## 2 Morphology Design of Graphene-Based Composites
### Graphene-Based Photonic Crystals
The role of graphene as IO PC material has been identified by [PERSON] et al., and some problems, e.g., charge carriers' recombination and slow electrons' pathway in \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\), have been overcome by utilizing the advantage of PC via trapping of photons, and improving the charge carriers' mobility via organized network [67]. \begin{table}
\begin{tabular}{c c c c c} \hline
**PCs** & **Loading Method** & **Applications** & **Findings** & **Ref.** \\ \hline graphene & - & biosensor & 14.8 times & [53] \\  & & & higher sensitivity * & \\ \hline \multirow{3}{*}{GO/TiO\({}_{2}\) IO} & \multicolumn{3}{c}{MB degradation} & \multirow{3}{*}{enhanced activity} & \multirow{3}{*}{[71]} \\  & immersion in GO & 150-W Xe lamp with & & \\ \cline{3-4}  & nanocolloid & 305 nm and 400 nm cut & & \\ \cline{1-1}  & & off filter & & \\ \hline GO/TiO\({}_{2}\) IO film & immersion in GO & \multirow{3}{*}{SERS detection} & \multirow{3}{*}{lower LOD} & \multirow{3}{*}{[54]} \\  & nanocolloid & & & \\ \hline \multirow{3}{*}{rGO/TiO\({}_{2}\)} & \multirow{3}{*}{immersion and calcination} & \multirow{3}{*}{150-W Xe lamp with 305 nm and 400 nm cut off filter} & \multirow{3}{*}{improved photodegradation} & \multirow{3}{*}{[56]} \\  & & & & \\ \cline{1-1} \cline{5-5}  & & organic pollutants & & \\ \cline{1-1} \cline{5-5}  & & adsorbents & & \\ \hline \end{tabular} \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)/GIO—coupling \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\) with a 3D graphene inverse opal; abs.—absorption; CVD—chemical vapor deposition; den. –density; ICPE—incident photon-to-current efficiency; LOD—limit of detection; MB—methylene blue; MO—methyl orange; NPS-IOC—3D nitrogen, phosphorus, and sulphur co-doped graphene-like carbon nanosphere with IO structure; PEC—photoelectrochemical; rGO/Pr/3 DOM TiO\({}_{2}\)—three dimensionally ordered macroporous TiO\({}_{2}\) with platinum (Pt) and reduced graphene oxide (rGO); SA—salicylic acid; SERS—surface-enhanced Raman scattering; * sensitivity in comparison with SPR based biosensor.  
\end{table} 
Table 1: _Cont._A novel ternary IO PC photocatalyst has been developed by [PERSON] et al., consisting of rGO, platinum (as co-catalyst) and titania as the backbone material [68]. It has been proposed that rGO improves the charge carrier's separation apart from enhanced light harvesting, as illustrated in Figure 11. Similarly, [PERSON] et al. have postulated that the excellent carriers' transport (extended lifetime of electrons) by rGO in ternary photocatalyst (rGO/Au/TiO\({}_{2}\)) and the synergistic effect between Au NP (SPR effect) and rGO for light harvesting are responsible for the amplified incident photon-to-electron conversion efficiency in the photoelectrochemical (PEC) study [69]. [PERSON] et al. have further confirmed the enhanced charge carriers' separation by rGO-functionalized on TiO\({}_{2}\) IO PC with the highest rate of salicylic acid photodegradation and the lowest photoluminescence intensity, as compared to GO-TiO\({}_{2}\) IO (without thermal treatment) and pristine PC, as shown in Figure 12 [56]. One of the prerequisite aspects in the case of G/rGO-modified PCs is the loading amount of G/rGO, which is critical for the enhancement of photocatalytic activity, and thus an optimum amount of G/rGO loaded on PC results in the best performance. For example, the highest photodegradation of methyl orange has been achieved in the presence  
Figure 11: Schematic illustrations of: (**a**) the morphology of TiO\({}_{2}\) IO co-modified with Pt NPs and reduced graphene oxide (r-GO), and (**b**) the proposed charge carriers’ separation and migration in rGO/Pt/TiO\({}_{2}\) (not plasmonic activation), rGO-green, Pt-red, TiO\({}_{2}\)-blue; Reprinted with permission from [68]. Copyright (2019) ACS. Figure 12: (**a**) Photocatalytic reaction rate of salicylic acid degradation and (**b**) photoluminescence spectra of pristine TiO\({}_{2}\) PC, GOnano-PC and rGOnano functionalized on TiO\({}_{2}\) PC. Reprinted with permission from [56]. Copyright (2013) Creative Commons Attribution.