The experiment was performed by taking different concentrations of IC dye solution (E-Merck) varying from [0.5 × 10⁻⁴ to 2.0 × 10⁻⁴ M] with constant current (4.6 mA). The change in concentration of the Indigocarmine was recorded by a change in % transmittance using a spectrophotometer. A plot of log%T (percentage transmittance of light) versus time was linear. Up to 60% of the reaction indicating degradation of IC follows first order kinetics. The rate constant values are given in Table 1 . The reaction rate decreased with the increase in [IC]. This is due to the accumulation of Indigocarmine molecules at the outermost layer of graphite anode as a result of the graphite electrode. Which decreases the concentration of OH free radicals. The pH value before and after the electrolysis remain constant. The COD for Indigocarmine solution before and after electrolysis was measured ( Table 1 , Figure 2 and Figure 3 ).

Applied Current = 4.6 mA, Temperature = 303 K, λ_max = 610 nm.

To investigate the impact of applied current, the experiment was conducted using four distinct current density ranging from 3.6 mA to 6.6 mA, while maintaining a constant 0.0001M Indigocarmine dye concentration. Notably, as the applied current increased, it observed a corresponding increase in the reaction rate. This phenomenon can be attributed to the higher current levels leading to elevated concentrations of oxidizing intermediates and OH free radicals, ultimately resulting in an accelerated degradation rate. The corresponding rate constant values can be found in Table 2 . Additionally, they conducted COD measurements for the Indigocarmine dye solution in various applied currents, both before and after degradation, with the results presented in Table 2 and Figure 4 .

[IC] = 1 × 10⁻⁴ M, Temperature = 303 K, λ_max = 610 nm.

To investigate the effect of temperature, the experiments were conducted at three distinct temperatures. As the temperature increased, it is observed that the rate of the reaction increased. It is observed that the rate of degradation of dye is not very significant at lower temperatures, however the reaction is more significantly influenced at higher temperatures. We determined the rate constant for degradation and COD values for both before and after degradation for the indigocarmine dye solution and these results are presented in Table 3 and Figure 5 . The increase in temperature can be attributed to an enhanced diffusion rate, potentially leading to a higher degradation rate. Thermodynamic parameters ΔH^#, ΔS^#, ΔG^# are calculated and are reported in Table 4 .

[IC] = 1 × 10⁻⁴ M, Current = 4.6 mA, λ_max = 610 nm.

The reaction has been carried out in the presence of Indigocarmine dye solution (0.0001 M), by keeping the applied current as constant (4.6 mA). The change in concentration of the Indigocarmine was recorded by a change in % transmittance of light using a spectrophotometer at λ_max = 610 nm. A plot of log%T (percentage transmittance of light) versus time was linear. Up to 65% of the reaction indicating the disappearance of Indigocarmine follows first order kinetics. The rate constant values are reported in Table 5 . The rate of the reaction is decreased with an increase in the concentration of Indigocarmine dye and the values of rate constants were higher compared to the graphite electrode as an anode. pH value was almost constant before and after degradation. The COD was measured for Indigocarmine solution before and after degradation and the values were reported in Table 5 and Figure 6 .

Applied Current = 4.6 mA, Temperature = 303 K, λ_max = 610 nm.

At constant [IC] the rate of reaction increased with increase in applied current. The current density varies from 3.6 mA - 6.6 mA. The increment of applied current builds the concentration of oxidizing intermediates and OH free radicles, which increases the rate of degradation. The rate of degradation efficiency was higher in Ni doped graphite modified electrode compared to the graphite electrode. The rate constant values are higher compared to graphite electrodes and are reported in Table 6 and Figure 7(a) . The COD was measured for both before and after degradation of dye solutions and is reported in Table 6 and Figure 7(b) .

[IC] = 1 × 10⁻⁴ M, Temperature = 303K, λ_max = 610 nm.

To investigate the effect of temperature, the degradation was carried out at three unique temperatures. Obviously, the increase in temperature increases the rate of reaction and shows that the rate of degradation is not extremely at low temperatures. However, the reaction was significantly increased at higher temperatures. The degradation efficiency was high for Ni/GME compared to graphite electrodes. Since the diffusion rate is increased with temperature, an increase in temperature could bring about an increase in the degradation rate. The rate constant values and COD values for before and after degradation are reported in Table 7 and Figure 8 . Thermodynamic parameters ΔH^#, ΔS^#, ΔG^# are calculated and are reported in Table 8 .

