Synthesis and Characterization of Activated Carbon from Coconut
Pulp via Physicochemical Activation and Its Potential for Biogas
Purification
Article
Yulizar Prawiranti
*
, Weni Mandasari
Chemistry Study Program, OSO University, Pontianak -78113, Indonesia
A
bstract
Coconut pulp is an abundant lignocellulosic byproduct with strong potential as a sustainable
precursor for activated carbon (AC). This study synthesized and characterized coconut-pulp-
derived
AC
via
an
integrated
physicochemical
route
and
assessed
adsorption-relevant
structural features for biogas upgrading (CO
₂
/H
₂
S). The process comprised carbonization at 400
°C, chemical activation with 3 N H
₃
PO
₄
and 3 N KOH, followed by physical activation at 600 °C.
Proximate analysis indicated low moisture (4.665%) and ash content (0.637%) with a yield of
12.38%, while the volatile fraction remained relatively high, consistent with the lignocellulosic
nature of the precursor. The produced AC exhibited a BET surface area of 345.57 m²/g with a
micropore-dominated structure, supported by an iodine number of 161.973 mg/g. FTIR spectra
suggested the formation of stable aromatic structures after activation, and SEM observations
revealed a well-developed pore network. As a key novelty, sequential dual chemical activation
(H
₃
PO
₄
+ KOH) combined with subsequent physical activation was employed to enhance pore
connectivity and carbon purity, which are critical for physisorption-driven adsorption. Overall,
coconut-pulp-derived AC prepared via integrated physicochemical activation shows promising
characteristics as a low-cost and sustainable adsorbent for biogas purification. Future work will
quantify CO
₂
/H
₂
S adsorption performance using real or synthetic biogas streams and optimize
activation parameters for scale-up.
Keywords:
Activated
carbon,
biogas,
coconut
pulp,
CO
₂
and
H
₂
S
adsorption,
physicochemical
activation
*
Corresponding author
Email addresses:
yulizarfery1987@gmail.com
(Yulizar Prawiranti)
DOI:
https://doi.org/10.22437/chp.v10i1.48610
Received
September 28
th
2025;
Accepted
April 02
nd
2026;
Available online
May 18
st
2026
Copyright © 2026 by Authors, Published by Chempublish Journal. This is an open access article under the CC BY License
(
https://creativecommons.org/licenses/by/4.0
)
1
Graphical Abstract
Introduction
The utilization of renewable energy is a key
pillar
in
the
global
transition
toward
sustainable
energy
systems.
In
Indonesia,
the
national
medium-term
development
plan
for
2025–2029
emphasizes
energy
independence
through
the
sustainable
use
of local resources. Among various renewable
energy
sources,
biogas
has
attracted
significant
attention
due
to
its
potential
to
simultaneously
provide
clean
energy
and
support
environmentally
friendly
waste
management.
Biogas
is
produced
through
the
anaerobic
fermentation
of
organic
waste;
however,
raw
biogas
typically
contains impurities such as carbon dioxide
(CO
₂
)
and
hydrogen
sulfide
(H
₂
S).
These
contaminants
are
corrosive
in
nature,
reduce
the
calorific
value
of
biogas,
and
accelerate
the
degradation
of
energy
conversion equipment, thereby limiting the
widespread
utilization
of
biogas
without
prior upgrading [1].
Various
technologies
have
been
developed
for biogas upgrading, including absorption,
membrane
separation,
and
adsorption.
Among
these
methods,
adsorption
using
activated
carbon
is
considered
a
relatively
simple, cost-effective, and flexible approach,
particularly
when
the
activated
carbon
is
synthesized
from
abundant
and
low-cost
biomass residues [2,3]. Indonesia, as one of
the
world’s
largest
coconut
producers,
generates
substantial
amounts
of
coconut-
processing residues, including coconut pulp
(or
coconut
dregs),
which
are
rich
in
lignocellulosic
components
and
therefore
promising
precursors
for
activated
carbon
production [4][5]. Previous studies have also
reported
that
coconut-based
residues
exhibit
favorable
performance
as
raw
materials
for
activated
carbon
in
various
adsorption applications [6].
Nevertheless, the performance of biomass-
derived
activated
carbon
is
strongly
influenced
by
the
activation
method
employed.
Recent
studies
have
demonstrated
that
activated
carbon
produced from coconut pulp via single-step
chemical
activation
using
phosphoric
acid
(H
₃
PO
₄
)
may
exhibit
an
extremely
high
volatile
matter
content,
reaching
up
to
94.86%,
which
far
exceeds
the
national
standard limit (SNI <25%). Excessive volatile
matter
can
block
active
pores,
hinder
adsorbate
diffusion,
and
ultimately
reduce
2
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
gas
adsorption
efficiency
[7].
In
contrast,
several
studies
have
reported
that
the
combination
of
chemical
activation
with
physical
or
thermal
activation
can
significantly
enhance
specific
surface
area,
improve
micro–mesopore
distribution,
and
reduce
volatile
components,
leading
to
improved
adsorption
performance
for
CO
₂
and H
₂
S [2]. Further empirical evidence has
shown
that
activated
carbon
derived
from
food
industry
residues
can
achieve
CO
₂
adsorption
capacities
of
up
to
495
mg
g
⁻
¹
under high-pressure conditions, highlighting
the
strong
potential
of
biomass-based
activated
carbon
for
biogas
purification
applications [8].
