Influence of the origin of carbon support on the structure and properties of TiO2 nanoparticles prepared by dip coating method

Abdessalem Omri; Mourad Benzina

doi:10.1016/j.arabjc.2015.06.027

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Original article

12 (

); 2926-2936

doi:

10.1016/j.arabjc.2015.06.027

Influence of the origin of carbon support on the structure and properties of TiO₂ nanoparticles prepared by dip coating method

Abdessalem Omri^⁎, Mourad Benzina

Laboratory of Water-Energy-Environment (LR3E), code: AD-10-02, National School of Engineers of Sfax, University of Sfax, BP W, 3038 Sfax, Tunisia

⁎Corresponding author. Tel.: +216 96803179. omriabdesslem@yahoo.fr (Abdessalem Omri)

Received: 2015-4-11, Accepted: 2015-6-16, Published: 2015-12-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

The study considered the preparation and catalytic properties of the TiO₂ particles supported on Date Stones Activated Carbon (TiO₂/DSAC) and Polyvinyl Alcohol (TiO₂/PVA). The prepared samples were characterized by different techniques. The photocatalyst obtained from DSAC support is better than the PVA one in a comparison of the physico-chemical properties, and was also confirmed by the photocatalytic degradation of Brilliant green (BG). The analysis results show that the TiO₂ particles were well dispersed in the DSAC surface and the size of the resulting TiO₂ crystallites reaches 18 nm. The 24.7 wt% of TiO₂ were deposited on the activated carbon whereas 18.5 wt% were agglomerated on the PVA surface. It was concluded that the higher photocatalytic activity in TiO₂/DSAC was due to parameters such as content of carbon, percentage of anatase, number of hydroxyl groups and surface area of the catalyst.

Keywords

Carbon content

Date stones activated carbon

Polyvinyl alcohol

Photocatalyst

Brilliant green

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1 Introduction

Advanced oxidation processes are useful adjuncts to conventional techniques such as, flocculation (Grĉíc et al., 2015), precipitation (Mahmoodi, 2011), adsorption on activated carbon (Wang et al., 2014a,b; Omri and Benzina, 2014; Omri et al., 2013a,b, 2012; Yang et al., 2015 ), reverse osmosis (Choi and Chung, 2015; Joo, 2014), the combustion and the aerobic biological oxidation (Punzi et al., 2015). These techniques may transfer the pollutant from the aqueous phase to a second phase without destroying them. The majority of the previous works were performed with photo-Fenton processes (Li et al., 2015a,b), ozonation/UV and a TiO₂ suspension (Mano et al., 2015; Baran et al., 2003). The use of TiO₂ as a photocatalyst to degrade compounds has received special attention. This technique is advantageous because it is inexpensive, non-polluting and allows working pressure and room temperature (Smits et al., 2013; Wang et al., 2012). It is common in catalytic processes (and also in the photolysis using crystalline TiO₂) that dispersion of catalyst remains in a straight relation with its catalytic efficiency. For that reason, finer particles of catalyst should exhibit a higher activity in catalytic processes. Hence, to obtain a proper dispersion of a catalyst, a great attention should be paid to the preparation conditions. To increase the photocatalytic activity, much recent work has focused on the use of supports. Several catalytic supports consist of carbonaceous materials (activated carbon (Omri et al., 2015, 2014), nanotubes (Bessegato et al., 2015), carbon nanofibers (Motlak et al., 2015)), a large number of ceramic materials (ceria (Furlani et al., 2014), zirconia (Shao et al., 2014), alumina (Wang et al., 2014a,b), silica (Li et al., 2008), perovskite (Ghiasi and Malekzadeh, 2014), silicon carbide (Wu et al., 2015)) but also to composite materials comprising a host matrix in which the nanostructures are associated. At present, the most often used supports in industrial units are still mainly consisting of alumina extrudates (Erol and Özbelge, 2008), silica (Cheshmeh Soltani et al., 2013), activated carbon or zeolites (Omri et al., 2015; Wang et al., 2008). TiO₂ supported on porous activated carbon increases its adsorption capacity of organic compounds (Meltem and Şadiye, 2012). Activated carbon is used mostly in industry for its large adsorption capacity, fast adsorption kinetic and relative ease of regeneration (Sheintuch and Matatov-Meytal, 1999). A variety of carbonaceous raw materials are used for the production of activated carbon such as almond shell (Omri and Benzina, 2012a,b), Ziziphus spina-christi seeds (Omri and Benzina, 2012a,b), coconut shell (Sunil et al., 2013), and date stones (Foo and Hameed, 2011). In this study, we have used of date stones to prepare the activated carbon. These seeds of date palm are a waste product of many industries, after technological transformation of the date fruits or their biological transformation (Mrabet et al., 2015). They are suitable for preparing activated carbon due to its excellent natural structure and low ash content (Bouchelta et al., 2008; Bouchenafa-Saib et al, 2005).

The goal of this work was to elucidate the effect exerted by the origin of carbon support on the amount of TiO₂ deposited for the photocatalytic degradation of Brilliant green (BG) from aqueous solution. However, two carbon supports were used: Activated Carbon prepared from Date Stones (DSAC) and Polyvinyl Alcohol (PVA). The prepared photocatalysts (TiO₂/DSAC and TiO₂/PVA) were subjected to instrumental techniques in order to study its surface morphology, structural and chemical properties.

