2.3. Adsorbent preparation and application

The precursor for the active carbon material was acquired by collecting avocado seeds. The avocado fruit waste seeds (AFWS) were air-dried and thoroughly washed before rinsing with deionized water. The washed seed residues were then oven-dried overnight at 100C. The seeds were then pulverized by ball milling it with laboratory hammer mill (Janke and Kunkel Micro-hammer Mill, Staufen IM Breisgau, Germany) to obtain fine powder. The bulky powdered material was later fractionated to diverse particle size using laboratory sieves. The resultant particles of different miniature diameters ranging from 38 to 150 μm were obtained in which 75 μm particle size was subsequently employed in production of active carbon material. The powdered form of avocado seed was then stored inside desiccator until application.

The adsorption studies were carried out to evaluate the efficiency of the avocado peel (bioadsorbent) for the removal of AsIII from the aqueous solution using the batch adsorption method. The batch adsorption experiments were carried out in 50 mL plastic bottles by shaking a constant mass of a predetermined size of adsorbent with arsenic standard solutions. The pH of the solutions was adjusted accordingly by adding either ammonium hydroxide or acetic acid solution. Each flask was sealed and kept in a state of agitation (200 rpm) using a mechanical laboratory shaker for the material to reach equilibrium. Upon equilibrium, the samples were filtered and analyzed using inductively coupled plasma optical emission spectroscopy (ICPOES). Parameters such as pH, concentration of solution, mass of adsorbent, contact time, and temperature were optimized.

The percentage removal of As(III) in solution was calculated using Eq. (1):

$$R\% = \frac{\mathbb{C}\_0 - \mathbb{C}\_\ell}{\mathbb{C}\_0} \times 100\tag{1}$$

at 2913 and 2848 cm<sup>1</sup> bands correspond to v(CdH) vibration in the alkane/alkyl aliphatic group which could be methylene [16–20]. The presence of alcohols and carbonyl groups was

composed of carboxylic group which is responsible for adsorption; similar results were

The surface morphology and the chemical composition of raw avocado seed was studied with scanning electron microscope coupled with energy dispersive spectroscopy (SEM-EDS). The image in Figure 2(a) showed that raw avocado seed material had a smooth surface with long

The EDS analyses performed on avocado seed revealed that the surface contained different mineral particles, such as carbon, oxygen, potassium, phosphorus, and chlorine (Figure 2b).

pH is one of the most important parameters that influence the adsorption of the analyte. In this study, the amount of AsIII adsorbed on avocado seed was the highest at pH 6 and gradually decreased as the pH increased up to 9 (Figure 3a) [7]. However, the highest removal was observed with avocado seed due to the presence of carboxylic group on the surface which increased the affinity toward arsenic to the adsorbent (Figure 1). Oxygen of the carbonyl group easily formed the complex with the arsenic [23]. Arsenic(III) adsorption decreased as the pH

The effect of the concentration was carried out by increasing the initial concentration from 5

percentage removal increased with the increasing concentration of the analyte; this is due to

, and the solutions were adjusted to pH 6 at 25C. It was observed that the

The highest content of oxygen may assist in adsorption due to electron lone pairs.

. This confirms that avocado seed is

http://dx.doi.org/10.5772/intechopen.73570

29

Bio-adsorbents for the Removal of Heavy Metals from Water

confirmed by the bond vibrations observed at 1633 cm<sup>1</sup>

ridges and a series of graphitic layers with various pores.

3.2. Optimization of adsorption parameters

goes below 6 due to the increasing ionic strength [24].

Figure 2. Avocado seed images of (a) SEM and (b) EDS.

to 30 mg L<sup>1</sup>

reported in the literature [21, 22].

where R is the percentage (%) removal and Co and Ce are the initial and equilibrium concentrations of the analyte, respectively.

The amount of metal adsorbed by adsorbent was calculated from the difference of metal quantity added to the biomass and metal content of the supernatant (Eq. (2) [14, 15]:

$$q\_{\epsilon} = \frac{(\mathbb{C}\_0 - \mathbb{C}\_{\epsilon})}{M} \times V \tag{2}$$

where qe is the metal uptake (mgg�<sup>1</sup> ), C<sup>0</sup> and Ce are the initial and equilibrium metal concentration (mgL�<sup>1</sup> ), V is the volume of the solution (mL), and M is the mass of the adsorbent (g).

#### 3. Results and discussion

#### 3.1. Characterization of the raw avocado seed and activated carbon material

The FTIR spectrum is an important technique which provides the surface functional groups that significantly contribute in the enhanced adsorption efficiency of the adsorbent. FTIR was used to determine the surface functional groups of raw avocado fruit waste seed. In Figure 1, the spectrum of the powdered avocado seed is represented, where the band located at 3259 cm�<sup>1</sup> corresponds to v (OdH) vibrations in the hydroxyl group, while the strong peaks

Figure 1. FTIR spectrum of avocado fruit waste seed (AFWS).

at 2913 and 2848 cm<sup>1</sup> bands correspond to v(CdH) vibration in the alkane/alkyl aliphatic group which could be methylene [16–20]. The presence of alcohols and carbonyl groups was confirmed by the bond vibrations observed at 1633 cm<sup>1</sup> . This confirms that avocado seed is composed of carboxylic group which is responsible for adsorption; similar results were reported in the literature [21, 22].

The surface morphology and the chemical composition of raw avocado seed was studied with scanning electron microscope coupled with energy dispersive spectroscopy (SEM-EDS). The image in Figure 2(a) showed that raw avocado seed material had a smooth surface with long ridges and a series of graphitic layers with various pores.

The EDS analyses performed on avocado seed revealed that the surface contained different mineral particles, such as carbon, oxygen, potassium, phosphorus, and chlorine (Figure 2b). The highest content of oxygen may assist in adsorption due to electron lone pairs.
