FTIR analysis was used to
identify some characteristics functional groups of adsorbent before and after
adsorption. Before MB adsorption, the FTIR spectrum contained several peaks.
Figure 4.1 showed that the broad and intense adsorption peak at 3449 cm-1
represents the O-H stretching of hydroxyl functional group. The weak band at
around 2923 cm-1 is assigned for stretching vibrations of C-H bond
in methyl group. The strong peak at 1654
cm-1 associated to C=O in carbonyl group and the peaks at 1342 cm-1
represent -NH bending vibration of primary
amines. The peak at 1114 cm-1 corresponds
to C-O stretching in primary alcohol.
However, after the dye
adsorption onto adsorbent FTIR revealed that some peaks were slightly shifted.
The peaks at 3449 cm-, 2923 cm-1 and 1342 cm-1 were
shifted to 3472 cm-1, 2920 cm-1 and 1384 cm-1 respectively
after the adsorption. This indicates that O-H, C-H and N-H group could be
involved in the adsorption of MB onto CFFS adsorbent (Amuda et al., 2014). The shift in the adsorption
peak also indicates that the interaction of MB dye molecules with the
functional groups of the adsorbent (Zhong et al., 2010).
The main change observed after
the adsorption of dye was the splitting of strong bending of C=O at around 1634
cm-1 into small splits. This splitting not only due to the
adsorption of dye but also due to the electrostatic interaction between MB
molecule and CFFS adsorbent (Gottipati & Mishra, 2010). The spectrum also showed no
new peak has been observed which indicates that no chemical bond is formed
between the adsorbate and adsorbent after adsorption and it showed that the
adsorption is due to physical forces (Kaur & Thakur, 2014). The point of zero charges (pHpzc) of CFFS adsorbent is
determined by using solid addition method in order to understand the influence
of solution pH on the adsorption process. The surface charge of adsorbent was
examined by comparing the pHpzc and pH of the adsorbent. Surface
charges arise from the presence of functional groups and their interactions
with the aqueous solution (Berrazoum et al.,
2015). The charge of
the functional group contributes to the
overall charge of the surface. When the solution pH is higher than the pHpzc,
the adsorbent surface has a negative charge
which favours the adsorption of cationic
species. Alternately, a solution pH below the pHpzc,
results in an overall positive charge and prefer an adsorption of anionic
species (Oyelude et al., 2015).
The pHpzc of CFFS adsorbent was 6.6
as shown in Figure 4.1. This value suggested that if the pH of the solution is higher that pHpzc, the
surface of the adsorbent become negatively charged and potentially for
attracting negatively charged molecules (Mei, 2016). Thus, the MB removal favoured at higher pH because at lower pH (pH < pHpzc), the adsorbent surface is positively charged where H+ ions become high thus compete with positively charged of MB cations for vacant adsorption site. This leads to a decrease in dye uptake on the adsorbent surface. (Jirekar et al., 2014). When pH of the solution is lower than pHpzc, adsorbent surface becomes negatively charged and the electrostatic force of attraction with MB molecule tend to be high, thus enhance the adsorption capacity of MB dye (Njoya, Nsami, Rahman, & Lekenengouateu, 2017)The result of physical characterization of the adsorbent was tabulated in Table 4.1 above. From the table, it was observed that CFFS adsorbent showed a low amount of bulk density, ash content, and moisture content. Bulk density refers to the weight per unit volume of sample. It provides a view regarding the floatability property of the adsorbent. Low bulk density indicates a high amount of pores thus enhance the adsorption capacity of the adsorbent (Bläker et al., 2017). Ash content analysis is important to determine the content of minerals residue as well as impurities that remain in the adsorbent by the heating process in the muffle furnace while moisture content referred as water content is an indicator used to determine the amount of water present in the adsorbent. The result shows that the ash content and moisture content in adsorbent is 7.21 % and 10.56% respectively. These values indicate that CFFS adsorbent has low ash content and moisture content. The results obtained not only shows a good property of effective adsorbent but also showing that this adsorbent was properly prepared and handled during the preparation stage (Ibrahim, 2013). An adsorbent with low ash content and moisture content also possess favourable properties of the precursor for the production of adsorbent because it increases the mechanical strength of adsorbent and increases the adsorptive capacity (Mohammed et al., 2012).