However,
systematic
studies
on
the
application
of
sequential
dual
chemical
activation
combined
with
subsequent
physical
activation
for
activated
carbon
derived
from
coconut
pulp
remain
very
limited.
In
particular,
the
relationships
between
integrated
activation
strategies,
volatile
matter
reduction,
pore
structure
development, and their implications for CO
₂
and
H
₂
S
adsorption
potential
in
biogas
upgrading
have
not
yet
been
comprehensively
reported.
This
knowledge
gap
provides
the
scientific
basis
for
the
present study.
Accordingly,
this
study
aims
to
synthesize
activated carbon from coconut pulp through
an
integrated
physicochemical
activation
approach
and
to
evaluate
its
key
physicochemical
characteristics
relevant
to
adsorption
processes,
including
specific
surface
area,
pore
structure,
and
surface
functional
groups.
In
addition,
the
theoretical
potential
of
the
synthesized
activated carbon for CO
₂
and H
₂
S adsorption
in biogas purification is assessed.
The
novelty
of
this
study
lies
in
the
first
systematic
application
of
sequential
dual
chemical
activation
using
H
₃
PO
₄
and
KOH
combined
with
subsequent
physical
activation on coconut pulp–derived activated
carbon,
as
well
as
in
the
analysis
of
the
relationship
between
volatile
matter
reduction
and
pore
structure
development
in relation to gas adsorption potential. This
approach
is
expected
to
produce
activated
carbon
with
superior
quality
compared
to
previously
reported
single-activation
methods
[2,7,8].
More
broadly,
this
study
contributes to the development of biomass-
based adsorbent materials while supporting
clean
energy
initiatives
and
sustainable
agricultural waste management.
Materials and Methods
Materials and Instrumentations
Coconut
pulp
was
used
as
the
main
precursor
for
activated
carbon
synthesis.
Chemical reagents included phosphoric acid
(H
₃
PO
₄
, 3 N), potassium hydroxide (KOH, 3
N),
hydrochloric
acid
(HCl,
5%),
iodine
solution (0.1 N), potassium iodate (KIO
₃
, 0.1
N), potassium iodide (KI, 10%), sulfuric acid
(H
₂
SO
₄
,
2
N),
sodium
thiosulfate
(Na
₂
S
₂
O
₃
,
0.1
N),
and
starch
indicator
(1%).
Distilled
and deionized water were used throughout
the
experiments.
The
main
instruments
consisted of a muffle furnace, drying oven,
mechanical
shaker,
FTIR
spectrometer
(Bruker
Alpha
II),
scanning
electron
microscope
equipped
with
EDX
(JEOL
JSM-
6510LA),
and
BET
surface
area
analyzer
(Quantachrome Autosorb-iQ).
Synthesis of Coconut Pulp–Based Activated
Carbon
Coconut
pulp
(1,043
g)
was
washed
thoroughly with water to remove impurities
and
sun-dried
until
constant
weight.
The
dried biomass was carbonized in a furnace
at
400
°C
for
2
h.
The
resulting
char
was
ground
and
sieved
to
a
particle
size
of
20
mesh prior to activation.
3
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
Sequential
chemical
activation
was
conducted by impregnating the char with 3
N
H
₃
PO
₄
(carbon-to-solution
ratio
1:2,
w/v)
for 24 h at room temperature. The sample
was
then
washed
with
distilled
water
until
neutral pH and dried at 110 °C for 3 h
[7].
Subsequently,
alkaline
activation
was
performed using 3 N KOH under the same
impregnation
ratio
and
duration,
followed
by washing and drying [9]. Physical activation
was
carried
out
by
heating
the
chemically
activated carbon at 600 °C for 1 h in a closed
furnace,
followed
by
natural
cooling.
The
activated
carbon
was
finally
washed
with
deionized water to remove residual ash
and dried at 110 °C [10].
Proximate Analysis and Iodine Number
Proximate
analysis,
including
moisture
content,
volatile
matter,
ash
content,
fixed
carbon, and yield, was performed according
to the Indonesian National Standard (SNI 06-
3730-1995).
All
measurements
were
conducted
in
triplicate,
and
average
values
were reported to ensure data reliability. The
iodine adsorption capacity was determined
using a standard titration method. Activated
carbon samples (0.5 g) were contacted with
standardized
iodine
solution
under
continuous shaking for 30 min, followed by
filtration
and
back-titration
using
standardized
Na
₂
S
₂
O
₃
solution.
Blank
and
sample
titrations
were
performed
in
triplicate,
and
iodine
numbers
were
calculated based on the difference between
blank and sample titration volumes.
Characterization
Fourier
Transform
Infrared
(FTIR)
spectroscopy
was
used
to
identify
surface
functional
groups
of
the
activated
carbon.
Surface
morphology
and
elemental
composition were examined using SEM–EDX
analysis.
Textural
properties,
including
specific surface area, pore volume, and pore
size
distribution,
were
evaluated
using
nitrogen
adsorption–desorption
isotherms
based on the BET and BJH methods.
