The XRD patterns of Fe(III)–Mt in comparison with
Na(I)–Mt and spent Fe(III)–Mt at relative humidity (RH) 40% are shown in Fig. 2
(a). The basal spacing, d001,
values are as follows: Fe(III)–Mt, 15.2 Å and Na–Mt, 12.1 Å. It is clear that
the divalent cation exchanged clay minerals showed higher d001 value due to larger layer of hydration when compared
to monovalent cation exchanged clay mineral.
FT–IR spectra of freshly prepared Fe(III)–Mt, Na(I)–Mt and spent
Fe(III)–Mt as shown in Fig. 2 (b). The FT-IR spectra of freshly prepared
Fe(II)–Mt is similar to that of Na(I)–Mt. The basic structure of clay mineral
has not undergone any significant change. For instance, the bending vibration
bands at ~ 520 cm–1 for Si–O–Al, and 920 cm–1 for Al2OH
are intact. However, stretching vibrations of Si–O group ~ 1046 cm–1
are slightly broadened. The vibration bands at 1628 cm–1 corresponds
to adsorbed water and 3429 cm–1 for water present at the interlayer.
However, XRD and FT–IR spectral values are in good agreement with the
previously reported values 24-26.
3.2 Removal of Rh B dye by Fe(III)–Mt
In order to determine the stoichiometric amount of
Fe(III)–Mt for the optimum dye removal, it was added to Rh B dye solution (Rh B
dye solution 0.025 mM, pH 5) by varying the amount of Fe(III)–Mt from 0.01 g to
0.07 g. The concentration of Rh B dye reduction was estimated from its optical
density at lmax = 554 nm using UV-Vis spectrophotometer. The effect of amount
Fe(III)–Mt on the rate of adsorption of Rh B solution is depicted in Fig. 3.
From the Fig. 3, it was observed that the required amount of Fe(III)–Mt for
100% dye removal was 0.07 g. It was observed that the rate of adsorption
increases with increase in amount of Fe(III)–Mt from 0.01 to 0.07 g.
Effect of pH
Fig. 4(a) shows the %
removal of Rh B dye by Fe(III)–Mt in stoichiometric amounts at different pH as
a function of time. In general, the dye removal by Fe(III)–Mt is very rapid
process. In each case, we saw a two-stage removal of Rh B dye by Fe(III)–Mt: A
rapid first stage followed by a slow second stage. A complete removal occurred
in about 7 &10 min at pH 3 and 5, whereas in basic medium complete
reduction was observed at pH 9 in 15 min. From the literature survey, it was
reported that the dye adsorption in acidic medium takes less time when compared
to basic medium 27, 28.
It is well-known that
the pH has a significant effect on the adsorption of dye on the surface of clay
mineral Fe(III)?Mt. Hou et al have
investigated the removal of Rh B dye using iron-pillared bentonite in aqueous
medium. However, the removal efficiency was higher at pH 3 – 5 (97%) while at
pH 6 – 10 only 70% dye removal was observed 28. Savitri Lodha et al have demonstrated the photodegradation
of Rh B dye using thiocyanate complex of iron and hydrogen peroxide. The effect
of initial pH of sample solutions on the degradation of Rh B dye was studied in
the range of 2 – 6. The experimental results revealed that maximum degradation of
dye was observed at pH 3 – 5 29. Furthermore UV-light emitting diodes
(UV-LEDs) were used for the photocatalytic degradation of Rhodamine B (RhB) dye
under UV-LED irradiation in different conditions. The experimental results have
shown that there was 74 – 82% degradation at pH 3 – 5, while at pH 5 – 8 dye
degradation was gradually decreased from 74% to 58% 30. Although these
heterogeneous reductants/adsorbents were used for degradation and adsorption
processes, there was an incomplete reduction and more time consumption.
Moreover, these are effective only in the presence of co-catalysts, sunlight
irradiation and/or presence of UV lamps. However, in the present
study we could achieve the efficient removal of Rh B dye solution both in
acidic as well as basic pH.
Effect of Temperature
The removal of Rh B dye by Fe(III)–Mt
was carried out in different temperatures (0 – 50 °C) at pH 5 as shown in Fig.
4(b). In general, the dye removal increased with temperature up to 50 °C. The
time taken for complete reduction at 0 °C, 30 °C & 50 °C are 15, 10 and 7
min respectively. Moreover, increase in temperature increases the amount of
Rhodamine B adsorbed on the surface of the clay mineral Fe(III)?Mt. Barka et al have
investigated factors influencing the photocatalytic degradation of Rhodamine B by TiO2-coated
non-woven paper. The results have shown that photocatalytic degradation was
temperature-dependent, the rate of degradation increases with the increase of
temperature (25 oC –
50 oC) 31. The application of heterogeneous
catalyst poly-hydroxyl-iron/sepiolite (H-Fe-S) for the degradation of Rh B dye
under visible light irradiation was investigated by Gao et al. It was found that photo catalytic degradation reaction rate
increase with the increase of the reaction temperature. For instance, 78.3%
removal of Rh B occurred at 25 oC with
irradiation of 40 min, compared to color removal of 86.3% at 30 oC and 99.0% at 45 oC,
respectively 32. Wang et al have
jet-induced cavitation combined with H2O2 was used for degradation of Rh
B dye in aqueous solution. It was found that the degradation of
rhodamine B is dependent on the solution temperature. The removal of rhodamine
B increased with increase of temperature from 30 to 50 oC 33. Decolorization of some organic pollutants in
water such as commercial dyes, Such as Malachite green (MG), Rhodamine B (Rh B)
and Methylene blue (MB) were studied using a fenton-like reagent. The results
clearly show that increase in decolourization of dye was observed when the
reaction temperature was raised (298 – 328K) 27, 34. However, in the present study, we see the 100 % removal
Rh B dye from aqueous solution by Fe(III)–Mt in all the temperatures ranging from 0 – 50 °C.