Journal of Scientific & Indu strial Research

Vol. 62, December 2003, pp 1138-1144

Electrochemical Degradation of Rhodamine B Dye in Textile and Paper Industries Effluent

Raj eev lain*, Nidhi Sharma and Meenakshi Bhargava

Department of Environmental Chemistry, Jiwaji University, Gwalior 474 0 II

Received : 09 Ma)1 2003; accepted: 22 September 2003

In the present paper, e lectrochemical behaviour of rhodamine B has been studied vo ltammetricall y using pl atinum and steel fo il as working electrodes. The cont ro lled potential e lectro lys is is carried out at e lectro lys is potential of - 1.20 V. The complete decolouri sation results within I to 2 h of electrolysis.

Keywords: Controlled potential e lectro lysis, Cycl ic voltammetry, Chemical ox idation demand , E lec trochemi cal treatment of industri al eftl uents, Industrial eftluents, Eftluents

Introduction

Rhodamines are an important class of compound s and find considerable commercial use in textile industries and al so in the preparation of red and pink lakes used as pigments, ,2. However, literature survey reveals that some of these extensive ly used commercial dyes are toxic on inh a lation and ingestion and may cause liver and th yro id damage. Rhodamine B is also an eye and skin irritant. Besides its toxicity effects the dye is also the maj or source of colour effluents from tex tile and paper dye ing industry3-s .

In view of thi s, it was considered worthwhile to carry out the comprehensive electrochemical tudy along with application of e lectrochemical methods for colour remova l and decrease in toxicity level with identifi cati on of decompositi on products.

Materials and Methods

For e lectrochemica l studies, synthetic dye (rhodamine B) obtained from Aldrich USA was used. 2.0 x 10-3 M stock solution of rhodamjne B was prepared in doubly di stilled water by di sso lving accurate ly we ighed compound in di stilled water. B R buffers in the pH range 2.5 to 12.0 were prepared in accordance with the stated method9

. For carrying out COD studi es, all the reagents viz. , K2Cr20 7, ferroin indicator, ferrous ammonium sulphate, and si lver

" Author fo r correspondence Telefax: 9 1-75 1-2346209 E-mail: gw lsosmica @sancharnet.in

su lphate-sulphuric acid were prepared as per standard method' o.

Experimental Procedure

Controlled potential e lectrolys is was carried out on a BAS CV-27 Cyclic Vol tammograph in connection with a Digital e lectronic 2000 Omnigraph x-ylt recorder. Conventional three-e lectrode sys tem was used in which electrodes to be electro lysed were dipped directly in the solution . Gal vanostat a ll owed a DC regulated power supply to fl ow between e lectrodes in the cell. For controlled potential

e lectrolysis, platinum foil (surface area 3 x 3 cm2) and

steel foil (surface area 4.5 x 3.5 cm2) were used as

working e lectrodes, SCE as reference and Pt wire as auxiliary electrode. CV studies were carried out on EG and G Potentiostat of Princeton Applied Research integrated with Applied E lectrochemi stry Software. pH metric measurements were made on Hach EC-40 Bench top pH/ISE meter. The absorbance kinetics was studied usmg Elico SL 159 UV-V isible Spectrophotometer.

Chemjcal oxidation demand (COD) was evaluated by the open reflux method using CO D digester from Spectra Lab (20 J5-S). Pre-coated TLC plate was obtained from E-Merck.

For the purpose of cyclic voltammetry and controlled potential electrolysis, 2 x 10-4 M of Stock solution was prepared in doubl y distilled water. Working solutions of rhodamine B were prepared by taking 1.0 mL of stock so lution , 8.0 mL of B R

'.

JAIN et at. : ELECTROCHEMICAL DEGRADATION OF RHODAM INE B DYE 11 39

buffer/di stilled water, and 1.0 mL of KC I. Nitrogen gas was purged so as to remove oxygen from the so lution. Cyclic voltammograms were recorded by carrying out studies at varying pH, scan rates, and concentrations.

Controlled potenti al electro lys is of dye so luti on was carried out at -1 .20 V . Progress of e lectrolys is was monitored by recording cyclic vo ltammograms at regu lar interva ls. Absorbance kinetics was monitored by recording absorbance of the solution at AmlX 554 .5 nm. The number of end products of e lectro lys is was determined by TLC.

