Journal of Advanced Oxidation Technologies 2018; 21(1) www.jaots.net DOI: 10.26802/jaots.2017.0022
Article ID- 20170022
Article:
Degradation of C.I. Acid Red 51 and C.I. Acid Blue 74 in Aqueous Solution by Combination of Hydrogen Peroxide, Nanocrystallite Zinc Oxide and Ultrasound Irradiation
Insaf Ould Brahim*1,3, Mohamed Belmedani1, Ahmed Haddad3, Hocine Hadoun2, Ahmed Belgacem1
1Laboratory of transfer phenomena, Faculty of Mechanical and Processes Engineering, University of Sciences and Technology Houari Boumediene, BP n 32 El Alia bab ezzouar 16111 Algiers, Algeria
2Nuclear Research Center of Algiers, 2 Bd Frantz Fanon, 16035, Algiers, Algeria
3Research Center in Industrial Technologies CRTI, P.O.Box 64, Cheraga 16014 Algiers, Algeria
*iouldbrahim@gmail.com Phone: 00213-20-77-67 Fax: 00213-21-34 -20-19 Abstract
This study illustrates the degradation of food dyes, C.I. Acid Red 51 (erythrosine E127) and C.I. Acid Blue 74 (indigo carmine E132) by sonocatalysis using an ultrasonic frequency of 37 kHz and a power of 150 W in the presence of heterogeneous catalysts ZnO and peroxide hydrogen (H2O2). The adsorption process for the two dyes on the ZnO nanocrystalline which satisfies the Freundlich model appears not effective because the elimination of the two food dyes does not exceed 35%.
In order to improve the removal, the sonocatalytic process (AD-OX) has been investigated. At this purpose, effect of operating parameters such as initial dye concentrations, H2O2 (0-0.75M) and initial pH on the sonochemical degradation was investigated.
It was observed that when the adsorption-catalysis was assisted by the ultrasonic and H2O2 a considerable yields has been achieved and about 86% and 97% of E127 and E132 were removed for 10 mg L-1 and 50 mg L-1 respectively.
To understand the behavior of dye degradation, structure of the zinc catalyst before and after the sonocatalytic process was characterized by mean X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM).
Results showed that the ZnO particles before and after sonocatalysis were crystallized in the hexagonal wurtzite phase and the size distribution indicates that most of the particles are in the range of 300 and 600 nm. Finally, ADMI and COD analysis were performed in order to quantify the residual color in solution and evaluate the efficiency of the dye mineralization. Results showed that the treatment of food dyes by US-ZnO-H2O2 process increased color degradation (ADMI) and mineralization efficiency (COD) by more than 50% and 76% respectively.
Keywords
Advanced Oxidation Process; Food Dyes (E127, E132); Sonocatalysis; H2O2; DCO; ADMI Received: March 06, 2017; Revised: June 10, 2017; Accepted: November 20, 2017
Introduction
The use of food dyes is not limited to aesthetic purposes [1], but its increase in industry especially, pharmaceutical industry (syrup against a cough, coating drugs...) and food industry (ice cream, sweets...) has become a serious
Access
problem causing harmful effects on human health and environmental pollution. Food dyes are not toxic but their degradation generate byproducts such as release of aromatic amines [2] which are suspected to be directly or indirectly responsible of several diseases such as endocrine disrupters, anemia nausea, hypertension, cancer, allergies [2]. Thus food dyes and colored effluent must be subject to regular controls [3-5] and treated before their discharge. Although, rigorous standard were established, the tolerance limit of the color change of the receiving environment should not exceed 100 mg Pt.L-1 (platinum-cobalt) [6], and the maximum daily intake (ADI) tolerated in humans is ranging between 30 and 500 ppm [7]. At this purpose, enormous efforts have been made to eliminate food dyes from effluents and conventional methods are often expensive for their implementation and maintenance, and fail to achieve a desired high yield [2, 8, 9]. Adsorption and oxidation are the most important processes used in industry for the treatment of food dyes [10] but unfortunately, most adsorbents have low adsorption capacity [11].
The advanced oxidation processes (AOPs) have proven and shown to be effective against various colorful and toxic pollutants. They rely on the formation of hydroxyl radicals •OH, which have a strong oxidizing power that makes them capable of degrading dyes and organic pollutants but can’t lead to a full mineralization *10+.
The sonocatalysis or catalysis assisted by ultrasound which is a part of the AOPs, is considered a clean and appropriate solution to food dye treatment [12, 13] because it generates very few secondary products requiring subsequent intervention but the degradation rate is rather slow using treatment with US alone (sonolysis) [14] and also energy consuming. Ultrasonic method coupled with a suitable heterogeneous catalyst semiconductor may improve the degradation of food coloring in the sonocatalytic process and a clear improvement in the degradation of dye was found by applying hybrid processes [15, 16].
The zinc oxide is the most suitable heterogeneous semiconductor catalyst for sonocatalysis. But the rapid rate of recombination of electron-hole pairs produced is the main limitation for the application of ZnO in the catalytic process (adsorption on ZnO). To prevent the electron-hole recombination, US-ZnO is combined with H2O2 in catalytic process [10, 17, 18]. In addition, the addition of H2O2 to sonocatalytic oxidation methods increases the efficiency of the decomposition and reduces the time required to remove food dyes [14, 19, 20].
In fact, it’s well known in the sonocatalytic systems that a light with strong energy is generated by the ultrasonic cavitation mechanism which excites ZnO semiconductor leading to the production of •OH radicals for dye degradation [10, 16, 21].
A simple mechanism for the formation of radicals during sonication of water is given by (Eqs. 1- 4) [22].
→ (1)
→ (2)
→ (3)
→ (4)
→ (5) In this study, two models of food dyes that have attracted considerable attention in many industrial processes were chosen, C.I. Acid Red 51 (erythrosine E127) and C.I. Acid Blue 74 (indigo carmine E132). It should be pointed out that these dyes present high toxicity and high potential risk to exceed the low acceptable daily intake (ADI), which is 0.1 mg/kg body weight (bw)/day for erythrosine (E127) [23, 24] and 5 mg/kg body weight (bw)/day for indigotine (E132) [25].
At this purpose, study of the adsorption of food dyes E127 and E132 on ZnO was investigated and then the improvement of the removal efficiency by adding H2O2 assisted by ultrasonic irradiation was considered. To understand the mechanism of dyes degradation structure of the zinc oxide before and after the US-ZnO-H2O2
process was carried out by XRD, SEM, and FTIR.
