Anal. Methods Environ. Chem. J. 5 (3) (2022) 40-54

Research Article, Issue 3

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

An efcient cheap source of activated carbon as solid phases for

extraction and removal of Congo Red from aqueous solutions

Tahrer N. Majid a and Ali A. Abdulwahid a,*

aUniversity of Basra, College of Science, Chemistry Department, PO Box 49, Basra, Iraq,

ABSTRACT

The present study reported the preparation of solid phases from

various available and cheap natural sources represented by activated

carbon to remove the polluting dye Congo Red (CR). Activated

carbon derived from the leaves of the Consocarpus plant (C/AC)

and Ziziphus Spina-Christi plant (Z/AC) and Myrtus plant (M/AC)

by chemical activation. The prepared solid phases were diagnosed

and examined using FTIR, FESE, and XRD. The results of the study

indicated that the best amount for the solid phase was 0.25 g for the

three solid phases used against dye, the optimal concentration of the

CR was 100 mg L-1, and the optimum acidity function was equal to 5

with a volume of 25 mL, as the optimization experiments indicated

that the best ow rate of the eluting solution was equal to 0.5 ml

min-1. The elution processes were carried out using several solvents

different in polarity and it was found that 8 mL of DMSO achieved

the best percentage of recovery (%R). Also, this study included

calculating adsorption capacity based on the optimal conditions

that were obtained by applying Langmuir and Freundlich isotherm

models, and qmax, according to the Langmuir model, was (21.74,

23.53, 22.17) mg g-1 for (Z/AC), (C/AC), and (M/AC) adsorbents,

respectively.

Keywords:

Solid phase extraction,

Active carbon,

Congo Red,

Enrichment factor,

UV-Vis technology

ARTICLE INFO:

Received 17 May 2022

Revised form 28 Jul 2022

Accepted 19 Aug 2022

Available online 29 Sep 2022

*Corresponding Author: Ali A. Abdulwahid

Email: ali.abdulwahid@uobasrah.edu.iq

https://doi.org/10.24200/amecj.v5.i03.205

1. Introduction

In recent years, human pollution of natural waters has

led to a signicant reduction in operational freshwater

resources on Earth [1]. These pollutants from multiple

sources have caused signicant environmental and

health problems that threaten society and living

organisms [2, 3]. Many contaminants such as toxic

heavy metals, and organic contaminants, such as

dyes, pesticides, drugs, degraded organic matter,

and so on, are present in polluted waters [4]. Among

these pollutants are dyed [5]. A dye is a coloring

substance that can be natural, semi-synthetic,

or fully synthetic and blend with the substrate to

which it is applied. Natural dyes can be non-toxic

compared to synthetic dyes due to their natural

origin. The primary sources of pollution of synthetic

dyes are the textile, rubber, paper, plastic, printing,

paint, and leather industries [6]. It is estimated that

about 10,000 types of articial and natural dyes are

produced annually worldwide, with a signicant

number of dyes being wasted during manufacturing

and application processes [7]. The main reason is

the incomplete adhesion of the paints to the layers

when painting. The amount of unstable dyes in

textile efuents is higher than that of efuents

discharged by other industries [8]. Many chemicals

and dyes remain unused during the dyeing process

of textiles, releasing excess liquid dye into the

environment. It is estimated that textiles subject

------------------------

Extraction and Removal of Congo Red by Activated carbon Tahrer N. Majid et al

to dyeing can absorb about 80% of dye liquor due

to their limited adsorption capacity [9]. Of all the

colors, "azo" colors are most often used to dye

different substrates. They are complex in nature

and are potentially carcinogenic. Due to the larger

molecular structures, their decomposition products

are also toxic [10]. If azo dyes are absorbed into the

soil from the water, they can alter the chemical and

physical properties of the soil. This can lead to the

destruction of the vegetation in the environment; if

the toxic chemical dyes remain in the soil for a long

time, they also kill benecial microorganisms in

the soil, signicantly affecting agricultural fertility

[11]. Therefore, these toxic dyes should be disposed

of from wastewater as much as possible before they

are released into terrestrial or aquatic resources in

an environmentally sound manner [12]. The search

for efcient and safe technologies for removing

organic paints from aquatic systems is of great

interest for environmental protection. The best

water treatment methods chosen depend on several

factors, including the nature, quantity and quality

of the paint materials in the systems analyzed

[13]. Great attention has been paid to technologies

for removing paint from wastewater, and many

chemical, biological and physical methods have

been developed for this purpose [14,15], including

adsorption, chemical oxidation, photocatalysis,

electrochemical oxidation, biodegradation, ion-

exchange ltration, coagulation/occulation,

membrane ltration, catalytic degradation

and so on. Most conventional methods have

major drawbacks of low selectivity, high power

consumption, and low color degradation [16].

