## 3 Results
Previous reports of RhB EF were in the range of \(10^{6}\)\(\sim\)\(10^{9}\)[38; 39]. This result shows an effective SERS enhancement, which can efficiently improve the SERS sensitivity and perform as a SERS substrate. Figure 3: Charge transfer scheme from Ag to ZnO. Apart from the sensitive SERS signals of RhB, the catalytic behavior of the substrate can also be exploited by taking advantage of plasmon effect. Plasmons provide more electrons (collective oscillations) to accelerate the rate of a chemical reaction. Moreover, plasmons serve as an efficient catalyst through \"hot electrons\", which are transferred to the excited state of molecules on the metallic surface and thus the required activation energy to initiate a chemical reaction is provided. Based on this assumption, we tested the photocatalytic activity of all the designed Ag/PDA/ZnO@GMF substrates by UV-induced degradation of RhB. We measured the SERS intensity under UV radiation and observed a gradual decrease in RhB intensities with increasing time of irradiation over all the substrates. However, among them, the requirement of a minimal irradiation time was observed for the substrate Ag-8h/PDA/ZnO@GMF. Therefore, the CT effect well contributed to the catalytic degradation of RhB upon UV radiation on Ag-8h/PDA/ZnO@GMF (Figure 6). In addition, we were interested to investigate whether a combination of Ag and ZnO was required to achieve efficient photocatalytic degradation of RhB, or if AgNPs alone on the PDA@GMF support was sufficient. For this purpose, Ag/PDA/ZnO@GMF and Ag/PDA@GMF were employed for the SERS signal measurements. The green line in Figure 7 is the substrate without ZnO and with an 8 h Ag  
Figure 4: SERS spectra of RhB on GMF, Ag/ZnO@GMF, ZnO@GMF, Ag/PDA@GMF, and Ag/PDA/ZnO@GMF. Ag-8h/PDA@GMF, we observed a significant SERS signal for RhB. However, the signal intensities were unaffected by UV radiation even after 40 min--indicating that the pure silver nanoparticle does not have catalytic degradation activity for RhB. The presence of ZnO led to a significant decrease in the SERS intensity under the same irradiation conditions (blue line). Therefore, from the controlled experiments, we confirmed that the presence of ZnO is required to drive the catalytic degradation of RhB. Next, we examined the reaction kinetics. For this purpose, we took the natural logarithm of intensities and plotted it against the reaction time. The samples with different deposition times were analyzed as regression curves, as shown in Figure A3a-f. The rate law by the first-order reaction can be written as below:  
\[(\mathrm{I_{t}}/\mathrm{I_{0}})_{1364}=-\mathrm{kt}\]  
where \(\mathrm{I_{0}}\) and \(\mathrm{I_{t}}\) are the SERS intensities before and after UV irradiation and k is the reaction rate constant for the degradation. We observed that an oblique line can be fitted at each deposition time. Further, we tried to determine the order of the degradation reaction. The reaction rate constant k value was calculated from the slope of each oblique line. Figure 5: SERS spectra of different Rhodamine B concentrations for substrate detection at increasing AgNP deposition times—(a) 2 h, (b) 4 h, (c) 6 h, (d) 8 h, (e) 10 h, and (f) 12 h.  
The rate constants and R squared values are listed in Figure 1:0 We observed that the substrate with a deposition time of 8 h had the largest linear slope, i.e., the maximum reaction rate constant (0.0391 min\({}^{-1}\)). The maximum rate constant for the catalytic degradation  
Figure 1:1 SERS monitoring of photocatalytic degradation of Rhodamine B (10\({}^{-3}\) M), substrate at different AgNP deposition times—(a) 2 h, (b) 4 h, (c) 6 h, (d) 8 h, (e) 10 h, and (f) 12 h.  
Figure 1:2 (I\({}_{\rm t}\)/I\({}_{\rm 0}\))\({}_{\rm 1364}\) vs. reaction time. Both samples had 8 h deposition time of Ag. The blue and green lines are with and without ZnO respectively. of RhB on the Ag-8h/PDA/ZnO@GMF can be attributed to the significant charge transfer between semiconductor and metal via the aromatic conjugated core of PDA.