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Colloids and Surfaces A: Physicochem. Eng. Aspects 362 (2010) 20–27

Contents lists available at ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

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olymer-templated mesoporous carbons with nickel nanoparticles

aura Sterk, Joanna Górka, Mietek Jaroniec ∗

epartment of Chemistry, Kent State University, Kent, OH 44240, USA

r t i c l e i n f o

rticle history:eceived 5 February 2010eceived in revised form 17 March 2010

a b s t r a c t

Soft-templating synthesis of mesoporous carbons in the presence of tetraethyl orthosilicate (TEOS) andnickel nitrate was carried out to introduce nickel nanoparticles and create additional microporosity inthese materials. This strategy was employed to synthesize phenolic resin-based mesoporous carbons with

ccepted 18 March 2010vailable online 27 March 2010

eywords:esoporous carbonsitrogen adsorptionickel nanoparticles

two different loadings of nickel nanoparticles and to obtain nickel-containing mesoporous carbon–silicahybrids. Removal of silica with NaOH solution from the hybrid composites gave mesoporous carbons withNi particles and inversely, burn off carbon from the aforementioned composites gave NiO-containingmesoporous silicas. Nitrogen adsorption, small and wide angle X-ray diffraction, transmission electronmicroscopy and thermogravimetric analysis showed good adsorption and structural properties of theaforementioned materials.

oft-templating synthesis

. Introduction

For years carbon materials have been used in many industrialpplications. Amorphous types of carbons are mostly derived frometroleum (carbon blacks) and/or organic sources. These carbonsre cheaply manufactured and readily available however the lack ofniformity and broad pore size distributions [1] make them unsuit-ble for advanced applications. Based on that, carbons with uniformnd ordered mesopores can expand applications of these materi-ls in various fields such as energy storage, catalysis, and electrodeaterials [2–4].In late 1990s, ordered mesoporous carbons (OMCs) have

een synthesized using hard-templating (HT) method [5–7], alsoeferred as nanocasting due to the fact that the final product is annverse replica of the template used. Since the beginning, ordered

esoporous silicas (OMSs) have been utilized as hard templatesor the synthesis of OMCs mostly because of easily tunable poros-ty in these materials and variety of morphologies available, e.g.,

CM-41, MCM-48, SBA-15, SBA-16, and FDU-1. According to theT strategy OMCs are obtained by filling the pores of siliceous

emplates with carbon precursors followed by their carbonization

nd subsequent silica dissolution. The first OMCs were reported byyoo’s group in 1999, using MCM-48 as the template and sucroses a carbon precursor [5]. The structural and adsorption propertiesf the final carbons depend not only on the properties of the tem-

∗ Corresponding author at: Department of Chemistry, Kent State University,illiams Hall, Room 201, Kent, OH 44242, USA. Tel.: +1 330 672 3790;

ax: +1 330 672 3816.E-mail address: jaroniec@kent.edu (M. Jaroniec).

927-7757/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfa.2010.03.028

© 2010 Elsevier B.V. All rights reserved.

plate used but also on the choice of carbon precursor. The latteris usually monomeric organic compound giving high carbon yieldat high carbonization temperatures [8]. Although, the nanocastingmethod has been widely studied for more than a decade, the mul-tistep process involving template removal with NaOH or HF is lessfeasible for scaling up.

In contrast to the HT synthesis, the recently reported the soft-templating (ST) synthesis of carbons has real potential to leaveacademic laboratories. This strategy is based on the self-assemblyprocess between triblock copolymers and polymerizing organics(used as template and carbon precursors, respectively) to formorganic–organic nanocomposites. The thermal treatment of the lat-ter at temperatures below 400 ◦C allows the thermosetting andcross-linking of carbon precursor, while higher temperatures resultin the template removal (triblock copolymer) and carbonizationof the thermosetting polymer (carbon precursor). The reducednumber of preparation steps, the use of biodegradable triblockcopolymers as templates and environmental friendly solvents(mostly water and ethanol) make this strategy feasible for a large-scale preparation.

