## 3 Environmental Applications of Graphene-Based Photocatalysts
### Antimicrobial Properties of Graphene-Based Composite Photocatalysts
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Preparation Method** & \begin{tabular}{c} **Experimental** \\ **Conditions** \\ \end{tabular} & **Findings** & **Ref.** \\ \hline GO-Ag & \begin{tabular}{c} AgNO\({}_{3}\) aq. added to GO \\ under constant stirring \\ \end{tabular} & DD; _E. coli_ or _S. aureus_ & conc. dependent inhibition & [113] \\ \hline GO & \begin{tabular}{c} HM (GO); GO, PVP, \\ \(\alpha_{\text{D}}\)-glucose, Ag/NH\({}_{3}\) at \\ 45\({}^{\circ}\)C. \\ \end{tabular} & EEMA, NR, LDH, ROS; AMNRLW & \begin{tabular}{c} Ag-GO \(>\) GO, dec. \\ EEAA/NR, LDH release and \\ ROS generation \\ \end{tabular} & [115] \\ \hline AgNPs/TETA-GO & \begin{tabular}{c} HM (GO)/ \\ self-assembly \\ using TETA as a bridging agent \\ \end{tabular} & CC; _E. coli_ or _S. aureus_ & MIC: 0.125 mg/mL (_E. coli_), 0.25 mg/mL (_S. aureus_) & [127] \\ \hline PVA/AgNPs-GO & \begin{tabular}{c} Ag\({}^{+}\) red. on PVA-GO by \\ L-ascorbic acid \\ \end{tabular} & EUCAST; _E. coli_ or _S. aureus_ & 2 wt\({}^{\circ}\)Ag—4 log red. _E. coli_/_S. aureus_ (24 h) & [128] \\ \hline GO/CS/TiO\({}_{2}\) & \begin{tabular}{c} HM (GO)/ \\ GO dropwise into CS, \\ TiO\({}_{2}\) addition \\ \end{tabular} & DD, L/D; _B. subtilis_ and _A. niger_ & \begin{tabular}{c} inh. colony formation; \\ most active \\ GO:CS:TiO\({}_{2}\) = 1:20:4 \\ \end{tabular} & [129] \\ \hline Cu\({}_{2}\)O-TiO\({}_{2}\)/rGO & \
\begin{tabular}{c} D and MIC; _S. aureus_, \\ _E. coli_, _S. oralis_, \\ _Pseudomonas aeruginosa_ \\ under vis \\ \end{tabular} &
\begin{tabular}{c} bactericidal activity: _S. aureus_ \\ _> P. aeruginosa_ \(\approx\)_E. coli_ \textgreater{} \\ \end{tabular} & [124] \\ \hline AMNRLW—Aquatic microorganisms in natural river/lake water; CC—colony-counting method; conc. –concentration; CS—chitosan; DD—disc & diffusion method; dec. —decensed; EEMA—extracellular enzyme activity assay; enh.—enhanced; EUCAST–EUCAST dilution method; HM—Hummers’ method; inh—inhibited; L/D—live/dead fluorescence assay; IDH—late dehydrogenase; MIC—minimum inhibitory concentration; NR—n nitrification rate; red.—reduction; ROS—reactive oxygen species, USR—ultrascine reduction WI—wet impregnation. \\ \end{tabular} & [125] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Graphene-based composites with metals and metal oxides for microbial disinfection. icals (\({}^{\bullet}\)O\({}_{2}\)\({}^{-}\)) and hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)). It should be pointed out that though ROS are detected only at the beginning stage for GO due to its further aggregation, Ag-GO generates ROS continuously for 48 h, indicating that Ag-GO has high stability in natural water. [PERSON] et al. have shown that uniformly deposited AgNPs NPs on triethylenetetramine (TETA)-functionalized GO (TGO) show significant antimicrobial efficiency for both gram-positive and gram-negative bacteria with higher efficiency against the latter [127]. Similarly, poly(vinyl alcohol)/Ag NPs-GO (PVA/AgNPs-GO) nanocomposite, fabricated through one-step environmentally friendly chemical reduction method, shows bactericidal activity towards both _E. coli_ and _S. aureus_, for 2 wt% of Ag, but the composite with lower content of silver is inactive [128]. Therefore, it has been proposed that GO stabilized metallic deposits and organic compounds. In addition to metal NPs, semiconductor photocatalysts, e.g., TiO\({}_{2}\)[124; 125; 126], ZnO [120; 121; 122; 123] and NiO [119], have also been used for graphene modifications, as shown in Table 3. Many studies have revealed that G/rGO/GO as a support for the photocatalysts could enhance the charge transport (as also discussed in previous sections), resulting in improved photocatalytic activity. [PERSON] et al. have demonstrated that GO/CS/TiO\({}_{2}\) composite exhibits significant suppression of colony-forming against bacteria _Bacillus subtilis_ and filamentous fungi _Aspergillus niger_ biofilm formation, despite the material does not show the cytotoxicity against mammalian and plant cells (Figure 13) [129].