2 Experimental

2.1

2.1 Materials

Activated Carbon (DSAC) was prepared from Tunisian Date Stones. Date Stones were first ground (<2 mm), dried overnight and then pyrolyzed a cylindrical electric furnace under inert atmosphere of nitrogen (flow rate 100 cm³/min) at 850 °C (heating rate 10 °C/min) for 2 h, then immediately activated with steam/N₂ for 1 h at the same temperature and left to cool at room temperature under inert atmosphere. The textural properties of the DSAC are listed in Table 1. This material was used as a catalytic support.

Table 1 Textural and structural properties of the samples.

	Sample
	DSAC	TiO₂/DSAC	TiO₂/PVA
S_BET (m²/g)	1044	670	148
Total pore volume (cm³/g)	0.76	0.54	0.16
Pore diameter (nm)	2.19	5.2	3.3
Crystallite size, D (nm)	–	22	18
Anatase content, A (%)	–	95	74
TiO₂ (wt%)	–	24.7	18.5
C (wt%)	74.25	38.2	12

Polyvinyl Alcohol, PVA (average polymerization degree of 1750 ± 50 and degree of hydrolysis of 98%) obtained from Sigma–Aldrich was used as a carbon precursor. This support was selected thanks to their low cost, eco-friendly hydrophilic polymer, revealed to be very attractive to immobilize TiO₂ (Lei et al., 2012).

Titanium isopropoxide, (Ti (OPrⁱ)₄, TTIP, Sigma–Aldrich, purity: 97%) and commercial TiO₂ (Degussa P25, Degussa Chemical) were used as titanium source for the preparation of photocatalysts.

Brilliant green (C₂₇H₃₄N₂O₄S) is used as a model cationic dye for photocatalytic studies; it is chiefly used in modern textile industries. In our work, Brilliant green was purchased from Sigma–Aldrich and used without further purification. A 10 mg/L Brilliant green solution was prepared through dissolving the BG powder in distilled water, and was immediately used. The BG solution has a pH 6.5. The dye was employed to investigate the photodegradation effect of the supported TiO₂.

2.2

2.2 Synthesis of photocatalysts by dip coating method

2.2.1

2.2.1 TiO₂/DSAC photocatalysts

A TiO₂ sol was prepared using the same method as described in our previous study (Omri et al., 2015). The sol was aged for 6 h at room temperature, and then was added drop by drop onto a 5 g Activated Carbon (DSAC) to be adsorbed. Then, it was dried at 80 °C in an oven, finally, calcined at 600 °C for 2 h in a nitrogen atmosphere.

2.2.2

2.2.2 TiO₂/PVA photocatalysts

Polyvinyl alcohol coating of TiO₂ particles was performed using the following protocol: Initially, Polyvinyl alcohol solution was prepared by adding 0.5 g of PVA powder in 50 ml of distilled water and this mixture was magnetically stirred at 85 °C for 2 h. After this, 0.5 g of TiO₂ powder is added to PVA solution (1:1 ratio) and stirred for 2 h followed by repeated ultrasonication until homogeneous dispersion of the solution was obtained. Precleaned glass substrates were dipped into the homogeneously dispersed PVA–TiO₂ solution for deposition of nanocomposite by dip coating technique. The synthesized photocatalysts are named TiO₂/PVA.

2.3

2.3 Characterization of the samples

The prepared samples were characterized using powder XRD, FT-IR, BET, Raman and SEM with EDX analysis. In order to determine the crystal phase composition and the TiO₂ crystallite size in the photocatalysts, X-ray diffraction measurements were carried out at room temperature using a X-ray diffractometer (Philips® PW 1710 diffractometer, Cu Kα, 40 kV/40 mA, scanning rate of 2 θ per min). The crystallite size was calculated by X-ray line broadening analysis using Scherrer equation (D = Kλ/β cos θ) (Bergeret and Gallezot, 1997).

The morphology of the products was explored using scanning electron microscope (SEM, Hitachi SU-70). The structural feature of these samples was observed at the accelerated voltage of 1.0 kV. Before observation, the samples were coated with gold in E-1010 Ion sputter. Energy dispersive X-ray analysis (EDX) was employed for the quantitative determination of TiO₂ contained in the carbon matrix. This was determined using Hitachi SU-70, SEM equipped with a microanalysis system EDX (Oxford X-Max 50 mm²).

The distribution of TiO₂ nanoparticles in the photocatalysts was characterized by transmission electron microscopy (TEM, FEI, Tecnai G20).

The surface functional groups were studied by FTIR spectroscopy. The FTIR spectra of the prepared materials were recorded between 500 and 4000 cm⁻¹ in a NICOET spectrometer. The transmission spectra of the samples were recorded using the KBr pallet containing 0.1% of the sample.

Nitrogen adsorption–desorption isotherms were measured at −196 °C on a Fisons Sorptomatic 1990 after out gassing (10⁻⁵ Pa) for 24 h at ambient temperature. The specific surface area, S_BET, was determined according to the Brunauer–Emmet–Teller (BET) equation, Dubinin’s theory, the comparison plot, and the DFT method (Stoeckli, 1995). The total surface area was estimated from the average values obtained using the Dubinin–Radushkevich theory, comparison plot and DFT methods.

The Raman spectra were studied (RM100 Confocal Raman Microscope, Renishaw) with argon ion laser excitation at λ₀ = 514.5 nm and a laser power at the sample of 4 mW focused on the sample by a 50 × N-plan objective lens.

