2. Experimental

#### 2.1 Materials and methods

The selected adsorbates comprise 21 compounds which are structurally differentiated with regard to the number, position, and type of the functional groups and length and spatial arrangement of the hydrocarbon part in a molecule. Not all of these substances are used as pesticides because of their low biological activity. However, due to complexity of the research issues, it seems to be reasonable to include them as a subject of the investigation.

Table 1 presents the physicochemical properties of the adsorbates collected on the basis of literature data or calculations using computer programs generally available. All the substances are analytical reagent grade purity. The chemical names and abbreviations of them are as follows: 4-chlorophenoxyacetic acid (4-CPA); 2,4 dichlorophenoxyacetic acid (2,4-D); 2,4,5-trichlorophenoxyacetic acid (2,4,5- CPA); 2,4,6-trichlorophenoxyacetic acid (2,4,6-CPA); 4-chloro-3-methylphenoxyacetic acid (4-CMPA); 4-chloro-2-methylphenoxyacetic acid (MCPA); 2,4 dibromophenoxypropionic acid (2,4-BrPA); 2,4,6-tribromophenoxypropionic acid (2,4,6-BrPA); 2-(3-chlorophenoxy)propionic acid (3-CPP); 3-(4-chlorophenoxy) propionic acid (4-CP); 2-(4-chlorophenoxy)propionic acid (4-CPP); 2-(2,4 dichlorophenoxy)propionic acid (2,4-CPP); 2-(2,5-dichlorophenoxy)propionic acid (2,5-CPP); 2-(3,4-dichlorophenoxy)propionic acid (3,4-CPP); 2-(2,4,5-trichlorophenoxy)propionic acid (2,4,5-CPP); 2-(4-chloro-2-methylphenoxy)propionic

acid (MCPP); 2-(4-chloro-3-methylphenoxy)propionic acid (4-CMPP); 2-(4 chlorophenoxy)-2-methylpropionic acid (CFA); 2-(4-chlorophenoxy)butanoic acid (4-CPB); 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB); and 2-(4-chloro-2-

The microporous activated carbon F300 was used as adsorbent (SBET = 762 m<sup>2</sup>

are given in the paper [8]. The methodology of equilibrium and kinetic measure-

/g; pHpzc 9.8). The characteristics of adsorbent

/g,

methylphenoxy)butanoic acid (4-CMPB).

ments is also described in the paper [8].

/g, Vmic = 0.28 cm<sup>3</sup>

Vt = 0.46 cm<sup>3</sup>

Table 1.

atoms.

3

Common name

pKa [9]

DOI: http://dx.doi.org/10.5772/intechopen.88726

Solubility g/dm<sup>3</sup> 20–25°C

4-CPA 3.14 0.848 [10] 1.88 1.63 1.85

Influence of Pesticide Properties on Adsorption Capacity and Rate on Activated Carbon…

2,4-D 2.80 0.682 [10] 2.46 1.03 2.37

2,4,5-CPA 2.56 0.268 [10] 3.04 0.42 2.89

2,4,6-CPA 2.57 0.247 [10] 3.04 0.42 2.89

MCPA 3.36 0.825 [10] 2.40 1.12 3.25

2,4,5-CPP 2.70 0.140 [10] 3.62 0.15 3.80

MCPP 3.47 0.895 [10] 2.97 0.55 3.13

CFA 3.37 0.582 [17] 2.89 0.63 2.84

MCPB 3.59 0.048 [10] 3.50 0.03 3.28

4-CMPA 3.36 0.650 [12] 2.40 1.12 5.42 8.96

2,4-BrPA 1.96 0.059 [14] 2.60 0.70 5.03 9 2,4,6-BrPA 1.50 0.015 [15] 3.12 0.07 5.71 9 3-CPP 3.27 1.200 [16] 2.45 1.06 5 7.79 4-CP 3.70 0.770 [12] 2.13 1.39 4.33 9.87 4-CPP 3.27 1.475 [10] 2.45 1.06 5.22 8.65 2,4-CPP 2.95 0.829 [10] 3.04 0.46 5.59 9.03 2,5-CPP 2.95 0.181 [14] 3.04 0.46 5.62 8.63 3,4-CPP 2.94 0.130 [12] 3.04 0.46 5.5 8.76

4-CMPP 3.46 0.690 [15] 2.97 0.55 5.86 7

4-CPB 3.42 0.315 [14] 2.98 0.54 5.22 9.7

4-CMPB 3.59 0.17 [12] 3.50 0.03 5.86 9.28

Physicochemical properties of the studied pesticides, where pKa is the value based on partial charge distribution in a molecule, log D is the octanol-water coefficient at a given pH, log P is the partition coefficient of a compound between octanol and water, and Dmin and Dmax are measures between the most distant molecule

Kow/log D [9] Kow/log

P

[11]

[11]

[11]

[11]

[13]

[13]

