C A R B O N 4 7 ( 2 0 0 9 ) 3 1 4 5 – 3 1 5 0

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Soluble activated charcoal

Arnab Mukherjee, Lawrence B. Alemany, Ryan Thaner, Wenh H. Guo, W.E. Billups*

Department of Chemistry and The Richard E. Smalley Institute for Nanoscale Science and Technology, Rice University,

6100 Main Street, MS 60, Houston, TX 77005, United States

A R T I C L E I N F O

Article history:

Received 28 February 2009

Accepted 13 June 2009

Available online 21 June 2009

0008-6223/$ - see front matter � 2009 Elsevidoi:10.1016/j.carbon.2009.06.035

* Corresponding author: Fax: +1 713 348 6355E-mail address: billups@rice.edu (W.E. Bil

A B S T R A C T

Reduction of activated charcoal by lithium in liquid ammonia yields charcoal salts that can

be reacted with dodecyl iodide to yield soluble dodecylated activated charcoal. Atomic force

microscopy images reveal a heterogeneous size distribution of nearly spherical nanoparti-

cles. High-resolution transmission electron microscopy images show a layered microcrys-

talline arrangement that becomes separated to form mostly single layered disordered

structures after dodecylation. A 1H–13C cross polarization magic angle spinning spectrum

of the charcoal revealed a broad, featureless signal from sp2 carbons and a much weaker

broad signal from aliphatic carbons.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Charcoal that is produced in natural fire plays an important

role in the carbon cycle of earth [1–4]. Naturally occurring

charcoal has also been used for radiocarbon dating [5]. Char-

coal is activated by heating in steam to approximately 1000 �Cin the absence of oxygen (O2). This treatment removes resid-

ual non-carbon elements and produces a porous internal

microstructure having an extremely high surface area [6].

Structural studies using both naturally occurring charcoal

[7–9] and artificially produced charcoal have been reported

[10,11]. As part of our research on the synthesis of soluble

nanomaterials [12,13], we have functionalized activated char-

coal by dodecyl groups, and we describe here the synthesis

and characterization of soluble dodecylated activated

charcoal.

2. Experimental

2.1. Materials

Wood-derived activated charcoal (5–10% fullerenes), lithium

(granules 99%), and 1-iodododecane (P98%) were purchased

from Aldrich.

er Ltd. All rights reserved

.lups).

2.2. Synthesis of dodecylated activated charcoal

The derivatization reactions [12–14] were carried out by

adding the raw activated charcoal (4.2 mmol) under an atmo-

sphere of argon to a dry 100 mL, three-neck, round-bottomed

flask fitted with a dry ice condenser. Ammonia (80 mL) was

then condensed into the flask followed by the addition of lith-

ium metal (42 mmol). Dodecyl iodide (6.3 mmol) was then

added, and the mixture stirred for 12 h. The ammonia was

then allowed to evaporate, and the flask was cooled in an

ice bath. The reaction mixture was quenched by the slow

addition of ethanol (30 mL) followed by water (30 mL). The

reaction mixture was acidified with 10% HCl, and the dodecy-

lated activated charcoal was extracted into hexane and

washed several times with water. The reddish-brown hexane

layer was then filtered through a 0.2 lm PTFE membrane and

washed with hexane and ethanol to remove unreacted start-

ing material. After drying overnight in vacuo at 80 �C, the dod-

ecylated activated charcoal was isolated in 55% yield.

2.3. Characterization of dodecylated activated charcoal

The dodecylated activated charcoal was characterized by

Raman spectroscopy [15,16], thermal gravimetric analysis

.

Fig. 1 – Photographs of (a) raw activated charcoal and (b)

dodecylated activated charcoal in chloroform (CHCl3).

500 1000 1500 2000 2500Wavenumber (cm ) -1

Raw CharcoalDodecylated Charcoal

Inte

nsity

(arb

.Uni

ts)

(a)

(b)

Fig. 2 – Raman spectra (785 nm) of (a) raw activated charcoal

and (b) dodecylated activated charcoal obtained by

dodecylation.

