DOI: 10.3303/CET24113021 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Paper Received: 20 April 2024; Revised: 13 September 2024; Accepted: 18 October 2024 
Please cite this article as: Min B.-C., Kang S.B., Ko G.-I., Won S.W., 2024, Removal of Dyes in Wastewater Using Pitch-based Carbon Waste 
Modified with Polyethylenimine, Chemical Engineering Transactions, 113, 121-126  DOI:10.3303/CET24113021 
  

 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 113, 2024 

A publication of 

 

The Italian Association 
of Chemical Engineering 
Online at www.cetjournal.it 

Guest Editors: Jeng Shiun Lim, Bohong Wang, Guo Ren Mong, Petar S. Varbanov 

Copyright © 2024, AIDIC Servizi S.r.l. 

ISBN 979-12-81206-14-4; ISSN 2283-9216 

Removal of Dyes in Wastewater Using Pitch-based Carbon 

Waste Modified with Polyethylenimine 

Byeong-Chan Mina, Su Bin Kangb, Gwang-II Koa, Sung Wook Wona,* 

aDepartment of Marine Environmental Engineering, Gyeongsang National University, 2 Tongyeonghaean-ro, Tongyeong,  

 Gyeongnam, Republic of Korea. 
bInstitute of Marine Industry, Gyeongsang National University, 2 Tongyeonghaean-ro, Tongyeong, Gyeongnam 53064,  

 Republic of Korea. 

 sungukw@gnu.ac.kr 

In this study, pitch-based carbon (PC) was modified with polyethylenimine (PEI) to produce PEI-modified PC 

(PEI-PC) for wastewater treatment. PEI, containing amine groups, shows advantages in adsorbing ionic dyes. 

The adsorption and desorption properties of PEC-PC for dyes were evaluated through pH edge, experiments, 

adsorption kinetics, isotherm studies, and desorption tests. We selected Cibacron Brilliant Yellow 3G-P 

(Reactive Yellow 2: RY2) as the model dye for our study. pH edge experiments were conducted in a pH range 

of 2-12 with an initial dye concentration of 100 mg/L. The results showed that dye uptake on PEI-PC increased 

as the pH value decreased. Adsorption kinetic experiments confirmed that adsorption equilibrium at pHs 2 and 

7 was achieved within 30 min. The adsorption isotherm experiments, conducted at initial dye concentrations 

ranging from 10 to 300 mg/L, revealed that the experimental data fit well with the Langmuir model. The dye-

loaded PEI-PC was desorbed using a 0.05 M NaOH solution, and this adsorption-desorption process was 

repeated. It was observed that when the adsorption-desorption cycles were repeated from 1 to 5 times, the 

adsorption efficiency decreased by 29 %. 

1. Introduction 

Water scarcity is one of the most pressing issues today, bringing the availability and quality of water supply into 

sharp focus. Many national policies now encourage companies to reduce water consumption and promote water 

reuse to ensure sustainable water resources (Waghchaure et al., 2022). Industrial processes are major 

contributors to water pollution, particularly through the release of organic compounds, which significantly impact 

the aquatic environment (Zhang et al., 2019). Various synthetic substances such as pesticides, persistent 

organic pollutants (POPs), and synthetic dyes have become significant environmental concerns. Among these, 

synthetic dyes are particularly prominent in the textile industry, where they are produced in large volumes 

worldwide. These dyes consume vast amounts of water and are highly toxic, causing health issues such as 

dermatitis, keratitis, and central nervous system damage (Zhang et al., 2023). They also severely impact 

ecosystems by blocking sunlight for aquatic plants. 

Despite regulations in many countries aimed at limiting dye wastewater discharge, more than 10,000 types of 

dyes are produced annually, totalling over 700,000 t, with more than 300 Mt of dye wastewater discharged each 

year (Waghmare et al., 2024). This highlights the inadequacy of current treatment methods and the urgent need 

for more effective solutions. Several techniques, including flocculation, biodegradation, filtration, oxidation, 

photolysis, and adsorption have been studied to remove dyes from water. Among these, adsorption is widely 

used due to its ease of use, low cost, and low energy requirements. 