Materials and Methods
Materials
All chemicals purchased for performing the present study were of analytical grade quality and used as received i.e.without further purification.
The feature of the two dyes (E127 and E132) chosen for the present work is summarized in Table 1 Stock solutions of food dyes of 1 g L-1 were prepared by using distilled water prepared in a “Lab tech water Still” distillatory.
TABLE 1STRUCTURES AND CHARACTERISTICS OF FOOD DYES (E127 AND E132)
Food dyes Formula Molecular weight (g mol-1) Structural formula λmax
(nm) E127
Xanthene dye
C20H6I4Na2O5 (H2O) 879.84 526
E132 indigoid dye
C16H8Na2N2O8S2 466.36 611
The desired concentration of the test solution was prepared by diluting the stock solution and the acidity of media was adjusted using diluted HCl and NaCl solutions.
In the case of sonolysis and sonocatalytic, the experiments were conducted at ultrasound wave of 37 kHz frequency and power of 150 W using an ultrasonic bath, model Elmasonic S60-H. The reactor was kept in the same position in the ultrasonic bath (Fig. 1) and the reaction temperature was maintained at 25 ±1 °C by means of bath refrigerant. A high-precision electronic balance (Kern ALS 220-4) with an accuracy of 10-4 g was used for taking the weight of catalyst ZnO and food dyes (E127 and E132).
FIG. 1 SCHEMATIC OF THE SONOCATALYTIC REACTOR USED.1: DOUBLE WALL REACTOR 2: ULTRASONIC BATH 3: DYE SOLUTION 4: DISTILLED WATER 5: ULTRASONIC WAVES (TRANSDUCER) 6: CRYOCOOLER 7: COOLING SYSTEM.
The absolute food dyes concentration was carried out by using a UV-visible spectrophotometer, model Specor 200.
A standard spectrometer quartz cell, 3.5 mL, was used as a solution container in the experiment.
The maximum absorption peak of E127 and E132 are 526 nm and 611 nm respectively.
I
I NaO
O
ONa I
I O
O
NH NH
S ONa O O
S O
O O NaO
O
Experimental Procedure 1) Adsorption test
The isotherm adsorption experiments were carried out at room temperature while the initial concentration of food dyes E127 and E132 ranged from 10 to 100 mg L-1 and 0.4 g and 2 g of ZnO for E132 and E127 respectively.
After 120 mn of adsorption, the mixture was centrifuged and the residual concentration in the supernatant was estimated by Eq. (6).
The amount of food dye adsorbed at time t, qt (mg g-1), was calculated using eq. (6):
( (6) qt (mg g-1) is the adsorbent amount at time t, C0 (mg L-1) is the initial concentration of food dye, Ct (mg L-1) is the concentration of food dye at time t, V is the volume of the solution (mL) and M the mass of the adsorbent (mg).
2) Sonocatalytic degradation
The dye degradation process was performed using 1L aqueous food dyes (E127 and E132) with desirable concentrations under constant stirring. The experimental procedure was conducted under four different conditions as described bellow:
a) Sonolysis of E127 and E132: Prepared dye solutions were irradiated by US waves with the frequency of 37 KHz for 60 min.
b) Catalyst of E127 and E132 using ZnO without sonication for 60 min.
c) Degradation of E127 and E132 in the presence of H2O2 and ZnO without sonication: Prepared dye solutions were contacted with H2O2 and simultaneously 2g and 0.4g of ZnO (optimum amount in the adsorption process on ZnO) were suspended in each medium of E127 and E132 respectively.
d) Sonocatalysis of E127 and E132 using ZnO in combination with US-H2O2 (advanced oxidation processes): A constant amount of ZnO (2g and 0.4g) was added to 1 L of food dye E127 and E132 solutions respectively to a specified concentration, and the prepared solution was sonicated in the dark to eliminate the photocatalysis effect. To study the effect of H2O2 on degradation efficiency, H2O2 solutions with concentration varying from 0 to 0.75 M was then added to prepared solutions and sonicated for 60 min.
The suspended catalyst particles were removed by centrifugation and the concentration of food dye (supernatant) E127 and E132 was analyzed by Spectrophotometry at 526 nm and 611 nm respectively.
The percentage of degradation was calculated by using the Eq. (7) given bellow:
Degradation efficiency (%) = ((C0-Ct)) /C0 *100 (7) Where: C0 and Ct are the initial and final concentration (mg L-1).
Analytical Methods
pH measurements were made using a pH meter, model Hanna instruments pH 211. A high-precision electronic balance (Kern ALS 220-4) with an accuracy of 10-4 g was used for taking the weight of catalyst ZnO and food dyes (E127 and E132).
The crystal phases of ZnO powders before and after removal food dyes E127 and E132 in combination with US- H2O2 were determined by X-ray diffraction (PANalytical diffractometer Model: X’Pert Pro Philips) using CuKα as the radiation source.
The particle size and morphology of the powders were investigated using Scanning Electron Microscopy type Philips XL30S-FEG, Model ESEM.
The infrared absorption spectra of the samples were recorded on KBr disks using a Nicolet 380 FT-IR spectrophotometer from Thermo Electron Corporation at frequency range of 4000-400 cm-1 and the patterns were
obtained by "OMNIC" software.
Color measured in the influent and effluent sample of catalytic and US treatments were measured by ADMI. ADMI color was determined spectrophotometrically in accordance with the ADMI tristimulus method. This Method for Color Measurement is used to quantify the residual color of waste water due to the presence of colored minerals and dyes. For the measurement of the true color, PtCo color unit was used according DIN ISO 6271.
The chemical oxygen demand (COD), which is generally used as parameter to evaluate the efficiency of the mineralization for the colored and decolorized solutions was determined using COD Digestion Apparatus Thermoreactor (AL125) and photometer AL200 [26].
Results and Discussion
Adsorption Isotherms
Adsorption behavior isotherms of food dyes E127 and E132, in the case where only ZnO was used, are shown in Fig. 2. The equilibrium adsorption data were fitted to most frequently used Langmuir and Freundlich models.