The electrochemical degradation of Indigocarmine dye solution was carried out by anodic oxidation. Further, the experiment was done in the presence of electrodes with platinum as cathode graphite or Ni/GME as anode. In the electrochemical method, OH free radical is formed by direct electrolysis and formed as an intermediate at the surface of a high ${\text{O}}_2^{-}$overvoltage anode from oxidation of water.

H₂O →. OH_ads + H⁺ + e⁻

The degradation of the IC takes place due to sequential electrochemical reduction and oxidation [17] . Graphite electrodes have the high affinity for IC with the implication that it will adversely affect electrode performance because of competitive adsorption and interaction such as electron shuttling may increase interactions. The strong oxidizing agent OH free radical, the sequential reduction and oxidation with graphite and the Pt electrodes. It has been found that Pt electrode possesses greater O₂ over voltage (+0.77 V), thus generating higher amounts of oxidant OH free radical. This reacts with IC converting into CO₂, H₂O and inorganic salts, until their total mineralization is reached. A colourless solution is obtained after degradation, which indicates the absence of formation of insoluble metal oxides. This suggests that oxidizing intermediates which are formed result in degradation of the dye. The graphite electrodes (GE) advantages such as commercial availability, low costs and easy modification [18] [19] . The present method can be used for remediation of waste water (Scheme 1).

The effect of applied current, [dye] and COD was estimated. In all these cases, the COD level decreased more than 90%. The instantaneous current effectiveness (ICE) for the anodic oxidation of Indigocarmine dye was calculated from the values of the COD using the equation,

$\text{ICE}\left(\%\right)=\frac{\left({\text{COD}}_{\text{i}}-{\text{COD}}_{\text{f}}\right)}{8\text{It}}\times \text{FV}$

Here, COD_i and COD_f are the chemical oxygen demands before and after degradation respectively; “I” the current, “F” the Faraday constant, “V” the volume of the electrolyte is the treatment time and “8” is the oxygen equivalent mass (geq − 1). The ICE data in Table 9 , Table 10 shows the efficiency of the process linearly related to ICE and indicates higher efficiency of the process for Ni/GME anode compared to GE anode [20] [21] .

The degradation of dye takes place in the absence of electrolyte HCl or NaOH. The degradation of dye depends on [dye], current density (I) and the surface active sites [S]. Since [S] remains constant, the rate of degradation in the present case is given by

$-\frac{\text{d}c}{\text{d}t}=\frac{k\left[I\right]}{\left[dye\right]}$

The rate constant for the degradation of the indigocarmine process was determined by plotting log%T versus time (t). Here “T” is the percentage transmission of the light obtained from a spectrophotometer, at λ_max 610 nm and it is inversely proportional to the concentration of the dye. A straight line was obtained for 60% of the degradation reaction and afterward deviation in linearity was observed.

The possibility of reusing the Ni/graphite modified electrode was tested to see the cost-effectiveness of the method adopted. After the degradation of the dye, the graphite modified electrode was washed with double distilled water and afterward reused for the degradation by taking the fresh dye solution. From the degradation study it is clear that the reuse of the graphite modified electrode to degrade the dye solution showed little less efficiency.

Figure 10(a) and Figure 10(b) represents UV-Visible spectra during the electrochemical degradation of Indigocarmine dye. A broad visible colour absorption spectra at 620 nm were totally eliminated at the end of the degradation cycle. However, the absorption in the UV-region indicates a less intense small peak which shows the presence of a minute concentration of organics (<48 mg/l COD).

Figure 11(a) & Figure 11(b) shows the SEM image of a graphite flake and its corresponding EDX profile. From the micrograph, the layered and homogenous nature of graphite was seen in different diameters. It is clear from Figure 11(a) before deposition, just graphite flakes are found. The observed size of the graphite flake ranged from 10 to 50 μm. From the EDX profile, the presence of carbon and oxygen content indicates the graphite present in the pure form in Figure 11(b) .

Figure 12(a) and Figure 12(b) show the SEM and EDX profile of Nickel encapsulated in a graphite rod. The SEM image of a nickel encapsulated graphite rod can clearly be distinguished from the graphite rod. Further, the heterogeneous block dots were seen on the surface, which show the nickel doped or encapsulated inside the graphite rod in Figure 12(a) . The corresponding EDX plot as shown in Figure 12(b) . From the EDX plot, we clearly noticed the presence of nickel peaks in different oxidation states along with graphite carbon peaks ( Table 11 and Table 12 ).