Continuous synthesis of precipitated calcium carbonate using a tubular reactor with the aid of aloe vera (Aloe barbadensis Miller) extract as a green morphological modifier

Green templating agents for evolving new morphologies and shapes of precipitated calcium carbonate (PCC) with wide-ranging potential applications are desirable. In this study, aloe vera (Aloe barbadensis Miller) extract (0.5%-5%, v/v) was utilized as a green modifier for the synthesis of a PCC composite with a new crystalline structure. A continuous PCC synthesis was conducted using a tall and narrow tubular column reactor with a favorable height-to-diameter ratio (l/d =150 cm/10 cm). The morphology, particle size, crystalline structure, and thermal characteristics of the synthesized PCC were studied by scanning electron microscopy, X-ray diffraction, particle size distribution, thermogravimetric analysis, differential thermal analysis, and Fourier transform infrared spectroscopy. Aloe vera extract concentrations above 0.5% (v/v) significantly influenced the particle size and morphology of the synthesized PCC but only marginally influenced the PCC yield. Under ambient temperature, and using aloe vera extract concentration above 0.5% (v/v), and 1 L/min CO2 flow rate, a rhombohedral calcite and aragonite composite with a polycrystalline dumbbell-like structure with radiating ends was produced. The morphology, particle size, and polymorphs of the CaCO3 crystals could be further tuned by varying the concentrations of the aloe vera extract. The synthesized PCC had a particle in the size range of 120-200 nm. (C) 2017 Elsevier Ltd. All rights reserved.