Mechanism of the pH-induced aggregation reaction between melamine and phosphate

The mechanism of the pH-induced aggregation reaction between melamine (Mel) and phosphate (Ps) has been studied using a combination of resonance Rayleigh scattering (RRS), FTIR, UV-visible spectra, and single-crystal X-ray and powder X-ray diffraction for the first time. The results confirm that the aggregation reaction between Mel and Ps is highly pH-dependent. Changes in pH dramatically influence the molar ratio of Mel to melaminium (Hmel(+)) and subsequently affect the synergistic nature of hydrogen bonding, electrostatic and pi-pi stacking interactions, resulting in the reversibility of the aggregation and dissolution process. The composition of the Mel-Ps aggregates has been characterized as 2[Hmel(+)]center dot[HPO42-]center dot 3H(2)O. Mechanism analysis demonstrated that there exist two different methods for the transformation of Mel into Hmel(+) by considering the aggregation reaction process and conditions.