The present work is devoted to the synthesis of a new photocatalyst ZnO (7.5%)/Bentonite prepared by impregnation method and its successful application for the degradation of Solophenyl Red 3BL (SR 3BL) under solar light (∼660 W/m2). The X-ray diffraction (XRD) indicates mixed phases of the nanocomposite catalyst (ZnO/Bentonite), characterized by scanning electron microscopy, X-ray fluorescence and attenuated total reflection. The optical properties confirm the presence of the Wurtzite ZnO phase with an optical gap of 3.27 eV. The catalyst dose (0.25–1 gL−1), pH solution (2.5–11) and initial dye concentration (5–75 mg/L) are optimized. The optimal pH (∼6.7) is close to the natural environment. The photodegradation yield increases with decreasing the SR 3BL concentration. The equilibrium is reached within 160 min and the data are well fitted by the Langmuir-Hinshelwood model; the SR 3BL disappearance obeys to a first-order kinetic with an apparent rate constant of 102 mn1. The best yield of SR 3BL photodegradation (92%) is achieved for a concentration of 5 mg/L and a catalyst dose of 0.75 gL−1 at free pH.

INTRODUCTION

The industries of textile, food, leather, plastics, paper and cosmetics use large amounts of dyes for coloring their final products (Djilani et al. 2015). With more than 10,000 types of dyes are used in the textile industry (Ohashi et al. 2012), about 10–15% are lost during the dyeing process and 2–20% are discharged as aqueous effluent in the aquatic medium with neither restriction nor control (Yuli Yanto et al. 2014).

Many of these dyes are not biodegradable; some of them are carcinogenic and can contaminate the aquatic environment (Noorimotlagh et al. 2014). Consequently, their presence in water even at low concentrations is a critical environmental concern because of the inhibition of photosynthesis and in the entire ecosystem (Hamdaoui & Chiha 2007).

The conventional techniques for the treatment of water polluted by dyes include chemical coagulation, ultra-filtration, extraction, chlorination, ozonation and adsorption. Such methods are expensive, often inefficient at low concentrations and not destructive enough. Accordingly, the search for low cost alternatives for the water treatment remains a topic of high priority (Boukhennoufa et al. 2011; Boumaza et al. 2013) and is currently debated all around the world. In this respect, the advanced oxidation processes (AOPs) are low-cost effective procedures for removing recalcitrant compounds including dyes (Andreozzi et al. 1999; Fatimah et al. 2011), drugs (Carabin et al. 2015) and pesticides (Saber et al. 2011). The main advantage of AOPs is the conversion of organic pollutants to less toxic molecules (Hou et al. 2015). The photocatalysis is a successful strategy for the degradation and mineralization of organic compounds in water (Carabin et al. 2015).

Solophenyl Red 3BL (SR 3BL), chosen for the photocatalytic tests, is a poly azo dye widely used in the textile industry. It is not biodegraded because of the complexity of the chemical structure (Damardji et al. 2009a) and its presence in water is harmful to human health (El Haddad et al. 2014). In addition, it attenuates the light penetration and inhibits considerably the photosynthesis and, in this way, aquatic life. Various treatments among which bioremediation (Neifar et al. 2011) and adsorption (Damardji et al. 2009a) have been used to remove SR 3BL from industrial effluents but remain inefficient because of the presence of the azo group (N=N). Consequently, SR 3BL is resistant to both chemical and biological oxidations. The purification of water contaminated by SR 3BL is a challenge for the scientists and low cost-effective technologies for its removal are highly recommended. In this regard, the photocatalysis is widely employed because of its easy operation and various photo-catalysts have been used for the SR 3BL removal using oxides (Habibi et al. 2005; Boukhennoufa et al. 2011) and clays supporting active semiconductors (Damardji et al. 2009b). Indeed, the conception of heterogeneous catalysts having hybrid structure represents a promising alternative for environmental protection (Bentouami et al. 2010). The clay-based catalysts are classified into ion exchanged catalysts, impregnated catalysts, acidic activated clay, intercalated catalysts, pillared interlayer clay, clay-supported catalysts, composites and hybrids catalysts (Hui Zhou 2011).

