Production of nano hydroxyapatite and Mg-Whitlockite from biowaste-derived products via continuous flow hydrothermal synthesis : a step towards circular economy

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Nigar, Farah and Johnston, Amy-Louise and Smith, Jacob and Oakley, William and Islam, Md Towhidul and Felfel, Reda and Grant, David and Lester, Edward and Ahmed, Ifty (2023) Production of nano hydroxyapatite and Mg-Whitlockite from biowaste-derived products via continuous flow hydrothermal synthesis : a step towards circular economy. Materials, 16 (6). 2138. ISSN 1996-1944 (https://doi.org/10.3390/ma16062138)

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Abstract

Biowastes from agriculture, sewage, household wastes, and industries comprise promising resources to produce biomaterials while reducing adverse environmental effects. This study focused on utilising waste-derived materials (i.e., eggshells as a calcium source, struvite as a phosphate source, and CH3COOH as dissolution media) to produce value-added products (i.e., calcium phosphates (CaPs) derived from biomaterials) using a continuous flow hydrothermal synthesis route. The prepared materials were characterised via XRD, FEG-SEM, EDX, FTIR, and TEM analysis. Magnesium whitlockite (Mg-WH) and hydroxyapatite (HA) were produced by single-phase or biphasic CaPs by reacting struvite with either calcium nitrate tetrahydrate or an eggshell solution at 200 °C and 350 °C. Rhombohedral-shaped Mg-WH (23–720 nm) along with tube (50–290 nm diameter, 20–71 nm thickness) and/or ellipsoidal morphologies of HA (273–522 nm width) were observed at 350 °C using HNO3 or CH3COOH to prepare the eggshell and struvite solutions, and NH4OH was used as the pH buffer. The Ca/P (atomic%) ratios obtained ranged between 1.3 and 1.7, indicating the formation of Mg-WH and HA. This study showed that eggshells and struvite usage, along with CH3COOH, are promising resources as potential sustainable precursors and dissolution media, respectively, to produce CaPs with varying morphologies.

ORCID iDs

Nigar, Farah, Johnston, Amy-Louise, Smith, Jacob, Oakley, William, Islam, Md Towhidul, Felfel, Reda ORCID logoORCID: https://orcid.org/0000-0003-4651-9759, Grant, David, Lester, Edward and Ahmed, Ifty;
CORE (COnnecting REpositories)