PAPER www.rsc.org/materials | Journal of Materials Chemistry

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Bottom-up tailoring of nonionic surfactant-templated mesoporous silicananomaterials by a novel composite liquid crystal templating mechanism

Qianjun He, Jianlin Shi,* Jinjin Zhao, Yu Chen and Feng Chen

Received 9th April 2009, Accepted 11th June 2009

First published as an Advance Article on the web 15th July 2009

DOI: 10.1039/b907266g

A bottom-up tailoring methodology was developed to successfully regulate the morphology and size of

novel composite micellar bunches with liquid crystal mesophases self-assembled from multivalent metal

ions (ZrIV) and nonionic surfactants (P123), and subsequently the morphologies and dimensions of

liquid crystal-templated mesoporous silica nanomaterials (MSNs). The composite micellar bunches

with liquid crystal mesophases were directly evidenced by TEM imaging and DLS measurements. By

virtue of these morphologically and dimensionally controllable composite micellar bunches as

templates, SBA-15 MSNs were well tailored from long nanorods of 645� 245 nm to short nanorods of

360 � 210 nm, and even to nanoplates of 310 � 740 nm and subsphaeroidal nanoparticles of 230 nm.

Introduction

The morphological and dimensional tailoring of nonionic

surfactant-templated MSNs have attracted increasing interest.

MCM-41-type mesoporous silica nanomaterials (MSNs) with

various controlled morphologies have been synthesized using

ionic surfactants as structure directing agents (SDA) by base-

catalyzed routes. However by acid-catalyzed routes, the

controllable tailoring for nonionic surfactant-templated MSNs

still remains a great challenge, mainly because of the difficulty of

regulating the dimensions and shapes of micelles. Nevertheless,

compared with other mesoporous silica materials, nonionic

surfactant-templated MSNs exhibit some prefect features in the

biomedical field for the load and delivery of nanocrystals,

quantum dots and large molecules such as DNA, siRNA,

proteins and enzymes.1 Recently, SBA-15 microrods (1.5 �1 mm),2 nanorods (500 � 100 nm)3 and nanospheres (300 nm)4

have been obtained by a salt-out method, a dilute solution

approach and a nonionic/ionic surfactant-templated route,

respectively. However, the discretional adjustment of particle

size and morphology of SBA-type mesoporous nanomaterials, as

far as we know, is still far away from satisfactory achievement,

and especially, the corresponding control mechanisms are not

well understood. Therefore, new morphological and dimensional

tailoring methodology for nonionic surfactant-templated meso-

porous nanomaterials needs to be developed.

A clear understanding of the mechanisms relating to the self-

assembly among organic and inorganic precursors and micelles

would ultimately make for a more rational and general approach

to the morphological and dimensional control of mesoporous

nanomaterials.5 There have been two popular mechanisms for

the formation of mesoporous materials well known as the liquid

crystal templating (LCT) mechanism and the cooperative self-

State Key Laboratory of High Performance Ceramics and SuperfineMicrostructure, Shanghai Institute of Ceramics, Chinese Academy ofSciences, 1295 DingXi Rd, Shanghai 200050, P. R. China. E-mail:jlshi@sunm.shcnc.ac.cn; Fax: +86 21 52413122; Tel: +86 21 52412714

6498 | J. Mater. Chem., 2009, 19, 6498–6503

assembly (CSA) mechanism, which were first proposed by Beck

and Stucky, respectively.6 There is a distinct difference between

the two mechanisms: a liquid crystal phase pre-exists prior to the

addition of silicate species according to the LCT mechanism,

however according to the CSA mechanism, the mesostructured

assembly would not occur until silicate species are added to

cooperate with. It can be thought that the mechanism which

would be applied to explaining the formation of a certain mes-

oporous material mainly depends on the micellization accessi-

bility from the used surfactant in a given reaction system. In

principle, both mechanisms can be viewed at three length scales:

the molecular scale which refers to the interactions between

organic and inorganic precursors, the mesoscale or nanoscale

which involves the growth and assembly of micelles, and the

microscale which is related to the morphology and dimension of

final products. It is evident that the interactions between organic

and inorganic precursors on the molecular scale determine the

growth, assembly, dimension and shape of micelles on the

mesoscale or nanoscale, which further influence the final

morphology and dimensions of the mesoporous material on the

nanoscale or microscale.7 This strategy is defined as a bottom-up

methodology of designing and tailoring materials.