Data Processing and Reproducibility
All
experimental
measurements
were
performed at least three times, and results
are
presented
as
mean
values.
Data
calculations were conducted using standard
analytical
equations,
while
graphical
analyses were processed using spreadsheet
software. Instrumental data (BET, FTIR, SEM–
EDX)
were
analyzed
using
manufacturer-
provided
software.
Reproducibility
was
ensured
through
consistent
operating
conditions and repeated measurements.
Figure 1.
Flowchart of coconut pulp–derived
activated
carbon
synthesis,
testing,
and
physicochemical characterization.
Results and Discussion
Synthesis of Coconut Pulp-Based Activated
Carbon
The
use
of
coconut
pulp
biomass
as
a
precursor for activated carbon offers an eco-
friendly
solution
to
reduce
organic
waste
4
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
while
adding
economic
value.
Activated
carbon’s
high
surface
area
and
porous
structure
make
it
suitable
for
adsorption,
purification, and energy applications. In this
study, 1043 g of coconut pulp was processed
through washing, drying, carbonization, and
sieving.
Washing
eliminated
impurities,
while
drying
(sun
and
oven
at
110°C)
ensured
moisture
reduction
for
product
stability [7].
Carbonization was performed at 400°C for 2
hours, which is sufficient for soft, low-density
coconut pulp to undergo effective pyrolysis
while
preserving
pore
development
[11].
Although
higher
temperatures
enhance
porosity [12], previous studies confirm that
even at 400°C, chemically activated coconut
residue
can
achieve
surface
areas
up
to
1187.61 m²/g with dominant microporosity.
The carbonized product was sieved through
a 20-mesh screen to obtain particles suitable
for adsorption applications, including biogas
purification. This mesh size supports optimal
CO
₂
and
H
₂
S
adsorption
while
maintaining
gas
flow
efficiency
in
fixed-bed
systems.
Similar results were achieved using banana
stem-based activated carbon (CO
₂
reduction
39.89%,
CH
₄
increased
to
64.79%)
[13]
and
tofu waste-based carbon (CH
₄
up to 76.86%)
[14],
confirming
the
effectiveness
of
20-
mesh particle sizing
Activation of Coconut Pulp Carbon
Chemical
activation
using
phosphoric
acid
(H
₃
PO
₄
)
successfully
produced
activated
carbon with a well-developed pore structure
and
high
surface
area.
The
introduction
of
phosphate-based
polar
functional
groups
enhanced
the
surface
affinity
for
polar
compounds
such
as
H
₂
S,
while
also
increasing CO
₂
adsorption capacity through
quadrupole
interactions
and
micropore
formation [15]. This was followed by alkaline
activation using a 3N KOH solution, known
for promoting micropore development and
further increasing surface area.
Physical
activation
was
subsequently
conducted
at
600°C
for
one
hour
in
the
absence
of
inert
gas,
aiming
to
open
pore
structures
and
eliminate
volatile
content.
Although
inert
gas
is
commonly
used
to
prevent
oxidation,
semi-closed
furnace
systems can still enable efficient activation,
as
supported
by
surface
area
values
reaching
548
m²/g
without
inert
protection
[16].
High-temperature
activation
in
such
conditions may increase ash content due to
the
presence
of inorganic minerals like Ca,
Mg,
and
K.
The
resulting
basicity
of
the
carbon
surface
enhances
interactions
with
acidic and polar gases such as H
₂
S and CO
₂
[9]. Similar outcomes have been reported in
studies
where
high
surface
pH
improved
adsorption
performance
despite
the
absence of inert gas [16]. In this study, the
surface
pH
was
measured
at
13–14,
indicating
substantial
ash
content.
As
a
preventive
measure,
deionized
water
washing was applied to reduce residual ash,
prevent
pore
blockage,
and
maintain
optimal adsorption efficiency.
Proximate Analysis
Proximate
analysis
evaluates
key
biomass
properties
moisture,
ash,
volatile
matter,
and
fixed
carbon
that
influence
thermal
stability, chemical reactivity, and micropore
formation. These parameters are critical for
determining
biomass
suitability
as
a
precursor
to
activated
carbon,
as
they
directly
affect
adsorption
capacity
and
carbon yield [17].
Yield Determination (SNI 06-3730-1995)
The
yield
of
activated
carbon
is
a
key
indicator
of
the
efficiency
of
biomass
conversion into porous materials with high
adsorption potential. From 485.45 g of dried
coconut
pulp,
60.11
g
of
activated
carbon
5
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
was
obtained
after
carbonization,
chemical
activation with H
₃
PO
₄
and KOH, and physical
activation at 600°C, resulting in a final yield
of 12.38%. Using dry mass as the calculation
basis
aligns
with
standard
practice
in
biomass-based activated carbon production,
as
only
the
solid
fraction
contributes
to
carbonization
and
pore
formation.
This
approach
ensures
greater
accuracy
and
consistency
across
studies,
avoiding
bias
from variable moisture content [18].
The
obtained
yield
is
consistent
with
the
range of 11.2–14.63% reported for coconut
residues [19]. Low yields are typically caused
by
mass
loss
during
carbonization
and
thermal degradation of organics, particularly
due to low lignin content. Nonetheless, yield
reduction is often accompanied by improved
pore
development
and
surface
area
expansion,
enhancing
adsorption
performance for applications such as water
purification and CO
₂
and H
₂
S capture [6].
