DSpace at VNU: Degradation of phenol using the mixed (Al-Fe) pillared bentonite as a heterogeneous photo-fenton catalyst

9 2011 490-493 Conference IWAMN2009 -Degradation of Phenol Using the Mixed Al-Fe Pillared Bentonite as a Heterogeneous Photo-Fenton Catalyst∗ Nguyen Thi Dieu Cam† Faculty of Chemistry,

e-Journal of Surface Science and Nanotechnology 27 December 2011

e-J Surf Sci Nanotech Vol 9 (2011) 490-493 Conference IWAMN2009

-Degradation of Phenol Using the Mixed (Al-Fe) Pillared Bentonite as a

Heterogeneous Photo-Fenton Catalyst∗

Nguyen Thi Dieu Cam†

Faculty of Chemistry, Quy Nhon University, 170 An Duong Vuong, Quy Nhon, Binh Dinh, Vietnam

Dao Thanh Phuong, Ha Van Tai, Nguyen Dinh Bang, and Nguyen Van Noi

Faculty of Chemistry, Hanoi University of Science VNU-Hanoi,

334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam

(Received 16 December 2009; Accepted 21 June 2010; Published 27 December 2011)

In this work the mixed Al-Fe pillared bentonite was developed and tested as a heterogeneous catalyst for the photo-Fenton oxidation of phenol under solar light irradiation The structural characteristics of the catalyst were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) The Al-Fe pillared clay exhibits higher basal distance than original bentonite The effect of pH to the degradation of phenol and the reusability of the catalyst were addressed.The results of photocatalytic experiments indicate that the heterogeneous photo-Fenton process employing the Al-Fe pillared clay as a photocatalyst possesses a high potential for phenol degradation During the photocatalytic reaction, the amount of iron leaching out increases as a function of time Significantly lower concentration of Fe2+and Fe3+in the solution after the treatment could give a great advantage to the mixed Al-Fe pillared bentonite/H2O2system over the homogeneous Fenton system [DOI: 10.1380/ejssnt.2011.490]

Keywords: Pillared clay; Heterogeneous Fenton; Phenol; Catalytic activity, Solar light irradiation

In Fenton reaction, hydroxyl radical - a strong oxidant

[1–4] - is produced OH• can oxidize non-biodegradable

pollutants into CO2 and H2O

Fe2++ H2O2→ Fe3++ OH−+ HO• (1)

Fe3++ H2O2 → Fe(OOH)2++ H+

→ Fe2++ HO•

Fe3++ HO•

Fe(OH)2++ hv → Fe2++ HO• (4)

However, homogeneous Fenton reaction requires high

con-centration of Fe (II), and iron ions must be treated after

used In addition, low pH condition of this reaction makes

it impractical because of the high cost of acidifying before

treatment and neutralizing after treatment Therefore,

immobilizing transition metal ions to improve efficient of

Fenton process is the objective of this project

In order to decrease the price and increase the

availabil-ity of catalysts, clay is one of the most promising carriers

to immobilize metal ions Pillared interlayered process

is employed to immobilize metal ions into interlayers of

clay Pillared interlayered clay is used as catalyst to

de-grade organic pollutants in Fenton process Clay can be

pillared with only iron cation [5, 6] or with the mixture of

iron and other cations, such as aluminum [7–9], zirconium

[10] In pillaring process, clays are swelled in water, and

∗This paper was presented at the International Workshop on

Ad-vanced Materials and Nanotechnology 2009 (IWAMN2009), Hanoi

University of Science, VNU, Hanoi, Vietnam, 24-25 November, 2009.

