Effect of magnetite transformations on degradation efficiency of cerium dioxide-magnetite composite

j m a e e s e c h n o l . 2 0 2 0;9(3):4431–4439 www.jm .com.b A ailable online a www.sciencedi ec .com O iginal a icle E ec o magne i e ans o ma ions on deg ada ion e ficiency o ce ium dioxide-magne i e composi e Y onna Ji asko aa,∗, Ji i Bu sika, Jakub Ede e b, Pa el Janosb, Jan Ju icac, Ji i Lunacekd, Ond ej Zi o skyd aCEITEC IPM, Ins i u e o Physics o Ma e ials, AS CR, ˇ Ziˇ zko a 22, 616 62 B no, Czech Republic bFacul y o he En i onmen , Uni e si y o Jan E angelis a Pu kynˇ e, K álo a V´ yˇ sina 7, 400 96 Ús í nad Labem, Czech Republic cRegional Ma e ials Science and Technology Cen e, Vˇ SB – Technical Uni e si y o Os a a, 17. Lis opadu 2172/15, 708 00 Os a a-Po uba, Czech Republic dDepa men o Physics, Vˇ SB – Technical Uni e si y o Os a a, 17. Lis opadu 2172/15, 708 00 Os a a-Po uba, Czech Republic a i c l e i n o A icle his o y: Recei ed 26 Decembe 2019 Accep ed 18 Feb ua y 2020 A ailable online 28 Feb ua y 2020 Keywo ds: CeO2 I on oxide Mic os uc u e Magne ic p ope y Mössbaue spec oscopy Deg ada ion e ficiency a b s a c P esen in es iga ions a e ocused on syn hesis o magne i e/ce ium dioxide eac i e so - ben s in a ious weigh a ios o componen s and hei cha ac e iza ion o chemical and magne ic p ope ies. The mo phology and changes in magne ic ans o ma ions in depen- dence on composi ion a e ollowed by elec on mic oscopy, X- ay di ac ion, Mössbaue spec oscopy and magne ic measu emen s a oom and low empe a u es. Deg ada ion e ficiency is e alua ed om a decomposi ion o he o ganophospho us pes icide pa a hion me hyl using p epa ed eac i e so ben s. The expe imen al esul s e eal ha he deg a- da ion e ficiency, exp essed by a e cons an (mol/h) in dependence on amoun o ce ium dioxide con en ( ol.%), is independen on kind o i on oxide bu inc eases wi h ce ium diox- ide con en . On he con a y, sa u a ion and emanen magne iza ions a e highly sensi i e o ela i e a io o i on oxides; magne i e, maghemi e and hema i e, o igina ing om he ini ial magne i e ans o ma ions in dependence on sample composi ion. © 2020 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/). 1. In oduc ion The a e ea h ce ium oxide o ce ium dioxide belongs p esen ly o equen ly s udied opic. I is p epa ed by a ious syn he ic p ocedu es and cha ac e ized wi h la ge numbe o expe imen al me hods. Among echnologies, e.g., sol-gel me hods, homogeneous hyd olysis [1], hyd o he mal syn he- ∗Co esponding au ho . E-mail: [email p o ec ed] (Y. Ji asko a). sis [2,3], p ecipi a ion me hods using oxala e, ammonium hyd oxide and ammonium ca bona e [4–6] can be men ioned. Ce ium dioxide and ce ium dioxide-based composi es a e used in di e en echnological applica ions [7]. These include a wide ange o ca aly ic applica ions [8], solid oxide uel cells [9,10], oxygen senso s [11], glass-polishing [12], an ul a io- le abso ben , e.g., o cosme ic use [13,14], eac i e so ben s [15–17]. The las decade assumes also impo ance in he medical field. Thanks o ce ium dioxide sel egene a ing an ioxidan p ope ies, i ep esen s a p omising an ioxidan o healing nume ous un ea able oxida i e-s ess- ela ed diseases [18–21]. h ps://doi.o g/10.1016/j.jm .2020.02.068 2238-7854/© 2020 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license (h p:// c ea i ecommons.o g/licenses/by-nc-nd/4.0/). 