Preparation, characterisation and modification of carbon-based monolithic rods for chromatographic...

Research Article

Preparation, characterisation andmodification of carbon-based monolithicrods for chromatographic applications

A range of porous carbon-based monolithic (PCM) rods with flow-through pore sizes of 1,

2, 5 and 10 mm, were produced using a silica particle template method. The rods were

characterised using SEM and energy-dispersive X-ray spectroscopy, BET surface area and

porous structure analysis, dilatometry and thermal gravimetry. SEM evaluation of the

carbon monolithic structures revealed an interconnected rigid bimodal porous structure

and energy-dispersive X-ray spectroscopy analysis verified the quantitative removal of the

embedded silica beads. The specific surface areas of the 1, 2, 5 and 10 mm rods were 178,

154, 84 and 125 m2/g after pyrolysis and silica removal, respectively. Shrinkage of the

monolithic rods during pyrolysis is proportional to the particle size of the silica used and

ranged from 9 to 12%. Mercury porosimetry showed a narrow distribution of pore sizes,

with an average of �700 nm for the 1 mm carbon monolith. The suitability of bare and

surface oxidised PCM rods for the use as a stationary phase for reversed and normal phase

LC was explored. The additional modification of PCM rods with gold micro-particles

followed by 6-mercaptohexanoic acid was performed and ion-exchange properties were

evaluated.

Keywords: Gold micro-particles / LC porous carbon monoliths / Silica geltemplateDOI 10.1002/jssc.200900845

1 Introduction

Monolithic porous columns have many advantageous

characteristics to be used in various LC techniques as

compared to traditional particle packed columns [1–3]. The

most significant of them is a relatively high flow through

porosity, leading to low-column pressure drops, with the

potential for use with elevated flow rates, leading to faster

separations. Early reports on the production and use of

monolithic columns in GC were made by Ross and

Jefferson [4]. The approach was extended to LC as early as

1974 by Hansen and Sievers [5]. Polymer monoliths quickly

gained popularity since their early demonstration in the late

1980s due to their relative ease of fabrication and have

shown specific advantages for application in bio-separations

[6, 7]. Nakanishi and Soga reported a significant advance in

1991 in the preparation of silica based monolithic rods,

produced via phase separation by polymerisation of tetra-

methoxysilane in the presence of poly(ethylene oxide) [8, 9].

A meso-porous structured silica skeleton was achieved

through hydrothermal treatment of the silica rod with

ammonium hydroxide. Since this pioneering work, silica-

based monolithic columns have arguably become the most

popular phases currently applied to small molecule separa-

tions [10, 11], including organic and inorganic ions [12–14].

Recently, other alternatives to silica materials for the

preparation of monolithic columns have been investigated,

including zirconia [15], hafnia [16], titania [17] and carbon

monoliths. These materials and corresponding columns

exhibit better hydrolytical and thermal stability properties

than their silica counterparts, but the inorganic oxide based

materials are more reactive.

Carbon monoliths exhibit the advantages of both inor-

ganic oxides and organic polymers, being resistant to swel-

ling and hydrolysis. Once formed, they are structurally rigid

and resistant to attack from strongly acidic or basic solu-

tions, and stable in almost all organic solvents. Additionally,

carbon monoliths exhibit a temperature stability well

beyond most normal LC operating conditions. Additionally,

being conductive materials PGC columns are also suitable

for the use in electrochemically modulated LC or, if

suitably functionalised, in electrochemically switched ion

exchange [18–22]. Various authors have recently reported

Ali H. Eltmimi1

Leon Barron1

Aran Rafferty2

John P. Hanrahan3

Olga Fedyanina4

Ekaterina Nesterenko1

Pavel N. Nesterenko4

Brett Paull1

1Irish Separation Science Cluster,National Centre for SensorResearch, Dublin City University,Glasnevin, Dublin, Ireland

2School of Mechanical andManufacturing Engineering,Dublin City University, Ireland

3Glantreo, Rubicon Centre, CITCampus, Bishoptown, Cork,Ireland

4ACROSS-Australian Centre forResearch on Separation Science,School of Chemical Sciences,University of Tasmania, Hobart,TAS, Australia

Received December 16, 2009Revised January 6, 2010Accepted January 8, 2010

Abbreviations: EDX, energy-dispersive X-ray spectroscopy;

HF, hydrofluoric acid; ICP-OES, inductively coupledplasma–optical emission spectroscopy; PCM, porouscarbon-based monolithic

Correspondence: Professor Brett Paull, Irish Separation ScienceCluster, National Centre for Sensor Research, Dublin CityUniversity, Glasnevin, Dublin 9, IrelandE-mail: [email protected]: 1353-1-7005503

& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com

J. Sep. Sci. 2010, 33, 1231–1243 1231

the preparation in various forms of porous carbon mono-

lithic structures [23–31]. Mareche et al. [32] proposed a new

kind of porous monolithic phase using exfoliated graphite

as a starting material. The exfoliated graphite material was

compressed into adjustable shapes and the porosity and

density of carbon block was shown to depend upon the

compression rate. Alvarez and Fuertes [33] prepared

carbon monoliths by using silica monoliths as sacrificial

templates. They retain the foamy vesicular structure and

exhibit a high surface area of 1800 m2/g, with a large

porosity made up of the framework-confined meso-pores of

around 3.4 nm. Recently, Xu et al. [34] reported a method for

the synthesis of a carbon monolith for chromatographic

applications with a tri-modal porous structure of macro/

macro/meso-pores by nano-casting and phase separation. In

this reported method a silica monolith was used as

the hard template and a mixture of styrene and divi-

nylbenzene, in the presence of initiator and porogenic

reagent (dodecanol), was filled into the void space of the

monolithic template.

The use of template particles, in particular silica based,

for the preparation of ordered nano- and micro-structured

carbon materials has been the topic of much attention in

recent years in the production of so-called ‘‘inverse opals’’.

For example, Zakhidov et al. [35] synthesised carbon inverse

opals by infiltrating silica opal plates with a phenolic resin.

They cured the resin at low temperature, pyrolysed the resin

then removed the silica with aqueous hydrofluoric acid

(HF). They also reported that the X-ray diffraction indicated

an amorphous structure consistent with a glassy carbon.

Further work followed in this area [36–39], and most

recently Guan et al. [40] in 2007 synthesised carbon micro-

particle arrays with different particle morphologies from

phenolic resin using a similar inverse opal templating

process.

The idea of using spherical particles as templates for the

preparation of monolithic rods of dimensions and physical

stability suitable for chromatographic application was first

generated in 1966 by John Knox, who proposed an ‘‘inverse

column’’ in which the stationary phase structure had the

same shape as the mobile phase (gas phase) in the particle

packed column [41]. Knox stated how such a structure could

be made ‘‘by filling a column with beads of some low

melting point substance, fusing the points of contact, filling

the gas space with a thermosetting resin, and, after curing,

melting out the original beads’’. However, it was only

recently that Liang et al. [42] using such an approach

reported on the preparation of a carbon-based monolithic

column for chromatography by pyrolysing a carbon rod

made of a copolymer of a resorcinol/iron(III) complex and

formaldehyde using silica particles as a template. SEM

images revealed macro-pores with diameters between 5 and

10 mm, while BET measurements show reasonable porosity

(0.5229 mL/g) for the monoliths and a developed surface

area of 163 m2/g. Preliminary separations of n-alkylben-

zenes were achieved with dichloromethane and methanol as

the mobile phase, with 1% n-hexane as an additive.

