Study of the Mechanism of the Influence of Surfactants on the Kinetics of Copper Ionization Discharge
Abstract Generated abstract
This study examines how the molecular surfactants n-amyl alcohol and camphor influence the kinetics of copper discharge and ionization in sulfate electrolyte. Using polarography with linearly varying potential on dropping mercury, stationary mercury drop, and solid copper electrodes, the authors measured cathodic and anodic currents, peak potentials, half-wave potentials, and electrocapillary behavior in 1 M sodium sulfate containing copper sulfate and varying surfactant concentrations. Increasing surfactant concentration reduced the copper limiting or peak currents, while peak potentials, half-wave potentials, and the slope characteristic of a reversible polarographic wave remained essentially unchanged. The results suggest that these surfactants do not appreciably alter the reversibility or electrochemical discharge step, but instead affect the delivery or removal of copper ions at the electrode interface.
Full Text
STUDY OF THE MECHANISM OF THE EFFECT OF SURFACTANTS ON THE KINETICS OF COPPER DISCHARGE–IONIZATION
V. E. GORODOVYKH, O. S. STEPANOVA, N. G. BROSHNIKOVA
(Presented by the scientific-methodological seminar of the CTF)
There is no consensus in the published literature on the mechanism by which additives of surfactants of organic origin affect electrode processes. Most researchers believe that the influence of organic substances on electrode processes is in many cases associated with their adsorption at the electrode–electrolyte-solution interface. But the effect of this film of adsorbed organic substance may be due to different causes [1].
First, it may be due to the slowed penetration of ions through the adsorbed film of the surfactant to the electrode surface [2]; second, to a slowed discharge–ionization process [3].
The aim of the present work is to study the mechanism of the influence of surfactants on the kinetics of copper discharge–ionization by the polarographic method.
A. G. Stromberg [3] proposes using the polarographic method to study the mechanism of the influence of surfactants (s.a.) on electrode processes. Surfactants may affect both the stage of delivery of the substance to the electrode and the discharge–ionization stage. According to Stromberg [3], if s.a. affect the stage of delivery of the substance to the electrode, then the limiting current should decrease and remain constant at constant filling \((\Theta)\). At desorption potentials, the waves should abruptly reach the initial value observed without surfactants. The half-wave potentials should remain constant at all values.
If, however, s.a. affect the electrochemical stage, i.e., the discharge–ionization stage, then the irreversibility of the electrode process increases and the shape of the anodic–cathodic wave changes. The value of the limiting current does not change, while the half-wave potentials shift. The retarding effect of s.a. on the kinetics of discharge–ionization should manifest itself through a decrease in the exchange current under the influence of s.a.
Experimental Method
To study the effect of s.a. on the kinetics of copper discharge–ionization, the method of polarography with a linearly varying potential was used. The studies were carried out successively using three electrodes: a dropping mercury electrode, \(\tau = 2.3\ \text{s}\); a stationary mercury drop, \(r = 0.04\ \text{cm}\); and a solid copper electrode, \(l = 3\ \text{mm}\), \(d = 0.5\ \text{mm}\). The studies were performed on an OH-101 polarograph in an electrolytic cell with insertable quartz beakers.
Oxygen was carefully removed from the solution under study with purified nitrogen.
The background solution was 1 M Na\(_2\)SO\(_4\). Standard copper solutions were prepared from “ch.p.” grade CuSO\(_4\) salt. Camphor and n-amyl alcohol were chosen as surfactants. The choice of these surfactants was determined by the fact that both camphor and n-amyl alcohol belong to surfactants of the molecular type and, as follows from literature data [1–3], exert a strong influence on electrode processes. In addition, n-amyl alcohol and camphor are reduced on a mercury electrode at very negative potentials and, in the range of potentials studied by us (from \(+0.1\) V to \(-0.9\) V), do not participate in the electrode process. The experiments were carried out in a solution of the following composition: \(n \cdot 10^{-3}\) M CuSO\(_4\); 1 M Na\(_2\)SO\(_4\); \(x\) (in fractions of saturation) surfactant at \(t = 20\)–22°C. A mercury sulfate electrode served as the reference electrode.
When working with a stationary electrode, the accumulation potential was \(-0.9\) V.
The electrolysis time was \(\tau = 2\) min.
Results Obtained and Their Discussion
The dependence of the cathodic and anodic currents and of the potentials of the copper peaks and half-waves on the concentration of n-amyl alcohol and camphor in 1 M Na\(_2\)SO\(_4\) solution was studied.