†Corresponding author: nguyendieucam@hus.edu.vn

TABLE I: Mineral composition of enriched Thanh Hoa clay Mineral concentration Concentration (% wt)

Zeolite (Heulandit +Chabazit) 3-5

then oligomeric metal cation complexes are added to ex-change with the interlayer cations After that, materials are dried and calcined, transforming metal polyoxocations into metal oxide pillared Properties of pillared clays de-pend on many conditions, such as origin, size of clays, polyoxocation solutions, and calcinating temperature, Pillared clay catalysts are easy to be collected after used

so that secondary pollution is prevented Moreover, the stability of catalysts is tested and this kind of catalyst is reusable

In this research, we present our results about catalytic properties of Al-Fe pillared clay We use this material to catalyze phenol degradation using advanced Fenton pro-cess with H2O2 Effects of pH on heterogeneous Fenton process are investigated

A Materials

Thanh Hoa bentonite (CEC = 71 meq/100g dried clay) provided by Truong Thinh company (mineral and chemi-cal composition is showed in Tables I, II and III), AlCl3, FeCl3, NaOH, phenol, H2O2(Merck), deionized water

e-Journal of Surface Science and Nanotechnology Volume 9 (2011)

TABLE II: Chemical composition of original Thanh Hoa clay

FIG 1: XRD pattern of (a) bentonite and (b) modified bentonite

B Al-Fe pillared clay preparation

1 Pillared solution

Pillared solution was prepared at 338K by adding

NaOH solution gradually into AlCl3 and FeCl3 solution

while continuously stirring until the molar ratio OH/(Al

+ Fe) is 2/1 The molar ratio Al/Fe was 8.5/1.5 The

pillared solution was aged overnight

2 Al-Fe pillared clays

A 2 wt% clay suspension was adjusted to pH 9.1 and

swelled for 2 days Pillared solution was added into clay

suspension until achieving 10 mmol Al-Fe/1g clay The

suspension was stirred in 4 hours and aged for one day

at room temperature After that, the suspension was

fil-tered and washed with deionized water repeatedly until

completely eliminate chloride ion, then dried at 313, 343

and 383 K in 12 hour Finally the dried solid was calcined

at 673 K in 3 hours

C Phenol photocatalytic oxidation

The reaction was carried out in a sequencing batch

re-actor 300 mL of approximate 100 mg/L phenol solution

was added to the 500 mL beaker, then 0.5 g pillared clay

was added, and the suspension was stirred continuously

to make uniform suspension H2O2was added to the

sus-pension at the beginning of solar light irradiation The pH

of the solution was adjusted by HCl and NaOH solution

Phenol and iron ion concentration was determined

D Analytical method

Catalytic characterization was investigated by X-ray

diffraction method using D8 ADVANCE instrument

(Bruker-Germany), SEM (JEOS JSM - 5410 LV, Japan)

TABLE III: Chemical composition of enriched Thanh Hoa clay

TABLE IV: Interlayer distances of bentonite and modified bentonite

Concentration of phenol was determined by spectropho-tometric method using UV-VIS Novaspec II instrument (Germany) with 4-amino antipyrine as a color agent at

510 nm Concentration of iron was measured using 1,10 – phenanthroline as a color agent Cation exchange capac-ity of clay was measured by methylene blue adsorption method according to American Petroleum Institute

III RESULTS AND DISCUSSION

A Material characterization

Chemical composition and physicochemical properties

of original bentonite and Al-Fe pillared clay were repre-sented in Tables I, II, III and IV

XRD patterns (Fig 1) showed that interlayer distance

FIG 2: SEM pattern of (a) bentonite and (b) modified ben-tonite

Volume 9 (2011) Cam, et al.

FIG 3: UV pattern of (a) initial phenol solution and (b) phenol solution after 3 h of treatment

