4.3. Activated carbons obtained from orange peels

Some studies have been done for the preparation of activated carbon from orange peel, Table 5 shows some reports and it is possible to appreciate the different activating agents used, temperature, and time of carbonization, as well as the surface area reported for those materials.

Some studies for the elaboration of activated carbons from orange peel are described below; these materials have been used for the removal of metals, dyes, among others. These reports indicate sorption capacities from 7.9 to 982 mg/g.

Quijano and Mejía [31] elaborated activated carbons from the residue obtained after pectin extraction from orange peels; they analyzed the effect of time and carbonization temperature on the carbonization percentage, using a 22 factorial design. They determined that temperature has significant influence on the carbonization yield; the optimum condition was obtained at 400C and 0.5 h for a 34.8% yield and a sorption capacity of methylene blue of 149.4 mg/g.

Annadurai et al. [32] prepared low-cost sorbents from orange peels for the sorption of several dyes in aqueous solution. The concentrations of dye and pH were varied and after the study they determined that sorption capacities decrease as follows: methyl orange > methylene blue > rhodamine B > red congo > methyl violet > black amino 10B, from 20.5 to 7.9 mg/g.

Khaled et al. [33, 34], in different studies, evaluated different conditions to obtain activated carbon; they used H2SO4 as an activating agent; a solution of this acid was in contact with the material for 96 h at 105C; after that, the sample was carbonized at 120C and 180C. Obtained activated carbons were evaluated using direct blue dye-106 and direct yellow-12, for which sorption capacities were 107.5 and 75.8 mg/g, respectively.

Materiala

Particle size

Temperature

Time

Activation

 Agent (

C)

(h)

(m2/g)

Temperature

Time

Surface area

Pore volume

Pore size

Sorption

Reference

capacity (mg/g)

(nm)

1.92

 680

[20]

(cm3 /g)

(mm)

Grapefruit

Banana

Yaca

Almond

 1–5

300 700 1200

300 700 1200

Rice

 6 103 aMaterials were considered Table 4. Organic waste used for the production

 as the husks of the mentioned

 fruits. CH: chemical activation and P: physical activation.

 of activated carbon.

650

1

 CH

 NaOH —

 —

253.4

 0.17

 1

1

1

Orange

 1

1

1

 P

 CO2

—

—

—

—

—

—

1

 240

13.5

12–14

2.62

 0.17

[22]

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211

1

 248

1

 225.6

 14.5

15

10

1

 342

15.5

15–25

7–14

 166.7

1

 385

16.92

10

1

 322

—

350

0.5

H3PO4 350

450 550

0.5

 1260

 0.733

19.5

8–12

 288.5

[21]

2

—

0.5

 1033

 0.664

—

1000

 8

ZnCl —

 —

0.5

 5

—

1.7

—

——

1650

 1.26

3.01

—

[11]

[12]

—

450

2

 CH

 KOH

 450, 800

 1.5,

1892.1

 1.095

2.5

(

C)

(h)


are displacing the zeolites, used frequently for this purpose. Another important application, which takes advantage of the properties of a molecular sieve of activated carbons, is the retention of nitrogen oxides (NOx) from different sources and sulfur that coals and oils contain and that when heated is transformed into toxic products, such as sulfur dioxide (SO2), hydro-

Recently, fruit husks as agroindustrial waste have been implemented in the production of activated carbons; investigation of sorption about selective specific size molecules has been done regarding these materials. The use of agroindustrial residues is a new alternative that provides a proposal of integral valorization, taking advantage of the waste abundance and the

Table 4 shows the results of some reports from which activated carbons have been elaborated; elaborating parameters as well as surface areas are shown. It is possible to see surface area

/g [26], activated carbon MT40 of 528 m<sup>2</sup>

Some studies have been done for the preparation of activated carbon from orange peel, Table 5 shows some reports and it is possible to appreciate the different activating agents used, temperature, and time of carbonization, as well as the surface area reported for those

Some studies for the elaboration of activated carbons from orange peel are described below; these materials have been used for the removal of metals, dyes, among others. These reports

Quijano and Mejía [31] elaborated activated carbons from the residue obtained after pectin extraction from orange peels; they analyzed the effect of time and carbonization temperature on the carbonization percentage, using a 22 factorial design. They determined that temperature has significant influence on the carbonization yield; the optimum condition was obtained at 400C and 0.5 h for a 34.8% yield and a sorption capacity of methylene blue of 149.4 mg/g.