The first report in the area of soft-templated carbons waspublished by Liang et al. [9]. The OMC films were obtainedby self-assembly of polystyrene-block-poly(4-vinylpyridine) (PS-P4VP) and resorcinol/formaldehyde. It was shown that the PS-P4VPblock copolymer can be used as a structure directing agent(soft template) for the formation of ordered phenolic resin

mesostructure. However, the use of quite expensive PS-P4VPcopolymer limited the applicability of this system. Tanaka et al.[10] as the first employed commercially available and inexpen-sive poly(ethylene oxide)–poly(propylene oxide)–poly(ethyleneoxide) triblock copolymer (EO106PO70EO106; Pluronic F127) as a

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L. Sterk et al. / Colloids and Surfaces A:

oft template in the synthesis of OMCs. This resulted in rapidevelopment of the soft-templating synthesis of carbons, whereain advances were made independently by Zhao and Dai groups

11,12]. Two alternative synthesis routes were proposed based onhe catalyst used for the self-assembly of triblock copolymer andhenolic resin-type carbon precursor. Zhao introduced the conceptf using sodium hydroxide for pre-polymerization of phenol andormaldehyde, which were later neutralized prior self-assemblyith block copolymer [11]. While, Dai’s procedure was based on theirect polymerization of phloroglucinol and formaldehyde in theydrophilic domains of triblock copolymer catalyzed by hydrochlo-ic acid [12]. Recent findings related to the synthesis of OMCs undercidic conditions show importance of high HCl concentration in theormation of ordered carbon mesostructures [13].

Mesoporous carbon materials with tunable properties such asore size distribution, BET surface area and pore volume can serves excellent supports for catalysis, energy storage, etc. Before theevelopment of soft-templating approach, extensive studies haveeen done towards preparation of OMCs with incorporated inor-anic nanoparticles on the basis of the hard-templating method. Forxample, the chemical vapor deposition of pyrrole into the pores ofron containing SBA-15 and SBA-16 templates resulted in nitrogen-oped carbon nanorods (CMK-3) with iron nanoparticles [14]. Also,ther methods afforded complete filling of pores of the templateith carbon precursor; however, the real challenge was to deposit a

hin film of carbon on the surface of a template, which will retain thetructure after template removal. It was demonstrated that SBA-15oated with 2,3-dihydroxynaphthalene (DHN) and then impreg-ated with concentrated Ni salt and heated, resulted in mesoporousarbons with ultra-thin carbon pore walls and evenly dispersed Nianoparticles [15].

In the case of soft-templated carbons, the incorporation of inor-anic species to the carbon framework can be done directly duringhe self-assembly process. One of the procedures involves the usef commercially available suspension of nanoparticles [16], whichan be added to the reaction mixture in desired quantities. Note-orthy, the addition of latter does not disturb organic–organic

elf-assembly and the system is able to adjust itself to host bigoadings of nanoparticles (up 50%) without noticeable structureeterioration [17]. The second method [18–26], which is widelysed, employs the addition of metal salts to the reaction mixture,hich during thermal treatment can be transformed into metalanoparticles embedded in the carbon matrix. For the first timehis concept was demonstrated for the synthesis of highly ordered

esoporous carbon–titania nanocomposites possessing “bricked-ortar” frameworks [18]. The use of TiCl4 as metal precursor, resol

s a carbon precursor, and Pluronic F127 as a template in the one-ot synthesis resulted in obtaining ordered carbon materials withigh surface area and evenly distributed TiO2 nanoparticles. Theame group recently modified this approach to obtain crystalline–TiO2 composites [19]. It was shown the use of acid–base pairTiCl4 and Ti(OC4H7)4) as titania precursors instead of single sourcean greatly improve the titania content in the sample even up to7 wt%. Moreover, the mesostructured composites still exhibitedood adsorption properties such as the relatively high specific sur-ace area of ∼200 m2/g and pore volume.

