Precursors calcined egg shell and agar are used to synthesize calcium carbonate particles by solvothermal method using ethylene glycol/water solvent system. The synthesized products are calcined at 700 and 900 °C for 5 hours. Calcination temperature has significantly influence the morphology and composition of particles. Calcium carbonate particles are converted into calcium hydroxide particles after calcining at 900 °C for 5 hours. Reitveld refinement is performed on XRD data of all products and their structural models are constructed. Data analysis shown that crystal system of all products is same, but the atomic coordinates have changed after calcination treatment. Scanning and transmission electron microscopic techniques are used for analysis of surface and internal morphology of products. Prepared products are used as catalyst for degradation of Congo red in aqueous medium. Prepared products are also used as fuel additive. Results indicate that the products possess significant potential to be used as catalyst and fuel additive. The product is comprised of oval shaped particles. The size of these oval shaped nanoparticles lies in the range of 80 to 120 nm.