In the work presented here, a detailed examination of

the production, and subsequent physical characterisation, of

carbon monolithic rods of 1–10 mm macro-pore size is

presented, based on an adapted and optimised templating

procedure first proposed by Liang et al. [42]. Synthetic

carbon rods of up to 10 cm in length were produced using a

simple thermally initiated process, based upon pyrolysing a

cast rod made of a copolymer of a 25:75 phenol resin mixed

with formaldehyde in the presence of silica beads (1, 2, 5

and 10 mm in particle size, respectively). These rods were

physically characterised, and then clad using a variety of

methods to ensure elimination of all housing voids and to

enable chromatographic evaluation. Finally, the surface

modification of the carbon rods with gold nano/micro-

particles for further chromatographic application was also

investigated.

2 Materials and methods

2.1 Chemicals

Resorcinol (99%), formaldehyde (37 wt% aqueous solution),

ethyl alcohol, toluene (99.9%), ethylbenzene (99.91%),

butylbenzene (99.9%) and HF acid (38–40%) were obtained

from Sigma-Aldrich (Gillingham, UK). 1-Butanol and ferric

chloride (99%) were obtained from Riedel-De Haen, Seelze

(Hannover, Germany). Nucleosil 5 and 10 mm silica beads

(surface area 5 359 and 124 m2/g, respectively, pore sizes

5 50 and 100 A, respectively) were obtained from Macher-

ey-Nagel (Duren, Germany) and 1 and 2 mm silica particles

(surface area 5 809 and 617 m2/g, respectively, pore sizes

5 47.5 and 50.1 A, respectively) were obtained from

Glantreo (The Rubicon Centre, CIT Campus, Bishopstown,

Ireland). The approximate particle size range measured

using SEM for each silica gel (1, 2, 5 and 10 mm) was

0.8–1.6 mm, 1.4–2.2 mm, 3.8–5.2 mm and 7.9–12.4 mm,

respectively. Araldite epoxy resin was obtained from Bostik

Findley (Stafford, UK). Gold(III) chloride 99.99% and 6-

mercaptohexanoic acid 90% were obtained from Sigma-

Aldrich. Reagent water was obtained from a Millipore Milli-

Q water purification unit (Millipore, Bedford, MA, USA)

and was 18.2 MO or better. All chemicals were used as

received from the manufacturers.

2.2 Instrumentation and characterisation

A GFL water bath, model 1013, from Laborgerateborse

GmbH (Burladingen, Germany) was used to prepare the

precursor carbon rod. An EHRET thermovacuum oven from

Ehret Labor and Pharmatechnik GmbH, KG, Emmendin-

gen, Germany was used to complete the polymerisation of

the precursor carbon rod. For the pyrolysis of the rod, a

desktop alumina tube furnace, model GSL1300X, from MTI

(Richmond, USA) was used. The surface morphology of the

carbon monoliths was examined using Hitachi SEM/

J. Sep. Sci. 2010, 33, 1231–12431232 A. H. Eltmimi et al.


energy-dispersive X-ray spectroscopy (SEM/EDX) model

S-3000N VP, Oxford, UK. High-resolution SEM images of

the monolith surface morphology were achieved using a

field emission Hitachi S-5500 SEM (Hitachi High Technol-

ogies America, USA). Inductively coupled plasma–optical

emission spectroscopy (ICP-OES) was used for the analysis

of gold, using a Liberty 220 series instrument (Varian, Palo

Alto, USA). To characterise the 1, 2, 5 and 10 mm templated

carbon monolith structures, a surface area analyzer, model

2375 (Micromeritics Gemini, Georgia, USA) was used to

measure the specific surface area and pore volume using the

nitrogen adsorption/desorption technique. Dilatometric

analysis was carried out using a programmable horizontal

pushrod dilatometer, model Dil 402-E (Netzsch, Emmen-

dingen, Germany) to study the effect of the pyrolysis on the

carbon monoliths. Thermal analysis was carried out using

differential thermal analysis/thermo gravimetric analysis

(DTA/TGA), model STA 1500 (Stanton Redcroft, UK).

Additionally, pore size distribution of the carbon monoliths

was characterised by mercury porosimetry, model Autoscan

33 (Quantachrome, UK) with a nominal measurement

range of 3.2 nm to 5 mm over a range of pressure from

atmospheric to 228 MPa. Infra-red spectra of the monolithic

carbon material surface were recorded using a Spectrum GX

FT-IR instrument (Perkin-Elmer, Milano, Italy). Monolith

cladding images were obtained using a SVM340 Syncro-

nised Video Microscope from LabSmith (Livermore, CA,

USA). The carbon monolithic rods were then sealed into

short chromatographic columns and evaluated for flow-

through porosity and backpressure profiles, retention

selectivity for a range of test solutes, and ruggedness over

extended use.

2.3 Preparation of the carbon monolith rods

A modified procedure [42] was used for the preparation of

the carbon monolithic rods. A 1 g portion of silica particles

(either 1, 2, 5 or 10 mm) was dispersed in 1.5 g of 1-butanol

and sonicated for 1 h. A 0.18 g portion of ferric chloride

followed by the addition of 0.367 g of resorcinol was then

added into the silica suspension and dissolved by gentle

shaking. After the addition of resorcinol, the mixture

solution directly turned dark and the resorcinol/Fe(III)

complex was formed. A 0.3 g portion of an ice cooled, 37%

formaldehyde solution in water was introduced into the

mixture in one step with further gentle agitation. The

mixture was kept in an ice-water bath for 1 h with constant

stirring. After removal from the ice-water bath, the mixture

was slowly transferred into 7 mm id glass tubes which were

capped when filled. These tubes were then placed in a 901C

hot water bath for 15 h. The mixture polymerised into a

solid rod inside the glass tube. The resin rod detached from

the glass tube wall due to shrinking caused by polymerisa-

tion. The polymer rods were aged in the glass tube overnight

in the hot-water bath. Crack-free phenolic resin/silica rods

were then removed from the glass tubes and kept within a

fumehood for 72 h to slowly evaporate the majority of

residual solvent. Finally, the rods were thoroughly dried in a

vacuum oven at 801C overnight and further cured at 1351C

for 4 h to ensure complete polymerisation.

A horizontal tube furnace purged with N2 gas was

employed to pyrolyse the rods. The temperature was first

ramped from room temperature to 8001C at 2.51C/min, and

then held at 8001C for 2 h, to ensure complete carbonisa-

tion. A second ramp took place from 800 to 12501C at 101C/

min. The temperature was kept constant at 12501C for a

further 1 h. Then the furnace was allowed to cool naturally

to room temperature.

