Optical Studies on Extraction of Some Transition Metal Cations Through Liquid Membrane Containing 1-Phenylazonaphth-2-Ol as Ionophore

Introduction

Dyes¹ have been extensively used in such as in ink-jet printing, imagining and in electronics. These required functional dyes which are able to form organized supramolecular assemblies², the properties of which can be controlled as a function of self-assembly process. Supramolecular control dye arrangement is important for providing the improved performance of existing devices and to create new dye-based materials with tunable optical and electronic properties. Now a dyes considerable efforts are being made towards the modification of the structure of organic dyes in the direction of the self-organization. These studies have generated a wealth of knowledge inthe designing of variety of materials and complexes with intriguing properties.

The field of supramolecular chemistry has brought to light of new binding sites with improved selectivity. Logically, the idea of coupling these ionophores to chromophores or fluorophores emerged some years later, leading to the so-called chromoionophore and fluoroionophore³.The chromo-and fluoro-ionophores form a particularly interesting class of probes since they can combine recognition properties with optical transduction, i.e. changing colour or fluorescence⁴.

Experimental

Extraction Studies In The Presence of Artificial Visible Light Source

To study the special effect of artificial light radiation on the extraction processes, theexperiments have been carried out in the following two conditions:

Extraction in presence of artificial visible light source (100W tungsten filament).

In total darkness.

These studies have been performed to assess the effect of light on the extraction of metal ions in the presence of visible light source.

In this method 10 mL of aqueous metal salt solution was vigorously stirred with 10 mL of ionophore solution in organic solvent (chloroform) in a small beaker. The solution was magnetically stirred using Teflon coated capsule. The beaker was covered by the paraffin to minimize the rate of evaporation. The photoirradiation was carried out using visible light source (100W tungsten filament) and intensity of light were measured by ms6610 Lux meter.  This process was continued up to 4 hours. After well stirring, the mixture was allowed to stand for 5 minutes for the separation of two phases. The depleted aqueous phase was removed and the metal content was analyzed by volumetric method. The amount of metal cation extracted by ionophore was measured by their difference in aqueous phase before and after extraction (tables- 1 to 4).

The extraction experiments were also carried out in complete darkness (absence of light).

Results and Discussion

Extraction Studies in the Presence of Artificial Visible Light Source

To study the effect of light radiation on extraction process the experiments have been carriedout at two different concentrations of ionophore (1.0 × 10^-3M and 1.0 × 10^-4M), in the following conditions.

Extraction in the presences of artificial visible light source (100 W tungsten filament)

In the natural light

In total darkness

The results of extraction of metal cations (Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with ionophore1-phenylazonaphth-2-olare listed in the tables (1 to 4).

On comparing the results of extraction of metal cations (Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with ionophore1-phenylazonaphth-2-olin the presence of artificial light source (100W) and natural light it is observed that this ionophore exhibit the photo responsive properties.

The experimentswere carried out at two different light intensities (126×10 Lux and 73×10 Lux) as measured by Lux meter⁵.The results indicate that 73×10 Lux is suitable intensity of light for extraction of metal cations with ionophore1-phenylazonaphth-2-ol shows higher extraction capacity at126×10 Lux.

The observed trend of extraction of selected metal cations (Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) by ionophore1-phenylazonaphth-2-ol in the presence of artificial light source and in natural light is found different.

The observed trend of extraction of selected metal cations by ionophores1-phenylazonaphth-2-ol in the presence of artificial light source (100W tungsten filament) is Zn²⁺>Ni²⁺>Cu²⁺while Co²⁺does not shows extraction in the presence of light source. The observed trend of extraction of selected metal cations by ionophore 1-phenylazonaphth-2-ol in the natural light is Co²⁺> Ni²⁺>Cu²⁺ while Zn²⁺does not shows extraction in the natural light with ionophore1-phenylazonaphth-2-ol (table- 2).

On the basis of results it can be concluded that the effect of light radiation on extraction process are opposite from the results obtained by the extraction process in the natural light source. The presence of chromophoric mono azo (-N=N-) and diazo moiety in the ionophore  1-phenylazonaphth-2-ol attributed for the same.

The trans– isomer of azobenzene can be photomerized to the cis-isomer, which can be converted thermally back to the trans form again.¹¹The isomerization is completely reversible, free from side reactions⁶. It can be concluded that in the presence of artificial light source these ionophore (1-phenylazonaphth-2-ol) form cis configuration and shows more selectivity towards the Zn²⁺ ions

Figure- 5.1: TransandCisgeometric isomers of azobenzene   Click here to View figure

 

The extraction experiments have also been carried out in the complete darkness. Furthermore, no any progress in extraction process is observed. These results also support that ionophore is photo-responsive in nature^7s.

