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Polarographic reduction of methylene blue in presence of clay minerals
SHORT
475
COMMUNICATIONS
REFERENCES
1. 2. 3. 4. 5. 6. 7.
R. B. Fischer and S. H. Simonsen, Anal. Chem., 1948,20, 1107. J. D. Hanna and 0. E. Hileman, Jr., Talanta, 1972, 19, 894. E. D. Salesin and L. Gordon, ibid., 1960, 5, 81. E. D. Salesin, E. W. Abrahamson and L. Gordon, ibzd., 1962,s 699. A. G. Walton, The Formation and Properties of Precipttates Intersczence, New York, 1967. H. Christopherson and E. B. Sandell, Anal. Chim. Acta, 1954, 10, 1. B. Jones, Analyst, 1929, 54, 582. Snnnnary-Spectrophotometric measurements of undissociated nickel dimethylglyoximate molecules in solution and electron-microscope observatzons of the precipitated particles have confirmed and extended previous information on the nucleation of nickel dimethylglyoximate precipitated from homogeneous solution. Supersaturated concentrations several hundred times the equilzbrium solubility may persist for as long as 2 hr. Nucleation occurs not all at one initial time but rather in multiple “bursts” spread out over several hours.
Talnnta.
Vol
22, pp 475-471
Pergamon
Press
1975 Prmted
m Great Brltam
POLAROGRAPHIC REDUCTION OF METHYLENE IN PRESENCE OF CLAY MINERALS
BLUE
(Received 5 September 1974. Accepted 17 October 1974)
Adsorption of the cationic dye Methylene Blue on clays has been studied by various workers.1-6 As the dye is known to give a well-defined polarographic wave in buffered media, the effect of clays on its polarographic reduction behaviour was investigated. This paper reports the possibility of estimating the clay fraction by a polarographzc method and the results obtained on the binding of the dye on clay particles. The method proposed here is simple, rapid, and needs only small samples.
EXPERIMENTAL
Reagents
Standard clays, bentonite, kaolinite and illne were obtained from Ward’s Natural Clay Corporation, New York. The Methylene Blue used was a B.D.H. product. Stock clay suspensions were prepared and converted into the hydrogen form by ion-exchange treatment (Amberlite IR-120) and the particle size was controlled by centrifugation. Apparatus
A Heyrovsky polarograph (Model LP 55 A) was operated manually in conjunction with a Pye Scalamp galvanometer (Model 7903/5). The capillary constant mzi3t”6 was 2.985; the drop time was 3.4 set (open circuit) and nitrogen was used for deaeration of solutions. All measurements were made at 30 + 0.01”. So far no suitable vessel has been developed’ which could be used for heterogeneous systems, and the vessel used by Beckmann* in gas analysis was therefore employed in these studies. In this cell the stream of gas and the circulating solution ensure uniform mixing of the suspension, pumping the solution at constant speed past the electrode, and maintaining of an inert atmosphere. It is worth mentioning that the vessels used for homogeneous kinetic investigations are useless for such systems as they permit investzgations of only static solutions. Preparation of solutzons
The requisite amount of dye (effectzve concentration 1 x 10m3and 8 x lO-‘M in the case of bentonite and 8 x lo-‘M in the case of kaolinite and illite) was taken in tubes along with different amounts of the clays and the total volume made up to 20 ml. The pH was adjusted to 2.9,4.9 and 9.2 (checked by pH-meter) in the case of bentonite-dye suspensions and 2.9 in the case of kaolinite-dye and illite-dye suspensions.
RESULTS
AND
DISCUSSION
Polarograms of Methylene Blue (1 x 10w3M) in the presence of different amounts of bentonite at pH 2.9, 4.9 and 9.2 are shown in Fig. 1. Similar curves are obtained at a concentration of 8 x lo- 5M and also for the polarograms of the dye in presence of varying amounts of kaolinite and illite at pH 29. The I?,,, values of the dye were found to be -002, -0.28 and -0.32 V at pH 2.9, 4.9 and 9.2 respectively, in good agreement with the half-wave potentials reported by Clark,’ who also found that the E,,, of the normal wave corresponds closely to the oxidation potential of the thermodynamically reversible Methylene Blue system.
