*6.3. Copper Oxide Nanoparticles (Cu2ONPs)*

In recent years, copper (Cu) has intrigued researchers for its application in nanoparticle synthesis, due to its readily available nature, and characteristics like catalytic, electrical, optical and mechanical properties [135–137]. Copper oxide, being a vital inorganic material, is predominantly used in modern technologies, especially in the field of catalysis, ceramics and superconductor applications. Moreover, it can also be used as electrode active materials for the degradation of nitrous oxide with ammonia, and oxidizing carbon monoxide, hydrocarbon and phenol in the formation of supercritical water [138]. The phytogenic synthesis of Cu2ONPs possessing antioxidant ability is compiled in Table 3. In 2019, Rajeshkumar and his colleagues also reported a similar radical scavenging property of copper nanoparticles synthesized using leaf extract of *Cissus arnotiana*, when compared with the standard ascorbic acid [102].