Also, the soft-templated mesoporous carbons containing irid-um particles have been reported [20]. It was found that the factorsuch as aging time of the gel and the molar ratio of resorcinol toormaldehyde, which usually affect carbon ordering, also governhe size of the nanoparticles formed. In this case, small (∼2 nm)

nd highly dispersed iridium particles were obtained. Also, ther–OMC catalysts proved their good performance for the hydrazineecomposition.

OMCs with magnetic properties are of the great interest dueo their possible applications, e.g., magnetic storage media [21].

ochem. Eng. Aspects 362 (2010) 20–27 21

Since the discovery of soft-templating synthesis of mesoporouscarbons, this easy and cost effective approach seems to be a goodalternative for quite laborious hard-templating method. In one ofthe recent reports the “one-pot” synthesis of �-Fe2O3-containingmesoporous carbons obtained by the coassembly of block copoly-mer with resol and ferric citrate was demonstrated [22]. It wasshown that the samples with low �-Fe2O3 content (such as 9.0 wt%)possessed an ordered 2D hexagonal (p6mm) structure, uniformmesopores (∼4.0 nm), high surface areas (up to 590 m2/g) and porevolumes (up to 0.48 cm3/g). All maghemite/carbon nanocompos-ites exhibited excellent magnetic properties, where the saturationmagnetization strength can be easily tuned by increasing the �-Fe2O3 loading. Although, the latter also lowered the values of theBET surface area and pore volume.

The ferromagnetic properties of Ni–OMC composites makethem attractive materials for magnetic separations [23]. Especiallythe fact of being self-protected against acid leaching makes themvaluable in magnetic separations. Also, for the first time the metal-containing carbons with a cubic structure of Im3m symmetry havebeen reported. Different synthesis conditions required for the for-mation of cages instead of channels also affect the growth of Ninanocrystals, which showed nearly the same size (∼20 nm) regard-less the amount of Ni salt used in the synthesis. In contrast, thework reported by Wang and Dai [24] shows that the average sizeof Ni particles increased with the metal loading. There is someevidence that the nanoparticles are formed in the carbon matrixand on the outer surface of hexagonally ordered carbons as well.Besides that, the resulting Ni–carbon composites exhibited goodstructural properties such as large and uniform mesopores (∼7 nm),total pore volume (0.46–0.68 cm3/g) and high BET surface area (upto 660 m2/g).

The idea of using metal salt for the generation of nanoparti-cles in OMCs and tetraethyl orthosilicate (TEOS) as a mesostructurereinforcing agent was reported by Zhou et al. [25]. Depending onthe NiCl2 concentration, the Ni–C composite obtained after silicadissolution exhibited high specific surface area (1220 m2/g). Theas-prepared Ni–C samples served as supports for Pt nanoparticlesformed under microwave conditions. The resulting binary cata-lyst (consisted of metallic Ni and Pt nanoparticles) has shown itscatalytic activity in the methanol electro-oxidation reaction. Also,the concept of using TEOS to reinforce the mesostructure forma-tion and to improve the overall structural parameters of sampleswas employed to obtain carbon-supported ruthenium catalyst forbenzene hydrogenation [26].

This paper reports the one-pot synthesis of soft-templatedordered mesoporous carbons and silicas with Ni nanoparticleson the surface and embedded in the carbon, silica and compos-ite frameworks. These composite materials were synthesized withaddition of TEOS to enhance their microporosity and facilitatethe access to Ni nanoparticles. An interesting feature of someNi–carbon composites is bimodal mesoporosity and substantialmicroporosity if the synthesis is carried in the presence of largeramounts of TEOS.

2. Materials and methods

2.1. Chemicals

Poly(ethylene oxide)–poly(propylene oxide)–poly(ethyleneoxide) triblock copolymer (EO106PO70EO106; Pluronic F127) was

provided by BASF Corp. Resorcinol (C6O2H6; 98%), formaldehyde(HCHO; 37%), nickel nitrate hexahydrate (Ni(NO3)2·6H2O; 99%)and tetraethyl orthosilicate (TEOS, 98%) were purchased fromArcos Organics. HCl (35–38%) was purchased from Fischer andethanol from Pharmco.

