Oxidation Of Tetracycline Research Articles

Enhanced degradation of tetracycline in water over Cu-doped hematite nanoplates by peroxymonosulfate activation under visible light irradiation

Herein, Cu-doped hematite nanoplates (named as CuHNPs) with abundant oxygen-vacancies were prepared through a facile one-pot solvothermal method and used for efficient peroxymonosulfate (PMS) activation to degrade tetracycline (TC) in water. The catalytic activity of optimal CuHNPs-7.5 catalyst to activate PMS for the degradation of TC in water under visible light irradiation is 7.74 and 2.93 times higher than that of pure one without and with visible light irradiation. CuHNPs-7.5 exhibited excellent degradation for TC in the broad pH range from 2.14 to 10.75, and the removal of TC was barely inhibited by co-anions. The combination of free radicals and non-radical pathway, including sulfate radicals (SO4·-), hydroxide radicals (·OH), superoxide radical (·O2-) and single oxygen (1O2), contributed to TC oxidation. The introduction of Cu2+ not only accelerated the transformation of Fe(III)/Fe(II) redox cycle but also induced rich oxygen defects in the structure of hematite, boosting more generation of reactive oxygen species (ROSs) for TC degradation. Density functional theory (DFT) calculation and electrochemical impedance spectroscopy (EIS) tests confirmed the accelerated electrons transfer of CuHNPs-7.5 in PMS activation. This study provides a strategy to construct effective catalysts of PMS activation combining radicals and non-radical pathways for environmental remediation.

Hydrothermal synthesis of Cu-doped ZnS for enhanced photocatalytic degradation of tetracycline under the visible light

Undoped and Cu-doped ZnS were sucessfully synthesized by hydrothermal method. X-ray diffraction, Fourier transform infrared spectrometer, scanning electron microscope, transmission electron microscopy and UV-vis spectrophotometer were used to characterize the synthesized products. Characterization results indicated that Cu has been successfully doped into ZnS, and the doped material was smaller and had looser surface. In addition, the band gap was decreased from 3.50 eV to 2.27 eV through doping of Cu. Photocatalytic degradation of tetracycline confirmed the superiority of Cu-doped ZnS compared with ZnS, and the electron paramagnetic resonance and quenching experiment were used to investigate the photocatalytic mechanism, ·OH was regarded as the dominant species for tetracycline oxidation degradation. The effects of tetracycline concentration and catalyst dosage were further studied. Also, the good stability of Cu-doped ZnS was demonstrated via the 5-cycle test.

Removal of Tetracycline Oxidation Products in the Nanofiltration Process

The possibility of removing tetracycline (TRC) from water in an integrated advanced oxidation and membrane filtration process was investigated. Ozonation and UV/H2O2 photooxidation were applied for the destruction of TRC. Six oxidation products (OPs) retaining the structural core of TRC have been identified. One new TRC oxidation product, not reported so far in the literature, was identified—ethyl 4-ethoxybenzoate. All identified OPs were effectively retained on the membrane in the nanofiltration process. However, chemical oxygen demand (COD) measurements of the filtrates showed that in the case of UV/H2O2 oxidation, the OPs passed through the membrane into the filtrate. Various water matrices were used in the research, including the river water untreated and after ozone treatment. It has been shown that organic matter present in surface water can improve pharmaceutical retention, although it contributes to significant membrane fouling. Pre-ozonation of the river water reduced the membrane fouling. The XPS analysis was used to show ozone and H2O2 influence on the top polymer layer of the membrane. It was shown that the oxidants can damage the amide bond of the polyamide.