0 20 40 60 80 100
0 1 2 3 4
Q Langmuir Q Experimental Q Freundlich
q (mg/L)
Ce(mg/L) E127
0 10 20 30 40 50 60 70
0 5 10 15 20 25 30 35 40
Q exerimental QLangmuir Q freundlish
q (mg/g)
Ce(mg/L) E132
0 2 4 6 8 10 12 14 16
0 5 10 15 20 25 30
E127 E132
Ce/qe
Ce(mg/L)
0 1 2 3 4 5
-1 0 1 2 3 4
E127 E132
ln(qe)
ln(Ce)
FIG. 2 ISOTHERM ACCORDING TO LANGMUIR AND FREUNDLICH APPLIED MODELS FOR FOOD DYES a) E127 AND b) E132 ADSORPTION ON ZnO; c) LANGMUIR AND d) FREUNDLICH ISOTHERMS FOR E127 AND E132 FOOD DYES WITH CONCENTRATION
IN THE RANGE OF 10-100 mg L-1 ON NANOCRYSTALLITE ZnO WITHOUT H2O2 AND ULTRASOUND V=1L, T=25±1°C , MZnO, E132=0.4G, MZnO, E127=2 G
The Langmuir model can be expressed by Eq. (8) where qm is the maximum adsorption capacity (mg g-1) and KL: is the Langmuir constant (L mg-1),
( ( (8) Freundlich model (Eq. (9)).
(9)
a) b)
c) d)
Where Kf is the adsorption capacity of the adsorbent and n giving an indication of how favorable the adsorption process is.
The linears form of the Langmuir and Freundlich models were given by Eqs. (10) and (11), respectively.
( ) ( ) (10) ( ( )log (Ce) (11) A plot of (Ce/qe vs Ce) resulted in a linear graphical relation indicating the applicability of the Langmuir model shown in Fig. 2c and a plot of (log qe vs log Ce) resulted in a linear graphical relation indicating the applicability of the Freundlich model shown in Fig. 2d.
Table 2 displays the results of the calculated isotherm constants [27, 28] and summarizes all the constants and correlation coefficient R² values obtained from the two isotherm models applied for adsorption of E127 and E132 food dyes on ZnO. On the basis of the R², Freundlich isotherm represents the equilibrium adsorption data with better fit as compared to Langmuir isotherm for E127 Fig. 2a. Freundlich and Langmuir isotherms are competitive for E132 Fig. 2b. The value n is greater than one, suggesting that both food dyes E127 and E132 were favorably adsorbed by ZnO [29].
TABLE 2ISOTHERMS CONSTANTS FOR FOOD DYE ADSORPTION ONTO ZNO
pH Variations in Removal of Food Dyes E127 and E132 in the Combination Process of US and H2O2
pH of the solution has an important implications on the sonochemical process. It can influence, at the same time, the chemical structure of adsorbent, absorbat as well as the mechanism of sonocatalysis and therefore the performance of the sonochemical process [30-33].
The pH affected the behavior of food dye E127 by influencing Platinum cobalt, as illustrated in Table 3. The effect was observed visually, mainly in acid medium (2≤pH≤ 5) in the form of, a loss of color turning the solution transparent. Thus, under these conditions a decrease in the absorption intensity corresponding to hypochromic phenomena was recorded (Fig. 3a and Fig. 3b).
TABLE 3PLATINCOBALT EFFECT ON PH FOOD DYE (E127,E132)
In the range of pH between 4 and 11 (4<pH<11) we observed a bathochromic phenomena and at lower values of pH less than 4 (2<pH<4) the band at 526 nm shifts to a lower energy or a longer wavelength.
For food dye E132, no effect of pH was observed and the value of Platinum cobalt is quasi constant. Similar results were reported by Mittal et al in their study on the adsorption of crystal violet dye onto waste materials, and Gupta et al, in their work adsorption of erythrosine over hen feathers [27, 34]
Therefore, this study will be limited to a pH range which does not affect the color of the E127, i.e. 5<pH <11, and 2<pH <11 (Fig. 3c and Fig. 3d).
Isotherms
Food dyes Langmuir Freundlich
E127 qmax
(mg.g-1)
b (L.mg-1)
R2 KF (L g-1) n R2
37.47 0,0584 0.853 1,3280 1.27 0.954
E132 4,11 17.96 0.932 0,324 1,832 0.940
pH 2 4 5 10 11
Platin Cobald according to DIN ISO 6271
E132 175.35 174.46 175.45 171.32 174.48
E127 190.10 214.89 327.98 333.92 325.96
The effect of the initial pH on the degradation of food dyes E127 and E132 is shown in Fig. 4. As it can be seen, the best removal efficiency was observed under acidic conditions and optimum pH (pHopt) is found to be 5 for E127 and 2 for E132 in sonocatalytic system.
FIG. 3 IMPACT OF pH ON THE ABSORPTION SPECTRUM OF THE FOOD DYES: [E127]=[E132]=50 mg L-1. [H2O2]=0.147 M, T=25±1°C, POWER=150 W, F=37 KHZ, MZnO =0.4 G AND 2G FOR [E132] AND [E127] RESPECTIVELY: A) EFFECT OF PH ON ERYTHROSINE 2D, B)
EFFECT OF pH ON ERYTHROSINE 3D, C) EFFECT OF PH ON INDIGOTINE 2D, D) EFFECT OF PH ON INDIGTINE 3D
FIG. 4 EFFECT OF pH ON SONOCATALYTIC DEGRADATION OF E127 AND E132, [E127]=[E132]=10 mg L-1, T=25°C, POWER=150W, F=37 KHZ
Effect of H202 Concentration on Sonocatalytic Systems
As described above, the use of ZnO or only ultrasonic irradiation showed little or no improvement in dye degradation.
The effect of H2O2 on degradation efficiency was studied by increasing the H2O2 concentration between 0 and 0.75 M while keeping all other conditions the same. Fig. 5 shows the effect of H2O2 on dye degradation.
In this case we observed a little more food dye removal due to the presence of H2O2 in the medium. In the aqueous solution, the decomposition of in a cavitation bubble leads to the formation of •OH, H• and HOO• radicals.
Scavenging of radicals in the bubble or at the interface and recombination reactions can inhibit the mass injection of the radicals into the solution.
The radicals may also reach the liquid bubble interface and may pass into the bulk solution where they can react with solutes. Therefore there is an increase in degradation yield compared to the case where only ZnO or only US were responsible for the degradation process [35, 36].
The optimal concentration of H2O2 was found to be 0.5 M. More dosage of H2O2 produces more hydroxyl radicals and the excess of H2O2 would produce scavenge •OH,Formation of radicals occurs via the following reaction:
→ (12) In addition excess of H2O2 could also contribute in the removal efficiency decline of dye due to the recombination of •OH, via the reaction:
→ (13) The presence of H2O2 is a key parameter for dye decomposition in AOPs technique, depending on its nature of reductants [21, 36, 37].
