The biosynthesis of high purity and crystalline CdO nanocrystals by green novel and environmental friendly process using the natural extract of H Sabdariffa as an effective chelating chemical agent was demonstrated. A thermal annealing at 500 °C during 2 h under normal air conditions allows the obtention of highly crystallized single phase CdO nanoparticles as substantiated by different technique. While the HRSEM showed that the CdO nanoparticles are of a cuboid shape with an average size of 113 nm, the HRTEM studies shed lighted on the fact that the nanoparticles consist of nano-crystals with a diameter ranging from 23 to 35 nm. The EDS showed that there are no other elements observed in the Cadmium oxide nanoparticles except Cd and O especially additional K or Na which can originate from residual organics of the natural extract Hibiscus Sabdarifa. Similar elemental spectrum has been noted on the non annealed initial deposited powder sustaining the pure chemical form of the formed CdxOy nanoparticles within the initial deposit. In terms of its intensity and its spectral selectivity, the observed strong photoluminescence emission centered at ∼551 nm can be utilized in the industry for high quality monochromatic sources. The optical band gap values of the CdO nanoparticles were deduced to be 2.1 eV and 2.7 eV for indirect and direct transitions respectively. From solar energy photoconversion, the CdO nanoparticles/p-Si heterojunction exhibited acceptable rectification characteristics with current saturating at Vf ∼1 V.
The follow up study will consist of identifying the mechanism and the dynamic of formation of the CdO NPs during the interaction of the Cadmium salt precursor and the H Sabdariffa extracts compounds. More specifically, the bioactive compounds would be identified. In addition, the synthesis of less stable oxides such as semi-metallic and metallic CdO NPs is being investigated.