230
Sh. Sohrabnezhad / Spectrochimica Acta Part A 81 (2011) 228–235
material. The molar composition of the reactant mixture is as fol-
lows:
In which C0 is the initial concentration of dye and C is the con-
centration of dye after irradiation in selected time interval.
TEOS: 0.31NaOH: 0.125HDTMABr: 1197H2O
2.6. Procedures of photodegradation of methylene blue
The nanoMCM-41 prepared was calcined at 550 ◦C for 5 h to
decompose the surfactant and obtain the white powder. This pow-
der was used as the parent material to prepare nanoAl-MCM-41
free surfactant materials by ion-exchange method with 0.1 M of
Al2(SO4)3·18H2O (Merck) solution. NanoAl-MCM-41 surfactant-
free was used for loading the nanoparticles.
Photodegrdation experiments were performed with a photo-
catalytic reactor system. This bench–scale system consisted of
cylindrical Pyrex–glass cell with 1.0 L capacity, 10 cm inside diam-
eter and 15 cm height. A 200 W tungsten filament Philips lamp
(ꢀ > 400 nm) was placed in a 5 cm diameter quartz tube with one
end tightly sealed by a Teflon stop. The lamp and the tube were
then immersed in the photoreactor cell with a light path of 3.0 cm.
The photoreactor was filled with 25 mL of 0.25–3.2 ppm of dye as
pollutant and 0.04–1.2 g/L of CoS/nanoAl-MCM-41 as nanophoto-
catalyst. The whole reactor was cooled with water-cooled jacket on
its outside and the temperature was kept at 25 ◦C. The reaction solu-
tion was continually purged with oxygen and magnetically stirred
at least for 15 min before any irradiation. To determine the per-
centage of dye destruction, the samples were collected at regular
intervals, and centrifuged to remove the nanocatalyst particles that
exist as undissolved particles in the samples.
2.3. Preparation of CoS/nanoAl-MCM-41 catalysts
The solution 0.1 M of Co(NO3) was prepared as precursors
of the CoS semiconductor. For ion- exchange, 0.5 g of nanoAl-
MCM-41 powder was suspended in 25 mL solution of cobalt
nitrate and stirred at room temperature for 5 h. After that, the
sample was washed to remove unexchanged Co ions and air-
dried. Finally, sulphurizing of Co ions was carried out with 0.1 M
Na2S solution. To make the reaction with the S2− ion, 0.5 g of
Co2+-exchanged mesopore sample was added to 25 mL of 0.1 M
Na2S solution at a fix temperature and magnetically stirred for
5 h. The sample was washed with deionized water and col-
lected by filtration. The obtained sample fin powder with grey
color prepared sample is called CoS/nanoAl-MCM-41. The sam-
ple was stable at ambient condition. CoS of 2–20 wt% loading over
nanoAl-MCM-41 support is prepared for its photocatalytic evolu-
tion.
In order to obtain maximum degradation efficiency, pH, con-
centration of dye and amount of photocatalyst were studied in
amplitudes of 2–12, 0.25–3.2 ppm and 0.04–1.2 g/L respectively.
The experimental were carried out in the presence of CoS nanopar-
ticles in nanoAl-MCM-41 material and for methylene blue dye.
2.7. Reaction of methylene blue with sodium sulfide
In a stoppered cuvette, an aqueous solution of methylene blue
(100 M) was mixed with sodium sulfide solution (100 mM) and
the final volume of the mixture was maintained to 3 mL. The mix-
ture was shaken well and the absorbance of the solution was
monitored at an interval of 2 min. It was found that the absorbance
value decreased in ꢀmax = 664, 614 and 292 nm gradually, indicating
the progress of the reaction.
In the same way, 2 mg of each nano catalyst (nanoAl-MCM-
41 and CoS/nanoAl-MCM-41 materials), was introduced separately
into methylene blue solution and was maintained to 3 mL. We
also carried out all the reactions in different pH. The pH solution
is adjusted by adding HCl or NaOH. In all cases the reaction was
monitored spectraphotometrically at the dye ꢀmax at 664 nm.
2.4. Preparation of nanoCoS particles
The major steps involved in this hydrothermal process were
carried out as follows: appropriate amount of cobalt salts and
Na2S were prepared to obtain cobalt sulfide. The mainly synthetic
process of CoS was presented as follows: 0.005 mol of Co(NO3)2
was dissolved in 30 mL distilled water and 0.006 mol of Na2S was
injected dropwise into this solution with a syringe. Then the solu-
tion was placed into a 50 mL Teflon-lined stainless steel autoclave
and was filled with about 18 mL ethylenediamine up to 95% of the
capacity (50 mL). The autoclaves were sealed carefully and put into
an oven maintained at 180 ◦C for 48 h, then cooled down to room
temperature gradually. The precipitates were separated from the
aqueous solution and washed with distilled water and absolute
ethanol repeatedly. The final products were dried in a vacuum for
further characterization.
3. Results and discussion
2.5. The measurement of the degradation efficiency of dye (%D)
The XRD pattern of nanoAl-MCM-41 support, CoS/nanoAl-
MCM-41 and nanoCoS loading on the support are shown in
Fig. 2.
The wavelengths absorbance maximum (ꢀmax) of methylene
blue dye is 664 nm. Therefore, photometric analysis of samples
before and after irradiation can be used for measurement of the
%D (degradation efficiency of dye). The absorption of solution
and solid samples was measured by a UV–vis spectro photome-
ter shimadzu model 1600 PC and UV–vis diffused reflectance
spectrometer UV–vis DRS Scinco model 4100, respectively. For
exploring the effect of pH, the solution’s pH was initially adjusted
by adding 0.01 M NaOH or 0.01 M HCl and by controlling with a pH
meter (Horiba-F12). Before determining optimum pH, the exper-
iments were carried out at the original pH of the dye solution
(pH 8).
2Â range, under the condition of 40 kV and 40 mA, at a step size
of 2Â = 0.02◦. The XRD patterns of nanoAlMCM-41 show typi-
cal characteristic three-peak pattern with a very strong one at a
low 2Â and two peaks at higher 2Â values [24,25]. The XRD pat-
(Fig. 2A). However, some differences, such as the boarding of the
diffraction peaks, decrease of some peaks intensity as well as the
shift to the peak positions to the lower angle can be observed
in the spectra. With limiting the range to 2Â = 25–45◦, two peaks
are observed (Fig. 2B) approximately at 2Â equal 31◦ and 46.5◦,
which are due to the reflection of the ∼30.5◦ (1 0 0) and ∼46◦
(1 0 1) planes, in the nanoCoS phase, respectively [26]. These shifts
of the peak position to the slightly lower angles are in agree-
ment with the reports made for other molecular sieves [27–29].
The percentage of degradation was calculated by using the equa-
tion given below:
ꢀ
ꢁ
C
%D = 100 × C0
−
C0