Degradation Pathways Of Ciprofloxacin Research Articles

Enhanced degradation of ciprofloxacin by graphitized mesoporous carbon (GMC)-TiO2 nanocomposite: Strong synergy of adsorption-photocatalysis and antibiotics degradation mechanism

In order to achieve remarkable synergy between adsorption and photocatalysis for antibiotics elimination from water, in this study, a graphitized mesoporous carbon (GMC)-TiO2 nanocomposite was successfully synthesized by an extended resorcinol-formaldehyde (R-F) method. In the composite, the lamellar GMC nanosheets possessed large specific surface area and mesoporous structure, and could adsorb and enrich antibiotics effectively. This could not only reduce the antibiotic concentration in water shortly, but also greatly increase the chances for antibiotics to contact with and be degraded by photocatalysts and active species. Interestingly, GMC could also facilitate the transportation of photogenerated electrons to further improve the photocatalytic efficiency of TiO2, and 15 mg/L ciprofloxacin (CIP) could be totally mineralized in 1.5 h. Meanwhile, the biological inhibition of reaction solution on luminescence bacteria decreased obviously with antibiotics degradation until non-toxicity, reinforcing the thorough elimination of antibiotics. Besides, from the viewpoint of organic chemistry, several plausible CIP degradation pathways were established using HPLC-MS technique, and an interesting intermediate with five-membered ring structure was firstly proposed, which is helpful to deeply understand CIP degradation. Strong synergy between adsorption and photocatalysis, along with quick and efficient antibiotics elimination, double confirm the great potential of GMC-TiO2 nanocomposite for practical antibiotic wastewater purification.

Degradation of ciprofloxacin antibiotic by Homogeneous Fenton oxidation: Hybrid AHP-PROMETHEE method, optimization, biodegradability improvement and identification of oxidized by-products

The main purpose of this experimental study was to optimize Homogeneous Fenton oxidation (HFO) and identification of oxidized by-products from degradation of Ciprofloxacin (CIP) using hybrid AHP-PROMETHEE, Response Surface Methodology (RSM) and High Performance Liquid Chromatography coupled with Mass Spectrometry (HPLC–MS). At the first step, an assessment was made for performances of two catalysts (FeSO4·7H2O and FeCl2·4H2O) based on hybrid AHP-PROMETHEE decision making method. Then, RSM was utilized to examine and optimize the influence of different variables including initial CIP concentration, Fe2+ concentration, [H2O2]/[ Fe2+] mole ratio and initial pH as independent variables on CIP removal, COD removal, and sludge to iron (SIR) as the response functions in a reaction time of 25 min. Weights of the mentioned responses as well as cost criteria were determined by AHP model based on pairwise comparison and then used as inputs to PROMETHEE method to develop hybrid AHP-PROMETHEE. Based on net flow results of this hybrid model, FeCl2·4H2O was more efficient because of its less environmental stability as well as lower SIR production. Then, optimization of experiments using Central Composite Design (CCD) under RSM was performed with the FeCl2·4H2O catalyst. Biodegradability of wastewater was determined in terms of BOD5/COD ratio, showing that HFO process is able to improve wastewater biodegradability from zero to 0.42. Finally, the main intermediaries of degradation and degradation pathways of CIP were investigated with (HPLC-MS). Major degradation pathways from hydroxylation of both piperazine and quinolonic rings, oxidation and cleavage of the piperazine ring, and defluorination (OH/F substitution) were suggested.

Photocatalytic degradation of fluoroquinolone antibiotics using ordered mesoporous g-C3N4 under simulated sunlight irradiation: Kinetics, mechanism, and antibacterial activity elimination

