Facet-Dependent Fe2O3/BiVO4(110)/BiVO4(010)/Fe2O3 Dual S-Scheme Photocatalyst as an Efficient Visible-Light-Driven Peroxymonosulfate Activator for Norfloxacin Degradation.

A lack of eco-friendly, highly active photocatalyst for peroxymonosulfate (PMS) activation and unclear environmental risks are significant challenges. Herein, we developed a double S-scheme Fe2O3/BiVO4(110)/BiVO4(010)/Fe2O3 photocatalyst to activate PMS and investigated its impact on wheat seed germination. We observed an improvement in charge separation by depositing Fe2O3 on the (010) and (110) surfaces of BiVO4. This enhancement is attributed to the formation of a dual S-scheme charge transfer mechanism at the interfaces of Fe2O3/BiVO4(110) and BiVO4(010)/Fe2O3. By introducing PMS into the system, photogenerated electrons effectively activate PMS, generating reactive oxygen species (ROS) such as hydroxyl radicals (·OH) and sulfate radicals (SO4·-). Among the tested systems, the 20% Fe2O3/BiVO4/Vis/PMS system exhibits the highest catalytic efficiency for norfloxacin (NOR) removal, reaching 95% in 40 min. This is twice the catalytic efficiency of the Fe2O3/BiVO4/PMS system, 1.8 times that of the Fe2O3/BiVO4 system, and 5 times that of the BiVO4 system. Seed germination experiments revealed that Fe2O3/BiVO4 heterojunction was beneficial for wheat seed germination, while PMS had a significant negative effect. This study provides valuable insights into the development of efficient and sustainable photocatalytic systems for the removal of organic pollutants from wastewater.

Rational Design and Synthesis of Fe-Doped Co-Based Coordination Polymer Composite Photocatalysts for the Degradation of Norfloxacin and Ciprofloxacin.

The solar light-responsive Fe-doped Co-based coordination polymer (Fe@Co-CP) photocatalyst was synthesized under mild conditions. [Co(4-padpe)(1,3-BDC)]n (Co-CP) was first constructed using mixed ligands through the hydrothermal method. Then, Fe was introduced into the Co-CP framework to achieve the enhanced photocatalytic activity. The optimal Fe@Co-CP-2 exhibited excellent catalytic degradation performance for norfloxacin and ciprofloxacin under sunlight irradiation without auxiliary oxidants, and the degradation rates were 91.25 and 92.66% in 120 min. These excellent photocatalytic properties were ascribed to the generation of the Fe-O bond, which not only enhanced the light absorption intensity but also accelerated the separation efficiency of electrons and holes, and hence significantly improved the photocatalytic property of the composites. Meanwhile, Fe@Co-CP-2 displayed excellent stability and reusability. In addition, the degradation pathways and intermediates of antibiotic molecules were effectively analyzed. The free radical scavenging experiment and ESR results confirmed that •OH, •O2-, and h+ active species were involved in the catalytic degradation reaction; the corresponding mechanisms were deeply investigated. This study provides a fresh approach for constructing Fe-doped Co-CP-based composite materials as photocatalysts for degradation of antibiotic contaminants.

Comparison of visible light driven H2O2 and peroxymonosulfate degradation of norfloxacin using Co/g-C3N4.

As common advanced oxidation processes, Fenton-like and peroxymonosulfate (PMS) processes have received enormous attention due to their high efficiency in the pollutants degradation. In this study, the Co/g-C3N4 photocatalyst was prepared by facial calcination strategy and used to evaluate the behavior of the Co/g-C3N4/H2O2 and Co/g-C3N4/PMS systems for norfloxacin (NOR) photocatalytic degradation under visible light irradiation. The composite photocatalysts exhibited better performance compared to that of pure g-C3N4 due to the efficient separation of electron-hole pairs and visible light absorption. The Co/g-C3N4/PMS system possessed better photocatalytic performance than the Co/g-C3N4/H2O2 system, where the degradation ratio of NOR and removal ratio of total organic carbon (TOC) were 96.4% and 54%, respectively, in 10 min. The photocatalytic mechanism was investigated using reactive species trapping experiments and electron spin-resonance spectroscopy (ESR). ⋅OH and SO4⋅- were the dominant reaction species in the Co/g-C3N4/H2O2 and Co/g-C3N4/PMS systems, respectively. According to the analysis of the NOR degradation path, SO4⋅- could attack the C-H bond on the piperazine ring or quinolone group of NOR, which resulted in it more active and accelerating the destruction of NOR with SO4⋅- and ⋅OH. The destruction of the quinolone group was the main pathway in the H2O2 process, while the destruction of the piperazine ring was the main pathway in the PMS process. In sum, the Co/g-C3N4/PMS process had a higher photocatalytic activity and economic applicability.