4432 j m a e e s e c h n o l . 2 0 2 0;9(3):4431–4439 Ce ium dioxide is he mos widely known compound o ce ium. I c ys allizes in fluo i e c ys al s uc u e wi h cc uni cell, space g oup Fm3m. I has pale yellow colou and is p ac ically insoluble in wa e and only mode a ely soluble in s ong mine al acids. I can abso b small amoun mois u e and ca bon dioxide om he a mosphe e. The p ope y ha is equen ly discussed a p esen is i s easy o ma ion o oxy- gen acancies which should be a eason o i s e omagne ic beha iou in he nanosized s a e (pa icle dimensions < 15 nm) [22,23] in spi e o i s diamagne ic s a e in he bulk o m. Ge and co-au ho s [24] e ified expe imen ally and heo e ically ha oxygen acancies cause an inc ease in magne iza ion o nanopa icles compa ed o bulk samples due o e ec - ing he su ounding o elec ons leading o an inc ease in magne ic momen s o pa icles. The oom- empe a u e e - omagne ism o ce ium dioxide is also influenced by ei he goal-di ec ed ansi ion me al doping [25–28] o by magne ic impu i ies [29,30]. P e ious s udies e ealed an unusual abili y o ce ium oxide o des oy oxic o ganophospha e compounds; his abil- i y demons a es no only in pu e nano-ce ium dioxide, bu also in magne ically sepa able composi es based on Fe-oxides and CeO2. Va ious chemical p ocedu es we e examined and sui able composi ions and he mal ea men s a e sea ched and s udied [15,31,32]. P esen wo k is also de o ed o magne ically sepa able so - ben s based on i on and ce ium oxides o di e en mu ual olume a ios and exposed o he same calcina ion ea - men . The mic os uc u al and physical cha ac e is ics o hese sys ems ha e been s udied in o de o co ela e hem wi h he sensing p ope ies owa ds haza dous o ganophos- pha es. 2. Expe imen al 2.1. Ma e ials and sample p epa a ion The inpu ma e ials o he sample p epa a ions we e pu - chased as eagen -g ade chemicals om Sigma Ald ich (S einheim, Ge many). The ce ium ca bona e was p epa ed om he comme cial Ce(NO3)3.6H2O (pu i y 99.9%) and NH4HCO3(pu i y 99.5%) by p ecipi a ion me hod published elsewhe e [15]. B iefly, he ca bona e p ecu so was p e- pa ed by p ecipi a ion o an aqueous solu ion o Ce(NO3)3 (0.2 mol L−1) wi h an excess o NH4HCO3(0.5 mol L−1) unde s i ing. A e he p ecipi a ion p ocess, he agi a ion con in- ued o one mo e hou and he p ecipi a e was le in he solu ion un il he nex day. The p ecipi a e was sepa a ed by fil a ion, washed wi h deionized wa e and d ied o e nigh a 110 ◦C. Subsequen ly he adequa e mass o ce ium ca bon- a e and a ificial magne i e (Fe3O4pa icle size 50–100 nm) was mechanically mixed in a ios om 0/100 up o 50/50 (CeO2/Fe3O4). The mix u es o ce ium ca bona e/Fe3O4we e subjec ed o annealing p ocess a 500 ◦C o 2 h in ai a mo- sphe e. Du ing annealing ce ium ca bona e ans o ms in o ce ium oxide (CeO2). 2.2. Scanning and ansmission elec on mic oscopy, X- ay di ac ion, pa icle size analyze The mo phology o samples we e ollowed by TESCAN LYRA 3XMU FEG/SEM scanning elec on mic oscope a accele a ing ol age o 20 kV, equipped wi h an X-Max80 Ox o d Ins u- men s de ec o o ene gy-dispe si e X- ay (EDX) analysis. FEI Ti an Themis 60–300 cubed high esolu ion ansmission elec- on mic oscope wi h a high sensi i i y EDX sys em (0.7 s ad solid angle) ope a ing a 300 kV was used o selec ed samples o see hei mo phology in mo e de ails. X’PERT PRO di ac ome e (Panaly ical) equiped