Article pubs.acs.org/cm
Versatile Surfactant/Swelling-Agent Template for Synthesis of LargePore Ordered Mesoporous Silicas and Related Hollow Nanoparticles Liang Huang† and Michal Kruk* Department of Chemistry, College of Staten Island, City University of New York, 2800 Victory Boulevard, Staten Island, New York 10314, United States Graduate Center, City University of New York, 365 Fifth Avenue, New York, New York 10016, United States S Supporting Information *
ABSTRACT: A surfactant/swelling-agent pair suitable for templating a variety of well-defined large-pore nanoporous silicas was identified. The pair includes a poly(ethylene oxide)poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, block copolymer surfactant (Pluronic F127, EO106PO70EO106) with a large fraction of long hydrophilic PEO blocks and a swelling agent (toluene) that strongly solubilizes in micelles of the PEO-PPO-PEO surfactant family. Such a combination affords micellar templates for both spherical and cylindrical mesopores with potential to hinder cross-linking of micelletemplated nanostructures due to stabilization of nanoparticles by long PEO chains. Under low-temperature conditions (11−12 °C), the Pluronic F127/toluene pair affords ultralarge-pore FDU-12 (ULP-FDU-12) silica with face-centered cubic structure of spherical mesopores and related hollow nanospheres, as well as large-pore SBA-15 (LP-SBA-15) with two-dimensional hexagonal structure of cylindrical mesopores and related silica nanotubes. ULP-FDU-12 reaches the unit-cell parameter of 69 nm, which is very large. LP-SBA-15 has a unit-cell parameter up to 26 nm and pore diameter up to ∼20 nm and is exceptionally well ordered. The hollow nanospheres and nanotubes are attainable through lowering of the silica-precursor/surfactant ratio. The materials templated by spherical micelles form when the surfactant/ swelling-agent solution is kept under stirring for extended periods of time before the addition of the silica precursor. The sizes of entrances to the hollow nanospheres can be continuously tuned by adjusting the hydrothermal treatment temperature. The ordered mesoporous silicas can be converted from open-pore to closed-pore materials through the thermally induced pore closing. The diversity in morphology, pore size, and pore connectivity makes the proposed surfactant/swelling-agent templating system unprecedented in the large mesopore domain.
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INTRODUCTION The surfactant-micelle-templated synthesis of ordered mesoporous solids1−15 has opened an avenue to a diverse family of well-defined materials with mesopores of diameter from 2 to ∼40 nm. The compatibility with many surfactant families1,3,13,16−18 and the structural robustness1,3,5,13,19 have placed silicas at the forefront of the ordered mesoporous materials development with respect to achievable structures,1,3−5,13,15,19−21 pore sizes,1,3,20−24 and pore connectivity,5,19,25,26 as well as surface functionalization.1,27 The micelletemplated periodically arranged voids in these materials may be cylinders1−3 or spheres of uniform size,3−5 networks with welldefined branching,1,20,28 or pores of two different sizes and similar5 or different29 shapes. The connecting micropores or/ and mesopores in the walls of the ordered mesopores19,30,31 of silicas templated by block copolymer surfactants (such as poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, commercially available as Pluronics) or oligomeric surfactants with hydrophilic blocks3 result in hierarchical pore systems, in which the ordered mesopores and their connections can both be tuned.25 Although the micelle © 2015 American Chemical Society
templating often gives rise to periodic silica nanostructures, it can also produce single-micelle-templated nanoporous entities, such as hollow nanospheres29,32−36 and nanotubes.35,37−40 This emerging strategy is an attractive addition to the current arsenal of strategies for the synthesis of hollow silica nanostructures, which includes hard templating by nanospheres,41−44 nanocubes,45 nanorods/nanotubes,46,47 and porous solids (including anodic aluminas),48,49 and soft templating by nanoemulsions,50 peptide (or other organic) nanofibers,51−55 and polymer brushes.56 While the applicability of some surfactants to template a variety of well-defined nanoporous silica morphologies is known, for instance, in the case of certain alkylammonium surfactants that can template two-dimensional (2-D) hexagonal, cubic, and lamellar structures,1 as well as closed-pore nanospheres,57 often a surfactant of a particular structure is selected to facilitate the formation of a desired pore Received: August 5, 2014 Revised: January 6, 2015 Published: January 12, 2015 679
DOI: 10.1021/cm5028749 Chem. Mater. 2015, 27, 679−689
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Chemistry of Materials morphology.3−5 This is particularly important in the large-pore domain (pore diameter above 12 nm),21−24,58−61 where the formation of a desired structure type with a sufficient degree of perfection has often been a challenge, no matter whether custom-made surfactants have been employed59 or common surfactants combined with micelle swelling agents23 have been utilized. High-molecular-weight block copolymer surfactants with a dominant fraction of hydrophilic blocks have been typically used to template large spherical mesopores,21,24,62 whereas high-molecular-weight surfactants with a major fraction of hydrophobic blocks have served as templates for large cylindrical mesopores.22,23 While the use of the swelling agents can dramatically change these considerations, allowing one to template spherical mesopores using a surfactant with a large proportion of hydrophobic domains as a microemulsion stabilizer,63 or cylindrical mesopores using a swollen surfactant with a large proportion of the hydrophilic blocks,64 these cases are less common and less predictable. Moreover, weakly ordered or disordered materials may form that way.63 Clearly, an approach in which a single surfactant can template a variety of large-pore silica morphologies would be highly desirable, especially as large-pore silicas are very useful as catalyst supports,65−69 adsorbents,70 templates for nanostructures,21 and media for immobilization of biomolecules.71,72 As discussed above, amphiphilic block copolymers, particularly the ones with hydrophilic poly(ethylene oxide), PEO, blocks are well-known as templates for ordered mesoporous materials.3,73 It is considered that in the case of silica-based materials, the framework forms primarily around the PEO blocks and thus is interpenetrated by them, allowing one to obtain mesoporous silicas with porous (typically microporous) walls.19 PEO blocks can be short, having several repeating units (as in the case of some oligomeric surfactants)3 or rather long, having 100 or more repeating units.3,29,74 Amphiphilic block copolymers with PEO blocks can also template individual or aggregated hollow nanoparticles, such as nanospheres34−36,75 or nanotubes,35,38,39 in the single-micelle-templating process mentioned above. It was considered that the PEO blocks on the periphery of the particles can afford the stabilization against aggregation and/or consolidation.35,76,77 At the same time, the framework is expected to form primarily in the PEO corona, as it is the case for ordered mesoporous materials.35 Block copolymers with longer PEO blocks are expected to be superior in the synthesis of single-micelle-templated nanoparticles, because such PEO blocks are more suitable as the environment for the framework condensation and the agent to stabilize the outer surface of the particle. In order to generate very large mesopores templated by large hydrophobic micelle cores, either surfactants with particularly long hydrophobic blocks are used59,78 or surfactants with quite large hydrophobic blocks assisted by micelle swelling agents are employed.21,23,24,60 The use of the swelling agents has an advantage of providing an opportunity to tune the volume ratio of the hydrophilic corona to the hydrophobic core of the micelles and thus opens an opportunity for the formation of micelles of different shapes, including spherical and cylindrical,79 especially if the swelling is significant. Therefore, it is postulated herein that a block copolymer surfactant with a large PEO block (or blocks) and a quite large hydrophobic block combined with a swelling agent that solubilizes strongly in the surfactant may template a variety of large-pore structures of ordered mesoporous materials and hollow nanoparticles. In addition, the large length of the hydrophilic block is expected to
lead to the formation of thick pore walls in the material, which is likely to make the material amenable to the thermally induced pore closing26,80 if the sample is not subjected to an extensive hydrothermal treatment. Therefore, not only open mesopores but also closed ones may be achievable in the considered case. Recently, we proposed that the synthesis of large-pore ordered mesoporous materials can be facilitated if a surfactant of choice is paired with a judiciously selected micelle swelling agent.23,24,60,62,81,82 The swelling agent can be selected from a series of compounds exhibiting gradually increasing extent of solubilization in a particular class of surfactants (see Supporting Information Scheme S1).23 For instance, alkylbenzenes with different number and/or size of alkyl substituents solubilize in common Pluronic PEO-PPO-PEO block copolymer surfactants to an extent that decreases as the size and/or number of alkyl substituents increases.83 A swelling agent should be selected for a particular surfactant in such a way that it solubilizes in the surfactant micelles to an appreciable, but not excessive, extent.23,24,60,82 These considerations paved an avenue to two-dimensional hexagonal SBA-15 silicas with ultralarge cylindrical mesopores of diameter up to ∼30 nm23,84 and large-pore periodic mesoporous organosilicas,60 as well as facecentered cubic FDU-12 silicas with ultralarge spherical mesopores of diameter up to ∼37 nm.24,62 This approach also afforded single-micelle-templated organosilica and silica nanospheres with fairly large mesopore interiors (up to ∼22 nm in diameter).35 Herein, it is shown that a block copolymer surfactant with a dominant fraction of long hydrophilic blocks combined with a micelle expander that solubilizes strongly in the surfactant micelles exhibits an unprecedented versatility as a template in the large-pore domain (pore diameter above 12 nm), allowing one to obtain highly ordered FDU-12 silicas with spherical pores and SBA-15 silicas with cylindrical pores (arranged in 2D hexagonal structure) (see Supporting Information Scheme S1), as well as hollow nanospheres and nanotubes. The resulting materials have widely tailorable mesopore size and accessibility.