The present work deals with the synthesis of the hetero-system ZnO/Bentonite; ZnO was supported on the clay using zinc acetate as a precursor which requires a low decomposition temperature (∼200 °C). The hetero-system has been tested successfully for the degradation of the recalcitrant dye SR 3BL under solar energy. The Bentonite is inexpensive, presents environmentally friendly characteristics (Motshekga et al. 2013), good adsorption properties (Toor et al. 2015), it has been successfully applied for the immobilization of some photocatalysts (Darvishi Cheshmeh Soltani et al. 2016) and is locally available. It is used in the food industry, animal feed, adhesives, ceramics and drilling muds (Murray 2000). On the other hand, ZnO is suitable for the photocatalytic applications because of its advantages like activity in the ultraviolet range, non-toxicity, thermal and chemical stabilities (Güy et al. 2016), strong oxidation ability and a large free-exciton binding energy (Lee et al. 2016). The influence of the catalyst dose, pH and initial SR 3BL concentration are investigated. The photocatalysis on wide band gap semiconductors occurs by an advanced oxidation process, leading to a partial mineralization where oxygen plays a crucial role (organic compounds + O2 → mineral products). Oxidation of water by photoholes through a valence band process produce OH radicals, concomitantly, the electrons in the conduction band react with dissolved oxygen, yielding O2 species. Both radicals contribute to the destruction of the organic molecule SR 3BL.

EXPERIMENTAL

Reagents and chemicals

All chemicals used in the present work were of AR grade. Zn (CH3CO2)2, 2H2O (Sigma Aldrich, 99%) and N, N-dimethylformamide (DMF) (VWR, 99.9%) were used without any further purification. The natural Bentonite was procured from the Algerian Bentonite Company while the SR 3BL commonly known as direct red 80 (CAS number: 2610-10-8) was obtained from the Algerian Textiles Company. Distilled water (resistivity ∼0.7 Ω cm) was used for the preparation of the solutions.

Photocatalyst preparation and characterization

The preparation procedure consists of the Bentonite purification followed by its impregnation with nanosized ZnO. The Bentonite was thoroughly washed with water and dried at 80 °C. The hetero-system ZnO (7.5%)/Bentonite was prepared by impregnation with a slightly modified protocol reported by Meshram et al. (2011): 1 g of Zn(CH3CO2)2, 2H2O was dissolved in 125 mL of DMF in presence of 5 g of the purified Bentonite; the mixture was stirred overnight and evaporated at 100 °C. Then, the powder was calcinated at 200 °C for 3 h, homogenized in an agate mortar and identified by X-ray diffraction (XRD, X'pert MPD diffractometer), equipped with Cu Kα radiation (λ = 0.154178 nm). The data were collected at room temperature over the 2θ range (5–120 °). The average crystallite size D (nm) of ZnO/Bentonite was calculated from the full width at half maximum (β): 
formula
1
where θ is the diffraction angle of the intense diffraction peak (Lalhriatpuia et al. 2015). The synthesis temperature can be selected on the basis of thermal analysis (TG), to prevent the formation of secondary phase like the spinel ZnFe2O4 and to maintain a large active surface, a desirable property in photocatalysis. The decomposition of Zn(CH3CO2)2,2H2O was investigated by TG analysis using a Setaram thermo analyzer (AG0084 LabSystem) at a heating rate of 10 °C min−1. The surface morphology of the samples was analyzed by scanning electron microscope (SEM, Fei Quanta 600). The chemical analysis of the catalysts was performed by the X-ray fluorescence (XRF) using Horiba XRF. The attenuated total reflection (ATR) spectra were recorded with a Perkin Elmer spectrometer (Spectrum One) over the range (450–4,000 cm1). The diffuse reflectance spectrum was plotted with a UV-Visible spectrophotometer (Specord 200 plus) using PTFE as reference. The point of zero charge (pzc) is obtained by measuring the equilibrium pH of an aqueous solution containing a suspension of finely powdered catalyst (Bellal et al. 2015).

Batch experiments

SR 3BL was selected for the photocatalytic tests, its chemical structure and UV-Visible absorption spectrum are illustrated in Figure SM1 (available with the online version of this paper). 250 mg of the catalyst powder were dispersed in 250 mL of aqueous SR 3BL solution at variable concentrations in an open borosilicate reactor exposed to sunlight on a clear day (in October) under magnetic stirring (350 rpm); the solar flux was measured with a MS-410 Pyranometer (Figure SM2, available online). The aliquots were withdrawn at regular time intervals and centrifuged twice (2,000 rpm, 10 mn) to separate the solid particles from the solution. The absorbance of the analyte is proportional to the concentration according to the Beer-Lambert law (λmax = 540 nm); the UV-Vis spectra were recorded with a double beam spectrophotometer (Shimadzu UV1800) for the determination of the residual SR 3BL concentration. The photodegradation yield (R) is calculated from the relation: 
formula
2
Co and Ct are the initial and equilibrium concentration of SR 3BL in the solution, respectively.

