estimated that the organic loading is about 16.1 wt. %). Elemental analysis was employed to quantitatively determine the loadings of two functionalities on the bifunctionalized MSP-NO(x) (Table 1). The loading of triamine on MSP-N is as high as 1.21 mmol/g. This value is much higher than that of the octyl on MSP-O (0.80
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Figure 3. (A) Appearance of water-air biphase systems in the presence of MSP-O, MSP-N, MSP-NO(x) (x=40, 50, 60, 70, 80, 85, 90 respectively): (a) distribution of samples in the water, (b) after high shear mixing of the samples and water under air, (c) after adding HCl. (B) Optical micrographs of water-air biphase systems in the presence of MSP-O, MSP-N, MSP-NO(x): (b’) after high shear mixing of the samples and water under air, and (c’) after adding HCl. Scale bar = 300 μm. mmol/g). The reason for such a difference is that alkaline triamine has ability to self-catalyze the surface silylation.22 Notably, for the set of functionalized MSP-NO(x) samples, the determined loading of triamine gradually decreased and the determined loading of octyl gradually increased with x increasing, which is in accordance with the amounts of two organosilane added in experiment. Interestingly, the molar ratio of octyl to triamine gradually increases from 0.21 to 3.13 for the set of samples (the last column, Table 1). These results suggest that the surface chemistry can
be finely tuned in a wide range by changing the molar fractions of these two chosen organosilanes. 2.2. Interfacial Activity. We next examined the interfacial activity of the synthesized samples. After addition of 5 wt. % of the sample (with respect to water) into 1 g water, distinctive phenomena appear, as shown in Figure 3a. MSP-N precipitates at the bottom, whereas MSP-O totally floats on water. Remarkably, depending on the molar fraction of octyl groups (x), the states for MSP-NO(x) were classified into three scenarios. When x=40, the particles precipitate at the bottom, as with
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Figure 4. Three phase contact angles of modified MSP and the phase transition with the three phase contact angle. Scale bar = 300 µm. MSP-N. When increasing the molar fraction of octyl groups (x) up to 50, 60, the samples were partially dispersed in water. When further increasing x up to 70, 80, 85, 90, they were all floated on water. More interestingly, after high shear mixing of these mixtures under air for 3 min at 1800 rpm (with a magnetic stirrer bar), different appearances were observed (Figure 3b and 3b’). For MSP-N and MSP-NO(40), the systems are aqueous suspension in which the solid particles were totally dispersed. For MSP-NO(50), there is an gas-in-water phase (termed Pickering foam) in the upper layer. As shown in optical microscopy, the size of bubbles was mainly several tens of micrometers. For x between 60 and 80, the mixture became what researchers termed soufflé-like.60 As seen in Figure 3b’, the particles comprising it were more aggregated and sticky compared with those in the powder. For MSP-O and MSP-NO(x=85, 90), the ‘dry water’ was obtained since it looks like powders. The optical microscopy confirmed that the mixture was completely in the form of powders (without any residual water phase), of which the grain size ranges from thirty to one hundred micrometers. These results demonstrated that we could successfully achieve the phase transition from air-in-water (Pickering foams) to water-in-air (‘dry waters’) by tailoring the molar fraction of two organosilanes. The variation of the water contact angle (θ) (wettability) may account for the difference in dispersion and interfacial activity. The measured results are shown in Figure 4. We failed to measure the water contact angle of bare MSP because the water droplet
spread rapidly on the material pellets. This is the direct evidence for the extremely high hydrophilicity of MSP. The water contact angles of MSP-O and MSP-N were determined to be 138.5° and 24.5°, respectively, confirming that MSP-O and MSP-N are hydrophobic and hydrophilic, respectively. Interestingly, the water contact angles of the set of MSP-NO(x) (x=40, 50, 60, 70, 80, 85, 90) samples increase gradually from 52° to 123°. These values fall just in between the values of MSP-O and MSP-N, and the increase in water contact angle is due to the increase in the molar fraction of octyl groups. The remarkable distinctness in water contact angle reflects the difference in the wettability of our synthesized mesoporous silica particles. As