476
SHORT COMMUNICATIONS
8(
I
I
I
I
I
I
(0) ;; 6( a al 6 : 5
(0 0)
4(
0 i $
2(
k :
Potentlol
(I Dv=O.l
Volt)--
801
Potent101 (I DIV=O
,
,
,
,
,
Potent101 (I Dlv=O
,
,
,
I Volt)-
,
I Volt)-
Fig. 1. Polarograms of Methylene Blue (1 x IO-‘M) in presence of various amounts of bentonite (g). (a) pH 2.9, (6) pH 49, (c) pH 9.2. All curves start at to.1 V applied potential.
A prewave with E,,, = -0.01 V is realized at pH 4.9 (Fig. lb). The normal reduction wave disappears below the concentration 6 x 10m5M and therefore a concentration higher than this was chosen for subsequent studies. The striking features of the reduction of the various clay-dye suspensions are as follows. (i) The diffusion current of the pure dye is considerably reduced in presence of clays. The effect is, however, most pronounced in the case of bentonite, as compared to the other two minerals. (ii) The decrease in the diffusion current increases with gradual increase in the amount of mineral added. (iii) The E,,, of the dye does not change. A decrease of 1.36 PA, in the diffusion current is observed on adding 40 mg of bentonite whereas reductions of 0.45 and 0.22 fi are obtained by adding the same amount of illite and kaolinite under identical conditions for the dye solution. Polarograms at pH 4.9 (Fig. lb) show that low amounts of bentonite added decrease the height of the normal reduction wave without causing any effect on the prewave. Higher amounts of this material, however, shift the half-wave potential of the prewave towards the more positive side, along with the decrease in the height of the normal reduction wave. A linear relationship is found between the decrease in wave height (id,-ld) and the amount of mineral present. It is thus possible to calculate the amount of free dye (from the values of idid,) as well as the amount of dye bound to the clay particles. The amount of dye bound to bentonite at different concentrations and pH are given in Tables 1 and 2. It is observed that the amount of dye bound to bentonite is abnormally high if the solution is as concentrated as 1 x 10W3j$4. Factors such as aggregation of dye molecules at such high concentrations, and multiple adsorption, account for this behaviour. As suggested by Bergmann and O’Konski lo there is a greater probability of the binding of aggregated species than monomers on the crystal surface. At lower concentration of the dye (8 x lo- 5?vf) and the dyexlay ratio mentioned in Table 2, the binding is small, being of the same order as required for exchange adsorption. Thus when the dye concentration is initially low there is no physical adsorption and even a single polarographic measurement can give an estimate of exchange capacity. The amount of bound dye 1s also found to increase with increase in pH. This can be explamed by assuming that the edges acquire a negative charge” at higher pH (through broken Si-0 and Al-O bonds) with the result that more of the cationic dye is adsorbed.
417
SHORTCOMMUNICATIONS
Table 1. Distribution of Methylene Blue (initial concentration
PH
Amount of bentonite added, g
2.9
0.07 0.10 0.24 0.26 0.28 0.30 0.08 @lo 0.18 0.20 0.22 0.24
9.2
1 x 10e3M)
Concentration of free dye, 10e3M
Concentration of bound dye. 10-3M
0.83 0.78 047 040 0.30 0.28 0.71 0.66 0.47 0.45 0.38 0.32
0.17 0.22 0.53 0.60 0.70 0.72 0.29 0.34 0.53 0.55 @62 0.58
Table 2. Distribution of Methylene Blue at pH 2.9 (initial concentration 8 x lo-‘M) Amount of bentonite added. g
Concentration of free dye, 10e5M
Concentration of bound dye, lo- ‘M
0.12 0.16 0.40 0.45 0.50 0.55
6.80 6.24 3.84 3.36 2.88 240
1.20 1.76 4.16 4.64 5.12 ,5.60
Various mixtures of bentonite, lllite or kaolinite with a non-clay material were prepared. These samples had different cation-exchange capacities depending on the amount of non-clay material present in them. Polarograms of Methylene Blue (8 x 10e5M, pH 2.9) in the presence of these samples were taken and a linear relationship was found between the mineral content of these samples and the decrease in the diffusion current (&-id). This goes to show that the reduction of Methylene Blue in the presence of various clays or soil samples can possibly be used in estimating the clay content and its exchange capacity, and in the identification of various minerals. Further work in this direction is in progress. Acknowledgement-Thanks are due to Professor W. U. Malik, Head of the Chemistry Department, for the facillties to carry out this work and to UGC India for a Junior Research Fellowship to P.R. Chemwry Department University of Roorkee Roorkee, V. P., India
S. K. SRIVASTAVA PUSHPATIRAZDAN
REFERENCES 1. S. B. Hendricks and L. T. Alexander, J. Am. Sot. Agron.,
2. 3. 4. 5. 6. 7.