The effect of Ultraviolet-B irradiation on the photodegradation of ciprofloxacin and norfloxacin as inhibitors of bacterial DNA replication and cell division in urea medium.

Ciprofloxacin hydrochloride and Norfloxacin are second-generation fluoroquinolone antibiotic against bacterial DNA gyrase, which reduces DNA strain throughout replication. As DNA gyrase is essential through DNA replication, subsequent DNA synthesis and cell division are inhibited. Direct photolysis of fluoroquinolones was studied by using UV irradiation in the presence or absence of other substances that generate free radicals. This study aimed to assess the effect of Ultraviolet B (UVB) irradiation in removing ciprofloxacin and norfloxacin by using a simulating model of wastewater contained urea at pH 4. A known concentration of ciprofloxacin and norfloxacin were prepared in an appropriate aqueous solution in presence or absence 0.2M urea and adjusted at pH 4. The dis-solved drugs were irradiated with UVB-lamp in a dark place for 60 minutes. The percent of removal and the rate of elimination (k) of each drug were calculated. The direct photolysis effect of UVB irradiation was observed with ciprofloxacin which amounted to 24.4% removal compared with12.4% removal of norfloxacin after 60 minutes of irradiation. The effect of UVB irradiation was enhanced by urea to reach 38.9% and 15% for ciprofloxacin and norfloxacin. The calculated k of ciprofloxacin has amounted to three folds of that of norfloxacin. Direct photolysis of ciprofloxacin and norfloxacin can be achieved simply by using a simulation model of 0.2 M urea and UVB irradiation at pH 4. UVB is highly effective in removing ciprofloxacin compared with norfloxacin by 2-3 folds.

Synthesis of Novel Ternary Dual Z-scheme AgBr/LaNiO3/g-C3N4 Composite with Boosted Visible-Light Photodegradation of Norfloxacin.

Promoting the separation of photogenerated charges and enhanced optical absorption capacity is the main means to modify photocatalytic capacities to advance semiconductor photocatalyst applications. For the first time, a novel ternary photocatalyst for dual Z-scheme system AgBr/LaNiO3/g-C3N4 (ALG) was prepared via a modest ultrasound-assisted hydrothermal method. The results indicated that LaNiO3 nanoballs and AgBr nanoparticles were successfully grown on the surface of g-C3N4 nanosheets. A dual Z-scheme photocatalytic reaction system could be constructed based on the energy band matching within AgBr, LaNiO3 and g-C3N4. Metallic Ag during the photocatalytic reaction process acted as the active electrons transfer center to enhance the photocatalytic charge pairs separation. The chemical composition of ALG was optimized and composites with 3% AgBr, 30% LaNiO3 and 100% g-C3N4 which was noted as 3-ALG displayed the best photocatalytic performance. A total of 92% of norfloxacin (NOR) was photodegraded within two hours over ALG and the photodegradation rate remained >90% after six cycles. The main active species during the degradation course were photogenerated holes, superoxide radical anion and hydroxyl radical. A possible mechanism was proposed based on the synergetic effects within AgBr, LaNiO3 and g-C3N4. This work would offer a credible theoretical basis for the application of dual Z-scheme photocatalysts in environment restoration.

Shuttle-like CeO2/g-C3N4 composite combined with persulfate for the enhanced photocatalytic degradation of norfloxacin under visible light.

In this work, the shuttle-like CeO2 modified g-C3N4 composite was synthesized and was combined with persulfate (PS) for the efficient photocatalytic degradation of norfloxacin (NOR) under visible light. Scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) emission spectra were used to characterize the structural and optical properties of the as-prepared catalysts. Active species trapping experiments demonstrated that additional sulfate radicals (·SO4-) formed upon the addition of PS which could cooperate with superoxide radicals (O2-), holes (h+) and hydroxyl radicals (OH) to decompose NOR. Singlet oxygen (1O2) was also formed during the reaction and acted as an important active species. The degradation products of NOR were also identified and analyzed by using LC-MS technology, and the possible degradation mechanism and pathways were proposed and discussed. This work indicated that the shuttle-like CeO2 modified g-C3N4 coupled with PS displayed promising applications in the field of pharmaceutical wastewater purification.

