PurposeThe purpose of this paper is to prepare calcium oxide (CaO) nanoparticles by green synthesis technique and study its structural, morphological and optical properties. The prepared samples were calcined at, 200°C, 300°C and 500°C, and the variation in the properties at different temperatures were investigated.Design/methodology/approachGreen approach has been used in the present work to synthesise the CaO nanoparticles using Murraya Koenigii leaf (curry leaves) extract as a capping agent. This technique involves the use of nontoxic reagents and natural products derived from various parts of plants.FindingsStudies reveal that CaO nanoparticles with good optical properties can be synthesized successfully by green approach. The optical absorbance spectra show a broad absorption peak around 400–500 nm. FTIR studies confirm the presence of different functional groups that help in the stabilization of CaO nanoparticles. PL emission spectra show a high intensity emission peak at around 231 nm in addition to peaks at 375 nm and 400 nm. XRD studies show planes of CaO cubic phase. SEM images show a nonuniform distribution of spherical particles along with some clusters. EDX spectra confirm the presence of calcium and oxygen.Practical implicationsCaO nanoparticles have wide applications in optical devices as well as in phototherapy. It is thus interesting to devise new and eco-friendly techniques to synthesise these nanoparticles to suit these applications.Originality/valueThis work would provide a new insight into the preparation of different metal oxide nanoparticles by a very simple and cost-effective green technique without the use of toxic reagents.

Nanoparticles (NPs) synthesized by green techniques have received reseachers attention due to their unique physicochemical characteristics and their immense applications in various field. In recent years, synthesis of metal nanoparticles (MNPs) by green technique using plant extracts has become centre of attraction researchers because these NPs have low hazardous effect on the environment and also low toxicity for the human body. The plant extract contains various secondary metabolites which act as a reducing and stabilizing for various metallic nanoparticles synthesis. The non-biological methods i.e. the conventional chemical and physical methods are highly toxic and have serious hazardous effect on human beings and other organisms. On the other hand, the biological or green synthesis of metallic nanoparticles is less expensive, single step process, eco-friendly and also shows effective result. Different plant extracts has been used successfully with various metallic nanoparticles such as, copper, silver, gold, palladium, platinum and zinc oxide. Also, these nanoparticles have potential to cure many diseases such as cancer, hepatitis, malaria, and other deadly diseases. This paper presents a review on plant mediated synthesis of metallic nanoparticles by green technology.