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EXPERIMENTAL SECTION
Materials. Ultralarge-Pore FDU-12 Silica. In a typical synthesis procedure, 1.00 g of Pluronic F127 (EO106PO70EO106, BASF) (and KCl, if used) was dissolved in 60 mL of 2 M HCl in a glass container with magnetic stirring, then 3 mL of toluene was added, and the mixture was stirred at 350 rpm (or higher rate) at 12 °C for 1 day (or 2 days) in a covered container. Next, 4.5 g of tetraethyl orthosilicate (TEOS) was added. The reaction mixture was stirred in the covered container at 12 °C for 1 day, and then it was transferred to a polypropylene (PP) bottle, capped, and kept at 100 °C for 1 day. The product was filtered and dried in a vacuum oven at 60 °C. The assynthesized material was calcined at 550 °C under air for 5 h to remove the surfactant template. The resulting samples were denoted FT, where F represents FDU-12 and T is the initial synthesis temperature (in degrees Celsius). If a sample was prepared in the presence of an inorganic salt (KCl), the amount of the salt used (relative to 2.5 g per 60 mL of the HCl solution, which was used in syntheses of FDU-12 in the presence of xylenes24 and ethylbenzene62) is expressed in % and added to the name of the sample as FT-Sx (for instance, FT-S50 means that 1.25 g KCl was used). For samples prepared in the absence of the salt, the ending -S0 is omitted. In some cases, a part of the dried as-synthesized material was subjected to an acid treatment,21,24,85 in which 0.5 g of the as-synthesized sample was placed in 30 mL of 2 M HCl solution and heated at 130 °C in a Teflon-lined autoclave for 2 days. Then the materials were filtered, 680
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spherical mesopores of FDU-12 was also calculated using a geometrical relation involving the mesopore volume, Vp, the pore wall volume (the volume of silica, 1/ρ, plus the volume of micropores in the walls, Vmi), and the unit-cell parameter, a:88
dried, and calcined. The acid-treated samples are denoted FT-AT′, where A denotes the acid treatment and T′ indicates the treatment temperature in °C. One of the samples was prepared without a hydrothermal treatment or an acid treatment, and it is denoted FTL, where L stands for low temperature only. In the cases where a sample was calcined at different temperatures (from 550 to 800 °C), the calcination temperature in °C is noted at the end of the sample name. Large-Pore SBA-15 Silica. 1.00 g of Pluronic F127 was dissolved in 60 mL of 2 M HCl in a glass container with magnetic stirring at 11 °C, and then a mixture of 4.5 g of TEOS and 3 mL of toluene was added. The synthesis mixture composition was the same as in the case of large-pore FDU-12. The solution was stirred at 250 rpm at 11 °C for 1 day in a covered container, and then it was transferred to a PP bottle, capped, and kept at 100 °C for 1 day or transferred to a Teflon-lined autoclave and kept at 130 °C for 2 days. The product was filtered and dried in a vacuum oven at 60 °C. The as-synthesized material was calcined at 550 °C under air for 5 h to remove the template. The samples were denoted S-HT-t, where S represents SBA-15, H represents the hydrothermal treatment, T is the hydrothermal treatment temperature, and t denotes its duration in days. One of the samples was prepared without a hydrothermal treatment, and it is denoted ST′, where T′ denotes its calcination temperature in °C (550−800 °C). Hollow Silica Nanospheres. 1.00 g of Pluronic F127 was dissolved in 60 mL of 2 M HCl in a glass container with magnetic stirring, and then 3 mL of toluene was added and the mixture was stirred at 350 rpm at 12 °C for 2 days in a covered container. Next, 3.1 g of TEOS (31% lower mass than in the case of FDU-12; otherwise the composition was the same) was added. The reaction mixture was stirred in the covered container at 12 °C for 1 day, and then it was transferred to a PP bottle and kept at 100 °C or sealed in a Teflonlined autoclave and heated at 110−140 °C for 1 day. The product was filtered and dried in a vacuum oven at 60 °C. The as-synthesized material was calcined at 550 °C under air for 5 h. The samples are denoted HS-HT, where HS represents hollow sphere, H represents the hydrothermal treatment, and T is its temperature in °C. Silica Nanotubes. 1.00 g of Pluronic F127 was dissolved in 60 mL of 2 M HCl in a glass container with magnetic stirring, and then a mixture of 3 mL of toluene and 2.8 g of TEOS (38% lower mass than in the case of SBA-15; otherwise the composition was the same) was added. The solution was stirred at 250 rpm at 11 °C for 1 day in a covered container. Then the mixture was transferred to a PP bottle, capped, and kept at 100 °C for a day. The resulting gel was dried under compressed air flow (until its volume decreased 3−4 times) and further dried in a vacuum oven at 60 °C. The as-synthesized material was calcined at 550 °C under air for 5 h. Characterization. Small-angle X-ray scattering (SAXS) patterns were measured on a Bruker Nanostar U instrument equipped with Cu Kα radiation source (rotating anode operated at 50 kV, 24 mA) and Vantec-2000 two-dimensional detector. Samples were placed in the hole of an aluminum sample holder and secured with a Kapton tape. Nitrogen adsorption isotherms were acquired at −196 °C on a Micromeritics ASAP 2020 volumetric adsorption analyzer. Before the analysis, samples were outgassed at 200 °C in the port of the adsorption analyzer. Transmission electron microscopy (TEM) images were collected on FEI Tecnai Spirit microscope operated at 120 kV. Before the imaging, samples were sonicated in ethanol and drop-casted on a carbon-coated copper grid, and ethanol was allowed to evaporate. The BET specific surface area86 (SBET) was determined from nitrogen adsorption isotherm in the relative pressure range from 0.04 to 0.20. Total pore volume86 (Vt) was determined from the amount adsorbed at a relative pressure of 0.99. The micropore volume (Vmi) and the primary mesopore volume (Vp) were evaluated using the αs plot method, as described elsewhere.62 The pore size distribution (PSD) was determined from adsorption branches of the isotherms using the Barrett−Joyner−Halenda (BJH) method with the KJS correction for cylindrical mesopores (accurately calibrated for pores of diameter up to 7 nm).87 This method is known to underestimate the diameter of spherical mesopores24,62 and to overestimate the diameter of large cylindrical mesopores.23 Therefore, the diameter, wd, of ordered
⎛ 6 wd = a⎜ ⎜ πv ⎝
⎞1/3 ⎟ + Vp + Vmi ⎟⎠ Vp
1 ρ
(1)
where v is the number of pores in the unit-cell (4 for face-centered cubic structure) and a is the unit-cell parameter calculated on the basis of the position of the (311) peak (see below). The above relation does not take into consideration that some FDU-12 samples exhibit octahedral holes between the close-packed hollow-sphere building blocks.29 However, the volume of these pores does not appear to be large. The diameter of cylindrical mesopores of SBA-15 was calculated using the following equation (d100 is the (100) interplanar spacing):89