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0 20 40 60
80 E127
E132
R%
H2O2 concentration (M)
FIG. 5 EFFECT OF [H2O2] ON DYE DEGRADATION UNDER OPTIMUM DOSAGE OF ZnO; MZnO E132=0.4G, MZnO E132=2 G, pH=5, T=25±1 °C , T=
60 MIN, [E127]=[E132]=10 mg L-1
Comparison of Removal Efficiency of Food Dyes using US, ZnO, ZnO-H2O2, ZnO-US and US-ZnO-H2O2
The degradation of food dyes E127 and E132 in the US, ZnO, US-H2O2, US-ZnO-H2O2 systems are compared in Fig.
6. However, the most ideal condition for dye degradation could be achieved by simultaneously using US, ZnO and H2O2 as it’s expected from the theoretical aspect *37+.
The maximum removal of E127 (10 mg L-1) and E132 (50 mg L-1) observed in the US-ZnO-H2O2 system are 83.66%
and 97.1% after 20 min and 8 min respectively.
In ultrasonic system, degradation efficiency of E127 and E132 was observed at 25%, 15%. In ZnO system, it was observed at 36.23% and 25% whereas, in ZnO-H2O2 system, it was observed at 59.35% and 38% respectively (Fig. 6).
H2O2 has led to an enhancement of US performance for heterogeneous sonocatalytic reaction. The highest removal, observed in the US-ZnO-H2O2 system compared with other systems is mainly attributed to the increased
production of •OH radicals due to the decomposition of H2O2 to form more active free radicals such as •OH radicals [38]. As reported above, the formation rate of •OH radicals occurs in two ways. Firstly, the reduction of H2O2 at the conduction band would produce •OH radicals. Secondly, the self-decomposition of H2O2 as a result of US irradiation would also produce •OH Radicals [39].
FIG. 6 DEGRADATION EFFICIENCY OF FOOD DYES: US, ZnO, ZnO/H2O2, ZnO/US AND US/ZnO/H2O2 [E127]= [E132]=10 mg L-1, [H2O2]
=0.147 M, pH=5, T=25±1°C , POWER=150 W, F= 37 kHz, MZnO=0.4 G AND 2G FOR [E132] AND [E127] RESPECTIVELY, T=60MIN
FIG. 7 UV-VIS SPECTRA (2 D) OF AQUEOUS SOLUTIONS DURING US/ZnO/H2O2 PROCESS 37 kHz, 150 W, T=25 ±1, C=50 mg. L-1, PHI=5, 60 MIN,OF THE FOLLOWING DYES A) E127, B) E132, BETWEEN 0 MIN UNTIL 60 MIN) IN A ZONES a) UV; b) VISIBLE AND c) IR REGION,
MZnO=0.4 G AND 2G FOR [E132] AND [E127] RESPECTIVELY
UV-Vis Monitoring of Degradation of Food Dyes in Aqueous Solution with ZnO in Combination with US-H2O2 Fig. 7 shows the UV-Vis spectra of the aqueous solutions of the two dyes before and after the application of the US- ZnO-H2O2 process. The spectra show a clear decrease in the maximum absorption wavelength in the visible region (λ max) for each dye and a hypsochromic shift occurred simultaneously with increasing sonication time *38, 40+.
Most importantly, after 30 min of reaction time, no emergence of new absorption bands for E132 and E127 was observed indicating a possible formation of by-products under these conditions as revealed by the low mineralization rates [10].
The variation of UV–visible spectra during the reaction relates color depletion and changes in the chemical structure of food dyes in US-H2O2-ZnO system. For an initial food dyes concentration of 50 mg L-1, approximately 37.14 % degradation efficiency was achieved within 10 min and 97.1 % degradation efficiency was achieved within 2 min for E127 and E132, respectively (inset graph in Fig. 7 and Fig. 8). Moreover, Fig. 7 shows that the color disappeared totally after 2 min for E132 and partially disappeared after 30 min for E127. The decrease in color with time is closely related to the characteristic of the absorbance peak at 525 nm and 611 nm for E127 and E132, respectively, in which the rapid decrease is related to the chmosphere-containig linkage of the food dye molecule partially-broken down for E127 and completely broken down for E132 (complete removal of the conjugated structure of E132) [41].
The quickest decay of the peak, within 2 min, in the ultraviolet region at 300 nm for E127 and 310 nm for E132 is associated with rings bonded in food molecules.
0 10 20 30 40 50 60
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
t (min)
C/C0
-10 0 10 20 30 40 50 60 70 80 90 100
R%
0 10 20 30 40 50 60
0.5 0.6 0.7 0.8 0.9 1.0
t (min)
C/C0
-10 0 10 20 30 40 50
R%
0 10 20 30 40 50 60
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
t (min)
C/C0
-10 0 10 20 30 40 50 60 70 80
R%
0 10 20 30 40 50 60
0.0 0.2 0.4 0.6 0.8 1.0
t (min)
C/C0
0 20 40 60 80 100
R%
FIG. 8 EFFECT OF ULTRASONIC IRRADIATION TIME FOR E127 AND E132 (POWER 150W, FREQUENCY 37 kHz, T=25±1°C, T=60 MIN, [ZnO] E127 =2 G. L-1, [ZnO] E132=0. 4G; [H2O2]=0. 147 M, a) [E127]= 10 mg L-1, b) [E127]=50 mg L-1, c) [E132]=10 MG L-1, d) [E132]=50 MG L-1
c) d)
b) a)
Effect of Initial Dye Concentration
As can be seen in Figures 7 and 8, the degradation ratios of the two dyes both increased gradually with the increase of ultrasonic irradiation time. The greatest degradation ratios, of 86.27%, and 37.14% were achieved, for 10 mg L-1 and 50 mg L-1, respectively, at 30 min irradiation time in the presence of ZnO and H2O2 for E127 dye. For E132, the degradation ratio in the presence of ZnO and H2O2 is 69.47 % at 2 min and 97.1% and at 10 min irradiation time for 10 mg L-1 and 50 mg L-1 respectively. Importantly, there was no emergence of new absorption bands after 8 min and 2 min reaction time for E127 and E132 respectively, thus suggesting the presence of by-products (possibly formed under these conditions) [10]. These results indicate that these food dyes can be degraded to a certain extent under ultrasonic dye combined with ZnO powder and H2O2. Ultrasonic waves are longitudinal and upon passing through a liquid medium produce cavitational bubbles. Formation and behavior of the cavitation bubbles upon the propagation of the acoustic wave in the liquid constitute the essential events that induce the sonochemical effects.