Table
1.
Presents
the
comparative
proximate
analysis
of
dried
coconut
pulp,
chemically
activated
coconut
pulp
carbon,
and
combined
chemical–physical
activation,
following
the
Indonesian National Standard (SNI 06-3730-1995).
Sample
Moisture
content
(%)
Ash content
(%)
Volatile matter
content
(%)
Fixed carbon
content
(%)
Dried coconut pulp
1.352
0.834
98.946
0.220
Coconut
pulp
activated
carbon-chemical
6.179
8.651
89.316
2.033
Coconut
pulp
activated
carbon-chemical-
physical
4.665
0.637
97.485
1878
SNI 06-3730-1995
Max 15
Max 10
Max 25
Min.65
Moisture
Content
Determination
(SNI
06-
3730-1995)
Moisture
content
is
a
critical
parameter
in
activated
carbon
characterization,
as
it
directly affects storage
stability, adsorption
efficiency,
and
susceptibility
to
microbial
growth. In this study, the measured moisture
contents
were
1.352%
for
dried
coconut
pulp, 6.179% for chemically activated carbon
(H
₃
PO
₄
–KOH),
and
4.665%
for
chemically–
physically
activated
carbon,
all
well
below
the SNI maximum limit of 15%.
The
low
value
for
dried
coconut
pulp
indicates effective initial dehydration, while
the
higher
level
in
chemically
activated
samples
is
attributed
to
the
hygroscopic
nature of KOH and moisture uptake during
immersion
and
washing.
In
contrast,
the
lower
value
in
chemically–physically
activated
carbon
suggests
that
high-
temperature
thermal
activation
effectively
removed residual water, enhancing stability.
These findings are consistent with [20], who
reported 9.57% moisture in natural coconut
fibers,
higher
than
the
values
obtained
in
this study, underscoring the efficiency of the
applied activation and drying methods. Low
moisture
content
in
activated
carbon
has
been
reported
to
enhance
shelf
life
and
adsorption
performance.
In
this
study,
the
low
moisture
level
indicates
successful
activation and drying processes, supporting
the
potential
of
coconut
pulp-based
activated
carbon
for
water
and
gas
purification applications [21].
6
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
Determination
of
Volatile
Matter
Content
(SNI 06-3730-1995)
Coconut pulp, a by-product of coconut milk
extraction,
contains
47.18%
cellulose,
12.10% hemicellulose, and 10.58% lignin [5].
Its soft parenchymal structure contributes to
low
density
and
a
high
surface
area,
accelerating
thermal
decomposition
during
carbonization. The low activation energies of
cellulose and hemicellulose [22] explain the
high
volatile
matter
content
recorded
at
different
stages:
98.946%
in
raw
coconut
pulp, 89.316% after chemical activation, and
97.485%
following
combined
chemical–
physical
activation.
These
results
are
consistent
with
[7],
who
reported
94.860%
volatile matter in phosphoric acid-activated
coconut pulp-based carbon.
The
decrease
to
89.316%
after
chemical
activation confirms the effectiveness of KOH
as a dehydrating and oxidizing agent. KOH
facilitates the removal of non-carbonaceous
substances,
promotes
aromatic
structure
formation,
and
supports
micropore
development,
enhancing
thermal
stability
and surface area for adsorption [23].
Combined
activation
showed
a
less
significant
reduction
to
97.485%,
likely
due
to
limited
pyrolysis
efficiency
under
semi-
closed conditions without inert gas [16]. All
samples still exceeded the SNI 06-3730-1995
volatile matter threshold of 25%, indicating
the
need
for
further
optimization
in
activation parameters.
High volatile content, however, may benefit
adsorption
by
introducing
active
functional
groups
like
–OH,
–COOH,
and
–C=O,
which
facilitate interactions with polar gases such
as CO
₂
and H
₂
S. Alkaline activation not only
reduces
volatile
matter
but
also
improves
carbon
structure
and
enhances
microporosity and adsorption capacity [6].
Determination of Ash Content (SNI 06-3730-
1995)
Ash
content
represents
the
residual
inorganic
compounds
remaining
after
combustion
and
is
a
key
determinant
of
activated
carbon
quality
and
purity,
particularly
due
to
elements
such
as
silica,
calcium,
and
magnesium that
are
resistant
to thermal degradation [24].
The analysis showed that dried coconut pulp
contained
0.834%
ash,
which
increased
to
8.651%
after
chemical
activation
but
decreased
to
0.637%
following
combined
chemical–physical
activation.
All
values
remained below the maximum threshold of
10% set by SNI 06-3730-1995. The higher ash
content
in
chemically
activated
samples
is
likely
attributed
to
residual
inorganic
salts
such
as
K
₂
CO
₃
and
K
₂
O
from
insufficient
washing of KOH, while efficient washing has
been
reported
to
reduce
ash
content
and
enhance
carbon
purity
[25].
Elevated
ash
content may also indicate the deposition of
minerals on the carbon surface or within its
pores,
potentially
hindering
adsorption
performance.
Therefore,
maintaining
low
ash
content
is
not
only
critical
to
meeting
quality
standards
but
also
to
ensuring
the
performance
and
chemical
stability
of
activated carbon.
