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Unveiling unusual coloration in amorphous phosphate pigments: a study inspired by the mineral Brazilianite
(2026-12-01)
Onoda, Hiroaki
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Higuchi, Kanata
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Charoonsuk, Thitirat
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Pulphol, Phieraya
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Muanglhua, Rangson
Brazilianite, with the formula NaAl<inf>3</inf>(PO<inf>4</inf>)<inf>2</inf>(OH)<inf>4</inf>, exhibits an intriguing pale yellow to green coloration, a phenomenon not readily explained by the absence of conventional d-block chromophoric metal ions. This study investigates the synthesis of amorphous phosphate-based pigments compositionally analogous to Brazilianite, aiming to replicate and understand the origin of its distinctive coloration through controlled precursor stoichiometry and thermal processing. Sodium, aluminum, and phosphate precursors were precisely mixed and thermally treated. X-ray diffraction (XRD) confirmed the predominantly amorphous nature of the synthesized materials, irrespective of achieving long-range crystalline order analogous to mineral Brazilianite. Despite this, samples processed at intermediate temperatures (e.g., 300–400 °C) exhibited a consistent yellowish hue. This non-conventional coloration, attributed to intrinsic electronic or structural features within the amorphous phosphate network rather than traditional chromophores, represents a significant scientific innovation. This coloration was found to be intrinsically linked to the phosphate network itself. Stability assessments in acidic (0.1 wt% H<inf>2</inf>SO<inf>4</inf>) and basic (0.1 wt% NaOH) environments revealed significant vulnerability, attributed to the facile dissolution of sodium and aluminum phosphate species. Notably, the yellowish coloration persisted across various Na/Al/P compositional ratios, even with systematic variations in aluminum or sodium content. This strongly suggests that the observed color is not critically dependent on a precise Na: Al stoichiometry but is fundamentally governed by the local electronic structure within the phosphate network, potentially involving defect centers or specific P-O-Al/Na linkages. These findings offer valuable insights into designing novel, non-toxic, color-stable pigments where coloration arises from mechanisms beyond traditional transition metal ion incorporation, highlighting the potential role of controlled disorder in phosphate-based materials for sustainable applications.
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The Y3+ Donor-Doped CCTO (Ca0.95Y0.05Cu3Ti4O12) Dielectric Fillers for Electrical Output Enhancement of Flexible Triboelectric Nanogenerator
(2026-06-03)
Saichompoo, Kittipan
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Rattanawongwiboon, Thitirat
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Kingkam, Wilasinee
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Pakawanit, Phakkhananan
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Sukkha, Usa
The escalating wearable electronic devices with their flexible energy sources demand has rendered the imperative scientific challenge on the development of materials for the flexible triboelectric nanogenerators (F-TENG), one of advanced energy harvesting systems. Dielectric material optimization, the Y3+ donor-doped calcium copper titanate based on exactly stoichiometric Ca<inf>0.95</inf>Y<inf>0.05</inf>Cu<inf>3</inf>Ti<inf>4</inf>O<inf>12</inf> (CCTYO), serves as a critical pathway in this work for achieving enhanced F-TENG via compositing with the polydimethylsiloxane (PDMS) polymer. The enhancement of electrical output has garnered substantial interest owing to its increased relative permittivity ((Formula presented.)). The influence of the loaded CCTYO amounts on structure, morphologies, dielectric properties, and electrical output, including open-circuit voltage (V<inf>OC</inf>), short-circuit current (I<inf>SC</inf>) and power density for PDMS/CCTYO composites is investigated. As compared with loading undoped CCTO, the additional Y3+ can improve higher F-TENG output by increasing the (Formula presented.) along with maintaining the loss tangent (tan δ < 0.02) at optimized condition. The appropriate amounts of CCTYO 0.75 wt% make the PDMS/CCTYO F-TENG to achieve V<inf>OC</inf> of ∼76.4 V (8.5 V/cm2) and I<inf>SC</inf> of ∼130.0 μA (14.4 μA/cm2), which were higher than pristine PDMS for 2.7 and 4.3 times. The power density of 53 µW/cm2 is 8.9 times higher than that of 6.3 µW/cm2 from the pristine PDMS. This study also provides a COMSOL multiphysics simulation, bridging laboratory experiments, for quantifying the triboelectric capability of dielectric materials.
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Titanate Nanosheets/Cellulose Composite Showing Improved Crystallinity and Decreased Water Wettability by Gamma-Irradiation
(2025-11-25)
Tariwong, Yaowaluk
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Pulphol, Phieraya
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Sangtawesin, Tanagorn
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Seriwattanachai, Chaowaphat
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Kanjanaboos, Pongsakorn
While molecularly thin nanosheets have been increasingly studied as functional coatings, their use as a hydrophobic and γ-irradiation-tolerant component in biologically derived matrices is to be demonstrated. Herein, simple dip-coating was employed to fabricate titanate nanosheets/cellulose composites, which were subjected to γ-irradiation up to 50 kGy. Their surface chemistry was evaluated by water contact angle (WCA) measurements and X-ray photoelectron spectroscopy (XPS). Upon irradiation, the WCA of all samples nonmonotonically increased in three stages from ∼29 to 50° (noncoated) and ∼46 to 80° (composite, optimized at ∼1.2 wt %Ti loading, or 0.2 mg·cm–2). The titanium content and the 4+ valence did not change with the dose, suggesting the radiolytic stability. The dual surface modification occurs while cellulose fiber morphology and nanoscale mechanical properties are preserved. The increased WCA at the cellulose-part is explained by the γ-irradiation-induced crystallization according to the increased crystallinity index and improved thermal stability. At the other component, nanosheet coating results in increased surface roughness and diminished water–surface interactions. The latter is deduced from DSC measurements of water evaporation from pristine and 50 kGy-irradiated Cs<inf>0.7</inf>Ti<inf>1.825</inf>O<inf>4</inf>layered crystal-a nanosheet precursor. Our work suggests further exploration of nanosheets with diverse structures and compositions as coatings or fillers, which could find applications in γ-irradiation-sterilized barrier films.
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Surface phosphatization of cerium-lanthanum oxides for catalytically inert white pigments
(2025-11-01)
Onoda, Hiroaki
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Wada, Takuma
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Charoonsuk, Thitirat
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Pulphol, Phieraya
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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
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Yamaoka, Kazuto
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Charoonsuk, Thitirat
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Pulphol, Phieraya
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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.

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