⎞1/2 ⎛ Vp ⎟ ⎜ wd = 1.213d100 1 ⎜ +V +V ⎟ p mi ⎠ ⎝ρ
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(2)
RESULTS AND DISCUSSION Selection of Surfactant/Swelling-Agent Pair. Herein, Pluronic F127 block copolymer (EO106PO70EO106) was selected, which is a commercially available surfactant with long hydrophilic PEO blocks and a rather large hydrophobic PPO block. This surfactant is widely known as a micellar template for the synthesis of materials with spherical mesopores, both periodic 3,31,90 and single-micelle-templated.34,35 While the uses of Pluronic F127 to template cylindrical mesopores or even gyroidal pore systems have been demonstrated,64,79 they have been rare. Herein, it is shown that the combination of Pluronic F127 with a powerful swelling agent, toluene, known to strongly solubilize in Pluronic surfactants,83 leads to unparalleled structural versatility in the large-mesopore domain. Synthesis of Ultralarge-Pore FDU-12 Silica Using Toluene as Swelling Agent. Toluene was predicted to solubilize in the micelles of Pluronic F127 to a greater extent than any other alkylbenzene.83 Because of the fact that Pluronic block copolymers with a rather low fraction of hydrophobic blocks (such as Pluronic F127, which has only ∼30 wt % of PPO) benefit from combining with swelling agents that solubilize strongly in the Pluronic micelles, toluene was expected by us to be a superior swelling agent in the synthesis of silicas with large spherical mesopores (such as FDU-12 silica21,24,62) when compared to other alkylaromatic swelling agents, such as trimethylbenzene (TMB)21 as well as xylene24 and ethylbenzene.62 However, our previous work showed that in the presence of an inorganic salt (KCl), which is used to facilitate the formation of a highly ordered block copolymertemplated product, xylene and ethylbenzene rendered ultralarge-pore FDU-12 silicas with particularly large unit-cell sizes,24,62 outperforming not only TMB but also toluene.24 This finding was inconsistent with our prediction and first associated with volatility of toluene.24 However, our work on the synthesis of periodic mesoporous organosilicas (PMOs) using Pluronic F127 and toluene showed that PMO formed in the presence of an appreciable concentration of an inorganic salt (KCl) had a moderate unit-cell size, which could be increased considerably by reducing the salt concentration.81 Therefore, the influence of the salt on the toluene-assisted synthesis of ULP-FDU-12 was examined at 14 °C with a silica 681
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the (311) reflection, because this position (and thus the corresponding interplanar spacing) was consistently related with the positions of other reflections (see Supporting Information Figures S2 and S3). On the other hand, the ratios of angular positions of the other peaks to the position of the strongest peak tended to decrease to some extent as the unitcell size increased, probably because the first peak was the (111) reflection overlapping with the (200) reflection,91 while the intensity of the latter increased as the unit-cell size increased (likely due to the increased pore-volume/pore-wallvolume ratio). For the considered samples, the (220) peak was either weak or not observed. The reason is not clear, but since relative peak intensities may depend on the ratio of the pore volume to the pore wall volume and on the type of periodic voids in the structure92 (here, spherical mesopores or the latter and octahedral holes), these factors are likely to contribute. The unit-cell enlargement for as-synthesized materials and the reduced shrinkage upon calcination with the decrease in the salt concentration resulted in a wide range of pore diameters in the large-pore domain (from 19 to 29 nm calculated using eq 1, see Supporting Information Table S1; BJH-KJS pore diameters were 16−25 nm, see Figure 2). It should be noted that as the amount of the salt was reduced and eventually the salt was eliminated, additional peaks appeared on the pore size distributions at ∼10 nm, which can be attributed to octahedral holes between close-packed hollow sphere building blocks in the material.29,91 The reduction of the shrinkage resulted in the increased pore volume of the materials (Supporting Information Table S1), as inferred from the increased adsorption capacity (Figure 2). On the basis of earlier studies of large-pore FDU-1221 and SBA-15 silicas 23 templated by Pluronic surfactants at subambient temperature in the presence of swelling agents, a further increase in the unit-cell size was attempted through a decrease in the initial synthesis temperature. When the temperature was lowered to 12 °C, the increase in the unitcell size was observed, but the synthesis was not fully reproducible in terms of the unit-cell size, and in some cases, a contamination with 2-D hexagonal silica (SBA-15) was observed. The increase in the stirring rate to 370−450 rpm (from 350 rpm) improved the reproducibility to an extent that good-quality FDU-12 materials were obtained 2−3 times more often than the materials significantly contaminated with SBA15. One of the well-ordered FDU-12 silicas (obtained with stirring rate of 450 rpm and denoted F12-U) obtained that way exhibited the unit-cell parameter of 67 nm for as-synthesized sample (see Supporting Information Figure S4) and pore diameter of 38 nm (Supporting Information Table S1). It should be noted that our sample exhibited the capillary condensation relative pressure (0.932; Supporting Information Figure S5) that was nearly the same as that of the carbon with spherical mesopores of diameter estimated as 40 nm based on the size of the template used to generate them and as 38 nm based on nitrogen adsorption data using DFT kernel for spherical mesopores.93 This comparison additionally confirms the reliability of our pore size assessment using eq 1. An appreciable unit-cell parameter decrease (10%) upon calcination was observed for the sample hydrothermally treated at 100 °C for 1 day (see Supporting Information Table S1). However, the shrinkage was reduced to 1% by using an acid treatment at 130 °C for 2 days and this allowed us to synthesize a sample with an exceptionally large unit-cell parameter of 68 nm and the pore diameter of 47 nm, as calculated using eq 1
precursor (TEOS) added 1 day after the introduction of toluene and the stirring rate of 350 rpm. When the salt concentration was lowered, the unit-cell parameter and the pore size systematically increased (see Figures 1 and 2 and
Figure 1. Small-angle X-ray scattering patters for calcined FDU-12 silicas formed at 14 °C in the presence of toluene and different amounts of KCl or in the absence of KCl.
Figure 2. (left) Pore size distributions and (right) nitrogen adsorption isotherms of FDU-12 silicas formed at 14 °C in the presence of toluene and different amounts of KCl or in the absence of KCl. The isotherms for F14−S50, F14−S25, and F14 were offset vertically by 100, 300, and 450 cm3 STP g−1, respectively, to facilitate comparison.
