Synthesis of Calcium Carbonate from Orange Peel Waste Extract: A Mechanistic Investigation

The present work reports the mechanism and synthesis of calcium carbonate (CaCO3) formation from orange peel, which is one of the most common agriculture waste generated throughout the globe. The zest of oranges was co-distilled with distilled water to separate the essential oil content. Further, the residue was washed twice with distilled water to get the desired extract. For the green synthesis of CaCO3, a saturated solution of calcium nitrate tetrahydrate (Ca(NO3)2 & sdot;4H2O) was mixed thoroughly with orange peel extract in the 1:3 proportion. This solution was kept on magnetic stirrer while maintaining temperature at 85 & ring;C, heated at 100 & ring;C for 13 h which was further annealed at 300 & ring;C, 500 & ring;C and 700 & ring;C. X-ray diffraction (XRD) shows the presence of calcite phase corresponding to CaCO3. Fourier transform infrared spectra (FTIR) exhibits the bands corresponding to Ca-O, C-O and vibrations of CO3-2 bonds whereas UV-Visible spectroscopy shows the optical behavior of CaCO3. The qualitative analysis of orange peel extract as well as the black-brown gel formed as a result of sol-gel synthesis method was examined using Gas Chromatography & Mass Spectrometry (GCMS). It revealed the presence of acidic groups (2,3-butanediol & 1,4-benzenediol) which led to the development of a mechanism, governing the formation of CaCO3.