A key factor in adsorption is finding a suitable adsorbent. Carbon materials are effective adsorbents because of 

their wide availability and high adsorption capacity. Coal tar pitch, a by-product of petroleum, is a carbon 

compound with excellent thermal stability, chemical resistance, and low cost (Kim et al., 2021). It is a high value-

added raw material and suitable as a carbon precursor for the adsorption of dye substances in water. 

In this study, pitch-based carbon (PC) was impregnated with polyethylenimine (PEI) and functionalized by 

coating its surface. The PEI-modified PC (PEI-PC) was analysed using scanning electron microscopy (SEM) 

121



and energy dispersive X-ray spectroscopy (EDS). Cibacron Brilliant Yellow 3G-P (Reactive Yellow 2) was used 

as a representative dye to evaluate the adsorption capacity. This uptake was assessed through isotherm, kinetic 

experiment, and pH edge test. Additionally, reuse experiments were conducted to determine the recyclability of 

PEI-PC in the wastewater treatment process. This study aims to investigate the effectiveness and reusability of 

PEI-PC as a novel adsorbent for dye removal contributing to the development of sustainable water treatment 

technologies. 

2. Materials and methods 

2.1 Materials 

The PC waste was obtained from Smart Korea Co., Ltd. (Daejeon, South Korea). PEI was purchased from 

Nippon Shokubai CO., Ltd. in Japan. Sigma-Aldrich provided the RY2. Other remaining chemicals used, such 

as isopropyl alcohol, methyl alcohol, HCl, and NaOH, were of analytical grade. 

2.2 Preparation of PEI-PC 

The PEI to use for PC modification was 1.25 g, filled with 50 mL of distilled water to make a 2.5 % PEI solution 

and dissolved for 1 h. To create PEI-PC, 2 g of PC was added to a 2.5 % PEI solution 50 mL and reacted in an 

incubator at 25 ℃ and 160 rpm for 3 days. Afterward, it was washed three times with distilled water and wet PEI-

PC was freeze-dried at -110 °C for 24 h. 

2.3 Analytical methods 

The surface morphologies and elemental compositions were examined using Field Emission Scanning Electron 

Microscopy combined with Energy Dispersive X-ray Spectroscopy (FE-SEM/EDS) on an Apreo S instrument 

(Thermo Fisher, USA). 

2.4 Adsorption experiments  

The UV-Vis spectroscopy (X-ma 3000pc, Human, Korea) was used to analyze the adsorption experiments. The 

wavelength of the dye was measured at 404 nm (for RY2). The calculation of dye adsorption q (mg/g) on PC 

and PEI-PC was performed using Eq(1). 

𝑞 =  
𝑉𝑖𝐶𝑖−𝑉𝑓𝐶𝑓

𝑚
  (1) 

The initial concentration (Ci) of dye solution was set at 100 mg/L, volume of 30 mL (Vi and Vf), and mass of the 

adsorbent (m) was 0.03 g. Each conical tube (50 mL) contained the dye and adsorbent and was shaken at 25 °C 

and 160 rpm for 24 h. The experiment for pH effects was evaluated in a range of 2 to 12, and the isotherm and 

kinetic experiments were evaluated at pH 2 with different contact times (ranging from 0 to 240 min) and initial 

concentrations of dye (ranging from 10 to 300 mg/L). Then, the relevant model equations were substituted for 

optimization and characterization. 

2.5 Reusability experiments  

The desorption process was performed by centrifuging the adsorbed mixture to remove the supernatant, adding 

30 mL of 0.05 M NaOH solution and reacting 24 h (Kang et al., 2023). The re-adsorption process was similar to 

desorption, with the mixture centrifuged to remove the supernatant and reacted under the same conditions as 

the initial adsorption. The adsorption-desorption process was repeated five times in succession. The UV-Vis 

spectroscopy was used to analyze the dye concentration after dilution. The adsorption-desorption efficiencies 

were calculated using Eq(2) and Eq(3). The adsorbed dye amount (mg) was measured by multiplying the uptake 

(mg/g) of dye and amount of adsorbent (g). The desorbed dye amount (mg) was measured by multiplying the 

concentration (mg/L) of dye after desorption and the volume of NaOH solution (mL). 