The silica particles and the iron catalyst were removed

from the rods by etching in concentrated HF acid (38–40%)

for 3 h and subsequently washed away with copious

amounts of distilled water. The porous carbon rods obtained

were finally thoroughly dried within a fumehood for 24 h.

2.4 Preparation of carbon/gold composite monolith

New carbon/gold composite monoliths were prepared

following a procedure adapted from that reported by

Dekanski et al. [43] detailing the modification of glassy

carbon surfaces with silver particles. The carbon monolithic

rod was immersed in a 100 mM chlorauric acid in pH 1.8

aqueous solution overnight followed by drying for 24 h. The

degree of gold functionalisation of the carbon rods was

evaluated through digestion in HCl and analysed for gold

content using ICP-OES. Carbon/gold composite monoliths

were further modified with 6-mercaptohexanoic acid,

following an adapted procedure reported by Huo and

Worden [44], by immersing the rod in 10 mM of the acid

solution overnight followed by drying for 24 h. A second

modification procedure was also investigated to modify

carbon rods after column cladding (see below), which

simply involved pumping 100 mM chlorauric acid (pH 1.8)

through the cladded carbon monolith overnight, followed by

flushing the column with deionised water.

2.5 Cladding of the carbon rod and chromatographic

characterisation

The initial range of monolithic carbon rods were clad in

heat-shrinkable PTFE tubing by heating at 3401C. Encased

carbon rods were then sealed (making sure all air pockets

were eliminated) into short PEEK HPLC columns (typically

30� 6 mm id) with epoxy resin. This column could then be

connected to a standard HPLC system. Later rods were

completely encased directly within epoxy resin of �5 mm

thickness, into which chromatographic tubing connections

were sealed directly interfacing with the end of the

monolithic rod.

Chromatographic characterisation of monoliths was

carried out on an Agilent 1200 chromatograph comprising a

vacuum degasser, quaternary pump, autosampler, column

J. Sep. Sci. 2010, 33, 1231–1243 Liquid Chromatography 1233


oven and UV-Vis detector. Both reversed-phase and normal-

phase chromatographic selectivity was evaluated for each

new column. Bare carbon monolithic columns were tested

for normal-phase selectivity through injections of 15 mL of

model mixtures containing 10 mg/mL each of butylbenzene,

acetophenone and nitrobenzene in hexane, with hexane as

the mobile phase delivered at 1 mL/min, with UV detection

at 254 nm. Reversed-phase chromatographic evaluation of

the monolithic rods was based on the retention of various

substituted phenols in a water–methanol (1:9) mobile

phase, delivered at 0.15 mL/min, with detection at 278 nm.

Methylbenzene exhibited no retention in either normal or

reversed-phase mode under the conditions used and so was

used as a dead-time marker for each new monolithic rod

produced. The gold and 6-mercaptohexanoic acid modified

carbon monoliths were tested for ion exchange capacity by

injection of 10 mL of a 1 mg/mL solution of imidazole in

1 mM sodium acetate, with photometric detection at

280 nm. 1 mM sodium acetate/acetic acid buffer solution

was used as an eluent at 1 mL/min flow-rate.

3 Results and discussion

The synthesis of porous carbon-based monolithic (PCM)

rods includes three main steps: preparation of silica particle

embedded polymer rods, drying and pyrolysis of the

organopolymer phase, and etching of silica phase. The

adapted method developed results in an intermediate glassy

carbon–graphite monolithic material, with a reported

graphite index value of �0.2 [42]. The intermediate structure

and degree of disorder would suggest some degree of

undesirable surface functionality, likely to negatively affect

upon chromatographic selectivity and efficiency. However,

PCM of the macro-porous dimensions produced here have

not previously been evaluated chromatographically, there-

fore potential selectivity and efficiency is unknown.

Physically, the ideal porous monolith for application as a

stationary phase within LC is of course one exhibiting a

completely homogeneous structure and uniform mono-

functional surface. Thus it is necessary to avoid any cracks

or large internal cavities formed by bubbles in the

preparation of the PCM rods. Both cracks and cavities can

appear during the drying and pyrolysis stages of forming

intermediate resorcinol-formaldehyde resin rods with

embedded silica particles, so the most critical part of this

synthetic process is the careful drying of such resin rods.

3.1 Preparation and pyrolysis of silica-embedded

precursor rods

As described in Section 2.3, silica particles of 1, 2, 5 and

10 mm diameters were used in this work. The support

surface area was typically in the range 300–900 m2/g, with

pore diameters in the range 4–40 nm. Using these silica

particles, monoliths were made according to the procedure

detailed in Section 2.3. To achieve crack-free and bubble-free

rods, the drying procedure was found to be critical. Rods

were aged overnight at 901C after the phenolic resin was

formed. Evolution of solvent molecules during aging from

within the resin creates stresses, which can result in cracks

within the wet gel. Slow aging allows the steady formation a

highly cross-linked bulk polymer to resist these stresses.

Additionally, keeping the ageing temperature below the

boiling point of the solvent used, here butanol, limits the

formation of bubbles inside the rod. The aged wet rod was

then dried slowly at room temperature inside a fumehood.

Careful control of the pyrolysis step, where carbonisa-

tion of phenol–formaldehyde resin occurs, is also a critical

aspect of monolith formation. The pyrolysis step carbonises

the inter-particulate phenolic resin to form the monolithic

structure, which is then subject to acid treatment to

remove the silica particles. Shrinkage will occur as a

result of carbonisation, as during this step water vapour,

carbon monoxide, and hydrogen gases are produced. Here,

dilatometry was used to investigate the shrinkage of

samples during the pyrolysis heating cycle. Figure 1 shows

the shrinkages measured for the four samples studied here.

For each of the rods, significant shrinkage was observed

during the pyrolysis process as shown in Fig. 1. Shrinkage

commenced at approximately 2001C and was rapid up to

approximately 8001C. During this step a slow heating rate of

2.51C/min was used, to minimise the potential for thermal

shock, rapid gas evolution and cracking. A plateau in the

shrinkage occurs coinciding with the 2 h isothermal hold at

8001C. The shrinkage slows down as the structure is

consolidated. After the isothermal hold, the heating rate is

increased to 101C/min and heating proceeds to 12501C.

During this new heating phase, a second phase of rapid

shrinkage is observed. The temperature is then held

constant at 12501C for 1 h. The observed behaviour was

different for the 1 and 2 mm samples, compared to the 5 and

10 mm samples. For the former samples, a sharp shrinkage

was observed during the 101C/min heating ramp to 12501C.

During the isothermal hold at 12501C these samples tended

to plateau out.