Many attempts have been made today to develop

new selective and sensitive techniques for the

purication of samples and separation of selected

materials, and solid phase extraction (SPE) is the

most widely used method [17], As SPE for sample

pretreatment offers several advantages, including

fast separation, low cost, low solvent consumption,

high enrichment efciency and recovery rates,

short processing times, no emulsion formation,

and the ability to combine with many advanced

detection methods [18], simple composition, high

recovery and high enrichment factor. The basic

principle of the elements/species of particular

interest is to transfer the target elements/species

from the sample matrix to the active site of the

SPE adsorbent. The sorbent is the main factor

that determines the selectivity, sensitivity, and

extraction/absorption dynamics of the relevant

method [19]. In this study, three natural materials

were selected to convert them into activated carbon

and use the products as a solid phase in the study of

the solid phase extraction technology (SPE), where

Ziziphus Spina-Christi leaves, Consocarpus leaves

and Myrtus Communis leaves were used. Materials

in the preparation of solid phases (Z/AC), (C/AC)

and (M/AC) respectively to remove Congo red

(CR) in aqueous solutions using SPE under optimal

conditions.

This paper aims to investigate the applicability of

activated carbon prepared from cheap and available

natural sources as a solid phase in SPE for the

purify water contaminated with organic Congo red

(CR) dye, [1-naphthalene sulfonic acid, 3, 30-(4,

40-biphenylenebis (azo)) bis (4-amino-) disodium

salt] (Fig. 1).

Fig. 1. Chemical structure of Congo red

2. Experimental

2.1. Chemicals and Materials

Chemical reagents including Congo Red (CR), 85%

dye content (C32H22N6Na2O6S2, Mw: 696.665 g mol-

1) purchased from (Pub Chem). A stock solution

(100 mg.L-1) of (CR) was prepared by dissolving the

required amount of dye in distilled water. The pH was

adjusted with 0.1 mol L-1 of NaOH (Univar) and 0.1

mol.L-1 HCl (AnalaR) and measured with a pH meter

(model SD 300, Germany). The potassium hydroxide

(KOH), (Sigma-Aldrich) was used to activate the

carbon that was prepared from multiple natural

sources (Ziziphus Spina-Christi leaves, Consocarpus

leaves, and Myrtus communis leave). The ethanol,

methanol, dimethyl sulfoxide (DMSO), n-Hexane,

and toluene (Sigma-Aldrich) were used in the solid

phase elution to recover the dye. Distilled water was

used throughout this study. AC was distinguished

by FT-IR, XRD, TEM and SEM technologies. The

absorbance of the CR dye solution was measured

at the wavelength of 494 nm, using a UV-visible

spectrophotometer (PG Instrument T80 + UV/VIS

model). The percentage of dye removal efciency, R

and the amount of CR dye adsorbed per unit weight

of adsorbent at time t, qt (mg g-1) was calculated as

Equation 1 and 2:

(Eq.1)

(Eq.2)

Where Ce is the concentration of CR at time t, C0 is

the initial dye concentration (mg L-1), M is the mass

of adsorbent (g) and V is the volume of solution (L).

2.2. Activated carbon preparation

Three categories of activated carbon were produced

from Ziziphus Spina Christi leaves, Consocarpus

leaves and Myrtus communis leaves, and were denoted

by (Z/AC), (C/AC) and (M/AC) respectively. The

leaves of the plants were collected and washed well

with distilled water; then each substance was boiled

in two liters of water for two hours, to remove other

water-soluble organic and phenolic compounds, then

dried at 70°C in Oven for 8 hours. Subsequently, they

were crushed and sieved (40–60 mesh). Afterward,

125 g of each type of dried plant leaf powder was

used as the initial amount to produce every kind of

activated carbon and impregnation of the plant leaves

in a potassium hydroxide KOH (25%) by using a

solution (KOH) to solid (plant leaves powder) ratio

of 3:1 for 24 h, and then rinsed with distilled water

several to reach the pH of the washing liquid. Then,

the washed solid samples were dried at 100 °C; then

pyrolyzed in a mufe furnace at 500 °C carbonization

temperature for 1 hour. After that, the samples were

washed with deionized water many times until the pH

of the solution was equal to the pH of the distilled

water. The resulting activated carbon was dried up

at 100 °C and kept dry till usage in the experiment

[20,21].