wi h Co K␣ adia ion (␭ =0.17902 nm) was used o di ac og am measu e- men s in he ange o 2 = 20◦–135◦, s eps = 0.01◦, and ime/s ep 5 s. Rie eld s uc u e efinemen me hod [33] using he High- Sco e Plus p og am and he ICSD da abase [34] we e applied o analyze he ela i e abundance o phases (A) and hei basic pa ame e s, la ice cons an (a) and mean mic o-domain size (d). Pa icle-size dis ibu ion was measu ed by lase di ac ion pa icle size analyze Mas e Size 3000, Mal e n Ins umen s L d. 2.3. Magne ic and Mössbaue measu emen s Room empe a u e magne ic measu emen s in an applied ex e nal field o ±1600 kA/m (±2 T) we e pe o med using ib a ing sample magne ome e (VSM) EZ9 (Mic osense, Massachuse s, USA). This equipmen was used also o measu emen s o he ini ial ( i gin) cu e, MVIR(H), and magne iza ions a inc easing (MUP) and dec easing (MDOWN) posi i e magne ic fields. These cha ac e is- ics a e needed o de e mina ion o he Henkel plo : M(H) = MVIR(H) − (MUP(H) + MDOWN(H))/2. A physical p ope y measu emen sys em (PPMS, Model P935A, San Diego, USA) quan um design was applied o mea- su emen s o hys e esis loops wi h maximal magne ic field o ±4000 kA/m (±5 T) and ze o-field-cooled (ZFC) and field- cooled (FC) cu es in he magne ic field o 8 kA/m and in he empe a u e ange (2–293 K). Mössbaue spec oscopy (MS) measu emen s we e done in ansmission geome y a oom empe a u e using a57Co (Rh) sou ce. Calib a ion o he eloci y scale was pe o med wi h ␣-Fe a RT and he isome shi s a e gi en wi h espec o i s Mössbaue spec um. All spec a we e e alua ed using he ansmission in eg al app oach in he p og am CONFIT [35]. The expe imen al poin s we e analysed by double- and single-line componen s yielding alues o isome shi (ı) and quad upole spli ing (). The ela i e ep esen a ion o hese subcomponen s is deno ed by A. 2.4. Deg ada ion e ficiency Deg ada ion e ficiency was de e mined om pa a hion me hyl (PM) decomposi ion in o 4-ni o enol (FN); see Re . [15] o mo e de ails. The simple eac ion PM⇒FN is assumed and kine ics o such eac ion is ollowed ei he on a weigh loss j m a e e s e c h n o l . 2 0 2 0;9(3):4431–4439 4433 Fig. 1 – Sample o nominal composi ion Fe3O4+10 w .% Ce2(CO3)3a e calcina ion ea men ; le panel – a ea EDX analyses om he sp ead powde , igh panel – local analyses om indi idual cons i uen s. The ob ained composi ions (in a .%) a e shown below. Fig. 2 – Mo phology as seen in SEM, seconda y elec ons (a) and XRD di ac og am (b) o magne i e in he ini ial s uc u al s a e. o PM o an inc ease o FN amoun . Unde p esump ion ha no o he eac ion exis s he loss o PM should be equal o he inc ease o FN. This was alid in p esen s udy. 3. Resul s and discussion 3.1. Mo phology, phase and chemical composi ion Chemical analysis was done by EDX in SEM on powde s sp ead on a conduc i e ape. Se e al a eas we e selec ed a each sam- ple and he in eg al alues we e measu ed. Along wi h la ge a ea analyses, he poin EDX analyses o indi idual phases we e measu ed as well. As an example, he sample o nom- inal composi ion Fe3O4+10 w .% Ce2(CO3)3a e calcina ion ea men (500 ◦C/2 h/ai ) is shown in Fig. 1. To ollow changes in phase composi ion o he mixed samples a e calcina ion ea men , bo h inpu powde s, i.e. magne i e and ce ium ca bona e, we e also ea ed sepa a ely by he same calcina ion pa ame e s. The mo phology o ini ial magne i e is seen in Fig. 2a and X- ay di ac og am anal- ysed using ICSD 20596 da a shee is depic ed in Fig. 2b. The 4434 j m a e e s e c h n o l . 