ISSN 0104-7760
Matheus Felipe Freire Pego1+, Janaína Carvalho1, Willian Borges1, Maria Lúcia Bianchi1
IMPACT OF CORONA TREATED ACTIVATED CARBON IN ANIONIC AND
CATIONIC DYE ADSORPTION
Keywords:
Corona treatment
Adsorption
Surface modification
Textural properties
Histórico:
Recebido 27/01/2017
Aceito 22/05/2017
ABSTRACT: Dye degradation is a significant topic in environmental science, since dyes can
bring several problems to the environment. Activated carbon (AC) is an important material
used as adsorbent of these hazardous substances, but need to be improved especially into
specific substances. This paper aimed to evaluate the impact of activated carbon surface
modified by corona treatment (electric discharge) on adsorption of different dyes. Activated
carbons were treated by corona treatment to cause surface modification, modifying
exposure time to treatment (2, 5, 8 and 10 minutes). Evaluation of adsorption was performed
by adsorption isotherms and kinetic adsorption. Dyes differed in their charge (anionic or
cationic) and molecular weight. Dyes used were Methylene Blue (cationic) and Congo Red
(anionic). Surface area and Scanning Electron Microscopy (SEM) were also conducted.
Surface chemistry was impacted by corona treatment and interfered in dye adsorption.
There was decrease of dye adsorption for both dyes according to time exposure. However,
the decrease of Methylene Blue (25%) was higher than Congo Red (14%), suggesting that
either charge or molecule weight interfere in the adsorption isotherms. In kinetic adsorption,
there was no difference between treatments, although there was a difference in adsorption
equilibrium. SEM showed that surface was impacted (pore destruction) by corona treatment.
Furthermore, estimated surface area was strongly impacted by the treatment, reducing with
the increase of time exposure. Thus, textural properties might have contributed to reduce
adsorption capacity of both dyes and play a higher role than chemical properties.
IMPACTO DE CARVÕES ATIVADOS TRATADOS COM DESCARGA CORONA
NA ADSORÇÃO DE CORANTES CATIÔNICOS E ANIÔNICOS
Palavras chave:
Tratamento corona
Adsorção
Modificação da superfície
Propriedades texturais
+
Correspondência:
matheuscura@hotmail.com
DOI:
10.1590/01047760201723022300
RESUMO: A degradação de corantes é um importante tópico nas ciências ambientais, já
que os corantes podem trazer diversos problemas para o meio ambiente. O carvão ativado
é um importante material usado como adsorvente dessas substâncias causadoras dos mais
diversos danos, mas precisam ser melhoradas especialmente quando envolve substâncias
específicas. Este manuscrito tem como objetivo avaliar o impacto da superfície de carvões
ativados modificados pelo tratamento corona (descarga elétrica) na adsorção de diferentes
corantes. Os carvões ativados foram tratados pelo tratamento corona para promover a
modificação na superfície, modificando os tempos de exposição ao tratamento (2, 5, 8 e 10
minutos). A avaliação da adsorção foi realizada pelas isotermas de adsorção e velocidade de
adsorção. Os corantes diferiram pelas suas cargas (aniônico e catiônico) e massa molecular.
Os corantes utilizados foram o Azul de Metileno (catiônico) e o Vermelho Congo (aniônico).
A área superficial e a microscopia eletrônica de varredura (MEV) também foram realizadas.
A superfície química foi impactada pelo tratamento corona e interferiu na adsorção dos
corantes. Houve decréscimo na adsorção dos corantes para ambos de acordo com o tempo
de exposição. No entanto, o decréscimo de Azul de Metileno (25%) foi maior que para o
Vermelho Congo (14%), sugerindo que a carga ou a massa molecular interferiram na isoterma
de adsorção. Na velocidade de adsorção, não houve nenhuma diferença entre os tratamentos,
embora houve diferença no equilíbrio da adsorção. A análise MEV mostrou que a superfície
foi impactada (destruição dos poros) pelo tratamento corona. Além disso, a área superficial
estimada foi fortemente impactada pelo tratamento, reduzindo com o aumento do tempo de
exposição. Assim, a propriedades texturais pode ter contribuído para a redução na capacidade
de adsorção de ambos corantes, desempenhando papel de maior importância comparado
com as propriedades químicas.
