## 2 Morphology Design of Graphene-Based Composites
### The Composites of Graphene with Faceted Particles
the improvement of photocatalytic activity is possibly caused by better charge separation at the interface of TiO\({}_{2}\) NCs and rGO layer, and enhanced optical absorption at vis range due to new donor levels inside titania bandgap, i.e., the defects, such as Vo and Ti\({}^{3+}\)[39]. [PERSON] et al. have prepared G-wrapped TiO\({}_{2}\) hollow core-shell structures, in which titania core is composed of mutually independent exposed (001) and (101) faceted nanocrystals [40]. This photocatalytic system has been used for simultaneous oxidative degradation of Rhodamine B and reduction Cr(VI). The observed photocatalytic efficiency, compared with pure TiO\({}_{2}\) microspheres and P25 (Figure 3a), has been explained by Z-scheme mechanism (2 nd generation Z-scheme), in which rGO acts as solid-state electron mediator, as shown in Figure 3b. Under irradiation, electrons are photoexcited from valence bands (VBs) of faceted titania nanocrystals ((001) and (101)) to their individual conduction bands (CBs). Then, rGO provides pathways for the photogenerated electrons from CB of (101) facets (possessing less positive potential) to VB of (001) facets (possessing less negative potential), and thus resulting in efficient separation of charge carriers with better redox properties, i.e., electrons in CB of (001) and holes in VB of (101) facets [40]. Figure 2: Schematic illustration for synthesis of TiO\({}_{2}\) NCs@RGO composites (RGO–rGO). Reprinted with permission from [39]. Copyright 2014 John Wiley and Sons. The research approaches on coupling of graphene with faceted particles have not been limited to faceted titania, but also other metal oxides, such as polyhedral Cu\({}_{2}\)O and BiVO\({}_{4}\), have been investigated. For example, [PERSON] have obtained a ternary rGO-wrapped octahedral Ag-Cu\({}_{2}\)O (Ag-Cu\({}_{2}\)O/rGO) photocatalyst [41]. In the proposed novel heterostructure, Cu\({}_{2}\)O octahedra are decorated with dense silver NPs, and wrapped with thin rGO nanosheets (Figures 4 and 5). It has been proposed that both Ag and rGO act as acceptor of photo-excited electrons from Cu\({}_{2}\)O, improving the separation of electron-hole pairs, and thus decreasing their recombination possibility. Furthermore, the incorporation of rGO does not only suppress the recombination of charge carriers, but also prevents the agglomeration of Ag NPs. Moreover, Ag NPs could also enhance activity due to the surface plasmon resonance at vis range of solar spectrum (plasmonic photocatalysis). Therefore, Ag-Cu\({}_{2}\)O/rGO photocatalyst has shown high photocatalytic activity and stability during photodegradation of phenol under vis irradiation [41]. Figure 4: Schematic illustration of synthesis and structure of the Ag-Cu\({}_{2}\)O/rGO composite. Reprinted with permission from [41]. Copyright 2018 Elsevier. Figure 3: (**a**) Photocatalytic conversion of Cr(VI) and Rh B in single system: TGHMs–graphene-wrapped TiO\({}_{2}\) hollow core-shell microspheres, PT–pure TiO\({}_{2}\) microspheres; (**b**) Schematic graph of proposed mechanism of synergistic removal of Cr(VI) and Rh B in a \(Z\)-scheme photocatalytic system consisting of rGO and titania nanocrystals with exposed (001) and (101) facets under stimulated solar light irradiation. Reprinted with permission from [40]. Copyright 2016 Creative Commons Attribution. In the research focusing on BiVO4, [PERSON] et al. have presented rGO/BiVO4 composites with maximized interfacial coupling by completely covering of BiVO4 polyhedrons with rGO sheets by an evaporation-induced self-assembly process. In rGO/BiVO4 composites, BiVO4 polyhedrons have a well-defined truncated bipyramid morphology with (040) facets exposed, and rGO layers conformally covering polyhedron surfaces to form well-defined rGO/BiVO4 composite (Figures 6 and 7) [42]. The as-prepared rGO/BiVO4 photocatalyst has shown obviously enhanced efficiency of charge separation and improved ability of surface adsorption, resulting in significantly higher photocatalytic activity.