Enhanced visible light photocatalytic efficiency of La-doped ZnO nanofibers via electrospinning-calcination technology

A series of La-doped ZnO(La/ZnO)nanofibers were prepared by electrospinning-calcination technology and characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),ultraviolet-visible(UV-Vis)absorption spectroscopy and specific surface area analysis.The effect of numerous operational parameters involving calcination temperature,La doping amount,La-doped ZnO concentration and initial Rhodamine B(Rh B)concentration on photocatalytic efficiency of the composite has been analyzed by using Rh B for degradation under the illumination of visible light.Under optimum conditions,ZnO doped with 1.5 at.%La achieved 94.31%Rh B degradation after 510 min of visible light illumination.The kinetic data of La/ZnO catalyst for Rh B photodegradation fitted the Langmuir-Hinshelwood first-order(LHFO)kinetic model well.

Photodegradation of new herbicide HW-02 in organic solvents

HW-02 is a new organophosphates herbicide which is discovered and developed in China. The kinetics and mechanism of HW-02 photodegradation in the organic solvents were studied at 25°C under the irradiation of ultraviolet light. The results showed that photochemical reaction of HW-02 in organic solvents such as n-hexane, methanol, dimethyl benzene and acetone under UV light could be well described by the first kinetic equation, and the photodegradation efficiency decreased with a order of n-hexane methanol xylene acetone. The photodegradation efficiency constant of HW-02 in n-hexane, methanol, xylene and acetone were 4.951 × 10^-2 , 3.253 × 10^-2 , 2.377 × 10^-2 and 1.628 × 10^-2 min 1 , and the corresponding half-lives were 13.99, 21.20, 29.15 and 42.56 min, respectively. By separation and identification of photoproducts using GC-MS, it could be concluded that HW-02 was photolyzed through ester cleavage, photo-dechlorination and photoisomerization of the molecule itself.

Aquatic photo-transformation and enhanced photoinduced toxicity of ionizable tetracycline antibiotics

Most antibiotics contain ionizable groups that undergo acid-base dissociation giving rise to diverse dissociated forms in aquatic systems depending on the pH of the system.In sunlit surface waters,photochemical transformation plays a crucial role in determining the fate of antibiotics.This study presents a comprehensive examination of the photo-transformation degradation kinetics,pathways and photoinduced toxicity of three widely detected tetracyclines(TCs):tetracycline(TC),oxytetracycline(OTC),and chlortetracycline(CTC).Under simulated sunlight(λ>290 nm),their apparent photolysis followed pseudo-first-order kinetics,with rate constants significantly increasing from H_(2)TCs^(0)to TCs^(2–).Through competition kinetic experiments and matrix calculations,it was found that the anions HTCs–or TCs^(2–)(pH~8–10)were more reactive toward hydroxyl radicals(•OH),while TCs^(2–)(pH~10)reacted the fastest with singlet oxygen(^(1)O_(2)).Considering the dissociated species,the total environmental photo-transformation half-lives of TCs were determined,revealing a strong dependence on the water pH and seasonal variation in sunlight.Generally,apparent photolysis was the dominant photochemical process,followed by^(1)O_(2)and•OH oxidation.Different transformation pathways for the three reactions were determined based on the key photoproducts identified using HPLC-MS/MS.Toxicity tests and ECOSAR software calculations confirmed that the intermediates produced by the•OH and 1O_(2)photo-oxidation processes were more toxic than the parent compounds.These findings significantly enhance our understanding of the complex photochemical fate and associated risks of TCs in aqueous environments.