Photocatalytic degradation of norfloxacin using N-doped TiO2: Optimization, mechanism, identification of intermediates and toxicity evaluation.

In this study, the photocatalytic degradation of Norfloxacin (NOR) has been studied using N-doped TiO2 (N-TiO2) under visible light irradiation, which was synthesized from a self-owned patent recipe and procedure. Subsequently, a three-factor five-level model, which was based on the central composite design (CCD), was developed to determine the optimal NOR concentration, N-TiO2 dosage, and initial pH in practical use. Meanwhile, the degradation pathway was identified by high-performance liquid chromatography-mass spectroscopy (HPLC-MS). Moreover, the toxicity of degradation intermediates was determined using the bacterium Escherichia coli so as to evaluate the health risk of the photocatalytic treated influent. The synthesized N-TiO2 nanoparticles were spherical, and the grain sizes were distributed from approximately 12 nm-20 nm, with a specific surface area of 148.52 m2/g. The light absorption is range from the ultraviolet region to the visible light region since the band gap was reduced to 2.92eV. It was demonstrated from the response surface method results that the initial NOR of 6.03 mg/L, N-TiO2 dose of 0.54 g/L, and pH of 6.37 could be the proposed optimal degradation conditions, which resulted in a 99.53% removal of NOR within 30 min under visible light irradiation. Two possible degradation pathways were proposed, including the replacement of F atoms by hydroxyl radicals, piperazinyl ring cleavage, hydroxylation, and decarboxylation. In the acute toxicity test, the toxicity declined 55% after photocatalytic treatment for 60 min. The results show the feasibility and novelty for photocatalytic treatment of antibiotics by N-TiO2 photocatalyst.

Photocatalytic oxidation of norfloxacin by Zn0.9Fe0.1S supported on Ni-foam under visible light irradiation.

Norfloxacin (NOR) is an emerging antibiotics contaminant due to its high resistance to microbial degradation and natural weathering. In this study, Fe-doped ZnS photocatalyst (Zn0.9Fe0.1S) was deposited on nickel foam (Ni-foam) to improve photocatalytic activity under visible light irradiation. The mass ratio of Zn0.9Fe0.1S and Ni-foam was optimized to be 0.03 g catalyst versus per g Ni-foam (0.03 Zn0.9Fe0.1S/Ni-foam), which led to the highest removal rate of 95%. The optimal degradation condition for NOR over 0.03 Zn0.9Fe0.1S/Ni-foam was pH at 7.0, initial NOR concentration of 5 mg L-1, and initial photocatalyst concentration of 11.7 g L-1, with the highest first-order reaction rate constant of 0.025 min-1 and mineralization rate of 63.1%. The NOR removal rate on 0.03 Zn0.9Fe0.1S/Ni-foam photocatalyst (95%) was approximately four times of that obtained on Zn0.9Fe0.1S photocatalyst (25%). The increased photocatalytic performance could be attributed to the function of Ni-foam as excellent electron collectors that provided efficient photoinduced charge separation from Zn0.9Fe0.1S. The reactive species responsible for the degradation of NOR were photo-generated holes, hydroxyl radical, and superoxide radicals. Nearly 90% of the photocatalytic efficiency was retained over seven cycles and the released metal ion concentrations were <0.3% of the total mass of photocatalyst, suggesting high stability of the photocatalyst during the photocatalytic reactions. The aqueous/solid mass transfer and intraparticle mass transfer for Zn0.9Fe0.1S/Ni-foam were not limiting factors for the degradation of NOR. Therefore the Zn0.9Fe0.1S/Ni-foam photocatalyst could be applied in the degradation of hazardous pollutants.

Microwave-Enhanced Photolysis of Norfloxacin: Kinetics, Matrix Effects, and Degradation Pathways.