Supporting Information Figure S1 and Table S1). FDU-12 silica obtained in the absence of the salt had a unit-cell parameter of 52.8 nm (for the as-synthesized sample), which is large, and the sample still exhibited highly ordered facecentered cubic structure (see SAXS patterns in Supporting Information Figures S1 and S2). The decrease in the salt concentration brought not only the unit-cell increase but also the decrease in shrinkage upon calcination (see Figure 1 and Supporting Information Table S1). In the case of samples hydrothermally treated at 100 °C for 1 day, the shrinkage (defined as the unit-cell parameter decrease) was 17% at a salt concentration typically used in FDU-12 synthesis, but it was reduced to 10% when the salt was not employed. It should be noted that the unit-cell parameter for the face-centered cubic FDU-12 structure was determined from the angular position of 682
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Chemistry of Materials (see Supporting Information Table S1 and Figures S4−S6; BJH-KJS pore diameter was 39.5 nm). These unit-cell sizes are significantly larger than those attained for face-centered cubic mesoporous silica powders prepared with any previously reported swelling agents (up to ∼56 nm, as calculated on the basis of the position of the first peak on SAXS patters;24,62 up to ∼58 nm, if the position of (311) peak is used) or with custom-made surfactants (up to ∼59 nm).58,69 Only a facecentered cubic thin film was recently reported on the basis of grazing incidence SAXS to have a larger unit-cell size (∼100 nm),94 but its adsorption properties were not characterized. TEM images of another FDU-12 sample with very large unitcell size (Supporting Information Figure S6; this sample was obtained with the stirring rate of 350 rpm) confirmed a highly ordered structure of the FDU-12 silica, but a minor contamination with 2-D hexagonal structure was seen (even though it was not apparent from SAXS and N2 adsorption). There was also some evidence of the presence of the hexagonal close-packed intergrowth in the material (see Supporting Information Figure S6),30,95,96 which is a common feature of silicas with cubic close-packed structures.30,96 No peaks related to the hexagonal close-packed structure were seen in SAXS patterns, which suggests that the population of this structure was minor. When the initial step of the synthesis was performed at 12 °C and TEOS was added 2 days (instead of one) after the addition of toluene or a small amount of KCl (0.125−0.25 g per 1 g Pluronic F127) was added to the synthesis mixture, the reproducibility of the synthesis was very good. In particular, when the time interval between the addition of toluene and TEOS was 2 days, FDU-12 silica with the unit-cell parameter of 60 nm (for as-synthesized sample; see Supporting Information Table S1 and Figure S7) was obtained. After calcination, the unit-cell parameter was 55 nm. The sample exhibited the pore diameter of 34 nm, as calculated using eq 1. Synthesis of Ultralarge-Pore SBA-15 Silica. As discussed above, the interval between the addition of toluene and TEOS was found to have an impact on the phase purity of the product in the synthesis of ULP-FDU-12. When TEOS was added 24 h or more after the addition of toluene, FDU-12 with facecentered cubic (fcc) structure of spherical mesopores was obtained even if there could be a contamination with the 2-D hexagonal structure, as inferred from TEM, but not apparent in SAXS and nitrogen adsorption (and thus expected to be minor). When the interval between addition of the swelling agent and the silica precursor was decreased, a mixture of facecentered cubic and 2-D hexagonal structures was observed (Supporting Information Figure S8). An almost pure 2-D hexagonal phase, as inferred from SAXS, was synthesized when TEOS was added together with toluene (Supporting Information Figure S8). When the initial synthesis temperature was lowered to 11 °C and the stirring rate was decreased to 250 rpm (from 350 rpm), SBA-15 silica with a highly ordered 2-D hexagonal structure was recovered, as seen from the appearance of four or more peaks on its small-angle X-ray scattering pattern (Figure 3). In fact, some of the higher-order reflections observed for this material are rarely seen for SBA-15 and were only sporadically reported for 2-D hexagonal MCM-41 silicas.97 The material hydrothermally treated at 100 °C for 1 day exhibited the BET specific surface area of 540 m2/g, the total pore volume of 0.55 cm3/g, the mesopore volume of 0.29 cm3/g, and the micropore volume of 0.19 cm3/g. There was a steep capillary condensation step on its nitrogen adsorption isotherm (Figure 4), which
Figure 3. Small-angle X-ray scattering patters for SBA-15 silicas formed at 11 °C. The samples were hydrothermally treated at 100 or 130 °C. AS and C denote as-synthesized and calcined samples.
Figure 4. (left) Nitrogen adsorption isotherms and (right) pore size distributions for calcined SBA-15 formed at 11 °C and hydrothermally treated at 100 and 130 °C.
revealed a narrow pore size distribution (wKJS = 16.7 nm; wd = 13.6 nm), but the adsorption−desorption hysteresis loop was broad and the desorption was primarily at the lower limit of adsorption−desorption hysteresis (relative pressure of ∼0.50), thus suggesting that the entrances to the cylindrical mesopores were of diameter below 5 nm.98 It is known that the cylindrical mesopores of SBA-15 can be capped or plugged,80 so the small entrance size is expected to be related to such structural features (while additional insight can be gained from the inspection of related silica nanotubes, see below). The material exhibited a (100) interplanar spacing, d100, of 20.1 nm, which is exceptionally large for such highly ordered SBA-15. The d100 value for as-synthesized material was even larger (22.5 nm). A hydrothermal treatment at 130 °C eliminated the constrictions and allowed us to obtain a highly ordered SBA-15 with a narrow hysteresis loop on its adsorption isotherm and with a BJH-KJS pore diameter of 23.1 nm and d100 of 22.2 nm (22.8 nm for as-synthesized sample). The material exhibited the BET specific surface area of 343 m2/g, the total pore volume of 0.91 cm3/g, the mesopore volume of 0.78 cm3/g, and a very low micropore volume of 0.01 cm3/g. As the BJH-KJS method overestimates the size of cylindrical mesopores in the considered range, eq 2 was used to render a more accurate pore diameter estimate of 21.3 nm, which is very large as for highly ordered SBA-15.23,84 The ordered structure of the material was clearly seen in TEM images (Supporting Information Figure S9). It should be noted that the images suggested a slight contamination of the material with hollow spheres (individual or their clusters, either ordered or disordered), primarily on the sides of elongated particles of SBA-15. However, SAXS patterns for samples prepared under 683
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Chemistry of Materials optimized conditions only featured peaks that could be rigorously indexed as peaks of 2-D hexagonal structure and the background at low angles was much lower than the peak intensity, which suggests that the content of the impurity was low. Moreover, the peak on the pore size distribution was narrow and additional peaks were absent in the relevant pore size range, which confirms the conclusion based on the SAXS patterns. Synthesis of Hollow Silica Nanospheres. The singlemicelle-templated hollow silica spheres were synthesized through the reduction of the ratio of the silica precursor (TEOS) to the surfactant template (Pluronic F127), following an approach proposed by us earlier and demonstrated to be successful, primarily for organosilicas.35 Following the synthesis procedure for ultralarge-pore FDU-12 that was outlined above, but with reduced amount of TEOS (to 69%), hollow silica nanospheres were obtained. The SAXS patterns for these materials (Supporting Information Figure S10) featured multiple broad peaks and were similar to the SAXS patterns reported for uniform single-micelle-templated nanospheres.35 TEM images (Figure 5 and Supporting Information Figure
Figure 6. Nitrogen adsorption isotherms and pore size distributions for hollow silica nanospheres prepared with different hydrothermal treatment temperatures. The isotherms for samples hydrothermally treated at 110, 120, 130, and 140 °C were offset vertically by 550, 1100, 1750, and 2350 cm3 STP g−1.
