a better control of the phenylphosphonate content was achieved by the direct precipitation approach, just varying the H2PP/H3PO4 molar ratio in the mother solution containing Zr(IV); it was observed that the fraction of PP groups in the solids was higher than that in the mother solution, indicating that the Zr(IV) affinity for the phenylphosphonate anion is higher than that for monohydrogen phosphate.