Degradation of norfloxacin (NOR) was studied using a combination of microwave and UV irradiation methods (MW/UV process). Remarkable synergistic effect was found between MW and UV light. The removal rate with the MW/UV process was much faster than that with UV light irradiation only. Degradation of NOR followed second-order kinetics and ~72% of NOR could be removed in the first 5 min of MW/UV reaction. Influence of inorganic ions (cations (K⁺, Mg2+, Ca2+, Cu2+) and anions (Cl-, SO42-, NO3-, CO32-)), humic acid (HA) and surfactants (cation, anion, and non-ionic) on the degradation of NOR by the MW/UV process was investigated. Among the ions, Cu2+ and NO3- ions inhibited the degradation of NOR. The presence of HA and surfactants in water showed a slight inhibition on the NOR removal. Furthermore, the NOR degradation in the MW/UV process was primarily caused by the ·OH-photosensitization steps. Seven intermediates formed by the oxidation of NOR were identified and three reaction pathways were proposed. Removals of NOR in tap water (TW), synthetic wastewater (WW), river water (RW), and seawater (SW) were also studied, which demonstrated that the MW/UV process was an effective oxidation technology for degrading fluoroquinolone antibiotics in different water matrices.

Sustained molecular oxygen activation by solid iron doped silicon carbide under microwave irradiation: Mechanism and application to norfloxacin degradation.

Sustained molecular oxygen activation by iron doped silicon carbide (Fe/SiC) was investigated under microwave (MW) irradiation. The catalytic performance of Fe/SiC for norfloxacin (NOR) degradation was also studied. Rapid mineralization in neutral solution was observed with a pseudo-first-order rate constant of 0.2239 min-1 under 540 W of MW irradiation for 20 min. Increasing Fe/SiC rod and MW power significantly enhanced the degradation and mineralization rate with higher yield of reactive oxygen species (ROS). Fe shell corrosion and subsequent Fe0/II oxidation by molecular oxygen with MW activation was the key factor for NOR degradation through two-electron-transfer by Fe0 under acidic conditions and single-electron-transfer by FeII under neutral-alkaline solution. Removal rate of NOR was significantly affected by solution pH, showing higher degradation rates at both acidic and alkaline conditions. The highest removal efficiencies and rates at alkaline pH values were ascribed to the contribution of bound FeII species on the Fe shell surface due to the hydroxylation of Fe/SiC. ·OH was the main oxidizing specie for NOR degradation, confirmed by density functional theory (DFT) calculations and radical scavenger tests. DFT calculations were conducted on the reaction/activation energies of the transition/final states of NOR/degradation products, combined with intermediate identification with high performance liquid chromatography coupled with a triple-quadruple mass spectrometer (HPLC-MS/MS), the piperazinyl ring was the most reactive site for ·OH attack, followed by further ring-opening and stepwise oxidation. In this study, Fe/SiC were proved to be an excellent catalyst for the treatment of fluoroquinolone antibiotics with MW activation.

Formulation and stabilization of norfloxacin in liposomal preparations.

A number of liposomal preparations of norfloxacin (NF) containing variable concentrations of phosphatidylcholine (PC) (10.8-16.2mM) have been formulated and an entrapment of NF to the extent of 41.7-56.2% was achieved. The values of apparent first-order rate constants (kobs) for the photodegradation of NF in liposomes (pH7.4) lie in the range of 1.05-2.40×10(-3)min(-1) compared to a value of 8.13×10(-3)min(-1) for the photodegradation of NF in aqueous solution (pH7.4). The values of kobs are a linear function of PC concentration indicating an interaction of PC and NF during the reaction. The second-order rate constant for the photochemical interaction of PC and NF has been determined as 8.92×10(-2)M(-1)min(-1). Fluorescence measurements on NF in liposomes indicate a decrease in fluorescence with an increase in PC concentration as a result of formation of NF(-) species which exhibits poor fluorescence. Dynamic light scattering has shown an increase in the size of NF encapsulated liposomes with an increase in PC concentration. The stabilization of NF in liposomes is achieved by the formation of a charge-transfer complex between NF and PC.

Degradation of quinolone antibiotic, norfloxacin, in aqueous solution using gamma-ray irradiation.

This study reports the efficiency of gamma-ray irradiation to degrade quinolone antibiotic, norfloxacin, in aqueous solution. Laboratory batch experiments were conducted to determine the "pseudo-first" order degradation kinetics of norfloxacin in the concentration ranges of 3.4-16.1 mg L(-1) by gamma-ray irradiation. The dose constant was found to be dependent on the initial concentration of norfloxacin and gamma-ray irradiation dose rate (D r). The saturation of norfloxacin sample solutions with N2, air or N2O, and the presence of tert-butanol and 2-propanol showed that (•)OH played more crucial role in the degradation of norfloxacin. The second order rate constants of (•)OH, eaq (-), and (•)H with norfloxacin were calculated to be 8.81 × 10(9), 9.54 × 10(8), and 1.10 × 10(9) M(-1) s(-1), respectively. The effects of various additives including CO3 (2-), HCO3 (-), NO3 (-), NO2 (-), and thiourea and the pH of the medium on the degradation of norfloxacin were also investigated. Norfloxacin degradation was lower in surface water and wastewater than in ultrapure water. Several degradation byproducts of norfloxacin were identified from which the possible degradation pathway was proposed.