Metal-organic framework-derived rodlike AgCl/Ag/In2O3: A plasmonic Z-scheme visible light photocatalyst

A novel metal–organic framework (MOF)-derived rodlike AgCl/Ag/In2O3 plasmonic photocatalyst has been successfully prepared by electrostatic self-assembly, co-precipitation, in-situ photoreduction, and calcination. The photocatalytic activity of the samples was systematically investigated by photocatalytic tetracycline (TC) oxidation and Cr(VI) reduction under visible light irradiation. Among the as-prepared samples, AgCl/Ag/In2O3-2 displayed the most effective photocatalytic activity. For photocatalytic TC oxidation, the apparent rate constant of AgCl/Ag/In2O3-2 was 0.5036 min−1, which was 2.7, 6.5, and 1.8 times higher than that of In2O3 (0.1845 min−1), AgCl/In2O3 (0.1544 min−1) and Ag/In2O3 (0.2850 min−1), respectively. In addition, AgCl/Ag/In2O3-2 also exhibited the highest activity for photocatalytic Cr(VI) reduction, and the photocatalytic Cr(VI) reduction rate of AgCl/Ag/In2O3-2 in 3hrs could reach 94.8%. The superior photocatalytic activity was due to the enhanced absorption in the visible light region caused by localized surface plasmon resonance (LSPR) and the efficient interfacial charge migration and separation in AgCl/Ag/In2O3 samples. Moreover, the intermediates formed in the photocatalytic TC oxidation were identified by GC–MS. Finally, a series of characterizations and simulations (density functional theory, cambridge serial total energy package, and finite difference time domain) were carried out to demonstrate the plasmonic Z-scheme photocatalytic mechanism.

Rational tailoring of the electronic structure for the SrxNaTayO3 semiconductor: Insights into its enhanced photoactivity and optical property

NaTaO3 (NTO), as a popular photocatalyst with the prominent redox ability, largely straddles across the conduction band minimum (CBM) and valence band maximum (VBM) edge over Fermi level. Pristine NTO exhibits the poor light-harvesting ability and the rapid recombination of electron-hole pairs. We proposed an effective method to improve the photocatalytic property of NTO (ABO3-type) by substituting B site with Sr. The SrxNaTayO3 (SNTO) exhibited the boosted photocatalytic activity toward tetracycline oxidation under solar light irradiation. The rate constant for S0.5NTO (molar ratio of Sr: Ta = 1 : 2) was 5.1 times higher than the pure NTO. DFT results indicated that the Sr 3d orbital combining the O 2p and Ta 5d hybrid orbitals, widened the VB of SNTO. The band gap was narrowed from 3.86 to 2.82 eV after Sr substitution, which enhanced its light-harvesting ability. The VBM moved upward for 1.42 V and the CBM moved upward for 0.38 V. The shifts of the CBM and VBM, together with the more stretched Ta–O–Ta configuration, highly facilitated the electron-hole pair separation in SNTO. These electronic structure changes accounted for the significant photocatalytic performance enhancement of NaTaO3 via Sr substitution for B-site-Ta.

Unraveling fundamental active units in carbon nitride for photocatalytic oxidation reactions

Covalently bonded carbon nitride (CN) has stimulated extensive attention as a metal-free semiconductor. However, because of the complexity of polymeric structures, the acquisition of critical roles of each molecular constituent in CN for photocatalysis remains elusive. Herein, we clarify the fundamental active units of CN in photocatalysis by synthesizing CN with more detailed molecular structures. Enabled by microwave synthesis, the as-prepared CN consists of distinguishable melem (M1) and its incomplete condensed form (M2). We disclose rather than the traditional opinion of being involved in the whole photocatalytic processes, M1 and M2 make primary contributions in light absorption and charge separation, respectively. Meanwhile, oxygen molecules are unusually observed to be activated by participating in the photoexcited processes via electronic coupling mainly to M2. As a result, such CN has a higher activity, which was up to 8 times that of traditional bulk CN for photocatalytic oxidation of tetracycline in water.

ELECTROCHEMICAL DETECTION OF TETRACYCLINE AS EMERGENT POLLUTANT IN WATER USING CARBON NANOFIBER-CoAl2O4 ELECTRODE

The aim of this study was to develop an electrochemical procedure for the advanced detection of tetracycline (TC) in water using CoAl2O4 dispersed onto carbon nanofiber-epoxy composite electrode substrate, which was selected from a series of tested carbon-based electrode substrates, i.e., commercial glassy-carbon and boron-doped diamond electrodes and home-made carbon nanotubeepoxy and carbon nanofiber-epoxy composites. Carbon nanofiber-epoxy composite electrode was found the best host for CoAl2O4 modifier based on the electrocatalytic effect towards TC oxidation and detection using cyclic voltammetry (CV) technique. The electrochemical techniques applied for electrochemical detection applications were CV, differential-pulse voltammetry (DPV), square-wave voltammetry (SWV) and chronoamperometry (CA). All the tested electrochemical techniques allowed TC determination and the electroanalytical parameters varied related to the technique type. DPV operated at the step potential of 50 mV and the modulation amplitude of 200 mV allowed the lowest limit of detection of 9 nM for TC determination. The recovery test applied for real surface water spiked with known TC concentrations among the reproducibility and the repeatability showed the great potential for the advanced quantitative determination of TC in real water or in pharmaceutical formulations.

