Novel green route synthesis of CdO nanostructures by using CdCO3 obtained by MICP and its application in photodegradation of methylene blue and Congo red

This research developed a new green route synthesis of cadmium oxide (CdO) nanostructures. First, the microbially induced carbonate precipitation was employed as a bioremediation strategy of Cd+2 in wastewater using granular sludge to precipitate it as cadmium carbonate (CdCO3) crystals. Then, the CdCO3 powder was subjected to calcination treatment at 450°C for 10, 20, 30, and 60 min to convert it to CdO and remove organic compounds. The characterization results showed that CdCO3 was converted entirely to CdO at 60 min of the thermal annealing at 450°C. CdO exhibited a simple cubic structure with an average crystallite size of 28 nm. Scanning electron microscopy images showed agglomerations composed of CdO tube-like nanostructures with an average of 60 nm in diameter. The optical energy band-gaps of the CdO nanostructures were 2.15 eV and 2.0 eV for direct and indirect transitions, respectively.