The photocatalytic activity of silver-doped TiO₂ (Ag-TiO₂) nanoparticles was studied by photocatalytic degradation of lomefloxacin (LMF) using a photoreactor with a mercury lamp (PHILIPS, TUV 8 W T5, E_max = 254 nm). The 1 and 2% silver-doped TiO₂ nanoparticles were synthesized by liquid impregnation (LI) method. The resulting nanoparticles were characterized by surface analytical methods such as X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis and transmission electron microscope (TEM). The study shows 2% Ag-TiO₂ nanoparticles exhibited better results (95% degradation) in 1 h for the degradation of lomeofloxacin compared to 1% Ag-TiO₂ and pure TiO₂. XRD analysis indicated that the crystallite size of TiO₂ was 17.00 nm, while the crystallite size of 1% Ag-TiO₂ and 2% Ag-TiO₂ was 13.07 to 14.17 nm. TEM images show the particle size of Ag-TiO₂ nanoparticles were in the range 40–45 nm in length and 10–15 nm in breadth. Pseudo-first-order rate constants were found to decrease with increase in pH. The effect of UV intensity, catalyst dosage and initial concentration of LMF on the degradation rate were also studied and elaborately discussed.

The kinetics and mechanism of removal of the fluoroquinolone antibacterial levofloxacin (LFC) by free available chlorine (FAC) during water chlorination processes have been investigated for the first time between pH values 4.2 and 8.5. The pH-dependent second-order rate constants were found to decrease with increase in pH ( e.g. apparent second order rate constant; k″_app = 20 dm³ mol ⁻¹ s ⁻¹ at pH 4.2 and k″_app = 1dm³ mol ⁻¹ s ⁻¹ at pH 8.5 and at 25°C). The products of the reaction were determined by liquid chromatography and high resolution mass spectrometry. There are two plausible pathways for the LFC chlorination. The major channel is electrophilic halodecarboxylation of the quinolone moiety in which HOCl reacts at tertiary N(4) amine to form a reactive chlorammonium intermediate (R₃N(4)Cl⁺) that can catalytically halogenate LFC, and the minor channel is chlorination at the piperazinyl moiety in which HOCl reacts at tertiary N(4) amine to form a reactive chlorammonium intermediate (R₃N(4)Cl⁺) followed by intermediate degradation both at the piperazinyl and quinolone moieties with successive chlorination. The effect of temperature on the rate of the reaction was studied at four different temperatures and rate constants were found to increase with increase in temperature and the thermodynamic activation parameters E_a, DL H≠, DL S≠ and Δ G≠ were evaluated and discussed.

The kinetic and mechanistic investigation of oxidation of emerging contaminant lomefloxacin (LMF) by alkaline permanganate was carried out spectrophotometrically. The oxidation product 7-amino-1-ethyl-6, 8-difluoro-4-oxo-quinoline-3-carboxylic acid was identified by Agilent 6130 Series Quadrupole LC/MS. The stoichiometry was found to be 1:2, that is, 1 mol of lomefloxacin reacted with 2 mol Mn(VII). Orders with respect to [LMF] and [OH⁻] were found to be fractional and less that one. The oxidation reaction proceeds via an alkali permanganate species that forms a complex with lomefloxacin and the complex then decomposes to give the product. The rate of reaction was found to decrease with decrease in the dielectric constant. The effects of initially added products and ionic strength have also been investigated. The kinetics of the reaction was also studied at four different temperatures, and the thermodynamic activation parameters for the reaction were evaluated and discussed. The geometry optimization of reactants and activated complex were carried out using density functional theory (DFT). The DFT calculations were accomplished with the TURBOMOLE program package (Version-6.4). The activation energy was found to be ~21 kJ/mol at RI-BP86.def 2-TZVPP level of theory.

Liquid Impregnation (LI) technique was developed to prepare 1% and 2% Ag doped Titania nanoparticles. The characterization of the prepared nanoparticles was achieved by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX) and Transmission Electron Microscopy (TEM). The crystallite size was obtained by Scherrer equation analysis of XRD main peak of doped and undoped nanoparticles. It was observed that crystallite size of bare TiO2 was 17.00 nm, whilst the crystallite size of 1% Ag doped titania and 2% Ag doped titania was 13.07 nm to 14.17 nm. TEM images ascertained that particle size of Ag-TiO2 nanoparticles were in the range 40-45 nm in length and 10-15 nm in width. The pH of the solution exerted a negative effect on photodegradation rate of sparfloxacin. The masking effect on the degradation of sparfloxacin was observed at higher catalyst dosages. The increase in UV intensity linearly enhanced the degradation rate of sparfloxacin and the influence of initial sparfloxacin concentration on the degradation rate was investigated and discussed. Copyright © 2018 VBRI Press.