Recently, €O. Dag and co-workers introduced transition metal

salts to induce the self-assembly of oligo(ethylene oxide)

surfactants into a lyotropic liquid crystal (LLC) system with an

extra small quantity of water, and then used this LLC system as

the template to synthesize mesostructured silica films and

monoliths.8 However, at such a high concentration of surfac-

tants, it is almost impossible to obtain well-dispersed MSNs.

Interestingly, at a relatively low concentration of surfactants,

whether a similar stable LLC system could be obtained or not,

and further, whether this system could be employed to direct the

formation of mesostructured silica nanomaterials is, as far as we

know, not explored and documented yet. In addition, no direct

microscopic imaging evidence before the addition of silicate

precursors is available to support the existence of any liquid

crystal mesophase in aqueous solutions as the template for

directing the formation of ordered mesoporous materials.

This journal is ª The Royal Society of Chemistry 2009

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Based on the bottom-up strategy, in the present work multi-

valent metal chlorides (ZrOCl2) were introduced to bind and

induce the oligo(ethylene oxide) surfactant Pluroinc P123

(EO20PO70EO20, Mw z 5800) of a relatively low concentration

to self-assemble into a stable LLC system of composite micelles.

The existence of stable LLC bunches self-assembled from

composite micelles of P123 and multivalent metal ions are clearly

evidenced by direct TEM observations, which are also supported

by direct measurements of micellar sizes by in situ dynamic light

scattering (DLS) analyses. In the present investigated systems,

the addition of multivalent metal ions is inferred to result in the

redistribution of the surface charges of composite micelles on the

molecular scale, subsequently the variation of the size and shape

of micelles, the thickness of double electrode layer and the elec-

trostatic interactions between hydrated micelles and silicate

species on the mesoscale, and finally the controllable tailoring of

the morphology and dimensions of MSNs on the nanoscale. A

series of SBA-15 MSNs with controlled morphologies and

dimensions from long nanorods to short nanorods, even to

nanoplates and smaller subsphaeroidal nanoparticles, have been

obtained. Comparative measurements and analyses of precursor

micelles and the final synthesized mesoporous nanomaterials

approve the high efficiency of the bottom-up tailoring for the

morphologically and dimensionally controlled SBA-15 MSNs.

Experimental

Synthesis of LLC systems and SBA-15 MSNs

In a typical synthetic procedure, a proper quantity (0.0644–0.322 g)

of ZrOCl2$8H2O was completely dissolved into 40 mL of 2 M

hydrochloric acid, and then 0.5 g of Pluroinc P123 was

added. These precursor solutions were continuously stirred for 8 h

at 35� 0.5 �C. The stable LLC systems were obtained, which were

used to synthesize the morphologically and dimensionally

controlled SBA-15 MSNs as follows.

1 g of tetraethyl orthosilicate (TEOS) was added dropwise into

the abovementioned precursor solutions. After 24 h, the as-

synthesized materials were centrifuged. In order to remove

surfactant, the as-synthesized materials were refluxed for 24 h

and repeated three times in a mixed solution of 250 mL ethanol

and 2 mL hydrochloric acid (36–38%) at 78 �C. The products

were then dried overnight at 120 �C in vacuum.