Femtosecond transient absorption spectroscopy study of the early events of norfloxacin in aqueous solutions with varying pH values.

The photophysics and photochemistry of norfloxacin (NF) have been investigated in aqueous solutions of different pH using femtosecond transient absorption spectroscopy (fs-TA). Resonance Raman spectroscopic experiments on NF have also been conducted in aqueous solutions of different pH to characterize the vibrational and structural information on the initial forms of NF. The experimental results in combination with density functional theory calculations of the key intermediates help us to elucidate the early events for NF after photoexcitation in aqueous solutions with varying pH values. The fs-TA results indicate that NF mainly underwent photophysical processes on the early delay time scale (before 3 ns), and no photochemical reactions occurred on this time scale. Specifically, after the irradiation of NF, the molecule reaches a higher excited singlet Sn and then decays to the lowest-lying excited singlet state S1 followed by intersystem crossing to transform into the lowest-lying triplet state T1 with a high efficiency, with an exception that there is a lower efficiency observed in basic aqueous solution due to the generation of an intramolecular electron transfer as an additional pathway to waste energy.

Photolytic degradation of norfloxacin, enrofloxacin and ciprofloxacin in various aqueous media.

The photolytic degradation of norfloxacin, enrofloxacin and ciprofloxacin, fluoroquinolone antibacterials widely used in human and veterinary medicine, was investigated under simulated solar irradiation in different water matrices (river water and synthetic wastewater similar by composition to wastewater of pharmaceutical industry). The results showed that investigated fluoroquinolones degrade very quickly and photodegradation followed pseudo first order kinetics. The slowest photodegradation rate was observed in river water for all three fluoroquinolones. In the case of pharmaceutical mixture irradiation, no significant differences in rate constants were observed compared to single-component experiments. The structures of photodegradation products were determined and photodegradation pathways were suggested. Two main processes occurred primary from enrofloxacin depending on pH values: (I) cyclopropane ring cleavage at pH 4 and (II) oxidative photodegradation at pH 8. The structures of the photoproducts E-1 to E-6 are unknown and have not been reported for this fluoroquinolone. For ciprofloxacin two main processes were also identified depending on experimental conditions. Under acidic conditions (pH 4), reactions involved rather the quinolone ring (cleavage of the cyclopropane ring and fluorine solvolysis), while at pH 8 the side-chain reactions took place. The photodegradation pathway of norfloxacin somewhat differed from the previous two. There was no significant dependence on reaction conditions and there were no two different pathways. Determination and identification of photodegradation products were performed by liquid chromatography-mass spectrometry (LC-MS/MS). The obtained results are of importance for assessing the environmental fate of fluoroquinolones in aqueous media.

Photodegradation of Norfloxacin in aqueous solution containing algae.

Photodegradation of Norfloxacin in aqueous solution containing algae under a medium pressure mercury lamp (15 W, lambda(max) = 365 nm) was investigated. Results indicated that the photodegradation of Norfloxacin could be induced by the algae in the heterogeneous algae-water systems. The photodegradation rate of Norfloxacin increased with increasing algae concentration, and was greatly influenced by the temperature and pH of solution. Meanwhile, the cooperation action of algae and Fe(III), and the ultrasound were beneficial to photodegradation of Norfloxacin. The degradation kinetics of Norfloxacin was found to follow the pseudo zero-order reaction in the suspension of algae. In addition, we discussed the photodegradation mechanism of Norfloxacin in the suspension of algae. This work will be helpful for understanding the photochemical degradation of antibiotics in aqueous environment in the presence of algae, for providing a new method to deal with antibiotics pollution.

Application of advanced oxidation processes to doxycycline and norfloxacin removal from water.