we know, the particles with θ < 90° prefer to stay in water while those with θ > 90° prefer to stay in air rather than in water. For MSP-N and MSP-NO(40), the particles are so highly hydrophilic that they prefer to disperse in water. Being moderately hydrophilic, the MSP-NO(50) particles lead to Pickering foams. For MSP-NO(60), MSP-NO(70), and MSP-NO(80), the particles are partially hydrophobic, so that the soufflé-like mixture is generated. MSP-NO(85), MSP-NO(90) and MSP-O exhibit hydrophobicity, resulting in water drops in air (‘dry water’). The excellent ability to enable the phase transition from Pickering foams and ‘dry waters’ is attributed to the controllable interface activity from high hydrophility to high hydrophobicity. To further evaluate the interfacial activity of our synthesized mesoporous silica particles, we compared them with nonporous silica nanoparticles. For example,
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nonporous silica nanoparticles with a size of ca. 350 nm (Figure S4) are modified by the same amounts of octyl organosilane as for MSP-O. The three-phase contact angle is measured to be 139°, which is roughly equal to MSP-O. Then a mixture of water (1 g) and these nonporous silica nanoparticles (0.005 g) was stirred under air at the same stirring speed as for MSP-NO(x). Notably, the soufflé-like mixture was formed instead of ‘dry water’ (Figure S4). These results highlight the importance of the presence of large pores in large particles for preparing ‘dry water’. 2.3. pH Response. Interestingly, we further found that the particles-stabilized Pickering foams or ‘dry waters’ could be facilely disassembled by tuning the water pH. As Figure 3c and 3c’ shows, for the samples MSP-N, MSP-NO(40), MSP-NO(70), MSP-NO(80), MSP-NO(90) and MSP-O, their systems were unchanged after addition of a small amount of acid. Interestingly, Pickering foams stabilized by MSP-NO(50) underwent complete disassembly after adding acid (The impact of the functional groups on the surface of MSP-NO(x) on the pH value of the system was not considered here.), becoming a aqueous suspension. Moreover, ‘dry water’ stabilized by MSP-NO(85) disassembled upon addition of acid and the powdery water droplets turned into aggregated and sticky particles, as seen in Figure 3c’.
Notably, the formed soufflé-like mixture stabilized by MSP-NO(60) turned into Pickering foams, which could be confirmed by the optical microscopy (Figure 3c’). These investigations demonstrate that the careful choice of modification protocol is of importance for obtaining pH-responsive ‘dry waters’ and foams. The driving force for the disassembly in response to pH is the change of the surface’s hydrophilicity/hydrophobicity caused by protonation of the amine groups on the surface. The hydrophobicity of MSP-O is almost unchangeable because of the absence of a pH-sensitive moiety. As for relatively hydrophilic particles MSP-NO(50), the surface becomes high hydrophilic after protonating triamine groups, so the solid particles depart from the gas-water interface to the water phase. Similarly, the hydrophobicity of MSP-NO(85) turns into partially hydrophobicity, thus driving disassembly of ‘dry waters’ and becoming soufflé-like mixtures. To our knowledge, it is the first report that ‘dry water’ stabilized by inorganic materials is pH-responsive.
2.4. Carbon Dioxide Adsorption Performance. Carbon dioxide has drawn significant attention as one of the main anthropogenic contributors to climate change. For the capture of CO2, the most common adsorbents are aqueous alkanolamine solutions. However, this adsorbent suffers from several disadvantages in
Figure 5. Carbon dioxide adsorption test. (a) The appearance and (b) the optical microscopy image of ‘dry K2CO3-containing water’(45), where the number in the bracket refers to the concentration of potassium carbonate, stabilized by MSP-NO(85), (c) CO2 pressure drop with time, black: the K2CO3 solution under stirring (600 rpm); blue: the K2CO3 solution without stirring, red: ‘dry K2CO3-containing water’(45) without stirring, (d) comparison of CO2 uptake capacity in ‘dry K2CO3-containing water’(30), ‘dry K2CO3-containing water’(45) and ‘dry K2CO3-containing water’(52.5) with their bulk solution with and without stirring, (e) recycling results for the carbon dioxide adsorption of ‘dry K2CO3-containing water’(45), (f) optical microscopy image of ‘dry K2CO3-containing water’(45) after three recycles. Scale bar = 300 µm. Adsorption conditions: 1 g ‘dry K2CO3-containing water’, 40 oC, 0.2 MPa, 60 min.