Characterization of LLC systems

One to three drops of the abovementioned precursor solutions,

prior to the addition of TEOS, were added on a copper net, and

residual liquid was absorbed with a filter paper. Then the copper

net was observed at once on a JEM-2010 electron microscope

attached with an Oxford Link ISIS energy-dispersive spectrometer

operating at 200 kV. Meanwhile, energy dispersive spectra (EDS)

were collected on observed micelles and out of observed micelles.

The mean zeta potentials and sizes of composite micelles in

these precursor solutions prior to the addition of TEOS were

detected at a constant temperature of 35 �C by the DLS method

via a zeta potential and particle-size analyzer (ZetaPlus,

Brookhaven Instrument Corp., Holtsville, N.Y., USA).

This journal is ª The Royal Society of Chemistry 2009

Characterization of SBA-15 MSNs

Transmission electron microscopy (TEM) and scanning electron

microscopy (SEM) images of SBA-15 MSNs obtained on a JEM-

2010 electron microscope operating at 200 kV and a JSM-6700F

electron microscope, respectively. The mean particle dimensions

in a and c directions were calculated from about 100 particles in

a TEM image.

Small-angle X-ray diffraction (SAXRD) data of SBA-15

MSNs were recorded on Rigaku D/Max-2550V diffractometer

using Cu Ka radiation (40 kV and 40 mA) at a scanning rate of

0.4�/min over the range 0.6–5.0� with a step width of 0.002�.

Nitrogen adsorption–desorption isotherms were carried out

on a Micromeritics Tristar 3000 analyzer at 77 K under

a continuous adsorption condition. All samples were pretreated

for 12 h at 120 �C under nitrogen before measurement. Average

pore diameter was calculated from desorption branches of

isotherms by the Barrett–Joyner–Halenda method. Specific

surface area and pore volume were calculated by Brunauer–

Emmett–Teller and Barrett–Joyner–Halenda methods, respec-

tively.

Results and discussion

The interactions among P123, hydronium, and introduced

multivalent metal salts are proposed as follows:

mH3O++P123/[P123$mH3O+]m + (1)

nZrOCl2 þ�

mþ 23n�

H3Oþ þ P123þ nH2O

/n

n�ZrCl2ðH2OÞ4

�2þ$P123$

�m� 4

3n�

H3Oþoðmþ2

3nÞþ

(2)

where the molar ratio of Cl to Zr is assumed to approximately be

2 according to the elemental analyses by EDS (see Table 1, Fig. 1

and Fig. 2).

Comparing eqn (1) and (2), the introduction of ZrOCl2 would

positively charge the micelles of [P123$mH3O+]m + (abbreviated

as H$P123) further, and the average charge density of

{n[ZrCl2(H2O)4]2+$P123$(m�4n/3)H3O+}(m+2n/3) + (abbreviated as

Zr$P123) composite micelles, which were reflected by the values

of (m + 2n/3), would increase with the increase of the ZrOCl2concentration because more [ZrCl2(H2O)4]2 + would be bound to

P123 and consequently the n value would increase. It was pre-

dicted that the mean lengths of rodlike micelles decrease with the

increase of salt concentration as well as their charge densities in

aqueous solutions of low ionic strength.9 In this way, the

dimension and zeta potential of rodlike composite micelles

would be tunable via the addition of ZrOCl2, or other similar

multivalent metal salts, which would determine the dimension,

morphology and dispersivity of SBA-15 MSNs.

Such inspired design and prediction based on the bottom-up

strategy are supported experimentally by TEM imaging and DSL

techniques in the present work. As listed in Table 1, with the

increase of the Zr concentrations, the mean charge densities

(ZP/LDLS) of Zr$P123 composite micelles increase according to

the zeta potential measurements, the mean lengths of rodlike

micelles also decrease according to the particle size measure-

ments by DLS and TEM methods (Fig. 1), and the mean lengths

J. Mater. Chem., 2009, 19, 6498–6503 | 6499

Fig. 1 TEM images of Zr$P123 composite micelles at the different Zr

concentrations: (A) 5 mM, (B) 12.5 mM, (C) 18.8 mM, and (D) 25 mM.