Effect of a novel one-dimensional zinc tungsten oxide nanorods anchored two-dimensional graphitic carbon nitride nanosheets for improved solar-light-driven photocatalytic removal of toxic pollutants and photoelectrochemical water splitting

In this study, one-dimensional zinc tungsten oxide (ZnWO4) was prepared by a simple hydrothermal procedure, and two-dimensional graphitic carbon nitride (g-C3N4) was prepared by a solid-state reaction method. The g-C3N4/ZnWO4 (CZO) heterostructure was prepared by a hydrothermal approach. Further, TEM, HRTEM, XRD, DRS, and electrochemical investigations were used to describe the formation of CZO heterostructure. The photocatalytic performance of a CZO nanocomposite shows promising properties for the degradation of tetracycline (TC). Further, the CZO nanocomposite was also used for the photoelectrochemical (PEC) water oxidation. The morphology and structural analysis demonstrated the successful dispersion of ZnWO4 nanorods over the g-C3N4 nanosheets. The tuning of CZO nanocomposite bandgap confirms the establishment of heterostructure. From the photocatalytic investigations, the CZO nanocomposite degrades the antibiotic TC within 70 min under solar-light irradiation. The detailed PEC investigations notify the CZO nanocomposite has lesser charge-transfer resistance, high response of photocurrent with good stability. The CZO electrolyte shows improved photocurrent density of 0.162 mA/cm2 vs. Ag/AgCl in 0.1 M Na2SO3 electrolyte under solar-light illumination. The detailed mechanisms of photocatalytic degradation of TC and PEC water oxidation were discussed with possible graphical diagrams.

Adsorptive stripping voltammetric determination of Tetracycline in pharmaceutical capsule formulation using Poly(Malachite green) modified glassy carbon electrode

A selective and sensitive electrochemical method based on glassy carbon electrode modified with poly(malachite green) was developed for determination of tetracycline in pharmaceutical capsule formulation. Cyclic voltammetry and electrochemical impedance spectroscopy using [Fe(CN)6]3-/4- as a probe were used to characterize the potentiodynamiclly deposited poly(malachite green) on the surface of glassy carbon electrode. In contrast to the unmodified glassy carbon electrode, the fabricated poly(malachite green) modified glassy carbon electrode showed catalytic property towards two steps irreversible oxidation of tetracycline. Better correlation of the oxidative peak current with the scan rate than with the square root of scan rate supported by slope of 0.60 for log(current) versus log(scan rate) indicated that the oxidation reaction of tetracycline at the modified electrode was predominantly controlled by electron exchange step at the solution polymer interface. Under optimized solution pH, and accumulation parameters, the square wave adsorptive anodic striping peak current response of the modified electrode showed linear dependence on concentration of tetracycline in the range 5–100 μM with determination coefficient, method detection limit, and quantification limit of 0.99588, 1.6 μM, and 5.3 μM, respectively. The tetracycline content of a capsule sample claimed to have 250 mg/capsule was found to be 250.53 mg/capsule with 0.21% deviation. Excellent spike recovery result of 99.80%, and 98.49–99.78% recovery of tetracycline in capsule sample in the presence of 50–200% of UA, AA, and ampicillin validated the applicability of the method for determination of tetracycline in real samples with complex matrix like capsule formulations.

