Spherical 10 nm rhabdophane (LaPO4·H2O) particles were made by controlled precipitation in water using lanthanum citrate chelate and phosphoric acid (La-Cit+/H3PO4) at a temperature of 30°C. Rod-shaped 10 nm × 100 nm rhabdophane particles were made by direct precipitation from lanthanum nitrate and phosphoric acid (La(NO3)3/H3PO4). The lanthanum nitrate to phosphoric acid molar ratios (La:P) were fixed at 1:1 and 1:5 for both methods to study their effect on particle size and shape. The particles were characterized with DTA/TGA, XRD, TEM, SEM, Fourier Transform infrared spectroscopy, and ζ potential measurements. The spherical particle surfaces had absorbed citric acid. The point of zero charge of the rod-shaped and spherical particles was pH 5.4 and 4.3, respectively. Formation mechanisms for the spherical particles are discussed.
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