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transport, the corrosion of the equipment and toxicity. In the context, ‘dry water’ could be a promising alternative for capturing CO2, benefitting transportation, dusting and low corrosivity. Moreover, the finely dispersed water droplet in ‘dry water’ could lead to enhanced adsorption kinetics as it has much higher surface-to-volume ratio than the bulk solutions. In order to verify the point above, a cheap potassium carbonate solution was chosen to prepare ‘dry K2CO3-containing water’ for CO2 capture. By vigorously stirring a mixture of 0.05 g of MSP-NO(85) and 1 g of 45 wt. % potassium carbonate solution, we successfully prepared ‘dry K2CO3-containing water’(45), where the number in the bracket refers to the concentration of potassium carbonate solution. The mechanical stability of ‘dry K2CO3-containing water’(45) was assessed by passing through a glass funnel under its own gravity. The photograph of the appearance virtually shows free-flowing powders with good mobility (Figure 5a). The optical micrograph of the samples after passing through the funnel further confirms the powders are intact in shape and in size, delivering high robustness (Figure 5b). CO2 captured by ‘dry K2CO3-containing water’ from simulated flue gas automatically (without stirring) proceeded under mild conditions (0.2 MPa and 40 oC). Based on the CO2 pressure drop with time (Figure 5c), one can find that the ‘dry K2CO3-containing water’ system showed remarkably enhanced uptake rate in comparison to the other two systems: bulk K2CO3 solution without stirring and bulk K2CO3 solution under stirring. The enhanced capture rate is attributed to the presence of ‘dry K2CO3-containing water’ powders that creates a large interface area available for CO2 capture. As listed in Figure 5d, the CO2 capture capacity of ‘dry K2CO3-containing water’(45) over a period of 1 hour reaches up to 8.86 wt. %, which is considerably larger than the bulk K2CO3 solution without stirring (0.85 wt. %) and the bulk K2CO3 solution under stirring (1.33 wt. %). The same trend is observed that the CO2 capture capacity of ‘dry K2CO3-containing water’ is better than the bulk solution with and without stirring whether the concentration of potassium carbonate solution is lower or higher (Figure 5d). Moreover, we found that the CO2 capture capacity of ‘dry K2CO3-containing water’(52.5) is less than ‘dry K2CO3-containing water’(45) because of some bigger and defective water droplets (Figure S5 in Supporting Information). These results clearly indicate that the resultant ‘dry K2CO3-containing water’ outperforms the conventional alkaline solution in CO2 capture. To evaluate the recyclability of ‘dry K2CO3-containing water’, the representative ‘dry K2CO3-containing water’(45) was desorbed under the constant flow of N2 at 100 oC for 60 min. As shown in Figure 5e, after desorption, the CO2 capture capacity of ‘dry K2CO3-containing water’(45) still reaches 5.70 wt. %, approximately 67% of the first adsorption. The decrease
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in adsorption capacity may be explained by an increase in the concentration K2CO3 solution because of the water loss during desorption, which is supported by the above result that the CO2 capture capacity of ‘dry K2CO3-containing water’(52.5) is less than that of ‘dry K2CO3-containing water’(45). In the third recycle the capture capacity of ‘dry K2CO3-containing water’(45) is 5.43 wt. %, which is almost close to the second recycle. Although the majority of powdery droplets after three recycles are slightly smaller than fresh ones because of slight loss of water, their shape and morphology are mostly maintained, as shown in Figure 5f and Figure S6. The results show clearly that the ‘dry water’ stabilized by the developed mesoporous silica particles is self-standing enough to sustain consecutive CO2 adsorption and desorption.
3. CONCLUSIONS In summary, we have successfully prepared large-sized, gas/water interface-active, mesoporous silica particles through modification with a mixture of hydrophobic octyl organosilane and hydrophilic triamine organosilane. Our synthesis protocol allows the phase transition from Pickering foams to ‘dry waters’ to be facilely achieved by tunning the interface-activity of mesoporous silica particles. Interestingly, these particles-stabilized foams and ‘dry waters’ could be disassembled in response to pH, due to the protonation of amines on the surface. Furthermore, the resultant ‘dry K2CO3-containing water’ was demonstrated to be an updated platform for CO2 capture. In comparison to bulk alkaline solutions, ‘dry K2CO3-containing water’ has significantly enhanced CO2 uptake capacity, faster kinetics, and is self-standing enough to sustain consecutive adsorption/desorption. We believe that the Pickering foams and ‘dry waters’ stabilized by the developed mesoporous silicas will be accessible to more innovative applications in colloidsome synthesis, gas absorption and catalysis.
