Potential use of waste foundry sand in dual process (photocatalysis and photo-Fenton) for the effective removal of phenazone from water: Slurry and fixed-bed approach

Solar-driven hybrid photo-Fenton degradation of persistent antibiotic ciprofloxacin by zinc ferrite-titania heterostructures: degradation pathway, intermediates, and toxicity analysis

Present work puts forward an efficient strategy to degrade one of the persistent antibiotic contaminants, ciprofloxacin (CIP). Hybrid advanced oxidation process (HAOP) is tailored with a synergy effect between photocatalysis and photo-Fenton catalysis on zinc ferrite-titania heterostructured composite (ZFO-TiO₂). The ZFO-TiO₂ heterostructured composite enables heterogenous surfaces for enhanced charge separation where HAOP is implemented for CIP degradation with the aid of class AAA solar simulator. The results reveal an enhanced degradation rate of CIP (k_obs = 0.255 min^-1), noticeably higher than the conventional TiO₂-based photocatalysis. The HAOP system strongly enhances the reaction rates showing five times higher performance as compared to TiO₂-based photocatalysis. The substitution reactions for degradation of CIP into its intermediates were analyzed by LC-MS/MS, and the plausible degradation pathways have been graphically modeled identifying 3-phenyl-1-propanol and phenol molecules as less toxic end products. Toxicity of the photodegraded samples reveal 18.1 ± 1.24% inhibition of V. fischeri at the end of 60-min treatment indicating reduced toxicity of CIP contaminated samples. Antimicrobial inhibition studies on E. coli also corroborate an effective CIP removal (~ 100%) in less than 90 min. The study puts forward a novel ZFO-TiO₂ composite HAOP system for efficient and rapid mineralization of an antibiotic pollutant, extendable towards wide range of pharmaceutical drug degradation studies.

Fly ash-, foundry sand-, clay-, and pumice-based metal oxide nanocomposites as green photocatalysts

Metal oxides possess exceptional physicochemical properties which make them ideal materials for critical photocatalytic applications. However, of major interest, their photocatalytic applications are hampered by several drawbacks, consisting of prompt charge recombination of charge carriers, low surface area, inactive under visible light, and inefficient as well as expensive post-treatment recovery. The immobilization of metal oxide semiconductors on materials possessing high binding strength eliminates the impractical and costly recovery of spent catalysts in large-scale operations. Notably, the synthesis of green material (ash, clay, foundry sand, and pumice)-based metal oxides could provide a synergistic effect of the superior adsorption capacity of supporting materials and the photocatalytic activity of metal oxides. This phenomenon significantly improves the overall degradation efficiency of emerging pollutants. Inspired by the novel concept of "treating waste with waste", this contribution highlights recent advances in the utilization of natural material (clay mineral and pumice)- and waste material (ash and foundry sand)-based metal oxide nanocomposites for photodegradation of various pollutants. First, principles, mechanism, challenges towards using metal oxide as photocatalysts, and immobilization techniques are systematically summarized. Then, sources, classifications, properties, and chemical composition of green materials are briefly described. Recent advances in the utilization of green materials-based metal oxide composites for the photodegradation of various pollutants are highlighted. Finally, in the further development of green materials-derived photocatalysts, we underlined the current gaps that are worthy of deeper research in the future.

Catalytic activity comparison of natural ferrous minerals in photo-Fenton oxidation for tertiary treatment of dyeing wastewater

Natural ferrous minerals are readily available and recyclable catalysts in photo-Fenton-like oxidation for wastewater treatment. In this work, typical ferrous oxide and sulfide minerals including magnetite, chalcopyrite, and pyrrhotite were exploited as catalysts in heterogeneous photo-Fenton oxidation for purification of biological effluent of dyeing wastewater. In a wide initial pH range (3.0~7.5), ferrous mineral-based heterogeneous photo-Fenton-like reactions were proven to be effective on the oxidation of recalcitrant pollutants. COD removals achieved 60.57%, 58.83%, and 57.41% using pyrrhotite, chalcopyrite, and magnetite, respectively, as catalyst under ultraviolet irradiation of 220~275 nm at H₂O₂ concentration of 9.8 mM. The corresponding COD removals were 51.75% and 34.09% with or without ferrous sulfate additions in UV/H₂O₂ systems. Minerals exhibited excellent stability and reusability with photo-catalytic activity reduction of less than 10% in the reuse of 5 cycles. Dissolved iron concentrations were determined to be 1.86 mg L^-1, 4.62 mg L^-1, and 7.53 mg L^-1 for magnetite, chalcopyrite, and pyrrhotite, respectively, at pH 3 and decreased to zero in neutral pH environment, which were much lower than those required for homogenous Fenton reaction. It was deduced that oxidation of recalcitrant pollutants was mainly catalyzed by Fe(II) on the mineral surface. The more reactive oxygen species such as hydroxyl radicals were resulted from the reaction of surface Fe (II) with H₂O₂, H₂O₂ photolysis, and charge separation of minerals under UV irradiation.

Microwave-Assisted Synthesis of Chalcopyrite/Silver Phosphate Composites with Enhanced Degradation of Rhodamine B under Photo-Fenton Process

A new composite by coupling chalcopyrite (CuFeS₂) with silver phosphate (Ag₃PO₄) (CuFeS₂/Ag₃PO₄) was proposed by using a cyclic microwave heating method. The prepared composites were characterized by scanning and transmission electron microscopy and X-ray diffraction, Fourier-transform infrared, UV–Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. Under optimum conditions and 2.5 W irradiation (wavelength length > 420 nm, power density = 0.38 Wcm⁻²), 96% of rhodamine B (RhB) was degraded by CuFeS₂/Ag₃PO₄ within a 1 min photo-Fenton reaction, better than the performance of Ag₃PO₄ (25% degradation within 10 min), CuFeS₂ (87.7% degradation within 1 min), and mechanically mixed CuFeS₂/Ag₃PO₄ catalyst. RhB degradation mainly depended on the amount of hydroxyl radicals generated from the Fenton reaction. The degradation mechanism of CuFeS₂/Ag₃PO₄ from the photo-Fenton reaction was deduced using a free radical trapping experiment, the chemical reaction of coumarin, and photocurrent and luminescence response. The incorporation of CuFeS₂ in Ag₃PO₄ enhanced the charge separation of Ag₃PO₄ and reduced Ag₃PO₄ photocorrosion as the photogenerated electrons on Ag₃PO₄ were transferred to regenerate Cu²⁺/Fe³⁺ ions produced from the Fenton reaction to Cu⁺/Fe²⁺ ions, thus simultaneously maintaining the CuFeS₂ intact. This demonstrates the synergistic effect on material stability. However, hydroxyl radicals were produced by both the photogenerated holes of Ag₃PO₄ and the Fenton reaction of CuFeS₂ as another synergistic effect in catalysis. Notably, the degradation performance and the reusability of CuFeS₂/Ag₃PO₄ were promoted. The practical applications of this new material were demonstrated from the effective performance of CuFeS₂/Ag₃PO₄ composites in degrading various dyestuffs (90–98.9% degradation within 10 min) and dyes in environmental water samples (tap water, river water, pond water, seawater, treated wastewater) through enhanced the Fenton reaction under sunlight irradiation.