𝐴𝑑𝑠𝑜𝑟𝑝𝑡𝑖𝑜𝑛 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 (%) =  
𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑦𝑒 𝑎𝑚𝑜𝑢𝑛𝑡 (𝑚𝑔)

𝐼𝑛𝑖𝑡𝑎𝑖𝑙𝑙𝑦 𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑦𝑒 𝑎𝑚𝑜𝑢𝑛𝑡 (𝑚𝑔)
 × 100 (2) 

𝐷𝑒𝑠𝑜𝑟𝑝𝑡𝑖𝑜𝑛 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 (%) =  
𝐷𝑒𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑦𝑒 𝑎𝑚𝑜𝑢𝑛𝑡 (𝑚𝑔)

𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑦𝑒 a𝑚𝑜𝑢𝑛𝑡 (𝑚𝑔)
 × 100 (3) 

122



3. Results and discussion 

3.1 Comparative dye adsorption capacity to the influencing factor at pH 2 

To identify the factors influencing the fabrication of PEI-PC, materials were produced using different molecular 

weights of PEI: low molecular weight PEI (L-PEI, m.w.=800) and high molecular weight PEI (H-PEI, 

m.w.=70,000). Additionally, the solvents used for impregnation—distilled water (DW), isopropyl alcohol (IPA), 

and methyl alcohol (MA)—were varied during the manufacturing and evaluation process (Figure 1). 

 

Figure 1: Comparison of dye uptakes in difference PEI molecular weight and solvents 

H-PEI-PC increased in dye uptake, ranging from 89.38 to 104.05 mg/g, in comparison to L-PEI-PC (ranging 

from 53.27 to 54.27 mg/g). The difference in adsorption capacity between the H- and L-PEI was 1.65 to 1.93 

times, indicating that molecular weight substantially affects RY2 adsorption capacity. The variations in solvent 

did not have a significant influence, with differences less than 1 mg/g for the L-PEI-PC and 15 mg/g for the H-

PEI-PC. All subsequent experiments and analyses were performed using PEI-PC prepared with 2.5 % PEI with 

a molecular weight 70,000 and distilled water as solvent, which showed the highest uptake in Figure 1. 

3.2 Characterization of PC, PEI-PC, and RY2 loaded PEI-PC 

SEM images were used to investigate the surface morphology of the adsorbents, and EDS analysis provided 

information on their elemental composition. 

 

Figure 2: SEM/EDS of (a) the raw PC, (b) PEI-PC, and (c) RY2 loaded PEI-PC (magnification  ×3000)  

The surface of the PC appeared non-porous and smooth surface and the elemental properties are mostly made 

of carbon and contain some oxygen (Figure 2a). In the PEI-PC, nitrogen was detected, which can be attributed 

raw PC

L_PEI/D
W

-P
C

L_PEI/M
T-P

C

L_PEI/IP
A-P

C

H_PEI/D
W

-P
C

H_PEI/IP
A-P

C

H_PEI/M
T-P

C

R
Y

2
 u

p
ta

k
e
 (

m
g

/g
)

0

20

40

60

80

100

120
Ci = 303.77

123



to the amine groups presented in PEI (Figure 2b). After RY2 adsorption on PEI-PC, the surface was observed 

roughly due to the effect of RY2 molecule, and additional elements such as sulfur and chlorine were detected 

(Figure 2c). This confirms that PEI has been functionalized on the surface of the PC, facilitating the adsorption 

of RY2 onto the developed adsorbent surface.  