RESULTS AND DISCUSSION

Photocatalyst characterization

The Bentonite (origin: west Algeria) has an average granulometry of 74 μm and a humidity degree of 6%. The mineralogical composition is evaluated as follows: SiO2 (55–56%), Al2O3 (12–18%), Na2O (1–3%), CaO (1–5%), K2O (0.76–1.75%), MgO (2–3%) and Fe2O3 (ppm). The thermal decomposition of Zn (CH3CO2)2, 2H2O was undertaken by thermal analysis to delimit its decomposition temperature and thermal stability range (Figure SM3, available with the online version of this paper). The process starts with an endothermic reaction accounting for ∼4.5% of the total weight loss in the TG curve up to ∼50 °C, due to the departure of adsorbed water with an enthalpy of 23 J/g. A second weight loss (∼11%) with two overlapped endothermic peaks is due to successful liberation of two crystallization water molecules at ∼125 °C (308 J/g). The endothermic peak at 262 °C is assigned to the acetate decomposition (82 J/g) with a weight loss of 55%, close to the theoretical one (58%). The plateau region observed above 350 °C indicates the formation of ZnO. However, this synthesis was done at 200 °C because the thermal analysis TG plot was plotted dynamically.

Figure 1 shows the XRD pattern of both the raw Bentonite and the hetero-system (ZnO/Bentonite). The latter indicates mixed phases and contains peaks of ZnO and Bentonite, indicating clearly the successful impregnation of ZnO. In addition to the XRD peaks of the Bentonite, new peaks appeared, attributed to ZnO (hexagonal wurzite) at 31.77, 34.42, 36.25, 47.53, 56.60, 62.86, 67.96 and 69.10, respectively, for the reticular plans (100), (002), (101), (102), (110), (103), (112) and (201) in agreement with the JCPDS card no 36–1451. The decreased intensity indicates the intercalation of ZnO with a decreasing of the basal spacing of the bentonite; similar behavior was obtained by Djellabi et al. (2014) on TiO2/montmorillonite.
Figure 1

XRD patterns of Bentonite and ZnO/Bentonite.

Figure 1

XRD patterns of Bentonite and ZnO/Bentonite.

The crystallite size of the catalyst, deduced from the intense XRD peak (Equation (1)) is found to be 21 nm. Such size should increase the active surface area of ZnO for the reception of more incident photons which consequently enhances the photocatalytic performance.

The optical gap (Eg) of the catalyst is crucial for the solar energy conversion. The gap of the hetero-system ZnO/Bentonite is obtained by extrapolating the linear part of (αhν)2 to the abscissa axis according to the Pankov relation (Lahmar & Trari 2015): 
formula
3
A value of 3.27 eV is obtained (Figure 2), attributed to ZnO with an intensity of ∼20. The zoom in the low energy region indicates a second transition at 2.21 eV with a weak intensity (∼0.1), due to the hematite phase Fe2O3, in conformity with its small percentage in the clay (ppm order). In contrast, the other oxides forming the Bentonite like SiO2 and Al2O3 possess higher transitions (>5 eV).
Figure 2

The optical transitions of the hetero-system ZnO/Bentonite.

Figure 2

The optical transitions of the hetero-system ZnO/Bentonite.

The SEM analysis was used to investigate the morphology of our samples; the images (Figure 3) show that the bentonite has a porous structure, suitable for ZnO immobilization. ZnO was successfully supported on the Bentonite surface. As observed in Figure 3(a), the structure of the hetero-system (Figure 3(b)) has evidently changed and the Bentonite matrix is covered by ZnO nano-particles which occupy the pores, thus decreasing the specific surface area. Similar results were obtained by Darvishi Cheshmeh Soltani & Haghighat (2015) on the hetero-system ZnO/diatomite.
Figure 3

SEM micrographs of (a) raw Bentonite and (b) ZnO/Bentonite.

Figure 3

SEM micrographs of (a) raw Bentonite and (b) ZnO/Bentonite.

