## 3 Results and Discussion
### The Electrocatalytic Reduction and Detection of 2,4-Dinitrotoluene  
#### Cyclic voltammetry  
Cyclic voltammograms were recorded to estimate the electrocatalytic activity of the synthesized Zn-MOF-8@Ag/Au modified electrode towards the reduction of 2,4 DNT. In Figure 5b, CV was performed in the presence and absence modified electrode in presence of the 2,4 DNT. The dynamic active surface area of the modified gold electrode was calculated by using Randles-Sevcik equation; utilizing cyclic voltammetric technique, 5 mM K\({}_{3}\)Fe (CN)\({}_{6}\) as a test solution and 0.1 M KCl as the supporting electrolyte, at different sweep rates. For a reversible process the equation is as follows:  
\[\text{Ip}=2.69\times 105\times\text{n}^{3/2}\text{ A}\times\text{D}_{0}\tfrac{1}{2}\times\text{v}^{1/2}\times\text{C}_{0}\]  
where Ip = peak current (\(\mu\)A), A = surface area of the electrode (cm\({}^{2}\)), C\({}_{0}\)= concentration of electroactive species (mol cm\({}^{-3}\)), n = number of electrons transferred, D\({}_{0}\) = diffusion coefficient (cm\({}^{2}\) s\({}^{-1}\)) and v = scan rate (V s\({}^{-1}\)). The value of the diffusion coefficient can be obtained, by plotting Ipa vs. v\({}^{1/2}\) (for 0.05 mol cm\({}^{-2}\) of K\({}_{3}\)[Fe(CN)\({}_{6}\)]\({}^{3/4}\)). Here, C\({}_{0}\) = 0.05, n = 1, D\({}_{0}\) = \(7.6\times 10^{-6}\) cm\({}^{2}\) s\({}^{-1}\). On substituting these values, the active surface area was calculated to be 0.056 cm\({}^{2}\) on a modified Au electrode [42]. The CV response was recorded for a modified Au electrode in 0.25 mM 2,4-DNT in 0.1 M, PBS (pH = 7.4), respectively, at a scan rate of 0.0050 mV/s. Figure 5b shows the CV curve of a Zn-MOF-8@Ag modified gold electrode in the absence gave no response (black line) and in presence afforded two reduction peaks (red line). The results indicated that the modified Au electrode showed negligible response in the absence of 2,4-DNT but gave two major reduction peaks in presence of 2,4-DNT. These reduction peak appeared at \(-\)0.50 V and \(-\)0.62 V which confirmed that the Zn-MOF-8@Ag modified Au electrode is much reactive towards 2,4-DNT and established that synthesized Zn-MOF-8@Ag is efficient for the reduction of 2,4-DNT. Further, the effect of scan rate of modified electrode was studied in detail by applying different scan rate dependent experiments. The scan rate experiments were performed (0.25 mM, 2,4 DNT, 0.1 M PBS) in scan rates ranging from 5 mA/s to 500 mA/s and are depicted in Figure 5c. The CV responses of modified electrodes increased with increase in the scan rate which confirmed that the reduction is diffusion controlled. The calibration curve of cathodic peak current and square root of scan rate is plotted in Figure 5d.  
Further, we have endorsed the effect of different concentrations of 2,4-DNT against the modified gold electrode; CV response showed that electrocatalytic current increased with increase in concentration (0.2 to 0.25 mM) of 2,4-DNT in PBS at pH 7.4 against the modified Au electrode (Figure 6a). The results reveal that with the increment in the concentration of the 2,4-DNT, the reduction peak (R\({}_{1}\) & R\({}_{2}\)) also increased, which confirmed that the modified electrode is sensitive towards 2,4 DNT. The irreversible electrochemical response shows that there is no anodic current observed in the reverse sweep, thus implying that Zn-MOF-8@AgQDs is an effective mediator for the reduction of 2,4-DNT.