For determinati on of number of electrons 'n' in vo lved in the reduction of the dye, KCI and buffe r were mi xed in same ratio as for cycl ic vo ltammetric studies. The soluti on was deaerated by passing nitrogen gas for 10-1 5 min . The solution thus prepared was e lectro lysed . The current decreased exponenti all y with time. From decrease in current during electro lys is the number of e lectrons transferred were calcul ated. Coulometer was used to read the quantity of coulombs direc tl y and 'n ' was calculated by using the expression Q = nFN.

Results and Discussion

Cyclic Vo ltammetry

The cyc lic vo ltammograms of the compound in aqueous neutral medium showed two broad reducti on peaks on fo rward scan and two ox idation peaks on

reverse scan at the scan rates ranging from 100 m V /s to 2000 mV/s (Figure 1). The peak potenti al (Ep ,Cl and Ep,Cll ) of both the cathodic peaks were found to shi ft towards negati ve potenti al with increasing scan rates but anodic peak potential (Ep,a) showed positi ve shift. Both the reduction peaks were found to be irreversible with the separation of peak potential greater than 0.059/n (ref. 11 and 12). Irreversability was also supported by shape of the vo ltammograms that were drawn out and fl atter" . The linear pl ot of ip,c vs concentration a lso supports irreversibility. With increased concentration of rhodamine B, peak potential shi fted towards more negati ve potent ial, thereby indicating the difficul ty in reduction" (Figure 2). Both cathodic and anodic peak currents of rhodamine B in di stilled water were fo und to be increas ing with increase in scan rate (Table I) .

At pH 2.5 the dye soluti on ex hib ited two cathodic peaks. The plots of ip,c VS V1/2 for both the cathodic peaks were found to be linear, pass ing through origin , indicating the e lectrode process to be entirely di ffusion-contro lled " which was fur ther supported by a plot of log ip vs log v with a s lope of 0.5 V suggesting a di ffusion contro lled peak l4 (Figure 3) .

Studies at Various pH

Cyc li c vo ltammetri c s tudies of rh odamine B we re carri ed out at pH 2 .5 to 10 .5 on Pt e lect rode .

-220.0 ,----..,-----,-------y-----.-----,.----~

- 190. 0 -

- 140.0

-100.0

"- -60.0 G:

3 H - 20 . 0

20.0

60.0

100 . 0

140. 0 L..-_ _ _ -L _ _ _ _ ..L.. ___ ----.l _ _ _ _ --L ___ _ L-_ __ -.l 1200.0 see. I! 400.0 11 . 0 -400.0 -800. 0 - 1200

Figure I - Cyclic voltammograms of rhodami ne B (2 x 1O-4M in d istilled water at platinum working electrode at varying scan rates . (mV/s) ( \ ) \00, (2) 200, (3) 500, (4) 1000, (5) \500, (6) 2000

1140 J SCI [ND RES VOL 62 DECEMBER 2003

25.0

20.13

-c :&

u

Jf 15.1)

~

10, Q

11.0 12.0 16.0 20.0 24.0

COfte. x 10"" M

Fi gure 2 - Plot of ip" vs cone. of rhodamine B at scan rate of 200mV /s at plati num fo il work ing electrode

Tab le I - Voitam metri c charac teristics o f rhodamin e. B (Cone. = 2.0 x 10.4 M) at vari ous scan rates in aqueous neutral med ium

SI No. pH Scan

VY2 ·Ep,cl ·Ep,cII

Rate (V) (V)