8. 9. 10. 11.
1940,32,455. V. L. Bossazza, Am. Min., 1944,29,23S. P. T. Haing and G. W. Brindley, Clays and Clay Minerals, 1970, 18, 203. P. E. Fairbairn and R. H. S. Robertson. Clay Min. Bull., 1957.3, 129. W. S. Ramchandran and K. P. Kacker, Am. Mzn., 1962,41, 165. W. Worrall. Trans. Brit. Ceram. Sot., 1958.51, 210. Z. P. Zagerskl, Aduances in Polarography. Interscience. New York, 1960. P. Beckmann, Chem. Ind. (London), 1948,9, 791. W. M. Clark, Pub. Health Reports, 1925.40, 1155. K. Bergmann and C. T. O’Konskl., J. Phys. Chem., 1963,67, 2169. Van Olphen, Clay Colloid Chemistry. p. 90. Interscience. New York, 1963. Summary-Clay-Methylene Blue suspensions have been examined polarographically. The degree of binding of the dye on the clay particles has been calculated. The possibility of using the data in estimating the clay content of a sample and identifying the mineral is suggested.
475
COMMUNICATIONS
REFERENCES
1. 2. 3. 4. 5. 6. 7.
R. B. Fischer and S. H. Simonsen, Anal. Chem., 1948,20, 1107. J. D. Hanna and 0. E. Hileman, Jr., Talanta, 1972, 19, 894. E. D. Salesin and L. Gordon, ibid., 1960, 5, 81. E. D. Salesin, E. W. Abrahamson and L. Gordon, ibzd., 1962,s 699. A. G. Walton, The Formation and Properties of Precipttates Intersczence, New York, 1967. H. Christopherson and E. B. Sandell, Anal. Chim. Acta, 1954, 10, 1. B. Jones, Analyst, 1929, 54, 582. Snnnnary-Spectrophotometric measurements of undissociated nickel dimethylglyoximate molecules in solution and electron-microscope observatzons of the precipitated particles have confirmed and extended previous information on the nucleation of nickel dimethylglyoximate precipitated from homogeneous solution. Supersaturated concentrations several hundred times the equilzbrium solubility may persist for as long as 2 hr. Nucleation occurs not all at one initial time but rather in multiple “bursts” spread out over several hours.
Talnnta.
Vol
22, pp 475-471
Pergamon
Press
1975 Prmted
m Great Brltam
POLAROGRAPHIC REDUCTION OF METHYLENE IN PRESENCE OF CLAY MINERALS
BLUE
(Received 5 September 1974. Accepted 17 October 1974)
Adsorption of the cationic dye Methylene Blue on clays has been studied by various workers.1-6 As the dye is known to give a well-defined polarographic wave in buffered media, the effect of clays on its polarographic reduction behaviour was investigated. This paper reports the possibility of estimating the clay fraction by a polarographzc method and the results obtained on the binding of the dye on clay particles. The method proposed here is simple, rapid, and needs only small samples.