3146 C A R B O N 4 7 ( 2 0 0 9 ) 3 1 4 5 – 3 1 5 0

(TGA) [17], solid-state 13C magic angle spinning (MAS) nu-

clear magnetic resonance (NMR) spectroscopy [13,18], atom-

ic force microscopy (AFM) [19] and high-resolution

transmission electron microscopy (HRTEM) [7,20]. Raman

spectra were collected from samples using a Renishaw

1000 micro-Raman system with a 785 nm laser source. Mul-

Fig. 3 – MAS 13C NMR spectra of raw activated charcoal. (a) 1H–1

FID, 5-s relaxation delay, 18,000 scans. FID processed with 50 Hz

obtained with 20.5-ms FID and 30-s relaxation delay, 7800 scan

sharp signal at 144.0 ppm results from C60.

tiple spectra (3–5) were obtained, normalized to the G band,

and averaged to present a comprehensive overview of the

material. TGA data were obtained using a model SDT 2960

TA instrument in an argon atmosphere. Samples were de-

gassed at 80 �C and then heated at 10 �C/min to 700 �Cand held there for 20 min. Solid state 13C MAS NMR spectra

3C CP spectrum obtained with a 1-ms contact time, 29.3-ms

(1 ppm) of line broadening. (b) Direct 90� pulse 13C spectrum

s. FID processed with 50 Hz (1 ppm) of line broadening. The

C A R B O N 4 7 ( 2 0 0 9 ) 3 1 4 5 – 3 1 5 0 3147

were acquired on a Bruker AVANCE-200 NMR spectrometer

(50.3 MHz 13C and 200.1 MHz 1H) using standard Bruker

pulse programs, as described previously [13,18]. Critical

parameters are given in the figure captions. AFM images

were taken using a Digital Instrument Nanoscope IIIa in

tapping mode with a 3045 JVW piezo tube scanner. A sam-

ple for AFM imaging was prepared by spin coating a chloro-

form solution onto mica. The tapping frequency was

between 270 and 310 kHz. HRTEM images were taken using

a HRTEM (JEM-2010F), operated at an accelerating voltage of

200 kV. A drop of activated charcoal (both raw and dodecy-

lated) in chloroform was placed on a TEM grid (mesh size

200 l), dried and examined.

Fig. 4 – MAS 13C NMR spectra of dodecylated activated charcoal. (

except for a contact time of only 0.2 ms, 22,800 scans. FID proces

(a) except for a contact time of 1.0 ms. (c) Same as (b) except for a

Same as (c) except for an 80-ls dephasing interval and 30,000 sc

FID and 10-s relaxation delay, 2600 scans. FID processed with 50

s relaxation delay. (g) Same as (e) except for a 90-s relaxation d

3. Results and discussion

‘‘Charcoal salts’’, prepared by treating activated charcoal with

lithium in liquid ammonia react readily with dodecyl iodide

to give charcoal functionalized by dodecyl groups as illus-

trated in the following reaction. Previous work with carbon

Activated charcoal

ð�5–10% of C60Þ���!Li=NH3

C12H25–I½Activated charcoal�–C12H25

nanotubes and graphite has shown that these materials can

also be dissolved in organic solvents after functionalization

by dodecyl groups [12,13].

Stable suspensions of the dodecylated charcoal in organic

solvents are formed after sonication for a few minutes.

a) 1H–13C CP spectrum. Same acquisition parameters as in (a)

sed with only 20 Hz (0.4 ppm) of line broadening. (b) Same as

50-ls dephasing interval between CP and FID acquisition. (d)

ans. (e) Direct 90� pulse 13C spectrum obtained with 20.5-ms

Hz (1 ppm) of line broadening. (f) Same as (e) except for a 30-

elay.