The 5 and 10 mm samples exhibited a steady rapid

shrinkage from 8001C to the end of the isothermal hold at

12501C. All of the samples continued to contract, almost

identically, during cooling. From Fig. 1 it can be seen that

the overall shrinkage of the rods ranged from approximately

9% to almost 12%. Shrinkage increased proportional to the

particle size of the silica used. The larger the particle size

the larger the gaps between particles. The shrinkage

observed in Fig. 1 can be partly attributed to carbonisation

of the resin located between the silica beads. Further

shrinkage can be attributed to the non-uniformity of silica

particles themselves. During pyrolysis the silica particles

will rearrange themselves and shift slightly until such time

as they become locked in position. Another possible reason

for high shrinkage could be non-uniform infiltration of

phenolic resin into the void spaces between silica particles.

Infiltration can be difficult to achieve and is dependent on



the conditions used to mix the phenolic resin and silica

beads (and achieve full wetting of the silica), including the

use of stirring or use of a vacuum to force the resin into the

voids. The viscosity of the resin solution is another variable

which can determine the degree of infiltration.

Ko et al. [45] have carried out an in-depth study of the

behaviour of phenolic resins during pyrolysis. Ko et al.showed how volatiles such as H2O, CO, CO2, H2 and

other gases were removed during pyrolysis, leading to

weight loss and shrinkage. Significantly, Ko et al. showed

that 91% of the total gases evolved during pyrolysis occurred

in the temperature range of 400–7001C. Below 7001C

shrinkage of the phenolic resin increased linearly with

temperature and was attributed to the rearrangement of the

carbon structure. Above 10001C the shrinkage neared

completion due to the packing and cross-linking of the

glassy carbon structure. Total shrinkage of approximately

17% was observed. In the study conducted by Ko et al., a

total weight loss of phenolic resin of 435% was observed up

to a temperature of 24001C. Briefly, 94% of this weight loss

occurred below 9001C.

DTA/TGA analysis was used to investigate thermal

behaviour and weight loss of the 1 mm silica powder and also

the 1 mm silica–carbon rod during pyrolysis. For the powder

sample, a weight loss of 7.4% was observed up to 12501C.

This is expected since porous silica generally acts as a

sponge for organics and contaminants.

For the combined silica–carbon sample, a total weight

loss of 50% was observed (Fig. 2). For the carbon–silica

sample, a sharp endothermic peak was observed at

approximately 551C. A broad endothermic peak occurred

between 240 and 4001C. The disturbances observed at 800

and 12501C are artefacts created by the pyrolysis profile

which contained isothermal dwell times at these tempera-

tures.

Clearly, the weight loss is dramatic and is accompanied

by a vigorous exothermic reaction, even at a heating rate of

2.51C/min. According to Ko et al. [45] the condensation

0

400

800

1200

1600

0 200 400 600 800

Time (min)

Tem

pera

ture

(°C

)

-0.15

-0.11

-0.07

-0.03

0.01

dL/L

o

Temp

dL/L0 1 µm

2 µm

5 µm

10 µm

Figure 1. Dilatometry profilesof the 1, 2, 5 and 10 mm silica-particle templated monolithicrods subjected to a tempera-ture programmed pyrolysiscycle.

40

50

60

70

80

90

100

20 220 420 620 820 1020 1220

Temperature (°C)

% W

eigh

t rem

aini

ng

-2.00E-05

-1.00E-05

0.00E+00

1.00E-05

2.00E-05

3.00E-05

4.00E-05

5.00E-05

6.00E-05

Del

ta T

(mic

rovo

lts)

% weight remaining

Delta T

Figure 2. Thermo-gravimetric beha-viour of the 1 mm silica–carbon rodduring pyrolysis under flowing nitro-gen.



of polymer structures results in gas evolution and pore

creation in the carbonised sample. Above 7001C the effects

of chemical densification is greater than the formation of

pores. It can be seen from Fig. 2 that above approximately

4001C the bulk of the burn-off activity and associated weight

loss has been completed. However, it would be reasonable to

suggest that even lower heating ramp rates than 2.51C/min

in the region up to 4001C could be beneficial, such is the

volatility of the reaction in this region.

3.2 Characterisation of porous structure of carbon

monoliths

The above careful control of monolith preparation and

pyrolysis conditions resulted in the ability to produce carbon

monoliths of up to 100 mm in length without internal and

surface fissures or cracks. Optical microscopy of the

monolith surface showed a smooth homogenous surface

structure along the complete length of the monolithic rod

(Fig. 3A). SEM analysis of the monolithic rods in cross-

section revealed interconnected rigid porous structures for

each version of the monolith and verified the quantitative

removal of the embedded silica particles using HF acid

(Fig. 3B, 1 mm particle templated rod; 3C, 2 mm particle

templated rod; 3D; 5 mm particle templated rod; and 3E,

10 mm particle templated rod). HR-SEM was used to image

the smooth carbon surface morphology, although the

presence of isolated pores in the carbon skeleton of the

order 10–20 nm could also be identified (Fig. 3F).

EDX analysis carried out on cross sections of the

carbon monolith samples (1, 2, 5 and 10 mm) gave further

evidence that the silica was totally removed from the carbon

rod after treatment in HF acid (Fig. 4). Only negligible trace

amounts of silica residue could be detected in the HF

treated rods.

Surface area analysis (BET) was employed to investigate

characteristics of the monoliths before and after pyrolysis.

The silica particles (powder) were also characterised. Table 1

summarises the measured surface areas and pore volumes

of the silica particles and monoliths investigated in this

study. The 1 mm silica particles exhibited a high surface area

of 934 m2/g, indicative of a highly porous powder. The

powder exhibited a classic Type 1 isotherm, indicative of

micro-porous materials. The pore volume distribution

peaked at 2.1 nm (Fig. 5A). A similar isotherm was observed

for the 2 mm particles (powder).

In terms of the monolithic carbon–silica samples, lower

surface areas, compared to the silica particles, were

observed. For the 1 mm carbon–silica monolith before

pyrolysis, a surface area of 315 m2/g was recorded. The

surface area in this case is made up of the non-porous

phenolic resin element and the accessible silica element of

the composite. In this case it may be expected that this

monolithic sample would show very similar characteristics

to the 1 mm particle sample. However, a Type 4 isotherm,

commonly associated with the presence of meso-porosity,

was observed (Fig. 5B). Capillary condensation gave rise to a

hysteresis loop at the mid-range of the pressures investi-

gated. A hysteresis loop was also observed close to unity,

similar to that observed for the 1 mm particle sample. A peak

was observed for pores between 2–9 nm. Presumably, this is

the same porosity as was found for the powder sample. In

this sample, however, there is a distinct uptake in volume

Figure 3. Top: (A) Photograph of a 90�4 mm porous carbonmonolith, with inset showing microscope image of homoge-nous surface. Middle: SEM images of carbon monoliths with (B)1 mm macro-pores, (C) 2 mm macro-pores, (D) 5 mm macro-poresand (E) 10 mm macro-pores after removal of the silica beads.Magnification equal for images (B)–(E). Bottom: HR-SEM imageof the carbon surface morphology of the 5 mm templatedmonolith.



absorbed beyond 15 nm and this continues to rise to 45 nm

and beyond. This could be attributed to pores formed by the

contact points between silica particles which were not

completely filled by phenolic resin.