1
Federal University of Lavras - Lavras, Minas Gerais, Brazil
CERNE | v. 23 n. 2 | p. 219-228 | 2017
IMPACT OF CORONA TREATED ACTIVATED CARBON IN ANIONIC AND CATIONIC DYE ADSORPTION
INTRODUCTION
Dyes are colored substances that are used
in several industries for many applications imparting
permanent color to their products. Dyes are essential,
especially to textile industries, which use their properties
to color many fabrics (GUARATINI; ZANONI, 1999).
However, the indiscriminate use of these substances
and the lack of well-treated waste generated by these
industries are a huge problem for the environment.
Dyes may disturb the environment, especially the
water environment. Dyes are toxic to micro-organisms,
may decrease oxygenation, prevent light penetration
through the water surface and significantly impact
aquatic ecosystem. Dyes can also cause visual pollution
(GOTTLIEB et al., 2003).
Water pollution is one of the issues of most concern
in environmental science. Governmental control, severe
legislation and effluent treatment have contributed to
decrease this problem (ROBINSON et al., 2001). Dye
pollution reduction has been exhaustively studied for
several years, yet, currently new technologies have been
developed to perform and improve dye degradation,
making the environment cleaner and reducing pollution.
The main and new methods to reduce dye pollution
involve activated carbon (GHAEDI et al., 2012), surface
modified activated carbons (MOHAMMED et al., 2015),
nanoadsorbents (KYZAS; MATIS, 2015), agricultural
adsorbent waste (PELÁEZ-CID et al., 2013), other
adsorbents (YAVUZ; SAKA, 2013), ozonation (CASTRO
et al., 2016), irradiation (HERNÁNDEZ-URESTI et al.,
2011), photocatalics (MAHMOODI, 2013), plasma
discharge (JIANG et al., 2014), biological methods
(KANAGARAJ et al., 2014) and others.
Activated carbons have a key role in reducing dye
pollution. Activated carbons are used as adsorbents for
many dyes and other substances. The main characteristics
which impact adsorption are the high surface area,
porosity and surface chemistry. Also, dye properties
have an important influence on the activated carbon
adsorption process (ACEVEDO et al., 2015).
Dyes properties directly affect adsorption capacity.
The main dye characteristics which can impact adsorption
capacity are polarity, molar mass, molecular size, acidity,
basicity, molecular charge and the relationship among
these properties and the surface structure of adsorbents.
Moreover, some factors can influence adsorption capacity
such as pH, dye concentration, adsorbent dosage, contact
time and temperature (SALLEH et al., 2011). Different
surface chemistries of activated carbons impact the
adsorption capacity of anionic and cationic dyes. Equilibrium
220
isotherms and other adsorption process are impacted
by the relationship of different dye groups and surface
chemistry. Thus, surface chemistry and dye properties play
an important role in dye adsorption (FARIA et al., 2004).
Molecule charge is one of the most studied
properties in the adsorption process. Basically, the
molecule charge can be anionic or cationic. An anionic
dye has a negative charge and a cationic dye has a
positive charge (WAN NGAH et al., 2011). Dye charges
directly interact with adsorbent surface chemistry.
Surface chemistry could be different depending on
surface modification and its surface functional groups,
which have different properties (SHAFEEYAN et al.,
2010). Thus, the relationship between molecule charge
and adsorbent surface chemistry impacts the adsorption
capacity of specific molecules differently.