Optical Effect on Extraction

Table 1: Amount of metal ion extracted after 4 hours with ionophore (concentration1.0 ×10^-3 M) in the absence and presence of artificial light source (100 W) at two different intensities in chloroform.

Metal Salts	Amount of cation extracted (in gm/ L)by ionophore	Amount of cation extracted (in gm/ L) by ionophore at 126×10 Lux	Amount of cation extracted (in gm/L) by ionophores at 73×10 Lux
	(absence of light source)	(Presence of light source) 100 W bulb
Co(NO3)2	2.9103	–	–
NiSO4	2.8085	–	8.4255
Cu(NO3)2	4.8320	4.8320	4.8320
ZnSO4	–	14.3770	20.1278

Concentration of metal salt = 1.0 × 10^-1 M,    Concentration of ionophore =1.0 × 10^-3 M

Intensity of light = 126 × 10 Lux,   Intensity of light = 73 × 10 Lux

Table 2: Comparative amount of metal ion extracted after 4 hours with ionophore (conc. 1.0 × 10^-4 M) in the absence and presence of artificial light source (100 W) at two different intensities in chloroform.

Metal Salts	Amount of cation extracted (in gm/ L) by ionophore	Amount of cation extracted (in gm/ L) by ionophore at 126×10 Lux	Amount of cation extracted (in gm/L) by ionophores at 73×10 Lux
	(absence of light source)	(Presence of light source) 100 W bulb
Co(NO3)2	17.4618	–	–
NiSO4	16.8510	–	5.6170
Cu(NO3)2	14.4960	4.8320	2.4160
ZnSO4	–	14.3770	17.2524

Concentration of metal salt = 1.0 × 10^-1 M,    Concentration of ionophore = 1.0 × 10^-4 M

Intensity of light = 126 × 10 Lux,        Intensity of light = 73 ×10 Lux

Table 3:  Comparative amount of metal ion extracted after 4 hours with ionophore(conc. 1.0 × 10^-3 M) in the absence and presence of artificial light source (100 W bulb) at two different intensities in chloroform.

Metal Salts	Amount of cation extracted (in gm/ L) by ionophore	Amount of cation extracted (in gm/ L) by ionophore at 126 × 10 Lux	Amount of cation extracted (in gm/L) by ionophore at 73 × 10 Lux
	(absence of light source)	(Presence of light source) 100 W bulb
Co(NO3)2	1.1641	–	0.2913
NiSO4	–	3.3702	1.1234
Cu(NO3)2	4.8320	2.4160	0.7248
ZnSO4	1.7252	3.4504	1.1501

Concentration of metal salt = 1.0 × 10^-2 M,    Concentration of ionophore  = 1.0 × 10^-3 M

Intensity of light = 126 × 10 Lux,      Intensity of light = 73 × 10 Lux

Table 4: Comparative amount of metal ion extracted after 4 hours with ionophore(conc. 1.0 × 10^-4 M) in the absence and presence of artificial light source (100 W bulb) at two different intensities in chloroform.

Metal Salts	Amount of cation extracted (in gm/ L) by ionophore	Amount of cation extracted (in gm/ L) by ionophore at 126 × 10 Lux	Amount of cation extracted (in gm/L) by ionophores at 73 × 10 Lux
	(absence of light source)	(Presence of light source) 100 W bulb
Co(NO3)2	2.9103	0.2910	–
NiSO4	–	4.2127	2.8085
Cu(NO3)2	–	2.4160	2.1744
ZnSO4	–	4.3131	2.5878

Concentration of metal salt = 1.0 × 10^-2 M,    Concentration of ionophore = 1.0 × 10^-4 M

Intensity of light = 126  ×  10 Lux,    Intensity of light = 73  ×  10 Lux

 

Conclusion

Ionophoreis better extractant for Co²⁺   and Cu²⁺   ions in the natural light.The selected ionophore shows better extraction selectivity for Zn²⁺ in the presence of artificial light source only.

On comparing the results of extraction of metal cations (Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with ionophore1-phenylazonaphth-2-ol in the presence of artificial light source (100W tungsten filament) and natural light it is observed that these ionophores have photo responsive properties.

The extraction experiments have also been carried out in the complete darkness, but no progress in the extraction is observed.

Acknowledgements

The authors are thankful to Dr. Ruplekha Vyas, Professor and Head, Govt. Auto. Holkar Science College, Indore (M.P.), for providing laboratory facilities.

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