**3. Graphene related materials (GRMs): Principles and strategies**

Graphene has attracted immense attention ever since 2010 Nobel prize in Physics was awarded to Andre Geim and Konstantin Novoselov for their pioneering work. Owing to exotic physicochemical properties, and wide industry application prospects including catalysis, electronics, sensing, energy conversion-storage and environmental remediation, constant attempts have been made in its synthesis, investigations and innovations. Basically, graphene is an allotrope of carbon (linked by sp2 bonds), a oneatom-thick layer arranged in two-dimensional honeycomb network exhibiting unique properties such as high thermal conductivity (5000 W m−1 K−1), large specific surface area (2630 m2 g−1) and high intrinsic electron mobility (200,000 cm2 V−1 s−1) [23, 24]. GRMs include graphene oxide (GO), reduced graphene oxide (rGO), and their derivatives (e.g., functionalized graphene or composites which can be used as building blocks

#### **Figure 4.**

*General synthesis strategies for preparation of graphene related materials. Reproduced with permission from Ambrosi et al. [25].*

to develop series of nanocomposites or hybrid photocatalysts via Vander Walls interaction and inherent surface active O2−/OH groups and oxo ligands chemistry.

#### **3.1 Preparation of graphene and related materials**

A wide range of synthesis techniques have been developed to yield graphene and related materials. It can be broadly classified into two distinct approaches: (i) topdown, and (ii) bottom-enabling different scale-up capability and variations in the properties (**Figure 4**). Top-down synthesis strategy relies on simple exfoliation of graphite via mechanical means (e.g., Scotch tape), chemical (e.g., solution-processed, graphite oxide exfoliation/reduction), and electrochemical (oxidation/reduction and exfoliation) methods and allows weakening the van der Waals forces between the graphene layers to form the graphene with single or few atom thick layers. A special graphene nanoribbons with tuneable band gaps and edge shapes have been achieved via opening of carbon nanotubes through chemical or thermal routes [26]. On the other hand, bottom-up strategies which rely on assembly of small molecular building blocks into few layer graphene nanostructures have been achieved through different chemical routes such as catalytic (e.g., CVD), thermal (e.g., SiC decomposition), or chemical (organic synthesis) processes. The readers are directed to several recent reviews for the details of synthesis of GRMs [25, 26].