2.4

2.4 Photo reactor system and experimental procedures

Experiments were carried out using a cylindrical batch photoreactor opened at air, 8 cm in diameter and 12 cm in working height, the water jacket has a diameter of 5 cm contains the UV-lamp and permits the water circulation (Fig. 1). The photoreactor was recovered inside with (11 cm × 25 cm) of the photocatalyst and was exposed to a luminous source composed of a HPK Philips UV-lamp (125 W), placed in axial position inside the water jacket. The required amount of photocatalyst was mixed in 200 mL of a BG solution. Before irradiation, the suspensions were stirred under dark conditions for 30 min. During the photocatalytic tests, the shaking of the suspensions was controlled to ensure that the suspension was homogeneous. At given time intervals, about 4 mL of aliquots was sampled, and filtered through the Millipore syringe filter (size = 0.45 μm). The absorbance of filtrates was then analyzed on a UV–visible spectrophotometer (UV-1650PC Shimadzu, Japan) at its maximum wavelength of 624 nm, to determine the residual concentration. The percentage of degradation of BG was calculated from the following equation:

(1)

Percentage of degradation (%) = \frac{C_{0} - C_{r}}{C_{0}} \times 100

where C₀ and C_r are the concentrations of initial and residual BG respectively.

3 Results and discussion

3.1

3.1 Specific surface areas and deposited TiO₂ amount of the photocatalysts

The adsorption–desorption isotherms and the inset corresponding pore size distribution profile for the prepared samples were given in Fig. 2. It can be observed in the isotherms that the DSAC has a wider knee and a higher N₂ adsorption capacity than the photocatalysts (TiO₂/DSAC and TiO₂/PVA). These isotherms exhibit a typical IUPAC type IV with a hysteresis loop at high relative pressure of P/P₀ = 0.5–1.0, thus indicating the presence of mesopores (Li et al., 2012; Yu et al., 2006). In addition, the pore size distribution profile shows that the TiO₂/DSAC owns more micropores and mesopores than the other samples. As shown in Table 1, the specific surface areas (S_BET) of the photocatalysts decrease with the significant content of TiO₂, indicating that TiO₂ coverage of pore becomes higher reflecting the important absorbed amount of titanium during the preparation.

N2 adsorption–desorption isotherms and the inset corresponding pore size distributions for the DSAC, TiO2/DSAC and TiO2/PVA samples.

The concentration of TiO₂ in the photocatalysts was clearly identified from EDX. In particular, the TiO₂/DSAC had the highest titania concentration of 24.7 wt.%, that is attributed to the significant quantity of carbon which supports the titanium (38.2 wt.%). The EDX analysis shown in Fig. 3, indicates qualitatively the presence of TiO₂ on the photocatalysts surface, also the existence of certain elements, such as Si, Mg, P, S, K, which are constituents of mineral compositions of the activated carbon used.

EDX diagrams of naked PVC, TiO2/DSAC and TiO2/PVA photocatalysts.

3.2

3.2 X-ray diffraction (XRD) analysis

X-ray diffraction (XRD) patterns of DSAC, TiO₂/DSAC and TiO₂/PVA catalysts are shown in Fig. 4. The two broad peaks of the DSAC sample indicate that this sample is not very crystallized, which is a typical characteristic of the activated carbon. The peak at 2 θ = 22° corresponds to reflexions in the (0 0 2) plane, whereas the peak at 2 θ = 43° corresponds to the (1 0 0) plane (Wang et al., 2011). The pattern for TiO₂/DSAC shows the diffraction peaks at 2 θ values of 25.3°, 37.75°, 48°, 53.8° and 54.9°. They are assigned to (1 0 1), (0 0 4), (2 0 0), (1 0 5) and (2 1 1) reflections of anatase phase of TiO₂ (JCPDS No. 21-1272). Both peaks at 2 θ values of 27.4° and 36.1° are characteristic of the TiO₂-rutile phase (JCPDS No. 21-1272). The XRD patterns of TiO₂/PVA catalysts showed three small crystalline characteristic peaks at 2 θ = 25°, 38° and 47° corresponding to (1 0 1), (0 0 4) and (2 0 0) planes indicating the crystal planes of anatase phase (Lu et al., 2007; Pourjafar et al., 2012). The absence of any intense peaks throughout the spectrum of the composite TiO₂/PVA indicated the predominantly amorphous nature of the structure (Kanarlou and Rafizadeh, 2011).

XRD patterns of DSAC, TiO2/DSAC and TiO2/PVA samples.

The relative content of anatase and rutile, as listed in Table 1, is estimated using the Spurr–Myers equation (2) (Spurr and Myers, 1957):

(2)

(A) % = \frac{I_{A}}{I_{A} + 1.265 I_{R}} \times 100

where A (%) is the relative content of anatase, I_A and I_R are the intensities of the anatase (1 0 1) peak at 2 θ = 25.3° and the rutile (1 1 0) peak at 2 θ = 27.4° (Nolan et al., 2009; Yu et al., 2006).

The anatase content of samples is equal to 95% and 74% for TiO₂/DSAC and TiO₂/PVA, respectively. These values show that the anatase is highly predominant in all samples. The main active crystal phases of TiO₂ are anatase and rutile. Among the two phases, anatase is typically more active (Kim and Ehrman, 2009). According to Ambrus et al. (2008), photocatalyst containing anatase phase is more efficient than rutile-only catalyst. This also suggests that the catalyst TiO₂/DSAC with >90% anatase shows improved photocatalyst activity.

