The discovery of synthetic Bi₃O(OH)(PO₄)₂ [BOHP] and its application towards photocatalytic oxidation of the water contaminant perfluorooctanoic acid (PFOA) has prompted further interest in development. Despite its high activity towards PFOA degradation, scarce appearance in the literature and lack of research have left a knowledge gap in the understanding of BOHP synthesis, formation, and photocatalytic activity. Herein, we explore the crystallization of BOHP microparticles via hydrothermal syntheses, focusing on the influence of ions and organics present in the reaction solution when using different hydroxide amendments (NaOH, NH₄OH, NMe₄OH, and NEt₄OH). To better understand the unique structure-activity aspects of BOHP, the related bismuth oxy phosphate (BOP) structural family was also explored, including A-BOP (A = N⁺, K⁺) and M-BOP derivatives (M = Ca²⁺, Sr²⁺, Pb²⁺). Results from materials characterization, including X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, indicated crystal structure, morphology, and atomic composition were significantly influenced by solution pH, inorganic metal cations (Na⁺, K⁺, Ca²⁺, Sr²⁺, Pb²⁺), and organic amines. Experiments involving ultraviolet photocatalytic destruction of PFOA by a BOHP suspension revealed that catalytic activity was influenced by of the choice of reagents and their variable effect on surface facet growth and crystal defects in the resulting microparticles. Together, this work provides a strategy for crystal facet and surface defect engineering with potential to expand to other metal oxides within the hydrothermal system.

Marc Mason

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