Corona treatment is an electric discharge that is
applied to some material to cause surface modification
and changes in materials properties. This treatment is
used in polymers, rubber, aluminum sheets and other
carbonaceous materials. Corona treatment is a treatment
that promotes surface oxidation thought the ionization
of gases (O3, O2) by electric discharge, causing covalent
chemical reactions on the surface which changes some
materials properties (STEPCZYÑSKA, 2015).
Corona treatment can be a surface modification
technique which changes surface structure and impacts
dye adsorption process. Therefore, this study aimed
to evaluate the impact of corona treatment on the
adsorption process of anionic and cationic dyes.
MATERIAL AND METHODS
Surface modification
In this study a powdered commercial activated
carbon was used. This activated carbon was used because
their large adsorption capacity. The activated carbon was
from Alphacarbo Company.
Corona treatment was used to cause surface
modification (oxidation) of activated carbons. The corona
equipment was from Plasma Tech - Corona Brazil (Figure
1), Model PT-1, 0.5 kW power, 220 V and frequency
of 60 Hz. Activated carbon were submitted to corona
discharge (high frequency and voltage) at four different
exposures times. Treatment one (T1) was the standard,
without treatment (virgin activated carbon). The other
treatments (T2, T3, T4 and T5) varied exposure time
2, 5, 8 and 10 minutes respectively. Head height was
established at 4.5 cm. An aluminum box was used to
reduce material losses during treatment, since agitation
was high during treatment.
CERNE | v. 23 n. 2 | p. 219-228 | 2017
PEGO et al.
FIGURE 1 Corona treatment scheme.
Adsorption isotherms
Adsorption isotherms are the most common way
to evaluate solid adsorption capacity. The evaluation of
activated carbon adsorption capacity was performed
using two kinds of dyes (Figure 2): one with negative
charge (anionic) and other with positive charge (cationic).
The anionic dye was Congo Red and cationic dye was
Methylene Blue.
FIGURE 2 Dye molecules used in activated carbon
adsorption tests A-Congo Red (anionic) BMethylene Blue (cationic)
The activated in 10mg carbons (treated and nontreated) were weighed. After, 10 mL solutions at different
concentration (25, 50, 100, 200, 400, 800, 1000 mg.L-1)
for Methylene Blue and (10, 25, 50, 75, 100, 200, and 400
mg.L-1) for Congo Red were added to obtain the adsorption
isotherms. The aliquots were kept under agitation for 24
hours at 200 rpm at room temperature in a Certomat
MO II orbital shaker. The materials were centrifuged
and the determination of equilibrium concentration was
performed by UV-visible analysis on a Biospectro SP-22
UV spectrophotometer in wavelengths of 665 nm for
Methylene Blue and 500 nm for Congo Red.
The dye solutions were prepared by weighing an
exact quantity of dye, being dissolved in distilled water to
prepare a 1000 mg.L-1 stock solution, which were diluted
according to concentration. Solutions preparation and
concentration determination to obtain the adsorption
isotherms were performed at room temperature
(22.5ºC) and pH 3.7 – 4.2 for Methylene Blue and room
temperature (20ºC) and pH (6.5-7) for Congo Red. The
pH was measured by a PG1800 digital pH meter.
Calibration curves were adjusted according to
known dye solution concentrations. The amount of dye
adsorbed per unit mass of activated carbon (mg.g-1) was
calculated according to Equation 1. Where: C0 (mg.L-1)
= initial dye concentration; Ceq (mg.L-1) = equilibrium
concentration; V (L) = solution volume;m (g) =
adsorbent mass.
[1]
Adsorption kinetics
Kinetics studies allow determining the time
necessary to attain adsorption equilibrium. These studies
are important to determine adsorption efficiency.
Methylene Blue and Congo Red were also used
as adsorbent. For each treatment 5 mg of activated
carbon were weighed together with 5 mL of adsorbates
at a concentration of 50 mg.L-1 for Methylene Blue and
25 mg.L-1 for Congo Red. In time intervals (5, 10, 15,
30, 60, 120, 240, 360, 720 and 1440 minutes), aliquots
were removed, centrifuged and their concentrations
were determined, using wavelengths of 665 nm for
Methylene Blue and 500 nm for Congo Red. Absorbance
readings were performed on a Biospectro SP-22 UV
spectrophotometer.