The data obtained are presented in Tables 1 and 2 and in Fig. 1. As can be seen, the cathodic and anodic copper current decreases with increasing concentration
Table 1
Effect of n-amyl alcohol and camphor on the current and potential of the cathodic copper peak on a stationary copper electrode
\((C_{\mathrm{Cu}^{2+}} = 1 \cdot 10^{-4}\ \mathrm{mol/l})\)
| Addition H—C\(_5\)H\(_{11}\)OH, mol/l | \(I\), μA | \(-\varphi_{\mathrm{p}}\), V | Camphor addition, mol/l | \(I\), μA | \(-\varphi_{\mathrm{p}}\), V |
|---|---|---|---|---|---|
| — | 72 | 0.55 | — | 70 | 0.55 |
| \(2.7 \cdot 10^{-2}\) | 60 | 0.55 | \(1.12 \cdot 10^{-3}\) | 65 | 0.55 |
| \(5.4 \cdot 10^{-2}\) | 58 | 0.55 | \(2.24 \cdot 10^{-3}\) | 59 | 0.55 |
| \(8.1 \cdot 10^{-2}\) | 56 | 0.55 | \(3.37 \cdot 10^{-3}\) | 48 | 0.55 |
| \(10.8 \cdot 10^{-2}\) | 52 | 0.55 | \(4.48 \cdot 10^{-3}\) | 40 | — |
| \(16.2 \cdot 10^{-2}\) | 52 | 0.55 | \(5.6 \cdot 10^{-3}\) | 32 | — |
| \(21.6 \cdot 10^{-2}\) | 50 | 0.55 | |||
| \(27 \cdot 10^{-2}\) | 50 | 0.55 |
Table 2
Effect of n-amyl alcohol and camphor on the current and potential of the anodic copper peak on a stationary mercury drop
\((C_{\mathrm{Cu}^{2+}} = 1 \cdot 10^{-4}\ \mathrm{mol/l};\ \tau = 2\ \mathrm{min},\ \varphi_{\mathrm{e}} = -0.9\ \mathrm{V})\)
| Addition H—C\(_5\)H\(_{11}\)OH, mol/l | \(I\), μA | \(-\varphi_{\mathrm{p}}\), V | Camphor addition, mol/l | \(I\), μA | \(-\varphi_{\mathrm{p}}\), V |
|---|---|---|---|---|---|
| — | 5.2 | 0.34 | — | 1.82 | 0.34 |
| \(0.54 \cdot 10^{-2}\) | 4.48 | 0.34 | \(1.12 \cdot 10^{-4}\) | 1.65 | 0.34 |
| \(1.08 \cdot 10^{-2}\) | 4.02 | 0.34 | \(2.24 \cdot 10^{-4}\) | 1.38 | 0.34 |
| \(1.62 \cdot 10^{-2}\) | 3.78 | 0.34 | \(3.36 \cdot 10^{-4}\) | 1.32 | 0.34 |
| \(2.16 \cdot 10^{-2}\) | 3.30 | 0.34 | \(4.48 \cdot 10^{-4}\) | 1.32 | 0.34 |
| \(2.70 \cdot 10^{-2}\) | 3.20 | 0.34 | \(5.6 \cdot 10^{-4}\) | 1.32 | 0.34 |
| \(3.34 \cdot 10^{-2}\) | 3.20 | 0.34 | |||
| \(3.38 \cdot 10^{-2}\) | 3.00 | 0.34 |
Fig. 1. Effect of n-amyl alcohol and camphor on the limiting current and half-wave potential of copper. ○ — addition of amyl alcohol; △ — addition of camphor
surfactants in the electrolyte, while the peak potentials and half-wave potentials remain constant.
The experimental data obtained on a dropping mercury electrode were processed according to the equation of the reversible polarographic wave
\[ \varphi=\varphi_{1/2}-\frac{RT}{zF}\ln\frac{i}{I-i}, \qquad b=\frac{0.059}{2}. \]
From the graphical dependence \(\lg \frac{i}{I-i}\)—\(\varphi\), the slope of the straight line was determined
\[ \left(b=\frac{2.3\cdot RT}{zF}=\frac{0.059}{z}=\sim 0.03,\ \text{for } z=2\right). \]
The value of the angular coefficient “\(b\)” in the equation of the reversible polarographic wave does not change for copper in a pure solution and in the presence of surfactants, which makes it possible to conclude that surfactants do not affect the reversibility of the electrode process.
To establish the desorption potentials of n-amyl alcohol and camphor, electrocapillary curves were recorded on mercury in a solution of \(1MNa_2SO_4\) (Fig. 2).
Fig. 2. Electrocapillary curves
1 — \(1M\ Na_2SO_4\);
2 — \(1M\ Na_2SO_4\); \(5.6\cdot10^{-3}\ M\) camphor;
3 — \(1M\ Na_2SO_4\) and \(0.27\ M\) n-amyl alcohol
On the basis of the data obtained and theoretical assumptions, it may be supposed that n-amyl alcohol and camphor, during the discharge–ionization of copper, affect the stage of delivery or removal of copper ions.
REFERENCES
- B. N. Kabanov. Electrochemistry of Metals and Adsorption. Khimiya Publishing House, Moscow, 1966.
- M. A. Loshkarev, A. A. Kryukova. Journal of Physical Chemistry, 23, 209, 1949.
- M. A. Loshkarev, A. A. Kryukova. Journal of Physical Chemistry, 23, 221, 1949.
- M. A. Loshkarev, A. A. Kryukova. Journal of Physical Chemistry, 26, 731, 1952.
- A. G. Stromberg, L. S. Zagainova. Journal of Physical Chemistry, 31, 1042, 1957.
- A. G. Stromberg. Report at the All-Union Electrochemical Conference, Dnepropetrovsk, 1967.