2 0 2 0;9(3):4431–4439 Fig. 3 – Mo phology as seen in SEM, seconda y elec ons (a) and XRD di ac og am (b) o magne i e a e calcina ion ea men a 500 ◦C/2 h/ai . calcina ion ea men a 500 ◦C o 2 h in ai did no b ing any isible changes in mo phology as seen in Fig. 3a. Ne - e heless he XRD measu emen (Fig. 3b) yielded a mix u e o h ee Fe-oxides, namely hema i e, ␣-Fe2O3, maghemi e, ␥- Fe2O3, and ini ial magne i e Fe3O4analysed using da a shee s 15840, 35643, and 20596, espec i ely. The calcina ion ea men has ans o med ce ium ca bon- a e in o ce ium dioxide o med by hin ela i ely la ge pla es seen in Fig. 4a simul aneously wi h i s di ac og am in Fig. 4b confi ming pu e ce ium oxide analysed by 28753 ICSD da a shee . The ela i e a ios o oxide phases measu ed by XRD a e summa ised in dependence on he ini ial nominal sam- ple composi ion in Table 1. The esul s show p edominan ly magne i e ans o ma ion du ing calcina ion ea men . EDX elemen al mapping in TEM was used o wo selec ed samples (S5 and S9) o isualize quali a i ely elemen s dis- ibu ion. In bo h samples (Fig. 5a,b) we could obse e la ge Ce- ich oxides and fine Fe- ich oxides wi h almos no chem- ical in e mixing and wi h mo phology simila o he ini ial s a e. The same image was ound in o he mixed samples: he mo phology and lay-ou was simila o ha seen in Fig. 1 igh . The pa icle size dis ibu ion is depic ed in Fig. 6. The sam- ple wi h he lowes ce ium dioxide con en (S4) ollows he dis ibu ion o Fe-oxide pa icles. A highe ce ium dioxide con en s he peaks o dis ibu ions ollow ei he peaks co - esponding o Fe- and Ce-oxides o he isible b oadening o dis ibu ions a e p esen eflec ing pa icle agglome a ions. The analysis o XRD pa e ns has yielded he size o mic odomains o ce ium dioxide a ying be ween 8 and 10 nm, while hose o Fe-oxide phases was app oxima ely en imes la ge . The la ice pa ame e s o indi idual phases in he sam- ples sligh ly fluc ua ed wi hin he ange o expe imen al e o . No sys ema ic elonga ion o con ac ion o la ice pa ame e s indica e subs i u ion o Fe3+(Fe2+) in CeO2o Ce4+ in Fe-oxide phases. The samples S5 and S7 ha e shown highe con en s o magne i e and maghemi e bu a eason o i is a p esen unclea . 3.2. Mac o- and mic omagne ic p ope ies The magne ic measu emen s a oom empe a u e we e used o de e mina ion o basic magne ic pa ame e s, sa u a ion and emanen magne iza ions and coe ci i y and pa ame- e s needed o Henkel plo s [36]. Hys e esis loops including de ail a low magne ic fields a e shown in Fig. 7 o ini ial magne i e (S1), magne i e a e calcina ions’ ea men (S2) in he le panel and hose o ce ium dioxide (S3) in he igh panel. The cu e o ce ium dioxide consis s o e omag- ne ic con ibu ion well isible in de ail and he diamagne ic con ibu ion eflec ed by dec easing magne isa ion a highe magne ic fields due o a nega i e magne ic suscep ibili y. A dec ease in sa u a ion magne iza ion o he S2 sample is due o ans o ma ion o magne i e in o mainly haema i e con- ibu ing wi h i s low alue o sa u a ion magne iza ion. The hys e esis loops o he mixed samples a e p esen ed he e by means o hei magne ic cha ac e is ics shown in dependence on sample composi ion in Fig. 8. A low sp ead o he coe ci i y alues in he samples co - esponds o he simila mo phology o he samples