The occurrence of fluoroquinolones (FQs) in the ambient environment has raised serious concerns. In this study, the photocatalytic degradation kinetics and mechanism of ciprofloxacin (CIP) was investigated in ordered mesoporous g-C3N4 (ompg-C3N4). Under simulated sunlight irradiation, ompg-C3N4 exhibited a 2.9 fold more rapid reaction for CIP degradation than bulk g-C3N4. This enhancement may be attributed to the large specific surface area and effective charge separation of ompg-C3N4. The eradication of CIP followed the Langmuir–Hinshelwood (L–H) kinetics model, and surface reactions played a significant role during the photocatalysis process. Further study of reactive species (RSs) by both ESR technology and RSs scavenging experiments revealed that the superoxide anion radical (O2−) and photohole (h+) were primarily responsible for the degradation of CIP. Based on the identification of intermediates using liquid chromatography with tandem mass spectrometry (HPLC-MS/MS), and the prediction of reactive sites via Frontier Electron Densities (FEDs), the degradation pathways of CIP were proposed. A comparison of the degradation among FQs revealed that the piperazine moiety showed a dramatic effect on the degradation of FQs during the photocatalysis process. A residual antibiotic activity experiment revealed that ompg-C3N4 provided a very desirable performance for the reduction of antibiotic activity. The sufficient photocatalytic degradation of CIP in ambient water revealed that a sunlight-driven ompg-C3N4 photocatalytic process may be efficiently applied for the remediation of CIP contaminated natural waters.

Enhanced catalytic degradation of ciprofloxacin with FeS2/SiO2 microspheres as heterogeneous Fenton catalyst: Kinetics, reaction pathways and mechanism

In this study, the application of FeS2/SiO2 microspheres as a catalyst to activate H2O2 for the degradation of ciprofloxacin (CIP) was systematically investigated. Results demonstrated that the presence of SiO2 microspheres on the surface of FeS2 could effectively make the reaction of aqueous Fe2+ and H2O2 smoothly continuous by controlling the release of aqueous Fe2+ from FeS2. Nearly 100% of CIP was degraded after 60min under the optimum conditions. A superior performance on the CIP degradation and high reusability of the catalyst was obtained in FeS2/SiO2 microspheres activated H2O2 system. A low concentration of ethylene diamine tetraacetie acid (EDTA) did positively affect the degradation rate of CIP. A synergetic effect between adsorption and oxidation processes contributed to the significant enhancement of CIP degradation. Seven oxidation intermediates were identified during the CIP degradation process, and the direct HO oxidation proved to be a main CIP degradation pathway. For degradation pathway of CIP, oxidation of piperazine ring would be its first step, followed by cleavage of the heterocyclic ring. Subsequently, the substitution, hydroxylation and decarboxylation processes occurred. This is the first report on the feasibility of FeS2/SiO2 microspheres activated H2O2 system for the enhanced degradation of CIP.

Degradation of ciprofloxacin and sulfamethoxazole by ferrous-activated persulfate: Implications for remediation of groundwater contaminated by antibiotics

The wide occurrence of antibiotics in groundwater raised great scientific interest as well as public awareness in recent years due to their potential ability to spread antibiotic resistant gene and pose risk to humans. The present study investigated the ferrous ion (Fe(II)) activated decomposition of persulfate (S2O82−), as a potential in situ chemical oxidation (ISCO) approach, for remediation of groundwater contaminated by antibiotics. Fe(II)-persulfate mediated ciprofloxacin (CIP) degradation was found to be more efficient than sulfamethoxazole (SMX) at near neutral pH (pH6.0), probably due to the higher electric density in CIP molecule and its ability to form complex with Fe(II) as a ligand. Hydroxyl (HO) and sulfate radical (SO4−) were determined to be responsible for the degradation of CIP and SMX in Fe(II)-persulfate system by molecular probes. No enhancement in the degradation of CIP was observed when citrate (CA), ethylenediaminetetraacetate (EDTA) and (S,S)-ethylenediamine-N,N′-disuccinate (EDDS) were used as Fe(II) chelating agents in Fe(II)-persulfate system. For SMX, CA and EDTA accelerated the degradation by Fe(II)-persulfate. Degradation of antibiotics in river water matrix was nearly the same as that in Milli-Q water, implying the possibility of using Fe(II)-persulfate for antibiotics depletion under environmentally relevant condition. A comparison of the degradation efficiency of SMX with other sulfonamides and sulfanilic acid indicated that the heterocyclic ring has a large impact on the degradation of sulfonamides. Transformation products of CIP and SMX by Fe(II)-persulfate were analyzed by solid phase extraction–liquid chromatography–mass spectrometry (SPE–LC–MS) technique. Based on the intermediate products, Fe(II)-persulfate mediated CIP degradation pathways were tentatively proposed.