Photodegradation of Indigo carmine in aqueous solution by zirconium phosphates

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Photodegradation of Indigo carmine in aqueous solution by zirconium phosphates

Zouhair Barhon

^a

, François Bozon-Verduraz

^b

, Nabil Saffaj

^c

, Abderahman Albizane

^d

, Mohamed Azzi

^a

, Mohamed Kacimi

^e

& Mahfoud Ziyad

^e

a

Laboratoire Interface Matériau et Environnement, Université Hassan II — Ain Chock, Km. 8, Route El Jadida, B.P. 5366, Maârif, Casablanca, Morocco

b

Groupe Nanomatériaux, ITODYS, UMR-CNRS 7086, Université Paris-Diderot (Paris 7), Bâtiment Lavoisier, 15, rue Jean-Antoine de Baïf, 75205, Paris Cedex 13, France

c

Université Ibn Zohr, Faculté Polydisciplinaire de Ouarzazate, Morocco Phone:

00212663323683 Fax: 00212663323683

d

Laboratoire de Matériaux, Environnement et Catalyse, Université Hassan II -B.P. 146, Avenue Hassan II, C.P. 20650, Mohammedia, Morocco

e

Faculté des Sciences, Laboratoire de Physico-chimie des Matériaux et Catalyse, Département de Chimie, Avenue Ibn Battouta, B.P. 1014, Rabat, Morocco

Version of record first published: 03 Aug 2012.

To cite this article: Zouhair Barhon, François Bozon-Verduraz, Nabil Saffaj, Abderahman Albizane, Mohamed Azzi, Mohamed Kacimi & Mahfoud Ziyad (2011): Photodegradation of Indigo carmine in aqueous solution by zirconium phosphates, Desalination and Water Treatment, 30:1-3, 69-73

To link to this article: http://dx.doi.org/10.5004/dwt.2011.1394

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Photodegradation of Indigo carmine in aqueous solution by zirconium phosphates

Zouhair Barhon

^a

, Franc¸ois Bozon-Verduraz

^b

, Nabil Saffaj

^c

, Abderahman Albizane

^d

, Mohamed Azzi

^a

, Mohamed Kacimi

^e

, Mahfoud Ziyad

^e

a

Laboratoire Interface Mate´riau et Environnement, Universite´ Hassan II – Ain Chock, Km. 8, Route El Jadida, B.P. 5366, Maaˆrif, Casablanca, Morocco

b

Groupe Nanomate´riaux, ITODYS, UMR-CNRS 7086, Universite´ Paris-Diderot (Paris 7), Baˆtiment Lavoisier, 15, rue Jean-Antoine de Baı¨f, 75205 Paris Cedex 13, France

c

Universite´ Ibn Zohr, Faculte´ Polydisciplinaire de Ouarzazate, Morocco Tel: 00212663323683; Fax: 0021224885801; Email: saffaj@gmail.com

d

Laboratoire de Mate´riaux, Environnement et Catalyse, Universite´ Hassan II - B.P. 146, Avenue Hassan II, C.P. 20650, Mohammedia, Morocco

e

Faculte´ des Sciences, Laboratoire de Physico-chimie des Mate´riaux et Catalyse, De´partement de Chimie, Avenue Ibn Battouta, B.P. 1014, Rabat, Morocco

Received 1 December 2009; accepted 20 January 2011

A B S T R A C T

The results of the photocatalytic degradation of Indigo carmine in aqueous solution indicated that the Ag-ZrP photocatalyst prepared by refluxing amorphous zirconium phosphate in silver nitrate method exhibited better photocatalytic performance than

a

-Zirconium Phosphate (

a

-ZrP). The reaction was studied by varying different parameters such as pH and irradiation time.

Keywords:

Indigo carmine; Zirconium phosphate; Silver nitrate; Photocatalytic degradation

1. Introduction

The Indigo carmine (IC) is considered as highly toxic indigoid class of dye. Contact with it can cause skin and eye irritations. It can also cause permanent injury to cornea and conjunctiva. The consumption of the dye can also prove fatal, as it is carcinogenic and can lead to reproductive, developmental, neuron and acute toxicity [1]. Hence, the removal of dyes from process or waste effluents becomes of fundamental importance to the environment. There are many techniques for removing dyes from waste water, such

as membrane process [2], coagulation [3], adsorption [4] and photodegradation [5].

Currently, the photocatalytic treatment is a more attractive alternative for the removal of soluble organic compounds. It does not require expensive oxidants and can be carried out at mild temperature and pressure.

Among various materials, semiconductors were used as photocatalysts under UV irradiation because of their physical and chemical stability, low cost, ease of availability, non-toxicity, and electronic and optical properties [6,7]. Furthermore, efforts have been made by many researchers to use new photochemically stable materials, such as zirconium phosphate, and introduce metal into the nanoporous materials to effectively

Corresponding author

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increase the catalytic activities. It was shown that silver has a beneficial influence on the photoactivity of nano- crystalline semiconductor photocatalysts [7].