100 10.00 0.439

2 200 14. 14 0.45 1 0 .640

3 500 22 .36 0.46 1 0.680 Dist illed

4 1000 3 1.62 0.482 0.720 Water

5 1500 38.72 0.503 0.750

6 2000 44.72 0.549 0.820

In pH range 3.8 to 10. 5, only a s in g le broad a nd not ve ry di stinct reducti on peak and a co rrespondin g ox idat ion peak was observed . Peak curre nt becomes a lmos t neglig ibl e a t pH 6 .5 , indi cat ing decrease in ra te of protonati on w ith inc rease in pH (Fi gure 4a). T he re was a lso an observed negative shi ft in the redu cti on peak pote ntial with pH . Thi s negati ve shi ft w ith pH indi cated proton pa rti c ipation in the e lec trode process. The negat ive shift in peak potentia l with pH was sw ift up to pH 4 .5 , the reafte r th e re was p rac ti ca l constancy in Ep,c with pH (Figure 4 b) as th e equ ilibrium shifted toward s un protonated fo rm . Th e two linear secrme nts b

inte rsec t a t pH 4.5 corresponding to the pKa va lue I 4

•17

.

· ip ,cl ·ip ,cII ·ip ,a l ·Ep,all il l ,(/1 II',a ll (~A) (~A) (V) (V) (pA) (~A )

4. 10 1 0 .860 0.259 09. 30 5.415

7.02 12.0 0 .845 0.262 10.79 9.079

15.8 1 22.0 0.827 0 .232 20. 18 17.1 3

28.9 40.3 0.802 0.232 28. 10 28.18

39.23 47.0 0.787 0 .229 33.23 34.69

52.4 1 70.2 0.749 0.229 3(J. 16 41.28

Controlled Potential Electrolysis

Contro lled potenti a l e lectro lysis of the dye

soluti on in aqueous neutra l med ium (Cone. = 2 .0 x 10.4 M ) in disti lled water and at diffe rent phosphate buffers was carried out. The initi al redox peak of rhodamine B in aqueous medium di sappears after cpe for 2 h, leading to complete colou r re moval but another reduction peak at lower potential was observed in e lectro lysed soluti on ind icating the formation of some other e lectroacti ve decompos iti on products, both in the case of platinu m and steel fb il e lec trodes (Figure 5).

E xhaustive contro lled potenti a l e lect ro lys is was also carried out in solu tions of various pH . At al l the

JAIN el al.: ELECTROCHEMICAL DEGRADATION OF RHODAMINE B DYE 1141

1000.0

I aoo.O

.. Ii ,. I 400.0

200.0

II Peak

I Peek

30.0 'O.D SO.O 10.0

JI~

Figure 3 - Plot of ip,c VS vl12 of rhodamine B at pH 2.5 at platinum foi l working electrode. conc. 2 x IO·4M

~ ~ . ,

.. w

250.0

I.)

200.0

150.0

100.0

50.0

2.0 '.0 1.0 10.0 12.D

pH -

II I b)

O.t

0.7

2.D I.D 10.0 12.0

Figure 4 - Plot of (a) ip,c vs pH (b) Ep.c vs pH. of rhodamine B at scan rate of IOOmV/s at pl at inum foil

working electrode. conc. 2 x 1O·4M

pH, total disappearance of cathodic and anodic peaks with drastic reduction in peak current was observed. The voltammetric characteristics of rhodamine B dye solution (in distilled water and at varying pH) before and after electrochemical treatment are given in Table 2.

.- .• r----.----.-----,----,-----,----.---~

.-1811. 1

- lZ8.B

H - 81 . 1

e. '

41.e

• . • L-__ ~ ____ ~ ____ L_ __ ~ ____ _L ____ L_ __ ~

14M. 1 1 .... 1 -688 . 8 -1".8 - 14M

E <.u)

Figure 5 - Cyclic voltammograms of rhodamine B (2 x 1O·4M• 8.8 pH) at platinum working electrode scan rate 50mV/s (A) Before electrochemical treatment (B) After electrochemi cal

treatment

The number of electrons 'n' involved in reduction of rhodamine B was determined at different pH / aqueous medium and were found to be 4 .0 ± 0.2.

Spectral Studies

The spectral changes of rhodamine B (Conc. =

2 x 10·4M) in aqueous neutral medium was recorded in the region 450 to 650 nm. The dye soluti on exhibited a single well-defined absorption band at 554.5 nm.