capillary condensation between the loosely arranged spherical particles. The specific surface areas, total pore volumes, micropore volumes, and pore sizes of the materials are listed in Supporting Information Table S2. It is notable that the hollow nanospheres have an unusually large pore diameter (36−48 nm; Figure 6) as for single-micelle-templated materials. Their inner diameter exceeded those attained earlier with Pluronics and custom-made block copolymer templates.35,36,61 Adjustment of Entrances to Hollow Nanospheres. While the size of pores in shells of relatively large nanospheres (∼200 nm in diameter) can be controlled in a wide range (3− 13 nm) in the selective etching process99,100 and the tunability of the entrance size to vesicle-templated silicas was recently achieved through a hydrothermal treatment,101 the ability to widely tune the entrance sizes to single-micelle-templated nanospheres has not been reported to our knowledge. In the case of the spherical mesopores of ordered silicas, the connections become larger as the temperature or duration of the hydrothermal treatment increases.25,30,31 Herein, a similar pore entrance adjustability for single-micelle-templated silica nanoparticles is demonstrated. The hollow silica nanospheres obtained after the hydrothermal treatment at 100 °C exhibited a broad adsorption−desorption hysteresis loop with a capillary evaporation step at the lower limit of adsorption−desorption hysteresis (relative pressure ∼0.50; see Figure 6), indicating that the entrances to their interiors were of diameter below ∼5 nm, if one estimates the entrance size on the basis of capillary evaporation pressure, comparing it to the capillary evaporation pressure for uniform cylindrical mesopores.98 As the temperature of the hydrothermal treatment was increased from 100 to 140 °C, the capillary evaporation step gradually shifted to much higher relative pressures and the hysteresis loops evolved from broad to narrow. This behavior indicates a significant enlargement in the nanoparticle entrance sizes (that is, dimensions of gaps in the nanoparticle shell, see below) from diameter below ∼5 nm to that close to the size of the interiors of the nanoparticles (the latter being inferred from the narrowness of the hysteresis loop for the sample treated at 140 °C). The observed pore entrance size adjustability is likely to be related to the aggregation of PEO chains in the silica framework as the temperature increases and/or the hydrothermal treat-
Figure 5. Transmission electron microscopy images of silica nanospheres prepared using Pluronic F127 surfactant and toluene as a swelling agent. The hydrothermal treatment temperature was (top left) 100 °C, (top right) 130 °C, and (bottom) 140 °C. Arrows point to gaps in the walls, that is, entrances to the nanospheres.
S11) clearly showed uniform nanospheres of large diameter, which formed loose aggregates with no periodicity. The capillary condensation steps centered at relative pressures of 0.94−0.96 on the adsorption isotherms (Figure 6) were related to the filling of the uniform spherical mesopores and the subsequent significant uptake close to the saturation vapor pressure (relative pressure of 1) can be attributed to the 684
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Chemistry of Materials ment is prolonged,25,30 thus being generally valid for the considered single-micelle-templated silica nanoparticles and the micelle-templated ordered mesoporous silicas. The enlargement in the size of the pore entrances was visualized by TEM (Figure 5). Images of hollow spherical nanoparticles hydrothermally treated at 130 °C and especially 140 °C showed more openings and/or larger openings in the nanosphere walls than for nanospheres treated at 100 °C (Figure 5). The openings were not uniform in size and shape and did not exhibit any regular arrangement on the nanoparticle surface. This insight is likely to be relevant to not only the spherical nanoparticles but also ordered mesoporous silicas. It needs to be pointed out that the occurrence of the capillary evaporation in a quite narrow relative pressure range (Figure 6) suggests that the size distribution of largest entrances to individual nanospheres is not particularly broad, which parallels an earlier work on ordered mesoporous silicas.25,102 As the pore entrance size dramatically increased with the temperature of the hydrothermal treatment, the pore diameter increased to some extent (from 36 to 48 nm, see Figure 6 and Supporting Information Table S2). It should be noted that, in the case of nanospheres prepared at different temperatures, pieces of broken or malformed nanospheres appeared to be visible. Additional work will be required to understand if the sonication used to disperse the nanoparticles leads to their damage. Synthesis of Hollow Silica Nanotubes. The hollow silica nanotubes (Figure 7 and Supporting Information Figure S12) were prepared by employing the synthesis conditions suitable for SBA-15 (11 °C; 250 rpm; TEOS added together with toluene), but with the ratio of TEOS to Pluronic F127 lowered to 62%. For a sample hydrothermally treated at 100 °C for 1 day, a mostly narrow adsorption−desorption hysteresis loop on the isotherm with a tail toward lower pressures (Figure 8) indicated that most nanotube interiors were without any major constrictions, although some were accessible through narrower entrances. A significant nitrogen uptake close to the saturation vapor pressure (Figure 8) can be attributed to the capillary condensation between loosely arranged nanotubes (see Figure 7). The silica nanotubes exhibited high specific surface area of 694 m2/g, the total pore volume of 2.20 cm3/g, the micropore volume of 0.06 cm3/g, and an unusually large BJH-KJS pore diameter of 19.9 nm. When the hydrothermal treatment was not employed, the adsorption isotherm (Figure 8) featured a broad hysteresis loop akin to that for the SBA-15 silica hydrothermally treated at 100 °C (Figure 4). The broadness of the hysteresis loop indicated that the nanotubes prepared at low temperature had narrow entrances and/or constrictions. Clearly, the hydrothermal treatment enlarged the entrances to the mesopores. SAXS patterns of the material before and after calcination revealed weak ordering (Supporting Information Figure S13). TEM images (Figure 7 and Supporting Information Figure S12) showed nanotubes, which were long (up to several micrometers) for as-synthesized sample prepared at low temperature only. However, the nanotubes aggregated and/or broke into short pieces during the calcination (and/or perhaps sonication). A surface modification of surfactant-containing nanotubes with trimethylchlorosilane to introduce trimethylsilyl (TMS) groups helped to improve the integrity of the silica nanotubes and to reduce the aggregation of these nanoparticles (Figure 7; the corresponding nitrogen adsorption characterization results are shown in Supporting Information Figure
Figure 7. Transmission electron microscopy images of silica nanotubes prepared using Pluronic F127 surfactant and toluene as a swelling agent. (top) As-synthesized sample prepared without a hydrothermal treatment; (middle) calcined (550 °C) sample prepared with hydrothermal treatment; (bottom) sample prepared without hydrothermal treatment, stabilized through the surface modification, and then calcined at 300 °C. 685
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pore FDU-12 silicas were prepared earlier through the thermally induced pore closing process. The pore-closing temperature was 400−650 °C for FDU-12 prepared in the presence of TMB as the swelling agent26,106 and 400−450 °C for FDU-12 prepared using ethylbenzene or xylene.24,62 In these earlier cases, a significant concentration of an inorganic salt (KCl) was present in the synthesis mixture. A higher pore closing temperature observed herein may be due to the lower extent of shrinkage during calcination at a particular temperature for the sample prepared in the absence of the salt. The closed-pore FDU-12 silicas retained a highly ordered facecentered cubic structure, as seen from SAXS (Supporting Information Figure S15) and TEM (Supporting Information Figure S16). As seen in Supporting Information Figure S15, the calcination at temperatures up to 800 °C did not decrease the resolution of SAXS patterns, even though SAXS peaks shifted to higher 2θ angles as the calcination temperature increased, indicating the decrease in the unit-cell size. The lowering of the unit-cell parameter by 18−19%, which was observed after calcination at 550−650 °C, was not accompanied by the pore closing (as seen from nitrogen adsorption isotherms and pore size distributions, see Supporting Information Figure S15), but the shrinkage of 24−25% observed after calcination at 750−800 °C was accompanied by complete (or nearly complete) mesopore closing. It should be noted that the considered ULP-FDU-12 appears to be a closed-packed array of hollow nanospheres that had octahedral holes between the nanospheres.29,91 The octahedral holes are likely to correspond to a peak at ∼9 nm (Supporting Information Figure S15), whereas the spherical mesopores (inside the spherical building blocks) correspond to the peak at 21−22 nm on the pore size distributions. It is interesting that the closing of the spherical mesopores (as seen from the disappearance of the peak at ∼20 nm) was accompanied by the loss of the peak corresponding to the octahedral holes, indicating their inaccessibility to nitrogen or elimination through sintering. The ordered mesopores of the ULP-FDU-12 sample calcined at 800 °C were clearly visible by TEM (Supporting Information Figure S16). The relatively high pore closing temperature observed for the present FDU-12 sample suggests that the presence of inorganic salts in the synthesis mixtures reported earlier24,62 (and presumably the presence of the salt’s residue in the final materials) promotes the shrinkage upon calcination and leads to the pore closing at a lower temperature. Synthesis of Closed-Pore SBA-15 Silica. For a large-pore SBA-15 silica templated by Pluronic P123 (EO20PO70EO20) and 1,3,5-triisopropylbenzene, the pore closing was at 950 °C.80 The constrictions existing in the channels and caps at the ends of the cylindrical pores were suggested to contribute to the pore-closing of SBA-15 silicas. For the highly ordered SBA-15 silicas prepared using Pluronic F127 and toluene, as described earlier herein, but at low temperature only (without the hydrothermal treatment), the mesopores were nearly completely closed at a much lower temperature of 700−750 °C. The total pore volume and BET specific surface area decreased from 0.22 cm3/g and 236 m2/g, respectively, for the sample calcined at 550 °C to 0.07 cm3/g and 53 m2/g, respectively, for the sample calcined at 700 °C (see adsorption isotherms in Supporting Information Figure S17), and even much lower adsorption was observed for the sample calcined at 750 °C, indicating nearly no pores accessible to nitrogen molecules. However, the highly ordered 2-D hexagonal structure was preserved (see SAXS patterns in Supporting Information Figure
Figure 8. Nitrogen adsorption isotherms and pore size distributions for silica nanotubes prepared without and with hydrothermal treatment.
