Synthesis of novel colored substrate-free pearlescent pigments of vanadium phosphates with large-size layered platelet morphology

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Novel colored substrate-free pearlescent pigments based on vanadium phosphates, VOPO 4 ·2H 2 O (VOP) and H 0.6 (VO) 3 (PO 4 ) 3 (H 2 O) 3 ·4H 2 O (HVP), with layered structures, were synthesized using solution process and hydrothermal synthesis. XRD and SAED analyses confirmed the single crystallinity of VOP and HVP. Hydrogen peroxide (H 2 O 2 ) was crucial for producing larger plate-like crystal grains of VOP and contributing to the phase formation of HVP. FE-SEM analysis revealed that VOP and HVP consist of layered plate-like particles (platelets) with smooth surfaces, achieving small thicknesses and high aspect ratios (diameter to thickness). Notably, this study is the first to report particle diameters of 221 µm for VOP and 220 µm for HVP and to propose VOP and HVP as potential substrate-free pearlescent pigments. The optical properties are characterized by optical reflectance spectra and CIE L ∗ a ∗ b ∗ coordinates, while the pearlescent effect was also evaluated. Under an optical microscope, all samples exhibited striking iridescent colors, visible even in different regions within the same particle. Furthermore, 1 wt% of the green HVP pearlescent pigments were successfully dispersed in the poly(methyl methacrylate) (PMMA) matrix, indicating a good suitability for PMMA colorization. • Novel colored substrate-free pearlescent pigments (VOP and HVP) were synthesized. • H 2 O 2 was crucial for larger particles of VOP and phase formation of HVP. • VOP and HVP exhibit layered plate-like particles with high aspect ratios. • These pigments demonstrate high gloss units and striking iridescent colors. • The compatibility of HVP with the PMMA polymer was evaluated.

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