Determination
of
Fixed
Carbon
Content
(Based on SNI 06-3730-1995)
The fixed carbon content of coconut residue-
based activated carbon was evaluated based
on
the
Indonesian
National
Standard
(SNI
06-3730-1995), which stipulates a minimum
of 65% as a quality benchmark. In this study,
all
samples
recorded
fixed
carbon
levels
below
the
standard,
indicating
incomplete
carbonization
due
to
high
volatile
matter.
Despite
this,
a
high
volatile
fraction
can
promote
pore
development
and
enhance
surface chemistry through the formation of
7
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
–OH,
–COOH,
and
–C=O
groups,
which
improve interactions with polar compounds.
Activated
carbon
with
substandard
fixed
carbon
levels
has
previously
shown
high
adsorption efficiency for iron ions, attributed
to oxygenated functional groups generated
during
carbonization
[7].
Similar
observations were made by previous study
[26],
who
reported
that
highly
porous
and
chemically active carbon materials achieved
superior
greenhouse
gas
adsorption
compared
to
commercial
activated
carbon,
regardless of fixed carbon content.
These
results
suggest
that,
although
the
samples
did
not
meet
the
fixed
carbon
requirement,
their
porous
structure
and
functionalized
surfaces
still
provide
significant
potential
for
adsorption
applications.
A
comprehensive
assessment
of activated carbon quality should therefore
include surface area, porosity, and chemical
functionality alongside fixed carbon content.
Iodine Number Determination
Activated
carbon
is
widely
used
to
remove
harmful
gases
like
CO
₂
and
H
₂
S,
with
the
iodine
number
(mg
I
₂
/g)
serving
as
a
key
indicator
of
micropore
content
and
adsorption
capacity.
Experimental
data
(Table 2) showed variations in iodine uptake
across the three samples
Table
2
.
Iodine
adsorption
capacity
of
various activated carbon samples
Sample
Iodine adsorption
capacity (mg/g)
Dried coconut pulp
141.057
Coconut
pulp
activated
carbon-
chemical
209.003
Coconut
pulp
activated
carbon-
chemical-physical
161.973
The elevated iodine number recorded in the
chemically
activated
coconut
pulp
sample
confirms
the
superior
efficacy
of
chemical
activation
in
enhancing
surface
area
and
promoting micropore formation. This aligns
with
findings
by
[26],
which
indicate
that
biomass-derived activated carbons with high
iodine
values
exhibit
enhanced
adsorption
of toxic and greenhouse gases.
Micro- and mesopores play a critical role in
the
physisorption
of
small
gas
molecules
such
as
CO
₂
and
H
₂
S.
The
adsorption
behavior varies with molecular polarity; H
₂
S,
being
polar,
and
CO
₂
,
non-polar,
require
optimized
pore
architecture
and
sufficient
surface area for effective capture.
With
an
iodine
number
exceeding
209.003
mg/g, the chemically activated coconut pulp
carbon
exhibits
strong
potential
for
application
in
air
purification
systems,
particularly
for
mitigating
CO
₂
and
H
₂
S
emissions from industrial and organic waste
sources.
Its
high
adsorption
capacity
and
modifiable surface chemistry position it as a
viable
material
for
advanced
selective
adsorbents or catalytic support platforms.
IR-Spectroscopy of Activated Carbon
FTIR
analysis
was
performed
to
evaluate
changes
in
surface
functional
groups
resulting
from
chemical
and
physical
activation
of
coconut
pulp–derived
carbon.
The
FTIR
spectra
of
dried
coconut
pulp,
chemically activated carbon, and chemically–
physically activated carbon are presented in
Figure 2. Figure 2 shows that dried coconut
pulp exhibits typical lignocellulosic features,
characterized
by
a
broad
–OH
stretching
band around 3400 cm
⁻
¹ and a C=O stretching
band
near
1740
cm
⁻
¹,
indicating
the
presence
of
hydroxyl
and
carbonyl
groups
associated with cellulose and hemicellulose.
Following
chemical
activation,
notable
spectral
changes
were
observed.
The
8
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
intensity
of
–OH
and
C=O
bands
markedly
decreased, indicating the decomposition of
oxygen-containing
functional
groups.
In
addition,
the
emergence
of
absorption
bands in the 750–880 cm
⁻
¹ region suggests
the
formation
of
substituted
aromatic
structures,
reflecting
increased
aromaticity
of
the
carbon
framework.
These
changes
indicate
that
chemical
activation
effectively
reduces
polar
functional
groups
while
promoting aromatic domain development.
Figure
2.
FTIR
spectra
of
dried
coconut
pulp,
coconut
pulp
activated
carbon-chemical,
and
coconut pulp activated carbon-chemical- physical, showing the transformation of functional
groups during the activation process.
Further
modification
was
evident
in
the
chemically–physically
activated
sample,
where the –OH and C=O bands were further
diminished
and
a
distinct
band
near
900
cm
⁻
¹ appeared, attributed to aromatic =C–H
vibrations.
This
progressive
reduction
of
polar groups and enhancement of aromatic
structures
suggest
more
extensive
devolatilization
and
structural
rearrangement during combined activation.