Scanning electron microscopy (SEM)
Treated and non-treated activated carbon
samples were submitted to surface microscopy analysis
to observe the changes occurred in the structure of
the materials. The analysis was performed on an Evo40
LEO XVP (25 kV) equipment. An aluminum support
was coated with aluminum foil. Samples were held on
double-sided carbon tape attached to aluminum support
and then covered by a thin layer of gold.
Estimated surface area
It is possible to estimate surface area of solid
materials using the Methylene Blue model molecule, when
it is not possible to use BET methodology. Estimated surface
area uses molecular properties, such as diameter, in order
to obtain a consistent result. The Methylene Blue molecules
have important properties which enable them to be used
as estimators of the surface area of activated carbons.
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IMPACT OF CORONA TREATED ACTIVATED CARBON IN ANIONIC AND CATIONIC DYE ADSORPTION
Using the surface area of a Methylene Blue molecule it is
possible to estimate surface area through Equation 2.
Where: SBM (m².g-¹) = Activated carbon area accessible to
Methylene Blue; S°BM = Methylene Blue surface area; qm
(mg.g-1) = Maximum adsorption capacity of Methylene Blue.
[2]
RESULTS AND DISCUSSION
Surface modifications of many materials are
impacted by corona treatment. Electric discharge with
high frequency and voltage supplied by corona treatment
provoke surface modification through the ionization
of gases located between surface material and corona
equipment. This ionization promotes liberation of photons
and electrons causing chemical reactions and oxidation in
materials surface. Different chemical reactions lead to
material surface different properties, since new structures
in surface are formed. Wettability, acidity, basicity, polarity,
reactivity, chemical and textural properties are the main
properties impacted by corona treatment.
Surface chemistry of treated AC was strongly
affected by the corona treatment. Comparing to nontreated AC, there was a tendency towards increasing
acidity, Oxygen content, Carboxyl acid and O/C ratio.
There was a tendency of decreasing Carbon content,
lactone and phenol groups. The differences are
related to time exposure. Thus, surface modification
was performed on activated carbon and resulted in
different properties that could impact the adsorption
process (PEGO, 2016).
Adsorption isotherms
Adsorption isotherms were performed aiming to
evaluate adsorption capacity and better understand dye
adsorption process. Adsorption isotherms demonstrated
the activated carbon capacity to adsorb a particular
substance (dye) at equilibrium.
Figure 3 and 4 show adsorption isotherms of
Methylene Blue and Congo Red dyes, respectively.
According to these Figures, there was a dye adsorption
decrease with increased of time exposure to the corona
treatment. Thus, generally, for these dyes, corona
treatment does not improve adsorption capacity of the
activated carbons.
Methylene Blue adsorption
Adsorption isotherms of the Methylene Blue
dye (cationic) on activated carbons is shown in Figure
3. According to this Figure, there was a decrease in
222
FIGURE 3 Adsorption isotherm of Methylene Blue in
the different treatments (10 mg de AC; 10 mL
solution; pH= 3.7 - 4.2; 200 rpm; concentration
25-1000 ppm; Room temperature= 22.5 ºC).
FIGURE 4 Adsorption isotherm of Congo Red in the
different treatments (10 mg of AC; 10 mL
solution; pH= 6.5-7; 200 rpm; concentration
10-400 ppm; Room temperature= 20 ºC).
adsorption capacity of the activated carbons with the
increase of time exposure to corona treatment. This
decrease is approximately 25% less, comparing nontreated AC and the AC which had the highest exposure
time and the lowest Qeq.