Based on the XRD results, the average crystal size of TiO₂ was calculated using the Debye–Scherrer equation (3):

(3)

D = \frac{K λ}{β \cos θ}

where D is the average crystallite size (nm), λ is the wavelength of the X-ray radiation (λ = 0.1540 nm), K is the Scherrer constant (K = 0.9), β is the full-width at half-maximum (FWHM) of the (1 0 1) plane and θ is the Bragg angle (rad) (Wang et al., 2009a,b). The size of TiO₂ crystallites is listed in Table 1 for all the samples. The observed broad hump in the XRD pattern of composite TiO₂/PVA indicated the presence of crystallites of low dimensions (Chopra, 1969).

3.3

3.3 Surface studies by microscopic techniques

SEM images of DSAC, TiO₂/DSAC and TiO₂/PVA are shown in Fig. 5a–c. As shown in Fig. 5(a), the DSAC sample presents an irregular and highly porous surface. Fig. 5(b) shows SEM micrograph where the presence of TiO₂ particles deposited on DSAC surface is observed with a good dispersity. Compared with Fig. 5(b), TiO₂ powders agglomerated on the surface of the sample, indicating the poor dispersion of TiO₂ nanoparticles in PVA matrix (Fig. 5c).

SEM images of DSAC (a), TiO2/DSAC (b) and TiO2/PVA (c) samples.

The TEM images (Fig. 6a and b) of the prepared samples showed the presence of TiO₂ particles deposited on the external surface of carbon. From Fig. 6a, the TiO₂ forms a thin layer surrounding and partially stabilizing the activated carbon aggregates. In Fig. 6b, it is clear that TiO₂ nanoparticles are uniformly dispersed in PVA matrix and aggregations are observed.

TEM images of TiO2/DSAC (a) and TiO2/PVA (b) samples.

3.4

3.4 Fourier transform infrared spectroscopy (FT-IR)

The FT-IR spectra of DSAC, TiO₂/DSAC and TiO₂/PVA are provided in Fig. 7. The peaks at 3400 cm⁻¹ and 1650 cm⁻¹ were attributed to OH stretching and bending of water, respectively. The peak observed at 2900 cm⁻¹ characterized the vibration of C–H bond. For both photocatalysts, the band at around 1060 cm⁻¹ was attributed to the vibration mode of Ti–O bond (Liu et al., 2007). Also, the intensity of the broad band between 500 and 800 cm⁻¹ characterizes the Ti–O–Ti bond in the anatase phase (Foo and Hameed, 2010). The results obtained from FT-IR analysis were in agreement with those obtained from XRD analysis.

FTIR spectra of DSAC, TiO2/DSAC and TiO2/PVA samples.

3.5

3.5 Raman spectroscopy

The Raman spectra of the prepared samples are displayed in Fig. 8. For both composites, the identical spectra show a series of five frequencies at 150.7, 201.4, 388.5, 505.4 and 629.2 cm⁻¹. These frequencies are characteristic of anatase phase TiO₂. Two peaks at 1335.3 and 1590.5 cm⁻¹ were attributed to (CH₂) wagging bond and (OH) bending in the carbon samples (Shadak Alee et al., 2013).

Raman spectra of DSAC, TiO2/DSAC and TiO2/PVA samples.

3.6

3.6 Photocatalytic activity

3.6.1

3.6.1 Mechanism of photodegradation

The mechanism of photocatalytic oxidation processes has been extensively discussed in the literatures (Baek et al., 2013; Ahmed et al., 2011). When the photocatalyst is exposed to UV radiation with light energy greater than its band gap energy (3.2 eV), an electron (e⁻) in the conduction band (CB) of the semiconductor can be transferred to the valance band (VB), remaining a positive hole (h⁺) in the valence band (Fig. 9).

(4)

{TiO}_{2} + h ν \to h^{+} (VB) + e^{-} (CB)

Under light irradiation, reactive oxygen species, such as HO^• and O₂^•− in the electron and hole are produced by H₂O and O₂ on the surface of TiO₂. The hydroxyl radicals (HO^•), which are most powerful oxidizing agent, can mineralize most of the organic pollutants to smaller and less harmful species, eventually producing CO₂, H₂O, and other degradation products through the various different paths (Ahmed et al., 2011).

(5)

h^{+} (VB) + H_{2} O \to {HO}^{•} + H^{+}

(6)

h^{+} (VB) + {OH}^{-} \to {HO}^{•}

(7)

e^{-} + (CB) + O_{2} \to O_{2}^{-}

(8)

{HO}^{•} + organic polluants \to int ermediates \to {CO}_{2} ↑ + H_{2} O + other deg radation products

Fig. 9 depicts possible structure of TiO₂/DSAC or TiO₂/PVA with adsorption capacity and photocatalytic activity. As mentioned in the previous section, a large amount of TiO₂ will be exposed on the surface of carbon. As a result, active site available on the surface of carbon will increase. This may also contribute to the high photocatalytic activity of TiO₂/DSAC or TiO₂/PVA. Thus, TiO₂ supported on activated carbon will degrade BG through photocatalytic oxidation process as mentioned above. HO^• will attack aromatic ring sites in organic compounds and result in the formation of ring-opened products. Ring-opened products may contribute to decrease in molecular size which may later yield CO₂ and H₂O and other degradation products (Gang et al., 2011). The breaking down of the benzene ring and subsequent mineralization leading to CO₂ and H₂O could be visualized by the decrease in BG during the photocatalytic process (Laura et al., 2010).

Mechanism of photocatalytic degradation of Brilliant green.