Fig. 2 EDS spectra on and out of Zr$P123 composite micelles under

TEM as shown in Fig. 1A.

Table 1 The dependencies of the mean surface charge density, the size of micelles and the dimension of SBA-15 MSNs on Zr concentration

CZra (mM) 0 (mM) 5 (mM) 12.5 (mM) 18.8 (mM) 25 (mM)

Ron(Zr/Cl)b — 0.50 0.52 0.49 0.50

Rout(Zr/Cl)b — 0.09 0.13 0.22 0.36

LDLSc (nm) 2158 2012 490 376 238

ZPd (mV) 100 108 122 108 95ZP/LDLS (mV nm�1) 0.046 0.054 0.25 0.29 0.40LM–TEM

e (nm) — 1900 � 800 550 � 250 400 � 100 270 � 40LS–TEM

f (nm) 730 � 100l 645 � 65 310 � 30 360 � 45 �230DM–TEM

e (nm) — 250 � 50 300 � 50 250 � 60 220 � 20DS–TEM

f (nm) 290 � 50 245 � 35 740 � 50 210 � 20 �230d100

g (nm) 8.8 9.2 9.4 9.4 9.6DBJH

h (nm) 5.3 5.1 5.0 4.9 4.9wi (nm) 3.5 4.1 4.4 4.5 4.7Sj (m2 g�1) 684 706 785 799 845Vk (cm3 g�1) 1.0 0.8 0.8 0.9 0.8

a The total Zr concentration in precursor solutions. b The molar ratio of Zr to Cl on micelles (Ron(Zr/Cl)) or out of micelles (Rout(Zr/Cl)) determined byEDS under TEM as shown in Fig. 1. c The mean size of micelles determined by DLS measurements at 35 �C. d The zeta potential per micelle calculatedfrom the minimal common divisor of zeta potential values of precursor solutions measured at 35 �C using a zeta potential analyzer. e The average length(LM–TEM) and diameter (DM–TEM) of micellar bunches calculated from TEM images as shown in Fig. 1. f The average length (LS–TEM) and diameter(DS–TEM) of SBA-15 MSNs calculated from TEM images as shown in Fig. 3. g The (100) plane spacing determined by SAXRD as indicated byFig. 5. h The average pore size of SBA-15 MSNs calculated from desorption branches of nitrogen adsorption–desorption isotherms by the Barrett–Joyner–Halenda method. i The thickness of mesoporous walls of SBA-15 MSNs determined by d100 and DBJH. j Specific surface area of SBA-15MSNs calculated by the Brunauer–Emmett–Teller and Barrett–Joyner–Halenda method. k Pore volume calculated by the Barrett–Joyner–Halendamethod. l The mean size of the subassembly of conglutinated SBA-15 micro-rods.

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of SBA-15 MSNs also correspondingly decrease according to

TEM and SEM observations (Fig. 3 and Fig. 4), as predicted.

The successful direct TEM imaging of the composite micelles

and the micelle self-assembled bunches, which is of novelty and

vital importance for revealing the self-assembly and tailoring

mechanism, should be attributed to the relatively strong binding

interactions among Zr$P123 composite micelles which enhance

the micelle electron density due to the enrichment of Zr on

micelles. Such an enrichment of ZrIV ions is supported by the

elementary analyses by EDS under TEM (Table 1, Fig. 1 and

6500 | J. Mater. Chem., 2009, 19, 6498–6503

Fig. 2). In spite of the different Zr concentrations in precursor

solutions, the molar ratios of Zr to Cl on composite micelles

almost keep constant at around 0.5, which are always remarkably

higher than those out of composite micelles (Table 1). Compar-

atively in the absence of ZrIV ions, the micelles of H$P123 cannot

be directly observed by TEM owing to the very low contrast

against the carbon membrane support for TEM imaging.