S14). For some nanotubes, round ends with somewhat higher diameter than the diameter along the tubes were observed, which is consistent with earlier experimental and theoretical studies of worm-like micelles103,104 and with our TEM observation of individual cylindrical mesopores for large-pore SBA-15 silicas80 and related organosilicas.60 Some nanotubes exhibited undulations close to their ends. A small fraction of hollow nanospheres was also present, perhaps as a result of a budding process104 that resulted in the fragmentation of the nanotubes to nanospheres, being additionally supported by the occurrence of the aforementioned undulations. Hemispherelike tips of nanotubes accompanied by nanospheres were reported by others in the case of silica nanotubes templated by poly(ethylene oxide)-polystyrene block copolymers, but they were attributed to nanospheres being building blocks for the nanotubes,40 which follows the work on elucidation of early stages of regular SBA-15 synthesis.105 It is suggested herein that the nanotubes templated by cylindrical micelles fragment into nanospheres, which does not preclude the possibility of the nanotube assembly from nanospheres at earlier stages of the synthesis. On the basis of the fact that under the conditions reported herein, SBA-15 and nanotubes are obtained in the case of slower stirring and/or shorter stirring time, while FDU-12 and nanospheres are obtained in the case of faster stirring and longer stirring times, it is proposed that the fragmentation of the cylindrical-micelle-templated nanotubes to the sphericalmicelle-templated nanospheres is facilitated or perhaps even caused by the shear force. As mentioned above, the silica nanotubes formed under conditions similar to those for SBA-15 silicas but at a lower relative amount of the framework precursor. Therefore, it is likely that the TEM observation of the nanotubes provides insight into the structure of building blocks that get together in the process of formation of SBA-15 (at least under the conditions studied herein). In particular, the building blocks of SBA-15 may have closed ends, which are restructured or lost at later stages of the synthesis, especially during the hydrothermal treatment. The ability to close the cylindrical mesopores of SBA-15 (demonstrated earlier80 and also discussed hereafter) is consistent with the above postulate. Synthesis of Closed-Pore FDU-12 Silica. The possibility of converting FDU-12 prepared under salt-free conditions studied herein to a closed-pore silica (that is, a material with mesopores inaccessible to nitrogen molecules) was evaluated by selecting a sample prepared at low temperature only (without hydrothermal treatment). The closed-pore material was obtained after calcination at 750 °C as inferred from nitrogen adsorption data (Supporting Information Figure S15). Closed686
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S17). The calcinations at 550−800 °C led to the (100) interplanar spacing decrease of 21−22% in comparison to d100 of the as-synthesized sample (20.3 nm). TEM clearly showed the retention of the periodic porous structure in this material (Supporting Information Figure S18), even though its pores were nearly inaccessible. It was argued elsewhere80 that the possibility of thermally induced closing of cylindrical mesopores arises because of the presence of caps at the mesopore ends and/or constrictions (porous plugs) in the mesopores. It is known that a transformation from spherical to cylindrical micelles and the elongation of the latter is involved in the formation of normal SBA-15.107 It can be hypothesized that entities present at early stages of the considered SBA-15 synthesis are similar in shape to the nanotubes that were described above but perhaps have lower aspect ratio. In general, it is expected that at early stages of the synthesis, the silicas (or organosilicas) templated by block copolymer−surfactant micelles exhibit mesopores closed in a sense that they are separated from the surroundings through a microporous wall in which the micropores (or small mesopores) are templated by PEO blocks of the surfactant. If such a structure is calcined, the mesopores (voids once occupied by hydrophobic cores of the micelles, that is, PPO domains) are accessible through the micropores (or small mesopores). This structure makes the mesopores susceptible for the thermally induced mesopore closing, which was documented herein and in previous studies.24,26,62,81
ACKNOWLEDGMENTS NSF is gratefully acknowledged for partial support of this research (Award DMR-0907487) and for funding the acquisition of the SAXS/WAXS system through Award CHE0723028. Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research (Award PRF No. 49093-DNI5). The Imaging Facility at CSI is acknowledged for providing access to TEM. Mr. Amanpreet S. Manchanda, CSI, is acknowledged for acquiring TEM images of some samples. BASF is acknowledged for the donation of the Pluronic F127 block copolymer. The investigation of the tailoring of entrances to the nanospheres was stimulated by the discussion with Professor Shuiqin Zhou, CSI.
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CONCLUSIONS The combination of an amphiphilic block copolymer surfactant having a dominant fraction of the long hydrophilic moieties with a micelle expander that strongly solubilizes in micelles is suitable as a template for the synthesis of a variety of welldefined large-pore silica nanostructures. Face-centered cubic arrays of spherical mesopores can be obtained, as well as highly ordered honeycomb structures. These two distinct large-pore morphologies can be obtained in open-pore and closed-pore variants. A decrease in the silica to surfactant ratio suppresses the consolidation into periodic structures and allows one to recover silica nanotubes and aggregated hollow nanospheres. The access to hollow nanospheres and nanotubes can be tuned through the hydrothermal treatment. These results provide access to very useful materials and conceptual understanding of how synthesis protocols to access these classes of materials can be designed. ASSOCIATED CONTENT
S Supporting Information *
Scheme. Tables with structural parameters. Figures with experimental SAXS patterns, nitrogen adsorption isotherms, and pore size distributions. TEM images. This material is available free of charge via the Internet at http://pubs.acs.org.