Fig. 5 – AFM (10 lm · 10 lm) image of dodecylated activated

charcoal spin coated onto freshly cleaved mica from

chloroform.

3148 C A R B O N 4 7 ( 2 0 0 9 ) 3 1 4 5 – 3 1 5 0

Although solutions of the raw and dodecylated activated

charcoal remain suspended in chloroform immediately after

sonication (Fig. 1), the raw activated charcoal precipitates

after a few minutes.

The extent of functionalization can be inferred from the

exceptionally strong disorder peak exhibited by the Raman

spectrum (Fig. 2). As shown in Fig. 2a, the Raman spectrum

of the starting activated charcoal exhibits a tangential mode

(G band) at 1590 cm�1 and a disorder band (D band) at

1290 cm�1 [21]. After functionalization, the relative intensity

of the D band was observed to increase (Fig. 2b) as a result

of the rehybridization of the carbon framework.

Thermogravimetric analysis (TGA) of degassed (80 �C for

30 min) dodecylated charcoal results in a sharp weight loss

in the range of 200–350 �C. The carbon/functional group ratio

determined from these data was found to be about 48.

The dodecylated activated charcoal was not sufficiently

soluble in CDCl3 to obtain 1H and DEPT-135 13C spectra

(500 MHz spectrometer) with much useful information. Sig-

nals consistent with the presence of long chain alkyl groups

were clearly evident in the 1H and DEPT-135 13C spectra. A

weak, broad signal at 3.65 ppm in the 1H spectrum (not pres-

ent in the deuterated solvent) indicated that some O-dodecy-

lation might have occurred. A 1H–13C cross polarization magic

angle spinning (CPMAS) spectrum of the charcoal revealed a

broad, featureless signal from sp2 carbons and a much weaker

broad signal from aliphatic carbons (Fig. 3a). However, this

spectrum is not representative of all the carbon in the sample,

as a direct 90� pulse 13C experiment indicated that the sample

contained a much higher percentage of sp2 carbons, including

some C60 that could not be detected in the CP experiment

(Fig. 3b). Lengthening the relaxation delay from 10 s to 30 s

in the direct 13C pulse experiment had only a small effect

on the relative signal intensities. Clearly, many of the carbons

had experienced little, if any, cross polarization in the initial

CP experiment. In the direct 13C pulse spectrum, the sp2 sig-

nal is also somewhat broader than in the CP spectrum.

Dodecylation resulted in a large increase in aliphatic

intensity in the CPMAS spectra (Fig. 4a and b), both in an

absolute sense and compared to the intensity of the sp2 car-

bon signal. The aliphatic signal intensity downfield of about

65 ppm is consistent with the presence of O–C(sp3) groups,

as suggested in the solution state 1H spectrum. Decreasing

the contact time from 1 ms (Fig. 4b) to 0.2 ms (Fig. 4a) caused,

as expected, a significant reduction in the relative intensity of

the sp2 carbon signal. The signal at 43 ppm apparently cross

polarizes somewhat more slowly than the signal at 32 ppm,

which suggests that the former signal results in part from

quaternary aliphatic carbons. The aliphatic signal intensity

downfield of 65 ppm remains, which would be consistent

with the presence of OCH2 groups [as opposed to O–C (quater-

nary aliphatic carbon)].

A dipolar dephasing spectrum [13,18,22] obtained with a

50-ls dephasing interval between the 1-ms contact time for

cross polarization and the FID acquisition exhibits a severely

attenuated aliphatic band, with a weak residual aliphatic sig-

nal at 30 ppm consistent with the interior carbons of the

dodecyl groups (Fig. 4c). In contrast, the sp2 carbons exhibit

a much less attenuated signal, consistent with most of the

sp2 carbons being fully substituted. Lengthening the dephas-

ing interval to 80 ls results in nearly complete elimination of

the aliphatic signal (Fig. 4d).

