Thermal degradation of calcium and sodium alginate: A greener synthesis towards calcium oxide micro/nanoparticles.

Processes for nanoparticle synthesis often use toxic solvents under aggressive conditions. A greener alternative is the burning of self-organized alginate systems. We followed the influence of the CaCl2 concentrations during gelation of sodium alginate and the heating rate on the synthesis of nanoparticles by the combustion method using TGA as a reactor vessel. Samples were collected after each main process of mass loss and characterized using the Scanning Electron Microscopy, Infrared Spectroscopy, and X-ray Diffraction. Samples treated at 50 °C·min-1 presented porous structures at temperatures more than 500 °C lower than the treatments at 10 °C·min-1. All calcium alginate samples presented changing from a predominantly amorphous to crystalline structures such as Ca(OH)2, CaCO3 in the calcite phase and CaO as a function of the temperature, while sodium alginate produced mainly Na2CO3, NaOH and NaO. We observed two main correlations: 1) between the porosity and the heating rate, and 2) between the formation of crystalline structure in intermediate temperatures and the CaCl2 concentration in the gelation step.