The XRF analysis (Table 1) clearly shows the presence of ZnO in the synthesized photocatalyst. The ATR spectra (Figure 4) of the Bentonite, ZnO-Bentonite, ZnO-Bentonite after adsorption, ZnO-Bentonite after photocatalysis and the dye SR 3BL (solid form) were recorded to confirm the impregnation of the sensitizer ZnO. The impregnation with ZnO have almost the same ATR bands except that the intensity of the peak at 1,470 cm1 has decreased, probably due to interactions between Zn—O and Si—O—Si, which suggest that ZnO is well impregnated in the clay. After dye adsorption, we have detected modifications in the spectrum within the region (3,200–3,600 cm1) whose bands belong to the domain of O—H and N—H groups. This clearly confirms that SR 3BL is adsorbed physically through electrostatic and hydrogen bonding between the oxides of the Bentonite and the hetero-atoms of the dye. More interestingly, after photocatalysis, the spectrum becomes similar to the initial state of the Bentonite/ZnO, thus indicating that the adsorbed dye was eliminated by photocatalysis. These results suggest that the decrease of SR 3BL concentration was not ascribed to its adsorption but mainly to the photodegradation through AOP process.
Table 1

XRF analysis of Bentonite and ZnO/Bentonite

ElementBentonite mass (%)ZnO/Bentonite mass (%)
Al 09.57 10.10 
Si 63.07 51.57 
06.72 04.64 
Ca 08.23 02.71 
Ti 00.40 00.44 
Fe 11.18 06.75 
Zn – 23.67 
ElementBentonite mass (%)ZnO/Bentonite mass (%)
Al 09.57 10.10 
Si 63.07 51.57 
06.72 04.64 
Ca 08.23 02.71 
Ti 00.40 00.44 
Fe 11.18 06.75 
Zn – 23.67 
Figure 4

ATR spectra of Bentonite, ZnO-Bentonite, ZnO-Bentonite after adsorption, ZnO-Bentonite after photocatalysis and SR 3BL.

Figure 4

ATR spectra of Bentonite, ZnO-Bentonite, ZnO-Bentonite after adsorption, ZnO-Bentonite after photocatalysis and SR 3BL.

Photoactivity of the hetero-system ZnO/Bentonite

It is worthwhile to outline that the Bentonite alone exhibits neither adsorption nor photodegradation for SR 3BL while the hetero-system ZnO/Bentonite shows a high removal under solar light. The Bentonite support plays a more active role by increasing the dispersion of ZnO particles which increases the active surface area, thus enhancing considerably the photocatalytic performance.

The interaction ZnO/Bentonite–SR 3BL is a preamble for the photoelectrochemical conversion. The pzc of the catalyst is found to be 9.20 and the catalyst surface may protonate or deprotonate, depending on the pH value. The surface catalyst is positively charged below pzc and negatively charged above pzc, SR 3BL is an anionic dye (Sahel et al. 2014) and its degradation is improved below pzc through electrostatic interaction through the nitrogen lone pair. The potential of the conduction band (ECB) of the sensitizer ZnO plays a key role and its value (−1.35 VSCE, pH ∼ 6.7), calculated from the relation ECB=e×Vfb+Ea–Eg, where Vfb and e are respectively the flat band potential of ZnO and the electron charge. The activation energy Ea (0.1 eV) is calculated from the electrical conductivity on sintered pellets. The potential of ZnO-CB is located below that of O2/O2 couple and should generate free radicals, responsible for the partial mineralization of SR 3BL. Concomitantly, the holes in the valence band (+1.92 VVSCE) are less anodic than the OH/H2O (∼2 V) level and react with dissolved oxygen to generate OH radicals. The spatial separation of oxidation and reduction half reactions occurs by the interfacial electric field on the opposite poles of the crystallites which behaves as a nano photoelectrochemical cell: 
formula
4
 
formula
5
 
formula
6
 
formula
7
 
formula
8
 
formula
9
Initially, SR 3BL adsorbs on the surface of the hetero-system ZnO/Bentonite (15%) which occurs in less than 1 h. More interestingly, under sunlight, the red color of the adsorbed dye disappears progressively and the catalyst retakes its original coloration (Figure 5), indicating the photodegradation of the adsorbed SR 3BL layers. The adsorbed layers are oxidized, after which the process becomes governed kinetically by the diffusion of SR 3BL toward the active sites at the interface in which the radicals are used for further adsorption/photodegradation.
Figure 5

Images of the catalyst (a) before treatment, (b) after adsorption and (c) after photodegradation.

Figure 5

Images of the catalyst (a) before treatment, (b) after adsorption and (c) after photodegradation.

