High consumption of mollusk shells generates many waste mollusk shells. To reduce and utilize these wastes, they can be cleaned and milled to produce calcium carbonate (CaCO3) powders, which can be further used as raw material for producing valuable products. This research presents a simple, cheap, and environmentally friendly preparation of calcium phosphates by using waste mollusk shells as a renewable source. All synthesized calcium phosphate samples were characterized and confirmed by X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The addition of phosphoric acid to mollusk-derived CaCO3 generated triple superphosphate (TSP), which consisted of two or more calcium phosphate compounds. After the TSP powder was dissolved in water, non-soluble powders were obtained and found to be dicalcium phosphate dihydrate (DCPD, CaHPO4·2H2O). After removing non-soluble compounds and then the self-evaporating process of the solution fraction to dryness, the recrystallized product was investigated and confirmed as monocalcium phosphate monohydrate (MCPM, Ca(H2PO4)2·H2O). This recrystallization process produced highly purified Ca(H2PO4)2·H2O with high solubility and phosphorus content that can be used as an effective fertilizer. The green and low-cost preparation of calcium phosphates proposed in this research will be valuable to reduce waste mollusk shells by reforming them into value-added products. This information points out the viewpoint of a zero-waste operation for obtaining sustainable development, which could be selected as an effective technique for waste management and recycling.
Discoveries of the correlation between the physical properties and structure of the materials are interesting in the field of the material science and chemical engineering. This work investigated the correlation between the structure, chromaticity, and dielectric properties of calcium copper pyrophosphates, Ca2−xCuxP2O7. The solid state thermal decomposition reaction was employed to synthesize the Ca2−xCuxP2O7 by varying the mole ratio between Ca and Cu. The structure and crystallography of the pyrophosphate compounds were identified and confirmed by using an X-ray diffraction (XRD) technique. The Rietveld refinement method and the extended X-ray absorption fine structure (EXAFS) least-squares fitting technique were also applied to refine the sample crystal structure. The bond angle and bond length of samples were also obtained from the refinement method. The X-ray absorption edge energies (E0) of the synthesized compounds were investigated and the obtained results confirmed the formation of the binary metal pyrophosphates (Ca2−xCuxP2O7). The image sensor result of the Cu2P2O7 sample (x = 2.00) illustrated a yellowish-green color, while other compounds (x = 0.50−1.50) presented color tones that changed from blue-green to bluish-green. The dielectric constant (εr) of the synthesized Ca2−xCuxP2O7 were calculated by using the Clausius-Mossotti relation, and the highest εr was observed for Ca2P2O7. The Raman and Fourier transform infrared (FTIR) spectrophotometers were employed to characterize and confirm the vibrational characteristics of the P2O74− group. The experimental results demonstrated that the changing in the crystal structure of Ca2−xCuxP2O7 (i.e., bond angle of P−O−P in P2O74− and distortion phenomena in M−O6 octahedral site) can cause the correlation between the dielectric and optical properties of the sample.
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