seen in SEM mic og aphs. On he o he hand, he non-mono onic changes in sa u a ion and emanen magne iza ions ollow changes in he Fe-oxide ep esen a ion. The highe ela i e ep esen a ion o magne i e and maghemi e s. haema i e in he samples S5 and S7 (Fig. 8 uppe panel) ma kedly influence he magne iza ion. While haema i e is weakly e omagne ic o sa u a ion magne iza ion 0.3 Am2/kg a oom empe a u e, he magne i e and maghemi e a e e imagne ic yielding isi- bly highe alues o sa u a ion magne iza ion anges be ween 60 up o 100 Am2/kg [37]. Thei highe con en in hese samples con ibu es o inc ease in magne iza ion. The same endency is documen ed in Henkel plo s in Fig. 9 ep esen ing he abo e men ioned o mula M(H) g aphically. The nega i e dependences documen p e ailing magne ic dipola (magne- os a ic dipole-dipole) in e ac ions. They a e p oduced by he magne ic momen o each g ain wi h p e ailing influence o he Fe-oxides. The highes peak in ensi y o he M(H), −4.87 Am2/kg, was ob ained o he ini ial magne i e (S1) sam- ple. As in p e ious obse a ions, he in ensi y o peaks o he S5 and S7 samples abundan in magne i e and maghemi e a e highe compa ed o he o he mixed composi ions. The eason o hese “anomalies” is unknown in his momen . I can be only specula ed ha i could come o an un hough -o condi ions du ing calcina ions ea men . The Mössbaue spec oscopy was applied and he phases and hype fine in e ac ions analysed o comple e mac oscopic magne ic p ope ies. The selec ed Mössbaue spec a mea- su ed a oom empe a u e a e shown in Fig. 10. The spec a j m a e e s e c h n o l . 2 0 2 0;9(3):4431–4439 4435 Fig. 4 – Mo phology as seen in SEM, seconda y elec ons (a) and XRD di ac og am (b) o ce ium dioxide ob ained om he ce ium ca bona e a e calcina ions’ ea men a 500 ◦C/2 h/ai . Table 1 – Phase composi ion o samples de e mined by XRD and Mössbaue phase analysis (MS, only e omagne ic phases). Nominal composi ion Sample Me hod Fe3O4␣-Fe2O3␥-Fe2O3␣-FeOOH CeO2 w .% Fe3O4S1 XRD 100.0 MS 74.5 18.7 5.0 Fe3O4/500 ◦C/2 h/ai S2 XRD 3.0 67.9 29.1 MS 8.1 66.8 22.6 1.7 CeO2(Ce2(CO3)3)/500 ◦C/2 h/ai S3 XRD 100.0 MS Fe3O4+5 w .% Ce2(CO3)3/500 ◦C/2 h/ai S4 XRD 3.2 70.3 21.9 4.6 MS 9.8 66.3 21.0 1.5 Fe3O4+10 w .% Ce2(CO3)3/500 ◦C/2 h/ai S5 XRD 10.3 34.9 46.5 8.3 MS 14.9 45.4 36.5 2.7 Fe3O4+20 w .% Ce2(CO3)3/500 ◦C/2 h/ai S6 XRD 7.1 59.9 9.1 23.9 MS 10.2 66.3 19.6 2.1 Fe3O4+30 w .% Ce2(CO3)3/500 ◦C/2 h/ai S7 XRD 15.2 21.1 26.0 37.7 MS 13.8 41.1 40.2 3.0 Fe3O4+40 w .% Ce2(CO3)3/500 ◦C/2 h/ai S8 XRD 9.2 29.6 16.1 45.1 MS 11.1 55.6 28.3 2.0 Fe3O4+50 w .% Ce2(CO3)3/500 ◦C/2 h/ai S9 XRD 0.0 24.5 26.0 49.5 MS 12.7 51.5 30.8 2.8 Fig. 5 – EDX maps o cons i uen elemen s dis ibu ion in calcina ed samples wi h nominal composi ion Fe3O4+10 w .% Ce2(CO3)3(a) and Fe3O4+50 w .% Ce2(CO3)3(b). 4436 j m a e e s e c h n o l . 2 0 2 0;9(3):4431–4439 Fig. 6 – Pa icle size dis ibu ion o inpu Fe- and Ce-oxides (S1, S3) and o mixed samples. Fig. 7 – Hys e esis loops o he ini ial magne i e (S1), calcina ed magne i e (S2) and ce ium ca bona e (S3) including de ails a low magne ic fields. o S1, S2, and mixed S4 up o S9 samples we e e alua ed wi h a se o Lo en zian sex uple s ep esen ed e omagne ic phases. Besides hem also he double-line componen s we e p esen in middle o all samples and hey a e seen also in spec a p esen ed in Fig. 10. Simila spec a a e seen and discussed in Re . [38]. In