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Author: search.filters.author.Pulphol, PhierayaSubject: search.filters.subject.Cerium dioxide

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    Surface phosphatization of cerium-lanthanum oxides for catalytically inert white pigments
    (2025-11-01)
    Onoda, Hiroaki
    ;
    Wada, Takuma
    ;
    Charoonsuk, Thitirat
    ;
    Pulphol, Phieraya
    ;
    Muanghlua, Rangson
    Cerium dioxide (CeO<inf>2</inf>) is a UV-scattering agent commonly employed in sunscreens but suffers from oxidative catalytic activity, raising concerns for dermal applications. To address this issue, surface passivation via phosphatization has been explored, although prior attempts with CeO<inf>2</inf> alone failed to eliminate its intrinsic yellow hue due to low reactivity with phosphoric acid. In this study, we introduce a novel white pigment synthesized via the phosphoric acid-mediated treatment of CeO<inf>2</inf>–La<inf>2</inf>O<inf>3</inf> mixtures. By co-utilizing lanthanum oxide, which readily forms lanthanum phosphate—a white, inert compound—we achieved enhanced suppression of oxidative activity alongside improved whiteness. The composite materials were systematically characterized via X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), particle size analysis, colorimetry (Lab*), and catalytic activity assays. The results reveal that phosphatization preferentially proceeds at lanthanum sites, forming phosphate-rich surface layers that diminish redox activity while maintaining favorable dispersion and smoothness properties. The pigment shows high acid resistance and negligible photocatalytic activity, indicating its potential as a safe, non-reactive alternative for cosmetic formulations. This work advances the development of rare-earth-based functional pigments via a scalable, low-temperature route.
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    Synthesis of cerium dioxide-based pigments with co-precipitated phosphate: tuning oxidation catalytic activity for cosmetic and paint applications
    (2025-09-01)
    Onoda, Hiroaki
    ;
    Yamaoka, Kazuto
    ;
    Charoonsuk, Thitirat
    ;
    Pulphol, Phieraya
    ;
    Vittayakorn, Naratip
    Cerium oxide, a popular ultraviolet screening agent in cosmetics, is hindered by its oxidation catalytic activity. Seeking an alternative to cerium phosphate, which increases particle size but lacks catalytic activity, we synthesized a novel cerium hydroxide-cerium oxide pigment by coprecipitating a small amount of phosphate. We chose a baseline Ce/P ratio of 10:1 based on preliminary tests showing that a moderate level of phosphate effectively reduces oxidation catalytic activity while still preserving key cerium oxide characteristics. We evaluated its composition, particle size, oxidation catalyst activity, and hue. Coprecipitation and subsequent heating yielded a yellowish pigment containing both cerium oxide and cerium phosphate. Compared to cerium oxide, our pigment exhibited superior smoothness. Additionally, samples prepared under low pH or high phosphate ratios demonstrated reduced oxidation catalytic activity. However, when applied as a pigment in oil paints, its hiding power was diminished. Our findings highlight a promising strategy for mitigating the catalytic drawbacks of cerium oxide while improving pigment properties, yet caution is warranted regarding its efficacy in paint applications. This study underscores the potential of cerium-based compounds in diverse fields, with room for optimization in specific applications. This study underscores the potential of systematically tuning cerium-based compounds for a range of applications, including cosmetics and paints, by exploring how pH and Ce/P ratio influence catalytic activity, coloration, and particle properties.