Following pyrolysis and HF treatment, the surface area

of the 1 mm sample dropped to 178 m2/g. This further drop

is due to the removal of the porous silica beads, which were

responsible for the high surface area prior to pyrolysis, thus,

leaving a skeleton of large pores (approximately 1 mm). The

adsorption-desorption isotherm for the sample after pyro-

lysis was also a Type 4 isotherm, but in this case it exhibited

hysteresis from relative pressure 0.4 to unity, indicative of

pores in the meso-range and beyond. Pores were shown to

exist at high volumes below 15 nm but also up to 200 nm

and further, beyond the range of the instrument. This was

expected since pores of approximately 1 mm were present

following removal of the silica.

Mercury porosimetry was carried out to further inves-

tigate the silica particles and monoliths. The 1 mm silica

powder was compacted to form a disc. This was done to

minimise the possibility of powder being sucked into the

mercury under vacuum. It also allowed for more direct

comparison with the monolithic samples. Powders behave

differently under conditions of mercury filling in terms of

filling of free space between particles. In terms of pore

volume, a large distribution peak was observed at approxi-

mately 500 nm. This was attributed to the spaces between

the contact points of the 1 mm silica spheres. No other pores

were observed for the volume distribution. However, a

different picture emerged when the pore number fraction

was taken into consideration. In this case, a very small peak

was observed at 500 nm. However, a sharp rise was observed

at approximately 30 nm and continued down to 6 nm,

something that was entirely absent from the volume

distribution. Clearly, large quantities of small pores exist,

but these possess a low pore volume. It is believed that these

pores correspond to the pores within the silica particles, as

found earlier by BET. In the volume distribution, the

presence of these small pores is being masked by a smaller

number of large volume pores.

Porosimetry was then carried out on the carbon–silica

(1 mm) monolith before pyrolysis. The pore distribution of

Figure 4. EDX images of carbonmonolith samples (left) before and(right) after HF treatment to removethe silica template particles.

Table 1. Surface area and pore volumes measurements of the silica powders and carbon monoliths

Nominal

particle size

Silica particles (mm) Surface area of

monolith (m2/g)

Pore volume of

monolith (mL/g)

Macro-pore size

distributiona) (mm)

Total

porosity

Measureda) average

particle size

Measureda) particle

size %RSD

Surface area

(m2/g)

Pre-

pyrolysis

Post-

pyrolysis

Pre-

pyrolysis

Post-

pyrolysis

Range Mean

1 1.3 19 934 315 178 0.24 0.23 0.5–1.2 0.7 0.25

2 1.8 16 616 235 154 0.48 0.23 1.5–2.0 1.6 0.66

5 4.0 34 359 196 84 0.30 0.095 4.5–6.0 5.3 0.70

10 9.9 16 339 195 125 0.57 0.32 9.2–10.1 9.7 –

a) Determined using SEM.



this sample is shown in Fig. 6A. This sample exhibited

pores of approximately 230 nm. This was somewhat unex-

pected, in that it may well have been reasonable to expect a

result similar to the compacted 1 mm silica powder,

assuming that the phenolic resin was non-porous. Pore

number fraction analysis (data not shown) revealed a minor

peak at approximately 230 nm, but the main activity occur-

red at 6–7 nm and 10–20 nm. These latter two peaks are

believed to correspond to the internal pores in the silica

beads. Less clear was the presence of the volumetric peak at

230 nm. There are a number of possible reasons for this as

previously mentioned, including impartial infiltration of

phenolic resin into the void spaces between silica particles,

or too-high viscosity of the resin solution affecting degree of

infiltration. The raw volume intruded for this sample was

1.23 cm3/g as compared with 2.36 cm3/g for the compacted

powder, adding weight to the assumption that the silica

particles were not totally coated, and the spaces between

silica particles were not completely filled.

Following pyrolysis and silica removal, the pore distri-

bution changes again, as shown in Fig. 6B. As can be seen,

the pore distribution forms a sharp peak at approximately

800 nm. The raw volume intruded has increased to

3.15 cm3/g indicative of the increase in pore size. The sharp

peak found at 250 nm prior to pyrolysis (attributed to inter-

particle voids) is no longer in evidence. However, the large

peak at 800 nm does possess a tail which extends to

approximately 150 nm. The large peak observed in Fig. 6B

ranges from 1200 to 500 nm, and is due to the pores left by

the removal of the 1 mm silica particles. The pores are

expected to be less than 1 mm in diameter due to shrinkage

during pyrolysis, which was shown in Fig. 1 to be approxi-

mately 9% for the sample made from 1 mm silica particles.

Other variances are expected due to the imperfect particle

size distribution of the silica particles, i.e. �0.8–1.6 mm from

SEM averaging measurements.

The pore number fraction data was examined. The pore

number fraction is the number of pores in a narrow range of

pore sizes relative to the total number of pores in the

measurement range. The pore number fraction is found by

dividing the number of pores in a small interval by the total

number of pores. The resulting number represents the

fractional amount of all the pores which are found in that

particular interval. The calculation of pore number fraction

is based on the assumptions that all pores are cylindrical

and are of equal length. Pore number fraction is a dimen-

sionless quantity. When the pore number fraction data was

examined, it is clear that many other fine pores also exist in

the pyrolysed sample (Fig. 7).

The predominant pore size (in volume terms) are the

pores remaining after the removal of the 1 mm silica parti-

cles. However, other pores also exist, ranging from 9 nm to

-10

65

140

215

290

365

0 2 4 6 8 10Pore Diameter (nm)

Incr

emen

tal P

ore

Are

a (m

2 .g-1

)

140

170

200

230

260

0 0.5 1Relative pressure (P/Po)

adsorption

desorption

0

0.009

0.018

0.027

0.036

0.045

0 10 20 30 40 50

Pore diameter (nm)

Incr

emen

tal p

ore

vol (

cm3 .

g-1

)

B

A

0

100

200

300

0 0.5 1Relative pressure (P/Po)

adsorption

desorption

Figure 5. (A) Adsorption-desorption isotherm (inset) and poredistribution of 1 mm silica powder. (B) Isotherm (inset) and poredistribution of the 1 mm carbon–silica monolith before pyrolysis.

-0.1

0.3

0.7

1.1

10 100 1000 10000Diameter (nm)

Max Ø = 753 nmB

-0.1

0.2

0.5

0.8

10 100 1000 10000Diameter (nm)

dV/d

log

(cm

3 .g-1

)

Max Ø = 231 nmA

Figure 6. Pore distribution for1 mm silica–resin monolith (A)before pyrolysis and (B) afterpyrolysis and removal of silicaparticles.



approximately 70 nm. This phenomenon has been observed

by other authors. For example, Liang et al. [42] reported four

types of pores in their final samples prepared using 10 mm

template silica. These were macro-pores formed from the

original silica spheres, macro-pores from the contact points

of the spheres, meso-pores formed by silica diffusion into

carbon and micro-pores formed by pyrolysis of phenol–

formaldehyde resin.