3.6.2

3.6.2 Effect of catalyst dosage

In the photocatalytic process, the determination of optimum amount of photocatalyst is a very important parameter. Experiments were carried by varying of the photocatalyst dosage between 0.1 and 0.3 g/L for a 10 mg/L solution of Brilliant green at 120 min under irradiation. Fig. 10 shows the variation of percentage degradation of the dye depending on the amount of TiO₂/PVA and TiO₂/DSAC. It can be observed that percentage removal increases proportionally with the catalyst dose to a tray indicating a progressive saturation of the photon absorption for a given incident flux. The dose of TiO₂/DSAC, most effective, is not the same for the TiO₂/PVA. The minimum dosage that provides the best photoefficiency of decomposition is 0.25 g/L and 0.2 g/L of TiO₂/PVA and TiO₂/DSAC respectively. This result is in correlation with the physico-chemical properties of materials, such as the anatase content in this sample is slightly higher (95%) than in both other TiO₂/PVA samples (84%).

Effect of catalyst dosage on photocatalytic degradation of BG in the presence of TiO2/DSAC and TiO2/PVA.

3.6.3

3.6.3 Effect of irradiation time

Experiments of BG degradation in the presence of optimum dosage of photocatalyst were performed. The results obtained are summarized in Fig. 11. Under dark conditions, adsorption yield, the catalyst activity depends on the carbon mass ratio. Under UV illumination, it is observed that the time required to degrade a solution concentration of 10 mg/l is more important in the case of the TiO₂/DSAC photocatalyst than in the TiO₂/PVA. The removal of BG using TiO₂/PVA reached 90.23% after 135 min irradiation time. By against for TiO₂/DSAC, the removal of this dye reached 95.75% after 90 min irradiation time. This is also in agreement with the fact that surface area which is higher for the TiO₂/DSAC and the significant percentage of carbon presented like support. The direct photolysis without solids could be neglected with less than 4% of conversion after 135 min of UV-irradiation.

Effect of irradiation time on photocatalytic degradation of BG.

The UV–Visible spectra of Brilliant green dye solutions after different intervals of photodegradation in the presence of (only) TiO₂/DSAC are shown in Fig. 12. The diminishing intensity of the bands at 624 nm reveals their removal by photodegradation.

UV–Vis absorption spectra of Brilliant green solution in the presence of TiO2/DSAC at different time.

3.6.4

3.6.4 Effect of cleaning under O₂/UV

O₂/UV is an effective method for removing a variety of contaminants from various surfaces. It is a simple-to-use dry process which is inexpensive to set up and operate. It can produce near-atomically clean surfaces in a vacuum system. Cleaning was performed on the TiO₂/DSAC photocatalyst only after use. With a well cleaned surface, decomposition of Brilliant green starts 15 min earlier than non-cleaned surface, as shown by the results of the comparative study presented in Fig. 13. This lag matches to time required to destroy the adsorbed impurities on the surface before starting the decomposition of Brilliant green. The percentage of BG photodegradation by treated TiO₂/DSAC reaches 89%.

Effect of cleaning under O2/UV on photocatalytic activity of TiO2/DSAC.

3.6.5

3.6.5 Kinetic degradation analysis

Several experimental results suggest that the rates of photocatalytic oxidation of various contaminants over illuminated TiO₂ occur via pseudo-first-order kinetics (Le et al., 2012; Li et al., 2015a,b ).

(9)

\ln (\frac{C_{0}}{C_{t}}) = k_{app} t

where C₀ is the initial concentration of Brilliant green, C_t is the concentration of this dye at illumination time t and k_app is the apparent rate constant of the first-order reaction (min⁻¹). A plot of ln(C₀/C_t) versus time represents a straight line, the slope equals the apparent first-order rate constant k_app. Table 2 lists the apparent first-order rate constants (k_app) for different photocatalysts, which were calculated from Fig. 10. k_app has been used as a comparison parameter because it is independent of the concentration used. The degradation rate of Brilliant green by the TiO₂/DSAC photocatalyst is higher than the other correlation coefficient. These results show that the prepared DSAC was a good support for TiO₂.

Table 2 Apparent first-order rate constants (k_app) for the different photocatalysts.

Photocatalyst	k_app (min⁻¹)	Correlation coefficient, R²
TiO₂/DSAC	0.023	0.992
TiO₂/PVA	0.017	0.981

3.7

3.7 Stability and reusability of prepared photocatalysts

In order to test the feasibility of cyclic use of prepared photocatalysts, three cycles of photocatalytic degradation of Brilliant green were carried out as shown in Fig. 14. The stability of photocatalysts was investigated in optimal condition in this study. The BG removal efficiency during photocatalytic degradation by TiO₂/DSAC decreased slightly as recycling number of runs increase. At the second cycles, 84% of the initial BG was degraded by TiO₂/DSAC. The efficiency of BG removal in the third cycles was similar to that of the second cycles. The results indicate that cyclic usage of these nanocomposites is feasible with satisfactory stability in treating organic compounds. That is, continuous photocatalytic degradation may well be realized.

BG degradation by repeated use of the prepared photocatalysts.

3.8

3.8 Comparison of degradation percentages of Brilliant green dye with literature

Table 3 compares the results obtained in terms of photodegradation of Brilliant green, in the presence of the photocatalyst presented in this work, to other previously published results considering TiO₂ based catalysts. As it can be seen, the obtained maximum BG degradation by prepared composites was more favorable than those of other catalysts. The high efficiency of our system was related to the choice of preparation method and the nature of catalytic support.

