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The role of the reactive oxygen species and the influence of KBiO3 synthesis method in the photodegradation of methylene blue and ciprofloxacin
摘要： KBiO3 was synthesized by three methods: chemical substitution, hydrothermal and sonochemical. All reaction products were analyzed by X-ray powder diffraction and reveal that KBiO3 presents a cubic structure. The morphology of each sample was analyzed with scanning electron microscopy (SEM), and the micrographs show particles with cube-like (chemical substitution), spheres-like (sonochemical) and flakes-like (hydrothermal) shape. HR-TEM technique was used to confirm the crystal structure and to determine the particle size of the samples, also it was used to corroborate the morphology. The photocatalytic activity of KBiO3 was evaluated on the reactions of the degradation of methylene blue (MB) and Ciprofloxacin (CPFX). An almost 100% discoloration of MB was reached at 120 min with KBiO3 obtained by the sonochemical method and a 67% degradation of CPFX was obtained by KBiO3 synthesized by the hydrothermal method. These results were associated with the catalyst morphology and organic adsorption on the surface of the catalyst. With the aim for a further understanding of the photocatalytic degradation of MB and CPFX, scavengers such as benzoquinone, isopropanol, and catalase were added to the photocatalytic reaction in order to identify the reactive oxygen species (ROS) involved. It has been found that hydrogen peroxide (H2O2) was the primary oxidizing species for the degradation of MB; meanwhile in the case of the oxidation of CPFX occurred by the presence of the superoxide radical (O2?·).
关键词： Photocatalysis,Organic pollutants,Reactive oxygen species,Scavengers,KBiO3
更新于2025-09-23 15:23:52
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Optimizing P25-rGO composites for pesticides degradation: Elucidation of photo-mechanism
摘要： The junction of graphene oxide with TiO2 particles can help develop more efficient photocatalysts capable to harvest radiation in a wider range of the electromagnetic spectrum for real photocatalytic applications. The synthesis procedure of TiO2 P25-rGO composites was optimized to photodegrade a selected mixture of pesticides classified by EU as priority pollutants (alachlor, diuron, atrazine and isoproturon). The influence of temperature and time of hydrothermal method, as well as the effect of graphene oxide (GO) percentage added in the synthesis, was studied to obtain the nanocomposite that showed the highest photoactivity. Long time and moderate temperature have offered the best interaction between TiO2 P25 and rGO. GO was quantitatively reduced to rGO during the hydrothermal treatment, but maintains a higher level of disorder. The optimal GO loading was found around 0.25 wt. %, which allowed the photocatalyst achieve high photocatalytic performance both in phenol and pesticides photodegradation. Finally, in order to try to elucidate the photocatalytic mechanism of the selected mixture of pesticides three scavengers were employed: methanol to scavenge hydroxyl radicals, formic acid for the photogenerated holes, and copper (II) nitrate to quench the electrons of the conduction band. In conclusion, all these pesticides were mostly photodegraded by the hydroxyl radicals (HO?) produced from the photo-induced holes (h+); given that the oxidant species generated from electrons or mediated by direct mechanism were not relevant.
关键词： Scavengers,TiO2P25-reduced graphene oxide composites,Pesticides,Photo-mechanism
更新于2025-09-23 15:23:52
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Synthesis?of?MgTiO <sub/>3</sub> ?Nanoparticles?for?Photocatalytic?Applications
摘要： Magnesium titanate (MgTiO3) has been successfully synthesized via the sonochemical method by using TiO2 (P25) and Magnesium nitrate (MgNO3)2.6H2O as precursors without any additional phases such as MgTi2O5 and Mg2TiO4. The synthesized nanoparticles were well characterized by optical methods using UV-Vis diffuse reflectance spectroscopy (DRS) and Photoluminescence spectroscopy (PL). The morphology of MgTiO3 nanoparticles is irregular in shape with serious agglomerations were confirmed through SEM analysis. XRD confirms crystal structure and phase purity of MgTiO3 nanoparticles calcined at 700 °C for 2 hours. The calculated band gap energy of MgTiO3 nanoparticles has been found to be 3.05 eV. Using the prepared MgTiO3 nanoparticles, the photocatalytic activities were evaluated by following the degradation of Congo red dye under visible light. Moreover, the influence of various scavengers on the photocatalytic reaction were studied.