3.3 Housing, modification and chromatographic

evaluation

Housing/cladding the carbon monoliths was carried out

using two approaches as detailed in Section 2.5. Both

approaches proved successful with evaluation using optical

microscopy confirming complete elimination of voids along

the monolithic edge (Fig. 8). Both cladding techniques were

subjected to applied column backpressures of up to

2.41 MPa without sign of stress-induced voids. Typical

monolith backpressures for the column housed/clad mono-

liths ranged from 0.77 MPa on a 5 mm templated

(30� 6 mm id) bare carbon monolith, to 2.21 MPa on a

1 mm templated (73� 4 mm id) carbon/gold composite

monolithic rod, with applied flow rates of 1 mL/min.

Column LC can provide important information on the

quality and properties of the prepared carbon monolith.

First, the right peak shape or elution profile of any retained

solute will confirm the absence of cracks or significant

internal cavities within the monolithic rod and reflect the

uniformity of the porous structures. Second, the recording

of backpressure at the top of carbon monolith column

provides information on the permeability of the material

and the interconnectivity of the pores within the monolith.

Finally, the evaluation of selectivity and retention of model

substances can provide information on adsorption proper-

ties of the surface of the bare monoliths.

All of the prepared monoliths had well-developed

surface areas of between 84 and 178 m2/g (Table 1).

However, pure glassy carbon is known to be a relatively poor

LC phase, showing only weak retention for both polar and

non-polar solutes under normal and reversed-phase condi-

tions [46]. Despite this limitation, here due to the inter-

mediate composition of the newly structured PCM rods, it

was important to evaluate the selectivity and efficiency

exhibited. Using a short 30� 6 mm id 5 mm PCM rod rela-

tively weak (ok 5 1) retention of aromatic hydrocarbons

including toluene, ethylbenzene and butylbenzene was

noted in hexane. These results are in a good agreement with

data reporting the weak retention of benzene, toluene and

xylenes on porous graphitic carbon (Hypercarb) in heptanes,

obtained by Kaliszan et al. [47].

The PCM phase exhibited stronger retention for more

polar molecules under normal-phase LC conditions (as

shown later in Fig. 11A). The conditioning of the carbon

surface using mineral acids was investigated to potentially

increase retention of polar solutes and homogenise the

surface functionality. The surface was conditioned sequen-

tially using 0.5 and 2 M solutions of sulphuric acid, followed

by a 2 M solution of 50:50 sulphuric/nitric acid. Following

such conditioning steps the retention factors for the more

polar species such as nitrobenzenene and acetophenone

were increased significantly in comparison with butylben-

zene under normal-phase conditions, indicating increased

presence of polar sites on the carbon surface (Table 2).

(These sites were confirmed through FT-IR evaluation of the

carbon surface showing the presence of various oxygen

containing functional groups. Figure 9 shows a typical FT-

IR spectrum obtained. The broad absorption peak at

Figure 7. Microscopy imagesof (A) epoxy resin clad 5 mmtemplated carbon monolithand (B) a 5 mm templatedcarbon monolithic rod cladwithin a heat-treated Teflonsheath with an epoxy exteriorsealing layer for housing with-in a PEEK column.

Figure 8. Pore number fraction of pores for the 1 mm carbonmonolith after pyrolysis.



3429 cm�1 corresponds to the stretching O–H vibrations.

The characteristic C 5 O stretching vibration band is seen at

1701 cm�1. One more broad band at 1152 cm�1 was prob-

ably caused by a superposition of bands associated with

vibrations of the C-O-C group. A the same time the presence

of very small bands associated with asymmetric methyl

group vibrations at 2960 cm�1 or with asymmetric methy-

lene group vibrations at 2930 cm�1 prove the almost

complete pyrolysis of the original polymer.)

The retention of polar molecules such as phenols on

carbonaceous stationary phases in methanol–water mobile

phases is mainly due to ‘‘the polar retention effect on

graphite’’ [48], when the charge of the polar adsorbate

approaching the surface induces the appearance of a dipole

at the surface. Under these conditions, hydrophobic inter-

actions play a less important role. Because of the presence of

numerous oxygen containing groups at the surface of the

PCM, the retention of phenols can be increased through the

formation of hydrogen bonds. To investigate the retention

mechanism further, the retention of a number of substi-

tuted phenols was determined on a 50� 6 mm id PCM

column. The obtained results (Table 3) show the retention

order of the various phenols on the PCM, which were of a

very similar order to that recently recorded on a porous

graphitic carbon column (Hypercarb) [49]. However,

obviously there was no strong correlation between the

retention of phenols and their hydrophobicity and pKa

values.

The PCM rods were further modified with gold nano-

particles by self-assembly in solution, following sponta-

neous induced reduction upon functional groups at the

surface. Initial modification of each rod was carried out by

simple immersion of the monolithic rods in 0.1 M tetra-

chloroauric acid. Initial experiments showed the dimen-

sions of the surface immobilised gold particles were

proportional to immersion time. Gold particles ranging

from 50 to 150 nm in high degrees of surface coverage could

be obtained using this technique, as shown in Fig. 10,

which compares a typical SEM of an unmodified (Fig. 10A)

and gold modified 5 mm templated PCM (Fig. 10B). A

typical gold-modified carbon monolith was subsequently

immersed in HCl and the digest was analysed for gold

Table 2. Retention factors for test solutes on glassy carbon

monolith following surface modification with mineral

acids

Monolith surface modification Retention factor, k

Butylbenzene Nitrobenzene

No modification 0.29 1.4

0.5 M H2SO4 0.32 2.0

2.0 M H2SO4 0.32 3.9

2.0 M HNO3/H2SO4 0.33 9.1

Figure 10. SEM images of the 5 mm templated carbon monolith (A) before modification and (B) after modification with gold nano/micro-particles (50–150 nm) through immersion of the carbon rod, (C) after modification through dynamic modification via pumpingtetrachloroauric acid solution through clad monolith.

Table 3. Retention volume (VR, mL) of phenols in methanol–-

water (9:1) eluent on porous glassy carbon monolith

and selectivity (k) for same on porous graphitic carbon

[49]

Phenol pKa log P VR (mL) k [38]

2-tert-Butyl-4-methylphenol 11.72 3.97 1.84 0.57

Phenol 9.99 1.46 3.27 0.30

4-Methylphenol 10.26 1.94 5.02 0.76

2-Methoxyphenol 9.98 1.32 5.69 0.83

4-Methoxyphenol 10.10 1.58 9.23 0.91

2-Chlorophenol 8.56 2.15 11.72 0.95

Figure 9. FT-IR spectrum of the carbon monolith surface.



content using ICP-OES. The results indicated a 1.62% w/w

Au content using the above modification method. Conduc-

tivity measurements confirmed the gold modified carbon

monolithic exhibited higher conductance (322 S/m) than

recorded for the bare PCM rod (176 S/m).

