Photocatalytic Processes for the Removal of Dye - Green Chemistry for Dyes Removal from Wastewater - page 183

Table 5.21 FTIR spectral characteristics of rejected tea before and after
adsorption [114].

IR Peak Frequency ( cm -1 ) Assignment

Before
adsorption

Ater
adsorption

Difference

1 3430 3414 ‒16 Bonded O‒H groups

2 ‒ 2920 Aliphatic C‒H groups

3 ‒ 1733 C=O stretching

4 1630 1600 ‒30 C=O stretching

5 1509 ‒ Aromatic nitro compound

6 1383 1385 +2 Symmetric bending of CH 3

7 ‒ 1333 Aromatic nitro compound

8 ‒ 1247 S=O stretching

9 1033 1035 +2 C‒O stretching

10 ‒ 884 C‒C stretching

11 608 557 ‒51 ‒C‒C‒ group

adsorption process. Similar surface area and surface functional groups on
Pu-erh tea were reported elsewhere [115]. Also, untreated coffee residues
have been proven to have a high uptake capacity. The characterization of
this waste illustrated that, similar to tea waste, the surface area of the cof-
fee waste was also very low [116]. The Boehm titration method illustrated
the presence of 0.94 mmol/g carboxylic and 0.91 mmol/g basic functional
groups, where small amounts of phenolic and lactonic moieties were also
observed. The experimental titration curves for point of zero charge (PZC)
determination are presented in Figure 5.24. The PZC value was observed
between 3.2-3.4, above which the adsorbent surface exhibits a predomi-
nantly negative surface charge. The PZC value played an important role in
explaining the mechanism of the dye adsorption. The study of the pH effect
showed that the adsorption of the Remazol Blue (RB) was decreased with
an increase in the pH level, whereas an opposite trend was observed for
Basic Blue (BB). The dissociation of the RB in the solution was presented
as follows:
D - SO 3 Na D - SO 3 - + Na + (5.2)
Also, the adsorbent surface was protonated at low pH values. Then
electrostatic interaction could occur between the positive surface of
the adsorbent and the negatively-charged adsorbate. As the pH value