Zirconium phosphate is an important inorganic material that is extensively studied in different chemical fields including ion exchange, catalysis and photodegra- dation, and has received considerable attention [8–11].

Photodegradation activity of synthetic zirconium phos- phates is related to their relatively no negligible surface area, swelling properties and high cation exchange capacity. The chemical treatment of synthetic zirconium phosphates has long been studied with the intention of modifying their texture, acidity and photochemical property in order to make them useful as adsorbents or catalysts supports [9–13]. Different metals such as Ag, Cu and Zn were used in the modification of zirco- nium phosphate [14,15].

The aim of this study is to examine the feasi- bility of discoloration of IC dye using a-ZrP and amorphous zirconium phosphate activated by nitrate silver. The factors that influence the dye photocataly- tic removal such as pH, time and silver effects were investigated.

2. Experimental

2.1. Preparation and characterization of zirconium phosphates Amorphous zirconium phosphate a-ZrP was prepared as described by Clearfield method [16].

a-Zirconium phosphate was prepared by refluxing amorphous zirconium phosphate a-ZrP in phosphoric acid H

₃

PO

4

for 24 h. The resulting crystalline a-ZrP was centrifuged, washed with deionised water and dried at 80

C for 48 h.

Silver activation was done as described in Ref [10], 5 g of amorphous a-ZrP was added to solution of silver nitrate AgNO

3

(400 mg; 200 cm

³

) and agitated for 1 h.

Then, 18 cm

³

of phosphoric acid H

3

PO

4

was added and the mixture was refluxed for 2 days to yield precipitate denoted Ag-ZrP for the simplicity. The samples were centrifuged, washed with deionised water and dried at 80

C for 2 days.

For all samples, the phases X-ray powder diffrac- tion (XRD) patterns were obtained by Philips X’Pert PRO with Cu Ka radiation and the FTIR measurements were performed with 4 cm

¹

resolution by VERTEX 70 spectrometer. Zeta potentials of suspension samples were measured at room temperature using a Malvern’s Zetasizer Nano.

2.2. Photocatalytic evaluation

IC, the chemical structure of which is shown in Fig. 1, was selected, as a model for the photocatalytic

degradation experiments because it is a non-volatile and common contaminant in the industrial waste- waters. The setup used for photocatalytic degradation experiment consists of a 250 mL beaker and 20 cm above it, a low-pressure mercury lamp UV (15 W, Philips) was used as an artificial light source. Moreover, the content of the beaker was stirred by a magnetic stirrer during irradiation. UV-VIS spectrophotometer (Standard UNICAM) was used to measure the UV–vis absorption spectra of IC as function of irradiation time.

To compare, we studied the adsorption of IC by these materials under the same conditions in the dark and the effect of UV radiation on the degradation of dye in the absence of catalysts.

The experiments were performed by suspending calculated amount of the catalyst into IC solution (100 ppm). The reaction was carried out isothermally at 25

C and samples of the reaction mixture were taken at time intervals for a total reaction time 2 h. The deco- lourisation was determined at the maximum 608 nm.

Removal efficiency (%) of IC was measured by apply- ing the following equation:

removal efficiency ð Þ ¼ % Co C

Co 100; ð1Þ

where Co is the original IC content and C is the retained IC in solution.

3. Results and discussion 3.1. Characterization

As mentioned in Ref [10], the XRD patterns of both materials a-ZrP and Ag-ZrP exhibit the same main reflections with different intensity and resolution. The interlayer spacing for all materials was retained at around 0.75 nm. The spectra of a-ZrP is well crystal- lized, whereas Ag-ZrP presents broad ill-defined reflections indicating its low crystallinity or the pre- sence of small size of crystallites. This low crystallinity can be due to the exchange of hydrogen ions by silver ions.

These results were confirmed by FTIR spectrum of both materials Ag-ZrP and a-ZrP which are the Fig. 1. Chemical structure of indigo carmine.

70 Z. Barhon et al. / Desalination and Water Treatment 30 (2011) 69–73

Downloaded by [University of Arizona] at 03:57 18 December 2012

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same with small difference in the intensities of some peaks concerning the OH bands (970, 1,619, 3,170, 3,509 and 3,598 cm

¹

). These bands were slightly reduced after activation of zirconium phosphate by sil- ver nitrate confirming probably the substitution of hydrogen by silver ions [10].

3.2. Catalytic activity 3.2.1. Effect of pH

The photocatalytic performance of IC on Ag-ZrP and a-ZrP at different pH values was shown in Fig. 2.

The pH of the solution was adjusted with diluted NaOH and HCl. It was found that the photocatalytic efficiency of the dye over Ag-ZrP and a-ZrP was highly pH dependent.

The photocatalytic efficiencies decreased with increasing pH values. But at pH > 8, the decolourisa- tion of the dye was negligible. The photocatalytic per- formance dramatically increased at the pH 3. The photocatalytic oxidation of organic compounds on Ag-ZrP and a-ZrP may be carried out in two processes:

(1) The diffusion of organic compound to the particle surface to forming a complex.

