Phase Transformation, Photocatalytic and Photoluminescent Properties of BiPO4 Catalysts Prepared by Solid-State Reaction: Degradation of Rhodamine B

Synthesis of Petitjeanite Bi3O(OH)(PO4)2 Photocatalytic Microparticles: Effect of Synthetic Conditions on the Crystal Structure and Activity toward Degradation of Aqueous Perfluorooctanoic Acid (PFOA)

The discovery of synthetic Bi₃O(OH)(PO₄)₂ [BOHP] and its application toward photocatalytic oxidation of the water contaminant perfluorooctanoic acid (PFOA) have prompted further interest in development. Despite its high activity toward PFOA degradation, the 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 = Na⁺ and K⁺) and M-BOP derivatives (M = Ca²⁺, Sr²⁺, and Pb²⁺). Results from materials characterization, including X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, indicated that the crystal structure, morphology, and atomic composition were significantly influenced by solution pH, inorganic metal cations (Na⁺, K⁺, Ca²⁺, Sr²⁺, and Pb²⁺), and organic amines. Experiments involving ultraviolet photocatalytic destruction of PFOA by a BOHP suspension revealed that catalytic activity was influenced by 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 the potential to expand to other metal oxides within the hydrothermal system.

ZIF-8 metal organic framework materials as a superb platform for the removal and photocatalytic degradation of organic pollutants: a review

Metal organic frameworks (MOFs) are attracting significant attention for applications including adsorption, chemical sensing, gas separation, photocatalysis, electrocatalysis and catalysis. In particular, zeolitic imidazolate framework 8 (ZIF-8), which is composed of zinc ions and imidazolate ligands, have been applied in different areas of catalysis due to its outstanding structural and textural properties. It possesses a highly porous structure and chemical and thermal stability under varying reaction conditions. When used alone in the reaction medium, the ZIF-8 particles tend to agglomerate, which inhibits their removal efficiency and selectivity. This results in their mediocre reusability and separation from aqueous conditions. Thus, to overcome these drawbacks, several well-designed ZIF-8 structures have emerged by forming composites and heterostructures and doping. This review focuses on the recent advances on the use of ZIF-8 structures (doping, composites, heterostructures, etc.) in the removal and photodegradation of persistent organic pollutants. We focus on the adsorption and photocatalysis of three main organic pollutants (methylene blue, rhodamine B, and malachite green). Finally, the key challenges, prospects and future directions are outlined to give insights into game-changing breakthroughs in this area.

Photodegradation under UV Light Irradiation of Various Types and Systems of Organic Pollutants in the Presence of a Performant BiPO4 Photocatalyst

In this study, we prepared spheroid microstructures of monoclinic bismuth phosphate BiPO4 by a facile solid-state reaction at 500 °C. The crystal structure was refined using the Rietveld method, where the crystal cell was resolved using a monoclinic system (parameters a, b, c, β) with space group P21/n. SEM images showed that the solid catalyst presented homogeneous morphologies. These BiPO4 microparticles (BiP-500) have been used as photocatalysts to photodegrade, under UV light irradiation, three cationic dyes (Rhodamine B, RhB; Methylene Blue, MB; and Toluidine Blue, TB), three anionic dyes (Congo Red, CR; Orange G, OG; and Methyl Orange, MO) and mixtures of RhB-MB, RhB-OG and MO-OG organic dyes. The photodegradation efficiency of these BiP-500 microparticles is found to be optimal in the case of RhB solutions, RhB-MB and RhB-OG binary mixtures. The BiP-500 catalyst shows a high selectivity for the conversion of the mixture of dyes into CO2 and H2O. Total organic carbon analysis of an anionic dye and a cationic dye (RhB, OG and RhB-MB) confirms the mineralization of the pollutants in the presence of BiP-500 particles. The photocatalytic efficiency of our BiP-500 photocatalyst has been confirmed, with a view to facilitate applications in the field of the depollution of wastewater in the agricultural environment by the degradation of parathion-methyl (PM) as a pollutant.

Fabrication of Hydrotalcite-like Copper Hydroxyl Salts as a Photocatalyst and Adsorbent for Hexavalent Chromium Removal

Cu-HyS-urea and Cu-HyS-NaOH, which are hydrotalcite-like copper hydroxyl salts, were prepared by two different methods, urea hydrolysis and precipitation, respectively. Both synthesis methods provided the successful formation of a copper hydroxyl salt, Cu2(OH)3NO3. From XRD and UV-DRS results, the product from the urea hydrolysis methods (Cu-HyS-urea) displayed higher crystallinity, small bandgap energy (Eg), and high light absorption ability because of some intercalated carbonate anions. For the Cr(VI) removal test, the Cu-HyS-NaOH showed superior adsorption of Cr(VI) than Cu-HyS-urea due to a higher specific surface area, confirmed by BET analysis. However, the Cu-HyS-urea presented higher photocatalytic Cr(VI) reduction under light irradiation than Cu-HyS-NaOH, owing to narrow Eg, less recombination, and a high transfer of the photogenerated charge carriers, proven by the results from photoluminescence, photocurrent density, and electrochemical impedance spectroscopy. Thus, this work provides a new function of the hydrotalcite-like copper hydroxyl salts (Cu-HyS-urea and Cu-HyS-NaOH) that can be utilized not only for adsorption of Cr(VI) but also as photocatalysts for Cr(VI) reduction under light irradiation.