2.3. Solid phase extraction

The solid phase extraction method includes three

basic stages, column preparation, loading, and elution

[22,23]. The column of the polypropylene cartridge

was prepared (Fig. 2). The column was lled with a

permeable polypropylene lm (disc) with a thickness

of 1 mm. Four layers of glass paper were placed

glass lter paper; then the column was lled with a

xed weight (0.5 gm) of the solid phase, which is the

activated carbon prepared in this study from different

natural sources (Z/AC), (C/AC), (M/AC). The steel

was homogeneous, so, that it was free of voids and of

equal height from the top, then a layer of glass paper

was placed over the solid phase. The CR dye solution

was passed at the pHpzc, where the dye is bound at

this stage to the solid phase pre-packed in the column

and the unbound part of the dye passes from the

column as well as the rest of the original components

and at a running rate depends on gravity. As for the

rinsing stage, it included passing the elution solution

through the separation column, which breaks the

link between the dye and the solid phase, and then

transfers the solution to measurement using UV-

Anal. Methods Environ. Chem. J. 5 (3) (2022) 40-54

visible technology to know the concentration

extracted from the dye. The ratio can be calculated

as the percentage of recovery % through Equation 3,

and this study included nding the ideal conditions

for the optimization of the extraction process as

shown below.

(Eq.3)

2.4. Characterization Methods

To investigate the surface characteristic of (Z/

AC), (C/AC), and (M/AC), FT IR, XRD, and SEM

spectra were studied. FT-IR spectroscopy was

carried out to determine the type and nature of the

functional groups present in the activated carbon.

The presence of these functional groups increases

heterogeneity and, thereby the extraction. The

spectra of (Z/AC), (C/AC), and (M/AC) samples

are shown in Table 1. To explore the crystal lattice

structure of activated carbon, an X-ray diffraction

pattern was carried out; Figure 3 shows the XRD

conguration of the three AC types (Z/AC), (C/

AC) and (M/AC). In this pattern, several peaks

were found corresponding to their semi-crystalline

nature. XRD spectra of the tted conditioners

revealed a sharp diffraction peak of 29.5° for all

solutions that (Z/AC), (C/AC), and (M/AC) and this

is evidence for the possible presence of potassium

compounds with high crystallinity after activation

with KOH. The SEM is a tool for characterizing

the surface morphology and physical properties

of the adsorbent surface. It helps determine the

particle shape, appropriate size distribution of the

adsorbent and porosity. The surface morphology

of the (Z/AC), (C/AC) and (M/AC) adsorbents are

shown in Figure 4a-c.

Fig. 2. Summary of preparation of activated carbon and extraction procedure

Extraction and Removal of Congo Red by Activated carbon Tahrer N. Majid et al

Table 1. FT-IR analysis (Z/AC), (C/AC) and (M/AC

Z\ACC\ACM\AC

3438.463754.733422.06O-H

3374.82-3302.5≡CH

3225.36-3267.79CH=

2369.12-2360.44≡CH

2948.63-2900.41CH-

1445.391432.851435.74C-O

-1609.13-C=C

Fig. 3. XRD pattern of a: (Z/AC), b: (C/AC) and c: (M/AC)

Anal. Methods Environ. Chem. J. 5 (3) (2022) 40-54

Fig. 4a. SEM of Ziziphus spina-christi (Z/AC)

Fig. 4c. SEM image of Myrtus plant (M/AC)

Fig. 4b. SEM of Consocarpus plant (C/AC)