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REFERENCES
(1) Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T. W.; Olson, D. H.; Sheppard, E. W.; McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. J. Am. Chem. Soc. 1992, 114, 10834. (2) Inagaki, S.; Fukushima, Y.; Kuroda, K. J. Chem. Soc., Chem. Commun. 1993, 680. (3) Zhao, D.; Huo, Q.; Feng, J.; Chmelka, B. F.; Stucky, G. D. J. Am. Chem. Soc. 1998, 120, 6024. (4) Huo, Q.; Leon, R.; Petroff, P. M.; Stucky, G. D. Science 1995, 268, 1324. (5) Sakamoto, Y.; Kaneda, M.; Terasaki, O.; Zhao, D. Y.; Kim, J. M.; Stucky, G.; Shin, H. J.; Ryoo, R. Nature 2000, 408, 449. (6) Attard, G. S.; Bartlett, P. N.; Coleman, N. R. B.; Elliott, J. M.; Owen, J. R.; Wang, J. H. Science 1997, 278, 838. (7) Braun, P. V.; Osenar, P.; Stupp, S. I. Nature 1996, 380, 325. (8) Sun, T.; Ying, J. Y. Nature 1997, 389, 704. (9) Tian, Z.-R.; Tong, W.; Wang, J.-Y.; Duan, N.-G.; Krishnan, V. V.; Suib, S. L. Science 1997, 276, 926. (10) Tanaka, S.; Nishiyama, N.; Egashira, Y.; Ueyama, K. Chem. Commun. 2005, 2125. (11) Meng, Y.; Gu, D.; Zhang, F.; Shi, Y.; Yang, H.; Li, Z.; Yu, C.; Tu, B.; Zhao, D. Angew. Chem., Int. Ed. 2005, 44, 7053. (12) Yang, P.; Zhao, D.; Margolese, D. I.; Chmelka, B. F.; Stucky, G. D. Nature 1998, 396, 152. (13) Che, S.; Garcia-Bennett, A. E.; Yokoi, T.; Sakamoto, K.; Kunieda, H.; Terasaki, O.; Tatsumi, T. Nat. Mater. 2003, 2, 801. (14) Che, S.; Liu, Z.; Ohsuna, T.; Sakamoto, K.; Terasaki, O.; Tatsumi, T. Nature 2004, 429, 281. (15) Han, Y.; Zhang, D.; Chng, L. L.; Sun, J.; Zhao, L.; Zou, X.; Ying, J. Y. Nat. Chem. 2009, 1, 123. (16) Tanev, P. T.; Pinnavaia, T. J. Science 1995, 267, 865. (17) Attard, G. S.; Glyde, J. C.; Goltner, C. G. Nature 1995, 378, 366. (18) Goltner, C. G.; Berton, B.; Kramer, E.; Antonietti, M. Chem. Commun. 1998, 2287. (19) Ryoo, R.; Ko, C. H.; Kruk, M.; Antochshuk, V.; Jaroniec, M. J. Phys. Chem. B 2000, 104, 11465. (20) Kleitz, F.; Choi, S. H.; Ryoo, R. Chem. Commun. 2003, 2136. (21) Fan, J.; Yu, C.; Lei, J.; Zhang, Q.; Li, T.; Tu, B.; Zhou, W.; Zhao, D. J. Am. Chem. Soc. 2005, 127, 10794. (22) Zhang, H.; Sun, J.; Ma, D.; Weinberg, G.; Su, D. S.; Bao, X. J. Phys. Chem. B 2006, 110, 25908. (23) Cao, L.; Man, T.; Kruk, M. Chem. Mater. 2009, 21, 1144. (24) Huang, L.; Yan, X.; Kruk, M. Langmuir 2010, 26, 14871. (25) Kim, T. W.; Ryoo, R.; Kruk, M.; Gierszal, K. P.; Jaroniec, M.; Kamiya, S.; Terasaki, O. J. Phys. Chem. B 2004, 108, 11480. (26) Kruk, M.; Hui, C. M. J. Am. Chem. Soc. 2008, 130, 1528. (27) Stein, A.; Melde, B. J.; Schroden, R. C. Adv. Mater. 2000, 12, 1403. (28) Monnier, A.; Schuth, F.; Huo, Q.; Kumar, D.; Margolese, D.; Maxwell, R. S.; Stucky, G. D.; Krishnamurty, M.; Petroff, P.; Firouzi, A.; Janicke, M.; Chmelka, B. F. Science 1993, 261, 1299.
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AUTHOR INFORMATION
Corresponding Author
*(M.K.) E-mail:
[email protected]. Present Address †
(L.H.) ATRP Solutions, Inc., 855 William Pitt Way, Pittsburgh, PA 15238.
Notes
The authors declare no competing financial interest. 687
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Article
Chemistry of Materials (29) Tang, J.; Zhou, X.; Zhao, D.; Lu, G. Q.; Zou, J.; Yu, C. J. Am. Chem. Soc. 2007, 129, 9044. (30) Matos, J. R.; Kruk, M.; Mercuri, L. P.; Jaroniec, M.; Zhao, L.; Kamiyama, T.; Terasaki, O.; Pinnavaia, T. J.; Liu, Y. J. Am. Chem. Soc. 2003, 125, 821. (31) Fan, J.; Yu, C.; Gao, F.; Lei, J.; Tian, B.; Wang, L.; Luo, Q.; Tu, B.; Zhou, W.; Zhao, D. Angew. Chem., Int. Ed. 2003, 42, 3146. (32) Khanal, A.; Inoue, Y.; Yada, M.; Nakashima, K. J. Am. Chem. Soc. 2007, 129, 1534. (33) Yuan, J.-J.; Mykhaylyk, O. O.; Ryan, A. J.; Armes, S. P. J. Am. Chem. Soc. 2007, 129, 1717. (34) Liu, J.; Yang, Q.; Zhang, L.; Yang, H.; Gao, J.; Li, C. Chem. Mater. 2008, 20, 4268. (35) Mandal, M.; Kruk, M. Chem. Mater. 2012, 24, 123. (36) Wei, J.; Li, Y.; Wang, M.; Yue, Q.; Sun, Z.; Wang, C.; Zhao, Y.; Deng, Y.; Zhao, D. J. Mater. Chem. A 2013, 1, 8819. (37) Wang, H.; Wang, Y.; Zhou, X.; Zhou, L.; Tang, J.; Lei, J.; Yu, C. Adv. Funct. Mater. 2007, 17, 613. (38) Ding, S.; Liu, N.; Li, X.; Peng, L.; Guo, X.; Ding, W. Langmuir 2010, 26, 4572. (39) Liu, X.; Li, X.; Guan, Z.; Liu, J.; Zhao, J.; Yang, Y.; Yang, Q. Chem. Commun. 2011, 47, 8073. (40) Wang, C.; Wei, J.; Yue, Q.; Luo, W.; Li, Y.; Wang, M.; Deng, Y.; Zhao, D. Angew. Chem., Int. Ed. 2013, 52, 11603. (41) Caruso, F.; Caruso, R. A.; Moehwald, H. Science 1998, 282, 1111. (42) Blas, H.; Save, M.; Pasetto, P.; Boissiere, C.; Sanchez, C.; Charleux, B. Langmuir 2008, 24, 13132. (43) Wu, S.-H.; Mou, C.-Y.; Lin, H.-P. Chem. Soc. Rev. 2013, 42, 3862. (44) Li, X.; Yang, Y.; Yang, Q. J. Mater. Chem. A 2013, 1, 1525. (45) Wang, T.; Chai, F.; Fu, Q.; Zhang, L.; Liu, H.; Li, L.; Liao, Y.; Su, Z.; Wang, C.; Duan, B.; Ren, D. J. Mater. Chem. 2011, 21, 5299. (46) Gao, C.; Lu, Z.; Yin, Y. Langmuir 2011, 27, 12201. (47) Wang, T.-T.; Chai, F.; Wang, C.-G.; Li, L.; Liu, H.-Y.; Zhang, L.Y.; Su, Z.-M.; Liao, Y. J. Colloid Interface Sci. 2011, 358, 109. (48) Mitchell, D. T.; Lee, S. B.; Trofin, L. C. M.; Li, N.; Nevanen, T. K.; Söderlund, H.; Martin, C. R. J. Am. Chem. Soc. 2002, 124, 11864. (49) Kovtyukhova, N. I.; Mallouk, T. E.; Mayer, T. S. Adv. Mater. 2003, 15, 780. (50) Lin, Y.-S.; Wu, S.-H.; Tseng, C.-T.; Hung, Y.; Chang, C.; Mou, C.-Y. Chem. Commun. 2009, 3542. (51) Harada, M.; Adachi, M. Adv. Mater. 2000, 12, 839. (52) Ji, Q.; Iwaura, R.; Shimizu, T. Chem. Lett. 2004, 33, 504. (53) Yuwono, V. M.; Hartgerink, J. D. Langmuir 2007, 23, 5033. (54) Li, D.-M.; Chen, Y.-C.; Zhang, C.; Song, S.; Zheng, Y.-S. J. Mater. Chem. B 2013, 1, 1622. (55) Sanwaria, S.; Pal, J.; Srivastava, R.; Formanek, P.; Stamm, M.; Horechyy, A.; Nandan, B. RSC Adv. 2013, 3, 24009. (56) Müllner, M.; Lunkenbein, T.; Breu, J.; Caruso, F.; Mueller, A. H. E. Chem. Mater. 2012, 24, 1802. (57) Zhao, D.; Huang, X.; Zhou, L.; Yu, C. J. Mater. Chem. 2012, 22, 11523. (58) Deng, Y.; Yu, T.; Wan, Y.; Shi, S.; Meng, Y.; Gu, D.; Zhang, L.; Huang, Y.; Liu, C.; Wu, X.; Zhao, D. J. Am. Chem. Soc. 2007, 129, 1690. (59) Chan, Y.-T.; Lin, H.-P.; Mou, C.-Y.; Liu, S.-T. Microporous Mesoporous Mater. 2009, 123, 331. (60) Mandal, M.; Kruk, M. J. Mater. Chem. 2010, 20, 7506. (61) Liu, D.; Sasidharan, M.; Nakashima, K. J. Colloid Interface Sci. 2011, 358, 354. (62) Huang, L.; Kruk, M. J. Colloid Interface Sci. 2012, 365, 137. (63) Lettow, J. S.; Han, Y. J.; Schmidt-Winkel, P.; Yang, P.; Zhao, D.; Stucky, G. D.; Ying, J. Y. Langmuir 2000, 16, 8291. (64) Feng, P.; Bu, X.; Stucky, G. D.; Pine, D. J. J. Am. Chem. Soc. 2000, 122, 994. (65) Roux, E. L.; Liang, Y.; Storz, M. P.; Anwander, R. J. Am. Chem. Soc. 2010, 132, 16368.