Therefore, the treatment that obtained higher
adsorption capacity was non-treated AC (T1), with Qeq
of 272.2 mg.g-1. After 24 hours, all treatments reached
equilibrium adsorption. Qeq values for T2, T3, T4 and
T5 treatments were respectively 230.2; 215.3; 211.4
and 205.1 mg.g-1.
This reduction could be explained by the fact of
activated carbon surface treatment and other substances,
which use similar surface modification processes such as
corona treatment, most often need special conditions,
like: specific atmosphere, different pressure conditions
CERNE | v. 23 n. 2 | p. 219-228 | 2017
PEGO et al.
and reactors. These characteristics provide alterations
in its properties or even protection in activated carbon
structure. Plasma surface modification and other physical
surface modifications methods are similar to corona
treatment. Generally, these treatments expose materials
to extreme conditions, causing damages or changes in
their structure.
Reduction of activated carbon adsorption can also
be related to adsorbate properties, the intrinsic relation
between adsorbent-adsorbate and to the change occurred
to porosity and textural characteristic caused by agitation
and high temperatures due to electric discharge.
It is possible to infer that surface characteristics
like acidity and basicity impact adsorption capacity.
There are some studies demonstrating that Methylene
Blue adsorption is potentiated in more basic surface
(WANG et al., 2005)methylene blue, from aqueous
solutions onto as-received activated carbons and acidtreated carbons was investigated. The physical and
surface chemical properties of the activated carbons
were characterized using BET-N2 adsorption, X-ray
photoelectron spectroscopy (XPS. Therefore, surfaces
which have large number of acidic groups, generally, are
not ideal for Blue Methylene. Treated activated carbons
have higher acidity and were related to time exposure,
culminating in the adsorption capacity decrease. Thus,
this may suggest that higher exposure time had higher
acidity and consequently lower adsorption capacity for
Methylene Blue.
The adsorption capacity behavior caused by other
similar surface treatments (plasma discharge) is different
depending on factors that may impact adsorption. Some
authors have increased adsorption capacity due to
treatment compared to virgin activated carbons (CHE
et al., 2013; QU et al., 2013). However, other authors
reported that electric discharge had a negative impact on
adsorption capacity. They attributed this to destruction
of surface functional groups (HAO et al., 2009; JI et
al., 2013). The adsorption capacity behavior especially
depends on methodology employed aiming to cause
the surface modification, since many factors can impact
adsorption capacity.
Congo red adsorption
Adsorption isotherm of Congo red dye (anionic)
on activated carbons is showed in Figure 4. According to
the Figure 4, as well as Methylene Blue adsorption, there
was a decrease in adsorption capacity due to the corona
treatment exposure time. It was expected that adsorption
capacity would be increased since there was an increase
of acidity. However, the decrease can be related to the
decrease of surface area. Also, textural properties can
play an important role on adsorption capacity. Thus,
considering factors that impact adsorption, chemical
properties was weaker than textural properties, as
showed in surface area and pore structure, observed in
the following topics.
The decrease is approximately of 14% comparing
non-treated AC and the treatment that had higher
exposure time and obtained the lowest Qeq value.
Thus, the AC which showed higher adsorption capacity
was non-treated AC (T1), with a Qeq of 256.2 mg.g-1.
The Qeq values for T2, T3, T4 and T5 treatments were
respectively of 256.1; 236.4; 223.6 and 220.3 mg.g-1. The
higher adsorption capacity of these activated carbons
may be due to their being commercial activated carbons.
According to these results, it is possible to infer
that Congo Red adsorption was less impacted than
Methylene Blue adsorption. This can be related to the
reaction occurred between adsorbent and adsorbate,
particularly in the influence of some variables such as pH
and temperature. According to (YAVUZ; SAKA, 2013)
pH has a high importance on the adsorption process and
strongly impacts adsorption capacity.
Nonetheless, dye charge may have been
responsible for adsorption differences between the
two types of dyes. Methylene Blue, by having a positive
charge, is more attracted to basic surfaces. The Congo
red molecule, by having negative charge, is more
attracted to acid surfaces.