Extraction and Removal of Congo Red by Activated carbon Tahrer N. Majid et al

3. Results and Discussion

3.1. Optimization of the extraction procedure

The study of nding the optimal conditions for any

analytical method includes the process of changing

one of the conditions of the experiment and xing

the rest of the other conditions that control the

efciency of the experiment. Adjusting the method

to all the optimal values for all factors, and to

nd the ideal conditions and obtain the maximum

efciency of the process of extraction and removal

of the dye, several experiments were conducted as

follows:

3.2. Amount of solid phase

The effect of the weight of the packed solid phase

in the separating column was studied, and the

results proved that the percentage of retrieval varies

according to the amount of the solid phase. Figure 5

shows an apparent behavior in increasing the retrieval

percentage with increasing phase weight for the

weights range (0.05-5.0) g, where the recovery

percentage reaches the maximum value when using

the weight of 0.25 g. Then the recovery percentages

stabilize in the largest weights down to 0.5 g. This

behavior was for all solid phases when studying the

CR dye, which leads to the weight of 0.25 g of the

solid phase being selected as a constant weight for

all phases in all subsequent experiments.

Fig. 5. Effect of the solid phase amount on the recovery

of Congo Red

3.3. Effect of Dye concentration

The effect of the concentration of the CR solution

was studied after packing the extraction column

with 0.25 g of activated carbon and loading CR

with a range of concentrations which is (50-400)

mg L-1 with the stabilization of the acidity function,

the volume of the dye solution, the ow rate, the

type and volume of the rinse solution, where a

concentration of 100 mg L-1 was chosen for the CR

dye towards the corresponding solid phases, where

this concentration achieves a recovery percentage

ranging from 60-65% for the dyes. This ratio is

necessary because the recovery efciency was not

at this stage at its maximum, and it is expected to

increase it when conducting experiments on other

factors affecting extraction. Due to Figure 6, the

effect of the concentration of the CR solutions was

shown.

Fig. 6. Effect of Congo Red concentration on the

recovery percentage

3.4. Effect of pH

The pH function is one of the critical factors in

the study of extraction, which affects the surface

charge of the solid phase and the composition of

the dye [38]. The effect of acid functions on the

solid phase extraction process with a range of (2-

12) was studied. Figure 7 represents the effect of

the acidity function on the percentage of recovery

of CR (anionic) dye when extracted by (Z/AC) and

(C/AC) and (M/AC) phases, as we notice that the

%R values increase directly for the range of the

acidic function (2-5) and then reach the optimal

100

0100 200 300 400 500

Recovery , %

Conc. of CR , mg/L

(Z/AC)KOH

(M/AC)KOH

(C/AC)KOH

0 0.1 0.2 0.3 0.4 0.5 0.6

Recovery , %

Active Carbon Weghit , gm

(Z/AC)KOH

(M/AC)KOH

(C/AC)KOH

Anal. Methods Environ. Chem. J. 5 (3) (2022) 40-54

acidity function pH = 5 and this increase in the %R

values is attributed to the hydrostatic interactions

between the solid phases and dyes, as for the acid

functions that follow the optimum value and within

the range (6-12), we notice a decrease in the values

of %R, and this can be attributed to the fact that

the hydroxyl radical OH- whose concentration

increases with the increase of the acidic function

competes with the dye molecules towards the solid

phases. The value of the optimal pH function in

extracting or removing the CR dye is equal to 5

and was identical to the results of previous studies

[24,25].

Fig. 7. Effect of pH on the recovery of Congo Red

3.5. Effect of dyes volume

Studying the effect of the target material

solution’s volume is essential in determining the

optimal conditions for the solid phase extraction

method [26,27]. Figure 8 showed that the

percentages of recovery of CR dye were close to

100% for volumes less than 100 mL within the

range of volumes (100-400) mL, the percentages

of recovery gradually decreased. This behavior

was very logical because the efciency of the

extraction decreases with the increase in the

volume of the solution, as the concentration of

the dye decreases with the increase in the volume

of the solution, and therefore the remaining dye

during the extraction process is more diluted

the more the volume of the solution was more

signicant the extraction efciency decreased.

So, the volume of 25 mL is considered to be the

optimum volume of the CR dye.

Fig. 8. Effect of Congo Red solution volume on the

recovery percentage

3.6. Effect of ow rate

The effect of the ow rate of the dye solution is

one of the critical factors affecting the efciency of

extraction in the solid phase. A balance in the ow

rate is necessary in the sense that low ow rates

do not achieve high rates of recovery of the target

material due to the possibility of disengagement

between the solid phase and the target material

during the passage of the solution. Thus, the

extraction efciency decreases, and high ow rates

are considered undesirable because they do not

provide sufcient time for the connection between

the solid phase and the material to be extracted.