(2) Exchange of electrons with the reactive surface of samples [17].

The zeta potential profile of both Ag-ZrP and a-ZrP suspensions are shown in Fig. 3. This figure shows that the catalysts surfaces are negatively charged and this charge becomes more important when pH increases.

IC is a dianionic dye in aqueous solution and it can keep its dianionic configuration in the pH range 3–11.

At low pH range, electrostatic interactions between the catalyst surface and dye anions lead to adsorption of the latter on the metal oxide support [17]. The photocatalytic activity is more important at pH 4, due to the surface charge of the catalyst which is almost zero. This overcomes the repulsion between the surface and the dye and allows their contact. This contact is confirmed by the low adsorption of IC obtained in the dark (Fig. 4).

The photocatalytic performance decreases with increasing pH due to the electrostatic repulsion between the dye species and the surface of the catalyst as a result of which the photocatalytic degradation percentage was found to be minimum at pH > 8.

In reality, the interpretation of pH effects on the efficiency of dye photodegradation process is a very

2 4 6 8 10

0 20 40 60 80 100

(a) (b)

Photocatalytic degradation %

pH

Fig. 2. Effect of pH on the photocatalytic performance of IC on (a)

a

-ZrP, and (b) Ag-ZrP. V

¼

200 ml, m

cat¼

100 mg, t

¼

2 h, [IC]

¼

100 ppm.

– 40 –35 –30 –25 –20 –15 –10 –5 0

2 4 6 8 10

(a) (b)

E (mV)

pH

Fig. 3. Zeta potential of IC on (a)

a

-ZrP, and (b) Ag-ZrP as a function of solution pH.

2 4 6 8 10

0 20

(a)

(b)

Adsorption %

pH

Fig. 4. Effect of pH on the adsorption of IC on (a)

a

-ZrP, and (b) Ag-ZrP. V¼ 200 ml, m

cat¼

100 mg, t

¼

2 h, [IC]

¼

100 ppm.

Downloaded by [University of Arizona] at 03:57 18 December 2012

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difficult task because three possible reaction mechan- isms can contribute to dye degradation, namely, hydro- xyl radical attack (Eq. (2)), direct oxidation by the positive hole (Eq. (3)), and direct reduction by the elec- tron in the conducting band (Eq. (4)) [11].

Catalystþh!h^þ_ðVBÞþe_ðCBÞ H2Oþh^þðVBÞ!H^þþOH

DyeþOH!degradation product 2ð Þ Dyeþh^þVB!oxidation products ð Þ3 DyeþeCB!reduction products ð Þ4 8<

:

It appears that the effect of pH on the degradation of the pollutants is variable and controversial, since the positive holes are considered to be the major oxidation species at low pH, whereas hydroxyl radicals are con- sidered as the predominant species at neutral or high pH levels [18].

Since the influence of the pH is dependent on dye type and surface properties of materials, this effect on photocatalytic performance must be accurately checked before any application. All further experiments were carried out at pH 3.

3.2.2. Effect of silver activation and time on photocatalytic performance of IC

Adsorption phenomena are less important in the dark (Fig. 4) and no photolytic degradation by UV light of IC has been observed in the same operating conditions, so dye disappearance represents exactly the photocatalytic degradation on the photocatalyst surface.

The refluxing of amorphous zirconium phosphate in silver salt lead to an increase of the degree of photocata- lytic performance of IC solution compared to a-ZrP.

Thus, enhanced degradation under UV irradiation maybe ascribed to the effects of Ag deposits acting as electron traps leading to better electron excitation [19].

In addition, the rate-determining step in photocatalytic oxidations is believed to be the electron transfer from Ag–ZrP surface to the adsorbed oxygen [19].

It can be seen that the dye uptake process was found to proceed through two stages as shown in Fig. 5:

(1) An initial rapid uptake for the first 10 min was found that 50% and 29% for Ag-ZrP and a-ZrP respectively of IC decolorized.

(2) The dye uptake attains saturation from 70 min and 100 min for Ag-ZrP and a-ZrP respectively.

As described by Othman et al., the high photode- gradation performance at the initial period (10 min) may be due to increasing the number of vacant sites available at the initial stage and as a result an expected variation in the concentration of adsorbate in solution and on adsorbent surface (concentration gradient) tends to enhance the dye sorption rate [17]. As time

proceeds, this concentration gradient decreases due to the intermediates of dye destruction which can block the surface of the catalyst and slow down the photoca- talytic process and also due to accumulation of dye molecules on vacant sites and thus saturation stage was almost perceived [17].

4. Conclusion

The results of our study have shown that the degra- dation of IC dye was successfully carried out using a-ZrP and Ag-ZrP. The presence of silver enhanced the photo- catalytic degradation due to its effect, which acts as elec- tron traps leading to better electron excitation. High photocatalytic activity was found at pH 3.

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0 20 40 60 80 100 120

0 20 40 60 80 100

(a) (b)

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t (min)

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