22 L. Sterk et al. / Colloids and Surfaces A: Physic

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cheme 1. Illustration of carbon micro-mesostructure with nickel nanoparticlesbtained by soft-templating.

.2. Materials

Synthesis of materials (see Scheme 1) was carried out accordingo a slightly modified recipe reported by Wang et al. [27]. Initially,.25 g of Pluronic F127, 1.25 g of resorcinol and Ni(NO3)2·6H2O inhe amount required to be 10 and 20 wt% with respect to carbonrecursors were dissolved in water/ethanol solution. After com-lete dissolution 1.1 ml of HCl was added under continued stirringor another 30 min. Then 1.25 ml of formaldehyde was introducedo the reaction mixture and stirred until the mixture turned milky.tirring was continued for 30 min to ensure phenolic resin for-ation. At this time, the mixing was stopped and the solutions

emained undisturbed until phase separation took place. The upperhase, which consisted mostly of ethanol and water, was removednd the lower phase was transferred onto a Pyrex dish to evaporatehe solvent for 16 h under ambient conditions followed by agingt 100 ◦C for 24 h. In the case of SiO2-containing samples, TEOS inmounts of 40 and 60 wt% with respect to the carbon precursor wasdded ∼30 min after formaldehyde addition.

Carbonization was done in a tube furnace under nitrogen atmo-phere using the heating rate of 2 ◦C/min up to 180 ◦C and holding athis temperature for 5 h, resuming heating with the same rate up to00 ◦C and with 5 ◦C/min up to 850 ◦C and holding at the latter tem-erature for 2 h. In order to remove silica, the samples were soakedith 3% sodium hydroxide (10 ml/1 g of the material) and kept at

0 ◦C for 16 h followed by washing with deionized water. The silicaaterials were obtained by burning off carbon in the silica–carbon

omposites in air at 850 ◦C for 2 h; this temperature was reachedsing 5 ◦C/min heating rate.

The final samples were denoted according to the for-ula: M − xNiyT, where M stands for the type of material

CS = carbon–silica nanocomposite, C = carbon, S = silica), x indicatest% of the nickel salt (Ni) used and y refers to wt% of TEOS (T) in

he sample.

.3. Measurements

Nitrogen adsorption isotherms were measured at −196 ◦C onSAP 2010 and 2020 volumetric analyzers (Micromeritics, Inc., GA).ll samples were outgassed at 200 ◦C for 2 h prior to adsorptioneasurements.Wide angle X-ray diffraction analysis was performed on PAN-

lytical X’Pert PRO MPD X-ray diffraction system using Cu K�adiation (40 kV, 40 mA). All patterns were recorded using 0.02◦

tep size and 4 s per step in the range of 15◦ ≤ 2� ≤ 80◦. Small angleRD analysis was performed in the range of 0.4◦ ≤ 2� ≤ 5◦.

Thermogravimetric analysis was made using a TA Instrumenti-Res TGA 2950 thermogravimetric analyzer from 30 to 800 ◦C

nder air flow with a heating rate of 10 ◦C/min.

TEM images of the samples were taken on a Hitachi HD-2000canning and transmission electron microscope (STEM). The unitas operated at an accelerating voltage of 200 kV and an emission

urrent at 30 mA.

ochem. Eng. Aspects 362 (2010) 20–27

2.4. Calculations

The BET specific surface area [28] was calculated from nitrogenadsorption isotherms in the relative pressure range of 0.05–0.2. Thetotal pore volume [29] was estimated from the amount adsorbedat a relative pressure of ∼0.99. The pore size distributions werecalculated from nitrogen adsorption isotherms at −196 ◦C using theimproved KJS method for cylindrical mesopores with diameters upto 10 nm [30].

