Effects of amino acids on the formation of hematite particles in a forced hydrolysis reaction

Abstract

The influence of amino acids on the formation of hematite particles from a forced hydrolysis reaction of acidic FeCl 3 solution was examined. The spherical particles were produced on the systems with L-phenylalanine ( L-Phe), L-serine ( L-Ser) and L-alanine ( L-Ala), though L-glutamine ( L-Gln) and L-glutamic acid ( L-Glu) gave ellipsoidal hematite particles. This morphological change in hematite particles is consistent with the order of stability constant of amino acids against to Fe 3+ ions ( K). The hematite particles produced with L-Glu, L-Gln and L-Ser were highly porous because they are formed by aggregation of cluster particles. These particles exhibited microporous behavior by outgassing the particles below 200 °C while they changed to mesoporous after treating above 300 °C by elimination of amino acids molecules remained between the cluster particles within the hematite particles. The hematite particles strongly depended on the nature of amino acids such as alternation of solution pH and adsorption affinity to β-FeOOH and/or polynuclear primary (PN) particles. The systems on L-Ala and L-Phe, showing very rapid phase transformation from β-FeOOH to hematite, exhibited the Ostwald ripening. A rotational particle preparation procedure suggested that the morphology of hematite particle is governed by the mode and strength of amino acid adsorption onto β-FeOOH and/or PN particles.