Overnight immersion of the gold modified monolithic

phase in 10 mM of 6-mercaptohexanoic acid solution,

followed by drying for 24 h, was carried out to convert the

surface of modified monolith to a weak cation exchanger.

The modified rod was then clad as described above and

evaluated chromatographically, using imidazole as a stan-

dard solute, with a 1 mM aqueous acetic acid/acetate mobile

phase (pH 3.96). Figure 11B shows the retention of the

imidazole cation on the short 30 mm gold particle modified

5 mm templated PCM. Although the efficiency was low,

calculated using N ¼ 5:55ðtR=W1=2Þ2 as 1270 N/m, for the

imidazole peak, it was clear that cation exchange based

retention was evident.

A 73� 4 mm id 1 mm templated PCM was clad within

an epoxy resin column and subsequently modified with gold

through pumping at 1 mL/min 100 mM tetrachlorauric acid

(pH 1.8) through the cladded carbon monolith overnight.

Further modification with 6-mercaptohexanoic acid was

achieved again through pumping the solution through the

previously modified monolith. Using this dynamic modifi-

cation technique a considerably lower degree of surface

coverage was achieved (equal to only 0.011% w/w Au for a

5 mm templated monolith, as shown in Fig. 10C). Using the

above moderately modified 1 mm templated column, the

retention of neutral resorcinol and cationic imidazole was

investigated.

The 1 mm templated monolith exhibited both a signifi-

cantly reduced void volume compared to the 5 mm templated

monolith. Given the total volumes of the two monolithic

rods, namely 0.849 cm3 for the short 5 mm templated

monolith compared to 0.917 cm3 for the longer 1 mm

templated rod, the observed void volumes correspond to a

large difference in both column density and overall porosity,

equivalent to �25% total porosity for the 1 mm rod

compared to �70% for the 5 mm templated material. Given

the surface areas of the two materials and the column

dimensions, based upon a glassy carbon density of 1.5 g

cm3, this corresponds to total surface areas of �180 m2 for

the 1 mm column and only �30 m2 for the 5 mm column.

This reflects the low surface area of the 5 mm material noted

in Table 1, indicative of non-ideal homogeneity and packing

density in the preparation of the original silica-polymer mix,

resulting in potential presence of internal voids and larger

than expected overall porosity. Chromatographically, this

difference is reflected in the observed peak shapes shown in

Fig. 11, where the 1 mm templated rod exhibited an

improvement in both peak width (approximately 2.1 min at

-0.5

0.5

1.5

2.5

3.5

4.5

5.5

6.5

0 2 4

Abs

(m

AU

)

A B C D

1.2 min

O

0.7 min

-0.15

0.05

0.25

0.45

0.65

0 2 4

t00.6 min

Imidazole1.6 min

NH

N

-20

30

80

130

180

230

0 1 2

30 oC Rt = 0.27 min

60 oC Rt = 0.30 min

-40

10

60

110

160

210

260

310

0 1 2Time (min)

NH

N

30 oC Rt = 0.23 min

60 oC Rt = 0.62 min

HO OH

Figure 11. (A) Separation of butylbenzene and acetophenone (100 mg/L) in hexane on a 30� 6 mm id 5 mm templated carbon monolithiccolumn. (B) Retention of imidazole cation (1 mg/L) on a gold-mercaptohexanoic acid modified 30� 6 mm id 5 mm templated carbonmonolithic column using a 1 mM sodium acetate mobile phase, with photometric detection at 280 nm. (C) Peak shape for resorcinol onthe gold-mercaptohexanoic acid modified 73� 4 mm id 1 mm templated carbon monolith over 30–601C. (D) Increasing retention ofimidazole on the gold-mercaptohexanoic acid modified 73�4 mm id 1 mm templated carbon monolith over 30–601C.



baseline for imidazole on the 5 mm modified rod compared

to �1.5 min on the 1 mm phase under similar conditions)

and symmetry (Fig. 11C and D), although a reduced overall

ion exchange capacity was apparent from direct retention

comparisons between the two gold modified monoliths

under similar chromatographic conditions.

The effect of temperature upon retention was investi-

gated to confirm the dominance of ion exchange in the

retention mechanism on the modified monoliths. Despite

low capacity the effect upon retention of imidazole

compared with the resorcinol was significant, with no

temperature effect upon retention or peak shape noted

between 30 and 601C for the later neutral solute, but a

significant increase in retention observed for the imidazole

cation. This effect was also seen with 5 and 10 mm templated

gold–mercaptohexanoic acid modified monoliths, with the

reproducibility of peak shapes for both retained and unre-

tained species following multiple temperature variations

confirming thermal stability of both the surface modifica-

tion and the carbon rod cladding itself (Fig. 11C shows six

overlaid chromatograms spanning the temperature range

30–601C).

The results show clearly that the potential for higher

capacity modified monoliths exists through utilising the

immersion based modification approach on the monoliths

of higher surface area and greater density, namely the 1 and

2 mm templated materials. This, together with alternative

applications for these modified glassy carbon monoliths,

including electrochemical studies, is the subject of ongoing

research.

4 Concluding remarks

The research shows the technical feasibility of production of

monolithic carbon monolithic rods of dimensions suited to

future potential chromatographic applications, based upon

template particles ranging from 1 to 10 mm. In this study,

the synthetic process described was reliable and can

reproducibly produce rods of specific physical characteris-

tics. At this stage in the work it is not possible to state how

minor differences in the physical structure of the rods

would ultimately show themselves, for example, in chro-

matographic performance. This would need to be deter-

mined in further work on covalently modified rods.

The physical properties of the intermediate glassy –

graphitic carbon monoliths has been fully characterised,

together with evaluation of simple surface modification

techniques resulting in a stable gold–mercaptohexanoic

acid modified material, which exhibits temperature stable

and reproducible ion exchange capacity. The results

obtained to-date show limited suitability to the efficient

separation of small molecules in the monolithic formats so

far investigated, although the potential application to larger

bio-molecules is under investigation, which may provide

better separation efficiencies. These new composite conduc-

tive materials have potential further novel application within

separation science, together with possibilities in flow

through electrodes, sensors and electrochemical micro-

reactors.

The authors acknowledge Science Foundation Ireland forfunding this project (Grant 05/RFP/CHE0011) and thankBrendan Twamley for his assistance with SEM imaging. BrettPaull would also like to thank the Royal Society of Chemistry forfunding provided to complete this work under the JournalsGrants for International Authors Scheme.

The authors have declared no conflict of interest.

5 References

[1] Minakuchi, H., Nakanishi, K., Soga, N., Ishizuka, N.,Tanaka, N., Anal. Chem. 1996, 68, 3498–3501.

[2] Tennikova, T. B., Belenkii, B. G., Svec, F., J. Liq. Chro-matogr. 1990, 13, 63–70.

[3] Paull, B., Nesterenko, P. N., Trends anal. Chem. 2005,24, 295–303.