3. Results

3.1. Carbon–nickel vs. carbon–nickel–silica composites

Nitrogen adsorption measurements were carried out to deter-mine changes in the porous structure of the materials studied,which were caused by increased loading of nickel and by additionof TEOS. The isotherms and the corresponding pore size distribu-tions (PSDs) curves are shown in Fig. 1. The first samples obtainedfrom two-component system (Ni salt and phenolic resin, denoted asC–10Ni and C–20Ni, respectively) exhibited adsorption isothermsof type IV with H1 hysteresis loop characteristic for uniform meso-pores. An increase in the Ni loading led to the reduction of the totaladsorption mostly due to the reduction of the amount of adsorb-ing carbon in the composite sample. When the third component(TEOS) was introduced to the reaction mixture, significant changesin the shape of hysteresis loops were observed only in the case ofthe samples possessing 60% of TEOS (Fig. 1C).

A two-step hysteresis loop is observed for the composites with60 wt% of TEOS, which translates to bimodal pore size distribution(Fig. 1D). The physicochemical properties of the materials studiedare listed in Table 1. This table shows that the BET surface areas ofthe Ni–carbon samples are 755 and 562 m2/g for lower and higherNi loadings, respectively. In the case of the tri-component systems,a gradual decrease in the BET surface area is observed as morenickel and TEOS is introduced to the system. Also, the microporevolumes reflect the same trend, except the fact that changes are lessnoticeable than in the case of the specific surface area. In general,small micropore volumes are typical for soft-templated carbonsand also in this case their contribution to the total pore volume isonly ∼10–15%.

As for the composite samples the total pore volume is relativelyhigh (0.53 and 0.68 cm3/g for CS–20Ni40T and CS–20Ni60T, respec-tively). The biggest differences between these samples are visiblein their mesoporosity, which seems to be affected by different con-tents of Ni and TEOS. The pore widths calculated from the PSDcurves were found to be ∼7.5 nm for the C–Ni and C–Ni–SiO2 sam-ples with 40% of TEOS. As mentioned above, the larger amount ofTEOS resulted in bimodal pore size distribution with peak maxima6.5 and 10.2 nm.

3.2. Carbon–nickel materials

Nitrogen adsorption isotherms for the carbons obtained aftersilica dissolution (Fig. 1E) retain the same shape as those for thecorresponding carbon–nickel–silica composites suggesting that themesopore structure was nearly untouched. However, the increasedadsorption at low p/po proves a significant enlargement of microp-orosity, which is clearly visible on the PSD curves (Fig. 1F). Based onthe data listed in Table 1, one can see the importance of adding TEOS

during the synthesis, which led to the carbons with high microp-ore volume and high BET surface area. The latter was found to be inthe range 860–1700 cm3/g, precisely reflecting different amountsof the TEOS used in the synthesis. Besides that, the effect of TEOS isclearly visible in the enlargement of the micropore volume, which

L. Sterk et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 362 (2010) 20–27 23

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ig. 1. Nitrogen adsorption isotherms (A, C and E) and the corresponding pore siztudied.

or C–10Ni–60T reached the value of 0.53 cm3/g. Note that theicroporosity created after silica dissolution can even double the

ontribution of micropores to the total pore volume (from 10–15%o 30% after silica etching). Also, the total and mesopore volumesncreased, especially for the samples with high TEOS content. Thehanges in the mesopore diameters observed after silica dissolutionre relatively small and will be discussed in the next section.

.3. Silica materials

Shown in Fig. 2 are nitrogen adsorption isotherms for the meso-orous silicas obtained after burning off the carbon component inhe carbon–silica composites to prove the formation of interpen-

ributions (B, D and F) for the nickel–silica–carbon and nickel–carbon composites

etrating carbon–silica network. The steep capillary condensationstep clearly indicates the existence of uniform mesopores. Theincreased adsorption close to unity indicates the existence of sec-ondary mesoporosity, which can be seen well on the PSD plots (seegraph in the inset). The characteristic features of the obtained silicasare high total and mesopore volumes, while the samples microp-orosity is low and comparable to that in the C–Ni–SiO2 composites.

3.4. TGA analysis

The actual amounts of nickel and silica introduced to the car-bon materials were obtained by thermogravimetric analysis. TheC–10Ni and C–20Ni samples showed residues of 3.0 and 6.2%,

24 L. Sterk et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 362 (2010) 20–27

Table 1Structural properties of the samples studieda.