Photocatalytic oxidation of tetracycline by magnetic carbon-supported TiO2 nanoparticles catalyzed peroxydisulfate: Performance, synergy and reaction mechanism studies

TiO2 decorated on ferroferric oxides coupled with activated carbon (TFOC), as a magnetic heterogeneous catalyst, was synthesized and its photocatalytic ability was assessed in coupling with UV light towards peroxydisulfate (PS) activation to degrade tetracycline (TC). Main properties of the catalyst were analyzed by using UV–visible DRS, FESEM, VSM, PL, EDS, TEM, XRD and BET techniques. A proposed reaction mechanism was suggested for activating PS and TC degradation. Both TiO2 and Fe3O4 (FO) were synthesized and dispersed successfully on the carbon surfaces in nano-sized scale. It was found that the photocatalytic activity of TiO2 was accelerated significantly after loading on the magnetic carbon. TFOC showed an excellent magnetic response in the presence of a magnet. According to PL analysis, FO nanoparticles and carbon played a critical role in the suppression of recombination of excited electrons and holes. TFOC in coupling with UV showed a best performance, compared to the other single and binary processes for TC decontamination. After 15 min reaction, the highest level of elimination, 96% TC (60 mg/L) and 72.1% TOC were obtained at optimum operational conditions: pH:5.0, TFOC: 0.3 g/L and PS:1.0 mM. A noticeable synergistic effect was found for TFOC in combination with UV and PS. Both negligible Fe leaching and high efficiency of degradation were achieved with reused times, illustrating that TFOC has an excellent durability and reusability. Based on trapping tests, the importance of involved oxidizing species during TC decontamination over TFOC/PS/UV system was in order of 1O2 > SO4•– > h+ > O2•– > HO•. Among studied anions, the highest quenching impact was observed for chloride ions. Particularly, TFOC composite showed the high catalytic activity as well excellent potential in recovery and its coupling with UV light and PS can be introduced as a promising strategy for efficient destroying TC antibiotic.

Carbon quantum dots decorated heteroatom co-doped core-shell Fe0@POCN for degradation of tetracycline via multiply synergistic mechanisms

In this study, novel core-shell catalyst with a new ternary heterostructure was synthesized (Fe0@POCN/CQDs) for the degradation of tetracycline (TC). The TEM results showed that the Fe0 particles were wrapped in POCN material and many nano CQDs were uniformly dispersed in the material. The new ternary nanocomposite exhibits excellent photocatalytic activity for the removal of TC, which was approximately 4.76 times higher than that of GCN. The enhancement of photocatalytic activity was attributed to the effective heterojunction as well as the multiply synergistic effects of POCN combined with Fe0 and CQDs, which was beneficial for retardation of recombination rate of photogenerated electron–hole pairs and generation of more free radicals for the oxidation of TC. Besides, the reactive oxygen species (ROS) of h+, •O2− and •OH played pivotal roles in the degradation of TC by Fe0@POCN/CQDs during the photocatalytic reaction. At the same times, sulfate radical (SO4•-) and hydroxyl radical (•OH) highlighted the dominant role in the degradation process compared with other free radicals under persulfate hybrid mixture system (PS system), which was further confirmed by radical scavenger experiments and electron spin resonance (ESR) analysis. The response surface methodology (RSM) study indicated that the optimal removal parameters of tetracycline could reach 97.57% within 30 min under PS system. In addition, the possible degradation pathway intermediates of TC were studied by HPLC-MS and the reaction catalytic activity mechanism of Fe0@POCN/CQDs/persulfate system was discussed.

Comparative testing of Ag/Au/Pt graphene electromodified electrodes in electrochemical detection of tetracycline-emerging pollutant

This study aimed to obtain new electrochemically modified electrodes with graphene and Au, Pt, Ag particles considering graphite (GP) and glassy carbon (GC) substrate by applying the chronoamperometry technique to develop the detection protocol of tetracycline (TC) considered as an emerging pollutant in water, using cyclic voltammetry (CV) technique. The graphite-based substrate used for Ag/ Au/ Pt electrodeposition led to the electrode compositions on which TC oxidation process was not diffusion-controlled and as consequence, TC detection failed. TC detection protocols were developed for all Ag/Au /Pt electrodeposited GC and GCGP electrodes. Better limits of TC detection was achieved for Ag electrodeposited on GC-GP at the cathodic potential of 0.460 V/SCE.