EXPERIMENTAL
Reagents
Standard clays, bentonite, kaolinite and illne were obtained from Ward’s Natural Clay Corporation, New York. The Methylene Blue used was a B.D.H. product. Stock clay suspensions were prepared and converted into the hydrogen form by ion-exchange treatment (Amberlite IR-120) and the particle size was controlled by centrifugation. Apparatus
A Heyrovsky polarograph (Model LP 55 A) was operated manually in conjunction with a Pye Scalamp galvanometer (Model 7903/5). The capillary constant mzi3t”6 was 2.985; the drop time was 3.4 set (open circuit) and nitrogen was used for deaeration of solutions. All measurements were made at 30 + 0.01”. So far no suitable vessel has been developed’ which could be used for heterogeneous systems, and the vessel used by Beckmann* in gas analysis was therefore employed in these studies. In this cell the stream of gas and the circulating solution ensure uniform mixing of the suspension, pumping the solution at constant speed past the electrode, and maintaining of an inert atmosphere. It is worth mentioning that the vessels used for homogeneous kinetic investigations are useless for such systems as they permit investzgations of only static solutions. Preparation of solutzons
The requisite amount of dye (effectzve concentration 1 x 10m3and 8 x lO-‘M in the case of bentonite and 8 x lo-‘M in the case of kaolinite and illite) was taken in tubes along with different amounts of the clays and the total volume made up to 20 ml. The pH was adjusted to 2.9,4.9 and 9.2 (checked by pH-meter) in the case of bentonite-dye suspensions and 2.9 in the case of kaolinite-dye and illite-dye suspensions.
RESULTS
AND
DISCUSSION
Polarograms of Methylene Blue (1 x 10w3M) in the presence of different amounts of bentonite at pH 2.9, 4.9 and 9.2 are shown in Fig. 1. Similar curves are obtained at a concentration of 8 x lo- 5M and also for the polarograms of the dye in presence of varying amounts of kaolinite and illite at pH 29. The I?,,, values of the dye were found to be -002, -0.28 and -0.32 V at pH 2.9, 4.9 and 9.2 respectively, in good agreement with the half-wave potentials reported by Clark,’ who also found that the E,,, of the normal wave corresponds closely to the oxidation potential of the thermodynamically reversible Methylene Blue system.
476
SHORT COMMUNICATIONS
8(
I
I
I
I
I
I
(0) ;; 6( a al 6 : 5
(0 0)
4(
0 i $
2(
k :
Potentlol
(I Dv=O.l
Volt)--
801
Potent101 (I DIV=O
,
,
,
,
,
Potent101 (I Dlv=O
,
,
,
I Volt)-
,
I Volt)-
Fig. 1. Polarograms of Methylene Blue (1 x IO-‘M) in presence of various amounts of bentonite (g). (a) pH 2.9, (6) pH 49, (c) pH 9.2. All curves start at to.1 V applied potential.
A prewave with E,,, = -0.01 V is realized at pH 4.9 (Fig. lb). The normal reduction wave disappears below the concentration 6 x 10m5M and therefore a concentration higher than this was chosen for subsequent studies. The striking features of the reduction of the various clay-dye suspensions are as follows. (i) The diffusion current of the pure dye is considerably reduced in presence of clays. The effect is, however, most pronounced in the case of bentonite, as compared to the other two minerals. (ii) The decrease in the diffusion current increases with gradual increase in the amount of mineral added. (iii) The E,,, of the dye does not change. A decrease of 1.36 PA, in the diffusion current is observed on adding 40 mg of bentonite whereas reductions of 0.45 and 0.22 fi are obtained by adding the same amount of illite and kaolinite under identical conditions for the dye solution. Polarograms at pH 4.9 (Fig. lb) show that low amounts of bentonite added decrease the height of the normal reduction wave without causing any effect on the prewave. Higher amounts of this material, however, shift the half-wave potential of the prewave towards the more positive side, along with the decrease in the height of the normal reduction wave. A linear relationship is found between the decrease in wave height (id,-ld) and the amount of mineral present. It is thus possible to calculate the amount of free dye (from the values of idid,) as well as the amount of dye bound to the clay particles. The amount of dye bound to bentonite at different concentrations and pH are given in Tables 1 and 2. It is observed that the amount of dye bound to bentonite is abnormally high if the solution is as concentrated as 1 x 10W3j$4. Factors such as aggregation of dye molecules at such high concentrations, and multiple adsorption, account for this behaviour. As suggested by Bergmann and O’Konski lo there is a greater probability of the binding of aggregated species than monomers on the crystal surface. At lower concentration of the dye (8 x lo- 5?vf) and the dyexlay ratio mentioned in Table 2, the binding is small, being of the same order as required for exchange adsorption. Thus when the dye concentration is initially low there is no physical adsorption and even a single polarographic measurement can give an estimate of exchange capacity. The amount of bound dye 1s also found to increase with increase in pH. This can be explamed by assuming that the edges acquire a negative charge” at higher pH (through broken Si-0 and Al-O bonds) with the result that more of the cationic dye is adsorbed.
