g-C3N4-promoted degradation of ofloxacin antibiotic in natural waters under simulated sunlight

This is the first report on the photodegradation of ofloxacin under simulated solar light and in actual environmental matrices in the presence of a g-C₃N₄ suspension. The catalyst, prepared from the polymerization of dicyandiamide (650 °C, reaction yield 60%), was characterized by means of powder X-ray diffraction (PXRD), UV-vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and BET surface area measurements. The experiments were carried out in a lab-scale batch reactor at concentrations in the range of micrograms/milligrams per liter. The course of the reaction was monitored by high-pressure liquid chromatography with UV-vis and fluorescence detectors. The g-C₃N₄-promoted photodegradation occurred at a rate 10 times faster than the direct photolysis and obeyed a first-order kinetics; in addition, the photodegradation kinetics of sonicated g-C₃N₄ resulted to be of the same order of that caused by P25 TiO₂. Finally, the photochemical paths and the photoproducts have been identified and compared to those obtained by using P25 TiO₂. From the results of this study, it can be concluded that g-C₃N₄ is a very attractive photocatalyst compared to P25 TiO₂ in view of its ease of preparation, low cost, excellent oxidizing properties, large fraction of solar radiation absorbed, and intrinsically layered structure.

Enhancement of TiO₂ NPs Activity by Fe₃O₄ Nano-Seeds for Removal of Organic Pollutants in Water

The enhancement of the photocatalytic activity of TiO₂ nanoparticles (NPs), synthesized in the presence of a very small amount of magnetite (Fe₃O₄) nanoparticles, is here presented and discussed. From X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses, the crystallinity of TiO₂ nanoparticles (NPs) seems to be affected by Fe₃O₄, acting as nano-seeds to improve the tetragonal TiO₂ anatase structure with respect to the amorphous one. Photocatalytic activity data, i.e., the degradation of methylene blue and the Ofloxacin fluoroquinolone emerging pollutant, give evidence that the increased crystalline structure of the NPs, even if correlated to a reduced surface to mass ratio (with respect to commercial TiO₂ NPs), enhances the performance of this type of catalyst. The achievement of a relatively well-defined crystal structure at low temperatures (T_max = 150 °C), preventing the sintering of the TiO₂ NPs and, thus, preserving the high density of active sites, seems to be the keystone to understand the obtained results.

Fluoroquinolone antibiotics in the environment

Fluoroquinolones (FQs) are used in large amounts for human and animal medical care. They are excreted as parent compound, as conjugates, or as oxidation, hydroxylation, dealkylation, or decarboxylation products of the parent compound. A considerable amount of FQs and their metabolites may reach the soil as constituents of urine, feces, or manure. The residues of FQs in foods of animal origin may pose hazards to consumers through emergence of drug-resistant bacteria. FQs bind strongly to topsoil, reducing the threat of surface water and groundwater contamination. The strong binding of FQs to soil and sediments delays their biodegradation and explains the recalcitrance of FQs. Wastewater treatment is an efficient elimination step (79%-87% removal) for FQs before they enter rivers. FQs are susceptible to photodegradation in aqueous medium, involving oxidation, dealkylation, and cleavage of the piperazine ring.

Oxidative transformation of fluoroquinolone antibacterial agents and structurally related amines by manganese oxide

Various members of the popular fluoroquinolone antibacterial agents (FQs) have been frequently detected in municipal wastewater and surface water bodies in recent years. This study was conducted to gain a better understanding of the fate of FQs in the sediment-water environment. Seven FQs were examined for adsorptive and oxidative interactions with delta-MnO2 under environmental conditions and exhibited reactivity in the order of ciprofloxacin approximately enrofloxacin approximately norfloxacin approximately ofloxacin > lomefloxacin > pipemidic acid >> flumequine. Four amines that are structurally related to the aniline and piperazine functional groups of FQs showed reactivity to oxidation by delta-MnO2 in the order of 1-phenylpiperazine > aniline > N-phenylmorpholine > 4-phenylpiperidine. Comparison among the above compounds clearly indicates thatthe piperazine moiety of FQs is the predominant adsorptive and oxidative site to MnO2. Product analyses showed that oxidation by MnO2 results in dealkylation and hydroxylation at the piperazine moiety of FQs, with the quinolone ring essentially intact. The reaction kinetics, reactivity comparison, and product characterization point to a surface reaction mechanism that likely begins with formation of a surface complex between FQ and the surface-bound MnIV, followed by oxidation at the aromatic N1 atom of FQ's piperazine moietyto generate an anilinyl radical intermediate. The radical intermediates subsequently undergo N-dealkylation, C-hydroxylation, and possibly coupling to yield a range of products. Even though the quinolone ring appears to be stable with respect to MnO2, it affects the overall reactivity and potentially product distribution of FQs via substituent effects. Results of this study strongly suggest that manganese oxides commonly present in soils will likely play an important role in the abiotic degradation of fluoroquinolone antibacterial agents in the environment.

Pharmaceutical impurities--a mini-review

The control of pharmaceutical impurities is currently a critical issue to the pharmaceutical industry. The International Conference on Harmonization (ICH) has formulated a workable guideline regarding the control of impurities. In this review, a description of different types and origins of impurities in relation to ICH guidelines and, degradation routes, including specific examples, are presented. The article further discusses measures regarding the control of impurities in pharmaceuticals.