Figure 9 shows a graphic relationship between the

percentages of dye recovery versus the rate of the

ow rate of the CR solution. We found that the

maximum ow rate was equal to 0.5 mL min.

Fig.9. Effect of ow rate on the recovery of Congo Red

100

0246810 12 14

Recovery , %

(Z/AC)KOH

(M/AC)KOH

(C/AC)KOH

100

010 20 30 40 50 60

Recovery , %

Volume of CR , mL

(Z/AC)KOH

(M/AC)KOH

(C/AC)KOH

100

0 1 23 4 5 6

Recovery , %

Flow Rate , ml/min

(Z/AC)KOH

(M/AC)KOH

(C/AC)KOH

Extraction and Removal of Congo Red by Activated carbon Tahrer N. Majid et al

3.7. Effect of type and volume of eluting solution

Table 2 shows the solvents used as eluent solutions

and their polarity index values, where the polarity

coefcient represents the ability of the solvent

to interfere with the solute[28], and Figure 10

shows the effect of the type of the solvent on the

percentages of recovery of the two dyes. We note

that the highest rate of recovery was achieved when

the elution solution was DMSO with a polarity

coefcient of 7.2 and the highest polarity among

the solvents. It may be attributed to the great

afnity of CR dyes towards the DMSO solvent

because it is a polar dye. It makes the dye leave as a

solid phase and moves with the more polar rinsing

solution (Figure 10). we note that the percentages

of recovery decrease with the decreasing polarity

of the eluting solution. The study also included

nding the optimum volume of the rinse solution;

when observing in Figure 11, which represents the

graphic relationship between the percentage of

recovery of the CR dye and the volume of the rinse

solution, we nd that the volume that achieves the

highest rate of recovery was equal to 8 mL. Finding

the optimal volume of the rinsing solution leads us

to calculate the enrichment factor, which evaluates

the extraction process, which can be calculated

from Equation 4 [29].

(Eq.4)

The enrichment coefcient can be calculated

depending on the initial dye volume and the volume

of the rinsing solution (Equation 4). Table 3 shows

the values of the calculated enrichment coefcients

for the extraction systems under study.

Fig. 11. Effect of DMSO volume on the recovery

of Congo Red

(Z/AC)KOH

(M/AC)KOH

(C/AC)KOH

100

DMSO

Methanol

Ethanol

Toluene

n-Hexane

Recovery , %

Eluent Type

Fig. 10. Effect of elution type on the recovery of Congo Red

100

0 2 4 6 8 10 12 14 16 18 20

Recovery , %

DMSO Volume , mL

(Z/AC)KOH

(M/AC)KOH

(C/AC)KOH

Anal. Methods Environ. Chem. J. 5 (3) (2022) 40-54

3.8. Isotherm study

One of the most important benets of the SPE

extraction process is the removal of the target

substance from its origin in which it is located

[30]. Therefore, the results obtained in the

extraction experiments can be employed in favor

of the removal operations of CR from its aqueous

solution. The residual concentration of the solutions

of the CR dye was calculated and thus the weight

adsorption capacity q (mg g-1) was calculated based

on Equation 5 [31, 32].

(Eq.5)

Through the study of the isotherm, it is possible

to clarify the relationship between the solid

phases and dye, and to suggest the mechanisms of

interaction [33]. The study of the isotherm includes

the application of many models, and the Langmuir

and Freundlich models were chosen in this study.

3.9. Langmuir isotherm model

The Langmuir equation [34] which was developed

in 1916 applies to monolayer or single-molecular

adsorption of the target material on the surface

of the adsorbent material or the solid phase

(Equation 6), where this equation assumes the

existence of homogeneous adsorption sites [35].

(Eq.6)

Figure 12 represents the Langmuir model for CR.