Ultra-small zinc oxide nanosheets anchored onto sodium bismuth sulfide nanoribbons as solar-driven photocatalysts for removal of toxic pollutants and phtotoelectrocatalytic water oxidation

Heterostructured nanohybrids were prepared from sodium bismuth sulfide (NaBiS2) and zinc oxide (ZnO) through hydrothermal process. The nanocomposite was used for tetracycline (TC) degradation as well as photoelectrochemical (PEC) water oxidation. Morphology and structural analyses were performed to confirm the dispersion of ultra-small ZnO nanosheets into the NaBiS2 nanoribbons. By tuning the band gap, it was possible to degrade tetracycline toxic pollutant within 90 min under the simulated solar light irradiation, while PEC suggested a lower charge-transfer resistance, high photocurrent response, and exceptionally good stability. The highest photocurrent density of 0.751 mAcm−2 vs. Ag/AgCl in 0.1 M Na2SO3 solution was observed under solar-light illumination. Detailed photocatalytic mechanisms for the degradation of TC and PEC water oxidation are discussed.

Electrochemical Detection of Tetracycline on Highly Sensitive Benzene Sourced CVD Graphene‐Gold Nanoparticles Nanointerfaces

AbstractThe development of sensitive, fast and efficient nanointerfaces as platforms for electrochemical sensing devices for the detection of environmental pollutant including antibiotic pollutant has become a matter of priority for public safety. We report herein a benzene sourced graphene‐gold nanoparticle sensor for the detection of tetracycline using chronoamperometry. Structural analysis using Raman Spectroscopy and x‐ray diffraction spectroscopy (XRD) confirmed the presense of few‐layer graphene. Atomic force (AFM) and scanning electron microscopy (SEM) characterization results confirmed the synthesized graphene to be thin flat sheet‐like material with wide surface area and a thickness of less than 1 nm. Cyclic voltammetry characterization of the fabricated modified electrodes showed diffusion controlled process for the oxidation of tetracycline. The modified electrode exhibited a fast response to the detection of tetracycline and a sensitivity of 1,86×102 μA/mM/cm2.The theoretical detection limit (S/N=3) was 1,60×10−1 μM and the linear dynamic range was from 2,90×101 μM to 1.53×103 μM.

Trace Ti3+- and N-codoped TiO2 nanotube array anode for significantly enhanced electrocatalytic degradation of tetracycline and metronidazole

A trace Ti3+- and N-codoped TiO2 nanotube array (TiON) anode is fabricated by electrochemical reduction after introducing nitrogen into the TiON. The TiON anode material is characterized by scanning electron microscopy, X-ray diffraction, Raman spectra and X-ray photoelectron spectroscopy. Electrochemical analyses of TiON, including cyclic voltammetry, electrochemical impedance spectroscopy and linear scan voltammetry, are conducted to confirm that the electrochemical performance could be significantly improved by electrochemical reduction and N doping. The achieved TiON anode is applied to the electrocatalytic oxidation of tetracycline (TC) and metronidazole (MNZ). The effect of applied current density, initial solution pH and initial TC/MNZ concentration on the reaction kinetics is systematically evaluated to obtain the optimal conditions. The degradation processes follow an apparent first-order kinetic model in all conditions. After 240 min of reaction time, the TC removal efficiency, chemical oxygen demand (COD) removal rate and total organic carbon (TOC) removal rate are >99%, 92.86% and 74.98%, respectively. The MNZ removal efficiency, COD and TOC removal rate achieved are >99%, 93.03% and 79.30%, respectively, after 240 min of degradation. The excellent removal efficiency of TC and MNZ indicates that this TiON anode is a promising material in the practical application of removing antibiotics from water.