Annadurai et al. [32] prepared low-cost sorbents from orange peels for the sorption of several dyes in aqueous solution. The concentrations of dye and pH were varied and after the study they determined that sorption capacities decrease as follows: methyl orange > methylene blue >

Khaled et al. [33, 34], in different studies, evaluated different conditions to obtain activated carbon; they used H2SO4 as an activating agent; a solution of this acid was in contact with the material for 96 h at 105C; after that, the sample was carbonized at 120C and 180C. Obtained activated carbons were evaluated using direct blue dye-106 and direct yellow-12, for which

rhodamine B > red congo > methyl violet > black amino 10B, from 20.5 to 7.9 mg/g.

/g [26].

/g; these values are comparable to those reported in literature for

/g [24]. These values are also comparable to

/g [25], Darco KB-B of 1608 m2

/g [27], activated carbon

/g

gen sulfide (SH2), carbon sulfide (S2C), and so on [17].

/g [23], as well as 1853 m2

commercial materials: PET activated carbons have 1170 m2

/g [27], and Fluka 03866 of 179 m2

4.3. Activated carbons obtained from orange peels

indicate sorption capacities from 7.9 to 982 mg/g.

sorption capacities were 107.5 and 75.8 mg/g, respectively.

low cost of the material [17].

values from 200 to 1800 m2

[26], Fluka 05120 of 1110 m<sup>2</sup>

lignite of 1300 m<sup>2</sup>

210 Wastewater and Water Quality

BW of 300 m<sup>2</sup>

materials.

Table 4. Organic waste used for the production of activated carbon.


Table 5. Preparation of activated carbon using orange peels.

Fernandez et al. [35] studied the effect of H3PO4 as an activating agent to prepare activated carbon; the carbonization procedure was carried out at 475C in 0.5 h. Authors report surface areas of 1090 m2 /g for the obtained materials. Methylene blue and rhodamine B were used to characterize sorption capacities and the values obtained were 320 and 522 mg/g, respectively.

the model pollutant in order to analyze sorption capacity of 2342.91 mg/g. This result was

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213

Figures 2 and 3 show a comparison of the surface morphology of orange peel and activated carbon obtained from orange peel. It can be seen that after the carbonization treatment the surface was modified, given by the thermal process and by the activation agent. The carboni-

On the other hand, Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the surface groups of activated carbon obtained from orange peel. Figure 4 shows the comparison of orange peel and activated carbon. It is possible to appreciate that the intensity of some signals decreases after carbonization process. Table 6 identifies functional groups associated

compared to dried orange peel that showed a sorption capacity of 149.26 mg/g.

Figure 4. Comparison of the FTIR spectrum of orange peel and orange peel-activated carbon.

zation process promotes the formation of new surface sites.

Figure 3. SEM micrography of activated carbon obtained from orange peel at 1000.

with the FTIR spectra of Figure 4.

Li et al. [20], studied the effect of KOH as an activating agent and the process of carbonization in an inert atmosphere, at 800C; the activated carbon obtained had a surface area greater than 1800 m2 / g, and a sorption capacity of 680 m/g was obtained using methyl orange as a model pollutant.

Ashtaputrey and Ashtaputrey [36] prepared activated carbon from orange peels by chemical activation using HCl; they also varied the carbonization temperature from 300 to 500C for 1 h. They analyzed the sorption capacity of iodine, and finally, they concluded that a carbonization temperature of 300C promotes a sorption capacity of up to 983 mg/g.
