Study On The Degradation Kinetics And Mechanism Of Diclofenac Sodium From Water By Ferrate

In recent years,due to the widespread use of pharmaceuticals and personal care products?PPCPs?,a large number of PPCPs have been discharged into environment.Diclofenac sodium?DCF?,a non-steroidal anti-inflammatory drug?NSAID?,is one of the most popular antipyretic and analgesic drugs in the world.With antibacterial property,DCF can't be removed completely by the traditional sewage treatment technologies,polluting the surface water,groundwater and drinking water and threatening the safety of ecosystem and human.Therefore,it is urgent to seek safe,efficient and environmentally friendly technologies for the degradation of DCF,which was used as model pollutants to investigate the reaction kinetics of DCF by K₂FeO₄.The main contents are as followed:?1?The solid K₂FeO₄ samples were characterized by X-ray photoelectron spectroscopy?XPS?,X-ray diffraction?XRD?and Fourier transform infrared spectroscopy?FT-IR?.The results showed that the valence state of Fe on the surface of the prepared samples was hexavalent.The XRD and FT-IR spectra of the samples were in good agreement with the standard spectra of K₂FeO₄,and the characteristic peaks responded obviously,which indicated that the samples were purified K₂FeO₄.In addition,the conventional quantitative determination methods of K₂FeO₄ were compared.It was found that the results measured by direct spectrophotometry showed only error of 1.9%and 0.34%with chromate titration and indirect spectrophotometry,respectively,indicating the feasibility for the rapid determination of the K₂FeO₄ purity using direct spectrophotometry.?2?The influences of temperature,pH and common ions on the stability of K₂FeO₄solution were investigated.The results indicated that the increase of temperature accelerated the self-decomposition of K₂FeO₄ solution,which was the most stable at the pH value of 10.SO₄^2-,Cl^-,NO₃^-,Ca²⁺,Mg²⁺and Na⁺showed nearly no effect on the stability of K₂FeO₄solution,which was improved by SiO₃^2-but reduced by Cu²⁺,Fe³⁺and Fe²⁺.?3?The degradation kinetics and reaction mechanism of DCF by K₂FeO₄ were investigated systematically.It was found that the reaction of DCF with K₂FeO₄ followed the second-order reaction kinetic model and the second-order rate constant of DCF(k_app)was decreased with increasing pH.The presence of CO₃^2-and NOM inhibited the oxidation of DCF due to the hydrolysis,radical scavenging effects and competition,respectively.Cu²⁺could incorporate into the crystal structure of iron?III?oxide or hydroxide nanoparticles,which formed by the decomposition of K₂FeO₄,and thus produced metal ferrites spinel phase CuFe₂O₄ with possessed catalytic activity,and thus enhanced the degradation of DCF.The other common water constituents(e.g.,SO₄^2-,Cl^-,NO₃^-,Mg²⁺and Ca²⁺)showed almost no effect.Based on the seven products detected by quadrupole-time of flight-mass spectrometer?QTOF/MS?,the potential degradation mechanism of DCF by K₂FeO₄ was proposed revealing six different reaction pathways,including hydroxylation,decarboxylation,C-N bond cleavage,dehydrogenation,formylation and dechlorination-hydroxylation.?4?The influencing factors and degradation kinetics of DCF by the joint systems of K₂FeO₄/Fe³⁺,K₂FeO₄/Fe²⁺and K₂FeO₄/Mn²⁺were investigated.The results showed that the degradation of DCF by joint systems followed the pseudo first-order kinetics.The observed pseudo first-order rate constant of DCF(k_obs)was significantly increased with the increasing dosage of Fe³⁺,Fe²⁺and Mn²⁺,which was closely related to the morphology distribution and redox potential of K₂FeO₄ at different pH values,and was positively correlated with the increase of temperature.The molar ratio of K₂FeO₄/Mn²⁺had a great influence on the action mechanism of Mn²⁺in this system.When the molar ratio was less than 2:3,the oxidation product of Mn²⁺was MnO₂,which catalyzed the degradation of DCF by K₂FeO₄.However,when the molar ratio was more than 2:3,the oxidation product of Mn²⁺transformed into KMnO₄,which enhanced the removal of DCF by the addition of oxidation properties.Presences of different water constituents showed different effect on DCF oxidation,with an obvious inhibition by CO₃^2-,but enhancement by Cu²⁺and Zn²⁺.In summary,K₂FeO₄ can effectively remove DCF from water.The self-catalysis of Fe³⁺and Fe²⁺,the catalysis of Mn²⁺and the superposition of oxidation capacity caused by it's reaction products?i.e.,MnO₂ and KMnO₄?make the joint systems of K₂FeO₄/Fe³⁺,K₂FeO₄/Fe²⁺and K₂FeO₄/Mn²⁺became efficient and feasible for practical application.Degrading the organic contaminants,the joint systems can meanwhile convert Fe³⁺and Mn²⁺to be non-toxic and harmless solid particles,which is of great significance for the treatment of actual water bodies.