ASSOCIATED CONTENT Supporting Information
Experimental details; Elemental analysis; N2 adsorption– desorption isotherms; TEM; The water contact angle; Optical microscopy image. This material is available free of charge via the Internet at http://pubs.acs.org.
Notes The authors declare no competing financial interests.
ACKNOWLEDGMENT This work is supported by the Natural Science Foundation of China (21573136 and U1510105), the foundation of the State Key Laboratory of Coal Conversions (INSTITUTE of COAL CHEMISTRY, No.J15-16-609), Program for the Key Research and Development Plan of Shanxi (201603D312003) and the
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(16) Dawson, R.; Stevens, L. A.; Williams, O. S. A.; Wang, W. X.; Carter, B. O.; Sutton, S.; Drage, T. C.; Blanc, F.; Adams, D. J.; Cooper, A. I. ‘Dry bases’: carbon dioxide capture using alkaline dry water. Energy Environ. Sci. 2014, 7, 1786−1791. doi:10.1039/c3ee44124e. (17) Du, K.; Glogowski, E.; Emrick, T.; Russell, T. P.; Dinsmore, A. D. Adsorption energy of nano- and microparticles at liquid-liquid interfaces. Langmuir 2010, 26, 12518−12522. doi:10.1021/la100497h. (18) Arbatan, T.; Li, L. Z.; Tian, J. F.; Shen, W. Liquid marbles as micro-bioreactors for rapid blood typing. Adv. Healthcare Mater. 2012, 1, 80−83. doi:10.1002/adhm.201100016. (19) Gao, W.; Lee, H. K.; Hobley, J.; Liu, T. X.; Phang, I. Y.; Ling, X. Y. Graphene liquid marbles as photothermal miniature reactors for reaction kinetics modulation. Angew. Chem. Int. Ed. 2015, 54, 3993−3996. doi:10.1002/anie.201412103. (20) Tian, J. F.; Arbatan, T.; Li, X.; Shen, W. Liquid marble for gas sensing. Chem. Commun. 2010, 46, 4734−4736. doi:10.1039/c001317j. (21) Wang, W. X.; Bray, C. L.; Adams, D. J.; Cooper, A. I. Methane storage in dry water gas hydrates. J. Am. Chem. Soc. 2008, 130, 11608−11609. doi:10.1021/ja8048173. (22) Huang, J. P.; Cheng, F. Q.; Binks, B. P.; Yang, H. Q. pH-Responsive gas-water-solid interface for multiphase catalysis. J. Am. Chem. Soc. 2015, 137, 15015−15025. doi:10.1021/jacs.5b09790. (23) Sheng, Y. F.; Sun, G. Q.; Wu, J.; Ma, G. H.; Ngai, T. Silica-based liquid marbles as microreactors for the silver mirror reaction. Angew. Chem. Int. Ed. 2015, 54, 7012−7017. doi:10.1002/anie.201500010. (24) Tian, J. F.; Arbatan, T.; Li, X.; Shen, W. Porous liquid marble shell offers possibilities for gas detection and gas reactions. Chem. Eng. J. 2010, 165, 347−353. doi:10.1016/j.cej.2010.06.036. (25) Park, J.; Shin, K.; Kim, J.; Lee, H.; Seo, Y.; Maeda, N.; Tian, W.; Wood, C. D. Effect of hydrate shell formation on the stability of dry water. J. Phys. Chem. C 2015, 119, 1690−1699. doi:10.1021/jp510603q. (26) Fletcher, P. D. I.; Holt, B. Controlled silanization of silica nanoparticles to stabilize foams, climbing films, and liquid marbles. Langmuir 2011, 27, 12869−12876. doi:10.1021/la2028725. (27) Bormashenko, E.; Pogreb, R.; Musin, A.; Balter, R.; Whyman, G.; Aurbach, D. Interfacial and conductive properties of liquid marbles coated with carbon black. Powder Technol. 2010, 203, 529−533. doi:10.1016/j.powtec.2010.06.019. (28) Bormashenko, E.; Bormashenko, Y.; Pogreb, R.; Gendelman, O. Janus droplets: liquid marbles coated with dielectric/semiconductor particles. Langmuir 2011, 27, 7−10. doi:10.1021/la103653p. (29) Kim, S. H.; Lee, S. Y.; Yang, S. M. Janus microspheres for a highly flexible and impregnable water-repelling interface. Angew. Chem. Int. Ed. 2010, 49, 2535−2538. doi:10.1002/anie.201000108. (30) Xue, Y. H.; Wang, H. X.; Zhao, Y.; Dai, L. M.; Feng, L. F.; Wang, X. G.; Lin, T. Magnetic liquid marbles: A "precise" miniature reactor. Adv. Mater. 2010, 22, 4814−4818. doi:10.1002/adma.201001898. (31) Zhao, Y.; Fang, J.; Wang, H. X.; Wang, X. G.; Lin, T. Magnetic liquid marbles: manipulation of liquid droplets using highly hydrophobic Fe3O4 nanoparticles. Adv. Mater. 2010, 22, 707−710. doi:10.1002/adma.200902512. (32) Zhang, S. G.; Zhang, Y.; Wang, Y.; Liu, S. M.; Deng, Y. Q. Sonochemical formation of iron oxide nanoparticles in ionic liquids for magnetic liquid marble. Phys. Chem. Chem. Phys. 2012, 14, 5132−5138. doi:10.1039/c2cp23675c.