Doxycycline (Dxy) and Norfloxacin (Nfx) have been oxidized by means of different technologies of increasing complexity. Preliminary experiments showed that activated carbon adsorption (1.0 g L⁻¹) of these antibiotics (C(Antibiotic) = 5 × 10⁻5 M) led to a 60 and 85 % of total organic carbon (TOC) removal, however, a significant decrease in adsorption capacity was experienced after several reuses of the adsorbent. UV-C irradiation of Dxy (20 % removal in 2 h) or Nfx (90 % removal in 2 h) did not affect the initial TOC content of the solution while single ozonation (C(O3) gas inlet concentration = 15.0 ppm) led to the instantaneous disappearance of the parent compounds while TOC conversion values in the proximity of 40 % were obtained. Complex systems based on the combination of ozone, UV-C radiation, titanium dioxide and activated carbon led to similar TOC removals of the order of 70 and 65 % for Dxy and Nfx, respectively. An attempt has been made to calculate the quantum yield and direct ozonation rate constants for doxycycline and norfloxacin. Additionally, the best systems, i.e., the O3 and O3/UV-C processes, have been simulated by a pseudoempirical model by considering TOC as a surrogate parameter.

Theoretical assessment of norfloxacin redox and photochemistry.

Norfloxacin, 1-ethyl-6-fluoro-1,4-dihydo-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid, NOR, is an antibiotic drug from the fluoroquinoline family. The different protonation states of this drug formed throughout the pH range is studied by means of density functional theory (DFT) and the spectra of the NOR species computed using time-dependent DFT. Details about their photochemistry are obtained from investigating the highest occupied and lowest unoccupied molecular orbitals. The predominant species under physiological pH, the zwitterion, is the most photoliable one, capable of producing singlet oxygen or/and superoxide radical anions from its triplet state. In addition, the main photodegradation step, defluorination, occurs more easily from this species compared with the other forms. The defluorination from the excited triplet state requires passing a barrier of 16.3 kcal/mol in the case of the zwitterion. The neutral and cationic forms display higher transition barriers, whereas the reaction path of defluorination is completely endothermic for the anionic species. The theoretical results obtained herein are in line with previous experimental data.

Studies of the photooxidant properties of antibacterial fluoroquinolones and their naphthalene derivatives.

We synthesized and determined the production of reactive oxygen species (ROS) as 1O2, *-O2, *OH, H2O2 during the photolysis with UV-A light of three antibacterial quinolones and their naphthyl ester derivatives. Singlet oxygen and ROS dose-dependant generation from norfloxacin (1), enoxacin (2), ciprofloxacin (3) and their respective naphthyl ester derivatives 4-6 were detecting in cell-free systems by the histidine assay and by luminol-enhanced chemiluminescence (LCL). Both the electronic absorption and emission spectra were quantified and their photostability determined. The antibacterial activity in darkness and under irradiation of compounds 4, 5 and 6 was tested on E. coli and compared with their parent drugs.

Laser flash photolysis study of photoionization in fluoroquinolones.

A laser flash photolysis investigation was carried out on the mechanism of electron photoejection in fluoroquinolone derivatives, bearing either electron donating or electron accepting substituents in position 8, laser excited at lambda(exc) = 355 nm in neutral aqueous solutions. The dependence of the hydrated electron absorption at 720 nm on the laser intensity and on the presence of N2O as electron scavenger evidenced that in enoxacin, norfloxacin, and lomefloxacin the photoionization is predominantly two-photon. With rufloxacin, besides the two-photon process, a one photon contribution with a quantum yield of 0.034 was measured.

Validation of a high-performance liquid chromatographic method for the determination of norfloxacin and its application to stability studies (photo-stability study of norfloxacin).

The development and validation study of a sensitive, rapid, reproducible, easy and precise reversed-phase high-performance liquid chromatographic assay for norfloxacin (NFLX) samples from photo-stability of solid dosage forms, without using gradient elution, extraction methods and without using counter-ion has been carried out. The method showed excellent linearity (r2> or =0.999) in the range 1-20 microg ml(-1) using a Lichrosorb-RP-8 column (10 microm, 20 cm x 4.6 mm) and UV-detection (278 nm) at ambient temperature. This method showed good efficiency for the analysis of photodegraded NFLX samples, and was applied to study the photo-stability of NFLX tablets under different conditions (direct sun light, ultraviolet light and fluorescent light). It was proven that the use of a disintegrant can increase the photo-stability of the NFLX in the tablets. This effect was studied in directly compressible tablets with microcrystalline cellulose (MCC) and mannitol for direct compression.