case o he S1 and S2 samples he hype fine pa ame e s, ı and , ∼0.23 mm/s and 0.35 mm/s, o Fig. 8 – Dependence o magne ic cha ac e is ics on olume concen a ion o he CeO2in he samples. double-line componen can be asc ibed o Fe3+ ions. In he mixed samples S4 up o S9 his sub-componen was p esen as well bu ano he pa amagne ic componen yielding he simila hype fine pa ame e as ob ained o ce ium dioxide in oduced he eina e was de ec ed. The ep esen a ions o hese componen s we e low usually a ound 1%. The spec um o ce ium dioxide (S3) sample was fi ed by double-line com- ponen wi h he isome shi ı = 0.12 mm/s and quad upole spli ing  = 0.58 mm/s (86%) and single-line componen wi h ı = 0.25 mm/s (14%) which, simila ly as in p e ious s udies [30], e iden ial o p esence o Fe-a oms. The e omagne ic componen s we e i) magne i e ep e- sen ed by alues o he hype fine induc ion B ∼ 48.6 T and ∼ 46.6 T, o he isome shi ı∼ 0.38 mm/s and ∼ 0.60 mm/s, and o he quad upole spli ing  ∼ −0.02 mm/s and ∼ 0.0 mm/s, ii) maghemi e o pa ame e s B ∼ 50.3 T, ı ∼ 0.27 mm/s, and  ∼ 0.04 mm/s, and iii) haema i e B ∼ 51.5 T, ı ∼ 0.37 mm/s, and  ∼ −0.18 mm/s. These Fe-oxide phases suppo he esul s ob ained abo e by XRD. Ne e heless, he o he componen o hype fine pa ame e s B ∼ 41 T, ı ∼ 0.47 mm/s, and  ∼ −0.25 mm/s was de ec ed. I could be asc ibed o goe hi e. The ela i e ep esen a ions o e omagne ic phases de ec ed by MS a e p esen oge he wi h XRD da a in Table 2. The j m a e e s e c h n o l . 2 0 2 0;9(3):4431–4439 4437 Fig. 9 – Henkel plo s o he ini ial (S1) and ea ed (S2) magne i e and he mixed Fe-oxide wi h a ious con en o ce ium dioxide om 5 w .% (S4) up o 50 w .% (S9). sligh di e ences in alues be ween bo h me hods a e due o highe sensi i i y o Mössbaue spec ome y on i on con ain- ing phases and hei o de ing. 3.3. Deg ada ion e ficiency As was men ioned abo e a sea ching o magne ically sepa- able so ben s is in p og ess o he se e al las yea s. He e, he deg ada ion e ficiency o se o he samples wi h a ying ini ial composi ions o magne i e/ce ium ca bona e and cal- cina ed a he same condi ions was es ed o he deg ada ion o pa a hion me hyl (PM) and i s con e sion in o 4-ni o enol (FN). Du ing his chemical p ocedu e he a e o chemical eac- ion de e mines he dec easing amoun o PM and inc easing amoun o FN. Bo h componen s can be measu ed simul a- neously. This eac ion can be exp essed by simplified ela ion cPM = cPM0 * exp(−k* ), whe e k is a e cons an and cPM0 is he ini ial concen a ion o PM compound and cPM is concen a- ion o PM compound a ime . The same dependence can be w i en also o FN componen . The changes o k in he es ed samples a e depic ed in Fig. 11. I seems ha cPM = cFN is alid up o app oxima ely 25 ol.% CeO2. The sligh di e ences obse ed a highe CeO2con en s can imply mo e complica ed eac ion. I appea s also ha p esence o Fe-oxides sligh ly mode a e he a e o decomposi ion. 4. Conclusions P esen in es iga ions a e de o ed o magne ically sepa able eac i e so ben s p epa ed as composi e o di e en weigh con en s o he magne i e/ce ium ca bona e (100/0 up o 50/50) subjec ed o calcina ion ea men s a 500 ◦C o 2 h in ai . Fig. 10 – Mössbaue spec a o ini ial (S1) and he mally ea ed (S2) magne i e, calcina ed ce ium ca bona e (S3) and selec ed mixed samples composed o Fe-oxide and o 30 w .% (S7) and 50 w .