## 3 Results and Discussion
### Photocatalytic Activity of AuNPs  
Studies that have investigated the photodegradation of dyes or other pollutants by AuNPs have reported some disadvantages of AuNPs use. First, high AuNPs concentration was required to achieve satisfactory efficiency; for example, 60-2000 mg/L biogenic AuNPs was required to degrade dye [20; 25; 35]. Second, only treatment with dilute dye concentration did not fulfil the actual requirements of dye treatment; for example, treatment with 5-22.4 mg/L MB was insufficient [20; 25; 36]. Finally, only in the presence of NaBH\({}_{4}\), strong photocatalytic activity was achieved for efficient degradation of dyes [24]. To solve these  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & _E. Coli_ & _S. Aureus_ & _P. Aerginosa_ & _C. albicans_ & _C. Acenes_ & _B. Cereus_ \\ \hline BLAuNPs & 6.25 \(\pm\) 0.01 & 12.5 \(\pm\) 0.02 & 6.25 \(\pm\) 0.01 & 3.125 \(\pm\) 0.01 & 12.5 \(\pm\) 0.02 & 12.5 \(\pm\) 0.02 \\ ECAuNPs & 6.25 \(\pm\) 0.01 & 6.25 \(\pm\) 0.01 & 6.25 \(\pm\) 0.01 & 3.125 \(\pm\) 0.01 & 6.25 \(\pm\) 0.01 & 6.25 \(\pm\) 0.01 \\ Chemicals-5 nm & 25 \(\pm\) 0.03 & 50 \(\pm\) 0.08 & 25 \(\pm\) 0.01 & 12.5 \(\pm\) 0.01 & 50 \(\pm\) 0.08 & 50 \(\pm\) 0.05 \\ \hline \end{tabular}
\end{table}
Table 1: Minimum inhibitory concentrations (mg/L) of BLAuNPs, ECAuNPs, and chemically synthesized AuNPs (5 nm) against tested strains.  
Figure 3: DPPH radical scavenging activity of BLAuNPs, ECAuNPs, and Chemicals-5 nm at different concentrations.  
problems, we evaluated the efficiency of 25 mg/L AuNPs in degrading 100 mg/L dye without the addition of NaBH4.  
Dye degradation of AuNPs can be ranked from the easiest to the hardest as follows (Figure 4): VBR, MG, and MB. This ranking might be attributed to differences in the chemical structures of the dyes. Furthermore, ECAuNPs exhibited the highest photocatalytic efficiency and Chemicals-5 nm exhibited the lowest removal efficiency. The reaction was of pseudo-first order, and the respective rate constants (k) for photocatalytic reactions by ECAuNPs for VBR, MG, and MB were 0.702, 0.452, and 0.357 min\({}^{-1}\) (r\({}^{2}\) > 0.97). The photodegradation of MB by ECAuNPs was more efficient than the photodegradation of MB by AuNPs synthesized by Longan fruit (k = 0.29 min\({}^{-1}\)) [25] and Lagerstroemia speciosa (k = 0.198 min\({}^{-1}\)) [37]. Moreover, 100% removal of 40 mg/L MG by 60 mg/L AuNPs synthesized by Enterococcus species required 48 h [35], but ECAuNPs and BLAuNPs could photodegrade 100 mg/L MG in only 8 and 12 min in this study, respectively. The high photocatalytic activity of the ECAuNPs can be attributed to their small size and spherical morphology. These results indicated that AuNPs synthesized in this study were competitive. [PERSON] et al. reported that a photocatalytic reaction is triggered by the excitation of electrons in AuNPs from the low energy valence band to the high energy conduction band in the presence of sunlight [24]. The electrons from the valence band on the AuNPs surface are transferred to these dyes, thereby degrading them. Briefly, biogenic AuNPs synthesized in this study exhibit high potential to be used in the removal of dyes or other environmental pollutants.  
Figure 4: Removal efficiencies of (**a**) VBR (**b**) MG and (**c**) MB by BLAuNPs, ECAuNPs, and Chemicals-5 nm during the 12 min treatment periods (dye concentration: 100 mg/L; AuNPs concentration: 25 mg/L).