(66) Martin, A.; Morales, G.; Martinez, F.; van Grieken, R.; Cao, L.; Kruk, M. J. Mater. Chem. 2010, 20, 8026. (67) Dacquin, J. P.; Lee, A. F.; Pirez, C.; Wilson, K. Chem. Commun. 2012, 48, 212. (68) Ma, G.; Yan, X.; Li, Y.; Xiao, L.; Huang, Z.; Lu, Y.; Fan, J. J. Am. Chem. Soc. 2010, 132, 9596. (69) Wei, J.; Wang, H.; Deng, Y.; Sun, Z.; Shi, L.; Tu, B.; Luqman, M.; Zhao, D. J. Am. Chem. Soc. 2011, 133, 20369. (70) Sanz, R.; Calleja, G.; Arencibia, A.; Sanz-Perez, E. S. J. Mater. Chem. A 2013, 1, 1956. (71) Ikemoto, H.; Tubasum, S.; Pullerits, T.; Ulstrup, J.; Chi, Q. J. Phys. Chem. C 2013, 117, 2868. (72) Shui, W.; Fan, J.; Yang, P.; Liu, C.; Zhai, J.; Lei, J.; Yan, Y.; Zhao, D.; Chen, X. Anal. Chem. 2006, 78, 4811. (73) Goltner, C. G.; Henke, S.; Weissenberger, M. C.; Antonietti, M. Angew. Chem., Int. Ed. 1998, 37, 613. (74) El-Safty, S. A.; Mizukami, F.; Hanaoka, T. J. Phys. Chem. B 2005, 109, 9255. (75) Tang, J.; Liu, J.; Wang, P.; Zhong, H.; Yang, Q. Microporous Mesoporous Mater. 2010, 127, 119. (76) Huo, Q.; Liu, J.; Wang, L.-Q.; Jiang, Y.; Lambert, T. N.; Fang, E. J. Am. Chem. Soc. 2006, 128, 6447. (77) Tan, H.; Liu, N. S.; He, B.; Wong, S. Y.; Chen, Z.-K.; Li, X.; Wang, J. Chem. Commun. 2009, 6240. (78) Kramer, E.; Forster, S.; Goltner, C.; Antonietti, M. Langmuir 1998, 14, 2027. (79) Chen, D.; Li, Z.; Wan, Y.; Tu, X.; Shi, Y.; Chen, Z.; Shen, W.; Yu, C.; Tu, B.; Zhao, D. J. Mater. Chem. 2006, 16, 1511. (80) Mandal, M.; Kruk, M. Chem. Mater. 2012, 24, 149. (81) Mandal, M.; Kruk, M. J. Phys. Chem. C 2010, 114, 20091. (82) Kruk, M. Acc. Chem. Res. 2012, 45, 1678. (83) Nagarajan, R. Colloids Surf., B 1999, 16, 55. (84) Cao, L.; Kruk, M. RSC Adv. 2014, 4, 331. (85) Yang, C.-M.; Schmidt, W.; Kleitz, F. J. Mater. Chem. 2005, 15, 5112. (86) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Pure Appl. Chem. 1985, 57, 603. (87) Kruk, M.; Jaroniec, M.; Sayari, A. Langmuir 1997, 13, 6267. (88) Ravikovitch, P. I.; Neimark, A. V. Langmuir 2002, 18, 1550. (89) Kim, S. S.; Karkamkar, A.; Pinnavaia, T. J.; Kruk, M.; Jaroniec, M. J. Phys. Chem. B 2001, 105, 7663. (90) Kleitz, F.; Liu, D.; Anilkumar, G. M.; Park, I.-S.; Solovyov, L. A.; Shmakov, A. N.; Ryoo, R. J. Phys. Chem. B 2003, 107, 14296. (91) Yuan, P.; Yang, J.; Bao, X.; Zhao, D.; Zou, J.; Yu, C. Langmuir 2012, 28, 16382. (92) Schmidt, W. Microporous Mesoporous Mater. 2009, 117, 372. (93) Cychosz, K. A.; Guo, X.; Fan, W.; Cimino, R.; Gor, G. Y.; Tsapatsis, M.; Neimark, A. V.; Thommes, M. Langmuir 2012, 28, 12647. (94) Yao, L.; Woll, A. R.; Watkins, J. J. Macromolecules 2013, 46, 6132. (95) Sakamoto, Y.; Diaz, I.; Terasaki, O.; Zhao, D.; Perez-Pariente, J.; Kim, J. M.; Stucky, G. D. J. Phys. Chem. B 2002, 106, 3118. (96) Thomas, A.; Schlaad, H.; Smarsly, B.; Antonietti, M. Langmuir 2003, 19, 4455. (97) Huo, Q.; Margolese, D. I.; Stucky, G. D. Chem. Mater. 1996, 8, 1147. (98) Kruk, M.; Jaroniec, M. Chem. Mater. 2003, 15, 2942. (99) Gao, Y.; Chen, Y.; Ji, X.; He, X.; Yin, Q.; Zhang, Z.; Shi, J.; Li, Y. ACS Nano 2011, 5, 9788. (100) Chen, Y.; Chu, C.; Zhou, Y.; Ru, Y.; Chen, H.; Chen, F.; He, Q.; Zhang, Y.; Zhang, L.; Shi, J. Small 2011, 7, 2935. (101) Zhang, J.; Karmakar, S.; Yu, M.; Mitter, N.; Zou, J.; Yu, C. Small 2014, 10, 5068. (102) Kruk, M.; Antochshuk, V.; Matos, J. R.; Mercuri, L. P.; Jaroniec, M. J. Am. Chem. Soc. 2002, 124, 768. (103) Geng, Y.; Discher, D. E. J. Am. Chem. Soc. 2005, 127, 12780. 688
DOI: 10.1021/cm5028749 Chem. Mater. 2015, 27, 679−689
Article
Chemistry of Materials (104) Loverde, S. M.; Ortiz, V.; Kamien, R. D.; Klein, M. L.; Discher, D. E. Soft Matter 2010, 6, 1419. (105) Flodstrom, K.; Wennerstrom, H.; Alfredsson, V. Langmuir 2004, 20, 680. (106) Morishige, K.; Kondou, Y. J. Phys. Chem. C 2012, 116, 3702. (107) Flodstrom, K.; Teixeira, C. V.; Amenitsch, H.; Alfredsson, V.; Linden, M. Langmuir 2004, 20, 4885.
689
DOI: 10.1021/cm5028749 Chem. Mater. 2015, 27, 679−689