The transient cavities in the bubbles, produced during ultrasonic irradiation, exist briefly, expanding to at least double their initial size before violently collapsing into smaller bubbles. The collapse of these bubbles can yield local pressure of hundreds of atmospheres and temperatures of thousands of degrees resulting in solute thermolysis [41]. When water was sonicated and were produced. A simple mechanism of radical formation and depletion (Equations 1-4) during sonication of water is given above [42, 43].
The principal agent for degradation of food dyes E127 and E132 was the excition of ZnO by light, emitted by sonoluminescence generated in US cavitation, resulting in the implosion of bubbles. This process occurs in multiple steps:
The first step is the excitation of the food dyes (FD) E127 and E132 adsorbed on the ZnO surface stands for an excited E127 or E132 ( ) molecule which is adsorbed on ZnO. The excited food dye molecule ( ) on the ZnO surface injects an electron to its conduction band, The trapped electron, ZnO (e) converts O2 absorbed on the surface to . The excited can also create an electron (e-)-hole (h+) pair in ZnO; this hole can react with a water molecule adsorbed on the ZnO surface to produce the •OH radical. Another route of generation of •OH can be through the formation of HO2•, which leads to formation of H2O2. The H2O2 adsorbed on ZnO can also lead to the formation of •OH.
Characterization of ZnO
In order to understand the mechanism of dye degradation by Ad-OX process, the structure of ZnO before and after degradation of food dyes was studied using XRD, FTIR and SEM. X-ray diffraction measurement has been taken in the range of 2 teta between 5 and 70°.
In order to determine crystal structure and morphology of ZnO; before and after degradation, food dyes E127 and E132 in combination with US and H2O2, DRX, FTIR and SEB were used.
The changes in the crystal structure affected by both US and H2O2, X-ray diffraction measurement has been taken in the range of 2 teta =5-70° for the ZnO after sonocatalysis with H2O2. The structural parameters of ZnO before and after sonocatalysis with H2O2 of food dyes E127 and E132) are shown in Fig. 9.
Representative X-Ray Diffraction patterns of ZnO before and after sonocatalysis with H2O2 are shown in Fig. 9. The spectra revealed the predominance of three peaks which can be assigned to the reflections from (100), (002) and (101) planes. The peak at position of (101) has the highest intensity indicating no preferred orientation.
In addition, we can observe a peaks broadening with the distribution of chemical compositions indicating that all particles are nanoscale as expected on the basis of the Williamson-Hall formula [46]. The dominant peaks for ZnO after food degradation, Fig. 9-a and Fig. 9-b were identified at 2θ=31.8°, 34.2°, 34.4°, 36.3°, 47.6°, 56.6°, 62.9°, 66.4°, 68° and 69.1°, which can be indexed to (100), (002), (101), (102), (110), (103), (200), (112), (220) and (004) reflections and associated with the diffractions of the hexagonal wurtzite phase. These positions are almost identical to those reported on the JCPDS 36-1451 ZnO card [8, 45, 46]. Compared to the spectrum of ZnO before food dyes treatment, figure 9-c, there is a slight shift to the right of diffraction positions indicating an increase in internal constraint due
to the phenomenon of degradation of food dye. The average crystallite size of ZnO before and after dyes treatment can be estimated by the application of Williams-Hall (WH) formula. The estimated sizes are found to be 31.43 nm, 24.36 nm and 23.04 nm for ZnO, ZnO-H2O2-E127 and ZnO-H2O2-E132 respectively.
FIG. 9 X-RAY POWDER DIFFRACTION PATTERN OF PURE ZnO BEFORE AND AFTER THE US-ZnO-H2O2 PROCESS OF FOOD DYES (E127 AND E132) a) PURE ZnO, b) ZnO AFTER US/ZnO/H2O2 PROCESS (E127) c) ZnO AFTER US/ZnO/H2O2 PROCESS (E132) POWER 150W,
FREQUENCY 37 kHz
The IR spectra of the ZnO samples before and after sonocatalysis are shown in Fig. 10. The FTIR spectrum after 60 min degradation treatment shows a major change in the fingerprint region which clearly indicates the degradation of initial dyes. A broad band at 3444 cm-1 is assigned to O-H stretching mode of the hydroxyl group. The characteristic band at 1550 cm-1 of E132 is assigned to C=C vibration of aromatical ring in benzene [47]. The peak at 1398 cm-1 is assigned to C-H stretching in –CH3 group. The peak at 1507 cm-1 for E127 is assigned to the N-H band.
The peaks at 1008 cm-1 for E127 1029 cm-1 for E132 can be assigned to the asymmetric strong band for C-O-C. The peak at 831 cm-1 is assigned to out of plane bending, the peak at 698.14 cm-1 to C-H deformation and finally, the broadband at 533 cm-1 for E132 is assigned to S-S disulfide.
FIG. 10 IR SPECTRA OF ZnO BEFORE AND AFTER SONOCATALYSIS OF FOOD DYES E127 AND E132 [H2O2]=0.147M , POWER 150W, FREQUENCY 37 kHz
0 10 20 30 40 50 60 70 80 90
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
100 004220112200
110102 103
101002
Relative intensity
a) b) c)
US ZnO E127 H2O2
Us ZnO H2O2 Sonocatalyse E 132 ZnO pur
2θ°
ZnO
ZnO/US/H2O2 :E132 ZnO/US/H2O2 : E127
The morphologies of the ZnO before and after sonocatalysis as revealed by SEM are illustrated in Fig.11. As can be seen, ZnO particles are quite irregular in size and shape. This non-uniformity can be attributed to adsorption of dyes E127 and E132 in the ZnO catalyst. Size distribution of ZnO particles in this figure was determined using Manual Microstructure distance Measurement (histogram) and is shown in Fig.11. Most of the particles have sizes in the range varying from 300 to 600 nm. The average size of the particles of the sample was 370 nm and the average size of this sample after sonocatalysis has been calculated about 461 nm and 605 nm for E127 and E132, respectively. The changes structural morphologies of ZnO may be caused by the US and H2O2 assisted catalysis of food dyes.