[4] Ross, W. D., Jefferson, R. T., J. Chromatogr. Sci. 1970, 8,386–389.

[5] Hansen, L. C., Sievers, R. E., J. Chromatogr. Sci. 1974,99, 123–140.

[6] Liao, J. L., Zhang, R., Hjerten, S., J. Chromatogr. 1991,586, 21–26.

[7] Svec, F., Frechet, J. M. J., Anal. Chem. 1992, 64,820–822.

[8] Nakanishi, K., Soga, N., J. Am. Ceram. Soc. 1991, 74,2518–2530.

[9] Nakanishi, K., Soga, N., J. Non-Cryst. Solids 1992, 139,1–13.

[10] Cabrera, K., J. Sep. Sci. 2004, 27, 843–852.

[11] Motokawa, M., Ohira, M., Minakuchi, H., Nakanishi, K.,Tanaka, N ., J. Sep. Sci. 2006, 29, 2471–2477.

[12] Glenn, K. M., Lucy, C. A., Haddad, P. R., J. Chromatogr.A 2007, 1155, 8–14.

[13] O’Riordain, C., Gillespie, E., Connolly, D., Nesterenko, P.N., Paull, B ., J. Chromatogr. A 2007, 1142, 185–193.

[14] Paull, B., Nesterenko, P. N., Trends Anal. Chem. 2005,24, 295–303.

[15] Randon, J., Huguet, S., Piram, A., Puy, G., Demesmay,C., Rocca, J. L., J. Chromatogr. A 2006, 1109,19–25.

[16] Hoth, D. C., Rivera, J. G., Colon, L. A., J. Chromatogr. A2005, 1079, 392–396.

[17] Zizkovsky, V., Kucera, R., Klimes, J., Dohnal, J.,J. Chromatogr. A 2008, 1189, 83–91.

[18] Antrim, R. F., Scherrer, R. A., Yacynych, A. M., Anal.Chim. Acta 1984, 164, 283–286.

[19] Ge, H. L., Wallace, G. G., J. Liq. Chrom. 1990, 13,3245–3260.

[20] Keller, D. W., Ponton, L. M., Porter, M. D., J. Chroma-togr. A 2005, 1089, 72–81.



[21] Keller, D. W., Porter, M. D., Anal. Chem. 2005, 77,7399–7407.

[22] Muna, G. W., Swope, V. M., Swain, G. M., Porter, M. D.,J. Chromatogr. A 2008, 1210, 154–159.

[23] Amadou, J., Begin, D., Nguyen, P., Tessonnier, J. P.,Dintzer, T., Vanhaecke, E., Ledoux, M. J., Pha-Huu, C.,Carbon 2006, 44, 2587–2589.

[24] Job, N., Thery, A., Pirard, R., Marien, J., Kocon, L.,Rouzaud, J. N., Beguin, F., Pirard, J. P., Carbon 2005, 43,2481–2494.

[25] Job, N., Sabatier, F., Pirard, J. P., Crine, M., Leonard, A.,Carbon 2006, 44, 2534–2542.

[26] Laszlo, K., Onyestyak, G., Rochas, C., Geissler, E.,Carbon 2005, 43, 2402–2405.

[27] Shi, Z. G., Feng, Y. Q., Xu, L., Da, S. L., Liu, Y., Mater.Chem. Phys. 2006, 97, 472–475.

[28] Siyasukh, A., Maneeprom, P., Larpkiattaworn, S.,Tonanon, N., Tanthapanichakoon, W., Tamon, H.,Charinpanitkul, T., Carbon 2008, 46, 1309–1315.

[29] Tonanon, N., Siyasukh, A., Wareenin, Y., Char-inpanitkul, T., Tanthapanichakoon, W., Nishihara, H.,Mukai, S. R., Tamon, H., Carbon 2005, 43, 2808–2811.

[30] Wang, D., Smith, N. L., Budd, P. M., Polym. Intern. 2005,54, 297–303.

[31] Lu, X., Caps, R., Fricke, J., Alviso, C. T., Pekala, R. W., J.Non-Cryst Solids 1995, 188, 226–234.

[32] Mareche, J. F., Begin, D., Furdin, G., Puricelli, S., Pajak,J., Albiniak, A., Jasienko-Halat, M., Siemieniewska, T.,Carbon 2001, 39, 771–773.

[33] Alvarez, S., Fuertes, A. B., Mater. Lett. 2007, 61,2378–2381.

[34] Xu, L. Y., Shi, Z. G., Feng, Y. Q., Microporous Meso-porous Mat. 2008, 115, 618–623.

[35] Zakhidov, A. A., Baughman, R. H., Iqbal, Z., Cui, C. X.,Khayrullin, I., Dantas, S. O., Marti, I., Ralchenko, V. G.,Science 1998, 282, 897–901.

[36] Zakhidov, A. A., Khayrullin, I. I., Baughman, R. H.,Iqbal, Z., Yoshino, K., Kawagishi, Y., Tatsuhara, S.,Nanostruct. Mater. 1999, 12, 1089–1095.

[37] Kajii, H., Take, H., Yoshino, K., Synthetic Met. 2001, 121,1315–1316.

[38] Take, H., Matsumoto, T., Hiwatashi, S., Nakayama, T.,Niihara, K., Yoshino, K., Jpn. J. Appl. Phys. 2004, 43,4453–4457.

[39] Aliev, A. E., Lee, S. B., Baughman, R. H., Zakhidov, A. A.,J. Luminesc. 2007, 125, 11.

[40] Guan, G. Q., Kusakabe, K., Ozono, H., Taneda, M.,Uehara, M., Maeda, H., J. Mater. Sci. 2007, 42,10196–10202.

[41] Knox, J. H., Anal. Chem. 1966, 38, 253–261.

[42] Liang, C., Dai, S., Guiochon, G., Anal. Chem. 2003, 75,4904–4912.

[43] Dekanski, A., Stevanovic, J., Stevanovic, R., Jovanovic,V. M., Carbon 2001, 39, 1207–1216.

[44] Huo, Q., Worden, J. G., J. Nanopart. Res. 2007, 9,1013–1025.

[45] Ko, T., Kuo, W., Chang, Y., J. Appl. Polym. Sci. 2000, 81,1084–1089.

[46] Gilbert, M. T., Knox, J. H., Kaur, B., Chromatographia1982, 16, 138–146.

[47] Kaliszan, R., Osmialowski, K., Bassler, B. J., Hartwick,R. A., J. Chromatogr. 1990, 499, 333–344.

[48] Knox, J. H., Ross, P., Advances in Chromatography,vol. 37, Marcel Dekker, New York 1997, p. 73.

[49] Fedyanina O. N., Nesterenko P. N., Russ. J. Phys. Chem.A 2010, 84, 476–480.



Preparation, characterisation and modification of carbon-based monolithic rods for chromatographic...

Documents

Transcript of Preparation, characterisation and modification of carbon-based monolithic rods for chromatographic...