Study on the Photocatalysis Mechanism of the Z-Scheme Cobalt Oxide Nanocubes/Carbon Nitride Nanosheets Heterojunction Photocatalyst with High Photocatalytic Performances

An efficient Z-scheme Co3O4/g-C3N4 heterojunction photocatalyst was developed via in-situ forming Co3O4 nanocubes on the g-C3N4 nanosheet in the hydrothermal process. The obtained photocatalyst exhibited high photocatalytic activity for the visible-light-driven catalytic reduction of Cr(VI) and catalytic oxidation of tetracycline (TC). Among the as-synthesized catalysts, Co3O4/g-C3N4-0.04 (the mass ratio of g-C3N4 to Co3O4 is 0.04) sample exhibits the most efficient catalytic activities. The photocatalytic reduction and photocatalytic oxidation efficiencies of Co3O4/g-C3N4-0.04 can obtain 81.3 and 92.6 %, respectively. Moreover, the TC is mineralized in the course of photocatalytic degradation, 72.2% of TOC is removed from the reaction system. In addition, the apparent quantum efficiency for the removal of Cr(VI) was also obtained and the the Co3O4/g-C3N4-0.04 could achieve the highest apparent quantum efficiency among the samples. The enhancing photocatalytic activities originated from the efficient interfacial charge migration and separation obtained in Co3O4/g-C3N4-0.04, which is preliminarily confirmed by the photoluminescence spectra, time-resolved photoluminescence spectra and the photoelectrochemical characterizations. Finally, we speculate that the Co3O4/g-C3N4 heterostructures follow a more reasonable Z-scheme charge transfer in this study, which is confirmed by analyzing the results of electron paramagnetic resonance, radical scavenging experiments, and theoretical calculations.

Novel Z-scheme Ag-C3N4/SnS2 plasmonic heterojunction photocatalyst for degradation of tetracycline and H2 production

A novel Z-scheme Ag-C3N4/SnS2 plasmonic heterojunction photocatalyst was developed for the first time by in situ forming 3D flower-like SnS2 microspheres on the 2D Ag-C3N4 nanosheet. The photocatalytic performances of the samples were systematically examined via the photocatalytic water splitting for H2 production and photocatalytic degradation of tetracycline (TC) under visible light irradiation. Among the as-prepared Ag-C3N4/SnS2 samples with various Ag content, 5Ag-C3N4/SnS2 (the mass ratio of Ag to g-C3N4 is 5 wt%) sample exhibited the most efficient photocatalytic performances. Theapparentreactionrateconstantof 5Ag-C3N4/SnS2 for the photocatalytic oxidation of TC was 0.0201 min−1, which was 7.2, 4.9 and 3.0 times higher than those of the bare SnS2 (0.0028 min−1), g-C3N4 (0.0041 min−1) and g-C3N4/SnS2 (0.0066 min−1), respectively. As for the H2 production, a maximum of 1104.5 μmol g−1.h−1 can be achieved for the 5Ag-C3N4/SnS2. The enhancing photocatalytic performance was attributed to the enhanced absorbance in the visible light region caused by localized surface plasmon resonance (LSPR) and the efficient interfacial charge migration and separation in Ag-C3N4/SnS2 samples. In addition, the photocatalytic degradation pathway of TC was proposed based on nine degradation products confirmed by GC–MS. Finally, there were a series of characterization, such as time-resolved fluorescence emission decay spectra, photoelectrochemical characterizations, and stimulation methods (DFT, CASTEP, and FDTD), to verify the Z-scheme plasmonic heterojunction photocatalysis mechanism.

3D hydrangea-like Mn3O4@(PSS/PDDA/Pt)n with ultrafine Pt nanoparticles modified anode for electrochemical oxidation of tetracycline

Three-dimensional (3D) hydrangea-like Mn3O4@(PSS/PDDA/Pt)n was prepared via in situ reduction of Pt4+ on sea-urchin-like MnO2 coated with lay-by-layer (LBL) films of polyelectrolytes. Combining of ultrafine Pt nanoparticles, 3D structure and manganese oxide support makes these Mn3O4@(PSS/PDDA/Pt)n particles suitable for anode-oxidation of tetracycline (TC) with both excellent mass activity and durability. The performance and possible mechanism of TC degradation on Mn3O4@(PSS/PDDA/Pt)n anode were investigated. The maximal TC removal efficiency on Mn3O4@(PSS/PDDA/Pt)n anode achieved 98.8% at a TC concentration of 60 mg L−1, pH 7.0 and 8 V in the presence of NaCl. The TC electrochemical oxidation on Mn3O4@(PSS/PDDA/Pt)n anode followed a pseudo-first-order kinetic. Additionally, the efficiency of TC removal on Mn3O4@(PSS/PDDA/Pt)1 anode maintained more than 95% after recycling for 5 times, indicating the considerable durability. We also evaluated the application for degradation of other antibiotics. Thus, our research provides a deep insight into the preparation of efficient anode based on 3D manganese oxides loaded with ultrafine Pt particles for potential application in electrochemical oxidation of TC and other antibiotics in contaminated water.