417
SHORTCOMMUNICATIONS
Table 1. Distribution of Methylene Blue (initial concentration
PH
Amount of bentonite added, g
2.9
0.07 0.10 0.24 0.26 0.28 0.30 0.08 @lo 0.18 0.20 0.22 0.24
9.2
1 x 10e3M)
Concentration of free dye, 10e3M
Concentration of bound dye. 10-3M
0.83 0.78 047 040 0.30 0.28 0.71 0.66 0.47 0.45 0.38 0.32
0.17 0.22 0.53 0.60 0.70 0.72 0.29 0.34 0.53 0.55 @62 0.58
Table 2. Distribution of Methylene Blue at pH 2.9 (initial concentration 8 x lo-‘M) Amount of bentonite added. g
Concentration of free dye, 10e5M
Concentration of bound dye, lo- ‘M
0.12 0.16 0.40 0.45 0.50 0.55
6.80 6.24 3.84 3.36 2.88 240
1.20 1.76 4.16 4.64 5.12 ,5.60
Various mixtures of bentonite, lllite or kaolinite with a non-clay material were prepared. These samples had different cation-exchange capacities depending on the amount of non-clay material present in them. Polarograms of Methylene Blue (8 x 10e5M, pH 2.9) in the presence of these samples were taken and a linear relationship was found between the mineral content of these samples and the decrease in the diffusion current (&-id). This goes to show that the reduction of Methylene Blue in the presence of various clays or soil samples can possibly be used in estimating the clay content and its exchange capacity, and in the identification of various minerals. Further work in this direction is in progress. Acknowledgement-Thanks are due to Professor W. U. Malik, Head of the Chemistry Department, for the facillties to carry out this work and to UGC India for a Junior Research Fellowship to P.R. Chemwry Department University of Roorkee Roorkee, V. P., India
S. K. SRIVASTAVA PUSHPATIRAZDAN
REFERENCES 1. S. B. Hendricks and L. T. Alexander, J. Am. Sot. Agron.,
2. 3. 4. 5. 6. 7.
8. 9. 10. 11.
1940,32,455. V. L. Bossazza, Am. Min., 1944,29,23S. P. T. Haing and G. W. Brindley, Clays and Clay Minerals, 1970, 18, 203. P. E. Fairbairn and R. H. S. Robertson. Clay Min. Bull., 1957.3, 129. W. S. Ramchandran and K. P. Kacker, Am. Mzn., 1962,41, 165. W. Worrall. Trans. Brit. Ceram. Sot., 1958.51, 210. Z. P. Zagerskl, Aduances in Polarography. Interscience. New York, 1960. P. Beckmann, Chem. Ind. (London), 1948,9, 791. W. M. Clark, Pub. Health Reports, 1925.40, 1155. K. Bergmann and C. T. O’Konskl., J. Phys. Chem., 1963,67, 2169. Van Olphen, Clay Colloid Chemistry. p. 90. Interscience. New York, 1963. Summary-Clay-Methylene Blue suspensions have been examined polarographically. The degree of binding of the dye on the clay particles has been calculated. The possibility of using the data in estimating the clay content of a sample and identifying the mineral is suggested.