关键词： MgTiO3,Scavengers,Congo red,Nanoparticles,Photocatalytic degradation,Sonochemical
更新于2025-09-19 17:15:36
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Complexation des acides aminés basiques arginine, histidine et lysine avec l’ADN plasmidique en solution aqueuse : participation à la capture de radicaux sous irradiation X à 1,5 keV
摘要： The chemical environment of DNA in real biological situation is complex notably due to the presence of histones, i.e. nuclear proteins which are linked approximately in equal mass balance to the DNA macromolecule to form chromatin. Histones have numerous terminal tails made up of basic (positively charged) amino acids arginine and lysine while DNA is a macro-anion which holds one negative charge per phosphate moiety all along the double-helix. As a first attempt, in this study, the complexity of the nuclear chromatin structure is mimicked through the formation of complexes made up of the basic amino acids Arg, His, Lys (which apart from His are protonated at physiological pH) and a DNA plasmid used as a probe. Those three amino acids, when free in aqueous solution are known to be effective radical scavengers, notably for the hydroxyl radical, they might therefore protect DNA against indirect effects when exposed to ionizing radiations. At fixed concentration, the scavenging capacities of free amino acids, σ, for the hydroxyl radical are typically such that σHis ≈σArg > σLys (σLys ≈ 0,1 × σArg). We have measured the yields of single strand breaks per plasmid and per Gray (χ) during exposure of aqueous solutions of complexes [amino acid –plasmid DNA] to ultra-soft X-rays (1,5 keV). At equal concentrations, the three complexed amino acids which also are present in large excess in the solutions do not exhibit DNA protection capabilities that are in line with their scavenging capacities ; we find indeed single strand break yields that follow the order χHis > χArg > χLys (χ Lys ≈ 0,01 × χArg). After having detailed our experimental protocol, we analyze the specific features of basic amino acids interactions with DNA, based on a bibliographic survey. The specificity of Arg interaction with DNA, especially its propensity to create bidentate contacts with bases (principally with the G base) makes it possible to propose a way by which high DNA single strand break damage is favored in the presence of Arg. An inter-molecular radical transfer is suggested which also seems to hold for the Lysine amino acid. As for the unexpected high single strand break yields observed with His, we suggest some possible pathways but complementary experiments still will have to be performed.
关键词： ultra-soft X-rays,chromatin,DNA,amino acids,single strand breaks,radical scavengers
更新于2025-09-10 09:29:36
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Pitfalls in the ABTS Peroxidase Activity Test: Interference of Photochemical Processes
摘要： ABTS (2,2′-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid) oxidation to form its radical cation in the presence of H2O2 is frequently used as a test for determining the peroxidase activity of enzyme mimics. Detailed studies using salen-type Mn(III) complexes show that photochemical processes involving H2O2, ABTS, and the complex itself can lead to erroneous results. The capability of the complexes to act as ?OH scavengers can be also relevant when the mechanism of their biological activity is considered.
关键词： photochemical processes,ABTS,peroxidase activity,?OH scavengers,Mn(III) complexes
更新于2025-09-09 09:28:46
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An unusual dependency on the hole-scavengers in photocatalytic reductions mediated by a titanium-based metal-organic framework
摘要： The reductive reactions driven by photo-generated electrons on photocatalysts were generally considered to be irrelevant to the employed hole-scavengers. Herein, we report an unexpected dependence of photocatalytic debromination of decabromodiphenyl ether (BDE 209) on the hole-scavengers catalyzed by amine-functionalized MIL-125(Ti). It was found that the debromination only occurred when triethanolamine, rather than the conventional alcohols, was used as the hole-scavenger. Further low-temperature ESR experiments indicate that triethanolamine participates in the formation of the active catalytic Ti (Ⅲ) species, which shuttle the electron to BDE 209, producing reductive debromination products.
关键词： Photocatalysis,Hole-scavengers,BDE 209,Metal-organic frameworks
更新于2025-09-04 15:30:14