Sample SBET (m2/g) Vt (cm3/g) Vmi (cm3/g) Vme (cm3/g) wKJS (nm) RTGA (%)

C–10Ni 755 0.69 0.07 0.49 7.3 3.0C–20Ni 562 0.53 0.06 0.37 7.3 6.2CS–10Ni40T 632 0.63 0.07 0.47 7.5 25.6CS–20Ni40T 553 0.53 0.06 0.38 7.4 25.5CS–10Ni60T 526 0.63 0.06 0.52 6.5; 10.2 61.2CS–20Ni60T 491 0.68 0.05 0.58 6.5; 10.2 52.3

C–10Ni40T 911 0.81 0.17 0.54 7.4 7.3C–20Ni40T 860 0.77 0.15 0.52 7.2 9.0C–10Ni60T 1692 1.59 0.53 1.09 6.8; 10.2 15.2C–20Ni60T 1273 1.38 0.34 1.00 6.9; 9.4 18.2

S–10Ni60T 676 1.06 0.06 0.91 7.6 –.05

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a lot of possibilities in terms of the incorporation of foreign species,carbon functionalization, etc. The ability of the phenolic resin-block copolymer system to self-adjust to the additional stressdue to high loadings of nanoparticles is impressive and can beeasily used to produce composites with pre-designed properties,

S–20Ni60T 597 1.09 0

a SBET, BET surface area; Vt , single-point pore volume; Vmi, volume of fine poresntegration of PSD in the range 4–20 nm; wKJS, mesopore diameter at the maximum

espectively, which is lower than expected. The composite analy-is revealed the residue of ∼25%, which includes both nickel andilica content in the CS–10Ni40T and CS–20Ni40T samples. Theemaining composite samples show accordingly higher values dueo larger amounts of the TEOS used during synthesis. For the carbonamples obtained after silica dissolution with NaOH, the TG resultshange from 7 to 18% depending on the sample. In this case, wexpected to obtain similar values to those for C–10Ni and C–20Niarbons. The much higher values strongly indicate the silica wasot completely removed.

.5. XRD and TEM

The small and wide angle XRD patterns are shown inigs. 3 and 4, respectively. The XRD patterns recorded at smallngles (Fig. 3) exhibit at least one distinct reflection peak indicat-ng the presence of uniform mesopores. The TEM images shown inig. 5 prove that these mesopores are ordered.

The wide angle XRD patterns shown in Fig. 4 (panels A–C) revealhe presence of crystalline nickel phase (*) in the amorphous car-on matrix. The diffraction patterns show (1 1 1), (2 0 0) and (2 2 0)

eflections attributed to the cubic (Fm3m) nickel phase accordingo the JCPDS card number 04-0850. The average crystallite size cal-ulated from Scherrer equation was found to be in the range from7 to 83 nm. The non-marked sharp peaks refer to aluminum as aesult of Al sample holder.

ig. 2. Nitrogen adsorption isotherms and the corresponding PSDs for the Ni-ontaining silica samples (inset).

0.80 7.6 –

ned by the integration of PSD up to 4 nm, Vme, volume of mesopores obtained bye PSD curve; RTGA, residue obtained by the TG analysis in air.

The wide angle XRD patterns for the corresponding silica sam-ples (Fig. 4D) show four distinct reflection peaks (1 1 1), (2 0 0),(2 2 0) and (3 1 1), which are identified as nickel oxide (Bunsenite)phase. The NiO crystallites were found to be ∼30 nm. As expected,the bigger nickel loading greatly improved the resolution of peaks.

4. Discussion

The soft-templating synthesis of mesoporous carbons can offer

Fig. 3. Small angle XRD patterns for the nickel–carbon and nickel–silica–carboncomposites; the latter were prepared using 40 wt% of TEOS in relation to the carbonprecursors.