Table 2 regroups the photodegradation yield (R) of SR 3BL onto various photocatalysts available in the literature, along with that obtained onto ZnO/Bentonite used in this study. It is clear that ZnO/Bentonite has the highest photocatalytic capacity compared to other catalysts.

Table 2

Comparison of the maximum photodegradation of SR 3BL for various catalysts

MaterialPhotodegradation yieldReference
TiO2 83% Boukhennoufa et al. (2011)  
TiO2- Montmorillonite 80% Damardji et al. (2009b)  
ZnO-Bentonite 92% Present study 
MaterialPhotodegradation yieldReference
TiO2 83% Boukhennoufa et al. (2011)  
TiO2- Montmorillonite 80% Damardji et al. (2009b)  
ZnO-Bentonite 92% Present study 

Effect of the dose of ZnO/Bentonite

The influence of the catalyst dose on the SR 3BL photodegradation, investigated over the range (0.25–1 gL1), is illustrated in Figure 6. The activity increases with raising the dose and the maximal degradation occurs for an optimal dose (mass of catalyst/volume of the solution) of 1 g L1. This is simply due to the increasing number of active sites of ZnO uniformly dispersed on the Bentonite which lead to a higher reception surface for incident photons and in this way to an increasing number of (e/h+) pairs. Above 1 g L1, the scattering effect predominates and inhibits the photocatalytic process, accounting for the regression of the photoactivity. It is worthwhile to outline that the optimal conversion occurs for dose of 1 g L1 (77%) is not far from that of 0.75 gL1 (74%). So, the tests were continued with the last dose for economic reasons and in order to decrease the turbidity of the solution.
Figure 6

Effect of the catalyst dose on the photodegradation of SR 3BL ([SR] = 10 ppm, free pH).

Figure 6

Effect of the catalyst dose on the photodegradation of SR 3BL ([SR] = 10 ppm, free pH).

Effect of pH

The textile effluents are produced over a broad pH range; therefore, the effect of pH on the efficiency of decolorization process is an important parameter to investigate (Ghoreishian et al. 2014). Given that the nature of the dye is pH-insensitive while ZnO exhibit pH dependent electronic bands with a linear slope of 0.06 V pH1, we have taken advantage of this property to have an optimal band bending (∼0.4 V) at the interface ZnO/dye solution for the charges separation. Further, the generation of hydroxyl radicals is also a function of pH (Neamtu et al. 2003). SR 3BL is chemically stable over a wide pH range (2.5–11) and Figure 7 shows a strong influence of pH, the photodegradation yield increases with raising pH up to pH ∼ 6.7 and then decreases.
Figure 7

Effect of pH on the removal of SR 3BL ([SR 3BL] = 10 mg/L, catalyst dose = 0.75 g L−1).

Figure 7

Effect of pH on the removal of SR 3BL ([SR 3BL] = 10 mg/L, catalyst dose = 0.75 g L−1).

The best efficiency occurs at free pH (6.7), close to that of the natural aquatic environment.

The mechanistic aspect involved at the solid/solution interface for the SR 3BL adsorption onto the hetero-system ZnO/Bentonite is determined from the pH study, closely related to the pzc. The pzc of the catalyst is found to be 9.20. The surface catalyst is positively charged below pzc and negatively charged above pzc. SR 3BL molecules have negative charges (anionic dye) in a wide pH value range. Therefore, when the SR 3BL solution pH value is below the pzc, the adsorption (first step in photocatalysis) of SR 3BL anions on the surface of catalyst particles is favored through electrostatic attraction and, in this way, the SR 3BL photo-oxidation. A similar behavior was obtained in the study carried out by Changchun et al. (2011).

Effect of initial SR 3BL concentration

The dyes are thrown in the aquatic environment at concentrations up to 20 mg/L and inhibit dramatically the aquatic life by blocking the photosynthesis with serious consequences on the eco-system. So, it is interesting to study the photodegradation by varying the initial SR 3BL concentration (Co) while all other parameters were kept constant at their optimal values; five concentrations ranging from 5 to 75 mg/L were selected; Figure 8 shows that the photodegradation efficiency of SR 3BL decreases with raising Co. For high concentrations, more dye molecules are adsorbed on the catalyst surface, and the generation of active radicals on the catalyst surface is reduced since the active sites are occupied by the dye molecules. In addition, the light penetration is strongly attenuated as the concentration Co increases; consequently, fewer photons reach the catalyst surface and the photodegradation decreases significantly (Wang et al. 2008). Hence, the optimal concentration is found to be 5 mg/L with a degradation yield of 92%.
Figure 8

Effect of initial concentration on the removal of SR 3BL (free pH, catalyst dose = 0.75 g L−1).