These
spectral
transformations
are
consistent with previous studies on coconut-
based
activated
carbons,
which
reported
that
activation
processes
reduce
hydroxyl
and carbonyl functionalities while enhancing
aromatic character due to hemicellulose and
lignin degradation [27]. Similar FTIR behavior
was
also
observed
for
H
₃
PO
₄
-activated
coconut
residue–based
activated
carbon,
where
the
formation
of
aromatic
=C–H
structures
was
correlated
with
improved
adsorption
performance
[7].
Overall,
the
FTIR
results
confirm
that
integrated
chemical–physical
activation
effectively
modifies
surface
chemistry
by
decreasing
polarity and increasing aromaticity, which is
favorable for adsorption applications.
Morphological of Activated Carbon
SEM–EDX
analysis
was
conducted
to
investigate
the
pore
morphology
and
chemical composition of dried coconut pulp,
coconut pulp activated carbon-chemical, and
coconut
pulp
activated
carbon-chemical-
physical. SEM images at 500× magnification
(Figure 3.a) revealed that the dried coconut
pulp
sample
exhibited
a
rough
surface
dominated
by
macropores,
which
likely
formed
due
to
the
evaporation
of
volatile
compounds
during
carbonization.
At
a
medium magnification of 5000× (Figure 3.b),
the emergence of mesopores was observed,
serving
as
transitional
diffusion
pathways.
However,
at
higher
magnification
(10,000×;
Figure
3.c),
only
a
few
micropores
were
visible,
with
uneven
distribution.
These
9
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
findings
are
consistent
with
[28],
who
reported
that
physically
activated
coconut
shell-based
carbon
typically
contains
macropores in the range of 0.8–1.0 µm and
exhibits limited micropore distribution.
[A]
[B]
[C]
Figure 3.
SEM images of dried coconut pulp at different magnifications: 500× [A], 5000× [B],
10,000× [C].
SEM analysis of chemically activated coconut
pulp
carbon
showed
a
more
open surface,
thinner
pore
walls,
and
well-developed
meso- and micropores. The presence of fine
particles
suggested
residual
activating
agents.
This
observation
is
in
line
with
the
findings
of
[29],
who
reported
that
KOH
activation
enhances
pore
quantity
and
connectivity
but
tends
to
leave
behind
mineral
residues
such
as
K
₂
O.
EDX
results
further
support
this,
showing
a
carbon
composition
of
69.44%
(PURE)
and
88.16%
(OXIDE),
along
with
a
relatively
high
potassium
content
of
5.72%
(PURE)
and
10.65% (OXIDE).
The coconut pulp activated carbon-chemical-
physical
exhibited
the
most
optimal
characteristics
among
the
samples.
SEM
images at various magnifications revealed a
well-organized
hierarchical
pore
structure
consisting of macropores serving as primary
transport
channels,
mesopores
facilitating
molecular diffusion, and densely distributed
micropores.
This
sponge-like
structure
indicates
a
high
specific
surface
area
and
excellent
pore
connectivity.
These
findings
are consistent with [30], who reported that
combined
activation
methods
can
produce
activated
carbon
with
high
porosity
and
hierarchical
structures
that
enhance
molecular
diffusion.
EDX
analysis
further
supports
these
results,
showing
dominant
carbon
content
(89.48%
PURE;
96.65%
OXIDE),
moderate
oxygen
content
(8.23%),
and
very
low
levels
of
residual
mineral
elements.
10
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
[A]
[B]
[C]
Figure 4.
SEM images of coconut pulp activated carbon-chemical at different magnifications:
500× [A], 5000× [B], 10,000× [C].
[A]
[B]
[C]
Figure
5.
SEM
images
of
coconut
pulp
activated
carbon-chemical-physical
at
different
magnifications: 500× [A], 5000× [B], 10,000× [C].
11
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
Comparatively,
the
dried
coconut
pulp
exhibits superior carbon purity but retains a
relatively simple pore structure. The coconut
pulp
activated
carbon-chemical
shows
improved
pore
development
and
the
presence
of
polar
functional
groups;
however, it also presents a decline in purity
due
to
potassium
residue.
In
contrast,
the
coconut
pulp
activated
carbon-chemical-
physical
offers
the
most
balanced
characteristics—exceptionally
high
carbon
purity,
an
optimized
hierarchical
pore
structure,
and
minimal
residual
mineral
content.
These
findings
are
not
only
consistent with previous literature but also
affirm that the combined activation method
is
a superior
approach
for
producing
high-
quality
activated
carbon
in
terms
of
both
structural
morphology
and
chemical
composition
Surface
Textural
Analysis
Using
BET–BJH
Methods
The
textural
properties
of
coconut
pulp–
derived
carbon
were
evaluated
using
BET–
BJH analysis, as summarized in Table 3. The
dried
coconut
pulp
sample
exhibited
a
relatively high specific surface area of 245.72
m²/g, dominated by microporous structures
(200.70
m²/g)
with
an
average
pore
size
of
2.085
nm.
This
behavior
is
consistent
with
previous
reports
indicating
that
lignocellulosic
coconut
residues
inherently
promote
micropore
formation
during
carbonization
due
to
the
decomposition
of
cellulose,
hemicellulose,
and
lignin
components [5,11].