Degradation of tetracycline by UV activated monochloramine process: Kinetics, degradation pathway, DBPs formation and toxicity assessment

The combination of UV and monochloramine (UV/NH2Cl) was investigated to eliminate tetracycline (TC) in water. The results indicated that TC degradation by UV/NH2Cl oxidation far exceeded that by UV photolysis and dark chloramination and these processes well fitted pseudo-first-order kinetics. With the increase of NH2Cl dosage, the pseudo-first-order rate constant (kobs) value increased linearly during TC chloramination, while the growth rate of kobs presented a gradual downward trend in UV/NH2Cl process. TC degradation by UV photolysis, dark chloramination and UV/NH2Cl oxidation displayed highly pH-dependent. As solution pH increased from 5.0 to 9.0, the TC removal increased during UV photolysis, while decreased during dark chloramination. For UV/NH2Cl process, the TC degradation showed a decreasing trend with increasing pH from 5.0 to 7.0, but further increasing pH to 9.0 presented an increasing trend. Reactive chlorine species acted as the major contributors to TC degradation in pH range of 6.0–8.0. TC degradation was not apparently affected after the introduction of HA and chloride, but was substantially accelerated in the presence of HCO3−. The proposed degradation pathways involved the hydroxylation, demethylation, dehydration and chlorine substitution processes. Compared with dark chloramination, the N-Nitrosodimethylamine (NDMA) generation was enhanced during TC oxidation by UV/NH2Cl process. The NDMA concentration increased with increasing solution pH from 6.0 to 8.0 and also elevated in the presences of humic acid (HA), nitrite, nitrate and ammonium during TC oxidation by chloramination and UV/NH2Cl. The results of acute toxicity test demonstrated that the toxicity of the reacted solution exhibited similar trends during dark chloramination and UV/NH2Cl treatment and was found to be obviously higher than UV photolysis.

Oxidation of tetracycline and oxytetracycline for the photo-Fenton process: Their transformation products and toxicity assessment

Advanced oxidation processes have gained significant attention for treating tetracycline (TC) and oxytetracycline (OTC), however, their oxidation using the photo-Fenton process has not been sufficiently studied. Although degradations of TC and OTC were enhanced by increasing H2O2 and Fe2+ within the ranges investigated (H2O2 = 20–50 mg/L and Fe = 1–10 mg/L) under UV irradiation, further experiments for the photo-Fenton process were conducted with 20 mg/L of H2O2 and 5 mg/L of Fe2+ to balance efficiency and cost. The photo-Fenton process (UV/H2O2/Fe2+) was shown to be more effective to remove TC and OTC than H2O2, ultraviolet (UV), and UV/H2O2 at the same doses of oxidants. Inorganic anions and cations were shown to inhibit the degradation of TC and OTC during the photo-Fenton process, in the following order: HPO42- > HCO3− ≫ SO42- > Cl− and Cu2+ ≫ Ca2+ > Na+. The TC and OTC degradation are generally improved by increasing pH, which is opposite to the kpCBA,obs values, caused by increasing the deprotonation degree of TC and OTC. Four and nine transformation products of TC and OTC, respectively, were detected over the treatment period. Among the transformation products, m/z 443.14 (C22H22N2O8) formed during TC degradation, and m/z 433.16 (C20H20N2O9) and m/z 415.15 (C20H18N2O8) formed during OTC degradation, were reported for the first time. Vibrio fischeri toxicity assessment indicated that the inhibition ratio was decreased with a decreasing TC concentration, while, OTC transformation lead to higher toxicity. The product (m/z 477.15b) was determined to be the compound causing toxicity during degradation of OTC by using the quantitative structure activity relationship (QSAR). This toxic transformation product caused higher inhibition ratios than its parental compound (OTC), but its further oxidization resulted in decreasing the inhibition ratios.