Controlled potential electrolysis (cpe) of the dye solution was carried out in conjunction with UV -Vis spectrophotometric studies. For thi s, kinetics of decay (absorbance kinetics) was monitored by recording absorbance till the end of the reaction. The progress of electrolysis was monitored by recording spectral changes at different duration. The absorbance band at A I11<IX 554.5 nm systematically decreased with electro­lysis. Decrease in absorbance was recorded with the passage of time, using both steel foil (Figure 6) and Pt foil (Figure 7) as working electrodes. The kinetics of decolourisation varied with initial dye concentration. The resulting absorbance vs time plots were exponential in nature. Using linear log AI vs time plots. Kinetics was found to be first order both in the case of steel (k = 1.2 x 10.2) and platinum foil (k = 1.4 x 10.2

) working electrodes .

Chromatographic Study

To substantiate electrochemical, spectrophoto­metric and kinetic evidences regarding the number of the end products, TLC studies were carried out. It was observed that electro lysed solution exhibited three spots in (9: 1) acetone: water system.

1142 J SCI IND RES VOL 62 DECEMBER 2003

Table 2 - Controlled potential electrolysis resul ts of rhodamine B in aqueous neutral medium and at varying pH, scan rate = 100 mV Is

SI No. Medium Working Before (A)/after (B) electrode electro-chemical treatment

Di still ed Pl atinum foil

A water B

2 Distilled

Steel foil A

water B

3 3.8 Platinum foil A B

4 8.8 Platinum foil A B

5 10.5 Platinum foil A B

A = Before e lectrochemical treatment B = After electrochemical treatment

.0.4

0

° " . 1-0.4 0 . ~

r -0.1

I ~

2.0

- 1.2

, ~ 40.0 10.0 120.0 110.0

i 1.2 --n.o,.,---... • 0.' e

u

40.0 10.0 120.0 110.0 200.0 240.0

Figure 6 - Plot of absorbance vs time and log absorbance vs time at 554.5 nm (A. max) during electroreduction of rhodamine B at steel foil working electrode, conc. 2: x 1004M in distilled water

COD Results

In the present work, COD results were taken as one of the important parameter to judge the feasibility

Solution cone. -Ep,c -ip,c -Er a ip,a (M) (V) (flA) (V) (flA )

2.0 x 1004 0.833 10.68 0.872 3 l.0 0.320 28.98 0.858 69.63

2.0 x 1004 0 .833 0.872 3 l.0

10.68 0.883 48 .90

2.0 x 1004 0.772 11 9 .0 0.516 47.7 1 0.610 50.0 0 .5 16 40.0

2.0 x 1004 0.932 42.85 0 .577 4l.03

2.0 x 1004 0.352 15.09 0.786 44.93

.0.4

I 0

"

I " - G.4

r - 0.1 " 2.0

" " U -1.2

• ~ 1.2 t £0.0 10.0 120.0 110.0

! --n.o,.,---

I o.a

, , 40.0 10.0 120.0 110.0 200.0 24000 210.0

--n.o,.,--_ Figu re 7 - Plot of absorbance vs time and log absorbance vs

time at 554.5nm (A max) during electroreduct ioll o f rhodam ine B at platinum foi l working electrode, cone. 2 x 10

0

<1 M in di stilled water

of the electrochemical process for the treatment of coloured dye effluent. The initial COD value of the coloured dye solution is 2240 mg/L at the cone. of 2 x 10-4 which after controll ed potenti a l e lec trolys is

Yo,

JAIN el al.: ELECTROCHEMICAL DEGRADATION OF RHODAMINE B DYE 1143

y 0

II , C - OH

Y ~ ~

, ~ + (CH3CH2h N N(CH2CH3h}CI-

[AJ

1 o OH y ~ ~

'" I_ f - OH + , , + H N(CH3CH2h }CI-

r [C]

J 2e-, 2H+ - H2O

0- 0

'" 1 ~ - H Y

I " I

~ +

[OJ , H

(CH3CH2h N NH - (CH 3CH2h }CI-

m/z =105

j [E]

[Fj m/z = 58

[Gj

Scheme I - Reaction scheme

11 44 J SCI IND RES VOL 62 DECEMBER 2003

decreases to 440 mg/L. COD reduction of 80.35 per cent was observed. This could be ascribed to the e lectroreduction of the initial dye into decomposition products, leading to decrease In COD value (Scheme I) .

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