L. Sterk et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 362 (2010) 20–27 25

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Fig. 4. Wide angle XRD patterns for the nickel–carbon, nicke

specially in relation to meso- and total pore volumes [17]. Themall microporosity observed usually for the soft-templated car-ons can be an issue for some applications. It has been shownhat the post-synthesis KOH activation is a great way to overcomehe aforementioned obstacle [31]. Although, this activation (if notontrolled) may lead to deterioration of the carbon mesostructure31] and sometimes it may affect the properties of nanoparti-

les. Because of that, the addition of a small molecule such asEOS, which can freely coassemble with phenolic resin and formmesostructure, with subsequent silica removal, seems to be a

ood alternative for the improvement of microporosity. Our stud-es showed that the addition of TEOS affects also mesoporosity.

a–carbon and nickel oxide–silica composite samples studied.

In the case of composites, all samples possess very small fractionof micropores, which is typical for phenolic resin-based carbons,regardless of the amount of TEOS loaded, suggesting that TEOS isincorporated uniformly into the carbon walls. This is also provedby obtaining very similar values of the mesopore volumes and porewidths for the C–Ni and C–Ni–SiO2 samples with 40% TEOS con-tent. In contrast, the nanocomposites obtained with larger amount

of TEOS exhibited bimodal mesopore size distributions and biggermesopore volumes. Between two systems of pores, these of about6.5 nm can be attributed to primary mesopores, while the pores ofabout 10.2 nm reflect some secondary mesoporosity. After NaOHtreatment the microporosity created by removing TEOS-generated

26 L. Sterk et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 362 (2010) 20–27

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ilica is clearly visible for all carbon samples. Moreover, in the com-lex systems like ours, the order of addition of the components,specially TEOS, which is most abundant compound in the synthe-is, seems to be important. The fact that the larger pores (∼10 nm)re present in the composites and carbon materials suggest thathese pores are created during initial self-assembly of composites;owever, further studies are required to fully explain the formationf two types of pores in these complex systems.

An increase in the nickel concentration resulted in a reductionf the BET surface area and the mesopore volume, which is prob-bly due to the presence of heavy component, Ni, in the samples;lthough, a partial pore blocking cannot be ruled out [15]. Whilehe amount of TEOS affects porosity of the composites and carbonstudied, in the case of nickel: (i) the mesopore widths are almosthe same, (ii) the changes in the mesopore volumes are moderate,hich stay in a good agreement with real Ni loadings obtained from

GA, and (iii) both aforementioned effects are true for all types ofhe materials studied. Moreover, the data obtained from the XRD

easurements show that the Ni nanoparticles formed are relativelyarger than those reported by Zhou et al. [25]. However, it seems toe some relation between the size of nanoparticles and the synthe-is conditions. Our studies show the organic–organic coassemblynder acidic media affords Ni nanoparticles in the range 30–83 nm,hich is in good agreement with data reported for the similar sys-

em also synthesized under acidic conditions but without TEOS24]. Based on that, it is suspected that nanoparticles can be formedot only in the carbon matrix but also on the external surface. The

atter can easily undergo agglomeration during carbonization pro-ess. These results also complement the findings obtained on theasis of adsorption data.

. Conclusions

In conclusion, the soft-templating was successfully employedor the preparation of mesoporous carbon–silica composites con-aining Ni nanoparticles. By changing the post-synthesis treatmentf silica–carbon–nickel composites the mesoporous carbons withi nanoparticles or silicas with NiO particles were easily obtained.he addition of TEOS, which generates additional microporosity, isimple and especially useful when the chemical activation cannote used to enlarge the BET surface area. The large and accessibleesopores and high BET surface areas make these carbons poten-

ially attractive for applications in catalysis and energy storage.

cknowledgments

This material is based upon work supported by the National Sci-nce Foundation under CHE-0848352. The authors thank BASF forroviding the triblock polymer. The TEM imaging was performed at

[

ains in the C–10Ni sample.

the Center for Nanophase Materials Sciences, which is sponsoredby the Oak Ridge National Laboratory, Division of Scientific UserFacilities of the US Department of Energy.

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