More important is that these rodlike Zr$P123 composite

micelles unexpectedly self-assemble into a kind of novel mono-

dispersed bunches in a certain order along a micellar longitudinal

c direction (see the inset of Fig. 1A). The intermicellar spacings

keep almost constant at 26 nm which is remarkably wider than

the (100) plane spacing of SBA-15 MSNs (Table 1 and Fig. 5),

and there is a very low contrast between two micelles which can

clearly be observed by TEM imaging especially in the inset of

This journal is ª The Royal Society of Chemistry 2009

Fig. 3 TEM images of SBA-15 MSNs synthesized at the different Zr

concentrations: (A) and (B) 0 mM, (C) 5 mM, (D) 12.5 mM, (E) 18.8 mM,

and (F) 25 mM.

Fig. 4 SEM images of SBA-15 MSNs synthesized at different Zr

concentrations: (A) 0 mM, (B) 5 mM, (C) and (D) 12.5 mM, (E) 18.8 mM,

(F) 25 mM. All scale bars are 1 mm except that of (C) (100 nm).

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Fig. 1A, implying no precipitation of zirconia in any form, which

was supported by the fact that all these precursor solutions prior

to the addition of silicate species are stable, transparent and clear

over two months. From Fig. 6, all SBA-15 MSNs have the

classical type-IV adsorption–desorption isotherms with type-H1

hystereses and well-defined step loops at relative pressures of

0.5–0.8, which also suggests that they possess uniform meso-

porous structures in accordance with the results obtained from

TEM images (Fig. 3) and SAXRD data (Fig. 5). As listed in

Table 1, they all possess a high surface area, large pore volume

and large mesopores.

Furthermore, with the increase of the Zr concentration, the

composite micellar bunches became more uniform in length with

their extra tails getting shorter or even disappeared, the bunches

became subsphaeroidal at 25 mM of relatively high Zr concen-

tration. Consequently and correspondingly, a kind of sub-

sphaeroidal mesoporous nanoparticles with a minimal

dimension of about 230 nm in the present reaction system was

obtained. Therefore, we strongly believe that these composite

micellar bunches are in a stable LLC state10 in the investigated

precursor solutions prior to the addition of silicate species. After

the addition of TEOS, these composite micellar bunches or LLC

mesophases direct the formation of SBA-15 MSNs and regulate

their dimensions and morphologies, because the dimensions in

This journal is ª The Royal Society of Chemistry 2009

either a or c direction of the composite micellar bunches and the

SBA-15 MSNs match very well with each other in a ratio of

about 1:1 (or about 2:1 and 1:2 under relatively low Zr concen-

trations of 5 mM and 12.5 mM, respectively) according to the

TEM observations (Fig. 1, Fig. 3 and Table 1). It can be inferred

that this bottom-up tailoring route obeys the LCT mechanism.

The entire tailoring process by this bottom-up route can be

schematically illustrated as shown in Scheme 1.

Noticeably, ZrIV ions play an important role in cutting,

conglutinating or dispersing mesoporous nanoparticles (Scheme

1). In the absence of any multivalent metal ion, SBA-15 nanorods

of about 730 nm in length and 290 nm in diameter were

conventionally conglutinated with each other in both a and c

directions into extra long rods of micrometre scale (Fig. 3A and

B and Fig. 4A). This heavy conglutination is considered a result

of the low charge density on the micelles. However in the pres-

ence of a small quantity of ZrIV ions, the composite micellar

bunches of several micrometres in length and a stable LLC

mesophase (see the inset in Fig. 1A) were assembled by virtue of

the hydrogen bonding and the electrostatic attraction between

Zr$P123 composite micelles and counterpart ions (Scheme 1).

