Maximising carbonate content in sodium-carbonate Co-substituted hydroxyapatites prepared by aqueous precipitation reaction

Potassium–carbonate co-substituted hydroxyapatite compositions: maximising the level of carbonate uptake for potential CO2 utilisation options

“…Synthesis of sodium/carbonate substituted hydroxyapatite compositions also observed lower than expected levels of sodium substitution, even though increasing amounts of sodium carbonate reactant added resulted in increasing levels of carbonate substitution. 25 NH 4 + ions are known to be capable of substituting for the calcium ions in hydroxyapatite 44 and it could therefore be hypothesised that perhaps some competition existed between K + ions and NH 4…”

“…Potassium-carbonate (K-CO 3 ) co-substituted apatites were synthesised at room temperature by aqueous precipitation reaction between calcium hydroxide (Ca(OH) 2 , 98% assay, VWR, UK), phosphoric acid (H 3 PO 4 , 85% solution in water, Merck) and either potassium carbonate (K 2 CO 3 , Z99% assay, Sigma-Aldrich, UK) or potassium hydrogen-carbonate (KHCO 3 , 99.7% assay, Sigma-Aldrich, UK), following a method described previously 25 that was based on an established precipitation reaction. 33 Briefly, two series of compositions were prepared with K 2 CO 3 as the source of potassium ions in Series I and KHCO 3 used in Series II.…”

“…Materials Advances previously 25 that was based on an established precipitation reaction. 33 Briefly, two series of compositions were prepared with K 2 CO 3 as the source of potassium ions in Series I and KHCO 3 used in Series II.…”

“…This mechanism focuses on balancing charge on the calcium and phosphate sites of HA, with any carbonate for hydroxyl substitution considered to occur independently. Our previous work showed that high levels of carbonate substitution, approximately 14 and 18 wt%, were achievable when sodium was the monovalent cation involved in the co-substitution, utilising NaCl and CO 2 gas 10 or the more conventional sodium carbonate/sodium hydrogen carbonate reactants, 25 respectively. In these compositions, however, the sodium counter ion does not provide any specific utilisation or benefit for an application of the material.…”