@article{5ee9ded5ffb54c33b7778da271c0ebf2,
title = "Ph-dependent degradation of diclofenac by a tunnel-structured manganese oxide",
abstract = "The mechanism of diclofenac (DIC) degradation by tunnel-structured γ-MnO2, with superior oxidative and catalytic abilities, was determined in terms of solution pH. High-performance liquid chromatography with mass spectroscopy (HPLC-MS) was used to identify intermediates and final products of DIC degradation. DIC can be efficiently oxidized by γ-MnO2 in an acidic medium, and the removal rate decreased significantly under neutral and alkaline conditions. The developed model can successfully fit DIC degradation kinetics and demonstrates electron transfer control under acidic conditions and precursor complex formation control mechanism under neutral to alkaline conditions, in which the pH extent for two mechanisms exactly corresponds to the distribution percentage of ionized species of DIC. We also found surface reactive sites (Srxn), a key parameter in the kinetic model for mechanism determination, to be exactly a function of solution pH and MnO2 dosage. The main products of oxidation with a highly active hydroxylation pathway on the tunnel-structured Mn-oxide are 5-iminoquinone DIC, hydroxyl-DIC, and 2,6-dichloro-N-o-tolylbenzenamine.",
keywords = "Diclofenac (DIC), Ph-dependent degradation mechanism, Reactive site, Tunnel-structured manganese oxide, γ-MnO",
author = "Hu, {Ching Yao} and Liu, {Yu Jung} and Kuan, {Wen Hui}",
note = "Funding Information: 4.ConTchluisssiotudnsy demonstrated that the pH of media highly influences DIC oxidative degradation on This study demonstrated that the pH of media highly influences DIC oxidative degradation on the tunnel-structured Mn-oxide (-MnO2).2The reduction potential of Mn-oxide, the number of the tunnel-structured Mn-oxide (-MnO2). The reduction potential of Mn-oxide, the number of surface reactive sites (S), and electrostatic affinity between DIC and -MnO22increase with a decrease surface reactive sites (S), and electrostatic affinity between DIC and -MnO2 increase with a decrease in pH value. Consequently, the electron-transfer control mechanism model successfully described in pH value. Consequently, the electron-transfer control mechanism model successfully described degradation evolution with time under acidic conditions (pH = 4–6). While under neutral-to-alkaline degradation evolution with time under acidic conditions (pH = 4–6). While under neutral-to-alkaline conditions (pH = 7–9), the precursor complex-formation control mechanism was highly fitting to the conditions (pH = 7–9), the precursor complex-formation control mechanism was highly fitting to the experimental data. At pH 7–9 the anionic species account for 100% DIC in solution and hence confront experimental data. At pH 7–9− the anionic species account for 100% DIC in solution and hence confront with the competition of OH −ions for the complex formation on the -MnO2 sur2 face. In contrast, the with the competition of OH ions for the complex formation on the -MnO2 surface. In contrast, the acid form of DIC with a sub−stantial ratio under pH 4–6 is favored for the surface complex formation acid form of DIC with a substantial ratio under pH 4–6 is favored for the surface complex formation with less competition. The results of the analysis of oxidative intermediates and products by using with less competition. The results of the analysis of oxidative intermediates and products by using HPLC–MS revealed decarboxylation, hydroxylation, and dimerization as the three main pathways HPLC–MS revealed decarboxylation, hydroxylation, and