3.3 Dye adsorption performance of PC and PEI-PC under different pHs 

The surface charge of the dye molecules and the adsorbent changes according to the pH of the solution (Wamba 

et al., 2018). The adsorption performance depends on the pH, which is a crucial factor (Figure 3a). It can be 

seen that the adsorption capacity of PEI-PC increased under the low pH conditions. The adsorption capacity 

was 92.51 mg/g at pH 2, and the adsorption capacity in the neutral solution (over pH 6) decreased rapidly to 

58.41 mg/g and 11.82 mg/g under alkaline conditions. 

3.4 Isotherm experiment 

The adsorption isotherm of RY2 onto PEI-PC is shown in Figure 3b. Isotherm is useful for investigating various 

aspects of adsorption, including maximum adsorption capacity, adsorbent properties, and adsorption 

mechanism. The Langmuir model and the Freundlich model were utilized to optimize the adsorption results and 

used each equation (Eq(4) and Eq(5)).  

Langmuir model: 𝑞𝑒 =
𝑞𝑚𝑎𝑥𝐾𝐿𝐶𝑒

1+𝐾𝐿𝐶𝑒
 (4) 

Freundlich model: 𝑞𝑒 = 𝐾𝐹𝐶𝑒
1 𝑛⁄

 (5) 

The model equations were characterized by several parameters including bL (L/mg), qmax (mg/g), qe (mg/g), KF 

(mg/g), Ce (mg/L), and 1/n of the adsorption strength. The isotherm models can sort the adsorption intensity as 

either cooperative (1/n > 1) or effective (0 < 1/n < 1). According to Table 1, the parameters of Langmuir model 

for PEI-PC at pH 2 indicate a qmax of 96.59 mg/g at pH 7, qmax is 60.76 mg/g. The Freundlich model parameters 

also reflect similar trends with KF value of 50.26 L/g at pH 2 and 36.07 L/g at pH 7. Analysis of the coefficient of 

determination (R²) suggests a better fit with the Langmuir model (R² = 0.969 at pH 2 and 0.968 at pH 7) 

compared to the Freundlich model (R² = 0.835 at pH 2 and 0.808 at pH 7). The higher Langmuir constant (bL), 

2.620 L/mg at pH 2 and 2.402 L/mg at pH 7, indicates a stronger affinity between the adsorbate (RY2) and the 

adsorbent (PEI-PC) under the experimental conditions (Wang et al., 2020). The notable difference in bL values 

between PEI-PC and raw PC underscores the enhanced interaction between PEI-PC and RY2. 

Table 1:  Adsorption isotherm parameters onto PEI-PC and raw PC 

  Langmuir model Freundlich model 

  bL (L/mg) R2 qmax (mg/g) KF (L/g) R2 1/n 

PEI-PC 
pH 2 2.620 0.969 96.59 50.26 0.835 0.141 

pH 7 2.402 0.968 60.76 36.07 0.808 0.111 

raw PC 
pH 2 4.792 0.919 46.95 10.43 0.992 0.112 

pH 7 0.366 0.991 13.38 7.415 0.980 0.119 

3.5 Kinetic studies 

The kinetics experiments were conducted with an initial dye concentration of 100 mg/L at pH 2 and pH 7. The 

pseudo-first and second models were used to analyze the kinetic results (Figure 3c, Eq(6), and Eq(7)). 

Pseudo-first-order model (PFO): 𝑞𝑡 = 𝑞1(1 − 𝑒𝑥𝑝(−𝑘1𝑡)) (6) 

Pseudo-second-order model (PSO): 𝑞𝑡 =
𝑞2

2𝑘2𝑡

1+𝑞2𝑘2𝑡
 (7) 

The equations variables of the kinetic models signify the number of dyes at the equilibrium adsorption state (q1 

and q2 (mg/g)), the number of dyes adsorbed at a given time (qt (mg/g)), t, and k1 (L/min) and k2 (g/(mg∙min)) 

are the rate constants. 