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REFERENCES (1) Crossley, S.; Faria, J.; Shen, M.; Resasco, D. E. Solid nanoparticles that catalyze biofuel upgrade reactions at the water/oil interface. Science 2010, 327, 68−72. doi:10.1126/science.1180769. (2) Zhang, M.; Wei, L. J.; Chen, H.; Du, Z. P.; Binks, B. P.; Yang, H. Q. Compartmentalized droplets for continuous flow liquid-liquid interface catalysis. J. Am. Chem. Soc. 2016, 138, 10173−10183. doi:10.1021/jacs.6b04265. (3) Liang, F. X.; Shen, K.; Qu, X. Z.; Zhang, C. L.; Wang, Q.; Li, J. L.; Liu, J. G.; Yang, Z. Z. Inorganic Janus nanosheets. Angew. Chem. Int. Ed. 2011, 50, 2379−2382. doi:10.1002/anie.201007519. (4) Tu, F. Q.; Lee, D. Shape-Changing and Amphiphilicity-reversing Janus particles with pH-responsive surfactant properties. J. Am. Chem. Soc. 2014, 136, 9999−10006. doi:10.1021/ja503189r. (5) Liu, H.; Wang, C. Y.; Zou, S. W.; Wei, Z. J.; Tong, Z. Simple, reversible emulsion system switched by pH on the basis of chitosan without any hydrophobic modification. Langmuir 2012, 28, 11017−11024. doi:10.1021/la3021113. (6) Shan, Y. Y.; Yu, C.; Yang, J.; Dong, Q.; Fan, X. M.; Qiu, J. S. Thermodynamically stable pickering emulsion configured with carbon-nanotube-bridged nanosheet-shaped layered double hydroxide for selective oxidation of benzyl alcohol. ACS Appl. Mater. Interfaces 2015, 7, 12203−12209. doi:10.1021/acsami.5b02595. (7) Yang, H. Q.; Fu, L. M.; Wei, L. J.; Liang, J. F.; Binks, B. P. Compartmentalization of incompatible reagents within Pickering emulsion droplets for one-pot cascade reactions. J. Am. Chem. Soc. 2015, 137, 1362−1371. doi:10.1021/ja512337z. (8) Lam, S.; Blanco, E.; Smoukov, S. K.; Velikov, K. P.; Velev, O. D. Magnetically responsive Pickering foams. J. Am. Chem. Soc. 2011, 133, 13856−13859. doi:10.1021/ja205065w. (9) Xie, L.; Shi, C.; Cui, X.; Zeng, H. B. Surface forces and interaction mechanisms of emulsion drops and gas bubbles in complex fluids. Langmuir 2017, 33, 3911−3925. doi:10.1021/acs.langmuir.6b04669. (10) Guevara, J. S.; Mejia, A. F.; Shuai, M.; Chang, Y. W.; Mannan, M. S.; Cheng, Z. D. Stabilization of Pickering foams by high-aspect-ratio nano-sheets. Soft Matter 2013, 9, 1327−1336. doi:10.1039/c2sm27061g. (11) Binks, B. P.; Horozov, T. S. Aqueous foams stabilized solely by silica nanoparticles. Angew. Chem. Int. Ed. 2005, 117, 3788−3791. doi:10.1002/ange.200462470. (12) Schulze-Zachau, F.; Braunschweig, B. Structure of polystyrenesulfonate/surfactant mixtures at air-water interfaces and their role as building blocks for macroscopic foam. Langmuir 2017, 33, 3499−3508. doi:10.1021/acs.langmuir.7b00400. (13) Aussillous, P.; Quere, D. Liquid marbles. Nature 2001, 411, 924−927. doi:10.1038/35082026. (14) Yildirim, A.; Budunoglu, H.; Daglar, B.; Deniz, H.; Bayindir, M. One-pot preparation of fluorinated mesoporous silica nanoparticles for liquid marble formation and superhydrophobic surfaces. ACS Appl. Mater. Interface 2011, 3, 1804−1808. doi:10.1021/am200359e. (15) Rykaczewski, K.; Chinn, J.; Walker, M. L.; Scott, J. H. J.; Chinn, A.; Jones, W. Dynamics of nanoparticle self-Assembly into superhydrophobic liquid marbles during water condensation. Acs Nano 2011, 5, 9746−9754. doi:10.1021/nn203268e.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 11
