Razi University

   Abstract In the first part, the synergistic photocatalytic activity of mixed bismuth oxyhalides (BiOI and BiOCl) and the critical role of iron doping in enhancing Cr(VI) reduction was investigated. By employing FeCl3 as both a chloride source and iron dopant precursor, we achieved in-situ Fe3+ incorporation into bismuth oxyhalides (BiOX; X = Cl/I) during a one-pot co-precipitation synthesis at room temperature. The resulting iron-doped BiOX formed flower-like particles integrated with NH2-UiO-66, a zirconium-based metal-organic framework (MOF), creating a Z-scheme heterojunction composite. The NH2-UiO-66/Fe-BiOX composite exhibited exceptional visible-light-driven Cr(VI) reduction, achieving 98% efficiency within 30 minutes (pH 2, 100 W LED). This performance surpasses the NH2-UiO-66/BiOI reference system (82% efficiency), highlighting the dual role of iron doping and mixed oxyhalide phases in promoting charge separation and suppressing recombination. Mechanistic studies revealed that photogenerated electrons and superoxide radicals (•O2–) act as primary reductants, with the Fe3+/Fe2+ redox cycle enhancing •O2– generation via efficient electron transfer.    In the second part, a one-pot strategy was employed to synthesize a Bi-MOF-based composite photocatalyst. In this system, the ionic liquid acted not only as a structure-directing and stabilizing agent but also as a halide source, leading to the in situ formation of BiOCl in the Bi-MOF matrix. The resulting hybrid exhibited a monolithic porous structure that enhanced light absorption, charge separation, and surface reactivity. Under visible light irradiation from a 100 W LED source, Bi-MOF@BiOCl/IL/PVP (Bi-MOF/BIP) showed a high efficiency of 97% in the degradation of rhodamine dye within 15 min, which was much more active compared to the pristine Bi-MOF. Radical scavenging experiments confirmed that superoxide radicals (?O??), electrons (e?), and holes (h?) generated by the photoreactive species were the dominant responsible for the degradation process. The synergistic interaction between Bi-MOF, BiOCl, PVP, and ionic liquid contributed to efficient charge transfer and enhanced visible light-induced redox activity, highlighting the potential of this composite as an effective photocatalyst for environmental remediation.    In the third part, we investigated the photodegradation of polystyrene using a novel photocatalyst based on NiCo-MOF/GN/SiO? under visible light. We performed the reaction both in the solid phase and in solution to see which conditions were more effective for breaking the polymer chain. The gel-permeation chromatography analysis showed that this composite, especially in the presence of THF, has a very high performance and drastically reduces the molecular weight of polystyrene; so that Mn decreased from the initial value of 67400 g mol?1 to 2377 g mol?1. This significant decrease indicates that the combination of NiCo-MOF and graphene-NH2/SiO2, along with the appropriate solvent, can decompose the polystyrene chain more rapidly and intensively. Investigation of the role of scavengers also showed that both electron and hole species are active in the process and the reaction mechanism proceeds according to the type I charge transfer model. These results prove that this photocatalyst can be an efficient method for degrading resistant polymers under visible light.