## 2 Morphology Design of Graphene-Based Composites
### Graphene-Based Photonic Crystals
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**PCs** & **Loading Method** & **Applications** & **Findings** & **Ref.** \\ \hline (GQD)-TiO\({}_{2}\) film & TiO\({}_{2}\) immersion in & SA degradation; & \\  & GQD suspension & \(\lambda>400\) nm & enhanced activity & [55] \\ \hline \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)/graphene & \begin{tabular}{c} spin coating and \\ thermal treatment \\ \end{tabular} & \begin{tabular}{c} ICPE measurement; \\ Xe lamp \\ \end{tabular} & 2.6-fold higher than reference & [66] \\ \hline graphene & - & optical absorption & enhanced abs. & [49] \\ \hline graphene PC fiber & - & optoelectronics & stronger broadband response & [50] \\ \hline \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)/GIO & \begin{tabular}{c} carburization; nickel \\ oxide IO and CVD \\ \end{tabular} & PEC water splitting & 1.4-fold higher photocurrent den. & [67] \\ \hline rGO/Pt/3 DOM TiO\({}_{2}\) & \
\begin{tabular}{c} immersion and \\ calcination to form r-GO \\ \end{tabular} &
\begin{tabular}{c} MO degradation; \\ \(\lambda>420\) nm; \\ \end{tabular} & 4-fold increase & [68] \\ \hline TiO\({}_{2}\)@ & immersion and & PEC water splitting; & 2-fold & [69] \\ rGO@Au & calcination & 300-W Xe lamp & enhancement & [70] \\ \hline IO-SnO\({}_{2}\)/G & immersion and & MO degradation & & \\ microspheres & calcination & 300-W Hg lamp; & enhanced activity & [70] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Graphene-modified PCs: preparation, properties and performance. For 2D structures, an interesting theoretical study has been performed on graphene/silver (with surface plasmon resonance, SPR) coated PC fiber, where graphene deposition has been identified as the promising method to prevent the oxidation of silver that might weaken the SPR effect for the sensor efficacy [52]. It is well known that though graphene has broad light absorption range in electromagnetic wave spectrum, the total optical absorption is still weak and requires some aid for enhancement, e.g., from supporting materials. In this sense, the coupling of graphene with PCs might significantly improve the ability of optical absorption, as already reported [50]. Accordingly, introduction of single layer of graphene into 2D PC (nanocavity) has been postulated to enhance the light-matter interaction, as confirmed by a model study carried out by [PERSON] et al. [58]. Controlled engineering that involves the design of IO heterostructures (3D), such as the coupling of conductor, semiconductor [67] and plasmonic nanomaterials [48; 73], has gained attention and been considered as an efficient method to enhance the performances of various materials, including graphene-based IO PCs, where graphene acts either as the backbone material of PCs or co-catalyst to improve the conductivity of the overall coupled PC-based materials. The fabrications of graphene-based PCs, where graphene-like materials (GO/rGO) act as co-catalysts, has been mostly carried out by immersing/dipping the IO PC into GO colloidal suspension with subsequent post-thermal treatment (calcination) [55; 68; 69; 71]. On the other hand, the formation of graphene-like materials as the backbone material of IO PC requires at least three-step procedure i.e., (i) preparation of template (opal), (ii) infiltration of opal with targeted material, and (iii) the removal of sacrificial template. For example, the opal template has been infiltrated with precursors of dopants (N, P, S) along with carbon (to form carbonaceous IO), and then pyrolyzed under inert conditions in order to form multi-heteroatom-doped graphene-like carbon nanospheres IO PC [72]. It has been shown that high temperature (700-1000 \({}^{\circ}\)C) is necessary for carbonization and carburization to fabricate graphene as the IO PC backbone material [67; 74].