ordered mesoporous silica-based materials. J. Am. Chem. Soc. 2006, 128, 8116−8117. doi:10.1021/ja062286z. (48) Clemments, A. M.; Botella, P.; Landry, C. C. Spatial mapping of protein adsorption on mesoporous silica nanoparticles by stochastic optical reconstruction microscopy. J. Am. Chem. Soc. 2017, 139, 3978−3981. doi:10.1021/jacs.7b01118. (49) Soler-Illia, G. J. A. A.; Azzaroni, O. Multifunctional hybrids by combining ordered mesoporous materials and macromolecular building blocks. Chem. Soc. Rev. 2011, 40, 1107−1150. doi:10.1039/c0cs00208a. (50) Argyo, C.; Weiss, V.; Brauchle, C.; Bein, T. Multifunctional mesoporous silica nanoparticles as a universal platform for drug delivery. Chem. Mater. 2014, 26, 435−451. doi:10.1021/cm402592t. (51) Paris, J. L.; Cabanas, M. V.; Manzano, M.; Vallet-Regi, M. Polymer-grafted mesoporous silica nanoparticles as ultrasound-responsive drug carriers. Acs Nano 2015, 9, 11023−11033. doi:10.1021/acsnano.5b04378. (52) Sinha, A.; Basiruddin, S. K.; Chakraborty, A.; Jana, N. R. β -Cyclodextrin functionalized magnetic mesoporous silica colloid for cholesterol separation. ACS Appl. Mater. Interfaces 2015, 7, 1340−1347. doi:10.1021/am507817b. (53) Xue, F.; Zhang, Y. B.; Zhang, F. W.; Ren, X. M.; Yang, H. Q. Tuning the interfacial activity of mesoporous silicas for biphasic interface catalysis reactions. ACS Appl. Mater. Interfaces 2017, 9, 8403−8412. doi:10.1021/acsami.6b16605. (54) Huo, C. L.; Li, M.; Huang, X.; Yang, H. M.; Mann, S. Membrane engineering of colloidosome microcompartments using partially hydrophobic mesoporous silica nanoparticles. Langmuir 2014, 30, 15047−15052. doi:10.1021/la503958d. (55) Fujii, S.; Yusa, S.; Nakamura, Y. Stimuli-responsive liquid marbles: controlling structure, shape, stability, and motion. Adv. Funct. Mater. 2016, 26, 7206−7223. doi:10.1002/adfm.201603223. (56) Nakai, K.; Fujii, S.; Nakamura, Y.; Yusa, S. Ultraviolet-light-responsive liquid marbles. Chem. Lett. 2013, 42, 586−588. doi:10.1246/cl.130119. (57) Sun, J. H.; Wei, W.; Zhao, D. H.; Hu, Q.; Liu, X. Y. Liquid marbles prepared from pH-responsive self-assembled micelles. Soft Matter 2015, 11, 1954−1961. doi:10.1039/c4sm02832e. (58) Sun, J. M.; Zhang, H.; Tian, R. J.; Ma, D.; Bao, X. H.; Su, D. S.; Zou, H F.. Ultrafast enzyme immobilization over large-pore nanoscale mesoporous silica particles. Chem. Commun. 2006, 1322−1324. doi:10.1039/b516930e. (59) Schmidt-Winkel, P.; Lukens, W. W.; Zhao, D. Y.; Yang, P. D.; Chmelka, B. F.; Stucky, G. D. Mesocellular siliceous foams with uniformly sized cells and windows. J. Am. Chem. Soc. 1999, 121, 254−255. doi:10.1021/ja983218i. (60) Binks, B. P.; Murakami, R. Phase inversion of particle-stabilized materials from foams to dry water. Nat. Mater. 2006, 5, 865−869. doi:10.1038/nmat1757.