5 285 565 845 1125 1405 1685 1965 2245 0
20 40 60 80 100 120
Frequency
Diameter (nm)
5 255 505 755 1005 1255 1505 1755 2005 2255 2505 0
2 4 6 8 10 12 14 16 18
Frequency
Diameter (nm)
5 505 1005 1505 2005 2505 3005 0
5 10 15 20
Frequency
Diameter (nm)
FIG. 11 SEM IMAGES AND SIZE DISTRIBUTION DIAGRAMS OF ZnO BEFORE AND AFTER THE US-ZnO-H2O2 PROCESS: a) ZnO, b) US/ZnO/H2O2 (E127), c) US/ZnO/H2O2 (E132), POWER 150W, FREQUENCY 37 kHz
The UV-Vis spectrum of E127 and E132 during the US-ZnO-H2O2 process shown in Fig. 7 clearly indicates peaks disappearance. Peaks corresponding to 260 nm, 310 nm and 360 nm for E127; and 250 nm, 288 nm, 345 nm and 611 nm for E132 disappear. The reasons for the peak disappearance in the UV- spectrum could be due to:
Cleavage of the conjugated π-bond systems, a transition that is destructive to the molecule;
b) a)
c)
Loss of the chromophore i.e. the group of atoms which control the color of the food dye; a functional group capable of having characteristic electronic transitions from the molecule;
Fragmentation of the molecules;The decrease in concentration (note that the color removal of food dye clearly indicates the decrease in concentration by hue and and ADMI index) Figs. 12 and 13.
FIG. 12 CHROMATICITY DIAGRAM OF THE TRISTIMULUS SYSTEM: CIE CHROMATICITY DIAGRAM OF FOOD DYES E127 AND E132 BEFORE AND AFTER TREATMENT US/ZnO/H2O2 FOR BOTH CONCENTRATIONS 10 mg L-1 AND 50 mg L-1, POWER 150W, FREQUENCY
37 kHz
0 10 20 30 40 50 60
0.0 0.2 0.4 0.6 0.8 1.0 1.2
10 mg/L 50 mg/L
ADMI/ADMI0
time (min)
0 10 20 30 40 50 60
0.4 0.6 0.8 1.0
1.2 50 mg/L
10 mg/L
ADMI/ADMI0
t (min)
FIG. 13 THE FRACTION OF RESIDUAL ADMI OF FOOD DYE SOLUTIONS UNDER US/ZnO/H2O2, POWER 150W, FREQUENCY 37 kHz FOR a) INITIAL ADMI OF 171.1 UNITS AND b) INITIAL ADMI OF 311 UNITS; CONCENTRATION OF H2O2=0.147 M, T=25±1°C, FREQUENCY 37
kHz, POWER 150 W a) E127 50 AND 10 mg L-1, b) E132 50 AND 10 mg L-1
A CIE chromaticity diagram which represents the mapping human color perception in terms of two CIE of parameters x and y by plotting y=f(x) (Fig. 12). All the spectral colors are distributed around the shape color space and is called CIE chromaticity diagram. Standard white light (approximative sunlight) is located at with coordinate of ( x=y=z=1/3). A picture of the CIE chromaticity diagram Fig. 12. It represents all visible colors and provides a graphical space on which we can map other color gamuts.
COD and ADMI analyses were performed in order to confirm that the decoloration of the solution is due to the disappearance of the chromophore groups of the of dye molecules.
The results of this series of tests using ZnO and US-ZnO-H2O2 for removal of food dyes are shown in Fig. 13 and Table 4. For E127, the ADMI value equilibrium decreases with the increase of ultrasonic irradiation time from 171.1
a) b)
to 129 and 311 to 129.8 ADMI for a concentration of 10 mg L-1 and 50 mg L-1 respectively. For E132, the ADMI value decreases with the increase of ultrasonic irradiation time from 187 to 112 ADMI for a concentration of 50 mg L-1. This value remains substantially constant and equal to 140 ADMI for a concentration of 10 mg L-1.
TABLE 4 EFFICIENCY OF US/ZNO/H2O2 OF FOOD DYE,ULTRASONIC POWER (W)=150,FREQUENCY=37 KHZ,T=25±1°C, PH=5.3,SONICATION TIME (MIN)=60,[H2O2]=0.147M
Dyes Treatments Experimental conditions Results degradation
E127 C=10 mg L-1 C= 50 mg L-1
Catalyst dosage ZnO (g L-1) =2 86.27%
37.14%
E132 C=10 mg L-1 C=50 mg L-1
Catalyst dosage ZnO (g L-1) =0. 4 69.47%
97.1%
In the present work, COD results were taken as one of the important parameters to judge the feasibility of the sonocatalysis with the H2O2 process for the treatment of food dyes E127 and E132.
The COD determination tests were performed according to the standard dichromate method using COD digester.
The mineralization efficiency, η,was calculated using the following equation:
( (14) Where CODi is the initial chemical oxygen demand and CODf is the COD of treated solution.
The initial and final COD tests which are necessary to measure the amount of oxygen in water consumed for chemical oxidation of food dyes (catalyzed and sonocatalyzed products formed) were determined by applying a Standard 2H open reflux method (ALPHA, Standard Methods for Water and Wastewater Examination).
Table 5 summarizes the ADMI and DCO values before and after treatment of food dyes. According to the obtained results, dye compounds have very high COD values along with intense color. Both catalyzed and sonocatalyzed solutions showed a significant decrease in COD value of the initial colored solution for food dyes. The greatest decrease in food dye concentration appeared in the sonocatalysis process combined to H2O2 for 50 mg L-1. Thus, less COD is found in aqueous solution after sonocatalytic treatment indicating the effectiveness of sonocatalytic treatment to degrade color.
TABLE 5DCO AND ADMI EFFICIENCY Catalysis process (ZnO) Food dye Concentration mg L-1 DCOi
mg O2/l
DCOf
mgO2/l
R% ADMIi ADMIf R%
E127 10 388 369 5 171.1 141 17.59
E127 50 755 596 23.09 311 263.44 15.29
E132 10 494 393 20.45 140 132.6574 5.24
E132 50 1218 612 49.75 187 176.5847 5.57
Sonocatalysis process (ZnO/H2O2/US)
E127 10 388 216.25 44.26 171.1 129 24.56
E127 50 755 376 50.20 311 129.8 58.26
E132 10 494 257 47.68 140 85 39.3
E132 50 1218 352.14 76 187 112 40.1
Conclusion
The system consisted of ZnO-H2O2 (0.147 M)-US (37 KHz frequency) shown to be quite efficient in degrading two food dyes (E127 and E132) largely employed by the food and pharmaceutical industry. It was demonstrated that the ultrasonic cavitations generates reactive species such as •OH, H•, O• and OOH•, which are able to oxidize food dyes in aqueous solution. US cause the disaggregation of the catalyst leading to an increase of the specific surface area which favors mass transfer of chemical species between liquid-solid. The maximum removal of E127 (10 mg L-
1) 86.27% and E132 (50 mg L-1) 97.1% was observed in the US-ZnO-H2O2 system at initial pH (pH=5) in a short
period of time, less than <20 min by using only a low mass of ZnO, 2 g and 0.4 g per liter for E127 and E132, respectively. The XRD patterns showed that ZnO particles before and after sonocatalysis were crystallized in the hexagonal wurtzite phase. Size distribution of ZnO by Scanning Microscopy (SEM) indicates that most of the particles have sizes in the range from 300 to 600 nm. The spectrophotometric method was applied successfully to the degradation of E127 and E132 from aqueous solution by US-ZnO-H2O2 process and clearly indicates the fragmentation of the molecule.