Adsorption kinetics
Adsorption kinetics differs from adsorption
isotherm. Adsorption kinetics shows adsorption
efficiency and provides information about the velocity of
the adsorption process.
As in adsorption isotherms, for the adsorption
kinetics study were used the same dyes. Figures 3 and 4
showed that there were no large differences in adsorption
velocity. In addition, the differences occurred seem not
to be correlated with time exposure. Yet, it is possible
to observe that the adsorption kinetics of Congo Red
showed fewer differences between treatments when
compared to Methylene Blue kinetics. All treatments
showed great initial dye adsorption speed. After a short
time, reaction equilibrium was reached for both dyes.
Methylene Blue adsorption kinetics
Adsorption kinetics of Methylene Blue is
presented in Figure 5. According to this Figure, there
223
IMPACT OF CORONA TREATED ACTIVATED CARBON IN ANIONIC AND CATIONIC DYE ADSORPTION
were no significant differences in kinetic behavior for the
treatments. It was not possible to relate kinetic behavior
to increasing exposure time and all AC adsorbed
approximately 100% of the dyes in a few minutes.
The initial Methylene Blue adsorption velocity
for all treatments was very fast, reaching adsorption
equilibrium after 16-18 minutes, indicating rapid filling of
sites for all activated carbons.
FIGURE 6 Congo Red Adsorption kinetics, 25 mg.L-1
concentration (5 mg of AC and 5 mL solution).
Scanning electron microscopy (SEM)
FIGURE 5 Methylene Blue Adsorption Kinetic, 50 mg.L-1
concentration (5 mg of AC and 5 mL of solution).
Congo Red adsorption kinetics
Congo Red adsorption kinetic is presented in
Figure 6. According to the Figure, as in the Methylene
Blue adsorption kinetics there were no significant
differences in kinetic behavior for the treatments. There
was no pattern in the kinetic behavior according to
increased corona treatment time exposure.
The adsorption kinetics of the Congo Red
molecule by the activated carbons were less than those
of Methylene Blue. Equilibrium adsorption was achieved
after approximately 4 hours, with more than 95% dye
removal. The differences between adsorption kinetics
may be related to the different molecular properties,
especially size and charge. The Congo Red molecule
(696.68 g.mol-1) has molecular mass higher than the
Methylene Blue molecule (356 g.mol-1). Furthermore,
the molecules present opposite charges that interfere
in adsorption kinetics until equilibrium is reached.
Chowdhury et al. (2009)especially for the treatment of
colored effluent generated from the dyeing and bleaching
industries. Low cost adsorbents have gained attention
over the decades as a means of achieving very high
removal efficiencies to meet effluent discharge standards.
The present article reports on batch investigations for
color removal from aqueous solutions of Methylene Blue
(MB observed differences between adsorption kinetics
patterns; Methylene Blue obtained faster adsorption
compared to Congo Red.
224
SEM analysis was performed in order to observe if
the structure of the activated carbons was impact by the
corona treatment, since the electric discharge decrease
adsorption capacity of both dyes. Analyzing Figure 7, it
is possible to observe that changes occurred in the AC
structure with the increase of exposure time. It is believed
that ruptures of the porous structures took place, making
the surface more irregular and heterogeneous. Figure 7
shows internal pore structure, its regularity and sizes.
According to this Figure, pores were damaged according
to the time exposure. The pore destruction occurred
both on the surface and the internal structure. Observing
T1 (Figure 7 A), the porous structure seems to be well
arranged, being a large structure with regular and intact
pores. On the other hand, T5 (Figure 7 E) had significant
porous structure destruction.
Porous structure destruction of activated carbons
might be related to the temperature that is generated
during treatment and agitation of AC inside the aluminum
box. Electric discharge promotes agitation, requiring the
use of an aluminum box. Material agitation was high due
low particle size and lightweight material. Besides, high
temperatures are generated by the equipment (high
voltage and frequency). These factors may impact pore
destruction of treatments. According to Yavuz and Saka
(2013), high exposure times to corona treatment can
destroy functional groups structure and porosity.