(33) McHale, G.; Herbertson, D. L.; Elliott, S. J.; Shirtcliffe, N. J.; Newton, M. I. Electrowetting of nonwetting liquids and liquid marbles. Langmuir 2007, 23, 918−924. doi:10.1021/la061920j. (34) Bormashenko, E.; Pogreb, R.; Whyman, G.; Musin, A.; Bormashenko, Y.; Barkay, Z. Shape, vibrations, and effective surface tension of water marbles. Langmuir 2009, 25, 1893−1896. doi:10.1021/la8028484. (35) Hashmi, A.; Strauss, A.; Xu, J. Freezing of a liquid marble. Langmuir 2012, 28, 10324−10328. doi:10.1021/la8028484. (36) Dupin, D.; Armes, S. P.; Fujii, S. Stimulus-responsive liquid marbles. J. Am. Chem. Soc. 2009, 131, 5386−5387. doi:10.1021/ja901641v. (37) Fujii, S.; Suzaki, M.; Armes, S. P.; Dupin, D.; Hamasaki, S.; Aono, K.; Nakamura, Y. Liquid marbles prepared from pH-responsive sterically stabilized latex particles. Langmuir 2011, 27, 8067−8074. doi:10.1021/la201317b. (38) Fujii, S.; Kameyama, S.; Armes, S. P.; Dupin, D.; Suzaki, M.; Nakamura, Y. pH-responsive liquid marbles stabilized with poly(2-vinylpyridine) particles. Soft Matter 2010, 6, 635−640. doi:10.1039/b914997j. (39) Ueno, K.; Hamasaki, S.; Wanless, E. J.; Nakamura, Y.; Fujii, S. Microcapsules fabricated from liquid marbles stabilized with latex particles. Langmuir 2014, 30, 3051−3059. doi:10.1021/la5003435. (40) Subramaniam, A. B.; Abkarian, M.; Stone, H. A. Controlled assembly of jammed colloidal shells on fluid droplets. Nat. Mater. 2005, 4, 553−556. doi:10.1038/nmat1412. (41) Nonomura, Y.; Komura, S.; Tsujii, K. Adsorption of microstructured particles at liquid-liquid interfaces. J Phys Chem B 2006, 110, 13124−13129. doi:10.1021/jp0617017. (42) Wan, Y.; Zhao, D. Y. On the controllable soft-templating approach to mesoporous silicates. Chem. Rev. 2007, 107, 2821−2860. doi:10.1021/cr068020s. (43) Niu, D. C.; Li, Y. S.; Shi, J. L. Silica/organosilica cross-linked block copolymer micelles: a versatile theranostic platform. Chem. Soc. Rev. 2017, 46, 569−585. doi:10.1039/c6cs00495d. (44) Wei, J.; Sun, Z. K.; Luo, W.; Li, Y. H.; Elzatahry, A. A.; Al-Enizi, A. M.; Deng, Y. H.; Zhao, D. Y. New insight into the Synthesis of Large-Pore Ordered Mesoporous Materials. J. Am. Chem. Soc. 2017, 139, 1706−1713. doi:10.1021/jacs.6b11411. (45) Jiang, H. L.; Tatsu, Y.; Lu, Z. H.; Xu, Q. Non-, micro-, and mesoporous metal-organic framework isomers: reversible transformation, fluorescence sensing, and large molecule separation. J. Am. Chem. Soc. 2010, 132, 5586−5587. doi:10.1021/ja101541s. (46) Kruk, M.; Jaroniec, M. Gas Adsorption characterization of ordered organic-inorganic nanocomposite materials. Chem. Mater. 2001, 13, 3169−3183. doi:10.1021/cm0101069. (47) Balas, F.; Manzano, M.; Horcajada, P.; Vallet-Regi, M. Confinement and controlled release of bisphosphonates on
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