REFERENCES
[1] Klaus, H., Index in: Industrial Dyes. Wiley-VCH Verlag GmbH & Co. KGaA,, 2004: p. 653-660.
[2] Pathania, D., S. Sharma, and P. Singh, Removal of methylene blue by adsorption onto activated carbon developed from Ficus carica bast. Arabian Journal of Chemistry, 2013.
[3] Cassano, A.; Molinari, R.; Romano, M.; Drioli, E.: Treatment of aqueous effluents of the leather industry by membrane processes: A review. Journal of Membrane Science 2001, 181, 111-126.
[4] Pokhrel, D. and T. Viraraghavan, Treatment of pulp and paper mill wastewater—a review. Science of The Total Environment, 2004. 333(1–3): p. 37-58.
[5] Matouq, M.A.-D. and Z.A. Al-Anber, The application of high frequency ultrasound waves to remove ammonia from simulated industrial wastewater. Ultrasonics Sonochemistry, 2007. 14(3): p. 393-397.
[6] Djelal, H., M. Rigail, and L. Boyer, Les effluents industriels et leur traitement. Management & Avenir, 2008. 6(20): p. p. 275- 288
[7] Kara, D., Spectrophotometric Determination of Tartrazine , Riboflavine and Carmoisine in drinks by Zero-order Spectrophotometric Method Using Determinant Calculation and First Derivative Spectrophotometric Method. Asian Journal of Chemistry, 2005. 17(2): p. 743-754.
[8] Gupta, V.K. and Suhas, Application of low-cost adsorbents for dye removal – A review. Journal of Environmental Management, 2009. 90(8): p. 2313-2342.
[9] Salleh, M.A.M., et al., Cationic and anionic dye adsorption by agricultural solid wastes: A comprehensive review.
Desalination, 2011. 280(1–3): p. 1-13.
[10]Pavanelli, S. P.; Bispo, G. L.; Nascentes, C. C.; Augusti, R.: Degradation of food dyes by zero-valent metals exposed to ultrasonic irradiation in water medium: optimization and electrospray ionization mass spectrometry monitoring. Journal of the Brazilian Chemical Society 2011, 22, 111-119.
[11]Klett, C.; Barry, A.; Balti, I.; Lelli, P.; Schoenstein, F.; Jouini, N.: Nickel doped Zinc oxide as a potential sorbent for decolorization of specific dyes, methylorange and tartrazine by adsorption process. Journal of Environmental Chemical Engineering 2014, 2, 914-926.
[12]Matouq, M. A.; Al-Anber, Z. A.; Tagawa, T.; Aljbour, S.; Al-Shannag, M.: Degradation of dissolved diazinon pesticide in water using the high frequency of ultrasound wave. Ultrasonics Sonochemistry 2008, 15, 869-874.
[13]Khataee, A.; Saadi, S.; Vahid, B.: Kinetic modeling of sonocatalytic degradation of reactive orange 29 in the presence of lanthanide-doped ZnO nanoparticles. Ultrasonics Sonochemistry 2017, 34, 98-106.
[14]Matouq M., T.T.a.S.N., High frequency ultrasound waves for degradation of amoxicillin in the presence of hydrogen peroxides for industrial pharmaceutical wastewater treatment. Global NEST journal, 2014. 16(05): p. 805-813.
[15]Wu, T. Y.; Guo, N.; Teh, C. Y.; Hay, J. X. W.: Applications of Ultrasound Technology in Environmental Remediation. In Advances in Ultrasound Technology for Environmental Remediation; Springer Netherlands: Dordrecht, 2013; pp 13-93.
[16]Song, L.; Chen, C.; Zhang, S.; Wei, Q.: Sonocatalytic degradation of amaranth catalyzed by La3+ doped TiO2 under ultrasonic irradiation. Ultrasonics Sonochemistry 2011, 18, 1057-1061.
[17]Morrison, S. R.; Freund, T.: Chemical reactions of electrons and holes at the ZnO/electrolyte-solution interface.
Electrochimica Acta 1968, 13, 1343-1349.
[18]Suslick, K.S., Sonochemistry, in Kirk-Othmer Encyclopedia of Chemical Technology2000, John Wiley & Sons, Inc.
[19]Ertugay, N.; Acar, F. N.: The degradation of Direct Blue 71 by sono, photo and sonophotocatalytic oxidation in the presence of ZnO nanocatalyst. Applied Surface Science 2014, 318, 121-126.
[20]Yan, D.; Hu, C.-L.; Mao, J.-G.: A2SbB3O8 (A = Na, K, Rb) and [small beta]-RbSbB2O6: two types of alkali boroantimonates with 3D anionic architectures composed of SbO6 octahedra and borate groups. CrystEngComm 2016, 18, 1655-1664.
[21]Matouq, M.; Al-Anber, Z.; Susumu, N.; Tagawa, T.; Karapanagioti, H.: The kinetic of dyes degradation resulted from food industry in wastewater using high frequency of ultrasound. Separation and Purification Technology 2014, 135, 42-47.
[22]Okitsu, K.; Iwasaki, K.; Yobiko, Y.; Bandow, H.; Nishimura, R.; Maeda, Y.: Sonochemical degradation of azo dyes in aqueous solution: a new heterogeneous kinetics model taking into account the local concentration of OH radicals and azo dyes. Ultrasonics Sonochemistry 2005, 12, 255-262.
[23]Abdel Aziz, A. H.; Shouman, S. A.; Attia, A. S.; Saad, S. F.: A study on the reproductive toxicity of erythrosine in male mice.
Pharmacological research 1997, 35, 457-62.
[24]Gardner, D. F.; Utiger, R. D.; Schwartz, S. L.; Witorsch, P.; Meyers, B.; Braverman, L. E.; Witorsch, R. J.: Effects of oral erythrosine (2′,4′,5′,7′-tetraiodofluorescein) on thyroid function in normal men. Toxicology and Applied Pharmacology 1987, 91, 299-304.