In contrast, the coconut pulp–derived carbon
subjected
solely
to
chemical
activation
exhibited
a
significant
reduction
in
BET
surface
area
(10.47
m²/g)
and
total
pore
volume,
accompanied
by
an
increase
in
average pore size to 7.262 nm. This decrease
can
be
scientifically
explained
by
pore
blockage
and
limited
pore
accessibility
caused
by
residual
activating
agents
and
volatile
compounds
that
were
not
completely
removed
in
the
absence
of
subsequent physical activation.
Table
3.
Textural
properties
of
activated
carbon
based
on
BET
and
BJH
analyses
(values
reported as mean ± standard deviation, n = 3).
Sample
BET surface
area (m²/g)
Total
pore
volume
(cc/g)
Average
pore
size
(nm)
Micropore
surface area
(m²/g)
Micropore
volume
(cc/g)
Dried
coconut
pulp
245.72
0.1281
2.085
200.70
0.0808
Coconut
pulp
activated
carbon-
chemical
10.47
0.01901
7.262
3.352
0.001468
Coconut
pulp
activated
carbon-
chemical-
physical
345.57
0.1595
1.846
282.80
0.1059
12
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
Previous
studies
have
reported
that
chemical
activation
using
strong
activating
agents
such
as
phosphoric
acid
or
alkaline
compounds
may
lead
to
the
formation
of
inorganic
residues
and
tarry
by-products,
which
can
partially
occupy
pore
channels
and suppress nitrogen adsorption, resulting
in
artificially
low
BET
surface
area
values
[7,9].
Furthermore,
chemical
activation
without
high-temperature
thermal
treatment
may
induce
pore widening
rather
than
effective
pore
development,
shifting
the
pore
structure from microporous to mesoporous
domains.
This
phenomenon
explains
the
drastic decrease in micropore surface area
(3.352
m²/g)
observed
for
the
chemically
activated sample. Similar trends have been
reported
in
coconut-based
activated
carbons,
where
insufficient
thermal
activation led to reduced microporosity due
to incomplete removal of activating residues
and unstable pore structures [10,19].
By
comparison,
the
coconut
pulp–derived
activated
carbon
produced
through
combined
chemical
and
physical
activation
exhibited
the
highest
BET
surface
area
(345.57
m²/g)
and
micropore
contribution
(282.80 m²/g), with a reduced average pore
size
of
1.846
nm.
The
subsequent
physical
activation
at
600
°C
effectively
removed
residual
activating
agents,
promoted
devolatilization,
and
reopened
blocked
pores,
resulting
in
a
well-developed
and
interconnected
microporous
structure.
The
critical
role
of
physical
activation
in
enhancing pore accessibility and stabilizing
pore architecture has been widely reported
for
biomass-based
activated
carbons
[3,10,
25].
Overall,
the
observed
reduction
in
BET
surface
area
for
the
chemically
activated
sample
does
not
indicate
inferior
material
quality, but rather reflects limited accessible
porosity
due
to
residual
chemical
species
and
the
absence
of
sufficient
thermal
activation.
The
substantial
recovery
and
enhancement
of
surface
area
achieved
through
integrated
chemical–physical
activation
confirm
that
dual
activation
strategies are essential for producing high-
quality
activated
carbon
with
enhanced
microporosity,
which
is
particularly
beneficial
for
gas
adsorption
applications
such
as
CO
₂
and
H
₂
S
removal
from
biogas
[2,8].
Evaluation
of
Adsorption
Potential
of
Coconut Pulp–Derived Activated Carbon for
CO
₂
and H
₂
S Removal in Biogas
Activated carbon synthesized from coconut
pulp residue exhibits strong potential as an
adsorbent
for
biogas
purification,
particularly
for
the
removal
of
carbon
dioxide
(CO
₂
)
and
hydrogen
sulfide
(H
₂
S).
This
evaluation
is
based
on
an
integrated
analysis of surface textural properties (BET–
BJH),
surface
chemistry
(FTIR),
iodine
number,
and
supporting
morphological
evidence (SEM–EDX). These parameters are
widely
recognized
as
key
indicators
governing
gas
adsorption
performance
in
porous carbon materials.
Surface textural analysis demonstrated that
the
chemically
and
physically
activated
carbon possessed a high BET specific surface
area
of
345.57
m²/g,
with
a
dominant
micropore surface area of 282.80 m²/g. The
prevalence
of
microporosity
is
particularly
advantageous
for
the
adsorption
of
small
gas molecules such as CO
₂
(kinetic diameter
≈
0.33
nm)
and
H
₂
S
(≈
0.36
nm),
which
preferentially
adsorb
within
narrow
micropores.
Previous
studies
have
shown
that activated carbon with a well-developed
microporous structure can achieve very high
CO
₂
removal
efficiency
under
optimized
adsorption
conditions,
highlighting
the
13
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
crucial role of micropore-dominated surface
area in gas separation processes [31].
The adsorption potential inferred from BET
analysis
is
further supported
by
the
iodine
number
of
161.973
mg/g,
which
quantitatively
reflects
the
abundance
of
accessible micropores. High iodine numbers
are
commonly
associated
with
enhanced
adsorption
capacity,
as
iodine
molecules
predominantly occupy microporous regions.