Some analysis of activated carbon surface using
methods similar to the corona treatment is divergent
regarding surface changes. Some author reported that
these methods can cause destruction of pores and other
benefit modifications. Thus, structural modifications
are dependent on the methodology of the treatment
that is applied to cause modifications. Che et al. (2013)
CERNE | v. 23 n. 2 | p. 219-228 | 2017
PEGO et al.
analyzing the surface of AC treated by plasma observed
that the external surface was impacted on a microscale
and became rough. In this regard, Ji et al. (2013) also
working with the same treatment, found that the surface
became irregular and heterogeneous. Vignesh et al.
(2016) using specific conditions, via SEM analysis verified
that plasma treatment does not cause structural damage
on AC and it maintained the same dimensions and mass
compared to non-treated activated carbon.
Thus, it is evident that the conditions under
treatment are carried out have a huge influence
on surface structure. Specific treatment conditions
determine properties and morphology of the activated
carbon surface. The main methods are the use of barriers,
reactors, pressure conditions and specific atmospheres.
Estimated surface area
The activated carbon surface area was estimated
using Methylene Blue adsorption. This is a simple and
rapid method that provides important information on
the structure of the adsorbent material. The estimated
surface area is presented in Table 1. According to
this Table, the increased exposure time of each
treatment decreased the estimated surface area of the
activated carbon, which was completely dependent
on the Methylene Blue adsorption capacity. The high
temperature reached and agitation received by corona
discharge may have caused the destruction of porous
structures, negatively contributing to the surface area.
TABLE 1 Surface area estimated values according to treatments.
Treatment
T1
T2
T3
T4
T5
Surface area (m2.g-1)
525.34
444.29
415.53
408.00
395.84
Surface modification using plasma discharge
(similar treatment) can cause reduction of surface area
and total pore volume. The reduction is conditioned
due to the time exposure acting on the surface, adding
new surface functional groups which can be allocated
to pore entrances, causing a reduction in surface area.
Furthermore, surface area reduction may be caused
by factors inherent to surface modification, such as
temperature, pressure, exposure (CHE et al., 2013).
CONCLUSION
FIGURE 7 Electron micrographs (759 x) of non-treated AC T1
(A) and treatments T2 (B), T3 (C), T4 (D) and T5 (E).
In this study the impact of corona treatment
on the activated carbon adsorption process of anionic
and cationic dyes was evaluated. Although the Corona
treatment caused surface modification of activated
225
IMPACT OF CORONA TREATED ACTIVATED CARBON IN ANIONIC AND CATIONIC DYE ADSORPTION
carbon, this modification was not able to improve
adsorption capacity of Methylene Blue and Congo Red,
it not being possible to infer about other adsorbates.
Higher exposure time resulted in lower adsorption
capacities. Blue Methylene adsorption had Qeq of
272.2 mg.g-1 (non-treated) and with the increase of
exposure time had 230.2; 215.3; 211.4 and 205.1 mg.g-1,
respectively. Congo Red adsorption had Qeq of 256.2
mg.g-1 (non-treated) and with the increase of exposure
time had 256.1; 236.4; 223.6 and 220.3 mg.g-1.
Kinetic adsorption was not different between treated
and non-treated activated carbons for both dyes. However,
Methylene Blue adsorption was faster than Congo Red,
possibly due to differences in molecule size and charge.
Dye charges have an influence on dye adsorption,
although this influence does not contribute to improve
dye adsorption. Decreasing adsorption capacity may
be related to decreasing surface area. The surface area
decrease is due to porous structure ruptures, making
the surface more irregular. Thus, surface chemistry was
not the main factor involved in the adsorption process.
Other factors may impact this, such as surface structure,
porosity, surface area and dye properties.
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