[25]Bell, D. R.; Clode, S.; Fan, M. Q.; Fernandes, A.; Foster, P. M. D.; Jiang, T.; Loizou, G.; MacNicoll, A.; Miller, B. G.; Rose, M.;
Tran, L.; White, S.: Interpretation of studies on the developmental reproductive toxicology of 2,3,7,8-tetrachlorodibenzo-p- dioxin in male offspring. Food and Chemical Toxicology 2010, 48, 1439-1447.
[26]Eaton, A. D.; Clesceri, L. S.; Greenberg, A. E.; Franson, M. A. H.; American Public Health, A.; American Water Works, A.;
Water Environment, F.: Standard methods for the examination of water and wastewater; American Public Health Association: Washington, DC, 1998.
[27]Mittal, A.; Mittal, J.; Malviya, A.; Kaur, D.; Gupta, V. K.: Adsorption of hazardous dye crystal violet from wastewater by waste materials. Journal of Colloid and Interface Science 2010, 343, 463-473.
[28]Annadurai, G.; Brintha, S. R.; Sivakavinesan, M.; Soranam, R.: Isotherm Studies on Adsorption of Crystal Violet Dye Using Zinc Oxide Adsorbents. International Journal of Chemical and Analytical Science 2012, 3
[29]Kataria, N.; Garg, V. K.; Jain, M.; Kadirvelu, K.: Preparation, characterization and potential use of flower shaped Zinc oxide nanoparticles (ZON) for the adsorption of Victoria Blue B dye from aqueous solution. Advanced Powder Technology 2016, 27, 1180-1188.
[30]Tauber, A.; Schuchmann, H.-P.; von Sonntag, C.: Sonolysis of aqueous 4-nitrophenol at low and high pH. Ultrasonics Sonochemistry 2000, 7, 45-52.
[31]De Bel, E.; Dewulf, J.; Witte, B. D.; Van Langenhove, H.; Janssen, C.: Influence of pH on the sonolysis of ciprofloxacin:
Biodegradability, ecotoxicity and antibiotic activity of its degradation products. Chemosphere 2009, 77, 291-295.
[32]Lan, R.-J.; Li, J.-T.; Chen, B.-H.: Ultrasonic Degradation of Fuchsin Basic in Aqueous Solution: Effects of Operating Parameters and Additives. International Journal of Photoenergy 2013, 2013, 7.
[33]Goel, M.; Hongqiang, H.; Mujumdar, A. S.; Ray, M. B.: Sonochemical decomposition of volatile and non-volatile organic compounds—a comparative study. Water Research 2004, 38, 4247-4261.
[34]Gupta, V. K.; Mittal, A.; Kurup, L.; Mittal, J.: Adsorption of a hazardous dye, erythrosine, over hen feathers. Journal of Colloid and Interface Science 2006, 304, 52-57.
[35]Wang, J.; Lv, Y.; Zhang, L.; Liu, B.; Jiang, R.; Han, G.; Xu, R.; Zhang, X.: Sonocatalytic degradation of organic dyes and comparison of catalytic activities of CeO2/TiO2, SnO2/TiO2 and ZrO2/TiO2 composites under ultrasonic irradiation.
Ultrasonics Sonochemistry 2010, 17, 642-648.
[36]Abbasi, M.; Asl, N. R.: Sonochemical degradation of Basic Blue 41 dye assisted by nanoTiO2 and H2O2. Journal of Hazardous Materials 2008, 153, 942-947.
[37]Golmohammadi, S. A. A., Mohammad%A Mohammadi, Aliakbar%A Alinejad, Azim%A Mirzaei, Nezam%A Ghaderpoori, Mansour%A Ghaderpoori, Afshin: Removal of blue cat 41 dye from aqueous solutions with ZnO nanoparticles in combination with US and US-H2O2 advanced oxidation processes. Environmental Health Engineering and Management Journal 2016, 3, 107-113.
[38]Behnajady, M. A.; Modirshahla, N.; Tabrizi, S. B.; Molanee, S.: Ultrasonic degradation of Rhodamine B in aqueous solution:
Influence of operational parameters. Journal of Hazardous Materials 2008, 152, 381-386.
[39]Muthukumari, B.; Selvam, K.; Muthuvel, I.; Swaminathan, M.: Photoassisted hetero-Fenton mineralisation of azo dyes by Fe(II)-Al2O3 catalyst. Chemical Engineering Journal 2009, 153, 9-15.
[40]Behnajady, M. A.; Modirshahla, N.: Kinetic modeling on photooxidative degradation of C.I. Acid Orange 7 in a tubular continuous-flow photoreactor. Chemosphere 2006, 62, 1543-1548.
[41]Ferkous, H.; Hamdaoui, O.; Merouani, S.: Sonochemical degradation of naphthol blue black in water: Effect of operating parameters. Ultrasonics Sonochemistry 2015, 26, 40-47.
[42]Kumar, P.; Govindaraju, M.; Senthamilselvi, S.; Premkumar, K.: Photocatalytic degradation of methyl orange dye using silver (Ag) nanoparticles synthesized from Ulva lactuca. Colloids and surfaces. B, Biointerfaces 2013, 103, 658-61.
[43]Suslick, K. S.: "Homogeneous Sonochemistry" in Ultrasound: Its Chemical, Physical and Biological Effects. VCH Publishers,New York 1988, 123-164.
[44]Khorsand Zak, A.; Majid, W. A.; Abrishami, M.; Yousefi, R.: X-ray analysis of ZnO nanoparticles by Williamson-Hall and size-strain plot methods. Solid State Sciences 2011, 13, 251-256.
[45]McMurdie, H. F.; Morris, M. C.; Evans, E. H.; Paretzkin, B.; Wong-Ng, W.; Ettlinger, L.; Hubbard, C. R.: Standard X-ray diffraction powder patterns from the JCPDS research associateship. Powder Diffraction 1986, 1, 64-77.
[46]Ahmad, M.; Ahmed, E.; Hong, Z. L.; Ahmed, W.; Elhissi, A.; Khalid, N. R.: Photocatalytic, sonocatalytic and sonophotocatalytic degradation of Rhodamine B using ZnO/CNTs composites photocatalysts. Ultrasonics Sonochemistry 2014, 21, 761-773.
[47]Saharan, P.; Chaudhary, G. R.; Lata, S.; Mehta, S. K.; Mor, S.: Ultra fast and effective treatment of dyes from water with the synergistic effect of Ni doped ZnO nanoparticles and ultrasonication. Ultrasonics Sonochemistry 2015, 22, 317-325.
