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A. Khataee et al. / Ultrasonics Sonochemistry xxx (2016) xxx–xxx
ꢀ
ꢀ
and pressure, which in turn convert H2O molecules to OH and H
radicals. The produced ꢀOH radicals attack and degrade the organic
pollutants [16,17]. (ii) Sonocatalysis: the presence of suitable par-
ticles can enhance the oxidation efficiency of the system by gener-
ating more nucleation sites for cavitation phenomena [17,18]. (iii)
Ultrasound-assisted enhanced adsorption: the resulted energy
from ultrasonic irradiation enhances the mass transfer efficiency
through convection pathway and also activates the surfaces sites
of aggregated particles [6,7]. Furthermore, it has been proven that
ultrasonic irradiation can be used as a very effective technique in
increasing the adsorption of dyes on adsorbent by enhancing the
affinity between adsorbent and adsorbate.
recorded by a Jeol JEM2011 microscope. The X-ray diffraction
patterns of samples were measured using a Rigaku D max 2000
system at 40 kV, 30 mA and 2h range of 10–90. FT-IR spectra of
the bare and Fe3O4-CHC were recorded using a Bruker Tensor 27
(Germany) FT-IR spectrophotometer in the wavenumber range of
400–4000 cmꢁ1 using KBr pellets. The textural characteristics of
the samples were determined by the N2 adsorption–desorption
isotherms at ꢁ196 °C (Micromeritics, TriStar 3000, USA). An Agi-
lent 6890 gas chromatography and 5973 mass spectrometer (Palo
Alto, Canada) was used to identify the generated intermediates of
AR17 in ultrasound-assisted process.
In this study, Fe3O4-loaded coffee waste hydrochar (Fe3O4-CHC)
was synthesized through a simple precipitation method. The syn-
thesized adsorbent was characterized by SEM, TEM, EDX, XRD,
BET and FT-IR analysis. The ultrasound-assisted process in the
presence of Fe3O4-CHC was used to remove AR17 dye from aque-
ous solution. The effects of adsorbent dosage, initial dye concentra-
tion, presence of inorganic anions and ultrasonic power on the dye
removal efficiency were investigated. The Langmuir and Freundlich
isotherms were used to justify the experimental data. The pro-
duced intermediates of degradation of AR17 were also identified
by GC–MS analysis.
2.3. Ultrasound-assisted process
Ultrasound-assisted experiments were carried out in a 250 mL
Erlenmeyer flask, which was placed in an ultrasonic bath (Sonica,
2200 EP S3, Italy). In a typical procedure, 0.1 g of prepared adsor-
bent was mixed with 100 mL of AR17 solution with distinct
concentration and then sonicated. The experiments were carried
out in the dark to remove the effect of photolysis. At reaction time
intervals of 10 min, 4 mL aliquots were obtained from the reaction
mixture to determine the remaining dye concentration.
2.4. Calculating the AR17 removal efficiency and isotherms
2. Materials and methods
The residual AR17 concentration in the solution was measured
using
a UV–Vis spectrophotometer (WPA lightwave S2000,
2.1. Materials
England) at a maximum wavelength of 510 nm. Eq. (1) was used
to determine the percent decolorization efficiency:
All the chemicals used in this study were of analytical grade and
used without further purifications. FeCl3ꢀ6H2O and FeCl2ꢀ4H2O, HCl
and NaOH were purchased from Sigma-Aldrich (Germany). Acid
Red 17 (AR17) as an azo dye was provided by Shimi Boyakhsaz
Co., Iran. The specifications of AR17 are given in Table 1.
RE ð%Þ ¼ ½ðCi ꢁ CeÞ=Ciꢂ ꢃ 100
ð1Þ
where Ci is the initial concentration of AR17 solution and Ce is its
concentration (mg/L) at time t.
The capacity of Fe3O4-CHC for adsorption of AR17 was
calculated using Eq. (2) [7,20]:
2.2. Preparation and characterization of Fe3O4-loaded hydrochar
ðCi ꢁ CeÞ ꢃ V
qe ¼
ð2Þ
Coffee waste hydrochar was produced via hydrothermal car-
bonization of spent coffee grounds at 200 °C with residence time
of 6 h [19]. Fe3O4-CHC was prepared as follows: 5 mL 5 M HCl,
40 mL water and 5 mL ethanol were mixed in a 100 mL flask. Then,
13.32 g FeCl3ꢀ6H2O and 19.88 g FeCl2ꢀ4H2O were added to the
above solution and heated at 40 °C to complete dissolution of the
salts. Then, 1 g hydrochar was added to 30 mL of the prepared
solution and stirred for 2 h at room temperature. The prepared sus-
pension was filtered and washed with distilled water and then
immediately transfer into 1 M ammonia solution. After 2 h stirring
at room temperature, the synthesized Fe3O4-CHC was collected
and washed with distilled water and dried under vacuum.
m
where qe is the adsorption capacity per gram of adsorbent, V(L) is
the volume of thesolution and m (g) is the mass of adsorbent.
The Langmuir and Freundlich adsorption isotherms are
frequently used isotherms to determine the interactions between
the adsorbent and adsorbate. The Langmuir isotherm can be
expressed by Eq. (3):
Ce
1
Ce
¼
þ
ð3Þ
qe KLqmax qmax
where qmax (mg/g) is the surface maximum adsorption capacity in
the monolayer cover and KL is the coefficient related to the energy
of adsorption.
The surface morphology of bare hydrochar and Fe3O4-CHC
samples was investigated using a SEM equipped with an EDX
microanalysis (Mira3 FEG-SEM Tescan, Czech). TEM images were
The Freundlich model is given by Eq. (4) [21]:
Table 1
Characteristics of Acid Red 17.
Chemical structure
Molecular formula
C20H12N2Na2O7S2
Color Index number
16180
kmax (nm)
Mw (g/mol)
502.435
510
Please cite this article in press as: A. Khataee et al., Ultrasound-assisted removal of Acid Red 17 using nanosized Fe3O4-loaded coffee waste hydrochar,
Khataee, Alireza