Table 4 also shows the results obtained from this

model. The values of the maximum adsorption

capacity qmax, Langmuir constant KL and correlation

coefcient R2 were calculated by plotting the

graphical relationship of the Langmuir equation

between Ce/qe on the Y-axis and Ce on the X-axis

as in Figure 12, where the slope of the straight line

represents (1/qmax) and the cutoff represents (1/

qmax. KL) and by noting the Table 4, we nd that

the maximum adsorption capacity of CR dye by

the solid phase (C/AC) is the highest in comparison

with the other two phases. This may be due to the

nature of the interaction between this dye and the

prepared solid phases, which certainly had the

advantage compared to the nature of the association

with CR dye, and also through Table 4 we nd that

the values of Langmuir constant rise in the same

pattern, which indicates the extent of the strong

interaction between the active sites in the dye and

between the solid phase. It is also noted the values

of the correlation coefcient very close to the right

one, which indicates the relative applicability of

the studied adsorption systems on the Langmuir

model.

Table 2. Solvents used as elution solution and their polarity index

Polarity indexSolvent

7.2DMSO

5.1Methanol

4.3Ethanol

2.4Toluene

0.1n-hexane

Table 3. Enrichment factors for extraction of CR

Enrichment factorSolid Phase

3.125(Z/AC)

3.125(M/AC)

3.125(C/AC)

Extraction and Removal of Congo Red by Activated carbon Tahrer N. Majid et al

3.10. Freundlich isotherm model

As Equation 7, the Freundlich equation developed

in 1926 [36] It explains the processes of interference

and adsorption that occur on heterogeneous

surfaces and assumes that adsorption occurs at sites

of varying adsorption energy [37].

(Eq.7)

The Figure 13 represent Freundlich model for

CR. Table 5 also shows the results obtained from

this model. The values of Freundlich constant KF

and correlation coefcient R2 were calculated by

plotting the graph of Freundlich equation between

lnqe on the Y-axis and lnCe on the X-axis as in Figure

13, where the slope of the straight line represents

(1/n) and the cut off represents (lnKF). By noting

the Table 5, we nd that the highest value of KF,

which represents the adsorption energy between the

solid phase and the dye [38] is for the adsorption

system of the solid phase (C/AC) and this result is

in agreement with the qmax values calculated from

the Langmuir model. The values of 1/n give an

indication that the adsorption process is preferred or

unfavorable, as if the values of 1/n = 0, this means

that the adsorption is irreversible, but when it is

0<1/n<1, this indicates that the adsorption between

the solid phase and target material is a preferred

process, and adsorption may not be favorable when

1/n>1 [39]. When observing the values of 1/n from

Table 5, we nd that they are greater than zero and

less than one for all solid phases. Thus, could be

concluded that the adsorption systems in this study

are preferred. After reviewing Tables 4 and 5, we

nd that the R2 values of the Freundlich model

for all systems are higher than the corresponding

values in the Langmuir model leading to suggest a

physisorption mechanism.

4. Conclusion

In conclusion, the efcient removal of the dyes

CR from aqueous solutions was observed when

using the active carbon (Z/AC), (C/AC) and (M/

AC) as solid phases. The optimization approach

y = 0.046x + 0.2958

R² = 0.9938

y = 0.0451x + 0.2364

R² = 0.9933

y = 0.0425x + 0.1692

R² = 0.9905

0.5

1.5

2.5

3.5

4.5

0 20 40 60 80 100

Ce /q , (g/L)

Ce , (mg/L)

(Z/AC)KOH

(M/AC)KOH

(C/AC)KOH

Fig. 12. Langmuir isotherm of adsorption of Congo Red

Table 4. Langmuir isotherm parameters for the adsorption of CR dye at 25 °C

qmax(mg. g-1)Solid Phase

1.55510.993821.7391(Z/AC)

1.907780.993322.1729(M/AC)

2.511820.990523.5294(C/AC)

Anal. Methods Environ. Chem. J. 5 (3) (2022) 40-54

for the extraction of CR observed that the optimum

amount of solid phases was 0. 25 g, the initial

concentration of dye solution was 100 mg L-1, the

optimum pH was 5, the volume of dye solution was

25.0 mL with a ow rate equal to 0.5 mL min-1,

and the optimum elution solution was DMSO with

a volume equal to 2.0 mL, from the linearized form

(from the calculation of the Langmuir equation,

qmax), values for the CR dye were (21.74, 23.53,

22.17) mg g-1 for (Z/AC), (C/AC), and (M/AC),

respectively.

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