Two different solutions, indicated

Two different solutions, indicated as A and B, respectively, were prepared individually by dissolving the precursors in deionized water. The pH of both solutions was adjusted toB10 (experimental value 9.9). To this purpose, either ammonium hydroxide (NH4OH 20%, Fisher Chemical) (method 1) or potassium hydroxide solution (KOH, Fisher Chemical) (method 2) wereutilized as mentioned in the text. As explained in the Result and discussion section, the Mg30-cACP powders were prepared according to both methods. To this purpose, di-ammoniumhydrogen phosphate (NH4)2HPO4 was also replaced in the initial solution B by di-potassium phosphate (K2HPO4), in the same proportion, leading to the sample denoted Mg30-cACP-K. Toreach pH 9.9, KOH solutions with pH = 13 or 15 were added to solutions A and B, respectively. Solution B containing HPO4 2 ions exhibited buffer properties, so that a stronger initial alkaline solution was required to increase its pH. The rest of the synthesis procedure was the same for both methods. In each case, solution A was added to solution B at room temperature (B22 1C). The resulting mixture was stirred for few minutes and then immediately filtered on a Buchner funnel, washed with alkalinized deionized