dimerization as the three main pathways of DIC transformation by -MnO2. Although the oxidation products obtained by -MnO2 are similar of DIC transformation by -MnO2. Although the oxidation products obtained by -MnO2 are similar to those obtained by other Mn-2oxides, hydroxylation of DIC by -MnO22is more active2than other to those obtained by other Mn-oxides, hydroxylation of DIC by -MnO2 is more active than other pathways because of an abundance of flexible corner-shared MnO66 for target pollutant degradation. pathways because of an abundance of flexible corner-shared MnO6 for target pollutant degradation. pathways because of an abundance of flexible corner-shared MnO6 for target pollutant degradation. Supplementary Materials: The following are available online: www.mdpi.com/xxx/s1, Figure S1: DIC species dFiisgturirbeuSti1o:nDvIeCrssupsescoielustdioisnt.rHibAutaionndvAe−rsruepsrseosleunttiothne. aHciAdandiAonizreepdrfeosremntotfh DeIaCc,idreasnpdecitoivneilzye.dTfhoermblaocfkDanICd, Supplementary Materials: The followin−g are available online: www.mdpi.com/xxx/s1, Figure S1: DIC species gray line were calculated based on pK− a = 4.15 of DIC [44]. When pH higher than 7, the ionized species (A ) distribution versus solu−tion. HA and A represent the acid and ionized form of DIC, respectively. The black and− accounts for 100% of DIC in solution pH+. Figure S2: LC–MS chromato+graphic patterns of degradatio−n gorafydleignreadwaetrieo ncailnctuelramteeddibaat+seesd(ao)nTpICKain=E4S.1I5 mofo DdeIC(b[)4+4M].SWphaettnerpnHs ihnigEhSeIr tmhaonde7,utnhde eironpiHze7d.0spfoercireesa(cAtio)n intermediates (a) TIC in ESI mode (b) MS patterns in ESI mode under pH 7.0 for reaction time = 24 h with initial aictimenctoerunm=teds24fioahrteswith1(a00) % initialTICof inDIMnOESCI+im2nloadingosdoe lu(bti) oMn200SppHmg.a.tterFingsuirne ESS2I:+ mLCod–e MSundcerhropmHa7t.o0gforarprheiacctpioanttterimnse =o2f 4dhegwriathdaintiiotinal MnO2 loading 200 mg. + + intermediates (a) TIC in ESI mode (b) MS patterns in ESI mode under pH 7.0 for reaction time = 24 h with initial MACnu.-OYth2.Holor.aaCdnoidngtWr2i.b0-H0utm.iKog.n.asn: aCly.-zYe.Hd .thcoendcaetiaveadndanwdrodteesitghneepdatpher.eAxplleraiumtheonrts.hYa.v-Je.Lr.epaderafonrdmaegdrethede etoxpthereimpuebnltis.hCe.d- Author Contributions: C.-Y.H. conceived and designed the experiments. Y.-J.L. performed the experiments. C.-Y.H. and W.-H.K. analyzed the data and wrote the paper. All authors read and approved the final manuscript. Author Contributions: C.-Y.H. conceived and designed the experiments. Y.-J.L. performed the experiments. C.-YF.Hun.danindgW:T.-hHis.Kre.saenaarclyhzreedcethivee datthaeafnudndwinrogtefr tohme pMaipneirs.trAylloaf uScthieonrcser eaandaTnedchanpoplroogvyeodf tthee fRineaplumblaincuosf cCrihpitn.a, Contract No. NSC 98-2221-E-038 -004, MOST 105-2221-E-131-001-MY3 and MOST 108-2221-E-131-024-MY3. Contract No. NSC 98-2221-E-038 -004, MOST 105-2221-E-131-001-MY3 and MOST 108-2221-E-131-024-MY3 . Funding: This research received the funding from Ministry of Science and Technology of the Republic of China, CCoonntrfalcicttNs of. NInStCer9e8st-:2T22h1e-Eau-0t3h8or-s00d4e,cMlaOreS nTo 1c0o5n-2fl2ic2t1-oEf -i1n3t1e-r0e0s1t.-MY3 and MOST 108-2221-E-131-024-MY3 . Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest. References References References Publisher Copyright: {\textcopyright} 2020 by the authors.",
year = "2020",
month = aug,
doi = "10.3390/W12082203",
language = "English",
volume = "12",
journal = "Water (Switzerland)",
issn = "2073-4441",
publisher = "Multidisciplinary Digital Publishing Institute (MDPI)",
number = "8",
}
