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Innovative simple method for the preparation of simonkolleite-TiO2 photocatalyst with different Zn contents was achieved. The prepared photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), FT-IR, Raman and diffuse reflectance spectroscopy techniques. The photocatalytic activities of the materials were evaluated for the simultaneous detoxification of hexavalent chromium (Cr(VI)) and oxidation of organic compounds commonly present in wastewater under simulated solar light. The best photoreduction efficiency of Cr(VI) has been achieved at 1000 ppm simonkolleite-TiO2 photocatalyst of 5% Zn/TiO2 weight ratio, and pH value of 2.5 to enhance the adsorption onto catalyst surface. Photoreduction was significantly improved by using formic acid as holes scavenger owing to its chemical adsorption on the catalyst surface. Finally, 100% photoreduction of Cr(VI) could be achieved using formic/simonkolleite-TiO2 systems under sunlight. [ABSTRACT FROM AUTHOR]

Multifunctional superparamagnetic magnetite/hydroxyapatite (Fe 3 O 4 /Ca 10 (PO 4) 6 (OH) 2 or MHAp) nano-composites were synthesized via a facile two-step co-precipitation method at room temperature. These magnetic nano-composites underwent heat treatment at various temperatures ranging (400°, 600°, and 900 °C), which were subsequently utilized as nanosorbents for removing Pb2+ ions. The XRD data revealed that both the magnetite and hydroxyapatite synthesized were in a pure phase. In the Fe 3 O 4 /HAp composites, there was an augmentation in the intensity peak of hydroxyapatite observed up to 600 °C. However, at 900 °C, a calcium iron phosphate phase emerged, and magnetite (Fe 3 O 4) transitioned into the hematite (Fe 2 O 3) phase. Elevating the heat treatment enhanced the crystallinity of the developed Fe 3 O 4 /HAp composites while diminishing the surface area. The prepared nanocomposites exhibited high adsorption efficiency across a wide pH range, with an optimal pH of 5.5. Notably, the adsorption rate of Pb2+ reached 94 % within the first 5 min, with complete metal adsorption progressively at 60 min. The kinetic and isotherm analysis of the adsorption process revealed that pseudo-second-order model and Langmuir model agreed well with the adsorption process. Also, FAH 0 demonstrated the highest adsorption capacity (263.2 mg/g) for Pb2+ ions. Furthermore, the Fe 3 O 4 /HAp composite NPs exhibited remarkable recyclability even after five cycles of reuse; retaining an efficiency of over 96 %, and allowing for easy separation without a significant loss of adsorption efficiency. The results of the current desorption study underscore the promising practical applications of these nano-composites in decontaminating aqueous media. [ABSTRACT FROM AUTHOR]