Moreover, during the condensation of silicate species, the

composites of the LLC composite micellar bunches and silicate

species would no longer conglutinate with each other along the c

direction due to the positively charged micelle ends, moreover,

the original very long composites could be cut shorter, e.g. in

half, probably owing to the combined effect of shearing strain by

stirring and the further attack from ZrIV ions. It is known that

charges would be distributed near the end caps of rodlike micelles

and that the charge density would increase when rodlike micelles

J. Mater. Chem., 2009, 19, 6498–6503 | 6501

Fig. 5 SAXRD patterns of SBA-15 MSNs synthesized at different Zr

concentrations: (A) 0 mM, (B) 5 mM, (C) 12.5 mM, (D) 18.8 mM, and

(E) 25 mM.

Fig. 6 Nitrogen adsorption–desorption isotherms of SBA-15

MSNs synthesized at different Zr concentrations: (A) 0 mM, (B) 5 mM,

(C) 12.5 mM, (D) 18.8 mM, and (E) 25 mM.

Scheme 1 The bottom-up morphological and dimensional tailoring of

SBA-15 MSNs by the controllable LLC composite micellar bunches.

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are continuously charged.9e Therefore, these highly charged

composites of the LLC composite micellar bunches and silicate

species have a higher end charge density than those not or less

charged by ZrIV ions, which, as we believe, leads to even shorter

micellar bunches/silicate meso-composites along the c direction

and a well-developed dispersivity of SBA-15 MSNs (Fig. 3 and

Fig. 4). Surprisingly, at the slightly increased Zr concentration of

12.5 mM, the shortened LLC composite micellar bunches can be

doubled in the a direction after the assembly with silicate species

so that a kind of mesoporous nanoplate could be obtained. When

the Zr concentrations were further increased, these composites

could not be doubled or cut shorter in either a or c direction. One

can think that these composites are too short in the c direction to

6502 | J. Mater. Chem., 2009, 19, 6498–6503

be further divided, and the greatly enhanced repulsive interaction

owing to the enhanced mean charge density, which is indirectly

supported by the increased thickness of mesoporous walls as

suggested by Table 1, results in the low probability of their

conglutination or growth in both a and c directions. Therefore

short rodlike and even subsphaeroidal mesoporous nanoparticles

have been obtained (Fig. 3E and F and Fig. 4) at relatively high

Zr concentrations of 18.8 mM and 25 mM, respectively.

This journal is ª The Royal Society of Chemistry 2009

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Conclusion

In summary, a liquid crystal templating route for the morpho-

logical and dimensional tailoring of nonionic surfactant-tem-

plated MSNs has been directly evidenced by TEM imaging

assisted by in situ DLS measurements by introducing multivalent

metal ions ZrIV to enhance the image contrast for the first time.

By virtue of introducing multivalent metal salts ZrOCl2, novel

LLC mesophases of metal ion–P123 composite micelles have

been assembled and their morphologies and dimensions can be

well controlled through varying the concentrations of the added

multivalent metal salts, and subsequently the morphologies and

dimensions of SBA-15 MSNs can correspondingly be well

tailored from long nanorods of 645 � 245 nm to short nanorods

of 360 � 210 nm, and even to nanoplates of 310 � 740 nm and

subsphaeroidal nanoparticles of 230 nm. This bottom-up

tailoring strategy can be extended to using other kinds of

multivalent metal salts, surfactants and inorganic resources to

prepare various mesoporous nanomaterials with expected

morphologies and dimensions.

Acknowledgements

We greatly thank Ms Meiling Ruan for the TEM measurements.

We greatly acknowledge financial supports from the National

Nature Science Foundation of China (Grant Nos. 20633090 and

50823007), National 863 High-Tech Program (Grant No.

This journal is ª The Royal Society of Chemistry 2009

2007AA03Z317), Shanghai Rising-Star Program(Grant No.

07QA14061), Shanghai Nano-Science Project (Grant No.

0852nm03900) and CASKJCX Projects (Grant No. KJCX2-

YW-M02 and KJCX2-YW-210).

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