Table 3 Comparison of degradation percentages of Brilliant green dye with literature.

Catalyst preparation method	Brilliant green conc. (mol/L)	Catalyst dose (g/L)	Highest degradation (%), time	Ref.
Sr–TiO₂, Ultrasonic–hydrothermal method	5.17 × 10⁻⁵	0.5	96%, 60 min	Sood et al. (2015)
Degussa P-25	2 × 10⁻³	0.5	95.5%, 8 h	Chen et al. (2008)
TiO₂/PVDF, Dry cast method	4.14 × 10⁻⁵	2.5	90%, 10 h	Alaoui et al. (2011)
TiO₂–SiO₂, Solvent EISA method	2.5 × 10⁻⁵	1	98%, 70 min	Dong et al. (2012)
TiO₂ nanoparticles, Sol–Gel method	4 × 10⁻⁵	0.4	93.6%, 120 min	Li et al. (2007)
TiO₂/Cu	8 × 10⁻⁶	3	44%, 180 min	Munusamy et al. (2013)
TiO₂/Zn	8 × 10⁻⁶	1	70%, 180 min	Munusamy et al. (2013)
TiO₂/DSAC, Dip coating method	2 × 10⁻⁵	0.2	96%, 90 min	This study
TiO₂/PVA, Dip coating method	2 × 10⁻⁵	0.25	90%, 135 min	This study

4 Conclusions

Two types of photocatalysts were synthesized by dip coating method using the date stones activated carbon and polyvinyl alcohol as support. This study has revealed that the origin of carbon support affects the formation and state of supported TiO₂. The prepared photocatalysts have demonstrated the porous structure, as determined from N₂ adsorption isotherms at 77 K. The XRD and Raman spectrum demonstrated that the deposited TiO₂ adhered to carbon support so that it increased the stability of titanium crystallites. Scanning electron microscopy has revealed the uniform distribution of TiO₂ over the activated carbon and agglomerated particles over the polymer. Analysis showed that the TiO₂ deposited amount is related to the percentage of carbon involved. The kinetics of the Brilliant green degradation in aqueous solution by the synthesized photocatalysts fit well a pseudo-first order kinetic. The photoactivity of TiO₂/DSAC composites is better than of TiO₂/PVA, possible because active carbon produces high concentration of Brilliant green near TiO₂ for its photocatalysis. The prepared nanocomposites still had good photocatalytic activity after three cycles and TiO₂ did not leach into the solution during photocatalytic reaction of Brilliant green.

Acknowledgments

We are grateful to the Ministry of Higher Education and Scientific Research for the financial support to the current work. The authors are indebted to Leila MAHFOUDHI for proofreading of English.

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Show Sections

[1] Ahmed S., Rasul M.G., Brown R., Hashib M.A., . Influence of parameters on the heterogeneous photocatalytic degradation of pesticides and phenolic contaminants in wastewater: a short review. J. Environ. Manage.. 2011;92:311-330.
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[2] Alaoui O.T., Nguyen Q.T., Schaetzel P., Mbareck C., . Dye and bacteria photodegradations with anatase-loaded microporous poly(vinylidene fluoride) membranes. Catal. Sci. Technol.. 2011;1:1412-1422.
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[3] Ambrus Z., Mogyorósi K., Szalai A., Alapi T., Demeter K., Dombi A., Sipos P., . Low temperature synthesis, characterization and substrate-dependent photocatalytic activity of nanocrystalline TiO2 with tailor-made rutile to anatase ratio. Appl. Catal. A: Gen.. 2008;340:153-161.
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[4] Baek M., Yoon J., Hong J., Suh J., . Application of TiO₂-containing mesoporous spherical activated carbon in a fluidized bed photoreactor-Adsorption and photocatalytic activity. Appl. Catal. A-Gen.. 2013;450:222-229.
[Google Scholar]

[5] Baran W., Makowski A., Wardas W., . The influence of FeCl₃ on the photocatalytic degradation of dissolved azo dyes in aqueous TiO₂ suspensions. Chemosphere. 2003;53:87-95.
[Google Scholar]

[6] Bergeret G., Gallezot P., . Ertl G., Knözinger H., Weitkamp J., eds. Handbook of Heterogeneous Catalysis. Weinheim: Wiley-VCH; 1997. p. :439.

[7] Bessegato G.G., Cardoso J.C., Zanoni M.V.B., . Enhanced photoelectrocatalytic degradation of an acid dye with boron-doped TiO₂ nanotube anodes. Catal. Today. 2015;240:100-106.
[Google Scholar]

[8] Bouchelta C., Medjram M.S., Bertrand O., Bellat J.P., . Preparation and characterization of activated carbon from date stones by physical activation with steam. J. Anal. Appl. Pyrol.. 2008;82:70-77.
[Google Scholar]

[9] Bouchenafa-Saib N., Grange P., Verhasselt P., Addoun F., Dubois V., . Effect of oxidant treatment of date pit active carbons used as Pd supports in catalytic hydrogenation of nitrobenzene. Appl. Catal. A. Gen.. 2005;286:167-174.
[Google Scholar]

[10] Chen C., Lu C., Fan H., Chung W., Jan J., Lin H.D., Lin W.Y., . Photocatalyzed N-de-ethylation and degradation of Brilliant Green in TiO₂ dispersions under UV irradiation. Desalination. 2008;219:89-100.
[Google Scholar]

[11] Cheshmeh Soltani R.D., Khataee A.R., Safari M., Joo S.W., . Preparation of bio-silica/chitosan nanocomposite for adsorption of a textile dye in aqueous solutions. Int. Biodeterior. Biodegrad.. 2013;85:383-391.
[Google Scholar]

[12] Choi J., Chung J., . Evaluation of potential for reuse of industrial wastewater using metal-immobilized catalysts and reverse osmosis. Chemosphere. 2015;125:139-146.
[Google Scholar]

[13] Chopra K.L., . Thin Film Phenomena. New York: Mcgraw Hill Book Company; 1969.

