## 3 Experimental Approach
### \(\gamma\)-Graphyne  
After the theoretical prediction of \(\gamma\)-graphyne, lots of successful methods, such as mechanochemical, ultrasonic methods, ball milling, catalyzed coupling reaction, etc., have been adopted for the synthesis. Some interesting, applied techniques, along with possible mechanisms, have been demonstrated here. For example, Yang et al. [102] synthesized \(\gamma\)-graphyne using a modified mechanochemical technique and then used it as an adsorbent to clean wastewater dyes. The synthesis process used calcium carbide (CaC\({}_{2}\)) and hexabromobenzene (PhBr\({}_{6}\)) as precursor materials and employed the ball milling method for the synthesis of \(\gamma\)-graphyne (as presented in Figure 7). According to them, initially, high mechanical stress breaks the lattice structure and molecular bonds of CaC\({}_{2}\), producing an abundance of [C\(\equiv\)C]\({}^{2}\)- and Ca\({}^{2+}\) in the medium. Then, highly negatively charged [C\(\equiv\)C]\({}^{2-}\) having strong surface energy reacts with carbon atoms of PhBr\({}_{6}\), leading to the formation of C-C bonds between them. Later, Br atoms in the PhBr\({}_{6}\) were gradually ousted by C\(\equiv\)C bonds. Furthermore, partially substituted hexabromobenzene retains its high  
Figure 6: General schematic of graphyne synthesis pathways, including experimental and chemical methods, such as cross-coupling reactions, mechanochemistry, and ultrasonic-assisted synthesis. activity due to the electron-withdrawing impact of C\(\equiv\)C groups, and cross-coupling nucleophilic substitution persists. Ultimately, acetylene bonds replace every Br atom to create \(\gamma\)-graphyne. In another work, Li et al. [103] also synthesized \(\gamma\)-graphyne through a similar mechanochemical method using benzene as a precursor material. They convert benzene into \(\gamma\)-graphyne by reacting it with CaC\({}_{2}\) through solid-liquid interphase reaction in the presence of ball milling (Figure 8). The prepared materials were used as electrocatalysts for the oxygen evolution reaction (OER). The authors estimated the Gibbs free energy change in this synthesis reaction and found that it is below zero at a standard temperature, demonstrating a spontaneous process in thermodynamics. Ding et al. [104] also synthesized \(\gamma\)-graphyne using CaC\({}_{2}\) and PhBr\({}_{6}\) as a starting material, but they employed ultrasonic force instead of ball milling as a driving force for the cross-coupling reaction. The plausible steps of the reaction are schematically presented in Figure 9 (Red arrows in the figure represent nucleophilic substitution.). The reaction pathway in the ultrasonic method is similar to that of the synthesis of \(\gamma\)-graphyne ball milling, as mentioned previously. Here, only instead of ball milling forces, ultrasound irradiation may rapidly disperse big particles of raw materials into small sizes, considerably increasing the contact area of the reactants. Meanwhile, the high energy given by ultrasonic irradiation's acoustic cavitation can fully initiate the chemical interaction between CaC\({}_{2}\) and PhBr\({}_{6}\). In another work, Yang et al. [105] employed mechanochemistry to synthesize \(\gamma\)-graphyne by cross-coupling reaction utilizing calcium carbide and 1,3,5-tribromobenzene as starting material. Figure 8: Schematic of \(\gamma\)-graphyne synthesis from benzene and CaC\({}_{2}\) under a solid–liquid mechanochemical interface reaction, used for electrocatalytic applications. Figure 7: Mechanistic diagram of \(\gamma\)-graphyne synthesis using CaC\({}_{2}\) and hexabromobenzene via ball milling, illustrating bond formation and substitution steps during the mechanochemical reaction. Reproduced with permission from reference [102] @ 2022 Elsevier. Recently, He et al. [106] employed a one-pot pproach for the synthesis of \(\gamma\)-graphyne utilizing hexabromobenzene and acetylenedicarboxylic acid through a Pd-catalyzed decarboxylative coupling process (as presented in Figure 10).