[13]

[13]

[18]

[9] pH = 1.81 pH = 10.38

Dmin /Å [9]

4.33 9.38

4.88 9.49

6.22 8.88

5.42 8.84

5.47 9.52

5.62 9

5.86 8.64

4.42 9.14

6.36 9.65

Dmax /Å


Influence of Pesticide Properties on Adsorption Capacity and Rate on Activated Carbon… DOI: http://dx.doi.org/10.5772/intechopen.88726

#### Table 1.

The influence of adsorbate substituents on adsorption mechanism is similar to that of surface groups of adsorbent. Depending on their nature, they can attract or repel electrons and affect the dispersive interactions between adsorbate aromatic ring and graphene layers of activated carbon. The adsorbate functional groups that are electron donors activate the aromatic ring by moving electrons toward it, and thereby they enhance the interactions between adsorbate molecule and π electrons of adsorbent graphene planes. On the other hand, the deactivating groups as electron acceptors reduce the electron density of aromatic ring; thus, interactions of

The research on effect of adsorbate properties on adsorption process is an extension of the studies already published in the paper [8]. The pesticides belonging to a group of chloride phenoxyacid derivatives were used as adsorbates in view of their common usage in agriculture and hence a high probability of infiltration to surface and underground waters. Their presence in water affects its quality, worsens its properties, and in some cases makes it unsuitable to consume. These pesticides show a carcinogenic activity on living organisms and a relatively long half-life time in the environment; therefore, the intensive study on their removal by adsorption process is very important for practical applications. The experimental studies include measurements of the adsorption isotherms and concentration rate profiles as well as their interpretation on the basis of the generalized Langmuir (GL) equation for equilibrium data and diffusion models (intraparticle diffusion model (IDM) and pore diffusion model (PDM)) and multi-exponential (m-exp) equation for kinetic data. Based on the obtained results, the correlations between adsorbate structure, its properties, and adsorption uptake and rate were analyzed. The evaluation of the theoretical equilibrium and kinetic equations and models based on a fitting quality and consistency with adsorption mechanism was also made.

The selected adsorbates comprise 21 compounds which are structurally differentiated with regard to the number, position, and type of the functional groups and length and spatial arrangement of the hydrocarbon part in a molecule. Not all of these substances are used as pesticides because of their low biological activity. However, due to complexity of the research issues, it seems to be reasonable to

Table 1 presents the physicochemical properties of the adsorbates collected on the basis of literature data or calculations using computer programs generally available. All the substances are analytical reagent grade purity. The chemical names and abbreviations of them are as follows: 4-chlorophenoxyacetic acid (4-CPA); 2,4 dichlorophenoxyacetic acid (2,4-D); 2,4,5-trichlorophenoxyacetic acid (2,4,5- CPA); 2,4,6-trichlorophenoxyacetic acid (2,4,6-CPA); 4-chloro-3-methylphenoxyacetic acid (4-CMPA); 4-chloro-2-methylphenoxyacetic acid (MCPA); 2,4 dibromophenoxypropionic acid (2,4-BrPA); 2,4,6-tribromophenoxypropionic acid (2,4,6-BrPA); 2-(3-chlorophenoxy)propionic acid (3-CPP); 3-(4-chlorophenoxy) propionic acid (4-CP); 2-(4-chlorophenoxy)propionic acid (4-CPP); 2-(2,4 dichlorophenoxy)propionic acid (2,4-CPP); 2-(2,5-dichlorophenoxy)propionic acid (2,5-CPP); 2-(3,4-dichlorophenoxy)propionic acid (3,4-CPP); 2-(2,4,5-trichlorophenoxy)propionic acid (2,4,5-CPP); 2-(4-chloro-2-methylphenoxy)propionic

adsorbate-adsorbent surface are weakened [1–7].

2. Experimental

Sorption in 2020s

2

2.1 Materials and methods

include them as a subject of the investigation.

Physicochemical properties of the studied pesticides, where pKa is the value based on partial charge distribution in a molecule, log D is the octanol-water coefficient at a given pH, log P is the partition coefficient of a compound between octanol and water, and Dmin and Dmax are measures between the most distant molecule atoms.

acid (MCPP); 2-(4-chloro-3-methylphenoxy)propionic acid (4-CMPP); 2-(4 chlorophenoxy)-2-methylpropionic acid (CFA); 2-(4-chlorophenoxy)butanoic acid (4-CPB); 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB); and 2-(4-chloro-2 methylphenoxy)butanoic acid (4-CMPB).

The microporous activated carbon F300 was used as adsorbent (SBET = 762 m<sup>2</sup> /g, Vt = 0.46 cm<sup>3</sup> /g, Vmic = 0.28 cm<sup>3</sup> /g; pHpzc 9.8). The characteristics of adsorbent are given in the paper [8]. The methodology of equilibrium and kinetic measurements is also described in the paper [8].