[14] Dong W., Sun Y., Ma Q., Zhu L., Hua W., Lu X., Zhuang G., Zhang S., Guo Z., Zhao D., . Excellent photocatalytic degradation activities of ordered mesoporous anatase TiO₂–SiO₂ nanocomposites to various organic contaminants. J. Hazard. Mater.. 2012;229:307-320.
[Google Scholar]

[15] Erol F., Özbelge T.A., . Catalytic ozonation with non-polar bonded alumina phases for treatment of aqueous dye solutions in a semi-batch reactor. Chem. Eng. J.. 2008;139:272-283.
[Google Scholar]

[16] Foo K.Y., Hameed B.H., . Decontamination of textile wastewater via TiO2/activated carbon composite materials. Adv. Colloid Interf. Sci.. 2010;159:130-143.
[Google Scholar]

[17] Foo K.Y., Hameed B.H., . Preparation of activated carbon from date stones by microwave induced chemical activation: application for methylene blue adsorption. Chem. Eng. J.. 2011;170:338-341.
[Google Scholar]

[18] Furlani E., Aneggi E., Leitenburg C.d., Maschio S., . High energy ball milling of titania and titania-ceria powder mixtures. Powder Technol.. 2014;254:591-596.
[Google Scholar]

[19] Gang X., Huanhuan L., Quanyuan C., Colin H., Mark T., Francis I., . Synergy between surface adsorption and photocatalysis during degradation of humic acid on TiO₂/activated carbon composites. J. Hazard. Mater.. 2011;186:765-772.
[Google Scholar]

[20] Ghiasi M., Malekzadeh A., . Solar photocatalytic degradation of methyl orange over La_0.7Sr0.3MnO₃ nano-perovskite. Sep. Purif. Technol.. 2014;134:12-19.
[Google Scholar]

[21] Grĉíc I., Vrsaljko D., Katanĉíc Z., Papíc S., . Purification of household grey water loaded with hair colorants by solar photocatalysis using TiO₂-coated textile fibers coupled flocculation with chitosan. J. Water Process Eng.. 2015;5:15-27.
[Google Scholar]

[22] Joo S.H., . Combined adsorbents and reactive oxygen species (ROS) generators in soil for treating reverse osmosis concentrates. Powder Technol.. 2014;264:9-21.
[Google Scholar]

[23] Kanarlou H., Rafizadeh S., . Investigation of optical and structural properties of titanium very thin layers under heat process. Aust. J. Basic. Appl. Sci.. 2011;5:1182-1187.
[Google Scholar]

[24] Kim S., Ehrman S.H., . Photocatalytic activity of a surface-modified anatase and rutile titania nanoparticle mixture. J. Colloid Interface Sci.. 2009;338:304-307.
[Google Scholar]

[25] Laura L.A., María-Teresa M.S., Jesús S.A., Arnaud S., Corinne F., Jean Marc C., . Photocatalytic degradation of boscalid in aqueous titanium dioxide suspension: identification of intermediates and degradation pathways. Appl. Catal. B: Environ.. 2010;98:122-131.
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[26] Le H.A., Linh L.T., Chin S., Jurng J., . Photocatalytic degradation of methylene blue by a combination of TiO₂-anatase and coconut shell activated carbon. Powder Technol.. 2012;225:167-175.
[Google Scholar]

[27] Lei P., Wang F., Gao X., Ding Y., Zhang S., Zhao J., Liu S., Yang M., . Immobilization of TiO₂ nanoparticles in polymeric substrates by chemical bonding for multicycle photodegradation of organic pollutants. J. Hazard. Mater.. 2012;227:185-194.
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[28] Li T., Tao Z., Guang-chun C., Ai-hua Y., . Preparation of nanometer TiO₂ and its application in basic brilliant green dye wastewater degradation. J. Environ. Sci. Technol.. 2007;5
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[29] Li J., Liu S., He Y., Wang J., . Adsorption and degradation of the cationic dyes over Co doped amorphous mesoporous titania-silica catalyst under UV and visible light irradiation. Micropor. Mesopor. Mater.. 2008;115:416-425.
[Google Scholar]

[30] Li Y., Li L., Li C., Chen W., Zeng M., . Carbon nanotube/titania composites prepared by a micro-emulsion method exhibiting improved photocatalytic activity. Appl. Catal. A-Gen.. 2012;427:1-7.
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[31] Li D., Zhu Q., Han C., Yang Y., Jiang W., Zhang Z., . Photocatalytic degradation of recalcitrant organic pollutants in water using a novel cylindrical multi-column photoreactor packed with TiO₂-coated silica gel beads. J. Hazard. Mater.. 2015;285:398-408.
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[32] Li H., Li Y., Xiang L., Huang Q., Qiu J., Zhang H., Sivaiah M.V., Baron F., Barrault J., Petit S., Valange S., . Heterogeneous photo-Fenton decolorization of Orange II over Al-pillared Fe-smectite: response surface approach, degradation pathway, and toxicity evaluation. J. Hazard. Mater.. 2015;287:32-41.
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[33] Liu S.X., Chen X.Y., Chen X., . A TiO₂/AC composite photocatalyst with high activity and easy separation prepared by a hydrothermal method. J. Hazard. Mater.. 2007;143:257-263.
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[34] Lu C.H., Wu W.H., Kale R.B., . Synthesis of photocatalytic TiO₂ thin films via the high-pressure crystallization process at low temperatures. J. Hazard. Mater.. 2007;147:213-218.
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[35] Mahmoodi N.M., . Photocatalytic ozonation of dyes using copper ferrite nanoparticle prepared by co-precipitation method. Desalination. 2011;279:332-337.
[Google Scholar]