The direct 90� pulse 13C experiment reveals a much

stronger aliphatic signal (Fig. 4e) than in the corresponding

spectrum of the starting material (Fig. 3b). Just as with the

starting material, a direct 90� pulse 13C experiment indicates

that the dodecylated activated charcoal contained a much

higher percentage of sp2 carbons than indicated by the basic1H–13C CPMAS spectrum (Fig. 4e and b). Note the absence of

C60 after reductive dodecylation. Lengthening the relaxation

delay from 10 s to 30 s (Fig. 4f) seems to increase the inten-

sity of the signal at 43 ppm and the intensity of the broad

sp2 signal relative to the aliphatic signal at 30 ppm. Length-

ening the relaxation delay to 90 s (Fig. 4g) seems to show a

further small increase in the intensity of the signal at

43 ppm. The increased intensity at 43 ppm would be consis-

tent with slowly relaxing quaternary aliphatic signals over-

lapping with more rapidly relaxing C-1 CH2 signals. Such a

conclusion is also consistent with the relative intensities

in the CPMAS spectra obtained with 0.2-ms and 1.0-ms con-

tact times (Fig. 4a and b). Quaternary aliphatic carbon sig-

nals could reasonably be expected to appear near 43 ppm

[13,18].

The sp2 signal in the direct 13C pulse spectrum (Fig. 4g) is

clearly broader than in the CP spectra (Fig. 4a and b) and

exhibits a more intense upfield component. In addition, the

peak maximum shifts noticeably upfield, from 133 ppm in

the CP spectrum to 126 ppm in the direct 13C pulse spectrum.

In contrast, the same comparison of the CP and direct 13C

pulse spectra for the starting material (Fig. 3) shows much

less difference. Clearly, significant structural changes oc-

curred upon dodecylation.

Although AFM microscopy has been utilized previously to

image the surface of solid activated charcoal [23], to the best

of our knowledge AFM images have not been recorded by spin

coating samples from solution. The atomic force microscopy

Fig. 6 – (a) HRTEM images of raw activated charcoal. (b) Layered arrangement of raw activated charcoal. (c) Dodecylated

activated charcoal with layers being separated. (d) Dodecylated activated charcoal with disordered lattice fringes. Scale bar for

6a, 6c and 6d is 5 nm. Scale bar for 6b is 2 nm.

C A R B O N 4 7 ( 2 0 0 9 ) 3 1 4 5 – 3 1 5 0 3149

(AFM) images presented in Fig. 5 were recorded by spin coat-

ing the charcoal from a chloroform solution onto mica. Solu-

ble dodecylated activated charcoal shows a heterogeneous

size distribution of nearly spherical nanoparticles. The hori-

zontal distances of the particles vary between 8 nm and

0.3 lm. The average height of the particles varies between

�2 nm and 5 nm with 80% having an average height of

3.5 nm.

HRTEM images (Fig. 6a and b) of the unfunctionalized acti-

vated charcoal show a layered microcrystalline arrangement

with lattice fringes of 3.5 A [24–26], similar to graphite where

the interlayer distance is approximately 3.5 A. Small fuller-

enes were also observed in the HRTEM images. Functionaliza-

tion of the charcoal salt (formed by electron transfer as

lithium intercalates into the activated charcoal layers) leads

to a disordered structure with short range ordering of the sep-

arated layers as shown in Fig. 6c and d. This observation is

strictly analogous to the debundling of carbon nanotubes

and graphite reported previously [12,27,28].

In conclusion, we describe a simple route to functionalized

activated charcoal that is soluble in aprotic organic solvents.

TGA data indicate that there is one dodecyl group for every

48 sp2 activated charcoal carbon atoms. Future studies will in-

volve the attachment of other functional groups that will en-

hance adsorptive properties of charcoal.

Acknowledgements

We thank the Robert A. Welch Foundation (C-0490), the Na-

tional Science Foundation (CHE-0450085) and the Houston

Area Research Council for support of this work.

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