TABLE V: Interlayer distances of bentonite and modified

ben-tonite

Phenol conversion (%) 56.42 93.81 99.00 -

-Iron leaching (mg/L) 1.04 1.04 2.62 3.24 4.36

of bentonite modified by Fe/Al mixture was higher than

that of original bentonite From SEM patterns (Fig 2),

there is difference between pillared clay and original

Ben-tonite It proves that pillared clay was successfully

syn-thesized

B Catalytic efficiency of Al-Fe pillared clay

Preliminary test proved that phenols can not be

de-graded by H2O2 without Al-Fe pillared clay Phenol

re-moval caused by adsorption process on pillared clay was

not significant in comparison with that caused by

oxi-dation process Experiments proved that unpillared

ben-tonite can not degrade phenol Experimental data of

phe-nol conversion degree is presented in Table V and Fig 3

Reaction condition: 129 mg/L phenol solution, room

tem-perature, sunlight

Figure 3 shows that Al-Fe/Bent material has high

ef-ficiency under sunlight and room temperature condition

This is a promising material to apply in practice to treat

wastewater polluted by phenol in particular, and by

or-ganic pollutants, in general

C Effect of pH on heterogeneous Fenton reaction

Fenton reaction takes place rapidly at pH < 3 (if higher,

Fe(II) is precipitated, so that the efficiency decreases

sig-nificantly) To investigate the effect of pH on catalytic

property of Al-Fe pillared clay, experiments were carried

out at different pH Reaction was carried out at room

tem-perature with sunlight irradiation Results are showed in

Fig 4

FIG 4: atalytic property of Al-Fe pillared clay versus phenol conversion

From obtained data it can be concluded that the

cat-alytic efficiency of the material is significant when pH >3,

while homogeneous Fenton process is not efficient How-ever, when increasing pH, the induction period increases,

so that time for phenol to degrade completely is longer When pH = 3, after only 90 mins, the phenol conver-sion is 93.80%, but when increasing pH to 3.5, 4 and 4.4, the conversion of phenol decreases to 88.73%, 86.53% and 6.42% respectively Consequently, induction period is a function of pH

Many scientists think that the induction periods occur

in condensed phase, involving polymers [11], and it is not

in solution state Aqueous Fenton reactions catalyzed by pillared clay were observed several times [12], but their mechanism can not be clarified yet, because of lack of de-tails and involvement of condensed phases and adsorption onto material surface There can be two factors in re-sponse for induction periods: activation processes of sur-face iron by formation of complex with reactant sursur-face before oxidation takes place; or the need of time to dis-solve iron so that homogeneous Fenton reaction can occur The second reason has less possibility because

concentra-tion of iron is small (<2.5 mg/L) Inducconcentra-tion period might

result from protonation of iron surface

e-Journal of Surface Science and Nanotechnology Volume 9 (2011)

FIG 5: Catalytic property of Al-Fe pillared clay versus phenol

conversion

FIG 6: Concentration of phenol and iron

D Test on the iron leaching

During reaction, iron from pillared clay is dissolved into

solution Concentration of iron tends to decrease when

in-creasing pH (Fig 5) Iron keeps leaching even when

phe-nol is completely degraded At higher pH, amount of iron

is smaller (at pH = 4.4, after reaction, concentration of

iron is 0.22 mg/L) It shows that amount of iron leaching

out and reusability not only depend on gradually oxida-tion between iron and phenol but also depend on pH In this work, concentration of iron after 7 hours of reaction

is smaller than 0.25 mg/L at pH 4.4 Consequently, the higher the pH, the smaller the leaching of iron However, optimum pH is chosen as 4.0 because of the shortest con-version time (1.5 h) and the lowest concentration of iron (0.48 mg/L)

E Reusability of Al-Fe – bent catalyst

The used material was collected, washed with large amount of deionized water and dried at room temper-ature It was then reused as catalyst for Fenton reac-tion Conditions were: 107.63 mg/L phenol solution, pH

4, room temperature, sunlight irradiation Results are presented in Fig 6

It can be seen from Fig 6 that Al-Fe-bent material still has catalytic activity, although it decreases For new material, it takes 1.5 hours to completely degrade phenol, but for reused material, it takes 2.5 hours

Al-Fe pillared clay was successfully synthesized from Thanh Hoa bentonite and Al, Fe ions Results proved that phenol treatment by adsorption is insignificant in comparison to that by catalysis process The experimen-tal data show that phenol degradation decreases while pH increases, and the optimum achieves at pH 4 Amount of iron leaching into wastewater strongly depends on pH, and it decreases sharply when pH increases

Acknowledgments

The support of this work by the National Foundation for Science and Technology Development (Project code 104.99.153.09) is gratefully acknowledged

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