A
positive
correlation
between
iodine
number
and
adsorption
performance
has
also
been
reported
for
biomass-derived
activated
carbons,
confirming
that
higher
iodine uptake corresponds to increased gas
adsorption efficiency [32]. In this study, the
consistency
between
high
BET
micropore
surface
area
and
iodine
number
strongly
indicates
favorable
adsorption
characteristics.
FTIR
analysis
provides
complementary
insight into the surface chemistry governing
adsorbate–adsorbent
interactions.
The
observed
reduction
in
polar
functional
groups such as hydroxyl (–OH) and carbonyl
(C=O), along with the formation of aromatic
C=C
bonds,
suggests
increased
surface
hydrophobicity and structural stability. A less
polar
surface
is
beneficial
for
selective
adsorption
of
non-polar
or
weakly
polar
gases such as CO
₂
and H
₂
S, as it minimizes
competitive
adsorption
with
water
vapor.
Similar
FTIR
characteristics
have
been
reported
to
significantly
enhance
H
₂
S
adsorption
performance
in
chemically
modified
coconut
shell–based
activated
carbons [33].
Morphological analysis using SEM revealed a
hierarchical
pore
structure
consisting
of
interconnected
macro-,
meso-,
and
micropores,
which
facilitates
gas
diffusion
toward active adsorption sites. EDX analysis
confirmed a high carbon content of 96.65%,
indicating
minimal
inorganic
residue
that
could
otherwise
block
pore
channels.
Comparable
structural
features
and
high
carbon
purity
have
been
reported
for
biomass-based activated carbons exhibiting
surface
areas
exceeding
400
m²/g
and
superior gas adsorption behavior [34].
From
an
application
perspective,
activated
carbon
has
been
demonstrated
to
significantly
improve
biogas
quality
by
increasing
methane
(CH
₄
)
concentration
to
approximately
91.6%
while
reducing
CO
₂
levels below 14% using adsorption columns
arranged in series [35]. Considering the high
micropore
surface
area,
elevated
iodine
number,
and
favorable
surface
chemistry
observed in this study, coconut pulp–derived
activated
carbon
is
expected
to
exhibit
comparable adsorption performance. These
results
confirm
that
the
material
is
technically
suitable
and
economically
promising for sustainable biogas upgrading
applications.
Conclusion
Activated carbon derived from coconut pulp
waste was successfully synthesized through
an
integrated
chemical–physical
activation
strategy,
resulting
in
significant
enhancement of physicochemical properties
relevant
to
gas
adsorption.
The
combined
activation approach effectively developed a
well-connected
hierarchical
pore
structure,
as evidenced by a high BET specific surface
area
of
345.57
m²/g
and
a
dominant
micropore
surface
area
of
282.80
m²/g,
which
are
particularly
favorable
for
the
adsorption
of
small
gas
molecules
such
as
CO
₂
and
H
₂
S.
The
high
carbon
purity
(96.65%), iodine number (161.973 mg/g), low
ash
content
(0.637%),
and
moderate
moisture
content
(4.665%)
further
confirm
the high quality and structural stability of the
synthesized
activated
carbon.
Scientifically,
this study demonstrates that sequential dual
14
Y. Prawiranti et al.,
Chempublish Journal, 10(1) 2026, 1 - 18
chemical
activation
followed
by
physical
activation
is
an
effective
strategy
to
overcome
pore
blockage
and
limited
microporosity
associated
with
single-step
activation,
thereby
strengthening
the
structure–property relationship of biomass-
based
adsorbents.
From
an
application
perspective, the results highlight the strong
potential of coconut pulp–derived activated
carbon
as
a
sustainable
and
low-cost
adsorbent
for
biogas
upgrading.
Nevertheless,
this
study
is
limited
to
physicochemical
indicators
of
adsorption
performance; therefore, future work should
focus
on
dynamic
adsorption
experiments
using
real
or
simulated
biogas
to
evaluate
adsorption
capacity,
selectivity,
and
long-
term
regenerability
under
practical
operating conditions.
Acknowledgement
The
authors
would
like
to
express
their
deepest
gratitude
to
the
Ministry
of
Education,
Culture,
Research,
and
Technology
for
the
support
and
funding
provided
for
this
research.
Sincere
thanks
are
also
extended
to
the
Institute
for
Research and Community Service (LPPM) of
OSO
University
for
the
facilities,
guidance,
and
assistance
that
greatly
contributed
to
the completion of this study.
Author Contributions
Conceptualization,
Y.P.;
Methodology,
Y.P.
and
W.M.;
Software,
W.M.;
Validation,
Y.P.
and
W.M.;
Formal
Analysis,
Y.P.;
Investigation, Y.P. and W.M.; Resources, Y.P.;
Data Curation, W.M.; Writing – Original Draft
Preparation, Y.P.; Writing – Review & Editing,
W.M.; Visualization, W.M.; Supervision, Y.P.;
Project
Administration,
Y.P.;
Funding
Acquisition, Y.P.
Conflict of Interest
The
authors declare
no conflict of interest.
The funders had no role in the design of the
study;
in
the
collection,
analysis,
or
interpretation of data; in the writing of the
manuscript; or in the decision to publish the
results.
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