% (S9) ce ium dioxide. Va ious cha ac e iza ion expe imen al me hods ha e e ealed a numbe o s uc u al and physical aspec s. The main conclusions can be summa ised subsequen ly. • Comme cial magne i e (Fe3O4) con ains also small amoun o maghemi e and ␣-FeOOH de ec ed by highly sensi i e Mössbaue spec oscopy. 4438 j m a e e s e c h n o l . 2 0 2 0;9(3):4431–4439 Fig. 11 – Deg ada ion e ficiency exp essed as he a e cons an o he pa a hion me hyl decomposi ion (PM, •) o o he 4-ni o enol c ea ion (FN, o) and amoun o Fe-oxides (夽) in dependence o CeO2con en in measu ed samples. • Tempe a u e ea men (500 ◦C/2 h/ai ) o magne i e leads o he ans o ma ion in o maghemi e and hema i e and dec eases he con en o ␣-FeOOH. • All hese i on-oxides a e p esen also in o he samples in di e en amoun s. • X- ay di ac ion o ea ed ce ium ca bona e (500 ◦C/2 h/ai ) confi ms i s ans o ma ion in o ce ium oxide o he fluo i e-like c ys alline s uc u e and flake- o m. • X- ay di ac og am analysis yields sligh ly di e en CeO2 con en compa ed o nominal one. • Di e ences be ween XRD and Mössbaue esul s in ep- esen a ion o indi idual phases a e due o dissimila sensi i i y o bo h expe imen al me hods. • Dispe sion in mic o-domain and pa icle size da a despi e he same ea ed pa ame e s o all samples (500 ◦C/2 h/ai ) imply ha mo e a en ion should be done o condi ions o sample p epa a ion and o hei subsequen ea men . • Magne ic cha ac e is ics, sa u a ion and emanen magne- iza ions, a e de e mined by ype and con en o i on-oxide. While magne i e (Ms = 90÷100 Am2/kg) and maghemi e (Ms = 60÷80 Am2/kg) a e e imagne ic wi h only sligh di - e ence in Ms a oom empe a u e, haema i e is weakly e omagne ic (Ms ∼ 0.3 Am2/kg) and i s highe con en in he samples (S2, S4, S6, S8, S9) con ibu es o he lowe alue o Ms. Hype fine induc ion alues (B) a e compa able o all h ee Fe-oxides and no impo an di e ences among sam- ples a e he e o e isible. • The deg ada ion e ficiency seems o be independen on ype o i on-oxide bu inc eases wi h con en o ce ium dioxide. • Insu ficiency o p esen s udies is ha no in o ma ion con- ce ning ce ium dioxide was ob ained in despi e o a ious expe imen al me hods. Some s udies o o he au ho s show ha ce ium dioxide can con ain besides dominan dia- magne ic Ce4+ ions also pa amagne ic Ce3+ ions mainly a pa icle su aces due o acancy- ype-de ec o ma ion. The a io o Ce4+ and Ce3+ ions could con ibu e o be e expla- na ion o he deg ada ion e ficiency. Conflic s o in e es The au ho s decla e no conflic s o in e es . Acknowledgemen s The au ho s hank M. Dosek om he Facul y o En i onmen , Uni e si y J.E. Pu kyne o his help wi h sample p epa a- ion. This wo k was unded by he Czech Science Founda ion ia he p ojec No. 19-07460S and by Minis y o Educa ion You h and Spo s o he Czech Republic ia he ollow- ing p ojec s: No. CZ.02.1.01/0.0/0.0/17 048/0007399 (ERDF/ESF New Composi e Ma e ials o En i onmen al Applica ions), No. LQ1601 (CEITEC 2020-Na ional Sus ainabili y P og amme II), ID LM2015041 (CEITEC Nano Resea ch In as uc u e), No. CZ.1.05/2.1.00/19.0387 (De elopmen o he Resea ch and De elopmen Base o RMSTC), and No. 2015073 (NanoEn iCz Resea ch In as uc u e). Appendix A. Supplemen a y da a Supplemen a y ma e ial ela ed o his a icle can be ound, in he online e sion, a doi:h ps://doi.o g/10.1016/j. jm .2020.02.068. e e e n c e s [1] Renuka NK, P a een AK, Aniz CU. 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