[36] Mano T., Nishimoto S., Kameshima Y., Miyake M., . Water treatment efficacy of various metal oxide semiconductors for photocatalytic ozonation under UV and visible light irradiation. Chem. Eng. J.. 2015;264:221-229.
[Google Scholar]

[37] Meltem A., Şadiye Ş., . TiO₂-activated carbon photocatalysts: preparation, characterization and photocatalytic activities. Chem. Eng. J.. 2012;180:354-363.
[Google Scholar]

[38] Motlak M., Barakat N.A.M., Akhtar M.S., Hamza A.M., Kim B., Kim C.S., Khalil K.A., Almajid A.A., . High performance of NiCo nanoparticles-doped carbon nanofibers as counter electrode for dye-sensitized solar cells. Electrochim. Acta. 2015;160:1-6.
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[39] Mrabet A., Rodríguez-Gutierrez G., Guill-en-Bejarano R., Rodríguez-Arcos R., Ferchichi A., Sindic M., Jim-enez-Araujo A., . LWT – Food Sci. Technol.. 2015;60:518-524.

[40] Munusamy S., Aparna R.s.l., Prasad R.g.s.v., . Photocatalytic effect of TiO2 and the effect of dopants on degradation of brilliant green. Sustain. Chem. Process.. 2013;1:4.
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[41] Nolan N., Pillai S., Seery M., . Spectroscopic investigation of the anatase-to-rutile transformation of sol−gel-synthesized TiO₂ photocatalysts. J. Phys. Chem. C. 2009;113:16151-16157.
[Google Scholar]

[42] Omri A., Benzina M., . Removal of manganese (II) ions from aqueous solutions by adsorption on activated carbon derived a new precursor: Ziziphus spin a-christi seeds. Alexandria Eng. J.. 2012;51:343-350.
[Google Scholar]

[43] Omri A., Benzina M., . Adsorption characteristics of silver ions onto activated carbon prepared from almond shell. Desalin. Water Treat. 2012:1-10.
[Google Scholar]

[44] Omri A., Benzina M., . Almond shell activated carbon: adsorbent and catalytic support in the phenol degradation. Environ. Monit. Assess.. 2014;186:3875-3890.
[Google Scholar]

[45] Omri, A., Wali, A., Benzina, M., 2012. Adsorption of bentazon on activated carbon prepared from Lawsonia inermis wood: Equilibrium, kinetic and thermodynamic studies. Arab. J. Chem. http://dx.doi.org/10.1016/j.arabjc.2012.04.047.

[46] Omri A., Benzina M., Ammar N., . Preparation, modification and industrial application of activated carbon from almond shell. J. Ind. Eng. Chem.. 2013;19:2092-2099.
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[47] Omri A., Benzina M., Trabelsi W., Ammar N., . Adsorptive removal of humic acid on activated carbon prepared from almond shell: approach for the treatment of industrial phosphoric acid solution. Desalin. Water Treat. 2013:1-12.
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[48] Omri A., Lambert S.D., Geens J., Bennour F., Benzina M., . Synthesis, surface characterization and photocatalytic activity of TiO₂ supported on almond shell activated carbon. J. Mater. Sci. Technol.. 2014;30:894-902.
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[49] Omri A., Benzina M., Bennour F., . Industrial application of photocatalysts prepared by hydrothermal and sol–gel methods. J. Ind. Eng. Chem.. 2015;21:356-362.
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[50] Pourjafar S., Rahimpour A., Jahanshahi M., . Synthesis and characterization of PVA/PES thin film composite nanofiltration membrane modified with TiO₂ nanoparticles for better performance and surface properties. J. Ind. Eng. Chem.. 2012;18:1398-1405.
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[51] Punzi M., Anbalagan A., Borner R.A., Svensson B., Jonstrup M., Mattiasson B., . Degradation of a textile azo dye using biological treatment followed by photo-Fenton oxidation: evaluation of toxicity and microbial community structure. Chem. Eng. J.. 2015;270:290-299.
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[52] Shadak Alee K., Kuladeep R., Narayana Rao D., . In-situ investigation of the formation of silver nanoparticles in polyvinyl alcohol through micro-Raman spectroscopy. Opt. Commun.. 2013;293:69-74.
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[53] Shao G.N., Imran S.M., Jeon S.J., Engole M., Abbas N., Salman Haider M., Kang S.J., Kim H.T., . Sol–gel synthesis of photoactive zirconia–titania from metal salts and investigation of their photocatalytic properties in the photodegradation of methylene blue. Powder Technol.. 2014;258:99-109.
[Google Scholar]

[54] Sheintuch M., Matatov-Meytal Y.I., . Comparison of catalytic processes with other regeneration methods of activated carbon. Catal. Today. 1999;53:73-80.
[Google Scholar]

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