Biosynthesis and characterization of CuO nanoparticles using mehandi and neem leaf extract and its relevance as a nanofluid for heat transfer

•Crystallite size of CuO NPs came around 15.69 nm.•Particle size of CuO NPs was around 43.81 nm.•Aggregated biosynthesized CuO NPs have a spherical shape.•Heat transfer strongly influenced by nanoparticle concentration and particle size.•Cooling rate increases as coolant nanoparticle concentration increases. The purpose of this research is to biosynthesis and characterization of cupric oxide nanoparticles (CuO NPs). The biosynthesis method has been used in the preparation of CuO NPs using plant leaf extract and copper nitrate trihydrate (Cu(NO3)2⋅3H2O) in a molar ratio of 1:4. The CuO NPs are confirmed by XRD, FTIR, SEM-EDS and UV–Visible Spectroscopy characterization techniques. The CuO NPs has been characterised and parameters such as stability, particle size and crystal size are studied. The experiment for stability and particle size was carried out using dynamic light scattering (DLS) and found that the value of zeta potential is around −38.84 mV. However, the average particle size of the nanoparticles is estimated to be43.81 nm using DLS, which also confirms by TEM analysis the size range of particle is 10–80 nm. Apart from particle size, the XRD characterization technique is used to calculate average crystallite size and crystalline structure of nanoparticles and it is found that the value of crystallite size is 15.69 nm. The SEM analysis confirms that the nanoparticles were composed of evenly dispersed, spherical particles in aggregated form. The prepared nanoparticles has been used in water (0.1 vol%) to prepare nanofluid and physical properties was measured and found it is suitable for cooling purpose.