Figure 8

Effect of initial concentration on the removal of SR 3BL (free pH, catalyst dose = 0.75 g L−1).

Kinetic analysis as a function of SR 3BL concentration

The kinetics of SR 3BL photodegradation under solar light is investigated. The surface adsorption has a direct effect on the photoactivity through the increasing number of photocatalytic sites (Mekatel et al. 2012). As mentioned above, the SR 3BL molecules are adsorbed on the hetero-system by electrostatic interaction of azoic groups through the lone electron pair. The kinetic process is clearly visible in Figure 9; the disappearance rate of SR 3BL depends on the initial concentration Co and the mechanism is well described by the pseudo-first-order kinetic: 
formula
10
where r is the rate, kapp (mn1) is the apparent pseudo-first-order rate constant and C is the concentration of the dye at the reaction time (t). By integration of Equation (10), one obtains: 
formula
11
Figure 9

The kinetic of SR 3BL photodegradation under sunlight ([SR 3BL] = 10 mg/L, free pH, catalyst dose = 0.75 g L−1).

Figure 9

The kinetic of SR 3BL photodegradation under sunlight ([SR 3BL] = 10 mg/L, free pH, catalyst dose = 0.75 g L−1).

To elucidate the photodegradation kinetic, the graphs -Ln (C/Co) versus time for different concentrations Co were plotted (Figure 10); the kinetic model fits well the experimental data and the rate constant kapp decreases with increasing Co (Table 3). Consequently, the pseudo-first-order kinetic can really be used to describe the photodegradation of SR 3BL onto the hetero-system ZnO/Bentonite in agreement with Zuniga-Benitez et al. (2016).
Table 3

First-order kinetic constant (kapp) and R2 for different initial concentrations

Co (mg/L)510255075
Kapp × 102 (min10. 5 0.2 0.1 0.07 
R2 0.989 0.992 0.979 0.975 0.970 
Co (mg/L)510255075
Kapp × 102 (min10. 5 0.2 0.1 0.07 
R2 0.989 0.992 0.979 0.975 0.970 
Figure 10

Kinetics of SR 3BL photodegradation; linear transform -Ln (C/Co) versus time at different concentrations (free pH and catalyst dose = 0.75 g L−1).

Figure 10

Kinetics of SR 3BL photodegradation; linear transform -Ln (C/Co) versus time at different concentrations (free pH and catalyst dose = 0.75 g L−1).

The Langmuir-Hinshelwood (L–H) model is successfully used to describe the kinetic of the photocatalytic degradation of organic compounds (Carabin et al. 2015) on zeolites (Krishna & Baur 2005) and clays (Mekatel et al. 2012) and is expressed by the following equation: 
formula
12
where kr and K are the reaction rate constant and the reactant adsorption constant, respectively. At low concentrations Co, there is no catalyst saturation and Equation (12) can be simplified to an apparent first-order kinetic model: 
formula
13
Therefore, the SR 3BL photodegradation is described by a pseudo-first-order kinetic, which is rationalized in terms of L–H model to accommodate the reactions.

CONCLUSION

The photocatalytic elimination of the SR 3BL dye on the hetero-system was successfully achieved under solar light. The XRD, optical properties, SEM images, XRF analysis and ATR spectra showed that the Wurtzite ZnO is well impregnated and homogeneously supported on the Bentonite, forming a novel and efficient hetero-system for the photocatalytic applications. The catalyst dose, pH solution and initial dye concentration were optimized. It has been found that the photodegradation increases with decreasing the SR 3BL concentration and the equilibrium is reached within 160 min. The experimental data are suitably described by the L–H model and the photodegradation follows a first-order kinetic. The best photoactivity is obtained for a concentration of 5 mg/L and a catalyst dose of 0.75 gL1 at natural pH.

ACKNOWLEDGEMENTS

The authors are thankful to Dr O. Arous for the interpretation of ATR spectra and Dr B. Bellal for his technical assistances. This work was financially supported by the Faculty of Chemistry (Algiers) and Unité de Développement des Equipements Solaires, UDES/Centre de Développement des Energies Renouvelables, CDER.

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Supplementary data