The adsorption equilibrium of PEI-PC for RY2 was reached within 60 min. For PEI-PC at pH 2, the PFO model 

showed an R2 of 0.974 with q1 at 79.53 mg/g and k1 at 2.082 L/min. The PSO model provided an R2 of 0.988, 

with q2 at 81.21 mg/g and k2 at 0.058 g/(mg·min), indicating a closer fit to the experimental values of qe at 84.08 

mg/g for RY2. Similarly, at pH 7, the q1 was 46.92 mg/g and k1 was 1.608 L/min with an R2 of 0.961 for the PFO 

model, while the PSO model yielded q2 at 48.22 mg/g and k2 at 0.064 g/(mg·min) with an R2 of 0.981. 

Comparatively, raw PC showed lower kinetic adsorption performance. At pH 2, the q1 value was 17.61 mg/g 

124



and k1 was 1.163 L/min (PFO: R2 of 0.949), while q2 was 18.22 mg/g with k2 at 0.113 g/(mg·min) and R2 of 0.979 

for the PSO model. At pH 7, the respective values for q1 and q2 were 13.25 mg/g and 13.75 mg/g, with R2 values 

of 0.967 and 0.970. These results confirm that the PSO model is more suitable for describing the adsorption 

kinetics of reactive dyes onto PEI-PC, reflecting higher compatibility with the experimental observations and a 

better understanding of the adsorption process (Kang et al, 2023). 

Table 2: Adsorption kinetic parameters onto PEI-PC and raw PC 

  Pseudo-first-order (PFO) model  Pseudo-second-order (PSO) model 

  q1 (mg/g) R2 k1 (L/min) q2 (mg/g) R2 k2 (g/mg min) 

PEI-PC 
pH 2 79.53 0.974 2.082 81.21 0.988 0.058 

pH 7 46.92 0.961 1.608 48.22 0.981 0.064 

raw PC 
pH 2 17.61 0.949 1.163 18.22 0.979 0.113 

pH 7 13.25 0.967 0.619 13.75 0.970 0.080 

 

 

Figure 3. (a) The pH effects on dyes uptakes by raw PC and PEI-PC (b) Adsorption isotherm of dyes on raw PC 

and PEI-PC at pH 2 and pH 7 (c) Adsorption kinetics of dyes on raw PC and PEI-PC at pH 2 and pH 7 

3.6 Reusability studies 

One critical aspect of adsorbents is their reusability, which offers significant economic benefits. As depicted in 

Figure 4, the reuse efficiency of the PEI-PC adsorbent was evaluated over five cycles using 0.05 M NaOH as 

the desorbing agent. 

The desorption efficiencies consistently exceeded 94 % throughout all cycles, demonstrating the adsorbent's 

capacity for effective regeneration. Subsequent re-adsorption tests showed that the PEI-PC retained between 

72.54 % and 81.37 % of its initial adsorption capacity after each cycle. These results confirm the robust 

reusability of PEI-PC, underlining its potential for cost-effective application in dye removal processes. 

 

125



 

Figure 4: Efficiency of repeated adsorption and desorption cycles 

4. Conclusions 

PEI-PC was prepared through the impregnation of PEI onto the surface of the PC. The amine groups from the 

PEI coating impart a positive charge to the PEI-PC adsorbents, which exhibit outstanding adsorption capabilities 

for anionic reactive dyes, particularly under acidic conditions. At a pH of 2, the Langmuir model appeared an 

adsorption capacity of 94.32 mg/g. Furthermore, the adsorption efficiency remained above 70 % through five 

cycles of reuse evaluations, demonstrating the robust reusability of the adsorbent. The simplicity of the 

manufacturing process, coupled with the absence of a specific pretreatment requirement, underscores the 

commercial viability of PEI-PC for dye removal applications. 

Acknowledgments 

This work was supported by the Technology development Program (S3366606) funded by the Ministry of SMEs 

and Startups (MSS, Korea) 

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Number of cycles

1 cycle 2 cycles 3 cycles 4 cycles 5 cycles

E
ff

ic
ie

n
c

y
 (

%
)

0

20

40

60

80

100

120
Adsorption

Desorption

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	Removal of Dyes in Wastewater Using Pitch-based Carbon Waste Modified with Polyethylenimine